WorldWideScience

Sample records for carrier sense multiple access

  1. Analisis Kerja Carrier Sense Multiple Access With Collison Avoidance (CSMA/CA) Dalam WLAN

    OpenAIRE

    Syafril

    2009-01-01

    Dewasa ini penggunaan Wireless Local Area Network (WLAN) lebih mengarah kepada protokol IEEE 802.11 yang bekerja pada lapis fisik dan Medium Access Control (MAC) dari OSI. Protokol utama pada layer MAC adalah Carier Sense Multiple Access with Collision Avoidance (CSMA/CA) yang prinsip kerjanya didasarkan pada metode Distributed Coordination Function (DCF). Protokol CSMA/CA ini menggunakan pertukaran paket RTS/CTS untuk mendeteksi terjadinya tubrukan paket sehingga pada saat pen...

  2. Cross-Layer Design of an Energy-Efficient Cluster Formation Algorithm with Carrier-Sensing Multiple Access for Wireless Sensor Networks

    Directory of Open Access Journals (Sweden)

    Buratti Chiara

    2005-01-01

    Full Text Available A new energy-efficient scheme for data transmission in a wireless sensor network (WSN is proposed, having in mind a typical application including a sink, which periodically triggers the WSN, and nodes uniformly distributed over a specified area. Routing, multiple access control (MAC, physical, energy, and propagation aspects are jointly taken into account through simulation; however, the protocol design is based on some analytical considerations reported in the appendix. Information routing is based on a clustered self-organized structure; a carrier-sensing multiple access (CSMA protocol is chosen at MAC layer. Two different scenarios are examined, characterized by different channel fading rates. Four versions of our protocol are presented, suitably oriented to the two different scenarios; two of them implement a cross-layer (CL approach, where MAC parameters influence both the network and physical layers. Performance is measured in terms of network lifetime (related to energy efficiency and packet loss rate (related to network availability. The paper discusses the rationale behind the selection of MAC protocols for WSNs and provides a complete model characterization spanning from the network layer to the propagation channel. The advantages of the CL approach, with respect to an algorithm which belongs to the well-known class of low-energy adaptive clustering hierarchy (LEACH protocols, are shown.

  3. Sensing Throughput Optimization in Fading Cognitive Multiple Access Channels With Energy Harvesting Secondary Transmitters

    OpenAIRE

    Biswas, Sinchan; Shirazinia, Amirpasha; Dey, Subhrakanti

    2016-01-01

    The paper investigates the problem of maximizing expected sum throughput in a fading multiple access cognitive radio network when secondary user (SU) transmitters have energy harvesting capability, and perform cooperative spectrum sensing. We formulate the problem as maximization of sum-capacity of the cognitive multiple access network over a finite time horizon subject to a time averaged interference constraint at the primary user (PU) and almost sure energy causality constraints at the SUs....

  4. Performance Analysis of Multiple Access 60 GHz System Using Frequency-shifted Gaussian Pulse and Non-carrier PSWF Pulse

    OpenAIRE

    Hao Zhang; Wei Shi; Tingting Lu; Jingjing Wang; Xinjie Wang

    2013-01-01

    In this paper, a kind of impulse radio (IR) 60 GHz pulse based on Prolate Spheroidal Wave Functions (PSWF) is proposed. The capacity and performance for multiple access 60 GHz communication system based on carrier pulse and impulse radio pulse are analyzed separately. Both frequency-shifted Gaussian pulse and Prolate Spheroidal Wave Functions (PSWF) pulse are considered and devised according to the federal communication commission (FCC) power constraints. Pulse position modulation (PPM) with ...

  5. Performance Analysis of Global Search Algorithm Based Multiuser Detector for Multi Carrier Code Division Multiple Access System under Clipping Noise

    Directory of Open Access Journals (Sweden)

    S. Sivanesskumar

    2011-01-01

    Full Text Available Problem statement: Multi Carrier Code Division Multiple Access (MC-CDMA, a promising technology for the 4G communication systems. The major limitation of MC-CDMA system is the Multiple Access Interference (MAI which is due to near-far effect, frequency offset and nonlinear power amplification due to clipping noise. Approach: The performance of MC-CDMA under clipping noise using Global search algorithm based Multiuser detector in AWGN, Rayleigh and Rician channel is analyzed in this study. Results: The proposed method is simulated using BPSK modulation, Walsh spreading code, number of subcarriers 64 and number of users 16 and clipping noise. Conclusion: By simulation result, BER in AWGN channel outperforms other channels as SNR is increased. The performance of Rician fading channel is better than that of Rayleigh fading channel, because of the LOS path.

  6. Efficient Detection Algorithm for a Multiple-Input and Multiple-Output Multiuser Multi-Carrier Code Division Multiple Access in Time-Varying Channels

    Directory of Open Access Journals (Sweden)

    Fares Sayadi

    2009-01-01

    Full Text Available Problem statement: Maximum Likelihood (ML decoding has been applied for the uplink ofappr a Multi-Carrier Code Division Multiple Access (MC-CDMA system based on Orthogonal Frequency Division Multiplexing (OFDM. Multiple-Input Multiple-Output (MIMO channel from k users, which moves at vehicular speed, to the Base-Station (BS is time-varying. For time-varying channels, Sphere Decoding (SD was introduced to perform ML decoding. Whereas, computational complexity of SD (due to a QR-factorization for each symbol, is nevertheless high. Modified SD had been proposed to achieve near optimum solutions that called Subspace-Sphere Decoder (SPSD. Approach: Proposed algorithm was based on subspace and orthogonal projection with very small dimensionality as robustness scheme in an iterative Multi-User Detection (MUD and Parallel Interference Cancelation (PIC method. Results: This approach had been achieved intense reduction of computational complexity for time-varying channel via one and more than one order of magnitude at channel estimation and multiuser detection respectively. Furthermore, SPSD was robustness to channel estimation error (about 3.8 dB as compared to the representative counterparts in literature. Conclusion: Effectiveness of proposed method was demonstrated by simulations.

  7. On the Optimality of Myopic Sensing in Multi-channel Opportunistic Access: the Case of Sensing Multiple Channels

    CERN Document Server

    Wang, Kehao

    2011-01-01

    Recent works have developed a simple and robust myopic sensing policy for multi-channel opportunistic communication systems where a secondary user (SU) can access one of N i.i.d. Markovian channels. The optimality of the myopic sensing policy in maximizing the SU's cumulated reward is established under certain conditions on channel parameters. This paper studies the generic case where the SU can sense more than one channel each time. By characterizing the myopic sensing policy in this context, we establish analytically its optimality for certain system setting when the SU is allowed to sense two channels. In the more generic case, we construct counterexamples to show that the myopic sensing policy, despite its simple structure, is non-optimal.

  8. Carrier sense data highway system

    Science.gov (United States)

    Frankel, Robert

    1984-02-14

    A data transmission system includes a transmission medium which has a certain propagation delay time over its length. A number of data stations are successively coupled to the transmission medium for communicating with one another. Each of the data stations includes a transmitter for originating signals, each signal beginning with a carrier of a duration which is at least the propagation delay time of the transmission medium. Each data station also includes a receiver which receives other signals from other data stations and inhibits operation of the transmitter at the same data station when a carrier of another signal is received.

  9. Is CSMA Able to Coordinate Multiple Access in Vehicular Radio Channels Effectively?

    OpenAIRE

    Mittag, J.; Hartenstein, H.

    2012-01-01

    The first generation of inter-vehicle communication networks will most likely be based on the IEEE 802.11p standard. That is, they are going to deploy Carrier Sense Multiple Access (CSMA) to coordinate channel access among neighboring vehicles. Recently, concerns have been raised that fast-fading propagation conditions, i.e. a time- and frequency-selective fading as reported by several measurement campaigns in highway environments, might challenge the effectiveness of CSMA. These concerns als...

  10. Multiple-Antenna Interference Cancellation for WLAN with MAC Interference Avoidance in Open Access Networks

    OpenAIRE

    Alexandr M. Kuzminskiy; Hamid Reza Karimi

    2007-01-01

    The potential of multiantenna interference cancellation receiver algorithms for increasing the uplink throughput in WLAN systems such as 802.11 is investigated. The medium access control (MAC) in such systems is based on carrier sensing multiple-access with collision avoidance (CSMA/CA), which itself is a powerful tool for the mitigation of intrasystem interference. However, due to the spatial dependence of received signal strengths, it is possible for the collision avoidance mechanism to fa...

  11. Carrier Sense Random Packet CDMA Protocol in Dual-Channel Networks

    Directory of Open Access Journals (Sweden)

    C. Du

    2015-06-01

    Full Text Available Code resource wastage is caused by the reason that many hopping frequency (FH sequences are unused, which occurs under the condition that the number of the actual subnets needed for the tactical network is far smaller than the networking capacity of code division net¬working. Dual-channel network (DCN, consisting of one single control channel and multiple data channels, can solve the code resource wastage effectively. To improve the anti-jamming capability of the control channel of DCN, code division multiple access (CDMA technology was introduced, and a carrier sense random packet (CSRP CDMA protocol based on random packet CDMA (RP-CDMA was proposed. In CSRP-CDMA, we provide a carrier sensing random packet mechanism and a packet-segment acknowledgement policy. Furthermore, an analytical model was developed to evaluate the performance of CSRP-CDMA networks. In this model, the impacts of multi-access interference from both inter-clusters and intra-clusters were analyzed, and the mathematical expressions of packet transmission success probability, normalized network throughput and signal interference to noise ratio, were also derived. Analytical and simulation results demonstrate that the normalized network throughput of CSRP-CDMA outperforms traditional RP-CDMA by 10%, which can guarantee the resource utilization efficiency of the control channel in DCNs.

  12. Blind Estimation of Multiple Carrier Frequency Offsets

    CERN Document Server

    Yu, Yuanning; Poor, H Vincent; Koivunen, Visa

    2007-01-01

    Multiple carrier-frequency offsets (CFO) arise in a distributed antenna system, where data are transmitted simultaneously from multiple antennas. In such systems the received signal contains multiple CFOs due to mismatch between the local oscillators of transmitters and receiver. This results in a time-varying rotation of the data constellation, which needs to be compensated for at the receiver before symbol recovery. This paper proposes a new approach for blind CFO estimation and symbol recovery. The received base-band signal is over-sampled, and its polyphase components are used to formulate a virtual Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system estimation techniques, the system response is estimated and used to subsequently transform the multiple CFOs estimation problem into many independent single CFO estimation problems. Furthermore, an initial estimate of the CFO is obtained from the phase of the MIMO system response. The Cramer-Rao Lower bound is also derived, and the la...

  13. Selective Sensing and Access Strategy to Maximize Throughput in Cognitive Radio Sensor Network

    OpenAIRE

    Weijun Li; Chao Yang; Zhenquan Wu; Beihai Tan; Yuli Fu

    2014-01-01

    This paper presents a selective spectrum sensing and access strategy in a cognitive radio sensor network (CRSN), in order to maximize the throughput of secondary user (SU) system. An SU senses multiple channels simultaneously via wideband spectrum sensing. To maximize the throughput and reduce the sensing energy consumption, not all of the channels are sensed. The SU selects some channels for spectrum sensing and accesses these channels based on the sensing results. The unselected channels ar...

  14. Combating Impairments in Multi-carrier Systems: A Compressed Sensing Approach

    KAUST Repository

    Al-Shuhail, Shamael

    2015-05-01

    Multi-carrier systems suffer from several impairments, and communication system engineers use powerful signal processing tools to combat these impairments and keep up with the capacity/rate demands. Compressed sensing (CS) is one such tool that allows recovering any sparse signal, requiring only a few measurements in a domain that is incoherent with the domain of sparsity. Almost all signals of interest have some degree of sparsity, and in this work we utilize the sparsity of impairments in orthogonal frequency division multiplexing (OFDM) and its variants (i.e., orthogonal frequency division multiplexing access (OFDMA) and single-carrier frequency-division multiple access (SC-FDMA)) to combat them using CS. We start with the problem of peak-to-average power ratio (PAPR) reduction in OFDM. OFDM signals suffer from high PAPR and clipping is the simplest PAPR reduction scheme. However, clipping introduces inband distortions that result in compromised performance and hence needs to be mitigated at the receiver. Due to the high PAPR nature of the OFDM signal, only a few instances are clipped, these clipping distortions can be recovered at the receiver by employing CS. We then extend the proposed clipping recovery scheme to an interleaved OFDMA system. Interleaved OFDMA presents a special structure that result in only self-inflicted clipping distortions. In this work, we prove that distortions do not spread over multiple users (while utilizing interleaved carrier assignment in OFDMA) and construct a CS system that recovers the clipping distortions on each user. Finally, we address the problem of narrowband interference (NBI) in SC-FDMA. Unlike OFDM and OFDMA systems, SC-FDMA does not suffer from high PAPR, but (as the data is encoded in time domain) is seriously vulnerable to information loss owing to NBI. Utilizing the sparse nature of NBI (in frequency domain) we combat its effect on SC-FDMA system by CS recovery.

  15. Code division multiple access (CDMA)

    CERN Document Server

    Buehrer, R Michael

    2006-01-01

    This book covers the basic aspects of Code Division Multiple Access or CDMA. It begins with an introduction to the basic ideas behind fixed and random access systems in order to demonstrate the difference between CDMA and the more widely understood TDMA, FDMA or CSMA. Secondly, a review of basic spread spectrum techniques are presented which are used in CDMA systems including direct sequence, frequency-hopping and time-hopping approaches. The basic concept of CDMA is presented, followed by the four basic principles of CDMA systems that impact their performance: interference averaging, universa

  16. Optimality of Multichannel Myopic Sensing in the Presence of Sensing Error for Opportunistic Spectrum Access

    Directory of Open Access Journals (Sweden)

    Xiaofeng Jiang

    2013-01-01

    Full Text Available The optimization problem for the performance of opportunistic spectrum access is considered in this study. A user, with the limited sensing capacity, has opportunistic access to a communication system with multiple channels. The user can only choose several channels to sense and decides whether to access these channels based on the sensing information in each time slot. Meanwhile, the presence of sensing error is considered. A reward is obtained when the user accesses a channel. The objective is to maximize the expected (discounted or average reward accrued over an infinite horizon. This problem can be formulated as a partially observable Markov decision process. This study shows the optimality of the simple and robust myopic policy which focuses on maximizing the immediate reward. The results show that the myopic policy is optimal in the case of practical interest.

  17. Open-access microcavities for chemical sensing.

    Science.gov (United States)

    Vallance, Claire; Trichet, Aurelien A P; James, Dean; Dolan, Philip R; Smith, Jason M

    2016-07-01

    The recent development of open-access optical microcavities opens up a number of intriguing possibilities in the realm of chemical sensing. We provide an overview of the different possible sensing modalities, with examples of refractive index sensing, optical absorption measurements, and optical tracking and trapping of nanoparticles. The extremely small mode volumes within an optical microcavity allow very small numbers of molecules to be probed: our current best detection limits for refractive index and absorption sensing are around 10(5) and 10(2) molecules, respectively, with scope for further improvements in the future. PMID:27242174

  18. Open-access microcavities for chemical sensing

    Science.gov (United States)

    Vallance, Claire; Trichet, Aurelien A. P.; James, Dean; Dolan, Philip R.; Smith, Jason M.

    2016-07-01

    The recent development of open-access optical microcavities opens up a number of intriguing possibilities in the realm of chemical sensing. We provide an overview of the different possible sensing modalities, with examples of refractive index sensing, optical absorption measurements, and optical tracking and trapping of nanoparticles. The extremely small mode volumes within an optical microcavity allow very small numbers of molecules to be probed: our current best detection limits for refractive index and absorption sensing are around 105 and 102 molecules, respectively, with scope for further improvements in the future.

  19. A Novel Multiple Access Protocol for Mobile Ad Hoc Network with Smart Antennas

    Institute of Scientific and Technical Information of China (English)

    YANGJun; LIJiandong; ZHOUXiaodong

    2004-01-01

    The approach to employ smart antennas in Mobile ad hoc network (MANET) nodes is presented. An adaptive beamforming-Carrier-Sense multiple access/collison avoidance) (ABF-CSMA/CA) protocol is proposed. In the ABF-CSMA/CA, Request-to-Send/Clear-to-Send (RTS/CTS) dialogue is used to distribute channel reservation information. Training sequences are transmitted just before RTS and CTS packets, so the Temporal reference beamforming (TRB) can be performed by the source node and the destination node.An improved virtual carrier-sense mechanism is also proposed to enhance Collision avoidance (CA) and obtain efficient Space division multiple access (SDMA). In this scheme, every node has two kinds of Network allocation vector (NAV): an oNAV maintains the interval of ongoing transmission of neighbors whose smart antennas operate in omnidirectional mode, and multiple bNAVs maintain those intervals of neighbors whose smart antennas operate in beamforming mode. Theoretical analysis of channel utilization of the proposed protocol is presented. Results show that ABF-CSMA/CA protocol combining with smart antennas can provide higher channel utilization.

  20. 47 CFR 36.381 - Carrier access charge billing and collecting expense.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Carrier access charge billing and collecting... Operating Expenses and Taxes Customer Operations Expenses § 36.381 Carrier access charge billing and... billing and collecting of access charges to interexchange carriers. (b) Of access charges other than...

  1. Remote Sensing Open Access Journal: Increasing Impact through Quality Publications

    Directory of Open Access Journals (Sweden)

    Prasad S. Thenkabail

    2014-08-01

    Full Text Available Remote Sensing, an open access journal (http://www.mdpi.com/journal/remotesensing has grown at rapid pace since its first publication five years ago, and has acquired a strong reputation. It is a “pathfinder” being the first open access journal in remote sensing. For those academics who were used to waiting a year or two for their peer-reviewed scientific work to be reviewed, revised, edited, and published, Remote Sensing offers a publication time frame that is unheard of (in most cases, less than four months. However, we do this after multiple peer-reviews, multiple revisions, much editorial scrutiny and decision-making, and professional editing by an editorial office before a paper is published online in our tight time frame, bringing a paradigm shift in scientific publication. As a result, there has been a swift increase in submissions of higher and higher quality manuscripts from the best authors and institutes working on Remote Sensing, Geographic Information Systems (GIS, Global Navigation Satellite System (GNSS, GIScience, and all related geospatial science and technologies from around the world. The purpose of this editorial is to update everyone interested in Remote Sensing on the progress made over the last year, and provide an outline of our vision for the immediate future. [...

  2. Enhancing Sensing and Channel Access in Cognitive Radio Networks

    KAUST Repository

    Hamza, Doha R.

    2014-06-18

    Cognitive radio technology is a promising technology to solve the wireless spectrum scarcity problem by intelligently allowing secondary, or unlicensed, users access to the primary, licensed, users\\' frequency bands. Cognitive technology involves two main tasks: 1) sensing the wireless medium to assess the presence of the primary users and 2) designing secondary spectrum access techniques that maximize the secondary users\\' benefits while maintaining the primary users\\' privileged status. On the spectrum sensing side, we make two contributions. First, we maximize a utility function representing the secondary throughput while constraining the collision probability with the primary below a certain value. We optimize therein the channel sensing time, the sensing decision threshold, the channel probing time, together with the channel sensing order for wideband primary channels. Second, we design a cooperative spectrum sensing technique termed sensing with equal gain combining whereby cognitive radios simultaneously transmit their sensing results to the fusion center over multipath fading reporting channels. The proposed scheme is shown to outperform orthogonal reporting systems in terms of achievable secondary throughput and to be robust against phase and synchronization errors. On the spectrum access side, we make four contributions. First, we design a secondary scheduling scheme with the goal of minimizing the secondary queueing delay under constraints on the average secondary transmit power and the maximum tolerable primary outage probability. Second, we design another secondary scheduling scheme based on the spectrum sensing results and the primary automatic repeat request feedback. The optimal medium access probabilities are obtained via maximizing the secondary throughput subject to constraints that guarantee quality of service parameters for the primary. Third, we propose a three-message superposition coding scheme to maximize the secondary throughput without

  3. Carrier multiplication in silicon nanocrystals: ab initio results

    Directory of Open Access Journals (Sweden)

    Ivan Marri

    2015-02-01

    Full Text Available One of the most important goals in the field of renewable energy is the development of original solar cell schemes employing new materials to overcome the performance limitations of traditional solar cell devices. Among such innovative materials, nanostructures have emerged as an important class of materials that can be used to realize efficient photovoltaic devices. When these systems are implemented into solar cells, new effects can be exploited to maximize the harvest of solar radiation and to minimize the loss factors. In this context, carrier multiplication seems one promising way to minimize the effects induced by thermalization loss processes thereby significantly increasing the solar cell power conversion. In this work we analyze and quantify different types of carrier multiplication decay dynamics by analyzing systems of isolated and coupled silicon nanocrystals. The effects on carrier multiplication dynamics by energy and charge transfer processes are also discussed.

  4. Multiple-Access Quantum-Classical Networks

    Science.gov (United States)

    Razavi, Mohsen

    2011-10-01

    A multi-user network that supports both classical and quantum communication is proposed. By relying on optical code-division multiple access techniques, this system offers simultaneous key exchange between multiple pairs of network users. A lower bound on the secure key generation rate will be derived for decoy-state quantum key distribution protocols.

  5. Extending the unambiguous velocity range using multiple carrier frequencies

    DEFF Research Database (Denmark)

    Zhang, Z.; Jakobsson, A.; Nikolov, Svetoslav; Chambers, J.A.

    2005-01-01

    Typically, velocity estimators based on the estimation of the Doppler shift will suffer from a limited unambiguous velocity range. Proposed are two novel multiple carrier based velocity estimators extending the velocity range above the Nyquist velocity limit. Numerical simulations indicate that the...

  6. Quantum internet using code division multiple access

    Science.gov (United States)

    Zhang, Jing; Liu, Yu-Xi; Özdemir, Şahin Kaya; Wu, Re-Bing; Gao, Feifei; Wang, Xiang-Bin; Yang, Lan; Nori, Franco

    2013-07-01

    A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.

  7. FODA: a novel efficient multiple access protocol for highly dynamic self-organizing networks

    Science.gov (United States)

    Li, Hantao; Liu, Kai; Zhang, Jun

    2005-11-01

    Based on the concept of contention reservation for polling transmission and collision prevention strategy for collision resolution, a fair on-demand access (FODA) protocol for supporting node mobility and multihop architecture in highly dynamic self-organizing networks is proposed. In the protocol, a distributed clustering network architecture formed by self-organizing algorithm and a main idea of reserving channel resources to get polling service are adopted, so that the hidden terminal (HT) and exposed terminal (ET) problems existed in traffic transmission due to multihop architecture and wireless transmission can be eliminated completely. In addition, an improved collision prevention scheme based on binary countdown algorithm (BCA), called fair collision prevention (FCP) algorithm, is proposed to greatly eliminate unfair phenomena existed in contention access of newly active ordinary nodes and completely resolve access collisions. Finally, the performance comparison of the FODA protocol with carrier sense multiple access with collision avoidance (CSMA/CA) and polling protocols by OPNET simulation are presented. Simulation results show that the FODA protocol can overcome the disadvantages of CSMA/CA and polling protocols, and achieve higher throughput, lower average message delay and less average message dropping rate.

  8. A Review of Packet Reservation Multiple Access

    Directory of Open Access Journals (Sweden)

    Varsha Sharma

    2011-05-01

    Full Text Available The rapid technological advances and innovations of the past few decades have pushed wireless communication from concept to reality. The popularity of wireless communication systems can be seen almost everywhere in the form of cellular networks, WLANs, and WPANs. Packet-switched technology has been demonstrated as effective in cellular radio systems with short propagation delay, not only for data, but also for voice transmission. In fact, packet voice can efficiently exploit speech on-off activity to improve bandwidth utilization over time division multiple access (TDMA. Such an approach has been first suggested in the packet reservation multiple-access (PRMA technique, an adaptation of the reservation ALOHA protocol to the cellular environment. PRMA can be viewed as a combination of TDMA and slotted ALOHA protocols. Recently modified versions of the PRMA protocol have been the subject of extensive research. This paper reviews a number of variations of PRMA protocol in literature.

  9. Proposition of an Unexploited Multiple Access Technique

    OpenAIRE

    Sidi Ahmed Djennas; Fethi Tarik Bendimerad

    2012-01-01

    Continual growth in number of telecommunication network users encourages engineers to bring solutions to avoid overload and conflict. The situation is remedied by multiple access techniques and protocols. In fact, several ideas were applied with success to overcome difficulties. Basically, these ideas are based on discrimination in time, frequency, space and modulating code or time management. Within the context, we propose in this paper a new technique which helps us to avoid the conflict be...

  10. The Gaussian Multiple Access Diamond Channel

    CERN Document Server

    Kang, Wei

    2011-01-01

    In this paper, we study the capacity of the diamond channel. We focus on the special case where the channel between the source node and the two relay nodes are two separate links of finite capacity and the link from the two relay nodes to the destination node is a Gaussian multiple access channel. We call this model the Gaussian multiple access diamond channel. We propose both an upper bound and a lower bound on the capacity. Since the upper and lower bounds take on similar forms, it is expected that they coincide for certain channel parameters. To show this, we further focus on the symmetric case where the separate links to the relays are of the same capacity and the power constraints of the two relays are the same. For the symmetric case, we give necessary and sufficient conditions that the upper and lower bounds meet. Thus, for a Gaussian multiple access diamond channel that satisfies these conditions, we have found its capacity.

  11. Multiple-Antenna Interference Cancellation for WLAN with MAC Interference Avoidance in Open Access Networks

    Directory of Open Access Journals (Sweden)

    Kuzminskiy Alexandr M

    2007-01-01

    Full Text Available The potential of multiantenna interference cancellation receiver algorithms for increasing the uplink throughput in WLAN systems such as 802.11 is investigated. The medium access control (MAC in such systems is based on carrier sensing multiple-access with collision avoidance (CSMA/CA, which itself is a powerful tool for the mitigation of intrasystem interference. However, due to the spatial dependence of received signal strengths, it is possible for the collision avoidance mechanism to fail, resulting in packet collisions at the receiver and a reduction in system throughput. The CSMA/CA MAC protocol can be complemented in such scenarios by interference cancellation (IC algorithms at the physical (PHY layer. The corresponding gains in throughput are a result of the complex interplay between the PHY and MAC layers. It is shown that semiblind interference cancellation techniques are essential for mitigating the impact of interference bursts, in particular since these are typically asynchronous with respect to the desired signal burst. Semiblind IC algorithms based on second- and higher-order statistics are compared to the conventional no-IC and training-based IC techniques in an open access network (OAN scenario involving home and visiting users. It is found that the semiblind IC algorithms significantly outperform the other techniques due to the bursty and asynchronous nature of the interference caused by the MAC interference avoidance scheme.

  12. Multiple-Antenna Interference Cancellation for WLAN with MAC Interference Avoidance in Open Access Networks

    Directory of Open Access Journals (Sweden)

    Alexandr M. Kuzminskiy

    2007-10-01

    Full Text Available The potential of multiantenna interference cancellation receiver algorithms for increasing the uplink throughput in WLAN systems such as 802.11 is investigated. The medium access control (MAC in such systems is based on carrier sensing multiple-access with collision avoidance (CSMA/CA, which itself is a powerful tool for the mitigation of intrasystem interference. However, due to the spatial dependence of received signal strengths, it is possible for the collision avoidance mechanism to fail, resulting in packet collisions at the receiver and a reduction in system throughput. The CSMA/CA MAC protocol can be complemented in such scenarios by interference cancellation (IC algorithms at the physical (PHY layer. The corresponding gains in throughput are a result of the complex interplay between the PHY and MAC layers. It is shown that semiblind interference cancellation techniques are essential for mitigating the impact of interference bursts, in particular since these are typically asynchronous with respect to the desired signal burst. Semiblind IC algorithms based on second- and higher-order statistics are compared to the conventional no-IC and training-based IC techniques in an open access network (OAN scenario involving home and visiting users. It is found that the semiblind IC algorithms significantly outperform the other techniques due to the bursty and asynchronous nature of the interference caused by the MAC interference avoidance scheme.

  13. Cooperation in Carrier Sense Based Wireless Ad Hoc Networks - Part II: Proactive Schemes

    CERN Document Server

    Munari, Andrea; Zorzi, Michele

    2012-01-01

    This work is the second of a two-part series of papers on the effectiveness of cooperative techniques in non-centralized carrier sense-based ad hoc wireless networks. While Part I extensively discussed reactive cooperation, characterized by relayed transmissions triggered by failure events at the intended receiver, Part II investigates in depth proactive solutions, in which the source of a packet exploits channel state information to preemptively coordinate with relays in order to achieve the optimal overall rate to the destination. In particular, this work shows by means of both analysis and simulation that the performance of reactive cooperation is reduced by the intrinsic nature of the considered medium access policy, which biases the distribution of the available relays, locating them in unfavorable positions for rate optimization. Moreover, the highly dynamic nature of interference that characterizes non-infrastructured ad hoc networks is proved to hamper the efficacy and the reliability of preemptively ...

  14. Induction Charge Detector with Multiple Sensing Stages

    Science.gov (United States)

    Gamero-Castano, Manuel

    2008-01-01

    An induction charge detector with multiple sensing stages has been conceived for use in characterizing sprayed droplets, dust particles, large ionized molecules, and the like. Like related prior single-stage devices, each stage yields a measurement of the electric charge and the time of flight of the particle. In effect, an n-stage sensor yields n independent sets of such measurements from the same particle. The benefit of doing this is to increase the effective signal-to-noise ratio and thereby lower the charge-detection limit and the standard error of the charge measurement.

  15. Quantum internet using code division multiple access

    CERN Document Server

    Zhang, Jing; Ozdemir, Sahin Kaya; Wu, Re-Bing; Wang, Xiang-Bin; Nori, Franco

    2012-01-01

    Code division multiple access (CDMA) is a spread-spectrum technology, in which a code is used to spread the spectral content of information to achieve larger network capacity. It has been widely used in classical communication and wireless networks. Here, we extend CDMA to the quantum case, where many pairs of nodes can transmit quantum information through a shared channel. This can be achieved by chaotic encoding of quantum information to spread its spectral content and by chaos synchronization, to separate different sender-receiver pairs. The proposed method is robust to low-frequency noise, and achieves faithful transmission with fidelities of up to 0.99.

  16. Basics of code division multiple access (CDMA)

    CERN Document Server

    Rao, Raghuveer

    2005-01-01

    Code division multiple access (CDMA) has proven to be a viable enabling technique for the simultaneous transmission and reception of data over a shared channel. Although associated mostly with wireless cellular communication, CDMA is also being considered for optical channels. This text, aimed at the reader with a basic background in electrical or optical engineering, covers CDMA fundamentals: from the basics of the communication process and digital data transmission, to the concepts of code division multiplexing, direct sequence spreading, diversity techniques, the near-far effect, and the IS

  17. Random-access distributed fiber sensing

    OpenAIRE

    Zadok, Avinoam; Antman, Yair; Primerov, Nikolay; Denisov, Andrey; SANCHO Juan; Thévenaz, Luc

    2012-01-01

    Optical sensing offers an attractive solution to the societal concern for prevention of natural and human-generated threats and for efficient use of natural resources. The unprecedented properties of optical fibers make them ideal for implementing a ‘nervous system’ in structural health monitoring: they are small, low-cost and electrically and chemically inert. In particular, the nonlinear interaction of stimulated Brillouin scattering allows for the distributed measurement of strain and temp...

  18. A novel velocity estimator using multiple frequency carriers

    DEFF Research Database (Denmark)

    Zhang, Zhuo; Jakobsson, Andreas; Nikolov, Svetoslav; Chambers, Jonathan

    -to-noise ratio is low, and some averaging in depth is applied to improve the estimate. Further, due to velocity gradients in space and time, the spectrum may get smeared. An alternative approach is to use a pulse with multiple frequency carriers, and do some form of averaging in the frequency domain. However......Most modern ultrasound scanners use the so-called pulsed-wave Doppler technique to estimate the blood velocities. Among the narrowband-based methods, the autocorrelation estimator and the Fourier-based method are the most commonly used approaches. Due to the low level of the blood echo, the signal......, the limited transducer bandwidth will limit the accuracy of the conventional Fourier-based estimator; this method is also known to have considerable variance. More importantly, both the mentioned methods suffer from the maximum axial velocity bound, vzmax = cfprf/4fc, where c is the speed of...

  19. Proposition of an Unexploited Multiple Access Technique

    Directory of Open Access Journals (Sweden)

    Sidi Ahmed Djennas

    2012-03-01

    Full Text Available Continual growth in number of telecommunication network users encourages engineers to bring solutions to avoid overload and conflict. The situation is remedied by multiple access techniques and protocols. In fact, several ideas were applied with success to overcome difficulties. Basically, these ideas are based on discrimination in time, frequency, space and modulating code or time management. Within the context, we propose in this paper a new technique which helps us to avoid the conflict between users and manage optimally the information convoy. The basic idea for the new technique, baptized on the occasion by FAT (Fundamentals Agreement Technique, is to develop every signal and to convert it into a form with fundamentals as components. Of course emission and reception parts are in agreement about fundamentals to allow signals recovery later.

  20. Resource Allocation in Multiple Access Channels

    CERN Document Server

    ParandehGheibi, Ali; Ozdaglar, Asuman; Medard, Muriel

    2008-01-01

    We consider the problem of rate allocation in a Gaussian multiple-access channel, with the goal of maximizing a utility function over transmission rates. In contrast to the literature which focuses on linear utility functions, we study general concave utility functions. We present a gradient projection algorithm for this problem. Since the constraint set of the problem is described by exponentially many constraints, methods that use exact projections are computationally intractable. Therefore, we develop a new method that uses approximate projections. We use the polymatroid structure of the capacity region to show that the approximate projection can be implemented by a recursive algorithm in time polynomial in the number of users. We further propose another algorithm for implementing the approximate projections using rate-splitting and show improved bounds on its convergence time.

  1. Multiple-Access Quantum Key Distribution Networks

    CERN Document Server

    Razavi, Mohsen

    2011-01-01

    This paper addresses multi-user quantum key distribution networks, in which any two users can mutually exchange a secret key without trusting any other nodes. The same network also supports conventional classical communications by assigning two different wavelength bands to quantum and classical signals. Time and code division multiple access (CDMA) techniques, within a passive star network, are considered. In the case of CDMA, it turns out that the optimal performance is achieved at a unity code weight. A listen-before-send protocol is then proposed to improve secret key generation rates in this case. Finally, a hybrid setup with wavelength routers and passive optical networks, which can support a large number of users, is considered and analyzed.

  2. Grant-free Rateless Multiple Access: A Novel Massive Access Scheme for Internet of Things

    OpenAIRE

    Zhang, Zhaoyang; Wang, Xianbin; Zhang, Yu; Chen, Yan

    2016-01-01

    Rateless Multiple Access (RMA) is a novel non-orthogonal multiple access framework that is promising for massive access in Internet of Things (IoT) due to its high efficiency and low complexity. In the framework, after certain \\emph{registration}, each active user respectively transmits to the access point (AP) randomly based on an assigned random access control function (RACf) until receiving an acknowledgement (ACK). In this work, by exploiting the intrinsic access pattern of each user, we ...

  3. An optimal probabilistic multiple-access scheme for cognitive radios

    KAUST Repository

    Hamza, Doha R.

    2012-09-01

    We study a time-slotted multiple-access system with a primary user (PU) and a secondary user (SU) sharing the same channel resource. The SU senses the channel at the beginning of the slot. If found free, it transmits with probability 1. If busy, it transmits with a certain access probability that is a function of its queue length and whether it has a new packet arrival. Both users, i.e., the PU and the SU, transmit with a fixed transmission rate by employing a truncated channel inversion power control scheme. We consider the case of erroneous sensing. The goal of the SU is to optimize its transmission scheduling policy to minimize its queueing delay under constraints on its average transmit power and the maximum tolerable primary outage probability caused by the miss detection of the PU. We consider two schemes regarding the secondary\\'s reaction to transmission errors. Under the so-called delay-sensitive (DS) scheme, the packet received in error is removed from the queue to minimize delay, whereas under the delay-tolerant (DT) scheme, the said packet is kept in the buffer and is retransmitted until correct reception. Using the latter scheme, there is a probability of buffer loss that is also constrained to be lower than a certain specified value. We also consider the case when the PU maintains an infinite buffer to store its packets. In the latter case, we modify the SU access scheme to guarantee the stability of the PU queue. We show that the performance significantly changes if the realistic situation of a primary queue is considered. In all cases, although the delay minimization problem is nonconvex, we show that the access policies can be efficiently obtained using linear programming and grid search over one or two parameters. © 1967-2012 IEEE.

  4. Performance of Joint Spectrum Sensing and MAC Algorithms for Multichannel Opportunistic Spectrum Access Ad Hoc Networks

    CERN Document Server

    Park, Jihoon; Čabrić, Danijela

    2009-01-01

    We present an analytical framework to assess the link layer throughput of multichannel Opportunistic Spectrum Access (OSA) ad hoc networks. Specifically, we focus on analyzing various combinations of collaborative spectrum sensing and Medium Access Control (MAC) protocol abstractions. In analysis we decompose collaborative spectrum sensing into layers, parametrize each layer, classify existing solutions, and propose a new protocol called Truncated Time Division Multiple Access (TTDMA) that supports efficient distribution of sensing results in "k out of N" fusion rule. In case of multichannel MAC protocols we evaluate two main approaches of control channel design with (i) dedicated and (ii) hopping channel. We propose to augment these protocols with options of handling SU connections preempted by PU either by (i) connection buffering until PU departure and (ii) connection switching to a vacant PU channels. By comparing and optimizing different design combinations we show that (i) it is generally better to buff...

  5. Carrier injection engineering in nanowire transistors via dopant and shape monitoring of the access regions

    Energy Technology Data Exchange (ETDEWEB)

    Berrada, Salim, E-mail: s.berrada@insa.ueuromed.org; Bescond, Marc, E-mail: marc.bescond@im2np.fr; Cavassilas, Nicolas; Raymond, Laurent; Lannoo, Michel [IM2NP UMR CNRS 7334, Aix-Marseille Université, Technopôle de Château Gombert, 60 Rue Frédéric Joliot Curie, Bâtiment Néel,13453 Marseille (France)

    2015-10-12

    This work theoretically studies the influence of both the geometry and the discrete nature of dopants of the access regions in ultra-scaled nanowire transistors. By means of self-consistent quantum transport simulations, we show that discrete dopants induce quasi-localized states which govern carrier injection into the channel. Carrier injection can be enhanced by taking advantage of the dielectric confinement occurring in these access regions. We demonstrate that the optimization of access resistance can be obtained by a careful control of shape and dopant position. These results pave the way for contact resistance engineering in forthcoming device generations.

  6. Carrier injection engineering in nanowire transistors via dopant and shape monitoring of the access regions

    International Nuclear Information System (INIS)

    This work theoretically studies the influence of both the geometry and the discrete nature of dopants of the access regions in ultra-scaled nanowire transistors. By means of self-consistent quantum transport simulations, we show that discrete dopants induce quasi-localized states which govern carrier injection into the channel. Carrier injection can be enhanced by taking advantage of the dielectric confinement occurring in these access regions. We demonstrate that the optimization of access resistance can be obtained by a careful control of shape and dopant position. These results pave the way for contact resistance engineering in forthcoming device generations

  7. Terahertz study of ultrafast carrier dynamics in InGa/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David;

    2009-01-01

    Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells is measured by time-resolved terahertz spectroscopy. The built-in piezoelectric field is initially screened by photoexcited, polarized carriers, and is gradullay restored as the carriers recombine. We observe a nonexponential decay of...

  8. Spectrum Sensing for Cognitive Radio Based on Multiple Antennas

    DEFF Research Database (Denmark)

    Nguyen, Huan Cong; De Carvalho, Elisabeth; Prasad, Ramjee

    2012-01-01

    Spectrum sensing is a key component for enabling the cognitive radio paradigm. In this paper, we propose a novel totally-blind spectrum sensing technique for cognitive radio device equipped with multiple antennas, namely the Space Frequency Cross Product Sensing (SFCPS) algorithm. Existing...

  9. Optical gas sensing responses in transparent conducting oxides with large free carrier density

    Science.gov (United States)

    Ohodnicki, P. R.; Andio, M.; Wang, C.

    2014-07-01

    Inherent advantages of optical-based sensing devices motivate a need for materials with useful optical responses that can be utilized as thin film functional sensor layers. Transparent conducting metal oxides with large electrical conductivities as typified by Al-doped ZnO (AZO) display attractive properties for high temperature optical gas sensing through strong optical transduction of responses conventionally monitored through changes in measured electrical resistivity. An enhanced optical sensing response in the near-infrared and ultraviolet/visible wavelength ranges is demonstrated experimentally and linked with characteristic modifications to the dielectric constant due to a relatively high concentration of free charge carriers. The impact of light scattering on the magnitude and wavelength dependence of the sensing response is also discussed highlighting the potential for tuning the optical sensing response by controlling the surface roughness of a continuous film or the average particle size of a nanoparticle-based film. The physics underpinning the optical sensing response for AZO films on planar substrates yields significant insight into the measured sensing response for optical fiber-based evanescent wave absorption spectroscopy sensors employing an AZO sensing layer. The physics of optical gas sensing discussed here provides a pathway towards development of sensing materials for extreme temperature optical gas sensing applications. As one example, preliminary results are presented for a Nb-doped TiO2 film with sufficient stability and relatively large sensing responses at sensing temperatures greater than 500 °C.

  10. Passive UHF RFID tag with multiple sensing capabilities.

    Science.gov (United States)

    Fernández-Salmerón, José; Rivadeneyra, Almudena; Martínez-Martí, Fernando; Capitán-Vallvey, Luis Fermín; Palma, Alberto J; Carvajal, Miguel A

    2015-01-01

    This work presents the design, fabrication, and characterization of a printed radio frequency identification tag in the ultra-high frequency band with multiple sensing capabilities. This passive tag is directly screen printed on a cardboard box with the aim of monitoring the packaging conditions during the different stages of the supply chain. This tag includes a commercial force sensor and a printed opening detector. Hence, the force applied to the package can be measured as well as the opening of the box can be detected. The architecture presented is a passive single-chip RFID tag. An electronic switch has been implemented to be able to measure both sensor magnitudes in the same access without including a microcontroller or battery. Moreover, the chip used here integrates a temperature sensor and, therefore, this tag provides three different parameters in every reading. PMID:26506353

  11. Passive UHF RFID Tag with Multiple Sensing Capabilities

    Directory of Open Access Journals (Sweden)

    José Fernández-Salmerón

    2015-10-01

    Full Text Available This work presents the design, fabrication, and characterization of a printed radio frequency identification tag in the ultra-high frequency band with multiple sensing capabilities. This passive tag is directly screen printed on a cardboard box with the aim of monitoring the packaging conditions during the different stages of the supply chain. This tag includes a commercial force sensor and a printed opening detector. Hence, the force applied to the package can be measured as well as the opening of the box can be detected. The architecture presented is a passive single-chip RFID tag. An electronic switch has been implemented to be able to measure both sensor magnitudes in the same access without including a microcontroller or battery. Moreover, the chip used here integrates a temperature sensor and, therefore, this tag provides three different parameters in every reading.

  12. Spectrum Sensing for Cognitive Radio Based on Multiple Antennas

    DEFF Research Database (Denmark)

    Nguyen, Huan Cong; De Carvalho, Elisabeth; Prasad, Ramjee

    Spectrum sensing is a key component for enabling the cognitive radio paradigm. In this paper, we propose a novel totally-blind spectrum sensing technique for cognitive radio device equipped with multiple antennas, namely the Space Frequency Cross Product Sensing (SFCPS) algorithm. Existing...... correlated and on which a sensing method is developed. SFCPS performs better than existing correlation-based techniques and with a lower computational complexity for small number of observed samples....

  13. Key issues of multiple access technique for LEO satellite communication systems

    Institute of Scientific and Technical Information of China (English)

    温萍萍; 顾学迈

    2004-01-01

    The large carrier frequency shift caused by the high-speed movement of satellite (Doppler effects) and the propagation delay on the up-down link are very critical issues in an LEO satellite communication system, which affects both the selection and the implementation of a suitable access method. A Doppler based multiple access technique is used here to control the flow and an MPRMA-HS protocol is proposed for the application in LEO satellite communication systems. The extended simulation trials prove that the proposed scheme seems to be a very promising access method.

  14. Optimal Sensing for Opportunistic Spectrum Access in Cognitive Radio

    Directory of Open Access Journals (Sweden)

    Nasrullah Armi

    2010-08-01

    Full Text Available Opportunistic Spectrum Access (OSA brings new research challenges in MAC protocol design. It allows unlicensed users to share licensed spectrum in space and time with no or little interference to Primary Users (PUs. When designing an OSA MAC protocol, one of the most difficult but important problem is how the unlicensed users decide when and which channel they should sense and access without conflicting the communications among PUs. To solve this problem, the unlicensed users should have the ability of adaptively and dynamically seeking and exploiting opportunities in both licensed and unlicensed spectrum and along both the time and the frequency dimensions. Secondary Users (SUs as unlicensed users are required to sense radio frequency band, and when PU are detected, they must vacate the channel immediately within certain amount of time. Due to hardware and energy constraints, full spectrum availability cannot be sensed as well as they do not monitor when there is no data to be transmitted. In this paper, we study MAC protocol design and optimal sensing for OSA in Cognitive Radio (CR ad hoc network under Partially Observable Markov Decision Process (POMDP algorithm that maximizes achievable throughput for SUs with sufficient protection to PUs. Furthermore, we study tractable greedy algorithm to reduce the complexity of POMDP calculation. The derivation of greedy approach proves that sensing problem can be solved either optimally or approximate the optimal solution. Computer simulation is used to evaluate the performances both of optimal and sub optimal strategy.

  15. Optimal Sensing for Opportunistic Spectrum Access in Cognitive Radio

    Directory of Open Access Journals (Sweden)

    Nasrullah Armi, Naufal M. Saad, M. Zuki Yusoff, Muhammad Arshad

    2010-08-01

    Full Text Available One of the most difficult thing but important problem when designing an OSA (Opportunistic Spectrum Access MAC protocol is how the unlicensed users decide when and which channel they should sense and access without conflicting the communications among PUs. To solve this problem, the unlicensed users should have the ability of adaptively and dynamically seeking and exploiting opportunities in both licensed and unlicensed spectrum and along both of the time and the frequency dimensions. Secondary Users (SUs as unlicensed users are required to sense radio frequency band, and when PU are detected, they must vacate the channel immediately within certain amount of time. Due to hardware and energy constraints, full spectrum availability cannot be sensed as well as they do not monitor when there is no data to be transmitted. In this paper, we study MAC protocol design and optimal sensing for OSA in Cognitive Radio (CR ad hoc network under Partially Observable Markov Decision Process (POMDP algorithm that maximizes achievable throughput for SUs with sufficient protection to PUs. The bandwith effect to number of bit transmitted in one slot and tractable greedy algorithm to reduce the complexity of POMDP calculation was studied as well. The derivation of greedy approach proves that sensing problem can be solved either optimally or approximate the optimal solution. Computer simulation is used to evaluate the performances both of optimal and sub optimal strategy.

  16. On Myopic Sensing for Multi-Channel Opportunistic Access

    CERN Document Server

    Zhao, Qing; Liu, Keqin

    2007-01-01

    We consider a multi-channel opportunistic communication system where the states of these channels evolve as independent and statistically identical Markov chains (the Gilbert-Elliot channel model). A user chooses one channel to sense and access in each slot and collects a reward determined by the state of the chosen channel. The objective is to design a sensing policy for channel selection to maximize the average reward. In this paper, we study the structure, optimality, and performance of the myopic sensing policy. We show that the myopic sensing policy has a simple robust structure that reduces channel selection to a counting procedure and obviates the need for knowing the channel transition probabilities. The optimality of this simple policy is established for the two-channel case and conjectured for the general case based on extensive simulations. The performance of the myopic sensing policy is analyzed, which, based on the optimality of myopic sensing, characterizes the maximum throughput of a multi-chan...

  17. Enhanced optical oxygen sensing using a newly synthesized ruthenium complex together with oxygen carriers.

    Science.gov (United States)

    Ertekin, Kadriye; Kocak, Suleyman; Sabih Ozer, M; Aycan, Sule; Cetinkaya, Bekir

    2003-11-12

    In this article, an emission based, simple and fast method is proposed for the determination of gaseous oxygen. A newly synthesized fluorophore, dichloro-{2,6-bis[1-(4-dimethylamino-phenylimino) ethyl]pyridine}ruthenium(II) has been used for oxygen sensing together with oxygen carrier perfluorochemicals (PFCs) in silicon matrix. It should be noted that the solubility of oxygen in fluorocarbons is about three to ten times large as that observed in the parent hydrocarbons or in water, respectively. Employed PFCs are chemically and biochemically inert, have high dissolution capacities for oxygen, and, once doped into sensing film, considerably enhance the response of sensing agent. PMID:18969220

  18. Multiple-input multiple-output symbol rate signal digital predistorter for non-linear multi-carrier satellite channels

    OpenAIRE

    Zenteno, Efrain; Piazza, Roberto; M. R. Bhavani Shankar; Rönnow, Daniel; Ottersten, Björn

    2015-01-01

    A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD ha...

  19. Orientation Sensing Using Multiple Passive RFID Tags

    DEFF Research Database (Denmark)

    Krigslund, Rasmus; Popovski, Petar; Pedersen, Gert Frølund

    2012-01-01

    Knowing the inclination of an object can be valuable information in a supply chain application, e.g. when handling orientation sensitive objects. In this work we present a method for sensing the inclination using Radio Frequency IDentification (RFID) technology. The method requires standard RFID...

  20. High power terahertz induced carrier multiplication in Silicon

    DEFF Research Database (Denmark)

    Tarekegne, Abebe Tilahun; Pedersen, Pernille Klarskov; Iwaszczuk, Krzysztof;

    2015-01-01

    The application of an intense THz field results a nonlinear transmission in high resistivity silicon. Upon increasing field strength, the transmission falls from 70% to 62% due to carrier generation through THz-induced impact ionization and subsequent absorption of the THz field by free electrons....

  1. Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David;

    We studied the THz conductivity of InGaN/GaN multiple quantum wells (MQWs)by time-resolved terahertz spectroscopy. A nonexponential carrier density decay is observed due to the restoration of a built-in piezoelectric field. Terahertz conductivity spectra show a nonmetallic behavior of the carriers....

  2. Reinforcement Learning Technique in Multiple Motorway Access Control Strategy Design

    OpenAIRE

    Veljanovska, Kostandina; M. Bombol, Kristi; Maher, Tomaž

    2010-01-01

    An appropriately designed motorway access control can decrease the total travel time spent in the system up to 30% and consequently increase the merging operations safety. To date, implemented traffic responsive motorway access control systems have been of local or regulatory type and not truly adaptive in the real sense of the meaning. Hence, traffic flow can be influenced positively by numerous intelligent transportation system (ITS) techniques. In this paper a contemporary approach is pres...

  3. Impact of sensing errors on the queueing delay and transmit power in cognitive radio access

    KAUST Repository

    Hamza, Doha R.

    2011-03-01

    We study a multiple-access system with a primary user (PU) and a secondary user (SU) utilizing the same frequency band and communicating with a common receiver. Both users transmit with a fixed transmission rate by employing a channel inversion power control scheme. The SU transmits with a certain probability that depends on the sensing outcome, its queue length and whether it has a new packet arrival. We consider the case of erroneous sensing. The goal of the SU is to find the optimal transmission scheduling policy so as to minimize its queueing delay under constraints on its average transmit power and the maximum tolerable primary outage probability caused by miss-detection. The access probabilities are obtained efficiently using linear programming. © 2011 IEEE.

  4. Performance of Multi-Carrier Access Schemes with Receiver Impairments in Down Link Indoor Environment

    DEFF Research Database (Denmark)

    Das, Suvra Sekhar; Rao, Raieshwar Kurapati; Prasad, Ramjee

    impairments, such as synchronization error and channel estimation errors. This work is targeted towards unified verification of performance of the schemes for different spreading gains, load conditions and sub carrier grouping schemes in quasi static realistic indoor channel environment in the presence of......Several multi-carrier spread spectrum (MC SS) access techniques which are based on Orthogonal Frequency Division Multiplexing (OFDM) have been developed till date. Different schemes are expected to perform optimally in different channel conditions. Their performance is also influenced by receiver...

  5. Marking sense of students' answers to multiple-choice questions

    Science.gov (United States)

    Dufresne, Robert J.; Leonard, William J.; Gerace, William J.

    2002-03-01

    A detailed example is used to illustrate the difficulties making sense of students' answers to multiple-choice questions. We explore how correct answers can be false indicators of student knowledge and understanding. We caution against excessive reliance on multiple-choice questions for instructional decisions.

  6. Orthogonal frequency division multiple access fundamentals and applications

    CERN Document Server

    Jiang, Tao; Zhang, Yan

    2010-01-01

    Supported by the expert-level advice of pioneering researchers, Orthogonal Frequency Division Multiple Access Fundamentals and Applications provides a comprehensive and accessible introduction to the foundations and applications of one of the most promising access technologies for current and future wireless networks. It includes authoritative coverage of the history, fundamental principles, key techniques, and critical design issues of OFDM systems. Covering various techniques of effective resource management for OFDM/OFDMA-based wireless communication systems, this cutting-edge reference:Add

  7. High accuracy localization of long term evolution based on a new multiple carrier noise model.

    Science.gov (United States)

    Lee, Wah Ching; Hung, Faan Hei; Tsang, Kim Fung; Wu, Chung Kit; Chi, Hao Ran; Chui, Kwok Tai; Lau, Wing Hong

    2014-01-01

    A high accuracy localization technique using Long Term Evolution (LTE) based on a new and accurate multiple carrier noise model has been developed. In the noise consideration, the LTE multiple carriers phase noise has been incorporated so that a new and accurate noise model is achieved. An experiment was performed to characterize the phase noise of carriers at 2 GHz. The developed noise model was incorporated into LTE localization analysis in a high traffic area in Hong Kong to evaluate the accuracy of localization. The evaluation and analysis reveals that the new localization method achieves an improvement of about 10% accuracy comparing to existing widely adopted schemes. PMID:25436658

  8. High Accuracy Localization of Long Term Evolution Based on a New Multiple Carrier Noise Model

    Directory of Open Access Journals (Sweden)

    Wah Ching Lee

    2014-11-01

    Full Text Available A high accuracy localization technique using Long Term Evolution (LTE based on a new and accurate multiple carrier noise model has been developed. In the noise consideration, the LTE multiple carriers phase noise has been incorporated so that a new and accurate noise model is achieved. An experiment was performed to characterize the phase noise of carriers at 2 GHz. The developed noise model was incorporated into LTE localization analysis in a high traffic area in Hong Kong to evaluate the accuracy of localization. The evaluation and analysis reveals that the new localization method achieves an improvement of about 10% accuracy comparing to existing widely adopted schemes.

  9. O2 sensing dynamics of BiFeO3 nanofibers: effect of minor carrier compensation.

    Science.gov (United States)

    Sobhan, Mushtaq; Xu, Qiang; Katoch, Akash; Anariba, Franklin; Kim, Sang Sub; Wu, Ping

    2015-05-01

    In this paper we investigate O(2) sensing dynamics in BiFeO(3) (BFO) nanofibers at various concentrations and temperatures, by using a combined experiment and computer simulation approach. Samples of pristine BFO, Ni-doped BFO, and Pb-doped BFO nanofibers were prepared. By incorporating Ni and Pb, additional acceptor states are introduced in BFO. Density functional theory calculations show that Ni prefers to substitute Fe site while Pb substitutes Bi site, resulting in a new deep donor originating from Ni interstitial defects, along with oxygen vacancies (V(o)). We find that both the sensing response and recovery time are shorter in samples made of pristine BFO nanofibers than in Ni- and Pb-doped nanofiber samples. We interpret the observed sensing dynamics through charge transport theory of the major (acceptors) and minor (donors) carriers, and found that the minor carrier compensation plays a significant role in determining the response and recovery time of the sensor device. This minor carrier compensation charge transport mechanism will provide new insights into more robust sensor development strategies, and into the research of ion-electron coupling in chemical dynamics of semiconductors. PMID:25850830

  10. ERP measures of semantic richness: The case of multiple senses

    Directory of Open Access Journals (Sweden)

    Vanessa eTaler

    2013-01-01

    Full Text Available Semantic richness refers to the amount of semantic information that a lexical item possesses. An important measure of semantic richness is the number of related senses that a word has (e.g., TABLE meaning a piece of furniture, a table of contents, to lay aside for future discussion, etc. We measured electrophysiological response to lexical items with many and few related senses in monolingual English-speaking young adults. Participants performed lexical decision on each item. Overall, high-sense words elicited shorter response latencies and smaller N400 amplitudes than low-sense words. These results constitute further evidence of the importance of semantic richness in lexical processing, and provide evidence that processing of multiple related senses begins as early as 200 milliseconds after stimulus onset.

  11. Multiple carrier transport in N-face indium nitride

    International Nuclear Information System (INIS)

    We present temperature (20-300 K) dependent multi-carrier measurements of electron species in N-face indium nitride. N-face InN samples were grown to different thicknesses (500-2000 nm) via plasma-assisted molecular beam epitaxy on C-face SiC substrates. Surface and bulk electron transport properties were extracted using a quantitative mobility spectrum analysis. Mobility of both bulk and surface electron species increase with film thickness. The temperature dependence of the mobility of both species differs to that of In-polar samples studied previously, while the mobility of surface electrons is more than twice that of In-polar samples with only a slight corresponding reduction in sheet concentration. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Multiple carriers of Q noble gases in primitive meteorites

    CERN Document Server

    Marrocchi, Yves; Estrade, Nicolas

    2015-01-01

    The main carrier of primordial heavy noble gases in chondrites is thought to be an organic phase, known as phase Q, whose precise characterization has resisted decades of investigation. Indirect techniques have revealed that phase Q might be composed of two subphases, one of them associated with sulfide. Here we provide experimental evidence that noble gases trapped within meteoritic sulfides present chemically- and thermally-driven behavior patterns that are similar to Q-gases. We therefore suggest that phase Q is likely composed of two subcomponents: carbonaceous phases and sulfides. In situ decay of iodine at concentrations levels consistent with those reported for meteoritic sulfides can reproduce the 129Xe excess observed for Q-gases relative to fractionated Solar Wind. We suggest that the Q-bearing sulfides formed at high temperature and could have recorded the conditions that prevailed in the chondrule-forming region(s).

