Beamforming-Based Physical Layer Network Coding for Non-Regenerative Multi-Way Relaying

Directory of Open Access Journals (Sweden)

Klein Anja

2010-01-01

Full Text Available We propose non-regenerative multi-way relaying where a half-duplex multi-antenna relay station (RS assists multiple single-antenna nodes to communicate with each other. The required number of communication phases is equal to the number of the nodes, N. There are only one multiple-access phase, where the nodes transmit simultaneously to the RS, and broadcast (BC phases. Two transmission methods for the BC phases are proposed, namely, multiplexing transmission and analog network coded transmission. The latter is a cooperation method between the RS and the nodes to manage the interference in the network. Assuming that perfect channel state information is available, the RS performs transceive beamforming to the received signals and transmits simultaneously to all nodes in each BC phase. We address the optimum transceive beamforming maximising the sum rate of non-regenerative multi-way relaying. Due to the nonconvexity of the optimization problem, we propose suboptimum but practical signal processing schemes. For multiplexing transmission, we propose suboptimum schemes based on zero forcing, minimising the mean square error, and maximising the signal to noise ratio. For analog network coded transmission, we propose suboptimum schemes based on matched filtering and semidefinite relaxation of maximising the minimum signal to noise ratio. It is shown that analog network coded transmission outperforms multiplexing transmission.

Tightness of Semidefinite Programming Relaxation to Robust Transmit Beamforming with SINR Constraints

Directory of Open Access Journals (Sweden)

Yanjun Wang

2013-01-01

Full Text Available This paper considers a multiuser transmit beamforming problem under uncertain channel state information (CSI subject to SINR constraints in a downlink multiuser MISO system. A robust transmit beamforming formulation is proposed. This robust formulation is to minimize the transmission power subject to worst-case signal-to-interference-plus-noise ratio (SINR constraints on the receivers. The challenging problem is that the worst-case SINR constraints correspond to an infinite number of nonconvex quadratic constraints. In this paper, a natural semidifinite programming (SDP relaxation problem is proposed to solve the robust beamforming problem. The main contribution of this paper is to establish the tightness of the SDP relaxation problem under proper assumption, which means that the SDP relaxation problem definitely yields rank-one solutions under the assumption. Then the SDP relaxation problem provides globally optimum solutions of the primal robust transmit beamforming problem under proper assumption and norm-constrained CSI errors. Simulation results show the correctness of the proposed theoretical results and also provide a counterexample whose solutions are not rank one. The existence of counterexample shows that the guess that the solutions of the SDP relaxation problem must be rank one is wrong, except that some assumptions (such as the one proposed in this paper hold.

Efficient high-performance ultrasound beamforming using oversampling

Science.gov (United States)

Freeman, Steven R.; Quick, Marshall K.; Morin, Marc A.; Anderson, R. C.; Desilets, Charles S.; Linnenbrink, Thomas E.; O'Donnell, Matthew

1998-05-01

High-performance and efficient beamforming circuitry is very important in large channel count clinical ultrasound systems. Current state-of-the-art digital systems using multi-bit analog to digital converters (A/Ds) have matured to provide exquisite image quality with moderate levels of integration. A simplified oversampling beamforming architecture has been proposed that may a low integration of delta-sigma A/Ds onto the same chip as digital delay and processing circuitry to form a monolithic ultrasound beamformer. Such a beamformer may enable low-power handheld scanners for high-end systems with very large channel count arrays. This paper presents an oversampling beamformer architecture that generates high-quality images using very simple; digitization, delay, and summing circuits. Additional performance may be obtained with this oversampled system for narrow bandwidth excitations by mixing the RF signal down in frequency to a range where the electronic signal to nose ratio of the delta-sigma A/D is optimized. An oversampled transmit beamformer uses the same delay circuits as receive and eliminates the need for separate transmit function generators.

Decentralized Group Sparse Beamforming for Multi-Cloud Radio Access Networks

KAUST Repository

Dhifallah, Oussama Najeeb

2015-12-06

Recent studies on cloud-radio access networks (CRANs) assume the availability of a single processor (cloud) capable of managing the entire network performance; inter-cloud interference is treated as background noise. This paper considers the more practical scenario of the downlink of a CRAN formed by multiple clouds, where each cloud is connected to a cluster of multiple-antenna base stations (BSs) via high-capacity wireline backhaul links. The network is composed of several disjoint BSs\\' clusters, each serving a pre-known set of single-antenna users. To account for both inter- cloud and intra-cloud interference, the paper considers the problem of minimizing the total network power consumption subject to quality of service constraints, by jointly determining the set of active BSs connected to each cloud and the beamforming vectors of every user across the network. The paper solves the problem using Lagrangian duality theory through a dual decomposition approach, which decouples the problem into multiple and independent subproblems, the solution of which depends on the dual optimization problem. The solution then proceeds in updating the dual variables and the active set of BSs at each cloud iteratively. The proposed approach leads to a distributed implementation across the multiple clouds through a reasonable exchange of information between adjacent clouds. The paper further proposes a centralized solution to the problem. Simulation results suggest that the proposed algorithms significantly outperform the conventional per-cloud update solution, especially at high signal-to-interference-plus- noise ratio (SINR) target.

A Delta-Sigma beamformer with integrated apodization

DEFF Research Database (Denmark)

Tomov, Borislav Gueorguiev; Stuart, Matthias Bo; Hemmsen, Martin Christian

2013-01-01

This paper presents a new design of a discrete time Delta-Sigma (ΔΣ) oversampled ultrasound beamformer which integrates individual channel apodization by means of variable feedback voltage in the Delta-Sigma analog to digital (A/D) converters. The output bit-width of each oversampled A/D converter...... remains the same as in an unmodified one. The outputs of all receiving channels are delayed and summed, and the resulting multi-bit sample stream is filtered and decimated to become an image line. The simplicity of this beamformer allows the production of high-channel-count or very compact beamformers....... The data are acquired using 12-bit flash A/D converters at a sampling rate of 70 MHz, and are then upsampled off-line to 560 MHz for input to the simulated ΔΣ beamformer. The latter generates a B-mode image which is compared to that produced by a digital beamformer that uses 10-bit A/D converters...

Near-field self-interference cancellation and quality of service multicast beamforming in full-duplex

Science.gov (United States)

Wu, Fei; Shao, Shihai; Tang, Youxi

2016-10-01

To enable simultaneous multicast downlink transmit and receive operations on the same frequency band, also known as full-duplex links between an access point and mobile users. The problem of minimizing the total power of multicast transmit beamforming is considered from the viewpoint of ensuring the suppression amount of near-field line-of-sight self-interference and guaranteeing prescribed minimum signal-to-interference-plus-noise-ratio (SINR) at each receiver of the multicast groups. Based on earlier results for multicast groups beamforming, the joint problem is easily shown to be NP-hard. A semidefinite relaxation (SDR) technique with linear program power adjust method is proposed to solve the NP-hard problem. Simulation shows that the proposed method is feasible even when the local receive antenna in nearfield and the mobile user in far-filed are in the same direction.

Analysis of Simulated and Measured Indoor Channels for mm-Wave Beamforming Applications

DEFF Research Database (Denmark)

Karstensen, Anders; Fan, Wei; Zhang, Fengchun

2018-01-01

was investigated using both single beam and multiple beams, with two different power allocation schemes applied to multi-beamforming. Channel measurements were performed at 28-30 GHz using a vector network analyzer equipped with a Biconical antenna as the transmit antenna and a rotated horn antenna as the receive...... antenna. 3D ray tracing simulations were carried out in the same replicated propagation environments. Based on measurement and ray tracing simulation data, it is shown that RT-assisted beamforming performs well both for single and multi-beamforming in these two representative indoor propagation...

Interference management with partial uplink/downlink spectrum overlap

KAUST Repository

Randrianantenaina, Itsikiantsoa

2016-07-26

Simultaneous reuse of spectral resources by uplink and downlink, denoted as in-band full duplex (FD) communication, is promoted to double the spectral efficiency when compared to its half-duplex (HD) counterpart. Interference management, however, remains challenging in FD cellular networks, especially when high disparity between uplink and downlink transmission powers exists. The uplink performance can be particularly deteriorated when operating on channels that are simultaneously occupied with downlink transmission. This paper considers a cellular wireless system with partial spectrum overlap between the downlink and uplink. The performance of the system becomes, therefore, a function of the overlap fraction, as well as the power levels of both the uplink and downlink transmissions. The paper considers the problem of maximizing an overall network utility to find the uplink/downlink transmission powers and the spectrum overlap fraction between the uplink and downlink spectrum in each cell, and proposes solving the problem using interior point method. Simulations results confirm the vulnerability of the uplink performance to the FD operation, and show the superiority of the proposed scheme over the FD and HD schemes. The results further show that explicit uplink and downlink performance should be considered for efficient design of cellular networks with overlapping uplink/downlink resources. © 2016 IEEE.

A Space-Time Signal Decomposition Algorithm for Downlink MIMO DS-CDMA Receivers

Science.gov (United States)

Wang, Yung-Yi; Fang, Wen-Hsien; Chen, Jiunn-Tsair

We propose a dimension reduction algorithm for the receiver of the downlink of direct-sequence code-division multiple access (DS-CDMA) systems in which both the transmitters and the receivers employ antenna arrays of multiple elements. To estimate the high order channel parameters, we develop a layered architecture using dimension-reduced parameter estimation algorithms to estimate the frequency-selective multipath channels. In the proposed architecture, to exploit the space-time geometric characteristics of multipath channels, spatial beamformers and constrained (or unconstrained) temporal filters are adopted for clustered-multipath grouping and path isolation. In conjunction with the multiple access interference (MAI) suppression techniques, the proposed architecture jointly estimates the direction of arrivals, propagation delays, and fading amplitudes of the downlink fading multipaths. With the outputs of the proposed architecture, the signals of interest can then be naturally detected by using path-wise maximum ratio combining. Compared to the traditional techniques, such as the Joint-Angle-and-Delay-Estimation (JADE) algorithm for DOA-delay joint estimation and the space-time minimum mean square error (ST-MMSE) algorithm for signal detection, computer simulations show that the proposed algorithm substantially mitigate the computational complexity at the expense of only slight performance degradation.

Transmit Power Optimisation in Wireless Network

Directory of Open Access Journals (Sweden)

Besnik Terziu

2011-09-01

Full Text Available Transmit power optimisation in wireless networks based on beamforming have emerged as a promising technique to enhance the spectrum efficiency of present and future wireless communication systems. The aim of this study is to minimise the access point power consumption in cellular networks while maintaining a targeted quality of service (QoS for the mobile terminals. In this study, the targeted quality of service is delivered to a mobile station by providing a desired level of Signal to Interference and Noise Ratio (SINR. Base-stations are coordinated across multiple cells in a multi-antenna beamforming system. This study focuses on a multi-cell multi-antenna downlink scenario where each mobile user is equipped with a single antenna, but where multiple mobile users may be active simultaneously in each cell and are separated via spatial multiplexing using beamforming. The design criteria is to minimize the total weighted transmitted power across the base-stations subject to SINR constraints at the mobile users. The main contribution of this study is to define an iterative algorithm that is capable of finding the joint optimal beamformers for all basestations, based on a correlation-based channel model, the full-correlation model. Among all correlated channel models, the correlated channel model used in this study is the most accurate, giving the best performance in terms of power consumption. The environment here in this study is chosen to be Non-Light of- Sight (NLOS condition, where a signal from a wireless transmitter passes several obstructions before arriving at a wireless receiver. Moreover there are many scatterers local to the mobile, and multiple reflections can occur among them before energy arrives at the mobile. The proposed algorithm is based on uplink-downlink duality using the Lagrangian duality theory. Time-Division Duplex (TDD is chosen as the platform for this study since it has been adopted to the latest technologies in Fourth

Impact of Users Identities and Access Conditions on Downlink Performance in Closed Small-Cell Networks

KAUST Repository

Radaydeh, Redha; Gaaloul, Fakhreddine; Alouini, Mohamed-Slim

2015-01-01

This paper investigates the effect of various operation parameters on the downlink user performance in overlaid small-cell networks. The case study considers closed-access small cells (e.g., femtocells), wherein only active authorized user

Optimal Multiuser Diversity in Multi-Cell MIMO Uplink Networks: User Scaling Law and Beamforming Design

Directory of Open Access Journals (Sweden)

Bang Chul Jung

2017-07-01

Full Text Available We introduce a distributed protocol to achieve multiuser diversity in a multicell multiple-input multiple-output (MIMO uplink network, referred to as a MIMO interfering multiple-access channel (IMAC. Assuming both no information exchange among base stations (BS and local channel state information at the transmitters for the MIMO IMAC, we propose a joint beamforming and user scheduling protocol, and then show that the proposed protocol can achieve the optimal multiuser diversity gain, i.e., KMlog(SNRlog N, as long as the number of mobile stations (MSs in a cell, N, scales faster than SNR K M − L 1 − ϵ for a small constant ϵ > 0, where M, L, K, and SNR denote the number of receive antennas at each BS, the number of transmit antennas at each MS, the number of cells, and the signal-to-noise ratio, respectively. Our result indicates that multiuser diversity can be achieved in the presence of intra-cell and inter-cell interference even in a distributed fashion. As a result, vital information on how to design distributed algorithms in interference-limited cellular environments is provided.

Distributed Multi-Cell Resource Allocation with Price Based ICI Coordination in Downlink OFDMA Networks

Science.gov (United States)

Lv, Gangming; Zhu, Shihua; Hui, Hui

Multi-cell resource allocation under minimum rate request for each user in OFDMA networks is addressed in this paper. Based on Lagrange dual decomposition theory, the joint multi-cell resource allocation problem is decomposed and modeled as a limited-cooperative game, and a distributed multi-cell resource allocation algorithm is thus proposed. Analysis and simulation results show that, compared with non-cooperative iterative water-filling algorithm, the proposed algorithm can remarkably reduce the ICI level and improve overall system performances.

Performance of Downlink UTRAN LTE under Control Channel Constraints

DEFF Research Database (Denmark)

López Villa, Dimas; Úbeda Castellanos, Carlos; Kovács, István Z.

2008-01-01

Dynamic time-frequency domain packet scheduling algorithms in the shared channel of downlink orthogonal Frequency Division Multiple Access (OFDMA) systems have been shown to achieve high multi-user diversity scheduling gains. However, the flexibility is obtained at the cost of additional control ...

SINR balancing in the downlink of cognitive radio networks with imperfect channel knowledge

KAUST Repository

Hanif, Muhammad Fainan

2010-01-01

In this paper we consider the problem of signal-to-interference-plus-noise ratio (SINR) balancing in the downlink of cognitive radio (CR) networks while simultaneously keeping interference levels at primary user (PU) receivers (RXs) below an acceptable threshold with uncertain channel state information available at the CR base-station (BS). We optimize the beamforming vectors at the CR BS so that the worst user SINR is maximized and transmit power constraints at the CR BS and interference constraints at the PU RXs are satisfied. With uncertainties in the channel bounded by a Euclidean ball, the semidefinite program (SDP) modeling the balancing problem is solved using the recently developed convex iteration technique without relaxing the rank constraints. Numerical simulations are conducted to show the effectiveness of the proposed technique in comparison to known approximations.

Synthetic aperture ultrasound Fourier beamformation using virtual sources

DEFF Research Database (Denmark)

Moghimirad, Elahe; Villagómez Hoyos, Carlos Armando; Mahloojifar, Ali

2016-01-01

An efficient Fourier beamformation algorithm is presented for multistatic synthetic aperture ultrasound imaging using virtual sources (FBV). The concept is based on the frequency domain wavenumber algorithm from radar and sonar and is extended to a multi-element transmit/receive configuration using...

Fundamentals of differential beamforming

CERN Document Server

Benesty, Jacob; Pan, Chao

2016-01-01

This book provides a systematic study of the fundamental theory and methods of beamforming with differential microphone arrays (DMAs), or differential beamforming in short. It begins with a brief overview of differential beamforming and some popularly used DMA beampatterns such as the dipole, cardioid, hypercardioid, and supercardioid, before providing essential background knowledge on orthogonal functions and orthogonal polynomials, which form the basis of differential beamforming. From a physical perspective, a DMA of a given order is defined as an array that measures the differential acoustic pressure field of that order; such an array has a beampattern in the form of a polynomial whose degree is equal to the DMA order. Therefore, the fundamental and core problem of differential beamforming boils down to the design of beampatterns with orthogonal polynomials. But certain constraints also have to be considered so that the resulting beamformer does not seriously amplify the sensors’ self noise and the mism...

An acousto-optic beamformer

DEFF Research Database (Denmark)

Torras Rosell, Antoni; Barrera Figueroa, Salvador; Jacobsen, Finn

2012-01-01

There is a great variety of beamforming techniques that can be used for localization of sound sources. The differences among them usually lie in the array layout or in the specific signal processing algorithm used to compute the beamforming output. Any beamforming system consists of a finite numb...

Performance analysis of coordination strategies in two-tier Heterogeneous Networks

KAUST Repository

Boukhedimi, Ikram; Kammoun, Abla; Alouini, Mohamed-Slim

2016-01-01

Large scale multi-tier Heterogeneous Networks (HetNets) are expected to ensure a consistent quality of service (QoS) in 5G systems. Such networks consist of a macro base station (BS) equipped with a large number of antennas and a dense overlay of small cells. The small cells could be deployed within the same coverage of the macro-cell BS, thereby causing high levels of inter-cell interference. In this regard, coordinated beamforming techniques are considered as a viable solution to counteract the arising interference. The goal of this work is to analyze the efficiency of coordinated beamforming techniques in mitigating both intra-cell and inter-cell interference. In particular, we consider the downlink of a Time-division duplexing (TDD) massive multiple-input-multiple-output (MIMO) tier-HetNet and analyze different beamforming schemes together with different degrees of coordination between the BSs. We exploit random matrix theory tools in order to provide, in explicit form, deterministic equivalents for the average achievable rates in the macro-cell and the micro-cells. We prove that our theoretical derivations allow us to draw some conclusions regarding the role played by coordination strategies in reducing the inter-cell interference. These findings are finally validated by a selection of some numerical results. © 2016 IEEE.

Performance analysis of coordination strategies in two-tier Heterogeneous Networks

KAUST Repository

Boukhedimi, Ikram

2016-08-11

Large scale multi-tier Heterogeneous Networks (HetNets) are expected to ensure a consistent quality of service (QoS) in 5G systems. Such networks consist of a macro base station (BS) equipped with a large number of antennas and a dense overlay of small cells. The small cells could be deployed within the same coverage of the macro-cell BS, thereby causing high levels of inter-cell interference. In this regard, coordinated beamforming techniques are considered as a viable solution to counteract the arising interference. The goal of this work is to analyze the efficiency of coordinated beamforming techniques in mitigating both intra-cell and inter-cell interference. In particular, we consider the downlink of a Time-division duplexing (TDD) massive multiple-input-multiple-output (MIMO) tier-HetNet and analyze different beamforming schemes together with different degrees of coordination between the BSs. We exploit random matrix theory tools in order to provide, in explicit form, deterministic equivalents for the average achievable rates in the macro-cell and the micro-cells. We prove that our theoretical derivations allow us to draw some conclusions regarding the role played by coordination strategies in reducing the inter-cell interference. These findings are finally validated by a selection of some numerical results. © 2016 IEEE.

Robustness Beamforming Algorithms

Directory of Open Access Journals (Sweden)

Sajad Dehghani

2014-04-01

Full Text Available Adaptive beamforming methods are known to degrade in the presence of steering vector and covariance matrix uncertinity. In this paper, a new approach is presented to robust adaptive minimum variance distortionless response beamforming make robust against both uncertainties in steering vector and covariance matrix. This method minimize a optimization problem that contains a quadratic objective function and a quadratic constraint. The optimization problem is nonconvex but is converted to a convex optimization problem in this paper. It is solved by the interior-point method and optimum weight vector to robust beamforming is achieved.

Multidimensional-DSP Beamformers Using the ROACH-2 FPGA Platform

Directory of Open Access Journals (Sweden)

Vishwa Seneviratne

2017-07-01

Full Text Available Antenna array-based multi-dimensional infinite-impulse response (IIR digital beamformers are employed in a multitude of radio frequency (RF applications ranging from electronically-scanned radar, radio telescopes, long-range detection and target tracking. A method to design 3D IIR beam filters using 2D IIR beam filters is described. A cascaded 2D IIR beam filter architecture is proposed based on systolic array architecture as an alternative for an existing radar application. Differential-form transfer function and polyphase structures are employed in the design to gain an increase in the speed of operation to gigahertz range. The feasibility of practical implementation of a 4-phase polyphase 2D IIR beam filter is explored. A digital hardware prototype is designed, implemented and tested using a ROACH-2 Field Programmable Gate Array (FPGA platform fitted with a Xilinx Virtex-6 SX475T FPGA chip and multi-input analog-to-digital converters (ADC boards set to a maximum sampling rate of 960 MHz. The article describes a method to build a 3D IIR beamformer using polyphase structures. A comparison of technical specifications of an existing radar application based on phased-array and the proposed 3D IIR beamformer is also explained to illustrate the proposed method to be a better alternative for such applications.

Synthetic Aperture Sequential Beamforming

DEFF Research Database (Denmark)

Kortbek, Jacob; Jensen, Jørgen Arendt; Gammelmark, Kim Løkke

2008-01-01

A synthetic aperture focusing (SAF) technique denoted Synthetic Aperture Sequential Beamforming (SASB) suitable for 2D and 3D imaging is presented. The technique differ from prior art of SAF in the sense that SAF is performed on pre-beamformed data contrary to channel data. The objective is to im......A synthetic aperture focusing (SAF) technique denoted Synthetic Aperture Sequential Beamforming (SASB) suitable for 2D and 3D imaging is presented. The technique differ from prior art of SAF in the sense that SAF is performed on pre-beamformed data contrary to channel data. The objective...... is to improve and obtain a more range independent lateral resolution compared to conventional dynamic receive focusing (DRF) without compromising frame rate. SASB is a two-stage procedure using two separate beamformers. First a set of Bmode image lines using a single focal point in both transmit and receive...... is stored. The second stage applies the focused image lines from the first stage as input data. The SASB method has been investigated using simulations in Field II and by off-line processing of data acquired with a commercial scanner. The performance of SASB with a static image object is compared with DRF...

Distributed Robust Power Minimization for the Downlink of Multi-Cloud Radio Access Networks

KAUST Repository

Dhifallah, Oussama Najeeb

2017-02-07

Conventional cloud radio access networks assume single cloud processing and treat inter-cloud interference as background noise. This paper considers the downlink of a multi-cloud radio access network (CRAN) where each cloud is connected to several base-stations (BS) through limited-capacity wireline backhaul links. The set of BSs connected to each cloud, called cluster, serves a set of pre-known mobile users (MUs). The performance of the system becomes therefore a function of both inter-cloud and intra-cloud interference, as well as the compression schemes of the limited capacity backhaul links. The paper assumes independent compression scheme and imperfect channel state information (CSI) where the CSI errors belong to an ellipsoidal bounded region. The problem of interest becomes the one of minimizing the network total transmit power subject to BS power and quality of service constraints, as well as backhaul capacity and CSI error constraints. The paper suggests solving the problem using the alternating direction method of multipliers (ADMM). One of the highlight of the paper is that the proposed ADMM-based algorithm can be implemented in a distributed fashion across the multi-cloud network by allowing a limited amount of information exchange between the coupled clouds. Simulation results show that the proposed distributed algorithm provides a similar performance to the centralized algorithm in a reasonable number of iterations.

Highly Reconfigurable Beamformer Stimulus Generator

Science.gov (United States)

Vaviļina, E.; Gaigals, G.

2018-02-01

The present paper proposes a highly reconfigurable beamformer stimulus generator of radar antenna array, which includes three main blocks: settings of antenna array, settings of objects (signal sources) and a beamforming simulator. Following from the configuration of antenna array and object settings, different stimulus can be generated as the input signal for a beamformer. This stimulus generator is developed under a greater concept with two utterly independent paths where one is the stimulus generator and the other is the hardware beamformer. Both paths can be complemented in final and in intermediate steps as well to check and improve system performance. This way the technology development process is promoted by making each of the future hardware steps more substantive. Stimulus generator configuration capabilities and test results are presented proving the application of the stimulus generator for FPGA based beamforming unit development and tuning as an alternative to an actual antenna system.

Compact Beamformer Design with High Frame Rate for Ultrasound Imaging

Directory of Open Access Journals (Sweden)

Jun Luo

2014-04-01

Full Text Available In medical field, two-dimension ultrasound images are widely used in clinical diagnosis. Beamformer is critical in determining the complexity and performance of an ultrasound imaging system. Different from traditional means implemented with separated chips, a compact beamformer with 64 effective channels in a single moderate Field Programmable Gate Array has been presented in this paper. The compactness is acquired by employing receive synthetic aperture, harmonic imaging, time sharing and linear interpolation. Besides that, multi-beams method is used to improve the frame rate of the ultrasound imaging system. Online dynamic configuration is employed to expand system’s flexibility to two kinds of transducers with multi-scanning modes. The design is verified on a prototype scanner board. Simulation results have shown that on-chip memories can be saved and the frame rate can be improved on the case of 64 effective channels which will meet the requirement of real-time application.

Adaptive Beamforming for Medical Ultrasound Imaging

DEFF Research Database (Denmark)

Holfort, Iben Kraglund

This dissertation investigates the application of adaptive beamforming for medical ultrasound imaging. The investigations have been concentrated primarily on the Minimum Variance (MV) beamformer. A broadband implementation of theMV beamformer is described, and simulated data have been used...... to demonstrate the performance. The MV beamformer has been applied to different sets of ultrasound imaging sequences; synthetic aperture ultrasound imaging and plane wave ultrasound imaging. And an approach for applying MV optimized apodization weights on both the transmitting and the receiving apertures...

Highly Reconfigurable Beamformer Stimulus Generator

Directory of Open Access Journals (Sweden)

Vaviļina E.

2018-02-01

Full Text Available The present paper proposes a highly reconfigurable beamformer stimulus generator of radar antenna array, which includes three main blocks: settings of antenna array, settings of objects (signal sources and a beamforming simulator. Following from the configuration of antenna array and object settings, different stimulus can be generated as the input signal for a beamformer. This stimulus generator is developed under a greater concept with two utterly independent paths where one is the stimulus generator and the other is the hardware beamformer. Both paths can be complemented in final and in intermediate steps as well to check and improve system performance. This way the technology development process is promoted by making each of the future hardware steps more substantive. Stimulus generator configuration capabilities and test results are presented proving the application of the stimulus generator for FPGA based beamforming unit development and tuning as an alternative to an actual antenna system.

ESPRIT with multiple-angle subarray beamforming

Science.gov (United States)

Xu, Wen; Jiang, Ying; Zhang, Huiquan

2012-12-01

This article presents a new approach of implementing signal direction-of-arrival estimation, in which subarray beamforming is applied prior to estimation of signal parameters via rotational invariance techniques (ESPRIT). Different from the previous approaches, the beam-domain data from multiple adjacent pointing angles are combined in a way that the displacement invariance structure required by ESPRIT is maintained. It is intended to further obtain a sub-beamwidth resolution for a conventional multi-beam system already having small beamwidths. Computer simulations show that for typical multi-beam system applications the new approach provides improved estimation mean-square errors over the original ESPRIT, on top of reduced requirements for signal-to-noise ratio, number of snapshots, and computational time.

Energy efficiency and SINR maximization beamformers for cognitive radio utilizing sensing information

KAUST Repository

Alabbasi, Abdulrahman

2014-06-01

In this paper we consider a cognitive radio multi-input multi-output environment in which we adapt our beamformer to maximize both energy efficiency and signal to interference plus noise ratio (SINR) metrics. Our design considers an underlaying communication using adaptive beamforming schemes combined with the sensing information to achieve an optimal energy efficient system. The proposed schemes maximize the energy efficiency and SINR metrics subject to cognitive radio and quality of service constraints. Since the optimization of energy efficiency problem is not a convex problem, we transform it into a standard semi-definite programming (SDP) form to guarantee a global optimal solution. Analytical solution is provided for one scheme, while the other scheme is left in a standard SDP form. Selected numerical results are used to quantify the impact of the sensing information on the proposed schemes compared to the benchmark ones.

Multiline 3D beamforming using micro-beamformed datasets for pediatric transesophageal echocardiography

Science.gov (United States)

Bera, D.; Raghunathan, S. B.; Chen, C.; Chen, Z.; Pertijs, M. A. P.; Verweij, M. D.; Daeichin, V.; Vos, H. J.; van der Steen, A. F. W.; de Jong, N.; Bosch, J. G.

2018-04-01

Until now, no matrix transducer has been realized for 3D transesophageal echocardiography (TEE) in pediatric patients. In 3D TEE with a matrix transducer, the biggest challenges are to connect a large number of elements to a standard ultrasound system, and to achieve a high volume rate (>200 Hz). To address these issues, we have recently developed a prototype miniaturized matrix transducer for pediatric patients with micro-beamforming and a small central transmitter. In this paper we propose two multiline parallel 3D beamforming techniques (µBF25 and µBF169) using the micro-beamformed datasets from 25 and 169 transmit events to achieve volume rates of 300 Hz and 44 Hz, respectively. Both the realizations use angle-weighted combination of the neighboring overlapping sub-volumes to avoid artifacts due to sharp intensity changes introduced by parallel beamforming. In simulation, the image quality in terms of the width of the point spread function (PSF), lateral shift invariance and mean clutter level for volumes produced by µBF25 and µBF169 are similar to the idealized beamforming using a conventional single-line acquisition with a fully-sampled matrix transducer (FS4k, 4225 transmit events). For completeness, we also investigated a 9 transmit-scheme (3  ×  3) that allows even higher frame rates but found worse B-mode image quality with our probe. The simulations were experimentally verified by acquiring the µBF datasets from the prototype using a Verasonics V1 research ultrasound system. For both µBF169 and µBF25, the experimental PSFs were similar to the simulated PSFs, but in the experimental PSFs, the clutter level was ~10 dB higher. Results indicate that the proposed multiline 3D beamforming techniques with the prototype matrix transducer are promising candidates for real-time pediatric 3D TEE.

Low-Complexity Interference-Free Downlink Channel Assignment with Improved Performance in Coordinated Small Cells

KAUST Repository

Radaydeh, Redha M.

2015-05-01

This paper proposes a low-complexity interference-free channel assignment scheme with improved desired downlink performance in coordinated multi-antenna small-coverage access points (APs) that employ the open-access control strategy. The adopted system treats the case when each user can be granted an access to one of the available channels at a time. Moreover, each receive terminal can suppress a limited number of resolvable interfering sources via its highly-correlated receive array. On the other hand, the operation of the deployed APs can be coordinated to serve active users, and the availability of multiple physical channels and the use of uncorrelated transmit antennas at each AP are exploited to improve the performance of supported users. The analysis provides new approaches to use the transmit antenna array at each AP, the multiple physical channels, the receive antenna array at each user in order to identify interference-free channels per each user, and then to select a downlink channel that provides the best possible improved performance. The event of concurrent interference-free channel identification by different users is also treated to further improve the desired link associated with the scheduled user. The analysis considers the practical scenario of imperfect identification of interference-free channel by an active user and/or the imperfectness in scheduling concurrent users requests on the same channel. The developed formulations can be used to study any performance metric and they are applicable for any statistical and geometric channel models. © 2015 IEEE.

Interference Mitigation and Sum Rate Optimization for MIMO Downlink Small Cells

Directory of Open Access Journals (Sweden)

H. H. Kha

2016-12-01

Full Text Available This paper addresses interference issues in multiuser multiple-input multiple-output (MIMO downlink heterogeneous networks in which multiple small cells are deployed in macrocell coverage. With the higher priority to access the frequency bands, the macro base station (MBS will exploit eigenmode transmission along with water-filling based power allocation to maximize its data rate. To avoid harmful interference to macro users, we propose structures of the precoders at the small cell BSs (SBSs as cascades of two precoding matrices. In addition, to mitigate intra-tier inference in small cells, the SBSs exploit the user scheduling schemes for their associated users. We investigate two user scheduling schemes using the minimum interference leakage and maximum signal to noise ratio criteria. The sum rate of the selected users can be further improved by power allocation. We develop an iterative algorithm using difference of convex functions (d.c. programming to tackle the mathematical challenges of the nonconvex power allocation problem, Numerical simulation results show that the proposed strategy outperforms the conventional methods in terms of the achievable sum rate.

Transmit Antenna Selection for Multi-User Underlay Cognitive Transmission with Zero-Forcing Beamforming

KAUST Repository

Hanif, Muhammad; Yang, Hong-Chuan; Alouini, Mohamed-Slim

2017-01-01

We present a transmit antenna subset selection scheme for an underlay cognitive system serving multiple secondary receivers. The secondary system employs zero-forcing beamforming to nullify the interference to multiple primary users and eliminate

Downlink Channel Estimation in Cellular Systems with Antenna Arrays at Base Stations Using Channel Probing with Feedback

Directory of Open Access Journals (Sweden)

Biguesh Mehrzad

2004-01-01

Full Text Available In mobile communication systems with multisensor antennas at base stations, downlink channel estimation plays a key role because accurate channel estimates are needed for transmit beamforming. One efficient approach to this problem is channel probing with feedback. In this method, the base station array transmits probing (training signals. The channel is then estimated from feedback reports provided by the users. This paper studies the performance of the channel probing method with feedback using a multisensor base station antenna array and single-sensor users. The least squares (LS, linear minimum mean square error (LMMSE, and a new scaled LS (SLS approaches to the channel estimation are studied. Optimal choice of probing signals is investigated for each of these techniques and their channel estimation performances are analyzed. In the case of multiple LS channel estimates, the best linear unbiased estimation (BLUE scheme for their linear combining is developed and studied.

Energy Efficiency and SINR Maximization Beamformers for Spectrum Sharing With Sensing Information

KAUST Repository

Alabbasi, Abdulrahman

2014-09-01

In this paper, we consider a cognitive radio multi-input-multi-output environment, in which we adapt our beamformer to maximize both energy efficiency (EE) and signal-to-interference-plus-noise ratio (SINR) metrics. Our design considers an underlaying communication using adaptive beamforming schemes combined with sensing information to achieve optimal energy-efficient systems. The proposed schemes maximize EE and SINR metrics subject to cognitive radio and quality-of-service constraints. The analysis of the proposed schemes is classified into two categories based on knowledge of the secondary-transmitter-to-primary-receiver channel. Since the optimizations of EE and SINR problems are not convex problems, we transform them into a standard semidefinite programming (SDP) form to guarantee that the optimal solutions are global. An analytical solution is provided for one scheme, while the second scheme is left in a standard SDP form. Selected numerical results are used to quantify the impact of the sensing information on the proposed schemes compared to the benchmark ones.

Digital Beamforming Synthetic Aperture Radar Developments at NASA Goddard Space Flight Center

Science.gov (United States)

Rincon, Rafael; Fatoyinbo, Temilola; Osmanoglu, Batuhan; Lee, Seung Kuk; Du Toit, Cornelis F.; Perrine, Martin; Ranson, K. Jon; Sun, Guoqing; Deshpande, Manohar; Beck, Jaclyn;

APES Beamforming Applied to Medical Ultrasound Imaging

DEFF Research Database (Denmark)

Blomberg, Ann E. A.; Holfort, Iben Kraglund; Austeng, Andreas

2009-01-01

Recently, adaptive beamformers have been introduced to medical ultrasound imaging. The primary focus has been on the minimum variance (MV) (or Capon) beamformer. This work investigates an alternative but closely related beamformer, the Amplitude and Phase Estimation (APES) beamformer. APES offers...... added robustness at the expense of a slightly lower resolution. The purpose of this study was to evaluate the performance of the APES beamformer on medical imaging data, since correct amplitude estimation often is just as important as spatial resolution. In our simulations we have used a 3.5 MHz, 96...... element linear transducer array. When imaging two closely spaced point targets, APES displays nearly the same resolution as the MV, and at the same time improved amplitude control. When imaging cysts in speckle, APES offers speckle statistics similar to that of the DAS, without the need for temporal...

Asymptotic analysis of downlink MISO systems over Rician fading channels

KAUST Repository

Falconet, Hugo

2016-06-24

In this work, we focus on the ergodic sum rate in the downlink of a single-cell large-scale multi-user MIMO system in which the base station employs N antennas to communicate with K single-antenna user equipments. A regularized zero-forcing (RZF) scheme is used for precoding under the assumption that each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming N and K grow large with a non trivial ratio and perfect channel state information is available at the base station. Recent results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signal-to-interference-plus-noise ratio as a function of the system parameters, the spatial correlation matrix and the Rician factor. Numerical results are used to evaluate the performance gap in the finite system regime under different operating conditions. © 2016 IEEE.

Asymptotic analysis of downlink MISO systems over Rician fading channels

KAUST Repository

Falconet, Hugo; Sanguinetti, Luca; Kammoun, Abla; Debbah, Merouane

2016-01-01

In this work, we focus on the ergodic sum rate in the downlink of a single-cell large-scale multi-user MIMO system in which the base station employs N antennas to communicate with K single-antenna user equipments. A regularized zero-forcing (RZF) scheme is used for precoding under the assumption that each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming N and K grow large with a non trivial ratio and perfect channel state information is available at the base station. Recent results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signal-to-interference-plus-noise ratio as a function of the system parameters, the spatial correlation matrix and the Rician factor. Numerical results are used to evaluate the performance gap in the finite system regime under different operating conditions. © 2016 IEEE.

On UWB beamforming

Directory of Open Access Journals (Sweden)

T. Kaiser

2004-01-01

Full Text Available Ultra-Wideband (UWB communication systems and Multi-Input-Multi-Output (MIMO techniques rank among the few emerging key technologies in wireless communications. For that reason the marriage of these two complementary approaches should deserve attention. Apparently, the extremely large ultra-wide bandwidth creates rich multipath diversity which calls, at a first glance, additional antenna elements into question. However, another point of view is as follows. The attenuation by solid materials usually increases with increasing frequency; e.g. frequencies above, say, 10 GHz are considered to be blocked by walls etc. Since UWB can occupy more than 7 GHz of bandwidth (according to FCC regularisation the performance of a communication link can be physically extended only by adding spatial information, i.e. multiple antennas, even if such extension may play a minor role. From this point of view UWB& MIMO presents an upper physical bound for indoor communications and is therefore at least worth to be investigated. In order to see the forest for the trees, we will focus in this limited contribution on beamforming among all alternative MIMO techniques (like space time coding or spatial multiplexing.

Parametric Beamformer for Synthetic Aperture Ultrasound Imaging

DEFF Research Database (Denmark)

Nikolov, Svetoslav; Tomov, Borislav Gueorguiev; Jensen, Jørgen Arendt

2006-01-01

. The beamformer consists of a number of identical beamforming blocks, each processing data from several channels and producing part of the image. A number of these blocks can be accommodated in a modern field-programmable gate array device (FPGA), and a whole synthetic aperture system can be implemented using...... with 255 levels. A beamforming block uses input data from 4 elements and produces a set of 10 lines. Linear interpolation is used to implement sub-sample delays. The VHDL code for the beamformer has been synthesized for a Xilinx V4FX100 speed grade 11 FPGA, where it can operate at a maximum clock frequency...

Impact of Users Identities and Access Conditions on Downlink Performance in Closed Small-Cell Networks

KAUST Repository

Radaydeh, Redha

2015-05-26

This paper investigates the effect of various operation parameters on the downlink user performance in overlaid small-cell networks. The case study considers closed-access small cells (e.g., femtocells), wherein only active authorized user equipments (UEs) can be served, and each of which is allocated single downlink channel at a time. On the other hand, the macrocell base station can unconditionally serve macrocell UEs that exist inside its coverage space. The available channels can be shared simultaneously in the macrocell network and the femtocell network. Moreover, a channel can be reused only at the macrocell base station. The analysis provides quantitative approaches to model UEs identities, their likelihoods of being active, and their likelihoods of producing interference, considering UEs classifications, locations, and access capabilities. Moreover, it develops models for various interference sources observed from effective interference femtocells, considering femtocells capacities and operation conditions. The associated formulations to describe a desired UE performance and the impact of the number of available channels as well as the adopted channel assignment approach are thoroughly investigated. The results are generally presented for any channel models of interference sources as well as the desired source of the served UE. Moreover, specific channel models are then adopted, for which generalized closedform analytical results for the desired UE outage probability performance are obtained. Numerical and simulation results are presented to further clarify the main outcomes of the developed analysis.

An object-oriented multi-threaded software beamformation toolbox

DEFF Research Database (Denmark)

Hansen, Jens Munk; Hemmsen, Martin Christian; Jensen, Jørgen Arendt

2011-01-01

Focusing and apodization are an essential part of signal processing in ultrasound imaging. Although the fun- damental principles are simple, the dramatic increase in computational power of CPUs, GPUs, and FPGAs motivates the development of software based beamformers, which further improves image...... new beam formation strategies. It is a general 3D implementation capable of handling a multitude of focusing methods, interpolation schemes, and parametric and dynamic apodization. Despite being exible, it is capable of exploiting parallelization on a single computer, on a cluster, or on both....... On a single computer, it mimics the parallization in a scanner containing multiple beam formers. The focusing is determined using the positions of the transducer elements, presence of virtual sources, and the focus points. For interpolation, a number of interpolation schemes can be chosen, e.g. linear, polyno...

Scalable Intersample Interpolation Architecture for High-channel-count Beamformers

DEFF Research Database (Denmark)

Tomov, Borislav Gueorguiev; Nikolov, Svetoslav I; Jensen, Jørgen Arendt

2011-01-01

Modern ultrasound scanners utilize digital beamformers that operate on sampled and quantized echo signals. Timing precision is of essence for achieving good focusing. The direct way to achieve it is through the use of high sampling rates, but that is not economical, so interpolation between echo...... samples is used. This paper presents a beamformer architecture that combines a band-pass filter-based interpolation algorithm with the dynamic delay-and-sum focusing of a digital beamformer. The reduction in the number of multiplications relative to a linear perchannel interpolation and band-pass per......-channel interpolation architecture is respectively 58 % and 75 % beamformer for a 256-channel beamformer using 4-tap filters. The approach allows building high channel count beamformers while maintaining high image quality due to the use of sophisticated intersample interpolation....

Downlink Performance of a Multi-Carrier MIMO System in a Bursty Traffic Cellular Network

DEFF Research Database (Denmark)

Nguyen, Hung Tuan; Kovacs, Istvan; Wang, Yuanye

2011-01-01

In this paper we analyse the downlink performance of a rank adaptive multiple input multiple output (MIMO) system in a busty traffic cellular network. A LTE-Advanced system with multiple component carriers was selected as a study case. To highlight the advantage of using MIMO techniques, we used ...

Synthetic Aperture Beamformation using the GPU

DEFF Research Database (Denmark)

Hansen, Jens Munk; Schaa, Dana; Jensen, Jørgen Arendt

2011-01-01

A synthetic aperture ultrasound beamformer is implemented for a GPU using the OpenCL framework. The implementation supports beamformation of either RF signals or complex baseband signals. Transmit and receive apodization can be either parametric or dynamic using a fixed F-number, a reference...

Ant Colony Optimization Algorithm for Centralized Dynamic Channel Allocation in Multi-Cell OFDMA Systems

Science.gov (United States)

Kim, Hyo-Su; Kim, Dong-Hoi

The dynamic channel allocation (DCA) scheme in multi-cell systems causes serious inter-cell interference (ICI) problem to some existing calls when channels for new calls are allocated. Such a problem can be addressed by advanced centralized DCA design that is able to minimize ICI. Thus, in this paper, a centralized DCA is developed for the downlink of multi-cell orthogonal frequency division multiple access (OFDMA) systems with full spectral reuse. However, in practice, as the search space of channel assignment for centralized DCA scheme in multi-cell systems grows exponentially with the increase of the number of required calls, channels, and cells, it becomes an NP-hard problem and is currently too complicated to find an optimum channel allocation. In this paper, we propose an ant colony optimization (ACO) based DCA scheme using a low-complexity ACO algorithm which is a kind of heuristic algorithm in order to solve the aforementioned problem. Simulation results demonstrate significant performance improvements compared to the existing schemes in terms of the grade of service (GoS) performance and the forced termination probability of existing calls without degrading the system performance of the average throughput.

Downlink Radio Resource Management for LTE-Advanced System with Combined MU-MIMO and Carrier Aggregation Features

DEFF Research Database (Denmark)

Nguyen, Hung Tuan; Kovacs, Istvan

2012-01-01

In this paper we study the performance enhancement of a downlink LTE-Advanced system with a combination of the multi-user MIMO and carrier aggregation transmission techniques. Radio resource management for the systems with the combined features are proposed, and the system performance is evaluate...

Robust regularized least-squares beamforming approach to signal estimation

KAUST Repository

Suliman, Mohamed Abdalla Elhag

2017-05-12

In this paper, we address the problem of robust adaptive beamforming of signals received by a linear array. The challenge associated with the beamforming problem is twofold. Firstly, the process requires the inversion of the usually ill-conditioned covariance matrix of the received signals. Secondly, the steering vector pertaining to the direction of arrival of the signal of interest is not known precisely. To tackle these two challenges, the standard capon beamformer is manipulated to a form where the beamformer output is obtained as a scaled version of the inner product of two vectors. The two vectors are linearly related to the steering vector and the received signal snapshot, respectively. The linear operator, in both cases, is the square root of the covariance matrix. A regularized least-squares (RLS) approach is proposed to estimate these two vectors and to provide robustness without exploiting prior information. Simulation results show that the RLS beamformer using the proposed regularization algorithm outperforms state-of-the-art beamforming algorithms, as well as another RLS beamformers using a standard regularization approaches.

Synthetic Aperture Sequential Beamformation applied to medical imaging

DEFF Research Database (Denmark)

Hemmsen, Martin Christian; Hansen, Jens Munk; Jensen, Jørgen Arendt

2012-01-01

Synthetic Aperture Sequential Beamforming (SASB) is applied to medical ultrasound imaging using a multi element convex array transducer. The main motivation for SASB is to apply synthetic aperture techniques without the need for storing RF-data for a number of elements and hereby devise a system...... with a reduced system complexity. Using a 192 element, 3.5 MHz, λ-pitch transducer, it is demonstrated using tissue-phantom and wire-phantom measurements, how the speckle size and the detail resolution is improved compared to conventional imaging....

Adaptive Beamforming Based on Complex Quaternion Processes

Directory of Open Access Journals (Sweden)

Jian-wu Tao

2014-01-01

Full Text Available Motivated by the benefits of array signal processing in quaternion domain, we investigate the problem of adaptive beamforming based on complex quaternion processes in this paper. First, a complex quaternion least-mean squares (CQLMS algorithm is proposed and its performance is analyzed. The CQLMS algorithm is suitable for adaptive beamforming of vector-sensor array. The weight vector update of CQLMS algorithm is derived based on the complex gradient, leading to lower computational complexity. Because the complex quaternion can exhibit the orthogonal structure of an electromagnetic vector-sensor in a natural way, a complex quaternion model in time domain is provided for a 3-component vector-sensor array. And the normalized adaptive beamformer using CQLMS is presented. Finally, simulation results are given to validate the performance of the proposed adaptive beamformer.

Single-station 6C beamforming

Science.gov (United States)

Nakata, N.; Hadziioannou, C.; Igel, H.

2017-12-01

Six-component measurements of seismic ground motion provide a unique opportunity to identify and decompose seismic wavefields into different wave types and incoming azimuths, as well as estimate structural information (e.g., phase velocity). By using the relationship between the transverse component and vertical rotational motion for Love waves, we can find the incident azimuth of the wave and the phase velocity. Therefore, when we scan the entire range of azimuth and slownesses, we can process the seismic waves in a similar way to conventional beamforming processing, without using a station array. To further improve the beam resolution, we use the distribution of amplitude ratio between translational and rotational motions at each time sample. With this beamforming, we decompose multiple incoming waves by azimuth and phase velocity using only one station. We demonstrate this technique using the data observed at Wettzell (vertical rotational motion and 3C translational motions). The beamforming results are encouraging to extract phase velocity at the location of the station, apply to oceanic microseism, and to identify complicated SH wave arrivals. We also discuss single-station beamforming using other components (vertical translational and horizontal rotational components). For future work, we need to understand the resolution limit of this technique, suitable length of time windows, and sensitivity to weak motion.

Hybrid Scheduling/Signal-Level Coordination in the Downlink of Multi-Cloud Radio-Access Networks

KAUST Repository

Douik, Ahmed

2016-03-28

In the context of resource allocation in cloud- radio access networks, recent studies assume either signal-level or scheduling-level coordination. This paper, instead, considers a hybrid level of coordination for the scheduling problem in the downlink of a multi-cloud radio- access network, so as to benefit from both scheduling policies. Consider a multi-cloud radio access network, where each cloud is connected to several base-stations (BSs) via high capacity links, and therefore allows joint signal processing between them. Across the multiple clouds, however, only scheduling-level coordination is permitted, as it requires a lower level of backhaul communication. The frame structure of every BS is composed of various time/frequency blocks, called power- zones (PZs), and kept at fixed power level. The paper addresses the problem of maximizing a network-wide utility by associating users to clouds and scheduling them to the PZs, under the practical constraints that each user is scheduled, at most, to a single cloud, but possibly to many BSs within the cloud, and can be served by one or more distinct PZs within the BSs\\' frame. The paper solves the problem using graph theory techniques by constructing the conflict graph. The scheduling problem is, then, shown to be equivalent to a maximum- weight independent set problem in the constructed graph, in which each vertex symbolizes an association of cloud, user, BS and PZ, with a weight representing the utility of that association. Simulation results suggest that the proposed hybrid scheduling strategy provides appreciable gain as compared to the scheduling-level coordinated networks, with a negligible degradation to signal-level coordination.

Low complexity symbol-wise beamforming for MIMO-OFDM systems

KAUST Repository

Lee, Hyun Ho

2011-12-01

In this paper, we consider a low complexity symbol-wise beamforming for MIMO-OFDM systems. We propose a non-iterative algorithm for the symbol-wise beamforming, which can provide the performance approaching that of the conventional symbol-wise beamforming based on the iterative algorithm. We demonstrate that our proposed scheme can reduce the computational complexity significantly. From our simulation results, it is evident that our proposed scheme leads to a negligible performance loss compared to the conventional symbol-wise beamforming regardless of spatial correlation or presence of co-channel interference. © 2011 IEEE.

MVDR Algorithm Based on Estimated Diagonal Loading for Beamforming

Directory of Open Access Journals (Sweden)

Yuteng Xiao

2017-01-01

Full Text Available Beamforming algorithm is widely used in many signal processing fields. At present, the typical beamforming algorithm is MVDR (Minimum Variance Distortionless Response. However, the performance of MVDR algorithm relies on the accurate covariance matrix. The MVDR algorithm declines dramatically with the inaccurate covariance matrix. To solve the problem, studying the beamforming array signal model and beamforming MVDR algorithm, we improve MVDR algorithm based on estimated diagonal loading for beamforming. MVDR optimization model based on diagonal loading compensation is established and the interval of the diagonal loading compensation value is deduced on the basis of the matrix theory. The optimal diagonal loading value in the interval is also determined through the experimental method. The experimental results show that the algorithm compared with existing algorithms is practical and effective.

Adaptive Beamforming using the Reconfigurable Montium TP

NARCIS (Netherlands)

van de Burgwal, M.D.; Rovers, K.C.; Blom, K.C.H.; Kokkeler, Andre B.J.; Smit, Gerardus Johannes Maria; López, S.

2010-01-01

Until a decade ago, the concept of phased array beamforming was mainly implemented with mechanical or analog solutions. Today, digital hardware has become powerful enough to perform the massive number of operations required for real-time digital beamforming. While more and more applications are

Optimal beamforming in MIMO systems with HPA nonlinearity

KAUST Repository

Qi, Jian

2010-09-01

In this paper, multiple-input multiple-output (MIMO) transmit beamforming (TB) systems under the consideration of nonlinear high-power amplifiers (HPAs) are investigated. The optimal beamforming scheme, with the optimal beamforming weight vector and combining vector, is proposed for MIMO systems with HPA nonlinearity. The performance of the proposed MIMO beamforming scheme in the presence of HPA nonlinearity is evaluated in terms of average symbol error probability (SEP), outage probability and system capacity, considering transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, namely, parameters of nonlinear HPA, numbers of transmit and receive antennas, and modulation order of phase-shift keying (PSK), on performance. ©2010 IEEE.

Optimal beamforming in MIMO systems with HPA nonlinearity

KAUST Repository

Qi, Jian; Aissa, Sonia

2010-01-01

In this paper, multiple-input multiple-output (MIMO) transmit beamforming (TB) systems under the consideration of nonlinear high-power amplifiers (HPAs) are investigated. The optimal beamforming scheme, with the optimal beamforming weight vector and combining vector, is proposed for MIMO systems with HPA nonlinearity. The performance of the proposed MIMO beamforming scheme in the presence of HPA nonlinearity is evaluated in terms of average symbol error probability (SEP), outage probability and system capacity, considering transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, namely, parameters of nonlinear HPA, numbers of transmit and receive antennas, and modulation order of phase-shift keying (PSK), on performance. ©2010 IEEE.

Optimal beamforming in ultrasound using the ideal observer.

Science.gov (United States)

Abbey, Craig K; Nguyen, Nghia Q; Insana, Michael F

2010-08-01

Beamforming of received pulse-echo data generally involves the compression of signals from multiple channels within an aperture. This compression is irreversible, and therefore allows the possibility that information relevant for performing a diagnostic task is irretrievably lost. The purpose of this study was to evaluate information transfer in beamforming using a previously developed ideal observer model to quantify diagnostic information relevant to performing a task. We describe an elaborated statistical model of image formation for fixed-focus transmission and single-channel reception within a moving aperture, and we use this model on a panel of tasks related to breast sonography to evaluate receive-beamforming approaches that optimize the transfer of information. Under the assumption that acquisition noise is well described as an additive wide-band Gaussian white-noise process, we show that signal compression across receive-aperture channels after a 2-D matched-filtering operation results in no loss of diagnostic information. Across tasks, the matched-filter beamformer results in more information than standard delay-and-sum beamforming in the subsequent radio-frequency signal by a factor of two. We also show that for this matched filter, 68% of the information gain can be attributed to the phase of the matched-filter and 21% can be attributed to the amplitude. A 1-D matched filtering along axial lines shows no advantage over delay-andsum, suggesting an important role for incorporating correlations across different aperture windows in beamforming. We also show that a post-compression processing before the computation of an envelope is necessary to pass the diagnostic information in the beamformed radio-frequency signal to the final envelope image.

Power-Controlled CDMA Cell Sectorization with Multiuser Detection: A Comprehensive Analysis on Uplink and Downlink

Directory of Open Access Journals (Sweden)

Aylin Yener

2007-12-01

Full Text Available We consider the joint optimization problem of cell sectorization, transmit power control and multiuser detection for a CDMA cell. Given the number of sectors and user locations, the cell is appropriately sectorized such that the total transmit power, as well as the receiver filters, is optimized. We formulate the corresponding joint optimization problems for both the uplink and the downlink and observe that in general, the resulting optimum transmit and receive beamwidth values for the directional antennas at the base station are different. We present the optimum solution under a general setting with arbitrary signature sets, multipath channels, realistic directional antenna responses and identify its complexity. We propose a low-complexity sectorization algorithm that performs near optimum and compare its performance with that of optimum solution. The results suggest that by intelligently combining adaptive cell sectorization, power control, and linear multiuser detection, we are able to increase the user capacity of the cell. Numerical results also indicate robustness of optimum sectorization against Gaussian channel estimation error.

