A Novel Multiuser Detector for Asynchronous CDMA System
LIANGXint; SHANGYong; LIANGQinglin; XIANGHaige
2004-01-01
The decorrelating and the MMSE (Minimum mean square error) multiuser detector for asynchronous CDMA (Code devision multiple access) system are ideally anticausal infinite memory-length detectors. Asa result~ in practice they have to be approximately implemented with finite-memory structure, and the process delay in detection is unavoidable. Based on the analysis of a new signal model for asynchronous system, a novel multiuser detector for asynchronous CDMA system is proposed in this paper~ which is termed as DF-IC-MMSE (Decision ,feedback interference cancellation-MMSE) detector. It's the detection statistics that makes the DF-IC-MMSE-detector basically different from other traditional ones. The DF-IC-MMSE detector can be ideally implemented with Causal finite memory-length structure, and cause no delay in symbol detection. Simulations show that the performance of DF-IC-MMSE detector is almost identical to that of the ideal MMSE detector.
Applications of Maximum Likelihood Algorithm in Asynchronous CDMA Systems
Xiao, P; Strom, E
2002-01-01
We treat the problems of propagation delay and channel estimation as well as data detection of orthogonally modulated signals in an asynchronous DS-CDMA system over fading channels using the maximum likelihood (ML) approach. The overwhelming computational complexity of the ML algorithm makes it unfeasible for implementation. The emphasis of this paper is to reduce its complexity by some approximation methods. The derived approximative ML schemes are compared with conventional algorithms as we...
Xiang, G; Ng, TS
1999-01-01
An asynchronous multicarrier (MC) direct-sequence (DS) code-division multiple-access (CDMA) scheme for the uplink of the mobile communication system operating in a frequency selective fading channel is analyzed. Bit error rate performance of the system with either equal-gain combining or maximum-ratio combining is obtained. Numerical results indicate that the system performs better than that of the conventional DS-CDMA system and another MC-DS-CDMA system.
Chia-Chang Hu
2005-04-01
Full Text Available A novel space-time adaptive near-far robust code-synchronization array detector for asynchronous DS-CDMA systems is developed in this paper. There are the same basic requirements that are needed by the conventional matched filter of an asynchronous DS-CDMA system. For the real-time applicability, a computationally efficient architecture of the proposed detector is developed that is based on the concept of the multistage Wiener filter (MWF of Goldstein and Reed. This multistage technique results in a self-synchronizing detection criterion that requires no inversion or eigendecomposition of a covariance matrix. As a consequence, this detector achieves a complexity that is only a linear function of the size of antenna array (J, the rank of the MWF (M, the system processing gain (N, and the number of samples in a chip interval (S, that is, Ã°ÂÂ’Âª(JMNS. The complexity of the equivalent detector based on the minimum mean-squared error (MMSE or the subspace-based eigenstructure analysis is a function of Ã°ÂÂ’Âª((JNS3. Moreover, this multistage scheme provides a rapid adaptive convergence under limited observation-data support. Simulations are conducted to evaluate the performance and convergence behavior of the proposed detector with the size of the J-element antenna array, the amount of the L-sample support, and the rank of the M-stage MWF. The performance advantage of the proposed detector over other DS-CDMA detectors is investigated as well.
Iterative Multiuser Receiver Based on Factor Graph for Asynchronous Coded CDMA Systems
无
2003-01-01
Factor graph, so named because it graphically represents function factorization, with which and its sum-product algorithm the iterative algorithm can be derived clearly. An iterative multiuser receiver based on factor graph for asynchronous coded CDMA system is proposed. In this paper, the a posteriori probability of users information bits conditioned on the noise-whitening filters output is represented by factor graphs, after numbers of iterations with the sum-product algorithm the information bits are estimated. The authors also propose a reduced complexity algorithm. Simulation results show that with this proposed receiver, near-single-user performance can be achieved, and small performance degradation for the reduced complexity algorithm with significant complexity reduction.
Performance comparison of asynchronous orthogonal multi-carrier CDMA in frequency selective channel
Xiang, G; Ng, TS
1998-01-01
Bit error rate (BER) performance of an asynchronous multi-carrier code division multiple access (MC-CDMA) system for the uplink of the mobile communication system with equal gain combining and maximum ratio combining are obtained. Given a fixed bandwidth frequency selective channel, performance of MC-CDMA is compared with that of conventional CDMA and MC-DS-CDMA in numerical results.
Xiang, G; Ng, TS
1998-01-01
Performance of an asynchronous orthogonal multi-carrier code division multiple access (MC-CDMA) system for the reverse link of the mobile communication system with equal gain combining is obtained. The performance of MC-CDMA is compared with that of conventional CDMA and MC-DS-CDMA in numerical results in a multipath Rayleigh fading channel.
Asynchronous CDMA Systems with Random Spreading-Part I: Fundamental Limits
Cottatellucci, Laura; Debbah, Merouane
2009-01-01
Spectral efficiency for asynchronous code division multiple access (CDMA) with random spreading is calculated in the large system limit allowing for arbitrary chip waveforms and frequency-flat fading. Signal to interference and noise ratios (SINRs) for suboptimal receivers, such as the linear minimum mean square error (MMSE) detectors, are derived. The approach is general and optionally allows even for statistics obtained by under-sampling the received signal. All performance measures are given as a function of the chip waveform and the delay distribution of the users in the large system limit. It turns out that synchronizing users on a chip level impairs performance for all chip waveforms with bandwidth greater than the Nyquist bandwidth, e.g., positive roll-off factors. For example, with the pulse shaping demanded in the UMTS standard, user synchronization reduces spectral efficiency up to 12% at 10 dB normalized signal-to-noise ratio. The benefits of asynchronism stem from the finding that the excess bandw...
A Particle Filter of Blind Equalization and Multiuser Detection in Asynchronous DS/CDMA Systems
ZHANG Jing; DONG Jian-ping; ZHANG Qian
2008-01-01
The particle filter (PF) is proposed to be the asynchronous direct-sequence eude-division multiple-access (DS/CDMA) multiuser detector without knowing the channel state information. The PF performs symbol detection according to the joint posterior density probability of simulated particles including relative delays, fading gains and symbols via sequential importance sample and resample. A simplified scheme is also proposed by separating the independent relative delays and fading with symbols. These parameters are modeled as the extended aggressive processes and estimated by the Kalman fdter, so as to provide their arbitrary importance distribution for symbol detection. Simulation results show that the bit error rate of the PF is less than convntional detectors.Moreover, the complexity of PF is moderate comaparable to other nonlinear suboptimal approaches.
Asynchronous Free-Space Optical CDMA Communications System for Last-mile Access Network
Jurado-Navas, Antonio; Raddo, Thiago R.; Sanches, Anderson L.;
2016-01-01
We propose a new hybrid asynchronous OCDMA-FSO communications system for access network solutions. New ABER expressions are derived under gamma-gamma scintillation channels, where all users can surprisingly achieve error-free transmissions when FEC is employed....