  13. A novel Modulation Topology for Power Converters utilizing Multiple Carrier Signals

    DEFF Research Database (Denmark)

    Knott, Arnold; Pfaffinger, Gerhard; Andersen, Michael Andreas E.

    2008-01-01

    waveform at the output. The multiple carriers are fed into multiple comparators and their outputs are intelligently combined by logic gates to get a single signal to drive one power stage of any type of converter. This commutation distinguishes between the four members of the novel family: the first one...

  14. Optical code division multiple access fundamentals and applications

    CERN Document Server

    Prucnal, Paul R

    2005-01-01

    Code-division multiple access (CDMA) technology has been widely adopted in cell phones. Its astonishing success has led many to evaluate the promise of this technology for optical networks. This field has come to be known as Optical CDMA (OCDMA). Surveying the field from its infancy to the current state, Optical Code Division Multiple Access: Fundamentals and Applications offers the first comprehensive treatment of OCDMA from technology to systems.The book opens with a historical perspective, demonstrating the growth and development of the technologies that would eventually evolve into today's

  15. On Optimality of Myopic Sensing Policy with Imperfect Sensing in Multi-channel Opportunistic Access

    CERN Document Server

    Wang, Kehao; Liu, Quan; Agha, Khaldoun Al

    2012-01-01

    We consider the channel access problem under imperfect sensing of channel state in a multi-channel opportunistic communication system, where the state of each channel evolves as an independent and identically distributed Markov process. The considered problem can be cast into a restless multi-armed bandit (RMAB) problem that is of fundamental importance in decision theory. It is well-known that solving the RMAB problem is PSPACE-hard, with the optimal policy usually intractable due to the exponential computation complexity. A natural alternative is to consider the easily implementable myopic policy that maximizes the immediate reward but ignores the impact of the current strategy on the future reward. In this paper, we perform an analytical study on the optimality of the myopic policy under imperfect sensing for the considered RMAB problem. Specifically, for a family of generic and practically important utility functions, we establish the closed-form conditions under which the myopic policy is guaranteed to b...

  16. Space Division Multiple Access with a Sum Feedback Rate Constraint

    OpenAIRE

    Huang, Kaibin; Heath, Jr, Robert W.; Andrews, Jeffrey G.

    2006-01-01

    On a multi-antenna broadcast channel, simultaneous transmission to multiple users by joint beamforming and scheduling is capable of achieving high throughput, which grows double logarithmically with the number of users. The sum rate for channel state information (CSI) feedback, however, increases linearly with the number of users, reducing the effective uplink capacity. To address this problem, a novel space division multiple access (SDMA) design is proposed, where the sum feedback rate is up...

  17. Recombination in liquid filled ionisation chambers with multiple charge carrier species: Theoretical and numerical results

    International Nuclear Information System (INIS)

    Liquid-filled ionisation chambers (LICs) are used in radiotherapy for dosimetry and quality assurance. Volume recombination can be quite important in LICs for moderate dose rates, causing non-linearities in the dose rate response of these detectors, and needs to be corrected for. This effect is usually described with Greening and Boag models for continuous and pulsed radiation respectively. Such models assume that the charge is carried by two different species, positive and negative ions, each of those species with a given mobility. However, LICs operating in non-ultrapure mode can contain different types of electronegative impurities with different mobilities, thus increasing the number of different charge carriers. If this is the case, Greening and Boag models can be no longer valid and need to be reformulated. In this work we present a theoretical and numerical study of volume recombination in parallel-plate LICs with multiple charge carrier species, extending Boag and Greening models. Results from a recent publication that reported three different mobilities in an isooctane-filled LIC have been used to study the effect of extra carrier species on recombination. We have found that in pulsed beams the inclusion of extra mobilities does not affect volume recombination much, a behaviour that was expected because Boag formula for charge collection efficiency does not depend on the mobilities of the charge carriers if the Debye relationship between mobilities and recombination constant holds. This is not the case in continuous radiation, where the presence of extra charge carrier species significantly affects the amount of volume recombination. - Highlights: • Analytical extension of Greening and Boag theories to multiple charge carriers. • Detailed numerical study of process of volume recombination in LICs. • Recombination in pulsed beams is independent of number and mobilities of carriers. • Multiple charge carriers have a significant effect in continuous

  18. Iterative Fusion of Distributed Decisions over the Gaussian Multiple-Access Channel Using Concatenated BCH-LDGM Codes

    OpenAIRE

    Crespo PedroM; Garcia-Frias Javier; Del Ser Javier; Manjarres Diana; Gil-Lopez Sergio

    2011-01-01

    This paper focuses on the data fusion scenario where nodes sense and transmit the data generated by a source to a common destination, which estimates the original information from more accurately than in the case of a single sensor. This work joins the upsurge of research interest in this topic by addressing the setup where the sensed information is transmitted over a Gaussian Multiple-Access Channel (MAC). We use Low Density Generator Matrix (LDGM) codes in order to keep the correlati...

  19. Performance Analysis of WBAN MAC Protocol under Different Access Periods

    OpenAIRE

    Pervez Khan; Niamat Ullah; Md. Nasre Alam; Kyung Sup Kwak

    2015-01-01

    The IEEE 802.15.6 is a new standard on wireless body area network (WBAN) for short-range, extremely low power wireless communication with high data rates in the vicinity of, or inside, a human body. The standard defines two contention-based channel access schemes: slotted ALOHA and carrier sense multiple access with collision avoidance (CSMA/CA) using an alternative binary exponential backoff procedure. The standard supports quality of service (QoS) differentiation through user priorities and...

  20. MIMO Multiple Access Channel with an Arbitrarily Varying Eavesdropper

    CERN Document Server

    He, Xiang; Yener, Aylin

    2012-01-01

    A two-transmitter Gaussian multiple access wiretap channel with multiple antennas at each of the nodes is investigated. The channel matrices at the legitimate terminals are fixed and revealed to all the terminals, whereas the channel matrix of the eavesdropper is arbitrarily varying and only known to the eavesdropper. The secrecy degrees of freedom (s.d.o.f.) region under a strong secrecy constraint is characterized. A transmission scheme that orthogonalizes the transmit signals of the two users at the intended receiver and uses a single-user wiretap code is shown to be sufficient to achieve the s.d.o.f. region. The converse involves establishing an upper bound on a weighted-sum-rate expression. This is accomplished by using induction, where at each step one combines the secrecy and multiple-access constraints associated with an adversary eavesdropping a carefully selected group of sub-channels.

  1. Empirical formulae for excess noise factor with dead space for single carrier multiplication

    KAUST Repository

    Dehwah, Ahmad H.

    2011-09-01

    In this letter, two empirical equations are presented for the calculation of the excess noise factor of an avalanche photodiode for single carrier multiplication including the dead space effect. The first is an equation for calculating the excess noise factor when the multiplication approaches infinity as a function of parameters that describe the degree of the dead space effect. The second equation can be used to find the minimum value of the excess noise factor for any multiplication when the dead space effect is completely dominant, the so called "deterministic" limit. This agrees with the theoretically known equation for multiplications less than or equal to two. © 2011 World Scientific Publishing Company.

  2. Distributed Learning Policies for Power Allocation in Multiple Access Channels

    OpenAIRE

    Mertikopoulos, Panayotis; Belmega, Elena V.; Moustakas, Aris L.; Lasaulce, Samson

    2011-01-01

    We analyze the problem of distributed power allocation for orthogonal multiple access channels by considering a continuous non-cooperative game whose strategy space represents the users' distribution of transmission power over the network's channels. When the channels are static, we find that this game admits an exact potential function and this allows us to show that it has a unique equilibrium almost surely. Furthermore, using the game's potential property, we derive a modified version of t...

  3. Accessing Applications from Multiple File Servers in a Computer Network

    OpenAIRE

    J.S.J. Daka; J. S. Isaac

    2005-01-01

    This study proposes a technique of accessing applications from multiple file servers in a computer network that caters for a large user community. The technique is a step towards creating a computer network system that is simple to implement, scalable, easy to manage, transparent to the user and suitable for a university-type environment. The proposed technique has some features of a distributed system, but is not as complex. It is built around a very popular commercial ne...

  4. Code division multiple access signaling for modulated reflector technology

    Science.gov (United States)

    Briles, Scott D.

    2012-05-01

    A method and apparatus for utilizing code division multiple access in modulated reflectance transmissions comprises the steps of generating a phase-modulated reflectance data bit stream; modifying the modulated reflectance data bit stream; providing the modified modulated reflectance data bit stream to a switch that connects an antenna to an infinite impedance in the event a "+1" is to be sent, or connects the antenna to ground in the event a "0" or a "-1" is to be sent.

  5. Distributed Storage Codes Meet Multiple-Access Wiretap Channels

    CERN Document Server

    Papailiopoulos, Dimitris S

    2010-01-01

    We consider {\\it i)} the overhead minimization of maximum-distance separable (MDS) storage codes for the repair of a single failed node and {\\it ii)} the total secure degrees-of-freedom (S-DoF) maximization in a multiple-access compound wiretap channel. We show that the two problems are connected. Specifically, the overhead minimization for a single node failure of an {\\it optimal} MDS code, i.e. one that can achieve the information theoretic overhead minimum, is equivalent to maximizing the S-DoF in a multiple-access compound wiretap channel. Additionally, we show that maximizing the S-DoF in a multiple-access compound wiretap channel is equivalent to minimizing the overhead of an MDS code for the repair of a departed node. An optimal MDS code maps to a full S-DoF channel and a full S-DoF channel maps to an MDS code with minimum repair overhead for one failed node. We also state a general framework for code-to-channel and channel-to-code mappings and performance bounds between the two settings. The underlyin...

  6. Spatially continuous distributed fiber optic sensing using optical carrier based microwave interferometry.

    Science.gov (United States)

    Huang, Jie; Lan, Xinwei; Luo, Ming; Xiao, Hai

    2014-07-28

    This paper reports a spatially continuous distributed fiber optic sensing technique using optical carrier based microwave interferometry (OCMI), in which many optical interferometers with the same or different optical path differences are interrogated in the microwave domain and their locations can be unambiguously determined. The concept is demonstrated using cascaded weak optical reflectors along a single optical fiber, where any two arbitrary reflectors are paired to define a low-finesse Fabry-Perot interferometer. While spatially continuous (i.e., no dark zone), fully distributed strain measurement was used as an example to demonstrate the capability, the proposed concept may also be implemented on other types of waveguide or free-space interferometers and used for distributed measurement of various physical, chemical and biological quantities. PMID:25089493

  7. Remote Sensing Image Feature Extracting Based Multiple Ant Colonies Cooperation

    Directory of Open Access Journals (Sweden)

    Zhang Zhi-long

    2014-02-01

    Full Text Available This paper presents a novel feature extraction method for remote sensing imagery based on the cooperation of multiple ant colonies. First, multiresolution expression of the input remote sensing imagery is created, and two different ant colonies are spread on different resolution images. The ant colony in the low-resolution image uses phase congruency as the inspiration information, whereas that in the high-resolution image uses gradient magnitude. The two ant colonies cooperate to detect features in the image by sharing the same pheromone matrix. Finally, the image features are extracted on the basis of the pheromone matrix threshold. Because a substantial amount of information in the input image is used as inspiration information of the ant colonies, the proposed method shows higher intelligence and acquires more complete and meaningful image features than those of other simple edge detectors.

  8. Subsurface Imaging and Sensing of Charge Carrier Movements in the Earth’s Crust

    Science.gov (United States)

    Dahlgren, R.; Freund, F. T.; Lazarus, M.; Wang, J. S.; Rekenthaler, D.; Peters, R. D.; Duma, G.

    2009-12-01

    The DUSEL facility will enable unique opportunities for field experiments that would otherwise not be possible at surface facilities (Lesko, K.T., TAUP, 2007) and support a host of undergraduate and graduate educational projects. In this presentation, some of the proposed geophysics experiments will be described as part of the subsurface Imaging and Sensing (SIS) project to study charge carrier movement in crustal rock as a function of various perturbations. The electric conductivity of the Earth’s crust is dominated by positive hole charge carriers, e.g. mobile electron vacancy defects (EVD) in the oxygen anion sublattice of minerals that make up the bulk of crustal rocks. We are interested in (i) coupling of fundamental processes linked to the activation of additional EVDs in rocks deep in the crust subjected to tectonic stresses and the outflow of these charge carriers into the surrounding rocks, (ii) their manifestation across the electromagnetic spectrum and other measuands, (iii) induced forces that arise when these charge carriers are subjected to the episodic or daily magnetic field variations coming from geomagnetic storms or from the ionospheric current vortex, and (iv) in the movement of positive holes in the shallow crust when a thunderstorm system drifts overhead, dragging along a charge cloud in the ground. We propose to conduct active rock stressing experiments in situ using expanding grout technique (performing electrical, electromagnetic, and VolksMeter tilt measurements) and to monitor the electric and magnetic field variations penetrating into the Earth’s crust. Additionally optical phenomena will be investigated (anomalous infrared signatures, visible light arising from atomic oxygen and corona discharge, and infrared imaging). If budget permits, measurement of changes of acoustic velocity, evolution of chemical species (H2, O*, Rn, etc) and radar reflectivity as a function of stresses will also be attempted. We propose to study the charge

  9. A Soft Sensing-Based Cognitive Access Scheme Exploiting Primary Feedback

    OpenAIRE

    Arafa Ahmed, M.; Seddik, Karim G.; Sultan Ahmed, K.; Elbatt, Tamer; El-Sherif, Amr

    2012-01-01

    Cognitive Radio International audience In this paper, we examine a cognitive spectrum access scheme in which secondary users exploit the primary feedback information. We consider an overlay secondary network employing a random access scheme in which secondary users access the channel by certain access probabilities that are function of the spectrum sensing metric. In setting our problem, we assume that secondary users can eavesdrop on the primary link's feedback. We study the cognitive ...

  10. Registration and Fusion of Multiple Source Remotely Sensed Image Data

    Science.gov (United States)

    LeMoigne, Jacqueline

    2004-01-01

    Earth and Space Science often involve the comparison, fusion, and integration of multiple types of remotely sensed data at various temporal, radiometric, and spatial resolutions. Results of this integration may be utilized for global change analysis, global coverage of an area at multiple resolutions, map updating or validation of new instruments, as well as integration of data provided by multiple instruments carried on multiple platforms, e.g. in spacecraft constellations or fleets of planetary rovers. Our focus is on developing methods to perform fast, accurate and automatic image registration and fusion. General methods for automatic image registration are being reviewed and evaluated. Various choices for feature extraction, feature matching and similarity measurements are being compared, including wavelet-based algorithms, mutual information and statistically robust techniques. Our work also involves studies related to image fusion and investigates dimension reduction and co-kriging for application-dependent fusion. All methods are being tested using several multi-sensor datasets, acquired at EOS Core Sites, and including multiple sensors such as IKONOS, Landsat-7/ETM+, EO1/ALI and Hyperion, MODIS, and SeaWIFS instruments. Issues related to the coregistration of data from the same platform (i.e., AIRS and MODIS from Aqua) or from several platforms of the A-train (i.e., MLS, HIRDLS, OMI from Aura with AIRS and MODIS from Terra and Aqua) will also be considered.

  11. Accessing Applications from Multiple File Servers in a Computer Network

    Directory of Open Access Journals (Sweden)

    J. S.J. Daka

    2005-01-01

    Full Text Available This study proposes a technique of accessing applications from multiple file servers in a computer network that caters for a large user community. The technique is a step towards creating a computer network system that is simple to implement, scalable, easy to manage, transparent to the user and suitable for a university-type environment. The proposed technique has some features of a distributed system, but is not as complex. It is built around a very popular commercial network operating system called NetWare.

  12. Optical multiple access techniques for on-board routing

    Science.gov (United States)

    Mendez, Antonio J.; Park, Eugene; Gagliardi, Robert M.

    1992-01-01

    The purpose of this research contract was to design and analyze an optical multiple access system, based on Code Division Multiple Access (CDMA) techniques, for on board routing applications on a future communication satellite. The optical multiple access system was to effect the functions of a circuit switch under the control of an autonomous network controller and to serve eight (8) concurrent users at a point to point (port to port) data rate of 180 Mb/s. (At the start of this program, the bit error rate requirement (BER) was undefined, so it was treated as a design variable during the contract effort.) CDMA was selected over other multiple access techniques because it lends itself to bursty, asynchronous, concurrent communication and potentially can be implemented with off the shelf, reliable optical transceivers compatible with long term unattended operations. Temporal, temporal/spatial hybrids and single pulse per row (SPR, sometimes termed 'sonar matrices') matrix types of CDMA designs were considered. The design, analysis, and trade offs required by the statement of work selected a temporal/spatial CDMA scheme which has SPR properties as the preferred solution. This selected design can be implemented for feasibility demonstration with off the shelf components (which are identified in the bill of materials of the contract Final Report). The photonic network architecture of the selected design is based on M(8,4,4) matrix codes. The network requires eight multimode laser transmitters with laser pulses of 0.93 ns operating at 180 Mb/s and 9-13 dBm peak power, and 8 PIN diode receivers with sensitivity of -27 dBm for the 0.93 ns pulses. The wavelength is not critical, but 830 nm technology readily meets the requirements. The passive optical components of the photonic network are all multimode and off the shelf. Bit error rate (BER) computations, based on both electronic noise and intercode crosstalk, predict a raw BER of (10 exp -3) when all eight users are

  13. OVERSAMPLED CHAOTIC BINARY SEQUENCES FOR MULTIPLE ACCESS COMMUNICATION

    Institute of Scientific and Technical Information of China (English)

    Zhang Hongtao; Wang Huiyun; Ding Runtao

    2002-01-01

    Noise interference and multiple access interference are the main impairment to the performance of DS/CDMA communication system. This letter presents that OverSampled Chaotic Map (OSCM) binary sequences are secure as spreading sequences, and based on the optimal quantizing method, the BER performance of the system has been derived in detail, the internal relationships among the number of users, the power of noise and the length of code chips are revealed in mathematical formulae. The performance of the system can be improved by employing these formulae. Numerical results conform the efficiency of discussion in this letter.

  14. Sequential Joint Spectrum Sensing and Channel Estimation for Dynamic Spectrum Access

    OpenAIRE

    Yilmaz, Yasin; Guo, Ziyu; Wang, Xiaodong

    2014-01-01

    Dynamic spectrum access under channel uncertainties is considered. With the goal of maximizing the secondary user (SU) throughput subject to constraints on the primary user (PU) outage probability we formulate a joint problem of spectrum sensing and channel state estimation. The problem is cast into a sequential framework since sensing time minimization is crucial for throughput maximization. In the optimum solution, the sensing decision rule is coupled with the channel estimator, making the ...

  15. 78 FR 2600 - Special Access for Price Cap Local Exchange Carriers; AT&T Corporation Petition for Rulemaking To...

    Science.gov (United States)

    2013-01-11

    ... providers' market shares, supply and demand elasticity, and carriers' cost structures, size, and access to... entry, the availability of reasonably substitutable services, the level of demand elasticity, and..., such as how to define markets or analyze demand and supply responsiveness, have been made irrelevant...

  16. 77 FR 57504 - Special Access for Price Cap Local Exchange Carriers; AT&T Corporation Petition for Rulemaking To...

    Science.gov (United States)

    2012-09-18

    ... flexibility grants for special access services, pending adoption of new rules. The Commission suspends its... hindering investment and innovation. Price cap carriers argue that they are still subject to burdensome... throughout an MSA. We therefore suspend, on an interim basis, the operation of those rules pending...

  17. Some New Results on the Multiple-AccessWiretap Channel

    Directory of Open Access Journals (Sweden)

    Bin Dai

    2014-08-01

    Full Text Available In this paper, some new results on the multiple-access wiretap channel (MAC-WT are provided. Specifically, first, we investigate the degraded MAC-WT, where two users transmit their corresponding confidential messages (no common message to a legitimate receiver via a multiple-access channel (MAC, while a wiretapper wishes to obtain the messages via a physically degraded wiretap channel. The secrecy capacity region of this model is determined for both the discrete memoryless and Gaussian cases. For the Gaussian case, we find that this secrecy capacity region is exactly the same as the achievable secrecy rate region provided by Tekin and Yener, i.e., Tekin–Yener’s achievable region is exactly the secrecy capacity region of the degraded Gaussian MAC-WT. Second, we study a special Gaussian MAC-WT, and find the power control for two kinds of optimal points (max-min point and single user point on the secrecy rate region of this special Gaussian model.

  18. Multiple Detectors Based Analytical Performance of Spectrum Sensing

    Directory of Open Access Journals (Sweden)

    S.Taruna

    2014-03-01

    Full Text Available A key challenge in operating cognitive radios (CRs in a self-organizing (ad hoc network is how to adaptively and efficiently utilize spectrum resources keeping in mind that no interference is caused to primary users and also that no spectrum is rendered unused when a secondary user is waiting for access. Detecting the spectrum holes using one detector can be insufficient for increasing secondary users. In the proposed paper, an attempt has been made to implement multiple detectors to improve the probability of detection by increasing the SNR. Multiple detector technique has been implemented using various methods like Selection Combining (SC, Equal Gain Combining (EGC, and Maximum Ratio Combining (MRC, to discover which of these methods provide better increase in SNR as the numbers of detectors are increased.

  19. Multiple hot-carrier collection in photo-excited graphene Moiré superlattices

    Science.gov (United States)

    Wu, Sanfeng; Wang, Lei; Lai, You; Shan, Wen-Yu; Aivazian, Grant; Zhang, Xian; Taniguchi, Takashi; Watanabe, Kenji; Xiao, Di; Dean, Cory; Hone, James; Li, Zhiqiang; Xu, Xiaodong

    2016-01-01

    In conventional light-harvesting devices, the absorption of a single photon only excites one electron, which sets the standard limit of power-conversion efficiency, such as the Shockley-Queisser limit. In principle, generating and harnessing multiple carriers per absorbed photon can improve efficiency and possibly overcome this limit. We report the observation of multiple hot-carrier collection in graphene/boron-nitride Moiré superlattice structures. A record-high zero-bias photoresponsivity of 0.3 A/W (equivalently, an external quantum efficiency exceeding 50%) is achieved using graphene’s photo-Nernst effect, which demonstrates a collection of at least five carriers per absorbed photon. We reveal that this effect arises from the enhanced Nernst coefficient through Lifshtiz transition at low-energy Van Hove singularities, which is an emergent phenomenon due to the formation of Moiré minibands. Our observation points to a new means for extremely efficient and flexible optoelectronics based on van der Waals heterostructures.

  20. Remote Sensing Open Access Journal: Leading a New Paradigm in Publishing

    Directory of Open Access Journals (Sweden)

    Prasad S. Thenkabail

    2011-12-01

    Full Text Available Remote Sensing is a pathfinding open access journal providing great opportunities for the growing community of remote sensing and geoscience scientists and practitioners to publish high quality research and practical papers expeditiously. It is a journal keeping up with the changing times we live in: open access, instant access, free access, and global access from whichever precise latitude and longitude you live in on the planet Earth or for that matter anywhere in space as long as we have internet access! So, open access journals are breaking many paradigms and setting forth new ones that will soon become the norm as we advance into the twenty-first century. The days of inordinate delays in publishing good science research articles are fast disappearing with open access journals. In remote sensing and geoscience, Remote Sensing (http://www.mdpi.com/journal/remotesensing/ is one of the pioneers, thanks to the vision of Dr. Shu-Kun Lin, the publisher. It started in the year 2009 with headquarters in Basel, Switzerland and a branch office in Beijing, China. It will soon complete Volume 3 by the end of 2011.

  1. Stability Properties of Network Diversity Multiple Access with Multiple-Antenna Reception and Imperfect Collision Multiplicity Estimation

    Directory of Open Access Journals (Sweden)

    Ramiro Samano-Robles

    2013-01-01

    Full Text Available In NDMA (network diversity multiple access, protocol-controlled retransmissions are used to create a virtual MIMO (multiple-input multiple-output system, where collisions can be resolved via source separation. By using this retransmission diversity approach for collision resolution, NDMA is the family of random access protocols with the highest potential throughput. However, several issues remain open today in the modeling and design of this type of protocol, particularly in terms of dynamic stable performance and backlog delay. This paper attempts to partially fill this gap by proposing a Markov model for the study of the dynamic-stable performance of a symmetrical and non-blind NDMA protocol assisted by a multiple-antenna receiver. The model is useful in the study of stability aspects in terms of the backlog-user distribution and average backlog delay. It also allows for the investigation of the different states of the system and the transition probabilities between them. Unlike previous works, the proposed approach considers the imperfect estimation of the collision multiplicity, which is a crucial process to the performance of NDMA. The results suggest that NDMA improves not only the throughput performance over previous solutions, but also the average number of backlogged users, the average backlog delay and, in general, the stability of random access protocols. It is also shown that when multiuser detection conditions degrade, ALOHA-type backlog retransmission becomes relevant to the stable operation of NDMA.

  2. A Frequency—Diversity Spread—Spectrum Multiple Access System with Random Signature Sequences

    Institute of Scientific and Technical Information of China (English)

    CaoYewen; XiangHaige

    1995-01-01

    A new scheme for the spread-spectrum multiple access system named Frequency-Diver-sity Spread-Spectrum Multiple Access(FD-DDMA)system,is proposed.In this FD-SSMA sys-tem,the same information will be modulated on a group of mutually orthogonal frequency compo-nents(carriers)with a random signature sequence at the same time,and it will be demodulated by a coherent receiver for every component and then incorporated (ad if using frequency diversity)on the basis of this random sequence.The spectrum of the modulated signal is very close to that of a white-noise in a wider frequency band due to orthogonality for all frequency components and prop-erty of the random sequence,the system becomes a spread-spectrum one.The (Inverse)Fast Froier Transform(IFFT,FFT)can be applied in the system ,which provides additional flexibility.The performance in an asynchronous mode,such as ability of multiusers,anti-interferences ,is an-alyzed.

  3. Making Authentic Data Accessible: The Sensing the Environment Inquiry Module

    Science.gov (United States)

    Griffis, Kathy; Thadani, Vandana; Wise, Joe

    2008-01-01

    We report on the development of a middle school life sciences inquiry module, Sensing the Environment. This "data-enriched" inquiry module includes a series of activities exploring the nature of science, photosynthesis, transpiration, and natural selection, which culminates in students' querying authentic environmental data to support a scientific…

  4. Hot carrier multiplication on graphene/TiO2 Schottky nanodiodes

    Science.gov (United States)

    Lee, Young Keun; Choi, Hongkyw; Lee, Hyunsoo; Lee, Changhwan; Choi, Jin Sik; Choi, Choon-Gi; Hwang, Euyheon; Park, Jeong Young

    2016-06-01

    Carrier multiplication (i.e. generation of multiple electron–hole pairs from a single high-energy electron, CM) in graphene has been extensively studied both theoretically and experimentally, but direct application of hot carrier multiplication in graphene has not been reported. Here, taking advantage of efficient CM in graphene, we fabricated graphene/TiO2 Schottky nanodiodes and found CM-driven enhancement of quantum efficiency. The unusual photocurrent behavior was observed and directly compared with Fowler’s law for photoemission on metals. The Fowler’s law exponent for the graphene-based nanodiode is almost twice that of a thin gold film based diode; the graphene-based nanodiode also has a weak dependence on light intensity—both are significant evidence for CM in graphene. Furthermore, doping in graphene significantly modifies the quantum efficiency by changing the Schottky barrier. The CM phenomenon observed on the graphene/TiO2 nanodiodes can lead to intriguing applications of viable graphene-based light harvesting.

  5. Diffuse optical tomography based on multiple access coding

    Science.gov (United States)

    Wang, Xuefeng; Wang, Yuanqing; Su, Jinshan; Xu, Fan

    2016-04-01

    Diffuse optical tomography (DOT) has the advantages of being a non-invasive, non-radiation emitting and low-cost biological tissue imaging method, and many recent studies have employed this technology. By improving the spatial resolution and developing a new method for constantly improving the flexibility of the experimental device, the system can perform data acquisition rapidly and conveniently. We propose a method for rapid data acquisition based on multiple access coding; it can acquire data in parallel, and the system can greatly improve the temporal resolution of the data acquisition step in diffuse optical tomography thereafter. We simulate the encoding and decoding process of the source-detector pair and successfully isolate the source signal from mixed signals. The DOT image reconstruction highlight the effectiveness of the system.

  6. Rate and Power Allocation in Fading Multiple Access Channels

    CERN Document Server

    ParandehGheibi, Ali; Ozdaglar, Asuman; Medard, Muriel

    2008-01-01

    We consider the problem of rate and power allocation in a fading multiple-access channel. Our objective is to obtain rate and power allocation policies that maximize a utility function defined over average transmission rates. In contrast with the literature, which focuses on the linear case, we present results for general concave utility functions. We consider two cases. In the first case, we assume that power control is possible and channel statistics are known. In this case, we show that the optimal policies can be obtained greedily by maximizing a linear utility function at each channel state. In the second case, we assume that power control is not possible and channel statistics are not available. In this case, we define a greedy rate allocation policy and provide upper bounds on the performance difference between the optimal and the greedy policy. Our bounds highlight the dependence of the performance difference on the channel variations and the structure of the utility function.

  7. Dynamic Rate Allocation in Fading Multiple-access Channels

    CERN Document Server

    ParandehGheibi, Ali; Ozdaglar, Asuman; Medard, Muriel

    2008-01-01

    We consider the problem of rate allocation in a fading Gaussian multiple-access channel (MAC) with fixed transmission powers. Our goal is to maximize a general concave utility function of transmission rates over the throughput capacity region. In contrast to earlier works in this context that propose solutions where a potentially complex optimization problem must be solved in every decision instant, we propose a low-complexity approximate rate allocation policy and analyze the effect of temporal channel variations on its utility performance. To the best of our knowledge, this is the first work that studies the tracking capabilities of an approximate rate allocation scheme under fading channel conditions. We build on an earlier work to present a new rate allocation policy for a fading MAC that implements a low-complexity approximate gradient projection iteration for each channel measurement, and explicitly characterize the effect of the speed of temporal channel variations on the tracking neighborhood of our p...

  8. Carrier localization effect in polarized InGaN multiple quantum wells

    International Nuclear Information System (INIS)

    Carrier localization effects in polarized InGaN/GaN multiple quantum wells (MQWs) were investigated as a function of well width, d, and In content, x. Using photoreflectance (PR), photoluminescence (PL), PL excitation (PLE), selective excitation of PL, PL excitation power, and time-resolved PL spectroscopy, the dominance of the localization effect against the built-in field effect on carrier recombination dynamics in InxGa1-xN MQWs of different well width (d = 2.0-4.0 nm, x ∼ 0.15) and In content (x ∼ 0.22-0.27, d = 2.5 nm) was revealed. Based on the modeling of the PL spectra by Monte Carlo simulation of exciton hopping and the spectroscopic reference provided by PR, increased In content and well width were found to increase the band potential fluctuations and carrier localization depth. The density of localized states deduced from the simulation was found to be in a fair agreement with the PLE data. The built-in field strength in InGaN QWs containing 15% of In was estimated to be of 0.5 MV/cm. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Carrier localization effect in polarized InGaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Zukauskas, A.; Kazlauskas, K.; Tamulaitis, G.; Mickevicius, J.; Jursenas, S.; Kurilcik, G.; Miasojedovas, S. [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9, Build. III, 10222 Vilnius (Lithuania); Springis, M.; Tale, I. [Institute of Solid State Physics, University of Latvia, Kengaraga iela 8, Riga 1063 (Latvia); Cheng, Yung-Chen; Wang, Hsiang-Chen; Huang, Chi-Feng; Yang, C.C. [Graduate Institute of Electro-Optical Engineering, National Taiwan University, 1 Roosevelt Road, Sec. 4, Taipei (Taiwan)

    2005-05-01

    Carrier localization effects in polarized InGaN/GaN multiple quantum wells (MQWs) were investigated as a function of well width, d, and In content, x. Using photoreflectance (PR), photoluminescence (PL), PL excitation (PLE), selective excitation of PL, PL excitation power, and time-resolved PL spectroscopy, the dominance of the localization effect against the built-in field effect on carrier recombination dynamics in In{sub x}Ga{sub 1-x}N MQWs of different well width (d = 2.0-4.0 nm, x {approx} 0.15) and In content (x {approx} 0.22-0.27, d = 2.5 nm) was revealed. Based on the modeling of the PL spectra by Monte Carlo simulation of exciton hopping and the spectroscopic reference provided by PR, increased In content and well width were found to increase the band potential fluctuations and carrier localization depth. The density of localized states deduced from the simulation was found to be in a fair agreement with the PLE data. The built-in field strength in InGaN QWs containing 15% of In was estimated to be of 0.5 MV/cm. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. A QUANTUM MULTIPLE ACCESS COMMUNICATIONS SCHEME USING ORBITAL ANGULAR MOMENTUM

    Institute of Scientific and Technical Information of China (English)

    Dong Xiaoliang; Zhao Shengmei; Zheng Baoyu

    2013-01-01

    We propose a quantum multiple access communications scheme using Orbital Angular Momentum (OAM) sector states in the paper.In the scheme,each user has an individual modified Poincare Bloch sphere and encodes his information with his own corresponding sector OAM states.A prepared entangled photon pairs are separated at transmitter and receiver.At the transmitter,each user encodes his information with the sector OAM states on the photons and the superposition of the different sector OAM states is carried by the photons.Then the photons are transmitted through quantum noiseless channel to the receiver.At the receiver,each user could retrieve his information by coincidently measuring the transmitted photons with the receiver side photons which are modulated by a special prepared measurement basis.The theoretical analysis and the numerical simulations show that each user could get his information from the superposition state without error.It seems that this scheme provides a novel method for quantum multiple users communications.

  11. Mitigation of multiple access interference using two-dimensional modified double weight codes for optical code division multiple access systems

    Science.gov (United States)

    Jamil Abdullah, Amir Razif Arief; Aljunid, Syed Alwee; Safar, Anuar Mat; Nordin, Junita Mohd; Ahmad, R. Badlishah

    2012-06-01

    We proposed newly two-dimensional (2-D) spectral amplitude coding optical code division multiple access (OCDMA) scheme using modified double weight (MDW) code capable of suppressing phase-induced intensity noise (PIIN). The architecture of the spectral/spatial MDW OCDMA system with the property of multi-access interference cancellation is presented. The proposed code exhibits good cross-correlation property. At the optimized data transmission rate of 0.745 Gbps, 2-D MDW, M=63, N=3, reaches maximum cardinality of 200% increases compared to 2-D perfect difference code, M=57, N=3. The performance is severely deteriorated if the data rate further increases above 0.745 Gbps. The proposed code meets the optical transmission requirements at 10-9 bit error rate error floor, with lowest effective transmitted power (Psr), -17.5 dBm, in comparison to the others through minimizing interference noise that result in PIIN suppression. The proposed system reaches optimum requirements performance in terms of cardinality, data transmission rate, and low effective transmitted power.

  12. A satellite mobile communication system based on Band-Limited Quasi-Synchronous Code Division Multiple Access (BLQS-CDMA)

    Science.gov (United States)

    Degaudenzi, R.; Elia, C.; Viola, R.

    1990-01-01

    Discussed here is a new approach to code division multiple access applied to a mobile system for voice (and data) services based on Band Limited Quasi Synchronous Code Division Multiple Access (BLQS-CDMA). The system requires users to be chip synchronized to reduce the contribution of self-interference and to make use of voice activation in order to increase the satellite power efficiency. In order to achieve spectral efficiency, Nyquist chip pulse shaping is used with no detection performance impairment. The synchronization problems are solved in the forward link by distributing a master code, whereas carrier forced activation and closed loop control techniques have been adopted in the return link. System performance sensitivity to nonlinear amplification and timing/frequency synchronization errors are analyzed.

  13. Coalitional Games in Partition Form for Joint Spectrum Sensing and Access in Cognitive Radio Networks

    CERN Document Server

    Saad, Walid; Zheng, Rong; Hjørungnes, Are; Başar, Tamer; Poor, H Vincent

    2012-01-01

    Unlicensed secondary users (SUs) in cognitive radio networks are subject to an inherent tradeoff between spectrum sensing and spectrum access. Although each SU has an incentive to sense the primary user (PU) channels for locating spectrum holes, this exploration of the spectrum can come at the expense of a shorter transmission time, and, hence, a possibly smaller capacity for data transmission. This paper investigates the impact of this tradeoff on the cooperative strategies of a network of SUs that seek to cooperate in order to improve their view of the spectrum (sensing), reduce the possibility of interference among each other, and improve their transmission capacity (access). The problem is modeled as a coalitional game in partition form and an algorithm for coalition formation is proposed. Using the proposed algorithm, the SUs can make individual distributed decisions to join or leave a coalition while maximizing their utilities which capture the average time spent for sensing as well as the capacity achi...

  14. Cyclostationary Beacon for Assisting Spectrum Sensing in Opportunistic Spectrum Access

    Directory of Open Access Journals (Sweden)

    Thomas Kaiser

    2011-03-01

    Full Text Available Cognitive radio is a promising solution to the problem of spectrum scarcity by means of allowing secondary radio networks access the spectrum opportunistically. One of the most important issues in cognitive radio is how to detect existing over-the-air signals reliably. Not a few literatures have reported that signals could be detected via their inherent or embedded properties. However, this approach may not be reliable and flexible enough for all kinds of signals with different modulation types. In this paper, we propose a type of multitone beacon signal carrying cyclostationary signatures, which is able to enhance the reliability and efficiency of signal detection at low cost of spectrum overhead. This beacon not only can indicate the presence or absence of user signal but also can reveal some other information helpful to opportunistic spectrum access through the information bits carried on its cyclostationary signatures. It could be applied to device/network identification, indication of spectrum allocation and spectrum rendezvous, both for primary and secondary users. Based on our previous work reported in [1], the generation and detection algorithm of the beacon signal are extended with improved spectral efficiency. Performance is discussed with both computer simulation and testbed validation.

  15. Investigation of Coherent Multicarrier Code Division Multiple Access for Optical Access Networks

    Directory of Open Access Journals (Sweden)

    Ali Tamini

    2016-01-01

    Full Text Available Orthogonal frequency division multiplexing (OFDM has proved to be a promising technique to increase the reach and bit rate both in long‑haul communications and in passive optical networks. This paper, for the first time, investigates the use of OFDM combined with electrical CDMA in presence of coherent detection as a multiple access scheme. The proposed multicarrier‑CDMA system is simulated using Walsh‑Hadamard codes and its performance is compared to that of coherent WDM-OFDM system in terms of bit‑error‑rate and bandwidth efficiency. It is shown that MC‑CDMA benefits from better spectral efficiency while its performance slightly deteriorates in comparison to WDM-OFDM when the number of users is increased.

  16. Multiple Access Techniques for Next Generation Wireless: Recent Advances and Future Perspectives

    Directory of Open Access Journals (Sweden)

    Shree Krishna Sharma

    2016-01-01

    Full Text Available The advances in multiple access techniques has been one of the key drivers in moving from one cellular generation to another. Starting from the first generation, several multiple access techniques have been explored in different generations and various emerging multiplexing/multiple access techniques are being investigated for the next generation of cellular networks. In this context, this paper first provides a detailed review on the existing Space Division Multiple Access (SDMA related works. Subsequently, it highlights the main features and the drawbacks of various existing and emerging multiplexing/multiple access techniques. Finally, we propose a novel concept of clustered orthogonal signature division multiple access for the next generation of cellular networks. The proposed concept envisions to employ joint antenna coding in order to enhance the orthogonality of SDMA beams with the objective of enhancing the spectral efficiency of future cellular networks.

  17. An Enhanced Multiple Random Access Scheme for Satellite Communications

    CERN Document Server

    Bui, Huyen-Chi; Boucheret, Marie-Laure

    2011-01-01

    In this paper, we introduce Multi-Slots Coded ALOHA (MuSCA) as a multiple random access method for satellite communications. This scheme can be considered as a generalization of the Contention Resolution Diversity Slotted Aloha (CRDSA) mechanism. Instead of transmitting replicas, this system replaces them by several parts of a single word of an error correcting code. It is also different from Coded Slotted ALOHA (CSA) as the assumption of destructive collisions is not adopted. In MuSCA, the entity in charge of the decoding mechanism collects all bursts of the same user (including the interfered slots) before decoding and implements a successive interference cancellation (SIC) process to remove successfully decoded signals. Simulations show that for a frame of 100 slots, the achievable total normalized throughput is greater than 1.25 and 1.4 for a frame of 500 slots, resulting in a gain of 80% and 75% with respect to CRDSA and CSA respectively. This paper is a first analysis of the proposed scheme and opens se...

  18. Enhancing Access to Land Remote Sensing Data through Mainstream Social Media Channels

    Science.gov (United States)

    Sohre, T.; Maiersperger, T.

    2011-12-01

    Social media tools are changing the way that people discover information, communicate, and collaborate. Government agencies supporting the Land Remote Sensing user community have begun taking advantage of standard social media tools and capabilities. National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) data centers have started providing outreach utilizing services including Facebook, Twitter, and YouTube videos. Really Simple Syndication (RSS) Feeds have become more standard means of sharing information, and a DataCasting tool was created as a NASA Technology Infusion effort to make RSS-based technology for accessing Earth Science information available. The United States Geological Survey (USGS) has also started using social media to allow the community access to news feeds and real-time earthquake alerts; listen to podcasts; get updates on new USGS publications, videos, and photographs; and more. Twitter feeds have been implemented in 2011 for the USGS Land Cover and Landsat user communities. In early 2011, the NASA Land Processes Distributed Active Archive Center (LP DAAC) user working group suggested the investigation of concepts for creating and distributing "bundles" of data, which would aggregate theme-based data sets from multiple sources. The LP DAAC is planning to explore the use of standard social bookmarking tools to support community developed bundles through the use of tools such as Delicious, Digg, or StumbleUpon. This concept would allow science users to organize and discover common links to data resources based on community developed tags, or a folksonomy. There are challenges that will need to be addressed such as maintaining the quality of tags but a social bookmarking system may have advantages over traditional search engines or formal ontologies for identifying and labeling various data sets relevant to a theme. As classification is done by the community of scientists who understand the data, the tagged data sets

  19. Blind Identification of Distributed Antenna Systems with Multiple Carrier Frequency Offsets

    CERN Document Server

    Yu, Yuanning; Poor, H Vincent

    2007-01-01

    In spatially distributed multiuser antenna systems, the received signal contains multiple carrier-frequency offsets (CFOs) arising from mismatch between the oscillators of transmitters and receivers. This results in a time-varying rotation of the data constellation, which needs to be compensated at the receiver before symbol recovery. In this paper, a new approach for blind CFO estimation and symbol recovery is proposed. The received base-band signal is over-sampled, and its polyphase components are used to formulate a virtual Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system estimation techniques, the system response can be estimated and decoupled versions of the user symbols can be recovered, each one of which contains a distinct CFO. By applying a decision feedback Phase Lock Loop (PLL), the CFO can be mitigated and the transmitted symbols can be recovered. The estimated MIMO system response provides information about the CFOs that can be used to initialize the PLL, speed up its ...

  20. PERFORMANCE OF OPPORTUNISTIC SPECTRUM ACCESS WITH SENSING ERROR IN COGNITIVE RADIO AD HOC NETWORKS

    Directory of Open Access Journals (Sweden)

    N. ARMI

    2012-04-01

    Full Text Available Sensing in opportunistic spectrum access (OSA has a responsibility to detect the available channel by performing binary hypothesis as busy or idle states. If channel is busy, secondary user (SU cannot access and refrain from data transmission. SU is allowed to access when primary user (PU does not use it (idle states. However, channel is sensed on imperfect communication link. Fading, noise and any obstacles existed can cause sensing errors in PU signal detection. False alarm detects idle states as a busy channel while miss-identification detects busy states as an idle channel. False detection makes SU refrain from transmission and reduces number of bits transmitted. On the other hand, miss-identification causes SU collide to PU transmission. This paper study the performance of OSA based on the greedy approach with sensing errors by the restriction of maximum collision probability allowed (collision threshold by PU network. The throughput of SU and spectrum capacity metric is used to evaluate OSA performance and make comparisons to those ones without sensing error as function of number of slot based on the greedy approach. The relations between throughput and signal to noise ratio (SNR with different collision probability as well as false detection with different SNR are presented. According to the obtained results show that CR users can gain the reward from the previous slot for both of with and without sensing errors. It is indicated by the throughput improvement as slot number increases. However, sensing on imperfect channel with sensing errors can degrade the throughput performance. Subsequently, the throughput of SU and spectrum capacity improves by increasing maximum collision probability allowed by PU network as well. Due to frequent collision with PU, the throughput of SU and spectrum capacity decreases at certain value of collision threshold. Computer simulation is used to evaluate and validate these works.

  1. Characterisation of multiple carrier transport in indium nitride grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Quantitative mobility spectrum analysis (QMSA) was performed on multiple magnetic field Hall effect measurements of indium nitride grown by molecular beam epitaxy. This enables two clearly distinct electron species to be identified, which are attributed to the bulk and a surface accumulation layer. In this material, single magnetic field data corresponds to neither electron species, as both contribute significantly to the total conduction. The bulk electron distribution has an extracted average Hall mobility of 3570 cm2/(Vs) at 300 K with a concentration of 1.5 x 1017 cm-3, while the surface electrons have sheet charge density that is an order of magnitude higher than previously reported surface concentrations. The high quality bulk characteristics revealed emphasise the importance of using multi-carrier analysis when performing transport measurements on InN. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

  2. Precise relative positioning of multiple moving platforms using GPS carrier phase observables

    Science.gov (United States)

    Luo, Ning

    Precise relative positioning of multiple moving platforms using GPS carrier phase observables has numerous applications. The essential point for this research is the fast and reliable OTF carrier phase ambiguity resolution. Algorithms for single baseline resolution cannot provide optimal performance for this application because it does not make use of the redundancy available in the configuration of multiple moving platforms. In this thesis, a novel method called MultiKin is proposed for OTF ambiguity resolution for multiple moving platforms. First, MultiKin applies Delaunay triangulation to select necessary baselines and to build an optimal structure of ambiguity constraints. Second, it improves the reliability of the OTF ambiguity resolution of single-baselines by optimizing the ambiguity monitoring algorithm. Finally, the resolved ambiguities from each baseline are processed using the multiple triangular constraints, which can speed up fixing ambiguity and detecting wrong fixes. To fully evaluate the performance of MultiKin, a sophisticated GPS software simulator is developed. Its significance lies in a GPS error simulator. New GPS error models are built based on the investigation of the existing models. The spatial correlation and temporal variation of errors are highlighted in the new models; thus, these models are proper for error simulation in both single-point and differential GPS systems. In addition, all the models have adjustable parameters that allow users to generate a wide range of testing conditions. The results of extensive simulation tests and field tests with MultiKin indicate that MultiKin is effective in speeding up ambiguity resolution. The time required to fix ambiguities can be reduced by up to 67% over the single-baseline method time. Also, MultiKin increases the limit on the distance by two to three kilometres over which ambiguity resolution can be performed. An increased magnitude of the GPS errors and weaker satellite visibility can

  3. Scalable Lunar Surface Networks and Adaptive Orbit Access

    Science.gov (United States)

    Wang, Xudong

    2015-01-01

    Teranovi Technologies, Inc., has developed innovative network architecture, protocols, and algorithms for both lunar surface and orbit access networks. A key component of the overall architecture is a medium access control (MAC) protocol that includes a novel mechanism of overlaying time division multiple access (TDMA) and carrier sense multiple access with collision avoidance (CSMA/CA), ensuring scalable throughput and quality of service. The new MAC protocol is compatible with legacy Institute of Electrical and Electronics Engineers (IEEE) 802.11 networks. Advanced features include efficiency power management, adaptive channel width adjustment, and error control capability. A hybrid routing protocol combines the advantages of ad hoc on-demand distance vector (AODV) routing and disruption/delay-tolerant network (DTN) routing. Performance is significantly better than AODV or DTN and will be particularly effective for wireless networks with intermittent links, such as lunar and planetary surface networks and orbit access networks.

  4. Secondary access based on sensing and primary ARQ feedback in spectrum sharing systems

    KAUST Repository

    Hamza, Doha R.

    2012-04-01

    In the context of primary/secondary spectrum sharing, we propose a randomized secondary access strategy with access probabilities that are a function of both the primary automatic repeat request (ARQ) feedback and the spectrum sensing outcome. The primary terminal operates in a time slotted fashion and is active only when it has a packet to send. The primary receiver can send a positive acknowledgment (ACK) when the received packet is decoded correctly. Lack of ARQ feedback is interpreted as erroneous reception or inactivity. We call this the explicit ACK scheme. The primary receiver may also send a negative acknowledgment (NACK) when the packet is received in error. Lack of ARQ feedback is interpreted as an ACK or no-transmission. This is called the explicit NACK scheme. Under both schemes, when the primary feedback is interpreted as a NACK, the secondary user assumes that there will be retransmission in the next slot and accesses the channel with a certain probability. When the primary feedback is interpreted as an ACK, the secondary user accesses the channel with either one of two probabilities based on the sensing outcome. Under these settings, we find the three optimal access probabilities via maximizing the secondary throughput given a constraint on the primary throughput. We compare the performance of the explicit ACK and explicit NACK schemes and contrast them with schemes based on either sensing or primary ARQ feedback only. © 2012 IEEE.

  5. Spatiotemporal access model based on reputation for the sensing layer of the IoT.

    Science.gov (United States)

    Guo, Yunchuan; Yin, Lihua; Li, Chao; Qian, Junyan

    2014-01-01

    Access control is a key technology in providing security in the Internet of Things (IoT). The mainstream security approach proposed for the sensing layer of the IoT concentrates only on authentication while ignoring the more general models. Unreliable communications and resource constraints make the traditional access control techniques barely meet the requirements of the sensing layer of the IoT. In this paper, we propose a model that combines space and time with reputation to control access to the information within the sensing layer of the IoT. This model is called spatiotemporal access control based on reputation (STRAC). STRAC uses a lattice-based approach to decrease the size of policy bases. To solve the problem caused by unreliable communications, we propose both nondeterministic authorizations and stochastic authorizations. To more precisely manage the reputation of nodes, we propose two new mechanisms to update the reputation of nodes. These new approaches are the authority-based update mechanism (AUM) and the election-based update mechanism (EUM). We show how the model checker UPPAAL can be used to analyze the spatiotemporal access control model of an application. Finally, we also implement a prototype system to demonstrate the efficiency of our model. PMID:25177731

  6. A Soft Sensing-Based Cognitive Access Scheme Exploiting Primary Feedback

    CERN Document Server

    Arafa, Ahmed M; Sultan, Ahmed K; ElBatt, Tamer; El-Sherif, Amr A

    2012-01-01

    In this paper, we examine a cognitive spectrum access scheme in which secondary users exploit the primary feedback information. We consider an overlay secondary network employing a random access scheme in which secondary users access the channel by certain access probabilities that are function of the spectrum sensing metric. In setting our problem, we assume that secondary users can eavesdrop on the primary link's feedback. We study the cognitive radio network from a queuing theory point of view. Access probabilities are determined by solving a secondary throughput maximization problem subject to a constraint on the primary queues' stability. First, we formulate our problem which is found to be non-convex. Yet, we solve it efficiently by exploiting the structure of the secondary throughput equation. Our scheme yields improved results in, both, the secondary user throughput and the primary user packet delay. In addition, it comes very close to the optimal genie-aided scheme in which secondary users act upon t...

  7. High-Frequency Link Inverter for Fuel Cells Based on Multiple-Carrier PWM (to continue)

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    C. Operation of a PWM Cycloconverter The concepts in Section Ⅱ-B, present a progression of solutions to known design difficulties. To incorporate these benefits and eliminate the redundant conversion step shown in Fig. 6, we propose the PWM cycloconverter shown in Fig. 7. It will be shown in Section Ⅲ. that the conventional PWM inverter can be unified through a multiple-carrier PWM framework. The control concept introduced is extended to demonstrate that multiple-carrier PWM methods lead to HF link inverters that are nearly as simple to control as conventional PWM inverters.

  8. A 433-MHz Rail-to-Rail Voltage Amplifier with Carrier Sensing Function for Wireless Sensor Networks

    Science.gov (United States)

    Takeuchi, Takashi; Mikami, Shinji; Lee, Hyeokjong; Kawaguchi, Hiroshi; Ohta, Chikara; Yoshimoto, Masahiko

    In this paper we propose a novel functional amplifier suitable for low-power wireless receivers in a wireless sensor network. This amplifier can change input threshold level as carrier sensing level, since it has a minimum input amplitude to be amplified. A simple rail-to-rail output is suitable for a subsequent digital interface. The target frequency is 433MHz, and the maximum voltage gain is 11dB. The standby power is 39.5nW, and the active power is 352µW. The chip area is 82 × 24µm2.

  9. Radio Access Sharing Strategies for Multiple Operators in Cellular Networks

    DEFF Research Database (Denmark)

    Popovska Avramova, Andrijana; Iversen, Villy Bæk

    2015-01-01

    Mobile operators are moving towards sharing network capacity in order to reduce capital and operational expenditures, while meeting the increasing demand for mobile broadband data services. Radio access network sharing is a promising technique that leads to reduced number of physical base station....... The model used to assess the sharing strategies is based on multidimensional loss systems, and blocking probability is considered as performance metrics....... deployments (required for coverage enhancement), increased base station utilization, and reduced overall power consumption. Today, network sharing in the radio access part is passive and limited to cell sites. With the introduction of Cloud Radio Access Network and Software Defined Networking adoption to the...

  10. Accessing and Utilizing Remote Sensing Data for Vectorborne Infectious Diseases Surveillance and Modeling

    Science.gov (United States)

    Kiang, Richard; Adimi, Farida; Kempler, Steven

    2008-01-01

    Background: The transmission of vectorborne infectious diseases is often influenced by environmental, meteorological and climatic parameters, because the vector life cycle depends on these factors. For example, the geophysical parameters relevant to malaria transmission include precipitation, surface temperature, humidity, elevation, and vegetation type. Because these parameters are routinely measured by satellites, remote sensing is an important technological tool for predicting, preventing, and containing a number of vectorborne infectious diseases, such as malaria, dengue, West Nile virus, etc. Methods: A variety of NASA remote sensing data can be used for modeling vectorborne infectious disease transmission. We will discuss both the well known and less known remote sensing data, including Landsat, AVHRR (Advanced Very High Resolution Radiometer), MODIS (Moderate Resolution Imaging Spectroradiometer), TRMM (Tropical Rainfall Measuring Mission), ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), EO-1 (Earth Observing One) ALI (Advanced Land Imager), and SIESIP (Seasonal to Interannual Earth Science Information Partner) dataset. Giovanni is a Web-based application developed by the NASA Goddard Earth Sciences Data and Information Services Center. It provides a simple and intuitive way to visualize, analyze, and access vast amounts of Earth science remote sensing data. After remote sensing data is obtained, a variety of techniques, including generalized linear models and artificial intelligence oriented methods, t 3 can be used to model the dependency of disease transmission on these parameters. Results: The processes of accessing, visualizing and utilizing precipitation data using Giovanni, and acquiring other data at additional websites are illustrated. Malaria incidence time series for some parts of Thailand and Indonesia are used to demonstrate that malaria incidences are reasonably well modeled with generalized linear models and artificial

  11. The biophysical model for accuracy of cellular sensing spatial gradients of multiple chemoattractants

    International Nuclear Information System (INIS)

    Spatial gradients of surrounding chemoattractants are the key factors in determining the directionality of eukaryotic cell movement. Thus, it is important for cells to accurately measure the spatial gradients of surrounding chemoattractants. Here, we study the precision of sensing the spatial gradients of multiple chemoattractants using cooperative receptor clusters. Cooperative receptors on cells are modeled as an Ising chain of Monod–Wyman–Changeux clusters subject to multiple chemical-gradient fields to study the physical limits of multiple chemoattractants spatial gradients sensing. We found that eukaryotic cells cannot sense each chemoattractant gradient individually. Instead, cells can only sense a weighted sum of surrounding chemical gradients. Moreover, the precision of sensing one chemical gradient is signicantly affected by coexisting chemoattractant concentrations. These findings can provide a further insight into the role of chemoattractants in immune response and help develop novel treatments for inflammatory diseases. (paper)

  12. Cognitive Spectrum Efficient Multiple Access Technique using Relay Systems

    DEFF Research Database (Denmark)

    Frederiksen, Flemming Bjerge; Prasad, Ramjee

    2007-01-01

    Methods to enhance the use of the frequency spectrum by automatical spectrum sensing plus spectrum sharing in a cognitive radio technology context will be presented and discussed in this paper. Ideas to increase the coverage of cellular systems by relay channels, relay stations and collaborate...... radio will be presented as well....

  13. Dynamic Channel Access Scheme for Interference Mitigation in Relay-assisted Intra-WBANs

    OpenAIRE

    Ali, Mohamad Jaafar; Moungla, Hassine; Mehaoua, Ahmed

    2016-01-01

    This work addresses problems related to interference mitigation in a single wireless body area network (WBAN). In this paper, We propose a distributed \\textit{C}ombined carrier sense multiple access with collision avoidance (CSMA/CA) with \\textit{F}lexible time division multiple access (\\textit{T}DMA) scheme for \\textit{I}nterference \\textit{M}itigation in relay-assisted intra-WBAN, namely, CFTIM. In CFTIM scheme, non interfering sources (transmitters) use CSMA/CA to communicate with relays. ...

  14. Pilotless recovery of clipped OFDM signals by compressive sensing over reliable data carriers

    KAUST Repository

    Al-Safadi, Ebrahim B.

    2012-06-01

    In this paper we propose a novel method of clipping mitigation in OFDM using compressive sensing that completely avoids using reserved tones or channel-estimation pilots. The method builds on selecting the most reliable perturbations from the constellation lattice upon decoding at the receiver (in the frequency domain), and performs compressive sensing over these observations in order to completely recover the sparse nonlinear distortion in the time domain. As such, the method provides a practical solution to the problem of initial erroneous decoding decisions in iterative ML methods, and the ability to recover the distorted signal in one shot. © 2012 IEEE.

  15. Joint Sensing and Power Allocation in Multiple-Channel Cognitive Radio Networks

    Science.gov (United States)

    Yu, Huogen; Tang, Wanbin; Li, Shaoqian

    This letter considers a multiple-channel cognitive radio network (CRN) which can simultaneously sense multiple narrowband channels at a time. Taking the maximization of the CRN's overall throughput as the design objective, the optimization problem of jointly designing sensing time, sensing thresholds and transmission power allocation is formulated under the total power constraint of the CRN and the average interference constraint of the primary network. An iterative algorithm is proposed to obtain the locally optimal values for these parameters. Finally, numerical results show that significant overall throughput gain is achieved through the joint design.