Power-Controlled CDMA Cell Sectorization with Multiuser Detection: A Comprehensive Analysis on Uplink and Downlink

Directory of Open Access Journals (Sweden)

Oh Changyoon

2007-01-01

Full Text Available We consider the joint optimization problem of cell sectorization, transmit power control and multiuser detection for a CDMA cell. Given the number of sectors and user locations, the cell is appropriately sectorized such that the total transmit power, as well as the receiver filters, is optimized. We formulate the corresponding joint optimization problems for both the uplink and the downlink and observe that in general, the resulting optimum transmit and receive beamwidth values for the directional antennas at the base station are different. We present the optimum solution under a general setting with arbitrary signature sets, multipath channels, realistic directional antenna responses and identify its complexity. We propose a low-complexity sectorization algorithm that performs near optimum and compare its performance with that of optimum solution. The results suggest that by intelligently combining adaptive cell sectorization, power control, and linear multiuser detection, we are able to increase the user capacity of the cell. Numerical results also indicate robustness of optimum sectorization against Gaussian channel estimation error.

Effective and versatile software beamformation toolbox

DEFF Research Database (Denmark)

Kortbek, Jacob; Nikolov, Svetoslav; Jensen, Jørgen Arendt

2007-01-01

Delay-and-sum array beamforming is an essential part of signal processing in ultrasound imaging. Although the principles are simple, there are many implementation details to consider for obtaining a reliable and computational efficient beamforming. Different methods for calculation of time......-delays are used for different waveforms. Various inter-sample interpolation schemes such as FIR-filtering, polynomial, and spline interpolation can be chosen. Apodization can be any preferred window function of fixed size applied on the channel signals or it can be dynamic with an expanding and contracting...... seconds using a transducer of 128 elements, dynamic apodization and 3rd order polynomial interpolation. This is a decrease in computation time of at least a factor of 15 compared to an implementation directly in MATLAB of a similar beamformer....

Toward a Reconfigurable MIMO Downlink Air Interface and Radio Resource Management

DEFF Research Database (Denmark)

Kovacs, Istvan Zsolt; Luis, Garcia Ordonez; Ferrández, Miguel Navarro

2010-01-01

This article presents a reconfigurable multiple-input multiple-output air interface design combined with radio resource management algorithms applicable to multi-user MIMO transmission in downlink orthogonal frequency-division multiple access systems. A low-complexity, adaptive, and channel...... scheduling. System-level performance analysis, including the effects of limited and imperfect feedback from the terminals, shows that the SURFACE air interface provides an attractive practical solution for operations with high-rate adaptive MIMO transmission schemes in the context of next-generation wireless......-aware single-user and multi-user MIMO transmission solution is proposed based on the findings of the SURFACE European Commission funded research project. The resulting cross-layer design covers the reconfigurable air interface, and practical layer 1 and layer 2 RRM mechanisms for time-frequency packet...

Photonic Beamformer Model Based on Analog Fiber-Optic Links’ Components

International Nuclear Information System (INIS)

Volkov, V A; Gordeev, D A; Ivanov, S I; Lavrov, A P; Saenko, I I

2016-01-01

The model of photonic beamformer for wideband microwave phased array antenna is investigated. The main features of the photonic beamformer model based on true-time-delay technique, DWDM technology and fiber chromatic dispersion are briefly analyzed. The performance characteristics of the key components of photonic beamformer for phased array antenna in the receive mode are examined. The beamformer model composed of the components available on the market of fiber-optic analog communication links is designed and tentatively investigated. Experimental demonstration of the designed model beamforming features includes actual measurement of 5-element microwave linear array antenna far-field patterns in 6-16 GHz frequency range for antenna pattern steering up to 40°. The results of experimental testing show good accordance with the calculation estimates. (paper)

Plane Wave Medical Ultrasound Imaging Using Adaptive Beamforming

DEFF Research Database (Denmark)

Holfort, Iben Kraglund; Gran, Fredrik; Jensen, Jørgen Arendt

2008-01-01

In this paper, the adaptive, minimum variance (MV) beamformer is applied to medical ultrasound imaging. The Significant resolution and contrast gain provided by the adaptive, minimum variance (MV) beamformer, introduces the possibility of plane wave (PW) ultrasound imaging. Data is obtained using...

Smart Antenna UKM Testbed for Digital Beamforming System

Directory of Open Access Journals (Sweden)

2009-03-01

Full Text Available A new design of smart antenna testbed developed at UKM for digital beamforming purpose is proposed. The smart antenna UKM testbed developed based on modular design employing two novel designs of L-probe fed inverted hybrid E-H (LIEH array antenna and software reconfigurable digital beamforming system (DBS. The antenna is developed based on using the novel LIEH microstrip patch element design arranged into 4×1 uniform linear array antenna. An interface board is designed to interface to the ADC board with the RF front-end receiver. The modular concept of the system provides the capability to test the antenna hardware, beamforming unit, and beamforming algorithm in an independent manner, thus allowing the smart antenna system to be developed and tested in parallel, hence reduces the design time. The DBS was developed using a high-performance TMS320C6711TM floating-point DSP board and a 4-channel RF front-end receiver developed in-house. An interface board is designed to interface to the ADC board with the RF front-end receiver. A four-element receiving array testbed at 1.88–2.22 GHz frequency is constructed, and digital beamforming on this testbed is successfully demonstrated.

An improved minimum variance beamforming applied to plane-wave imaging in medical ultrasound

DEFF Research Database (Denmark)

Deylami, Ali Mohades; Asl, Babak Mohammadzadeh; Jensen, Jørgen Arendt

2016-01-01

Minimum variance beamformer (MVB) is an adaptive beamformer which provides images with higher resolution and contrast in comparison with non-adaptive beamformers like delay and sum (DAS). It finds weight vector of beamformer by minimizing output power while keeping the desired signal unchanged. We...

Fourier beamformation of multistatic synthetic aperture ultrasound imaging

DEFF Research Database (Denmark)

Moghimirad, Elahe; Villagómez Hoyos, Carlos Armando; Mahloojifar, Ali

2015-01-01

A new Fourier beamformation (FB) algorithm is presented for multistatic synthetic aperture ultrasound imaging. It can reduce the number of computations by a factor of 20 compared to conventional Delay-and-Sum (DAS) beamformers. The concept is based on the wavenumber algorithm from radar and sonar...

Synthetic aperture flow imaging using dual stage beamforming

DEFF Research Database (Denmark)

Li, Ye; Jensen, Jørgen Arendt

2013-01-01

A method for synthetic aperture flow imaging using dual stage beamforming has been developed. The main motivation is to increase the frame rate and still maintain a beamforming quality sufficient for flow estimation that is possible to implement in a commercial scanner. This method can generate...

Double Minimum Variance Beamforming Method to Enhance Photoacoustic Imaging

OpenAIRE

Paridar, Roya; Mozaffarzadeh, Moein; Nasiriavanaki, Mohammadreza; Orooji, Mahdi

2018-01-01

One of the common algorithms used to reconstruct photoacoustic (PA) images is the non-adaptive Delay-and-Sum (DAS) beamformer. However, the quality of the reconstructed PA images obtained by DAS is not satisfying due to its high level of sidelobes and wide mainlobe. In contrast, adaptive beamformers, such as minimum variance (MV), result in an improved image compared to DAS. In this paper, a novel beamforming method, called Double MV (D-MV) is proposed to enhance the image quality compared to...

Transmit Antenna Selection for Multi-User Underlay Cognitive Transmission with Zero-Forcing Beamforming

KAUST Repository

Hanif, Muhammad

2017-03-20

We present a transmit antenna subset selection scheme for an underlay cognitive system serving multiple secondary receivers. The secondary system employs zero-forcing beamforming to nullify the interference to multiple primary users and eliminate inter-user interference to the secondary users simultaneously. Simulation results show that the proposed scheme achieves near-optimal performance with low computational complexity. Lastly, an optimal power allocation strategy is also introduced to improve the secondary network throughput.

Minimizing Sum-MSE Implies Identical Downlink and Dual Uplink Power Allocations

OpenAIRE

Tenenbaum, Adam J.; Adve, Raviraj S.

2009-01-01

In the multiuser downlink, power allocation for linear precoders that minimize the sum of mean squared errors under a sum power constraint is a non-convex problem. Many existing algorithms solve an equivalent convex problem in the virtual uplink and apply a transformation based on uplink-downlink duality to find a downlink solution. In this letter, we analyze the optimality criteria for the power allocation subproblem in the virtual uplink, and demonstrate that the optimal solution leads to i...

FPGA implementation of adaptive beamforming in hearing aids.

Science.gov (United States)

Samtani, Kartik; Thomas, Jobin; Varma, G Abhinav; Sumam, David S; Deepu, S P

2017-07-01

Beamforming is a spatial filtering technique used in hearing aids to improve target sound reception by reducing interference from other directions. In this paper we propose improvements in an existing architecture present for two omnidirectional microphone array based adaptive beamforming for hearing aid applications and implement the same on Xilinx Artix 7 FPGA using VHDL coding and Xilinx Vivado ® 2015.2. The nulls are introduced in particular directions by combination of two fixed polar patterns. This combination can be adaptively controlled to steer the null in the direction of noise. The beamform patterns and improvements in SNR values obtained from experiments in a conference room environment are analyzed.

Robust regularized least-squares beamforming approach to signal estimation

KAUST Repository

Suliman, Mohamed Abdalla Elhag; Ballal, Tarig; Al-Naffouri, Tareq Y.

2017-01-01

In this paper, we address the problem of robust adaptive beamforming of signals received by a linear array. The challenge associated with the beamforming problem is twofold. Firstly, the process requires the inversion of the usually ill

Robust distributed cognitive relay beamforming

KAUST Repository

Pandarakkottilil, Ubaidulla

2012-05-01

In this paper, we present a distributed relay beamformer design for a cognitive radio network in which a cognitive (or secondary) transmit node communicates with a secondary receive node assisted by a set of cognitive non-regenerative relays. The secondary nodes share the spectrum with a licensed primary user (PU) node, and each node is assumed to be equipped with a single transmit/receive antenna. The interference to the PU resulting from the transmission from the cognitive nodes is kept below a specified limit. The proposed robust cognitive relay beamformer design seeks to minimize the total relay transmit power while ensuring that the transceiver signal-to-interference- plus-noise ratio and PU interference constraints are satisfied. The proposed design takes into account a parameter of the error in the channel state information (CSI) to render the performance of the beamformer robust in the presence of imperfect CSI. Though the original problem is non-convex, we show that the proposed design can be reformulated as a tractable convex optimization problem that can be solved efficiently. Numerical results are provided and illustrate the performance of the proposed designs for different network operating conditions and parameters. © 2012 IEEE.

Non-Orthogonal Opportunistic Beamforming: Performance Analysis and Implementation

KAUST Repository

Xia, Minghua

2012-04-01

Aiming to achieve the sum-rate capacity in multi-user multi-antenna systems where $N_t$ antennas are implemented at the transmitter, opportunistic beamforming (OBF) generates~$N_t$ orthonormal beams and serves $N_t$ users during each channel use, which results in high scheduling delay over the users, especially in densely populated networks. Non-orthogonal OBF with more than~$N_t$ transmit beams can be exploited to serve more users simultaneously and further decrease scheduling delay. However, the inter-beam interference will inevitably deteriorate the sum-rate. Therefore, there is a tradeoff between sum-rate and scheduling delay for non-orthogonal OBF. In this context, system performance and implementation of non-orthogonal OBF with $N>N_t$ beams are investigated in this paper. Specifically, it is analytically shown that non-orthogonal OBF is an interference-limited system as the number of users $K \\\\to \\\\infty$. When the inter-beam interference reaches its minimum for fixed $N_t$ and~$N$, the sum-rate scales as $N\\\\ln\\\\left(\\\\frac{N}{N-N_t}\\ ight)$ and it degrades monotonically with the number of beams $N$ for fixed $N_t$. On the contrary, the average scheduling delay is shown to scale as $\\\\frac{1}{N}K\\\\ln{K}$ channel uses and it improves monotonically with $N$. Furthermore, two practical non-orthogonal beamforming schemes are explicitly constructed and they are demonstrated to yield the minimum inter-beam interference for fixed $N_t$ and $N$. This study reveals that, if user traffic is light and one user can be successfully served within a single transmission, non-orthogonal OBF can be applied to obtain lower worst-case delay among the users. On the other hand, if user traffic is heavy, non-orthogonal OBF is inferior to orthogonal OBF in terms of sum-rate and packet delay.

New perspective on single-radiator multiple-port antennas for adaptive beamforming applications.

Science.gov (United States)

Byun, Gangil; Choo, Hosung

2017-01-01

One of the most challenging problems in recent antenna engineering fields is to achieve highly reliable beamforming capabilities in an extremely restricted space of small handheld devices. In this paper, we introduce a new perspective on single-radiator multiple-port (SRMP) antenna to alter the traditional approach of multiple-antenna arrays for improving beamforming performances with reduced aperture sizes. The major contribution of this paper is to demonstrate the beamforming capability of the SRMP antenna for use as an extremely miniaturized front-end component in more sophisticated beamforming applications. To examine the beamforming capability, the radiation properties and the array factor of the SRMP antenna are theoretically formulated for electromagnetic characterization and are used as complex weights to form adaptive array patterns. Then, its fundamental performance limits are rigorously explored through enumerative studies by varying the dielectric constant of the substrate, and field tests are conducted using a beamforming hardware to confirm the feasibility. The results demonstrate that the new perspective of the SRMP antenna allows for improved beamforming performances with the ability of maintaining consistently smaller aperture sizes compared to the traditional multiple-antenna arrays.

New perspective on single-radiator multiple-port antennas for adaptive beamforming applications.

Directory of Open Access Journals (Sweden)

Gangil Byun

Full Text Available One of the most challenging problems in recent antenna engineering fields is to achieve highly reliable beamforming capabilities in an extremely restricted space of small handheld devices. In this paper, we introduce a new perspective on single-radiator multiple-port (SRMP antenna to alter the traditional approach of multiple-antenna arrays for improving beamforming performances with reduced aperture sizes. The major contribution of this paper is to demonstrate the beamforming capability of the SRMP antenna for use as an extremely miniaturized front-end component in more sophisticated beamforming applications. To examine the beamforming capability, the radiation properties and the array factor of the SRMP antenna are theoretically formulated for electromagnetic characterization and are used as complex weights to form adaptive array patterns. Then, its fundamental performance limits are rigorously explored through enumerative studies by varying the dielectric constant of the substrate, and field tests are conducted using a beamforming hardware to confirm the feasibility. The results demonstrate that the new perspective of the SRMP antenna allows for improved beamforming performances with the ability of maintaining consistently smaller aperture sizes compared to the traditional multiple-antenna arrays.

Iterative Minimum Variance Beamformer with Low Complexity for Medical Ultrasound Imaging.

Science.gov (United States)

Deylami, Ali Mohades; Asl, Babak Mohammadzadeh

2018-06-04

Minimum variance beamformer (MVB) improves the resolution and contrast of medical ultrasound images compared with delay and sum (DAS) beamformer. The weight vector of this beamformer should be calculated for each imaging point independently, with a cost of increasing computational complexity. The large number of necessary calculations limits this beamformer to application in real-time systems. A beamformer is proposed based on the MVB with lower computational complexity while preserving its advantages. This beamformer avoids matrix inversion, which is the most complex part of the MVB, by solving the optimization problem iteratively. The received signals from two imaging points close together do not vary much in medical ultrasound imaging. Therefore, using the previously optimized weight vector for one point as initial weight vector for the new neighboring point can improve the convergence speed and decrease the computational complexity. The proposed method was applied on several data sets, and it has been shown that the method can regenerate the results obtained by the MVB while the order of complexity is decreased from O(L 3 ) to O(L 2 ). Copyright © 2018 World Federation for Ultrasound in Medicine and Biology. Published by Elsevier Inc. All rights reserved.

Low complexity non-iterative coordinated beamforming in 2-user broadcast channels

KAUST Repository

Park, Kihong

2010-10-01

We propose a new non-iterative coordinated beamforming scheme to obtain full multiplexing gain in 2-user MIMO systems. In order to find the beamforming and combining matrices, we solve a generalized eigenvector problem and describe how to find generalized eigenvectors according to the Gaussian broadcast channels. Selected simulation results show that the proposed method yields the same sum-rate performance as the iterative coordinated beamforming method, while maintaining lower complexity by non-iterative computation of the beamforming and combining matrices. We also show that the proposed method can easily exploit selective gain by choosing the best combination of generalized eigenvectors. © 2006 IEEE.

Low complexity non-iterative coordinated beamforming in 2-user broadcast channels

KAUST Repository

Park, Kihong; Ko, Youngchai; Alouini, Mohamed-Slim

2010-01-01

We propose a new non-iterative coordinated beamforming scheme to obtain full multiplexing gain in 2-user MIMO systems. In order to find the beamforming and combining matrices, we solve a generalized eigenvector problem and describe how to find generalized eigenvectors according to the Gaussian broadcast channels. Selected simulation results show that the proposed method yields the same sum-rate performance as the iterative coordinated beamforming method, while maintaining lower complexity by non-iterative computation of the beamforming and combining matrices. We also show that the proposed method can easily exploit selective gain by choosing the best combination of generalized eigenvectors. © 2006 IEEE.

Capacity Bounds on the Downlink of Symmetric, Multi-Relay, Single-Receiver C-RAN Networks

Directory of Open Access Journals (Sweden)

Shirin Saeedi Bidokhti

2017-11-01

Full Text Available The downlink of symmetric Cloud Radio Access Networks (C-RANs with multiple relays and a single receiver is studied. Lower and upper bounds are derived on the capacity. The lower bound is achieved by Marton’s coding, which facilitates dependence among the multiple-access channel inputs. The upper bound uses Ozarow’s technique to augment the system with an auxiliary random variable. The bounds are studied over scalar Gaussian C-RANs and are shown to meet and characterize the capacity for interesting regimes of operation.

Analog Gradient Beamformer for a Wireless Ultrasound Scanner

DEFF Research Database (Denmark)

di Ianni, Tommaso; Hemmsen, Martin Christian; Bagge, Jan Peter

2016-01-01

This paper presents a novel beamformer architecture for a low-cost receiver front-end, and investigates if the image quality can be maintained. The system is oriented to the development of a hand-held wireless ultrasound probe based on Synthetic Aperture Sequential Beamforming, and has the advant......This paper presents a novel beamformer architecture for a low-cost receiver front-end, and investigates if the image quality can be maintained. The system is oriented to the development of a hand-held wireless ultrasound probe based on Synthetic Aperture Sequential Beamforming, and has...... the advantage of effectively reducing circuit complexity and power dissipation. The array of transducers is divided into sub-apertures, in which the signals from the single channels are aligned through a network of cascaded gradient delays, and summed in the analog domain before A/D conversion. The delay values...... are quantized to simplify the shifting unit, and a single A/D converter is needed for each sub-aperture yielding a compact, low-power architecture that can be integrated in a single chip. A simulation study was performed using a 3.75 MHz convex array, and the point spread function (PSF) for different...

Adaptive Priority-Based Downlink Scheduling for WiMAX Networks

OpenAIRE

Wu, Shih-Jung; Huang, Shih-Yi; Huang, Kuo-Feng

2012-01-01

Supporting quality of service (QoS) guarantees for diverse multimedia services are the primary concerns for WiMAX (IEEE 802.16) networks. A scheduling scheme that satisfies QoS requirements has become more important for wireless communications. We propose a downlink scheduling scheme called adaptive priority-based downlink scheduling (APDS) for providing QoS guarantees in IEEE 802.16 networks. APDS comprises two major components: priority assignment and resource allocation. Different service-...

A beamforming system based on the acousto-optic effect

DEFF Research Database (Denmark)

Torras Rosell, Antoni; Barrera Figueroa, Salvador; Jacobsen, Finn

2012-01-01

Beamforming techniques are usually based on microphone arrays. The present work uses a beam of light as a sensor element, and describes a beamforming system that locates sound sources based on the acousto-optic effect, this is, the interaction between sound and light. The use of light as a sensin...

Robust Frequency Invariant Beamforming with Low Sidelobe for Speech Enhancement

Science.gov (United States)

Zhu, Yiting; Pan, Xiang

2018-01-01

Frequency invariant beamformers (FIBs) are widely used in speech enhancement and source localization. There are two traditional optimization methods for FIB design. The first one is convex optimization, which is simple but the frequency invariant characteristic of the beam pattern is poor with respect to frequency band of five octaves. The least squares (LS) approach using spatial response variation (SRV) constraint is another optimization method. Although, it can provide good frequency invariant property, it usually couldn’t be used in speech enhancement for its lack of weight norm constraint which is related to the robustness of a beamformer. In this paper, a robust wideband beamforming method with a constant beamwidth is proposed. The frequency invariant beam pattern is achieved by resolving an optimization problem of the SRV constraint to cover speech frequency band. With the control of sidelobe level, it is available for the frequency invariant beamformer (FIB) to prevent distortion of interference from the undesirable direction. The approach is completed in time-domain by placing tapped delay lines(TDL) and finite impulse response (FIR) filter at the output of each sensor which is more convenient than the Frost processor. By invoking the weight norm constraint, the robustness of the beamformer is further improved against random errors. Experiment results show that the proposed method has a constant beamwidth and almost the same white noise gain as traditional delay-and-sum (DAS) beamformer.

Impact of Beamforming on the Path Connectivity in Cognitive Radio Ad Hoc Networks

Directory of Open Access Journals (Sweden)

Le The Dung

2017-03-01

Full Text Available This paper investigates the impact of using directional antennas and beamforming schemes on the connectivity of cognitive radio ad hoc networks (CRAHNs. Specifically, considering that secondary users use two kinds of directional antennas, i.e., uniform linear array (ULA and uniform circular array (UCA antennas, and two different beamforming schemes, i.e., randomized beamforming and center-directed to communicate with each other, we study the connectivity of all combination pairs of directional antennas and beamforming schemes and compare their performances to those of omnidirectional antennas. The results obtained in this paper show that, compared with omnidirectional transmission, beamforming transmission only benefits the connectivity when the density of secondary user is moderate. Moreover, the combination of UCA and randomized beamforming scheme gives the highest path connectivity in all evaluating scenarios. Finally, the number of antenna elements and degree of path loss greatly affect path connectivity in CRAHNs.

Laser beam-forming by deformable mirror for laser isotope separation

International Nuclear Information System (INIS)

Nemoto, Koshichi; Fujii, Takashi; Goto, Naohiko

1995-01-01

A rectangular laser beam of uniform intensity is very suitable for laser isotope separation. In this paper, we propose a beam-forming system which consists two deformable mirrors. One of the mirrors changes the beam intensity and the other compensates for phase distortion. We developed a deformable mirror for beam-forming. Its deformed surface is similar to the ideal mirror surface for beam-forming. We reshaped a Gaussian-like He-Ne laser beam into a beam with a more uniform intensity profile by a simple deformable mirror. (author)

Digital Beamforming Scatterometer

Science.gov (United States)

Rincon, Rafael F.; Vega, Manuel; Kman, Luko; Buenfil, Manuel; Geist, Alessandro; Hillard, Larry; Racette, Paul

2009-01-01

This paper discusses scatterometer measurements collected with multi-mode Digital Beamforming Synthetic Aperture Radar (DBSAR) during the SMAP-VEX 2008 campaign. The 2008 SMAP Validation Experiment was conducted to address a number of specific questions related to the soil moisture retrieval algorithms. SMAP-VEX 2008 consisted on a series of aircraft-based.flights conducted on the Eastern Shore of Maryland and Delaware in the fall of 2008. Several other instruments participated in the campaign including the Passive Active L-Band System (PALS), the Marshall Airborne Polarimetric Imaging Radiometer (MAPIR), and the Global Positioning System Reflectometer (GPSR). This campaign was the first SMAP Validation Experiment. DBSAR is a multimode radar system developed at NASA/Goddard Space Flight Center that combines state-of-the-art radar technologies, on-board processing, and advances in signal processing techniques in order to enable new remote sensing capabilities applicable to Earth science and planetary applications [l]. The instrument can be configured to operate in scatterometer, Synthetic Aperture Radar (SAR), or altimeter mode. The system builds upon the L-band Imaging Scatterometer (LIS) developed as part of the RadSTAR program. The radar is a phased array system designed to fly on the NASA P3 aircraft. The instrument consists of a programmable waveform generator, eight transmit/receive (T/R) channels, a microstrip antenna, and a reconfigurable data acquisition and processor system. Each transmit channel incorporates a digital attenuator, and digital phase shifter that enables amplitude and phase modulation on transmit. The attenuators, phase shifters, and calibration switches are digitally controlled by the radar control card (RCC) on a pulse by pulse basis. The antenna is a corporate fed microstrip patch-array centered at 1.26 GHz with a 20 MHz bandwidth. Although only one feed is used with the present configuration, a provision was made for separate corporate

Nonfeedback Distributed Beamforming Using Spatial-Temporal Extraction

Directory of Open Access Journals (Sweden)

Pongnarin Sriploy

2016-01-01

Full Text Available So far, major phase synchronization techniques for distributed beamforming suffer from the problem related to the feedback procedure as a base station has to send the feedback reference signal back to the transmitting nodes. This requires stability of communication channel or a number of retransmissions, introducing a complicated system to both transmitter and receiver. Therefore, this paper proposes an alternative technique, so-called nonfeedback beamforming, employing an operation in both space and time domains. The proposed technique is to extract a combined signal at the base station. The concept of extraction is based on solving a simultaneous linear equation without the requirement of feedback or reference signals from base station. Also, the number of retransmissions is less compared with the ones available in literatures. As a result, the transmitting nodes are of low complexity and also low power consumption. The simulation and experimental results reveal that the proposed technique provides the optimum beamforming gain. Furthermore, it can reduce Bit Error Rate to the systems.

Chip-Level Channel Equalization in WCDMA Downlink

Directory of Open Access Journals (Sweden)

Kari Hooli

2002-08-01

Full Text Available The most important third generation (3G cellular communications standard is based on wideband CDMA (WCDMA. Receivers based on TDMA style channel equalization at the chip level have been proposed for a WCDMA downlink employing long spreading sequences to ensure adequate performance even with a high number of active users. These receivers equalize the channel prior to despreading, thus restoring the orthogonality of users and resulting in multiple-access interference (MAI suppression. In this paper, an overview of chip-level channel equalizers is delivered with special attention to adaptation methods suitable for the WCDMA downlink. Numerical examples on the equalizers′ performance are given in Rayleigh fading frequency-selective channels.

Relaxed Binaural LCMV Beamforming

NARCIS (Netherlands)

Koutrouvelis, A.; Hendriks, R.C.; Heusdens, R.; Jensen, Jesper Rindom

2017-01-01

In this paper, we propose a new binaural beamforming technique, which can be seen as a relaxation of the linearly constrained minimum variance (LCMV) framework. The proposed method can achieve simultaneous noise reduction and exact binaural cue preservation of the target source, similar to the

Beam-Forming Concentrating Solar Thermal Array Power Systems

Science.gov (United States)

Cwik, Thomas A. (Inventor); Dimotakis, Paul E. (Inventor); Hoppe, Daniel J. (Inventor)

2016-01-01

The present invention relates to concentrating solar-power systems and, more particularly, beam-forming concentrating solar thermal array power systems. A solar thermal array power system is provided, including a plurality of solar concentrators arranged in pods. Each solar concentrator includes a solar collector, one or more beam-forming elements, and one or more beam-steering elements. The solar collector is dimensioned to collect and divert incoming rays of sunlight. The beam-forming elements intercept the diverted rays of sunlight, and are shaped to concentrate the rays of sunlight into a beam. The steering elements are shaped, dimensioned, positioned, and/or oriented to deflect the beam toward a beam output path. The beams from the concentrators are converted to heat at a receiver, and the heat may be temporarily stored or directly used to generate electricity.

An Improved Overloading Scheme for Downlink CDMA

Directory of Open Access Journals (Sweden)

Marc Moeneclaey

2005-04-01

Full Text Available An improved overloading scheme is presented for single-user detection in the downlink of multiple-access systems based on OCDMA/OCDMA (O/O. By displacing in time the orthogonal signatures of the two user sets that make up the overloaded system, the cross-correlation between the users of the two sets is reduced. For random O/O with square-root cosine rolloff chip pulses, the multiuser interference can be decreased by up to 50% (depending on the chip pulse bandwidth as compared to quasiorthogonal sequences (QOS that are presently part of the downlink standard of Cdma2000. This reduction of the multiuser interference gives rise to an increase of the achievable signal-to-interference-plus-noise ratio for a particular channel load.

A Novel Beamforming Technique for Highways Coverage Using High-Altitude Platforms

Directory of Open Access Journals (Sweden)

Yasser Albagory

2007-01-01

Full Text Available This paper proposes a novel beamforming technique to form an arbitrary-shaped cell for the high-altitude platforms (HAPs mobile communications. The new technique is based on pattern summation of individual low-sidelobe, narrow beams which constitute the desired cell pattern weighted by an amplitude correcting function. The new cell pattern can be adapted to cover the main highways forming worm-shaped cells which may cover the highway for long distances up to 100 km and it will have an important role in reducing frequent handoffs and signaling traffic of location updating from moving users over the long highways.

Distributed cognitive two-way relay beamformer designs under perfect and imperfect CSI

KAUST Repository

Pandarakkottilil, Ubaidulla

2011-09-01

In this paper, we present distributed two-way relay beamformer designs for a cognitive radio network (CRN) in which a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relay nodes. The secondary nodes share the spectrum with a licensed primary user (PU) node, and each node is assumed to be equipped with a single transmit/receive antenna. The interference to the PU resulting from the transmission from the cognitive nodes is kept below a specified limit. First, we consider relay beamformer designs assuming the availability of perfect channel state information (CSI). For this case, a mean-square error (MSE)-constrained beamformer that minimizes the total relay transmit power, and an MSE-balancing beamformer with a constraint on the total relay transmit power are proposed. Next, we consider relay beamformer designs assuming that the available CSI is imperfect. For this case too, we consider the same problems as those in the case of perfect CSI, and propose beamformer designs that are robust to the errors in the CSI. We show that the proposed designs can be reformulated as convex optimization problems that can be solved efficiently. Through numerical simulations, we illustrate the performance of the proposed designs. © 2011 IEEE.

Enhanced linear-array photoacoustic beamforming using modified coherence factor

Science.gov (United States)

Mozaffarzadeh, Moein; Yan, Yan; Mehrmohammadi, Mohammad; Makkiabadi, Bahador

2018-02-01

Photoacoustic imaging (PAI) is a promising medical imaging modality providing the spatial resolution of ultrasound imaging and the contrast of optical imaging. For linear-array PAI, a beamformer can be used as the reconstruction algorithm. Delay-and-sum (DAS) is the most prevalent beamforming algorithm in PAI. However, using DAS beamformer leads to low-resolution images as well as high sidelobes due to nondesired contribution of off-axis signals. Coherence factor (CF) is a weighting method in which each pixel of the reconstructed image is weighted, based on the spatial spectrum of the aperture, to mainly improve the contrast. We demonstrate that the numerator of the formula of CF contains a DAS algebra and propose the use of a delay-multiply-and-sum beamformer instead of the available DAS on the numerator. The proposed weighting technique, modified CF (MCF), has been evaluated numerically and experimentally compared to CF. It was shown that MCF leads to lower sidelobes and better detectable targets. The quantitative results of the experiment (using wire targets) show that MCF leads to for about 45% and 40% improvement, in comparison with CF, in the terms of signal-to-noise ratio and full-width-half-maximum, respectively.

Multicarrier Block-Spread CDMA for Broadband Cellular Downlink

Directory of Open Access Journals (Sweden)

Leus Geert

2004-01-01

Full Text Available Effective suppression of multiuser interference (MUI and mitigation of frequency-selective fading effects within the complexity constraints of the mobile constitute major challenges for broadband cellular downlink transceiver design. Existing wideband direct-sequence (DS code division multiple access (CDMA transceivers suppress MUI statistically by restoring the orthogonality among users at the receiver. However, they call for receive diversity and multichannel equalization to improve the fading effects caused by deep channel fades. Relying on redundant block spreading and linear precoding, we design a so-called multicarrier block-spread- (MCBS-CDMA transceiver that preserves the orthogonality among users and guarantees symbol detection, regardless of the underlying frequency-selective fading channels. These properties allow for deterministic MUI elimination through low-complexity block despreading and enable full diversity gains, irrespective of the system load. Different options to perform equalization and decoding, either jointly or separately, strike the trade-off between performance and complexity. To improve the performance over multi-input multi-output (MIMO multipath fading channels, our MCBS-CDMA transceiver combines well with space-time block-coding (STBC techniques, to exploit both multiantenna and multipath diversity gains, irrespective of the system load. Simulation results demonstrate the superior performance of MCBS-CDMA compared to competing alternatives.

Energy Efficient Precoding C-RAN Downlink with Compression at Fronthaul

OpenAIRE

Nguyen, Kien-Giang; Vu, Quang-Doanh; Juntti, Markku; Tran, Le-Nam

2017-01-01

This paper considers a downlink transmission of cloud radio access network (C-RAN) in which precoded baseband signals at a common baseband unit are compressed before being forwarded to radio units (RUs) through limited fronthaul capacity links. We investigate the joint design of precoding, multivariate compression and RU-user selection which maximizes the energy efficiency of downlink C-RAN networks. The considered problem is inherently a rank-constrained mixed Boolean nonconvex program for w...

Analysis of Sleep-Mode Downlink Scheduling Operations in EPON Systems

OpenAIRE

Yan, Ying; Dittmann, Lars

2011-01-01

Energy management strategy has been considered as an important component in the future Ethernet Passive Optical Networks (EPONs). In this paper, a sleeping mode operation is studied, and a downlink packet scheduling scheme is analyzed to preserve energy consumption and maintain the required QoS. This paper proposes a novel sleep-mode downlink packet scheduling scheme in order to enhance the sleep control function. Simulation results confirm that the proposed approach offers effective power ma...

Beamforming applied to surface EEG improves ripple visibility.

Science.gov (United States)

van Klink, Nicole; Mol, Arjen; Ferrier, Cyrille; Hillebrand, Arjan; Huiskamp, Geertjan; Zijlmans, Maeike

2018-01-01

Surface EEG can show epileptiform ripples in people with focal epilepsy, but identification is impeded by the low signal-to-noise ratio of the electrode recordings. We used beamformer-based virtual electrodes to improve ripple identification. We analyzed ten minutes of interictal EEG of nine patients with refractory focal epilepsy. EEGs with more than 60 channels and 20 spikes were included. We computed ∼79 virtual electrodes using a scalar beamformer and marked ripples (80-250 Hz) co-occurring with spikes in physical and virtual electrodes. Ripple numbers in physical and virtual electrodes were compared, and sensitivity and specificity of ripples for the region of interest (ROI; based on clinical information) were determined. Five patients had ripples in the physical electrodes and eight in the virtual electrodes, with more ripples in virtual than in physical electrodes (101 vs. 57, p = .007). Ripples in virtual electrodes predicted the ROI better than physical electrodes (AUC 0.65 vs. 0.56, p = .03). Beamforming increased ripple visibility in surface EEG. Virtual ripples predicted the ROI better than physical ripples, although sensitivity was still poor. Beamforming can facilitate ripple identification in EEG. Ripple localization needs to be improved to enable its use for presurgical evaluation in people with epilepsy. Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Low bandwidth binaural beamforming

NARCIS (Netherlands)

Srinivasan, S.

2008-01-01

An efficient beamforming scheme for wireless binaural hearing aids is proposed that provides a trade-off between the transmission bit rate and the amount of noise reduction. It is proposed to transmit only the low-frequency part of the signal from one hearing aid to the other, which is used in a

A phantom study on temporal and subband Minimum Variance adaptive beamforming

DEFF Research Database (Denmark)

Diamantis, Konstantinos; Voxen, Iben Holfort; Greenaway, Alan H.

2014-01-01

This paper compares experimentally temporal and subband implementations of the Minimum Variance (MV) adaptive beamformer for medical ultrasound imaging. The performance of the two approaches is tested by comparing wire phantom measurements, obtained by the research ultrasound scanner SARUS. A 7 MHz...... BK8804 linear transducer was used to scan a wire phantom in which wires are separated by 10 mm. Performance is then evaluated by the lateral Full-Width-Half-Maximum (FWHM), the Peak Sidelobe Level (PSL), and the computational load. Beamformed single emission responses are also compared with those...... from conventional Delay-and-Sum (DAS) beamformer. FWHM measured at the depth of 46.6 mm, is 0.02 mm (0.09λ) for both adaptive methods while the corresponding values for Hanning and Boxcar weights are 0.64 and 0.44 mm respectively. Between the MV beamformers a -2 dB difference in PSL is noticed in favor...

Robust Adaptive LCMV Beamformer Based On An Iterative Suboptimal Solution

Directory of Open Access Journals (Sweden)

Xiansheng Guo

2015-06-01

Full Text Available The main drawback of closed-form solution of linearly constrained minimum variance (CF-LCMV beamformer is the dilemma of acquiring long observation time for stable covariance matrix estimates and short observation time to track dynamic behavior of targets, leading to poor performance including low signal-noise-ratio (SNR, low jammer-to-noise ratios (JNRs and small number of snapshots. Additionally, CF-LCMV suffers from heavy computational burden which mainly comes from two matrix inverse operations for computing the optimal weight vector. In this paper, we derive a low-complexity Robust Adaptive LCMV beamformer based on an Iterative Suboptimal solution (RAIS-LCMV using conjugate gradient (CG optimization method. The merit of our proposed method is threefold. Firstly, RAIS-LCMV beamformer can reduce the complexity of CF-LCMV remarkably. Secondly, RAIS-LCMV beamformer can adjust output adaptively based on measurement and its convergence speed is comparable. Finally, RAIS-LCMV algorithm has robust performance against low SNR, JNRs, and small number of snapshots. Simulation results demonstrate the superiority of our proposed algorithms.

An applicable 5.8 GHz wireless power transmission system with rough beamforming to Project Loon

Directory of Open Access Journals (Sweden)

Chang-Jun Ahn

2016-06-01

Full Text Available In recent, Google proposed the Project Loon being developed with the mission of providing internet access to rural and remote areas using high-altitude balloons. In this paper, we describe an applicable prototype of 5.8 GHz wireless power transmission system with rough beamforming method to Project Loon. From the measurement results, transmit beamforming phased array antenna can transmit power more efficiently compared to a horn antenna and array antenna without beamforming with increasing the transmission distance. For the transmission distance of 1000 mm, transmit beamforming phased array antenna can obtain higher received power about 1.46 times compared to array antenna without transmit beamforming.

Linear-Array Photoacoustic Imaging Using Minimum Variance-Based Delay Multiply and Sum Adaptive Beamforming Algorithm

OpenAIRE

Mozaffarzadeh, Moein; Mahloojifar, Ali; Orooji, Mahdi; Kratkiewicz, Karl; Adabi, Saba; Nasiriavanaki, Mohammadreza

2017-01-01

In Photoacoustic imaging (PA), Delay-and-Sum (DAS) beamformer is a common beamforming algorithm having a simple implementation. However, it results in a poor resolution and high sidelobes. To address these challenges, a new algorithm namely Delay-Multiply-and-Sum (DMAS) was introduced having lower sidelobes compared to DAS. To improve the resolution of DMAS, a novel beamformer is introduced using Minimum Variance (MV) adaptive beamforming combined with DMAS, so-called Minimum Variance-Based D...

Analysis of Beamformer Directed Single-Channel Noise Reduction System for Hearing Aid Applications

DEFF Research Database (Denmark)

Jensen, Jesper; Pedersen, Michael Syskind

2015-01-01

We study multi-microphone noise reduction systems consisting of a beamformer and a single-channel (SC) noise reduction stage. In particular, we present and analyse a maximum likelihood (ML) method for jointly estimating the target and noise power spectral densities (psd's) entering the SC filter....... We show that the estimators are minimum variance and unbiased, and provide closed-form expressions for their mean-square error (MSE). Furthermore, we show that the MSE of the noise psd estimator is particularly simple: it is independent of target signal characteristics, frequency, and microphone...

Robust distributed cognitive relay beamforming

KAUST Repository

Pandarakkottilil, Ubaidulla; Aissa, Sonia

2012-01-01

design takes into account a parameter of the error in the channel state information (CSI) to render the performance of the beamformer robust in the presence of imperfect CSI. Though the original problem is non-convex, we show that the proposed design can

Highly Efficient Multi Channel Packet Forwarding with Round Robin Intermittent Periodic Transmit for Multihop Wireless Backhaul Networks

Science.gov (United States)

Furukawa, Hiroshi

2017-01-01

Round Robin based Intermittent Periodic Transmit (RR-IPT) has been proposed which achieves highly efficient multi-hop relays in multi-hop wireless backhaul networks (MWBN) where relay nodes are 2-dimensionally deployed. This paper newly investigates multi-channel packet scheduling and forwarding scheme for RR-IPT. Downlink traffic is forwarded by RR-IPT via one of the channels, while uplink traffic and part of downlink are accommodated in the other channel. By comparing IPT and carrier sense multiple access with collision avoidance (CSMA/CA) for uplink/downlink packet forwarding channel, IPT is more effective in reducing packet loss rate whereas CSMA/CA is better in terms of system throughput and packet delay improvement. PMID:29137164

Enhanced linear-array photoacoustic beamforming using modified coherence factor.

Science.gov (United States)

Mozaffarzadeh, Moein; Yan, Yan; Mehrmohammadi, Mohammad; Makkiabadi, Bahador

2018-02-01

Photoacoustic imaging (PAI) is a promising medical imaging modality providing the spatial resolution of ultrasound imaging and the contrast of optical imaging. For linear-array PAI, a beamformer can be used as the reconstruction algorithm. Delay-and-sum (DAS) is the most prevalent beamforming algorithm in PAI. However, using DAS beamformer leads to low-resolution images as well as high sidelobes due to nondesired contribution of off-axis signals. Coherence factor (CF) is a weighting method in which each pixel of the reconstructed image is weighted, based on the spatial spectrum of the aperture, to mainly improve the contrast. We demonstrate that the numerator of the formula of CF contains a DAS algebra and propose the use of a delay-multiply-and-sum beamformer instead of the available DAS on the numerator. The proposed weighting technique, modified CF (MCF), has been evaluated numerically and experimentally compared to CF. It was shown that MCF leads to lower sidelobes and better detectable targets. The quantitative results of the experiment (using wire targets) show that MCF leads to for about 45% and 40% improvement, in comparison with CF, in the terms of signal-to-noise ratio and full-width-half-maximum, respectively. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Downlink User Selection and Resource Allocation for Semi-Elastic Flows in an OFDM Cell

OpenAIRE

Yang, Chao; Jordan, Scott

2013-01-01

We are concerned with user selection and resource allocation in wireless networks for semi-elastic applications such as video conferencing. While many packet scheduling algorithms have been proposed for elastic applications, and many user selection algorithms have been proposed for inelastic applications, little is known about optimal user selection and resource allocation for semi-elastic applications in wireless networks. We consider user selection and allocation of downlink transmission po...

Beamforming design with proactive interference cancelation in MISO interference channels

Science.gov (United States)

Li, Yang; Tian, Yafei; Yang, Chenyang

2015-12-01

In this paper, we design coordinated beamforming at base stations (BSs) to facilitate interference cancelation at users in interference networks, where each BS is equipped with multiple antennas and each user is with a single antenna. By assuming that each user can select the best decoding strategy to mitigate the interference, either canceling the interference after decoding when it is strong or treating it as noise when it is weak, we optimize the beamforming vectors that maximize the sum rate for the networks under different interference scenarios and find the solutions of beamforming with closed-form expressions. The inherent design principles are then analyzed, and the performance gain over passive interference cancelation is demonstrated through simulations in heterogeneous cellular networks.

Simulation Study of Real Time 3-D Synthetic Aperture Sequential Beamforming for Ultrasound Imaging

DEFF Research Database (Denmark)

Hemmsen, Martin Christian; Rasmussen, Morten Fischer; Stuart, Matthias Bo

2014-01-01

in the main system. The real-time imaging capability is achieved using a synthetic aperture beamforming technique, utilizing the transmit events to generate a set of virtual elements that in combination can generate an image. The two core capabilities in combination is named Synthetic Aperture Sequential......This paper presents a new beamforming method for real-time three-dimensional (3-D) ultrasound imaging using a 2-D matrix transducer. To obtain images with sufficient resolution and contrast, several thousand elements are needed. The proposed method reduces the required channel count from...... Beamforming (SASB). Simulations are performed to evaluate the image quality of the presented method in comparison to Parallel beamforming utilizing 16 receive beamformers. As indicators for image quality the detail resolution and Cystic resolution are determined for a set of scatterers at a depth of 90mm...

On the power amplifier nonlinearity in MIMO transmit beamforming systems

KAUST Repository

Qi, Jian

2012-03-01

In this paper, single-carrier multiple-input multiple-output (MIMO) transmit beamforming (TB) systems in the presence of high-power amplifier (HPA) nonlinearity are investigated. Specifically, due to the suboptimality of the conventional maximal ratio transmission/maximal ratio combining (MRT/MRC) under HPA nonlinearity, we propose the optimal TB scheme with the optimal beamforming weight vector and combining vector, for MIMO systems with nonlinear HPAs. Moreover, an alternative suboptimal but much simpler TB scheme, namely, quantized equal gain transmission (QEGT), is proposed. The latter profits from the property that the elements of the beamforming weight vector have the same constant modulus. The performance of the proposed optimal TB scheme and QEGT/MRC technique in the presence of the HPA nonlinearity is evaluated in terms of the average symbol error probability and mutual information with the Gaussian input, considering the transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects on the performance of several system parameters, namely, the HPA parameters, numbers of antennas, quadrature amplitude modulation modulation order, number of pilot symbols, and cardinality of the beamforming weight vector codebook for QEGT. © 2012 IEEE.

Numerical analysis of biosonar beamforming mechanisms and strategies in bats.

Science.gov (United States)

Müller, Rolf

2010-09-01

Beamforming is critical to the function of most sonar systems. The conspicuous noseleaf and pinna shapes in bats suggest that beamforming mechanisms based on diffraction of the outgoing and incoming ultrasonic waves play a major role in bat biosonar. Numerical methods can be used to investigate the relationships between baffle geometry, acoustic mechanisms, and resulting beampatterns. Key advantages of numerical approaches are: efficient, high-resolution estimation of beampatterns, spatially dense predictions of near-field amplitudes, and the malleability of the underlying shape representations. A numerical approach that combines near-field predictions based on a finite-element formulation for harmonic solutions to the Helmholtz equation with a free-field projection based on the Kirchhoff integral to obtain estimates of the far-field beampattern is reviewed. This method has been used to predict physical beamforming mechanisms such as frequency-dependent beamforming with half-open resonance cavities in the noseleaf of horseshoe bats and beam narrowing through extension of the pinna aperture with skin folds in false vampire bats. The fine structure of biosonar beampatterns is discussed for the case of the Chinese noctule and methods for assessing the spatial information conveyed by beampatterns are demonstrated for the brown long-eared bat.

On the power amplifier nonlinearity in MIMO transmit beamforming systems

KAUST Repository

Qi, Jian; Aissa, Sonia

2012-01-01

In this paper, single-carrier multiple-input multiple-output (MIMO) transmit beamforming (TB) systems in the presence of high-power amplifier (HPA) nonlinearity are investigated. Specifically, due to the suboptimality of the conventional maximal ratio transmission/maximal ratio combining (MRT/MRC) under HPA nonlinearity, we propose the optimal TB scheme with the optimal beamforming weight vector and combining vector, for MIMO systems with nonlinear HPAs. Moreover, an alternative suboptimal but much simpler TB scheme, namely, quantized equal gain transmission (QEGT), is proposed. The latter profits from the property that the elements of the beamforming weight vector have the same constant modulus. The performance of the proposed optimal TB scheme and QEGT/MRC technique in the presence of the HPA nonlinearity is evaluated in terms of the average symbol error probability and mutual information with the Gaussian input, considering the transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects on the performance of several system parameters, namely, the HPA parameters, numbers of antennas, quadrature amplitude modulation modulation order, number of pilot symbols, and cardinality of the beamforming weight vector codebook for QEGT. © 2012 IEEE.

In-Band Full-Duplex Communications for Cellular Networks with Partial Uplink/Downlink Overlap

KAUST Repository

Alammouri, Ahmad; Elsawy, Hesham; Amin, Osama; Alouini, Mohamed-Slim

2015-01-01

In-band full-duplex (FD) communications have been optimistically promoted to improve the spectrum utilization in cellular networks. However, the explicit impact of spatial interference, imposed by FD communications, on uplink and downlink transmissions has been overlooked in the literature. This paper presents an extensive study of the explicit effect of FD communications on the uplink and downlink performances. For the sake of rigorous analysis, we develop a tractable framework based on stochastic geometry toolset. The developed model accounts for uplink truncated channel inversion power control in FD cellular networks. The study shows that FD communications improve the downlink throughput at the expense of significant degradation in the uplink throughput. Therefore, we propose a novel fine-grained duplexing scheme, denoted as α-duplex scheme, which allows a partial overlap between uplink and downlink frequency bands. To this end, we show that the amount of the overlap can be optimized via adjusting α to achieve a certain design objective.

In-Band Full-Duplex Communications for Cellular Networks with Partial Uplink/Downlink Overlap

KAUST Repository

AlAmmouri, Ahmad

2015-12-06

In-band full-duplex (FD) communications have been optimistically promoted to improve the spectrum utilization in cellular networks. However, the explicit impact of spatial interference, imposed by FD communications, on uplink and downlink transmissions has been overlooked in the literature. This paper presents an extensive study of the explicit effect of FD communications on the uplink and downlink performances. For the sake of rigorous analysis, we develop a tractable framework based on stochastic geometry toolset. The developed model accounts for uplink truncated channel inversion power control in FD cellular networks. The study shows that FD communications improve the downlink throughput at the expense of significant degradation in the uplink throughput. Therefore, we propose a novel fine-grained duplexing scheme, denoted as α-duplex scheme, which allows a partial overlap between uplink and downlink frequency bands. To this end, we show that the amount of the overlap can be optimized via adjusting α to achieve a certain design objective.

Minimum Variance Beamforming for High Frame-Rate Ultrasound Imaging

DEFF Research Database (Denmark)

Holfort, Iben Kraglund; Gran, Fredrik; Jensen, Jørgen Arendt

2007-01-01

, a 7 MHz, 128-element, phased array transducer with lambda/2-spacing was used. Data is obtained using a single element as the transmitting aperture and all 128 elements as the receiving aperture. A full SA sequence consisting of 128 emissions was simulated by gliding the active transmitting element...... weights for each frequency sub-band. As opposed to the conventional, Delay and Sum (DS) beamformer, this approach is dependent on the specific data. The performance of the proposed MV beamformer is tested on simulated synthetic aperture (SA) ultrasound data, obtained using Field II. For the simulations...... across the array. Data for 13 point targets and a circular cyst with a radius of 5 mm were simulated. The performance of the MV beamformer is compared to DS using boxcar weights and Hanning weights, and is quantified by the Full Width at Half Maximum (FWHM) and the peak-side-lobe level (PSL). Single...

Characterizing CDMA downlink feasibility via effective interference

NARCIS (Netherlands)

Endrayanto, A.I.; van den Berg, Hans Leo; Boucherie, Richardus J.

2003-01-01

This paper models and analyses downlink power assignment feasibility in Code Division Multiple Access (CDMA) mobile networks. By discretizing the area into small segments, the power requirements are characterized via a matrix representation that separates user and system characteristics. We obtain a

Modeling virtualized downlink cellular networks with ultra-dense small cells

KAUST Repository

Ibrahim, Hazem

2015-09-11

The unrelenting increase in the mobile users\\' populations and traffic demand drive cellular network operators to densify their infrastructure. Network densification increases the spatial frequency reuse efficiency while maintaining the signal-to-interference-plus-noise-ratio (SINR) performance, hence, increases the spatial spectral efficiency and improves the overall network performance. However, control signaling in such dense networks consumes considerable bandwidth and limits the densification gain. Radio access network (RAN) virtualization via control plane (C-plane) and user plane (U-plane) splitting has been recently proposed to lighten the control signaling burden and improve the network throughput. In this paper, we present a tractable analytical model for virtualized downlink cellular networks, using tools from stochastic geometry. We then apply the developed modeling framework to obtain design insights for virtualized RANs and quantify associated performance improvement. © 2015 IEEE.

Analysis of Sleep-Mode Downlink Scheduling Operations in EPON Systems

DEFF Research Database (Denmark)

Yan, Ying; Dittmann, Lars

2011-01-01

Energy management strategy has been considered as an important component in the future Ethernet Passive Optical Networks (EPONs). In this paper, a sleeping mode operation is studied, and a downlink packet scheduling scheme is analyzed to preserve energy consumption and maintain the required Qo......S. This paper proposes a novel sleep-mode downlink packet scheduling scheme in order to enhance the sleep control function. Simulation results confirm that the proposed approach offers effective power management on the basis of the traffic conditions. The trade-off between network performances and the power...

Delay and Standard Deviation Beamforming to Enhance Specular Reflections in Ultrasound Imaging.

Science.gov (United States)

Bandaru, Raja Sekhar; Sornes, Anders Rasmus; Hermans, Jeroen; Samset, Eigil; D'hooge, Jan

2016-12-01

Although interventional devices, such as needles, guide wires, and catheters, are best visualized by X-ray, real-time volumetric echography could offer an attractive alternative as it avoids ionizing radiation; it provides good soft tissue contrast, and it is mobile and relatively cheap. Unfortunately, as echography is traditionally used to image soft tissue and blood flow, the appearance of interventional devices in conventional ultrasound images remains relatively poor, which is a major obstacle toward ultrasound-guided interventions. The objective of this paper was therefore to enhance the appearance of interventional devices in ultrasound images. Thereto, a modified ultrasound beamforming process using conventional-focused transmit beams is proposed that exploits the properties of received signals containing specular reflections (as arising from these devices). This new beamforming approach referred to as delay and standard deviation beamforming (DASD) was quantitatively tested using simulated as well as experimental data using a linear array transducer. Furthermore, the influence of different imaging settings (i.e., transmit focus, imaging depth, and scan angle) on the obtained image contrast was evaluated. The study showed that the image contrast of specular regions improved by 5-30 dB using DASD beamforming compared with traditional delay and sum (DAS) beamforming. The highest gain in contrast was observed when the interventional device was tilted away from being orthogonal to the transmit beam, which is a major limitation in standard DAS imaging. As such, the proposed beamforming methodology can offer an improved visualization of interventional devices in the ultrasound image with potential implications for ultrasound-guided interventions.