Zhang Wei
2005-01-01
Full Text Available The optimum and many suboptimum iterative soft-input soft-output (SISO multiuser detectors require a priori information about the multiuser system, such as the users' transmitted signature waveforms, relative delays, as well as the channel impulse response. In this paper, we employ adaptive algorithms in the SISO multiuser detector in order to avoid the need for this a priori information. First, we derive the optimum SISO parallel decision-feedback detector for asynchronous coded DS-CDMA systems. Then, we propose two adaptive versions of this SISO detector, which are based on the normalized least mean square (NLMS and recursive least squares (RLS algorithms. Our SISO adaptive detectors effectively exploit the a priori information of coded symbols, whose soft inputs are obtained from a bank of single-user decoders. Furthermore, we consider how to select practical finite feedforward and feedback filter lengths to obtain a good tradeoff between the performance and computational complexity of the receiver.
CDMA systems capacity engineering
Kim, Kiseon
2004-01-01
This new hands-on resource tackles capacity planning and engineering issues that are crucial to optimizing wireless communication systems performance. Going beyond the system physical level and investigating CDMA system capacity at the service level, this volume is the single-source for engineering and analyzing systems capacity and resources.
Singh, Jaswinder
2013-12-01
The analysis of a three-dimensional (3-D) wavelength/time/space (W-T-S) asynchronous optical CDMA code family is presented considering MAI only under relaxed cross-correlation (λc ⩾ 1). Based on the code performance, it is shown that for code-limited systems (when W and/or T are non-prime), the number of generated codes and hence the supported users can be significantly increased by relaxing the cross-correlation constraint if a slight degradation in code performance can be tolerated.
On the Uplink Performance of Asynchronous LAS-CDMA
H. Wei; Hanzo, L
2005-01-01
In this paper closed-form formulae are derived for characterizing the BER performance of Large Area Synchronous CDMA (LAS-CDMA) as a function of both the number of resolvable paths Lp and the maximum delay difference ?max, as well as the number of users K, when communicating over a Nakagami-m fading channel. Moreover, we comparatively studies the performance of LAS-CDMA and the traditional random code based DS-CDMA.
Compositional asynchronous membrane systems
Cosmin Bonchis; Cornel Izbasa; Gabriel Ciobanu
2007-01-01
This paper presents an algorithmic way of building complex membrane systems by coupling elementary membranes. Its application seems particularly valuable in the case of asynchronous membrane systems, since the resulting membrane system remains asynchronous. The composition method is based on a handshake mechanism implemented by using antiport rules and promoters.
This book is comprised of summary of mobile communication : CT, TRS, Cellular mobile communication, digital communication, Is-95 and Friedns and PCS system, Basic concept : tools of mathematics, system, signal analysis of Fourier, Sampling, DB and Bandwidth, noise and OSI 7 Layer, DSSS and Code theory : spread spectrum, CDM/CDMA communication mode, code theory and PN code, CDMA Demodulator : Searcher engine, function by searcher engine, Finger demodulator and searcher task, control power : the reason for forward control power and reverse control power, open loop power control, closed loop power control and outer loop power control, Hand off : Parameter for hand off MASHO, new soft hand off, hard hand off, MAHHO and Access hand off, Radio transmission technique : interleaving and Modulation, Is-95, COMA 2000 : COMA 2000 System, Idle state and registration, vocoder : voice source coding and QCELP
Carey, Daniel
2006-01-01
La plupart des instances de normalisation ont basé leur système cellulaire 3G sur le DS-CDMA (W-CDMA, UMTS, cdma2000). Les systèmes 4G désirant des services améliorés, cette thèse examine le Multicarrier CDMA (MC-CDMA) comme un candidat possible pour l'interface air des générations futures. Un modèle statistique de la puissance d'interférence totale sur canal asynchrone a été développé et suit une distribution de Nakagami pour les techniques asynchrones DS-CDMA et MC-CDMA. Deux nouvelles tech...
Redundant Asynchronous Microprocessor System
Meyer, G.; Johnston, J. O.; Dunn, W. R.
1985-01-01
Fault-tolerant computer structure called RAMPS (for redundant asynchronous microprocessor system) has simplicity of static redundancy but offers intermittent-fault handling ability of complex, dynamically redundant systems. New structure useful wherever several microprocessors are employed for control - in aircraft, industrial processes, robotics, and automatic machining, for example.
OV-CDMA System: Concept and Implementation
Inaty Elie
2008-01-01
Full Text Available A new method is proposed to achieve a multirate overlapped code division multiple access system (OV-CDMA based on a novel code overlapping procedure. The signal-to-interference ratio (SIR performance has been investigated for such system. A channel model that allows multirate overlapped transmission is presented based on which a closed form solution for the SIR has been derived. In addition, a simple yet very efficient block diagram of the transmitter and the receiver architecture has been proposed for such a system. Based on the proposed block diagram, the encoder-decoder has been implemented using an FPGA. Numerical results show that the newly proposed OV-CDMA scheme outperforms the classical variable processing gain fast frequency hopping CDMA (VPG-FFH-CDMA for different system scenarios. Finally, real-time measurements have been successfully obtained using a hardware prototype utilizing the simple Xilinx Spartan IIE (XC2S200E FPGA.
OV-CDMA System: Concept and Implementation
Rafic Ayoubi
2008-04-01
Full Text Available A new method is proposed to achieve a multirate overlapped code division multiple access system (OV-CDMA based on a novel code overlapping procedure. The signal-to-interference ratio (SIR performance has been investigated for such system. A channel model that allows multirate overlapped transmission is presented based on which a closed form solution for the SIR has been derived. In addition, a simple yet very efficient block diagram of the transmitter and the receiver architecture has been proposed for such a system. Based on the proposed block diagram, the encoder-decoder has been implemented using an FPGA. Numerical results show that the newly proposed OV-CDMA scheme outperforms the classical variable processing gain fast frequency hopping CDMA (VPG-FFH-CDMA for different system scenarios. Finally, real-time measurements have been successfully obtained using a hardware prototype utilizing the simple Xilinx Spartan IIE (XC2S200E FPGA.
A MATCHED FILTER BANK BASED DOA ESTIMATION FOR ASYNCHRONOUS MULTIPATH CDMA CHANNELS
Yang Wei; Chen Junshi; Tan Zhenhui; Takis Mathiopoulos
2005-01-01
In this paper, a Direction Of Arrival (DOA) estimation algorithm is proposed for multiuser signals through uplink asynchronous multipath Code Division Multiple Access (CDMA)channels. The algorithm is based directly on the correlation matrices of matched filter bank outputs of desired user's multipath signals and it does not require that the elements of base station antenna array outnumber the multipath signals, which is necessary for the conventional sub-space based direction-finding algorithm. Simulation results show that the proposed algorithm estimates the DOA of multipath signals effectively and acceptably. The proposed algorithm has the prominent advantages of low complexity, simpleness and practicality, which make it much more suitable for practical application.
Sequence Selection and Performance in DS/CDMA Systems
Jefferson Santos Ambrosio
2016-03-01
Full Text Available In this work key concepts on coding division multiple access (CDMA communication systems have been discussed. The sequence selection impact on the performance and capacity of direct sequence CDMA (DS/CDMA systems under AWGN and increasing system loading, as well as under multiple antennas channels was investigated.
Sequence Selection and Performance in DS/CDMA Systems
Jefferson Santos Ambrosio; Franscisco de Assis Scannavino Junior; Taufik Abrão
2016-01-01
In this work key concepts on coding division multiple access (CDMA) communication systems have been discussed. The sequence selection impact on the performance and capacity of direct sequence CDMA (DS/CDMA) systems under AWGN and increasing system loading, as well as under multiple antennas channels was investigated.