  16. Generating free charges by carrier multiplication in quantum dots for highly efficient photovoltaics.

    Science.gov (United States)

    Ten Cate, Sybren; Sandeep, C S Suchand; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J; Schins, Juleon M; Siebbeles, Laurens D A

    2015-02-17

    CONSPECTUS: In a conventional photovoltaic device (solar cell or photodiode) photons are absorbed in a bulk semiconductor layer, leading to excitation of an electron from a valence band to a conduction band. Directly after photoexcitation, the hole in the valence band and the electron in the conduction band have excess energy given by the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor, the initially hot charges rapidly lose their excess energy as heat. This heat loss is the main reason that the theoretical efficiency of a conventional solar cell is limited to the Shockley-Queisser limit of ∼33%. The efficiency of a photovoltaic device can be increased if the excess energy is utilized to excite additional electrons across the band gap. A sufficiently hot charge can produce an electron-hole pair by Coulomb scattering on a valence electron. This process of carrier multiplication (CM) leads to formation of two or more electron-hole pairs for the absorption of one photon. In bulk semiconductors such as silicon, the energetic threshold for CM is too high to be of practical use. However, CM in nanometer sized semiconductor quantum dots (QDs) offers prospects for exploitation in photovoltaics. CM leads to formation of two or more electron-hole pairs that are initially in close proximity. For photovoltaic applications, these charges must escape from recombination. This Account outlines our recent progress in the generation of free mobile charges that result from CM in QDs. Studies of charge carrier photogeneration and mobility were carried out using (ultrafast) time-resolved laser techniques with optical or ac conductivity detection. We found that charges can be extracted from photoexcited PbS QDs by bringing them into contact with organic electron and hole accepting materials. However, charge localization on the QD produces a strong Coulomb attraction to its counter charge in the organic material. This limits the production

  17. DWDM Fiber-Wireless Access System with Centralized Optical Frequency Comb-based RF Carrier Generation

    DEFF Research Database (Denmark)

    Pang, Xiaodan; Beltrán, Marta; Sánchez, José;

    2013-01-01

    We propose and experimentally demonstrate an optical wireless DWDM system at 60 GHz with optical incoherent heterodyne up-conversion using an optical frequency comb. Multiple users with wireline and wireless services are simultaneously supported.......We propose and experimentally demonstrate an optical wireless DWDM system at 60 GHz with optical incoherent heterodyne up-conversion using an optical frequency comb. Multiple users with wireline and wireless services are simultaneously supported....

  18. Adaptive Information Access on Multiple Applications Support Wireless Sensor Networks

    DEFF Research Database (Denmark)

    Tobgay, Sonam; Olsen, Rasmus Løvenstein; Prasad, Ramjee

    2014-01-01

    information is challenged by dynamic nature of information elements. These challenges are more prominent in case of wireless sensor network (WSN) applications, as the information that the sensor node collects are mostly dynamic in nature (say, temperature). Therefore, it is likely that there can be a mismatch...... of information between the one which user uses and the one which is available at the source at the same instant of time. This leads to unreliable information being used by the application user for processing. Information accessing with minimal mismatch is desired by the WSN applications especially when WSN...

  19. Integrated Web-Based Access to and use of Satellite Remote Sensing Data for Improved Decision Making in Hydrologic Applications

    Science.gov (United States)

    Teng, W.; Chiu, L.; Kempler, S.; Liu, Z.; Nadeau, D.; Rui, H.

    2006-12-01

    Using NASA satellite remote sensing data from multiple sources for hydrologic applications can be a daunting task and requires a detailed understanding of the data's internal structure and physical implementation. Gaining this understanding and applying it to data reduction is a time-consuming task that must be undertaken before the core investigation can begin. In order to facilitate such investigations, the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) has developed the GES-DISC Interactive Online Visualization ANd aNalysis Infrastructure or "Giovanni," which supports a family of Web interfaces (instances) that allow users to perform interactive visualization and analysis online without downloading any data. Two such Giovanni instances are particularly relevant to hydrologic applications: the Tropical Rainfall Measuring Mission (TRMM) Online Visualization and Analysis System (TOVAS) and the Agricultural Online Visualization and Analysis System (AOVAS), both highly popular and widely used for a variety of applications, including those related to several NASA Applications of National Priority, such as Agricultural Efficiency, Disaster Management, Ecological Forecasting, Homeland Security, and Public Health. Dynamic, context- sensitive Web services provided by TOVAS and AOVAS enable users to seamlessly access NASA data from within, and deeply integrate the data into, their local client environments. One example is between TOVAS and Florida International University's TerraFly, a Web-enabled system that serves a broad segment of the research and applications community, by facilitating access to various textual, remotely sensed, and vector data. Another example is between AOVAS and the U.S. Department of Agriculture Foreign Agricultural Service (USDA FAS)'s Crop Explorer, the primary decision support tool used by FAS to monitor the production, supply, and demand of agricultural commodities worldwide. AOVAS is also part of GES DISC

  20. Optimal Random Access and Random Spectrum Sensing for an Energy Harvesting Cognitive Radio with and without Primary Feedback Leveraging

    Directory of Open Access Journals (Sweden)

    Ahmed El Shafie

    2014-07-01

    Full Text Available We consider a secondary user (SU with energy harvesting capability. We design access schemes for the SU which incorporate random spectrum sensing and random access, and which make use of the primary automatic repeat request (ARQ feedback. We study two problem-formulations. In the first problemformulation, we characterize the stability region of the proposed schemes. The sensing and access probabilities are obtained such that the secondary throughput is maximized under the constraints that both the primary and secondary queues are stable. Whereas in the second problem-formulation, the sensing and access probabilities are obtained such that the secondary throughput is maximized under the stability of the primary queue and that the primary queueing delay is kept lower than a specified value needed to guarantee a certain quality of service (QoS for the primary user (PU. We consider spectrum sensing errors and assume multipacket reception (MPR capabilities. Numerical results show the enhanced performance of our proposed systems.

  1. Performance analysis of electronic code division multiple access based virtual private networks over passive optical networks

    Science.gov (United States)

    Nadarajah, Nishaanthan; Nirmalathas, Ampalavanapillai

    2008-03-01

    A solution for implementing multiple secure virtual private networks over a passive optical network using electronic code division multiple access is proposed and experimentally demonstrated. The multiple virtual private networking capability is experimentally demonstrated with 40 Mb/s data multiplexed with a 640 Mb/s electronic code that is unique to each of the virtual private networks in the passive optical network, and the transmission of the electronically coded data is carried out using Fabry-Perot laser diodes. A theoretical scalability analysis for electronic code division multiple access based virtual private networks over a passive optical network is also carried out to identify the performance limits of the scheme. Several sources of noise such as optical beat interference and multiple access interference that are present in the receiver are considered with different operating system parameters such as transmitted optical power, spectral width of the broadband optical source, and processing gain to study the scalability of the network.

  2. Multi-user interference cancellation schemes for carrier frequency offset compensation in uplink OFDMA

    DEFF Research Database (Denmark)

    Nguyen, Huan Cong; De Carvalho, Elisabeth; Prasad, Ramjee

    2014-01-01

    Each user in the uplink of an Orthogonal Frequency Division Multiple Access (OFDMA) system may experience a different carrier frequency offset (CFO). These uncorrected CFOs destroy the orthogonality among subcarriers, causing inter-carrier interference and multi-user interference, which degrade t...... cancellation techniques for Orthogonal Frequency Division Multiple Access (OFDMA) available in literature with comparable or lower complexity....

  3. Low-Cost Encoding Device for Optical Code Division Multiple Access System

    Directory of Open Access Journals (Sweden)

    Mohammad S. Ab-Rahman

    2009-01-01

    Full Text Available Problem statement: Instead of using Fiber Bragg Grating (FBG to develop the coded spectrums, which consist of expensive elements, the grating also are highly sensitive to environmental changes and this will contribute to the increment of capital and operational expenditures (CAPEX and OPEX. Approach: This study presented the development of low-cost 16-ports encoding device for Optical Code Division Multiple Access (OCDMA systems based on Arrayed Waveguide Grating (AWG devices and optical switches. The encoding device is one of the new technologies that used to transmit the coded data in the optical communication system by using AWG and optical switches. It provided a high security for data transmission due to all data will be transmitted in binary code form. The output signals from AWG were coded with a binary code that given to an optical switch before it signal modulate with the carrier and transmitted to the receiver. The 16-ports encoding device used 16 Double Pole Double Throw (DPDT toggle switches to control the polarization of voltage source from +5 V to -5 V for 16 optical switches. When +5 V was given, the optical switch will give code '1' and vice versa. Results: We found that the insertion loss, crosstalk, uniformity and Optical Signal-Noise-Ratio (OSNR for the developed prototype are Conclusion: We had successful developed the AWG-based OCDMA encoding device prototype and characterized using linearity testing and continuous signal testing. The developed prototype was expected to be applied in the optical communication system on Passive Optical Networks (PONs.

  4. User—dependent Perfect—scheduling Multiple Access (UPMA) for Wireless Ad Hoc Networ

    Institute of Scientific and Technical Information of China (English)

    LIJiandong; LIWeiying; YANGJiawei; WENGJiwei

    2003-01-01

    A new multiple access protocol for wireless Internet access, called user-dependent perfect-scheduling multiple access (UPMA), is proposed. Packet transmis-sions are scheduled according to the number of active users,packet queue length and round-robin service rule. The proposed self-organizing algorithm is used to determine the number of active users. Users in ad h0c network are divided into clusters by the self-organizing algorithm. In each cluster an independent UPMA is used. UPMA al-gorithms for star and ad hoc wireless network are given.Performance analysis shows that UPMA have stable and very high throughnut.

  5. Optimum Access Analysis of Collaborative Spectrum Sensing in Cognitive Radio Network using MRC

    Directory of Open Access Journals (Sweden)

    Risala Tasin Khan

    2016-07-01

    Full Text Available The performance of cognitive radio network mainly depends on the finest sensing of the presence or absence of Primary User (PU. The throughput of a Secondary User (SU can be reduced because of the false detection of PU which causes an SU from its transmission opportunity. The factorization of the probability of correct decision is a really hard job when the special false alarm is incorporated into it. Previous works focus on collaborative sensing on the normal environment. In this paper, we have proposed a collaborative sensing method in Cognitive radio network for optimal access of PU licensed band by SU. It is shown performance analysis of energy detection through different cognitive users and conducts a clear comparison between local and collaborative sensing. In this paper, the maximal ratio combining diversity technique with energy detection has been employed to reduce the false alarm probability in the collaborative environment. The simulation result shows significant reduction of the probability of misdetection with increasing in the number of collaborative users. We also analyze that MRC scheme exhibits the best detection performance in collaborative environment.

  6. Adaptive Information Access in Multiple Applications Support Wireless Sensor Network

    DEFF Research Database (Denmark)

    Tobgay, Sonam; Olsen, Rasmus Løvenstein; Prasad, Ramjee

    2012-01-01

    Nowadays, due to wide applicability of Wireless Sensor Network (WSN) added by the low cost sensor devices, its popularity among the researchers and industrialists are very much visible. A substantial amount of works can be seen in the literature on WSN which are mainly focused on application...... specific WSN considering its resource constraints, neglecting the return-of-investment and usefulness of the system. In this paper, we bring out the WSN scenario which supports multiple applications and study the challenges that would pose in implementation as each specific application has its own specific...

  7. Mof-Tree: A Spatial Access Method To Manipulate Multiple Overlapping Features.

    Science.gov (United States)

    Manolopoulos, Yannis; Nardelli, Enrico; Papadopoulos, Apostolos; Proietti, Guido

    1997-01-01

    Investigates the manipulation of large sets of two-dimensional data representing multiple overlapping features, and presents a new access method, the MOF-tree. Analyzes storage requirements and time with respect to window query operations involving multiple features. Examines both the pointer-based and pointerless MOF-tree representations.…

  8. Performance analysis of spectrum sensing with multiple status changes in primary user traffic

    KAUST Repository

    Tang, Liang

    2012-06-01

    In this letter, the impact of primary user traffic with multiple status changes on the spectrum sensing performance is analyzed. Closed-form expressions for the probabilities of false alarm and detection are derived. Numerical results show that the multiple status changes of the primary user cause considerable degradation in the sensing performance. This degradation depends on the number of changes, the primary user traffic model, the primary user traffic intensity and the signal-to-noise ratio of the received signal. Numerical results also show that the amount of degradation decreases when the number of changes increases, and converges to a minimum sensing performance due to the limited sensing period and primary holding time. © 2012 IEEE.

  9. A Multiple-Reception Access Protocol with Interruptions with Mixed Priorities in CDMA Networks

    Institute of Scientific and Technical Information of China (English)

    Lu Xiaowen; Zhu Jinkang

    2003-01-01

    A novel access protocol called Multiple-Reception Access Protocol (MRAP) and its modification MRAP/WI are proposed. In this protocol, all colliding users with a common code can be identified by the base station due to the offset of arrival time Thus they can retransmit access requests under the base station's control. Furthermore new arrivals with higher priority level can interrupt the lower retransmission in order to reduce its access delay although it increases the lower priority's delay. Simulation results of MRAP and MRAP/WI are given in order to highlight the superior performance of the proposed approach.

  10. Centralized optical-frequency-comb-based RF carrier generator for DWDM fiber-wireless access systems

    DEFF Research Database (Denmark)

    Pang, Xiaodan; Beltran, Marta; Sanchez, Jose;

    2014-01-01

    In this paper, we report on a gigabit capacity fiber-wireless system that enables smooth integration between high-speed wireless networks and dense wavelength-division-multiplexing (DWDM) access networks. By employing a centralized optical frequency comb, both the wireline and the wireless services...... applications. For demonstration, we transmit a 2.5 Gbit/s signal through the proposed system and successfully achieve a bit-error-rate (BER) performance well below the 7% overhead forward error correction limit of the BER of 2 × 10¿3 for both the wireline and the wireless signals in the 60 GHz band after 25 km...... single-mode fiber plus up to 6 m wireless distance....

  11. Using Multiple Senses in Tourism Marketing: The Helsinki Expert, Eckero Line and Linnanmaki Amusement Park Cases

    OpenAIRE

    Isacsson, Annica; Alakoski, Leena; Bäck, Asta

    2009-01-01

    In order to create awareness & motivation among future travellers, tourism communication, should, according to our understanding, not only appeal to the visuals, but to all user senses in an inter medial mix. Hence, smell, sound, touch, taste and sight must be touched, in order for communication to be perceived valuable and interesting, as we argue that the activation of multiple senses enhances the feeling of authenticity and experience. If combined with ration and need, in addition to the i...

  12. Linear Precoding for the MIMO Multiple Access Channel with Finite Alphabet Inputs and Statistical CSI

    OpenAIRE

    Wu, Yongpeng; Wen, Chao-Kai; Xiao, Chengshan; Gao, Xiqi; Schober, Robert

    2014-01-01

    In this paper, we investigate the design of linear precoders for the multiple-input multiple-output (MIMO) multiple access channel (MAC). We assume that statistical channel state information (CSI) is available at the transmitters and consider the problem under the practical finite alphabet input assumption. First, we derive an asymptotic (in the large system limit) expression for the weighted sum rate (WSR) of the MIMO MAC with finite alphabet inputs and Weichselberger's MIMO channel model. S...

  13. Performance Analysis of Optical Code Division Multiple Access (OCDMA System

    Directory of Open Access Journals (Sweden)

    Amandeep Sukhija

    2014-08-01

    Full Text Available With the concept of 3G & 4G services OCDMA is one of the important technologies, that provide a very high speed communication. In this technology multiple users can communicate simultaneously to transfer different kind of data. OCDMA enables the best use of available bandwidth and the spectrum to represent a cost efficient network. But in a network there is always the requirement to increase the security and the efficiency or the throughput of a multiuser communication in the OCDMA network. The proposed work is about to increase the efficiency in a Noisy channel. Here the work will be performed on impulse noised network. We are here proposing the orthogonal approach along with OCDMA to improve the throughput. We are trying to show the results in terms of noise ratio and the derived throughput. The proposed work is about to reduce this packet loss and to increase the throughput in the noisy network. To overcome this drawback and to increase the throughput we are using the concept of OFDM along with CDMA. This concept is represented as the Orthogonal CDMA.

  14. Multiple stimulated emission fluorescence photoacoustic sensing and spectroscopy

    Science.gov (United States)

    Li, Gaoming; Gao, Fei; Qiu, Yishen; Feng, Xiaohua; Zheng, Yuanjin

    2016-07-01

    Multiple stimulated emission fluorescence photoacoustic (MSEF-PA) phenomenon is demonstrated in this letter. Under simultaneous illumination of pumping light and stimulated emission light, the fluorescence emission process is speeded up by the stimulated emission effect. This leads to nonlinear enhancement of photoacoustic signal while the quantity of absorbed photons is more than that of fluorescent molecules illuminated by pumping light. The electronic states' specificity of fluorescent molecular can also be labelled by the MSEF-PA signals, which can potentially be used to obtain fluorescence excitation spectrum in deep scattering tissue with nonlinearly enhanced photoacoustic detection. In this preliminary study, the fluorescence excitation spectrum is reconstructed by MSEF-PA signals through sweeping the wavelength of exciting light, which confirms the theoretical derivation well.

  15. Multiple access protocol for supporting multimedia services in wireless ATM networks

    DEFF Research Database (Denmark)

    Liu, Hong; Dittmann, Lars; Gliese, Ulrik Bo;

    1999-01-01

    . In this paper, we propose a multiple access protocol using centralized and distributed channel access control techniques to provide QoS guarantees for multimedia services by taking advantage of the characteristics of different kinds of ATM traffics. Multimedia traffic, including constant bit rate......The furture broadband wireless asynchronous transfer mode (ATM) networks must provide seamless extension of multimedia services from the wireline ATM networks. This requires an effecient wireless access protocol to fulfill varying Quality-og-Service (QoS) requirements for multimedia applications...... (CBR), variable bit rate (VBR) and available bit rate (ABR) with different kinds of applications, such as voice, video-conferening, MPEG video and Web-browising, is considered to evaluate the proposed protocol. Simulation results show that the proposed multiple access protocol can support a wide range...

  16. Employing optical code division multiple access technology in the all fiber loop vibration sensor system

    Science.gov (United States)

    Tseng, Shin-Pin; Yen, Chih-Ta; Syu, Rong-Shun; Cheng, Hsu-Chih

    2013-12-01

    This study proposes a spectral amplitude coding-optical code division multiple access (SAC-OCDMA) framework to access the vibration frequency of a test object on the all fiber loop vibration sensor (AFLVS). Each user possesses an individual SAC, and fiber Bragg grating (FBG) encoders/decoders using multiple FBG arrays were adopted, providing excellent orthogonal properties in the frequency domain. The system also mitigates multiple access interference (MAI) among users. When an optical fiber is bent to a point exceeding the critical radius, the fiber loop sensor becomes sensitive to external physical parameters (e.g., temperature, strain, and vibration). The AFLVS involves placing a fiber loop with a specific radius on a designed vibration platform.

  17. Prospective Mathematics Teachers' Sense Making of Polynomial Multiplication and Factorization Modeled with Algebra Tiles

    Science.gov (United States)

    Caglayan, Günhan

    2013-01-01

    This study is about prospective secondary mathematics teachers' understanding and sense making of representational quantities generated by algebra tiles, the quantitative units (linear vs. areal) inherent in the nature of these quantities, and the quantitative addition and multiplication operations--referent preserving versus referent…

  18. Low-sampling-rate M-ary multiple access UWB communications in multipath channels

    KAUST Repository

    Alkhodary, Mohammad T.

    2015-08-31

    The desirable characteristics of ultra-wideband (UWB) technology are challenged by formidable sampling frequency, performance degradation in the presence of multi-user interference, and complexity of the receiver due to the channel estimation process. In this paper, a low-rate-sampling technique is used to implement M-ary multiple access UWB communications, in both the detection and channel estimation stages. A novel approach is used for multiple-access-interference (MAI) cancelation for the purpose of channel estimation. Results show reasonable performance of the proposed receiver for different number of users operating many times below Nyquist rate.

  19. Integrated reconfigurable multiple-input–multiple-output antenna system with an ultra-wideband sensing antenna for cognitive radio platforms

    KAUST Repository

    Hussain, Rifaqat

    2015-06-18

    © The Institution of Engineering and Technology 2015. A compact, novel multi-mode, multi-band frequency reconfigurable multiple-input-multiple-output (MIMO) antenna system, integrated with ultra-wideband (UWB) sensing antenna, is presented. The developed model can be used as a complete antenna platform for cognitive radio applications. The antenna system is developed on a single substrate area of dimensions 65 × 120 mm2. The proposed sensing antenna is used to cover a wide range of frequency bands from 710 to 3600 MHz. The frequency reconfigurable dual-element MIMO antenna is integrated with P-type, intrinsic, N-type (PIN) diodes for frequency agility. Different modes of selection are used for the MIMO antenna system reconfigurability to support different wireless system standards. The proposed MIMO antenna configuration is used to cover various frequency bands from 755 to 3450 MHz. The complete system comprising the multi-band reconfigurable MIMO antennas and UWB sensing antenna for cognitive radio applications is proposed with a compact form factor.

  20. AquaUsers: Improving access to remotely sensed data for non-specialists

    Science.gov (United States)

    Clements, Oliver; Walker, Peter; Calton, Ben; Miller, Peter

    2015-04-01

    In recent years more and more complex remotely sensed data have been made available to the public by national and international agencies. These data are also reprocessed by different organisations to produce secondary products that are of specific need to a community. For instance the production of chlorophyll concentration maps from ocean colour data provided by NASA for the marine community. Providing access to such data has normally been focused on simply making the data available with appropriate metadata so that domain specialists can make use of it. One area that has seen significant investment, both of time and money, has been in the production of web based data portals. Primarily these have focused on spatial data. By providing a web map visualisation users are able to quickly assess both spatial coverage and data values. Data portal improvements have been possible thanks to advancements in back end data servers such as Thredds and ncWMS as well as improvements in front-end libraries for data visualisation including OpenLayers and D3. Data portals that make use of these technological advancements have aimed at improving the access and use of data by trained scientific domain specialists. There is now a push to improve access to these systems by non-scientific domain specialists through several European Commission funded projects, including OPEC and AquaUsers. These projects have improved upon an open source web GIS portal created by Plymouth Marine Laboratory [https://github.com/pmlrsg/GISportal]. We will present the latest version of our GIS portal, discuss the designs steps taken to achieve the latest build and share user stories as to how non-domain specialists are now able to utilise the system and get benefits from remotely sensed data. A first version was produced and disseminated to end users for feedback. At this stage the end users included government advisors, fish farmers and scientific groups with no specific GIS training or knowledge. This

  1. Secure Communications in High Speed Fiber Optical Networks Using Code Division Multiple Access (CDMA) Transmission

    Energy Technology Data Exchange (ETDEWEB)

    Han, I; Bond, S; Welty, R; Du, Y; Yoo, S; Reinhardt, C; Behymer, E; Sperry, V; Kobayashi, N

    2004-02-12

    This project is focused on the development of advanced components and system technologies for secure data transmission on high-speed fiber optic data systems. This work capitalizes on (1) a strong relationship with outstanding faculty at the University of California-Davis who are experts in high speed fiber-optic networks, (2) the realization that code division multiple access (CDMA) is emerging as a bandwidth enhancing technique for fiber optic networks, (3) the realization that CDMA of sufficient complexity forms the basis for almost unbreakable one-time key transmissions, (4) our concepts for superior components for implementing CDMA, (5) our expertise in semiconductor device processing and (6) our Center for Nano and Microtechnology, which is where the majority of the experimental work was done. Here we present a novel device concept, which will push the limits of current technology, and will simultaneously solve system implementation issues by investigating new state-of-the-art fiber technologies. This will enable the development of secure communication systems for the transmission and reception of messages on deployed commercial fiber optic networks, through the CDMA phase encoding of broad bandwidth pulses. CDMA technology has been developed as a multiplexing technology, much like wavelength division multiplexing (WDM) or time division multiplexing (TDM), to increase the potential number of users on a given communication link. A novel application of the techniques created for CDMA is to generate secure communication through physical layer encoding. Physical layer encoding devices are developed which utilize semiconductor waveguides with fast carrier response times to phase encode spectral components of a secure signal. Current commercial technology, most commonly a spatial light modulator, allows phase codes to be changed at rates of only 10's of Hertz ({approx}25ms response). The use of fast (picosecond to nanosecond) carrier dynamics of semiconductors

  2. VCSEL-based gigabit IR-UWB link for converged communication and sensing applications in optical metro-access networks

    DEFF Research Database (Denmark)

    Pham, Tien Thang; Gibbon, Timothy Braidwood; Tafur Monroy, Idelfonso

    2012-01-01

    We report on experimental demonstration of an impulse radio ultrawideband (IR-UWB) based converged communication and sensing system. A 1550-nm VCSEL-generated IR-UWB signal is used for 2-Gbps wireless data distribution over 800-m and 50-km single mode fiber links which present short-range in...... sensing application, paving the way forward for the development and deployment of converged UWB VCSEL-based technologies in access and in-building networks of the future....

  3. Implementation of Multiple Host Nodes in Wireless Sensing Node Network System for Landslide Monitoring

    International Nuclear Information System (INIS)

    This paper proposes multiple host nodes in Wireless Sensing Node Network System (WSNNS) for landslide monitoring. As landslide disasters damage monitoring system easily, one major demand in landslide monitoring is the flexibility and robustness of the system to evaluate the current situation in the monitored area. For various reasons WSNNS can provide an important contribution to reach that aim. In this system, acceleration sensors and GPS are deployed in sensing nodes. Location information by GPS, enable the system to estimate network topology and enable the system to perceive the location in emergency by monitoring the node mode. Acceleration sensors deployment, capacitate this system to detect slow mass movement that can lead to landslide occurrence. Once deployed, sensing nodes self-organize into an autonomous wireless ad hoc network. The measurement parameter data from sensing nodes is transmitted to Host System via host node and ''Cloud'' System. The implementation of multiple host nodes in Local Sensing Node Network System (LSNNS), improve risk- management of the WSNNS for real-time monitoring of landslide disaster

  4. Implementation of Multiple Host Nodes in Wireless Sensing Node Network System for Landslide Monitoring

    Science.gov (United States)

    Abas, Faizulsalihin bin; Takayama, Shigeru

    2015-02-01

    This paper proposes multiple host nodes in Wireless Sensing Node Network System (WSNNS) for landslide monitoring. As landslide disasters damage monitoring system easily, one major demand in landslide monitoring is the flexibility and robustness of the system to evaluate the current situation in the monitored area. For various reasons WSNNS can provide an important contribution to reach that aim. In this system, acceleration sensors and GPS are deployed in sensing nodes. Location information by GPS, enable the system to estimate network topology and enable the system to perceive the location in emergency by monitoring the node mode. Acceleration sensors deployment, capacitate this system to detect slow mass movement that can lead to landslide occurrence. Once deployed, sensing nodes self-organize into an autonomous wireless ad hoc network. The measurement parameter data from sensing nodes is transmitted to Host System via host node and "Cloud" System. The implementation of multiple host nodes in Local Sensing Node Network System (LSNNS), improve risk- management of the WSNNS for real-time monitoring of landslide disaster.

  5. Experimental demonstration of 2.5 Gbit/S incoherent two-dimensional optical code division multiple access system

    International Nuclear Information System (INIS)

    We demonstrated error-free operation of 4 simultaneous users in a fast frequency-hopping time-spreading optical code division multiple access system operating at 2.5 Gbit/s a Star architecture. Effective power penalty was ≤0.5dB. Novel optical code division multiple access receiver based on Terahertz Optical Asymmetric Demultiplexer was demonstrated to eliminate multiple access interference (Authors)

  6. Dispersion-flattened-fiber based optical thresholder for multiple-access-interference suppression in OCDMA system.

    Science.gov (United States)

    Wang, Xu; Hamanaka, Taro; Wada, Naoya; Kitayama, Ken-Ichi

    2005-07-11

    An optical thresholding technique based on super-continuum generation in dispersion flattened fiber is proposed and experimentally demonstrated to enable data-rate detection in optical code division multiple access networks. The proposed scheme exhibits an excellent discrimination between a desired signal and interference signals with features of pulse reshaping, low insertion loss, polarization independency as well as reasonable operation power. PMID:19498545

  7. Optical receiver sensitivity analysis for electronic code division multiple access over passive optical network

    Science.gov (United States)

    Han, Yamei; Liang, Siyuan; Wang, Liqian; Chen, Xue

    2010-12-01

    Optical receiver sensitivity for electronic code division multiple access over a passive optical network (ECDMA-PON) is analyzed theoretically. Compared with TDM system, ECDMA-PON offers better receiver sensitivity due to coding gain. Fundamental simulation results are provided to show its validity.

  8. Knowledge-Based Multiple Access Protocol in Broadband Wireless ATM Networks

    DEFF Research Database (Denmark)

    Liu, Hong; Gliese, Ulrik Bo; Dittmann, Lars

    1999-01-01

    In this paper, we propose a knowledge-based multiple access protocol for the extension of wireline ATM to wireless networks. The objective is to enable effecient transmission of all kinds of ATM traffic in the wireless channel with guaranteed QoS.The proposed protocol utilixes knowledge of the main...... guaranteed QoS requirements to a variety of ATM applications....

  9. Electro-optical time gating based on Mach-Zehnder modulator for multiple access interference elimination in optical code-division multiple access networks

    Science.gov (United States)

    Chen, Yinfang; Wang, Rong; Fang, Tao; Pu, Tao; Xiang, Peng; Zheng, Jilin; Zhu, Huatao

    2014-05-01

    An electro-optical time gating technique, which is based on an electrical return-to-zero (RZ) pulse driven Mach-Zehnder modulator (MZM) for eliminating multiple access interference (MAI) in optical code-division multiple access (OCDMA) networks is proposed. This technique is successfully simulated in an eight-user two-dimensional wavelength-hopping time-spreading system, as well as in a three-user temporal phase encoding system. Results show that in both systems the MAI noise is efficiently removed and the average received power penalty improved. Both achieve error-free transmissions at a bit rate of 2.5 Gb/s. In addition, we also individually discuss effects of parameters in two systems, such as the extinction ratio of the MZM, the duty cycle of the driven RZ pulse, and the time misalignment between the driven pulse and the decoded autocorrelation peak, on the output bit error rate performance. Our work shows that employing a common MZM as a thresholder provides another probability and an interesting cost-effective choice for a smart size, low energy, and less complex thresholding technique for integrated detection in OCDMA networks.

  10. Ultrafast Supercontinuum Spectroscopy of Carrier Multiplication and Biexcitonic Effects in Excited States of PbS Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Sfeir M. Y.; Gesuele, F.; Koh, W.-K.; Murray, C.B.; Heinz, T.F.; Wong, C.W.

    2012-06-01

    We examine the population dynamics of multiple excitons in PbS quantum dots using spectrally resolved ultrafast supercontinuum transient absorption (SC-TA) measurements. We simultaneously probe the first three excitonic transitions. The transient spectra show the presence of bleaching of absorption for the 1S{sub h}-1S{sub e} transition, as well as transients associated with the 1P{sub h}-1P{sub e} transition. We examine signatures of carrier multiplication (multiple excitons arising from a single absorbed photon) from analysis of the bleaching features in the limit of low absorbed photon numbers (multiple-exciton generation is discussed both in terms of the ratio between early- to long-time transient absorption signals and of a broadband global fit to the data. Analysis of the population dynamics shows that bleaching associated with biexciton population is red shifted with respect to the single exciton feature, which is in accordance with a positive binding energy for the biexciton.

  11. OPTIMIZATION OF MULTIPLE-CHANNEL COOPERATIVE SPECTRUM SENSING WITH DATA FUSION RULE IN COGNITIVE RADIO NETWORKS

    Institute of Scientific and Technical Information of China (English)

    Yu Huogen; Tang Wanbin; Li Shaoqian

    2012-01-01

    This paper focuses on multi-channel Cooperative Spectrum Sensing (CSS) where Secondary Users (SUs) are assigned to cooperatively sense multiple channels simultaneously.A multi-channel CSS optimization problem of joint spectrum sensing and SU assignment based on data fusion rule is formulated,which maximizes the total throughput of the Cognitive Radio Network (CRN) subject to the constraints of probabilities of detection and false alarm.To address the optimization problem,a Branch and Bound (BnB) algorithm and a greedy algorithm are proposed to obtain the optimal solutions.Simulation results are presented to demonstrate the effectiveness of our proposed algorithms and show that the throughput improvement is achieved through the joint design.It is also shown that the greedy algorithm with a low complexity achieves the comparable performance to the exhaustive algorithm.

  12. Influence of Rapid Thermal Annealing on Carrier Dynamics in GaInNAs/GaAs Multiple Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    ZHOU Wei; YANG Jie; XIA Su-Jing; LI Xiang; TANG Wu

    2011-01-01

    The excitation intensity and time-resolved photoluminescence spectroscopy are used to investigate the impact of annealing on the carrier dynamics in the Ga0.66In0.34N0.013As0.987 /GaAs multiple quantum well structure grown by metalorganic chemical vapor deposition.The measurement of excitation intensity photoluminescence (PL),performed for as-grown and annealed samples at different temperatures,indicates that the localized potential has come down slightly after annealing but does not alter the fact that PL emission at low temperature is dominated by localized exciton recombination.In contrast,free carrier recombination is magnified by post-grown annealing at room temperature.Our results show that the decay times are 0.587 and 0.327ns at 10K for the as-grown and annealed samples,and radiative decay times also shorten significantly after annealing at all temperatures.Hence the improvement of luminescence efficiency after annealing is caused by the reduction of localization and enhancement of radiative recombination rate.The reduction of the density of nonradiative centers is demonstrated indirectly after annealing.Recently,GaInNAs alloys have attracted an increasing amount of attention,driven by not only their potential applications in various electronic and optoelectronics devices but also their intriguing physical properties.[1] It has been demonstrated that the optical quality of GaInNAs/GaAs quantum wells can be improved by rapid thermal annealing (RTA).[2,3]%The excitation intensity and time-resolved photoluminescence spectroscopy are used to investigate the impact of annealing on the carrier dynamics in the Ga0.66ln0.34N0.013As0.987/GaAs multiple quantum well structure grown by metalorganic chemical vapor deposition. The measurement of excitation intensity photoluminescence (PL), performed for as-grown and annealed samples at different temperatures, indicates that the localized potential has come down slightly after annealing but does not alter the fact that PL

  13. 78 FR 2571 - Special Access for Price Cap Local Exchange Carriers; AT&T Corporation Petition for Rulemaking To...

    Science.gov (United States)

    2013-01-11

    ... Local Exchange Carriers; AT&T Corporation Petition for Rulemaking To Reform Regulation of Incumbent... Petition for Rulemaking To Reform Regulation of Incumbent Local Exchange Carrier Rates for Interstate.... One way to assess potential competition is by obtaining structural, pricing, and demand data over...

  14. Iterative Fusion of Distributed Decisions over the Gaussian Multiple-Access Channel Using Concatenated BCH-LDGM Codes

    Directory of Open Access Journals (Sweden)

    Crespo PedroM

    2011-01-01

    Full Text Available This paper focuses on the data fusion scenario where nodes sense and transmit the data generated by a source to a common destination, which estimates the original information from more accurately than in the case of a single sensor. This work joins the upsurge of research interest in this topic by addressing the setup where the sensed information is transmitted over a Gaussian Multiple-Access Channel (MAC. We use Low Density Generator Matrix (LDGM codes in order to keep the correlation between the transmitted codewords, which leads to an improved received Signal-to-Noise Ratio (SNR thanks to the constructive signal addition at the receiver front-end. At reception, we propose a joint decoder and estimator that exchanges soft information between the LDGM decoders and a data fusion stage. An error-correcting Bose, Ray-Chaudhuri, Hocquenghem (BCH code is further applied suppress the error floor derived from the ambiguity of the MAC channel when dealing with correlated sources. Simulation results are presented for several values of and diverse LDGM and BCH codes, based on which we conclude that the proposed scheme outperforms significantly (by up to 6.3 dB the suboptimum limit assuming separation between Slepian-Wolf source coding and capacity-achieving channel coding.

  15. Cognitive Spectrum Sensing with Multiple Primary Users in Rayleigh Fading Channels

    Directory of Open Access Journals (Sweden)

    Salam Al-Juboori

    2014-09-01

    Full Text Available Accurate detection of white spaces is crucial in cognitive radio networks. Initial investigations show that the accurate detection in a multiple primary users environment is challenging, especially under severe multipath conditions. Among many techniques, recently proposed eigenvalue-based detectors that use random matrix theories to eliminate the need of prior knowledge of the signals proved to be a solid approach. In this work, we study the effect of Rayleigh multipath fading channels on spectrum sensing in a multiple primary user environment for a pre-proposed detector called the spherical detector using the eigenvalue approach. Simulation results show interesting outcomes.

  16. Achieving Uniform Carriers Distribution in MBE Grown Compositionally Graded InGaN Multiple-Quantum-Well LEDs

    KAUST Repository

    Mishra, Pawan

    2015-05-06

    We investigated the design and growth of compositionally-graded InGaN multiple quantum wells (MQW) based light-emitting diode (LED) without an electron-blocking layer (EBL). Numerical investigation showed uniform carrier distribution in the active region, and higher radiative recombination rate for the optimized graded-MQW design, i.e. In0→xGa1→(1-x)N / InxGa(1-x)N / Inx→0Ga(1-x)→1N, as compared to the conventional stepped-MQW-LED. The composition-grading schemes, such as linear, parabolic, and Fermi-function profiles were numerically investigated for comparison. The stepped- and graded-MQW-LED were then grown using plasma assisted molecular beam epitaxy (PAMBE) through surface-stoichiometry optimization based on reflection high-energy electron-diffraction (RHEED) in-situ observations. Stepped- and graded-MQW-LED showed efficiency roll over at 160 A/cm2 and 275 A/cm2, respectively. The extended threshold current density roll-over (droop) in graded-MQW-LED is due to the improvement in carrier uniformity and radiative recombination rate, consistent with the numerical simulation.

  17. Resource allocation using time division multiple access over wireless relay networks

    Institute of Scientific and Technical Information of China (English)

    DAI Qin-yun; RONG Lu; HU Hong-lin; SU Gang

    2008-01-01

    This article considers a wireless network consisting of multiple sources that communicate with the corresponding destination utilizing a single half-duplex relay, whereas, the sources use the relay opportunistically. By integrating the information theory with the concept of effective capacity, this article proposes a dynamic time allocation strategy over the wireless relay network that aims at maximizing the relay network throughput, subject to a given delay quality of service (QoS) constraint, where time division multiple access (TDMA) is applied in the relay network. The simulation results show that the proposed allocation strategy can significantly improve the effective capacity as compared to the traditional equal time allocation strategy.

  18. Fairness for Non-Orthogonal Multiple Access in 5G Systems

    Science.gov (United States)

    Timotheou, Stelios; Krikidis, Ioannis

    2015-10-01

    In non-orthogonal multiple access (NOMA) downlink, multiple data flows are superimposed in the power domain and user decoding is based on successive interference cancellation. NOMA's performance highly depends on the power split among the data flows and the associated power allocation (PA) problem. In this letter, we study NOMA from a fairness standpoint and we investigate PA techniques that ensure fairness for the downlink users under i) instantaneous channel state information (CSI) at the transmitter, and ii) average CSI. Although the formulated problems are non-convex, we have developed low-complexity polynomial algorithms that yield the optimal solution in both cases considered.

  19. Forward error correcting codes in fiber-optic synchronous code-division multiple access networks

    Science.gov (United States)

    Srivastava, Anand; Kar, Subrat; Jain, V. K.

    2002-02-01

    In optical code-division multiple access (OCDMA) networks, the performance is limited by optical multiple access interference (OMAI), amplified spontaneous emission (ASE) noise and receiver noise. To reduce OMAI and noise effects, use of forward error correcting (FEC) (18880, 18865) and (2370, 2358) Hamming codes are explored for STM-1 (155 Mbps) bit stream. The encoding is carried out at the multiplex-section layer. The check bits are embedded in the unused bytes of multiplex section overhead (MSOH). The expression for probability of error is derived taking into consideration OMAI, various sources of noise and effect of group velocity dispersion (GVD). It is observed that for a BER of 10 -9, use of FEC gives a coding gain of 1.4-2.1 dB depending upon the type of coding scheme used. It is also seen that there is a sensitivity improvement of about 3 dB if the source is suitably pre-chirped.

  20. A distributed Synchronous reservation multiple access control protocol for mobile Ad hoc networks

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yanling; SUN Xianpu; LI Jiandong

    2007-01-01

    This study proposes a new multiple access control protocol named distributed synchronous reservation multiple access control protocol.in which the hidden and exposed terminal problems are solved,and the quality of service(QoS)requirements for real-time traffic are guaranteed.The protocol is founded on time division multiplex address and a different type of traffic is assigned to difierent priority,according to which a node should compete for and reserve the free slots in a different method.Moreover,there is a reservation acknowledgement process before data transmit in each reserved slot,so that the intruded terminal problem is solved.The throughput and average packets drop probability of this protocol are analyzed and simulated in a fully connected network.the results of which indicate that this protocol is efficient enough to support the real-time traffic.and it is more suitable to MANETs.

  1. Information Theory vs. Queueing Theory for Resource Allocation in Multiple Access Channels

    CERN Document Server

    ParandehGheibi, Ali; Ozdaglar, Asuman; Eryilmaz, Atilla

    2008-01-01

    We consider the problem of rate allocation in a fading Gaussian multiple-access channel with fixed transmission powers. The goal is to maximize a general concave utility function of the expected achieved rates of the users. There are different approaches to this problem in the literature. From an information theoretic point of view, rates are allocated only by using the channel state information. The queueing theory approach utilizes the global queue-length information for rate allocation to guarantee throughput optimality as well as maximizing a utility function of the rates. In this work, we make a connection between these two approaches by showing that the information theoretic capacity region of a multiple-access channel and its stability region are equivalent. Moreover, our numerical results show that a simple greedy policy which does not use the queue-length information can outperform queue-length based policies in terms of convergence rate and fairness.

  2. Distributed Joint Source-Channel Coding on a Multiple Access Channel with Side Information

    CERN Document Server

    Rajesh, R

    2008-01-01

    We consider the problem of transmission of several distributed sources over a multiple access channel (MAC) with side information at the sources and the decoder. Source-channel separation does not hold for this channel. Sufficient conditions are provided for transmission of sources with a given distortion. The source and/or the channel could have continuous alphabets (thus Gaussian sources and Gaussian MACs are special cases). Various previous results are obtained as special cases. We also provide several good joint source-channel coding schemes for a discrete/continuous source and discrete/continuous alphabet channel. Channels with feedback and fading are also considered. Keywords: Multiple access channel, side information, lossy joint source-channel coding, channels with feedback, fading channels.

  3. On Resource Allocation in Fading Multiple Access Channels - An Efficient Approximate Projection Approach

    CERN Document Server

    ParandehGheibi, Ali; Ozdaglar, Asuman; Medard, Muriel

    2008-01-01

    We consider the problem of rate and power allocation in a multiple-access channel. Our objective is to obtain rate and power allocation policies that maximize a general concave utility function of average transmission rates on the information theoretic capacity region of the multiple-access channel. Our policies does not require queue-length information. We consider several different scenarios. First, we address the utility maximization problem in a nonfading channel to obtain the optimal operating rates, and present an iterative gradient projection algorithm that uses approximate projection. By exploiting the polymatroid structure of the capacity region, we show that the approximate projection can be implemented in time polynomial in the number of users. Second, we consider resource allocation in a fading channel. Optimal rate and power allocation policies are presented for the case that power control is possible and channel statistics are available. For the case that transmission power is fixed and channel ...

  4. Throughput Analysis Model for IEEE 802.11e EDCA with Multiple Access Categories

    Directory of Open Access Journals (Sweden)

    Y. Lee

    2013-08-01

    Full Text Available IEEE 802.11e standard has been specified to support differentiated quality of service (QoS, one of the critical issues on the conventional IEEE 802.11 wireless local area networks (WLANs. Enhanced Distributed Channel Access (EDCA is the fundamental and mandatory contention-based channel access method of IEEE 802.11e, and delivers traffic based on differentiated Access Categories (ACs. A general three dimensional Markov chain model of IEEE 802.11e EDCA for performance analysis is proposed in this paper. The analytical model considers multiple stations with an arbitrary number of different ACs. It also differentiates the contention window (CW sizes and the arbitration interframe spaces (AIFSs, and considers virtual collision mechanism. Based on the model, the saturation throughput of EDCA is derived, and the accuracy of the proposed model is validated via simulations.

  5. Distributed Joint Source-Channel Coding on a Multiple Access Channel with Side Information

    OpenAIRE

    R. Rajesh; Sharma, Vinod

    2008-01-01

    We consider the problem of transmission of several distributed sources over a multiple access channel (MAC) with side information at the sources and the decoder. Source-channel separation does not hold for this channel. Sufficient conditions are provided for transmission of sources with a given distortion. The source and/or the channel could have continuous alphabets (thus Gaussian sources and Gaussian MACs are special cases). Various previous results are obtained as special cases. We also pr...

  6. Analysis of Coded FHSS Systems with Multiple Access Interference over Generalized Fading Channels

    OpenAIRE

    Zummo SalamA

    2008-01-01

    Abstract We study the effect of interference on the performance of coded FHSS systems. This is achieved by modeling the physical channel in these systems as a block fading channel. In the derivation of the bit error probability over Nakagami fading channels, we use the exact statistics of the multiple access interference (MAI) in FHSS systems. Due to the mathematically intractable expression of the Rician distribution, we use the Gaussian approximation to derive the error probability of coded...

  7. Parity-Check Network Coding for Multiple Access Relay Channel in Wireless Sensor Cooperative Communications

    OpenAIRE

    Bing Du; Jun Zhang

    2010-01-01

    A recently developed theory suggests that network coding is a generalization of source coding and channel coding and thus yields a significant performance improvement in terms of throughput and spatial diversity. This paper proposes a cooperative design of a parity-check network coding scheme in the context of a two-source multiple access relay channel (MARC) model, a common compact model in hierarchical wireless sensor networks (WSNs). The scheme uses Low-Density Parity-Check (LDPC) as the ...

  8. Performance analysis of slotted fiber-optic code-division multiple-access (CDMA) packet networks

    OpenAIRE

    Hsu, CS; Li, VOK

    1997-01-01

    This paper examines code-division multiple-access (CDMA) techniques used in slotted fiber-optic packet networks. Since the inherent properties and signal processing of the conventional communication channels are different from those of the fiber-optic channels, new code sequences must be constructed for fiber-optic applications. The goal of our research is to analyze the performance of fiber-optic CDMA packet networks using code sequences with given orthogonality properties. © 1997 IEEE.

  9. Performance analysis of unslotted fiber-optic code-division multiple-access (CDMA) packet networks

    OpenAIRE

    Hsu, CS; Li, VOK

    1997-01-01

    This paper examines code-division multiple-access (CDMA) techniques used in unslotted fiber-optic packet networks. Since the inherent properties and signal processing of the conventional communication channels are different from those of the fiber-optic channels, new code sequences must be constructed for fiber-optic applications. In unslotted systems, the exact solution is very difficult to obtain. Therefore, two approximation methods are presented to analyze the performance of such systems....

  10. Active microdisk resonators in an optical code division multiple access system

    Science.gov (United States)

    Akhavan, Hooman

    2013-02-01

    An optical code division multiple access design consisting of a set of active microdisks coupled to a waveguide bus for both encoder and decoder is presented. This integrated design is beneficial for secure transmission of data through an optical fiber channel. Device optimization and performance analysis shows dependence of the output signal quality on number of users and necessity of proper adjustment of quality factor of the resonators considering intended transmitted data rate.

  11. Cascaded holographic polymer reflection grating filters for optical-code-division multiple-access applications.

    Science.gov (United States)

    Kostuk, Raymond K; Maeda, Wendi; Chen, Chia-Hung; Djordjevic, Ivan; Vasic, Bane

    2005-12-10

    We evaluate the use of edge-illuminated holographic Bragg filters formed in phenanthrenequinone-doped poly(methyl methacrylate) for optical-code-division multiple-access (OCDMA) coding and decoding applications. Experimental cascaded Bragg filters are formed to select two different wavelengths with a fixed distance between the gratings and are directly coupled to a fiber-measurement system. The configuration and tolerances of the cascaded gratings are shown to be practical for time-wavelength OCDMA applications. PMID:16363782

  12. Strict optical orthogonal codes for purely asynchronous code-division multiple-access applications.

    Science.gov (United States)

    Zhang, J G

    1996-12-10

    Strict optical orthogonal codes are presented for purely asynchronous optical code-division multiple-access (CDMA) applications. The proposed code can strictly guarantee the peaks of its cross-correlation functions and the sidelobes of any of its autocorrelation functions to have a value of 1 in purely asynchronous data communications. The basic theory of the proposed codes is given. An experiment on optical CDMA systems is also demonstrated to verify the characteristics of the proposed code. PMID:21151299

  13. Analysis of large area synchronous codedivision multiple access (LAS-CDMA)

    OpenAIRE

    Brooks, Stephen A.

    2002-01-01

    Large area synchronous code-division multiple access (LAS-CDMA) is a proposed fourth generation cellular standard. Similar to cdma2000, the distinguishing feature of LAS-CDMA is the new set of spreading codes used to separate users in the wireless channel. This thesis examines the properties of the new spreading codes. Unlike Walsh functions, which are orthogonal only when perfectly synchronized, LAS-CDMA spreading codes are orthogonal when synchronized within a nine-chip interference-free ti...

  14. Applications of superstructure fibre Bragg gratings for optical code division multiple access and packet switched networks

    OpenAIRE

    Teh, P.C.

    2003-01-01

    This thesis describes the research on the implementation of all-optical code generation and recognition based on superstructure fibre Bragg grating (SSFBG) for use in Optical Code Division Multiple Access (OCDMA) systems and also in high-speed all-optical packet switched networks.These results highlight the precision and flexibility of the continuous grating writing process and show that the SSFBG technology represents a promising technology not just for OCDMA but an extended range of other p...

  15. Joint Source-Channel Coding over a Fading Multiple Access Channel with Partial Channel State Information

    CERN Document Server

    Rajesh, R

    2009-01-01

    In this paper we address the problem of transmission of correlated sources over a fast fading multiple access channel (MAC) with partial channel state information available at both the encoders and the decoder. We provide sufficient conditions for transmission with given distortions. Next these conditions are specialized to a Gaussian MAC (GMAC). We provide the optimal power allocation strategy and compare the strategy with various levels of channel state information. Keywords: Fading MAC, Power allocation, Partial channel state information, Correlated sources.

  16. Nonadditivity of quantum capacities of quantum multiple-access channels and the butterfly network

    International Nuclear Information System (INIS)

    Multipartite quantum information transmission without additional classical resources is investigated. We show purely quantum superadditivity of quantum capacity regions of quantum memoryless multiple-access (MA) channels, which are not entanglement breaking. Also, we find that the superadditivity holds when the MA channel extends to the quantum butterfly network, which can achieve quantum network coding. The present widespread effects for the channels which enable entanglement distribution have not been revealed for multipartite scenarios.

  17. Polarization division multiple access with polarization modulation for LOS wireless communications

    Directory of Open Access Journals (Sweden)

    Cao Bin

    2011-01-01

    Full Text Available Abstract In this paper, we discuss a potential multiple access and modulation scheme based on polarized states (PS of electromagnetic (EM waves for line-of-sight (LOS communications. The proposed scheme is theoretic different from the existing polar modulation for EDGE and WCDMA systems. We propose the detailed bit representation (modulation and multiple access scheme using PS. Because of the inflexibility of polarization information in the time and frequency domains, as well as independence of frequency and space, the polarization information can be used independently for wireless communications, i.e., another independent resource domain that can be utilized. Due to the independence between the PS and the specific features of signals (such as waveform, bandwidth and data rate, the discussed polarization division multiple access (PDMA and polarization modulation (PM are expected to improve the spectrum utilization effectively. It is proved that the polarization filtering technique can be adopted in the PDMA-PM wireless communications to separate the multiuser signals and demodulate the bit information representing by PS for desired user. Some theoretical analysis is done to demonstrate the feasibility of the proposed scheme, and the simulation results are made to evaluate the performance of the suggested system.

  18. High security chaotic multiple access scheme for visible light communication systems with advanced encryption standard interleaving

    Science.gov (United States)

    Qiu, Junchao; Zhang, Lin; Li, Diyang; Liu, Xingcheng

    2016-06-01

    Chaotic sequences can be applied to realize multiple user access and improve the system security for a visible light communication (VLC) system. However, since the map patterns of chaotic sequences are usually well known, eavesdroppers can possibly derive the key parameters of chaotic sequences and subsequently retrieve the information. We design an advanced encryption standard (AES) interleaving aided multiple user access scheme to enhance the security of a chaotic code division multiple access-based visible light communication (C-CDMA-VLC) system. We propose to spread the information with chaotic sequences, and then the spread information is interleaved by an AES algorithm and transmitted over VLC channels. Since the computation complexity of performing inverse operations to deinterleave the information is high, the eavesdroppers in a high speed VLC system cannot retrieve the information in real time; thus, the system security will be enhanced. Moreover, we build a mathematical model for the AES-aided VLC system and derive the theoretical information leakage to analyze the system security. The simulations are performed over VLC channels, and the results demonstrate the effectiveness and high security of our presented AES interleaving aided chaotic CDMA-VLC system.

  19. Partial Interference and Its Performance Impact on Wireless Multiple Access Networks

    Directory of Open Access Journals (Sweden)

    Lau WingCheong

    2010-01-01

    Full Text Available To determine the capacity of wireless multiple access networks, the interference among the wireless links must be accurately modeled. In this paper, we formalize the notion of the partial interference phenomenon observed in many recent wireless measurement studies and establish analytical models with tractable solutions for various types of wireless multiple access networks. In particular, we characterize the stability region of IEEE 802.11 networks under partial interference with two potentially unsaturated links numerically. We also provide a closed-form solution for the stability region of slotted ALOHA networks under partial interference with two potentially unsaturated links and obtain a partial characterization of the boundary of the stability region for the general M-link case. Finally, we derive a closed-form approximated solution for the stability region for general M-link slotted ALOHA system under partial interference effects. Based on our results, we demonstrate that it is important to model the partial interference effects while analyzing wireless multiple access networks. This is because such considerations can result in not only significant quantitative differences in the predicted system capacity but also fundamental qualitative changes in the shape of the stability region of the systems.

  20. A simple and accessible synthetic lectin for glucose recognition and sensing

    Science.gov (United States)

    Ke, Chenfeng; Destecroix, Harry; Crump, Matthew P.; Davis, Anthony P.

    2012-09-01

    Binding carbohydrates from water is a difficult task, even for the natural carbohydrate-binding proteins known as lectins. The design of synthetic lectin mimics is correspondingly challenging, especially if good selectivities are required. In previous work we showed that success is possible, but only for complex polycyclic architectures that require lengthy and low-yielding syntheses; for example, one glucose-selective system was made in 21 steps and only 0.1% overall yield. Here we report the discovery of a simple monocyclic host that matches the earlier designs, but is far more accessible as it is prepared in just five steps and 23% overall yield. The new synthetic lectin binds glucose with excellent selectivity versus other common monosaccharides (for example, ∼50:1 versus galactose) and sufficient affinity for glucose sensing at the concentrations found in blood. It also features a built-in signalling system in the form of strong and guest-dependent fluorescence emission. The effectiveness and simplicity of this molecule suggests the potential for development into a new methodology for practical glucose monitoring.

  1. ASIC3 Channels Integrate Agmatine and Multiple Inflammatory Signals through the Nonproton Ligand Sensing Domain

    Directory of Open Access Journals (Sweden)

    Cao Hui

    2010-12-01

    Full Text Available Abstract Background Acid-sensing ion channels (ASICs have long been known to sense extracellular protons and contribute to sensory perception. Peripheral ASIC3 channels represent natural sensors of acidic and inflammatory pain. We recently reported the use of a synthetic compound, 2-guanidine-4-methylquinazoline (GMQ, to identify a novel nonproton sensing domain in the ASIC3 channel, and proposed that, based on its structural similarity with GMQ, the arginine metabolite agmatine (AGM may be an endogenous nonproton ligand for ASIC3 channels. Results Here, we present further evidence for the physiological correlation between AGM and ASIC3. Among arginine metabolites, only AGM and its analog arcaine (ARC activated ASIC3 channels at neutral pH in a sustained manner similar to GMQ. In addition to the homomeric ASIC3 channels, AGM also activated heteromeric ASIC3 plus ASIC1b channels, extending its potential physiological relevance. Importantly, the process of activation by AGM was highly sensitive to mild acidosis, hyperosmolarity, arachidonic acid (AA, lactic acid and reduced extracellular Ca2+. AGM-induced ASIC3 channel activation was not through the chelation of extracellular Ca2+ as occurs with increased lactate, but rather through a direct interaction with the newly identified nonproton ligand sensing domain. Finally, AGM cooperated with the multiple inflammatory signals to cause pain-related behaviors in an ASIC3-dependent manner. Conclusions Nonproton ligand sensing domain might represent a novel mechanism for activation or sensitization of ASIC3 channels underlying inflammatory pain-sensing under in vivo conditions.

  2. The Vibrio harveyi quorum-sensing system uses shared regulatory components to discriminate between multiple autoinducers

    Science.gov (United States)

    Waters, Christopher M.; Bassler, Bonnie L.