Non-invasive beamforming add-on module

KAUST Repository

Bader, Ahmed; Alouini, Mohamed-Slim

2017-01-01

An embodiment of a non-invasive beamforming add-on apparatus couples to an existing antenna port and rectifies the beam azimuth in the upstream and downstream directions. The apparatus comprises input circuitry that is configured to receive one

Beamforming under Quantization Errors in Wireless Binaural Hearing Aids

Directory of Open Access Journals (Sweden)

Srinivasan Sriram

2008-01-01

Full Text Available Improving the intelligibility of speech in different environments is one of the main objectives of hearing aid signal processing algorithms. Hearing aids typically employ beamforming techniques using multiple microphones for this task. In this paper, we discuss a binaural beamforming scheme that uses signals from the hearing aids worn on both the left and right ears. Specifically, we analyze the effect of a low bit rate wireless communication link between the left and right hearing aids on the performance of the beamformer. The scheme is comprised of a generalized sidelobe canceller (GSC that has two inputs: observations from one ear, and quantized observations from the other ear, and whose output is an estimate of the desired signal. We analyze the performance of this scheme in the presence of a localized interferer as a function of the communication bit rate using the resultant mean-squared error as the signal distortion measure.

Beamforming under Quantization Errors in Wireless Binaural Hearing Aids

Directory of Open Access Journals (Sweden)

Kees Janse

2008-09-01

Full Text Available Improving the intelligibility of speech in different environments is one of the main objectives of hearing aid signal processing algorithms. Hearing aids typically employ beamforming techniques using multiple microphones for this task. In this paper, we discuss a binaural beamforming scheme that uses signals from the hearing aids worn on both the left and right ears. Specifically, we analyze the effect of a low bit rate wireless communication link between the left and right hearing aids on the performance of the beamformer. The scheme is comprised of a generalized sidelobe canceller (GSC that has two inputs: observations from one ear, and quantized observations from the other ear, and whose output is an estimate of the desired signal. We analyze the performance of this scheme in the presence of a localized interferer as a function of the communication bit rate using the resultant mean-squared error as the signal distortion measure.

Interference management with partial uplink/downlink spectrum overlap

KAUST Repository

Randrianantenaina, Itsikiantsoa; Elsawy, Hesham; Dahrouj, Hayssam; Alouini, Mohamed-Slim

2016-01-01

Simultaneous reuse of spectral resources by uplink and downlink, denoted as in-band full duplex (FD) communication, is promoted to double the spectral efficiency when compared to its half-duplex (HD) counterpart. Interference management, however

Downlink scheduling using non-orthogonal uplink beams

KAUST Repository

Eltayeb, Mohammed E.

2014-04-01

Opportunistic schedulers rely on the feedback of the channel state information of users in order to perform user selection and downlink scheduling. This feedback increases with the number of users, and can lead to inefficient use of network resources and scheduling delays. We tackle the problem of feedback design, and propose a novel class of nonorthogonal codes to feed back channel state information. Users with favorable channel conditions simultaneously transmit their channel state information via non-orthogonal beams to the base station. The proposed formulation allows the base station to identify the strong users via a simple correlation process. After deriving the minimum required code length and closed-form expressions for the feedback load and downlink capacity, we show that i) the proposed algorithm reduces the feedback load while matching the achievable rate of full feedback algorithms operating over a noiseless feedback channel, and ii) the proposed codes are superior to the Gaussian codes.

Downlink scheduling using non-orthogonal uplink beams

KAUST Repository

Eltayeb, Mohammed E.; Al-Naffouri, Tareq Y.; Bahrami, Hamid Reza Talesh

2014-01-01

Opportunistic schedulers rely on the feedback of the channel state information of users in order to perform user selection and downlink scheduling. This feedback increases with the number of users, and can lead to inefficient use of network resources and scheduling delays. We tackle the problem of feedback design, and propose a novel class of nonorthogonal codes to feed back channel state information. Users with favorable channel conditions simultaneously transmit their channel state information via non-orthogonal beams to the base station. The proposed formulation allows the base station to identify the strong users via a simple correlation process. After deriving the minimum required code length and closed-form expressions for the feedback load and downlink capacity, we show that i) the proposed algorithm reduces the feedback load while matching the achievable rate of full feedback algorithms operating over a noiseless feedback channel, and ii) the proposed codes are superior to the Gaussian codes.

An Integrated Real-Time Beamforming and Postfiltering System for Nonstationary Noise Environments

Directory of Open Access Journals (Sweden)

Gannot Sharon

2003-01-01

Full Text Available We present a novel approach for real-time multichannel speech enhancement in environments of nonstationary noise and time-varying acoustical transfer functions (ATFs. The proposed system integrates adaptive beamforming, ATF identification, soft signal detection, and multichannel postfiltering. The noise canceller branch of the beamformer and the ATF identification are adaptively updated online, based on hypothesis test results. The noise canceller is updated only during stationary noise frames, and the ATF identification is carried out only when desired source components have been detected. The hypothesis testing is based on the nonstationarity of the signals and the transient power ratio between the beamformer primary output and its reference noise signals. Following the beamforming and the hypothesis testing, estimates for the signal presence probability and for the noise power spectral density are derived. Subsequently, an optimal spectral gain function that minimizes the mean square error of the log-spectral amplitude (LSA is applied. Experimental results demonstrate the usefulness of the proposed system in nonstationary noise environments.

Robust distributed two-way relay beamforming in cognitive radio networks

KAUST Repository

Pandarakkottilil, Ubaidulla

2012-04-01

In this paper, we present distributed beamformer designs for a cognitive radio network (CRN) consisting of a pair of cognitive (or secondary) transceiver nodes communicating with each other through a set of secondary non-regenerative two-way relays. The secondary network shares the spectrum with a licensed primary user (PU), and operates under a constraint on the maximum interference to the PU, in addition to its own resource and quality of service (QoS) constraints. We propose beamformer designs assuming that the available channel state information (CSI) is imperfect, which reflects realistic scenarios. The performance of proposed designs is robust to the CSI errors. Such robustness is critical in CRNs given the difficulty in acquiring perfect CSI due to loose cooperation between the PUs and the secondary users (SUs), and the need for strict enforcement of PU interference limit. We consider a mean-square error (MSE)-constrained beamformer that minimizes the total relay transmit power and an MSE-balancing beamformer with a constraint on the total relay transmit power. We show that the proposed designs can be reformulated as convex optimization problems that can be solved efficiently. Through numerical simulations, we illustrate the improved performance of the proposed robust designs compared to non-robust designs. © 2012 IEEE.

PHASED ARRAY FEED CALIBRATION, BEAMFORMING, AND IMAGING

International Nuclear Information System (INIS)

Landon, Jonathan; Elmer, Michael; Waldron, Jacob; Jones, David; Stemmons, Alan; Jeffs, Brian D.; Warnick, Karl F.; Richard Fisher, J.; Norrod, Roger D.

2010-01-01

Phased array feeds (PAFs) for reflector antennas offer the potential for increased reflector field of view and faster survey speeds. To address some of the development challenges that remain for scientifically useful PAFs, including calibration and beamforming algorithms, sensitivity optimization, and demonstration of wide field of view imaging, we report experimental results from a 19 element room temperature L-band PAF mounted on the Green Bank 20 Meter Telescope. Formed beams achieved an aperture efficiency of 69% and a system noise temperature of 66 K. Radio camera images of several sky regions are presented. We investigate the noise performance and sensitivity of the system as a function of elevation angle with statistically optimal beamforming and demonstrate cancelation of radio frequency interference sources with adaptive spatial filtering.

Stochastic Beamforming via Compact Antenna Arrays

DEFF Research Database (Denmark)

Alrabadi, Osama; Pedersen, Gert Frølund

2012-01-01

The paper investigates the average beamforming (BF) gain of compact antenna arrays when statistical channel knowledge is available. The optimal excitation (precoding vector) and impedance termination that maximize the average BF gain are a compromise between the ones that maximize the array...

Multicell Downlink Capacity with Coordinated Processing

Directory of Open Access Journals (Sweden)

Roberto Padovani

2008-07-01

Full Text Available We study the potential benefits of base-station (BS cooperation for downlink transmission in multicell networks. Based on a modified Wyner-type model with users clustered at the cell-edges, we analyze the dirty-paper-coding (DPC precoder and several linear precoding schemes, including cophasing, zero-forcing (ZF, and MMSE precoders. For the nonfading scenario with random phases, we obtain analytical performance expressions for each scheme. In particular, we characterize the high signal-to-noise ratio (SNR performance gap between the DPC and ZF precoders in large networks, which indicates a singularity problem in certain network settings. Moreover, we demonstrate that the MMSE precoder does not completely resolve the singularity problem. However, by incorporating path gain fading, we numerically show that the singularity problem can be eased by linear precoding techniques aided with multiuser selection. By extending our network model to include cell-interior users, we determine the capacity regions of the two classes of users for various cooperative strategies. In addition to an outer bound and a baseline scheme, we also consider several locally cooperative transmission approaches. The resulting capacity regions show the tradeoff between the performance improvement and the requirement for BS cooperation, signal processing complexity, and channel state information at the transmitter (CSIT.

Employing beam-forming for estimating the direction of arrival in a multi-path propagation environment

Directory of Open Access Journals (Sweden)

M. Bresch

2005-01-01

Full Text Available Due to recent researches on traffic accidents with vulnerable road users (VRUs, several measures revealed a great opportunity of reduction. However, all measures applied so far failed to reduce the number of traffic accidents if there is no line-of-sight. Therefore, a transponder signal is utilized to make the VRU visible. The motor vehicle carries a mobile receiver for VRU detection and location. The receiver employs digital beam-forming for estimating the direction of arrival (DOA with an antenna array for RF ISM band. A sequence of DOA estimations is used for location and motion estimation purposes.

Spatially Controlled Relay Beamforming

Science.gov (United States)

Kalogerias, Dionysios

This thesis is about fusion of optimal stochastic motion control and physical layer communications. Distributed, networked communication systems, such as relay beamforming networks (e.g., Amplify & Forward (AF)), are typically designed without explicitly considering how the positions of the respective nodes might affect the quality of the communication. Optimum placement of network nodes, which could potentially improve the quality of the communication, is not typically considered. However, in most practical settings in physical layer communications, such as relay beamforming, the Channel State Information (CSI) observed by each node, per channel use, although it might be (modeled as) random, it is both spatially and temporally correlated. It is, therefore, reasonable to ask if and how the performance of the system could be improved by (predictively) controlling the positions of the network nodes (e.g., the relays), based on causal side (CSI) information, and exploitting the spatiotemporal dependencies of the wireless medium. In this work, we address this problem in the context of AF relay beamforming networks. This novel, cyber-physical system approach to relay beamforming is termed as "Spatially Controlled Relay Beamforming". First, we discuss wireless channel modeling, however, in a rigorous, Bayesian framework. Experimentally accurate and, at the same time, technically precise channel modeling is absolutely essential for designing and analyzing spatially controlled communication systems. In this work, we are interested in two distinct spatiotemporal statistical models, for describing the behavior of the log-scale magnitude of the wireless channel: 1. Stationary Gaussian Fields: In this case, the channel is assumed to evolve as a stationary, Gaussian stochastic field in continuous space and discrete time (say, for instance, time slots). Under such assumptions, spatial and temporal statistical interactions are determined by a set of time and space invariant

Robust Transceiver Design for Multiuser MIMO Downlink with Channel Uncertainties

Science.gov (United States)

Miao, Wei; Li, Yunzhou; Chen, Xiang; Zhou, Shidong; Wang, Jing

This letter addresses the problem of robust transceiver design for the multiuser multiple-input-multiple-output (MIMO) downlink where the channel state information at the base station (BS) is imperfect. A stochastic approach which minimizes the expectation of the total mean square error (MSE) of the downlink conditioned on the channel estimates under a total transmit power constraint is adopted. The iterative algorithm reported in [2] is improved to handle the proposed robust optimization problem. Simulation results show that our proposed robust scheme effectively reduces the performance loss due to channel uncertainties and outperforms existing methods, especially when the channel errors of the users are different.

Microwave beamforming for non-invasive patient-specific hyperthermia treatment of pediatric brain cancer

International Nuclear Information System (INIS)

Burfeindt, Matthew J; Zastrow, Earl; Hagness, Susan C; Van Veen, Barry D; Medow, Joshua E

2011-01-01

We present a numerical study of an array-based microwave beamforming approach for non-invasive hyperthermia treatment of pediatric brain tumors. The transmit beamformer is designed to achieve localized heating-that is, to achieve constructive interference and selective absorption of the transmitted electromagnetic waves at the desired focus location in the brain while achieving destructive interference elsewhere. The design process takes into account patient-specific and target-specific propagation characteristics at 1 GHz. We evaluate the effectiveness of the beamforming approach using finite-difference time-domain simulations of two MRI-derived child head models from the Virtual Family (IT'IS Foundation). Microwave power deposition and the resulting steady-state thermal distribution are calculated for each of several randomly chosen focus locations. We also explore the robustness of the design to mismatch between the assumed and actual dielectric properties of the patient. Lastly, we demonstrate the ability of the beamformer to suppress hot spots caused by pockets of cerebrospinal fluid (CSF) in the brain. Our results show that microwave beamforming has the potential to create localized heating zones in the head models for focus locations that are not surrounded by large amounts of CSF. These promising results suggest that the technique warrants further investigation and development.

Linear-array photoacoustic imaging using minimum variance-based delay multiply and sum adaptive beamforming algorithm

Science.gov (United States)

Mozaffarzadeh, Moein; Mahloojifar, Ali; Orooji, Mahdi; Kratkiewicz, Karl; Adabi, Saba; Nasiriavanaki, Mohammadreza

2018-02-01

In photoacoustic imaging, delay-and-sum (DAS) beamformer is a common beamforming algorithm having a simple implementation. However, it results in a poor resolution and high sidelobes. To address these challenges, a new algorithm namely delay-multiply-and-sum (DMAS) was introduced having lower sidelobes compared to DAS. To improve the resolution of DMAS, a beamformer is introduced using minimum variance (MV) adaptive beamforming combined with DMAS, so-called minimum variance-based DMAS (MVB-DMAS). It is shown that expanding the DMAS equation results in multiple terms representing a DAS algebra. It is proposed to use the MV adaptive beamformer instead of the existing DAS. MVB-DMAS is evaluated numerically and experimentally. In particular, at the depth of 45 mm MVB-DMAS results in about 31, 18, and 8 dB sidelobes reduction compared to DAS, MV, and DMAS, respectively. The quantitative results of the simulations show that MVB-DMAS leads to improvement in full-width-half-maximum about 96%, 94%, and 45% and signal-to-noise ratio about 89%, 15%, and 35% compared to DAS, DMAS, MV, respectively. In particular, at the depth of 33 mm of the experimental images, MVB-DMAS results in about 20 dB sidelobes reduction in comparison with other beamformers.

A scalable-low cost architecture for high gain beamforming antennas

KAUST Repository

Bakr, Omar; Johnson, Mark; Jungdong Park,; Adabi, Ehsan; Jones, Kevin; Niknejad, Ali

2010-01-01

Many state-of-the-art wireless systems, such as long distance mesh networks and high bandwidth networks using mm-wave frequencies, require high gain antennas to overcome adverse channel conditions. These networks could be greatly aided by adaptive beamforming antenna arrays, which can significantly simplify the installation and maintenance costs (e.g., by enabling automatic beam alignment). However, building large, low cost beamforming arrays is very complicated. In this paper, we examine the main challenges presented by large arrays, starting from electromagnetic and antenna design and proceeding to the signal processing and algorithms domain. We propose 3-dimensional antenna structures and hybrid RF/digital radio architectures that can significantly reduce the complexity and improve the power efficiency of adaptive array systems. We also present signal processing techniques based on adaptive filtering methods that enhance the robustness of these architectures. Finally, we present computationally efficient vector quantization techniques that significantly improve the interference cancellation capabilities of analog beamforming architectures. © 2010 IEEE.

A scalable-low cost architecture for high gain beamforming antennas

KAUST Repository

Bakr, Omar

2010-10-01

Many state-of-the-art wireless systems, such as long distance mesh networks and high bandwidth networks using mm-wave frequencies, require high gain antennas to overcome adverse channel conditions. These networks could be greatly aided by adaptive beamforming antenna arrays, which can significantly simplify the installation and maintenance costs (e.g., by enabling automatic beam alignment). However, building large, low cost beamforming arrays is very complicated. In this paper, we examine the main challenges presented by large arrays, starting from electromagnetic and antenna design and proceeding to the signal processing and algorithms domain. We propose 3-dimensional antenna structures and hybrid RF/digital radio architectures that can significantly reduce the complexity and improve the power efficiency of adaptive array systems. We also present signal processing techniques based on adaptive filtering methods that enhance the robustness of these architectures. Finally, we present computationally efficient vector quantization techniques that significantly improve the interference cancellation capabilities of analog beamforming architectures. © 2010 IEEE.

Downlink Multihop Transmission Technique for Asymmetric Traffic Accommodation in DS-CDMA/FDD Cellular Communications

Science.gov (United States)

Mori, Kazuo; Naito, Katsuhiro; Kobayashi, Hideo

This paper proposes an asymmetric traffic accommodation scheme using a multihop transmission technique for CDMA/FDD cellular communication systems. The proposed scheme exploits the multihop transmission to downlink packet transmissions, which require the large transmission power at their single-hop transmissions, in order to increase the downlink capacity. In these multihop transmissions, vacant uplink band is used for the transmissions from relay stations to destination mobile stations, and this leads more capacity enhancement in the downlink communications. The relay route selection method and power control method for the multihop transmissions are also investigated in the proposed scheme. The proposed scheme is evaluated by computer simulation and the results show that the proposed scheme can achieve better system performance.

Robust Nearfield Wideband Beamforming Design Based on Adaptive-Weighted Convex Optimization

Directory of Open Access Journals (Sweden)

Guo Ye-Cai

2017-01-01

Full Text Available Nearfield wideband beamformers for microphone arrays have wide applications in multichannel speech enhancement. The nearfield wideband beamformer design based on convex optimization is one of the typical representatives of robust approaches. However, in this approach, the coefficient of convex optimization is a constant, which has not used all the freedom provided by the weighting coefficient efficiently. Therefore, it is still necessary to further improve the performance. To solve this problem, we developed a robust nearfield wideband beamformer design approach based on adaptive-weighted convex optimization. The proposed approach defines an adaptive-weighted function by the adaptive array signal processing theory and adjusts its value flexibly, which has improved the beamforming performance. During each process of the adaptive updating of the weighting function, the convex optimization problem can be formulated as a SOCP (Second-Order Cone Program problem, which could be solved efficiently using the well-established interior-point methods. This method is suitable for the case where the sound source is in the nearfield range, can work well in the presence of microphone mismatches, and is applicable to arbitrary array geometries. Several design examples are presented to verify the effectiveness of the proposed approach and the correctness of the theoretical analysis.

Scheduling Algorithms for Maximizing Throughput with Zero-Forcing Beamforming in a MIMO Wireless System

Science.gov (United States)

Foronda, Augusto; Ohta, Chikara; Tamaki, Hisashi

Dirty paper coding (DPC) is a strategy to achieve the region capacity of multiple input multiple output (MIMO) downlink channels and a DPC scheduler is throughput optimal if users are selected according to their queue states and current rates. However, DPC is difficult to implement in practical systems. One solution, zero-forcing beamforming (ZFBF) strategy has been proposed to achieve the same asymptotic sum rate capacity as that of DPC with an exhaustive search over the entire user set. Some suboptimal user group selection schedulers with reduced complexity based on ZFBF strategy (ZFBF-SUS) and proportional fair (PF) scheduling algorithm (PF-ZFBF) have also been proposed to enhance the throughput and fairness among the users, respectively. However, they are not throughput optimal, fairness and throughput decrease if each user queue length is different due to different users channel quality. Therefore, we propose two different scheduling algorithms: a throughput optimal scheduling algorithm (ZFBF-TO) and a reduced complexity scheduling algorithm (ZFBF-RC). Both are based on ZFBF strategy and, at every time slot, the scheduling algorithms have to select some users based on user channel quality, user queue length and orthogonality among users. Moreover, the proposed algorithms have to produce the rate allocation and power allocation for the selected users based on a modified water filling method. We analyze the schedulers complexity and numerical results show that ZFBF-RC provides throughput and fairness improvements compared to the ZFBF-SUS and PF-ZFBF scheduling algorithms.

An evaluation of the performance of two binaural beamformers in complex and dynamic multitalker environments.

Science.gov (United States)

Best, Virginia; Mejia, Jorge; Freeston, Katrina; van Hoesel, Richard J; Dillon, Harvey

2015-01-01

Binaural beamformers are super-directional hearing aids created by combining microphone outputs from each side of the head. While they offer substantial improvements in SNR over conventional directional hearing aids, the benefits (and possible limitations) of these devices in realistic, complex listening situations have not yet been fully explored. In this study we evaluated the performance of two experimental binaural beamformers. Testing was carried out using a horizontal loudspeaker array. Background noise was created using recorded conversations. Performance measures included speech intelligibility, localization in noise, acceptable noise level, subjective ratings, and a novel dynamic speech intelligibility measure. Participants were 27 listeners with bilateral hearing loss, fitted with BTE prototypes that could be switched between conventional directional or binaural beamformer microphone modes. Relative to the conventional directional microphones, both binaural beamformer modes were generally superior for tasks involving fixed frontal targets, but not always for situations involving dynamic target locations. Binaural beamformers show promise for enhancing listening in complex situations when the location of the source of interest is predictable.

Linear-array photoacoustic imaging using minimum variance-based delay multiply and sum adaptive beamforming algorithm.

Science.gov (United States)

Mozaffarzadeh, Moein; Mahloojifar, Ali; Orooji, Mahdi; Kratkiewicz, Karl; Adabi, Saba; Nasiriavanaki, Mohammadreza

2018-02-01

In photoacoustic imaging, delay-and-sum (DAS) beamformer is a common beamforming algorithm having a simple implementation. However, it results in a poor resolution and high sidelobes. To address these challenges, a new algorithm namely delay-multiply-and-sum (DMAS) was introduced having lower sidelobes compared to DAS. To improve the resolution of DMAS, a beamformer is introduced using minimum variance (MV) adaptive beamforming combined with DMAS, so-called minimum variance-based DMAS (MVB-DMAS). It is shown that expanding the DMAS equation results in multiple terms representing a DAS algebra. It is proposed to use the MV adaptive beamformer instead of the existing DAS. MVB-DMAS is evaluated numerically and experimentally. In particular, at the depth of 45 mm MVB-DMAS results in about 31, 18, and 8 dB sidelobes reduction compared to DAS, MV, and DMAS, respectively. The quantitative results of the simulations show that MVB-DMAS leads to improvement in full-width-half-maximum about 96%, 94%, and 45% and signal-to-noise ratio about 89%, 15%, and 35% compared to DAS, DMAS, MV, respectively. In particular, at the depth of 33 mm of the experimental images, MVB-DMAS results in about 20 dB sidelobes reduction in comparison with other beamformers. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Analisis Quality of Service (QoS Jaringan Telekomunikasi High-Speed Downlink Packet Access (HSDPA pada Teknologi 3.5G

Directory of Open Access Journals (Sweden)

Mey Fenny Wati Simanjuntak

2016-01-01

Full Text Available Sejak layanan teknologi 3G pertama kali diperkenalkan, permintaan akan layanan berbasis paket data dari tahun ke tahun mengalami peningkatan yang pesat. Menanggapi hal tersebut, para penyedian jaringan telekomunikasi terus berusaha untuk meningkatkan kemampuan jaringannya. Salah satu solusinya menerapkan teknologi High-Speed Downlink Packet Access yang direkomendasikan oleh 3GPP Release 5. Penelitian ini dikhususkan untuk menganalisis Quality of Service jaringan telekomunikasi High-Speed Downlink Packet Access di Kecamatan Tembalang Kota Semarang. Analisis Quality of Service jaringan telekomunikasi High-Speed Downlink Packet Access pada penelitian ini bertujuan untuk memberikan gambaran kualitas jaringan telekomunikasi High-Speed Downlink Packet Access dari sisi bandwidth, throughput, packet loss dan delay. Metode penelitian yang dibahas dalam penelitian ini yaitu penelitian kualitatif observatif, dimana akan dilakukan pengamatan tentang bagaimana QoS jaringan telekomunikasi High-Speed Downlink Packet Access pada teknologi 3.5G di Kecamatan Tembalang Kota Semarang. Proses pengamatan dalam menganalisis Quality of Service jaringan telekomunikasi High-Speed Downlink Packet Access di Kecamatan Tembalang Kota Semarang berdasarkan 4 parameter diantaranya bandwidth, throughput, packet loss dan delay. Aplikasi yang digunakan yaitu monitoring application Elnus Bandwidth Meter dan Axence NetTools Professional 4.0. Selain itu, Quality of Service jaringan telekomunikasi High- Speed Downlink Packet Access di Kecamatan Tembalang Kota Semarang diamati berdasarkan waktu yaitu harian, mingguan dan bulanan.

DS-CDMA satellite diversity reception for personal satellite communication: Downlink performance analysis

Science.gov (United States)

DeGaudenzi, Riccardo; Giannetti, Filippo

1995-01-01

The downlink of a satellite-mobile personal communication system employing power-controlled Direct Sequence Code Division Multiple Access (DS-CDMA) and exploiting satellite-diversity is analyzed and its performance compared with a more traditional communication system utilizing single satellite reception. The analytical model developed has been thoroughly validated by means of extensive Monte Carlo computer simulations. It is shown how the capacity gain provided by diversity reception shrinks considerably in the presence of increasing traffic or in the case of light shadowing conditions. Moreover, the quantitative results tend to indicate that to combat system capacity reduction due to intra-system interference, no more than two satellites shall be active over the same region. To achieve higher system capacity, differently from terrestrial cellular systems, Multi-User Detection (MUD) techniques are likely to be required in the mobile user terminal, thus considerably increasing its complexity.

Development of an acoustic steam generator leak detection system using delay-and-sum beamformer

International Nuclear Information System (INIS)

Chikazawa, Yoshitaka

2009-01-01

A new acoustic steam generator leak detection system using delay-and-sum beamformer is proposed. The major advantage of the delay-and-sum beamformer is it could provide information of acoustic source direction. An acoustic source of a sodium-water reaction is supposed to be localized while the background noise of the steam generator operation is uniformly distributed in the steam generator tube region. Therefore the delay-and-sum beamformer could distinguish the acoustic source of the sodium-water reaction from steam generator background noise. In this paper, results from numerical analyses are provided to show fundamental feasibility of the new method. (author)

Joint Transmitter-Receiver Optimization in the Downlink CDMA Systems

Directory of Open Access Journals (Sweden)

Mohammad Saquib

2002-08-01

Full Text Available To maximize the downlink code-division multiple access (CDMA system capacity, we propose to minimize the total transmitted power of the system subject to users′ signal-to-interference ratio (SIR requirements via designing optimum transmitter sequences and utilizing linear optimum receivers (minimum mean square error (MMSE receiver. In our work on joint transmitter-receiver design for the downlink CDMA systems with multiple antennas and multipath channels, we develop several optimization algorithms by considering various system constraints and prove their convergence. We empirically observed that under the optimization algorithm with no constraint on the system, the optimum receiver structure matches the received transmitter sequences. A simulation study is performed to see how the different practical system constraints penalize the system with respect to the optimum algorithm with no constraint on the system.

Strong reflector-based beamforming in ultrasound medical imaging.

Science.gov (United States)

Szasz, Teodora; Basarab, Adrian; Kouamé, Denis

2016-03-01

This paper investigates the use of sparse priors in creating original two-dimensional beamforming methods for ultrasound imaging. The proposed approaches detect the strong reflectors from the scanned medium based on the well known Bayesian Information Criteria used in statistical modeling. Moreover, they allow a parametric selection of the level of speckle in the final beamformed image. These methods are applied on simulated data and on recorded experimental data. Their performance is evaluated considering the standard image quality metrics: contrast ratio (CR), contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). A comparison is made with the classical delay-and-sum and minimum variance beamforming methods to confirm the ability of the proposed methods to precisely detect the number and the position of the strong reflectors in a sparse medium and to accurately reduce the speckle and highly enhance the contrast in a non-sparse medium. We confirm that our methods improve the contrast of the final image for both simulated and experimental data. In all experiments, the proposed approaches tend to preserve the speckle, which can be of major interest in clinical examinations, as it can contain useful information. In sparse mediums we achieve a highly improvement in contrast compared with the classical methods. Copyright © 2015 Elsevier B.V. All rights reserved.

Adaptive optics correction into single mode fiber for a low Earth orbiting space to ground optical communication link using the OPALS downlink.

Science.gov (United States)

Wright, Malcolm W; Morris, Jeffery F; Kovalik, Joseph M; Andrews, Kenneth S; Abrahamson, Matthew J; Biswas, Abhijit

2015-12-28

An adaptive optics (AO) testbed was integrated to the Optical PAyload for Lasercomm Science (OPALS) ground station telescope at the Optical Communications Telescope Laboratory (OCTL) as part of the free space laser communications experiment with the flight system on board the International Space Station (ISS). Atmospheric turbulence induced aberrations on the optical downlink were adaptively corrected during an overflight of the ISS so that the transmitted laser signal could be efficiently coupled into a single mode fiber continuously. A stable output Strehl ratio of around 0.6 was demonstrated along with the recovery of a 50 Mbps encoded high definition (HD) video transmission from the ISS at the output of the single mode fiber. This proof of concept demonstration validates multi-Gbps optical downlinks from fast slewing low-Earth orbiting (LEO) spacecraft to ground assets in a manner that potentially allows seamless space to ground connectivity for future high data-rates network.

SVD-BASED TRANSMIT BEAMFORMING FOR VARIOUS MODULATIONS WITH CONVOLUTION ENCODING

Directory of Open Access Journals (Sweden)

M. Raja

2011-09-01

Full Text Available This paper present a new beamforming technique using singular value decomposition (SVD for closed loop Multiple-input, multiple-output (MIMO wireless systems with various modulation techniques such as BPSK, 16-QAM, 16-PSK, DPSK and PAM along with convolution encoder. The channel matrix is decomposed into a number of independent orthogonal modes of excitation, which refer to as eigenmodes of the channel. Transmit precoding is performed by multiplying the input symbols with unitary matrix to produce the transmit beamforming, and the precoded symbols are transmitted over Rayleigh fading channel. At the receiver, combining process is performed by using maximum ratio combiner (MRC, and the receiver shaping is performed to retrieve the original input symbols by multiplying the received signal with conjugate transpose of the unitary matrix. Furthermore, the expressions for average bit error rate (BER for M-PSK and average BER for M-QAM are derived. The superiority of the proposed work is proved by simulation results and the proposed work is compared to the other beamforming methods.

Optically beamformed beam-switched adaptive antennas for fixed and mobile broadband wireless access networks

NARCIS (Netherlands)

Piqueras, M.A.; Grosskopf, G.; Vidal, B.; Herrera Llorente, J.; Martinez, J.M.; Sanchis, P.; Polo, V.; Corral, J.L.; Marceaux, A.; Galière, J.; Lopez, J.; Enard, A.; Valard, J.-L.; Parillaud, O.; Estèbe, E.; Vodjdani, N.; Choi, M.-S.; Besten, den J.H.; Soares, F.M.; Smit, M.K.; Marti, J.

2006-01-01

In this paper, a 3-bit optical beamforming architecture based in 2×2 optical switches and dispersive media is proposed and demonstrated. The performance of this photonic beamformer is experimentally demonstrated at 42.7 GHz in both transmission and reception modes. The progress achieved for

Polarized Uniform Linear Array System: Beam Radiation Pattern, Beamforming Diversity Order, and Channel Capacity

Directory of Open Access Journals (Sweden)

Xin Su

2015-01-01

Full Text Available There have been many studies regarding antenna polarization; however, there have been few publications on the analysis of the channel capacity for polarized antenna systems using the beamforming technique. According to Chung et al., the channel capacity is determined by the density of scatterers and the transmission power, which is obtained based on the assumption that scatterers are uniformly distributed on a 3D spherical scattering model. However, it contradicts the practical scenario, where scatterers may not be uniformly distributed under outdoor environment, and lacks the consideration of fading channel gain. In this study, we derive the channel capacity of polarized uniform linear array (PULA systems using the beamforming technique in a practical scattering environment. The results show that, for PULA systems, the channel capacity, which is boosted by beamforming diversity, can be determined using the channel gain, beam radiation pattern, and beamforming diversity order (BDO, where the BDO is dependent on the antenna characteristics and array configurations.

A combinatorial approximation algorithm for CDMA downlink rate allocation

NARCIS (Netherlands)

Boucherie, Richardus J.; Bumb, A.F.; Endrayanto, A.I.; Woeginger, Gerhard; Raghavan, S.; Anandalingam, G.

2006-01-01

This paper presents a combinatorial algorithm for downlink rate allocation in Code Division Multiple Access (CDMA) mobile networks. By discretizing the coverage area into small segments, the transmit power requirements are characterized via a matrix representation that separates user and system

A combinatorial approximation algorithm for CDMA downlink rate allocation

NARCIS (Netherlands)

Boucherie, Richardus J.; Bumb, A.F.; Endrayanto, A.I.; Woeginger, Gerhard

2004-01-01

This paper presents a combinatorial algorithm for downlink rate allocation in Code Division Multiple Access (CDMA) mobile networks. By discretizing the coverage area into small segments, the transmit power requirements are characterized via a matrix representation that separates user and system

Ad Hoc Microphone Array Beamforming Using the Primal-Dual Method of Multipliers

DEFF Research Database (Denmark)

Tavakoli, Vincent Mohammad; Jensen, Jesper Rindom; Heusdens, Richard

2016-01-01

In the recent years, there have been increasing amount of researches aiming at optimal beamforming with ad hoc microphone arrays, mostly with fusion-based schemes. However, huge amount of computational complexity and communication overhead impede many of these algorithms from being useful in prac...... the distributed linearly-constrained minimum variance beamformer using the the state of the art primal-dual method of multipliers. We study the proposed algorithm with an experiment....

Novel ring resonator-based integrated photonic beamformer for broadband phased array receive antennas - part 1: design and performance analysis

NARCIS (Netherlands)

Meijerink, Arjan; Roeloffzen, C.G.H.; Meijerink, Roland; Zhuang, L.; Marpaung, D.A.I.; Bentum, Marinus Jan; Burla, M.; Verpoorte, Jaco; Jorna, Pieter; Huizinga, Adriaan; van Etten, Wim

2010-01-01

A novel optical beamformer concept is introduced that can be used for seamless control of the reception angle in broadband wireless receivers employing a large phased array antenna (PAA). The core of this beamformer is an optical beamforming network (OBFN), using ring resonator-based broadband

Concentric artificial impedance surface for directional sound beamforming

Directory of Open Access Journals (Sweden)

Kyungjun Song

2017-03-01

Full Text Available Utilizing acoustic metasurfaces consisting of subwavelength resonant textures, we design an artificial impedance surface by creating a new boundary condition. We demonstrate a circular artificial impedance surface with surface impedance modulation for directional sound beamforming in three-dimensional space. This artificial impedance surface is implemented by revolving two-dimensional Helmholtz resonators with varying internal coiled path. Physically, the textured surface has inductive surface impedance on its inner circular patterns and capacitive surface impedance on its outer circular patterns. Directional receive beamforming can be achieved using an omnidirectional microphone located at the focal point formed by the gradient-impeding surface. In addition, the uniaxial surface impedance patterning inside the circular aperture can be used for steering the direction of the main lobe of the radiation pattern.

Sum Rate Maximization using Linear Precoding and Decoding in the Multiuser MIMO Downlink

OpenAIRE

Tenenbaum, Adam J.; Adve, Raviraj S.

2008-01-01

We propose an algorithm to maximize the instantaneous sum data rate transmitted by a base station in the downlink of a multiuser multiple-input, multiple-output system. The transmitter and the receivers may each be equipped with multiple antennas and each user may receive more than one data stream. We show that maximizing the sum rate is closely linked to minimizing the product of mean squared errors (PMSE). The algorithm employs an uplink/downlink duality to iteratively design transmit-recei...

Microcomb-Based True-Time-Delay Network for Microwave Beamforming With Arbitrary Beam Pattern Control

Science.gov (United States)

Xue, Xiaoxiao; Xuan, Yi; Bao, Chengying; Li, Shangyuan; Zheng, Xiaoping; Zhou, Bingkun; Qi, Minghao; Weiner, Andrew M.

2018-06-01

Microwave phased array antennas (PAAs) are very attractive to defense applications and high-speed wireless communications for their abilities of fast beam scanning and complex beam pattern control. However, traditional PAAs based on phase shifters suffer from the beam-squint problem and have limited bandwidths. True-time-delay (TTD) beamforming based on low-loss photonic delay lines can solve this problem. But it is still quite challenging to build large-scale photonic TTD beamformers due to their high hardware complexity. In this paper, we demonstrate a photonic TTD beamforming network based on a miniature microresonator frequency comb (microcomb) source and dispersive time delay. A method incorporating optical phase modulation and programmable spectral shaping is proposed for positive and negative apodization weighting to achieve arbitrary microwave beam pattern control. The experimentally demonstrated TTD beamforming network can support a PAA with 21 elements. The microwave frequency range is $\\mathbf{8\\sim20\\ {GHz}}$, and the beam scanning range is $\\mathbf{\\pm 60.2^\\circ}$. Detailed measurements of the microwave amplitudes and phases are performed. The beamforming performances of Gaussian, rectangular beams and beam notch steering are evaluated through simulations by assuming a uniform radiating antenna array. The scheme can potentially support larger PAAs with hundreds of elements by increasing the number of comb lines with broadband microcomb generation.

Uplink transmit beamforming design for SINR maximization with full multiuser channel state information

Science.gov (United States)

Xi, Songnan; Zoltowski, Michael D.

2008-04-01

Multiuser multiple-input multiple-output (MIMO) systems are considered in this paper. We continue our research on uplink transmit beamforming design for multiple users under the assumption that the full multiuser channel state information, which is the collection of the channel state information between each of the users and the base station, is known not only to the receiver but also to all the transmitters. We propose an algorithm for designing optimal beamforming weights in terms of maximizing the signal-to-interference-plus-noise ratio (SINR). Through statistical modeling, we decouple the original mathematically intractable optimization problem and achieved a closed-form solution. As in our previous work, the minimum mean-squared error (MMSE) receiver with successive interference cancellation (SIC) is adopted for multiuser detection. The proposed scheme is compared with an existing jointly optimized transceiver design, referred to as the joint transceiver in this paper, and our previously proposed eigen-beamforming algorithm. Simulation results demonstrate that our algorithm, with much less computational burden, accomplishes almost the same performance as the joint transceiver for spatially independent MIMO channel and even better performance for spatially correlated MIMO channels. And it always works better than our previously proposed eigen beamforming algorithm.

A comparison between temporal and subband minimum variance adaptive beamforming

Science.gov (United States)

Diamantis, Konstantinos; Voxen, Iben H.; Greenaway, Alan H.; Anderson, Tom; Jensen, Jørgen A.; Sboros, Vassilis

2014-03-01

This paper compares the performance between temporal and subband Minimum Variance (MV) beamformers for medical ultrasound imaging. Both adaptive methods provide an optimized set of apodization weights but are implemented in the time and frequency domains respectively. Their performance is evaluated with simulated synthetic aperture data obtained from Field II and is quantified by the Full-Width-Half-Maximum (FWHM), the Peak-Side-Lobe level (PSL) and the contrast level. From a point phantom, a full sequence of 128 emissions with one transducer element transmitting and all 128 elements receiving each time, provides a FWHM of 0.03 mm (0.14λ) for both implementations at a depth of 40 mm. This value is more than 20 times lower than the one achieved by conventional beamforming. The corresponding values of PSL are -58 dB and -63 dB for time and frequency domain MV beamformers, while a value no lower than -50 dB can be obtained from either Boxcar or Hanning weights. Interestingly, a single emission with central element #64 as the transmitting aperture provides results comparable to the full sequence. The values of FWHM are 0.04 mm and 0.03 mm and those of PSL are -42 dB and -46 dB for temporal and subband approaches. From a cyst phantom and for 128 emissions, the contrast level is calculated at -54 dB and -63 dB respectively at the same depth, with the initial shape of the cyst being preserved in contrast to conventional beamforming. The difference between the two adaptive beamformers is less significant in the case of a single emission, with the contrast level being estimated at -42 dB for the time domain and -43 dB for the frequency domain implementation. For the estimation of a single MV weight of a low resolution image formed by a single emission, 0.44 * 109 calculations per second are required for the temporal approach. The same numbers for the subband approach are 0.62 * 109 for the point and 1.33 * 109 for the cyst phantom. The comparison demonstrates similar

Beamforming using subspace estimation from a diagonally averaged sample covariance.

Science.gov (United States)

Quijano, Jorge E; Zurk, Lisa M

2017-08-01

The potential benefit of a large-aperture sonar array for high resolution target localization is often challenged by the lack of sufficient data required for adaptive beamforming. This paper introduces a Toeplitz-constrained estimator of the clairvoyant signal covariance matrix corresponding to multiple far-field targets embedded in background isotropic noise. The estimator is obtained by averaging along subdiagonals of the sample covariance matrix, followed by covariance extrapolation using the method of maximum entropy. The sample covariance is computed from limited data snapshots, a situation commonly encountered with large-aperture arrays in environments characterized by short periods of local stationarity. Eigenvectors computed from the Toeplitz-constrained covariance are used to construct signal-subspace projector matrices, which are shown to reduce background noise and improve detection of closely spaced targets when applied to subspace beamforming. Monte Carlo simulations corresponding to increasing array aperture suggest convergence of the proposed projector to the clairvoyant signal projector, thereby outperforming the classic projector obtained from the sample eigenvectors. Beamforming performance of the proposed method is analyzed using simulated data, as well as experimental data from the Shallow Water Array Performance experiment.

Downlink Multicell Processing with Limited-Backhaul Capacity

Directory of Open Access Journals (Sweden)

O. Simeone

2009-01-01

Full Text Available Multicell processing in the form of joint encoding for the downlink of a cellular system is studied under the assumption that the base stations (BSs are connected to a central processor (CP via finitecapacity links (finite-capacity backhaul. To obtain analytical insight into the impact of finite-capacity backhaul on the downlink throughput, the investigation focuses on a simple linear cellular system (as for a highway or a long avenue based on theWyner model. Several transmission schemes are proposed that require varying degrees of knowledge regarding the system codebooks at the BSs. Achievable rates are derived in closed-form and compared with an upper bound. Performance is also evaluated in asymptotic regimes of interest (high backhaul capacity and extreme signal-to-noise ratio, SNR and further corroborated by numerical results. The major finding of this work is that even in the presence of oblivious BSs (that is, BSs with no information about the codebooks multicell processing is able to provide ideal performance with relatively small backhaul capacities, unless the application of interest requires high data rate (i.e., high SNR and the backhaul capacity is not allowed to increase with the SNR. In these latter cases, some form of codebook information at the BSs becomes necessary.

Performance analysis of distributed beamforming in a spectrum sharing system

KAUST Repository

Yang, Liang; Alouini, Mohamed-Slim; Qaraqe, Khalid A.

2012-01-01

In this paper, we consider a distributed beamforming scheme (DBF) in a spectrum sharing system where multiple secondary users share the spectrum with the licensed primary users under an interference temperature constraint. We assume that DBF is applied at the secondary users. We first consider optimal beamforming and compare it with the user selection scheme in terms of the outage probability and bit-error rate performance. Since perfect feedback is difficult to obtain, we then investigate a limited feedback DBF scheme and develop an outage probability analysis for a random vector quantization (RVQ) design algorithm. Numerical results are provided to illustrate our mathematical formalism and verify our analysis. © 2012 IEEE.

Performance analysis of distributed beamforming in a spectrum sharing system

KAUST Repository

Yang, Liang

2012-09-01

In this paper, we consider a distributed beamforming scheme (DBF) in a spectrum sharing system where multiple secondary users share the spectrum with the licensed primary users under an interference temperature constraint. We assume that DBF is applied at the secondary users. We first consider optimal beamforming and compare it with the user selection scheme in terms of the outage probability and bit-error rate performance. Since perfect feedback is difficult to obtain, we then investigate a limited feedback DBF scheme and develop an outage probability analysis for a random vector quantization (RVQ) design algorithm. Numerical results are provided to illustrate our mathematical formalism and verify our analysis. © 2012 IEEE.

Coordinated scheduling for the downlink of cloud radio-access networks

KAUST Repository

Douik, Ahmed S.; Dahrouj, Hayssam; Al-Naffouri, Tareq Y.; Alouini, Mohamed-Slim

2015-01-01

This paper addresses the coordinated scheduling problem in cloud-enabled networks. Consider the downlink of a cloud-radio access network (CRAN), where the cloud is only responsible for the scheduling policy and the synchronization of the transmit

Aliasing-free wideband beamforming using sparse signal representation

NARCIS (Netherlands)

Tang, Z.; Blacquière, G.; Leus, G.

2011-01-01

Sparse signal representation (SSR) is considered to be an appealing alternative to classical beamforming for direction-of-arrival (DOA) estimation. For wideband signals, the SSR-based approach constructs steering matrices, referred to as dictionaries in this paper, corresponding to different

Directional hearing aid using hybrid adaptive beamformer (HAB) and binaural ITE array

Science.gov (United States)

Shaw, Scott T.; Larow, Andy J.; Gibian, Gary L.; Sherlock, Laguinn P.; Schulein, Robert

2002-05-01

A directional hearing aid algorithm called the Hybrid Adaptive Beamformer (HAB), developed for NIH/NIA, can be applied to many different microphone array configurations. In this project the HAB algorithm was applied to a new array employing in-the-ear microphones at each ear (HAB-ITE), to see if previous HAB performance could be achieved with a more cosmetically acceptable package. With diotic output, the average benefit in threshold SNR was 10.9 dB for three HoH and 11.7 dB for five normal-hearing subjects. These results are slightly better than previous results of equivalent tests with a 3-in. array. With an innovative binaural fitting, a small benefit beyond that provided by diotic adaptive beamforming was observed: 12.5 dB for HoH and 13.3 dB for normal-hearing subjects, a 1.6 dB improvement over the diotic presentation. Subjectively, the binaural fitting preserved binaural hearing abilities, giving the user a sense of space, and providing left-right localization. Thus the goal of creating an adaptive beamformer that simultaneously provides excellent noise reduction and binaural hearing was achieved. Further work remains before the HAB-ITE can be incorporated into a real product, optimizing binaural adaptive beamforming, and integrating the concept with other technologies to produce a viable product prototype. [Work supported by NIH/NIDCD.

Indoor Off-Body Wireless Communication: Static Beamforming versus Space-Time Coding

Directory of Open Access Journals (Sweden)

Patrick Van Torre

2012-01-01

Full Text Available The performance of beamforming versus space-time coding using a body-worn textile antenna array is experimentally evaluated for an indoor environment, where a walking rescue worker transmits data in the 2.45 GHz ISM band, relying on a vertical textile four-antenna array integrated into his garment. The two transmission scenarios considered are static beamforming at low-elevation angles and space-time code based transmit diversity. Signals are received by a base station equipped with a horizontal array of four dipole antennas providing spatial receive diversity through maximum-ratio combining. Signal-to-noise ratios, bit error rate characteristics, and signal correlation properties are assessed for both off-body transmission scenarios. Without receiver diversity, the performance of space-time coding is generally better. In case of fourth-order receiver diversity, beamforming is superior in line-of-sight conditions. For non-line-of-sight propagation, the space-time codes perform better as soon as bit error rates are low enough for a reliable data link.

Equalization of Multiuser Wireless CDMA Downlink Considering Transmitter Nonlinearity Using Walsh Codes

Directory of Open Access Journals (Sweden)

Pinter Stephen Z

2007-01-01

Full Text Available Transmitter nonlinearity has been a major issue in many scenarios: cellular wireless systems have high power RF amplifier (HPA nonlinearity at the base station; satellite downlinks have nonlinear TWT amplifiers in the satellite transponder and multipath conditions in the ground station; and radio-over-fiber (ROF systems consist of a nonlinear optical link followed by a wireless channel. In many cases, the nonlinearity is simply ignored if there is no out-of-band emission. This results in poor BER performance. In this paper we propose a new technique to estimate the linear part of the wireless downlink in the presence of a nonlinearity using Walsh codes; Walsh codes are commonly used in CDMA downlinks. Furthermore, we show that equalizer performance is significantly improved by taking into account the presence of the nonlinearity during channel estimation. This is shown by using a regular decision feedback equalizer (DFE with both wireless and RF amplifier noise. We perform estimation in a multiuser CDMA communication system where all users transmit their signal simultaneously. Correlation analysis is applied to identify the channel impulse response (CIR and the derivation of key correlation relationships is shown. A difficulty with using Walsh codes in terms of their correlations (compared to PN sequences is then presented, as well as a discussion on how to overcome it. Numerical evaluations show a good estimation of the linear system with 54 users in the downlink and a signal-to-noise ratio (SNR of 25 dB. Bit error rate (BER simulations of the proposed identification and equalization algorithms show a BER of achieved at an SNR of dB.

In Vivo Evaluation of Synthetic Aperture Sequential Beamforming

DEFF Research Database (Denmark)

Hemmsen, Martin Christian; Hansen, Peter Møller; Lange, Theis

2012-01-01

Ultrasound in vivo imaging using synthetic aperture sequential beamformation (SASB) is compared with conventional imaging in a double blinded study using side-by-side comparisons. The objective is to evaluate if the image quality in terms of penetration depth, spatial resolution, contrast...

Application of a Beamforming Technique to the Measurement of Airfoil Leading Edge Noise

Directory of Open Access Journals (Sweden)

Thomas Geyer

2012-01-01

Full Text Available The present paper describes the use of microphone array technology and beamforming algorithms for the measurement and analysis of noise generated by the interaction of a turbulent flow with the leading edge of an airfoil. Experiments were performed using a setup in an aeroacoustic wind tunnel, where the turbulent inflow is provided by different grids. In order to exactly localize the aeroacoustic noise sources and, moreover, to separate airfoil leading edge noise from grid-generated noise, the selected deconvolution beamforming algorithm is extended to be used on a fully three-dimensional source region. The result of this extended beamforming are three-dimensional mappings of noise source locations. Besides acoustic measurements, the investigation of airfoil leading edge noise requires the measurement of parameters describing the incident turbulence, such as the intensity and a characteristic length scale or time scale. The method used for the determination of these parameters in the present study is explained in detail. To demonstrate the applicability of the extended beamforming algorithm and the experimental setup as a whole, the noise generated at the leading edge of airfoils made of porous materials was measured and compared to that generated at the leading edge of a common nonporous airfoil.

Improved Plane-Wave Ultrasound Beamforming by Incorporating Angular Weighting and Coherent Compounding in Fourier Domain.

Science.gov (United States)

Chen, Chuan; Hendriks, Gijs A G M; van Sloun, Ruud J G; Hansen, Hendrik H G; de Korte, Chris L

2018-05-01

In this paper, a novel processing framework is introduced for Fourier-domain beamforming of plane-wave ultrasound data, which incorporates coherent compounding and angular weighting in the Fourier domain. Angular weighting implies spectral weighting by a 2-D steering-angle-dependent filtering template. The design of this filter is also optimized as part of this paper. Two widely used Fourier-domain plane-wave ultrasound beamforming methods, i.e., Lu's f-k and Stolt's f-k methods, were integrated in the framework. To enable coherent compounding in Fourier domain for the Stolt's f-k method, the original Stolt's f-k method was modified to achieve alignment of the spectra for different steering angles in k-space. The performance of the framework was compared for both methods with and without angular weighting using experimentally obtained data sets (phantom and in vivo), and data sets (phantom) provided by the IEEE IUS 2016 plane-wave beamforming challenge. The addition of angular weighting enhanced the image contrast while preserving image resolution. This resulted in images of equal quality as those obtained by conventionally used delay-and-sum (DAS) beamforming with apodization and coherent compounding. Given the lower computational load of the proposed framework compared to DAS, to our knowledge it can, therefore, be concluded that it outperforms commonly used beamforming methods such as Stolt's f-k, Lu's f-k, and DAS.

Experimental performance assessment of the sub-band minimum variance beamformer for ultrasound imaging

DEFF Research Database (Denmark)

Diamantis, Konstantinos; Greenaway, Alan H.; Anderson, Tom

2017-01-01

Recent progress in adaptive beamforming techniques for medical ultrasound has shown that current resolution limits can be surpassed. One method of obtaining improved lateral resolution is the Minimum Variance (MV) beamformer. The frequency domain implementation of this method effectively divides...... the broadband ultrasound signals into sub-bands (MVS) to conform with the narrow-band assumption of the original MV theory. This approach is investigated here using experimental Synthetic Aperture (SA) data from wire and cyst phantoms. A 7 MHz linear array transducer is used with the SARUS experimental...... ultrasound scanner for the data acquisition. The lateral resolution and the contrast obtained, are evaluated and compared with those from the conventional Delay-and-Sum (DAS) beamformer and the MV temporal implementation (MVT). From the wire phantom the Full-Width-at-Half-Maximum (FWHM) measured at a depth...

Blind information-theoretic multiuser detection algorithms for DS-CDMA and WCDMA downlink systems.

Science.gov (United States)

Waheed, Khuram; Salem, Fathi M

2005-07-01

Code division multiple access (CDMA) is based on the spread-spectrum technology and is a dominant air interface for 2.5G, 3G, and future wireless networks. For the CDMA downlink, the transmitted CDMA signals from the base station (BS) propagate through a noisy multipath fading communication channel before arriving at the receiver of the user equipment/mobile station (UE/MS). Classical CDMA single-user detection (SUD) algorithms implemented in the UE/MS receiver do not provide the required performance for modern high data-rate applications. In contrast, multi-user detection (MUD) approaches require a lot of a priori information not available to the UE/MS. In this paper, three promising adaptive Riemannian contra-variant (or natural) gradient based user detection approaches, capable of handling the highly dynamic wireless environments, are proposed. The first approach, blind multiuser detection (BMUD), is the process of simultaneously estimating multiple symbol sequences associated with all the users in the downlink of a CDMA communication system using only the received wireless data and without any knowledge of the user spreading codes. This approach is applicable to CDMA systems with relatively short spreading codes but becomes impractical for systems using long spreading codes. We also propose two other adaptive approaches, namely, RAKE -blind source recovery (RAKE-BSR) and RAKE-principal component analysis (RAKE-PCA) that fuse an adaptive stage into a standard RAKE receiver. This adaptation results in robust user detection algorithms with performance exceeding the linear minimum mean squared error (LMMSE) detectors for both Direct Sequence CDMA (DS-CDMA) and wide-band CDMA (WCDMA) systems under conditions of congestion, imprecise channel estimation and unmodeled multiple access interference (MAI).

Synthetic Aperture Flow Imaging Using a Dual Beamformer Approach

DEFF Research Database (Denmark)

Li, Ye

Color flow mapping systems have become widely used in clinical applications. It provides an opportunity to visualize the velocity profile over a large region in the vessel, which makes it possible to diagnose, e.g., occlusion of veins, heart valve deficiencies, and other hemodynamic problems....... However, while the conventional ultrasound imaging of making color flow mapping provides useful information in many circumstances, the spatial velocity resolution and frame rate are limited. The entire velocity distribution consists of image lines from different directions, and each image line...... on the current commercial ultrasound scanner. The motivation for this project is to develop a method lowering the amount of calculations and still maintaining beamforming quality sufficient for flow estimation. Synthetic aperture using a dual beamformer approach is investigated using Field II simulations...