Comparison between MC-CDMA and CDMA-OFDM/OQAM systems in presence of MIMO channel
Radhia Gharsallah; Ridha Bouallegue
2012-01-01
In this paper, we present a comparison between MC-CDMA and CDMA-OFDM/OQAM systems in the case of MIMO channel. The advanced Multi Carrier CDMA OFDM/OQAM modulation is a combination of CDMA and OFDM/OQAM. This combination takes advantages from multicarrier modulation and spread spectrum. Indeed, the use of OFDM has proved its ability to fight against frequency selective channels but the insertion of guard interval yields spectral efficiency loss and sensitivity to frequency dispersion due to t...
A mean field theory of coded CDMA systems
We present a mean field theory of code-division multiple-access (CDMA) systems with error-control coding. On the basis of the relation between the free energy and mutual information, we obtain an analytical expression of the maximum spectral efficiency of the coded CDMA system, from which a mean-field description of the coded CDMA system is provided in terms of a bank of scalar Gaussian channels whose variances in general vary at different code symbol positions. Regular low-density parity-check (LDPC)-coded CDMA systems are also discussed as an example of the coded CDMA systems
A mean field theory of coded CDMA systems
Yano, Toru [Graduate School of Science and Technology, Keio University, Hiyoshi, Kohoku-ku, Yokohama-shi, Kanagawa 223-8522 (Japan); Tanaka, Toshiyuki [Graduate School of Informatics, Kyoto University, Yoshida Hon-machi, Sakyo-ku, Kyoto-shi, Kyoto 606-8501 (Japan); Saad, David [Neural Computing Research Group, Aston University, Birmingham B4 7ET (United Kingdom)], E-mail: yano@thx.appi.keio.ac.jp
2008-08-15
We present a mean field theory of code-division multiple-access (CDMA) systems with error-control coding. On the basis of the relation between the free energy and mutual information, we obtain an analytical expression of the maximum spectral efficiency of the coded CDMA system, from which a mean-field description of the coded CDMA system is provided in terms of a bank of scalar Gaussian channels whose variances in general vary at different code symbol positions. Regular low-density parity-check (LDPC)-coded CDMA systems are also discussed as an example of the coded CDMA systems.
Comparison between MC-CDMA and CDMA-OFDM/OQAM systems in presence of MIMO channel
Radhia Gharsallah
2012-07-01
Full Text Available In this paper, we present a comparison between MC-CDMA and CDMA-OFDM/OQAM systems in the case of MIMO channel. The advanced Multi Carrier CDMA OFDM/OQAM modulation is a combination of CDMA and OFDM/OQAM. This combination takes advantages from multicarrier modulation and spread spectrum. Indeed, the use of OFDM has proved its ability to fight against frequency selective channels but the insertion of guard interval yields spectral efficiency loss and sensitivity to frequency dispersion due to the use of rectangular pulse shape. Thus, cyclic prefix OFDM is replaced by an advanced #64257;lterbank-based multicarrier system OFDM/OQAM that operates without guard interval. However, OFDM/OQAM provides orthogonality only on the real domain, so transmitted symbols must be real valued. In the other hand, the CDMA component has two advantages: multiple access interference cancellation and providing orthogonality in the complex domain. From the orthogonality property provided, the Alamouti ST code can be combined with MC-CDMA-OQAM system in order to exploit space and time diversity. Numerical results show the utility of this new wireless communication system MIMO-CDMA-OFDM/OQAM in comparison with MIMO-MC-CDMA system
Tamer A. Kadous
2003-01-01
Full Text Available The goal of this paper is to compare the performance of the linear minimum mean square error (MMSE detector for a class of code division multiple access (CDMA systems in time and frequency selective channels. Specifically, we consider direct sequence (DS-CDMA, multicarrier (MC-CDMA, and the MC-DS-CDMA systems. Two key tools are used in our development. First, a general time-frequency framework that includes the different CDMA systems as special cases. Second, the duality between time and frequency domains that is used to derive equivalences between the different CDMA systems operating over purely frequency selective and purely time selective channels. We then combine the insights obtained from these special cases to assess the performance of CDMA systems over time and frequency selective channels. We provide sufficient conditions for the codes employed by the CDMA systems for the equivalences to hold. Numerical results are presented to illustrate the results.
Diversity Analysis in CDMA Based Broadband Wireless System
Hemalatha, M.; V. Prithviraj; S. Jayalalitha; K. Thenmozhi
2012-01-01
This proposed study exploits transmit and receive diversity to mitigate multipath propagation and interference in CDMA system which is characterized by multipath interference. Code Division Multiple Access (CDMA) is the vital technology for modern wireless communication systems to share the available finite amount of radio bandwidth expeditiously. The CDMA system has soft capacity which polishes off the problem of limitation on the number of users in a system. In this paper the simulated resu...
Asynchronous interactive control systems
Vuskovic, M. I.; Heer, E.
1980-01-01
A class of interactive control systems is derived by generalizing interactive manipulator control systems. The general structural properties of such systems are discussed and an appropriate general software implementation is proposed. This is based on the fact that tasks of interactive control systems can be represented as a network of a finite set of actions which have specific operational characteristics and specific resource requirements, and which are of limited duration. This has enabled the decomposition of the overall control algorithm into a set of subalgorithms, called subcontrollers, which can operate simultaneously and asynchronously. Coordinate transformations of sensor feedback data and actuator set-points have enabled the further simplification of the subcontrollers and have reduced their conflicting resource requirements. The modules of the decomposed control system are implemented as parallel processes with disjoint memory space communicating only by I/O. The synchronization mechanisms for dynamic resource allocation among subcontrollers and other synchronization mechanisms are also discussed in this paper. Such a software organization is suitable for the general form of multiprocessing using computer networks with distributed storage.
Use of CDMA access technology in mobile satellite systems
Ramasastry, Jay; Wiedeman, Bob
1995-01-01
Use of Code Division Multiple Access (CDMA) technology in terrestrial wireless systems is fairly well understood. Similarly, design and operation of Power Control in a CDMA-based system in a terrestrial environment is also well established. Terrestrial multipath characteristics, and optimum design of the CDMA receiver to deal with multipath and fading conditions are reliably established. But the satellite environment is different. When the CDMA technology is adopted to the satellite environment, other design features need to be incorporated (for example; interleaving, open-loop and closed-loop power control design, diversity characteristics) to achieve comparable level of system performance. In fact, the GLOBALSTAR LEO/MSS system has incorporated all these features. Contrary to some published reports, CDMA retains the advantages in the satellite environment that are similar to those achieved in the terrestrial environment. This document gives a description of the CDMA waveform and other design features adopted for mobile satellite applications.
Tamer A. Kadous; Sayeed, Akbar M.
2003-01-01
The goal of this paper is to compare the performance of the linear minimum mean square error (MMSE) detector for a class of code division multiple access (CDMA) systems in time and frequency selective channels. Specifically, we consider direct sequence (DS)-CDMA, multicarrier (MC)-CDMA, and the MC-DS-CDMA systems. Two key tools are used in our development. First, a general time-frequency framework that includes the different CDMA systems as special cases. Second, the duality between time and...