    2006-01-01

    The quorum-sensing bacterium Vibrio harveyi produces and responds to three autoinducers (AIs), and this sensory information converges to control the expression of bioluminescence, biofilm formation, type III secretion (TTS), and protease production. The AIs are detected by cognate sensor histidine kinases that all relay phosphate to the shared response regulator LuxO. LuxO indirectly represses the master regulator of quorum sensing, LuxR, through the activation of multiple genes encoding small regulatory RNAs (called qrr genes for Quorum Regulatory RNA). Here we use differential fluorescence induction to identify 50 quorum-sensing-controlled promoters. Some promoters only showed significant responses in the simultaneous presence of all three AIs, while others displayed substantial responses to the individual AIs. A differential response to each AI input state was also observed for qrr and luxR expression and LuxR protein production. Individual cell analyses revealed that, in each case, all the bacteria in the population respond in unison to the various AI inputs. We propose that the V. harveyi quorum-sensing transition is not switch-like but rather operates in a graded manner, and that this signaling arrangement, which uses shared regulatory proteins, nonetheless provides V. harveyi a mechanism to respond uniquely to different AI input states. PMID:17015436

  3. Dual-mode on-demand droplet routing in multiple microchannels using a magnetic fluid as carrier phase.

    Science.gov (United States)

    Kim, Jitae; Won, June; Song, Simon

    2014-09-01

    We present dual-mode, on-demand droplet routing in a multiple-outlet microfluidic device using an oil-based magnetic fluid. Magnetite (Fe3O4) nanoparticle-contained oleic acid (MNOA) was used as a carrier phase for droplet generation and manipulation. The water-in-MNOA droplets were selectively distributed in a curved microchannel with three branches by utilizing both a hydrodynamic laminar flow pattern and an external magnetic field. Without the applied magnetic field, the droplets travelled along a hydrodynamic centerline that was displaced at each bifurcating junction. However, in the presence of a permanent magnet, they were repelled from the centerline and diverted into the desired channel when the repelled distance exceeded the minimum offset allocated to the channel. The repelled distance, which is proportional to the magnetic field gradient, was manipulated by controlling the magnet's distance from the device. To evaluate routing performance, three different sizes of droplets with diameters of 63, 88, and 102 μm were directed into designated outlets with the magnet positioned at varying distances. The result demonstrated that the 102-μm droplets were sorted with an accuracy of ∼93%. Our technique enables on-demand droplet routing in multiple outlet channels by simply manipulating magnet positions (active mode) as well as size-based droplet separation with a fixed magnet position (passive mode). PMID:25332742

  4. 一种自适应功率控制的信道预约多址接入协议%Channel reservation MAC protocol with adaptive power control mechanism carrier sensing

    Institute of Scientific and Technical Information of China (English)

    袁韵洁; 李波; 闫中江

    2013-01-01

    提出了一种动态调整发送功率和载波侦听门限的信道预约多址接入协议(PC-CRM).该协议将功率控制技术应用于信道预约机制,通过对预约节点发送功率的优化设定和载波侦听门限的动态调整,使得相邻节点可以同时复用信道,从而在增强预约稳定性的基础上,提升了网络容量,降低了节点能耗.仿真结果显示,与IEEE 802.11 DCF和基本信道预约协议相比,PC-CRM协议在网络吞吐率、能量消耗效率和分组延迟抖动方面均有明显优势.%vA channel reservation MAC protocol with the adjustable transmission power and carrier sensing threshold, called PC-CRM, is proposed. PC-CRM solves the problems of poor transmission quality, low network capacity and high energy consumption, which are caused by the distributed contention based channel access scheme in Ad Hoc networks. By employing power control into the channel reservation schemes, PC-CRM adjusts the transmission power and carrier sensing threshold to the optimum values, such that the channel is multiplexed in space. Additionally, PC-CRM is also capable of stabilizing the channel reservation, improving the network capacity, and reducing the energy cost. Simulation results show that, compared with IEEE 802. 11DCF and the basic channel reservation scheme, PC-CRM performs better in terms of the throughput, energy efficiency and delay jitter.

  5. Impact of optical hard limiter on the performance of an optical overlapped-code division multiple access system

    Science.gov (United States)

    Inaty, Elie; Raad, Robert; Tablieh, Nicole

    2011-08-01

    Throughout this paper, a closed form expression of the multiple access interference (MAI) limited bit error rate (BER) is provided for the multiwavelength optical code-division multiple-access system when the system is working above the nominal transmission rate limit imposed by the passive encoding-decoding operation. This system is known in literature as the optical overlapped code division multiple access (OV-CDMA) system. A unified analytical framework is presented emphasizing the impact of optical hard limiter (OHL) on the BER performance of such a system. Results show that the performance of the OV-CDMA system may be highly improved when using OHL preprocessing at the receiver side.

  6. Polarization diversity scheme on spectral polarization coding optical code-division multiple-access network

    Science.gov (United States)

    Yen, Chih-Ta; Huang, Jen-Fa; Chang, Yao-Tang; Chen, Bo-Hau

    2010-12-01

    We present an experiment demonstrating the spectral-polarization coding optical code-division multiple-access system introduced with a nonideal state of polarization (SOP) matching conditions. In the proposed system, the encoding and double balanced-detection processes are implemented using a polarization-diversity scheme. Because of the quasiorthogonality of Hadamard codes combining with array waveguide grating routers and a polarization beam splitter, the proposed codec pair can encode-decode multiple code words of Hadamard code while retaining the ability for multiple-access interference cancellation. The experimental results demonstrate that when the system is maintained with an orthogonal SOP for each user, an effective reduction in the phase-induced intensity noise is obtained. The analytical SNR values are found to overstate the experimental results by around 2 dB when the received effective power is large. This is mainly limited by insertion losses of components and a nonflattened optical light source. Furthermore, the matching conditions can be improved by decreasing nonideal influences.

  7. UNAPPROVED ACCESS POINT ELIMINATION IN WLAN USING MULTIPLE AGENTS AND SKEW INTERVALS

    Directory of Open Access Journals (Sweden)

    Prof.S.B.Vanjale

    2012-02-01

    Full Text Available For the Wireless Networks, presence of unapproved access points is becoming the major security issue. If this kind of network threats are not detected and mitigated on time, those will lead to the serious network damage and data loss. There are many researchers proposed solutions to overcome this security problem of WLAN, but those proposed tools having limitations or maybe they not automated to adopt the frequent changes in WLAN. We are into this research to present the new approach based on Master and Slave agents. Thisproposed approach not only looking for fast detection of Rough Access points in the network but also presenting the solution to mitigate the WLAN from them. In short new framework is dealing with detecting as well as eliminating the Unapproved Access Points in the network. In proposed approach, the Master and slave agents are automatically scanning the networks for any unauthorized access points using the skew intervals. This Methodology has the following outstanding properties: (1 it doesn’t require any specialized hardware; (2 the proposed algorithm detects and completely eliminates the unapproved aps from network; (3 it provides a cost-effective solution; (4 due to multiple master agents possibility of network congestion or delaysis reduced. The proposed technique can block unapproved APs as well as remove them from the networks both in form of Unauthorized APs or as a Rogue Clients Acting as APs.

  8. Reset-sensing quasi-V2 single-inductor multiple-output buck converter with reduced cross-regulation

    OpenAIRE

    Lee, ATL; Tan, SC; Hui, SYR; Chan, PCH; Sin, JKO

    2015-01-01

    This paper proposes a reset-sensing quasi-V2 single-inductor multiple-output (SIMO) converter with minimal cross-regulation. The conventional quasi-V2 sensing scheme in SIMO converters suffers from serious cross-regulation which is primarily induced by the load differentiation with unbalanced loads. It is shown that the proposed reset-sensing quasi-V2 control scheme can significantly reduce cross-regulation by completely discharging the feed-forward sensing node to zero volts during the idle ...

  9. Analyzing Medium Access Techniques in Wireless Body Area Networks

    Directory of Open Access Journals (Sweden)

    N. Javaid

    2014-01-01

    Full Text Available This paper presents comparison of Access Techniques used in Medium Access Control (MAC protocol for Wireless Body Area Networks (WBANs. Comparison is performed between Time Division Multiple Access (TDMA, Frequency Division Multiple Access (FDMA, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA, Pure ALOHA and Slotted ALOHA (S-ALOHA. Performance metrics used for comparison are Throughput (T, Delay (D and Offered Load (G. The main goal for comparison is to show which technique gives highest Throughput and lowest Delay with increase in Load. Energy efficiency is major issue in WBAN that is why there is need to know which technique performs best for energy conservation and also gives minimum delay. Simulations are performed for different scenarios and results are compared for all techniques. We suggest TDMA as best technique to be used in MAC protocol for WBANs due to its high throughput and minimum delay with increase in load. MATLAB is the tool that is used for simulation.

  10. USING MULTIPLE SENSES IN TOURISM MARKETING: THE HELSINKI EXPERT, ECKERÖ LINE AND LINNANMÄKI AMUSEMENT PARK CASES

    Directory of Open Access Journals (Sweden)

    Asta Bäck

    2009-11-01

    Full Text Available In order to create awareness & motivation among future travellers, tourism communication, should, according to our understanding, not only appeal to the visuals, but to all user senses in an inter medial mix. Hence, smell, sound, touch, taste and sight must be touched, in order for communication to be perceived valuable and interesting, as we argue that the activation of multiple senses enhances the feeling of authenticity and experience. If combined with ration and need, in addition to the involvement of other users, only then can tourism marketing claim to be future-oriented and engaging. According to Lindstrom and Kotler our understanding of the world, for the most part, is experienced through multiple senses. Our senses are the link to memory and can tap right into emotion. After sight, smell appears to be the most persuasive sense. We will, in this article present a few related cases, our findings and discuss the implications of our findings.

  11. Optical code division multiple access secure communications systems with rapid reconfigurable polarization shift key user code

    Science.gov (United States)

    Gao, Kaiqiang; Wu, Chongqing; Sheng, Xinzhi; Shang, Chao; Liu, Lanlan; Wang, Jian

    2015-09-01

    An optical code division multiple access (OCDMA) secure communications system scheme with rapid reconfigurable polarization shift key (Pol-SK) bipolar user code is proposed and demonstrated. Compared to fix code OCDMA, by constantly changing the user code, the performance of anti-eavesdropping is greatly improved. The Pol-SK OCDMA experiment with a 10 Gchip/s user code and a 1.25 Gb/s user data of payload has been realized, which means this scheme has better tolerance and could be easily realized.

  12. Code extraction from encoded signal in time-spreading optical code division multiple access.

    Science.gov (United States)

    Si, Zhijian; Yin, Feifei; Xin, Ming; Chen, Hongwei; Chen, Minghua; Xie, Shizhong

    2010-01-15

    A vulnerability that allows eavesdroppers to extract the code from the waveform of the noiselike encoded signal of an isolated user in a standard time-spreading optical code division multiple access communication system using bipolar phase code is experimentally demonstrated. The principle is based on fine structure in the encoded signal. Each dip in the waveform corresponds to a transition of the bipolar code. Eavesdroppers can get the code by analyzing the chip numbers between any two transitions; then a decoder identical to the legal user's can be fabricated, and they can get the properly decoded signal. PMID:20081977

  13. Quantum superadditivity in linear optics networks: Sending bits via multiple-access Gaussian channels

    International Nuclear Information System (INIS)

    Superadditivity effects of communication capacities are known in the case of discrete variable quantum channels. We describe the continuous variable analog of one of these effects in the framework of Gaussian multiple access channels (MACs). Classically, superadditivity-type effects are strongly restricted: For example, adding resources to one sender is never advantageous to other senders in sending their respective information to the receiver. We show that this rule can be surpassed using quantum resources, giving rise to a type of truly quantum superadditivity. This is illustrated here for two examples of experimentally feasible Gaussian MACs.

  14. TELEMEDICINE NETWORK BASED ON CODE-DIVISION MULTIPLE ACCESS WIRELESS TECHNOLOGY

    Institute of Scientific and Technical Information of China (English)

    同鸣; 卞正中; 张亮

    2003-01-01

    Objective To satisfy the need of reliable and efficient telemedicine in many mobile and ambulance situations. Methods A practical telemedicine system bases on code-division multiple access (CDMA) wireless communication technology has been developed, which has never been mentioned before. The design scheme for the proposed system is described and detailed analysis of the network protocol stacks and the data flow is presented. Results Experiments on real time transmission of medical images using developed system have demonstrated that the system performance is satisfactory and acceptable. Conclusion The telemedicine system based on CDMA is easy to implement and has high quality of transmitted images. It would be a prospective solution to mobile telemedicine.

  15. Variable-length coding for short packets over a multiple access channel with feedback

    DEFF Research Database (Denmark)

    Trillingsgaard, Kasper Fløe; Popovski, Petar

    2014-01-01

    significantly larger for variable-length stop-feedback codes compared to fixed-blocklength codes. This is analogous to the result by Polyanskiy et al. (2011) for the point-to-point channel. An important conclusion is the following. In the asymptotic case the capacity region can be achieved by joint decoding......We consider a two-user discrete memoryless multiple access channel with a common stop-feedback signal from the receiver to both transmitters. The achievable regions are characterized using joint decoding and successive cancellation decoding and, it is shown that the achievable regions are...

  16. Rendering Intelligence at Physical Layer for Smart Addressing and Multiple Access

    DEFF Research Database (Denmark)

    Sanyal, Rajarshi; Prasad, Ramjee; Cianca, Ernestina

    2010-01-01

    addressing of a node. For a typical closed user group type of network, we propose a multiple access mechanism and network topology which will not only eliminate the need of intelligent core network equipments in the network area , but to use this intelligent physical layer to directly reach any node over......The primary objective of this work is to propose a technique of wireless communication, where we render intelligence to the physical layer. We aim to realize a physical layer that can take part in some processes which is otherwise confined to higher layer signalling activities, like for example...

  17. Achievable Rate of a Cognitive MIMO Multiple Access Channel With Multi-Secondary Users

    KAUST Repository

    Sboui, Lokman

    2015-03-01

    We study the secondary sum-rate of an underlay cognitive multiple access channel consisting of a primary user and multiple secondary users (SUs) communicating with a common destination. We propose a particular linear precoding and SU selection scheme that maximize the cognitive sum-rate. This scheme is based on space alignment strategy allowing SUs to share the spectrum without interfering with each other. We derive the optimal power allocation for each selected SU after applying perfect or imperfect successive interference cancellation. Numerical results show that the proposed scheme provides a significant sum-rate improvement as the number of SUs increases. In addition, it achieves almost the same performance as an exhaustive search selection, mainly in low and high power ranges. © 1997-2012 IEEE.

  18. Effective use of multibeam antenna and space-time multiple access technology in modern mobile communication systems

    OpenAIRE

    Moskalets, N. V.

    2015-01-01

    A possibility for efficient use of radio-frequency spectrum and of corresponding increase in productivity of mobile communication system with space-time multiple access obtained by use of multibeam antenna of base station is considered.

  19. An investigation into the accuracy of the kriging method for multiple Wi-Fi access point RSSI estimation

    OpenAIRE

    Joubert, P.J.; Helberg, A.S.J.

    2014-01-01

    Kriging was originally developed for geographical interpolation purposes, but has proven to be a powerful tool in many other applications as well. In this study we evaluate the accuracy of kriging for Wi-Fi signal strength estimation in a complex indoor environment using multiple Wi-Fi Access Points. The empirical investigation of several scenarios is described and the results analysed. Kriging is shown to be a valid method for multiple access point Wi-Fi signal strength ...

  20. The Impact of Facebook Access in Creating a Sense of Community in Tourism and Recreation Classes

    Science.gov (United States)

    Tuma, Lorie A.

    2012-01-01

    Previous research has indicated that college students use social networking sites such as Facebook to establish friendships, maintain communication, and foster a sense of community; research also has indicated that many college instructors do not. Many college faculty acknowledge the importance of a sense of community in the classroom but are…

  1. Diagonal Eigenvalue Unity (DEU) code for spectral amplitude coding-optical code division multiple access

    Science.gov (United States)

    Ahmed, Hassan Yousif; Nisar, K. S.

    2013-08-01

    Code with ideal in-phase cross correlation (CC) and practical code length to support high number of users are required in spectral amplitude coding-optical code division multiple access (SAC-OCDMA) systems. SAC systems are getting more attractive in the field of OCDMA because of its ability to eliminate the influence of multiple access interference (MAI) and also suppress the effect of phase induced intensity noise (PIIN). In this paper, we have proposed new Diagonal Eigenvalue Unity (DEU) code families with ideal in-phase CC based on Jordan block matrix with simple algebraic ways. Four sets of DEU code families based on the code weight W and number of users N for the combination (even, even), (even, odd), (odd, odd) and (odd, even) are constructed. This combination gives DEU code more flexibility in selection of code weight and number of users. These features made this code a compelling candidate for future optical communication systems. Numerical results show that the proposed DEU system outperforms reported codes. In addition, simulation results taken from a commercial optical systems simulator, Virtual Photonic Instrument (VPI™) shown that, using point to multipoint transmission in passive optical network (PON), DEU has better performance and could support long span with high data rate.

  2. Bit Error Rate Performance Analysis on Modulation Techniques of Wideband Code Division Multiple Access

    CERN Document Server

    Masud, M A; Rahman, M A

    2010-01-01

    In the beginning of 21st century there has been a dramatic shift in the market dynamics of telecommunication services. The transmission from base station to mobile or downlink transmission using M-ary Quadrature Amplitude modulation (QAM) and Quadrature phase shift keying (QPSK) modulation schemes are considered in Wideband-Code Division Multiple Access (W-CDMA) system. We have done the performance analysis of these modulation techniques when the system is subjected to Additive White Gaussian Noise (AWGN) and multipath Rayleigh fading are considered in the channel. The research has been performed by using MATLAB 7.6 for simulation and evaluation of Bit Error Rate (BER) and Signal-To-Noise Ratio (SNR) for W-CDMA system models. It is shows that the analysis of Quadrature phases shift key and 16-ary Quadrature Amplitude modulations which are being used in wideband code division multiple access system, Therefore, the system could go for more suitable modulation technique to suit the channel quality, thus we can d...

  3. A Low-Complexity Source Encoding Assisted Multiple Access Protocol for Voice/Data Integrated Networks

    Directory of Open Access Journals (Sweden)

    Nariman Farvardin

    2005-02-01

    Full Text Available We present and evaluate the performance of a reduced complexity variation to the source encoding assisted multiple access (SEAMA protocol for integrating voice and data over a wireless network. This protocol, denoted as slow movable-boundary SEAMA (SMB-SEAMA, uses the same embedded and multistate voice encoder used in the original SEAMA protocol. However, in SMB-SEAMA, the movable voice/data boundary is not set based on the frame-by-frame bandwidth demand of the voice subsystem, but on the number of ongoing voice calls and the acceptable average distortion level. This results in a protocol that, at the network layer, is packet switched for both voice and data; however, from the data traffic point of view, voice looks like circuit switched. Analytical results show that SMB-SEAMA is a very efficient MAC protocol and present a model for analyzing the performance of queuing systems with a variable number of servers, each with constant service time. Consequently, while reducing the refreshing rate of the movable boundary by three orders of magnitude, simulation results demonstrate that SMB-SEAMA does not significantly degrade the system performance (less than 8% reduction in throughput and it still performs better than packet reservation multiple access (PRMA, the other known packet-switched scheme, which updates the boundary during every transmit frame.

  4. Efficient traffic grooming with dynamic ONU grouping for multiple-OLT-based access network

    Science.gov (United States)

    Zhang, Shizong; Gu, Rentao; Ji, Yuefeng; Wang, Hongxiang

    2015-12-01

    Fast bandwidth growth urges large-scale high-density access scenarios, where the multiple Passive Optical Networking (PON) system clustered deployment can be adopted as an appropriate solution to fulfill the huge bandwidth demands, especially for a future 5G mobile network. However, the lack of interaction between different optical line terminals (OLTs) results in part of the bandwidth resources waste. To increase the bandwidth efficiency, as well as reduce bandwidth pressure at the edge of a network, we propose a centralized flexible PON architecture based on Time- and Wavelength-Division Multiplexing PON (TWDM PON). It can provide flexible affiliation for optical network units (ONUs) and different OLTs to support access network traffic localization. Specifically, a dynamic ONU grouping algorithm (DGA) is provided to obtain the minimal OLT outbound traffic. Simulation results show that DGA obtains an average 25.23% traffic gain increment under different OLT numbers within a small ONU number situation, and the traffic gain will increase dramatically with the increment of the ONU number. As the DGA can be deployed easily as an application running above the centralized control plane, the proposed architecture can be helpful to improve the network efficiency for future traffic-intensive access scenarios.

  5. Efficiency droop effects of GaN-based light-emitting diodes on the performance of code division multiple access visible-light communication system

    Science.gov (United States)

    Lu, Huimin; Yan, Chaowen; Gao, Wei; Yu, Tongjun; Wang, Jianping

    2016-02-01

    The physical mechanism in efficiency droop of GaN-based light-emitting diodes (LEDs) was investigated using a modified rate equation model considering inhomogeneous carrier distribution and was compared with the measured result. On this basis, the efficiency droop effect on the performance of a code division multiple access (CDMA) visible-light communication (VLC) system using GaN-based LEDs was also analyzed. The results reveal that the obvious transmitted signal error under the effect of LED efficiency droop leads to performance deterioration of multiuser CDMA VLC systems. Also, the performance of CDMA VLC systems is reduced with the user number increase due to LED efficiency droop. The bit error rate of a CDMA VLC system was further calculated for different branch signal levels and bias currents. It is demonstrated that the efficiency droop effect on the performance of CDMA VLC systems can be alleviated by adjusting the branch signal level and the bias current.

  6. Multiple fiber Bragg grating sensor network with a rapid response and wide spectral dynamic range using code division multiple access

    Science.gov (United States)

    Kim, Youngbok; Jeon, Sie-Wook; Park, Chang-Soo

    2011-05-01

    Fiber Bragg grating (FBG) sensor networks have been intensively researched in optical sensor area and it developed in wavelength division multiplexing (WDM) and time division multiplexing (TDM) technologies which was adopted for its interrogating many optical sensors. In particular, WDM technology can be easily employed to interrogate FBG sensor however, the number of FBG sensors is limited. On the other hand, the TDM technique can extremely expand the number of sensor because the FBG sensors have same center wavelength. However, it suffers from a reduced sensor output power due to low reflectivity of FBG sensor. In this paper, we proposed and demonstrated the FBG sensor network based on code division multiple access (CDMA) with a rapid response and wide spectral dynamic range. The reflected semiconductor optical amplifier (RSOA) as a light source was directly modulated by the generated pseudorandom binary sequence (PRBS) code and the modulated signal is amplified and goes through FBG sensors via circulator. When the modulated optical signal experienced FBG sensor array, the optical signal which was consistent with center wavelength of FBGs is reflected and added from each sensors. The added signal goes into dispersion compensating fiber (DCF) as a dispersion medium. After through the DCF, the optical signal is converted into electrical signal by using photodetector (PD). For separate individual reflected sensor signal, the sliding correlation method was used. The proposed method improves the code interference and it also has advantages such as a large number of sensors, continuously measuring individual sensors, and decreasing the complexity of the sensor network.

  7. Accessing, Utilizing and Visualizing NASA Remote Sensing Data for Malaria Modeling and Surveillance

    Science.gov (United States)

    Kiang, Richard K.; Adimi, Farida; Kempler, Steven

    2007-01-01

    This poster presentation reviews the use of NASA remote sensing data that can be used to extract environmental information for modeling malaria transmission. The authors discuss the remote sensing data from Landsat, Advanced Very High Resolution Radiometer (AVHRR), Moderate Resolution Imaging Spectroradiometer (MODIS), Tropical Rainfall Measuring Mission (TRMM), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Earth Observing One (EO-1), Advanced Land Imager (ALI) and Seasonal to Interannual Earth Science Information Partner (SIESIP) dataset.

  8. Understanding droop effect by analysis on carrier density dependence in InGaN/GaN multiple-quantum-well light-emitting diodes

    Science.gov (United States)

    Liu, Wei; Zhao, Degang; Jiang, Desheng; Chen, Ping; Liu, Zongshun; Zhu, Jianjun; Yang, Jing; He, Xiaoguang; Li, Xiaojing; Li, Xiang; Liang, Feng; Liu, Jianping; Zhang, Liqun; Yang, Hui; Zhang, Yuantao; Du, Guotong

    2016-08-01

    The droop behaviors of two InGaN/GaN multiple-quantum-well blue-green light-emitting diodes grown on c-plane sapphires with different In content are investigated. The higher-In-content sample exhibits a lower efficiency, followed by a more significant droop as current increases in comparison with the lower-In-content diode. However, it is found that for both samples their efficiency reduction trend with increasing carrier density is nearly the same. Combining with the recombination rate equations, an analysis reveals that at the same injection current level, the carrier density in the higher-In-content quantum wells which have stronger polarization effect is larger due to the smaller bimolecular recombination coefficient, resulting in a more significant droop with current. Therefore, a study on the dependence of efficiency on carrier density can provide a clear elucidation to the physical mechanism of the efficiency droop behavior.

  9. Color coded multiple access scheme for bidirectional multiuser visible light communications in smart home technologies

    Science.gov (United States)

    Tiwari, Samrat Vikramaditya; Sewaiwar, Atul; Chung, Yeon-Ho

    2015-10-01

    In optical wireless communications, multiple channel transmission is an attractive solution to enhancing capacity and system performance. A new modulation scheme called color coded multiple access (CCMA) for bidirectional multiuser visible light communications (VLC) is presented for smart home applications. The proposed scheme uses red, green and blue (RGB) light emitting diodes (LED) for downlink and phosphor based white LED (P-LED) for uplink to establish a bidirectional VLC and also employs orthogonal codes to support multiple users and devices. The downlink transmission for data user devices and smart home devices is provided using red and green colors from the RGB LEDs, respectively, while uplink transmission from both types of devices is performed using the blue color from P-LEDs. Simulations are conducted to verify the performance of the proposed scheme. It is found that the proposed bidirectional multiuser scheme is efficient in terms of data rate and performance. In addition, since the proposed scheme uses RGB signals for downlink data transmission, it provides flicker-free illumination that would lend itself to multiuser VLC system for smart home applications.

  10. Multihop Medium Access Control for WSNs: An Energy Analysis Model

    Directory of Open Access Journals (Sweden)

    Haapola Jussi

    2005-01-01

    Full Text Available We present an energy analysis technique applicable to medium access control (MAC and multihop communications. Furthermore, the technique's application gives insight on using multihop forwarding instead of single-hop communications. Using the technique, we perform an energy analysis of carrier-sense-multiple-access (CSMA- based MAC protocols with sleeping schemes. Power constraints set by battery operation raise energy efficiency as the prime factor for wireless sensor networks. A detailed energy expenditure analysis of the physical, the link, and the network layers together can provide a basis for developing new energy-efficient wireless sensor networks. The presented technique provides a set of analytical tools for accomplishing this. With those tools, the energy impact of radio, MAC, and topology parameters on the network can be investigated. From the analysis, we extract key parameters of selected MAC protocols and show that some traditional mechanisms, such as binary exponential backoff, have inherent problems.

  11. Palm Swamp Wetland Ecosystems of the Upper Amazon: Characterizing their Distribution and Inundation State Using Multiple Resolution Microwave Remote Sensing

    Science.gov (United States)

    Podest, E.; McDonald, K. C.; Schröder, R.; Pinto, N.; Zimmermann, R.; Horna, V.

    2011-12-01

    Palm swamp wetlands are prevalent in the Amazon basin, including extensive regions in northern Peru. These ecosystems are characterized by constant surface inundation and moderate seasonal water level variation. The combination of constantly saturated soils, giving rise to low oxygen conditions, and warm temperatures year-round can lead to considerable methane release to the atmosphere. Because of the widespread occurrence and expected sensitivity of these ecosystems to climate change, knowledge of their spatial extent and inundation state is crucial for assessing the associated land-atmosphere carbon exchange. Precise spatio-temporal information on palm swamps is difficult to gather because of their remoteness and difficult accessibility. Spaceborne microwave remote sensing is an effective tool for characterizing these ecosystems since it is sensitive to surface water and vegetation structure and allows monitoring large inaccessible areas on a temporal basis regardless of atmospheric conditions or solar illumination. We are developing a remote sensing methodology using multiple resolution microwave remote sensing data to determine palm swamp distribution and inundation state over focus regions in the Amazon basin in northern Peru. For this purpose, two types of multi-temporal microwave data are used: 1) high-resolution (100 m) data from the Advanced Land Observing Satellite (ALOS) Phased Array L-Band Synthetic Aperture Radar (PALSAR) to derive maps of palm swamp extent and inundation from dual-polarization fine-beam and multi-temporal HH-polarized ScanSAR, and 2) coarse resolution (25 km) combined active and passive microwave data from QuikSCAT and AMSR-E to derive inundated area fraction on a weekly basis. We compare information content and accuracy of the coarse resolution products to the PALSAR-based datasets to ensure information harmonization. The synergistic combination of high and low resolution datasets will allow for characterization of palm swamps and

  12. Inter-comparison of multiple angle remotely sensed data across different spatial resolutions and sensors for determination of albedo

    OpenAIRE

    Khavarian Nehzak, Hassan

    2012-01-01

    Surface albedo is one of the critical parameters required by studies of surface energy balance and climate models. Albedo is defined as the ratio of outgoing radiances to incoming irradiances over hemispherical view-illumination geometry. Remotely sensed albedo is usually based on multiple view angle observations and a Bidirectional Reflectance Distribution Function (BRDF) model. The accuracy of remotely sensed albedo depends on a variety of factors of which the main ones are the accuracy of ...

  13. USING MULTIPLE SENSES IN TOURISM MARKETING: THE HELSINKI EXPERT, ECKERÖ LINE AND LINNANMÄKI AMUSEMENT PARK CASES

    OpenAIRE

    Asta Bäck; Leena Alakoski; Annica Isacsson

    2009-01-01

    In order to create awareness & motivation among future travellers, tourism communication, should, according to our understanding, not only appeal to the visuals, but to all user senses in an inter medial mix. Hence, smell, sound, touch, taste and sight must be touched, in order for communication to be perceived valuable and interesting, as we argue that the activation of multiple senses enhances the feeling of authenticity and experience. If combined with ration and need, in addition to the i...

  14. Multiple Sparse Measurement Gradient Reconstruction Algorithm for DOA Estimation in Compressed Sensing

    Directory of Open Access Journals (Sweden)

    Weijian Si

    2015-01-01

    Full Text Available A novel direction of arrival (DOA estimation method in compressed sensing (CS is proposed, in which the DOA estimation problem is cast as the joint sparse reconstruction from multiple measurement vectors (MMV. The proposed method is derived through transforming quadratically constrained linear programming (QCLP into unconstrained convex optimization which overcomes the drawback that l1-norm is nondifferentiable when sparse sources are reconstructed by minimizing l1-norm. The convergence rate and estimation performance of the proposed method can be significantly improved, since the steepest descent step and Barzilai-Borwein step are alternately used as the search step in the unconstrained convex optimization. The proposed method can obtain satisfactory performance especially in these scenarios with low signal to noise ratio (SNR, small number of snapshots, or coherent sources. Simulation results show the superior performance of the proposed method as compared with existing methods.

  15. Adaptive Code Division Multiple Access Protocol for Wireless Network-on-Chip Architectures

    Science.gov (United States)

    Vijayakumaran, Vineeth

    Massive levels of integration following Moore's Law ushered in a paradigm shift in the way on-chip interconnections were designed. With higher and higher number of cores on the same die traditional bus based interconnections are no longer a scalable communication infrastructure. On-chip networks were proposed enabled a scalable plug-and-play mechanism for interconnecting hundreds of cores on the same chip. Wired interconnects between the cores in a traditional Network-on-Chip (NoC) system, becomes a bottleneck with increase in the number of cores thereby increasing the latency and energy to transmit signals over them. Hence, there has been many alternative emerging interconnect technologies proposed, namely, 3D, photonic and multi-band RF interconnects. Although they provide better connectivity, higher speed and higher bandwidth compared to wired interconnects; they also face challenges with heat dissipation and manufacturing difficulties. On-chip wireless interconnects is one other alternative proposed which doesn't need physical interconnection layout as data travels over the wireless medium. They are integrated into a hybrid NOC architecture consisting of both wired and wireless links, which provides higher bandwidth, lower latency, lesser area overhead and reduced energy dissipation in communication. However, as the bandwidth of the wireless channels is limited, an efficient media access control (MAC) scheme is required to enhance the utilization of the available bandwidth. This thesis proposes using a multiple access mechanism such as Code Division Multiple Access (CDMA) to enable multiple transmitter-receiver pairs to send data over the wireless channel simultaneously. It will be shown that such a hybrid wireless NoC with an efficient CDMA based MAC protocol can significantly increase the performance of the system while lowering the energy dissipation in data transfer. In this work it is shown that the wireless NoC with the proposed CDMA based MAC protocol

  16. Downscaling remotely sensed imagery using area-to-point cokriging and multiple-point geostatistical simulation

    Science.gov (United States)

    Tang, Yunwei; Atkinson, Peter M.; Zhang, Jingxiong

    2015-03-01

    A cross-scale data integration method was developed and tested based on the theory of geostatistics and multiple-point geostatistics (MPG). The goal was to downscale remotely sensed images while retaining spatial structure by integrating images at different spatial resolutions. During the process of downscaling, a rich spatial correlation model in the form of a training image was incorporated to facilitate reproduction of similar local patterns in the simulated images. Area-to-point cokriging (ATPCK) was used as locally varying mean (LVM) (i.e., soft data) to deal with the change of support problem (COSP) for cross-scale integration, which MPG cannot achieve alone. Several pairs of spectral bands of remotely sensed images were tested for integration within different cross-scale case studies. The experiment shows that MPG can restore the spatial structure of the image at a fine spatial resolution given the training image and conditioning data. The super-resolution image can be predicted using the proposed method, which cannot be realised using most data integration methods. The results show that ATPCK-MPG approach can achieve greater accuracy than methods which do not account for the change of support issue.

  17. Performance analysis of multiple interference suppression over asynchronous/synchronous optical code-division multiple-access system based on complementary/prime/shifted coding scheme

    Science.gov (United States)

    Nieh, Ta-Chun; Yang, Chao-Chin; Huang, Jen-Fa

    2011-08-01

    A complete complementary/prime/shifted prime (CPS) code family for the optical code-division multiple-access (OCDMA) system is proposed. Based on the ability of complete complementary (CC) code, the multiple-access interference (MAI) can be suppressed and eliminated via spectral amplitude coding (SAC) OCDMA system under asynchronous/synchronous transmission. By utilizing the shifted prime (SP) code in the SAC scheme, the hardware implementation of encoder/decoder can be simplified with a reduced number of optical components, such as arrayed waveguide grating (AWG) and fiber Bragg grating (FBG). This system has a superior performance as compared to previous bipolar-bipolar coding OCDMA systems.

  18. A localized cooperative wideband spectrum sensing for dynamic access of TV bands using RF sensor networks

    KAUST Repository

    Mirza, Mohammed

    2011-07-01

    In this paper we address and simulate a Radio Frequency (RF) sensor network for a cooperative spectrum sensing and localization scheme. The proposed method integrates a Wavelet based Multi-Resolution Spectrum Sensing (MRSS), an N-bit hard combination technique for cooperative decision making and a Received Signal Strength (RSS) based localization algorithm to detect the availability of frequency bands and the location of the usable base station. We develop an N-bit hard combination technique and compare its performance to a traditionally used 2-bit hard combination for cooperative sensing. The key idea is to design a novel RF sensor network based cooperative wideband spectrum sensing and localization scheme by using a wavelet based Multi-Resolution Spectrum Sensing (MRSS) and Received Signal Strength (RSS) Localization techniques which were originally proposed for cognitive radio applications. The performance evaluations are also done to show the different detection accuracies for varying parameters such as number of sensor nodes, Signal to Noise Ratios (SNR) and number of averaged Power Spectral Densities (PSD). The proposed scheme improves the problems of shadowing, fading and noise. In addition, the RSS based localization technique was shown to be an acceptable means of estimating the position of the available transmitter. © 2011 IEEE.

  19. A New Time-Hopping Multiple Access Communication System Simulator: Application to Ultra-Wideband

    Directory of Open Access Journals (Sweden)

    José M. Páez-Borrallo

    2005-03-01

    Full Text Available Time-hopping ultra-wideband technology presents some very attractive features for future indoor wireless systems in terms of achievable transmission rate and multiple access capabilities. This paper develops an algorithm to design time-hopping system simulators specially suitable for ultra-wideband, which takes advantage of some of the specific characteristics of this kind of systems. The algorithm allows an improvement of both the time capabilities and the achievable sampling rate and can be used to research into the influence of different parameters on the performance of the system. An additional result is the validation of a new general performance formula for time-hopping ultra-wideband systems with multipath channels.

  20. Analysis of Coded FHSS Systems with Multiple Access Interference over Generalized Fading Channels

    Directory of Open Access Journals (Sweden)

    Zummo SalamA

    2008-01-01

    Full Text Available Abstract We study the effect of interference on the performance of coded FHSS systems. This is achieved by modeling the physical channel in these systems as a block fading channel. In the derivation of the bit error probability over Nakagami fading channels, we use the exact statistics of the multiple access interference (MAI in FHSS systems. Due to the mathematically intractable expression of the Rician distribution, we use the Gaussian approximation to derive the error probability of coded FHSS over Rician fading channel. The effect of pilot-aided channel estimation is studied for Rician fading channels using the Gaussian approximation. From this, the optimal hopping rate in coded FHSS is approximated. Results show that the performance loss due to interference increases as the hopping rate decreases.

  1. Analysis of Coded FHSS Systems with Multiple Access Interference over Generalized Fading Channels

    Directory of Open Access Journals (Sweden)

    Salam A. Zummo

    2009-02-01

    Full Text Available We study the effect of interference on the performance of coded FHSS systems. This is achieved by modeling the physical channel in these systems as a block fading channel. In the derivation of the bit error probability over Nakagami fading channels, we use the exact statistics of the multiple access interference (MAI in FHSS systems. Due to the mathematically intractable expression of the Rician distribution, we use the Gaussian approximation to derive the error probability of coded FHSS over Rician fading channel. The effect of pilot-aided channel estimation is studied for Rician fading channels using the Gaussian approximation. From this, the optimal hopping rate in coded FHSS is approximated. Results show that the performance loss due to interference increases as the hopping rate decreases.

  2. A Bayesian Game-Theoretic Approach for Distributed Resource Allocation in Fading Multiple Access Channels

    Directory of Open Access Journals (Sweden)

    Gaoning He

    2010-01-01

    Full Text Available A Bayesian game-theoretic model is developed to design and analyze the resource allocation problem in K-user fading multiple access channels (MACs, where the users are assumed to selfishly maximize their average achievable rates with incomplete information about the fading channel gains. In such a game-theoretic study, the central question is whether a Bayesian equilibrium exists, and if so, whether the network operates efficiently at the equilibrium point. We prove that there exists exactly one Bayesian equilibrium in our game. Furthermore, we study the network sum-rate maximization problem by assuming that the users coordinate according to a symmetric strategy profile. This result also serves as an upper bound for the Bayesian equilibrium. Finally, simulation results are provided to show the network efficiency at the unique Bayesian equilibrium and to compare it with other strategies.

  3. Filter multiplexing by use of spatial Code Division Multiple Access approach.

    Science.gov (United States)

    Solomon, Jonathan; Zalevsky, Zeev; Mendlovic, David; Monreal, Javier Garcia

    2003-02-10

    The increasing popularity of optical communication has also brought a demand for a broader bandwidth. The trend, naturally, was to implement methods from traditional electronic communication. One of the most effective traditional methods is Code Division Multiple Access. In this research, we suggest the use of this approach for spatial coding applied to images. The approach is to multiplex several filters into one plane while keeping their mutual orthogonality. It is shown that if the filters are limited by their bandwidth, the output of all the filters can be sampled in the original image resolution and fully recovered through an all-optical setup. The theoretical analysis of such a setup is verified in an experimental demonstration. PMID:12593478

  4. All-optical code-division multiple-access applications: 2(n) extended-prime codes.

    Science.gov (United States)

    Zhang, J G; Kwong, W C; Mann, S

    1997-09-10

    A new family of 2(n) codes, called 2(n) extended-prime codes, is proposed for all-optical code-division multiple-access networks. Such 2(n) codes are derived from so-called extended-prime codes so that their cross-correlation functions are not greater than 1, as opposed to 2 for recently proposed 2(n) prime codes. As a result, a larger number of active users can now be supported by the new codes for a given bit-error rate than can be by 2(n) prime codes, while power-efficient, waveguide-integrable all-serial coding and correlating configurations proposed for the 2(n) prime codes can still be employed. PMID:18259529

  5. Isolated user security enhancement in optical code division multiple access network against eavesdropping

    Science.gov (United States)

    Jyoti, Vishav; Kaler, Rajinder Singh

    2012-09-01

    A novel virtual user system is modeled for enhancing the security of an optical code division multiple access (OCDMA) network. Although the OCDMA system implementing code shift keying (CSK) is secure against a conventional power detector, it is susceptible to differential eavesdropping. An analytical framework is developed for the CSK-OCDMA system to show eavesdropper's code interception performance for a single transmitting user in the presence of a virtual user. It is shown that the eavesdropper's probability of correct bit interception decreases from 7.1×10-1 to 1.85×10-5 with the inclusion of the virtual user. Furthermore, the results confirm that the proposed virtual user scheme increases the confidentiality of the CSK-OCDMA system and outperforms the conventional OCDMA scheme in terms of security.

  6. System and method for integrating and accessing multiple data sources within a data warehouse architecture

    Science.gov (United States)

    Musick, Charles R.; Critchlow, Terence; Ganesh, Madhaven; Slezak, Tom; Fidelis, Krzysztof

    2006-12-19

    A system and method is disclosed for integrating and accessing multiple data sources within a data warehouse architecture. The metadata formed by the present method provide a way to declaratively present domain specific knowledge, obtained by analyzing data sources, in a consistent and useable way. Four types of information are represented by the metadata: abstract concepts, databases, transformations and mappings. A mediator generator automatically generates data management computer code based on the metadata. The resulting code defines a translation library and a mediator class. The translation library provides a data representation for domain specific knowledge represented in a data warehouse, including "get" and "set" methods for attributes that call transformation methods and derive a value of an attribute if it is missing. The mediator class defines methods that take "distinguished" high-level objects as input and traverse their data structures and enter information into the data warehouse.

  7. A Low Complexity VCS Method for PAPR Reduction in Multicarrier Code Division Multiple Access

    Institute of Scientific and Technical Information of China (English)

    Si-Si Liu; Yue Xiao; Qing-Song Wen; Shao-Qian Li

    2007-01-01

    This paper investigatesa peak to average power ratio (PAPR) reduction method in multicarrier code division multiple access (MC-CDMA) system. Variable code sets (VCS), a spreading codes selection scheme, can improve the PAPR property of the MC-CDMA signals, but this technique requires an exhaustive search over the combinations of spreading code sets. It is observed that when the number of active users increases, the search complexity will increase exponentially. Based on this fact, we propose a low complexity VCS (LC-VCS) method to reduce the computational complexity. The basic idea of LC-VCS is to derive new signals using the relationship between candidature signals. Simulation results show that the proposed approach can reduce PAPR with lower computational complexity. In addition, it can be blindly received without any side information.

  8. New code match strategy for wideband code division multiple access code tree management

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Orthogonal variable spreading factor channelization codes are widely used to provide variable data rates for supporting different bandwidth requirements in wideband code division multiple access (WCDMA) systems. A new code match scheme for WCDMA code tree management was proposed. The code match scheme is similar to the existing crowed-first scheme. When choosing a code for a user, the code match scheme only compares the one up layer of the allocated codes, unlike the crowed-first scheme which perhaps compares all up layers. So the operation of code match scheme is simple, and the average time delay is decreased by 5.1%. The simulation results also show that the code match strategy can decrease the average code blocking probability by 8.4%.

  9. Satellite-matrix-switched, time-division-multiple-access network simulator

    Science.gov (United States)

    Ivancic, William D.; Andro, Monty; Nagy, Lawrence A.; Budinger, James M.; Shalkhauser, Mary JO

    1990-01-01

    A versatile experimental Ka-band network simulator has been implemented at the NASA Lewis Research Center to demonstrate and evaluate a satellite-matrix-switched, time-division-multiple-access (SMS-TDMA) network and to evaluate future digital ground terminals and radiofrequency (RF) components. The simulator was implemented by using proof-of-concept RF components developed under NASA contracts and digital ground terminal and link simulation hardware developed at Lewis. This simulator provides many unique capabilities such as satellite range delay and variation simulation and rain fade simulation. All network parameters (e.g., signal-to-noise ratio, satellite range variation rate, burst density, and rain fade) are controlled and monitored by a central computer. The simulator is presently configured as a three-ground-terminal SMS-TDMA network.

  10. On the Capacity Region for Cognitive Multiple Access over White Space Channels

    CERN Document Server

    Zhang, Huazi; Zhang, Zhaoyang

    2012-01-01

    Cognitive Radio (CR) has stirred great interest with its potential to exploit the already scarce spectrum resource. The cognitive multiple access channels (CogMAC) are commonly seen in many applications, such as the Cognitive Radio Sensor Networks (CRSN), and the 802.22 cognitive Wireless Regional Area Networks (WRAN). In this paper, the primary user (PU) activities are treated as on/off side information, which can be obtained causally or non-causally. The cognitive MAC channels are then modeled as multi-switch channels and their rate regions are characterized. Explicit forms of outer and inner bounds of this rate region are derived by assuming additional side information, and they are shown to be tight in some special cases. An optimal rate and power allocation scheme that maximizes the sum rate is also proposed. The numerical results show the importance of side information in enhancing the capacity and the effectiveness of our rate allocation scheme.

  11. Secret Key Agreement Using Correlated Sources over the Generalized Multiple Access Channel

    CERN Document Server

    Salimi, Somayeh

    2012-01-01

    A secret key agreement setup between three users is considered in which each of the users 1 and 2 intends to share a secret key with user 3 and users 1 and 2 are eavesdroppers with respect to each other. The three users observe i.i.d. outputs of correlated sources and there is a generalized discrete memoryless multiple access channel (GDMMAC) from users 1 and 2 to user 3 for communication between the users. The secret key agreement is established using the correlated sources and the GDMMAC. In this setup, inner and outer bounds of the secret key capacity region are investigated. Moreover, for a special case where the channel inputs and outputs and the sources form Markov chains in some order, the secret key capacity region is derived. Also a Gaussian case is considered in this setup.

  12. Optical Shared Memory Computing and Multiple Access Protocols for Photonic Networks

    Science.gov (United States)

    Li, Kuang-Yu.

    In this research we investigate potential applications of optics in massively parallel computer systems, especially focusing on design issues in three-dimensional optical data storage and free-space photonic networks. An optical implementation of a shared memory uses a single photorefractive crystal and can realize the set of memory modules in a digital shared memory computer. A complete instruction set consists of R sc EAD, W sc RITE, S sc ELECTIVE E sc RASE, and R sc EFRESH, which can be applied to any memory module independent of (and in parallel with) instructions to the other memory modules. In addition, a memory module can execute a sequence of R sc EAD operations simultaneously with the execution of a W sc RITE operation to accommodate differences in optical recording and readout times common to optical volume storage media. An experimental shared memory system is demonstrated and its projected performance is analyzed. A multiplexing technique is presented to significantly reduce both grating- and beam-degeneracy crosstalk in volume holographic systems, by incorporating space, angle, and wavelength as the multiplexing parameters. In this approach, each hologram, which results from the interference between a single input node and an object array, partially overlaps with the other holograms in its neighborhood. This technique can offer improved interconnection density, optical throughput, signal fidelity, and space-bandwidth product utilization. Design principles and numerical simulation results are presented. A free-space photonic cellular hypercube parallel computer, with emphasis on the design of a collisionless multiple access protocol, is presented. This design incorporates wavelength-, space-, and time-multiplexing to achieve multiple access, wavelength reuse, dense connectivity, collisionless communications, and a simple control mechanism. Analytic models based on semi-Markov processes are employed to analyze this protocol. The performance of the

  13. An Adaptive Time-Spread Multiple-Access Policy for Wireless Sensor Networks

    Directory of Open Access Journals (Sweden)

    Konstantinos Oikonomou

    2007-05-01

    Full Text Available Sensor networks require a simple and efficient medium access control policy achieving high system throughput with no or limited control overhead in order to increase the network lifetime by minimizing the energy consumed during transmission attempts. Time-spread multiple-access (TSMA policies that have been proposed for ad hoc network environments, can also be employed in sensor networks, since no control overhead is introduced. However, they do not take advantage of any cross-layer information in order to exploit the idiosyncrasies of the particular sensor network environment such as the presence of typically static nodes and a common destination for the forwarded data. An adaptive probabilistic TSMA-based policy, that is proposed and analyzed in this paper, exploits these idiosyncrasies and achieves higher system throughput than the existing TSMA-based policies without any need for extra control overhead. As it is analytically shown in this paper, the proposed policy always outperforms the existing TSMA-based policies, if certain parameter values are properly set; the analysis also provides for these proper values. It is also shown that the proposed policy is characterized by a certain convergence period and that high system throughput is achieved for long convergence periods. The claims and expectations of the provided analysis are supported by simulation results presented in this paper.

  14. Method for Multiple Targets Tracking in Cognitive Radar Based on Compressed Sensing

    Directory of Open Access Journals (Sweden)

    Yang Jun

    2016-02-01

    Full Text Available A multiple targets cognitive radar tracking method based on Compressed Sensing (CS is proposed. In this method, the theory of CS is introduced to the case of cognitive radar tracking process in multiple targets scenario. The echo signal is sparsely expressed. The designs of sparse matrix and measurement matrix are accomplished by expressing the echo signal sparsely, and subsequently, the restruction of measurement signal under the down-sampling condition is realized. On the receiving end, after considering that the problems that traditional particle filter suffers from degeneracy, and require a large number of particles, the particle swarm optimization particle filter is used to track the targets. On the transmitting end, the Posterior Cramér-Rao Bounds (PCRB of the tracking accuracy is deduced, and the radar waveform parameters are further cognitively designed using PCRB. Simulation results show that the proposed method can not only reduce the data quantity, but also provide a better tracking performance compared with traditional method.

  15. Parity-Check Network Coding for Multiple Access Relay Channel in Wireless Sensor Cooperative Communications

    Directory of Open Access Journals (Sweden)

    Du Bing

    2010-01-01

    Full Text Available A recently developed theory suggests that network coding is a generalization of source coding and channel coding and thus yields a significant performance improvement in terms of throughput and spatial diversity. This paper proposes a cooperative design of a parity-check network coding scheme in the context of a two-source multiple access relay channel (MARC model, a common compact model in hierarchical wireless sensor networks (WSNs. The scheme uses Low-Density Parity-Check (LDPC as the surrogate to build up a layered structure which encapsulates the multiple constituent LDPC codes in the source and relay nodes. Specifically, the relay node decodes the messages from two sources, which are used to generate extra parity-check bits by a random network coding procedure to fill up the rate gap between Source-Relay and Source-Destination transmissions. Then, we derived the key algebraic relationships among multidimensional LDPC constituent codes as one of the constraints for code profile optimization. These extra check bits are sent to the destination to realize a cooperative diversity as well as to approach MARC decode-and-forward (DF capacity.

  16. High photo-excited carrier multiplication by charged InAs dots in AlAs/GaAs/AlAs resonant tunneling diode

    OpenAIRE

    Wang, Wangping; Hou, Ying; Xiong, Dayuan; Li, Ning; Lu, Wei

    2007-01-01

    We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs/GaAs/AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10nA photocurrent in this structure, corresponding to the photo-excited carrier multiplication factor of 10^7. This high multiplication factor is achieved by the ...

  17. Mapping of government land encroachment in Cameron Highlands using multiple remote sensing datasets

    Science.gov (United States)

    Zin, M. H. M.; Ahmad, B.

    2014-02-01

    The cold and refreshing highland weather is one of the factors that give impact to socio-economic growth in Cameron Highlands. This unique weather of the highland surrounded by tropical rain forest can only be found in a few places in Malaysia. It makes this place a famous tourism attraction and also provides a very suitable temperature for agriculture activities. Thus it makes agriculture such as tea plantation, vegetable, fruits and flowers one of the biggest economic activities in Cameron Highlands. However unauthorized agriculture activities are rampant. The government land, mostly forest area have been encroached by farmers, in many cases indiscriminately cutting down trees and hill slopes. This study is meant to detect and assess this encroachment using multiple remote sensing datasets. The datasets were used together with cadastral parcel data where survey lines describe property boundary, pieces of land are subdivided into lots of government and private. The general maximum likelihood classification method was used on remote sensing image to classify the land-cover in the study area. Ground truth data from field observation were used to assess the accuracy of the classification. Cadastral parcel data was overlaid on the classification map in order to detect the encroachment area. The result of this study shows that there is a land cover change of 93.535 ha in the government land of the study area between years 2001 to 2010, nevertheless almost no encroachment took place in the studied forest reserve area. The result of this study will be useful for the authority in monitoring and managing the forest.

  18. Mapping of government land encroachment in Cameron Highlands using multiple remote sensing datasets

    International Nuclear Information System (INIS)

    The cold and refreshing highland weather is one of the factors that give impact to socio-economic growth in Cameron Highlands. This unique weather of the highland surrounded by tropical rain forest can only be found in a few places in Malaysia. It makes this place a famous tourism attraction and also provides a very suitable temperature for agriculture activities. Thus it makes agriculture such as tea plantation, vegetable, fruits and flowers one of the biggest economic activities in Cameron Highlands. However unauthorized agriculture activities are rampant. The government land, mostly forest area have been encroached by farmers, in many cases indiscriminately cutting down trees and hill slopes. This study is meant to detect and assess this encroachment using multiple remote sensing datasets. The datasets were used together with cadastral parcel data where survey lines describe property boundary, pieces of land are subdivided into lots of government and private. The general maximum likelihood classification method was used on remote sensing image to classify the land-cover in the study area. Ground truth data from field observation were used to assess the accuracy of the classification. Cadastral parcel data was overlaid on the classification map in order to detect the encroachment area. The result of this study shows that there is a land cover change of 93.535 ha in the government land of the study area between years 2001 to 2010, nevertheless almost no encroachment took place in the studied forest reserve area. The result of this study will be useful for the authority in monitoring and managing the forest

  19. Hardware-In-the-Loop Measurements of the Multi-Carrier Compressed Sensing Multi-User Detection (MCSM) System

    OpenAIRE

    Bockelmann, Carsten; Monsees, Fabian; Woltering, Matthias; Dekorsy, Armin

    2015-01-01

    MCSM is a recently proposed novel system concept to solve the massive access problem envisioned in future communication systems like 5G and industry 4.0 systems. This work focuses on the practical verification of the theoretical gains that MCSM provides using a Hardware-In-the-Loop (HIL) measurement setup. We present results in two different scenarios: (i) a LoS lab setup and (ii) a non-LoS machine hall. In both scenarios MCSM shows promising performance in terms of the number of supported us...

  20. Entanglement distribution over quantum code-division multiple-access networks

    Science.gov (United States)

    Zhu, Chang-long; Yang, Nan; Liu, Yu-xi; Nori, Franco; Zhang, Jing

    2015-10-01

    We present a method for quantum entanglement distribution over a so-called code-division multiple-access network, in which two pairs of users share the same quantum channel to transmit information. The main idea of this method is to use different broadband chaotic phase shifts, generated by electro-optic modulators and chaotic Colpitts circuits, to encode the information-bearing quantum signals coming from different users and then recover the masked quantum signals at the receiver side by imposing opposite chaotic phase shifts. The chaotic phase shifts given to different pairs of users are almost uncorrelated due to the randomness of chaos and thus the quantum signals from different pair of users can be distinguished even when they are sent via the same quantum channel. It is shown that two maximally entangled states can be generated between two pairs of users by our method mediated by bright coherent lights, which can be more easily implemented in experiments compared with single-photon lights. Our method is robust under the channel noises if only the decay rates of the information-bearing fields induced by the channel noises are not quite high. Our study opens up new perspectives for addressing and transmitting quantum information in future quantum networks.

  1. Primary user localisation and uplink resource allocation in orthogonal frequency division multiple access cognitive radio systems

    KAUST Repository

    Nam, Haewoon

    2015-05-21

    In cognitive radio networks, secondary users (SUs) can share spectrum with primary users (PUs) under the condition that no interference is caused to the PUs. To evaluate the interference imposed to the PUs, the cognitive systems discussed in the literature usually assume that the channel state information (CSI) of the link from a secondary transmitter to a primary receiver (interference link) is known at the secondary transmitter. However, this assumption may often be impractical in cognitive radio systems, since the PUs need to be oblivious to the presence of the SUs. The authors first discuss PU localisation and then introduce an uplink resource allocation algorithm for orthogonal frequency division multiple access-based cognitive radio systems, where relative location information between primary and SUs is used instead of CSI of the interference link to estimate the interference. Numerical and simulation results show that it is indeed effective to use location information as a part of resource allocation and thus a near-optimal capacity is achieved. © The Institution of Engineering and Technology 2015.

  2. NCSA: A New Protocol for Random Multiple Access Based on Physical Layer Network Coding

    CERN Document Server

    Bui, Huyen Chi; Boucheret, Marie-Laure

    2010-01-01

    This paper introduces a random multiple access method for satellite communications, named Network Coding-based Slotted Aloha (NCSA). The goal is to improve diversity of data bursts on a slotted-ALOHA-like channel thanks to error correcting codes and Physical-layer Network Coding (PNC). This scheme can be considered as a generalization of the Contention Resolution Diversity Slotted Aloha (CRDSA) where the different replicas of this system are replaced by the different parts of a single word of an error correcting code. The performance of this scheme is first studied through a density evolution approach. Then, simulations confirm the CRDSA results by showing that, for a time frame of $400$ slots, the achievable total throughput is greater than $0.7\\times C$, where $C$ is the maximal throughput achieved by a centralized scheme. This paper is a first analysis of the proposed scheme which open several perspectives. The most promising approach is to integrate collided bursts into the decoding process in order to im...

  3. Satellite range delay simulator for a matrix-switched time division multiple-access network simulator

    Science.gov (United States)

    Nagy, Lawrence A.

    1989-01-01

    The Systems Integration, Test, and Evaluation (SITE) facility at NASA Lewis Research Center is presently configured as a satellite-switched time division multiple access (SS-TDMA) network simulator. The purpose of SITE is to demonstrate and evaluate advanced communication satellite technologies, presently embodied by POC components developed under NASA contracts in addition to other hardware, such as ground terminals, designed and built in-house at NASA Lewis. Each ground terminal in a satellite communications system will experience a different aspect of the satellite's motion due mainly to daily tidal effects and station keeping, hence a different duration and rate of variation in the range delay. As a result of this and other effects such as local oscillator instability, each ground terminal must constantly adjust its transmit burst timing so that data bursts from separate ground terminals arrive at the satellite in their assigned time slots, preventing overlap and keeping the system in synchronism. On the receiving end, ground terminals must synchronize their local clocks using reference transmissions received through the satellite link. A feature of the SITE facility is its capability to simulate the varying propagation delays and associated Doppler frequency shifts that the ground terminals in the network have to cope with. Delay is achieved by means of two NASA Lewis designed and built range delay simulator (RDS) systems, each independently controlled locally with front panel switches or remotely by an experiment control and monitor (EC/M) computer.