Adaptive Port-Starboard Beamforming of Triplet Sonar Arrays

NARCIS (Netherlands)

Groen, J.; Beerens, S.P.; Been, R.; Doisy, Y.

2005-01-01

Abstract—For a low-frequency active sonar (LFAS) with a triplet receiver array, it is not clear in advance which signal processing techniques optimize its performance. Here, several advanced beamformers are analyzed theoretically, and the results are compared to experimental data obtained in sea

Adaptive Beamforming Algorithms for Tow Ship Noise Canceling

NARCIS (Netherlands)

Robert, M.K.; Beerens, S.P.

2002-01-01

In towed array sonar, the directional noise originating from the tow ship, mainly machinery and hydrodynamic noise, often limits the sonar performance. When processed with classical beamforming techniques, loud tow ship noise induces high sidelobes that may hide detection of quiet targets in forward

Space-Time Chip Equalization for Maximum Diversity Space-Time Block Coded DS-CDMA Downlink Transmission

Directory of Open Access Journals (Sweden)

Petré Frederik

2004-01-01

Full Text Available In the downlink of DS-CDMA, frequency-selectivity destroys the orthogonality of the user signals and introduces multiuser interference (MUI. Space-time chip equalization is an efficient tool to restore the orthogonality of the user signals and suppress the MUI. Furthermore, multiple-input multiple-output (MIMO communication techniques can result in a significant increase in capacity. This paper focuses on space-time block coding (STBC techniques, and aims at combining STBC techniques with the original single-antenna DS-CDMA downlink scheme. This results into the so-called space-time block coded DS-CDMA downlink schemes, many of which have been presented in the past. We focus on a new scheme that enables both the maximum multiantenna diversity and the maximum multipath diversity. Although this maximum diversity can only be collected by maximum likelihood (ML detection, we pursue suboptimal detection by means of space-time chip equalization, which lowers the computational complexity significantly. To design the space-time chip equalizers, we also propose efficient pilot-based methods. Simulation results show improved performance over the space-time RAKE receiver for the space-time block coded DS-CDMA downlink schemes that have been proposed for the UMTS and IS-2000 W-CDMA standards.

A New Codebook Design for Hybrid Beamforming Systems using ...

African Journals Online (AJOL)

pc

2018-03-05

Mar 5, 2018 ... wireless personal area networks (WPANs) operating at the ... antenna element, is not practical in terms of the cost and power consumption [4]. To overcome ... hybrid beamformers for data transmission were designed under.

Balancing Uplink and Downlink under Asymmetric Traffic Environments Using Distributed Receive Antennas

Science.gov (United States)

Sohn, Illsoo; Lee, Byong Ok; Lee, Kwang Bok

Recently, multimedia services are increasing with the widespread use of various wireless applications such as web browsers, real-time video, and interactive games, which results in traffic asymmetry between the uplink and downlink. Hence, time division duplex (TDD) systems which provide advantages in efficient bandwidth utilization under asymmetric traffic environments have become one of the most important issues in future mobile cellular systems. It is known that two types of intercell interference, referred to as crossed-slot interference, additionally arise in TDD systems; the performances of the uplink and downlink transmissions are degraded by BS-to-BS crossed-slot interference and MS-to-MS crossed-slot interference, respectively. The resulting performance unbalance between the uplink and downlink makes network deployment severely inefficient. Previous works have proposed intelligent time slot allocation algorithms to mitigate the crossed-slot interference problem. However, they require centralized control, which causes large signaling overhead in the network. In this paper, we propose to change the shape of the cellular structure itself. The conventional cellular structure is easily transformed into the proposed cellular structure with distributed receive antennas (DRAs). We set up statistical Markov chain traffic model and analyze the bit error performances of the conventional cellular structure and proposed cellular structure under asymmetric traffic environments. Numerical results show that the uplink and downlink performances of the proposed cellular structure become balanced with the proper number of DRAs and thus the proposed cellular structure is notably cost-effective in network deployment compared to the conventional cellular structure. As a result, extending the conventional cellular structure into the proposed cellular structure with DRAs is a remarkably cost-effective solution to support asymmetric traffic environments in future mobile cellular

Mobile Ultrasound Plane Wave Beamforming on iPhone or iPad using Metal- based GPU Processing

Science.gov (United States)

Hewener, Holger J.; Tretbar, Steffen H.

Mobile and cost effective ultrasound devices are being used in point of care scenarios or the drama room. To reduce the costs of such devices we already presented the possibilities of consumer devices like the Apple iPad for full signal processing of raw data for ultrasound image generation. Using technologies like plane wave imaging to generate a full image with only one excitation/reception event the acquisition times and power consumption of ultrasound imaging can be reduced for low power mobile devices based on consumer electronics realizing the transition from FPGA or ASIC based beamforming into more flexible software beamforming. The massive parallel beamforming processing can be done with the Apple framework "Metal" for advanced graphics and general purpose GPU processing for the iOS platform. We were able to integrate the beamforming reconstruction into our mobile ultrasound processing application with imaging rates up to 70 Hz on iPad Air 2 hardware.

Digitally assisted analog beamforming for millimeter-wave communication

NARCIS (Netherlands)

Kokkeler, Andre B.J.; Smit, Gerardus Johannes Maria

2015-01-01

The paper addresses the research question on how digital beamsteering algorithms can be combined with analog beamforming in the context of millimeter-wave communication for next generation (5G) cellular systems. Key is the use of coarse quantisation of the individual antenna signals next to the

Low complexity symbol-wise beamforming for MIMO-OFDM systems

KAUST Repository

Lee, Hyun Ho; Park, Kihong; Yang, Hongchuan; Ko, Youngchai

2011-01-01

-wise beamforming based on the iterative algorithm. We demonstrate that our proposed scheme can reduce the computational complexity significantly. From our simulation results, it is evident that our proposed scheme leads to a negligible performance loss compared

Communication costs in a multi-tiered MPSoC

NARCIS (Netherlands)

van de Burgwal, M.D.; Smit, Gerardus Johannes Maria

2008-01-01

The amount of digital processing required for phased array beamformers is very large. It requires many parallel processors, which can be organized in a multi-tiered structure. Communication costs differ for each of the stages in such an architecture. For example, communication costs from the antenna

Compact FPGA-based beamformer using oversampled 1-bit A/D converters

DEFF Research Database (Denmark)

Tomov, Borislav Gueorguiev; Jensen, Jørgen Arendt

2005-01-01

A compact medical ultrasound beamformer architecture that uses oversampled 1-bit analog-to-digital (A/D) converters is presented. Sparse sample processing is used, as the echo signal for the image lines is reconstructed in 512 equidistant focal points along the line through its in-phase and quadr......% of the available logic resources in a commercially available midrange FPGA, and to be able to operate at 129 MHz. Simulation of the architecture at 140 MHz provides images with a dynamic range approaching 60 dB for an excitation frequency of 3 MHz.......A compact medical ultrasound beamformer architecture that uses oversampled 1-bit analog-to-digital (A/D) converters is presented. Sparse sample processing is used, as the echo signal for the image lines is reconstructed in 512 equidistant focal points along the line through its in......-phase and quadrature components. That information is sufficient for presenting a B-mode image and creating a color flow map. The high sampling rate provides the necessary delay resolution for the focusing. The low channel data width (1-bit) makes it possible to construct a compact beamformer logic. The signal...

Terahertz plasmonic Bessel beamformer

International Nuclear Information System (INIS)

Monnai, Yasuaki; Shinoda, Hiroyuki; Jahn, David; Koch, Martin; Withayachumnankul, Withawat

2015-01-01

We experimentally demonstrate terahertz Bessel beamforming based on the concept of plasmonics. The proposed planar structure is made of concentric metallic grooves with a subwavelength spacing that couple to a point source to create tightly confined surface waves or spoof surface plasmon polaritons. Concentric scatterers periodically incorporated at a wavelength scale allow for launching the surface waves into free space to define a Bessel beam. The Bessel beam defined at 0.29 THz has been characterized through terahertz time-domain spectroscopy. This approach is capable of generating Bessel beams with planar structures as opposed to bulky axicon lenses and can be readily integrated with solid-state terahertz sources

Pipeline Implementation of Polyphase PSO for Adaptive Beamforming Algorithm

Directory of Open Access Journals (Sweden)

Shaobing Huang

2017-01-01

Full Text Available Adaptive beamforming is a powerful technique for anti-interference, where searching and tracking optimal solutions are a great challenge. In this paper, a partial Particle Swarm Optimization (PSO algorithm is proposed to track the optimal solution of an adaptive beamformer due to its great global searching character. Also, due to its naturally parallel searching capabilities, a novel Field Programmable Gate Arrays (FPGA pipeline architecture using polyphase filter bank structure is designed. In order to perform computations with large dynamic range and high precision, the proposed implementation algorithm uses an efficient user-defined floating-point arithmetic. In addition, a polyphase architecture is proposed to achieve full pipeline implementation. In the case of PSO with large population, the polyphase architecture can significantly save hardware resources while achieving high performance. Finally, the simulation results are presented by cosimulation with ModelSim and SIMULINK.

A recurrent neural network for adaptive beamforming and array correction.

Science.gov (United States)

Che, Hangjun; Li, Chuandong; He, Xing; Huang, Tingwen

2016-08-01

In this paper, a recurrent neural network (RNN) is proposed for solving adaptive beamforming problem. In order to minimize sidelobe interference, the problem is described as a convex optimization problem based on linear array model. RNN is designed to optimize system's weight values in the feasible region which is derived from arrays' state and plane wave's information. The new algorithm is proven to be stable and converge to optimal solution in the sense of Lyapunov. So as to verify new algorithm's performance, we apply it to beamforming under array mismatch situation. Comparing with other optimization algorithms, simulations suggest that RNN has strong ability to search for exact solutions under the condition of large scale constraints. Copyright © 2016 Elsevier Ltd. All rights reserved.

A new architecture for a single-chip multi-channel beamformer based on a standard FPGA

DEFF Research Database (Denmark)

Tomov, Borislav Gueorguiev; Jensen, Jørgen Arendt

2001-01-01

) modulation analog-to-digital converters (ADC). Second, simple second-order ΔΣ modulation ADC with classic topology is used. This allows for simple analog circuitry and a very compact design. Several tens of these together with the corresponding preamplifiers can be fitted together onto a single analog......A new architecture for a compact medical ultrasound beamformer has been developed. Combination of novel and known principles has been utilized, leading to low processing power requirements and simple analog circuitry. Usage of a field programmable gate array (FPGA) for the digital signal processing...... integrated circuit. Third, parameter driven delay generation is used, using 3 input parameters per line per channel for either linear array imaging or phased array imaging. The delays are generated on the fly. The delay generation logic also determines the digital apodization by using 2 additional parameters...

Double-Stage Delay Multiply and Sum Beamforming Algorithm Applied to Ultrasound Medical Imaging.

Science.gov (United States)

Mozaffarzadeh, Moein; Sadeghi, Masume; Mahloojifar, Ali; Orooji, Mahdi

2018-03-01

In ultrasound (US) imaging, delay and sum (DAS) is the most common beamformer, but it leads to low-quality images. Delay multiply and sum (DMAS) was introduced to address this problem. However, the reconstructed images using DMAS still suffer from the level of side lobes and low noise suppression. Here, a novel beamforming algorithm is introduced based on expansion of the DMAS formula. We found that there is a DAS algebra inside the expansion, and we proposed use of the DMAS instead of the DAS algebra. The introduced method, namely double-stage DMAS (DS-DMAS), is evaluated numerically and experimentally. The quantitative results indicate that DS-DMAS results in an approximately 25% lower level of side lobes compared with DMAS. Moreover, the introduced method leads to 23%, 22% and 43% improvement in signal-to-noise ratio, full width at half-maximum and contrast ratio, respectively, compared with the DMAS beamformer. Copyright © 2018. Published by Elsevier Inc.

Improving source discrimination performance by using an optimized acoustic array and adaptive high-resolution CLEAN-SC beamforming

NARCIS (Netherlands)

Luesutthiviboon, S.; Malgoezar, A.M.N.; Snellen, M.; Sijtsma, P.; Simons, D.G.

2018-01-01

Beamforming performance can be improved in two ways: optimizing the location of microphones on the acoustic array and applying advanced beamforming algorithms. In this study, the effects of the two approaches are studied. An optimization method is developed to optimize the location of microphones

Active control of passive acoustic fields: passive synthetic aperture/Doppler beamforming with data from an autonomous vehicle.

Science.gov (United States)

D'Spain, Gerald L; Terrill, Eric; Chadwell, C David; Smith, Jerome A; Lynch, Stephen D

2006-12-01

The maneuverability of autonomous underwater vehicles (AUVs) equipped with hull-mounted arrays provides the opportunity to actively modify received acoustic fields to optimize extraction of information. This paper uses ocean acoustic data collected by an AUV-mounted two-dimensional hydrophone array, with overall dimension one-tenth wavelength at 200-500 Hz, to demonstrate aspects of this control through vehicle motion. Source localization is performed using Doppler shifts measured at a set of receiver velocities by both single elements and a physical array. Results show that a source in the presence of a 10-dB higher-level interferer having exactly the same frequency content (as measured by a stationary receiver) is properly localized and that white-noise-constrained adaptive beamforming applied to the physical aperture data in combination with Doppler beamforming provides greater spatial resolution than physical-aperture-alone beamforming and significantly lower sidelobes than single element Doppler beamforming. A new broadband beamformer that adjusts for variations in vehicle velocity on a sample by sample basis is demonstrated with data collected during a high-acceleration maneuver. The importance of including the cost of energy expenditure in determining optimal vehicle motion is demonstrated through simulation, further illustrating how the vehicle characteristics are an integral part of the signal/array processing structure.

Double-Stage Delay Multiply and Sum Beamforming Algorithm: Application to Linear-Array Photoacoustic Imaging

OpenAIRE

Mozaffarzadeh, Moein; Mahloojifar, Ali; Orooji, Mahdi; Adabi, Saba; Nasiriavanaki, Mohammadreza

2018-01-01

Photoacoustic imaging (PAI) is an emerging medical imaging modality capable of providing high spatial resolution of Ultrasound (US) imaging and high contrast of optical imaging. Delay-and-Sum (DAS) is the most common beamforming algorithm in PAI. However, using DAS beamformer leads to low resolution images and considerable contribution of off-axis signals. A new paradigm namely Delay-Multiply-and-Sum (DMAS), which was originally used as a reconstruction algorithm in confocal microwave imaging...

Dynamic Downlink Spectrum Access for D2D-Enabled Heterogeneous Networks

KAUST Repository

Radaydeh, Redha Mahmoud Mesleh; Al-Qahtani, Fawaz S.; Celik, Abdulkadir; Alouini, Mohamed-Slim

2018-01-01

This paper proposes new approaches for underlay device- to-device (D2D) communication in spectrum-shared het- erogeneous cellular networks. It considers devices that share downlink resources and have an enabled D2D feature to improve coverage

The Vienna LTE-advanced simulators up and downlink, link and system level simulation

CERN Document Server

Rupp, Markus; Taranetz, Martin

2016-01-01

This book introduces the Vienna Simulator Suite for 3rd-Generation Partnership Project (3GPP)-compatible Long Term Evolution-Advanced (LTE-A) simulators and presents applications to demonstrate their uses for describing, designing, and optimizing wireless cellular LTE-A networks. Part One addresses LTE and LTE-A link level techniques. As there has been high demand for the downlink (DL) simulator, it constitutes the central focus of the majority of the chapters. This part of the book reports on relevant highlights, including single-user (SU), multi-user (MU) and single-input-single-output (SISO) as well as multiple-input-multiple-output (MIMO) transmissions. Furthermore, it summarizes the optimal pilot pattern for high-speed communications as well as different synchronization issues. One chapter is devoted to experiments that show how the link level simulator can provide input to a testbed. This section also uses measurements to present and validate fundamental results on orthogonal frequency division multiple...

Computational Acoustic Beamforming for Noise Source Identification for Small Wind Turbines.

Science.gov (United States)

Ma, Ping; Lien, Fue-Sang; Yee, Eugene

2017-01-01

This paper develops a computational acoustic beamforming (CAB) methodology for identification of sources of small wind turbine noise. This methodology is validated using the case of the NACA 0012 airfoil trailing edge noise. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of noise sources generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz.

Ein Beitrag zur Erweiterung von Beamforming-Methoden

OpenAIRE

Kern, Marcus

2008-01-01

Im automobilen Entwicklungsprozess haben sich akustische Messsysteme etabliert, die mit einer Anordnung von Mikrofonen, einer optischen Kamera und einer nachgeschalteten Signalverarbeitung die Schalleinfallsrichtung detektieren und dadurch die Schalldruckverteilung auf Quellorte im Fernfeld zurückrechnen und visualisieren können. Die Signalverarbeitung beruht i. A. auf dem Delay&Sum-Beamforming, deren Umsetzung im Zeit- oder Frequenzbereich erfolgt. Die Schwächen dieser Messtechnik bezüglich ...

Modeling and Characterization of the Uplink and Downlink Exposure in Wireless Networks

Directory of Open Access Journals (Sweden)

Anis Krayni

2017-01-01

Full Text Available This paper deals with a new methodology to assess the exposure induced by both uplink and downlink of a cellular network using 3D electromagnetic simulations. It aims to analyze together the exposure induced by a personal device (uplink exposure and that induced by a base station (downlink exposure. The study involved the major parameters contributing to variability and uncertainty in exposure assessment, such as the user’s posture, the type of wireless device, and the propagation environment. Our approach is relying basically on the modeling of the power radiated by the personal device and the ambient electric field, while taking into account the effects of human body shadowing and the propagation channel fluctuations. The exposure assessment as well as the human-wave interactions has been simulated using the finite difference in time domain method (FDTD. In uplink scenarios, four FDTD simulations were performed with a child model, used in two postures (sitting and standing and in two usage scenarios (voice and data, which aimed to examine the exposure induced by a mobile phone and a tablet emitting, respectively, at 900 MHz and 1940 MHz. In the downlink scenario, a series of FDTD simulations of an exposure to a single plane wave and multiplane waves have been conducted, and an efficient metamodeling of the exposure using the Polynomial Chaos approach has been developed.

Eigenspace-Based Minimum Variance Adaptive Beamformer Combined with Delay Multiply and Sum: Experimental Study

OpenAIRE

Mozaffarzadeh, Moein; Mahloojifar, Ali; Nasiriavanaki, Mohammadreza; Orooji, Mahdi

2017-01-01

Delay and sum (DAS) is the most common beamforming algorithm in linear-array photoacoustic imaging (PAI) as a result of its simple implementation. However, it leads to a low resolution and high sidelobes. Delay multiply and sum (DMAS) was used to address the incapabilities of DAS, providing a higher image quality. However, the resolution improvement is not well enough compared to eigenspace-based minimum variance (EIBMV). In this paper, the EIBMV beamformer has been combined with DMAS algebra...

Beamspace Adaptive Beamforming for Hydrodynamic Towed Array Self-Noise Cancellation

National Research Council Canada - National Science Library

Premus, Vincent

2001-01-01

... against signal self-nulling associated with steering vector mismatch. Particular attention is paid to the definition of white noise gain as the metric that reflects the level of mainlobe adaptive nulling for an adaptive beamformer...

Beamspace Adaptive Beamforming for Hydrodynamic Towed Array Self-Noise Cancellation

National Research Council Canada - National Science Library

Premus, Vincent

2000-01-01

... against signal self-nulling associated with steering vector mismatch. Particular attention is paid to the definition of white noise gain as the metric that reflects the level of mainlobe adaptive nulling for an adaptive beamformer...

Distributed Hybrid Scheduling in Multi-Cloud Networks using Conflict Graphs

KAUST Repository

Douik, Ahmed; Dahrouj, Hayssam; Al-Naffouri, Tareq Y.; Alouini, Mohamed-Slim

2017-01-01

Recent studies on cloud-radio access networks assume either signal-level or scheduling-level coordination. This paper considers a hybrid coordinated scheme as a means to benefit from both policies. Consider the downlink of a multi-cloud radio access

Experimental performance assessment of the sub-band minimum variance beamformer for ultrasound imaging

DEFF Research Database (Denmark)

Diamantis, Konstantinos; Greenaway, Alan H.; Anderson, Tom

2017-01-01

Recent progress in adaptive beamforming techniques for medical ultrasound has shown that current resolution limits can be surpassed. One method of obtaining improved lateral resolution is the Minimum Variance (MV) beamformer. The frequency domain implementation of this method effectively divides...... the broadband ultrasound signals into sub-bands (MVS) to conform with the narrow-band assumption of the original MV theory. This approach is investigated here using experimental Synthetic Aperture (SA) data from wire and cyst phantoms. A 7 MHz linear array transducer is used with the SARUS experimental...

Scheduling for Multiuser MIMO Downlink Channels with Ranking-Based Feedback

Science.gov (United States)

Kountouris, Marios; Sälzer, Thomas; Gesbert, David

2008-12-01

We consider a multi-antenna broadcast channel with more single-antenna receivers than transmit antennas and partial channel state information at the transmitter (CSIT). We propose a novel type of CSIT representation for the purpose of user selection, coined as ranking-based feedback. Each user calculates and feeds back the rank, an integer between 1 and W + 1, of its instantaneous channel quality information (CQI) among a set of W past CQI measurements. Apart from reducing significantly the required feedback load, ranking-based feedback enables the transmitter to select users that are on the highest peak (quantile) with respect to their own channel distribution, independently of the distribution of other users. It can also be shown that this feedback metric can restore temporal fairness in heterogeneous networks, in which users' channels are not identically distributed and mobile terminals experience different average signal-to-noise ratio (SNR). The performance of a system that performs user selection using ranking-based CSIT in the context of random opportunistic beamforming is analyzed, and we provide design guidelines on the number of required past CSIT samples and the impact of finite W on average throughput. Simulation results show that feedback reduction of order of 40-50% can be achieved with negligible decrease in system throughput.

Improving beamforming by optimization of acoustic array microphone positions

NARCIS (Netherlands)

Malgoezar, A.M.N.; Snellen, M.; Sijtsma, P.; Simons, D.G.

2016-01-01

Assigning proper positions to microphones within arrays is essential in order to reduce or eliminate side- and grating lobes in 2D beamform images. In this paper an objective function is derived providing a measure for the presence of artificial sources. Using the global optimization method

Hardware dependencies of GPU-accelerated beamformer performances for microwave breast cancer detection

Directory of Open Access Journals (Sweden)

Salomon Christoph J.

2016-09-01

Full Text Available UWB microwave imaging has proven to be a promising technique for early-stage breast cancer detection. The extensive image reconstruction time can be accelerated by parallelizing the execution of the underlying beamforming algorithms. However, the efficiency of the parallelization will most likely depend on the grade of parallelism of the imaging algorithm and of the utilized hardware. This paper investigates the dependencies of two different beamforming algorithms on multiple hardware specification of several graphics boards. The parallel implementation is realized by using NVIDIA’s CUDA. Three conclusions are drawn about the behavior of the parallel implementation and how to efficiently use the accessible hardware.

Zero-Outage Cellular Downlink with Fixed-Rate D2D Underlay

DEFF Research Database (Denmark)

Kiilerich Pratas, Nuno; Popovski, Petar

2015-01-01

. D2D connections can be instrumental in localized aggregation of uplink M2M traffic to a more capable cellular device, before being finally delivered to the Base Station (BS). In this paper we show that a fixed M2M rate is an enabler of efficient Machine-Type D2D underlay operation taking place......, but not the interfering channels from the MTDs to U, we prove that there is a positive downlink rate that can always be decoded by U, leading to zero-outage of the downlink signal. This is a rather surprising consequence of the features of the multiple access channel and the fixed rate RM. We also consider the case...... of a simpler, single-user decoder at U with successive interference cancellation. However, with single-user decoder, a positive zero-outage rate exists only when NM = 1 and is zero when NM > 1. This implies that joint decoding is instrumental in enabling fixed-rate underlay operation....

Dynamic Downlink Spectrum Access for D2D-Enabled Heterogeneous Networks

KAUST Repository

Radaydeh, Redha Mahmoud Mesleh

2018-01-15

This paper proposes new approaches for underlay device- to-device (D2D) communication in spectrum-shared het- erogeneous cellular networks. It considers devices that share downlink resources and have an enabled D2D feature to improve coverage. The mode of operation classifies devices according to their experienced base station (BS) coverage, potential to be served by BS, ability of BS to meet their quality of service (QoS), and their downlink resources occupancy. The initiation of D2D cooperation is conditioned on proposed provisional access by an active device, wherein its serving BS attempts to meet its QoS using as low number of spectrum channels as possible, while treating remaining channels for feasible D2D cooperation. Detailed formulations for the mode of operation and a proposed D2D path allocation scheme are presented under perfect and imperfect operation scenarios. The developed results are generally applicable for any performance metric and network model.

TX-RX isolation method based on polarization diversity, spatial diversity and TX beamforming

DEFF Research Database (Denmark)

Foroozanfard, Ehsan; Carvalho, Elisabeth De; Pedersen, Gert F.

2016-01-01

In this paper, the feasibility of an antenna isolation technique based on null-steer beamforming, polarization diversity and spatial diversity is investigated. The proposed system consists of six patch antennas which are fed by a feeding network to obtain a null-steer beamformer. To achieve spatial...... diversity, antenna elements are located on two layers, facing in a different direction. Moreover, the antenna elements in two layers use different polarization. The measured results of the antenna system present a high TX-RX isolation in the order of 70 dB which shows the feasibility of such a system...

Sum-Rate Maximization of Coordinated Direct and Relay Systems

DEFF Research Database (Denmark)

Sun, Fan; Popovski, Petar; Thai, Chan

2012-01-01

Joint processing of multiple communication flows in wireless systems has given rise to a number of novel transmission techniques, notably the two-way relaying based on wireless network coding. Recently, a related set of techniques has emerged, termed coordinated direct and relay (CDR) transmissions......, where the constellation of traffic flows is more general than the two-way. Regardless of the actual traffic flows, in a CDR scheme the relay has a central role in managing the interference and boosting the overall system performance. In this paper we investigate the novel transmission modes, based...... on amplify-and-forward, that arise when the relay is equipped with multiple antennas and can use beamforming. We focus on one representative traffic type, with one uplink and one downlink users and consider the achievable sum-rate maximization relay beamforming. The beamforming criterion leads to a non...

Robust distributed two-way relay beamforming in cognitive radio networks

KAUST Repository

Pandarakkottilil, Ubaidulla; Aissa, Sonia

2012-01-01

. The secondary network shares the spectrum with a licensed primary user (PU), and operates under a constraint on the maximum interference to the PU, in addition to its own resource and quality of service (QoS) constraints. We propose beamformer designs assuming

Multiple and single snapshot compressive beamforming

DEFF Research Database (Denmark)

Gerstoft, Peter; Xenaki, Angeliki; Mecklenbrauker, Christoph F.

2015-01-01

and multiple snapshots. CS does not require inversion of the data covariance matrix and thus works well even for a single snapshot where it gives higher resolution than conventional beamforming. For multiple snapshots, CS outperforms conventional high-resolution methods even with coherent arrivals and at low......-lagged superposition of source amplitudes at all hypothetical DOAs. Regularizing with an ‘1-norm constraint renders the problem solvable with convex optimization, and promoting sparsity gives highresolution DOA maps. Here the sparse source distribution is derived using maximum a posteriori estimates for both single...

Compressive Sound Speed Profile Inversion Using Beamforming Results

Directory of Open Access Journals (Sweden)

Youngmin Choo

2018-05-01

Full Text Available Sound speed profile (SSP significantly affects acoustic propagation in the ocean. In this work, the SSP is inverted using compressive sensing (CS combined with beamforming to indicate the direction of arrivals (DOAs. The travel times and the positions of the arrivals can be approximately linearized using their Taylor expansion with the shape function coefficients that parameterize the SSP. The linear relation between the travel times/positions and the shape function coefficients enables CS to reconstruct the SSP. The conventional objective function in CS is modified to simultaneously exploit the information from the travel times and positions. The SSP is estimated using CS with beamforming of ray arrivals in the SWellEx-96 experimental environment, and the performance is evaluated using the correlation coefficient and mean squared error (MSE between the true and recovered SSPs, respectively. Five hundred synthetic SSPs were generated by randomly choosing the SSP dictionary components, and more than 80 percent of all the cases have correlation coefficients over 0.7 and MSE along depth is insignificant except near the sea surface, which shows the validity of the proposed method.

Modeling a content-aware LTE MAC downlink scheduler with heterogeneous traffic

DEFF Research Database (Denmark)

Artuso, Matteo; Christiansen, Henrik Lehrmann

2013-01-01

The scheduling policy adopted in the LTE (Long Term Evolution) MAC layer is the most valuable degree of freedom left from the 3GPP (3rd Generation Partnership Project) consortium to the industry and the research community . This paper presents an OPNET model of the downlink scheduling in a one...

Oscillatory neuronal dynamics associated with manual acupuncture: a magnetoencephalography study using beamforming analysis

Directory of Open Access Journals (Sweden)

Aziz eAsghar

2012-11-01

Full Text Available Magnetoencephalography (MEG enables non-invasive recording of neuronal activity, with reconstruction methods providing estimates of underlying brain source locations and oscillatory dynamics from externally recorded neuromagnetic fields. The aim of our study was to use MEG to determine the effect of manual acupuncture on neuronal oscillatory dynamics. A major problem in MEG investigations of manual acupuncture is the absence of onset times for each needle manipulation. Given that beamforming (spatial filtering analysis is not dependent upon stimulus-driven responses being phase-locked to stimulus onset, we postulated that beamforming could reveal source locations and induced changes in neuronal activity during manual acupuncture. In a beamformer analysis, a two-minute period of manual acupuncture needle manipulation delivered to the ipsilateral right LI-4 (Hegu acupoint was contrasted with a two-minute baseline period. We considered oscillatory power changes in the theta (4-8Hz, alpha (8-13Hz, beta (13-30Hz and gamma (30-100Hz frequency bands. We found significant decreases in beta band power in the contralateral primary somatosensory cortex and superior frontal gyrus. In the ipsilateral cerebral hemisphere, we found significant power decreases in beta and gamma frequency bands in only the superior frontal gyrus. No significant power modulations were found in theta and alpha bands. Our results indicate that beamforming is a useful analytical tool to reconstruct underlying neuronal activity associated with manual acupuncture. Our main finding was of beta power decreases in primary somatosensory cortex and superior frontal gyrus, which opens up a line of future investigation regarding whether this contributes towards an underlying mechanism of acupuncture.

On the input distribution and optimal beamforming for the MISO VLC wiretap channel

KAUST Repository

Arfaoui, Mohamed Amine; Rezki, Zouheir; Ghrayeb, Ali; Alouini, Mohamed-Slim

2017-01-01

We investigate in this paper the achievable secrecy rate of the multiple-input single-output (MISO) visible light communication (VLC) Gaussian wiretap channel with single user and single eavesdropper. We consider the cases when the location of eavesdropper is known or unknown to the transmitter. In the former case, we derive the optimal beamforming in closed form, subject to constrained inputs. In the latter case, we apply robust beamforming. Furthermore, we study the achievable secrecy rate when the input follows the truncated generalized normal (TGN) distribution. We present several examples which demonstrate the substantial improvements in the secrecy rates achieved by the proposed techniques.

On the input distribution and optimal beamforming for the MISO VLC wiretap channel

KAUST Repository

Arfaoui, Mohamed Amine

2017-05-12

We investigate in this paper the achievable secrecy rate of the multiple-input single-output (MISO) visible light communication (VLC) Gaussian wiretap channel with single user and single eavesdropper. We consider the cases when the location of eavesdropper is known or unknown to the transmitter. In the former case, we derive the optimal beamforming in closed form, subject to constrained inputs. In the latter case, we apply robust beamforming. Furthermore, we study the achievable secrecy rate when the input follows the truncated generalized normal (TGN) distribution. We present several examples which demonstrate the substantial improvements in the secrecy rates achieved by the proposed techniques.

Cobalt: A GPU-based correlator and beamformer for LOFAR

Science.gov (United States)

Broekema, P. Chris; Mol, J. Jan David; Nijboer, R.; van Amesfoort, A. S.; Brentjens, M. A.; Loose, G. Marcel; Klijn, W. F. A.; Romein, J. W.

2018-04-01

For low-frequency radio astronomy, software correlation and beamforming on general purpose hardware is a viable alternative to custom designed hardware. LOFAR, a new-generation radio telescope centered in the Netherlands with international stations in Germany, France, Ireland, Poland, Sweden and the UK, has successfully used software real-time processors based on IBM Blue Gene technology since 2004. Since then, developments in technology have allowed us to build a system based on commercial off-the-shelf components that combines the same capabilities with lower operational cost. In this paper, we describe the design and implementation of a GPU-based correlator and beamformer with the same capabilities as the Blue Gene based systems. We focus on the design approach taken, and show the challenges faced in selecting an appropriate system. The design, implementation and verification of the software system show the value of a modern test-driven development approach. Operational experience, based on three years of operations, demonstrates that a general purpose system is a good alternative to the previous supercomputer-based system or custom-designed hardware.

Performance Analysis of Diversity-Controlled Multi-User Superposition Transmission for 5G Wireless Networks.

Science.gov (United States)

Yeom, Jeong Seon; Chu, Eunmi; Jung, Bang Chul; Jin, Hu

2018-02-10

In this paper, we propose a novel low-complexity multi-user superposition transmission (MUST) technique for 5G downlink networks, which allows multiple cell-edge users to be multiplexed with a single cell-center user. We call the proposed technique diversity-controlled MUST technique since the cell-center user enjoys the frequency diversity effect via signal repetition over multiple orthogonal frequency division multiplexing (OFDM) sub-carriers. We assume that a base station is equipped with a single antenna but users are equipped with multiple antennas. In addition, we assume that the quadrature phase shift keying (QPSK) modulation is used for users. We mathematically analyze the bit error rate (BER) of both cell-edge users and cell-center users, which is the first theoretical result in the literature to the best of our knowledge. The mathematical analysis is validated through extensive link-level simulations.

Downlink Transmission of Short Packets

DEFF Research Database (Denmark)

Trillingsgaard, Kasper Fløe; Popovski, Petar

2017-01-01

Cellular wireless systems rely on frame-based transmissions. The frame design is conventionally based on heuristics, consisting of a frame header and a data part. The frame header contains control information that provides pointers to the messages within the data part. In this paper, we revisit...... the principles of frame design and show the impact of the new design in scenarios that feature short data packets, which are central to various 5G and Internet of Things applications. We~treat framing for downlink transmission in an AWGN broadcast channel with $K$ users, where the sizes of the messages....... This requires changes in the way control information is sent, and it requires that the users need to spend power decoding other messages, thereby increasing the average power consumption. We~show that the common heuristic design is only one point on a curve that represents the tradeoff between latency and power...

SINR balancing in the downlink of cognitive radio networks with imperfect channel knowledge

KAUST Repository

Hanif, Muhammad Fainan; Smith, Peter J.; Alouini, Mohamed-Slim

2010-01-01

an acceptable threshold with uncertain channel state information available at the CR base-station (BS). We optimize the beamforming vectors at the CR BS so that the worst user SINR is maximized and transmit power constraints at the CR BS and interference

Millimetre Level Accuracy GNSS Positioning with the Blind Adaptive Beamforming Method in Interference Environments

Directory of Open Access Journals (Sweden)

Saeed Daneshmand

2016-10-01

Full Text Available The use of antenna arrays in Global Navigation Satellite System (GNSS applications is gaining significant attention due to its superior capability to suppress both narrowband and wideband interference. However, the phase distortions resulting from array processing may limit the applicability of these methods for high precision applications using carrier phase based positioning techniques. This paper studies the phase distortions occurring with the adaptive blind beamforming method in which satellite angle of arrival (AoA information is not employed in the optimization problem. To cater to non-stationary interference scenarios, the array weights of the adaptive beamformer are continuously updated. The effects of these continuous updates on the tracking parameters of a GNSS receiver are analyzed. The second part of this paper focuses on reducing the phase distortions during the blind beamforming process in order to allow the receiver to perform carrier phase based positioning by applying a constraint on the structure of the array configuration and by compensating the array uncertainties. Limitations of the previous methods are studied and a new method is proposed that keeps the simplicity of the blind beamformer structure and, at the same time, reduces tracking degradations while achieving millimetre level positioning accuracy in interference environments. To verify the applicability of the proposed method and analyze the degradations, array signals corresponding to the GPS L1 band are generated using a combination of hardware and software simulators. Furthermore, the amount of degradation and performance of the proposed method under different conditions are evaluated based on Monte Carlo simulations.

Improved Channel Allocation and RLC block scheduling for Downlink traffic in GPRS

DEFF Research Database (Denmark)

Wang, Haibo; Devendra, Devendra; Zhou, Xin

This paper investigates the Radio Resource Management (RRM) approaches for GSM/GPRS networks. The effort was put on Access Control(AC), Time-Slot (TS) allocation, and Radio Link Control (RLC) packet scheduling for down-link performance enhancement. A new credit-based algorithm was proposed...

Effects of imperfect CSIT on downlink MU-MIMO Fair SLNR scheduling algorithm

NARCIS (Netherlands)

Debbarma, D.; Wang, Q.; Heemstra de Groot, S.M.; Lo, A.C.C.

2013-01-01

Indoor downlink communication contributes to a large part of the data traffic generated in today’s world. The demand for high rate wireless indoor coverage while providing complete support to the existing wireless technologies is a big challenge. The future proof centralized optical fiber indoor

Performance Evaluation of Analog Beamforming with Hardware Impairments for mmW Massive MIMO Communication in an Urban Scenario

Directory of Open Access Journals (Sweden)

Sonia Gimenez

2016-09-01

Full Text Available The use of massive multiple-input multiple-output (MIMO techniques for communication at millimeter-Wave (mmW frequency bands has become a key enabler to meet the data rate demands of the upcoming fifth generation (5G cellular systems. In particular, analog and hybrid beamforming solutions are receiving increasing attention as less expensive and more power efficient alternatives to fully digital precoding schemes. Despite their proven good performance in simple setups, their suitability for realistic cellular systems with many interfering base stations and users is still unclear. Furthermore, the performance of massive MIMO beamforming and precoding methods are in practice also affected by practical limitations and hardware constraints. In this sense, this paper assesses the performance of digital precoding and analog beamforming in an urban cellular system with an accurate mmW channel model under both ideal and realistic assumptions. The results show that analog beamforming can reach the performance of fully digital maximum ratio transmission under line of sight conditions and with a sufficient number of parallel radio-frequency (RF chains, especially when the practical limitations of outdated channel information and per antenna power constraints are considered. This work also shows the impact of the phase shifter errors and combiner losses introduced by real phase shifter and combiner implementations over analog beamforming, where the former ones have minor impact on the performance, while the latter ones determine the optimum number of RF chains to be used in practice.

Performance analysis of distributed beamforming in a spectrum sharing system

KAUST Repository

Yang, Liang

2013-05-01

In this paper, we consider a distributed beamforming scheme (DBF) in a spectrum sharing system where multiple secondary users share the spectrum with some licensed primary users under an interference temperature constraint. We assume that the DBF is applied at the secondary users. We first consider optimal beamforming and compare it with the user selection scheme in terms of the outage probability and bit error rate performance metrics. Since perfect feedback is difficult to obtain, we then investigate a limited feedback DBF scheme and develop an analysis for a random vector quantization design algorithm. Specifically, the approximate statistics functions of the squared inner product between the optimal and quantized vectors are derived. With these statistics, we analyze the outage performance. Furthermore, the effects of channel estimation error and number of primary users on the system performance are investigated. Finally, optimal power adaptation and cochannel interference are considered and analyzed. Numerical and simulation results are provided to illustrate our mathematical formalism and verify our analysis. © 2012 IEEE.

A Two-Stage MMSE Beamformer for Underdetermined Signal Separation

Czech Academy of Sciences Publication Activity Database

Koldovský, Zbyněk; Tichavský, Petr; Phan, A. H.; Cichocki, A.

2013-01-01

Roč. 20, č. 12 (2013), s. 1227-1230 ISSN 1070-9908 Grant - others:GA ČR(CZ) GAP103/11/1947 Program:GA Institutional support: RVO:67985556 Keywords : beamforming * underdetermined mixtures * blind source separation Subject RIV: BB - Applied Statistics, Operational Research Impact factor: 1.639, year: 2013 http://library.utia.cas.cz/separaty/2014/SI/koldovsky-0424112.pdf

Body Loss Study of Beamforming Mode in LTE MIMO Mobile Terminals

DEFF Research Database (Denmark)

Zhang, Shuai; Zhao, Kun; Ying, Zhinong

2015-01-01

This paper mainly focuses on the investigation of the body loss of beamforming mode in LTE MIMO mobile terminals with CTIA user effects. The research of the body loss and radiation efficiency is carried out over different phase differences between two ports of each MIMO antenna. During studies......, four kinds of typical LTE MIMO antennas are used, namely, collocated ground free (GF), parallel GF, parallel on ground (OG) and orthogonal OG MIMO antennas, under four mobile terminal lengths at low and high frequencies. Two kinds of CTIA user effects are included in the research. From the studies......, the parallel GF MIMO antenna type exhibits the best beamforming performance in the four MIMO antenna types. In order to verify the simulations, envelope correlation coefficients of two MIMO antenna prototypes are measured. All the measured results agree well with the simulated....

Comparisons of receive array interference reduction techniques under erroneous generalized transmit beamforming

KAUST Repository

Radaydeh, Redha Mahmoud; Alouini, Mohamed-Slim

2014-01-01

information for the desired user spatially uncorrelated transmit channels on the effectiveness of transmit beamforming for different interference reduction techniques is investigated. The case of over-loaded receive array with closely-spaced elements

Energy Efficiency and SINR Maximization Beamformers for Spectrum Sharing With Sensing Information

KAUST Repository

Alabbasi, AbdulRahman; Rezki, Zouheir; Shihada, Basem

2014-01-01

an underlaying communication using adaptive beamforming schemes combined with sensing information to achieve optimal energy-efficient systems. The proposed schemes maximize EE and SINR metrics subject to cognitive radio and quality-of-service constraints

Clinical evaluation of Synthetic Aperture Sequential Beamforming and Tissue Harmonic Imaging

DEFF Research Database (Denmark)

Brandt, Andreas Hjelm; Hemmsen, Martin Christian; Hansen, Peter Møller

2014-01-01

This study determines if the data reduction achieved by the combination Synthetic Aperture Sequential Beamforming (SASB) and Tissue Harmonic Imaging (THI) affects image quality. SASB-THI was evaluated against the combination of Dynamic Received Focusing and Tissue Harmonic Imaging (DRF-THI). A BK...... equally good image quality although a data reduction of 64 times is achieved with SASB-THI.......This study determines if the data reduction achieved by the combination Synthetic Aperture Sequential Beamforming (SASB) and Tissue Harmonic Imaging (THI) affects image quality. SASB-THI was evaluated against the combination of Dynamic Received Focusing and Tissue Harmonic Imaging (DRF-THI). A BK...... liver pathology were scanned to set a clinical condition, where ultrasonography is often performed. A total of 114 sequences were recorded and evaluated by five radiologists. The evaluators were blinded to the imaging technique, and each sequence was shown twice with different left-right positioning...

Directional synthetic aperture flow imaging using a dual stage beamformer approach

DEFF Research Database (Denmark)

Li, Ye; Jensen, Jørgen Arendt

2011-01-01

. The new method has been studied using the Field II simulations and experimental flow rig measurements. A linear array transducer with 7 MHz center frequency is used, and 64 elements are active to transmit and receive signals. The data is processed in two stages. The first stage has a fixed focus point......A new method for directional synthetic aperture flow imaging using a dual stage beamformer approach is presented. The velocity estimation is angle independent and the amount of calculations is reduced compared to full synthetic aperture, but still maintains all the advantages at the same time....... In the second stage, focal points are considered as virtual sources and data is beamformed along the flow direction. Then the velocities are estimated by finding the spatial shift between two signals. In the experimental measurements the angle between the transmit beam and flow vessel was 70 and a laminar flow...

Compressive Sound Speed Profile Inversion Using Beamforming Results

OpenAIRE

Youngmin Choo; Woojae Seong

2018-01-01

Sound speed profile (SSP) significantly affects acoustic propagation in the ocean. In this work, the SSP is inverted using compressive sensing (CS) combined with beamforming to indicate the direction of arrivals (DOAs). The travel times and the positions of the arrivals can be approximately linearized using their Taylor expansion with the shape function coefficients that parameterize the SSP. The linear relation between the travel times/positions and the shape function coefficients enables CS...

Energy efficiency and SINR maximization beamformers for cognitive radio utilizing sensing information

KAUST Repository

Alabbasi, AbdulRahman; Rezki, Zouheir; Shihada, Basem

2014-01-01

communication using adaptive beamforming schemes combined with the sensing information to achieve an optimal energy efficient system. The proposed schemes maximize the energy efficiency and SINR metrics subject to cognitive radio and quality of service

Computational modelling of multi-cell migration in a multi-signalling substrate

International Nuclear Information System (INIS)

Mousavi, Seyed Jamaleddin; Doblaré, Manuel; Doweidar, Mohamed Hamdy

2014-01-01

Cell migration is a vital process in many biological phenomena ranging from wound healing to tissue regeneration. Over the past few years, it has been proven that in addition to cell–cell and cell-substrate mechanical interactions (mechanotaxis), cells can be driven by thermal, chemical and/or electrical stimuli. A numerical model was recently presented by the authors to analyse single cell migration in a multi-signalling substrate. That work is here extended to include multi-cell migration due to cell–cell interaction in a multi-signalling substrate under different conditions. This model is based on balancing the forces that act on the cell population in the presence of different guiding cues. Several numerical experiments are presented to illustrate the effect of different stimuli on the trajectory and final location of the cell population within a 3D heterogeneous multi-signalling substrate. Our findings indicate that although multi-cell migration is relatively similar to single cell migration in some aspects, the associated behaviour is very different. For instance, cell–cell interaction may delay single cell migration towards effective cues while increasing the magnitude of the average net cell traction force as well as the local velocity. Besides, the random movement of a cell within a cell population is slightly greater than that of single cell migration. Moreover, higher electrical field strength causes the cell slug to flatten near the cathode. On the other hand, as with single cell migration, the existence of electrotaxis dominates mechanotaxis, moving the cells to the cathode or anode pole located at the free surface. The numerical results here obtained are qualitatively consistent with related experimental works. (paper)

Ka-Band Digital Beamforming and SweepSAR Demonstration for Ice and Solid Earth Topography

Science.gov (United States)

Sadowy, Gregory; Ghaemi, Hirad; Heavy, Brandon; Perkovic, Dragana; Quddus, Momin; Zawadzki, Mark; Moller, Delwyn

2010-01-01

GLISTIN is an instrument concept for a single-pass interferometric SAR operating at 35.6 GHz. To achieve large swath widths using practical levels of transmitter power, a digitally-beamformed planar waveguide array is used. This paper describes results from a ground-based demonstration of a 16-receiver prototype. Furthermore, SweepSAR is emerging as promising technique for achieving very wide swaths for surface change detection. NASA and DLR are studying this approach for the DESDynI and Tandem-L missions. SweepSAR employs a reflector with a digitally-beamformed array feed. We will describe development of an airborne demonstration of SweepSAR using the GLISTIN receiver array and a reflector.

Fetal MEG evoked response latency from beamformer with random field theory.

Science.gov (United States)

McCubbin, J; Vrba, J; Murphy, P; Temple, J; Eswaran, H; Lowery, C L; Preissl, H

2010-01-01

Analysis of fetal magnetoencephalographic brain recordings is restricted by low signal to noise ratio (SNR) and non-stationarity of the sources. Beamformer techniques have been applied to improve SNR of fetal evoked responses. However, until now the effect of non-stationarity was not taken into account in detail, because the detection of evoked responses is in most cases determined by averaging a large number of trials. We applied a windowing technique to improve the stationarity of the data by using short time segments recorded during a flash-evoked study. In addition, we implemented a random field theory approach for more stringent control of false-positives in the statistical parametric map of the search volume for the beamformer. The search volume was based on detailed individual fetal/maternal biometrics from ultrasound scans and fetal heart localization. Average power over a sliding window within the averaged evoked response against a randomized average background power was used as the test z-statistic. The significance threshold was set at 10% over all members of a contiguous cluster of voxels. There was at least one significant response for 62% of fetal and 95% of newborn recordings with gestational age (GA) between 28 and 45 weeks from 29 subjects. We found that the latency was either substantially unchanged or decreased with increasing GA for most subjects, with a nominal rate of about -11 ms/week. These findings support the anticipated neurophysiological development, provide validation for the beamformer model search as a methodology, and may lead to a clinical test for fetal cognitive development.

Coordinated SLNR based Precoding in Large-Scale Heterogeneous Networks

KAUST Repository

Boukhedimi, Ikram

2017-03-06

This work focuses on the downlink of large-scale two-tier heterogeneous networks composed of a macro-cell overlaid by micro-cell networks. Our interest is on the design of coordinated beamforming techniques that allow to mitigate the inter-cell interference. Particularly, we consider the case in which the coordinating base stations (BSs) have imperfect knowledge of the channel state information. Under this setting, we propose a regularized SLNR based precoding design in which the regularization factor is used to allow better resilience with respect to the channel estimation errors. Based on tools from random matrix theory, we provide an analytical analysis of the SINR and SLNR performances. These results are then exploited to propose a proper setting of the regularization factor. Simulation results are finally provided in order to validate our findings and to confirm the performance of the proposed precoding scheme.

Coordinated SLNR based Precoding in Large-Scale Heterogeneous Networks

KAUST Repository

Boukhedimi, Ikram; Kammoun, Abla; Alouini, Mohamed-Slim

2017-01-01

This work focuses on the downlink of large-scale two-tier heterogeneous networks composed of a macro-cell overlaid by micro-cell networks. Our interest is on the design of coordinated beamforming techniques that allow to mitigate the inter-cell interference. Particularly, we consider the case in which the coordinating base stations (BSs) have imperfect knowledge of the channel state information. Under this setting, we propose a regularized SLNR based precoding design in which the regularization factor is used to allow better resilience with respect to the channel estimation errors. Based on tools from random matrix theory, we provide an analytical analysis of the SINR and SLNR performances. These results are then exploited to propose a proper setting of the regularization factor. Simulation results are finally provided in order to validate our findings and to confirm the performance of the proposed precoding scheme.

Prediction and comparison of down-link electric field and uplink localised SAR values for realistic indoor wireless planning

International Nuclear Information System (INIS)

Plets, David; Joseph, Wout; Aerts, Sam; Vanhecke, Kris; Vermeeren, Guenter; Martens, Luc

2014-01-01

In this paper, for the first time a heuristic network calculator for both whole-body exposure due to indoor base station antennas or access points (down-link exposure) and localised exposure due to the mobile device (uplink exposure) in indoor wireless networks is presented. As an application, three phone call scenarios are investigated (Universal Mobile Telecommunications System (UMTS) macro-cell, UMTS femto-cell and WiFi voice-over-IP) and compared with respect to the electric-field strength and localised specific absorption rate (SAR) distribution. Prediction models are created and successfully validated with an accuracy of 3 dB. The benefits of the UMTS power control mechanisms are demonstrated. However, dependent on the macro-cell connection quality and on the user's average phone call connection time, also the macro-cell solution might be preferential from an exposure point of view for the considered scenario. (authors)

Integrated 60GHz RF beamforming in CMOS

CERN Document Server

Yu, Yikun; van Roermund, Arthur H M

2011-01-01

""Integrated 60GHz RF Beamforming in CMOS"" describes new concepts and design techniques that can be used for 60GHz phased array systems. First, general trends and challenges in low-cost high data-rate 60GHz wireless system are studied, and the phased array technique is introduced to improve the system performance. Second, the system requirements of phase shifters are analyzed, and different phased array architectures are compared. Third, the design and implementation of 60GHz passive and active phase shifters in a CMOS technology are presented. Fourth, the integration of 60GHz phase shifters

RF-to-RF Characterization of a Phased Array Receive Antenna Steering System Using a Novel Ring Resonator-Based Integrated Photonic Beamformer

NARCIS (Netherlands)

Zhuang, L.; Burla, M.; Roeloffzen, C.G.H.; Meijerink, Arjan; Marpaung, D.A.I.; Khan, M.R.H.; van Etten, Wim; Leinse, Arne; Hoekman, M.; Heideman, Rene

2009-01-01

A novel ring resonator-based photonic beamformer has been developed for continuous and squint-free control of the reception angle of broadband phased array antenna systems. The core of the system is a ring resonator based optical beamforming network (OBFN) used for delay synchronization and coherent

Comparison of Beam-Forming and Relaying in Sparse Sensor Networks

Directory of Open Access Journals (Sweden)

Mikuláš Krebs

2015-12-01

Full Text Available This study focuses on the differences in power consumption between beam-forming and relaying data transmission methods in a sparse wireless ad-hoc network. These two methods are observed for the same parameters using an identical network topology in a simulation programme that was developed as a part of this study.

Cognitive two-way relay beamforming: Design with resilience to channel state uncertainties

KAUST Repository

Ubaidulla, P.; Alouini, Mohamed-Slim; Aissa, Sonia

2016-01-01

In this paper, we propose a robust distributed relay beamformer design for cognitive radio network operating under uncertainties in the available channel state information. The cognitive network consists of a pair of transceivers and a set of non

Artificial lateral-line system for imaging dipole sources using Beamforming techniques

NARCIS (Netherlands)

Dagamseh, A.M.K.; Wiegerink, Remco J.; Lammerink, Theodorus S.J.; Krijnen, Gijsbertus J.M.

In nature, fish have the ability to localize prey, school, navigate, etc. using the lateral-line organ [1]. Here we present the use of biomimetic artificial hair-based flow-sensors arranged as lateral-line system in combination with beamforming techniques for dipole source localization in air.

An Enhanced Feedback-Base Downlink Packet Scheduling Algorithm for Mobile TV in WIMAX Networks

Directory of Open Access Journals (Sweden)

Joseph Oyewale

2013-06-01

Full Text Available With high speed access network technology like WIMAX, there is the need for efficient management of radio resources where the throughput and Qos requirements for Multicasting Broadcasting Services (MBS for example TV are to be met. An enhanced  feedback-base downlink Packet scheduling algorithm  that can be used in IEEE 802.16d/e networks for mobile TV “one way traffic”(MBS is needed to support many users utilizing multiuser diversity of the  broadband of WIMAX systems where a group of users(good/worst channels share allocated resources (bandwidth. This paper proposes a WIMAX framework feedback-base (like a channel-awareness downlink packet scheduling algorithm for Mobile TV traffics in IEEE806.16, in which network Physical Timing Slots (PSs resource blocks are allocated in a dynamic way to mobile TV subscribers based on the Channel State information (CSI feedback, and then considering users with worst channels with the aim of improving system throughput while system coverage is being guaranteed. The algorithm was examined by changing the PSs bandwidth allocation of the users and different number of users of a cell. Simulation results show our proposed algorithm performed better than other algorithms (blind algorithms in terms of improvement in system throughput performance. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso

Enhancing Network Quality using Baseband Frequency Hopping, Downlink Power Control and DTX in a Live GSM Network

DEFF Research Database (Denmark)

Nielsen, Thomas Toftegaard; Wagard, Jeroen; Skjærris, Søren

1998-01-01

Baseband frequency hopping in the combination with downlink power control and discontinuous transmission has been investigated as a quality improving feature in a live GSM network. Using the dropped call rate and the frame erasure rate to measure the network quality, the use of frequency hopping...... to the statistical inaccuracy with discontinuous transmission in GSM and maybe due to poor performance of the mobile stations, was encountered. The current status is therefore to reject the use of downlink discontinuous transmission until more information about the performance of the mobile stations is found...