An Adaptive Multiuser Chip-Rate Equalizer for CDMA Underwater Communication System
HAN Jing; HUANG Jian-guo; SHEN Xiao-hong
2008-01-01
Direct-sequence code-division multiple access (CDMA) is considered for multiuser communication network in underwater acoustic channel, where extended multipath and rapid time-variability are encountered. To track and compensate the channel distortion, a decentralized hypothesis-feedback equalization (HFE) algorithm based on chip-rate update has been used[1]. But due to multiple access interference (MAI), its performance suffers degradation. For this reason, successive interference cancellation hypothesis-feedback equalization (SIC-HFE) algorithm is proposed, which combines the capabilities of HFE to track the time-varying channel and SIC implemented by cross-over feedback filters to cancel out the MAI effects between users. Simulation and experiment results show that the proposed algorithm can significantly improve the performance of asynchronous multiuser CDMA underwater communication system.
Diversity Analysis in CDMA Based Broadband Wireless System
M. Hemalatha
2012-03-01
Full Text Available This proposed study exploits transmit and receive diversity to mitigate multipath propagation and interference in CDMA system which is characterized by multipath interference. Code Division Multiple Access (CDMA is the vital technology for modern wireless communication systems to share the available finite amount of radio bandwidth expeditiously. The CDMA system has soft capacity which polishes off the problem of limitation on the number of users in a system. In this paper the simulated results of CDMA system deployed with transmit diversity using Alamouti code and receiver diversity with Maximum Ratio Combining (MRC technique are presented. The proposed system optimizes the effect of multipath propagation and concludes the way to improve BER.
Asynchronous control for networked systems
Rubio, Francisco; Bencomo, Sebastián
2015-01-01
This book sheds light on networked control systems; it describes different techniques for asynchronous control, moving away from the periodic actions of classical control, replacing them with state-based decisions and reducing the frequency with which communication between subsystems is required. The text focuses specially on event-based control. Split into two parts, Asynchronous Control for Networked Systems begins by addressing the problems of single-loop networked control systems, laying out various solutions which include two alternative model-based control schemes (anticipatory and predictive) and the use of H2/H∞ robust control to deal with network delays and packet losses. Results on self-triggering and send-on-delta sampling are presented to reduce the need for feedback in the loop. In Part II, the authors present solutions for distributed estimation and control. They deal first with reliable networks and then extend their results to scenarios in which delays and packet losses may occur. The novel ...
Multi-user MIMO CDMA systems using complete complementary sequences.
Khirallah, C.; Coulton, Paul; Rashvand, P.; Zein, N
2006-01-01
The authors propose a novel use of complete complementary (CC) sequences for increased spectral efficiency in a multiple-input–multiple-output (MIMO) code division multiple access (CDMA) system. The new method overcomes many of the problems and limitations persistent in single-input–single-output (SISO) and proves that under the proposed MIMO CC-CDMA system, the capacity for the number of supported users increases linearly by the number of transmitters. The paper also shows that the MIMO CC-C...
Analysis of MC-CDMA System in Mobile Communications
M. F. Ghanim
2012-11-01
Full Text Available Wireless communication plays an important role in our daily life. One of the most important techniques which is Candidate for the fourth generation is Multicarrier Code Division Multiple Access (MC-CDMA due to its high data rate. This research paper presents the MC-CDMA system using different modulation techniques. The variety of modulation types are depended in order to show the effects of modulation index and type on broadcasting data. The bit error rate of the system is plotted for a range of signal to noise ratio so that the effect of modulation on the MC-CDMA system will be evident. Actually, the simulation results show that QAM gives less bit error rate that makes MC-CDMA more flexible and suitable for mobile communication next generation technology. Also, the peak-to-average power (PAPR of MC-CDMA is analyzed to show that high PAPR is the main disadvantage of MC-CDMA system then the possible solutions for this problem are discussed in this research paper.
Space Time Block Coded Multi-user CDMA Systems over Rayleigh Fading Channel
Mamun, M. Shahriar; Hussain, Jamil; Haque, Md. Hasibul; Shafik, Rishad Ahmed
2008-01-01
This paper investigates the performance and capacity of space time block coded (STBC) multi-user CDMA system over Rayleigh fading channel condition using multiple transmit antennas. Using simulation and analytical approach, we show that STBC CDMA system has increased performance in cellular networks. We also compare the performance of this system with the typical CDMA system and show that STBC and multiple transmit antennas for multi-user CDMA system provide performance gain without any need ...
Arifianto, M. S.; Chekima, A.; Hamid, M. Y.; Barukang, L.; Viswacheda, D. V.
This paper proposes multiple-access schemes based on Overloaded Minimum Total Squared Correlation (TSC) signatures, namely Pilot Aided Multi-Carrier Code-Division Multiple-Access (MC-CDMA) and Pilot Aided Space Time Block Codes (STBC) MC-CDMA. Since overloaded minimum TSC signatures were used as the spreading codes, a number of sub-channels in the MC-CDMA and STBC MC-CDMA schemes were not utilized for data transmission. These empty sub-channels can be exploited for comb-type pilot signaling. To maintain low system complexity, for the pilot sub-channels Least Square (LS) estimation was employed and for interpolating the characteristics of the data sub-channels linear interpolator was applied. The validity of the schemes is confirmed by comparing them with the original MC-CDMA method using Walsh-Hadamard orthogonal codes and also with Walsh-Hadamard based STBC MC-CDMA with block-type pilot. All systems use Equal Gain Combining (EGC) or Maximum Ratio Combining (MRC) in the MC-CDMA block at the receiver. The simulation result shows that although the spreading codes of interest are not fully orthogonal codes, for a low number of users the systems under investigation performed better than their Walsh-Hadamard based counterpart. This will be valuable for Wireless Personal Area Network (PAN) where the number of users is typically low.
New Power Estimation Methods for Highly Overloaded Synchronous CDMA Systems
Nashtaali, Damoun; Pad, Pedram; Moghadasi, Seyed Reza; Marvasti, Farokh
2011-01-01
In CDMA systems, the received user powers vary due to moving distance of users. Thus, the CDMA receivers consist of two stages. The first stage is the power estimator and the second one is a Multi-User Detector (MUD). Conventional methods for estimating the user powers are suitable for underor fully-loaded cases (when the number of users is less than or equal to the spreading gain). These methods fail to work for overloaded CDMA systems because of high interference among the users. Since the bandwidth is becoming more and more valuable, it is worth considering overloaded CDMA systems. In this paper, an optimum user power estimation for over-loaded CDMA systems with Gaussian inputs is proposed. We also introduce a suboptimum method with lower complexity whose performance is very close to the optimum one. We shall show that the proposed methods work for highly over-loaded systems (up to m(m + 1) =2 users for a system with only m chips). The performance of the proposed methods is demonstrated by simulations. In ...
On Analyzing LDPC Codes over Multiantenna MC-CDMA System
S. Suresh Kumar
2014-01-01
Full Text Available Multiantenna multicarrier code-division multiple access (MC-CDMA technique has been attracting much attention for designing future broadband wireless systems. In addition, low-density parity-check (LDPC code, a promising near-optimal error correction code, is also being widely considered in next generation communication systems. In this paper, we propose a simple method to construct a regular quasicyclic low-density parity-check (QC-LDPC code to improve the transmission performance over the precoded MC-CDMA system with limited feedback. Simulation results show that the coding gain of the proposed QC-LDPC codes is larger than that of the Reed-Solomon codes, and the performance of the multiantenna MC-CDMA system can be greatly improved by these QC-LDPC codes when the data rate is high.