  4. Optical Code-Division Multiple-Access and Wavelength Division Multiplexing: Hybrid Scheme Review

    Directory of Open Access Journals (Sweden)

    P. Susthitha Menon

    2012-01-01

    Full Text Available Problem statement: Hybrid Optical Code-Division Multiple-Access (OCDMA and Wavelength-Division Multiplexing (WDM have flourished as successful schemes for expanding the transmission capacity as well as enhancing the security for OCDMA. However, a comprehensive review related to this hybrid system are lacking currently. Approach: The purpose of this paper is to review the literature on OCDMA-WDM overlay systems, including our hybrid approach of one-dimensional coding of SAC OCDMA with WDM signals. In addition, we present an additional review of other categorios of hybrid WDM/OCDMA schemes, where codes of OCDMA can be employed on each WDM wavelength. Furthermore, an essential background of OCDMA, recent coding techniques and security issues are also presented. Results: Our results indicate that the feasibility of transmitting both OCDMA and WDM users on the same spectrum band can be achieved using MQC family code with an acceptable performance as well as good data confidentiality. In addition, the WDM interference signals can be suppressed properly for detection of optical broadband CDMA using notch filters. Conclusion: The paper provides a comprehensive overview of hybrid OCDMA-WDM systems and can be used as a baseline study for other scientists in the similar scope of research.

  5. Enhanced Seamless Handoff Using Multiple Access Points in Wireless Local Area Network

    Directory of Open Access Journals (Sweden)

    Prabhavathy . G,

    2015-06-01

    Full Text Available The Mobility in wireless cellular communication systems is its backbone so as to enhance the quality of service and maintain the continuous service. Handoff is an important task in maintaining the continuity of call in cellular systems and its failure can result in ongoing call termination. In cellular mobile networks, the coverage region is divided into smaller cells in order to achieve high system capacity. Each cell has a Base-Station (BS, which provides the service to the Mobile Terminals (MTs, i.e. users equipped with phones, within its region. Before a mobile user can communicate with other user(s in the network, a group of the frequency bands or channels should usually be assigned. The MTs is free to move across cells. When the mobile user crossing a cell boundary or by deterioration in quality of the signal in the current channel, handoff process is initiated. The scope of this project is to design 802.11 handoff schemes to solve the handoff problems in closely-spaced WLANs.The major problem in multiple WLANs are so many users trying to use same access point(AP, and interferences from nearby WLAN. The better hand off scheme based on signal strength and velocity of the nodes is proposed. The simulation results show that the proposed handoff scheme significantly reduces packet losses compared with existing handoff schemes.

  6. A Design and Development of Word Sense Disambiguation Algorithm for English Language Understanding for Database Access

    Directory of Open Access Journals (Sweden)

    M. Munusamy

    2011-01-01

    Full Text Available Problem statement: This study attempts to present an object-net method for word sense disambiguation. It is proposed to model the elementary meanings which assist the machine to autonomously undertake the analysis and synthesis processes of meaning. Approach: In the proposed methodology, the disambiguation process was performed in context manner. Starting from natural text, the context of the sentence was identified, then the actual meaning identified using correlation of elementary object meanings existed in object-net database. It was because even ambiguous word will have only one meaning based on the context or object or domain on which the sentence was written. Results: This object-net approach disambiguates original text with high precision of 96% of the verbs and 97% of nouns for data extraction from the database and reporting in terms of graphs. Conclusion: The accuracy of finding the sense of a word and extracting data from the database and projecting into graphs was based on number of trained objects in object-net database. Due to this object-net database plays a major role in this proposed method.

  7. A USER-DEPENDENT PERFECT-SCHEDULING MULTIPLE ACCESS PROTOCOL FOR VOICE-DATA INTEGRATION IN WIRELESS NETWORKDS

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A novel Multiple Access Control(MAC) protocol-User-dependent Perfect-scheduling Multiple Access(UPMA) protocol,which supports joint transmission of voice and data packets,is proposed.By this protocol,the bandwidth can be allocated dynamically to the uplink and downlink traffic with on-demand assignment and the transmission of Mobile Terminals(MTs) can be perfectly scheduled by means of polling.Meanwhile.a unique frame stucture is designed to guarantee Quality of Service(QoS) in voice traffic supporting.An effective colision resolution algorthm is also proposed to guarantee rapid channel access for activated MTs.Finally,performance of UPMA protocol is evaluated by simulation and compared with MPRMA protocol.Simulation results show that UPMA protocol has better performance.

  8. A USER-DEPENDENT PERFECT-SCHEDULING MULTIPLE ACCESS PROTOCOL FOR VOICE-DATA INTEGRATION IN WIRELESS NETWORKS

    Institute of Scientific and Technical Information of China (English)

    Zhou Yajian; Li Jiandong; Liu Kai

    2002-01-01

    A novel Multiple Access Control (MAC) protocol - User-dependent Perfect-scheduling Multiple Access (UPMA) protocol, which supports joint transmission of voice and data packets,is proposed. By this protocol, the bandwidth can be allocated dynamically to the uplink and downlink traffic with on-demand assignment and the transmission of Mobile Terminals (MTs)can be perfectly scheduled by means of polling. Meanwhile, a unique frame structure is designed to guarantee Quality of Service (QoS) in voice traffic supporting. An effective collision resolution algorithm is also proposed to guarantee rapid channel access for activated MTs. Finally, performance of UPMA protocol is evaluated by simulation and compared with MPRMA protocol.Simulation results show that UPMA protocol has better performance.

  9. Performance Study of Hybrid DS/FFH Spread-Spectrum Systems in the Presence of Frequency-Selective Fading and Multiple-Access Interference

    Energy Technology Data Exchange (ETDEWEB)

    Olama, Mohammed M [ORNL; Smith, Stephen Fulton [ORNL; Kuruganti, Phani Teja [ORNL; Ma, Xiao [ORNL

    2012-01-01

    Hybrid spread-spectrum (HSS) systems have recently received considerable interest in commercial, Smart Grid, and military communication systems because they accommodate high data rates with high link integrity, even in the presence of significant multipath effects and interfering signals. A highly useful form of this modulation scheme is the specific code-related combination of standard direct-sequence spread spectrum (DSSS) with fast frequency-hopping (FFH) spread spectrum, denoted hybrid DS/FFH, wherein multiple frequency hops occur within a single data-bit time. In this paper we perform a simulation-based study of the DS/FFH performance as compared to the existing standard DSSS and FHSS wireless networks. The performance metrics are bit-error probability and multiple-access capability. The parameter space of DS/FFH, including the DS spreading rate, frequency hopping rate, carrier frequencies, and numbers of users, is explored to show its performance under frequency-selective Rayleigh fading environments and multiuser interference. Direct digital synthesizers to achieve fast hopping speeds are also considered in our study.

  10. Web-based interactive access, analysis and comparison of remotely sensed and in situ measured temperature data

    Science.gov (United States)

    Eberle, Jonas; Urban, Marcel; Hüttich, Christian; Schmullius, Christiane

    2014-05-01

    Numerous datasets providing temperature information from meteorological stations or remote sensing satellites are available. However, the challenging issue is to search in the archives and process the time series information for further analysis. These steps can be automated for each individual product, if the pre-conditions are complied, e.g. data access through web services (HTTP, FTP) or legal rights to redistribute the datasets. Therefore a python-based package was developed to provide data access and data processing tools for MODIS Land Surface Temperature (LST) data, which is provided by NASA Land Processed Distributed Active Archive Center (LPDAAC), as well as the Global Surface Summary of the Day (GSOD) and the Global Historical Climatology Network (GHCN) daily datasets provided by NOAA National Climatic Data Center (NCDC). The package to access and process the information is available as web services used by an interactive web portal for simple data access and analysis. Tools for time series analysis were linked to the system, e.g. time series plotting, decomposition, aggregation (monthly, seasonal, etc.), trend analyses, and breakpoint detection. Especially for temperature data a plot was integrated for the comparison of two temperature datasets based on the work by Urban et al. (2013). As a first result, a kernel density plot compares daily MODIS LST from satellites Aqua and Terra with daily means from GSOD and GHCN datasets. Without any data download and data processing, the users can analyze different time series datasets in an easy-to-use web portal. As a first use case, we built up this complimentary system with remotely sensed MODIS data and in situ measurements from meteorological stations for Siberia within the Siberian Earth System Science Cluster (www.sibessc.uni-jena.de). References: Urban, Marcel; Eberle, Jonas; Hüttich, Christian; Schmullius, Christiane; Herold, Martin. 2013. "Comparison of Satellite-Derived Land Surface Temperature and Air

  11. Advanced mobile networking, sensing, and controls.

    Energy Technology Data Exchange (ETDEWEB)

    Feddema, John Todd; Kilman, Dominique Marie; Byrne, Raymond Harry; Young, Joseph G.; Lewis, Christopher L.; Van Leeuwen, Brian P.; Robinett, Rush D. III; Harrington, John J.

    2005-03-01

    This report describes an integrated approach for designing communication, sensing, and control systems for mobile distributed systems. Graph theoretic methods are used to analyze the input/output reachability and structural controllability and observability of a decentralized system. Embedded in each network node, this analysis will automatically reconfigure an ad hoc communication network for the sensing and control task at hand. The graph analysis can also be used to create the optimal communication flow control based upon the spatial distribution of the network nodes. Edge coloring algorithms tell us that the minimum number of time slots in a planar network is equal to either the maximum number of adjacent nodes (or degree) of the undirected graph plus some small number. Therefore, the more spread out that the nodes are, the fewer number of time slots are needed for communication, and the smaller the latency between nodes. In a coupled system, this results in a more responsive sensor network and control system. Network protocols are developed to propagate this information, and distributed algorithms are developed to automatically adjust the number of time slots available for communication. These protocols and algorithms must be extremely efficient and only updated as network nodes move. In addition, queuing theory is used to analyze the delay characteristics of Carrier Sense Multiple Access (CSMA) networks. This report documents the analysis, simulation, and implementation of these algorithms performed under this Laboratory Directed Research and Development (LDRD) effort.

  12. A Bio-Inspired Two-Layer Sensing Structure of Polypeptide and Multiple-Walled Carbon Nanotube to Sense Small Molecular Gases

    Directory of Open Access Journals (Sweden)

    Li-Chun Wang

    2015-03-01

    Full Text Available In this paper, we propose a bio-inspired, two-layer, multiple-walled carbon nanotube (MWCNT-polypeptide composite sensing device. The MWCNT serves as a responsive and conductive layer, and the nonselective polypeptide (40 mer coating the top of the MWCNT acts as a filter into which small molecular gases pass. Instead of using selective peptides to sense specific odorants, we propose using nonselective, peptide-based sensors to monitor various types of volatile organic compounds. In this study, depending on gas interaction and molecular sizes, the randomly selected polypeptide enabled the recognition of certain polar volatile chemical vapors, such as amines, and the improved discernment of low-concentration gases. The results of our investigation demonstrated that the polypeptide-coated sensors can detect ammonia at a level of several hundred ppm and barely responded to triethylamine.

  13. Integrating Multiple Knowledge Sources to Disambiguate Word Sense: An Exemplar-Based Approach

    OpenAIRE

    Ng, Hwee Tou; Lee, Hian Beng

    1996-01-01

    In this paper, we present a new approach for word sense disambiguation (WSD) using an exemplar-based learning algorithm. This approach integrates a diverse set of knowledge sources to disambiguate word sense, including part of speech of neighboring words, morphological form, the unordered set of surrounding words, local collocations, and verb-object syntactic relation. We tested our WSD program, named {\\sc Lexas}, on both a common data set used in previous work, as well as on a large sense-ta...

  14. Integrating Multiple Knowledge Sources to Disambiguate Word Sense An Exemplar-Based Approach

    CERN Document Server

    Ng, H T; Ng, Hwee Tou; Lee, Hian Beng

    1996-01-01

    In this paper, we present a new approach for word sense disambiguation (WSD) using an exemplar-based learning algorithm. This approach integrates a diverse set of knowledge sources to disambiguate word sense, including part of speech of neighboring words, morphological form, the unordered set of surrounding words, local collocations, and verb-object syntactic relation. We tested our WSD program, named {\\sc Lexas}, on both a common data set used in previous work, as well as on a large sense-tagged corpus that we separately constructed. better than the most frequent heuristic on the highly ambiguous words in the large corpus tagged with the refined senses of {\\sc WordNet}.

  15. Compressed sensing of roller bearing fault based on multiple down-sampling strategy

    International Nuclear Information System (INIS)

    Roller bearings are essential components of rotating machinery and are often exposed to complex operating conditions, which can easily lead to their failures. Thus, to ensure normal production and the safety of machine operators, it is essential to detect the failures as soon as possible. However, it is a major challenge to maintain a balance between detection efficiency and big data acquisition given the limitations of sampling theory. To overcome these limitations, we try to preserve the information pertaining to roller bearing failures using a sampling rate far below the Nyquist sampling rate, which can ease the pressure generated by the large-scale data. The big data of a faulty roller bearing’s vibration signals is firstly reduced by a down-sample strategy while preserving the fault features by selecting peaks to represent the data segments in time domain. However, a problem arises in that the fault features may be weaker than before, since the noise may be mistaken for the peaks when the noise is stronger than the vibration signals, which makes the fault features unable to be extracted by commonly-used envelope analysis. Here we employ compressive sensing theory to overcome this problem, which can make a signal enhancement and reduce the sample sizes further. Moreover, it is capable of detecting fault features from a small number of samples based on orthogonal matching pursuit approach, which can overcome the shortcomings of the multiple down-sample algorithm. Experimental results validate the effectiveness of the proposed technique in detecting roller bearing faults. (paper)

  16. Compressed sensing of roller bearing fault based on multiple down-sampling strategy

    Science.gov (United States)

    Wang, Huaqing; Ke, Yanliang; Luo, Ganggang; Tang, Gang

    2016-02-01

    Roller bearings are essential components of rotating machinery and are often exposed to complex operating conditions, which can easily lead to their failures. Thus, to ensure normal production and the safety of machine operators, it is essential to detect the failures as soon as possible. However, it is a major challenge to maintain a balance between detection efficiency and big data acquisition given the limitations of sampling theory. To overcome these limitations, we try to preserve the information pertaining to roller bearing failures using a sampling rate far below the Nyquist sampling rate, which can ease the pressure generated by the large-scale data. The big data of a faulty roller bearing’s vibration signals is firstly reduced by a down-sample strategy while preserving the fault features by selecting peaks to represent the data segments in time domain. However, a problem arises in that the fault features may be weaker than before, since the noise may be mistaken for the peaks when the noise is stronger than the vibration signals, which makes the fault features unable to be extracted by commonly-used envelope analysis. Here we employ compressive sensing theory to overcome this problem, which can make a signal enhancement and reduce the sample sizes further. Moreover, it is capable of detecting fault features from a small number of samples based on orthogonal matching pursuit approach, which can overcome the shortcomings of the multiple down-sample algorithm. Experimental results validate the effectiveness of the proposed technique in detecting roller bearing faults.

  17. Constructing a two bands optical code-division multiple-access network of bipolar optical access codecs using Walsh-coded liquid crystal modulators

    Science.gov (United States)

    Yen, Chih-Ta; Huang, Jen-Fa; Chih, Ping-En

    2014-08-01

    We propose and experimentally demonstrated the two bands optical code-division multiple-access (OCDMA) network over bipolar Walsh-coded liquid-crystal modulators (LCMs) and driven by green light and red light lasers. Achieving system performance depends on the construction of a decoder that implements a true bipolar correlation using only unipolar signals and intensity detection for each band. We took advantage of the phase delay characteristics of LCMs to construct a prototype optical coder/decoder (codec). Matched and unmatched Walsh signature codes were evaluated to detect correlations among multiuser data in the access network. By using LCMs, a red and green laser light source was spectrally encoded and the summed light dots were complementary decoded. Favorable contrast on auto- and cross-correlations indicates that binary information symbols can be properly recovered using a balanced photodetector.

  18. Multi-User Interference Cancellation Scheme(s) for Muliple Carrier Frequency Offset Compensation in Uplink OFDMA

    DEFF Research Database (Denmark)

    Nguyen, Huan Cong; Carvalho, Elisabeth De; Prasad, Ramjee

    2006-01-01

    We consider the uplink of an Orthogonal Frequency Division Multiple Access (OFDMA)-based system, where each Mobile Station (MS) experiences a different Carrier Frequency Offset (CFO). Uncorrected CFO destroy the orthogonality among subcarriers, which could cause severe Inter-Carrier Interference ...

  19. Ultra Wide Wavelength Division Multiplexing Optical Code Division Multiple Access Communication Systems in Wide Area Optical Communication Networks

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2013-01-01

    Full Text Available The effect of dispersion of fiber on the performance of OCDMA systemand to find the limitations imposed by dispersion on number of user and length of transmission. It has been observed that in the bit error rate performance curve the error is decreased when the number of subscriber is increased side by side the optical power is reduced when the users is added. This paper has presented the ultra wide wavelength division multiplexing optical code division multiple access (OCDMA communication systems in wide area optical communication networks and the transmission efficiency to be evaluated in order to determine the impact ofmulti access interference.

  20. Multiple small RNAs act additively to integrate sensory information and control quorum sensing in Vibrio harveyi

    Science.gov (United States)

    Tu, Kimberly C.; Bassler, Bonnie L.

    2007-01-01

    Quorum sensing is a cell–cell communication mechanism that bacteria use to collectively regulate gene expression and, at a higher level, to coordinate group behavior. In the bioluminescent marine bacterium Vibrio harveyi, sensory information from three independent quorum-sensing systems converges on the shared response regulator LuxO. When LuxO is phosphorylated, it activates the expression of a putative repressor that destabilizes the mRNA encoding the master quorum-sensing transcriptional regulator LuxR. In the closely related species Vibrio cholerae, this repressor was revealed to be the RNA chaperone Hfq together with four small regulatory RNAs (sRNAs) called Qrr1–4 (quorum regulatory RNA). Here, we identify five Qrr sRNAs that control quorum sensing in V. harveyi. Mutational analysis reveals that only four of the five Qrrs are required for destabilization of the luxR mRNA. Surprisingly, unlike in V. cholerae where the sRNAs act redundantly, in V. harveyi, the Qrr sRNAs function additively to control quorum sensing. This latter mechanism produces a gradient of LuxR that, in turn, enables differential regulation of quorum-sensing target genes. Other regulators appear to be involved in control of V. harveyi qrr expression, allowing the integration of additional sensory information into the regulation of quorum-sensing gene expression. PMID:17234887

  1. Highly accessible Pt nanodots homogeneously decorated on Au nanorods surface for sensing

    International Nuclear Information System (INIS)

    Highlights: • Seed-growth of highly-dispersed catalytic Pt nanodot on Au nanorod (PtND@AuNR). • Good accessibility of catalytic sites was evidenced by its peroxidase-like activity. • Excellent assay performances of H2O2 at PtND@AuNR-based sensor. - Abstract: Some nanostructures are reported to possess enzyme-mimetic activities similar to those of natural enzymes. Herein, highly-dispersed Pt nanodots on Au nanorods (HD- PtNDs@AuNRs) with mimetic peroxidase activity were designed as an active electrode modifier for fabrication of a hydrogen peroxide (H2O2) electrochemical sensor. The HD-PtNDs@AuNRs were synthesized by a seed-mediated growth approach and confirmed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and UV–vis spectroscopy. The electrochemical and catalytical performances of HD-PtNDs@AuNRs towards H2O2 reduction were investigated in detail by cyclic voltammetry and amperometry. The HD-PtNDs@AuNRs modified electrode displayed a high catalytic activity to H2O2 at −0.10 V (versus SCE), a rapid response within 5 s, a wide linear range of 2.0–3800.0 μM, a detection limit of 1.2 μM (S/N = 3), and a high sensitivity of 181 μA mM−1 cm−2. These results suggested a promising potential of fabricating H2O2 electrochemical sensor using HD- PtNDs@AuNRs

  2. Highly accessible Pt nanodots homogeneously decorated on Au nanorods surface for sensing

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Xun [College of Chemistry, Jilin University, Changchun 130012 (China); Li, Xin [College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Shi, Hongyan; Huang, Hao [College of Chemistry, Jilin University, Changchun 130012 (China); Wu, Xiaochun [CAS Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing 100190 (China); Song, Wenbo, E-mail: wbsong@jlu.edu.cn [College of Chemistry, Jilin University, Changchun 130012 (China)

    2014-12-10

    Highlights: • Seed-growth of highly-dispersed catalytic Pt nanodot on Au nanorod (PtND@AuNR). • Good accessibility of catalytic sites was evidenced by its peroxidase-like activity. • Excellent assay performances of H{sub 2}O{sub 2} at PtND@AuNR-based sensor. - Abstract: Some nanostructures are reported to possess enzyme-mimetic activities similar to those of natural enzymes. Herein, highly-dispersed Pt nanodots on Au nanorods (HD- PtNDs@AuNRs) with mimetic peroxidase activity were designed as an active electrode modifier for fabrication of a hydrogen peroxide (H{sub 2}O{sub 2}) electrochemical sensor. The HD-PtNDs@AuNRs were synthesized by a seed-mediated growth approach and confirmed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and UV–vis spectroscopy. The electrochemical and catalytical performances of HD-PtNDs@AuNRs towards H{sub 2}O{sub 2} reduction were investigated in detail by cyclic voltammetry and amperometry. The HD-PtNDs@AuNRs modified electrode displayed a high catalytic activity to H{sub 2}O{sub 2} at −0.10 V (versus SCE), a rapid response within 5 s, a wide linear range of 2.0–3800.0 μM, a detection limit of 1.2 μM (S/N = 3), and a high sensitivity of 181 μA mM{sup −1} cm{sup −2}. These results suggested a promising potential of fabricating H{sub 2}O{sub 2} electrochemical sensor using HD- PtNDs@AuNRs.

  3. Effect of Yoga Exercise on General Health Status (GHS and Sense of Life in Patients with Multiple Sclerosis

    Directory of Open Access Journals (Sweden)

    SH Najafi doulatabad

    2011-08-01

    Full Text Available Introduction & Objective: Multiple sclerosis (MS is a type of progressing and degenerating disease of myelin membrane of nervous cells in the Central Nervous System (CNS which could cause the incidence of many signs and complications in patients. The disease could affect different aspects of an individual’s life and disturb his/her normal life. This study was carried out in order to survey the effect of yoga exercise on general health status (GHS and sense of life in patients with multiple sclerosis. Materials & Methods: This research was a clinical trial study carried out at Yasouj University of Medical Sciences on 60 female patients with multiple sclerosis from Kohgiloyeh and Boyerahmad province in 2009.The data collecting tool consisted was MSQoL-54 questionnaire contained demographic information of patients. Patients were randomly divided into two control and case groups (30 persons in each group. Then, the general health status (GHS and sense of life of the subjects were evaluated. Yoga therapy was done in the case group for three months and each month included eight sessions of 1-1.5 hours while no intervention was carried out on the control group. One month after Yoga therapy, the general health status (GHS and sense of life for both groups were evaluated and compared with each other. Collected data were analyzed using descriptive tests, statistical independent t-test and paired t-test by the SPSS software. Results: The mean age of samples was 31.6±8.0 with the range of 18-45 years. Forty two (70% of the subjects were married and 18 (30% were single. Forty four (73.3% had high school education and 16 (26.6% had a university degree. Regarding occupation, most of them (63.3% were housewives. Results of the study showed that after Yoga therapy, the mean rate of general health status (GHS and sense of life as a whole had significant statistical difference between two groups (P<0.05. Conclusion: Yoga has improved the general health status

  4. Comparison of a Ring On-Chip Network and a Code-Division Multiple-Access On-Chip Network

    OpenAIRE

    Xin Wang; Jari Nurmi

    2007-01-01

    Two network-on-chip (NoC) designs are examined and compared in this paper. One design applies a bidirectional ring connection scheme, while the other design applies a code-division multiple-access (CDMA) connection scheme. Both of the designs apply globally asynchronous locally synchronous (GALS) scheme in order to deal with the issue of transferring data in a multiple-clock-domain environment of an on-chip system. The two NoC designs are compared with each other by their network structures, ...

  5. Data Management for Flexible Access - Implementation and Lessons Learned from work with Multiple User Communities

    Science.gov (United States)

    Benedict, K. K.; Scott, S.; Hudspeth, W. B.

    2012-12-01

    There is no shortage of community-specific and generic data discovery and download platforms and protocols (e.g. CUAHSI HIS, DataONE, GeoNetwork Open Source, GeoPortal, OGC CSW, OAI PMH), documentation standards (e.g. FGDC, ISO 19115, EML, Dublin Core), data access and visualization standards and models (e.g. OGC WxS, OpenDAP), and general-purpose web service models (i.e. REST & SOAP) upon which Geo-informatics cyberinfrastructure (CI) may be built. When attempting to develop a robust platform that may service a wide variety of users and use cases the challenge is one of identifying which existing platform (if any) may support those current needs while also allowing for future expansion for additional capabilities. In the case of the implementation of a data storage, discovery and delivery platform to support the multiple projects at the Earth Data Analysis Center at UNM, no single platform or protocol met the joint requirements of two initial applications (the New Mexico Resource Geographic Information System [http://rgis.unm.edu] and the New Mexico EPSCoR Data Portal [http://nmepscor.org/dataportal]) and furthermore none met anticipated additional requirements as new applications of the platform emerged. As a result of this assessment three years ago EDAC embarked on the development of the Geographic Storage, Transformation, and Retrieval Engine (GSToRE) platform as a general purpose platform upon which n-tiered geospatially enabled data intensive applications could be built. When initially released in 2010 the focus was on the publication of dynamically generated Open Geospatial Consortium services based upon a PostgreSQL/PostGIS backend database. The identification of additional service interface requirements (implementation of the DataONE API and CUAHSI WaterML services), use cases provided by the NM EPSCoR education working group, and expanded metadata publication needs have led to a significant update to the underlying data management tier for GSToRE - the

  6. Performance analysis of 2D asynchronous hard-limiting optical code-division multiple access system through atmospheric scattering channel

    Science.gov (United States)

    Zhao, Yaqin; Zhong, Xin; Wu, Di; Zhang, Ye; Ren, Guanghui; Wu, Zhilu

    2013-09-01

    Optical code-division multiple access (OCDMA) systems usually allocate orthogonal or quasi-orthogonal codes to the active users. When transmitting through atmospheric scattering channel, the coding pulses are broadened and the orthogonality of the codes is worsened. In truly asynchronous case, namely both the chips and the bits are asynchronous among each active user, the pulse broadening affects the system performance a lot. In this paper, we evaluate the performance of a 2D asynchronous hard-limiting wireless OCDMA system through atmospheric scattering channel. The probability density function of multiple access interference in truly asynchronous case is given. The bit error rate decreases as the ratio of the chip period to the root mean square delay spread increases and the channel limits the bit rate to different levels when the chip period varies.

  7. Reducing BER of spectral-amplitude coding optical code-division multiple-access systems by single photodiode detection technique

    Science.gov (United States)

    Al-Khafaji, H. M. R.; Aljunid, S. A.; Amphawan, A.; Fadhil, H. A.; Safar, A. M.

    2013-03-01

    In this paper, we present a single photodiode detection (SPD) technique for spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems. The proposed technique eliminates both phase-induced intensity noise (PIIN) and multiple-access interference (MAI) in the optical domain. Analytical results show that for 35 simultaneous users transmitting at data rate of 622 Mbps, the bit-error rate (BER) = 1.4x10^-28 for SPD technique is much better compared to 9.3x10^-6 and 9.6x10^-3 for the modified-AND as well as the AND detection techniques, respectively. Moreover, we verified the improved performance afforded by the proposed technique using data transmission simulations.

  8. Contention Resolution in Optical Burst Switched Networks using Spectral- Amplitude-Coding Optical Code Division Multiple Access

    CERN Document Server

    Sowailem, Mohamed Y S; Shalaby, Hossam M H

    2008-01-01

    We propose the implementation of spectral-amplitude-coding optical code division multiple access (SC-OCDMA) as a contention resolution technique in optical burst switched (OBS) networks. The new system architecture is presented in details where an all-optical methodology for cancelling multiple access interference is proposed. Performance evaluation of the proposed OBS/SC-OCDMA system is introduced where two performance measures are derived, namely, the steady-state throughput and the burst loss probability, in two cases: the presence and absence of code conversion capability. In addition, the performance of the proposed system is compared to that of the corresponding system that uses WDM instead of OCDMA. Our results reveal that a considerable performance improvement is achieved by using SCOCDMA instead of WDM in the optical layer below OBS in the MAC layer.

  9. Minimizing correlation effect using zero cross correlation code in spectral amplitude coding optical code division multiple access

    Science.gov (United States)

    Safar, Anuar Mat; Aljunid, Syed Alwee; Arief, Amir Razif; Nordin, Junita; Saad, Naufal

    2012-01-01

    The use of minimal multiple access interference (MAI) in code design is investigated. Applying a projection and mapping techniques, a code that has a zero cross correlation (ZCC) between users in optical code division multiple access (OCDMA) is presented in this paper. The system is based on an incoherent light source—LED, spectral amplitude coding (SAC), and direct detection techniques at the receiver. Using power spectral density (PSD) function and Gaussian approximation, we obtain the signal-to-noise ratio (SNR) and the bit-error rate (BER) to measure the code performance. Making a comparison with other existing codes, e.g., Hadamard, MFH and MDW codes, we show that our code performs better at BER 10-9 in terms of number of simultaneous users. We also demonstrate the comparison between the theoretical and simulation analyses, where the results are close to one another.

  10. Integrated photonic decoder with complementary code processing and balanced detection for two-dimensional optical code division multiple access.

    Science.gov (United States)

    Takiguchi, K; Okuno, M; Takahashi, H; Moriwaki, O

    2007-04-01

    We propose a novel integrated photonic decoder for two-dimensional (time spreading, wavelength hopping) optical code division multiple access. The decoder is composed of multiplexers-demultiplexers, variable delay lines, and a coupler, which processes complementary codes and utilizes balanced detection to reduce unwanted cross-correlation interference. We successfully carried out a 10 Gbit/s transmission that demonstrated its effectiveness. PMID:17339936

  11. Nonadditivity of quantum and classical capacities for entanglement breaking multiple-access channels and the butterfly network

    International Nuclear Information System (INIS)

    We analyze quantum network primitives which are entanglement breaking. We show superadditivity of quantum and classical capacity regions for quantum multiple-access channels and the quantum butterfly network. Since the effects are especially visible at high noise they suggest that quantum information effects may be particularly helpful in the case of the networks with occasional high noise rates. The present effects provide a qualitative borderline between superadditivities of bipartite and multipartite systems.

  12. Bit Error Rate Performance for Multicarrier Code Division Multiple Access over Generalized η-μ Fading Environment

    Directory of Open Access Journals (Sweden)

    James Osuru Mark

    2011-01-01

    Full Text Available The multicarrier code division multiple access (MC-CDMA system has received a considerable attention from researchers owing to its great potential in achieving high data rates transmission in wireless communications. Due to the detrimental effects of multipath fading the performance of the system degrades. Similarly, the impact of non-orthogonality of spreading codes can exist and cause interference. This paper addresses the performance of multicarrier code division multiple access system under the influence of frequency selective generalized η-µ  fading channel and multiple access interference caused by other active users to the desired one. We apply Gaussian approximation technique to analyse the performance of the system. The avearge bit error rate is derived and expressed in Gauss hypergeometic functions. Maximal ratio combining diversity technique is utilized to alleviate the deleterious effect of multipath fading. We observed that the system performance improves when the parameter η increase or decreasse in format 1 or format 2 conditions respectively.

  13. Hybrid bidirectional radio-over-fiber-based orthogonal frequency division multiple access-passive optical network supporting 60/120 GHz using offset quadrate phase shift keying

    Science.gov (United States)

    Zhang, Chongfu; Chen, Chen; Qiu, Kun

    2015-09-01

    A hybrid bidirectional orthogonal frequency division multiple access-passive optical network (OFDMA-PON) based on offset quadrate phase shift keying (OQPSK) to support 60- and 120-GHz radio-over-fiber system is proposed. The system can support wired/wireless applications and enable the dynamic bandwidth allocation according to a subscriber's application. It is successfully achieved by using the millimeter waves (MMWs) generation and the carrier-reuse technique. In the proposed scheme, the MMW bands used for downlink (DL) and uplink transmissions are generated at the optical line terminal by the dual-arm Mach-Zehnder modulators. Both 60- and 120-GHz MMWs are obtained for the transmission of the high bit-rate services in source-free optical network units (ONUs), only using a single 15-GHz sinusoidal wave source. The Rayleigh backscattering effect is considered in the proposed OQPSK-based OFDMA-PON. For DL transmission over a 30-km single-mode fiber, the power penalties are less than 0.8 and 1 dB for the OQPSK-OFDM wired data at 10 Gb/s and the OQPSK-OFDM wireless data at 5 Gb/s, respectively.

  14. Acetone Gas Sensing Properties of a Multiple-Networked Fe2O3-Functionalized CuO Nanorod Sensor

    Directory of Open Access Journals (Sweden)

    Sunghoon Park

    2015-01-01

    Full Text Available Fe2O3-decorated CuO nanorods were prepared by Cu thermal oxidation followed by Fe2O3 decoration via a solvothermal route. The acetone gas sensing properties of multiple-networked pristine and Fe2O3-decorated CuO nanorod sensors were examined. The optimal operating temperature of the sensors was found to be 240°C. The pristine and Fe2O3-decorated CuO nanorod sensors showed responses of 586 and 1,090%, respectively, to 1,000 ppm of acetone at 240°C. The Fe2O3-decorated CuO nanorod sensor also showed faster response and recovery than the latter sensor. The acetone gas sensing mechanism of the Fe2O3-decorated CuO nanorod sensor is discussed in detail. The origin of the enhanced sensing performance of the multiple-networked Fe2O3-decorated CuO nanorod sensor to acetone gas was explained by modulation of the potential barrier at the Fe2O3-CuO interface, highly catalytic activity of Fe2O3 for acetone oxidation, and the creation of active adsorption sites by Fe2O3 nanoparticles.

  15. Synthesis, structure, and room-temperature gas sensing of multiple-networked Pd-doped Ga2O3 nanowires

    International Nuclear Information System (INIS)

    Ga2O3-based gas sensors are known to show very poor performance at room temperature even though recent studies on Ga2O3 thin film-based gas sensors demonstrated that they detected O2, H2, CO, and CH4 gases efficiently at high temperatures of 600 - 1000 .deg. C. This high working temperature limits the practical usage of Ga2O3-based gas sensors. In this study, the NO2 gas sensing properties of multiple-networked Pd-doped Ga2O3 nanowire sensors were examined. Scanning electron microscopy showed nanowires with diameters of 50 - 100 nm and lengths of a few micrometers. Transmission electron microscopy and X-ray diffraction showed that the nanowires were monoclinic single-crystal Ga2O3. The Pd-doped Ga2O3 nanowire sensors showed far enhanced sensing performance to NO2 gas at room temperature compared to bare-Ga2O3 nanowire sensors. No appreciable dynamic sensing behaviors were observed for bare-Ga2O3 nanowire sensors at room temperature. In contrast, the sensors showed sensitivities of 26.86, 30.19, and 41.44% at NO2 concentrations of 10, 50, and 100 ppm, respectively. In addition, the origin of the enhancement of the sensing properties of the Ga2O3 nanowires by Pd doping is discussed.

  16. Popular Content Distribution in CR-VANETs with Joint Spectrum Sensing and Channel Access using Coalitional Games

    Directory of Open Access Journals (Sweden)

    Tianyu Wang

    2014-07-01

    Full Text Available Driven by both safety concerns and commercial interests, popular content distribution (PCD, as one of the key services offered by vehicular networks, has recently received considerable attention. In this paper, we address the PCD problem in highway scenarios, in which a popular file is distributed to a group of onboard units (OBUs driving through an area of interest (AoI. Due to high speeds of vehicles and deep fading of vehicle-to-roadside (V2R channels, the OBUs may not finish downloading the entire file. Consequently, a peer-to-peer (p2p network should be constructed among the OBUs for completing the file delivery process. Here, we apply the cognitive radio technique for vehicle-to-vehicle communications and propose a cooperative approach based on coalition formation games, which jointly considers the spectrum sensing and channel access performance. Simulation results show that our approach presents a considerable performance improvement compared with the non-cooperative case.

  17. Inhibition of human immunodeficiency virus type 1 multiplication by antisense and sense RNA expression.

    OpenAIRE

    Joshi, S; Van Brunschot, A; Asad, S.; van der Elst, I; Read, S. E.; Bernstein, A

    1991-01-01

    Human immunodeficiency virus type 1 (HIV-1) primarily infects CD4+ lymphocytes and macrophages and causes AIDS in humans. Retroviral vectors allowing neomycin phosphotransferase (npt) gene expression were engineered to express 5' sequences of HIV-1 RNA in the antisense or sense orientation and used to transform the human CD4+ lymphocyte-derived MT4 cell line. Cells expressing antisense or sense RNA to the HIV-1 tat mRNA leader sequence, as part of the 3' untranslated region of the npt mRNA, r...

  18. Local charge neutrality condition, Fermi level and majority carrier density of a semiconductor with multiple localized multi-level intrinsic/impurity defects

    Institute of Scientific and Technical Information of China (English)

    Ken K. Chin

    2011-01-01

    For semiconductors with localized intrinsic/impurity defects,intentionally doped or unintentionally incorporated,that have multiple transition energy levels among charge states,the general formulation of the local charge neutrality condition is given for the determination of the Fermi level and the majority carrier density.A graphical method is used to illustrate the solution of the problem.Relations among the transition energy levels of the multi-level defect are derived using the graphical method.Numerical examples are given for p-doping of the CdTe thin film used in solar panels and semi-insulating Si to illustrate the relevance and importance of the issues discussed in this work.

  19. Acetone Gas Sensing Properties of a Multiple-Networked Fe2O3-Functionalized CuO Nanorod Sensor

    OpenAIRE

    Sunghoon Park; Hyejoon Kheel; Gun-Joo Sun; Taegyung Ko; Wan In Lee; Chongmu Lee

    2015-01-01

    Fe2O3-decorated CuO nanorods were prepared by Cu thermal oxidation followed by Fe2O3 decoration via a solvothermal route. The acetone gas sensing properties of multiple-networked pristine and Fe2O3-decorated CuO nanorod sensors were examined. The optimal operating temperature of the sensors was found to be 240°C. The pristine and Fe2O3-decorated CuO nanorod sensors showed responses of 586 and 1,090%, respectively, to 1,000 ppm of acetone at 240°C. The Fe2O3-decorated CuO nanorod sensor also s...

  20. Multiple Perspectives on the Accessibility of E-Learning in Canadian Colleges and Universities

    Science.gov (United States)

    Asuncion, Jennison V.; Fichten, Catherine S.; Ferraro, Vittoria; Chwojka, Caroline; Barile, Maria; Nguyen, Mai Nhu; Wolforth, Joan

    2010-01-01

    An exploratory study identified and compared the views of 77 campus disability service providers, 38 professors, and 45 e-learning professionals from Canadian colleges and universities regarding their experiences with e-learning and its accessibility to students with disabilities. Findings indicate that all groups saw benefit in having someone who…

  1. Architecture of Wireless Sensor Networks with Mobile Sinks: Multiple Access Case

    OpenAIRE

    Liang Song; Dimitrios Hatzinakos

    2007-01-01

    We propose to develop Wireless Sensor Networks with Mobile Sinks (MSSN), under high sensor node density, where multiple sensor nodes need to share one single communication channel in the node-to-sink transmission. By exploiting the tradeoff between the successful information retrieval probability and the nodes energy consumption, a number of multiple nodes transmission scheduling algorithms are proposed. Both optimal and suboptimal algorithms, which exhibit exponential and linear complexity r...

  2. 39% access time improvement, 11% energy reduction, 32 kbit 1-read/1-write 2-port static random-access memory using two-stage read boost and write-boost after read sensing scheme

    Science.gov (United States)

    Yamamoto, Yasue; Moriwaki, Shinichi; Kawasumi, Atsushi; Miyano, Shinji; Shinohara, Hirofumi

    2016-04-01

    We propose novel circuit techniques for 1 clock (1CLK) 1 read/1 write (1R/1W) 2-port static random-access memories (SRAMs) to improve read access time (tAC) and write margins at low voltages. Two-stage read boost (TSR-BST) and write word line boost (WWL-BST) after the read sensing schemes have been proposed. TSR-BST reduces the worst read bit line (RBL) delay by 61% and RBL amplitude by 10% at V DD = 0.5 V, which improves tAC by 39% and reduces energy dissipation by 11% at V DD = 0.55 V. WWL-BST after read sensing scheme improves minimum operating voltage (V min) by 140 mV. A 32 kbit 1CLK 1R/1W 2-port SRAM with TSR-BST and WWL-BST has been developed using a 40 nm CMOS.

  3. Multi-parameter sensing with a single magnetoelastic sensor by applying loads on the null locations of multiple resonant modes

    Science.gov (United States)

    DeRouin, Andrew; Ghee Ong, Keat

    2016-03-01

    Magnetoelastic sensors are mass sensitive sensors commonly used for stress and pressure measurement, as well as chemical and biological monitoring when combined with a functionalized coating. Magnetoelastic sensors are typically made of free-standing, rectangular strips of magnetoelastic materials that exhibit longitudinal, extensional vibrations due to the excitation of magnetic fields. A single magnetoelastic sensor is generally used to monitor one parameter since only the fundamental resonant frequency is measured. Multiple-parameter sensing in close proximity has previously been achieved by using multiple magnetoelastic sensors of different dimensions and tracking their resonant frequencies independently. However, this requires a large surface area and inconvenient layout of dissimilarly shaped sensors. This paper presents a technique for monitoring multiple parameters with a single magnetoelastic sensor by applying separate mass loads at the null points (points of zero vibration) of multiple resonant modes. Applying a load at a null location does not affect the corresponding resonant mode but alters the resonant frequencies of other modes. Therefore, by isolating the variables of interest to multiple null points and simultaneously measuring the resonant frequency shifts of related resonant modes, the masses at each null location can be calculated. Results showed that changing the coverage at a null location along the width of the sensor can be used to minimize the loading effect on the corresponding resonant mode. In contrast, changing the lengthwise coverage can maximize the loading effect on other resonant modes, thus increasing the mass sensitivity of the sensor. Furthermore, simultaneously applying loads to null points of multiple resonant modes had a nearly additive effect, allowing detection of multiple parameters with a single magnetoelastic sensor.

  4. Interpolated Compressed Sensing for 2D Multiple Slice Fast MR Imaging

    OpenAIRE

    Yong Pang; Xiaoliang Zhang

    2013-01-01

    Sparse MRI has been introduced to reduce the acquisition time and raw data size by undersampling the k-space data. However, the image quality, particularly the contrast to noise ratio (CNR), decreases with the undersampling rate. In this work, we proposed an interpolated Compressed Sensing (iCS) method to further enhance the imaging speed or reduce data size without significant sacrifice of image quality and CNR for multi-slice two-dimensional sparse MR imaging in humans. This method utilizes...

  5. Road Extraction from High-resolution Remote Sensing Images Based on Multiple Information Fusion

    Directory of Open Access Journals (Sweden)

    LI Xiao-feng

    2016-02-01

    Full Text Available Road extraction from high-resolution remote sensing images has been considered to be a significant but very difficult task.Especially the spectrum of some buildings is similar with that of roads,which makes the surfaces being connect with each other after classification and difficult to be distinguished.Based on the cooperation between road surfaces and edges,this paper presents an approach to purify roads from high-resolution remote sensing images.Firstly,we try to improve the extraction accuracy of road surfaces and edges respectively.The logic cooperation between these two binary images is used to separate road and non-road objects.Then the road objects are confirmed by the cooperation between surfaces and edges.And the effective shape indices(e.g.polar moment of inertia and narrow extent index are applied to eliminate non-road objects.So the road information is refined.The experiments indicate that the proposed approach is efficient for eliminating non-road information and extracting road information from high-resolution remote sensing image.

  6. Multiple Temperature-Sensing Behavior of Green and Red Upconversion Emissions from Stark Sublevels of Er3+

    Directory of Open Access Journals (Sweden)

    Baosheng Cao

    2015-12-01

    Full Text Available Upconversion luminescence properties from the emissions of Stark sublevels of Er3+ were investigated in Er3+-Yb3+-Mo6+-codoped TiO2 phosphors in this study. According to the energy levels split from Er3+, green and red emissions from the transitions of four coupled energy levels, 2H11/2(I/2H11/2(II, 4S3/2(I/4S3/2(II, 4F9/2(I/4F9/2(II, and 2H11/2(I + 2H11/2(II/4S3/2(I + 4S3/2(II, were observed under 976 nm laser diode excitation. By utilizing the fluorescence intensity ratio (FIR technique, temperature-dependent upconversion emissions from these four coupled energy levels were analyzed at length. The optical temperature-sensing behaviors of sensing sensitivity, measurement error, and operating temperature for the four coupled energy levels are discussed, all of which are closely related to the energy gap of the coupled energy levels, FIR value, and luminescence intensity. Experimental results suggest that Er3+-Yb3+-Mo6+-codoped TiO2 phosphor with four pairs of energy levels coupled by Stark sublevels provides a new and effective route to realize multiple optical temperature-sensing through a wide range of temperatures in an independent system.

  7. BioZone Exploting Source-Capability Information for Integrated Access to Multiple Bioinformatics Data Sources

    Energy Technology Data Exchange (ETDEWEB)

    Liu, L; Buttler, D; Paques, H; Pu, C; Critchlow

    2002-01-28

    Modern Bioinformatics data sources are widely used by molecular biologists for homology searching and new drug discovery. User-friendly and yet responsive access is one of the most desirable properties for integrated access to the rapidly growing, heterogeneous, and distributed collection of data sources. The increasing volume and diversity of digital information related to bioinformatics (such as genomes, protein sequences, protein structures, etc.) have led to a growing problem that conventional data management systems do not have, namely finding which information sources out of many candidate choices are the most relevant and most accessible to answer a given user query. We refer to this problem as the query routing problem. In this paper we introduce the notation and issues of query routing, and present a practical solution for designing a scalable query routing system based on multi-level progressive pruning strategies. The key idea is to create and maintain source-capability profiles independently, and to provide algorithms that can dynamically discover relevant information sources for a given query through the smart use of source profiles. Compared to the keyword-based indexing techniques adopted in most of the search engines and software, our approach offers fine-granularity of interest matching, thus it is more powerful and effective for handling queries with complex conditions.

  8. BioZoom: Exploiting Source-Capability Information for Integrated Access to Multiple Bioinformatics Data Sources

    Energy Technology Data Exchange (ETDEWEB)

    Liu, L; Buttler, D; Critchlow, T J; Han, W; Paques, H; Pu, C; Rocco, D

    2003-01-09

    Modern Bioinformatics data sources are widely used by molecular biologists for homology searching and new drug discovery. User-friendly and yet responsive access is one of the most desirable properties for integrated access to the rapidly growing, heterogeneous, and distributed collection of data sources. The increasing volume and diversity of digital information related to bioinformatics (such as genomes, protein sequences, protein structures, etc.) have led to a growing problem that conventional data management systems do not have, namely finding which information sources out of many candidate choices are the most relevant and most accessible to answer a given user query. We refer to this problem as the query routing problem. In this paper we introduce the notation and issues of query routing, and present a practical solution for designing a scalable query routing system based on multi-level progressive pruning strategies. The key idea is to create and maintain source-capability profiles independently, and to provide algorithms that can dynamically discover relevant information sources for a given query through the smart use of source profiles. Compared to the keyword-based indexing techniques adopted in most of the search engines and software, our approach offers fine-granularity of interest matching, thus it is more powerful and effective for handling queries with complex conditions.

  9. Evaluating remote sensing of deciduous forest phenology at multiple spatial scales using PhenoCam imagery

    Directory of Open Access Journals (Sweden)

    S. T. Klosterman

    2014-02-01

    Full Text Available Plant phenology regulates ecosystem services at local and global scales and is a sensitive indicator of global change. Estimates of phenophase transition dates, such as the start of spring or end of autumn, can be derived from sensor-based time series data at the near-surface and remote scales, but must be interpreted in terms of biologically relevant events. We use the PhenoCam archive of digital repeat photography to implement a consistent protocol for visual assessment of canopy phenology at 13 temperate deciduous forest sites throughout eastern North America, as well as to perform digital image analysis for time series-based estimates of phenology dates. We then compare these near-surface results to remote sensing metrics of phenology at the landscape scale, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS and Advanced Very High Resolution Radiometer (AVHRR sensors. We present a new type of curve fit, using a generalized sigmoid, to estimate phenology dates. We quantify the statistical uncertainty of phenophase transition dates estimated using this method and show that the generalized sigmoid results in less statistical uncertainty than other curve-fitting methods. Additionally, we find that dates derived from analysis of high-frequency PhenoCam imagery have smaller uncertainties than remote sensing metrics of phenology, and that dates derived from the remotely-sensed enhanced vegetation index (EVI have smaller uncertainty than those derived from the normalized difference vegetation index (NDVI. Near-surface time series estimates for the start of spring are found to closely match visual assessment of leaf out, as well as remote sensing-derived estimates of the start of spring. However late spring and autumn phenology exhibit larger differences between near-surface and remote scales. Differences in late spring phenology between near-surface and remote scales are found to correlate with a landscape metric of deciduous

  10. A New Performance Analysis Method of Optical Code Division Multiple Access Systems with An Optical Hard-Limiter

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new performance analysis method of Optical Code Division Multiple Access (OCDMA) systems with an optical hard-limiter is studied. The bit error probability of the OCDMA system is derived, and the numerical results of the system with and without an ideal optical hard-limiter are analyzed respectively. The results show that although the derived expression is different from the one derived by J A Salehi[1], the numerical results are the same as those analyzed by J A Salehi, and the numerical result can be easily achieved in this expression.

  11. On the Performance of Non-Orthogonal Multiple Access in 5G Systems with Randomly Deployed Users

    Science.gov (United States)

    Ding, Zhiguo; Yang, Zheng; Fan, Pingzhi; Poor, H. Vincent

    2014-12-01

    In this letter, the performance of non-orthogonal multiple access (NOMA) is investigated in a cellular downlink scenario with randomly deployed users. The developed analytical results show that NOMA can achieve superior performance in terms of ergodic sum rates; however, the outage performance of NOMA depends critically on the choices of the users' targeted data rates and allocated power. In particular, a wrong choice of the targeted data rates and allocated power can lead to a situation in which the user's outage probability is always one, i.e. the user's targeted quality of service will never be met.

  12. Multiple psychological senses of community in Afghan context: exploring commitment and sacrifice in an underground resistance community.

    Science.gov (United States)

    Brodsky, Anne E

    2009-12-01

    The study of positive outcomes associated with strong psychological sense of community (PSOC) has grown worldwide. Yet most research explores PSOC as a uni-dimensional (positive) variable operating in a single referent community. Theoretical and empirical literature has suggested, however, that PSOC can be positive, neutral or negative (Brodsky in J Commun Psychol 24(4):347-363, 1996; Brodsky et al. in Psychological sense of community: Research, applications and implications. Kluwer, New York 2002) and since people live in multiple physical and relational communities, there may be multiple PSOCs (M-PSOC) operating simultaneously and interactively (Brodsky and Marx in J Commun Psychol 29(2):1-18, 2001). This paper explores the operation of M-PSOC in the lives of Afghan women, and male supporters, who belonged to a resistance organization before, during and after the Taliban regime. Decisions to join and stay in this community can be explained, in part, through the differentiation of positive, organizational-level PSOC from negative, macro-community-level PSOC. In addition, M-PSOC suggests unique cultural meanings of the terms "community" and "choice." Findings have implications for cross-cultural community work and for fostering resilient sub-communities in the face of macro and societal-level risks and oppression. PMID:19838788

  13. Source coherence impairments in a direct detection direct sequence optical code-division multiple-access system.

    Science.gov (United States)

    Fsaifes, Ihsan; Lepers, Catherine; Lourdiane, Mounia; Gallion, Philippe; Beugin, Vincent; Guignard, Philippe

    2007-02-01

    We demonstrate that direct sequence optical code- division multiple-access (DS-OCDMA) encoders and decoders using sampled fiber Bragg gratings (S-FBGs) behave as multipath interferometers. In that case, chip pulses of the prime sequence codes generated by spreading in time-coherent data pulses can result from multiple reflections in the interferometers that can superimpose within a chip time duration. We show that the autocorrelation function has to be considered as the sum of complex amplitudes of the combined chip as the laser source coherence time is much greater than the integration time of the photodetector. To reduce the sensitivity of the DS-OCDMA system to the coherence time of the laser source, we analyze the use of sparse and nonperiodic quadratic congruence and extended quadratic congruence codes. PMID:17230236

  14. Use of information visualization methods eliminating cross talk in multiple sensing units investigated for a light-addressable potentiometric sensor.

    Science.gov (United States)

    Siqueira, José R; Maki, Rafael M; Paulovich, Fernando V; Werner, Carl F; Poghossian, Arshak; de Oliveira, Maria C F; Zucolotto, Valtencir; Oliveira, Osvaldo N; Schöning, Michael J

    2010-01-01

    The integration of nanostructured films containing biomolecules and silicon-based technologies is a promising direction for reaching miniaturized biosensors that exhibit high sensitivity and selectivity. A challenge, however, is to avoid cross talk among sensing units in an array with multiple sensors located on a small area. In this letter, we describe an array of 16 sensing units of a light-addressable potentiometric sensor (LAPS), which was made with layer-by-layer (LbL) films of a poly(amidomine) dendrimer (PAMAM) and single-walled carbon nanotubes (SWNTs), coated with a layer of the enzyme penicillinase. A visual inspection of the data from constant-current measurements with liquid samples containing distinct concentrations of penicillin, glucose, or a buffer indicated a possible cross talk between units that contained penicillinase and those that did not. With the use of multidimensional data projection techniques, normally employed in information visualization methods, we managed to distinguish the results from the modified LAPS, even in cases where the units were adjacent to each other. Furthermore, the plots generated with the interactive document map (IDMAP) projection technique enabled the distinction of the different concentrations of penicillin, from 5 mmol L(-1) down to 0.5 mmol L(-1). Data visualization also confirmed the enhanced performance of the sensing units containing carbon nanotubes, consistent with the analysis of results for LAPS sensors. The use of visual analytics, as with projection methods, may be essential to handle a large amount of data generated in multiple sensor arrays to achieve high performance in miniaturized systems. PMID:20041720

  15. Performance Analysis of Ultra Wideband Multiple Access Time Hopping – Pulse Shape Modulation in Presence of Timing Jitter

    Directory of Open Access Journals (Sweden)

    D. Adhikari

    2014-09-01

    Full Text Available In short-range networks such as wireless personal area networks (WPAN, multiple user wireless connectivity for surveillance would require a wireless technology that supports multiple streams of high-speed data and consumes very little power. Ultra wideband (UWB technology enables wireless connectivity across multiple devices (users addressing the need for high-speed WPAN. Apart from having a distinct advantage of higher data rate over Bluetooth v4.0 (24 Mbps, the UWB technology is also found to be tolerant to frequency-selective multipath fading. In this paper authors discuss a time-hopping pulse shape modulation UWB signalling scheme for ad-hoc high bit rate wireless connectivity for defence applications. Authors analyse multiple access interference for both Gaussian channel and frequency selective multipath fading channel to compare the effects of timing jitter on two types of pulse shapes, namely modified Hermite pulse (MHP and prolate spheroidal wave functions (PSWF. Authors make a comparative analysis of the system performance with respect to PSWF and MHP to ascertain robustness to timing jitter. In the process, authors introduced a new metric of decision factor in timing jitter analysis.Defence Science Journal, Vol. 64, No. 5, September 2014, pp.464-470, DOI:http://dx.doi.org/10.14429/dsj.64.5787

  16. Radiative recombination mechanism of carriers in InGaN/AlInGaN multiple quantum wells with varying aluminum content

    International Nuclear Information System (INIS)

    Highlights: • Structural and optical properties of In GaN/AlxInyGa1−x−yN MQWs were investigated. • The existence of In-rich clusters has been verified by Raman spectra. • The degree of localization effect increase with increasing Al content in barriers. • The origin of the deep localized states could be assigned to the larger QCSE. • Recombination mechanism of carriers with increasing temperature has been proposed. - Abstract: The structural and optical properties of In0.20Ga0.80N/AlxInyGa1−x−yN multiple quantum wells samples with varying Al content in barrier layers grown on sapphire substrates by metalorganic chemical vapor deposition have been investigated by means of high-resolution X-ray diffraction, Raman scattering measurements and temperature-dependent photoluminescence. Raman measurements verified the existence of In-rich clusters in ternary and quaternary layers. At 10 K and 300 K, the PL spectrum of each sample is dominated by a sharp emission peak arising from In0.20Ga0.80N well layers. The anomalous temperature-dependent S-shaped behaviors of emission energies have been observed, indicating the presence of localized states induced by the potential fluctuations in the quantum wells due to the inhomogeneous distribution of In-rich clusters. The degree of the localization effect and the transition temperatures between different temperature regions can be enhanced by increasing Al content in barrier layers. The improvement of the localized states emission has been observed at the lower energy side of band gap emission of quantum wells with increasing Al content. The origin of the deep localized states could be attributed to the larger quantum-confined Stark effect in the quantum wells with higher Al content. The recombination mechanism of carriers between band edge and localized states was proposed for interpreting of the emission characteristics

  17. Throughput-Delay Trade-Off for Slotted Aloha Multiple Access with Capture Effect

    Directory of Open Access Journals (Sweden)

    A. Chehri

    2009-01-01

    Full Text Available Problem statement: Medium Access Control (MAC protocols are one of most important research issues in communication and networking. There have been proposed several MAC protocols in wireless as well in wired networks. Approach: ALOHA-based protocol is the simplest one, being able to provide prompt access, reliable channels and support for quality of service. However its limited capacity, low throughput and excessive delays make it not suitable for several applications. Results: So there had been many efforts devoted to increase its performance, one of them is the capture effect. With capture effect, the packets arriving with the highest power had a good chance to be detected accurately, even when other packets were present. Conclusion: In this study, a throughput-delay trade-off was investigated to improve the network performance. The capture threshold was assigned to the highest throughout/time delay ratio. Therefore, the capture threshold which provided a high throughput and low time delay was selected by a central node.