Downlink Error Rates of Half-duplex Users in Full-duplex Networks over a Laplacian Inter-User Interference Limited and EGK fading

KAUST Repository

Soury, Hamza

2017-03-14

This paper develops a mathematical framework to study downlink error rates and throughput for half-duplex (HD) terminals served by a full-duplex (FD) base station (BS). The developed model is used to motivate long term pairing for users that have non-line of sight (NLOS) interfering link. Consequently, we study the interferer limited problem that appears between NLOS HD users-pair that are scheduled on the same FD channel. The distribution of the interference is first characterized via its distribution function, which is derived in closed form. Then, a comprehensive performance assessment for the proposed pairing scheme is provided by assuming Extended Generalized- $cal{K}$ (EGK) fading for the downlink and studying different modulation schemes. To this end, a unified closed form expression for the average symbol error rate is derived. Furthermore, we show the effective downlink throughput gain harvested by the pairing NLOS users as a function of the average signal-to-interferenceratio when compared to an idealized HD scenario with neither interference nor noise. Finally, we show the minimum required channel gain pairing threshold to harvest downlink throughput via the FD operation when compared to the HD case for each modulation scheme.

Distributed cognitive two-way relay beamformer designs under perfect and imperfect CSI

KAUST Repository

Pandarakkottilil, Ubaidulla; Aissa, Sonia

2011-01-01

In this paper, we present distributed two-way relay beamformer designs for a cognitive radio network (CRN) in which a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relay nodes

Noise Quantification with Beamforming Deconvolution: Effects of Regularization and Boundary Conditions

DEFF Research Database (Denmark)

Lylloff, Oliver Ackermann; Fernandez Grande, Efren

Delay-and-sum (DAS) beamforming can be described as a linear convolution of an unknown sound source distribution and the microphone array response to a point source, i.e., point-spread function. Deconvolution tries to compensate for the influence of the array response and reveal the true source...

Outage probability of distributed beamforming with co-channel interference

KAUST Repository

Yang, Liang

2012-03-01

In this letter, we consider a distributed beamforming scheme (DBF) in the presence of equal-power co-channel interferers for both amplify-and-forward and decode-and-forward relaying protocols over Rayleigh fading channels. We first derive outage probability expressions for the DBF systems. We then present a performance analysis for a scheme relying on source selection. Numerical results are finally presented to verify our analysis. © 2011 IEEE.

Robust Adaptive Beamforming with Sensor Position Errors Using Weighted Subspace Fitting-Based Covariance Matrix Reconstruction.

Science.gov (United States)

Chen, Peng; Yang, Yixin; Wang, Yong; Ma, Yuanliang

2018-05-08

When sensor position errors exist, the performance of recently proposed interference-plus-noise covariance matrix (INCM)-based adaptive beamformers may be severely degraded. In this paper, we propose a weighted subspace fitting-based INCM reconstruction algorithm to overcome sensor displacement for linear arrays. By estimating the rough signal directions, we construct a novel possible mismatched steering vector (SV) set. We analyze the proximity of the signal subspace from the sample covariance matrix (SCM) and the space spanned by the possible mismatched SV set. After solving an iterative optimization problem, we reconstruct the INCM using the estimated sensor position errors. Then we estimate the SV of the desired signal by solving an optimization problem with the reconstructed INCM. The main advantage of the proposed algorithm is its robustness against SV mismatches dominated by unknown sensor position errors. Numerical examples show that even if the position errors are up to half of the assumed sensor spacing, the output signal-to-interference-plus-noise ratio is only reduced by 4 dB. Beam patterns plotted using experiment data show that the interference suppression capability of the proposed beamformer outperforms other tested beamformers.

Non-invasive beamforming add-on module

KAUST Repository

Bader, Ahmed

2017-02-23

An embodiment of a non-invasive beamforming add-on apparatus couples to an existing antenna port and rectifies the beam azimuth in the upstream and downstream directions. The apparatus comprises input circuitry that is configured to receive one or more signals from a neighboring node of the linear wireless sensor network; first amplifier circuitry configured to adjust an amplitude of a respective received signal in accordance with a weighting coefficient and invoke a desired phase to a carrier frequency of the received signal thereby forming a first amplified signal; and second amplifier circuitry configured to adjust a gain of the first amplified signal towards upstream and downstream neighbors of the linear wireless sensor in the linear wireless sensor network.

An analytical model for CDMA downlink rate optimization taking into account uplink coverage restriction

NARCIS (Netherlands)

Endrayanto, A.I.; van den Berg, Hans Leo; Boucherie, Richardus J.

2003-01-01

This paper models and analyzes downlink and uplink power assignment in Code Division Multiple Access (CDMA) mobile networks. By discretizing the area into small segments, the power requirements are characterized via a matrix representation that separates user and system characteristics. We obtain a

An analytical model for CDMA downlink rate optimization taking into account uplink coverage restrictions

NARCIS (Netherlands)

Endrayanto, A.I.; van den Berg, Hans Leo; Boucherie, Richardus J.

2005-01-01

This paper models and analyzes downlink and uplink power assignment in code division multiple access (CDMA) mobile networks. By discretizing the area into small segments, the power requirements are characterized via a matrix representation that separates user and system characteristics. We obtain a

Optimal OFDMA Downlink Scheduling Under a Control Signaling Cost Constraint

OpenAIRE

Larsson, Erik G.

2010-01-01

This paper proposes a new algorithm for downlink scheduling in OFDMA systems. The method maximizes the throughput, taking into account the amount of signaling needed to transmit scheduling maps to the users. A combinatorial problem is formulated and solved via a dynamic programming approach reminiscent of the Viterbi algorithm. The total computational complexity of the algorithm is upper boundedby O(K^4N) where K is the number of users that are being considered for scheduling in a frame and N...

Clinical evaluation of synthetic aperture sequential beamforming ultrasound in patients with liver tumors

DEFF Research Database (Denmark)

Hansen, Peter Møller; Hemmsen, Martin Christian; Brandt, Andreas Hjelm

2014-01-01

Medical ultrasound imaging using synthetic aperture sequential beamforming (SASB) has for the first time been used for clinical patient scanning. Nineteen patients with cancer of the liver (hepatocellular carcinoma or colorectal liver metastases) were scanned simultaneously with conventional...

Securing Communication via Transmission of Artificial Noise by Both Sides: Bipolar-Beamforming Optimization

Directory of Open Access Journals (Sweden)

Yongkai Zhou

2013-01-01

Full Text Available The paper considers the secure transmission in a wireless environment in which both the transmitter (Alice and the legitimate receiver (Bob send artificial noise (AN to interfere with the eavesdropper (Eve. Optimal design is analyzed in detail for this AN-by-both-side model to deal with Eve’s stochastic channel condition and random spatial distribution. Bipolar-beamforming is first proposed to jointly design Alice and Bob’s transmitting signals. By optimally assigning the transmitting antenna for Bob and allocating the power ratio between Alice’s information and the AN signal, maximum secrecy capacity can be achieved. Simulation is done to illustrate the process of bipolar-beamforming optimization. Results show that the AN-by-both-side model has good secrecy performance on both average and extreme conditions as Eve approaches Alice or Bob.

A spatial interference minimization strategy for the correlated LTE downlink channel

OpenAIRE

Nordin, R; Armour, SMD; McGeehan, JP

2010-01-01

In a downlink transmission, users can benefit from the high capacity gain achieved by transmitting independent data streams from multiple antennas to multiple users sharing the same physical time-frequency resources. This technique is known as multiuser MIMO (MU-MIMO). However, performance of MU-MIMO is sensitive towards propagation imperfections, such as time dispersion and inter-stream interference due to antenna correlation. In this paper we investigate the performance of MUMIMO operation ...

3-component beamforming analysis of ambient seismic noise field for Love and Rayleigh wave source directions

Science.gov (United States)

Juretzek, Carina; Hadziioannou, Céline

2014-05-01

Our knowledge about common and different origins of Love and Rayleigh waves observed in the microseism band of the ambient seismic noise field is still limited, including the understanding of source locations and source mechanisms. Multi-component array methods are suitable to address this issue. In this work we use a 3-component beamforming algorithm to obtain source directions and polarization states of the ambient seismic noise field within the primary and secondary microseism bands recorded at the Gräfenberg array in southern Germany. The method allows to distinguish between different polarized waves present in the seismic noise field and estimates Love and Rayleigh wave source directions and their seasonal variations using one year of array data. We find mainly coinciding directions for the strongest acting sources of both wave types at the primary microseism and different source directions at the secondary microseism.

Energy Efficient Power Allocation in Multi-tier 5G Networks Using Enhanced Online Learning

KAUST Repository

Alqerm, Ismail

2017-07-25

The multi-tier heterogeneous structure of 5G with dense small cells deployment, relays, and device-to-device (D2D) communications operating in an underlay fashion is envisioned as a potential solution to satisfy the future demand for cellular services. However, efficient power allocation among dense secondary transmitters that maintains quality of service (QoS) for macro (primary) cell users and secondary cell users is a critical challenge for operating such radio. In this paper, we focus on the power allocation problem in the multi-tier 5G network structure using a non-cooperative methodology with energy efficiency consideration. Therefore, we propose a distributive intuition-based online learning scheme for power allocation in the downlink of the 5G systems, where each transmitter surmises other transmitters power allocation strategies without information exchange. The proposed learning model exploits a brief state representation to account for the problem of dimensionality in online learning and expedite the convergence. The convergence of the proposed scheme is proved and numerical results demonstrate its capability to achieve fast convergence with QoS guarantee and significant improvement in system energy efficiency.

Acoustic Emission Beamforming for Detection and Localization of Damage

Science.gov (United States)

Rivey, Joshua Callen

The aerospace industry is a constantly evolving field with corporate manufacturers continually utilizing innovative processes and materials. These materials include advanced metallics and composite systems. The exploration and implementation of new materials and structures has prompted the development of numerous structural health monitoring and nondestructive evaluation techniques for quality assurance purposes and pre- and in-service damage detection. Exploitation of acoustic emission sensors coupled with a beamforming technique provides the potential for creating an effective non-contact and non-invasive monitoring capability for assessing structural integrity. This investigation used an acoustic emission detection device that employs helical arrays of MEMS-based microphones around a high-definition optical camera to provide real-time non-contact monitoring of inspection specimens during testing. The study assessed the feasibility of the sound camera for use in structural health monitoring of composite specimens during tensile testing for detecting onset of damage in addition to nondestructive evaluation of aluminum inspection plates for visualizing stress wave propagation in structures. During composite material monitoring, the sound camera was able to accurately identify the onset and location of damage resulting from large amplitude acoustic feedback mechanisms such as fiber breakage. Damage resulting from smaller acoustic feedback events such as matrix failure was detected but not localized to the degree of accuracy of larger feedback events. Findings suggest that beamforming technology can provide effective non-contact and non-invasive inspection of composite materials, characterizing the onset and the location of damage in an efficient manner. With regards to the nondestructive evaluation of metallic plates, this remote sensing system allows us to record wave propagation events in situ via a single-shot measurement. This is a significant improvement over

Ultrasonic Fingerprint Sensor With Transmit Beamforming Based on a PMUT Array Bonded to CMOS Circuitry.

Science.gov (United States)

Jiang, Xiaoyue; Tang, Hao-Yen; Lu, Yipeng; Ng, Eldwin J; Tsai, Julius M; Boser, Bernhard E; Horsley, David A

2017-09-01

In this paper, we present a single-chip 65 ×42 element ultrasonic pulse-echo fingerprint sensor with transmit (TX) beamforming based on piezoelectric micromachined ultrasonic transducers directly bonded to a CMOS readout application-specific integrated circuit (ASIC). The readout ASIC was realized in a standard 180-nm CMOS process with a 24-V high-voltage transistor option. Pulse-echo measurements are performed column-by-column in sequence using either one column or five columns to TX the ultrasonic pulse at 20 MHz. TX beamforming is used to focus the ultrasonic beam at the imaging plane where the finger is located, increasing the ultrasonic pressure and narrowing the 3-dB beamwidth to [Formula: see text], a factor of 6.4 narrower than nonbeamformed measurements. The surface of the sensor is coated with a poly-dimethylsiloxane (PDMS) layer to provide good acoustic impedance matching to skin. Scanning laser Doppler vibrometry of the PDMS surface was used to map the ultrasonic pressure field at the imaging surface, demonstrating the expected increase in pressure, and reduction in beamwidth. Imaging experiments were conducted using both PDMS phantoms and real fingerprints. The average image contrast is increased by a factor of 1.5 when beamforming is used.

A PSF-Shape-Based Beamforming Strategy for Robust 2D Motion Estimation in Ultrafast Data

Directory of Open Access Journals (Sweden)

Anne E. C. M. Saris

2018-03-01

Full Text Available This paper presents a framework for motion estimation in ultrafast ultrasound data. It describes a novel approach for determining the sampling grid for ultrafast data based on the system’s point-spread-function (PSF. As a consequence, the cross-correlation functions (CCF used in the speckle tracking (ST algorithm will have circular-shaped peaks, which can be interpolated using a 2D interpolation method to estimate subsample displacements. Carotid artery wall motion and parabolic blood flow simulations together with rotating disk experiments using a Verasonics Vantage 256 are used for performance evaluation. Zero-degree plane wave data were acquired using an ATL L5-12 (fc = 9 MHz transducer for a range of pulse repetition frequencies (PRFs, resulting in 0–600 µm inter-frame displacements. The proposed methodology was compared to data beamformed on a conventionally spaced grid, combined with the commonly used 1D parabolic interpolation. The PSF-shape-based beamforming grid combined with 2D cubic interpolation showed the most accurate and stable performance with respect to the full range of inter-frame displacements, both for the assessment of blood flow and vessel wall dynamics. The proposed methodology can be used as a protocolled way to beamform ultrafast data and obtain accurate estimates of tissue motion.

Analog 65/130 nm CMOS 5 GHz Sub-Arrays with ROACH-2 FPGA Beamformers for Hybrid Aperture-Array Receivers

Science.gov (United States)

2017-03-20

factor, where c is the wave speed . Proposed two-level hybrid beamforming architecture consists of an analog sub-array at level-1 (L-element analog...gigabit transceivers, to support 4x10Ge links (SFP+) for high- speed communication. ROACH-2 also supports two ZDOk+ interfaces supporting high speed ADCs...antenna systems with hybrid analog and digital beamforming for millimeter wave 5G ,” IEEE Communications Magazine, vol. 53, no. 1, pp. 186–194, January

Multi-Capacity Load Cell Concept

Directory of Open Access Journals (Sweden)

Seif. M. OSMAN

2014-09-01

Full Text Available Force measuring systems are usually used to calibrate force generated systems, it is not preferable to use load cells to measure forces less than 10 % of its nominal capacity. Several load cells are required to offer calibration facilities at sites to cover different ranges, this lead to difficulties in handling procedures, through the need for several carrying cases to carry this overweight in addition to the over cost of purchasing several load cells. This article concerns with introducing a new concept for designing a multi-capacity load cell as a new force standard in the field of measuring the force. This multi-capacity load cell will replace a set of load cells and reflects economically on the total cost and on easiness of handling procedures.

A multiple-choice knapsack based algorithm for CDMA downlink rate differentiation under uplink coverage restrictions

NARCIS (Netherlands)

Endrayanto, A.I.; Bumb, A.F.; Boucherie, Richardus J.

2004-01-01

This paper presents an analytical model for downlink rate allocation in Code Division Multiple Access (CDMA) mobile networks. By discretizing the coverage area into small segments, the transmit power requirements are characterized via a matrix representation that separates user and system

Loudness estimation of simultaneous sources using beamforming

DEFF Research Database (Denmark)

Song, Woo-keun; Ellermeier, Wolfgang; Minnaar, Pauli

2006-01-01

An algorithm is proposed for estimating the loudness of several simultaneous sound sources by means of microphone-array beamforming. The algorithm is derived from two listening experiments in which the loudness of two simultaneous sounds (narrow-band noises with 1-kHz and 3.15-kHz center...... frequencies) was matched to a single sound (2-kHz narrow-band noise). The simultaneous sounds were presented from either one sound source or two spatially separated sources, whereas the single sound was presented from the frontal direction. The results indicate that overall loudness can be calculated...... by summing the loudnesses of the individual sources according to a simple psychophysical relationship....

Beamforming Through Regularized Inverse Problems in Ultrasound Medical Imaging.

Science.gov (United States)

Szasz, Teodora; Basarab, Adrian; Kouame, Denis

2016-12-01

Beamforming (BF) in ultrasound (US) imaging has significant impact on the quality of the final image, controlling its resolution and contrast. Despite its low spatial resolution and contrast, delay-and-sum (DAS) is still extensively used nowadays in clinical applications, due to its real-time capabilities. The most common alternatives are minimum variance (MV) method and its variants, which overcome the drawbacks of DAS, at the cost of higher computational complexity that limits its utilization in real-time applications. In this paper, we propose to perform BF in US imaging through a regularized inverse problem based on a linear model relating the reflected echoes to the signal to be recovered. Our approach presents two major advantages: 1) its flexibility in the choice of statistical assumptions on the signal to be beamformed (Laplacian and Gaussian statistics are tested herein) and 2) its robustness to a reduced number of pulse emissions. The proposed framework is flexible and allows for choosing the right tradeoff between noise suppression and sharpness of the resulted image. We illustrate the performance of our approach on both simulated and experimental data, with in vivo examples of carotid and thyroid. Compared with DAS, MV, and two other recently published BF techniques, our method offers better spatial resolution, respectively contrast, when using Laplacian and Gaussian priors.

Performance of Adaptive Antennas in FH-GSM Using Conventional Beamforming

DEFF Research Database (Denmark)

Mogensen, Preben Elgaard; Leth-Espensen, P; Zetterberg, P.

2000-01-01

This paper presents the performance of adaptive antennas in a 1/3 reuse frequency hopping GSM network using conventional beamforming. It mainly focuses on C/I improvement for the purpose of capacity enhancement. The performance evaluation has been conducted by means of network computer simulations...... implementation facilitates a potential capacity gain of x3 in a 1/3 reuse FH-GSM network for an array size of M = 4-6....

Space-Time Chip Equalization for Maximum Diversity Space-Time Block Coded DS-CDMA Downlink Transmission

NARCIS (Netherlands)

Leus, G.; Petré, F.; Moonen, M.

2004-01-01

In the downlink of DS-CDMA, frequency-selectivity destroys the orthogonality of the user signals and introduces multiuser interference (MUI). Space-time chip equalization is an efficient tool to restore the orthogonality of the user signals and suppress the MUI. Furthermore, multiple-input

Enhancing the beamforming map of spherical arrays at low frequencies using acoustic holography

DEFF Research Database (Denmark)

Tiana Roig, Elisabet; Torras Rosell, Antoni; Fernandez Grande, Efren

2014-01-01

Recent studies have shown that the localization of acoustic sources based on circular arrays can be improved at low frequencies by combining beamforming with acoustic holography. This paper extends this technique to the three dimensional case by making use of spherical arrays. The pressure captur...

Reducing Downlink Signaling Traffic in Wireless Systems Using Mobile-Assisted Scheduling

OpenAIRE

Moosavi, Reza; Larsson, Erik G.

2010-01-01

We present an idea to reduce the part of the downlink signaling traffic in wireless multiple access systems that contains scheduling information. The theoretical basis of the scheme is that the scheduling decisions made by the base station are correlated with the CSI reports from the mobiles. This correlation can be exploited by the source coding scheme that is used to compress the scheduling maps before they are sent to the mobiles. In the proposed scheme, this idea is implemented by letting...

Cooperative joint precoding in a downlink cellular system with shared relay: Design and performance evaluation

KAUST Repository

Kwon, JaeWoo; Park, Kihong; Ko, Youngchai; Yang, Hongchuan

2012-01-01

In this paper, we investigate a relay enhanced cellular system, where a relay station is located in the overlap area served by two base stations. We propose cooperative joint precoding schemes for the downlink transmission of such relay enhanced cellular system to maximize the system capacity while minimizing the interference at both the relay station and the mobile stations. We formulate the optimization problems to maximize the system capacity and design the multiuser precoding vectors at each base station and the relay station. We quantify the ergodic rate performance of the proposed multiuser precoding schemes through statistical analysis. The extensively derived ergodic expressions will facilitate the accurate performance evaluation of the proposed transmission schemes. Numerical results show that the proposed schemes can effectively cancel the interference and improve the sum rate and the outage performance for cell edge users. © 2002-2012 IEEE.

Cooperative joint precoding in a downlink cellular system with shared relay: Design and performance evaluation

KAUST Repository

Kwon, JaeWoo

2012-10-01

In this paper, we investigate a relay enhanced cellular system, where a relay station is located in the overlap area served by two base stations. We propose cooperative joint precoding schemes for the downlink transmission of such relay enhanced cellular system to maximize the system capacity while minimizing the interference at both the relay station and the mobile stations. We formulate the optimization problems to maximize the system capacity and design the multiuser precoding vectors at each base station and the relay station. We quantify the ergodic rate performance of the proposed multiuser precoding schemes through statistical analysis. The extensively derived ergodic expressions will facilitate the accurate performance evaluation of the proposed transmission schemes. Numerical results show that the proposed schemes can effectively cancel the interference and improve the sum rate and the outage performance for cell edge users. © 2002-2012 IEEE.

High Resolution Ultrasound Imaging Using Adaptive Beamforming with Reduced Number of Active Elements

DEFF Research Database (Denmark)

Holfort, Iben Kraglund; Gran, Fredrik; Jensen, Jørgen Arendt

2009-01-01

is proposed. By reducing the number of active sensor elements, an increased resolution can be obtained with the MV beamformer. This observation is directly opposite the well-known relation between the spatial extent of the aperture and the achievable resolution. The investigations are based on Field II...

Downlinks for DBS - Design and engineering considerations

Science.gov (United States)

Blecker, M.; Martin, E. R.

1985-01-01

The subsystem interrelationships and design parameters choice procedures for a DBS downlink design are discussed from a business decisions point of view. The image quality is determined by customer satisfaction, which is translated to a required carrier/noise (C/N) ratio. The C/N ratio defines acceptable levels of signal fading, a subjective value which is modified by the demographics of the service area. Increasing the satellite on-board transmitting power to meet acceptable broadcast reliability places burdens on the start-up capitalization of the business. Larger receiving antennas in rural areas ameliorates some of the power requirements. The dish size, however, affects the labor costs of installation, but must be kept small enough to be used in heavily populated areas. The satellites must be built, as far as is possible, from off-the-shelf components to keep costs down. Design selections for a sample complete system are listed.

Multiuser Scheduling on the Downlink of an LTE Cellular System

Directory of Open Access Journals (Sweden)

Raymond Kwan

2008-01-01

Full Text Available The challenge of scheduling user transmissions on the downlink of a long-term evolution (LTE cellular communication system is addressed. In particular, a novel optimalmultiuser scheduler is proposed. Numerical results show that the system performance improves with increasing correlation among OFDMA subcarriers. It is found that only a limited amount of feedback information is needed to achieve relatively good performance. A suboptimal reduced-complexity scheduler is also proposed and shown to provide good performance. The suboptimal scheme is especially attractive when the number of users is large, in which case the complexity of the optimal scheme is high.

Eigenspace-based minimum variance adaptive beamformer combined with delay multiply and sum: experimental study

Science.gov (United States)

Mozaffarzadeh, Moein; Mahloojifar, Ali; Nasiriavanaki, Mohammadreza; Orooji, Mahdi

2018-02-01

Delay and sum (DAS) is the most common beamforming algorithm in linear-array photoacoustic imaging (PAI) as a result of its simple implementation. However, it leads to a low resolution and high sidelobes. Delay multiply and sum (DMAS) was used to address the incapabilities of DAS, providing a higher image quality. However, the resolution improvement is not well enough compared to eigenspace-based minimum variance (EIBMV). In this paper, the EIBMV beamformer has been combined with DMAS algebra, called EIBMV-DMAS, using the expansion of DMAS algorithm. The proposed method is used as the reconstruction algorithm in linear-array PAI. EIBMV-DMAS is experimentally evaluated where the quantitative and qualitative results show that it outperforms DAS, DMAS and EIBMV. The proposed method degrades the sidelobes for about 365 %, 221 % and 40 %, compared to DAS, DMAS and EIBMV, respectively. Moreover, EIBMV-DMAS improves the SNR about 158 %, 63 % and 20 %, respectively.

Compact beamforming in medical ultrasound scanners

DEFF Research Database (Denmark)

Tomov, Borislav Gueorguiev

2003-01-01

for high-quality imaging is large, and compressing it leads to better compactness of the beamformers. The existing methods for compressing and recursive generation of focusing data, along with original work in the area, are presented in Chapter 4. The principles and the performance limitations...... quality is comparable to that of the very good scanners currently on the market. The performance results have been achieved with the use of a simple oversampled converter of second order. The use of a higher order oversampled converter will allow higher pulse frequency to be used while the high dynamic...... channels, and even more channels are necessary for 3-dimensional (3D) diagnostic imaging. On the other hand, there is a demand for inexpensive portable devices for use outside hospitals, in field conditions, where power consumption and compactness are important factors. The thesis starts...

Multi-crystalline II-VI based multijunction solar cells and modules

Science.gov (United States)

Hardin, Brian E.; Connor, Stephen T.; Groves, James R.; Peters, Craig H.

2015-06-30

Multi-crystalline group II-VI solar cells and methods for fabrication of same are disclosed herein. A multi-crystalline group II-VI solar cell includes a first photovoltaic sub-cell comprising silicon, a tunnel junction, and a multi-crystalline second photovoltaic sub-cell. A plurality of the multi-crystalline group II-VI solar cells can be interconnected to form low cost, high throughput flat panel, low light concentration, and/or medium light concentration photovoltaic modules or devices.

Downlink Radio Resource Management for QoS Provisioning in OFDMA Systems

DEFF Research Database (Denmark)

Monghal, Guillaume Damien

Admission Control solution for a realistic OFDMA based system in downlink where LTE is taken as a case study. In the frame of the thesis work, a detailed system model of LTE dedicated to Radio Resource Management study has been developed and implemented in a semi-static system level simulator. In a first...... phase, the study focuses on the dual time / frequency domain packet scheduling concept which allows a linear complexity. Fundamental design principles for throughput control are highlighted. Using those principles, the design of a complete Quality of Service aware packet scheduling algorithm based...

Hierarchical Downlink Resource Management Framework for OFDMA based WiMAX Systems

DEFF Research Database (Denmark)

Wang, Hua; Iversen, Villy Bæk

2008-01-01

IEEE 802.16, known as WiMAX, has received much attention for its capability to support multiple types of applications with diverse QoS requirements. Beyond what the standard has defined, radio resource management (RRM) still remains an open issue. In this paper, we propose a hierarchical downlink...... belonging to different service classes with the objective of increasing the spectral efficiency while satisfying the diverse QoS requirements in each service class. CAC highlights how to limit the number of ongoing connections preventing the system capacity from being overused. Through system...

Multi-cellular logistics of collective cell migration.

Directory of Open Access Journals (Sweden)

Masataka Yamao

Full Text Available During development, the formation of biological networks (such as organs and neuronal networks is controlled by multicellular transportation phenomena based on cell migration. In multi-cellular systems, cellular locomotion is restricted by physical interactions with other cells in a crowded space, similar to passengers pushing others out of their way on a packed train. The motion of individual cells is intrinsically stochastic and may be viewed as a type of random walk. However, this walk takes place in a noisy environment because the cell interacts with its randomly moving neighbors. Despite this randomness and complexity, development is highly orchestrated and precisely regulated, following genetic (and even epigenetic blueprints. Although individual cell migration has long been studied, the manner in which stochasticity affects multi-cellular transportation within the precisely controlled process of development remains largely unknown. To explore the general principles underlying multicellular migration, we focus on the migration of neural crest cells, which migrate collectively and form streams. We introduce a mechanical model of multi-cellular migration. Simulations based on the model show that the migration mode depends on the relative strengths of the noise from migratory and non-migratory cells. Strong noise from migratory cells and weak noise from surrounding cells causes "collective migration," whereas strong noise from non-migratory cells causes "dispersive migration." Moreover, our theoretical analyses reveal that migratory cells attract each other over long distances, even without direct mechanical contacts. This effective interaction depends on the stochasticity of the migratory and non-migratory cells. On the basis of these findings, we propose that stochastic behavior at the single-cell level works effectively and precisely to achieve collective migration in multi-cellular systems.

Fractional Programming for Communication Systems—Part I: Power Control and Beamforming

Science.gov (United States)

Shen, Kaiming; Yu, Wei

2018-05-01

This two-part paper explores the use of FP in the design and optimization of communication systems. Part I of this paper focuses on FP theory and on solving continuous problems. The main theoretical contribution is a novel quadratic transform technique for tackling the multiple-ratio concave-convex FP problem--in contrast to conventional FP techniques that mostly can only deal with the single-ratio or the max-min-ratio case. Multiple-ratio FP problems are important for the optimization of communication networks, because system-level design often involves multiple signal-to-interference-plus-noise ratio terms. This paper considers the applications of FP to solving continuous problems in communication system design, particularly for power control, beamforming, and energy efficiency maximization. These application cases illustrate that the proposed quadratic transform can greatly facilitate the optimization involving ratios by recasting the original nonconvex problem as a sequence of convex problems. This FP-based problem reformulation gives rise to an efficient iterative optimization algorithm with provable convergence to a stationary point. The paper further demonstrates close connections between the proposed FP approach and other well-known algorithms in the literature, such as the fixed-point iteration and the weighted minimum mean-square-error beamforming. The optimization of discrete problems is discussed in Part II of this paper.

Duplex Schemes in Multiple Antenna Two-Hop Relaying

Directory of Open Access Journals (Sweden)

Anja Klein

2008-04-01

Full Text Available A novel scheme for two-hop relaying defined as space division duplex (SDD relaying is proposed. In SDD relaying, multiple antenna beamforming techniques are applied at the intermediate relay station (RS in order to separate downlink and uplink signals of a bi-directional two-hop communication between two nodes, namely, S1 and S2. For conventional amplify-and-forward two-hop relaying, there appears a loss in spectral efficiency due to the fact that the RS cannot receive and transmit simultaneously on the same channel resource. In SDD relaying, this loss in spectral efficiency is circumvented by giving up the strict separation of downlink and uplink signals by either time division duplex or frequency division duplex. Two novel concepts for the derivation of the linear beamforming filters at the RS are proposed; they can be designed either by a three-step or a one-step concept. In SDD relaying, receive signals at S1 are interfered by transmit signals of S1, and receive signals at S2 are interfered by transmit signals of S2. An efficient method in order to combat this kind of interference is proposed in this paper. Furthermore, it is shown how the overall spectral efficiency of SDD relaying can be improved if the channels from S1 and S2 to the RS have different qualities.

Comparisons of receive array interference reduction techniques under erroneous generalized transmit beamforming

KAUST Repository

Radaydeh, Redha Mahmoud

2014-02-01

This paper studies generalized single-stream transmit beamforming employing receive array co-channel interference reduction algorithms under slow and flat fading multiuser wireless systems. The impact of imperfect prediction of channel state information for the desired user spatially uncorrelated transmit channels on the effectiveness of transmit beamforming for different interference reduction techniques is investigated. The case of over-loaded receive array with closely-spaced elements is considered, wherein it can be configured to specified interfering sources. Both dominant interference reduction and adaptive interference reduction techniques for statistically ordered and unordered interferers powers, respectively, are thoroughly studied. The effect of outdated statistical ordering of the interferers powers on the efficiency of dominant interference reduction is studied and then compared against the adaptive interference reduction. For the system models described above, new analytical formulations for the statistics of combined signal-to-interference-plus-noise ratio are presented, from which results for conventional maximum ratio transmission and single-antenna best transmit selection can be directly deduced as limiting cases. These results are then utilized to obtain quantitative measures for various performance metrics. They are also used to compare the achieved performance of various configuration models under consideration. © 1972-2012 IEEE.

Low-Complexity Transmit Antenna Selection and Beamforming for Large-Scale MIMO Communications

Directory of Open Access Journals (Sweden)

Kun Qian

2014-01-01

Full Text Available Transmit antenna selection plays an important role in large-scale multiple-input multiple-output (MIMO communications, but optimal large-scale MIMO antenna selection is a technical challenge. Exhaustive search is often employed in antenna selection, but it cannot be efficiently implemented in large-scale MIMO communication systems due to its prohibitive high computation complexity. This paper proposes a low-complexity interactive multiple-parameter optimization method for joint transmit antenna selection and beamforming in large-scale MIMO communication systems. The objective is to jointly maximize the channel outrage capacity and signal-to-noise (SNR performance and minimize the mean square error in transmit antenna selection and minimum variance distortionless response (MVDR beamforming without exhaustive search. The effectiveness of all the proposed methods is verified by extensive simulation results. It is shown that the required antenna selection processing time of the proposed method does not increase along with the increase of selected antennas, but the computation complexity of conventional exhaustive search method will significantly increase when large-scale antennas are employed in the system. This is particularly useful in antenna selection for large-scale MIMO communication systems.

Interference Robust Transmission for the Downlink of an OFDM-Based Mobile Communications System

Directory of Open Access Journals (Sweden)

Markus Konrad

2008-01-01

Full Text Available Radio networks for future mobile communications systems, for example, 3GPP Long-Term Evolution (LTE, are likely to use an orthogonal frequency division multiplexing- (OFDM- based air interface in the downlink with a frequency reuse factor of one to avoid frequency planning. Therefore, system capacity is limited by interference, which is particularly crucial for mobile terminals with a single receive antenna. Nevertheless, next generation mobile communications systems aim at increasing downlink throughput. In this paper, a single antenna interference cancellation (SAIC algorithm is introduced for amplitude-shift keying (ASK modulation schemes in combination with bit-interleaved coded OFDM. By using such a transmission strategy, high gains in comparison to a conventional OFDM transmission with quadrature amplitude modulation (QAM can be achieved. The superior performance of the novel scheme is confirmed by an analytical bit-error probability (BEP analysis of the SAIC receiver for a single interferer, Rayleigh fading, and uncoded transmission. For the practically more relevant multiple interferer case we present an adaptive least-mean-square (LMS and an adaptive recursive least-squares (RLS SAIC algorithm. We show that in particular the RLS approach enables a good tradeoff between performance and complexity and is robust even to multiple interferers.

Improved Interference-Free Channel Allocation in Coordinated Multiuser Multi-Antenna Open-Access Small Cells

KAUST Repository

Radaydeh, Redha; Zafar, Ammar; Al-Qahtani, Fawaz; Alouini, Mohamed-Slim

2016-01-01

This paper investigates low-complexity joint interference avoidance and desired link improvement for single channel allocation in multiuser multi-antenna access points (APs) for open-access small cells. It is considered that an active user is equipped with an atenna array that can be used to suppress interference sources but not to provide spatial diversity. On the other hand, the operation of APs can be coordinated to meet design requirements, and each of which can unconditionally utilize assigned physical channels. Moreover, each AP is equipped with uncorrelated antennas that can be reused simultaneously to serve many active users. The analysis provides new approaches to exploit physical channels, transmit antennas, and APs to mitigate interference, while providing the best possible link gain to an active user through the most suitable interference-free channel. The event of concurrent service requests placed by active users on a specific interference-free channel is discussed for either interference avoidance through identifying unshared channels or desired link improvement via multiuser scheduling. The applicability of the approaches to balance downlink loads is explained, and practical scenarios due to imperfect identification of interference-free channels and/or scheduled user are thoroughly investigated. The developed results are applicable for any statistical and geometric models of the allocated channel to an active user as well as channel conditions of interference users. They can be used to study various performance measures. Numerical and simulation results are presented to explain some outcomes of this work.

Improved Interference-Free Channel Allocation in Coordinated Multiuser Multi-Antenna Open-Access Small Cells

KAUST Repository

Radaydeh, Redha

2016-02-16

This paper investigates low-complexity joint interference avoidance and desired link improvement for single channel allocation in multiuser multi-antenna access points (APs) for open-access small cells. It is considered that an active user is equipped with an atenna array that can be used to suppress interference sources but not to provide spatial diversity. On the other hand, the operation of APs can be coordinated to meet design requirements, and each of which can unconditionally utilize assigned physical channels. Moreover, each AP is equipped with uncorrelated antennas that can be reused simultaneously to serve many active users. The analysis provides new approaches to exploit physical channels, transmit antennas, and APs to mitigate interference, while providing the best possible link gain to an active user through the most suitable interference-free channel. The event of concurrent service requests placed by active users on a specific interference-free channel is discussed for either interference avoidance through identifying unshared channels or desired link improvement via multiuser scheduling. The applicability of the approaches to balance downlink loads is explained, and practical scenarios due to imperfect identification of interference-free channels and/or scheduled user are thoroughly investigated. The developed results are applicable for any statistical and geometric models of the allocated channel to an active user as well as channel conditions of interference users. They can be used to study various performance measures. Numerical and simulation results are presented to explain some outcomes of this work.

Reduced feedback opportunistic and layered random beamforming for MIMO-OFDMA systems

OpenAIRE

Han, C; Nicolaou, M; Doufexi, A; Armour, SMD

2007-01-01

This paper considers a number of techniques employed in opportunistic and layered random beamforming OFDMA schemes that aim to reduce the feedback required to perform scheduling whilst also minimising the throughput degradations resulting from this reduced throughput (due to the lack of full CSI at the Base Station (BS). Frequency response correlation among subcarriers can be exploited to group adjacent subcarriers into clusters which can then be treated as a single unit for feedback purposes...

Simulation of a ring resonator-based optical beamformer system for phased array receive antennas

NARCIS (Netherlands)

Tijmes, M.R.; Meijerink, Arjan; Roeloffzen, C.G.H.; Bentum, Marinus Jan

2009-01-01

A new simulator tool is described that can be used in the field of RF photonics. It has been developed on the basis of a broadband, continuously tunable optical beamformer system for phased array receive antennas. The application that is considered in this paper is airborne satellite reception of

47 CFR 25.147 - Licensing provision for NGSO MSS feeder downlinks in the band 6700-6875 MHz.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Licensing provision for NGSO MSS feeder downlinks in the band 6700-6875 MHz. 25.147 Section 25.147 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Applications and Licenses Space...

Clinical evaluation of synthetic aperture sequential beamforming

DEFF Research Database (Denmark)

Hansen, Peter Møller; Hemmsen, Martin Christian; Lange, Theis

2012-01-01

In this study clinically relevant ultrasound images generated with synthetic aperture sequential beamforming (SASB) is compared to images generated with a conventional technique. The advantage of SASB is the ability to produce high resolution ultrasound images with a high frame rate and at the same...... time massively reduce the amount of generated data. SASB was implemented in a system consisting of a conventional ultrasound scanner connected to a PC via a research interface. This setup enables simultaneous recording with both SASB and conventional technique. Eighteen volunteers were ultrasound...... scanned abdominally, and 84 sequence pairs were recorded. Each sequence pair consists of two simultaneous recordings of the same anatomical location with SASB and conventional B-mode imaging. The images were evaluated in terms of spatial resolution, contrast, unwanted artifacts, and penetration depth...

ASTC-MIMO-TOPS Mode with Digital Beam-Forming in Elevation for High-Resolution Wide-Swath Imaging

Directory of Open Access Journals (Sweden)

Pingping Huang

2015-03-01

Full Text Available Future spaceborne synthetic aperture radar (SAR missions require complete and frequent coverage of the earth with a high resolution. Terrain Observation by Progressive Scans (TOPS is a novel wide swath mode but has impaired azimuth resolution. In this paper, an innovative extended TOPS mode named Alamouti Space-time Coding multiple-input multiple-output TOPS (ASTC-MIMO-TOPS mode combined with digital beam-forming (DBF in elevation and multi-aperture SAR signal reconstruction in azimuth is proposed. This innovative mode achieves wide-swath coverage with a high geometric resolution and also overcomes major drawbacks in conventional MIMO SAR systems. The data processing scheme of this imaging scheme is presented in detail. The designed system example of the proposed ASTC-MIMO-TOPS mode, which has the imaging capacity of a 400 km wide swath with an azimuth resolution of 3 m, is given. Its system performance analysis results and simulated imaging results on point targets demonstrate the potential of the proposed novel spaceborne SAR mode for high-resolution wide-swath (HRWS imaging.

Clustering and Beamforming for Efficient Communication in Wireless Sensor Networks

Directory of Open Access Journals (Sweden)

Francisco Porcel-Rodríguez

2016-08-01

Full Text Available Energy efficiency is a critical issue for wireless sensor networks (WSNs as sensor nodes have limited power availability. In order to address this issue, this paper tries to maximize the power efficiency in WSNs by means of the evaluation of WSN node networks and their performance when both clustering and antenna beamforming techniques are applied. In this work, four different scenarios are defined, each one considering different numbers of sensors: 50, 20, 10, five, and two nodes per scenario, and each scenario is randomly generated thirty times in order to statistically validate the results. For each experiment, two different target directions for transmission are taken into consideration in the optimization process (φ = 0° and θ = 45°; φ = 45°, and θ = 45°. Each scenario is evaluated for two different types of antennas, an ideal isotropic antenna and a conventional dipole one. In this set of experiments two types of WSN are evaluated: in the first one, all of the sensors have the same amount of power for communications purposes; in the second one, each sensor has a different amount of power for its communications purposes. The analyzed cases in this document are focused on 2D surface and 3D space for the node location. To the authors’ knowledge, this is the first time that beamforming and clustering are simultaneously applied to increase the network lifetime in WSNs.

Closing the uplink/downlink loop on the new Horizons Mission to Pluto

Science.gov (United States)

Peterson, Joseph G.; Birath, Emma; Carcich, Brian; Harch, Ann

Commanding the payload on a spacecraft (“ uplink” sequencing and command generation) and processing the instrument data returned (“ downlink” data processing) are two primary functions of Science Operations on a mission. While vitally important, it is sometimes surprisingly difficult to connect data returned from a spacecraft to the corresponding commanding and sequencing information that created the data, especially when data processing is done via an automated science data pipeline and not via a manual process with humans in the loop. For a variety of reasons it is necessary to make such a connection and close this loop. Perhaps the most important reason is to ensure that all data asked for has arrived safely on the ground. This is especially critical when the mission must erase parts of the spacecraft memory to make room for new data; mistakes here can result in permanent loss of data. Additionally, there are often key pieces of information (such as intended observation target or certain instrument modes that are not included in housekeeping, etc.) that are known only at the time of commanding and never makes it down in the telemetry. Because missions like New Horizons strive to be frugal with how much telemetry is sent back to Earth, and the telemetry may not include unambiguous identifiers (like observation ids, etc.), connecting downlinked data with uplink command information in an automated way can require creative approaches and heuristics. In this paper, we describe how these challenges were overcome on the New Horizons Mission to Pluto. The system developed involves ingesting uplink information into a database and automatically correlating it with downlinked data products. This allows for more useful data searches and the ability to attach the original intent of each observation to the processed science data. Also a new data tracking tool is now being developed to help in planning data playback from the spacecraft and to ensu- e data is verified

Leakage based precoding for multi-user MIMO-OFDM systems

KAUST Repository

Sadek, Mirette

2011-08-01

In downlink multi-user multiple-input multiple-output (MIMO) transmissions, several precoding schemes have been proposed to decrease interference among users. Notable among these precoding schemes is one that uses the signal-to-leakage-plus-noise ratio (SLNR) as an optimization criterion. In this paper, leveraging the efficiency of the SLNR optimization, we generalize this precoding scheme to MIMO orthogonal frequency division multiplexing (OFDM) multi-user systems where the OFDM is used to overcome the inter-symbol- interference (ISI) introduced by multipath channels. We also introduce a channel compensation technique that reconstructs the channel at the transmitter for every time instant given a significantly lower channel feedback rate by the receiver. © 2006 IEEE.

Diversity-Multiplexing Trade-off for Coordinated Relayed Uplink and Direct Downlink Transmissions

DEFF Research Database (Denmark)

Thai, Chan; Popovski, Petar; Sun, Fan

2013-01-01

Abstract—There are two basic principles used in wireless network coding to design throughput-efficient schemes: (1) aggregation of communication flows and (2) interference is embraced and subsequently cancelled or mitigated. These principles inspire design of Coordinated Direct/Relay (CDR) schemes......, where each basic transmission involves two flows to a direct and a relayed user. Considering a scenario with relayed uplink and direct downlink, we analyze the Diversity-Multiplexing Tradeoff (DMT) calculating either the exact value or both upper/lower bounds. The CDR scheme is shown to have a higher...

Robust Transceivers Design for Multi-stream Multi-user MIMO Visible Light Communication

KAUST Repository

Sifaou, Houssem

2017-11-27

Visible light communication (VLC) is an emerging technique that uses light-emitting diodes to combine communication and illumination. It is considered as a promising scheme for indoor wireless communication that can be deployed at reduced costs, while offering high data rate performance. This paper focuses on the design of precoding and receiving schemes for downlink multi-user multiple-input multiple-output VLC systems using angle diversity receivers. Two major concerns need to be considered while solving such a problem. The first one is related to the inter-user interference, basically inherent to our consideration of a multi-user system, while the second results from the users’ mobility, causing imperfect channel estimates. To address both concerns, we propose robust precoding and receiver that solve the max-min SINR problem. The performance of the proposed VLC design is studied under different working conditions, where a significant gain of the proposed robust transceivers over their non-robust counterparts has been observed.

Robust Transceivers Design for Multi-stream Multi-user MIMO Visible Light Communication

KAUST Repository

Sifaou, Houssem; Kammoun, Abla; Park, Kihong; Alouini, Mohamed-Slim

2017-01-01

Visible light communication (VLC) is an emerging technique that uses light-emitting diodes to combine communication and illumination. It is considered as a promising scheme for indoor wireless communication that can be deployed at reduced costs, while offering high data rate performance. This paper focuses on the design of precoding and receiving schemes for downlink multi-user multiple-input multiple-output VLC systems using angle diversity receivers. Two major concerns need to be considered while solving such a problem. The first one is related to the inter-user interference, basically inherent to our consideration of a multi-user system, while the second results from the users’ mobility, causing imperfect channel estimates. To address both concerns, we propose robust precoding and receiver that solve the max-min SINR problem. The performance of the proposed VLC design is studied under different working conditions, where a significant gain of the proposed robust transceivers over their non-robust counterparts has been observed.

Graphene-based fine-tunable optical delay line for optical beamforming in phased-array antennas.

Science.gov (United States)

Tatoli, Teresa; Conteduca, Donato; Dell'Olio, Francesco; Ciminelli, Caterina; Armenise, Mario N

2016-06-01

The design of an integrated graphene-based fine-tunable optical delay line on silicon nitride for optical beamforming in phased-array antennas is reported. A high value of the optical delay time (τg=920  ps) together with a compact footprint (4.15  mm2) and optical loss graphene-based Mach-Zehnder interferometer switches and two vertically stacked microring resonators between which a graphene capacitor is placed. The tuning range is obtained by varying the value of the voltage applied to the graphene electrodes, which controls the optical path of the light propagation and therefore the delay time. The graphene provides a faster reconfigurable time and low values of energy dissipation. Such significant advantages, together with a negligible beam-squint effect, allow us to overcome the limitations of conventional RF beamformers. A highly efficient fine-tunable optical delay line for the beamsteering of 20 radiating elements up to ±20° in the azimuth direction of a tile in a phased-array antenna of an X-band synthetic aperture radar has been designed.

Speech understanding in background noise with the two-microphone adaptive beamformer BEAM in the Nucleus Freedom Cochlear Implant System.

Science.gov (United States)

Spriet, Ann; Van Deun, Lieselot; Eftaxiadis, Kyriaky; Laneau, Johan; Moonen, Marc; van Dijk, Bas; van Wieringen, Astrid; Wouters, Jan

2007-02-01

This paper evaluates the benefit of the two-microphone adaptive beamformer BEAM in the Nucleus Freedom cochlear implant (CI) system for speech understanding in background noise by CI users. A double-blind evaluation of the two-microphone adaptive beamformer BEAM and a hardware directional microphone was carried out with five adult Nucleus CI users. The test procedure consisted of a pre- and post-test in the lab and a 2-wk trial period at home. In the pre- and post-test, the speech reception threshold (SRT) with sentences and the percentage correct phoneme scores for CVC words were measured in quiet and background noise at different signal-to-noise ratios. Performance was assessed for two different noise configurations (with a single noise source and with three noise sources) and two different noise materials (stationary speech-weighted noise and multitalker babble). During the 2-wk trial period at home, the CI users evaluated the noise reduction performance in different listening conditions by means of the SSQ questionnaire. In addition to the perceptual evaluation, the noise reduction performance of the beamformer was measured physically as a function of the direction of the noise source. Significant improvements of both the SRT in noise (average improvement of 5-16 dB) and the percentage correct phoneme scores (average improvement of 10-41%) were observed with BEAM compared to the standard hardware directional microphone. In addition, the SSQ questionnaire and subjective evaluation in controlled and real-life scenarios suggested a possible preference for the beamformer in noisy environments. The evaluation demonstrates that the adaptive noise reduction algorithm BEAM in the Nucleus Freedom CI-system may significantly increase the speech perception by cochlear implantees in noisy listening conditions. This is the first monolateral (adaptive) noise reduction strategy actually implemented in a mainstream commercial CI.

Motion compensated beamforming in synthetic aperture vector flow imaging

DEFF Research Database (Denmark)

Oddershede, Niels; Jensen, Jørgen Arendt

2006-01-01

. In this paper, these motion effects are considered. A number of Field II simulations of a single scatterer moving at different velocities are performed both for axial and lateral velocities from 0 to 1 m/s. Data are simulated at a pulse repetition frequency of 5 kHz. The signal-to-noise ratio (SNR....... Here the SNR is -10 dB compared to the stationary scatterer. A 2D motion compensation method for synthetic aperture vector flow imaging is proposed, where the former vector velocity estimate is used for compensating the beamforming of new data. This method is tested on data from an experimental flow...

MIMO Beamforming for Secure and Energy-Efficient Wireless Communication

Science.gov (United States)

Nghia, Nguyen T.; Tuan, Hoang D.; Duong, Trung Q.; Poor, H. Vincent

2017-02-01

Considering a multiple-user multiple-input multiple-output (MIMO) channel with an eavesdropper, this letter develops a beamformer design to optimize the energy efficiency in terms of secrecy bits per Joule under secrecy quality-of-service constraints. This is a very difficult design problem with no available exact solution techniques. A path-following procedure, which iteratively improves its feasible points by using a simple quadratic program of moderate dimension, is proposed. Under any fixed computational tolerance the procedure terminates after finitely many iterations, yielding at least a locally optimal solution. Simulation results show the superior performance of the obtained algorithm over other existing methods.

Propagation testing multi-cell batteries.

Energy Technology Data Exchange (ETDEWEB)

Orendorff, Christopher J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lamb, Joshua [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Steele, Leigh Anna Marie [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Spangler, Scott Wilmer [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2014-10-01

Propagation of single point or single cell failures in multi-cell batteries is a significant concern as batteries increase in scale for a variety of civilian and military applications. This report describes the procedure for testing failure propagation along with some representative test results to highlight the potential outcomes for different battery types and designs.

Optimized scheduling technique of null subcarriers for peak power control in 3GPP LTE downlink.

Science.gov (United States)

Cho, Soobum; Park, Sang Kyu

2014-01-01

Orthogonal frequency division multiple access (OFDMA) is a key multiple access technique for the long term evolution (LTE) downlink. However, high peak-to-average power ratio (PAPR) can cause the degradation of power efficiency. The well-known PAPR reduction technique, dummy sequence insertion (DSI), can be a realistic solution because of its structural simplicity. However, the large usage of subcarriers for the dummy sequences may decrease the transmitted data rate in the DSI scheme. In this paper, a novel DSI scheme is applied to the LTE system. Firstly, we obtain the null subcarriers in single-input single-output (SISO) and multiple-input multiple-output (MIMO) systems, respectively; then, optimized dummy sequences are inserted into the obtained null subcarrier. Simulation results show that Walsh-Hadamard transform (WHT) sequence is the best for the dummy sequence and the ratio of 16 to 20 for the WHT and randomly generated sequences has the maximum PAPR reduction performance. The number of near optimal iteration is derived to prevent exhausted iterations. It is also shown that there is no bit error rate (BER) degradation with the proposed technique in LTE downlink system.

Energy efficient downlink MIMO transmission with linear precoding

Institute of Scientific and Technical Information of China (English)

XU Jie; LI ShiChao; QIU Ling; SLIMANE Ben S.; YU ChengWen

2013-01-01

Energy efficiency （EE） is becoming increasingly important for wireless cellular networks. This paper addresses EE optimization problems in downlink multiuser MIMO systems with linear precoding. Referring to different active transmit/receive antenna sets and transmission schemes as different modes, we propose a joint bandwidth/power optimization and mode switching scheme to maximize EE. With a specific mode, we prove that the optimal bandwidth and transmit power is either full transmit power or full bandwidth. After deriving the optimal bandwidth and transmit power, we further propose mode switching to select the mode with optimal EE. Since the optimal mode switching, i.e. exhaustive search, is too complex to implement, an alternative heuristic method is developed to decrease the complexity through reducing the search size and avoiding the EE calculation during each search. Through simulations, we demonstrate that the proposed methods can significantly improve EE and the performance is similar to the optimal exhaustive search.

Limit values for Downlink Mobile Telephony in Denmark

DEFF Research Database (Denmark)

Pedersen, Gert Frølund

2012-01-01

The purpose of this report is to set limits on the minimum average field-strength need in the downlink (from the mobile base-station to the mobile phone) for the mobile systems GSM900 and GSM1800 as well as the CDMA based UMTS900 and UMTS2100 systems in Denmark. The main assumptions made...... is obtained largely by the measured bodyloss for the most popular phones in the network, here taken as the most sold phones in 2011 [Mob12]. 6. The limits given can be used both for outdoor, in a car and indoor but values given by the mobile operators are often given for outdoor radio coverage only...... called the bodyloss. The basic sensitivity requirements of e.g. the GSM system for the mobile terminals are -102 dBm but here the measured values will be used for the phones in talk mode. The measured values will be obtained with the phone placed next to the head and a hand holding the phone....

System Level Analysis of LTE-Advanced

DEFF Research Database (Denmark)

Wang, Yuanye

This PhD thesis focuses on system level analysis of Multi-Component Carrier (CC) management for Long Term Evolution (LTE)-Advanced. Cases where multiple CCs are aggregated to form a larger bandwidth are studied. The analysis is performed for both local area and wide area networks. In local area...... reduction. Compared to the case of reuse-1, they achieve a gain of 50∼500% in cell edge user throughput, with small or no loss in average cell throughput. For the wide area network, effort is devoted to the downlink of LTE-Advanced. Such a system is assumed to be backwards compatible to LTE release 8, i...... scheme is recommended. It reduces the CQI by 94% at low load, and 79∼93% at medium to high load, with reasonable loss in downlink performance. To reduce the ACK/NACK feedback, multiple ACK/NACKs can be bundled, with slightly degraded downlink throughput....