Channel Estimation for MIMO MC-CDMA Systems
Sureshkumar, K; Vetrikanimozhi, A
2011-01-01
The concepts of MIMO MC-CDMA are not new but the new technologies to improve their functioning are an emerging area of research. In general, most mobile communication systems transmit bits of information in the radio space to the receiver. The radio channels in mobile radio systems are usually multipath fading channels, which cause inter-symbol interference (ISI) in the received signal. To remove ISI from the signal, there is a need of strong equalizer. In this thesis we have focused on simulating the MIMO MC-CDMA systems in MATLAB and designed the channel estimation for them.
CAPACITY CALCULATION OF TD-CDMA HIGH ALTITUDE PLATFORM SYSTEM
Wang Zhenyong; Liu Xiaowei; Li Zhuoshi
2011-01-01
A capacity calculation method of High Altitude Platform System (HAPS) is proposed in which TD-CDMA multiple access schemes are applied.With the influence of both power limit and bandwidth limit on capacity integrated,the paper derives the equations by which the capacity of TD-CDMA systems can be calculated,and performs calculation on a practical system.This calculation method is quite simple and effective with a comparatively small error,which is essential to the designing and research on HAPS.
Evaluation of CDMA system capacity for mobile satellite system applications
Smith, Partrick O.; Geraniotis, Evaggelos A.
1988-01-01
A specific Direct-Sequence/Pseudo-Noise (DS/PN) Code-Division Multiple-Access (CDMA) mobile satellite system (MSAT) architecture is discussed. The performance of this system is evaluated in terms of the maximum number of active MSAT subscribers that can be supported at a given uncoded bit-error probability. The evaluation decouples the analysis of the multiple-access capability (i.e., the number of instantaneous user signals) from the analysis of the multiple-access mutliplier effect allowed by the use of CDMA with burst-modem operation. We combine the results of these two analyses and present numerical results for scenarios of interest to the mobile satellite system community.
Partial interference subspace rejection in CDMA systems
Hansen, Henrik; Affes, Sofiene; Mewelstein, Paul
2001-01-01
Previously presented interference subspace rejection (ISR) proposed a family of new efficient multiuser detectors for CDMA. We reconsider in this paper the modes of ISR using decision feedback (DF). DF modes share similarities with parallel interference cancellation (PIC) but attempt to cancel...
Throughput of Coded Optical CDMA Systems with AND Detectors
Memon, Kehkashan A.; Umrani, Fahim A.; Umrani, A. W.; Umrani, Naveed A.
2012-09-01
Conventional detection techniques used in optical code-division multiple access (OCDMA) systems are not optimal and result in poor bit error rate performance. This paper analyzes the coded performance of optical CDMA systems with AND detectors for enhanced throughput efficiencies and improved error rate performance. The results show that the use of AND detectors significantly improve the performance of an optical channel.
Optical CDMA system using bacteriorhodopsin for optical data storage
Bae; Yang; Jin; Lee; Park
1999-11-01
An optical CDMA (code division multiple access) system for the optical data storage using bacteriorhodopsin (BR) is reported as an application of the BR materials. The desired signal of multiple input can be recorded and reconstructed by use of orthogonal codes. An experimental setup is proposed and demonstrated. PMID:10585180
Improving performance of DS-CDMA systems using chaotic complex Bernoulli spreading codes
Farzan Sabahi, Mohammad; Dehghanfard, Ali
2014-12-01
The most important goal of spreading spectrum communication system is to protect communication signals against interference and exploitation of information by unintended listeners. In fact, low probability of detection and low probability of intercept are two important parameters to increase the performance of the system. In Direct Sequence Code Division Multiple Access (DS-CDMA) systems, these properties are achieved by multiplying the data information in spreading sequences. Chaotic sequences, with their particular properties, have numerous applications in constructing spreading codes. Using one-dimensional Bernoulli chaotic sequence as spreading code is proposed in literature previously. The main feature of this sequence is its negative auto-correlation at lag of 1, which with proper design, leads to increase in efficiency of the communication system based on these codes. On the other hand, employing the complex chaotic sequences as spreading sequence also has been discussed in several papers. In this paper, use of two-dimensional Bernoulli chaotic sequences is proposed as spreading codes. The performance of a multi-user synchronous and asynchronous DS-CDMA system will be evaluated by applying these sequences under Additive White Gaussian Noise (AWGN) and fading channel. Simulation results indicate improvement of the performance in comparison with conventional spreading codes like Gold codes as well as similar complex chaotic spreading sequences. Similar to one-dimensional Bernoulli chaotic sequences, the proposed sequences also have negative auto-correlation. Besides, construction of complex sequences with lower average cross-correlation is possible with the proposed method.
Joint Transmitter-Receiver Optimization in the Downlink CDMA Systems
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 usersÃ¢Â€Â² 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.
Optimal admission control algorithms for scheduling burst data in CDMA multimedia systems
Kwok, YK; Lau, VKN
2001-01-01
3rd generation mobile systems are mostly based on the wideband CDMA platform to support high bit rate packet data services. One important component to offer packet data service in CDMA is a burst admission control algorithm. In this paper, we propose and study a novel jointly adaptive burst admission algorithm, namely the jointly adaptive burst admission-spatial dimension algorithm (JABA-SD) to effectively allocate valuable resources in wideband CDMA systems to burst requests. In the physical...
Performance of MC-MC CDMA Systems with Nonlinear Models of HPA
Labib Francis Gergis
2011-01-01
A new wireless communication system denoted as Multi-Code Multi-Carrier CDMA (MC-MC CDMA), which is the combination of Multi-Code CDMA and Multi-Carrier CDMA, is analyzed in this paper. This system can satisfy multi-rate services using multi-code schemes and muti-carrier services used for high rate transmission. The system is evaluated using Traveling Wave Tube Amplifier (TWTA). This type of amplifiers continue to offer the best microwave high power amplifiers (HPA) performance in terms of po...
Adaptive Denoising and Equalization of Infrared Wireless CDMA System
Fernando Xavier N.
2005-01-01
Full Text Available Infrared has abundant, unregulated bandwidth enabling rapid deployment at low cost. However, safety limits on power emission levels (IEC825, large noise due to ambient lighting, and multipath dispersion remain as hurdles in diffused indoor environments. Especially, the high-frequency periodic interference produced by fluorescent lights is a major concern. Spread spectrum techniques enable low-power operation and noise rejection, at the expense of large processing gain. In this paper, we quantify the noise received and propose an adaptive FIR filter to jointly cancel the multipath dispersion and the fluorescent light noise in an infrared CDMA system. From analytical and simulation results, the adaptive filter significantly enhances the noise rejection capability of the CDMA system and tracks well the quasistationary indoor wireless channel. Our results show tenfold improvement in the BER for a given SNR and processing gain due to the adaptive filter. The filter also performs well in the multiuser environment.
Adaptive Rate DS-CDMA Systems using Variable Spreading Factors
Yang, L-L.; Hanzo, L.
2004-01-01
Abstract—In this contribution, adaptive rate transmissions are investigated in the context of direct-sequence code-division multiple-access (DS-CDMA) systems using variable spreading factors (VSFs). In the context of the recently established family of adaptive rate-transmission schemes, the transmission rate is typically adapted in response to the channel’s fading-induced quality fluctuation. By contrast, in this contribution the transmission rate is adapted in response to the multiuser inter...