  18. Ultrasonic Multiple-Access Ranging System Using Spread Spectrum and MEMS Technology for Indoor Localization

    Directory of Open Access Journals (Sweden)

    Laurent Segers

    2014-02-01

    Full Text Available Indoor localization of persons and objects poses a great engineering challenge. Previously developed localization systems demonstrate the use of wideband techniques in ultrasound ranging systems. Direct sequence and frequency hopping spread spectrum ultrasound signals have been proven to achieve a high level of accuracy. A novel ranging method using the frequency hopping spread spectrum with finite impulse response filtering will be investigated and compared against the direct sequence spread spectrum. In the first setup, distances are estimated in a single-access environment, while in the second setup, two senders and one receiver are used. During the experiments, the micro-electromechanical systems are used as ultrasonic sensors, while the senders were implemented using field programmable gate arrays. Results show that in a single-access environment, the direct sequence spread spectrum method offers slightly better accuracy and precision performance compared to the frequency hopping spread spectrum. When two senders are used, measurements point out that the frequency hopping spread spectrum is more robust to near-far effects than the direct sequence spread spectrum.

  19. Multiple-access interference in 2-D wavelength/time optical CDMA system with optical hard-limiters

    Science.gov (United States)

    Chovan, Jozef; Uherek, František

    2005-08-01

    In this paper we present the proposed modification of 2-D wavelength/time (WIT) decoder1 by placing the second optical hard-limiter (0-HL) after decoder"s last optical coupler. The MA1 improvement of the 2-D W/T Optical Code Division Multiple Access (0-CDMA) system for the cases of 2D WIT decoder with one and with two 0-HLs is analyzed. Average value of signal-to-interference difference (SID) is used as the MA1 merit. The model of such 2D W/T 0-CDMA system for numerical calculation of the SID is proposed and presented in this paper. In the analyzed system, 2-D WIT Generalized Multiwavelength Prime Codewords (GMWPC), which are generated by algorithm reported in2 are used for achieving multiple-access. We assume the implemented 0-HL proposed in 3. The properties of such 0-HL were approximated [4] and its two ideality parameters, which characterize the measure of its ideality, were defined. The input and output time optical pulses sequence of W/T 0-CDMA decoder is numerical simulated. Dependencies of SID versus the weight of codeword and the number of active users in the system are presented. The influence of the properties used 0-HLs is evaluated.

  20. Transmission Analysis of Optical Code Division Multiple Access Communication Systems in the Presence of Noise in Local Area Network Applications

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2013-04-01

    Full Text Available OCDMA is an essential part of the digital communication system now days for long haul, high speed networks. The biggest challenge with Optical CDMA system is to maintain the performance of the system and offer high bandwidth in case of higher number of users at minimum cost. As the number of users increase, the input requirements i.e. transmitted power, bit rate etc start increasing sharply which contribute to the additional cost. It has recently attracted significant research interest because of the advantages it offers in terms of the flexibility in the management of the system resources. We have taken into account the system design parameters are determined such as BER (bit error rate, signal to noise ratio (SNR, transmission bit rates, and optical received power for different code lengths. The Optical CDMA systems suffer from the problem of multiple access interference (MAI.As the number of users increase the BER error rate degrades because the effect of MAI (multiple access interference increases. So, there is a limitation in number of users, as the number of users increase SNR decrease and probability of error increases.

  1. Design and Cost Performance of Decoding Technique for Hybrid Subcarrier Spectral Amplitude Coding-Optical Code Division Multiple Access System

    Directory of Open Access Journals (Sweden)

    R. K.Z. Sahbudin

    2011-01-01

    Full Text Available Problem statement: A hybrid technique combining subcarrier multiplexed and Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA deploying the Khazani-Syed code was proposed. It was proposed as a mean of increasing the maximum number of simultaneous active users by increasing the subcarrier and/or the SAC-OCDMA code word. Multiple Access Interference (MAI is the most dominant cause of performance degradation in SACOCDMA systems. Approach: A decoding technique which was simple and easy to build named Spectral Direct Decoding (SDD technique was proposed for the hybrid system of subcarrier SACOCDMA. Results: The comparison between the complementary subtraction and proposed SDD techniques for hybrid subcarrier SAC-OCDMA system in terms of cost performance was presented here. Results showed that the cost performance of the SDD technique offers a significant improvement over the complementary subtraction detection technique. Conclusion: It is shown that the cost performance of the hybrid system using SDD technique is significantly better than using the Complementary subtraction technique.

  2. Performance of a Frequency-Hopped Real-Time Remote Control System in a Multiple Access Scenario

    Science.gov (United States)

    Cervantes, Frank

    A recent trend is observed in the context of the radio-controlled aircrafts and automobiles within the hobby grade category and Unmanned Aerial Vehicles (UAV) applications moving to the well-known Industrial, Scientific and Medical (ISM) band. Based on this technological fact, the present thesis evaluates an individual user performance by featuring a multiple-user scenario where several point-to-point co-located real-time Remote Control (RC) applications operate using Frequency Hopping Spread Spectrum (FHSS) as a medium access technique in order to handle interference efficiently. Commercial-off-the-shelf wireless transceivers ready to operate in the ISM band are considered as the operational platform supporting the above-mentioned applications. The impact of channel impairments and of different critical system engineering issues, such as working with real clock oscillators and variable packet duty cycle, are considered. Based on the previous, simulation results allowed us to evaluate the range of variation for those parameters for an acceptable system performance under Multiple Access (MA) environments.

  3. On the De-Common-Sense Validity of the Multiple Choice Questions in the Reading Comprehension of College English Test Band 4

    OpenAIRE

    Jun Liu

    2014-01-01

    The researcher selected 10 multiple choice questions from the Reading Comprehension of College English Test Band 4, and asked 102 freshmen and 126 postgraduates to answer the questions without reading the source passages. The result shows that the percentage of the correct choice of each of the 7 multiple choice questions out of 10 exceeds the average percentage of the 4 choices for each question. This suggests that the students’ common sense does play a role when they answer the multiple cho...

  4. Multiple choice exams of medical knowledge with open books and web access? A validity study

    DEFF Research Database (Denmark)

    O'Neill, Lotte; Simonsen, Eivind Ortind; Knudsen, Ulla Breth;

    2015-01-01

    Background: Open book tests have been suggested to lower test anxiety and promote deeper learning strategies. In the Aarhus University medical program, ¼ of the curriculum assess students’ medical knowledge with ‘open book, open web’ (OBOW) multiple choice examinations. We found little existing e...... pass/fail rates for the groups will be compared. Results: The results will be available for and discussed at the AMEE 2015 conference....

  5. ECR Browser: A Tool For Visualizing And Accessing Data From Comparisons Of Multiple Vertebrate Genomes

    Energy Technology Data Exchange (ETDEWEB)

    Loots, G G; Ovcharenko, I; Stubbs, L; Nobrega, M A

    2004-01-06

    The increasing number of vertebrate genomes being sequenced in draft or finished form provide a unique opportunity to study and decode the language of DNA sequence through comparative genome alignments. However, novel tools and strategies are required to accommodate this increasing volume of genomic information and to facilitate experimental annotation of genome function. Here we present the ECR Browser, a tool that provides an easy and dynamic access to whole genome alignments of human, mouse, rat and fish sequences. This web-based tool (http://ecrbrowser.dcode.org) provides the starting point for discovery of novel genes, identification of distant gene regulatory elements and prediction of transcription factor binding sites. The genome alignment portal of the ECR Browser also permits fast and automated alignment of any user-submitted sequence to the genome of choice. The interconnection of the ECR browser with other DNA sequence analysis tools creates a unique portal for studying and exploring vertebrate genomes.

  6. Change Analysis of Antarctic Ice Shelves Based on Multiple Remote Sensing Products

    Science.gov (United States)

    Tian, Yixiang; Weng, Hexia; Lv, Da; Tong, Xiaohua; Li, Rongxing

    2016-06-01

    The Antarctic ice sheet is well known as the most sensitive and key issue in the global climate change research and is playing a more and more important role for the global sea level change. Measurement of changes in area and mass of the Antarctic ice sheet is critically important and has been made by using different remote sensing technologies and ground exploration data. Sequential mapping of Antarctic boundaries provides a simple and direct method for measuring the area and volume if ice sheet or ice shelves advances or retreats in the Antarctic coasts. Our results show that the total ice shelf area is retreated between 1963 and 2009. However, the trend for each ice shelf is quite different.

  7. Access to Care for Multiple Sclerosis in Times of Economic Crisis in Greece – the HOPE II Study

    Directory of Open Access Journals (Sweden)

    Kyriakos Souliotis

    2016-02-01

    Full Text Available Background While there is currently no cure for multiple sclerosis (MS, treatment with biologic diseasemodifying drugs (bDMDs can reduce the impact of the condition on the lives of patients. In Greece, the regulatory change in the distribution system of bDMDs, limited their administration through the designated pharmacies of the National Organization for Healthcare Services Provision (EOPYY or the National Health System (ESY hospitals, thus potentially impacting access to MS treatment. In this context, the aim of this paper was to assess the barriers to bDMDs, by recording MS patients’ experiences. Methods A survey research was conducted between January and February 2014 in Athens and 5 other major Greek cities with the methods of personal and telephone interview. A structured questionnaire was used to elicit socio-economic and medical information, information related to obstacles in accessing bDMDs and medical treatment, from MS patients that visited EOPYY pharmacies during the study period. Results During the last year 69% of 179 participants reported that the distribution system of bDMDs has improved. Thirteen percent of participants encountered problems in accessing their medication, and 16.9% of participants in accessing their physician, with the obstacles being more pronounced for non-Athens residents. Frequent obstacles to bDMDs were the distance from EOPYY pharmacies and difficulties in obtaining a diagnosis from an EOPYY/ESY physician, while obstacles to medical care were delays in appointment booking and travel difficulties. Conclusion Even though the major weaknesses of the distribution system of bDMDs have improved, further amelioration of the system could be achieved through the home delivery of medicines to patients living in remote areas, and through the development of a national MS registry.

  8. GLONASS-R: GNSS reflectometry with a Frequency Division Multiple Access-based satellite navigation system

    Science.gov (United States)

    Hobiger, T.; Haas, R.; Löfgren, J. S.

    2014-04-01

    The information from reflected Global Navigation Satellite System (GNSS) signals can become a valuable data source, from which geophysical properties can be deduced. This approach, called GNSS Reflectometry (GNSS-R), can be used to develop instruments that act like an altimeter when arrival times of direct and reflected signals are compared. Current GNSS-R systems usually entirely rely on signals from the Global Positioning Service (GPS), and field experiments could demonstrate that information from such systems can measure sea level with an accuracy of a few centimeters. However, the usage of the Russian GLONASS system has the potential to simplify the processing scheme and to allow handling of direct and reflected signals like a bistatic radar. Thus, such a system has been developed and deployed for test purposes at the Onsala Space Observatory, Sweden, that has an operational GPS-based GNSS-R system. Over a period of 2 weeks in October 2013, GPS-based GNSS-R sea level monitoring and measurements with the newly developed GLONASS-R system were carried out in parallel. In addition, data from colocated tide gauge measurements were available for comparison. It can be shown that precision and accuracy of the GLONASS-based GNSS-R system is comparable to, or even better than, conventional GPS-based GNSS-R solutions. Moreover, the simplicity of the newly developed GLONASS-R system allows to make it a cheap and valuable tool for various remote sensing applications.

  9. Post-Coma Persons with Extensive Multiple Disabilities Use Microswitch Technology to Access Selected Stimulus Events or Operate a Radio Device

    Science.gov (United States)

    Lancioni, Giulio E.; Singh, Nirbhay N.; O'Reilly, Mark F.; Sigafoos, Jeff; Alberti, Gloria; Oliva, Doretta; Megna, Gianfranco; Iliceto, Carla; Damiani, Sabino; Ricci, Irene; Spica, Antonella

    2011-01-01

    The present two studies extended research evidence on the use of microswitch technology by post-coma persons with multiple disabilities. Specifically, Study I examined whether three adults with a diagnosis of minimally conscious state and multiple disabilities could use microswitches as tools to access brief, selected stimulus events. Study II…

  10. Uncorrelated multiple conductive filament nucleation and rupture in ultra-thin high-κ dielectric based resistive random access memory

    KAUST Repository

    Wu, Xing

    2011-08-29

    Resistive switching in transition metal oxides could form the basis for next-generation non-volatile memory (NVM). It has been reported that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only individually, limiting our understanding of the possibility of multiple conductive filaments nucleation and rupture and the correlation kinetics of their evolution. In this study, direct visualization of uncorrelated multiple conductive filaments in ultra-thin HfO2-based high-κ dielectricresistive random access memory (RRAM) device has been achieved by high-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy(EELS), for nanoscale chemical analysis. The locations of these multiple filaments are found to be spatially uncorrelated. The evolution of these microstructural changes and chemical properties of these filaments will provide a fundamental understanding of the switching mechanism for RRAM in thin oxide films and pave way for the investigation into improving the stability and scalability of switching memory devices.

  11. On Low-Complexity Full-diversity Detection In Multi-User MIMO Multiple-Access Channels

    KAUST Repository

    Ismail, Amr

    2014-01-28

    Multiple-input multiple-output (MIMO) techniques are becoming commonplace in recent wireless communication standards. This newly introduced dimension (i.e., space) can be efficiently used to mitigate the interference in the multi-user MIMO context. In this paper, we focus on the uplink of a MIMO multiple access channel (MAC) where perfect channel state information (CSI) is only available at the destination. We provide new sufficient conditions for a wide range of space-time block codes (STBC)s to achieve full-diversity under partial interference cancellation group decoding (PICGD) with or without successive interference cancellation (SIC) for completely blind users. Interference cancellation (IC) schemes for two and three users are then provided and shown to satisfy the full-diversity criteria. Beside the complexity reduction due to the fact that PICGD enables separate decoding of distinct users without sacrificing the diversity gain, further reduction of the decoding complexity may be obtained. In fact, thanks to the structure of the proposed schemes, the real and imaginary parts of each user\\'s symbols may be decoupled without any loss of performance. Our new IC scheme is shown to outperform recently proposed two-user IC scheme especially for high spectral efficiency while requiring significantly less decoding complexity.

  12. Social Representations Of Violence Against Rural Women: Unveiling Senses In Multiple Views

    Directory of Open Access Journals (Sweden)

    Marta Cocco Costa

    2014-04-01

    Full Text Available We analyze the social representations of violence against women from the perspective of city managers, professionals and health workers in rural settings of the southern half of Rio Grande do Sul. The study has a qualitative approach and adds a theoretical/methodological perspective of social representations. The data were generated by means of the associative method, question-stimulus of words and expressions emergence. The analysis of word association was performed with EVOC software, considering frequency and order of association with inducing terms. Participants recognize violence against women as gender destination that induces consent, resignation, guilt and fear, and results in naturalization and trivialization of this social phenomenon. We highlight the need to produce ruptures in established and traditional forms of health care, in the conservative and stereotypical views of violence, favoring access to friendly service and avoiding the reproduction of gender inequalities.

  13. IPAT: a freely accessible software tool for analyzing multiple patent documents with inbuilt landscape visualizer.

    Science.gov (United States)

    Ajay, Dara; Gangwal, Rahul P; Sangamwar, Abhay T

    2015-01-01

    Intelligent Patent Analysis Tool (IPAT) is an online data retrieval tool, operated based on text mining algorithm to extract specific patent information in a predetermined pattern into an Excel sheet. The software is designed and developed to retrieve and analyze technology information from multiple patent documents and generate various patent landscape graphs and charts. The software is C# coded in visual studio 2010, which extracts the publicly available patent information from the web pages like Google Patent and simultaneously study the various technology trends based on user-defined parameters. In other words, IPAT combined with the manual categorization will act as an excellent technology assessment tool in competitive intelligence and due diligence for predicting the future R&D forecast. PMID:26452016

  14. A Sensing Error Aware MAC Protocol for Cognitive Radio Networks

    CERN Document Server

    Hu, Donglin

    2011-01-01

    Cognitive radios (CR) are intelligent radio devices that can sense the radio environment and adapt to changes in the radio environment. Spectrum sensing and spectrum access are the two key CR functions. In this paper, we present a spectrum sensing error aware MAC protocol for a CR network collocated with multiple primary networks. We explicitly consider both types of sensing errors in the CR MAC design, since such errors are inevitable for practical spectrum sensors and more important, such errors could have significant impact on the performance of the CR MAC protocol. Two spectrum sensing polices are presented, with which secondary users collaboratively sense the licensed channels. The sensing policies are then incorporated into p-Persistent CSMA to coordinate opportunistic spectrum access for CR network users. We present an analysis of the interference and throughput performance of the proposed CR MAC, and find the analysis highly accurate in our simulation studies. The proposed sensing error aware CR MAC p...

  15. Classification of hyperspectral remote sensing images based on simulated annealing genetic algorithm and multiple instance learning

    Institute of Scientific and Technical Information of China (English)

    高红民; 周惠; 徐立中; 石爱业

    2014-01-01

    A hybrid feature selection and classification strategy was proposed based on the simulated annealing genetic algorithm and multiple instance learning (MIL). The band selection method was proposed from subspace decomposition, which combines the simulated annealing algorithm with the genetic algorithm in choosing different cross-over and mutation probabilities, as well as mutation individuals. Then MIL was combined with image segmentation, clustering and support vector machine algorithms to classify hyperspectral image. The experimental results show that this proposed method can get high classification accuracy of 93.13%at small training samples and the weaknesses of the conventional methods are overcome.

  16. Interpolated compressed sensing for 2D multiple slice fast MR imaging.

    Directory of Open Access Journals (Sweden)

    Yong Pang

    Full Text Available Sparse MRI has been introduced to reduce the acquisition time and raw data size by undersampling the k-space data. However, the image quality, particularly the contrast to noise ratio (CNR, decreases with the undersampling rate. In this work, we proposed an interpolated Compressed Sensing (iCS method to further enhance the imaging speed or reduce data size without significant sacrifice of image quality and CNR for multi-slice two-dimensional sparse MR imaging in humans. This method utilizes the k-space data of the neighboring slice in the multi-slice acquisition. The missing k-space data of a highly undersampled slice are estimated by using the raw data of its neighboring slice multiplied by a weighting function generated from low resolution full k-space reference images. In-vivo MR imaging in human feet has been used to investigate the feasibility and the performance of the proposed iCS method. The results show that by using the proposed iCS reconstruction method, the average image error can be reduced and the average CNR can be improved, compared with the conventional sparse MRI reconstruction at the same undersampling rate.

  17. ECOHAB: Culver_M- NOAA CSC/Coastal Remote Sensing West Florida Coast Cruise, April 1999 (NODC Accession 0000535)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Abstract: The Coastal Services Center's (CSC) Coastal Remote Sensing (CRS) program is involved with programs to validate satellite algorithms for ocean properties....

  18. Chemosensors — Welcome to a New Open Access Journal Intended to Cover All Aspects of Chemical Sensing

    OpenAIRE

    Medintz, Igor L.

    2012-01-01

    It gives me great pleasure to welcome you to Chemosensors, a new online-only journal established by the Multidisciplinary Digital Publishing Institute (MDPI, Basel, Switzerland) with the intent of covering all aspects of chemical sensing. The ability to sense or detect/identify and quantitate a chemical entity, and in particular accomplish this through the use of chemical means, has never been a more important part of our society. Chemosensing permeates diverse fields including healthcare (e....

  19. Using multiple hydrogen bonding cross-linkers to access reversibly responsive three dimensional graphene oxide architecture

    Science.gov (United States)

    Han, Junkai; Shen, Yongtao; Feng, Wei

    2016-07-01

    Three-dimensional (3D) graphene materials have attracted a lot of attention for efficiently utilizing inherent properties of graphene sheets. However, 3D graphene materials reported in the previous literature are constructed through covalent or weak non-covalent interactions, causing permanent structure/property changes. In this paper, a novel 3D graphene material of dynamic interactions between lamellas with 2-ureido-4[1H]-pyrimidinone as a supra-molecular motif has been synthesized. This 3D graphene material shows enhanced sheet interactions while the cross-linking takes place. With proper solvent stimulation, the integrated 3D graphene material can disassemble as isolated sheets. The driving force for the 3D structure assembly or disassembly is considered to be the forming or breaking of the multiple hydrogen bonding pairs. Furthermore, the 3D material is used as an intelligent dye adsorber to adsorb methylene blue and release it. The controllable and reversible characteristic of this 3D graphene material may open an avenue to the synthesis and application of novel intelligent materials.Three-dimensional (3D) graphene materials have attracted a lot of attention for efficiently utilizing inherent properties of graphene sheets. However, 3D graphene materials reported in the previous literature are constructed through covalent or weak non-covalent interactions, causing permanent structure/property changes. In this paper, a novel 3D graphene material of dynamic interactions between lamellas with 2-ureido-4[1H]-pyrimidinone as a supra-molecular motif has been synthesized. This 3D graphene material shows enhanced sheet interactions while the cross-linking takes place. With proper solvent stimulation, the integrated 3D graphene material can disassemble as isolated sheets. The driving force for the 3D structure assembly or disassembly is considered to be the forming or breaking of the multiple hydrogen bonding pairs. Furthermore, the 3D material is used as an

  20. Securing optical code-division multiple-access networks with a postswitching coding scheme of signature reconfiguration

    Science.gov (United States)

    Huang, Jen-Fa; Meng, Sheng-Hui; Lin, Ying-Chen

    2014-11-01

    The optical code-division multiple-access (OCDMA) technique is considered a good candidate for providing optical layer security. An enhanced OCDMA network security mechanism with a pseudonoise (PN) random digital signals type of maximal-length sequence (M-sequence) code switching to protect against eavesdropping is presented. Signature codes unique to individual OCDMA-network users are reconfigured according to the register state of the controlling electrical shift registers. Examples of signature reconfiguration following state switching of the controlling shift register for both the network user and the eavesdropper are numerically illustrated. Dynamically changing the PN state of the shift register to reconfigure the user signature sequence is shown; this hinders eavesdroppers' efforts to decode correct data sequences. The proposed scheme increases the probability of eavesdroppers committing errors in decoding and thereby substantially enhances the degree of an OCDMA network's confidentiality.

  1. Asynchronous detection of optical code division multiple access signals using a bandwidth-efficient and wavelength-aware receiver.

    Science.gov (United States)

    Fok, Mable P; Deng, Yanhua; Prucnal, Paul R

    2010-04-01

    We experimentally demonstrate what we believe to be a novel detection scheme for interfacing asynchronous optical code division multiple access (CDMA) signals with an electronic clock and data recovery system that operates only at the baseband bandwidth. This allows using a large optical bandwidth expansion factor in which the optical chip rate is much larger than the bandwidth of the optoelectronic receiver. The received optical CDMA signal is launched into a four-wave-mixing-based wavelength-aware all-optical front end that rejects multiaccess interference, followed by an amplitude-noise suppression stage comprised of a semiconductor optical amplifier. The clean signal is then converted into a non-return-to-zero-like signal by a baseband receiver. Using the proposed detection scheme, asynchronous transmission and detection of optical CDMA signals is implemented. With the novel detection scheme, the classic CDMA near-far problem is mitigated, and error-free detection is easily obtained. PMID:20364229

  2. Demonstration of a novel optical code-division multiple-access system at 800 megachips per second.

    Science.gov (United States)

    Vethanayagam, N; Macdonald, R I

    1991-07-01

    A novel optical code-division multiple-access system using Alberta codes and complementary correlation is demonstrated at 800 megachips per second. Completely passive optical multiplexing and demultiplexing is performed throughout the process. Complementary correlation permits code orthogonality because bipolar electrical signals are generated from unipolar optical ones. The correlator is implemented optoelectronically with an array of metal-semiconductor-metal photodiodes. We show that the bit-error-rate performance of the system is not degraded by interfering signals and that zero cross talk is nominally achieved. An unusual property of such systems is confirmed: The bit error rate on a channel can be reduced by the presence of an interfering channel if the two transmitters are not chip asynchronous. PMID:19776859

  3. A design of a wavelength-hopping time-spreading incoherent optical code division multiple access system

    International Nuclear Information System (INIS)

    We present the architecture and code design for a highly scalable, 2.5 Gb/s per user optical code division multiple access (OCDMA) system. The system is scalable to 100 potential and more than 10 simultaneous users, each with a bit error rate (BER) of less than 10-9. The system architecture uses a fast wavelength-hopping, time-spreading codes. Unlike frequency and phase sensitive coherent OCDMA systems, this architecture utilizes standard on off keyed optical pulses allocated in the time and wavelength dimensions. This incoherent OCDMA approach is compatible with existing WDM optical networks and utilizes off the shelf components. We discuss the novel optical subsystem design for encoders and decoders that enable the realization of a highly scalable incoherent OCDMA system with rapid reconfigurability. A detailed analysis of the scalability of the two dimensional code is presented and select network deployment architectures for OCDMA are discussed (Authors)

  4. Novel WLL Architecture Based on Color Pixel Multiple Access Implemented on a Terrestrial Video Network as the Overlay

    DEFF Research Database (Denmark)

    Sanyal, Rajarshi; Cianca, Ernestina; Prasad, Ramjee

    2013-01-01

    for conveying data symbols from one end to other. The big question is: Is it feasible to implement color synthesized by the video systems for the purpose of telecommunications? In this paper we propose the ‘Color Pixel Multiple Access’ scheme for the radio access network and Color Pixel Multiplexing for core...... network, by implementing electronic color as a tool for addressing and bearing data overhead. The present day video systems that can generate millions of colors, in its electronic form have been utilized to set up a wireless network, serving mobile stations or computers as its nodes. The state of the art...... Wireless Local Loop deployments are based on the traditional cellular technologies. However there are limitations in terms of intricacy, cost and time to deploy .In this paper, the authors introduce a Wireless Local Loop architecture employing the proposed CPMA technique on existing overlay video...

  5. Performance analysis for a chaos-based code-division multiple access system in wide-band channel

    Directory of Open Access Journals (Sweden)

    Ciprian Doru Giurcăneanu

    2015-08-01

    Full Text Available Code-division multiple access technology is widely used in telecommunications and its performance has been extensively investigated in the past. Theoretical results for the case of wide-band transmission channel were not available until recently. The novel formulae which have been published in 2014 can have an important impact on the future of wireless multiuser communications, but limitations come from the Gaussian approximations used in their derivation. In this Letter, the authors obtain more accurate expressions of the bit error rate (BER for the case when the model of the wide-band channel is two-ray, with Rayleigh fading. In the authors’ approach, the spreading sequences are assumed to be generated by logistic map given by Chebyshev polynomial function of order two. Their theoretical and experimental results show clearly that the previous results on BER, which rely on the crude Gaussian approximation, are over-pessimistic.

  6. Optimal Throughput and Energy Efficiency for Wireless Sensor Networks: Multiple Access and Multipacket Reception

    Directory of Open Access Journals (Sweden)

    Li Wenjun

    2005-01-01

    Full Text Available We investigate two important aspects in sensor network design—the throughput and the energy efficiency. We consider the uplink reachback problem where the receiver is equipped with multiple antennas and linear multiuser detectors. We first assume Rayleigh flat-fading, and analyze two MAC schemes: round-robin and slotted-ALOHA. We optimize the average number of transmissions per slot and the transmission power for two purposes: maximizing the throughput, or minimizing the effective energy (defined as the average energy consumption per successfully received packet subject to a throughput constraint. For each MAC scheme with a given linear detector, we derive the maximum asymptotic throughput as the signal-to-noise ratio goes to infinity. It is shown that the minimum effective energy grows rapidly as the throughput constraint approaches the maximum asymptotic throughput. By comparing the optimal performance of different MAC schemes equipped with different detectors, we draw important tradeoffs involved in the sensor network design. Finally, we show that multiuser scheduling greatly enhances system performance in a shadow fading environment.

  7. Using multiple hydrogen bonding cross-linkers to access reversibly responsive three dimensional graphene oxide architecture.

    Science.gov (United States)

    Han, Junkai; Shen, Yongtao; Feng, Wei

    2016-08-01

    Three-dimensional (3D) graphene materials have attracted a lot of attention for efficiently utilizing inherent properties of graphene sheets. However, 3D graphene materials reported in the previous literature are constructed through covalent or weak non-covalent interactions, causing permanent structure/property changes. In this paper, a novel 3D graphene material of dynamic interactions between lamellas with 2-ureido-4[1H]-pyrimidinone as a supra-molecular motif has been synthesized. This 3D graphene material shows enhanced sheet interactions while the cross-linking takes place. With proper solvent stimulation, the integrated 3D graphene material can disassemble as isolated sheets. The driving force for the 3D structure assembly or disassembly is considered to be the forming or breaking of the multiple hydrogen bonding pairs. Furthermore, the 3D material is used as an intelligent dye adsorber to adsorb methylene blue and release it. The controllable and reversible characteristic of this 3D graphene material may open an avenue to the synthesis and application of novel intelligent materials. PMID:27378190

  8. Ultrafast carrier relaxation in GaN, In_(0.05)Ga_(0.95)N and an In_(0.05)Ga_(0.95)/In_(0.15)Ga_(0.85)N Multiple Quantum Well

    OpenAIRE

    Ozgur, Umit; Everitt, Henry O.

    2002-01-01

    Room temperature, wavelength non-degenerate ultrafast pump/probe measurements were performed on GaN and InGaN epilayers and an InGaN multiple quantum well structure. Carrier relaxation dynamics were investigated as a function of excitation wavelength and intensity. Spectrally-resolved sub-picosecond relaxation due to carrier redistribution and QW capture was found to depend sensitively on the wavelength of pump excitation. Moreover, for pump intensities above a threshold of 100 microJ/cm2, al...

  9. Radiative recombination mechanism of carriers in InGaN/AlInGaN multiple quantum wells with varying aluminum content

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Tong [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Jiao, Shujie, E-mail: shujiejiao@gmail.com [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Key Laboratory for Photonic and Electric Bandgap Materials, Ministry of Education, Harbin Normal University, Harbin 150001 (China); Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Wang, Dongbo [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Gao, Shiyong, E-mail: gaoshiyong@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Yang, Tianpeng [EpiTop Optoelectronic Co., Ltd., Pingxiang 337000 (China); Liang, Hongwei [School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China); Zhao, Liancheng [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2015-02-05

    Highlights: • Structural and optical properties of In GaN/Al{sub x}In{sub y}Ga{sub 1−x−y}N MQWs were investigated. • The existence of In-rich clusters has been verified by Raman spectra. • The degree of localization effect increase with increasing Al content in barriers. • The origin of the deep localized states could be assigned to the larger QCSE. • Recombination mechanism of carriers with increasing temperature has been proposed. - Abstract: The structural and optical properties of In{sub 0.20}Ga{sub 0.80}N/Al{sub x}In{sub y}Ga{sub 1−x−y}N multiple quantum wells samples with varying Al content in barrier layers grown on sapphire substrates by metalorganic chemical vapor deposition have been investigated by means of high-resolution X-ray diffraction, Raman scattering measurements and temperature-dependent photoluminescence. Raman measurements verified the existence of In-rich clusters in ternary and quaternary layers. At 10 K and 300 K, the PL spectrum of each sample is dominated by a sharp emission peak arising from In{sub 0.20}Ga{sub 0.80}N well layers. The anomalous temperature-dependent S-shaped behaviors of emission energies have been observed, indicating the presence of localized states induced by the potential fluctuations in the quantum wells due to the inhomogeneous distribution of In-rich clusters. The degree of the localization effect and the transition temperatures between different temperature regions can be enhanced by increasing Al content in barrier layers. The improvement of the localized states emission has been observed at the lower energy side of band gap emission of quantum wells with increasing Al content. The origin of the deep localized states could be attributed to the larger quantum-confined Stark effect in the quantum wells with higher Al content. The recombination mechanism of carriers between band edge and localized states was proposed for interpreting of the emission characteristics.

  10. Radionuclide carriers

    International Nuclear Information System (INIS)

    A new carrier for radionuclide technetium 99m has been prepared for scintiscanning purposes. The new preparate consists of physiologically acceptable water-insoluble Tcsup(99m)-carrier containing from 0.2 to 0.8 weight percent of stannic ion as reductor, bound to an anionic starch derivative with about 1-20% of phosphate substituents. (EG)

  11. Aircraft Carriers

    DEFF Research Database (Denmark)

    Nødskov, Kim; Kværnø, Ole

    the majority of its foreign trade, as well as its oil imports, upon which the country is totally dependent. China therefore has good reasons for acquiring an aircraft carrier to enable it to protect its national interests. An aircraft carrier would also be a prominent symbol of China’s future status...... information is pieced together, then a picture is created of a Chinese aircraft carrier program, where Varyag will be made operational for training purposes. With this as the model, China will build a similar sized carrier themselves. If this project does become a reality, then it will take many years for...... Kuznetsov carrier. The SU-33 is, in its modernized version, technologically at the same level as western combat aircraft in both the offensive as well as the defensive roles. But Russia and China currently have an arms trade 6 dispute that is likely to prevent a deal, unless the dispute is resolved. As an...

  12. Mapping Woody Plant Encroachment in Grassland Using Multiple Source Remote Sensing images: Case Study in Oklahoma

    Science.gov (United States)

    Wang, J.; Xiao, X.; Qin, Y.; Dong, J.; Zhang, G.; Zhang, Y.; Zou, Z.; Zhou, Y.; Wu, X.; Bajgain, R.

    2015-12-01

    Woody plant encroachment (mainly Juniperus virginiana, a coniferous evergreen tree) in the native grassland has been rapidly increasing in the U.S. Southern Great Plains, largely triggered by overgrazing domestic livestock, fire suppression, and changing rainfall regimes. Increasing dense woody plants have significant implications for local grassland ecosystem dynamics, such as carbon storage, soil nutrient availability, herbaceous forage production, livestock, watershed hydrology and wildlife habitats. However, very limited data are available about the spatio-temporal dynamics of woody plant encroachment to the native grassland at regional scale. Data from remotes sensing could potentially provide relevant information and improve the conversion of native grassland to woody plant encroachment. Previous studies on woody detection in grassland mainly conducted at rangeland scale using airborne or high resolution images, which is sufficient to monitor the dynamics of woody plant encroachment in local grassland. This study examined the potential of medium resolution images to detect the woody encroachment in tallgrass prairie. We selected Cleveland county, Oklahoma, US. as case study area, where eastern area has higher woody coverage than does the western area. A 25-m Phased Array Type L-band Synthetic Aperture Radar (PALSAR, N36W98) image was used to map the trees distributed in the grassland. Then, maximum enhanced vegetation index (EVI) and normalized difference vegetation index (NDVI) in the winter calculated from time-series Landsat images was used to identify the invaded woody species (Juniperus virginiana) through phenology-based algorithm. The resulting woody plant encroachment map was compared with the results extracted from the high resolution images provided by the National Agriculture Imagery Program (NAIP). Field photos were also used to validate the accuracy. These results showed that integrating PALSAR and Landsat had good performance to identify the

  13. Performance comparison of asynchronous orthogonal multi-carrier CDMA in frequency selective channel

    OpenAIRE

    Xiang, G; Ng, TS

    1998-01-01

    Bit error rate (BER) performance of an asynchronous multi-carrier code division multiple access (MC-CDMA) system for the uplink of the mobile communication system with equal gain combining and maximum ratio combining are obtained. Given a fixed bandwidth frequency selective channel, performance of MC-CDMA is compared with that of conventional CDMA and MC-DS-CDMA in numerical results.

  14. Asynchronous Orthogonal Multi-Carrier CDMA Using Equal Gain Combining in Multipath Rayleigh Fading Channel

    OpenAIRE

    Xiang, G; Ng, TS

    1998-01-01

    Performance of an asynchronous orthogonal multi-carrier code division multiple access (MC-CDMA) system for the reverse link of the mobile communication system with equal gain combining is obtained. The performance of MC-CDMA is compared with that of conventional CDMA and MC-DS-CDMA in numerical results in a multipath Rayleigh fading channel.

  15. An Efficient Medium Access Control Protocol with Parallel Transmission for Wireless Sensor Networks

    Directory of Open Access Journals (Sweden)

    Mitsuji Matsumoto

    2012-08-01

    Full Text Available In this paper, we present a novel low power medium access control protocol for wireless sensor networks (WSNs. The proposed protocol, EP-MAC (Efficient MAC with Parallel Transmission achieves high energy efficiency and high packet delivery ratio under different traffic load. EP-MAC protocol is basically based on the Time Division Multiple Access (TDMA approach. The power of Carrier Sense Multiple Access (CSMA is used in order to offset the fundamental problems that the stand-alone TDMA method suffers from, i.e., problems such as lack of scalability, adaptability to varying situations, etc. The novel idea behind the EP-MAC is that it uses the parallel transmission concept with the TDMA link scheduling. EP-MAC uses the methods for the transmission power adjustment, i.e., uses the minimum level power necessary to reach the intended neighbor within a specified bit error rate [BER] target. This reduces energy consumption, as well as further enhances the scope of parallel transmission of the protocol. The simulation studies support the theoretical results, and validate the efficiency of our proposed EP-MAC protocol.

  16. On optimal contention-based access scheme in WLAN for next generation networks

    Science.gov (United States)

    Yeh, Hsi-Hsun; Cheng, Chih-Chuan; Chen, Mau-Shi; Cheng, Bo-Chou; Chen, Huan

    2007-09-01

    A contention-based access scheme, Distributed Coordination Function (DCF), is the basic access technology and it works as the basis for 802.11 MAC and its extensions. Using the Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism and the Binary Exponential Backoff (BEB) mechanism, DCF can efficiently avoid multiple stations to transmit data at the same time and thus reduces the collision probability. In addition to BEB, Exponential Increase Exponential Decrease (EIED) is another well known backoff mechanism to avoid retransmission collision. In literature, many researches show that BEB algorithm may result in a poor throughput in a heavy load environment, while the EIED scheme does not perform as well as BEB under a light traffic condition. The emphasis of this paper is to address the shortcomings of the above two schemes and pose a solution to select a better random backoff timer in order to maximize the throughput under various traffic load. In this work, a novel backoff mechanism, Optimal Backoff (OB) mechanism, is proposed. OB can choose an optimal contention window according to current traffic conditions. Analytical and simulation results show that proposed Optimal Backoff mechanism always has highest throughput and lowest packet delay than those of the BEB and EIED mechanisms under both light and heavy traffic scenarios. With the deployment of the proposed OB, we believe that Wireless LAN is able to work perfectly as an extension of legacy mobile networks in t he context of upcoming Next Generation Networks.

  17. Performance Analysis of Direct-Sequence Code-Division Multiple-Access Communications with Asymmetric Quadrature Phase-Shift-Keying Modulation

    Science.gov (United States)

    Wang, C.-W.; Stark, W.

    2005-01-01

    This article considers a quaternary direct-sequence code-division multiple-access (DS-CDMA) communication system with asymmetric quadrature phase-shift-keying (AQPSK) modulation for unequal error protection (UEP) capability. Both time synchronous and asynchronous cases are investigated. An expression for the probability distribution of the multiple-access interference is derived. The exact bit-error performance and the approximate performance using a Gaussian approximation and random signature sequences are evaluated by extending the techniques used for uniform quadrature phase-shift-keying (QPSK) and binary phase-shift-keying (BPSK) DS-CDMA systems. Finally, a general system model with unequal user power and the near-far problem is considered and analyzed. The results show that, for a system with UEP capability, the less protected data bits are more sensitive to the near-far effect that occurs in a multiple-access environment than are the more protected bits.

  18. Mixing stream and datagram traffic on satellite: A FIFO Order-based Demand Assignment (FODA) Time Division Multiple Access (TDMA) scheme

    Science.gov (United States)

    Beltrame, R.; Bonito, A. B.; Celandroni, N.; Ferro, E.

    1985-11-01

    A FIFO Order based Demand Assignment (FODA) access scheme was designed to handle packetized data and voice traffic in a multiple access satellite broadcast channel of Mbits band. The channel is shared by as many as 64 simultaneously active stations in a range of 255 addressable stations. A sophisticated traffic environment is assumed, including different types of service requirements and an arbitrary load distribution among the stations. The results of 2Mbit/sec simulation tests for an existing hardware environment are presented.

  19. Aircraft Carriers

    DEFF Research Database (Denmark)

    Nødskov, Kim; Kværnø, Ole

    as a great power in Asia and will balance the carrier acquisitions of the United States, the United Kingdom, Russia and India. China’s current military strategy is predominantly defensive, its offensive elements being mainly focused on Taiwan. If China decides to acquire a large carrier with...... offensive capabilities, then the country will also acquire the capability to project military power into the region beyond Taiwan, which it does not possess today. In this way, China will have the military capability to permit a change of strategy from the mainly defensive, mainland, Taiwan-based strategy...... to a more assertive strategy, with potentially far-reaching consequences for the countries of the region. The Chinese have bought several retired carriers, which they have studied in great detail. The largest is the Russian-built carrier Varyag of the Kuznetsov class, which today is anchored in the...

  20. Energy-Based Cooperative Spectrum Sensing of SC-FDMA Systems

    Directory of Open Access Journals (Sweden)

    Fucheng Yang

    2014-07-01

    Full Text Available In this paper, we propose a frequency-hopping M-ary frequency-shift keying spectrum sensing network (FH/MFSK SSN for identifying the on/off states of the users supported by a single-carrier frequency-division multiple assess (SC-FDMA primary radio (PR system. Specifically, the spectrums of an uplink interleaved frequency-division multiple access (IFDMA PR system are monitored by a number of cognitive radio sensing nodes (CRSNs. These CRSNs distributedly detect the on/off states of users based on one of the three energy detection schemes. After the local spectrum sensing, the CRSNs transmit their detected states to a fusion centre (FC with the aid of FH/MFSK techniques. At the FC, the on/off states of the users supported the IFDMA PR system are finally classified according to either the conventional equal-gain combining (EGC scheme or the novel erasure-supported EGC (ES-EGC scheme. In this way, the on/off information about the spectrums occupied by an IFDMA PR systemcan be obtained, so that they can be exploited by a cognitive radio (CR system. For local spectrum sensing, in this paper, we consider four synchronisation scenarios concerning the synchronisation between the received IFDMA signals and the CRSNs. The performance of the FH/MFSK SSN associated with various schemes is investigated by simulations. Our studies show that the FH/MFSK SSN constitutes one of the highly reliable spectrum sensing schemes, which are capable of exploiting both the space diversity provided by local CRSNs and the frequency diversity provided by the subcarriers of IFDMA system.

  1. Circulation in the southern Great Barrier Reef studied through an integration of multiple remote sensing and in situ measurements

    Science.gov (United States)

    Mao, Yadan; Luick, John L.

    2014-03-01

    New mechanisms for stratification and upwelling in the southern Great Barrier Reef (GBR) are identified, and dynamic details of Capricorn Eddy, a transient feature located off the shelf at the southern extremity of the GBR, are revealed using the newly available surface current from High Frequency (HF) radar combined with other remote sensing and mooring data. The HF radar surface currents were used for tidal harmonic analysis and current-wind correlation analysis. These analyses, combined with Sea Surface Temperature (SST) data, mooring data, and altimetry-based geostrophic currents, enabled the effects of forcing from the large-scale oceanic currents (including the East Australian Current (EAC)), wind, and tides in a topographically complex flow regime to be separately identified. Within the indentation region where the width of the shelf abruptly narrows, current is strongly coupled with the EAC. Here strong residual flows, identified on current maps and SST images, fall into three patterns: southward flow, northwestward flow, and an eddy. Multiple data sets shed light on the prerequisite for the formation of the eddy, the reasons for its geometric variation, and its evolution with time. Intrusions of the eddy onto the shelf result in stratification characterized by a significant increase of surface temperature. Upwelling driven by wind or oceanic inflow is shown to cause stratification of previously well-mixed shelf water. The upwelling appears to be associated with equatorward-traveling coastal-trapped waves. The integrative method of analysis embodied here is applicable to other coastal regions with complex circulation.

  2. Strategies of Building a Stronger Sense of Community for Sustainable Neighborhoods: Comparing Neighborhood Accessibility with Community Empowerment Programs

    OpenAIRE

    Te-I Albert Tsai

    2014-01-01

    New Urbanist development in the U.S. aims at enhancing a sense of community and seeks to return to the design of early transitional neighborhoods which have pedestrian-oriented environments with retail shops and services within walking distances of housing. Meanwhile, 6000 of Taiwan’s community associations have been running community empowerment programs supported by the Council for Cultural Affairs that have helped many neighborhoods to rebuild so-called community cohesion. This research ...

  3. Quantum Multiple Access Channel

    Institute of Scientific and Technical Information of China (English)

    侯广; 黄民信; 张永德

    2002-01-01

    We consider the transmission of classical information over a quantum channel by many senders, which is a generalization of the two-sender case. The channel capacity region is shown to be a convex hull bound by the yon Neumann entropy and the conditional yon Neumann entropies. The result allows a reasonable distribution of channel capacity over the senders.

  4. Chemosensors — Welcome to a New Open Access Journal Intended to Cover All Aspects of Chemical Sensing

    Directory of Open Access Journals (Sweden)

    Igor L. Medintz

    2012-12-01

    Full Text Available It gives me great pleasure to welcome you to Chemosensors, a new online-only journal established by the Multidisciplinary Digital Publishing Institute (MDPI, Basel, Switzerland with the intent of covering all aspects of chemical sensing. The ability to sense or detect/identify and quantitate a chemical entity, and in particular accomplish this through the use of chemical means, has never been a more important part of our society. Chemosensing permeates diverse fields including healthcare (e.g., blood chemistry analysis, food safety (e.g., detecting contamination and spoilage, environmental monitoring (e.g., air and water quality, product and manufacturing assurance (e.g., purity and efficacy, household safety (e.g., smoke detection, forensics (e.g., drug analysis, and biological research (e.g., quantitating DNA or monitoring intracellular homeostasis, to name but a paltry few areas. Indeed, the application of chemosensing has become such an integrated aspect of modern society that trying to compile a comprehensive list of where it is utilized or relied on is almost impossible. Equally daunting is trying to compile a comprehensive list of all the different sensing techniques, types of analysis, modes of signal transduction, instruments and similar type aspects. The pace of new developments in this field is both remarkable and continuously accelerating with new products and applications being developed on an almost unceasing basis. [...

  5. Strategies of Building a Stronger Sense of Community for Sustainable Neighborhoods: Comparing Neighborhood Accessibility with Community Empowerment Programs

    Directory of Open Access Journals (Sweden)

    Te-I Albert Tsai

    2014-05-01

    Full Text Available New Urbanist development in the U.S. aims at enhancing a sense of community and seeks to return to the design of early transitional neighborhoods which have pedestrian-oriented environments with retail shops and services within walking distances of housing. Meanwhile, 6000 of Taiwan’s community associations have been running community empowerment programs supported by the Council for Cultural Affairs that have helped many neighborhoods to rebuild so-called community cohesion. This research attempts to evaluate whether neighborhoods with facilities near housing and shorter travel distances within a neighborhood would promote stronger social interactions and form a better community attachment than neighborhoods that have various opportunities for residents to participate in either formal or informal social gatherings. After interviewing and surveying residents from 19 neighborhoods in Taipei’s Beitou District, and correlating the psychological sense of community with inner neighborhood’s daily travel distances and numbers of participatory activities held by community organizations under empowerment programs together with frequencies of regular individual visits and casual meetings, statistical evidence yielded that placing public facilities near residential locations is more effective than providing various programs for elevating a sense of community.

  6. Solving the Near-Far Problem in Dynamic Frequency Hopping-Optical Code Division Multiple Access using Power Control

    Directory of Open Access Journals (Sweden)

    W. J.M. Al-galbi

    2009-01-01

    Full Text Available Problem statement: In this study, a distributed power control algorithm is proposed for Dynamic Frequency Hopping Optical-CDMA (DFH-OCDMA system. Approach: In general, the DFH-OCDMA can support higher number of simultaneous users compared to other OCDMA techniques. However, the performance of such system degrades significantly as the received power does lower than its minimum threshold. Results: This may obviously occur in a DFH-OCDMA network with near-far problem which consist of different fiber lengths among the users, that resulting to unequal power attenuation. The power misdistribution among simultaneous active users at the star coupler would degrade the Bit Error Rate (BER performance for users whose transmitting signals with longer fiber lengths. In order to solve these problems, we propose an adaptive distributed power control technique for DFH-OCDMA to satisfy the target Signal to Noise Ratio (SNR for all users. Conclusion: Taking into account the noise effects of Multiple Access Interference (MAI, Phase Induced Intensity Noise (PIIN and shot noise, the system can support 100% of users with power control as compared to 33% without power control when the initial transmitted power was -1dBm with 30 simultaneous users.

  7. Spatial-phase code-division multiple-access system with multiplexed Fourier holography switching for reconfigurable optical interconnection.

    Science.gov (United States)

    Takasago, K; Takekawa, M; Shirakawa, A; Kannari, F

    2000-05-10

    A new, to our knowledge, space-variant optical interconnection system based on a spatial-phase code-division multiple-access technique with multiplexed Fourier holography is described. In this technique a signal beam is spread over wide spatial frequencies by an M-sequence pseudorandom phase code. At a receiver side a selected signal beam is properly decoded, and at the same time its spatial pattern is shaped with a Fourier hologram, which is recorded by light that is encoded with the same M-sequence phase mask as the desired signal beam and by light whose spatial beam pattern is shaped to a signal routing pattern. Using the multiplexed holography, we can simultaneously route multisignal flows into individually specified receiver elements. The routing pattern can also be varied by means of switching the encoding phase code or replacing the hologram. We demonstrated a proof-of-principle experiment with a doubly multiplexed hologram that enables simultaneous routing of two signal beams. Using a numerical model, we showed that the proposed scheme can manage more than 250 routing patterns for one signal flow with one multiplexed hologram at a signal-to-noise ratio of ~5. PMID:18345134

  8. Solving the Near-Far Problem in Dynamic Frequency Hopping-Optical Code Division Multiple Access using Power Control

    Directory of Open Access Journals (Sweden)

    Wamidh J. M. ALgalbi

    2011-12-01

    Full Text Available In this study, a distributed power control algorithm is proposed for Dynamic Frequency Hopping Optical-CDMA (DFH-OCDMA system. In general, the DFH-OCDMA can support higher number of simultaneous users compared to other OCDMA techniques. However, the performance of such system degrades significantly as the received power does lower than its minimum threshold. This may obviously occur in a DFH-OCDMA network with near-far problem which consist of different fiber lengths among the users, that resulting to unequal power attenuation. The power misdistribution among simultaneous active users at the star coupler would degrade the Bit Error Rate (BER performance for users whose transmitting signals with longer fiber lengths. In order to solve these problems, we propose an adaptive distributed power control technique for DFH-OCDMA to satisfy the target Signal to oise Ratio (SR for all users. Taking into account the noise effects of Multiple Access Interference (MAI, Phase Induced Intensity oise (PII and shot noise, the system can support 100% of users with power control as compared to 33% without power control when the initial transmitted power was -1dBm with 30 simultaneous users. Ke

  9. Satellite range delay simulator for a matrix-switched time division multiple-access network simulation system

    Science.gov (United States)

    Nagy, Lawrence A.

    1990-01-01

    The Systems Integration, Test, and Evaluation (SITE) facility at NASA Lewis Research Center is presently configured as a satellite-switched time division multiple access (SS-TDMA) network simulator. The purpose of SITE is to demonstrate and evaluate advanced communication satellite technologies, presently embodied by POC components developed under NASA contracts in addition to other hardware, such as ground terminals, designed and built in-house at NASA Lewis. Each ground terminal in a satellite communications system will experience a different aspect of the satellite's motion due mainly to daily tidal effects and station keeping, hence a different duration and rate of variation in the range delay. As a result of this and other effects such as local oscillator instability, each ground terminal must constantly adjust its transmit burst timing so that data bursts from separate ground terminals arrive at the satellite in their assigned time slots, preventing overlap and keeping the system in synchronism. On the receiving end, ground terminals must synchronize their local clocks using reference transmissions received through the satellite link. A feature of the SITE facility is its capability to simulate the varying propagation delays and associated Doppler frequency shifts that the ground terminals in the network have to cope with. Delay is ahcieved by means of two NASA Lewis designed and built range delay simulator (RDS) systems, each independently controlled locally with front panel switches or remotely by an experiment control and monitor (EC/M) computer.

  10. 一种基于子载波侦听的宽带无线网络接入控制策略%A Subcarrier-Sensing-Based Medium Access Control Scheme in Wireless Broadband Networks

    Institute of Scientific and Technical Information of China (English)

    尹杰晨; 毛玉明; 冷鹏

    2014-01-01

    In the orthogonal frequency division multiple access (OFDMA)wireless broadband networks ,the efficiency of ran-dom access can be improved by distributing contention onto multiple channels .However ,due to the multichannel property ,the tradi-tional systems based on request-to-send (RTS )control frame have to encounter the idleness of subchannel ,the extension of RTS transmission time and the complex synchronization of uplink communication .To solve these problems ,in our scheme ,the users send signals on random subcarrier to request transmission opportunity .The access point senses these request signals ,and determines which user is permitted to access channel according to the busy state of the subcarriers .The theoretical analysis and simulation results both show that our scheme outperforms the traditional RTS-based schemes in term of the throughput .%在基于正交频分多址技术的宽带网络中,通过把竞争分散到多个子信道能有效改善随机接入的性能。然而多信道特性也会使传统基于Request-To-Send (RTS )控制帧的随机接入协议面临子信道空闲、RTS传输时间延长、上行复杂的问题。针对这些问题,在本文所提出的接入方法中,用户在没有被分配到资源时通过在随机子载波上发送信号来请求传输机会,与此同时,接入点对这些信号侦听,并根据子载波忙闲状态确定哪些用户可以接入。理论分析及仿真结果表明,相比传统依靠RTS的接入方法,采用子载波侦听,系统将获得更高的吞吐量。

  11. A multiple regrowth process for monolithically-integrated InP-based mode-locked laser diodes with uni-travelling carrier absorber

    Science.gov (United States)

    Lohe, Hans-Jörg; Scollo, Riccardo; Vogt, Werner; Gini, Emilio; Robin, Franck; Erni, Daniel; Harbers, Rik; Jäckel, Heinz

    2006-04-01

    Progress in photonics by monolithic integration for higher functional density, performance and reduced cost faces challenging hurdles due to technological and functional heterogeneities. Advanced local material growth techniques are enabling concepts towards high-density photonic integration, unprecedented performance and multi-functionality and ultimately optical systems-on-a-chip. For example mode-locked laser diodes (MLLDs) are key devices for ultra-short pulse generation for all-optical Tbit/s communication networks. MLLDs suffer from material compromises and will benefit from the possibility to design the gain, absorber and passive-waveguiding sections independently. We have proposed and demonstrated the integration of a saturable absorber with a fast absorption recovery time based on an InP/InGaAsP uni-traveling-carrier structure (UTC) to achieve pulses below 1 ps with repetition rates up to 40 GHz. The use of the UTC absorber instead of the commonly employed reverse-biased gain material requires however the heterogeneous growth of multiple layer stacks on the same chip with the butt-coupled regrowth technique.Critical for the MLLD performance are the reflections and the optical coupling between the different monolithic integrated layer structures of passive, absorbing and amplifying sections. 2D FDTD simulations of the optical waveguides demonstrate that to minimize reflections an angled interface between the different structures is preferable and can lead to reflection coefficients as low as 10^-6. To obtain an angled interface we used a wet chemical etching process sequence of selective and non-selective etchants, which is sensitive to crystal orientation and yields a 55° tilted interface. In addition we can conclude from our simulations that in order to minimize both, insertion loss and reflections, a bending of the light guiding layers has to be prevented. Bendings can lead to measured losses of 5-7 dB per interface whereas correctly aligned light

  12. Multi-channel Dual Clocks three-dimensional probability Random Multiple Access protocol for Wireless Public Bus Networks based on RTS/CTS mechanism

    Directory of Open Access Journals (Sweden)

    Zhou Sheng Jie

    2016-01-01

    Full Text Available A MAC protocol for public bus networks, called Bus MAC protocol, designed to provide high quality Internet service for bus passengers. The paper proposed a multi-channel dual clocks three-demission probability random multiple access protocol based on RTS/CTS mechanism, decreasing collisions caused by multiple access from multiple passengers. Use the RTS/CTS mechanism increases the reliability and stability of the system, reducing the collision possibility of the information packets to a certain extent, improves the channel utilization; use the multi-channel mechanism, not only enables the channel load balancing, but also solves the problem of the hidden terminal and exposed terminal. Use the dual clocks mechanism, reducing the system idle time. At last, the different selection of the three-dimensional probabilities can make the system throughput adapt to the network load which could realize the maximum of the system throughput.

  13. System and method for determination of the reflection wavelength of multiple low-reflectivity bragg gratings in a sensing optical fiber

    Science.gov (United States)

    Moore, Jason P. (Inventor)

    2009-01-01

    A system and method for determining a reflection wavelength of multiple Bragg gratings in a sensing optical fiber comprise: (1) a source laser; (2) an optical detector configured to detect a reflected signal from the sensing optical fiber; (3) a plurality of frequency generators configured to generate a signal having a frequency corresponding to an interferometer frequency of a different one of the plurality of Bragg gratings; (4) a plurality of demodulation elements, each demodulation element configured to combine the signal produced by a different one of the plurality of frequency generators with the detected signal from the sensing optical fiber; (5) a plurality of peak detectors, each peak detector configured to detect a peak of the combined signal from a different one of the demodulation elements; and (6) a laser wavenumber detection element configured to determine a wavenumber of the laser when any of the peak detectors detects a peak.

  14. Analysis of tumor template from multiple compartments in a blood sample provides complementary access to peripheral tumor biomarkers.