Downlink resource allocation for multichannel TDMA visible light communications

KAUST Repository

Abdelhady, Amr Mohamed Abdelaziz; Amin, Osama; Chaaban, Anas; Alouini, Mohamed-Slim

2017-01-01

Optical wireless communications (OWC) in general and resource allocation in OWC networks particularly have gained lots of attention recently. In this work, we consider the resource allocation problem of a visible light communication downlink transmission system based on time division multiple access with the objective of maximizing spectral efficiency (SE). As for the operational conditions, we impose constraints on the average optical intensity, the energy consumption and the quality-of-service. To solve the non-convex problem, we transform the objective function into a difference of concave functions by solving a second order differential inequality. Then, we propose a low-complexity algorithm to solve the resource allocation problem. Finally, we show by simulations the SE performance gains achieved by optimizing the power allocation over equal power allocation in the considered system. Numerical results show the SE gains achieved by using this solution.

Downlink resource allocation for multichannel TDMA visible light communications

KAUST Repository

Abdelhady, Amr Mohamed Abdelaziz

2017-05-12

Optical wireless communications (OWC) in general and resource allocation in OWC networks particularly have gained lots of attention recently. In this work, we consider the resource allocation problem of a visible light communication downlink transmission system based on time division multiple access with the objective of maximizing spectral efficiency (SE). As for the operational conditions, we impose constraints on the average optical intensity, the energy consumption and the quality-of-service. To solve the non-convex problem, we transform the objective function into a difference of concave functions by solving a second order differential inequality. Then, we propose a low-complexity algorithm to solve the resource allocation problem. Finally, we show by simulations the SE performance gains achieved by optimizing the power allocation over equal power allocation in the considered system. Numerical results show the SE gains achieved by using this solution.

Pulse Splitting for Harmonic Beamforming in Time-Modulated Linear Arrays

Directory of Open Access Journals (Sweden)

Lorenzo Poli

2014-01-01

Full Text Available A novel strategy for harmonic beamforming in time-modulated linear arrays is proposed. The pulse splitting technique is exploited to simultaneously generate two harmonic patterns, one at the central frequency and another at a preselected harmonic of arbitrary order, while controlling the maximum level of the remaining sideband radiations. An optimization strategy based on the particle swarm optimizer is developed in order to determine the optimal parameters describing the pulse sequence used to modulate the excitation weights of the array elements. Representative numerical results are reported and discussed to point out potentialities and limitations of the proposed approach.

Multi-chamber and multi-layer thiol-ene microchip for cell culture

DEFF Research Database (Denmark)

Tan, H. Y.; Hemmingsen, Mette; Lafleur, Josiane P.

2014-01-01

We present a multi-layer and multi-chamber microfluidic chip fabricated using two different thiol-ene mixtures. Sandwiched between the thiol-ene chip layers is a commercially available membrane whose morphology has been altered with coatings of thiol-ene mixtures. Experiments have been conducted ...... with the microchip and shown that the fabricated microchip is suitable for long term cell culture....

Multi-fuel reformers for fuel cells used in transportation. Phase 1: Multi-fuel reformers

Science.gov (United States)

1994-05-01

DOE has established the goal, through the Fuel Cells in Transportation Program, of fostering the rapid development and commercialization of fuel cells as economic competitors for the internal combustion engine. Central to this goal is a safe feasible means of supplying hydrogen of the required purity to the vehicular fuel cell system. Two basic strategies are being considered: (1) on-board fuel processing whereby alternative fuels such as methanol, ethanol or natural gas stored on the vehicle undergo reformation and subsequent processing to produce hydrogen, and (2) on-board storage of pure hydrogen provided by stationary fuel processing plants. This report analyzes fuel processor technologies, types of fuel and fuel cell options for on-board reformation. As the Phase 1 of a multi-phased program to develop a prototype multi-fuel reformer system for a fuel cell powered vehicle, the objective of this program was to evaluate the feasibility of a multi-fuel reformer concept and to select a reforming technology for further development in the Phase 2 program, with the ultimate goal of integration with a DOE-designated fuel cell and vehicle configuration. The basic reformer processes examined in this study included catalytic steam reforming (SR), non-catalytic partial oxidation (POX) and catalytic partial oxidation (also known as Autothermal Reforming, or ATR). Fuels under consideration in this study included methanol, ethanol, and natural gas. A systematic evaluation of reforming technologies, fuels, and transportation fuel cell applications was conducted for the purpose of selecting a suitable multi-fuel processor for further development and demonstration in a transportation application.

Code-modulated visual evoked potentials using fast stimulus presentation and spatiotemporal beamformer decoding.

Science.gov (United States)

Wittevrongel, Benjamin; Van Wolputte, Elia; Van Hulle, Marc M

2017-11-08

When encoding visual targets using various lagged versions of a pseudorandom binary sequence of luminance changes, the EEG signal recorded over the viewer's occipital pole exhibits so-called code-modulated visual evoked potentials (cVEPs), the phase lags of which can be tied to these targets. The cVEP paradigm has enjoyed interest in the brain-computer interfacing (BCI) community for the reported high information transfer rates (ITR, in bits/min). In this study, we introduce a novel decoding algorithm based on spatiotemporal beamforming, and show that this algorithm is able to accurately identify the gazed target. Especially for a small number of repetitions of the coding sequence, our beamforming approach significantly outperforms an optimised support vector machine (SVM)-based classifier, which is considered state-of-the-art in cVEP-based BCI. In addition to the traditional 60 Hz stimulus presentation rate for the coding sequence, we also explore the 120 Hz rate, and show that the latter enables faster communication, with a maximal median ITR of 172.87 bits/min. Finally, we also report on a transition effect in the EEG signal following the onset of the stimulus sequence, and recommend to exclude the first 150 ms of the trials from decoding when relying on a single presentation of the stimulus sequence.

Antireflection coating design for series interconnected multi-junction solar cells

International Nuclear Information System (INIS)

Aiken, Daniel J.

1999-01-01

AR coating design for multi-junction solar cells can be more challenging than in the single junction case. Reasons for this are discussed. Analytical expressions used to optimize AR coatings for single junction solar cells are extended for use in monolithic, series interconnected multi-junction solar cell AR coating design. The result is an analytical expression which relates the solar cell performance (through J(sub SC)) directly to the AR coating design through the device reflectance. It is also illustrated how AR coating design can be used to provide an additional degree of freedom for current matching multi-junction devices

Matched-filtering generalized phase contrast using LCoS pico-projectors for beam-forming

OpenAIRE

Bañas, Andrew Rafael; Palima, Darwin; Glückstad, Jesper

2012-01-01

We report on a new beam-forming system for generating high intensity programmable optical spikes using so-called matched-filtering Generalized Phase Contrast (mGPC) applying two consumer handheld pico-projectors. Such a system presents a low-cost alternative for optical trapping and manipulation, optical lattices and other beam-shaping applications usually implemented with high-end spatial light modulators. Portable pico-projectors based on liquid crystal on silicon (LCoS) devices are used as...

Adaptive multi-channel downlink assignment for overloaded spectrum-shared multi-antenna overlaid cellular networks

KAUST Repository

Radaydeh, Redha  Mahmoud; Alouini, Mohamed-Slim; Qaraqe, Khalid

2012-01-01

setup is expected to reduce the operational power and to function satisfactorily with the existing cellular architecture. Among the possible deployments of small-cell access points is to manage many of them to serve specific spatial locations, while

Signal processing approaches to secure physical layer communications in multi-antenna wireless systems

CERN Document Server

Hong, Y-W Peter; Kuo, C-C Jay

2013-01-01

This book introduces various signal processing approaches to enhance physical layer secrecy in multi-antenna wireless systems. Wireless physical layer secrecy has attracted much attention in recent years due to the broadcast nature of the wireless medium and its inherent vulnerability to eavesdropping. While most articles on physical layer secrecy focus on the information-theoretic aspect, we focus specifically on the signal processing aspects, including beamforming and precoding techniques for data transmission and discriminatory training schemes for channel estimation. The discussions will c

Novel ring resonator-based integrated photonic beamformer for broadband phased array receive antennas - part 2: experimental prototype

NARCIS (Netherlands)

Zhuang, L.; Roeloffzen, C.G.H.; Meijerink, Arjan; Burla, M.; Marpaung, D.A.I.; Leinse, Arne; Hoekman, M.; Heideman, Rene; van Etten, Wim

2010-01-01

An experimental prototype is presented that illustrates the implementation aspects and feasibility of the novel ring resonator-based optical beamformer concept that has been developed and analyzed in Part I of this paper . This concept can be used for seamless control of the reception angle in

Speech Intelligibility Advantages using an Acoustic Beamformer Display

Science.gov (United States)

Begault, Durand R.; Sunder, Kaushik; Godfroy, Martine; Otto, Peter

2015-01-01

A speech intelligibility test conforming to the Modified Rhyme Test of ANSI S3.2 "Method for Measuring the Intelligibility of Speech Over Communication Systems" was conducted using a prototype 12-channel acoustic beamformer system. The target speech material (signal) was identified against speech babble (noise), with calculated signal-noise ratios of 0, 5 and 10 dB. The signal was delivered at a fixed beam orientation of 135 deg (re 90 deg as the frontal direction of the array) and the noise at 135 deg (co-located) and 0 deg (separated). A significant improvement in intelligibility from 57% to 73% was found for spatial separation for the same signal-noise ratio (0 dB). Significant effects for improved intelligibility due to spatial separation were also found for higher signal-noise ratios (5 and 10 dB).

Analysis and compensation for the joint effects of HPA nonlinearity, I/Q imbalance and crosstalk in MIMO beamforming systems

KAUST Repository

Qi, Jian; Aissa, Sonia

2011-01-01

In this paper, we investigate the joint effects of high-power amplifier (HPA) nonlinearity, in-phase/quadrature-phase (I/Q) imbalance and crosstalk, on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems

Description and Performance of an L-Band Radiometer with Digital Beamforming

Directory of Open Access Journals (Sweden)

Juan F. Marchan-Hernandez

2010-12-01

Full Text Available This paper presents the description and performance tests of an L-band microwave radiometer with Digital Beamforming (DBF, developed for the Passive Advanced Unit (PAU for ocean monitoring project. PAU is an instrument that combines, in a single receiver and without time multiplexing, a microwave radiometer at L-band (PAU-RAD and a GPS-reflectometer (PAU-GNSS-R. This paper focuses on the PAU‑RAD beamformer’s first results, analyzing the hardware and software required for the developed prototype. Finally, it discusses the first results measured in the Universitat Politècnica de Catalunya (UPC anechoic chamber.

Error performance analysis in downlink cellular networks with interference management

KAUST Repository

Afify, Laila H.

2015-05-01

Modeling aggregate network interference in cellular networks has recently gained immense attention both in academia and industry. While stochastic geometry based models have succeeded to account for the cellular network geometry, they mostly abstract many important wireless communication system aspects (e.g., modulation techniques, signal recovery techniques). Recently, a novel stochastic geometry model, based on the Equivalent-in-Distribution (EiD) approach, succeeded to capture the aforementioned communication system aspects and extend the analysis to averaged error performance, however, on the expense of increasing the modeling complexity. Inspired by the EiD approach, the analysis developed in [1] takes into consideration the key system parameters, while providing a simple tractable analysis. In this paper, we extend this framework to study the effect of different interference management techniques in downlink cellular network. The accuracy of the proposed analysis is verified via Monte Carlo simulations.

Feedback Compression Schemes for Downlink Carrier Aggregation in LTE-Advanced

DEFF Research Database (Denmark)

Nguyen, Hung Tuan; Kovac, Istvan; Wang, Yuanye

2011-01-01

With full channel state information (CSI) available, it has been shown that carrier aggregation (CA) in the downlink can significantly improve the data rate experienced at the user equipments (UE) [1], [2], [3], [4]. However, full CSI feedback in all component carriers (CCs) requires a large...... portion of the uplink bandwidth and the feedback information increases linearly with the number of CCs. Therefore, the performance gain brought by deploying CA could be easily hindered if the amount of CSI feedback is not thoroughly controlled. In this paper we analyze several feedback overhead...... compression schemes in CA systems. To avoid a major re-design of the feedback schemes, only CSI compression schemes closely related to the ones specified in LTE-Release 8 and LTE-Release 9 are considered. Extensive simulations at system level were carried out to evaluate the performance of these feedback...

COOPERATIVE ROUTING FOR DYNAMIC AERIAL LAYER NETWORKS

Science.gov (United States)

2018-03-01

considered in underlay systems and miss detection constraints are considered in overlay systems. Neither of these constraints can directly measure ...GLOBECOM’ 16).  S. Mosleh, J. Ashdown, J. Matyjas, M. Medley, J. Zhang, and L. Liu, "Interference Alignment for Downlink Multi-Cell LTE -Advanced Systems

Practical Considerations in the Implementation of Collaborative Beamforming on Wireless Sensor Networks.

Science.gov (United States)

Felici-Castell, Santiago; Navarro, Enrique A; Pérez-Solano, Juan J; Segura-García, Jaume; García-Pineda, Miguel

2017-01-26

Wireless Sensor Networks (WSNs) are composed of spatially distributed autonomous sensor devices, named motes. These motes have their own power supply, processing unit, sensors and wireless communications However with many constraints, such as limited energy, bandwidth and computational capabilities. In these networks, at least one mote called a sink, acts as a gateway to connect with other networks. These sensor networks run monitoring applications and then the data gathered by these motes needs to be retrieved by the sink. When this sink is located in the far field, there have been many proposals in the literature based on Collaborative Beamforming (CB), also known as Distributed or Cooperative Beamforming, for these long range communications to reach the sink. In this paper, we conduct a thorough study of the related work and analyze the requirements to do CB. In order to implement these communications in real scenarios, we will consider if these requirements and the assumptions made are feasible from the point of view of commercial motes and their constraints. In addition, we will go a step further and will consider different alternatives, by relaxing these requirements, trying to find feasible assumptions to carry out these types of communications with commercial motes. This research considers the nonavailability of a central clock that synchronizes all motes in the WSN, and all motes have identical hardware. This is a feasibility study to do CB on WSN, using a simulated scenario with randomized delays obtained from experimental data from commercial motes.

Joint interference management and resource allocation for device-to-device (D2D) communications underlying downlink/uplink decoupled (DUDe) heterogeneous networks

KAUST Repository

Celik, Abdulkadir; Radaydeh, Redha Mahmoud Mesleh; Al-Qahtani, Fawaz S.; Alouini, Mohamed-Slim

2017-01-01

known as downlink (DL)/UL decoupling (DUDe). Subject to quality of service (QoS) requirements and power constraints, we formulate a joint SB assignment and resource block (RB) allocation optimization as a mixed integer non-linear programming (MINLP

FPGA-Based Sonar Processing

National Research Council Canada - National Science Library

Graham, Paul; Nelson, Brent

1998-01-01

This paper presents the application of time-delay sonar beamforming and discusses a multi-board FPGA system for performing several variations of this beamforming method in real-time for realistic sonar arrays...

Fractional Programming for Communication Systems—Part II: Uplink Scheduling via Matching

Science.gov (United States)

Shen, Kaiming; Yu, Wei

2018-05-01

This two-part paper develops novel methodologies for using fractional programming (FP) techniques to design and optimize communication systems. Part I of this paper proposes a new quadratic transform for FP and treats its application for continuous optimization problems. In this Part II of the paper, we study discrete problems, such as those involving user scheduling, which are considerably more difficult to solve. Unlike the continuous problems, discrete or mixed discrete-continuous problems normally cannot be recast as convex problems. In contrast to the common heuristic of relaxing the discrete variables, this work reformulates the original problem in an FP form amenable to distributed combinatorial optimization. The paper illustrates this methodology by tackling the important and challenging problem of uplink coordinated multi-cell user scheduling in wireless cellular systems. Uplink scheduling is more challenging than downlink scheduling, because uplink user scheduling decisions significantly affect the interference pattern in nearby cells. Further, the discrete scheduling variable needs to be optimized jointly with continuous variables such as transmit power levels and beamformers. The main idea of the proposed FP approach is to decouple the interaction among the interfering links, thereby permitting a distributed and joint optimization of the discrete and continuous variables with provable convergence. The paper shows that the well-known weighted minimum mean-square-error (WMMSE) algorithm can also be derived from a particular use of FP; but our proposed FP-based method significantly outperforms WMMSE when discrete user scheduling variables are involved, both in term of run-time efficiency and optimizing results.

Downlink Error Rates of Half-duplex Users in Full-duplex Networks over a Laplacian Inter-User Interference Limited and EGK fading

KAUST Repository

Soury, Hamza; Elsawy, Hesham; Alouini, Mohamed-Slim

2017-01-01

This paper develops a mathematical framework to study downlink error rates and throughput for half-duplex (HD) terminals served by a full-duplex (FD) base station (BS). The developed model is used to motivate long term pairing for users that have

Organic tandem and multi-junction solar cells

NARCIS (Netherlands)

Hadipour, Afshin; de Boer, Bert; Blom, Paul W. M.

2008-01-01

The emerging field of stacked layers (double- and even multi-layers) in organic photovoltaic cells is reviewed. Owing to the limited absorption width of organic molecules and polymers, only a small fraction of the solar flux can be harvested by a single-layer bulk hetero-junction photovoltaic cell.

Time-domain beamforming and blind source separation speech input in the car environment

CERN Document Server

Bourgeois, Julien

2009-01-01

The development of computer and telecommunication technologies led to a revolutioninthewaythatpeopleworkandcommunicatewitheachother.One of the results is that large amount of information will increasingly be held in a form that is natural for users, as speech in natural language. In the presented work, we investigate the speech signal capture problem, which includes the separation of multiple interfering speakers using microphone arrays. Adaptive beamforming is a classical approach which has been developed since the seventies. However it requires a double-talk detector (DTD) that interrupts th

Practical Considerations in the Implementation of Collaborative Beamforming on Wireless Sensor Networks

Directory of Open Access Journals (Sweden)

Santiago Felici-Castell

2017-01-01

Full Text Available Wireless Sensor Networks (WSNs are composed of spatially distributed autonomous sensor devices, named motes. These motes have their own power supply, processing unit, sensors and wireless communications However with many constraints, such as limited energy, bandwidth and computational capabilities. In these networks, at least one mote called a sink, acts as a gateway to connect with other networks. These sensor networks run monitoring applications and then the data gathered by these motes needs to be retrieved by the sink. When this sink is located in the far field, there have been many proposals in the literature based on Collaborative Beamforming (CB, also known as Distributed or Cooperative Beamforming, for these long range communications to reach the sink. In this paper, we conduct a thorough study of the related work and analyze the requirements to do CB. In order to implement these communications in real scenarios, we will consider if these requirements and the assumptions made are feasible from the point of view of commercial motes and their constraints. In addition, we will go a step further and will consider different alternatives, by relaxing these requirements, trying to find feasible assumptions to carry out these types of communications with commercial motes. This research considers the nonavailability of a central clock that synchronizes all motes in the WSN, and all motes have identical hardware. This is a feasibility study to do CB on WSN, using a simulated scenario with randomized delays obtained from experimental data from commercial motes.

Dynamic Resource Management in MC-CDMA Based Cellular Wireless Networks

Directory of Open Access Journals (Sweden)

Bala Jeevitha Vani

2009-10-01

Full Text Available Most of the multimedia and Internet services today are asymmetric in nature, and require high data rate support. Allocating equal band width in both uplink and downlink is not prudent solution, as most of the time user requirement is more either in uplink or downlink. The Multi Carrier Code Division Multiple Access (MC-CDMA system with time division duplex mode can easily met this requirement by dynamically declaring traffic direction in TDD slot, and adaptively allocating the sub channels. In this paper, we propose a adaptive slot and sub carrier allocation algorithm, that can be independently implemented in each cell of mobile communication network. Our analytical model is generalization of two cell concept to represent a multi cell model. Based on two cell concept four cases of interference pattern has been considered and simulated separately in presence of Additive White Gaussian Noise (AWGN and Rayleigh Channel. The simulated result suggests the requirement of approximately 9dB of Signal to Noise Ratio (SNR to maintain Bit Error Rate below 10-3. We also analyze the average delay incurred by the proposed algorithm in allocating resources.

Innovative architecture design for high performance organic and hybrid multi-junction solar cells

Science.gov (United States)

Li, Ning; Spyropoulos, George D.; Brabec, Christoph J.

2017-08-01

The multi-junction concept is especially attractive for the photovoltaic (PV) research community owing to its potential to overcome the Schockley-Queisser limit of single-junction solar cells. Tremendous research interests are now focused on the development of high-performance absorbers and novel device architectures for emerging PV technologies, such as organic and perovskite PVs. It has been predicted that the multi-junction concept is able to boost the organic and perovskite PV technologies approaching the 20% and 30% benchmarks, respectively, showing a bright future of commercialization of the emerging PV technologies. In this contribution, we will demonstrate innovative architecture design for solution-processed, highly functional organic and hybrid multi-junction solar cells. A simple but elegant approach to fabricating organic and hybrid multi-junction solar cells will be introduced. By laminating single organic/hybrid solar cells together through an intermediate layer, the manufacturing cost and complexity of large-scale multi-junction solar cells can be significantly reduced. This smart approach to balancing the photocurrents as well as open circuit voltages in multi-junction solar cells will be demonstrated and discussed in detail.

Estimating cell capacity for multi-cell electrical energy system

Science.gov (United States)

Hashemi, Iman Ahari

A Multi-Cell Electrical Energy System is a set of batteries that are connected in series. The series batteries provide the required voltage necessary for the contraption. After using the energy that is provided by the batteries, some cells within the system tend to have a lower voltage than the other cells. Also, other factors, such as the number of times a battery has been charged or discharged, how long it has been within the system and many other factors, result in some cells having a lesser capacity compared to the other cells within the system. The outcome is that it lowers the required capacity that the electrical energy system is required to provide. By having an unknown cell capacity within the system, it is unknown how much of a charge can be provided to the system so that the cells are not overcharged or undercharged. Therefore, it is necessary to know the cells capacity within the system. Hence, if we were dealing with a single cell, the capacity could be obtained by a full charge and discharge of the cell. In a series system that contains multiple cells a full charging or discharging cannot happen as it might result in deteriorating the structure of some cells within the system. Hence, to find the capacity of a single cell within an electrical energy system it is required to obtain a method that can estimate the value of each cell within the electrical energy system. To approach this method an electrical energy system is required. The electrical energy system consists of rechargeable non-equal capacity batteries to provide the required energy to the system, a battery management system (BMS) board to monitor the cells voltages, an Arduino board that provides the required communication to BMS board, and the PC, and a software that is able to deliver the required data obtained from the Arduino board to the PC. The outcome, estimating the capacity of a cell within a multi-cell system, can be used in many battery related technologies to obtain unknown

Downlink resource management for QoS scheduling in IEEE 802.16 WiMAX networks

DEFF Research Database (Denmark)

Wang, Hua; Dittmann, Lars

2010-01-01

IEEE 802.16, also known as WiMAX, has received much attention recently for its capability to support multiple types of applications with diverse Quality-of-Service (QoS) requirements. Beyond what the standard has defined, radio resource management (RRM) still remains an open issue, which plays...... an important role in QoS provisioning for different types of services. In this paper, we propose a downlink resource management framework for QoS scheduling in OFDMA based WiMAX systems. Our framework consists of a dynamic resource allocation (DRA) module and a connection admission control (CAC) module. A two...

Beamforming with a circular array of microphones mounted on a rigid sphere (L)

DEFF Research Database (Denmark)

Tiana Roig, Elisabet; Jacobsen, Finn; Fernandez Grande, Efren

2011-01-01

Beamforming with uniform circular microphone arrays can be used for localizing sound sources over 360. Typically, the array microphones are suspended in free space or they are mounted on a solid cylinder. However, the cylinder is often considered to be infinitely long because the scattering problem...... has no exact solution for a finite cylinder. Alternatively one can use a solid sphere. This investigation compares the performance of a circular array mounded on a rigid sphere with that of such an array in free space and mounted on an infinite cylinder, using computer simulations. The examined...

Performance Analysis of Downlink Inter-band Carrier Aggregation in LTE-Advanced

DEFF Research Database (Denmark)

Wang, Hua; Rosa, Claudio; Pedersen, Klaus

2011-01-01

CC can be different. In this paper, we investigate the downlink resource allocation for inter-band CA, i.e., how to assign carrier(s) to different UEs. A simple yet effective G-factor based carrier selection algorithm, which takes both traffic load and radio channel characteristics......Carrier aggregation (CA) is one of the most distinct features for LTE-Advanced systems, which can support a much wider transmission bandwidth up to 100 MHz by aggregating two or more individual component carriers (CCs) belonging to the same (intra-band) or different (inter-band) frequency bands....... With CA, it is possible to schedule a user equipment (UE) on multiple CCs simultaneously. From radio resource management (RRM) perspective, CC selection plays an important role in optimizing the system performance, especially in the case of inter-band CA where the radio propagation characteristics of each...

Adaptive digital beamforming for a CDMA mobile communications payload

Science.gov (United States)

Munoz-Garcia, Samuel G.; Ruiz, Javier Benedicto

1993-01-01

In recent years, Spread-Spectrum Code Division Multiple Access (CDMA) has become a very popular access scheme for mobile communications due to a variety of reasons: excellent performance in multipath environments, high scope for frequency reuse, graceful degradation near saturation, etc. In this way, a CDMA system can support simultaneous digital communication among a large community of relatively uncoordinated users sharing a given frequency band. Nevertheless, there are also important problems associated with the use of CDMA. First, in a conventional CDMA scheme, the signature sequences of asynchronous users are not orthogonal and, as the number of active users increases, the self-noise generated by the mutual interference between users considerably degrades the performance, particularly in the return link. Furthermore, when there is a large disparity in received powers - due to differences in slant range or atmospheric attenuation - the non-zero cross-correlation between the signals gives rise to the so-called near-far problem. This leads to an inefficient utilization of the satellite resources and, consequently, to a drastic reduction in capacity. Several techniques were proposed to overcome this problem, such as Synchronized CDMA - in which the signature sequences of the different users are quasi-orthogonal - and power control. At the expense of increased network complexity and user coordination, these techniques enable the system capacity to be restored by equitably sharing the satellite resources among the users. An alternative solution is presented based upon the use of time-reference adaptive digital beamforming on board the satellite. This technique enables a high number of independently steered beams to be generated from a single phased array antenna, which automatically track the desired user signal and null the unwanted interference source. In order to use a time-reference adaptive antenna in a communications system, the main challenge is to obtain a

MIMO wireless networks channels, techniques and standards for multi-antenna, multi-user and multi-cell systems

CERN Document Server

Clerckx, Bruno

2013-01-01

This book is unique in presenting channels, techniques and standards for the next generation of MIMO wireless networks. Through a unified framework, it emphasizes how propagation mechanisms impact the system performance under realistic power constraints. Combining a solid mathematical analysis with a physical and intuitive approach to space-time signal processing, the book progressively derives innovative designs for space-time coding and precoding as well as multi-user and multi-cell techniques, taking into consideration that MIMO channels are often far from ideal. Reflecting developments

An Efficient Downlink Scheduling Strategy Using Normal Graphs for Multiuser MIMO Wireless Systems

Science.gov (United States)

Chen, Jung-Chieh; Wu, Cheng-Hsuan; Lee, Yao-Nan; Wen, Chao-Kai

Inspired by the success of the low-density parity-check (LDPC) codes in the field of error-control coding, in this paper we propose transforming the downlink multiuser multiple-input multiple-output scheduling problem into an LDPC-like problem using the normal graph. Based on the normal graph framework, soft information, which indicates the probability that each user will be scheduled to transmit packets at the access point through a specified angle-frequency sub-channel, is exchanged among the local processors to iteratively optimize the multiuser transmission schedule. Computer simulations show that the proposed algorithm can efficiently schedule simultaneous multiuser transmission which then increases the overall channel utilization and reduces the average packet delay.

Uplink Contention-based CSI Feedback with Prioritized Layers for a Multi-Carrier System

DEFF Research Database (Denmark)

Kaneko, Megumi; Hayashi, Kazunori; Popovski, Petar

2012-01-01

, several works have considered contention-based CSI feedback in the UL control channel. We propose such a feedback scheme for a generic MC system, based on the idea of variable collision protection, where the probability that a feedback information experiences a collision depends on its importance......Optimized resource allocation of the Downlink (DL) in wireless systems utilizing Multi-Carrier (MC) transmission requires Channel State Information (CSI) feedback for each user/subchannel to the Base Station (BS), consuming a high amount of Uplink (UL) radio resources. To alleviate this problem...

Downlink power distributions for 2G and 3G mobile communication networks.

Science.gov (United States)

Colombi, Davide; Thors, Björn; Persson, Tomas; Wirén, Niklas; Larsson, Lars-Eric; Jonsson, Mikael; Törnevik, Christer

2013-12-01

Knowledge of realistic power levels is key when conducting accurate EMF exposure assessments. In this study, downlink output power distributions for radio base stations in 2G and 3G mobile communication networks have been assessed. The distributions were obtained from network measurement data collected from the Operations Support System, which normally is used for network monitoring and management. Significant amounts of data were gathered simultaneously for large sets of radio base stations covering wide geographical areas and different environments. The method was validated with in situ measurements. For the 3G network, the 90th percentile of the averaged output power during high traffic hours was found to be 43 % of the maximum available power. The corresponding number for 2G, with two or more transceivers installed, was 65 % or below.

Applicability of new radio technologies for advanced UMTS networks

Directory of Open Access Journals (Sweden)

A. Dekorsy

2004-01-01

Full Text Available An expanded effort is under the way to support the evolution of UMTS (Universal Mobile Telecommunication System. Apart from delivering high data rates, future UMTS releases will also require to provide high network performance in terms of system capacity, low radiated power, and high coverage. Well promising performance-enhancing technologies are smart antennas as well as multiuser detection. Although these new radio technologies have recently been subject to intense research, main UMTS network integration aspects with their specific constraints have been neglected in many cases. Especially the interaction with UMTS radio resource control being required to meet Quality of Service (QoS constraints has to be included to assess the applicability of these technologies for UMTS. In this paper, we study the interaction of beamforming concepts as well as multiuser detection with load and power control. We also work out UMTS specific constraints like signal-to-interference-plus-noise ratio (SINR operating points, pilot power pollution or channel estimation, all strongly limiting network performance. Results are shown for capacity gains and power reduction for all beamforming concepts of interest as well as linear multiuser detection schemes. The results show that fix as well as user-specific beamforming significantly improves network performance gains in downlink. In uplink multiuser detection indicates fairly modest system capacity gains, while it reduces tremendously mobile station power.

An absorptive single-pole four-throw switch using multiple-contact MEMS switches and its application to a monolithic millimeter-wave beam-forming network

International Nuclear Information System (INIS)

Lee, Sanghyo; Kim, Jong-Man; Kim, Yong-Kweon; Kwon, Youngwoo

2009-01-01

In this paper, a new absorptive single-pole four-throw (SP4T) switch based on multiple-contact switching is proposed and integrated with a Butler matrix to demonstrate a monolithic beam-forming network at millimeter waves (mm waves). In order to simplify the switching driving circuit and reduce the number of unit switches in an absorptive SP4T switch, the individual switches were replaced with long-span multiple-contact switches using stress-free single-crystalline-silicon MEMS technology. This approach improves the mechanical stability as well as the manufacturing yield, thereby allowing successful integration into a monolithic beam former. The fabricated absorptive SP4T MEMS switch shows insertion loss less than 1.3 dB, return losses better than 11 dB at 30 GHz and wideband isolation performance higher than 39 dB from 20 to 40 GHz. The absorptive SP4T MEMS switch is integrated with a 4 × 4 Butler matrix on a single chip to implement a monolithic beam-forming network, directing beam into four distinct angles. Array factors from the measured data show that the proposed absorptive SPnT MEMS switch can be effectively used for high-performance mm-wave beam-switching systems. This work corresponds to the first demonstration of a monolithic beam-forming network using switched beams

3-D Imaging Using Row–Column-Addressed Arrays With Integrated Apodization. Part I: Apodization Design and Line Element Beamforming

DEFF Research Database (Denmark)

Rasmussen, Morten Fischer; Christiansen, Thomas Lehrmann; Thomsen, Erik Vilain

2015-01-01

-integrated apodization increased the apparent diameter of the vessel from 2.0 mm to 2.4 mm, corresponding to an increase from 67% to 80% of the true vessel diameter. The line element beamforming approach is shown to be essential for achieving correct time-of-flight calculations, and hence avoid geometrical distortions...

Multiplier-free DCT approximations for RF multi-beam digital aperture-array space imaging and directional sensing

International Nuclear Information System (INIS)

Potluri, U S; Madanayake, A; Rajapaksha, N; Cintra, R J; Bayer, F M

2012-01-01

Multi-beamforming is an important requirement for broadband space imaging applications based on dense aperture arrays (AAs). Usually, the discrete Fourier transform is the transform of choice for AA electromagnetic imaging. Here, the discrete cosine transform (DCT) is proposed as an alternative, enabling the use of emerging fast algorithms that offer greatly reduced complexity in digital arithmetic circuits. We propose two novel high-speed digital architectures for recently proposed fast algorithms (Bouguezel, Ahmad and Swamy 2008 Electron. Lett. 44 1249–50) (BAS-2008) and (Cintra and Bayer 2011 IEEE Signal Process. Lett. 18 579–82) (CB-2011) that provide good approximations to the DCT at zero multiplicative complexity. Further, we propose a novel DCT approximation having zero multiplicative complexity that is shown to be better for multi-beamforming AAs when compared to BAS-2008 and CB-2011. The far-field array pattern of ideal DCT, BAS-2008, CB-2011 and proposed approximation are investigated with error analysis. Extensive hardware realizations, implementation details and performance metrics are provided for synchronous field programmable gate array (FPGA) technology from Xilinx. The resource consumption and speed metrics of BAS-2008, CB-2011 and the proposed approximation are investigated as functions of system word size. The 8-bit versions are mapped to emerging asynchronous FPGAs leading to significantly increased real-time throughput with clock rates at up to 925.6 MHz implying the fastest DCT approximations using reconfigurable logic devices in the literature. (paper)

Rank-Constrained Beamforming for MIMO Cognitive Interference Channel

Directory of Open Access Journals (Sweden)

Duoying Zhang

2016-01-01

Full Text Available This paper considers the spectrum sharing multiple-input multiple-output (MIMO cognitive interference channel, in which multiple primary users (PUs coexist with multiple secondary users (SUs. Interference alignment (IA approach is introduced that guarantees that secondary users access the licensed spectrum without causing harmful interference to the PUs. A rank-constrained beamforming design is proposed where the rank of the interferences and the desired signals is concerned. The standard interferences metric for the primary link, that is, interference temperature, is investigated and redesigned. The work provides a further improvement that optimizes the dimension of the interferences in the cognitive interference channel, instead of the power of the interference leakage. Due to the nonconvexity of the rank, the developed optimization problems are further approximated as convex form and are solved via choosing the transmitter precoder and receiver subspace iteratively. Numerical results show that the proposed designs can improve the achievable degree of freedom (DoF of the primary links and provide the considerable sum rate for both secondary and primary transmissions under the rank constraints.

Primal Decomposition-Based Method for Weighted Sum-Rate Maximization in Downlink OFDMA Systems

Directory of Open Access Journals (Sweden)

Weeraddana Chathuranga

2010-01-01

Full Text Available We consider the weighted sum-rate maximization problem in downlink Orthogonal Frequency Division Multiple Access (OFDMA systems. Motivated by the increasing popularity of OFDMA in future wireless technologies, a low complexity suboptimal resource allocation algorithm is obtained for joint optimization of multiuser subcarrier assignment and power allocation. The algorithm is based on an approximated primal decomposition-based method, which is inspired from exact primal decomposition techniques. The original nonconvex optimization problem is divided into two subproblems which can be solved independently. Numerical results are provided to compare the performance of the proposed algorithm to Lagrange relaxation based suboptimal methods as well as to optimal exhaustive search-based method. Despite its reduced computational complexity, the proposed algorithm provides close-to-optimal performance.

Individual motile CD4+ T cells can participate in efficient multi-killing through conjugation to multiple tumor cells

Science.gov (United States)

Liadi, Ivan; Singh, Harjeet; Romain, Gabrielle; Rey-Villamizar, Nicolas; Merouane, Amine; Adolacion, Jay R T.; Kebriaei, Partow; Huls, Helen; Qiu, Peng; Roysam, Badrinath; Cooper, Laurence J.N.; Varadarajan, Navin

2015-01-01

T cells genetically modified to express a CD19-specific chimeric antigen receptor (CAR) for the investigational treatment of B-cell malignancies comprise a heterogeneous population, and their ability to persist and participate in serial killing of tumor cells is a predictor of therapeutic success. We implemented Timelapse Imaging Microscopy In Nanowell Grids (TIMING) to provide direct evidence that CD4+CAR+ T cells (CAR4 cells) can engage in multi-killing via simultaneous conjugation to multiple tumor cells. Comparisons of the CAR4 cells and CD8+CAR+ T cells (CAR8 cells) demonstrate that while CAR4 cells can participate in killing and multi-killing, they do so at slower rates, likely due to the lower Granzyme B content. Significantly, in both sets of T cells, a minor sub-population of individual T cells identified by their high motility, demonstrated efficient killing of single tumor cells. By comparing both the multi-killer and single killer CAR+ T cells it appears that the propensity and kinetics of T-cell apoptosis was modulated by the number of functional conjugations. T cells underwent rapid apoptosis, and at higher frequencies, when conjugated to single tumor cells in isolation and this effect was more pronounced on CAR8 cells. Our results suggest that the ability of CAR+ T cells to participate in multi-killing should be evaluated in the context of their ability to resist activation induced cell death (AICD). We anticipate that TIMING may be utilized to rapidly determine the potency of T-cell populations and may facilitate the design and manufacture of next-generation CAR+ T cells with improved efficacy. PMID:25711538

Identifying EGFR-Expressed Cells and Detecting EGFR Multi-Mutations at Single-Cell Level by Microfluidic Chip

Science.gov (United States)

Li, Ren; Zhou, Mingxing; Li, Jine; Wang, Zihua; Zhang, Weikai; Yue, Chunyan; Ma, Yan; Peng, Hailin; Wei, Zewen; Hu, Zhiyuan

2018-03-01

EGFR mutations companion diagnostics have been proved to be crucial for the efficacy of tyrosine kinase inhibitor targeted cancer therapies. To uncover multiple mutations occurred in minority of EGFR-mutated cells, which may be covered by the noises from majority of un-mutated cells, is currently becoming an urgent clinical requirement. Here we present the validation of a microfluidic-chip-based method for detecting EGFR multi-mutations at single-cell level. By trapping and immunofluorescently imaging single cells in specifically designed silicon microwells, the EGFR-expressed cells were easily identified. By in situ lysing single cells, the cell lysates of EGFR-expressed cells were retrieved without cross-contamination. Benefited from excluding the noise from cells without EGFR expression, the simple and cost-effective Sanger's sequencing, but not the expensive deep sequencing of the whole cell population, was used to discover multi-mutations. We verified the new method with precisely discovering three most important EGFR drug-related mutations from a sample in which EGFR-mutated cells only account for a small percentage of whole cell population. The microfluidic chip is capable of discovering not only the existence of specific EGFR multi-mutations, but also other valuable single-cell-level information: on which specific cells the mutations occurred, or whether different mutations coexist on the same cells. This microfluidic chip constitutes a promising method to promote simple and cost-effective Sanger's sequencing to be a routine test before performing targeted cancer therapy.[Figure not available: see fulltext.

Cross-Layer Admission Control Policy for CDMA Beamforming Systems

Directory of Open Access Journals (Sweden)

Sheng Wei

2007-01-01

Full Text Available A novel admission control (AC policy is proposed for the uplink of a cellular CDMA beamforming system. An approximated power control feasibility condition (PCFC, required by a cross-layer AC policy, is derived. This approximation, however, increases outage probability in the physical layer. A truncated automatic retransmission request (ARQ scheme is then employed to mitigate the outage problem. In this paper, we investigate the joint design of an AC policy and an ARQ-based outage mitigation algorithm in a cross-layer context. This paper provides a framework for joint AC design among physical, data-link, and network layers. This enables multiple quality-of-service (QoS requirements to be more flexibly used to optimize system performance. Numerical examples show that by appropriately choosing ARQ parameters, the proposed AC policy can achieve a significant performance gain in terms of reduced outage probability and increased system throughput, while simultaneously guaranteeing all the QoS requirements.

Covert, Intelligent, and Spectrally-Efficient MIMO-Based Noise Radar Networks

Science.gov (United States)

2009-01-31

differentiate signals from various transmitters. Generalized Likelihood Ratio Test (GLRT) and Tapped Delay Line (TDL) beamforming were integrated. 2. RF tag...signjH From Tx 1 XCORR otfeljtion’ • y b«jmfotftiiri9 exx Eft . i igriji2 Ftorn T*2 (b) Fig. 8: MIMO radar using orthogonal sequences: (a...water-filling approach further. Generalized Likelihood Ratio Test and Tapped Delay Line Beamforming: Multi-input and multi-output (MIMO) radar

Reduced-complexity adaptive multi-channel assignment for shared access points in over-loaded small-cell networks

KAUST Repository

Radaydeh, Redha Mahmoud

2013-06-01

This paper proposes a reduced-complexity downlink multi-channel assignment scheme when feedback links are capacity-limited. The system model treats the case when multiple access points are allocated to serve scheduled users in over-loaded (i.e. dense) pico/femtocell networks. It assumes that the deployed access points can be shared simultaneously and employ isotropic antenna arrays of arbitrary sizes. Moreover, they transmit their data on a common physical channel and can not coordinate their transmissions. On the other hand, each scheduled user can be served by single transmit channel from each active access point at a time, and it lacks coordination with concurrent active users. The scheme operates according to the occupancy of available transmit channels, wherein extensively occupied access points are avoided adaptively, while reducing the load of processing. The operation is linked to a target performance via controlling the observed aggregate interference from the projected set of serving points. Through the analysis, results for the scheduled user outage performance, and the average number of active access points are presented. Numerical and simulations studies clarify the gains of the proposed scheme for different operating conditions. © 2013 IEEE.

Reduced-complexity adaptive multi-channel assignment for shared access points in over-loaded small-cell networks

KAUST Repository

Radaydeh, Redha Mahmoud; Qaraqe, Khalid A.; Alouini, Mohamed-Slim

2013-01-01

This paper proposes a reduced-complexity downlink multi-channel assignment scheme when feedback links are capacity-limited. The system model treats the case when multiple access points are allocated to serve scheduled users in over-loaded (i.e. dense) pico/femtocell networks. It assumes that the deployed access points can be shared simultaneously and employ isotropic antenna arrays of arbitrary sizes. Moreover, they transmit their data on a common physical channel and can not coordinate their transmissions. On the other hand, each scheduled user can be served by single transmit channel from each active access point at a time, and it lacks coordination with concurrent active users. The scheme operates according to the occupancy of available transmit channels, wherein extensively occupied access points are avoided adaptively, while reducing the load of processing. The operation is linked to a target performance via controlling the observed aggregate interference from the projected set of serving points. Through the analysis, results for the scheduled user outage performance, and the average number of active access points are presented. Numerical and simulations studies clarify the gains of the proposed scheme for different operating conditions. © 2013 IEEE.

Multi-grid Particle-in-cell Simulations of Plasma Microturbulence

International Nuclear Information System (INIS)

Lewandowski, J.L.V.

2003-01-01

A new scheme to accurately retain kinetic electron effects in particle-in-cell (PIC) simulations for the case of electrostatic drift waves is presented. The splitting scheme, which is based on exact separation between adiabatic and on adiabatic electron responses, is shown to yield more accurate linear growth rates than the standard df scheme. The linear and nonlinear elliptic problems that arise in the splitting scheme are solved using a multi-grid solver. The multi-grid particle-in-cell approach offers an attractive path, both from the physics and numerical points of view, to simulate kinetic electron dynamics in global toroidal plasmas

Multipath diffuse routing over heterogeneous mesh networks of web devices and sensors

NARCIS (Netherlands)

Vitale, G.; Stassen, M.L.A.; Colak, S.B.; Pronk, V.; Macq, B.; Quisquater, J.-.J.

2002-01-01

In this paper we present a new data flow algorithm based on physical diffusion for dense device networks needed for future ubiquitous communications. This diffuse data routing concept is based on multi-path signal propagation aided with adaptive beam-forming methods. Adaptation for beam-forming at

Exposure assessment of one-year-old child to 3G tablet in uplink mode and to 3G femtocell in downlink mode using polynomial chaos decomposition

International Nuclear Information System (INIS)

Liorni, I; Parazzini, M; Ravazzani, P; Varsier, N; Hadjem, A; Wiart, J

2016-01-01

So far, the assessment of the exposure of children, in the ages 0–2 years old, to relatively new radio-frequency (RF) technologies, such as tablets and femtocells, remains an open issue. This study aims to analyse the exposure of a one year-old child to these two sources, tablets and femtocells, operating in uplink (tablet) and downlink (femtocell) modes, respectively. In detail, a realistic model of an infant has been used to model separately the exposures due to (i) a 3G tablet emitting at the frequency of 1940 MHz (uplink mode) placed close to the body and (ii) a 3G femtocell emitting at 2100 MHz (downlink mode) placed at a distance of at least 1 m from the infant body. For both RF sources, the input power was set to 250 mW. The variability of the exposure due to the variation of the position of the RF sources with respect to the infant body has been studied by stochastic dosimetry, based on polynomial chaos to build surrogate models of both whole-body and tissue specific absorption rate (SAR), which makes it easy and quick to investigate the exposure in a full range of possible positions of the sources. The major outcomes of the study are: (1) the maximum values of the whole-body SAR (WB SAR) have been found to be 9.5 mW kg −1 in uplink mode and 65 μW kg −1 in downlink mode, i.e. within the limits of the ICNIRP 1998 Guidelines; (2) in both uplink and downlink mode the highest SAR values were approximately found in the same tissues, i.e. in the skin, eye and penis for the whole-tissue SAR and in the bone, skin and muscle for the peak SAR; (3) the change in the position of both the 3G tablet and the 3G femtocell significantly influences the infant exposure. (paper)

Exposure assessment of one-year-old child to 3G tablet in uplink mode and to 3G femtocell in downlink mode using polynomial chaos decomposition

Science.gov (United States)

Liorni, I.; Parazzini, M.; Varsier, N.; Hadjem, A.; Ravazzani, P.; Wiart, J.

2016-04-01

So far, the assessment of the exposure of children, in the ages 0-2 years old, to relatively new radio-frequency (RF) technologies, such as tablets and femtocells, remains an open issue. This study aims to analyse the exposure of a one year-old child to these two sources, tablets and femtocells, operating in uplink (tablet) and downlink (femtocell) modes, respectively. In detail, a realistic model of an infant has been used to model separately the exposures due to (i) a 3G tablet emitting at the frequency of 1940 MHz (uplink mode) placed close to the body and (ii) a 3G femtocell emitting at 2100 MHz (downlink mode) placed at a distance of at least 1 m from the infant body. For both RF sources, the input power was set to 250 mW. The variability of the exposure due to the variation of the position of the RF sources with respect to the infant body has been studied by stochastic dosimetry, based on polynomial chaos to build surrogate models of both whole-body and tissue specific absorption rate (SAR), which makes it easy and quick to investigate the exposure in a full range of possible positions of the sources. The major outcomes of the study are: (1) the maximum values of the whole-body SAR (WB SAR) have been found to be 9.5 mW kg-1 in uplink mode and 65 μW kg-1 in downlink mode, i.e. within the limits of the ICNIRP 1998 Guidelines; (2) in both uplink and downlink mode the highest SAR values were approximately found in the same tissues, i.e. in the skin, eye and penis for the whole-tissue SAR and in the bone, skin and muscle for the peak SAR; (3) the change in the position of both the 3G tablet and the 3G femtocell significantly influences the infant exposure.

Low-Complexity Hyperspectral Image Compression on a Multi-tiled Architecture

NARCIS (Netherlands)

Walters, K.H.G.; Kokkeler, Andre B.J.; Gerez, Sabih H.; Smit, Gerardus Johannes Maria

2009-01-01

The increasing amount of data produced in satellites poses a downlink communication problem due to the limited data rate of the downlink. This bottleneck is solved by introducing more and more processing power on-board to compress data to a satisfiable rate. Currently, this processing power is often

Performance of multi-junction cells due to illumination distribution across the cell surface

International Nuclear Information System (INIS)

Schultz, R.D.; Vorster, F.J; Dyk, E.E van

2012-01-01

This paper addresses the influence of illumination distribution on the performance of a high concentration photovoltaic (HCPV) module. CPV systems comprise of optical elements as well as mechanical tracking to concentrate the solar flux onto the solar receiver as well as to keep the system on track with the sun. The performance of the subcells of the multi-junction concentrator cell depends on the optical alignment of the system. Raster scanning of the incident intensity in the optical plane of the receiver and corresponding I–V measurements were used to investigate the influence of illumination distribution on performance. The results show that the illumination distribution that differs between cells does affect the performance of the module. The performance of the subcells of the multi-junction concentrator cell also depends on the optical alignment of the system.

Performance of multi-junction cells due to illumination distribution across the cell surface

Energy Technology Data Exchange (ETDEWEB)

Schultz, R.D., E-mail: s206029578@live.nmmu.ac.za [Nelson Mandela University, Physics Department, P.O. Box 77000, 6031, Port Elizabeth (South Africa); Vorster, F.J; Dyk, E.E van [Nelson Mandela University, Physics Department, P.O. Box 77000, 6031, Port Elizabeth (South Africa)

2012-05-15

This paper addresses the influence of illumination distribution on the performance of a high concentration photovoltaic (HCPV) module. CPV systems comprise of optical elements as well as mechanical tracking to concentrate the solar flux onto the solar receiver as well as to keep the system on track with the sun. The performance of the subcells of the multi-junction concentrator cell depends on the optical alignment of the system. Raster scanning of the incident intensity in the optical plane of the receiver and corresponding I-V measurements were used to investigate the influence of illumination distribution on performance. The results show that the illumination distribution that differs between cells does affect the performance of the module. The performance of the subcells of the multi-junction concentrator cell also depends on the optical alignment of the system.

Double-Stage Delay Multiply and Sum Beamforming Algorithm: Application to Linear-Array Photoacoustic Imaging.

Science.gov (United States)

Mozaffarzadeh, Moein; Mahloojifar, Ali; Orooji, Mahdi; Adabi, Saba; Nasiriavanaki, Mohammadreza

2018-01-01

Photoacoustic imaging (PAI) is an emerging medical imaging modality capable of providing high spatial resolution of Ultrasound (US) imaging and high contrast of optical imaging. Delay-and-Sum (DAS) is the most common beamforming algorithm in PAI. However, using DAS beamformer leads to low resolution images and considerable contribution of off-axis signals. A new paradigm namely delay-multiply-and-sum (DMAS), which was originally used as a reconstruction algorithm in confocal microwave imaging, was introduced to overcome the challenges in DAS. DMAS was used in PAI systems and it was shown that this algorithm results in resolution improvement and sidelobe degrading. However, DMAS is still sensitive to high levels of noise, and resolution improvement is not satisfying. Here, we propose a novel algorithm based on DAS algebra inside DMAS formula expansion, double stage DMAS (DS-DMAS), which improves the image resolution and levels of sidelobe, and is much less sensitive to high level of noise compared to DMAS. The performance of DS-DMAS algorithm is evaluated numerically and experimentally. The resulted images are evaluated qualitatively and quantitatively using established quality metrics including signal-to-noise ratio (SNR), full-width-half-maximum (FWHM) and contrast ratio (CR). It is shown that DS-DMAS outperforms DAS and DMAS at the expense of higher computational load. DS-DMAS reduces the lateral valley for about 15 dB and improves the SNR and FWHM better than 13% and 30%, respectively. Moreover, the levels of sidelobe are reduced for about 10 dB in comparison with those in DMAS.

Beamforming transmission in IEEE 802.11ac under time-varying channels.

Science.gov (United States)

Yu, Heejung; Kim, Taejoon

2014-01-01

The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes.

Design and analysis of a multi-cell subscale tank for liquid hydrogen storage

NARCIS (Netherlands)

Tapeinos, I.; Koussios, S.; Groves, R.M.

2015-01-01

This paper outlines the structural performance of a conformable pressurizable tank consisting of intersecting spherical shells (multi-cell tank). Multi-cell tanks outrival conventional multiple cylindrical tanks in volumetric efficiency when required to fit in a rectangular envelope in the

Down-link power distributions for 2G and 3G mobile communication networks

International Nuclear Information System (INIS)

Colombi, D.; Thors, B.; Persson, T.; Wiren, N.; Larsson, L. E.; Jonsson, M.; Toernevik, C.

2013-01-01

Knowledge of realistic power levels is key when conducting accurate EMF exposure assessments. In this study, down-link output power distributions for radio base stations in 2G and 3G mobile communication networks have been assessed. The distributions were obtained from network measurement data collected from the Operations Support System, which normally is used for network monitoring and management. Significant amounts of data were gathered simultaneously for large sets of radio base stations covering wide geographical areas and different environments. The method was validated with in situ measurements. For the 3G network, the 90. percentile of the averaged output power during high traffic hours was found to be 43 % of the maximum available power. The corresponding number for 2G, with two or more transceivers installed, was 65 % or below. (authors)

A Diagonal-Steering-Based Binaural Beamforming Algorithm Incorporating a Diagonal Speech Localizer for Persons With Bilateral Hearing Impairment.

Science.gov (United States)

Lee, Jun Chang; Nam, Kyoung Won; Jang, Dong Pyo; Kim, In Young

2015-12-01

Previously suggested diagonal-steering algorithms for binaural hearing support devices have commonly assumed that the direction of the speech signal is known in advance, which is not always the case in many real circumstances. In this study, a new diagonal-steering-based binaural speech localization (BSL) algorithm is proposed, and the performances of the BSL algorithm and the binaural beamforming algorithm, which integrates the BSL and diagonal-steering algorithms, were evaluated using actual speech-in-noise signals in several simulated listening scenarios. Testing sounds were recorded in a KEMAR mannequin setup and two objective indices, improvements in signal-to-noise ratio (SNRi ) and segmental SNR (segSNRi ), were utilized for performance evaluation. Experimental results demonstrated that the accuracy of the BSL was in the 90-100% range when input SNR was -10 to +5 dB range. The average differences between the γ-adjusted and γ-fixed diagonal-steering algorithms (for -15 to +5 dB input SNR) in the talking in the restaurant scenario were 0.203-0.937 dB for SNRi and 0.052-0.437 dB for segSNRi , and in the listening while car driving scenario, the differences were 0.387-0.835 dB for SNRi and 0.259-1.175 dB for segSNRi . In addition, the average difference between the BSL-turned-on and the BSL-turned-off cases for the binaural beamforming algorithm in the listening while car driving scenario was 1.631-4.246 dB for SNRi and 0.574-2.784 dB for segSNRi . In all testing conditions, the γ-adjusted diagonal-steering and BSL algorithm improved the values of the indices more than the conventional algorithms. The binaural beamforming algorithm, which integrates the proposed BSL and diagonal-steering algorithm, is expected to improve the performance of the binaural hearing support devices in noisy situations. Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Low-Cost Multi-Junction Photovoltaic Cells, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — The proposed SBIR project will provide a pathway to dramatically reduce the cost of multi-junction solar cells. The project leverages a TRL6 micropackaging process...