Fair channel-dependent scheduling in CDMA systems
Bruin, de, W.; Heijenk, Geert; El Zarki, Magda; Zan, Jasmine Lei
2003-01-01
In this study a scheduling algorithm for CDMA systems is presented which is a trade-off between two extreme ways of scheduling: C/I based and Round-Robin scheduling. The simulation results indeed display that the advantages of both these extremes have been combined in the new algorithm: a good fairness, comparable to that of the Round-Robin scheduling, together with almost the same power gain as reached in the C/I based scheduling.
New multitarget constant modulus array for CDMA systems
Zhang Jidong; Zheng Baoyu
2006-01-01
A new multitarget constant modulus array is proposed for CDMA systems based on least squares constant modulus algorithm. The new algorithm is called pre-despreading decision directed least squares constant modulus algorithm (DDDLSCMA). In the new algorithm, the pre-despreading is first applied for multitarget arrays to remove some multiple access signals, then the despreaded signal is processed by the algorithm which united the constant modulus algorithm and decision directed method. Simulation results illustrate the good performance for the proposed algorithm.
Strict optical orthogonal codes for purely asynchronous code-division multiple-access applications.
Zhang, J G
1996-12-10
Strict optical orthogonal codes are presented for purely asynchronous optical code-division multiple-access (CDMA) applications. The proposed code can strictly guarantee the peaks of its cross-correlation functions and the sidelobes of any of its autocorrelation functions to have a value of 1 in purely asynchronous data communications. The basic theory of the proposed codes is given. An experiment on optical CDMA systems is also demonstrated to verify the characteristics of the proposed code. PMID:21151299
CCS, locations and asynchronous transition systems
Mukund, Madhavan; Nielsen, Mogens
system for CCS by introducing labels on the transitions with information about the locations of events. We then show that the resulting transition system is an asynchronous transition system which has the additional property of being elementary, which means that it can also be represented by a 1-safe net...
Duration of asynchronous operations in distributed systems
Makhaniok, Mikhail; Männer, Reinhard
1995-01-01
A distributed asynchronous system is investigated. Its processing elements execute common operations concurrently and distributively. They are implemented as combinatorial circuits and exchange data via open collector bus lines. A method is presented to identify and to minimize the duration of an operation and therefore to increase the performance of the system. No hardware modifications are required.
Comparison of CDMA and FDMA for the MobileStar(sm) system
Jacobs, I. M.; Gilhousen, K. S.; Weaver, L. A.; Renshaw, K.; Murphy, T.
1988-01-01
Spread-spectrum code division multiple access (CDMA) and single channel per carrier frequency division multiple access (FDMA) systems are compared for spectrum efficiency. CDMA is shown to have greater maximum throughput than FDMA for the MobileStar(sm) system which uses digital voice activated carriers and directive circularly polarized satellite antennas.
The non-anticipation of the asynchronous systems
Vlad, Serban E.
2008-01-01
The asynchronous systems are the models of the asynchronous circuits from the digital electrical engineering and non-anticipation is one of the most important properties in systems theory. Our present purpose is to introduce several concepts of non-anticipation of the asynchronous systems.
An optical CDMA system based on chaotic sequences
Liu, Xiao-lei; En, De; Wang, Li-guo
2014-03-01
In this paper, a coherent asynchronous optical code division multiple access (OCDMA) system is proposed, whose encoder/decoder is an all-optical generator. This all-optical generator can generate analog and bipolar chaotic sequences satisfying the logistic maps. The formula of bit error rate (BER) is derived, and the relationship of BER and the number of simultaneous transmissions is analyzed. Due to the good property of correlation, this coherent OCDMA system based on these bipolar chaotic sequences can support a large number of simultaneous users, which shows that these chaotic sequences are suitable for asynchronous OCDMA system.
Adaptive Multiuser Detectors for DS-CDMA Systems
Paul Jean Etienne Jeszensky
2006-02-01
Full Text Available This work makes a review of the main Adaptives Multi-user Detectors (MuD-Adpt for Direct Sequence - Code Division Multiple Access (DS-CDMA systems. The MuD-Adpt based on Minimum Mean Square Error (MMSE and Decorrelator (MuD-Dec are focused. Multi-user detectors show great resistance to the near-far effect and combat effectively the Multiple Access Interference (MAI. Comparative numeric results characterize the substantial performance improvement of those detectors in relation to the matched filter conventional receiver (Conv.
Performance Evaluation of Space-Time Turbo Code Concatenated With Block Code MC-CDMA Systems
Lokesh Kumar Bansal; Aditya Trivedi
2011-01-01
In this paper, performance of a space-time turbo code (STTuC) in concatenation with space-time block code (STBC) in multi-carrier code-division multiple-access (MCCDMA) system with multi-path fading channel is considered. The performance in terms of bit error rate (BER) is evaluated through simulations. The corresponding BER of the concatenated STTuC-STBC-MC-CDMA system is compared with STTuC-MC-CDMA system and STBC-MC-CDMA system. The simulation results show that the STTuC-MCCDMA system perf...
An Efficient Paging Algorithm for Multi-Carrier CDMA System
Mostafa, Sheikh Shanawaz; Rashid, Gazi Maniur; Moinuddin, Muhammad; Amin, Md Ziaul; Nahid, Abdullah Al
2011-01-01
To cope with the increasing demand of wireless communication services multi-carrier systems are being used. Radio resources are very limited and efficient usages of these resources are inevitable to get optimum performance of the system. Paging channel is a low-bandwidth channel and one of the most important channels on which system performance depends significantly. Therefore it is vulnerable to even moderate overloads. In this paper, an efficient paging algorithm, Concurrent Search, is proposed for efficient use of paging channel in Multi- carrier CDMA system instead of existing sequential searching algorithm. It is shown by the simulation that the paging performance in proposed algorithm is far better than the existing system.
An Efficient Paging Algorithm for Multi-Carrier CDMA System
Sheikh Shanawaz Mostafa
2011-05-01
Full Text Available To cope with the increasing demand of wireless communication services multi-carrier systems are being used. Radio resources are very limited and efficient usages of these resources are inevitable to get optimum performance of the system. Paging channel is a low-bandwidth channel and one of the most important channels on which system performance depends significantly. Therefore it is vulnerable to even moderate overloads. In this paper, an efficient paging algorithm, Concurrent Search, is proposed for efficient use of paging channel in Multi- carrier CDMA system instead of existing sequential searching algorithm. It is shown by the simulation that the paging performance in proposed algorithm is far better than the existing system.
Diversity reception for advanced multi-satellite networks: A CDMA approach
Colzi, E.; Degaudenzi, R.; Elia, C.; Giannetti, F.; Viola, R.
1993-01-01
Diversity reception for Synchronous CDMA (S-CDMA) is introduced and analyzed. A Gaussian co-channel synchronous and asynchronous interference approximation is derived to evaluate the effects on the system bit error rate. Numerical results are provided for a simple mobile communication system where the signals transmitted by two distinct satellites in visibility are coherently combined by a three fingers Rake receiver. A second example showing performance of an integrated ground/satellite single frequency network for digital audio broadcasting is presented. Results show the capacity advantage of utilizing S-CDMA in combination with diversity reception.