    Science.gov (United States)

    Strauss, William M; Carter, Chris; Simmons, Jill; Klem, Erich; Goodman, Nathan; Vahidi, Behrad; Romero, Juan; Masterman-Smith, Michael; O'Regan, Ruth; Gogineni, Keerthi; Schwartzberg, Lee; Austin, Laura K; Dempsey, Paul W; Cristofanilli, Massimo

    2016-05-01

    Targeted cancer therapeutics are promised to have a major impact on cancer treatment and survival. Successful application of these novel treatments requires a molecular definition of a patient's disease typically achieved through the use of tissue biopsies. Alternatively, allowing longitudinal monitoring, biomarkers derived from blood, isolated either from circulating tumor cell derived DNA (ctcDNA) or circulating cell-free tumor DNA (ccfDNA) may be evaluated. In order to use blood derived templates for mutational profiling in clinical decisions, it is essential to understand the different template qualities and how they compare to biopsy derived template DNA as both blood-based templates are rare and distinct from the gold-standard. Using a next generation re-sequencing strategy, concordance of the mutational spectrum was evaluated in 32 patient-matched ctcDNA and ccfDNA templates with comparison to tissue biopsy derived DNA template. Different CTC antibody capture systems for DNA isolation from patient blood samples were also compared. Significant overlap was observed between ctcDNA, ccfDNA and tissue derived templates. Interestingly, if the results of ctcDNA and ccfDNA template sequencing were combined, productive samples showed similar detection frequency (56% vs 58%), were temporally flexible, and were complementary both to each other and the gold standard. These observations justify the use of a multiple template approach to the liquid biopsy, where germline, ctcDNA, and ccfDNA templates are employed for clinical diagnostic purposes and open a path to comprehensive blood derived biomarker access. PMID:27049831

  15. Effect of number of stack on the thermal escape and non-radiative and radiative recombinations of photoexcited carriers in strain-balanced InGaAs/GaAsP multiple quantum-well-inserted solar cells

    Science.gov (United States)

    Aihara, Taketo; Fukuyama, Atsuhiko; Suzuki, Hidetoshi; Fujii, Hiromasa; Sugiyama, Masakazu; Nakano, Yoshiaki; Ikari, Tetsuo

    2015-02-01

    Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) and radiative and non-radiative carrier recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although the optical absorbance signal intensity was proportional to the number of QW stack, the signal intensities of the SPV and PPT methods decreased at high number of stack. To explain the temperature dependency of these signal intensities, we proposed a model that considers the three carrier dynamics: the thermal escape from the QW, and the non-radiative and radiative carrier recombinations within the QW. From the fitting procedures, it was estimated that the activation energies of the thermal escape ΔEb a r r and non-radiative recombination ΔEN R were 68 and 29 meV, respectively, for a 30-stacked MQW sample. The estimated ΔEb a r r value agreed well with the difference between the first electron subband and the top of the potential barrier in the conduction band. We found that ΔEb a r r remained constant at approximately 70 meV even with increasing QW stack number. However, the ΔENR value monotonically increased with the increase in the number of stack. Since this implies that non-radiative recombination becomes improbable as the number of stack increases, we found that the radiative recombination probability for electrons photoexcited within the QW increased at a large number of QW stack. Additional processes of escaping and recapturing of carriers at neighboring QW were discussed. As a result, the combination of the three non-destructive methodologies provided us new insights for optimizing the MQW components to further improve the cell performance.

  16. Effect of number of stack on the thermal escape and non-radiative and radiative recombinations of photoexcited carriers in strain-balanced InGaAs/GaAsP multiple quantum-well-inserted solar cells

    International Nuclear Information System (INIS)

    Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) and radiative and non-radiative carrier recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although the optical absorbance signal intensity was proportional to the number of QW stack, the signal intensities of the SPV and PPT methods decreased at high number of stack. To explain the temperature dependency of these signal intensities, we proposed a model that considers the three carrier dynamics: the thermal escape from the QW, and the non-radiative and radiative carrier recombinations within the QW. From the fitting procedures, it was estimated that the activation energies of the thermal escape ΔEbarr and non-radiative recombination ΔENR were 68 and 29 meV, respectively, for a 30-stacked MQW sample. The estimated ΔEbarr value agreed well with the difference between the first electron subband and the top of the potential barrier in the conduction band. We found that ΔEbarr remained constant at approximately 70 meV even with increasing QW stack number. However, the ΔENR value monotonically increased with the increase in the number of stack. Since this implies that non-radiative recombination becomes improbable as the number of stack increases, we found that the radiative recombination probability for electrons photoexcited within the QW increased at a large number of QW stack. Additional processes of escaping and recapturing of carriers at neighboring QW were discussed. As a result, the combination of the three non-destructive methodologies provided us new insights for optimizing the MQW components to further improve the cell performance

  17. Effect of number of stack on the thermal escape and non-radiative and radiative recombinations of photoexcited carriers in strain-balanced InGaAs/GaAsP multiple quantum-well-inserted solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, Taketo; Fukuyama, Atsuhiko; Ikari, Tetsuo [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen-Kibanadai-Nishi, Miyazaki 889-2192 (Japan); Suzuki, Hidetoshi [Interdisciplinary Research Organization, University of Miyazaki, 1-1 Gakuen-Kibanadai-Nishi, Miyazaki 889-2192 (Japan); Fujii, Hiromasa; Nakano, Yoshiaki [Research Center for Advanced Science and Technology, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032 (Japan); Sugiyama, Masakazu [School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032 (Japan)

    2015-02-28

    Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) and radiative and non-radiative carrier recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although the optical absorbance signal intensity was proportional to the number of QW stack, the signal intensities of the SPV and PPT methods decreased at high number of stack. To explain the temperature dependency of these signal intensities, we proposed a model that considers the three carrier dynamics: the thermal escape from the QW, and the non-radiative and radiative carrier recombinations within the QW. From the fitting procedures, it was estimated that the activation energies of the thermal escape ΔE{sub barr} and non-radiative recombination ΔE{sub NR} were 68 and 29 meV, respectively, for a 30-stacked MQW sample. The estimated ΔE{sub barr} value agreed well with the difference between the first electron subband and the top of the potential barrier in the conduction band. We found that ΔE{sub barr} remained constant at approximately 70 meV even with increasing QW stack number. However, the ΔE{sub NR} value monotonically increased with the increase in the number of stack. Since this implies that non-radiative recombination becomes improbable as the number of stack increases, we found that the radiative recombination probability for electrons photoexcited within the QW increased at a large number of QW stack. Additional processes of escaping and recapturing of carriers at neighboring QW were discussed. As a result, the combination of the three non-destructive methodologies provided us new insights for optimizing the MQW components to further improve the cell performance.

  18. Structuring waveguide-grating-based wavelength-division multiplexing/optical code division multiple access network codecs over topology of concentric circles

    Science.gov (United States)

    Huang, Jen-Fa; Nieh, Ta-Chun; Chen, Kai-Sheng

    2013-01-01

    The cyclic period and free spectral range of arrayed-waveguide gratings (AWG) in a wavelength-division multiplexing/optical code division multiple access optical code division multiple access network are exploited. The total optical network unit (ONU) of network capacity is partitioned into groups of different wavelength in accordance with the geographical location of subscribers based on the radial distance of the ONU to the optical line terminal. Combining concentric circles round by round for ONU groups enables a fixed round-trip time in the data transmission and a significant increase in system performance. Using AWG router, the proposed topology of concentric circles retains signature orthogonality and minimizes wavelength collisions on the photo-detector. Furthermore, the adoption of extended M-sequence codes corresponding to the AWG codec provides a simpler, more efficient coding procedure and accommodates more users in a single group.

  19. System performances of optical space code-division multiple-access-based fiber-optic two-dimensional parallel data link.

    Science.gov (United States)

    Nakamura, M; Kitayama, K

    1998-05-10

    Optical space code-division multiple access is a scheme to multiplex and link data between two-dimensional processors such as smart pixels and spatial light modulators or arrays of optical sources like vertical-cavity surface-emitting lasers. We examine the multiplexing characteristics of optical space code-division multiple access by using optical orthogonal signature patterns. The probability density function of interference noise in interfering optical orthogonal signature patterns is calculated. The bit-error rate is derived from the result and plotted as a function of receiver threshold, code length, code weight, and number of users. Furthermore, we propose a prethresholding method to suppress the interference noise, and we experimentally verify that the method works effectively in improving system performance. PMID:18273237

  20. Recirculating photonic filter: a wavelength-selective time delay for phased-array antennas and wavelength code-division multiple access.

    Science.gov (United States)

    Yegnanarayanan, S; Trinh, P D; Jalali, B

    1996-05-15

    A novel wavelength-selective photonic time-delay filter is proposed and demonstrated. The device consists of an optical phased-array waveguide grating in a recirculating feedback configuration. It can function as a true-time-delay generator for squint-free beam steering in optically controlled phased-array antennas and as an encoding-decoding filter for wavelength code-division multiple access. PMID:19876143

  1. Wavelength-encoding/temporal-spreading optical code division multiple-access system with in-fiber chirped moiré gratings.

    Science.gov (United States)

    Chen, L R; Smith, P W; de Sterke, C M

    1999-07-20

    We propose an optical code division multiple-access (OCDMA) system that uses in-fiber chirped moiré gratings (CMG's) for encoding and decoding of broadband pulses. In reflection the wavelength-selective and dispersive nature of CMG's can be used to implement wavelength-encoding/temporal-spreading OCDMA. We give examples of codes designed around the constraints imposed by the encoding devices and present numerical simulations that demonstrate the proposed concept. PMID:18323934

  2. A point-wise fiber Bragg grating displacement sensing system and its application for active vibration suppression of a smart cantilever beam subjected to multiple impact loadings

    International Nuclear Information System (INIS)

    In this work, active vibration suppression of a smart cantilever beam subjected to disturbances from multiple impact loadings is investigated with a point-wise fiber Bragg grating (FBG) displacement sensing system. An FBG demodulator is employed in the proposed fiber sensing system to dynamically demodulate the responses obtained by the FBG displacement sensor with high sensitivity. To investigate the ability of the proposed FBG displacement sensor as a feedback sensor, velocity feedback control and delay control are employed to suppress the vibrations of the first three bending modes of the smart cantilever beam. To improve the control performance for the first bending mode when the cantilever beam is subjected to an impact loading, we improve the conventional velocity feedback controller by tuning the control gain online with the aid of information from a higher vibration mode. Finally, active control of vibrations induced by multiple impact loadings due to a plastic ball is performed with the improved velocity feedback control. The experimental results show that active vibration control of smart structures subjected to disturbances such as impact loadings can be achieved by employing the proposed FBG sensing system to feed back out-of-plane point-wise displacement responses with high sensitivity. (paper)

  3. Preconception Carrier Screening

    Science.gov (United States)

    ... Events Advocacy For Patients About ACOG Preconception Carrier Screening Home For Patients Search FAQs Preconception Carrier Screening ... Screening FAQ179, August 2012 PDF Format Preconception Carrier Screening Pregnancy What is preconception carrier screening? What is ...

  4. Responsible implementation of expanded carrier screening.

    Science.gov (United States)

    Henneman, Lidewij; Borry, Pascal; Chokoshvili, Davit; Cornel, Martina C; van El, Carla G; Forzano, Francesca; Hall, Alison; Howard, Heidi C; Janssens, Sandra; Kayserili, Hülya; Lakeman, Phillis; Lucassen, Anneke; Metcalfe, Sylvia A; Vidmar, Lovro; de Wert, Guido; Dondorp, Wybo J; Peterlin, Borut

    2016-06-01

    This document of the European Society of Human Genetics contains recommendations regarding responsible implementation of expanded carrier screening. Carrier screening is defined here as the detection of carrier status of recessive diseases in couples or persons who do not have an a priori increased risk of being a carrier based on their or their partners' personal or family history. Expanded carrier screening offers carrier screening for multiple autosomal and X-linked recessive disorders, facilitated by new genetic testing technologies, and allows testing of individuals regardless of ancestry or geographic origin. Carrier screening aims to identify couples who have an increased risk of having an affected child in order to facilitate informed reproductive decision making. In previous decades, carrier screening was typically performed for one or few relatively common recessive disorders associated with significant morbidity, reduced life-expectancy and often because of a considerable higher carrier frequency in a specific population for certain diseases. New genetic testing technologies enable the expansion of screening to multiple conditions, genes or sequence variants. Expanded carrier screening panels that have been introduced to date have been advertised and offered to health care professionals and the public on a commercial basis. This document discusses the challenges that expanded carrier screening might pose in the context of the lessons learnt from decades of population-based carrier screening and in the context of existing screening criteria. It aims to contribute to the public and professional discussion and to arrive at better clinical and laboratory practice guidelines. PMID:26980105

  5. Content Distribution for Telecom Carriers

    Directory of Open Access Journals (Sweden)

    Ben Falchuk

    2006-08-01

    Full Text Available Distribution of digital content is a key revenue opportunity for telecommunications carriers. As media content moves from analog and physical media-based distribution to digital on-line distribution, a great opportunity exists for carriers to claim their role in the media value chain and grow revenue by enhancing their broadband “all you can eat” high speed Internet access offer to incorporate delivery of a variety of paid content. By offering a distributed peer to peer content delivery capability with authentication, personalization and payment functions, carriers can gain a larger portion of the revenue paid for content both within and beyond their traditional service domains. This paper describes an approach to digital content distribution that leverages existing Intelligent Network infrastructure that many carriers already possess, as well as Web Services.

  6. Effects of pre-existing anti-carrier immunity and antigenic element multiplicity on efficacy of a modular virus-like particle vaccine.

    Science.gov (United States)

    Chuan, Yap P; Rivera-Hernandez, Tania; Wibowo, Nani; Connors, Natalie K; Wu, Yang; Hughes, Fiona K; Lua, Linda H L; Middelberg, Anton P J

    2013-09-01

    Modularization of a peptide antigen for presentation on a microbially synthesized murine polyomavirus (MuPyV) virus-like particle (VLP) offers a new alternative for rapid and low-cost vaccine delivery at a global scale. In this approach, heterologous modules containing peptide antigenic elements are fused to and displayed on the VLP carrier, allowing enhancement of peptide immunogenicity via ordered and densely repeated presentation of the modules. This study addresses two key engineering questions pertaining to this platform, exploring the effects of (i) pre-existing carrier-specific immunity on modular VLP vaccine effectiveness and (ii) increase in the antigenic element number per VLP on peptide-specific immune response. These effects were studied in a mouse model and with modular MuPyV VLPs presenting a group A streptococcus (GAS) peptide antigen, J8i. The data presented here demonstrate that immunization with a modular VLP could induce high levels of J8i-specific antibodies despite a strong pre-existing anti-carrier immune response. Doubling of the J8i antigenic element number per VLP did not enhance J8i immunogenicity at a constant peptide dose. However, the strategy, when used in conjunction with increased VLP dose, could effectively increase the peptide dose up to 10-fold, leading to a significantly higher J8i-specific antibody titer. This study further supports feasibility of the MuPyV modular VLP vaccine platform by showing that, in the absence of adjuvant, modularized GAS antigenic peptide at a dose as low as 150 ng was sufficient to raise a high level of peptide-specific IgGs indicative of bactericidal activity. PMID:23532896

  7. Maximizing System Throughput by Cooperative Sensing in Cognitive Radio Networks

    OpenAIRE

    Li, Shuang; Zheng, Zizhan; Ekici, Eylem; Shroff, Ness

    2011-01-01

    Cognitive Radio Networks allow unlicensed users to opportunistically access the licensed spectrum without causing disruptive interference to the primary users (PUs). One of the main challenges in CRNs is the ability to detect PU transmissions. Recent works have suggested the use of secondary user (SU) cooperation over individual sensing to improve sensing accuracy. In this paper, we consider a CRN consisting of a single PU and multiple SUs to study the problem of maximizing the total expected...

  8. A Silicon Micromachined Gyroscope Driven by the Rotating Carrier Self

    Institute of Scientific and Technical Information of China (English)

    Fuxue Zhang; Xu Mao; Yu Liu; Nan Zhang; Wei Zhang

    2006-01-01

    This paper reported a silicon micromachined gyroscope which is driven by the rotating carrier's angular velocity, the silicon was manufactured by anisotropy etching. The design, fabrication and packing of the sensing element were introduced in the paper. The imitation experimentation and performance test have certificated that the principle of the gyroscope is correct and the gyroscope can be used to sense yawing or pitching angular velocity of the rotating carrier, and the angular velocity of the rotating carrier itself.

  9. Optimized Sharable-Slot Allocation Using Multiple Channels to Reduce Data-Gathering Delay in Wireless Sensor Networks.

    Science.gov (United States)

    Van Vinh, Phan; Oh, Hoon

    2016-01-01

    The demand for event-driven real-time applications for timely and reliable data acquisition is growing in industrial sectors. However, it is challenging to satisfy the requirements since constraints such as limited available energy and bandwidth are inherent in a wireless sensor network. To deal with timely delivery, one desirable approach is to improve network throughput so that more real-time applications with tighter time constraints can be satisfied in any given network. To deal with reliable delivery, the use of a carrier sense multiple access mechanism for data transmission is preferred, along with the use of a sharable slot within which multiple nodes compete to send data. Thus, we present a method of using multiple channels and a way to optimize the size of the sharable slot. The proposed channel-slot-scheduling algorithm tries to optimize the size of a sharable slot when multiple channels are used. The algorithm also deals with situations where nodes generate multiple data packets in each round of a data-gathering period. It is shown through simulation that our approach greatly outperforms others on some selected metrics. PMID:27070619

  10. Inducible operation of the erythropoietin 3' enhancer in multiple cell lines: evidence for a widespread oxygen-sensing mechanism.

    OpenAIRE

    Maxwell, P H; Pugh, C. W.; Ratcliffe, P. J.

    1993-01-01

    Adaptive responses to hypoxia occur in many biological systems. A well-characterized example is the hypoxic induction of the synthesis of erythropoietin, a hormone which regulates erythropoiesis and hence blood oxygen content. The restricted expression of the erythropoietin gene in subsets of cells within kidney and liver has suggested that this specific oxygen-sensing mechanism is restricted to specialized cells in those organs. Using transient transfection of reporter genes coupled to a tra...

  11. An application of the edge effect in measuring accessibility to multiple food retailer types in Southwestern Ontario, Canada

    Directory of Open Access Journals (Sweden)

    Arku Godwin

    2011-05-01

    Full Text Available Abstract Background Trends in food retailing associated with the consolidation of smaller-format retailers into fewer, larger-format supercentres have left some rural areas with fewer sources of nutritious, affordable food. Access to nutritious, affordable food is essential for good dietary habits and combating health issues such as type-2 diabetes, obesity, and cardiovascular disease. Many studies on food environments use inaccurate or incomplete methods for locating food retailers, which may be responsible for mischaracterising food deserts. This study uses databases of every residence in and every food retailer in and around Middlesex County, Ontario, Canada. Residences were geocoded to their precise address, and network analysis techniques were performed in a geographic information system (GIS to determine distances between every residence and different types of food retailers (grocery stores, fast food, fruit and vegetable sources, grocery stores plus fruit and vegetable sources, variety stores, both when considering and neglecting facilities outside the area of study, to account for a deficiency in analysis termed the 'edge effect'. Results Analysis of household accessibility to food outlets by neighbourhood socioeconomic distress level indicated that residents in the most distressed neighbourhoods tended to have better accessibility to all types of food retailers. In the most distressed neighbourhoods, 79 percent of residences were within walking distance of a grocery store, compared to only 10 percent in the least distressed neighbourhoods. When the edge effect was neglected, 37 percent of distance estimates proved inaccurate. Average accessibility to all food retailer types improved dramatically when food outlets adjacent to the study area were considered, thereby controlling for the edge effect. Conclusion By neglecting to consider food retailers just outside study area boundaries, previous studies may significantly over-report the

  12. In Situ Live Cell Sensing of Multiple Nucleotides Exploiting DNA/RNA Aptamers and Graphene Oxide Nanosheets

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Ying; Li, Zhaohui; Weber, Thomas J.; Hu, Dehong; Lin, Chiann Tso; Li, Jinghong; Lin, Yuehe

    2013-07-23

    Adenosine-5’-triphosphate (ATP) and guanosine-5’-triphosphate (GTP) are primary energy resources and function coordinately for numerous reactions such as microtubule assembly, insulin secretion and ion channel regulation. We have developed a novel DNA/RNA aptamer- graphene oxide nanosheet (GO-nS) sensing platform that can selectively and simultaneously detect ATP and GTP in live cells. A fluorescent tag is covalently attached to aptamers and fluorescence is quenched upon binding of aptamer to the GO-nS. Fluorescently tagged aptamers that selectively bind ATP or GTP were isolated from an aptamer library and were adsorbed onto GO-nS. Upon incubation with targets (ATP and/or GTP), the aptamers readily dissociated from GO-nS and the fluorescent signal was recovered. By covalently attaching fluorophores, both ATP and GTP sensing aptamers could be exploited to simultaneously visualize aptamer dissociation in live cells. In addition, the GO-nS appear to be biocompatible and protect the adsorbed DNA/RNA aptamers from enzymatic cleavage. Our results support the application of aptamer/GO-nS as a sensing platform for nucleotides in living cells and have implications for the development of additional sensor platforms for other bio-molecules that show selective interactions with aptamers and other biomarkers.

  13. A mechanism of oxygen sensing in yeast. Multiple oxygen-responsive steps in the heme biosynthetic pathway affect Hap1 activity.

    Science.gov (United States)

    Hon, Thomas; Dodd, Athena; Dirmeier, Reinhard; Gorman, Nadia; Sinclair, Peter R; Zhang, Li; Poyton, Robert O

    2003-12-12

    Heme plays central roles in oxygen sensing and utilization in many living organisms. In yeast, heme mediates the effect of oxygen on the expression of many genes involved in using or detoxifying oxygen. However, a direct link between intracellular heme level and oxygen concentration has not been vigorously established. In this report, we have examined the relationships among oxygen levels, heme levels, Hap1 activity, and HAP1 expression. We found that Hap1 activity is controlled in vivo by heme and not by its precursors and that heme activates Hap1 even in anoxic cells. We also found that Hap1 activity exhibits the same oxygen dose-response curves as Hap1-dependent aerobic genes and that these dose-response curves have a sharp break at approximately 1 microM O2. The results show that the intracellular signaling heme level, reflected as Hap1 activity, is closely correlated with oxygen concentration. Furthermore, we found that bypass of all heme synthetic steps but ferrochelatase by deuteroporphyrin IX does not circumvent the need for oxygen in Hap1 full activation by heme, suggesting that the last step of heme synthesis, catalyzed by ferrochelatase, is also subjected to oxygen control. Our results show that multiple heme synthetic steps can sense oxygen concentration and provide significant insights into the mechanism of oxygen sensing in yeast. PMID:14512429

  14. An application of the edge effect in measuring accessibility to multiple food retailer types in Southwestern Ontario, Canada

    OpenAIRE

    Arku Godwin; Gilliland Jason A; Sadler Richard C

    2011-01-01

    Abstract Background Trends in food retailing associated with the consolidation of smaller-format retailers into fewer, larger-format supercentres have left some rural areas with fewer sources of nutritious, affordable food. Access to nutritious, affordable food is essential for good dietary habits and combating health issues such as type-2 diabetes, obesity, and cardiovascular disease. Many studies on food environments use inaccurate or incomplete methods for locating food retailers, which ma...

  15. Universal optical line terminal encoding and decoding architecture in two-code keying for noncoherent spectral amplitude coding optical code division multiple access systems

    Science.gov (United States)

    Yeh, Bih-Chyun; Lin, Cheing-Hong; Yang, De-Nian

    2014-01-01

    We propose a new code family, called extended shifted prime codes, and the universal encoding architecture for spectral amplitude coding optical code division multiple access systems using a two-code keying scheme. The proposed system can eliminate multiuser interference and suppress phase-induced intensity noise. In addition, we design the ESP codes to be an encoding/decoding architecture based on the array waveguide grating architecture and reduce the power loss and the complexity of the optical line terminal. The numerical results demonstrate that the proposed system with ESP codes outperforms the existing one-dimensional shifted prime codes system.

  16. Multiple Stable States and Catastrophic Shifts in Coastal Wetlands: Progress, Challenges, and Opportunities in Validating Theory Using Remote Sensing and Other Methods

    Directory of Open Access Journals (Sweden)

    Kevan B. Moffett

    2015-08-01

    Full Text Available Multiple stable states are established in coastal tidal wetlands (marshes, mangroves, deltas, seagrasses by ecological, hydrological, and geomorphological feedbacks. Catastrophic shifts between states can be induced by gradual environmental change or by disturbance events. These feedbacks and outcomes are key to the sustainability and resilience of vegetated coastlines, especially as modulated by human activity, sea level rise, and climate change. Whereas multiple stable state theory has been invoked to model salt marsh responses to sediment supply and sea level change, there has been comparatively little empirical verification of the theory for salt marshes or other coastal wetlands. Especially lacking is long-term evidence documenting if or how stable states are established and maintained at ecosystem scales. Laboratory and field-plot studies are informative, but of necessarily limited spatial and temporal scope. For the purposes of long-term, coastal-scale monitoring, remote sensing is the best viable option. This review summarizes the above topics and highlights the emerging promise and challenges of using remote sensing-based analyses to validate coastal wetland dynamic state theories. This significant opportunity is further framed by a proposed list of scientific advances needed to more thoroughly develop the field.

  17. Cooperation Scheme For Distributed Spectrum Sensing In Cognitive Radio Networks

    Directory of Open Access Journals (Sweden)

    Ying Dai

    2014-09-01

    Full Text Available Spectrum sensing is an essential phase in cognitive radio networks (CRNs. It enables secondary users (SUs to access licensed spectrum, which is temporarily not occupied by the primary users (PUs. The widely used scheme of spectrum sensing is cooperative sensing, in which an SU shares its sensing results with other SUs to improve the overall sensing performance, while maximizing its throughput. For a single SU, if its sensing results are shared early, it would have more time for data transmission, which improves the throughput. However, when multiple SUs send their sensing results early, they are more likely to send out their sensing results simultaneously over the same signaling channel. Under these conditions, conflicts would likely happen. Then, both the sensing performance and throughput would be affected. Therefore, it is important to take when-to-share into account. We model the spectrum sensing as an evolutionary game. Different from previous works, the strategy set for each player in our game model contains not only whether to share its sensing results, but also when to share. The payoff for each player is defined based on the throughput, which considers the influence of the time spent both on sensing and sharing. We prove the existence of the evolutionarily stable strategy (ESS. In addition, we propose a practical algorithm for each secondary user to converge to the ESS. We conduct experiments on our testbed consisting of 4 USRP N200s. The experimental results verify for our model, including the convergence to the ESS.

  18. Layers of Identity: Multiple Psychological Senses of Community Within a Community Setting Niveles de la Identidad: Múltiples Sentidos Psicológicos de Comunidad en un Entorno Comunitario

    Directory of Open Access Journals (Sweden)

    Anne E Brodsky

    2004-11-01

    Full Text Available This article explores psychological sense of community (PSOC, a feeling of belonging to, importance of, and identification with a community. In much of the research on PSOC, there has been a focus on identifying a single PSOC for an individual in a setting. Qualitative and quantitative data are used here to investigate the presence and operation of multiple psychological senses of community for individuals. These multiple PSOCs are explored in two macro, territorial settings and a subcommunity of one of these settings: a job training and education center for underserved women in Baltimore City. Exploration of multiple PSOCs at the macro- and subcommunity levels expands our conceptualization of the operation of PSOC and has real-life implications for fostering positive outcomes in multicultural communities. © 2001 John Wiley & Sons, Inc.El presente artículo explora el sentido psicológico de comunidad (PSOC, un sentimiento de pertenencia, importancia e identificación con la comunidad. Gran parte de la investigación realizada sobre el PSOC se ha focalizado en identificar un único sentido de comunidad para un individuo en un contexto determinado. Datos cualitativos y cuantitativos son usados aquí para investigar la presencia de múltiples sentidos psicológicos de comunidad para los individuos. Estos múltiples PSOCs son explorados en dos contextos territoriales a nivel macro, y en una subcomunidad de uno de estos contextos: un centro de capacitación laboral y educación para mujeres de escasos recursos en la ciudad de Baltimore. La exploración de múltiples PSOCs en los niveles macro y subcomunitario expande nuestra conceptualización del funcionamiento del PSOC y tiene implicancias en la vida real, para promover resultados positivos en comunidades multiculturales.

  19. Spatial and Temporal Distribution of Multiple Cropping Indices in the North China Plain Using a Long Remote Sensing Data Time Series

    Science.gov (United States)

    Zhao, Yan; Bai, Linyan; Feng, Jianzhong; Lin, Xiaosong; Wang, Li; Xu, Lijun; Ran, Qiyun; Wang, Kui

    2016-01-01

    Multiple cropping provides China with a very important system of intensive cultivation, and can effectively enhance the efficiency of farmland use while improving regional food production and security. A multiple cropping index (MCI), which represents the intensity of multiple cropping and reflects the effects of climate change on agricultural production and cropping systems, often serves as a useful parameter. Therefore, monitoring the dynamic changes in the MCI of farmland over a large area using remote sensing data is essential. For this purpose, nearly 30 years of MCIs related to dry land in the North China Plain (NCP) were efficiently extracted from remotely sensed leaf area index (LAI) data from the Global LAnd Surface Satellite (GLASS). Next, the characteristics of the spatial-temporal change in MCI were analyzed. First, 2162 typical arable sample sites were selected based on a gridded spatial sampling strategy, and then the LAI information was extracted from the samples. Second, the Savizky-Golay filter was used to smooth the LAI time-series data of the samples, and then the MCIs of the samples were obtained using a second-order difference algorithm. Finally, the geo-statistical Kriging method was employed to map the spatial distribution of the MCIs and to obtain a time-series dataset of the MCIs of dry land over the NCP. The results showed that all of the MCIs in the NCP showed an increasing trend over the entire study period and increased most rapidly from 1982 to 2002. Spatially, MCIs decreased from south to north; also, high MCIs were mainly concentrated in the relatively flat areas. In addition, the partial spatial changes of MCIs had clear geographical characteristics, with the largest change in Henan Province. PMID:27104536

  20. What Is Carrier Screening?

    Science.gov (United States)

    ... you want to learn. Search form Search Carrier screening You are here Home Testing & Services Testing for ... help you make the decision. What Is Carrier Screening? Carrier screening checks if a person is a " ...

  1. Investigation of in-band transmission of both spectral amplitude coding/optical code division multiple-access and wavelength division multiplexing signals

    Science.gov (United States)

    Ashour, Isaac A. M.; Shaari, Sahbudin; Shalaby, Hossam M. H.; Menon, P. Susthitha

    2011-06-01

    The transmission of both optical code division multiple-access (OCDMA) and wavelength division multiplexing (WDM) users on the same band is investigated. Code pulses of spectral amplitude coding (SAC)/optical code division multiple-access (CDMA) are overlaid onto a multichannel WDM system. Notch filters are utilized in order to suppress the WDM interference signals for detection of optical broadband CDMA signals. Modified quadratic congruence (MQC) codes are used as the signature codes for the SAC/OCDMA system. The proposed system is simulated and its performance in terms of both the bit-error rate and Q-factor are determined. In addition, eavesdropper probability of error-free code detection is evaluated. Our results are compared to traditional nonhybrid systems. It is concluded that the proposed hybrid scheme still achieves acceptable performance. In addition, it provides enhanced data confidentiality as compared to the scheme with SAC/OCDMA only. It is also shown that the performance of the proposed system is limited by the interference of the WDM signals. Furthermore, the simulation illustrates the tradeoff between the performance and confidentiality for authorized users.

  2. Accessibility, Demography and Protection: Drivers of Forest Stability and Change at Multiple Scales in the Cauvery Basin, India

    OpenAIRE

    Jane Southworth; Harini Nagendra; Nikhil Lele

    2010-01-01

    The Cauvery basin of Karnataka State encompasses a range of land cover types, from dense forest areas and plantations in the Western Ghats hills, to fertile agricultural lands in the river valley. Recent demographic changes, rapid economic development and urbanization have led to the conversion of vast stretches of forested land into plantations and permanent agriculture. We examine the human drivers of forest cover change between 2001 and 2006, using MODIS 250 m data at multiple spatial scal...

  3. Investigation of code reconfigurable fibre Bragg gratings for Optical Code Division Multiple Access (OCDMA) and Optical Packet Switching (OPS) Networks

    OpenAIRE

    Tian, Chun

    2009-01-01

    This thesis documents my work in the telecommunication system laboratory at the Optoelectronics Research Centre, towards the implementation of code reconfigurable OCDMA and all-optical packet switching nodes based on fibre Bragg grating (FBG) technology. My research work involves characterizing the performance of various gratings, specifically high reflectivity, short chip duration, long code sequences, multiple phase level and tunable superstructured fiber Bragg gratings (SSFBGs), by using t...

  4. Use of external cavity quantum cascade laser compliance voltage in real-time trace gas sensing of multiple chemicals

    Energy Technology Data Exchange (ETDEWEB)

    Phillips, Mark C.; Taubman, Matthew S.; Kriesel, Jason M.

    2015-02-08

    We describe a prototype trace gas sensor designed for real-time detection of multiple chemicals. The sensor uses an external cavity quantum cascade laser (ECQCL) swept over its tuning range of 940-1075 cm-1 (9.30-10.7 µm) at a 10 Hz repetition rate.

  5. Beyond simple point sets to the indistinguishable point-set tensorial limits of R-W algebras: multiple G-invariants and the carrier-map-based quantal-basis completeness of uniform NMR spin systems

    International Nuclear Information System (INIS)

    Augmented quasiparticle (QP) mappings, as applied to indistinguishable point sets of (Liouvillian) democratic-recoupled (DR) tensors, provide for a 1:1 invariant labelling of the underlying (disjoint) dual projective map carrier subspaces, where the Liouville pattern basis set is defined via superboson unit-tensor actions on a null space, | )). The co-operative-action Liouville algebras described here imply parallel limitations to Jucys graph recoupling and its related Racah-Wigner (R-W) algebras once DR indistinguishable point tensorial sets are involved, as in non-SR Sn,n>=4 dominant (NMR) spin symmetry. The importance of Sn G-invariants, as labels for disjoint carrier subspaces in such automorphic spin symmetries, arises from their essential role in defining the quantal-completeness of indistinguishable point sets. From the established properties of augmented-QPs as super-bosons (Temme 2002 Int. J. Quantum Chem. 89 429) (i.e., beyond the earlier Hilbert-space-based Louck and Biedenharn boson pattern views), insight into Atiyah and Sutcliffe's (A-S) assertions (Atiyah and Sutcliffe 2002 Proc. R. Soc. A 458 1089) on the limitations of graph recoupling theory to distinct point sets is obtained. This clarifies the wider analytic intractible of automorphic DR spin systems-beyond the Levi-Civita cyclic-commutation (R-W) approach (Levy-Leblond and Levy-Nahas 1965 J. Math. Phys. 6 1372) which holds for a mono-invariant problem. For (rotating-frame) density matrix approaches to [A]n, [A]n(X) and [AX]n(SU(2) x Sn) (dual) NMR systems, the focus is necessarily on the specialized nature of indistinguishable point sets within multiple invariant-theoretic-based, dynamical spin physics. Here, the GI(s) (GI-cardinality) constitute an important part of the dual irrep set, {Dk(U-tilde) x Γ-tilde[λ](v-tilde)(P)}, with combinatorics, as a central facet of invariant theory, playing a crucial role in the concept of 'quantal completeness' and the impact of A-S's assertion on the

  6. On the capacity of multiple access and broadcast fading Channels with full channel state information at low power regime

    KAUST Repository

    Rezki, Zouheir

    2013-07-01

    We study the throughput capacity region of the Gaussian multi-access (MAC) fading channel with perfect channel state information (CSI) at the receiver and at the transmitters (CSI-TR), at low power regime. We show that it has a multidimensional rectangle structure and thus is simply characterized by single user capacity points. More specifically, we show that at low power regime, the boundary surface of the capacity region shrinks to a single point corresponding to the sum-rate maximizer and that the coordinates of this point coincide with single user capacity bounds. Using the duality of Gaussian MAC and broadcast channels (BC), we provide a simple characterization of the BC capacity region at low power regime. © 2013 IEEE.

  7. A Sensing Error Aware MAC Protocol for Cognitive Radio Networks

    Directory of Open Access Journals (Sweden)

    Donglin Hu

    2012-08-01

    Full Text Available Cognitive radios (CR are intelligent radio devices that can sense the radio environment and adapt to changes in the radio environment. Spectrum sensing and spectrum access are the two key CR functions. In this paper, we present a spectrum sensing error aware MAC protocol for a CR network collocated with multiple primary networks. We explicitly consider both types of sensing errors in the CR MAC design, since such errors are inevitable for practical spectrum sensors and more importantly, such errors could have significant impact on the performance of the CR MAC protocol. Two spectrum sensing polices are presented, with which secondary users collaboratively sense the licensed channels. The sensing policies are then incorporated into p-Persistent CSMA to coordinate opportunistic spectrum access for CR network users.We present an analysis of the interference and throughput performance of the proposed CR MAC, and find the analysis highly accurate in our simulation studies. The proposed sensing error aware CR MAC protocol outperforms two existing approaches with considerable margins in our simulations, which justify the importance of considering spectrum sensing errors in CR MAC design.

  8. Cross-Product Comparison of Multiple Resolution Microwave Remote Sensing Data Sets Supporting Global Mapping of Inundated Wetlands

    Science.gov (United States)

    Podest, E.; Schroeder, R.; McDonald, K. C.; Pinto, N.; Willacy, K.; Whitcomb, J.; Moghaddam, M.; Hess, L. L.; Zimmermann, R.

    2010-12-01

    Inundated vegetation and open water bodies are common features across the landscape and exert major impacts on hydrologic processes and surface-atmosphere carbon exchange. Their carbon dioxide and methane emissions can have a large impact on global climate. It is therefore of great importance to assess their spatial extent and temporal variations in order to improve upon carbon balance estimates. Despite their importance in the global cycling of carbon and water and climate forecasting, they remain poorly characterized and modeled, primarily because of the scarcity of suitable regional-to-global remote sensing data for characterizing wetlands distribution and dynamics. Spaceborne synthetic aperture radar (SAR) offers an effective tool for characterizing these ecosystems since it is particularly sensitive to surface water and to vegetation structure, and it allows monitoring large inaccessible areas on a temporal basis regardless of atmospheric conditions or solar illumination. We are assembling a multi-year Earth System Data Record (ESDR) of global inundated wetlands to facilitate investigations on their role in climate, biogeochemistry, hydrology, and biodiversity. The ESDR is comprised of (1) fine-resolution (100m) maps of wetland extent, vegetation type, and seasonal inundation extent, derived from L-band SAR data from the Advanced Land Observing Satellite (ALOS) Phased Array L-Band SAR (PALSAR) and the Japanese Earth Resources Satellite (JERS) SAR, for continental-scale areas covering crucial wetland regions, and (2) global multi-temporal mappings of inundation extent at 25 km resolution derived from data sets from combined passive and active microwave remote sensing instruments (AMSR-E, QuikSCAT). We present a comparative analysis of the high-resolution SAR-based data sets and the coarse resolution inundation data sets for wetland ecosystems in the Amazonian tropics and the northern high latitudes of Alaska, Canada, and Eurasia. We compare information content

  9. On the capacity of multiple access and broadcast fading channels with full channel state information at low SNR

    KAUST Repository

    Rezki, Zouheir

    2014-01-01

    We study the throughput capacity region of the Gaussian multi-access (MAC) fading channel with perfect channel state information (CSI) at the receiver and at the transmitters, at low power regime. We show that it has a multidimensional rectangle structure and thus is simply characterized by single user capacity points.More specifically, we show that at low power regime, the boundary surface of the capacity region shrinks to a single point corresponding to the sum rate maximizer and that the coordinates of this point coincide with single user capacity bounds. Inspired from this result, we propose an on-off scheme, compute its achievable rate, and show that this scheme achieves single user capacity bounds of the MAC channel for a wide class of fading channels at asymptotically low power regime. We argue that this class of fading encompasses all known wireless channels for which the capacity region of the MAC channel has even a simpler expression in terms of users\\' average power constraints only. Using the duality of Gaussian MAC and broadcast channels (BC), we deduce a simple characterization of the BC capacity region at low power regime and show that for a class of fading channels (including Rayleigh fading), time-sharing is asymptotically optimal. © 2014 IEEE.

  10. A new two dimensional spectral/spatial multi-diagonal code for noncoherent optical code division multiple access (OCDMA) systems

    Science.gov (United States)

    Kadhim, Rasim Azeez; Fadhil, Hilal Adnan; Aljunid, S. A.; Razalli, Mohamad Shahrazel

    2014-10-01

    A new two dimensional codes family, namely two dimensional multi-diagonal (2D-MD) codes, is proposed for spectral/spatial non-coherent OCDMA systems based on the one dimensional MD code. Since the MD code has the property of zero cross correlation, the proposed 2D-MD code also has this property. So that, the multi-access interference (MAI) is fully eliminated and the phase induced intensity noise (PIIN) is suppressed with the proposed code. Code performance is analyzed in terms of bit error rate (BER) while considering the effect of shot noise, PIIN, and thermal noise. The performance of the proposed code is compared with the related MD, modified quadratic congruence (MQC), two dimensional perfect difference (2D-PD) and two dimensional diluted perfect difference (2D-DPD) codes. The analytical and the simulation results reveal that the proposed 2D-MD code outperforms the other codes. Moreover, a large number of simultaneous users can be accommodated at low BER and high data rate.

  11. GSR-TDMA: A Geometric Spatial Reuse-Time Division Multiple Access MAC Protocol for Multihop Underwater Acoustic Sensor Networks

    Directory of Open Access Journals (Sweden)

    Changho Yun

    2016-01-01

    Full Text Available The nonnegligible propagation delay of acoustic signals causes spatiotemporal uncertainty that occasionally enables simultaneous, collision-free packet transmission among underwater nodes (UNs. These transmissions can be handled by efficiently managing the channel access of the UNs in the data-link layer. To this end, Geometric Spatial Reuse-TDMA (GSR-TDMA, a new TDMA-based MAC protocol, is designed for use in centralized, multihop underwater acoustic sensor networks (UASNs, and in this case all UNs are periodically scheduled after determining a geometric map according to the information on their location. The scheduling strategy increases the number of UNs that send packets coincidentally via two subscheduling configurations (i.e., interhop and intrahop scheduling. Extensive simulations are used to investigate the reception success rate (RSR and the multihop delay (MHD of GSR-TDMA, and the results are compared to those of previous approaches, including C-MAC and HSR-TDMA. GSR-TDMA outperforms C-MAC; the RSR of GSR-TDMA is 15% higher than that of C-MAC, and the MHD of GSR-TDMA is 30% lower than that of C-MAC at the most. In addition, GSR-TDMA provides even better performance improvements over HSR-TDMA; the RSR of GSR-TDMA is 50% higher than that of HSR-TDMA, and the MHD of GSR-TDMA is an order of 102 lower than that of HSR-TDMA at the most.

  12. Airborne multispectral and thermal remote sensing for detecting the onset of crop stress caused by multiple factors

    Science.gov (United States)

    Huang, Yanbo; Thomson, Steven J.

    2010-10-01

    Remote sensing technology has been developed and applied to provide spatiotemporal information on crop stress for precision management. A series of multispectral images over a field planted cotton, corn and soybean were obtained by a Geospatial Systems MS4100 camera mounted on an Air Tractor 402B airplane equipped with Camera Link in a Magma converter box triggered by Terraverde Dragonfly® flight navigation and imaging control software. The field crops were intentionally stressed by applying glyphosate herbicide via aircraft and allowing it to drift near-field. Aerial multispectral images in the visible and near-infrared bands were manipulated to produce vegetation indices, which were used to quantify the onset of herbicide induced crop stress. The vegetation indices normalized difference vegetation index (NDVI) and soil adjusted vegetation index (SAVI) showed the ability to monitor crop response to herbicide-induced injury by revealing stress at different phenological stages. Two other fields were managed with irrigated versus nonirrigated treatments, and those fields were imaged with both the multispectral system and an Electrophysics PV-320T thermal imaging camera on board an Air Tractor 402B aircraft. Thermal imagery indicated water stress due to deficits in soil moisture, and a proposed method of determining crop cover percentage using thermal imagery was compared with a multispectral imaging method. Development of an image fusion scheme may be necessary to provide synergy and improve overall water stress detection ability.

  13. Four-Channel, 8 x 8 Bit, Two-Dimensional Parallel Transmission by use of Space-Code-Division Multiple-Access Encoder and Decoder Modules.

    Science.gov (United States)

    Nakamura, M; Kitayama, K; Igasaki, Y; Kaneda, K

    1998-07-10

    We experimentally demonstrate four-channel multiplexing of 64-bit (8 x 8) two-dimensional (2-D) parallel data links on the basis of optical space-code-division multiple access (CDMA) by using new modules of optical spatial encoders and a decoder with a new high-contrast 9-m-long image fiber with 3 x 10(4) cores. Each 8 x 8 bit plane (64-bit parallel data) is optically encoded with an 8 x 8, 2-D optical orthogonal signature pattern. The encoded bit planes are spatially multiplexed and transmitted through an image fiber. A receiver can recover the intended input bit plane by means of an optical decoding process. This result should encourage the application of optical space-CDMA to future high-throughput 2-D parallel data links connecting massively parallel processors. PMID:18285889

  14. Performance improvement of spectral amplitude coding-optical code division multiple access systems using NAND detection with enhanced double weight code

    Science.gov (United States)

    Ahmed, Nasim; Aljunid, Syed Alwee; Ahmad, R. Badlishah; Fadhil, Hilal A.; Rashid, Mohd Abdur

    2012-01-01

    The bit-error rate (BER) performance of the spectral amplitude coding-optical code division multiple access (SACOCDMA) system has been investigated by using NAND subtraction detection technique with enhanced double weight (EDW) code. The EDW code is the enhanced version of double weight (DW) code family where the code weight is any odd number and greater than one with ideal cross-correlation. In order to evaluate the performance of the system, we used mathematical analysis extensively along with the simulation experiment. The evaluation results obtained using the NAND subtraction detection technique was compared with those obtained using the complementary detection technique for the same number of active users. The comparison results revealed that the BER performance of the system using NAND subtraction detection technique has greatly been improved as compared to the complementary technique.

  15. A wide dynamics and fast scan interrogating method for a fiber Bragg grating sensor network implemented using code division multiple access.

    Science.gov (United States)

    Kim, Youngbok; Jeon, Sie-Wook; Kwon, Won-Bae; Park, Chang-Soo

    2012-01-01

    We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 με and a low crosstalk of 950:1. PMID:22778619

  16. A Wide Dynamics and Fast Scan Interrogating Method for a Fiber Bragg Grating Sensor Network Implemented Using Code Division Multiple Access

    Directory of Open Access Journals (Sweden)

    Chang-Soo Park

    2012-05-01

    Full Text Available We propose and demonstrate a fiber Bragg grating (FBG sensor network employing the code division multiple access (CDMA technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 μe and a low crosstalk of 950:1.

  17. A genetic polymorphism (rs17251221 in the calcium-sensing receptor gene (CASR is associated with stone multiplicity in calcium nephrolithiasis.

    Directory of Open Access Journals (Sweden)

    Yii-Her Chou

    Full Text Available Calcium nephrolithiasis is one of the most common causes of renal stones. While the prevalence of this disease has increased steadily over the last 3 decades, its pathogenesis is still unclear. Previous studies have indicated that a genetic polymorphism (rs17251221 in the calcium-sensing receptor gene (CASR is associated with the total serum calcium levels. In this study, we collected DNA samples from 480 Taiwanese subjects (189 calcium nephrolithiasis patients and 291 controls for genotyping the CASR gene. Our results indicated no significant association between the CASR polymorphism (rs17251221 and the susceptibility of calcium nephrolithiasis. However, we found a significant association between rs17251221 and stone multiplicity. The risk of stone multiplicity was higher in patients with the GG+GA genotype than in those with the AA genotype (chi-square test: P = 0.008; odds ratio  =  4.79; 95% confidence interval, 1.44-15.92; Yates' correction for chi-square test: P = 0.013. In conclusion, our results provide evidence supporting the genetic effects of CASR on the pathogenesis of calcium nephrolithiasis.

  18. Multiple Defects of Cell Cycle Checkpoints in U937-ASPI3K, an U937 Cell Mutant Stably Expressing Anti-Sense ATM Gene cDNA

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    (Ataxia-telangiectasia mutated gene (ATM) functions in control of cell cycle checkpoints in responding to DNA damage and protects cells from undergoing apoptosis. Knock-out within tumor cells of endogenous ATM will achieve therapeutic benefits and nable a better understanding of the decisive mechanisms of cell death or survival in response to DNA damaging agents. ) In present paper, we sought to characterize the cell cycle checkpoint profiles in U937-ASPI3K, a U937 cell mutant that was previously established with endogenous ATM knock-out phenotype. Synchronized U937-ASPI3K was exposed to 137Cs irradiation, G1, S, G2/M cell cycle checkpoint profiles were evaluated by determining cell cycle kinetics, p53/p21 protein, cyclin dependent kinase 2 (CDK2) and p34CDC2 kinase activity in response to irradiation. U937-ASPI3K exhibited multiple defects in cell cycle checkpoints as defined by failing to arrest cells upon irradiation. The accumulation of cellular p53/p21 protein and inhibition of CDK kinase was also abolished in U937-ASPI3K. It was concluded that the stable expression of anti-sense PI3K cDNA fragment completely abolished multiple cell cycle checkpoints in U937-ASPI3K, and hence U937-ASPI3K with an AT-like phenotype could serves as a valuable model system for investigating the signal transduction pathway in responding to DNA damaging-based cancer therapy.

  19. A Multi-Carrier Scheduling Algorithm for LTE-Advanced

    DEFF Research Database (Denmark)

    Vulpe, Alexander; Mihovska, Albena D.; Prasad, Ramjee; Fratu, Octavian

    LTE-Advanced aims to provide a transmission bandwidth of 100 MHz by using Carrier Aggregation to aggregate LTE Rel. 8 carriers. In order to increase the system capacity, resource allocation becomes a very good tool, and, in the context of the existence of multiple Component Carriers in LTE...

  20. Terahertz carrier dynamics in graphene and graphene nanostructures

    DEFF Research Database (Denmark)

    Jensen, Søren A.; Turchinovich, Dmitry; Tielrooij, Klaas Jan;

    2014-01-01

    Photoexcited charge carriers in 2D graphene and in 1D graphene nanostructures were studied with optical pump-THz probe spectroscopy. We find efficient hot-carrier multiplication in 2D graphene, and predominantly free carrier early time response in 1D nanostructures. © 2014 OSA....

  1. NODC Standard Format Coastal Ocean Wave and Current (F181) Data from the Atlantic Remote Sensing Land/Ocean Experiment (ARSLOE) (1980) (NODC Accession 0014202)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains time series coastal ocean wave and current data collected during the Atlantic Remote Sensing Land/Ocean Experiment (ARSLOE). ARSLOE was...

  2. Attack Prevention for Collaborative Spectrum Sensing in Cognitive Radio Networks

    CERN Document Server

    Duan, Lingjie; Huang, Jianwei; Shin, Kang G

    2011-01-01

    Collaborative spectrum sensing can significantly improve the detection performance of secondary unlicensed users (SUs). However, the performance of collaborative sensing is vulnerable to sensing data falsification attacks, where malicious SUs (attackers) submit manipulated sensing reports to mislead the fusion center's decision on spectrum occupancy. Moreover, attackers may not follow the fusion center's decision regarding their spectrum access. This paper considers a challenging attack scenario where multiple rational attackers overhear all honest SUs' sensing reports and cooperatively maximize attackers' aggregate spectrum utilization. We show that, without attack-prevention mechanisms, honest SUs are unable to transmit over the licensed spectrum, and they may further be penalized by the primary user for collisions due to attackers' aggressive transmissions. To prevent such attacks, we propose two novel attack-prevention mechanisms with direct and indirect punishments. The key idea is to identify collisions...

  3. Dedicated Carrier Deployment in Heterogeneous Networks with Inter-site Carrier Aggregation

    DEFF Research Database (Denmark)

    Wang, Hua; Rosa, Claudio; Pedersen, Klaus I.

    picos with dedicated carrier deployment. Collaborative inter-site carrier aggregation (CA) is proposed in scenarios with macro+RRH deployment to make an efficient use of the fragmented spectrum from multiple cells. While in scenarios with macro+pico deployment, UEs can only connect to either the...

  4. Accessibility and sensory experiences

    DEFF Research Database (Denmark)

    Ryhl, Camilla

    2010-01-01

    This article introduces a new design concept; sensory accessibility. While acknowledging the importance of sensory experiences in architectural quality, as well as the importance of accommodating user needs the concept combines three equally important factors; architecture, the senses and...... accessibility. Sensory accessibility accommodates aspects of a sensory disability and describes architectural design requirements needed to ensure access to architectural experiences. In the context of architecture accessibility has become a design concept of its own. It is generally described as ensuring...... physical access to the built environment by accommodating physical disabilities. While the existing concept of accessibility ensures the physical access of everyone to a given space, sensory accessibility ensures the choice of everyone to stay and be able to participate and experience....

  5. MAC Protocols for Optimal Information Retrieval Pattern in Sensor Networks with Mobile Access

    Directory of Open Access Journals (Sweden)

    Yang Zhiyu

    2005-01-01

    Full Text Available In signal field reconstruction applications of sensor network, the locations where the measurements are retrieved from affect the reconstruction performance. In this paper, we consider the design of medium access control (MAC protocols in sensor networks with mobile access for the desirable information retrieval pattern to minimize the reconstruction distortion. Taking both performance and implementation complexity into consideration, besides the optimal centralized scheduler, we propose three decentralized MAC protocols, namely, decentralized scheduling through carrier sensing, Aloha scheduling, and adaptive Aloha scheduling. Design parameters for the proposed protocols are optimized. Finally, performance comparison among these protocols is provided via simulations.

  6. Nitrogen-doped multiple graphene aerogel/gold nanostar as the electrochemical sensing platform for ultrasensitive detection of circulating free DNA in human serum.

    Science.gov (United States)

    Ruiyi, Li; Ling, Liu; Hongxia, Bei; Zaijun, Li

    2016-05-15

    Graphene aerogel has attracted increasing attention due to its large specific surface area, high-conductivity and electronic interaction. The paper reported a facile synthesis of nitrogen-doped multiple graphene aerogel/gold nanostar (termed as N-doped MGA/GNS) and its use as the electrochemical sensing platform for detection of double stranded (dsDNA). On the one hand, the N-doped MGA offers a much better electrochemical performance compared with classical graphene aerogel. Interestingly, the performance can be enhanced by only increasing the cycle number of graphene oxide gelation. On the other hand, the hybridization with GNS further enhances the electrocatalytic activity towards Fe(CN)6(3-/4-). In addition, the N-doped MGA/GNS provides a well-defined three-dimensional architecture. The unique structure make it is easy to combine with dsDNA to form the electroactive bioconjugate. The integration not only triggers an ultrafast DNA electron and charge transfer, but also realizes a significant synergy between N-doped MGA, GNS and dsDNA. As a result, the electrochemical sensor based on the hybrid exhibits highly sensitive differential pulse voltammetric response (DPV) towards dsDNA. The DPV signal linearly increases with the increase of dsDNA concentration in the range from 1.0×10(-)(21) g ml(-)(1) to 1.0×10(-16) g ml(-1) with the detection limit of 3.9×10(-22) g ml(-1) (S/N=3). The sensitivity is much more than that of all reported DNA sensors. The analytical method was successfully applied in the electrochemical detection of circulating free DNA in human serum. The study also opens a window on the electrical properties of multiple graphene aerogel and DNA as well their hybrids to meet the needs of further applications as special nanoelectronics in molecule diagnosis, bioanalysis and catalysis. PMID:26745792

  7. 多预约信息转发的协作信道预约多址接入协议%A Multiple Access Control Protocol with Multiple Reservation Information Relay and Cooperative Channel Reservation

    Institute of Scientific and Technical Information of China (English)

    袁韵洁; 李波

    2012-01-01

    针对Ad Hoc网络中实时业务在背景业务繁重时信道接入效率低的问题,提出一种邻节点协作转发信道预约信息(CRI)的多址接入协议(M-CCRM).节点在发送数据分组前,选取多条CRI作为其数据开销,在控制该开销不超过预先设定门限的基础上,将这些CRI随分组一起发送;收到数据分组的邻节点提取其携带的CRI,记录下那些自己位于其预约范围内的CRI,避免在这些CRI的预约时段内接入信道.M-CCRM协议扩大了CRI的覆盖范围,解决了由于信道衰落和(或)分组冲突导致的CRI丢失问题,提高了实时业务的信道接入效率.仿真结果表明,当开销门限为0.02时,M-CCRM协议的实时业务发送失败概率比基本信道预约协议和基本协作预约协议分别降低了31%和20%.%A new multiple access control (MAC) protocol called M-CCRM is proposed to solve the problem of poor channel access efficiency for real-time traffic in Ad Hoc networks with heavy background traffic loads. The proposed protocol bases on the idea of distributing channel reservation information (CRI) through cooperative relays of neighboring nodes. Before a node transmits a packet, multiple CRIs are carefully selected and piggy-backed with the packet so as to limit the corresponding overheads caused by carrying CRIs to be lower than a predefined threshold. By o-verhearing the packet, neighboring nodes record some of the CRIs as long as they are within the channel reservation distance of the CRIs, and then avoid to access the channel while the traffic indicated by the CRIs are carrying on. The proposed MAC protocol enlarges the coverage area of the announced CRIs, and avoids the possible missing of CRIs caused by channel fading and (or) packet collisions. Therefore, the channel access efficiency for real-time traffic is significantly increased. Simulations and comparisons with the basic channel reservation protocol and the basic cooperative channel reservation

  8. Performance of asynchronous fiber-optic code division multiple access system based on three-dimensional wavelength/time/space codes and its link analysis.