Performance of Overlaid MIMO Cellular Networks with TAS/MRC under Hybrid-Access Small Cells and Poisson Field Interference

KAUST Repository

AbdelNabi, Amr A.

2018-02-12

This paper presents new approaches to characterize the achieved performance of hybrid control-access small cells in the context of two-tier multi-input multi-output (MIMO) cellular networks with random interference distributions. The hybrid scheme at small cells (such as femtocells) allows for sharing radio resources between the two network tiers according to the densities of small cells and their associated users, as well as the observed interference power levels in the two network tiers. The analysis considers MIMO transceivers at all nodes, for which antenna arrays can be utilized to implement transmit antenna selection (TAS) and receive maximal ratio combining (MRC) under MIMO point-to-point channels. Moreover, it tar-gets network-level models of interference sources inside each tier and between the two tiers, which are assumed to follow Poisson field processes. To fully capture the occasions for Poisson field distribution on MIMO spatial domain. Two practical scenarios of interference sources are addressed including highly-correlated or uncorrelated transmit antenna arrays of the serving macrocell base station. The analysis presents new analytical approaches that can characterize the downlink outage probability performance in any tier. Furthermore, the outage performance in high signal-to-noise (SNR) regime is also obtained, which can be useful to deduce diversity and/or coding gains.

Performance of Overlaid MIMO Cellular Networks with TAS/MRC under Hybrid-Access Small Cells and Poisson Field Interference

KAUST Repository

AbdelNabi, Amr A.; Al-Qahtani, Fawaz S.; Radaydeh, Redha Mahmoud Mesleh; Shaqfeh, Mohammad; Manna, Raed F.

2018-01-01

This paper presents new approaches to characterize the achieved performance of hybrid control-access small cells in the context of two-tier multi-input multi-output (MIMO) cellular networks with random interference distributions. The hybrid scheme at small cells (such as femtocells) allows for sharing radio resources between the two network tiers according to the densities of small cells and their associated users, as well as the observed interference power levels in the two network tiers. The analysis considers MIMO transceivers at all nodes, for which antenna arrays can be utilized to implement transmit antenna selection (TAS) and receive maximal ratio combining (MRC) under MIMO point-to-point channels. Moreover, it tar-gets network-level models of interference sources inside each tier and between the two tiers, which are assumed to follow Poisson field processes. To fully capture the occasions for Poisson field distribution on MIMO spatial domain. Two practical scenarios of interference sources are addressed including highly-correlated or uncorrelated transmit antenna arrays of the serving macrocell base station. The analysis presents new analytical approaches that can characterize the downlink outage probability performance in any tier. Furthermore, the outage performance in high signal-to-noise (SNR) regime is also obtained, which can be useful to deduce diversity and/or coding gains.

Multi-cellular natural killer (NK) cell clusters enhance NK cell activation through localizing IL-2 within the cluster

Science.gov (United States)

Kim, Miju; Kim, Tae-Jin; Kim, Hye Mi; Doh, Junsang; Lee, Kyung-Mi

2017-01-01

Multi-cellular cluster formation of natural killer (NK) cells occurs during in vivo priming and potentiates their activation to IL-2. However, the precise mechanism underlying this synergy within NK cell clusters remains unclear. We employed lymphocyte-laden microwell technologies to modulate contact-mediated multi-cellular interactions among activating NK cells and to quantitatively assess the molecular events occurring in multi-cellular clusters of NK cells. NK cells in social microwells, which allow cell-to-cell contact, exhibited significantly higher levels of IL-2 receptor (IL-2R) signaling compared with those in lonesome microwells, which prevent intercellular contact. Further, CD25, an IL-2R α chain, and lytic granules of NK cells in social microwells were polarized toward MTOC. Live cell imaging of lytic granules revealed their dynamic and prolonged polarization toward neighboring NK cells without degranulation. These results suggest that IL-2 bound on CD25 of one NK cells triggered IL-2 signaling of neighboring NK cells. These results were further corroborated by findings that CD25-KO NK cells exhibited lower proliferation than WT NK cells, and when mixed with WT NK cells, underwent significantly higher level of proliferation. These data highlights the existence of IL-2 trans-presentation between NK cells in the local microenvironment where the availability of IL-2 is limited.

Imperfect generalized transmit beamforming with co-channel interference cancelation

KAUST Repository

Radaydeh, Redha Mahmoud Mesleh

2010-10-01

The performance of a generalized single-stream transmit beamforming scheme employing receive co-channel interference -steering algorithms in slowly varying and flat fading channels is analyzed. The impact of imperfect prediction of channel state information (CSI) for the desired user spatially uncorrelated transmit channels is considered. Both dominant interference cancelation and adaptive arbitrary interference cancelation algorithms for closely spaced receive antennas are used. The impact of outdated statistical ordering of the interferers instantaneous powers on the effectiveness of dominant interference cancelation is investigated against the less complex adaptive arbitrary cancelation scheme. For the system models described above, new exact formulas for the statistics of combined signal-to-interference-plus-noise ratio (SINR) are derived, from which results for conventional maximum ratio transmission (MRT) and best transmit channel selection schemes can be deduced as limiting cases. The results presented herein can be used to obtain quantitative measure for various performance metrics, and in addition to investigate the performance-complexity tradeoff for different multiple-antenna system models. © 2010 IEEE.

Sum rate maximization in the uplink of multi-cell OFDMA networks

KAUST Repository

Tabassum, Hina; Alouini, Mohamed-Slim; Dawy, Zaher

2012-01-01

of each cell, while ignoring the significant effect of inter-cell interference. This paper investigates the problem of resource allocation (i.e., subcarriers and powers) in the uplink of a multi-cell OFDMA network. The problem has a non

Aspects of multiuser MIMO for cell throughput maximization

DEFF Research Database (Denmark)

Bauch, Gerhard; Tejera, Pedro; Guthy, Christian

2007-01-01

We consider a multiuser MIMO downlink scenario where the resources in time, frequency and space are allocated such that the total cell throughput is maximized. This is achieved by exploiting multiuser diversity, i.e. the physical resources are allocated to the user with the highest SNR. We assume...

Statistical multi-path exposure method for assessing the whole-body SAR in a heterogeneous human body model in a realistic environment.

Science.gov (United States)

Vermeeren, Günter; Joseph, Wout; Martens, Luc

2013-04-01

Assessing the whole-body absorption in a human in a realistic environment requires a statistical approach covering all possible exposure situations. This article describes the development of a statistical multi-path exposure method for heterogeneous realistic human body models. The method is applied for the 6-year-old Virtual Family boy (VFB) exposed to the GSM downlink at 950 MHz. It is shown that the whole-body SAR does not differ significantly over the different environments at an operating frequency of 950 MHz. Furthermore, the whole-body SAR in the VFB for multi-path exposure exceeds the whole-body SAR for worst-case single-incident plane wave exposure by 3.6%. Moreover, the ICNIRP reference levels are not conservative with the basic restrictions in 0.3% of the exposure samples for the VFB at the GSM downlink of 950 MHz. The homogeneous spheroid with the dielectric properties of the head suggested by the IEC underestimates the absorption compared to realistic human body models. Moreover, the variation in the whole-body SAR for realistic human body models is larger than for homogeneous spheroid models. This is mainly due to the heterogeneity of the tissues and the irregular shape of the realistic human body model compared to homogeneous spheroid human body models. Copyright © 2012 Wiley Periodicals, Inc.

BEAM-FORMING ERRORS IN MURCHISON WIDEFIELD ARRAY PHASED ARRAY ANTENNAS AND THEIR EFFECTS ON EPOCH OF REIONIZATION SCIENCE

Energy Technology Data Exchange (ETDEWEB)

Neben, Abraham R.; Hewitt, Jacqueline N.; Dillon, Joshua S.; Goeke, R.; Morgan, E. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Bradley, Richard F. [Dept. of Electrical and Computer Engineering, University of Virginia, Charlottesville, VA, 22904 (United States); Bernardi, G. [Square Kilometre Array South Africa (SKA SA), Cape Town 7405 (South Africa); Bowman, J. D. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Briggs, F. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Cappallo, R. J.; Corey, B. E.; Lonsdale, C. J.; McWhirter, S. R. [MIT Haystack Observatory, Westford, MA 01886 (United States); Deshpande, A. A. [Raman Research Institute, Bangalore 560080 (India); Greenhill, L. J. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Hazelton, B. J.; Morales, M. F. [Department of Physics, University of Washington, Seattle, WA 98195 (United States); Johnston-Hollitt, M. [School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6140 (New Zealand); Kaplan, D. L. [Department of Physics, University of Wisconsin–Milwaukee, Milwaukee, WI 53201 (United States); Mitchell, D. A. [CSIRO Astronomy and Space Science (CASS), P.O. Box 76, Epping, NSW 1710 (Australia); and others

2016-03-20

Accurate antenna beam models are critical for radio observations aiming to isolate the redshifted 21 cm spectral line emission from the Dark Ages and the Epoch of Reionization (EOR) and unlock the scientific potential of 21 cm cosmology. Past work has focused on characterizing mean antenna beam models using either satellite signals or astronomical sources as calibrators, but antenna-to-antenna variation due to imperfect instrumentation has remained unexplored. We characterize this variation for the Murchison Widefield Array (MWA) through laboratory measurements and simulations, finding typical deviations of the order of ±10%–20% near the edges of the main lobe and in the sidelobes. We consider the ramifications of these results for image- and power spectrum-based science. In particular, we simulate visibilities measured by a 100 m baseline and find that using an otherwise perfect foreground model, unmodeled beam-forming errors severely limit foreground subtraction accuracy within the region of Fourier space contaminated by foreground emission (the “wedge”). This region likely contains much of the cosmological signal, and accessing it will require measurement of per-antenna beam patterns. However, unmodeled beam-forming errors do not contaminate the Fourier space region expected to be free of foreground contamination (the “EOR window”), showing that foreground avoidance remains a viable strategy.

Feasibility Studies on the Use of Higher Frequency Bands and Beamforming Selection Scheme for High Speed Train Communication

Directory of Open Access Journals (Sweden)

Ayotunde O. Laiyemo

2017-01-01

Full Text Available With increasing popularity of high speed trains and traffic forecast for future cellular networks, the need to provide improved data rates using higher frequency bands (HFBs for train passengers is becoming crucial. In this paper, we modify the OFDM frame structure for HST, taking into account the increasing sensitivity to speed at HFBs. A lower bound on the SNR/SINR for a given rate for reliable communication was derived considering the physical layer parameters from the OFDM frame. We also analyze different pathloss models in the context of examining the required gain needed to achieve the same performance as with microwave bands. Finally, we present a time-based analogue beamforming selection approach for HST. We observed that, irrespective of the pathloss models used, the required gains are within the same range. For the same SNR/SINR at different frequency bands, the achievable data rate varies with respect to the frequency bands. Our results show the potential of the use of HFBs. However, due to the increased sensitivity of some channel parameters, a maximum frequency band of 38 GHz is suggested. Evaluation of our proposed beamforming scheme indicates a close performance to the optimal SVD scheme with a marginal rate gap of less than 2 b/s/Hz.

Mobile Satellite Reception with a Virtual Satellite Dish based on a Reconfigurable Multi-Processor Architecture

NARCIS (Netherlands)

van de Burgwal, M.D.; Rovers, K.C.; Blom, K.C.H.; Kokkeler, Andre B.J.; Smit, Gerardus Johannes Maria

2011-01-01

Traditionally, mechanically steered dishes or analog phased array beamforming systems have been used for radio frequency receivers, where strong directivity and high performance were much more important than low-cost requirements. Real-time controlled digital phased array beamforming could not be

Cross-Layer Design and Analysis of Downlink Communications in Cellular CDMA Systems

Directory of Open Access Journals (Sweden)

Sun Jin Yuan

2006-01-01

Full Text Available A cellular CDMA network with voice and data communications is considered. Focusing on the downlink direction, we seek for the overall performance improvement which can be achieved by cross-layer analysis and design, taking physical layer, link layer, network layer, and transport layer into account. We are concerned with the role of each single layer as well as the interaction among layers, and propose algorithms/schemes accordingly to improve the system performance. These proposals include adaptive scheduling for link layer, priority-based handoff strategy for network admission control, and an algorithm for the avoidance of TCP spurious timeouts at the transport layer. Numerical results show the performance gain of each proposed scheme over independent performance of an individual layer in the wireless mobile network. We conclude that the system performance in terms of capacity, throughput, dropping probability, outage, power efficiency, delay, and fairness can be enhanced by jointly considering the interactions across layers.

The promise of downlink MU-MIMO for high-capacity next generation mobile broadband networks based on IEEE 802.16 m

OpenAIRE

Papathanassiou Apostolos; Davydov Alexei

2011-01-01

Abstract The dramatic increase of the demand for mobile broadband services poses stringent requirements on the performance evolution of currently deployed mobile broadband networks, such as Mobile WiMAX Release 1 and 3GPP LTE Release 8. Although the combination of single-user multiple-input multiple-output (SU-MIMO) and orthogonal frequency division multiple access (OFDMA) provide the appropriate technologies for improving the downlink performance of third generation (3G) code division multip...

Bi-directional 35-Gbit/s 2D beam steered optical wireless downlink and 5-Gbit/s localized 60-GHz communication uplink for hybrid indoor wireless systems

NARCIS (Netherlands)

Khalid, A.M.; Baltus, P.G.M.; Dommele, A.R.; Mekonnen, K.A.; Cao, Z.; Oh, C.W.; Matters, M.K.; Koonen, A.M.J.

2017-01-01

We present a full-duplex dynamic indoor optical wireless system using 2D passive optical beam steering for downlink and 60-GHz communication for upstream transmission. We demonstrate 35-Gb/s NRZ-OOK downstream multicasting and 5-Gb/s NRZ-ASK upstream communication.

Performance analysis of high-concentrated multi-junction solar cells in hot climate

Science.gov (United States)

Ghoneim, Adel A.; Kandil, Kandil M.; Alzanki, Talal H.; Alenezi, Mohammad R.

2018-03-01

Multi-junction concentrator solar cells are a promising technology as they can fulfill the increasing energy demand with renewable sources. Focusing sunlight upon the aperture of multi-junction photovoltaic (PV) cells can generate much greater power densities than conventional PV cells. So, concentrated PV multi-junction solar cells offer a promising way towards achieving minimum cost per kilowatt-hour. However, these cells have many aspects that must be fixed to be feasible for large-scale energy generation. In this work, a model is developed to analyze the impact of various atmospheric factors on concentrator PV performance. A single-diode equivalent circuit model is developed to examine multi-junction cells performance in hot weather conditions, considering the impacts of both temperature and concentration ratio. The impacts of spectral variations of irradiance on annual performance of various high-concentrated photovoltaic (HCPV) panels are examined, adapting spectra simulations using the SMARTS model. Also, the diode shunt resistance neglected in the existing models is considered in the present model. The present results are efficiently validated against measurements from published data to within 2% accuracy. Present predictions show that the single-diode model considering the shunt resistance gives accurate and reliable results. Also, aerosol optical depth (AOD) and air mass are most important atmospheric parameters having a significant impact on HCPV cell performance. In addition, the electrical efficiency (η) is noticed to increase with concentration to a certain concentration degree after which it decreases. Finally, based on the model predictions, let us conclude that the present model could be adapted properly to examine HCPV cells' performance over a broad range of operating conditions.

Scalability of multi-junction organic solar cells for large area organic solar modules

Science.gov (United States)

Xiao, Xin; Lee, Kyusang; Forrest, Stephen R.

2015-05-01

We investigate the scalability of multi-junction organic photovoltaic cells (OPV) with device areas ranging from 1 mm2 to 1 cm2, as well as 25 cm2 active area solar modules. We find that the series resistance losses in 1 cm2 vs. 1 mm2 OPV cell efficiencies are significantly higher in single junction cells than tandem, triple, and four junction cells due to the lower operating voltage and higher current of the former. Using sub-electrodes to reduce series resistance, the power conversion efficiency (PCE) of multi-junction cells is almost independent of area from 1 mm2 to 1 cm2. Twenty-five, 1 cm2 multi-junction cell arrays are integrated in a module and connected in a series-parallel circuit configuration. A yield of 100% with a deviation of PCE from cell to cell of <10% is achieved. The module generates an output power of 162 ± 9 mW under simulated AM1.5G illumination at one sun intensity, corresponding to PCE = 6.5 ± 0.1%, slightly lower than PCE of discrete cells ranging from 6.7% to 7.2%.

Neutral- and Multi-Colored Semitransparent Perovskite Solar Cells.

Science.gov (United States)

Lee, Kyu-Tae; Guo, L Jay; Park, Hui Joon

2016-04-11

In this review, we summarize recent works on perovskite solar cells with neutral- and multi-colored semitransparency for building-integrated photovoltaics and tandem solar cells. The perovskite solar cells exploiting microstructured arrays of perovskite "islands" and transparent electrodes-the latter of which include thin metallic films, metal nanowires, carbon nanotubes, graphenes, and transparent conductive oxides for achieving optical transparency-are investigated. Moreover, the perovskite solar cells with distinctive color generation, which are enabled by engineering the band gap of the perovskite light-harvesting semiconductors with chemical management and integrating with photonic nanostructures, including microcavity, are discussed. We conclude by providing future research directions toward further performance improvements of the semitransparent perovskite solar cells.

Compensation for HPA nonlinearity and I/Q imbalance in MIMO beamforming systems

KAUST Repository

Qi, Jian; Aissa, Sonia

2010-01-01

In this paper, we investigate the effects of high-power amplifier (HPA) nonlinearity and in-phase and quadrature-phase (I/Q) imbalance on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems. Specifically, we propose a compensation method for HPA nonlinearity and I/Q imbalance together in MIMO TB systems. The performance of the MIMO TB system under study is evaluated in terms of the average symbol error probability (SEP) and system capacity, considering transmission over uncorrelated frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, such as the HPA parameters, image-leakage ratio, numbers of transmit and receive antennas, length of pilot symbols, and modulation order of phase-shift keying (PSK), on performance. © 2010 IEEE.

Compensation for HPA nonlinearity and I/Q imbalance in MIMO beamforming systems

KAUST Repository

Qi, Jian

2010-10-01

In this paper, we investigate the effects of high-power amplifier (HPA) nonlinearity and in-phase and quadrature-phase (I/Q) imbalance on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems. Specifically, we propose a compensation method for HPA nonlinearity and I/Q imbalance together in MIMO TB systems. The performance of the MIMO TB system under study is evaluated in terms of the average symbol error probability (SEP) and system capacity, considering transmission over uncorrelated frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects of several system parameters, such as the HPA parameters, image-leakage ratio, numbers of transmit and receive antennas, length of pilot symbols, and modulation order of phase-shift keying (PSK), on performance. © 2010 IEEE.

Multi-cell disk-and-ring tapered structure for compact RF linacs

Energy Technology Data Exchange (ETDEWEB)

Smirnov, A.V.; Boucher, S.; Kutsaev, S. [RadiaBeam Systems LLC, 1713 Stewart Street, Santa Monica, CA 90404, US (United States); Hartzell, J. [RadiaBeam Technologies, LLC, 1717 Stewart Street, Santa Monica, CA 90404, US (United States); Savin, E. [RadiaBeam Technologies, LLC, 1717 Stewart Street, Santa Monica, CA 90404, US (United States); National Research Nuclear University “MEPhI”, Moscow 115409 (Russian Federation)

2016-09-11

A tubular disk-and-ring, tapered accelerating structure for small electron linacs and MicroLinacs is considered. It consists of metal and dielectric elements inserted into a metallic tube to eliminate multi-cell, multi-step brazing. The structure enables a wide range of phase velocities (including non-relativistic), a wide bandwidth allowing large number of cells (for standing wave mode) or short filling time (for traveling wave mode), combination of compensated and purely π-mode cells, alternative periodic focusing built-in to the RF structure (the disks), and combining of RF and vacuum windows. RF and accelerating performance of such a long structure having up to four dozens cells is analyzed. Some of beam dynamics, thermal, and vacuum aspects of the structure and MicroLinac performance are considered as well.

Multi-cell disk-and-ring tapered structure for compact RF linacs

International Nuclear Information System (INIS)

Smirnov, A.V.; Boucher, S.; Kutsaev, S.; Hartzell, J.; Savin, E.

2016-01-01

A tubular disk-and-ring, tapered accelerating structure for small electron linacs and MicroLinacs is considered. It consists of metal and dielectric elements inserted into a metallic tube to eliminate multi-cell, multi-step brazing. The structure enables a wide range of phase velocities (including non-relativistic), a wide bandwidth allowing large number of cells (for standing wave mode) or short filling time (for traveling wave mode), combination of compensated and purely π-mode cells, alternative periodic focusing built-in to the RF structure (the disks), and combining of RF and vacuum windows. RF and accelerating performance of such a long structure having up to four dozens cells is analyzed. Some of beam dynamics, thermal, and vacuum aspects of the structure and MicroLinac performance are considered as well.

Function of bunching segment in multi-cell RF gun

International Nuclear Information System (INIS)

Yang Xingfan; Xu Zhou Liu Xisan

2001-01-01

With a bunching segment and a shortened first cell, the 4 + 1/2 cell RF gun produced in CAEP has been proved experimentally to be effective in reducing electron back bombardment. The analysis of the electric field distribution and electron motion in bunching segment of multi-cell RF gun is presented. The electron capture efficiency and electron trajectory with different initial phase are calculated using Runge-Kutta method. The function of the bunching segment is discussed. The calculated parameters of the 4 + 1/2 cell RF gun agree well with the experimental results

Coordinated scheduling for the downlink of cloud radio-access networks

KAUST Repository

Douik, Ahmed S.

2015-09-11

This paper addresses the coordinated scheduling problem in cloud-enabled networks. Consider the downlink of a cloud-radio access network (CRAN), where the cloud is only responsible for the scheduling policy and the synchronization of the transmit frames across the connected base-stations (BS). The transmitted frame of every BS consists of several time/frequency blocks, called power-zones (PZ), maintained at fixed transmit power. The paper considers the problem of scheduling users to PZs and BSs in a coordinated fashion across the network, by maximizing a network-wide utility under the practical constraint that each user cannot be served by more than one base-station, but can be served by one or more power-zones within each base-station frame. The paper solves the problem using a graph theoretical approach by introducing the scheduling graph in which each vertex represents an association of users, PZs and BSs. The problem is formulated as a maximum weight clique, in which the weight of each vertex is the benefit of the association represented by that vertex. The paper further presents heuristic algorithms with low computational complexity. Simulation results show the performance of the proposed algorithms and suggest that the heuristics perform near optimal in low shadowing environments. © 2015 IEEE.

Design of an 8-40 GHz Antenna for the Wideband Instrument for Snow Measurements (WISM)

Science.gov (United States)

Durham, Timothy E.; Vanhille, Kenneth J.; Trent, Christopher R.; Lambert, Kevin M.; Miranda, Felix A.

2015-01-01

This poster describes the implementation of a 6x6 element, dual linear polarized array with beamformer that operates from about 8-40 GHz. It is implemented using a relatively new multi-layer microfabrication process. The beamformer includes baluns that feed dual-polarized differential antenna elements and reactive splitters that cover the full frequency range of operation. This fixed beam array (FBA) serves as the feed for a multi-band instrument designed to measure snow water equivalent (SWE) from an airborne platform known as the Wideband Instrument for Snow Measurements (WISM).

CINR Performance of Downlink Mobile WiMAX IEEE 802.16e Deployed Using Coexistence Cellular Terrestrial and HAPS

Directory of Open Access Journals (Sweden)

I. Iskandar

2014-11-01

Full Text Available Deploying WiMAX through High Altitude Platform Station (HAPS system is a new means of wireless delivery method and thus attracting much the attention in a telecommunication society. However delivering WiMAX through the terrestrial network has already been started a few years ago. Therefore, we need to look at the scenario of coexistence system both of HAPS and terrestrial in delivering WiMAX services. This paper evaluates the performance of coexistence system between cellular HAPS and terrestrial for the downlink scenario when they are transmitting WiMAX mobile 802.16e services. Our evaluation is based on the performance simulation of coexistence model using two methods. First method is a footprint exchange between the two systems.The second method is a combination of footprint exchange and HAPS footprint enhancement. The proposed methodsare then evaluated by computer simulation in terms of carrier to interference plus noise ratio (CINR performance. In general, both methods resulting performance enhancement in CINR quality compared with coexistence deployment with normal scenario of the cell configuration used by HAPS and terrestrial. The method of combining footprint exchange and HAPS footprint enhancement is able to improve CINR more than 10 dB compared with the normal footprint configuration for all users location inside the coverage.

Mode Theory of Multi-Armed Spiral Antennas and Its Application to Electronic Warfare Antennas

Science.gov (United States)

Radway, Matthew J.

with exceptionally stable and clean radiation patterns without use of an absorbing cavity. The multiarming technique allows the spiral to retain its pattern integrity at frequencies well below those of comparable two-armed spiral antennas. A quadrifilar helix-type of end-loading is applied to the end of the spiral, resulting in dramatically-improved low-frequency gain. Careful application of resistive end-loading allows good impedance matching at frequencies as low as one-half of the Mode 1 cutoff frequency, while providing acceptable radiation efficiency due to effective use of the available antenna volume. A novel dual-layering technique for reducing the spiral's modal impedance is presented, allowing the antenna to present a good impedance match to a 50 ohm system. The third application of mode theory has been to exploit the wideband multi-mode capability of the multi-armed spiral antenna to implement a simple wide-band radiation pattern nulling technique on a multi-armed spiral antenna. It is shown that wideband nulling is possible and that, in contrast to traditional array antennas, grating lobes do not appear even over extremely wide bandwidths. Simple techniques for addressing the phenomenon of null rotation with frequency are discussed. Finally, mode theory has been used to analyze beamformer non-idealities. This has led to the revelation that the spectral distribution of beamformer errors is at least as important as the magnitude of those errors. Proper choice of beamformer topology can result in noticeable improvement in the antenna performance.

A three dimensional anatomical view of oscillatory resting-state activity and functional connectivity in Parkinson's disease related dementia: An MEG study using atlas-based beamforming

NARCIS (Netherlands)

Ponsen, M.M.; Stam, C.J.; Bosboom, J.L.W.; Berendse, H.W.; Hillebrand, A.

2013-01-01

Parkinson's disease (PD) related dementia (PDD) develops in up to 80% of PD patients. The present study was performed to further unravel the underlying pathophysiological mechanisms by applying a new analysis approach that uses an atlas-based MEG beamformer to provide a detailed anatomical mapping

Effects of line fiducial parameters and beamforming on ultrasound calibration.

Science.gov (United States)

Ameri, Golafsoun; Baxter, John S H; McLeod, A Jonathan; Peters, Terry M; Chen, Elvis C S

2017-01-01

Ultrasound (US)-guided interventions are often enhanced via integration with an augmented reality environment, a necessary component of which is US calibration. Calibration requires the segmentation of fiducials, i.e., a phantom, in US images. Fiducial localization error (FLE) can decrease US calibration accuracy, which fundamentally affects the total accuracy of the interventional guidance system. Here, we investigate the effects of US image reconstruction techniques as well as phantom material and geometry on US calibration. It was shown that the FLE was reduced by 29% with synthetic transmit aperture imaging compared with conventional B-mode imaging in a Z-bar calibration, resulting in a 10% reduction of calibration error. In addition, an evaluation of a variety of calibration phantoms with different geometrical and material properties was performed. The phantoms included braided wire, plastic straws, and polyvinyl alcohol cryogel tubes with different diameters. It was shown that these properties have a significant effect on calibration error, which is a variable based on US beamforming techniques. These results would have important implications for calibration procedures and their feasibility in the context of image-guided procedures.

Performance of velocity vector estimation using an improved dynamic beamforming setup

DEFF Research Database (Denmark)

Munk, Peter; Jensen, Jørgen Arendt

2001-01-01

control of the acoustic field, based on the Pulsed Plane Wave Decomposition (PPWD), is presented. The PPWD gives an unambigious relation between a given acoustic field and the time functions needed on an array transducer for transmission. Applying this method for the receive beamformation results in a set...... and experimental data. The simulation setup is an attempt to approximate the situation present when performing a scanning of the carotid artery with a linear array. Measurement of the flow perpendicular to the emission direction is possible using the approach of transverse spatial modulation. This is most often...... the case in a scanning of the carotid artery, where the situation is handled by an angled Doppler setup in the present ultrasound scanners. The modulation period of 2 mm is controlled for a range of 20-40 mm which covers the typical range of the carotid artery. A 6 MHz array on a 128-channel system...

A Multi-Modality CMOS Sensor Array for Cell-Based Assay and Drug Screening.

Science.gov (United States)

Chi, Taiyun; Park, Jong Seok; Butts, Jessica C; Hookway, Tracy A; Su, Amy; Zhu, Chengjie; Styczynski, Mark P; McDevitt, Todd C; Wang, Hua

2015-12-01

In this paper, we present a fully integrated multi-modality CMOS cellular sensor array with four sensing modalities to characterize different cell physiological responses, including extracellular voltage recording, cellular impedance mapping, optical detection with shadow imaging and bioluminescence sensing, and thermal monitoring. The sensor array consists of nine parallel pixel groups and nine corresponding signal conditioning blocks. Each pixel group comprises one temperature sensor and 16 tri-modality sensor pixels, while each tri-modality sensor pixel can be independently configured for extracellular voltage recording, cellular impedance measurement (voltage excitation/current sensing), and optical detection. This sensor array supports multi-modality cellular sensing at the pixel level, which enables holistic cell characterization and joint-modality physiological monitoring on the same cellular sample with a pixel resolution of 80 μm × 100 μm. Comprehensive biological experiments with different living cell samples demonstrate the functionality and benefit of the proposed multi-modality sensing in cell-based assay and drug screening.

Hydrogen passivation of multi-crystalline silicon solar cells

Institute of Scientific and Technical Information of China (English)

胡志华; 廖显伯; 刘祖明; 夏朝凤; 陈庭金

2003-01-01

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper.Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.

Analytical Evaluation of Chunk-Based Tractable Multi-cell OFDMA system

Directory of Open Access Journals (Sweden)

P.Kavitha

2018-04-01

Full Text Available This paper evaluates thoroughly the performance of multi-cell OFDMA system. The two types of deployment in multi-cell OFDMA system, such as Strict Fractional Frequency Reuse (FFR and Soft FFR (SFR were evaluated. In order to model the base station locations, homogeneous Poisson point processes were used, i.e. tractable model instead of hexagonal grid was considered. In order to reduce complexity, chunk-based resource allocation scheme was embedded. Each cell divides the users into the users of the central cell area and the users of the cell edge area according to their average received Signal to Interference and Noise Ratio (SINR compared with FFR threshold. The primary stage of the analysis includes the spectral efficiency’s expression deriving from these two deployment scenarios, followed by the analysis with the use of coverage probability. However, the improvement of spectral efficiency is achieved in the case of SFR. On the contrary, coverage probability is far improved by using strict FFR scheme. Through numerical anaysis, We have shown that the optimal FFR threshold to achieve the highest spectral efficiency was 12 dB for both Strict FFR as well as SFR.

Application Research of Horn Array Multi-Beam Antenna in Reference Source System for Satellite Interference Location

Science.gov (United States)

Zhou, Ping; Lin, Hui; Zhang, Qi

2018-01-01

The reference source system is a key factor to ensure the successful location of the satellite interference source. Currently, the traditional system used a mechanical rotating antenna which leaded to the disadvantages of slow rotation and high failure-rate, which seriously restricted the system’s positioning-timeliness and became its obvious weaknesses. In this paper, a multi-beam antenna scheme based on the horn array was proposed as a reference source for the satellite interference location, which was used as an alternative to the traditional reference source antenna. The new scheme has designed a small circularly polarized horn antenna as an element and proposed a multi-beamforming algorithm based on planar array. Moreover, the simulation analysis of horn antenna pattern, multi-beam forming algorithm and simulated satellite link cross-ambiguity calculation have been carried out respectively. Finally, cross-ambiguity calculation of the traditional reference source system has also been tested. The comparison between the results of computer simulation and the actual test results shows that the scheme is scientific and feasible, obviously superior to the traditional reference source system.

A Measure Based on Beamforming Power for Evaluation of Sound Field Reproduction Performance

DEFF Research Database (Denmark)

Chang, Ji-ho; Jeong, Cheol-Ho

2017-01-01

This paper proposes a measure to evaluate sound field reproduction systems with an array of loudspeakers. The spatially-averaged squared error of the sound pressure between the desired and the reproduced field, namely the spatial error, has been widely used, which has considerable problems in two...... conditions. First, in non-anechoic conditions, room reflections substantially deteriorate the spatial error, although these room reflections affect human localization to a lesser degree. Second, for 2.5-dimensional reproduction of spherical waves, the spatial error increases consistently due...... to the difference in the amplitude decay rate, whereas the degradation of human localization performance is limited. The measure proposed in this study is based on the beamforming powers of the desired and the reproduced fields. Simulation and experimental results show that the proposed measure is less sensitive...

Near-optimal downlink precoding for two-tier priority-based wireless networks

KAUST Repository

Park, Kihong; Alouini, Mohamed-Slim

2015-01-01

In this paper, we study a two-tier priority-based wireless cellular network in which the primary base station (BS) has multiple antennas and the other terminals have a single antenna. We assume that we have two classes of users: high priority users and low priority users. We consider a rate maximization problem of the low priority users under signal-to-interference-plus-noise-ratio constraints on the high priority user to guarantee a certain quality-of-service for the high priority user. Since the interference due to the low priority users which communicate with each other via direct transmission may severely degrade the performance of the high priority user, we propose a BS-aided two-way relaying approach in which the BS helps relay the low priority users' signals instead of allowing them to communicate with each other via a direct path between them. In addition, an algorithm to find a near-optimal beamforming solution at the BS is proposed. The asymptotic results in the high power regime are derived to verify the average sum rate performance in the proposed scheme. Finally, based on some selected numerical results, we show that the proposed scheme outperforms the direct transmission scheme over a wide transmit power range.

Near-optimal downlink precoding for two-tier priority-based wireless networks

KAUST Repository

Park, Kihong

2015-02-01

In this paper, we study a two-tier priority-based wireless cellular network in which the primary base station (BS) has multiple antennas and the other terminals have a single antenna. We assume that we have two classes of users: high priority users and low priority users. We consider a rate maximization problem of the low priority users under signal-to-interference-plus-noise-ratio constraints on the high priority user to guarantee a certain quality-of-service for the high priority user. Since the interference due to the low priority users which communicate with each other via direct transmission may severely degrade the performance of the high priority user, we propose a BS-aided two-way relaying approach in which the BS helps relay the low priority users\\' signals instead of allowing them to communicate with each other via a direct path between them. In addition, an algorithm to find a near-optimal beamforming solution at the BS is proposed. The asymptotic results in the high power regime are derived to verify the average sum rate performance in the proposed scheme. Finally, based on some selected numerical results, we show that the proposed scheme outperforms the direct transmission scheme over a wide transmit power range.

A Low-Complexity UEP Methodology Demonstrated on a Turbo-Encoded Wavelet Image Satellite Downlink

Directory of Open Access Journals (Sweden)

Salemi Eric

2008-01-01

Full Text Available Realizing high-quality digital image transmission via a satellite link, while optimizing resource distribution and minimizing battery consumption, is a challenging task. This paper describes a methodology to optimize a turbo-encoded wavelet-based satellite downlink progressive image transmission system with unequal error protection (UEP techniques. To achieve that goal, we instantiate a generic UEP methodology onto the system, and demonstrate that the proposed solution has little impact on the average performance, while greatly reducing the run-time complexity. Based on a simple design-time distortion model and a low-complexity run-time algorithm, the provided solution can dynamically tune the system's configuration to any bitrate constraint or channel condition. The resulting system outperforms in terms of peak signal-to-noise ratio (PSNR, a state-of-the-art, fine-tuned equal error protection (EEP solution by as much as 2 dB.

A Low-Complexity UEP Methodology Demonstrated on a Turbo-Encoded Wavelet Image Satellite Downlink

Directory of Open Access Journals (Sweden)

Eric Salemi

2008-01-01

Full Text Available Realizing high-quality digital image transmission via a satellite link, while optimizing resource distribution and minimizing battery consumption, is a challenging task. This paper describes a methodology to optimize a turbo-encoded wavelet-based satellite downlink progressive image transmission system with unequal error protection (UEP techniques. To achieve that goal, we instantiate a generic UEP methodology onto the system, and demonstrate that the proposed solution has little impact on the average performance, while greatly reducing the run-time complexity. Based on a simple design-time distortion model and a low-complexity run-time algorithm, the provided solution can dynamically tune the system's configuration to any bitrate constraint or channel condition. The resulting system outperforms in terms of peak signal-to-noise ratio (PSNR, a state-of-the-art, fine-tuned equal error protection (EEP solution by as much as 2 dB.

A large multi-cell threshold gas Cerenkov counter

International Nuclear Information System (INIS)

Declais, Y.; Aubert, J.J.; Bassompierre, G.; Payre, P.; Thenard, J.M.; Urban, L.

1980-08-01

A large multi-cell threshold gas Cerenkov counter consisting of 78 cells has been built for use in a high energy muon scattering experiment at CERN (European Muon Collaboration). It is used with neon, nitrogen or a mixture of those two gases, allowing the pion threshold to be varied between 6 and 20 GeV/c. The sensitive region of the counter has a length of 4.0 m and entrance and exit windows of 1.1 x 2.4 m 2 and 2.4 x 5.0 m 2 , respectively

Relay-aided multi-cell broadcasting with random network coding

DEFF Research Database (Denmark)

Lu, Lu; Sun, Fan; Xiao, Ming

2010-01-01

We investigate a relay-aided multi-cell broadcasting system using random network codes, where the focus is on devising efficient scheduling algorithms between relay and base stations. Two scheduling algorithms are proposed based on different feedback strategies; namely, a one-step scheduling...

Max-Min SINR in Large-Scale Single-Cell MU-MIMO: Asymptotic Analysis and Low Complexity Transceivers

KAUST Repository

Sifaou, Houssem; Kammoun, Abla; Sanguinetti, Luca; Debbah, Merouane; Alouini, Mohamed-Slim

2016-01-01

This work focuses on the downlink and uplink of large-scale single-cell MU-MIMO systems in which the base station (BS) endowed with M antennas communicates with K single-antenna user equipments (UEs). Particularly, we aim at reducing the complexity

Rapid fabricating technique for multi-layered human hepatic cell sheets by forceful contraction of the fibroblast monolayer.

Directory of Open Access Journals (Sweden)

Yusuke Sakai

Full Text Available Cell sheet engineering is attracting attention from investigators in various fields, from basic research scientists to clinicians focused on regenerative medicine. However, hepatocytes have a limited proliferation potential in vitro, and it generally takes a several days to form a sheet morphology and multi-layered sheets. We herein report our rapid and efficient technique for generating multi-layered human hepatic cell (HepaRG® cell sheets using pre-cultured fibroblast monolayers derived from human skin (TIG-118 cells as a feeder layer on a temperature-responsive culture dish. Multi-layered TIG-118/HepaRG cell sheets with a thick morphology were harvested on day 4 of culturing HepaRG cells by forceful contraction of the TIG-118 cells, and the resulting sheet could be easily handled. In addition, the human albumin and alpha 1-antitrypsin synthesis activities of TIG-118/HepaRG cells were approximately 1.2 and 1.3 times higher than those of HepaRG cells, respectively. Therefore, this technique is considered to be a promising modality for rapidly fabricating multi-layered human hepatocyte sheets from cells with limited proliferation potential, and the engineered cell sheet could be used for cell transplantation with highly specific functions.

An Approach to Optimum Joint Beamforming Design in a MIMO-OFDM Multiuser System

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Pascual-Iserte Antonio

2004-01-01

Full Text Available This paper describes a multiuser scenario with several terminals acceding simultaneously to the same frequency channel. The objective is to design an optimal multiuser system that may be used as a comparative framework when evaluating other suboptimal solutions and to contribute to the already published works on this topic. The present work assumes that a centralized manager knows perfectly all the channel responses between all the terminals. According to this, the transmitters and receivers, using antenna arrays and leading to the so-called multiple-input-multiple-output (MIMO channels, are designed in a joint beamforming approach, attempting to minimize the total transmit power subject to quality of service (QoS constraints. Since this optimization problem is not convex, the use of the simulated annealing (SA technique is proposed to find the optimum solution.

Site-Specific Study of In-Building Wireless Solutions with Poisson Traffic

DEFF Research Database (Denmark)

Liu, Zhen; Sørensen, Troels Bundgaard; Mogensen, Preben

2011-01-01

Due to the poor outdoor-to-indoor propagation into buildings, dedicated wireless systems installed inside the buildings is often preferred for providing indoor users with high-data-rate services. We study the typical in-building wireless solutions - distributed antenna system and small cell Femto...... system - together with another multi-cell system using our proposed centralized scheduling scheme. In our previous work, their performance is evaluated and compared in the LTE downlink context with full buffer traffic. Compared to real mobile networks, the full buffer traffic model is usually a worst...

Compressive MIMO Beamforming of Data Collected in a Refractive Environment

Science.gov (United States)

Wagner, Mark; Nannuru, Santosh; Gerstoft, Peter

2017-12-01

The phenomenon of ducting is caused by abnormal atmospheric refractivity patterns and is known to allow electromagnetic waves to propagate over the horizon with unusually low propagation loss. It is unknown what effect ducting has on multiple input multiple output (MIMO) channels, particularly its effect on multipath propagation in MIMO channels. A high-accuracy angle-of-arrival and angle-of-departure estimation technique for MIMO communications, which we will refer to as compressive MIMO beamforming, was tested on simulated data then applied to experimental data taken from an over the horizon MIMO test bed located in a known ducting hot spot in Southern California. The multipath channel was estimated from the receiver data recorded over a period of 18 days, and an analysis was performed on the recorded data. The goal is to observe the evolution of the MIMO multipath channel as atmospheric ducts form and dissipate to gain some understanding of the behavior of channels in a refractive environment. This work is motivated by the idea that some multipath characteristics of MIMO channels within atmospheric ducts could yield important information about the duct.

Cognitive two-way relay beamforming: Design with resilience to channel state uncertainties

KAUST Repository

Ubaidulla, P.

2016-07-26

In this paper, we propose a robust distributed relay beamformer design for cognitive radio network operating under uncertainties in the available channel state information. The cognitive network consists of a pair of transceivers and a set of non-regenerative two-way relays that assist the communication between the transceiver pair. The secondary nodes share the spectrum with a licensed primary user node while ensuring that the interference to the primary receiver is maintained below a certain threshold. The proposed robust design maximizes the worst-case signal-to-interference-plus-noise ratio at the secondary transceivers while satisfying constraints on the interference to the primary user and on the total relay transmit power. Though the robust design problem is not a convex problem in its original form, we show that it can be reformulated as a convex optimization problem, which can be solved efficiently. Numerical results are provided and illustrate the merits of the proposed design for various operating conditions and parameters. © 2016 IEEE.

A Utility-Based Downlink Radio Resource Allocation for Multiservice Cellular DS-CDMA Networks

Directory of Open Access Journals (Sweden)

Mahdi Shabany

2007-03-01

Full Text Available A novel framework is proposed to model downlink resource allocation problem in multiservice direct-sequence code division multiple-access (DS-CDMA cellular networks. This framework is based on a defined utility function, which leads to utilizing the network resources in a more efficient way. This utility function quantifies the degree of utilization of resources. As a matter of fact, using the defined utility function, users' channel fluctuations and their delay constraints along with the load conditions of all BSs are all taken into consideration. Unlike previous works, we solve the problem with the general objective of maximizing the total network utility instead of maximizing the achieved utility of each base station (BS. It is shown that this problem is equivalent to finding the optimum BS assignment throughout the network, which is mapped to a multidimensional multiple-choice knapsack problem (MMKP. Since MMKP is NP-hard, a polynomial-time suboptimal algorithm is then proposed to develop an efficient base-station assignment. Simulation results indicate a significant performance improvement in terms of achieved utility and packet drop ratio.

Next Generation Multi-mode Remote Sensing Radar

Data.gov (United States)

National Aeronautics and Space Administration — The objective of this work is to demonstrate a new generation of digital beamforming synthetic aperture instrument technology (DBSAR-2) which has the potential of...

Demonstration of 575-Mb/s downlink and 225-Mb/s uplink bi-directional SCM-WDM visible light communication using RGB LED and phosphor-based LED.

Science.gov (United States)

Wang, Yuanquan; Wang, Yiguang; Chi, Nan; Yu, Jianjun; Shang, Huiliang

2013-01-14

We propose and experimentally demonstrate a novel full-duplex bi-directional subcarrier multiplexing (SCM)-wavelength division multiplexing (WDM) visible light communication (VLC) system based on commercially available red-green-blue (RGB) light emitting diode (LED) and phosphor-based LED (P-LED) with 575-Mb/s downstream and 225-Mb/s upstream transmission, employing various modulation orders of quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM). For the downlink, red and green colors/wavelengths are assigned to carry useful information, while blue chip is just kept lighting to maintain the white color illumination, and for the uplink, the low-cost P-LED is implemented. In this demonstration, pre-equalization and post-equalization are also adopted to compensate the severe frequency response of LEDs. Using this scheme, 4-user downlink and 1-user uplink transmission can be achieved. Furthermore, it can support more users by adjusting the bandwidth of each sub-channel. Bit error rates (BERs) of all links are below pre-forward-error-correction (pre-FEC) threshold of 3.8x 10(-3) after 66-cm free-space delivery. The results show that this scheme has great potential in the practical VLC system.

A Fair Resource Allocation Algorithm for Data and Energy Integrated Communication Networks

Directory of Open Access Journals (Sweden)

Qin Yu

2016-01-01

Full Text Available With the rapid advancement of wireless network technologies and the rapid increase in the number of mobile devices, mobile users (MUs have an increasing high demand to access the Internet with guaranteed quality-of-service (QoS. Data and energy integrated communication networks (DEINs are emerging as a new type of wireless networks that have the potential to simultaneously transfer wireless energy and information via the same base station (BS. This means that a physical BS is virtualized into two parts: one is transferring energy and the other is transferring information. The former is called virtual energy base station (eBS and the latter is named as data base station (dBS. One important issue in such setting is dynamic resource allocation. Here the resource concerned includes both power and time. In this paper, we propose a fair data-and-energy resource allocation algorithm for DEINs by jointly designing the downlink energy beamforming and a power-and-time allocation scheme, with the consideration of finite capacity batteries at MUs and power sensitivity of radio frequency (RF to direct current (DC conversion circuits. Simulation results demonstrate that our proposed algorithm outperforms the existing algorithms in terms of fairness, beamforming design, sensitivity, and average throughput.

Three-dimensional cell manipulation and patterning using dielectrophoresis via a multi-layer scaffold structure.

Science.gov (United States)

Chu, H K; Huan, Z; Mills, J K; Yang, J; Sun, D

2015-02-07

Cell manipulation is imperative to the areas of cellular biology and tissue engineering, providing them a useful tool for patterning cells into cellular patterns for different analyses and applications. This paper presents a novel approach to perform three-dimensional (3D) cell manipulation and patterning with a multi-layer engineered scaffold. This scaffold structure employed dielectrophoresis as the non-contact mechanism to manipulate cells in the 3D domain. Through establishing electric fields via this multi-layer structure, the cells in the medium became polarized and were attracted towards the interior part of the structure, forming 3D cellular patterns. Experiments were conducted to evaluate the manipulation and the patterning processes with the proposed structure. Results show that with the presence of a voltage input, this multi-layer structure was capable of manipulating different types of biological cells examined through dielectrophoresis, enabling automatic cell patterning in the time-scale of minutes. The effects of the voltage input on the resultant cellular pattern were examined and discussed. Viability test was performed after the patterning operation and the results confirmed that majority of the cells remained viable. After 7 days of culture, 3D cellular patterns were observed through SEM. The results suggest that this scaffold and its automated dielectrophoresis-based patterning mechanism can be used to construct artificial tissues for various tissue engineering applications.

Fluctuations of the peak current of tunnel diodes in multi-junction solar cells

International Nuclear Information System (INIS)

Jandieri, K; Baranovskii, S D; Stolz, W; Gebhard, F; Guter, W; Hermle, M; Bett, A W

2009-01-01

Interband tunnel diodes are widely used to electrically interconnect the individual subcells in multi-junction solar cells. Tunnel diodes have to operate at high current densities and low voltages, especially when used in concentrator solar cells. They represent one of the most critical elements of multi-junction solar cells and the fluctuations of the peak current in the diodes have an essential impact on the performance and reliability of the devices. Recently we have found that GaAs tunnel diodes exhibit extremely high peak currents that can be explained by resonant tunnelling through defects homogeneously distributed in the junction. Experiments evidence rather large fluctuations of the peak current in the diodes fabricated from the same wafer. It is a challenging task to clarify the reason for such large fluctuations in order to improve the performance of the multi-junction solar cells. In this work we show that the large fluctuations of the peak current in tunnel diodes can be caused by relatively small fluctuations of the dopant concentration. We also show that the fluctuations of the peak current become smaller for deeper energy levels of the defects responsible for the resonant tunnelling.

Cell motility dynamics: a novel segmentation algorithm to quantify multi-cellular bright field microscopy images.

Directory of Open Access Journals (Sweden)

Assaf Zaritsky

Full Text Available Confocal microscopy analysis of fluorescence and morphology is becoming the standard tool in cell biology and molecular imaging. Accurate quantification algorithms are required to enhance the understanding of different biological phenomena. We present a novel approach based on image-segmentation of multi-cellular regions in bright field images demonstrating enhanced quantitative analyses and better understanding of cell motility. We present MultiCellSeg, a segmentation algorithm to separate between multi-cellular and background regions for bright field images, which is based on classification of local patches within an image: a cascade of Support Vector Machines (SVMs is applied using basic image features. Post processing includes additional classification and graph-cut segmentation to reclassify erroneous regions and refine the segmentation. This approach leads to a parameter-free and robust algorithm. Comparison to an alternative algorithm on wound healing assay images demonstrates its superiority. The proposed approach was used to evaluate common cell migration models such as wound healing and scatter assay. It was applied to quantify the acceleration effect of Hepatocyte growth factor/scatter factor (HGF/SF on healing rate in a time lapse confocal microscopy wound healing assay and demonstrated that the healing rate is linear in both treated and untreated cells, and that HGF/SF accelerates the healing rate by approximately two-fold. A novel fully automated, accurate, zero-parameters method to classify and score scatter-assay images was developed and demonstrated that multi-cellular texture is an excellent descriptor to measure HGF/SF-induced cell scattering. We show that exploitation of textural information from differential interference contrast (DIC images on the multi-cellular level can prove beneficial for the analyses of wound healing and scatter assays. The proposed approach is generic and can be used alone or alongside traditional

Cell motility dynamics: a novel segmentation algorithm to quantify multi-cellular bright field microscopy images.

Science.gov (United States)

Zaritsky, Assaf; Natan, Sari; Horev, Judith; Hecht, Inbal; Wolf, Lior; Ben-Jacob, Eshel; Tsarfaty, Ilan

2011-01-01

Confocal microscopy analysis of fluorescence and morphology is becoming the standard tool in cell biology and molecular imaging. Accurate quantification algorithms are required to enhance the understanding of different biological phenomena. We present a novel approach based on image-segmentation of multi-cellular regions in bright field images demonstrating enhanced quantitative analyses and better understanding of cell motility. We present MultiCellSeg, a segmentation algorithm to separate between multi-cellular and background regions for bright field images, which is based on classification of local patches within an image: a cascade of Support Vector Machines (SVMs) is applied using basic image features. Post processing includes additional classification and graph-cut segmentation to reclassify erroneous regions and refine the segmentation. This approach leads to a parameter-free and robust algorithm. Comparison to an alternative algorithm on wound healing assay images demonstrates its superiority. The proposed approach was used to evaluate common cell migration models such as wound healing and scatter assay. It was applied to quantify the acceleration effect of Hepatocyte growth factor/scatter factor (HGF/SF) on healing rate in a time lapse confocal microscopy wound healing assay and demonstrated that the healing rate is linear in both treated and untreated cells, and that HGF/SF accelerates the healing rate by approximately two-fold. A novel fully automated, accurate, zero-parameters method to classify and score scatter-assay images was developed and demonstrated that multi-cellular texture is an excellent descriptor to measure HGF/SF-induced cell scattering. We show that exploitation of textural information from differential interference contrast (DIC) images on the multi-cellular level can prove beneficial for the analyses of wound healing and scatter assays. The proposed approach is generic and can be used alone or alongside traditional fluorescence single-cell

Groundwater management under uncertainty using a stochastic multi-cell model

Science.gov (United States)

Joodavi, Ata; Zare, Mohammad; Ziaei, Ali Naghi; Ferré, Ty P. A.

2017-08-01

The optimization of spatially complex groundwater management models over long time horizons requires the use of computationally efficient groundwater flow models. This paper presents a new stochastic multi-cell lumped-parameter aquifer model that explicitly considers uncertainty in groundwater recharge. To achieve this, the multi-cell model is combined with the constrained-state formulation method. In this method, the lower and upper bounds of groundwater heads are incorporated into the mass balance equation using indicator functions. This provides expressions for the means, variances and covariances of the groundwater heads, which can be included in the constraint set in an optimization model. This method was used to formulate two separate stochastic models: (i) groundwater flow in a two-cell aquifer model with normal and non-normal distributions of groundwater recharge; and (ii) groundwater management in a multiple cell aquifer in which the differences between groundwater abstractions and water demands are minimized. The comparison between the results obtained from the proposed modeling technique with those from Monte Carlo simulation demonstrates the capability of the proposed models to approximate the means, variances and covariances. Significantly, considering covariances between the heads of adjacent cells allows a more accurate estimate of the variances of the groundwater heads. Moreover, this modeling technique requires no discretization of state variables, thus offering an efficient alternative to computationally demanding methods.

Automatic Loss Adjustment for CDMA2000 and 1xEV-DO Standard for Downlink and Uplink

Directory of Open Access Journals (Sweden)

Jiri Kominek

2014-01-01

Full Text Available The functional and thermal testing of the mobile phone is always performed under various conditions that vary in terms of the connection between the DUT (Device Under Test and the measuring instrument. To achieve repeatable measurements under such conditions, it is necessary to adjust uplink and downlink loss using the instrument's external attenuation. While for GSM, WCDMA and LTE this is a relatively easy task, CDMA2000 and 1xEV-DO make automation of the adjustment process somewhat challenging due to the nature of the CDMA standard. An especially forward link is more complicated as those tests are run in signaling mode and not all instruments provide an FER value measured by an MS. This paper describes the algorithm for forward link loss adjustment and its implementation using Rohde & Schwarz CMW500.