Capacity of Synchronous CDMA Systems with Near-Far Effects and Design of Suboptimum Signature Codes
Kabir, P; Pad, P; Marvasti, F
2011-01-01
This paper deals with near-far effects on various aspects of Code Division Multiple Access (CDMA) systems. Initially, we propose a new class of codes for over-loaded synchronous wireless CDMA systems that are robust against near-far effects; and then we provide a low complexity decoder for a subclass of such codes. Moreover, bounds for the sum capacity of CDMA systems in the presence of near-far effects are derived. An important contributions of this paper is the development of a method that translates a near-far sum capacity problem with imperfect channel state estimation to the evaluation of the capacity for a CDMA system with perfect channel state estimation. To show the power and utility of the results, a number of sum capacity bounds for special cases are numerically evaluated.
A Charrelation Matrix-Based Blind Adaptive Detector for DS-CDMA Systems.
Luo, Zhongqiang; Zhu, Lidong
2015-01-01
In this paper, a blind adaptive detector is proposed for blind separation of user signals and blind estimation of spreading sequences in DS-CDMA systems. The blind separation scheme exploits a charrelation matrix for simple computation and effective extraction of information from observation signal samples. The system model of DS-CDMA signals is modeled as a blind separation framework. The unknown user information and spreading sequence of DS-CDMA systems can be estimated only from the sampled observation signals. Theoretical analysis and simulation results show that the improved performance of the proposed algorithm in comparison with the existing conventional algorithms used in DS-CDMA systems. Especially, the proposed scheme is suitable for when the number of observation samples is less and the signal to noise ratio (SNR) is low. PMID:26287209
Tides in asynchronous binary systems
Toledano, Oswaldo; Moreno, Edmundo; Koenigsberger, Gloria; Detmers, R.; Langer, Norbert
2006-01-01
Stellar oscillations are excited in non-synchronously rotating stars in binary systems due to the tidal forces. Tangential components of the tides can drive a shear flow which behaves as a differentially forced rotating structure in a stratified outer medium. In this paper we show that our single-layer approximation for the calculation of the forced oscillations yields results that are consistent with the predictions for the synchronization timescales in circular orbits. In addition, calibrat...
Intelligent Paging Strategy for Multi-Carrier CDMA System
Mostafa, Sheikh Shanawaz; Amin, Md Ziaul; Ahmad, Mohiuddin
2011-01-01
Subscriber satisfaction and maximum radio resource utilization are the pivotal criteria in communication system design. In multi-Carrier CDMA system, different paging algorithms are used for locating user within the shortest possible time and best possible utilization of radio resources. Different paging algorithms underscored different techniques based on the different purposes. However, low servicing time of sequential search and better utilization of radio resources of concurrent search can be utilized simultaneously by swapping of the algorithms. In this paper, intelligent mechanism has been developed for dynamic algorithm assignment basing on time-varying traffic demand, which is predicted by radial basis neural network; and its performance has been analyzed are based on prediction efficiency of different types of data. High prediction efficiency is observed with a good correlation coefficient (0.99) and subsequently better performance is achieved by dynamic paging algorithm assignment. This claim is sub...
A European mobile satellite system concept exploiting CDMA and OBP
Vernucci, A.; Craig, A. D.
1993-01-01
This paper describes a novel Land Mobile Satellite System (LMSS) concept applicable to networks allowing access to a large number of gateway stations ('Hubs'), utilizing low-cost Very Small Aperture Terminals (VSAT's). Efficient operation of the Forward-Link (FL) repeater can be achieved by adopting a synchronous Code Division Multiple Access (CDMA) technique, whereby inter-code interference (self-noise) is virtually eliminated by synchronizing orthogonal codes. However, with a transparent FL repeater, the requirements imposed by the highly decentralized ground segment can lead to significant efficiency losses. The adoption of a FL On-Board Processing (OBP) repeater is proposed as a means of largely recovering this efficiency impairment. The paper describes the network architecture, the system design and performance, the OBP functions and impact on implementation. The proposed concept, applicable to a future generation of the European LMSS, was developed in the context of a European Space Agency (ESA) study contract.
Performance of MC-MC CDMA Systems with Nonlinear Models of HPA
Gergis, Labib Francis
2011-01-01
A new wireless communication system denoted as Multi-Code Multi-Carrier CDMA (MC-MC CDMA), which is the combination of Multi-Code CDMA and Multi-Carrier CDMA, is analyzed in this paper. This system can satisfy multi-rate services using multi-code schemes and muti-carrier services used for high rate transmission. The system is evaluated using Traveling Wave Tube Amplifier (TWTA). This type of amplifiers continue to offer the best microwave high power amplifiers (HPA) performance in terms of power efficiency, size and cost, but lag behind Solid State Power Amplifiers (SSPA's) in linearity. This paper presents a technique for improving TWTA linearity. The use of predistorter (PD) linearization technique is described to provide TWTA performance comparable or superior to conventional SSPA's. The characteristics of the PD scheme is derived based on the extension of Saleh's model for HPA.
Physical Layer Built-In Security Analysis and Enhancement Algorithms for CDMA Systems
Li Tongtong
2007-01-01
Full Text Available Historically developed for secure communication and military use, CDMA has been identified as a major modulation and multiple-access technique for 3G systems and beyond. In addition to the wide bandwidth and low power-spectrum density which make CDMA signals robust to narrowband jamming and easy to be concealed within the noise floor, the physical layer built-in information privacy of CDMA system is provided by pseudorandom scrambling. In this paper, first, security weakness of the operational and proposed CDMA airlink interfaces is analyzed. Second, based on the advanced encryption standard (AES, we propose to enhance the physical layer built-in security of CDMA systems through secure scrambling. Performance analysis demonstrates that while providing significantly improved information privacy, CDMA systems with secure scrambling have comparable computational complexity and overall system performance with that of conventionally scrambled systems. Moreover, it is shown that by scrambling the training sequence and the message sequence separately with two independent scrambling sequences, both information privacy and system performance can be further improved. The proposed scheme can readily be applied to 3G systems and beyond.
CDMA Technology for Intelligent Transportation Systems
Bera, Rabindranath; Bera, Jitendranath; Sil, Sanjib; Mondal, Dipak; Dhar, Sourav; Kandar, Debdatta
2007-01-01
Scientists and Technologists involved in the development of radar and remote sensing systems all over the world are now trying to involve themselves in saving of manpower in the form of developing a new application of their ideas in Intelligent Transport system(ITS). The world statistics shows that by incorporating such wireless radar system in the car would decrease the world road accident by 8-10% yearly. The wireless technology has to be chosen properly which is capable of tackling the sev...
CDMA Technology for Intelligent Transportation Systems
Bera, Rabindranath; Sil, Sanjib; Mondal, Dipak; Dhar, Sourav; Kandar, Debdatta
2007-01-01
Scientists and Technologists involved in the development of radar and remote sensing systems all over the world are now trying to involve themselves in saving of manpower in the form of developing a new application of their ideas in Intelligent Transport system(ITS). The world statistics shows that by incorporating such wireless radar system in the car would decrease the world road accident by 8-10% yearly. The wireless technology has to be chosen properly which is capable of tackling the severe interferences present in the open road. A combined digital technology like Spread spectrum along with diversity reception will help a lot in this regard. Accordingly, the choice is for FHSS based space diversity system which will utilize carrier frequency around 5.8 GHz ISM band with available bandwidth of 80 MHz and no license. For efficient design, the radio channel is characterized on which the design is based. Out of two available modes e.g. Communication and Radar modes, the radar mode is providing the conditiona...