    Science.gov (United States)

    Singh, Jaswinder

    2010-03-10

    A novel family of three-dimensional (3-D) wavelength/time/space codes for asynchronous optical code-division-multiple-access (CDMA) systems with "zero" off-peak autocorrelation and "unity" cross correlation is reported. Antipodal signaling and differential detection is employed in the system. A maximum of [(W x T+1) x W] codes are generated for unity cross correlation, where W and T are the number of wavelengths and time chips used in the code and are prime. The conditions for violation of the cross-correlation constraint are discussed. The expressions for number of generated codes are determined for various code dimensions. It is found that the maximum number of codes are generated for S codes is compared to the earlier reported two-dimensional (2-D)/3-D codes for asynchronous systems. The codes have a code-set-size to code-size ratio greater than W/S. For instance, with a code size of 2065 (59 x 7 x 5), a total of 12,213 users can be supported, and 130 simultaneous users at a bit-error rate (BER) of 10(-9). An arrayed-waveguide-grating-based reconfigurable encoder/decoder design for 2-D implementation for the 3-D codes is presented so that the need for multiple star couplers and fiber ribbons is eliminated. The hardware requirements of the coders used for various modulation/detection schemes are given. The effect of insertion loss in the coders is shown to be significantly reduced with loss compensation by using an amplifier after encoding. An optical CDMA system for four users is simulated and the results presented show the improvement in performance with the use of loss compensation. PMID:20220892

  9. Hot carrier solar cell absorbers: investigation of carrier cooling properties of candidate materials

    Science.gov (United States)

    Conibeer, G.; Shrestha, Santosh; Huang, Shujuan; Patterson, Robert; Xia, Hongze; Feng, Yu; Zhang, Pengfei; Gupta, Neeti; Smyth, Suntrana; Liao, Yuanxun; Lin, Shu; Wang, Pei; Dai, Xi; Chung, Simon; Yang, Jianfeng; Zhang, Yi

    2015-09-01

    The hot carrier cell aims to extract the electrical energy from photo-generated carriers before they thermalize to the band edges. Hence it can potentially achieve a high current and a high voltage and hence very high efficiencies up to 65% under 1 sun and 86% under maximum concentration. To slow the rate of carrier thermalisation is very challenging, but modification of the phonon energies and the use of nanostructures are both promising ways to achieve some of the required slowing of carrier cooling. A number of materials and structures are being investigated with these properties and test structures are being fabricated. Initial measurements indicate slowed carrier cooling in III-Vs with large phonon band gaps and in multiple quantum wells. It is expected that soon proof of concept of hot carrier devices will pave the way for their development to fully functioning high efficiency solar cells.

  10. AntiJam: Efficient Medium Access despite Adaptive and Reactive Jamming

    CERN Document Server

    Richa, Andrea; Schmid, Stefan; Zhang, Jin

    2010-01-01

    Intentional interference constitutes a major threat for communication networks operating over a shared medium and where availability is imperative. Jamming attacks are often simple and cheap to implement. In particular, today's jammers can perform physical carrier sensing in order to disrupt communication more efficiently, specially in a network of simple wireless devices such as sensor nodes, which usually operate over a single frequency (or a limited frequency band) and which cannot benefit from the use of spread spectrum or other more advanced technologies. This paper proposes the medium access (MAC) protocol \\textsc{AntiJam} that is provably robust against a powerful reactive adversary who can jam a $(1-\\epsilon)$-portion of the time steps, where $\\epsilon$ is an arbitrary constant. The adversary uses carrier sensing to make informed decisions on when it is most harmful to disrupt communications; moreover, we allow the adversary to be adaptive and to have complete knowledge of the entire protocol history....

  11. Passive RFID based sensing

    OpenAIRE

    Capdevila Cascante, Santiago; Jofre Roca, Lluís; Romeu Robert, Jordi; Bolomey, J.Ch

    2011-01-01

    The principle of communication of passive RFID, which relies on the Modulated Scattering Technique (MST) to transmit the information from the tag to the reader, opens a way to enable conventional RFID for sensing purposes, without any additional circuitry. In this paper a short description of the physical principle behind the sensing is presented along with measurements of RFID tags used for sensing in multiple applications, such as electromagnetic field measurement temperature or presence de...

  12. Quality of service modeling and analysis for carrier ethernet

    NARCIS (Netherlands)

    Malhotra, R.

    2008-01-01

    Today, Ethernet is moving into the mainstream evolving into a carrier grade technology. Termed as Carrier Ethernet it is expected to overcome most of the shortcomings of native Ethernet. It is envisioned to carry services end-to-end serving corporate data networking and broadband access demands as w

  13. Performance of Uplink Carrier Aggregation in LTE-Advanced Systems

    DEFF Research Database (Denmark)

    Wang, Hua; Rosa, Claudio; Pedersen, Klaus

    2010-01-01

    paper, we evaluate the performance of uplink CA in LTE-Advanced systems with different CC allocation schemes. We first present the radio resource management (RRM) framework of multi-component carrier LTE-Advanced systems, with special attention on CC selection, adaptive transmission bandwidth, and......Carrier aggregation (CA) has been proposed to aggregate two or more component carriers (CCs) to support a much wider transmission bandwidth for LTE-Advanced systems. With carrier aggregation, it is possible to schedule a user equipment (UE) on multiple component carriers simultaneously. In this...... traffic conditions....

  14. Peptide-Carrier Conjugation

    DEFF Research Database (Denmark)

    Hansen, Paul Robert

    To produce antibodies against synthetic peptides it is necessary to couple them to a protein carrier. This chapter provides a nonspecialist overview of peptide-carrier conjugation. Furthermore, a protocol for coupling cysteine-containing peptides to bovine serum albumin is outlined.......To produce antibodies against synthetic peptides it is necessary to couple them to a protein carrier. This chapter provides a nonspecialist overview of peptide-carrier conjugation. Furthermore, a protocol for coupling cysteine-containing peptides to bovine serum albumin is outlined....

  15. Demonstration of high-speed multi-user multi-carrier CDMA visible light communication

    Science.gov (United States)

    Yang, Chao; Wang, Yuanquan; Wang, Yiguang; Huang, Xingxing; Chi, Nan

    2015-02-01

    We experimentally demonstrated a high-speed multi-user multi-carrier code-division multiple access (MC-CDMA) visible light communication (VLC) system. By employing a commercially available red light emitting diode (LED) and an avalanche photo diode (APD), we achieved a 16-user VLC system enabled by MC-CDMA, pre- and post-equalization, with an overall bit rate of 750 Mb/s over 1.5 m free-space transmission. The measured bit error ratio (BER) of each user is below the 7% pre-forward-error-correction (pre-FEC) threshold of 3.8×10-3.

  16. SOARAN: A Service-oriented Architecture for Radio Access Network Sharing in Evolving Mobile Networks

    OpenAIRE

    He, Jun; Song, Wei

    2015-01-01

    Mobile networks are undergoing fast evolution to software-defined networking (SDN) infrastructure in order to accommodate the ever-growing mobile traffic and overcome the network management nightmares caused by unremitting acceleration in technology innovations and evolution of the service market.Enabled by virtualized network functionalities, evolving carrier wireless networks tend to share radio access network (RAN) among multiple (virtual) network operators so as to increase network capaci...

  17. Impact of Carrier Frequency Offsets on Block-IFDMA Systems

    Directory of Open Access Journals (Sweden)

    Simon EP

    2009-01-01

    Full Text Available Recently, a new multiple access (MA scheme called block-interleaved frequency division multiple access (B-IFDMA is under consideration as an MA scheme candidate for 4G wireless applications. In this paper, the two variants of B-IFDMA are considered, the joint- DFT B-IFDMA and the added-signal B-IFDMA, and compared in terms of sensitivity to carrier frequency offsets (CFOs for both uplink and downlink. CFO gives rise to multiuser interference and self-user interference. We derive analytical expressions for the power of these interferences, and we quantify their detrimental effect through the evaluation of the signal-to-interference-plus-noise ratio (SINR degradation. We point out that both variants of B-IFDMA are not similarly affected by CFO. Hence, joint-DFT B-IFDMA provides a better robustness to multiuser interference than added-signal B-IFDMA, and so is better suited for the uplink. Then we show by means of numerical results that added-signal B-IFDMA is less sensitive to CFO in the downlink.

  18. Asymmetric Carrier Random PWM

    DEFF Research Database (Denmark)

    Mathe, Laszlo; Lungeanu, Florin; Rasmussen, Peter Omand;

    2010-01-01

    This paper presents a new fixed carrier frequency random PWM method, where a new type of carrier wave is proposed for modulation. Based on the measurements, it is shown that the spread effect of the discrete components from the motor current spectra is very effective independent of the modulation...

  19. Determination of Orbiter and Carrier Aerodynamic Coefficients from Load Cell Measurements

    Science.gov (United States)

    Glenn, G. M.

    1976-01-01

    A method of determining orbiter and carrier total aerodynamic coefficients from load cell measurements is required to support the inert and the captive active flights of the ALT program. A set of equations expressing the orbiter and carrier total aerodynamic coefficients in terms of the load cell measurements, the sensed dynamics of the Boeing 747 (carrier) aircraft, and the relative geometry of the orbiter/carrier is derived.

  20. Distributed and adaptive access mechanism supporting multiple-priority levels of throughput%支持优先等级的分布式自适应接入方案

    Institute of Scientific and Technical Information of China (English)

    石春; 何书前; 邓正杰; 张洁

    2015-01-01

    By studying the adjustment rules and ranges of access parameters ,a distributed and adaptive access mechanism was proposed based on channel status information .By sensing and counting channel busy status ,a node adjusting contention window linearly according to different access categories was designed ,which separated the adjustment rules of parameters from the status of data transmissions and alleviated the effect of fixed ranges of contention window on performance .The simulation results demonstrate the validity and scalability of the proposed access mechanism .%对接入参数调整策略和参数范围进行研究,基于信道状态信息,提出支持不同优先等级业务类型的分布式自适应接入方案。通过感知并统计信道状态数据,设计适合不同业务类型的线性调整竞争窗口的方法,解决接入参数调整对于数据传输状态的依赖和固定竞争窗口范围对性能的影响。仿真结果验证了该算法的有效性和良好的可扩展性能。

  1. Make electricity a complete and efficient carrier for energy accessibility - Hydro-Quebec strategic R & D; Faire de l'electricite un vecteur complet et efficace pour l'accessibilite de l'energie - La R&D strategique a Hydro-Quebec

    Energy Technology Data Exchange (ETDEWEB)

    Naggar, Raouf

    2010-09-15

    In an energy context dominated by the evolution of needs, the availability of resources and the respect of the environment, electricity will play a role increasingly important in order to make accessible most of the energy resources that are harnessed in real time and not already existing as a portable and storable form. However, to become a complete and efficient accessibility carrier, it will still have to rise to many more challenges in development, exploitation, maintenance and commercial exchanges. The Hydro Quebec research institute (IREQ) has begun several strategic R&D projects to raise to these challenges. [French] Dans un contexte energetique domine par l'evolution des besoins, la disponibilite des ressources et le respect de l'environnement, l'electricite jouera un role de plus en plus important pour rendre accessibles la plupart des ressources energetiques qui sont captees en temps reel et qui ne sont pas deja sous une forme stockable et transportable. Cependant, pour devenir un vecteur d'accessibilite complet et efficace, elle devra encore relever plusieurs defis au niveau du developpement, de l'exploitation, de la maintenance et des echanges commerciaux. L'institut de recherche d'Hydro-Quebec (IREQ) a entrepris plusieurs projets de R&D strategique visant a relever ces defis.

  2. Structural and bioinformatic characterization of an Acinetobacter baumannii type II carrier protein

    International Nuclear Information System (INIS)

    The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented. Microorganisms produce a variety of natural products via secondary metabolic biosynthetic pathways. Two of these types of synthetic systems, the nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs), use large modular enzymes containing multiple catalytic domains in a single protein. These multidomain enzymes use an integrated carrier protein domain to transport the growing, covalently bound natural product to the neighboring catalytic domains for each step in the synthesis. Interestingly, some PKS and NRPS clusters contain free-standing domains that interact intermolecularly with other proteins. Being expressed outside the architecture of a multi-domain protein, these so-called type II proteins present challenges to understand the precise role they play. Additional structures of individual and multi-domain components of the NRPS enzymes will therefore provide a better understanding of the features that govern the domain interactions in these interesting enzyme systems. The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented here. Comparison with the closest structural homologs of other carrier proteins identifies the requirements for a conserved glycine residue and additional important sequence and structural requirements within the regions that interact with partner proteins

  3. Structural and bioinformatic characterization of an Acinetobacter baumannii type II carrier protein

    Energy Technology Data Exchange (ETDEWEB)

    Allen, C. Leigh; Gulick, Andrew M., E-mail: gulick@hwi.buffalo.edu [University at Buffalo, Buffalo, NY 14203 (United States)

    2014-06-01

    The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented. Microorganisms produce a variety of natural products via secondary metabolic biosynthetic pathways. Two of these types of synthetic systems, the nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs), use large modular enzymes containing multiple catalytic domains in a single protein. These multidomain enzymes use an integrated carrier protein domain to transport the growing, covalently bound natural product to the neighboring catalytic domains for each step in the synthesis. Interestingly, some PKS and NRPS clusters contain free-standing domains that interact intermolecularly with other proteins. Being expressed outside the architecture of a multi-domain protein, these so-called type II proteins present challenges to understand the precise role they play. Additional structures of individual and multi-domain components of the NRPS enzymes will therefore provide a better understanding of the features that govern the domain interactions in these interesting enzyme systems. The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented here. Comparison with the closest structural homologs of other carrier proteins identifies the requirements for a conserved glycine residue and additional important sequence and structural requirements within the regions that interact with partner proteins.

  4. Near-Infrared Resonance Energy Transfer Glucose Biosensors in Hybrid Microcapsule Carriers

    Directory of Open Access Journals (Sweden)

    Mike McShane

    2008-09-01

    Full Text Available Fluorescence-based sensing systems offer potential for noninvasive monitoring with implantable devices, but require carrier technologies that provide suitable immobilization, accessibility, and biocompatibility. Recent developments towards this goal include a competitive binding assay for glucose that has been encapsulated in semipermeable microcapsule carriers. This paper describes an extension of this work to increase the applicability to in vivo monitoring, wherein two significant developments are described: (1 a near-infrared resonance energy transfer system for transducing glucose concentration, and (2 novel hybrid organic-inorganic crosslinked microcapsules as carriers. The quenching-based assay is a competitive binding (CB system based on apo-glucose oxidase (AG as the receptor and dextran as the competitive ligand. The encapsulated quencher-labeled dextran and near infrared donor-labeled glucose receptor showed a stable and reversible response with tunable sensitivity of 1–5%/mM over the physiological range, making these transducers attractive for continuous monitoring for biomedical applications.

  5. Integrated Coherent Radio-over-Fiber Units for Millimeter-Wave Wireless Access

    DEFF Research Database (Denmark)

    Stöhr, A.; Babiel, S.; Chuenchom, M.;

    2015-01-01

    next generation optical and wireless access services and high-capacity fixed wireless links for mobile backhaul. Proof-of-concept system experiments are reported including the wireless transmission of a 2.5 Gb/s data signal over 40 m (limited by lab space) at 76 GHz carrier frequency after 20 km fiber......-dense WDM. We propose and demonstrate novel radio access units (RAU) using coherent optical heterodyne detection for the generation of the millimeter-wave radio signals in the RAUs. The proposed CRoF concept supports the provision of multiple services over a single optical distribution network including......-optic transmission....

  6. 社会实践:大学生社会责任感培养的重要载体%Social practice:the important carrier of cultivating the students' sense of social responsibility

    Institute of Scientific and Technical Information of China (English)

    赵曙光

    2013-01-01

    The contemporary college students social responsibility in the mainstream is healthy and positive, but there are also some problems that can not be ignored. Mainly displays in: pay attention to self value, despise social value; social responsibility consciousness and behavior are not unified;pay attention to protect their own rights and obligations, desalination. Carry out social practice can strengthen the students' sense of social responsibility cognition, improve the ability of students to fulfill their social responsibilities, fostering and enhancing the effectiveness of college students' sense of social responsibility.%  当代大学生社会责任感主流是健康的、积极向上的,但是也存在着一些不容忽视的问题。主要表现在:注重自我价值,轻视社会价值;社会责任意识与行为表现不统一;注重维护自身权利,淡化应该履行的义务。深入开展社会实践能强化大学生社会责任感认知,提高大学生履行社会责任的能力,增强培养大学生社会责任感的实效性。

  7. Electroactive polymers for sensing

    Science.gov (United States)

    2016-01-01

    Electromechanical coupling in electroactive polymers (EAPs) has been widely applied for actuation and is also being increasingly investigated for sensing chemical and mechanical stimuli. EAPs are a unique class of materials, with low-moduli high-strain capabilities and the ability to conform to surfaces of different shapes. These features make them attractive for applications such as wearable sensors and interfacing with soft tissues. Here, we review the major types of EAPs and their sensing mechanisms. These are divided into two classes depending on the main type of charge carrier: ionic EAPs (such as conducting polymers and ionic polymer–metal composites) and electronic EAPs (such as dielectric elastomers, liquid-crystal polymers and piezoelectric polymers). This review is intended to serve as an introduction to the mechanisms of these materials and as a first step in material selection for both researchers and designers of flexible/bendable devices, biocompatible sensors or even robotic tactile sensing units. PMID:27499846

  8. Electroactive polymers for sensing.

    Science.gov (United States)

    Wang, Tiesheng; Farajollahi, Meisam; Choi, Yeon Sik; Lin, I-Ting; Marshall, Jean E; Thompson, Noel M; Kar-Narayan, Sohini; Madden, John D W; Smoukov, Stoyan K

    2016-08-01

    Electromechanical coupling in electroactive polymers (EAPs) has been widely applied for actuation and is also being increasingly investigated for sensing chemical and mechanical stimuli. EAPs are a unique class of materials, with low-moduli high-strain capabilities and the ability to conform to surfaces of different shapes. These features make them attractive for applications such as wearable sensors and interfacing with soft tissues. Here, we review the major types of EAPs and their sensing mechanisms. These are divided into two classes depending on the main type of charge carrier: ionic EAPs (such as conducting polymers and ionic polymer-metal composites) and electronic EAPs (such as dielectric elastomers, liquid-crystal polymers and piezoelectric polymers). This review is intended to serve as an introduction to the mechanisms of these materials and as a first step in material selection for both researchers and designers of flexible/bendable devices, biocompatible sensors or even robotic tactile sensing units. PMID:27499846

  9. Joint Iterative Carrier Synchronization and Signal Detection Employing Expectation Maximization

    DEFF Research Database (Denmark)

    Zibar, Darko; de Carvalho, Luis Henrique Hecker; Estaran Tolosa, Jose Manuel;

    2014-01-01

    . The algorithm is tested in a mixed line rate optical transmission scenario employing dual polarization 448 Gb/s 16-QAM signal surrounded by eight on-off keying channels in a 50 GHz grid. It is shown that joint carrier synchronization and data detection are more robust towards optical transmitter......In this paper, joint estimation of carrier frequency, phase, signal means and noise variance, in a maximum likelihood sense, is performed iteratively by employing expectation maximization. The parameter estimation is soft decision driven and allows joint carrier synchronization and data detection...... impairments and nonlinear phase noise, compared to digital phase-locked loop (PLL) followed by hard decisions. Additionally, soft decision driven joint carrier synchronization and detection offers an improvement of 0.5 dB in terms of input power compared to hard decision digital PLL based carrier...

  10. Remote sensing; Fernerkundung

    Energy Technology Data Exchange (ETDEWEB)

    Glaessler, C.

    2001-07-01

    The potential of different multitemporal and multispectral airborne and spaceborne remote sensing methods for assessment and monitoring of the lignite open-cast mining areas are discussed in this chapter. Emphasis is placed on the successful use of different remote sensing data in variable vegetation structures for dumped sediments with different mineralogical and geochemical properties and for hydrochemical properties of the residual lakes. Multiple remote sensing data are a cost and time efficient tool for the assessment of environmental impacts, supervising of reclamation activities as well as for long term monitoring of the mining area. The airborne data are well suited for large scale detailed research and mapping in smaller sites and the satellite data for the overview scale 1:50 000. An integrated remote sensing-GIS-system including all field and lab data, DTM and other graphical data, improve the results of the remote sensing data classification for the lignite mining region in Central Germany and the Lausitz. (orig.)

  11. Arctic phytoplankton and zooplankton abundance, temperature and salinity measurements collected from multiple platforms from 1903-02-22 to 1970-09-30 (NODC Accession 0069178)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Arctic phytoplankton and zooplankton abundance, temperature and salinity measurements collected from multiple platforms from 1903-02-22 to 1970-09-30 by Zoological...

  12. Temperature profile data from XBT casts from MULTIPLE PLATFORMS from a World-Wide distribution from 02 January 1990 to 31 December 1995 (NODC Accession 0001268)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — XBT data were collected from MULTIPLE PLATFORMS from a World-Wide distribution from 02 January 1990 to 31 December 1995. Data were submitted by the UK Hydrographic...

  13. Temperature profiles from MBT casts from a World-Wide distribution from MULTIPLE PLATFORMS from 08 April 1948 to 14 December 1968 (NODC Accession 9300131)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature profile data were collected from MBT casts from a World-Wide distribution. Data were collected from MULTIPLE PLATFORMS from 08 April 1948 to 14 Decmeber...

  14. Oceanographic profile temperature, salinity, oxygen measurements collected using bottle from multiple platforms in the Azov, Black Seas from 1924-1990 (NODC Accession 0002717)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Oceanographic profile temperature, salinity, oxygen measurements collected using bottle from multiple platforms in the Azov, Black Seas from 1924-1990

  15. Temperature profile and oxygen data collected from multiple ships using CTD casts in a world wide distribution from 04 September 1979 to 15 April 1998 (NODC Accession 0002716)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature profile and oxygen data were collected using CTD casts in a world wide distribution from multiple platforms from 04 September 1979 to 15 April 1998....

  16. A Comparative Study on Evaluating the Service Quality Attributes based on Kano Model: A Case of Low-cost Carrier and Full-service Carrier

    OpenAIRE

    Byun Hyojeong; Lee Byeongcheol; Rye Jaehee

    2014-01-01

    The emergence and development of low-cost carriers(LCC) with competitive price is heating up the competition in the aviation market more, especially between low-cost carriers(LCC) and full-service carriers(FSC). Therefore, it became more important than ever to implement service differentiation strategies of each airline for securing customers and competitiveness. In this sense, the purpose of this study is to compare and assess the different expectations of the customers for airline service a...

  17. Remote optical sensing network for gas monitoring based on laser spectroscopy over hybrid TDM/WDM-PONs

    Science.gov (United States)

    Huang, Ming-Fang; Plant, Genevieve; Tanaka, Akihiro; Cvijetic, Neda; Tian, Yue; Wysocki, Gerard; Wang, Ting

    2015-09-01

    We propose an optical gas sensing network directly overlaid onto optical access networks, hybrid TDM/WDM-PONs. Centralized remote gas monitoring is demonstrated using three different sensing technologies: Chirp Laser Dispersion Spectroscopy (CLaDS), Direct Laser Absorption Spectroscopy (DLAS) and tunable diode laser absorption spectroscopy (TDLS). DLAS performs fast threshold detection while CLaDS provides quantitative information about the gas. Additionally, TDLS utilizes a cost-effective solution for multiple gases detection. The results confirm that centralized remote gas sensing can be realized in optical communication networks using standard single-mode fiber (SMF), which provides a real time, low cost, and maintenance-free solution.

  18. Duchenne muscular dystrophy carriers

    International Nuclear Information System (INIS)

    By means of magnetic resonance imaging (MRI), the proton spin-lattice relaxation times (T1 values) of the skeletal muscles were measured in Duchenne muscular dystrophy (DMD) carriers and normal controls. The bound water fraction (BWF) was calculated from the T1 values obtained, according to the fast proton diffusion model. In the DMD carriers, T1 values of the gluteus maximus and quadriceps femoris muscles were significantly higher, and BWFs of these muscles were significantly lower than in normal control. Degenerative muscular changes accompanied by interstitial edema were presumed responsible for this abnormality. No correlation was observed between the muscle T1 and serum creatine kinase values. The present study showed that MRI could be a useful method for studying the dynamic state of water in both normal and pathological skeletal muscles. Its possible utility for DMD carrier detection was discussed briefly. (orig.)

  19. Carrier Load Balancing and Packet Scheduling for Multi-Carrier Systems

    DEFF Research Database (Denmark)

    Wang, Yuanye; Pedersen, Klaus; Sørensen, Troels Bundgaard;

    2010-01-01

    Abstract-In this paper we focus on resource allocation for next generation wireless communication systems with aggregation of multiple Component Carriers (CCs), i.e., how to assign the CCs to each user, and how to multiplex multiple users in each CC. We first investigate two carrier load balancing...... methods for allocating the CCs to the users- Round Robin (RR) and Mobile Hashing (MH) balancing by means of a simple theoretical formulation, as well as system level simulations. At Layer-2 we propose a simple cross-CC packet scheduling algorithm that improves the coverage performance and the resource...... allocation fairness among users, as compared to independent scheduling per CC. The Long Term Evolution (LTE)-Advanced is selected for the case study of a multi-carrier system. In such a system, RR provides better performance than MH balancing, and the proposed simple scheduling algorithm is shown to be...

  20. Demonstration of two-user, 10-Gbits/s optical code-division multiple-access system implemented by using cascaded longperiod fiber gratings formed in dispersion-compensating fiber with inner-cladding structure

    DEFF Research Database (Denmark)

    Kim, Sun-Jong; Eom, T.J.; Kim, T.Y.; Lee, B.H.; Park, C.S.

    2005-01-01

    A two-user, 10-Gbits/s optical code-division multiple-access system implemented by using cascaded long-period fiber gratings formed in a dispersion-compensating fiber (DCF) is demonstrated. Our results show that the sensitivity of cladding modes to the refractive index change on the cladding...... surface is greatly reduced by utilizing the inner-cladding mode of the DCF. Two pairs of encoder/decoder are constructed and the performance is evaluated by measuring bit error rate (BER). With an interferer, a BER of 1.5 X 10(-12) is measured at a received optical power of -6 dBm....

  1. Mucosal genetic immunization through microsphere–based oral carriers

    OpenAIRE

    Rosli, Rozita; Nograles, Nadine; Hanafi, Aimi; Nor Shamsudin, Mariana; Abdullah, Syahril

    2013-01-01

    Polymeric carriers in the form of cellulose acetate phthalate (CAP) and alginate (ALG) microspheres were used for encapsulation of plasmid DNA for oral mucosal immunization. Access into the intestinal mucosa by pVAX1 eukaryotic expression plasmid vectors carrying gene-coding sequences, either for the cholera enterotoxin B subunit (ctxB) immunostimulatory antigen or the green fluorescent protein (GFP), delivered from both types of microsphere carriers were examined in orally immunized BALB/c m...

  2. Carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool

    Science.gov (United States)

    Cai, Yu; Sha, Shuang

    2016-09-01

    This paper proposes a new carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool used in a cylindrical borehole environment during oil-based mud drilling processes. The new tool is an orthogonal frequency division multiplexing access-based contactless multi-measurand detection tool. The tool can measure formation resistivity in different azimuthal angles and elevational depths. It can measure many more measurands simultaneously in a specified bandwidth than the legacy frequency division multiplexing multi-measurand tool without a channel-select filter while avoiding inter-carrier interference. The paper also shows that formation resistivity is not sensitive to frequency in certain frequency bands. The average resistivity collected from N subcarriers can increase the measurement of the signal-to-noise ratio (SNR) by N times given no amplitude clipping in the current-injection electrode. If the clipping limit is taken into account, with the phase rotation of each single carrier, the amplitude peak-to-average ratio can be reduced by 3 times, and the SNR can achieve a 9/N times gain over the single-carrier system. The carrier-interleaving technique is also introduced to counter the carrier frequency offset (CFO) effect, where the CFO will cause inter-pad interference. A qualitative analysis and simulations demonstrate that block-interleaving performs better than tone-interleaving when coping with a large CFO. The theoretical analysis also suggests that increasing the subcarrier number can increase the measurement speed or enhance elevational resolution without sacrificing receiver performance. The complex orthogonal multi-pad multi-carrier resistivity logging tool, in which all subcarriers are complex signals, can provide a larger available subcarrier pool than other types of transceivers.

  3. Multiple symmetric lipomas with high levels of mtDNA with the tRNA(Lys) A-->G(8344) mutation as the only manifestation of disease in a carrier of myoclonus epilepsy and ragged-red fibers (MERRF) syndrome.

    OpenAIRE

    Holme, E; Larsson, N G; Oldfors, A; Tulinius, M; Sahlin, P; Stenman, G

    1993-01-01

    We have investigated the morphology, cytogenetics, and the fraction of mtDNA with the tRNA(Lys) A-->G(8344) mutation in three lipomas in a carrier of this mutation. The son of the patient had myoclonus epilepsy and ragged-red fibers syndrome. The fraction of mtDNA with the tRNA(Lys) mutation varied between 62% and 80% in cultured skin fibroblasts, lymphocytes, normal adipose tissue, and muscle. In the three lipomas the mean fraction of mutated mtDNA was 90%, 94%, and 94%. Ultrastructural exam...

  4. Intestinal solute carriers

    DEFF Research Database (Denmark)

    Steffansen, Bente; Nielsen, Carsten Uhd; Brodin, Birger; Eriksson, André Huss; Andersen, Rikke; Frokjaer, Sven

    2004-01-01

    A large amount of absorptive intestinal membrane transporters play an important part in absorption and distribution of several nutrients, drugs and prodrugs. The present paper gives a general overview on intestinal solute carriers as well as on trends and strategies for targeting drugs and...

  5. Glycosylation of solute carriers

    DEFF Research Database (Denmark)

    Pedersen, Nis Borbye; Carlsson, Michael C; Pedersen, Stine Helene Falsig

    2016-01-01

    Solute carriers (SLCs) are one of the largest groups of multi-spanning membrane proteins in mammals and include ubiquitously expressed proteins as well as proteins with highly restricted tissue expression. A vast number of studies have addressed the function and organization of SLCs as well as...

  6. Information and Its Carriers.

    Science.gov (United States)

    Herrmann, F.; And Others

    1985-01-01

    Describes: (1) the structure of a data transmission source, carrier, and receiver; (2) a quantitative measure for the amount of data, followed by some quantitative examples of data transmission processes; (3) the concept of data current; (4) data containers; and (5) how this information can be used to structure physics courses. (JN)

  7. Market Access and Welfare

    DEFF Research Database (Denmark)

    Raimondos-Møller, Pascalis; Woodland, Alan D.

    objectives of trade policy is problematic and calls for finding alternative tariff reform rules that can achieve both objectives at the same time. The present paper contributes to this aim by using a new set of tariff reforms that are based on local optimality. Using such reforms it is shown that market......According to the literature, well known tariff reform rules that are guaranteed to increase welfare will not necessarily increase market access, while rules that are guaranteed to increase market access will not necessarily increase welfare. Such conflict between welfare and market access...... access and consumer welfare will always be weakly compatible, in the sense that reforms based on each objective have the same signed effect on the other objective. For strong compatibility, whereby both objectives increase as a result of a locally optimal tariff reform, we derive both a necessary and...

  8. Estudio del protooncogen Ret en neoplasia endocrina multiple 2A y en carcinoma medular en tiroides familiar: Hallazgos clínico-patológicos en portadores asintomáticos Analysis of the RET protooncogene in multiple endocrine neoplasia 2A and in familial medullary thyroid carcinoma: Clinical-pathological findings in asymptomatic carriers

    Directory of Open Access Journals (Sweden)

    S. Belli

    2003-01-01

    Full Text Available El 25% de los carcinomas medulares de tiroides son hereditarios. Se presentan en forma de familiar (CMTF 5% o como neoplasia endocrina múltiple (MEN tipo 2A (17% o 2B (3%, y comparten la herencia, autosómica dominante, de una mutación germinal en el protooncogen RET en uno de 12 codones conocidos. Estudiamos 7 familias (5 CMTF y 2 MEN 2A con el objeto de detectar la mutación familiar e identificar a los portadores asintomáticos. Seis de las siete mutaciones (4 CMTF y 2 MEN 2A fueron en el codón más frecuente, el 634, y una familia con CMTF presentó una mutación germinal novel: una transición T>C en el codón 630, resultando el cambio C630A. De los 57 individuos estudiados, 25 (43.85 % fueron portadores de la mutación, 7 de éstos (28% eran portadores asintomáticos de los cuales 5 eran niños, con una edad X-=11±3.2 años y fueron tiroidectomizados. Presentaron hiperplasia de células C y focos de microcarcinoma en ambos lóbulos tiroideos aun cuando la calcitonina basal o estimulada con pentagastrina fueron normales. En conclusión, describimos una mutación germinal novel en el protooncogen RET: C630A y el hallazgo de enfermedad de la célula C en los portadores asintomáticos, que enfatiza la importancia de la tiroidectomía profiláctica tan pronto como se confirma el diagnóstico molecular.Twenty five percent of the medullary thyroid carcinoma (MTC is hereditary and 5% is familiar (FMTC, or considered as multiple endocrine neoplasia (MEN type 2A (17% or 2B (3%. These diseases are the result of the autosomic dominant inheritance of a mutation in the RET protooncogene, in one out of 12 different known codons. We analyzed 7 families (2 MEN 2A and 5 FMTC. Six mutations were detected in the most frequent codon, 634 (2 MEN 2A y 4 FMTC and one family with FMTC presented a novel mutation: a transition T>C at codon 630, resulting a C630A change. Among 57 individuals studied, 25 (43.85% presented the mutation. Seven (28% were asymptomatic

  9. Uptake Carriers and Oncology Drug Safety

    OpenAIRE

    Sprowl, Jason A.; Sparreboom, Alex

    2014-01-01

    Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics in multiple tissues. Many of these transporters are highly expressed in the gastrointestinal tract, liver, and kidney and are considered to be of particular importance in governing drug absorption, elimination, and cellular sensitivity of specific organs to a wide variety of oncology drugs. Although the majority of studies on the interacti...

  10. Distributed Multiuser Sequential Channel Sensing Schemes in Multichannel Cognitive Radio Networks

    CERN Document Server

    Shokri-Ghadikolaei, Hossein; Nasiri-Kenari, Masoumeh

    2012-01-01

    Effective spectrum sensing strategies enable cognitive radios (CRs) to identify and opportunistically transmit on under-utilized spectral resources. In this paper, sequential channel sensing problems for single and multiple secondary users (SUs) cases are effectively modeled through finite state Markovian processes. More specifically, a model for single user case is introduced and validated through analytical analysis. In order to address multiple SUs, this model is extended to modified p-persistent access (MPPA) and its generalized version. While the introduced analytical framework facilitates the process of performance evaluation, these algorithms experience a high level of collision among the SUs. To mitigate this problem appropriately, p-persistent random access (PPRA) scheme is proposed, which offers higher average throughput for SUs by statistically distributing their loads among all channels. The structure and performance of the proposed schemes are discussed in detail, and a set of illustrative numeri...

  11. Optimisation and common sense

    International Nuclear Information System (INIS)

    This note builds on recent articles about the development of new ICRP recommendations by supporting the use of common sense in optimisation; use of an additional criterion relating to technology-based principles is suggested to support utility- and equity-based criteria. This is taken forward by use of authoritative good practice safety precautions and a need to consider safety in an integrated manner. It is noted that use of common sense in ALARP or ALARA decisions is liable to rely on access to information and training. (author)

  12. Collision-free prioritized medium access control in wireless networks with hidden nodes

    OpenAIRE

    Andersson, Björn; Pereira, Nuno; Tovar, Eduardo

    2006-01-01

    We propose a collision-free medium access control (MAC) protocol, which implements static-priority scheduling and works in the presence of hidden nodes. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to sense the channel while transmitting to the channel. Our protocol is collision-free even in...

  13. Sensing via optical interference

    OpenAIRE

    Bailey, Ryan C.; Mohammed Parpia; Hupp, Joseph T.

    2005-01-01

    Chemical and biological sensing are problems of tremendous contemporary technological importance in multiple regulatory and human health contexts, including environmental monitoring, water quality assurance, workplace air quality assessment, food quality control, many aspects of biodiagnostics, and, of course, homeland security. Frequently, what is needed, or at least wanted, are sensors that are simultaneously cheap, fast, reliable, selective, sensitive, robust, and easy to use. Unfortunatel...

  14. Single Carrier Cyclic Prefix-Assisted CDMA System with Frequency Domain Equalization for High Data Rate Transmission

    Directory of Open Access Journals (Sweden)

    Madhukumar A. S.

    2004-01-01

    Full Text Available Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.

  15. Hungarian students’ carrier aspirations

    Directory of Open Access Journals (Sweden)

    A.S. Gubik

    2014-06-01

    Full Text Available The article analyzes the students’ carrier aspiration, right after their graduation and five years after their studies. It examines the differences arising from the students’ family business background and their most important social variables (gender, age. Then the study highlights the effects of study field on the students’ intention. The direct effect of education on starting an enterprise is undiscovered in the literature, the paper deals with the influence of availability and services use, offered by higher institutions.

  16. Remote Sensing

    CERN Document Server

    Khorram, Siamak; Koch, Frank H; van der Wiele, Cynthia F

    2012-01-01

    Remote Sensing provides information on how remote sensing relates to the natural resources inventory, management, and monitoring, as well as environmental concerns. It explains the role of this new technology in current global challenges. "Remote Sensing" will discuss remotely sensed data application payloads and platforms, along with the methodologies involving image processing techniques as applied to remotely sensed data. This title provides information on image classification techniques and image registration, data integration, and data fusion techniques. How this technology applies to natural resources and environmental concerns will also be discussed.

  17. Comparison of human solute carriers

    OpenAIRE

    Schlessinger, Avner; Matsson, Pär; Shima, James E.; Pieper, Ursula; Yee, Sook Wah; Kelly, Libusha; Apeltsin, Leonard; Stroud, Robert M.; Ferrin, Thomas E; Giacomini, Kathleen M.; Sali, Andrej

    2010-01-01

    Solute carriers are eukaryotic membrane proteins that control the uptake and efflux of solutes, including essential cellular compounds, environmental toxins, and therapeutic drugs. Solute carriers can share similar structural features despite weak sequence similarities. Identification of sequence relationships among solute carriers is needed to enhance our ability to model individual carriers and to elucidate the molecular mechanisms of their substrate specificity and transport. Here, we desc...

  18. Participatory sensing as an enabler for self-organisation in future cellular networks

    International Nuclear Information System (INIS)

    In this short review paper we summarise the emerging challenges in the field of participatory sensing for the self-organisation of the next generation of wireless cellular networks. We identify the potential of participatory sensing in enabling the self-organisation, deployment optimisation and radio resource management of wireless cellular networks. We also highlight how this approach can meet the future goals for the next generation of cellular system in terms of infrastructure sharing, management of multiple radio access techniques, flexible usage of spectrum and efficient management of very small data cells

  19. Carrier transport uphill. I. General

    DEFF Research Database (Denmark)

    Rosenberg, T; Wilbrandt, W

    1963-01-01

    A quantitative treatment of a carrier pump operating with two carrier forms C and Z is presented. Asymmetric metabolic reactions are assumed to transform Z into C on one and C into Z on the other side of the membrane, establishing a carrier cycle. The kinetical consequences of this mechanism are...

  20. Online Remote Sensing Interface

    Science.gov (United States)

    Lawhead, Joel

    2007-01-01

    BasinTools Module 1 processes remotely sensed raster data, including multi- and hyper-spectral data products, via a Web site with no downloads and no plug-ins required. The interface provides standardized algorithms designed so that a user with little or no remote-sensing experience can use the site. This Web-based approach reduces the amount of software, hardware, and computing power necessary to perform the specified analyses. Access to imagery and derived products is enterprise-level and controlled. Because the user never takes possession of the imagery, the licensing of the data is greatly simplified. BasinTools takes the "just-in-time" inventory control model from commercial manufacturing and applies it to remotely-sensed data. Products are created and delivered on-the-fly with no human intervention, even for casual users. Well-defined procedures can be combined in different ways to extend verified and validated methods in order to derive new remote-sensing products, which improves efficiency in any well-defined geospatial domain. Remote-sensing products produced in BasinTools are self-documenting, allowing procedures to be independently verified or peer-reviewed. The software can be used enterprise-wide to conduct low-level remote sensing, viewing, sharing, and manipulating of image data without the need for desktop applications.

  1. Multiple Perspectives / Multiple Readings

    Directory of Open Access Journals (Sweden)

    Simon Biggs

    2005-01-01

    Full Text Available People experience things from their own physical point of view. What they see is usually a function of where they are and what physical attitude they adopt relative to the subject. With augmented vision (periscopes, mirrors, remote cameras, etc we are able to see things from places where we are not present. With time-shifting technologies, such as the video recorder, we can also see things from the past; a time and a place we may never have visited.In recent artistic work I have been exploring the implications of digital technology, interactivity and internet connectivity that allow people to not so much space/time-shift their visual experience of things but rather see what happens when everybody is simultaneously able to see what everybody else can see. This is extrapolated through the remote networking of sites that are actual installation spaces; where the physical movements of viewers in the space generate multiple perspectives, linked to other similar sites at remote locations or to other viewers entering the shared data-space through a web based version of the work.This text explores the processes involved in such a practice and reflects on related questions regarding the non-singularity of being and the sense of self as linked to time and place.

  2. A parallel-pipelined architecture for a multi carrier demodulator

    Science.gov (United States)

    Kwatra, S. C.; Jamali, M. M.; Eugene, Linus P.

    1991-03-01

    Analog devices have been used for processing the information on board the satellites. Presently, digital devices are being used because they are economical and flexible as compared to their analog counterparts. Several schemes of digital transmission can be used depending on the data rate requirement of the user. An economical scheme of transmission for small earth stations uses single channel per carrier/frequency division multiple access (SCPC/FDMA) on the uplink and time division multiplexing (TDM) on the downlink. This is a typical communication service offered to low data rate users in commercial mass market. These channels usually pertain to either voice or data transmission. An efficient digital demodulator architecture is provided for a large number of law data rate users. A demodulator primarily consists of carrier, clock, and data recovery modules. This design uses principles of parallel processing, pipelining, and time sharing schemes to process large numbers of voice or data channels. It maintains the optimum throughput which is derived from the designed architecture and from the use of high speed components. The design is optimized for reduced power and area requirements. This is essential for satellite applications. The design is also flexible in processing a group of a varying number of channels. The algorithms that are used are verified by the use of a computer aided software engineering (CASE) tool called the Block Oriented System Simulator. The data flow, control circuitry, and interface of the hardware design is simulated in C language. Also, a multiprocessor approach is provided to map, model, and simulate the demodulation algorithms mainly from a speed view point. A hypercude based architecture implementation is provided for such a scheme of operation. The hypercube structure and the demodulation models on hypercubes are simulated in Ada.

  3. Maintainable substrate carrier for electroplating

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Chen-An; Abas, Emmanuel Chua; Divino, Edmundo Anida; Ermita, Jake Randal G.; Capulong, Jose Francisco S.; Castillo, Arnold Villamor; Ma, Diana Xiaobing

    2016-08-02

    One embodiment relates to a substrate carrier for use in electroplating a plurality of substrates. The carrier includes a non-conductive carrier body on which the substrates are placed and conductive lines embedded within the carrier body. A plurality of conductive clip attachment parts are attached in a permanent manner to the conductive lines embedded within the carrier body. A plurality of contact clips are attached in a removable manner to the clip attachment parts. The contact clips hold the substrates in place and conductively connecting the substrates with the conductive lines. Other embodiments, aspects and features are also disclosed.

  4. Equal gain combining for cooperative spectrum sensing in cognitive radio networks

    KAUST Repository

    Hamza, Doha R.

    2014-08-01

    Sensing with equal gain combining (SEGC), a novel cooperative spectrum sensing technique for cognitive radio networks, is proposed. Cognitive radios simultaneously transmit their sensing results to the fusion center (FC) over multipath fading reporting channels. The cognitive radios estimate the phases of the reporting channels and use those estimates for coherent combining of the sensing results at the FC. A global decision is made at the FC by comparing the received signal with a threshold. We obtain the global detection probabilities and secondary throughput exactly through a moment generating function approach. We verify our solution via system simulation and demonstrate that the Chernoff bound and central limit theory approximation are not tight. The cases of hard sensing and soft sensing are considered and we provide examples in which hard sensing is advantageous to soft sensing. We contrast the performance of SEGC with maximum ratio combining of the sensors\\' results and provide examples where the former is superior. Furthermore, we evaluate the performance of SEGC against existing orthogonal reporting techniques such as time division multiple access (TDMA). SEGC performance always dominates that of TDMA in terms of secondary throughput. We also study the impact of phase and synchronization errors and demonstrate the robustness of the SEGC technique against such imperfections. © 2002-2012 IEEE.

  5. The plant mitochondrial carrier family: functional and evolutionary aspects

    OpenAIRE

    Ilka eHaferkamp; Stephan eSchmitz-Esser

    2012-01-01

    Mitochondria play a key role in respiration and energy production and are involved in multiple eukaryotic but also in several plant specific metabolic pathways. Solute carriers in the inner mitochondrial membrane connect the internal metabolism with that of the surrounding cell. Because of their common basic structure, these transport proteins affiliate to the mitochondrial carrier family (MCF). Generally, MCF proteins consist of six membrane-spanning helices, exhibit typical conserved domain...

  6. Decision feedback loop for tracking a polyphase modulated carrier

    Science.gov (United States)

    Simon, M. K. (Inventor)

    1974-01-01

    A multiple phase modulated carrier tracking loop for use in a frequency shift keying system is described in which carrier tracking efficiency is improved by making use of the decision signals made on the data phase transmitted in each T-second interval. The decision signal is used to produce a pair of decision-feedback quadrature signals for enhancing the loop's performance in developing a loop phase error signal.

  7. Living in a 'fat swamp': exposure to multiple sources of accessible, cheap, energy-dense fast foods in a deprived community.

    Science.gov (United States)

    Saunders, Patrick; Saunders, Annie; Middleton, John

    2015-06-14

    This study assesses the levels of fats, including trans-fatty acids, and salt in common takeaway fast foods in a deprived urban municipality in the West Midlands, England, and implications in the context of the spatial distribution of fast food takeaways. The results of the compositional analysis of over 250 take-out foods were compared with established and derived standards. About 70% of products exceeded the recommendation that a meal should contain less than 30% of a Guideline Daily Amount (GDA). More than half of them exceeded 50% GDA for at least one metric, including 81% of all analyses for SFA. And 17% of samples exceeded the GDA for SFA, including each of two meals that contained about twice the GDA. Over 30% samples exceeded the children's GDA for total fat or SFA. 27% of salt analyses exceeded the GDA. People in Sandwell are exposed to large portion sizes and high levels of fats and salt in takeaway foods, with levels in some foods having increased since 2010. Given this population's limited options to break out of a highly compromising environment of living simultaneously in a 'swamp' of unhealthy, readily accessible and cheap takeaways, and a 'desert' of healthy options, an immediate and innovative package of interventions is required. PMID:25885785

  8. Glucose Sensing

    CERN Document Server

    Geddes, Chris D

    2006-01-01

    Topics in Fluorescence Spectroscopy, Glucose Sensing is the eleventh volume in the popular series Topics in Fluorescence Spectroscopy, edited by Drs. Chris D. Geddes and Joseph R. Lakowicz. This volume incorporates authoritative analytical fluorescence-based glucose sensing reviews specialized enough to be attractive to professional researchers, yet also appealing to the wider audience of scientists in related disciplines of fluorescence. Glucose Sensing is an essential reference for any lab working in the analytical fluorescence glucose sensing field. All academics, bench scientists, and industry professionals wishing to take advantage of the latest and greatest in the continuously emerging field of glucose sensing, and diabetes care & management, will find this volume an invaluable resource. Topics in Fluorescence Spectroscopy Volume 11, Glucose Sensing Chapters include: Implantable Sensors for Interstitial Fluid Smart Tattoo Glucose Sensors Optical Enzyme-based Glucose Biosensors Plasmonic Glucose Sens...

  9. Autonomous component carrier selection

    DEFF Research Database (Denmark)

    Garcia, Luis Guilherme Uzeda; Pedersen, Klaus; Mogensen, Preben

    2009-01-01

    in local areas, basing our study case on LTE-Advanced. We present extensive network simulation results to demonstrate that a simple and robust interference management scheme, called autonomous component carrier selection allows each cell to select the most attractive frequency configuration; improving...... management and efficient system operation. Due to the expected large number of user-deployed cells, centralized network planning becomes unpractical and new scalable alternatives must be sought. In this article, we propose a fully distributed and scalable solution to the interference management problem...

  10. Force sensing

    OpenAIRE

    Sanders, David

    2007-01-01

    A young child can explore and learn and compensate for unknown dynamics by prodding, pushing, touching, grasping and feeling. Force sensing and software research could soon allow artificial mechanisms to do the same. Force sensing has its roots in strain gauges, piezoelectrics, Wheatstone bridges, automation, robotics, grippers and virtual reality. That force sensing research has now become commonplace and has expanded from those roots to include so much more: video games, athletic equipment,...

  11. Fundamental Analysis of the Linear Multiple Regression Technique for Quantification of Water Quality Parameters from Remote Sensing Data. Ph.D. Thesis - Old Dominion Univ.

    Science.gov (United States)

    Whitlock, C. H., III

    1977-01-01

    Constituents with linear radiance gradients with concentration may be quantified from signals which contain nonlinear atmospheric and surface reflection effects for both homogeneous and non-homogeneous water bodies provided accurate data can be obtained and nonlinearities are constant with wavelength. Statistical parameters must be used which give an indication of bias as well as total squared error to insure that an equation with an optimum combination of bands is selected. It is concluded that the effect of error in upwelled radiance measurements is to reduce the accuracy of the least square fitting process and to increase the number of points required to obtain a satisfactory fit. The problem of obtaining a multiple regression equation that is extremely sensitive to error is discussed.

  12. Multiple emulsions: an overview.

    Science.gov (United States)

    Khan, Azhar Yaqoob; Talegaonkar, Sushama; Iqbal, Zeenat; Ahmed, Farhan Jalees; Khar, Roop Krishan

    2006-10-01

    Multiple emulsions are complex polydispersed systems where both oil in water and water in oil emulsion exists simultaneously which are stabilized by lipophillic and hydrophilic surfactants respectively. The ratio of these surfactants is important in achieving stable multiple emulsions. Among water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) type multiple emulsions, the former has wider areas of application and hence are studied in great detail. Formulation, preparation techniques and in vitro characterization methods for multiple emulsions are reviewed. Various factors affecting the stability of multiple emulsions and the stabilization approaches with specific reference to w/o/w type multiple emulsions are discussed in detail. Favorable drug release mechanisms and/or rate along with in vivo fate of multiple emulsions make them a versatile carrier. It finds wide range of applications in controlled or sustained drug delivery, targeted delivery, taste masking, bioavailability enhancement, enzyme immobilization, etc. Multiple emulsions have also been employed as intermediate step in the microencapsulation process and are the systems of increasing interest for the oral delivery of hydrophilic drugs, which are unstable in gastrointestinal tract like proteins and peptides. With the advancement in techniques for preparation, stabilization and rheological characterization of multiple emulsions, it will be able to provide a novel carrier system for drugs, cosmetics and pharmaceutical agents. In this review, emphasis is laid down on formulation, stabilization techniques and potential applications of multiple emulsion system. PMID:17076645

  13. LWS/SET Technology Experiment Carrier

    Science.gov (United States)

    Sherman, Barry; Giffin, Geoff

    2002-01-01

    This paper examines the approach taken to building a low-cost, modular spacecraft bus that can be used to support a variety of technology experiments in different space environments. It describes the techniques used and design drivers considered to ensure experiment independence from as yet selected host spacecraft. It describes the technology experiment carriers that will support NASA's Living With a Star Space Environment Testbed space missions. NASA has initiated the Living With a Star (LWS) Program to develop a better scientific understanding to address the aspects of the connected Sun-Earth system that affect life and society. A principal goal of the program is to bridge the gap between science, engineering, and user application communities. The Space Environment Testbed (SET) Project is one element of LWS. The Project will enable future science, operational, and commercial objectives in space and atmospheric environments by improving engineering approaches to the accommodation and/or mitigation of the effects of solar variability on technological systems. The SET Project is highly budget constrained and must seek to take advantage of as yet undetermined partnering opportunities for access to space. SET will conduct technology validation experiments hosted on available flight opportunities. The SET Testbeds will be developed in a manner that minimizes the requirements for accommodation, and will be flown as flight opportunities become available. To access the widest range of flight opportunities, two key development requirements are to maintain flexibility with respect to accommodation constraints and to have the capability to respond quickly to flight opportunities. Experiments, already developed to the technology readiness level of needing flight validation in the variable Sun-Earth environment, will be selected on the basis of the need for the subject technology, readiness for flight, need for flight resources and particular orbit. Experiments will be

  14. Cooperatively active sensing system

    International Nuclear Information System (INIS)

    Aiming at development of a strong and flexible sensing system, a study on a sensing technology prepared with cooperativity, activity, and real time workability has been promoted. In the former period, together with preparation of plural moving robot group with real time processing capacity of a lot of sensor informations composing of platform, a parallel object direction language Eus Lisp effectively capable of describing and executing cooperative processing and action therewith was developed. And, it was also shown that capacity to adaptively act even at dynamic environment could be learnt experientially. And, on processing of individual sensor information, application of a photographing system with multiple resolution property similar to human visual sense property was attempted. In the latter period, together with intending of upgrading on adaptability of sensing function, by using moving robot group in center of a moving robot loaded with active visual sense, a cooperative active sensing prototype system was constructed to show effectiveness of this study through evaluation experiment of patrolling inspection at plant simulating environment. (G.K.)

  15. "I'm Healthy, It's Not Going To Be Me": Exploring experiences of carriers identified through a population reproductive genetic carrier screening panel in Australia.

    Science.gov (United States)

    Beard, Catherine A; Amor, David J; Di Pietro, Louisa; Archibald, Alison D

    2016-08-01

    Advancing genetic testing technologies mean that population-based carrier screening for multiple inherited conditions is now available. As the number of genetic conditions being screened increases, there is a need for research into how people experience these screening programs. This research aimed to explore how women experience simultaneous carrier screening for three inherited conditions: cystic fibrosis (CF), spinal muscular atrophy (SMA), and fragile X syndrome (FXS). A qualitative approach was adopted using in-depth semi-structured interviews to explore the experiences of ten female participants: five SMA carriers, three CF carriers, and two FXS premutation carriers. Eight participants were pregnant when offered screening by their general practitioner or obstetrician and the decision to have screening was described as straightforward. Participants reported experiencing emotional responses such as anxiety and stress while waiting for either their partner's carrier screen result (CF or SMA carriers) or the pregnancy's CVS result (FXS carrier) and sought additional information about the relevant condition during this time. Most participants were in favor of population carrier screening for these conditions, preferably prior to conception. Genetic counselors played an essential role in supporting couples after they received a carrier result given the variable consent processes undertaken when screening was offered. Further research should focus on the development of reliable online information tailored to people receiving carrier results and strategies for raising awareness of the availability of population carrier screening within the community. © 2016 Wiley Periodicals, Inc. PMID:27150953

  16. Health Participatory Sensing Networks

    Directory of Open Access Journals (Sweden)

    Andrew Clarke

    2014-01-01

    Full Text Available The use of participatory sensing in relation to the capture of health-related data is rapidly becoming a possibility due to the widespread consumer adoption of emerging mobile computing technologies and sensing platforms. This has the potential to revolutionize data collection for population health, aspects of epidemiology, and health-related e-Science applications and as we will describe, provide new public health intervention capabilities, with the classifications and capabilities of such participatory sensing platforms only just beginning to be explored. Such a development will have important benefits for access to near real-time, large-scale, up to population-scale data collection. However, there are also numerous issues to be addressed first: provision of stringent anonymity and privacy within these methodologies, user interface issues, and the related issue of how to incentivize participants and address barriers/concerns over participation. To provide a step towards describing these aspects, in this paper we present a first classification of health participatory sensing models, a novel contribution to the literature, and provide a conceptual reference architecture for health participatory sensing networks (HPSNs and user interaction example case study.

  17. Broadband Wireline Provider Service: Optical Carrier - Fiber to the End User; BBRI_fiber12

    Data.gov (United States)

    University of Rhode Island Geospatial Extension Program — This dataset represents the availability of wireline broadband Internet access in Rhode Island via "Optical Carrier - Fiber to the End User" technology. Broadband...

  18. Decision Analysis of Dynamic Spectrum Access Rules

    Energy Technology Data Exchange (ETDEWEB)

    Juan D. Deaton; Luiz A. DaSilva; Christian Wernz

    2011-12-01

    A current trend in spectrum regulation is to incorporate spectrum sharing through the design of spectrum access rules that support Dynamic Spectrum Access (DSA). This paper develops a decision-theoretic framework for regulators to assess the impacts of different decision rules on both primary and secondary operators. We analyze access rules based on sensing and exclusion areas, which in practice can be enforced through geolocation databases. Our results show that receiver-only sensing provides insufficient protection for primary and co-existing secondary users and overall low social welfare. On the other hand, using sensing information between the transmitter and receiver of a communication link, provides dramatic increases in system performance. The performance of using these link end points is relatively close to that of using many cooperative sensing nodes associated to the same access point and large link exclusion areas. These results are useful to regulators and network developers in understanding in developing rules for future DSA regulation.

  19. Enhancing Carrier-To-Noise Ratio In Optical Cdma-Based Fiber Radio Networks

    Directory of Open Access Journals (Sweden)

    Surya.R

    2013-06-01

    Full Text Available A Bi-Directional fiber radio networks based on spectral Amplitude Coding (SAC optical Code Division Multiple Access (OCDMA with interference elimination is proposed. Here in this scheme hybrid ring/star topology is used with partial self healing ability and its key feature is to eliminate addition of direct current signal before the optical encoding process. As compared to previous SAC- based fiber radio network the proposed scheme improves both power efficiency and Carrier-to –noise ratio at the decoder. Adding to these improvement simple encoding / decoding structures with small sizes in the control base station is proposed to reduce the cost of the today’s mobile radio networks with large number of remote base stations.

  20. Commerical Remote Sensing Data Contract

    Science.gov (United States)

    U.S. Geological Survey

    2005-01-01

    The U. S. Geological Survey's (USGS) Commercial Remote Sensing Data Contracts (CRSDCs) provide government agencies with access to a broad range of commercially available remotely sensed airborne and satellite data. These contracts were established to support The National Map partners, other Federal Civilian agency programs, and Department of Defense programs that require data for the United States and its territories. Experience shows that centralized procurement of remotely sensed data leads to considerable cost savings to the Federal government through volume discounts, reduction of redundant contract administrative costs, and avoidance of duplicate purchases. These contracts directly support the President's Commercial Remote Sensing Space Policy, signed in 2003, by providing a centralized mechanism for civil agencies to acquire commercial remote sensing products to support their mission needs in an efficient and coordinated way. CRSDC administration is provided by the USGS Mid-Continent Mapping Center in Rolla, Missouri.