Multi-bits memory cell using degenerated magnetic states in a synthetic antiferromagnetic reference layer

International Nuclear Information System (INIS)

Fukushima, Akio; Yakushiji, Kay; Konoto, Makoto; Kubota, Hitoshi; Imamura, Hiroshi; Yuasa, Shinji

2016-01-01

We newly developed a magnetic memory cell having multi-bit function. The memory cell composed of a perpendicularly magnetized magnetic tunnel junction (MB-pMTJ) and a synthetic antiferromagnetic reference layer. The multi-bit function is realized by combining the freedom of states of the magnetic free layer and that in the antiferromagnetically coupled reference layer. The structure of the reference layer is (FeB/Ta/[Co/Pt]_3)/Ru/([Co/Pt]_6); the top and the bottom layers are coupled through Ru layer where the reference layer has two degrees of freedom of a head-to-head and a bottom-to-bottom magnetic configuration. A four-state memory cell is realized by combination of both degrees of freedom. The states in the reference layer however is hardly detected by the total resistance of MB-pMTJ, because the magnetoresistance effect in the reference layer is negligibly small. That implies that the resistance values for the different states in the reference layer are degenerated. On the other hand, the two different states in the reference layer bring different stray fields to the free layer, which generate two different minor loop with different switching fields. Therefore, the magnetic states in the reference layer can be differentiated by the two-step reading, before and after applying the appropriately pulsed magnetic field which can identify the initial state in the reference layer. This method is similar to distinguishing different magnetic states in an in-plane magnetized spin-valve element. We demonstrated that four different states in the MB-pMTJ can be distinguished by the two-step read-out. The important feature of the two-step reading is a practically large operation margins (large resistance change in reading) which is equal to that of a single MTJ. Even though the two-step reading is a destructive method by which 50% of the magnetic state is changed, this MB-pMTJ is promising for high density non-volatile memory cell with a minor cost of operation speed

Solar energy converters based on multi-junction photoemission solar cells.

Science.gov (United States)

Tereshchenko, O E; Golyashov, V A; Rodionov, A A; Chistokhin, I B; Kislykh, N V; Mironov, A V; Aksenov, V V

2017-11-23

Multi-junction solar cells with multiple p-n junctions made of different semiconductor materials have multiple bandgaps that allow reducing the relaxation energy loss and substantially increase the power-conversion efficiency. The choice of materials for each sub-cell is very limited due to the difficulties in extracting the current between the layers caused by the requirements for lattice- and current-matching. We propose a new vacuum multi-junction solar cell with multiple p-n junctions separated by vacuum gaps that allow using different semiconductor materials as cathode and anode, both activated to the state of effective negative electron affinity (NEA). In this work, the compact proximity focused vacuum tube with the GaAs(Cs,O) photocathode and AlGaAs/GaAs-(Cs,O) anode with GaAs quantum wells (QWs) is used as a prototype of a vacuum single-junction solar cell. The photodiode with the p-AlGaAs/GaAs anode showed the spectral power-conversion efficiency of about 1% at V bias  = 0 in transmission and reflection modes, while, at V bias  = 0.5 V, the efficiency increased up to 10%. In terms of energy conservation, we found the condition at which the energy cathode-to-anode transition was close to 1. Considering only the energy conservation part, the NEA-cell power-conversion efficiency can rich a quantum yield value which is measured up to more than 50%.

A 15-meter Multi-Gigabit W-band Bidirectional Wireless Bridge in Fiber-Optic Access Networks

DEFF Research Database (Denmark)

Pang, Xiaodan; Vegas Olmos, Juan José; Lebedev, Alexander

2013-01-01

. The down-converted signal is re-modulated on to the lightwave and transmit further through the fiber-optic system. In the uplink, both up-and down-conversion are performed by electrical means. Furthermore, we investigate both passive and active wireless transmitters in this work for both downlink......We present a bidirectional wireless bridge in the W-band enabling the seamless convergence between the wireless and fiber-optic access networks. In the downlink, a 16 Gbit/s QPSK signal is photonically up-converted at the wireless transmitter and electrically down-converted at the wireless receiver...... and uplink transmissions. With an active wireless transmitter, up to 15 meters wireless transmission is successfully achieved with a BER below the 7% FEC limit in the downlink....

Resonant-frequency discharge in a multi-cell radio frequency cavity

International Nuclear Information System (INIS)

Popović, S.; Upadhyay, J.; Nikolić, M.; Vušković, L.; Mammosser, J.

2014-01-01

We are reporting experimental results on a microwave discharge operating at resonant frequency in a multi-cell radio frequency (RF) accelerator cavity. Although the discharge operated at room temperature, the setup was constructed so that it could be used for plasma generation and processing in fully assembled active superconducting radio-frequency cryo-module. This discharge offers a mechanism for removal of a variety of contaminants, organic or oxide layers, and residual particulates from the interior surface of RF cavities through the interaction of plasma-generated radicals with the cavity walls. We describe resonant RF breakdown conditions and address the issues related to resonant detuning due to sustained multi-cell cavity plasma. We have determined breakdown conditions in the cavity, which was acting as a plasma vessel with distorted cylindrical geometry. We discuss the spectroscopic data taken during plasma removal of contaminants and use them to evaluate plasma parameters, characterize the process, and estimate the volatile contaminant product removal

Resonant-frequency discharge in a multi-cell radio frequency cavity

Energy Technology Data Exchange (ETDEWEB)

Popovic, S; Upadhyay, J; Mammosser, J; Nikolic, M; Vuskovic, L

2014-11-07

We are reporting experimental results on microwave discharge operating at resonant frequency in a multi-cell radio frequency (RF) accelerator cavity. Although the discharge operated at room temperature, the setup was constructed so that it could be used for plasma generation and processing in fully assembled active superconducting radio-frequency (SRF) cryomodule (in situ operation). This discharge offers an efficient mechanism for removal of a variety of contaminants, organic or oxide layers, and residual particulates from the interior surface of RF cavities through the interaction of plasma-generated radicals with the cavity walls. We describe resonant RF breakdown conditions and address the problems related to generation and sustaining the multi-cell cavity plasma, which are breakdown and resonant detuning. We have determined breakdown conditions in the cavity, which was acting as a plasma vessel with distorted cylindrical geometry. We discuss the spectroscopic data taken during plasma removal of contaminants and use them to evaluate plasma parameters, characterize the process, and estimate the volatile contaminant product removal.

Frequency-domain beamformers using conjugate gradient techniques for speech enhancement.

Science.gov (United States)

Zhao, Shengkui; Jones, Douglas L; Khoo, Suiyang; Man, Zhihong

2014-09-01

A multiple-iteration constrained conjugate gradient (MICCG) algorithm and a single-iteration constrained conjugate gradient (SICCG) algorithm are proposed to realize the widely used frequency-domain minimum-variance-distortionless-response (MVDR) beamformers and the resulting algorithms are applied to speech enhancement. The algorithms are derived based on the Lagrange method and the conjugate gradient techniques. The implementations of the algorithms avoid any form of explicit or implicit autocorrelation matrix inversion. Theoretical analysis establishes formal convergence of the algorithms. Specifically, the MICCG algorithm is developed based on a block adaptation approach and it generates a finite sequence of estimates that converge to the MVDR solution. For limited data records, the estimates of the MICCG algorithm are better than the conventional estimators and equivalent to the auxiliary vector algorithms. The SICCG algorithm is developed based on a continuous adaptation approach with a sample-by-sample updating procedure and the estimates asymptotically converge to the MVDR solution. An illustrative example using synthetic data from a uniform linear array is studied and an evaluation on real data recorded by an acoustic vector sensor array is demonstrated. Performance of the MICCG algorithm and the SICCG algorithm are compared with the state-of-the-art approaches.

A Measure Based on Beamforming Power for Evaluation of Sound Field Reproduction Performance

Directory of Open Access Journals (Sweden)

Ji-Ho Chang

2017-03-01

Full Text Available This paper proposes a measure to evaluate sound field reproduction systems with an array of loudspeakers. The spatially-averaged squared error of the sound pressure between the desired and the reproduced field, namely the spatial error, has been widely used, which has considerable problems in two conditions. First, in non-anechoic conditions, room reflections substantially deteriorate the spatial error, although these room reflections affect human localization to a lesser degree. Second, for 2.5-dimensional reproduction of spherical waves, the spatial error increases consistently due to the difference in the amplitude decay rate, whereas the degradation of human localization performance is limited. The measure proposed in this study is based on the beamforming powers of the desired and the reproduced fields. Simulation and experimental results show that the proposed measure is less sensitive to room reflections and the amplitude decay than the spatial error, which is likely to agree better with the human perception of source localization.

Robotic multi-well planar patch-clamp for native and primary mammalian cells

Science.gov (United States)

Milligan, Carol J; Li, Jing; Sukumar, Piruthivi; Majeed, Yasser; Dallas, Mark L; English, Anne; Emery, Paul; Porter, Karen E; Smith, Andrew M; McFadzean, Ian; Beccano-Kelly, Dayne; Bahnasi, Yahya; Cheong, Alex; Naylor, Jacqueline; Zeng, Fanning; Liu, Xing; Gamper, Nikita; Jiang, Lin-Hua; Pearson, Hugh A; Peers, Chris; Robertson, Brian; Beech, David J

2009-01-01

Multi-well robotic planar patch-clamp has become common in drug development and safety programmes because it enables efficient and systematic testing of compounds against ion channels during voltage-clamp. It has not, however, been adopted significantly in other important areas of ion channel research, where conventional patch-clamp remains the favoured method. Here we show the wider potential of the multi-well approach with the capability for efficient intracellular solution exchange, describing protocols and success rates for recording from a range of native and primary mammalian cells derived from blood vessels, arthritic joints, and the immune and central nervous systems. The protocol involves preparing a suspension of single cells to be dispensed robotically into 4-8 microfluidic chambers each containing a glass chip with a small aperture. Under automated control, giga-seals and whole-cell access are achieved followed by pre-programmed routines of voltage paradigms and fast extracellular or intracellular solution exchange. Recording from 48 chambers usually takes 1-6 hr depending on the experimental design and yields 16-33 cell recordings. PMID:19197268

Single and multi-frequency impedance characterization of symmetric activated carbon single capacitor cells

Directory of Open Access Journals (Sweden)

Suzana Sopčić

2018-05-01

Full Text Available Electrochemical impedance spectroscopy (EIS technique is used for characterization of single cell symmetric capacitors having different mass loadings of activated carbon (AC. Relevant values of charge storage capacitance (CT and internal resistance (ESR were evaluated by the single frequency and multi-frequency analyses of measured impedance spectra. Curve fittings were based on the non-ideal R-C model that takes into account the parasitic inductance, contributions from electrode materials/contacts and the effects of AC porosity. Higher CT and lower ESR values were obtained not only for the cell with higher mass of AC, but also using the single vs. multi-frequency approach. Lower CT and higher values of ESR that are generally obtained using the multi-frequency method and curve fittings should be related to the not ideal capacitive response of porous AC material and too high frequency chosen in applying the single frequency analysis.

Magnetic MIMO Signal Processing and Optimization for Wireless Power Transfer

Science.gov (United States)

Yang, Gang; Moghadam, Mohammad R. Vedady; Zhang, Rui

2017-06-01

In magnetic resonant coupling (MRC) enabled multiple-input multiple-output (MIMO) wireless power transfer (WPT) systems, multiple transmitters (TXs) each with one single coil are used to enhance the efficiency of simultaneous power transfer to multiple single-coil receivers (RXs) by constructively combining their induced magnetic fields at the RXs, a technique termed "magnetic beamforming". In this paper, we study the optimal magnetic beamforming design in a multi-user MIMO MRC-WPT system. We introduce the multi-user power region that constitutes all the achievable power tuples for all RXs, subject to the given total power constraint over all TXs as well as their individual peak voltage and current constraints. We characterize each boundary point of the power region by maximizing the sum-power deliverable to all RXs subject to their minimum harvested power constraints. For the special case without the TX peak voltage and current constraints, we derive the optimal TX current allocation for the single-RX setup in closed-form as well as that for the multi-RX setup. In general, the problem is a non-convex quadratically constrained quadratic programming (QCQP), which is difficult to solve. For the case of one single RX, we show that the semidefinite relaxation (SDR) of the problem is tight. For the general case with multiple RXs, based on SDR we obtain two approximate solutions by applying time-sharing and randomization, respectively. Moreover, for practical implementation of magnetic beamforming, we propose a novel signal processing method to estimate the magnetic MIMO channel due to the mutual inductances between TXs and RXs. Numerical results show that our proposed magnetic channel estimation and adaptive beamforming schemes are practically effective, and can significantly improve the power transfer efficiency and multi-user performance trade-off in MIMO MRC-WPT systems.

Cell growth characterization using multi-electrode bioimpedance spectroscopy

International Nuclear Information System (INIS)

Lu, Yi-Yu; Huang, Yu-Jie; Cheng, Kuo-Sheng; Huang, Ji-Jer

2013-01-01

Cell growth characterization during culturing is an important issue in a variety of biomedical applications. In this study an electrical bioimpedance spectroscopy-based multi-electrode culture monitoring system was developed to characterize cell growth. A PC12 cell line was cultured for the cell growth study. The bioimpedance variations for PC12 cell growth within the initial 12 h were measured over a range between 1 kHz and 4 MHz at three different medium concentrations. Within this frequency range, the largest bioimpedance value was 1.9 times the smallest bioimpedance value. The phase angle decreased over the range from 1 to 10 kHz when cells were growing. Then, the phase angle approached a constant over the frequency range between 10 kHz and 2 MHz. Thereafter, the phase angle increased rapidly from 20 to 52 degrees during cell culturing between 8 and 12 h at 4 MHz. The maximum cell number after culturing for 12 h increased by 25.8% for the control sites with poly-D-lysine (PDL) pastes. For the normal growth factor, the cell number increased up to 4.78 times from 8 to 12 h, but only 0.96 and 1.60 times for the other two medium growth factors. The correlation coefficients between impedance and cell number were 0.868 (coating with PDL), and 0.836 (without PDL) for the normal concentration medium. Thus, impedance may be used as an index for cell growth characterization. (paper)

Designs of precoding for LTE TDD using cell specific reference signals

DEFF Research Database (Denmark)

Sun, Fan; Lu, Lu; Sørensen, Troels Bundgaard

2010-01-01

We design non-codebook-based Multiple-Input Multiple-Output (MIMO) precoding schemes using multiple cell-specific reference signals patterns for the time division duplex (TDD) mode of LTE, where channel reciprocity can be exploited. Previously proposed non-codebookbased precoding schemes typically...... use UE specific reference signals for demodulation. Cell specific reference signals are however always allocated for the transmission of common control signalling, mobility measurements and downlink channel quality measurements. In order to save the resources occupied by UE specific reference signals...

Radiation resistant low bandgap InGaAsP solar cell for multi-junction solar cells

International Nuclear Information System (INIS)

Khan, Aurangzeb; Yamaguchi, Masafumi; Dharmaras, Nathaji; Yamada, Takashi; Tanabe, Tatsuya; Takagishi, Shigenori; Itoh, Hisayoshi; Ohshima, Takeshi

2001-01-01

We have explored the superior radiation tolerance of metal organic chemical vapor deposition (MOCVD) grown, low bandgap, (0.95eV) InGaAsP solar cells as compared to GaAs-on-Ge cells, after 1 MeV electron irradiation. The minority carrier injection due to forward bias and light illumination under low concentration ratio, can lead to enhanced recovery of radiation damage in InGaAsP n + -p junction solar cells. An injection anneal activation energy (0.58eV) of the defects involved in damage/recovery of the InGaAsP solar cells has been estimated from the resultant recovery of the solar cell properties following minority carrier injection. The results suggest that low bandgap radiation resistant InGaAsP (0.95eV) lattice matched to InP substrates provide an alternative to use as bottom cells in multi-junction solar cells instead of less radiation ressitant conventional GaAs based solar cells for space applications. (author)

Downlink Linear Precoders Based on Statistical CSI for Multicell MIMO-OFDM

Directory of Open Access Journals (Sweden)

Ebrahim Baktash

2017-01-01

Full Text Available With 5G communication systems on the horizon, efficient interference management in heterogeneous multicell networks is more vital than ever. This paper investigates the linear precoder design for downlink multicell multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM systems, where base stations (BSs coordinate to reduce the interference across space and frequency. In order to minimize the overall feedback overhead in next-generation systems, we consider precoding schemes that require statistical channel state information (CSI only. We apply the random matrix theory to approximate the ergodic weighted sum rate of the system with a closed form expression. After formulating the approximation for general channels, we reduce the results to a more compact form using the Kronecker channel model for which several multicarrier concepts such as frequency selectivity, channel tap correlations, and intercarrier interference (ICI are rigorously represented. We find the local optimal solution for the maximization of the approximate rate using a gradient method that requires only the covariance structure of the MIMO-OFDM channels. Within this covariance structure are the channel tap correlations and ICI information, both of which are taken into consideration in the precoder design. Simulation results show that the rate approximation is very accurate even for very small MIMO-OFDM systems and the proposed method converges rapidly to a near-optimal solution that competes with networked MIMO and precoders based on instantaneous full CSI.

On the Impact of Multi-User Traffic Dynamics on Low Latency Communications

DEFF Research Database (Denmark)

Gerardino, Guillermo Andrés Pocovi; Pedersen, Klaus I.; Alvarez, Beatriz Soret

2016-01-01

In this paper we study the downlink latency performance in a multi-user cellular network. We use a flexible 5G radio frame structure, where the TTI size is configurable on a per-user basis according to their specific service requirements. Results show that at low system loads using a short TTI (e.......g. 0.25 ms) is an attractive solution to achieve low latency communications (LLC). The main benefits come from the low transmission delay required to transmit the payloads. However, as the load increases, longer TTI configurations with lower relative control overhead (and therefore higher spectral...... efficiency) provide better performance as these better cope with the non-negligible queuing delay. The presented results allow to conclude that support for scheduling with different TTI sizes is important for LLC and should be included in the future 5G....

Three-dimensional wet-electrospun poly(lactic acid)/multi-wall carbon nanotubes scaffold induces differentiation of human menstrual blood-derived stem cells into germ-like cells.

Science.gov (United States)

Eyni, Hossein; Ghorbani, Sadegh; Shirazi, Reza; Salari Asl, Leila; P Beiranvand, Shahram; Soleimani, Masoud

2017-09-01

Infertility caused by the disruption or absence of germ cells is a major and largely incurable medical problem. Germ cells (i.e., sperm or egg) play a key role in the transmission of genetic and epigenetic information across generations. Generation of gametes derived in vitro from stem cells hold promising prospects which could potentially help infertile men and women. Menstrual blood-derived stem cells are a unique stem cell source. Evidence suggests that menstrual blood-derived stem cells exhibit a multi-lineage potential and have attracted extensive attention in regenerative medicine. To maintain the three-dimensional structure of natural extra cellular matrices in vitro, scaffolds can do this favor and mimic a microenvironment for cell proliferation and differentiation. According to previous studies, poly(lactic acid) and multi-wall carbon nanotubes have been introduced as novel and promising biomaterials for the proliferation and differentiation of stem cells. Some cell types have been successfully grown on a matrix containing carbon nanotubes in tissue engineering but there is no report for this material to support stem cells differentiation into germ cells lineage. This study designed a 3D wet-electrospun poly(lactic acid) and poly(lactic acid)/multi-wall carbon nanotubes composite scaffold to compare infiltration, proliferation, and differentiation potential of menstrual blood-derived stem cells toward germ cell lineage with 2D culture. Our primary data revealed that the fabricated scaffold has mechanical and biological suitable qualities for supporting and attachments of stem cells. The differentiated menstrual blood-derived stem cells tracking in scaffolds using scanning electron microscopy confirmed cell attachment, aggregation, and distribution on the porous scaffold. Based on the differentiation assay by RT-PCR analysis, stem cells and germ-like cells markers were expressed in 3D groups as well as 2D one. It seems that poly(lactic acid)/multi

GaSb solar cells grown on GaAs via interfacial misfit arrays for use in the III-Sb multi-junction cell

Science.gov (United States)

Nelson, George T.; Juang, Bor-Chau; Slocum, Michael A.; Bittner, Zachary S.; Laghumavarapu, Ramesh B.; Huffaker, Diana L.; Hubbard, Seth M.

2017-12-01

Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial misfit arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial misfit arrays could achieve higher efficiency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buffer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g efficiency of 5.5% and a 44-sun AM1.5d efficiency of 8.9%. The GaSb-on-GaAs cell was 1.0% efficient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute efficiency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the effectiveness of the GaSb junction was a function of concentration.

Progress in the development of metamorphic multi-junction III-V space solar cells

Energy Technology Data Exchange (ETDEWEB)

Sinharoy, S.; Patton, M.O.; Valko, T.M.; Weizer, V.G. [Essential Research Inc., Cleveland, OH (United States)

2002-07-01

Theoretical calculations have shown that highest-efficiency III-V multi-junction solar cells require alloy structures that cannot be grown on a lattice-matched substrate. Ever since the first demonstration of high efficiency metamorphic single-junction 1.1 and 1.2 eV InGaAs solar cells, interest has grown in the development of multi-junction cells of this type, using graded buffer layer technology. Essential Research Incorporated (ERI) is currently developing a dual-junction 1.6 eV InGaP/1.1 eV InGaAs tandem cell (projected practical air-mass zero (AMO), one-sun efficiency of 27%, and 100-sun efficiency of 31.1%) under a Ballistic Missile Defense Command (BMDO) SBIR Phase II program. A second ongoing research effort involves the development of a 2.1 eV A1GaInP/1.6 eV InGaAsP/1.2 eV InGaAs triple-junction concentrator tandem cell (projected practical AMO efficiency 36.5% under 100 suns) under a SBIR Phase II program funded by the Air Force. We are in the process of optimizing the dual-junction cell performance. For the triple-junction cell, we have developed the bottom and the middle cell, and are in the process of developing the layer structures needed for the top cell. A progress report is presented in this paper. (author)

Virtual MIMO Beamforming and Device Pairing Enabled by Device-to-Device Communications for Multidevice Networks

Directory of Open Access Journals (Sweden)

Yeonjin Jeong

2017-01-01

Full Text Available We consider a multidevice network with asymmetric antenna configurations which supports not only communications between an access point and devices but also device-to-device (D2D communications for the Internet of things. For the network, we propose the transmit and receive beamforming with the channel state information (CSI for virtual multiple-input multiple-output (MIMO enabled by D2D receive cooperation. We analyze the sum rate achieved by a device pair in the proposed method and identify the strategies to improve the sum rate of the device pair. We next present a distributed algorithm and its equivalent algorithm for device pairing to maximize the throughput of the multidevice network. Simulation results confirm the advantages of the transmit CSI and D2D cooperation as well as the validity of the distributive algorithm.

Strong adhesion of Saos-2 cells to multi-walled carbon nanotubes

International Nuclear Information System (INIS)

Matsuoka, Makoto; Akasaka, Tsukasa; Totsuka, Yasunori; Watari, Fumio

2010-01-01

In recent years, carbon nanotubes (CNTs) have been considered potential biomedical materials because of their unique character. The aim of this study was to investigate the response of a human osteoblast-like cell line - Saos-2 - on single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs). The surface of a culture dish was coated with CNTs, and Saos-2 cells were cultured for three days. Cell morphology, viability, alkaline phosphatase (ALP) activity, adhesion, and vinculin expression were evaluated. The result showed high cell viability and strong adhesion to MWCNTs. Saos-2 cultured on MWCNTs exhibited vinculin expression throughout the cell body, while the cells attached to SWCNTs and glass were mostly limited to their periphery. Our results suggest that CNT coatings promote cell activity and adhesiveness. These findings indicate that MWCNTs could be used as surface coating materials to promote cell adhesion.

A multi-scale model for correlation in B cell VDJ usage of zebrafish

International Nuclear Information System (INIS)

Pan, Keyao; Deem, Michael W

2011-01-01

The zebrafish (Danio rerio) is one of the model animals used for the study of immunology because the dynamics in the adaptive immune system of zebrafish are similar to that in higher animals. In this work, we built a multi-scale model to simulate the dynamics of B cells in the primary and secondary immune responses of zebrafish. We use this model to explain the reported correlation between VDJ usage of B cell repertoires in individual zebrafish. We use a delay ordinary differential equation (ODE) system to model the immune responses in the 6-month lifespan of a zebrafish. This mean field theory gives the number of high-affinity B cells as a function of time during an infection. The sequences of those B cells are then taken from a distribution calculated by a 'microscopic' random energy model. This generalized NK model shows that mature B cells specific to one antigen largely possess a single VDJ recombination. The model allows first-principle calculation of the probability, p, that two zebrafish responding to the same antigen will select the same VDJ recombination. This probability p increases with the B cell population size and the B cell selection intensity. The probability p decreases with the B cell hypermutation rate. The multi-scale model predicts correlations in the immune system of the zebrafish that are highly similar to that from experiment

A multi-scale model for correlation in B cell VDJ usage of zebrafish

Science.gov (United States)

Pan, Keyao; Deem, Michael W.

2011-10-01

The zebrafish (Danio rerio) is one of the model animals used for the study of immunology because the dynamics in the adaptive immune system of zebrafish are similar to that in higher animals. In this work, we built a multi-scale model to simulate the dynamics of B cells in the primary and secondary immune responses of zebrafish. We use this model to explain the reported correlation between VDJ usage of B cell repertoires in individual zebrafish. We use a delay ordinary differential equation (ODE) system to model the immune responses in the 6-month lifespan of a zebrafish. This mean field theory gives the number of high-affinity B cells as a function of time during an infection. The sequences of those B cells are then taken from a distribution calculated by a 'microscopic' random energy model. This generalized NK model shows that mature B cells specific to one antigen largely possess a single VDJ recombination. The model allows first-principle calculation of the probability, p, that two zebrafish responding to the same antigen will select the same VDJ recombination. This probability p increases with the B cell population size and the B cell selection intensity. The probability p decreases with the B cell hypermutation rate. The multi-scale model predicts correlations in the immune system of the zebrafish that are highly similar to that from experiment.

Multi-color imaging of fluorescent nanodiamonds in living HeLa cells using direct electron-beam excitation.

Science.gov (United States)

Nawa, Yasunori; Inami, Wataru; Lin, Sheng; Kawata, Yoshimasa; Terakawa, Susumu; Fang, Chia-Yi; Chang, Huan-Cheng

2014-03-17

Multi-color, high spatial resolution imaging of fluorescent nanodiamonds (FNDs) in living HeLa cells has been performed with a direct electron-beam excitation-assisted fluorescence (D-EXA) microscope. In this technique, fluorescent materials are directly excited with a focused electron beam and the resulting cathodoluminescence (CL) is detected with nanoscale resolution. Green- and red-light-emitting FNDs were employed for two-color imaging, which were observed simultaneously in the cells with high spatial resolution. This technique could be applied generally for multi-color immunostaining to reveal various cell functions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Joint interference management and resource allocation for device-to-device (D2D) communications underlying downlink/uplink decoupled (DUDe) heterogeneous networks

KAUST Repository

Celik, Abdulkadir

2017-07-31

In this paper, resource allocation and co-tier/cross-tier interference management are investigated for D2D-enabled heterogeneous networks (HetNets) where tiers 1, 2, and 3 consist of macrocells, smallcells, and D2D pairs, respectively. We first propose a D2D-enabled fractional frequency reuse scheme for uplink (UL) HetNets where macrocell subregions are preassigned to different subbands (SBs) in order to mitigate the tier-1↔tier-1 interference. Nevertheless, cell-edge macrocell user equipments (MUEs) with high transmission powers still form dead-zones for nearby smallcell UEs (SUEs) and D2D UEs (DUEs). One of the simple but yet novel means of the dead-zone alleviation is associating the cell-edge MUEs with nearby smallcells, which is also known as downlink (DL)/UL decoupling (DUDe). Subject to quality of service (QoS) requirements and power constraints, we formulate a joint SB assignment and resource block (RB) allocation optimization as a mixed integer non-linear programming (MINLP) problem to maximize the D2D sum rate and minimize the co-tier/cross-tier interference. Based on tolerable interference limit, we propose a fast yet high-performance suboptimal solution to jointly assign available SBs and RBs to smallcells. A D2D mode selection and resource allocation framework is then developed for DUEs. As traditional DL/UL Coupled (DUCo) scheme generates significant interference proportional to cellular user density and user association bias factor, results obtained from the combination of proposed methods and developed algorithms reveal the potential of DUDe for co-tier/cross-tier interference mitigation which opens more room for spectrum reuse of DUEs.

Cyclic Communication and the Inseparability of MIMO Multi-way Relay Channels

KAUST Repository

Chaaban, Anas; Sezgin, Aydin

2015-01-01

The K-user MIMO multi-way relay channel (Ychannel) consisting of K users with M antennas each and a common relay node with N antennas is studied in this paper. Each user wants to exchange messages with all the other users via the relay. A transmission strategy is proposed for this channel. The proposed strategy is based on two steps: channel diagonalization and cyclic communication. The channel diagonalization is applied by using zero-forcing beam-forming. After channel diagonalization, the channel is decomposed into parallel sub-channels. Cyclic communication is then applied, where signal-space alignment for network-coding is used over each sub-channel. The proposed strategy achieves the optimal DoF region of the channel if N M. To prove this, a new degrees-of-freedom outer bound is derived. As a by-product, we conclude that the MIMO Y-channel is not separable, i.e., independent coding on separate sub-channels is not enough, and one has to code jointly over several sub-channels.

Cyclic Communication and the Inseparability of MIMO Multi-way Relay Channels

KAUST Repository

Chaaban, Anas

2015-10-27

The K-user MIMO multi-way relay channel (Ychannel) consisting of K users with M antennas each and a common relay node with N antennas is studied in this paper. Each user wants to exchange messages with all the other users via the relay. A transmission strategy is proposed for this channel. The proposed strategy is based on two steps: channel diagonalization and cyclic communication. The channel diagonalization is applied by using zero-forcing beam-forming. After channel diagonalization, the channel is decomposed into parallel sub-channels. Cyclic communication is then applied, where signal-space alignment for network-coding is used over each sub-channel. The proposed strategy achieves the optimal DoF region of the channel if N M. To prove this, a new degrees-of-freedom outer bound is derived. As a by-product, we conclude that the MIMO Y-channel is not separable, i.e., independent coding on separate sub-channels is not enough, and one has to code jointly over several sub-channels.

A Novel Algorithm for Efficient Downlink Packet Scheduling for Multiple-Component-Carrier Cellular Systems

Directory of Open Access Journals (Sweden)

Yao-Liang Chung

2016-11-01

Full Text Available The simultaneous aggregation of multiple component carriers (CCs for use by a base station constitutes one of the more promising strategies for providing substantially enhanced bandwidths for packet transmissions in 4th and 5th generation cellular systems. To the best of our knowledge, however, few previous studies have undertaken a thorough investigation of various performance aspects of the use of a simple yet effective packet scheduling algorithm in which multiple CCs are aggregated for transmission in such systems. Consequently, the present study presents an efficient packet scheduling algorithm designed on the basis of the proportional fair criterion for use in multiple-CC systems for downlink transmission. The proposed algorithm includes a focus on providing simultaneous transmission support for both real-time (RT and non-RT traffic. This algorithm can, when applied with sufficiently efficient designs, provide adequate utilization of spectrum resources for the purposes of transmissions, while also improving energy efficiency to some extent. According to simulation results, the performance of the proposed algorithm in terms of system throughput, mean delay, and fairness constitute substantial improvements over those of an algorithm in which the CCs are used independently instead of being aggregated.

Matched-filtering generalized phase contrast using LCoS pico-projectors for beam-forming.

Science.gov (United States)

Bañas, Andrew; Palima, Darwin; Glückstad, Jesper

2012-04-23

We report on a new beam-forming system for generating high intensity programmable optical spikes using so-called matched-filtering Generalized Phase Contrast (mGPC) applying two consumer handheld pico-projectors. Such a system presents a low-cost alternative for optical trapping and manipulation, optical lattices and other beam-shaping applications usually implemented with high-end spatial light modulators. Portable pico-projectors based on liquid crystal on silicon (LCoS) devices are used as binary phase-only spatial light modulators by carefully setting the appropriate polarization of the laser illumination. The devices are subsequently placed into the object and Fourier plane of a standard 4f-setup according to the mGPC spatial filtering configuration. Having a reconfigurable spatial phase filter, instead of a fixed and fabricated one, allows the beam shaper to adapt to different input phase patterns suited for different requirements. Despite imperfections in these consumer pico-projectors, the mGPC approach tolerates phase aberrations that would have otherwise been hard to overcome by standard phase projection. © 2012 Optical Society of America

Reference Beam Pattern Design for Frequency Invariant Beamforming Based on Fast Fourier Transform

Directory of Open Access Journals (Sweden)

Wang Zhang

2016-09-01

Full Text Available In the field of fast Fourier transform (FFT-based frequency invariant beamforming (FIB, there is still an unsolved problem. That is the selection of the reference beam to make the designed wideband pattern frequency invariant (FI over a given frequency range. This problem is studied in this paper. The research shows that for a given array, the selection of the reference beam pattern is determined by the number of sensors and the ratio of the highest frequency to the lowest frequency of the signal (RHL. The length of the weight vector corresponding to a given reference beam pattern depends on the reference frequency. In addition, the upper bound of the weight length to ensure the FI property over the whole frequency band of interest is also given. When the constraints are added to the reference beam, it does not affect the FI property of the designed wideband beam as long as the symmetry of the reference beam is ensured. Based on this conclusion, a scheme for reference beam design is proposed.

Artifact removal algorithms for stroke detection using a multistatic MIST beamforming algorithm.

Science.gov (United States)

Ricci, E; Di Domenico, S; Cianca, E; Rossi, T

2015-01-01

Microwave imaging (MWI) has been recently proved as a promising imaging modality for low-complexity, low-cost and fast brain imaging tools, which could play a fundamental role to efficiently manage emergencies related to stroke and hemorrhages. This paper focuses on the UWB radar imaging approach and in particular on the processing algorithms of the backscattered signals. Assuming the use of the multistatic version of the MIST (Microwave Imaging Space-Time) beamforming algorithm, developed by Hagness et al. for the early detection of breast cancer, the paper proposes and compares two artifact removal algorithms. Artifacts removal is an essential step of any UWB radar imaging system and currently considered artifact removal algorithms have been shown not to be effective in the specific scenario of brain imaging. First of all, the paper proposes modifications of a known artifact removal algorithm. These modifications are shown to be effective to achieve good localization accuracy and lower false positives. However, the main contribution is the proposal of an artifact removal algorithm based on statistical methods, which allows to achieve even better performance but with much lower computational complexity.

Joint Utility-Based Power Control and Receive Beamforming in Decentralized Wireless Networks

Directory of Open Access Journals (Sweden)

Angela Feistel

2010-01-01

Full Text Available This paper addresses the problem of joint resource allocation in general wireless networks and its practical implementation aspects. The objective is to allocate transmit powers and receive beamformers to the users in order to maximize a network-wide utility that represents the attained QoS and is a function of the signal-to-interference ratios. This problem is much more intricate than the corresponding QoS-based power control problem. In particular, it is not known which class of utility functions allows for a convex formulation of this problem. In case of perfect synchronization, the joint power and receiver control problem can be reformulated as a power control problem under optimal receivers. Standard gradient projection methods can be applied to solve this problem. However, these algorithms are not applicable in decentralized wireless networks. Therefore, we decompose the problem and propose a convergent alternate optimization that is amenable to distributed implementation. In addition, in real-world networks noisy measurements and estimations occur. Thus, the proposed algorithm has to be investigated in the framework of stochastic approximation. We discuss practical implementation aspects of the proposed stochastic algorithm and investigate its convergence properties by simulations.

Automatic Cell Segmentation in Fluorescence Images of Confluent Cell Monolayers Using Multi-object Geometric Deformable Model.

Science.gov (United States)

Yang, Zhen; Bogovic, John A; Carass, Aaron; Ye, Mao; Searson, Peter C; Prince, Jerry L

2013-03-13

With the rapid development of microscopy for cell imaging, there is a strong and growing demand for image analysis software to quantitatively study cell morphology. Automatic cell segmentation is an important step in image analysis. Despite substantial progress, there is still a need to improve the accuracy, efficiency, and adaptability to different cell morphologies. In this paper, we propose a fully automatic method for segmenting cells in fluorescence images of confluent cell monolayers. This method addresses several challenges through a combination of ideas. 1) It realizes a fully automatic segmentation process by first detecting the cell nuclei as initial seeds and then using a multi-object geometric deformable model (MGDM) for final segmentation. 2) To deal with different defects in the fluorescence images, the cell junctions are enhanced by applying an order-statistic filter and principal curvature based image operator. 3) The final segmentation using MGDM promotes robust and accurate segmentation results, and guarantees no overlaps and gaps between neighboring cells. The automatic segmentation results are compared with manually delineated cells, and the average Dice coefficient over all distinguishable cells is 0.88.

Numerical investigation of a double-junction a:SiGe thin-film solar cell including the multi-trench region

International Nuclear Information System (INIS)

Kacha, K.; Djeffal, F.; Ferhati, H.; Arar, D.; Meguellati, M.

2015-01-01

We present a new approach based on the multi-trench technique to improve the electrical performances, which are the fill factor and the electrical efficiency. The key idea behind this approach is to introduce a new multi-trench region in the intrinsic layer, in order to modulate the total resistance of the solar cell. Based on 2-D numerical investigation and optimization of amorphous SiGe double-junction (a-Si:H/a-SiGe:H) thin film solar cells, in the present paper numerical models of electrical and optical parameters are developed to explain the impact of the multi-trench technique on the improvement of the double-junction solar cell electrical behavior for high performance photovoltaic applications. In this context, electrical characteristics of the proposed design are analyzed and compared with conventional amorphous silicon double-junction thin-film solar cells. (paper)

Synthesis of a multi-functional DNA nanosphere barcode system for direct cell detection.

Science.gov (United States)

Han, Sangwoo; Lee, Jae Sung; Lee, Jong Bum

2017-09-28

Nucleic acid-based technologies have been applied to numerous biomedical applications. As a novel material for target detection, DNA has been used to construct a barcode system with a range of structures. This paper reports multi-functionalized DNA nanospheres (DNANSs) by rolling circle amplification (RCA) with several functionalized nucleotides. DNANSs with a barcode system were designed to exhibit fluorescence for coding enhanced signals and contain biotin for more functionalities, including targeting through the biotin-streptavidin (biotin-STA) interaction. Functionalized deoxynucleotide triphosphates (dNTPs) were mixed in the RCA process and functional moieties can be expressed on the DNANSs. The anti-epidermal growth factor receptor antibodies (anti-EGFR Abs) can be conjugated on DNANSs for targeting cancer cells specifically. As a proof of concept, the potential of the multi-functional DNANS barcode was demonstrated by direct cell detection as a simple detection method. The DNANS barcode provides a new route for the simple and rapid selective recognition of cancer cells.

The effect of Cytochalasin D on F-Actin behavior of single-cell electroendocytosis using multi-chamber micro cell chip

KAUST Repository

Lin, Ran

2012-03-01

Electroendocytosis (EED) is a pulsed-electric-field (PEF) induced endocytosis, facilitating cells uptake molecules through nanometer-sized EED vesicles. We herein investigate the effect of a chemical inhibitor, Cytochalasin D (CD) on the actin-filaments (F-Actin) behavior of single-cell EED. The CD concentration (C CD) can control the depolymerization of F-actin. A multi-chamber micro cell chip was fabricated to study the EED under different conditions. Large-scale single-cell data demonstrated EED highly depends on both electric field and C CD. © 2012 IEEE.

The effect of Cytochalasin D on F-Actin behavior of single-cell electroendocytosis using multi-chamber micro cell chip

KAUST Repository

Lin, Ran; Chang, Donald C.; Lee, Yi Kuen

2012-01-01

Electroendocytosis (EED) is a pulsed-electric-field (PEF) induced endocytosis, facilitating cells uptake molecules through nanometer-sized EED vesicles. We herein investigate the effect of a chemical inhibitor, Cytochalasin D (CD) on the actin-filaments (F-Actin) behavior of single-cell EED. The CD concentration (C CD) can control the depolymerization of F-actin. A multi-chamber micro cell chip was fabricated to study the EED under different conditions. Large-scale single-cell data demonstrated EED highly depends on both electric field and C CD. © 2012 IEEE.

A method for producing transgenic cells using a multi-integrase system on a human artificial chromosome vector.

Directory of Open Access Journals (Sweden)

Shigeyuki Yamaguchi

Full Text Available The production of cells capable of expressing gene(s of interest is important for a variety of applications in biomedicine and biotechnology, including gene therapy and animal transgenesis. The ability to insert transgenes at a precise location in the genome, using site-specific recombinases such as Cre, FLP, and ΦC31, has major benefits for the efficiency of transgenesis. Recent work on integrases from ΦC31, R4, TP901-1 and Bxb1 phages demonstrated that these recombinases catalyze site-specific recombination in mammalian cells. In the present study, we examined the activities of integrases on site-specific recombination and gene expression in mammalian cells. We designed a human artificial chromosome (HAC vector containing five recombination sites (ΦC31 attP, R4 attP, TP901-1 attP, Bxb1 attP and FRT; multi-integrase HAC vector and de novo mammalian codon-optimized integrases. The multi-integrase HAC vector has several functions, including gene integration in a precise locus and avoiding genomic position effects; therefore, it was used as a platform to investigate integrase activities. Integrases carried out site-specific recombination at frequencies ranging from 39.3-96.8%. Additionally, we observed homogenous gene expression in 77.3-87.5% of colonies obtained using the multi-integrase HAC vector. This vector is also transferable to another cell line, and is capable of accepting genes of interest in this environment. These data suggest that integrases have high DNA recombination efficiencies in mammalian cells. The multi-integrase HAC vector enables us to produce transgene-expressing cells efficiently and create platform cell lines for gene expression.

Benefit of the UltraZoom beamforming technology in noise in cochlear implant users.

Science.gov (United States)

Mosnier, Isabelle; Mathias, Nathalie; Flament, Jonathan; Amar, Dorith; Liagre-Callies, Amelie; Borel, Stephanie; Ambert-Dahan, Emmanuèle; Sterkers, Olivier; Bernardeschi, Daniele

2017-09-01

The objectives of the study were to demonstrate the audiological and subjective benefits of the adaptive UltraZoom beamforming technology available in the Naída CI Q70 sound processor, in cochlear-implanted adults upgraded from a previous generation sound processor. Thirty-four adults aged between 21 and 89 years (mean 53 ± 19) were prospectively included. Nine subjects were unilaterally implanted, 11 bilaterally and 14 were bimodal users. The mean duration of cochlear implant use was 7 years (range 5-15 years). Subjects were tested in quiet with monosyllabic words and in noise with the adaptive French Matrix test in the best-aided conditions. The test setup contained a signal source in front of the subject and three noise sources at +/-90° and 180°. The noise was presented at a fixed level of 65 dB SPL and the level of speech signal was varied to obtain the speech reception threshold (SRT). During the upgrade visit, subjects were tested with the Harmony and with the Naída CI sound processors in omnidirectional microphone configuration. After a take-home phase of 2 months, tests were repeated with the Naída CI processor with and without UltraZoom. Subjective assessment of the sound quality in daily environments was recorded using the APHAB questionnaire. No difference in performance was observed in quiet between the two processors. The Matrix test in noise was possible in the 21 subjects with the better performance. No difference was observed between the two processors for performance in noise when using the omnidirectional microphone. At the follow-up session, the median SRT with the Naída CI processor with UltraZoom was -4 dB compared to -0.45 dB without UltraZoom. The use of UltraZoom improved the median SRT by 3.6 dB (p noise and for speech understanding in noise (p noise. The use of UltraZoom beamforming technology, available on the new sound processor Naída CI, improves speech performance in difficult and realistic noisy conditions when the

Characterization of cell mismatch in a multi-crystalline silicon photovoltaic module

International Nuclear Information System (INIS)

Crozier, J.L.; Dyk, E.E. van; Vorster, F.J.

2012-01-01

In this study the causes and effects of cell mismatch were identified in a multi-crystalline silicon photovoltaic module. Different techniques were used to identify the causes of the mismatch, including Electroluminescence (EL) imaging, Infrared (IR) imaging, current–voltage (I–V) characteristics, worst-case cell determination and Large Area Laser Beam Induced Current (LA-LBIC) scans. In EL images the cracked cells, broken fingers and material defects are visible. The presence of poorly contacted cells results in the formation of hot-spots. LA-LBIC line scans give the relative photoresponse of the cells in the module. However, this technique is limited due to the penetration depth of the laser beam. The worst case cell determination compares the I–V curves of the whole module with the I–V curve of the module with one cell covered, allowing the evaluation of the performance of each cell in a series-connected string. These methods allowed detection of the poorly performing cells in the module. Using all these techniques an overall view of the photoresponse in the cells and their performance is obtained.

Characterization of cell mismatch in a multi-crystalline silicon photovoltaic module

Energy Technology Data Exchange (ETDEWEB)

Crozier, J.L., E-mail: s207094248@live.nmmu.ac.za [Department of Physics, P.O. Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6031 (South Africa); Dyk, E.E. van; Vorster, F.J. [Department of Physics, P.O. Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6031 (South Africa)

2012-05-15

In this study the causes and effects of cell mismatch were identified in a multi-crystalline silicon photovoltaic module. Different techniques were used to identify the causes of the mismatch, including Electroluminescence (EL) imaging, Infrared (IR) imaging, current-voltage (I-V) characteristics, worst-case cell determination and Large Area Laser Beam Induced Current (LA-LBIC) scans. In EL images the cracked cells, broken fingers and material defects are visible. The presence of poorly contacted cells results in the formation of hot-spots. LA-LBIC line scans give the relative photoresponse of the cells in the module. However, this technique is limited due to the penetration depth of the laser beam. The worst case cell determination compares the I-V curves of the whole module with the I-V curve of the module with one cell covered, allowing the evaluation of the performance of each cell in a series-connected string. These methods allowed detection of the poorly performing cells in the module. Using all these techniques an overall view of the photoresponse in the cells and their performance is obtained.

Multi-region and single-cell sequencing reveal variable genomic heterogeneity in rectal cancer.

Science.gov (United States)

Liu, Mingshan; Liu, Yang; Di, Jiabo; Su, Zhe; Yang, Hong; Jiang, Beihai; Wang, Zaozao; Zhuang, Meng; Bai, Fan; Su, Xiangqian

2017-11-23

Colorectal cancer is a heterogeneous group of malignancies with complex molecular subtypes. While colon cancer has been widely investigated, studies on rectal cancer are very limited. Here, we performed multi-region whole-exome sequencing and single-cell whole-genome sequencing to examine the genomic intratumor heterogeneity (ITH) of rectal tumors. We sequenced nine tumor regions and 88 single cells from two rectal cancer patients with tumors of the same molecular classification and characterized their mutation profiles and somatic copy number alterations (SCNAs) at the multi-region and the single-cell levels. A variable extent of genomic heterogeneity was observed between the two patients, and the degree of ITH increased when analyzed on the single-cell level. We found that major SCNAs were early events in cancer development and inherited steadily. Single-cell sequencing revealed mutations and SCNAs which were hidden in bulk sequencing. In summary, we studied the ITH of rectal cancer at regional and single-cell resolution and demonstrated that variable heterogeneity existed in two patients. The mutational scenarios and SCNA profiles of two patients with treatment naïve from the same molecular subtype are quite different. Our results suggest each tumor possesses its own architecture, which may result in different diagnosis, prognosis, and drug responses. Remarkable ITH exists in the two patients we have studied, providing a preliminary impression of ITH in rectal cancer.

Multi-membrane chitosan hydrogels as chondrocytic cell bioreactors.

Science.gov (United States)

Ladet, S G; Tahiri, K; Montembault, A S; Domard, A J; Corvol, M-T M

2011-08-01

We investigated the bioactivity of new chitosan-based multi-membrane hydrogel (MMH) architectures towards chondrocyte-like cells. The microstructure of the hydrogels constituting the membranes precludes any living cell penetration, whereas their lower scale architecture allows the protein diffusion. The biological behavior of chondrocytes implanted within the MMH inter-membrane spaces was studied for 45 days in culture. Chondrocytes formed cell aggregates and proliferated without loosing their chondrogenic phenotype as illustrated by collagen II and aggrecan expressions at the mRNA and protein levels. Cells produced neo-formed alcyan blue matrix proteins filling MMH interspaces. The HiF-2α/SOX9 pattern of expression suggested that the elevated chondrocytic phenotype in MMH could be related to a better hypoxic local environment than in classical culture conditions. Pro-inflammatory markers were not expressed during the period of culture. The low level of nitric oxide accumulation within the inter-membrane spaces and in the incubation medium implied that chitosan consumed nitrites produced by entrapped chondrocytes, in relation with the decrease of its molecular weight of 50%. Our data suggest that MMH structures may be considered as complex chondrocytic cell bioreactors; "active decoys of biological media", potentially promising for various biomedical applications like the inter-vertebral disk replacement. Copyright © 2011 Elsevier Ltd. All rights reserved.

Wireless coordinated multicell systems architectures and precoding designs

CERN Document Server

Nguyen, Duy H N

2014-01-01

This SpringerBrief discusses the current research on coordinated multipoint transmission/reception (CoMP) in wireless multi-cell systems. This book analyzes the structure of the CoMP precoders and the message exchange mechanism in the CoMP system in order to reveal the advantage of CoMP. Topics include interference management in wireless cellular networks, joint signal processing, interference coordination, uplink and downlink precoding and system models. After an exploration of the motivations and concepts of CoMP, the authors present the architectures of a CoMP system. Practical implementati

Analysis and compensation for the joint effects of HPA nonlinearity, I/Q imbalance and crosstalk in MIMO beamforming systems

KAUST Repository

Qi, Jian

2011-03-01

In this paper, we investigate the joint effects of high-power amplifier (HPA) nonlinearity, in-phase/quadrature-phase (I/Q) imbalance and crosstalk, on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems, and propose a compensation method for the three impairments together. The performance of the MIMO TB system equipped with the proposed compensation scheme is evaluated in terms of average symbol error probability and capacity when transmissions are performed over uncorrelated Rayleigh fading channels. Numerical results are provided and show the effects on performance of several system parameters, namely, the HPA parameters, image-leakage ratio, crosstalk, numbers of antennas, length of pilot symbols and phase-shift keying modulation order. © 2011 IEEE.

Multi-stage high cell continuous fermentation for high productivity and titer.

Science.gov (United States)

Chang, Ho Nam; Kim, Nag-Jong; Kang, Jongwon; Jeong, Chang Moon; Choi, Jin-dal-rae; Fei, Qiang; Kim, Byoung Jin; Kwon, Sunhoon; Lee, Sang Yup; Kim, Jungbae

2011-05-01

We carried out the first simulation on multi-stage continuous high cell density culture (MSC-HCDC) to show that the MSC-HCDC can achieve batch/fed-batch product titer with much higher productivity to the fed-batch productivity using published fermentation kinetics of lactic acid, penicillin and ethanol. The system under consideration consists of n-serially connected continuous stirred-tank reactors (CSTRs) with either hollow fiber cell recycling or cell immobilization for high cell-density culture. In each CSTR substrate supply and product removal are possible. Penicillin production is severely limited by glucose metabolite repression that requires multi-CSTR glucose feeding. An 8-stage C-HCDC lactic acid fermentation resulted in 212.9 g/L of titer and 10.6 g/L/h of productivity, corresponding to 101 and 429% of the comparable lactic acid fed-batch, respectively. The penicillin production model predicted 149% (0.085 g/L/h) of productivity in 8-stage C-HCDC with 40 g/L of cell density and 289% of productivity (0.165 g/L/h) in 7-stage C-HCDC with 60 g/L of cell density compared with referring batch cultivations. A 2-stage C-HCDC ethanol experimental run showed 107% titer and 257% productivity of the batch system having 88.8 g/L of titer and 3.7 g/L/h of productivity. MSC-HCDC can give much higher productivity than batch/fed-batch system, and yield a several percentage higher titer as well. The productivity ratio of MSC-HCDC over batch/fed-batch system is given as a multiplication of system dilution rate of MSC-HCDC and cycle time of batch/fed-batch system. We suggest MSC-HCDC as a new production platform for various fermentation products including monoclonal antibody.

A Study of an Optical Lunar Surface Communications Network with High Bandwidth Direct to Earth Link

Science.gov (United States)

Wilson, K.; Biswas, A.; Schoolcraft, J.

2011-01-01

Analyzed optical DTE (direct to earth) and lunar relay satellite link analyses, greater than 200 Mbps downlink to 1-m Earth receiver and greater than 1 Mbps uplink achieved with mobile 5-cm lunar transceiver, greater than 1Gbps downlink and greater than 10 Mpbs uplink achieved with 10-cm stationary lunar transceiver, MITLL (MIT Lincoln Laboratory) 2013 LLCD (Lunar Laser Communications Demonstration) plans to demonstrate 622 Mbps downlink with 20 Mbps uplink between lunar orbiter and ground station; Identified top five technology challenges to deploying lunar optical network, Performed preliminary experiments on two of challenges: (i) lunar dust removal and (ii)DTN over optical carrier, Exploring opportunities to evaluate DTN (delay-tolerant networking) over optical link in a multi-node network e.g. Desert RATS.

Extracellular Bio-imaging of Acetylcholine-stimulated PC12 Cells Using a Calcium and Potassium Multi-ion Image Sensor.

Science.gov (United States)

Matsuba, Sota; Kato, Ryo; Okumura, Koichi; Sawada, Kazuaki; Hattori, Toshiaki

2018-01-01

In biochemistry, Ca 2+ and K + play essential roles to control signal transduction. Much interest has been focused on ion-imaging, which facilitates understanding of their ion flux dynamics. In this paper, we report a calcium and potassium multi-ion image sensor and its application to living cells (PC12). The multi-ion sensor had two selective plasticized poly(vinyl chloride) membranes containing ionophores. Each region on the sensor responded to only the corresponding ion. The multi-ion sensor has many advantages including not only label-free and real-time measurement but also simultaneous detection of Ca 2+ and K + . Cultured PC12 cells treated with nerve growth factor were prepared, and a practical observation for the cells was conducted with the sensor. After the PC12 cells were stimulated by acetylcholine, only the extracellular Ca 2+ concentration increased while there was no increase in the extracellular K + concentration. Through the practical observation, we demonstrated that the sensor was helpful for analyzing the cell events with changing Ca 2+ and/or K + concentration.

A 1 MHz BW 34.2 fJ/step Continuous Time Delta Sigma Modulator With an Integrated Mixer for Cardiac Ultrasound.

Science.gov (United States)

Kaald, Rune; Eggen, Trym; Ytterdal, Trond

2017-02-01

Fully digitized 2D ultrasound transducer arrays require one ADC per channel with a beamforming architecture consuming low power. We give design considerations for per-channel digitization and beamforming, and present the design and measurements of a continuous time delta-sigma modulator (CTDSM) for cardiac ultrasound applications. By integrating a mixer into the modulator frontend, the phase and frequency of the input signal can be shifted, thereby enabling both improved conversion efficiency and narrowband beamforming. To minimize the power consumption, we propose an optimization methodology using a simulated annealing framework combined with a C++ simulator solving linear electrical networks. The 3rd order single-bit feedback type modulator, implemented in a 65 nm CMOS process, achieves an SNR/SNDR of 67.8/67.4 dB across 1 MHz bandwidth consuming 131 [Formula: see text] of power. The achieved figure of merit of 34.2 fJ/step is comparable with state-of-the-art feedforward type multi-bit designs. We further demonstrate the influence to the dynamic range when performing dynamic receive beamforming on recorded delta-sigma modulated bit-stream sequences.