A Novel Space-time Spreading Transmit Diversity Scheme for Wireless CDMA System
ZOU Yong-zhong; LI Dao-ben
2004-01-01
This paper presents a new two-branch space-time spreading transmit diversity scheme for wireless CDMA systems, which differs from Space-Time Spreading (STS) of CDMA-2000. Using two transmit and M receiving antennas, the new scheme provides diversity order of 2M. This new technique does not require any bandwidth expansion and any feed back from the receiver to the transmitter and its computation complexity is similar to the Maximal-Ratio Combining (MRC).
Monte-Carlo Simulation for PDC-Based Optical CDMA System
FAHIM AZIZ UMRANI; AHSAN AHMED URSANI; ABDUL WAHEED UMRANI
2010-01-01
This paper presents the Monte-Carlo simulation of Optical CDMA (Code Division Multiple Access) systems, and analyse its performance in terms of the BER (Bit Error Rate). The spreading sequence chosen for CDMA is Perfect Difference Codes. Furthermore, this paper derives the expressions of noise variances from first principles to calibrate the noise for both bipolar (electrical domain) and unipolar (optical domain) signalling required for Monte-Carlo simulation. The simulated res...
Performance Enhancement of MC-CDMA Systems through MAP based Multiuser Detection
K. Rasadurai
2012-05-01
Full Text Available The joint Multiuser Detection (MUD and turbo coding are the two powerful techniques for enhancing the performance of the MC-CDMA systems. The Multiple Access Interference (MAI is one of the factors that affect the Bit Error Rate (BER performance of the MC-CDMA systems. Maximum a posteriori (MAP criterion based multi user detector greatly improves the system performance and mitigates the effects of MAI. However its complexity increases exponentially with increase in number of users. In this paper a Logarithmic-MAP (LOGMAP based MUD is proposed for the MC-CDMA systems. It is shown that the proposed LOG-MAP based MUD scheme improves the BER of the system greatly and it also reduces the MAI and complexity of the system.
Rotated Walsh-Hadamard Spreading with Robust Channel Estimation for a Coded MC-CDMA System
Raulefs Ronald
2004-01-01
Full Text Available We investigate rotated Walsh-Hadamard spreading matrices for a broadband MC-CDMA system with robust channel estimation in the synchronous downlink. The similarities between rotated spreading and signal space diversity are outlined. In a multiuser MC-CDMA system, possible performance improvements are based on the chosen detector, the channel code, and its Hamming distance. By applying rotated spreading in comparison to a standard Walsh-Hadamard spreading code, a higher throughput can be achieved. As combining the channel code and the spreading code forms a concatenated code, the overall minimum Hamming distance of the concatenated code increases. This asymptotically results in an improvement of the bit error rate for high signal-to-noise ratio. Higher convolutional channel code rates are mostly generated by puncturing good low-rate channel codes. The overall Hamming distance decreases significantly for the punctured channel codes. Higher channel code rates are favorable for MC-CDMA, as MC-CDMA utilizes diversity more efficiently compared to pure OFDMA. The application of rotated spreading in an MC-CDMA system allows exploiting diversity even further. We demonstrate that the rotated spreading gain is still present for a robust pilot-aided channel estimator. In a well-designed system, rotated spreading extends the performance by using a maximum likelihood detector with robust channel estimation at the receiver by about 1 dB.
Application of Zero Correlation Zone Sequences in Quasi-synchronous CDMA Systems
LI Shu-feng; JIA Zhi-cheng; WANG Jing; LI Qi
2007-01-01
In a quasi-synchronous code division multiple access(QS-CDMA) system, the correlation functions around the origin influence the system performance and odd functions are as important as the even functions. Three kinds of zero correlation zone(ZCZ) sequences are used to analyze and compare the correlation functions. Binary phase shift keying(BPSK) simulations of QS-CDMA system with the three kinds of QS sequences as spreading codes on additive white Gaussian noise(AWGN) channel show that these sequences are quasi-orthogonal, so they are suitable for QS-CDMA system. The correlation between the system performance and the zero correlation zone of the sequence is also proved.
New Parallel Interference Cancellation for Convolutionally Coded CDMA Systems
Xu Guo-xiong; Gan Liang-cai; Huang Tian-xi
2004-01-01
Based on BCJR algorithm proposed by Bahl et al and linear soft decision feedback, a reduced-complexity parallel interference cancellation (simplified PIC) for convolutionally coded DS CDMA systems is proposed. By computer simulation, we compare the simplified PIC with the exact PIC. It shows that the simplified PIC can achieve the performance close to the exact PIC if the mean values of coded symbols are linearly computed in terms of the sum of initial a prior log-likelihood rate (LLR) and updated a prior LLR, while a significant performance loss will occur if the mean values of coded symbols are linearly computed in terms of the updated a prior LLR only. Meanwhile, we also compare the simplified PIC with MF receiver and conventional PICs. The simulation results show that the simplified PIC dominantly outperforms the MF receiver and conventional PICs, at signal-noise rate (SNR) of 7 dB, for example, the bit error rate is about 10-4 for the simplified PIC, which is far below that of matched-filter receiver and conventional PIC.
Performance Analysis of Handoff in CDMA Cellular System
Dr. Dalveer Kaur
2013-07-01
Full Text Available Handoff mechanism is extremely important in cellular network because of the cellular architecture employed to maximize spectrum utilization. This unique feature has driven the rapid growth in the mobile network industry, changing it from a new technology into a massive industry within less than two decades. Handoff is the essential functionality for dealing with the mobility of the mobile users. This paper shows the soft handoff effects on the uplink direction of IS-95 CDMA networks is carried out, leading to optimize soft handoff for capacity under perfect power control approach. In practical systems, there is a nonzero handoff completion delay and soft handoff provides the required robustness to delays, although it comes at the expense of additional network resources. Thus, there is a tradeoff between the extent of soft handoff required and the handoff execution delay. This paper presents an analytical framework to study this tradeoff and also discuss simulation results simulated with the help of Matlab. For this, handoff dropping probability is minimized up to 0.1%.
On the Capacity Degradation Due to Coexistence of WCDMA and CDMA2000 Systems
WU Jiang; LIANG Shuang-chun; NIU Kai; WU Wei-ling
2004-01-01
In this paper, we investigate the capacity degradation due to the coexistence of WCDMA and CDMA2000 networks by system-level Monte Carlo simulation. Both systems are simulated according to the deployment of macro cells, and speech service is considered. The capacity losses under different carrier spacing and different geographical offset are evaluated. Simulation results show that considerable capacity loss is seen when WCDMA is the victim system, while the influence of WCDMA to CDMA2000 is slight. Increasing carrier-to-carrier spacing and decreasing geographical offset lead to less capacity loss and co-locating the base stations of both systems is a preferred solution.
Blind Identification and Equalization of MC-CDMA Systems Using Higher Order Cumulants
Mohammed Zidane
2014-04-01
Full Text Available In this work we propose an algorithm based on fourth order cumulants for identification of the linear system (Finite- Impulse Response (FIR with Non Minimum Phase (NMP excited by non-Gaussian sequences, independent identically distributed (i.i.d. In order to test its efficiency, we have compared with the Safi et al. algorithm, for that we considered three practical frequency-selective fading channel, called Broadband Radio Access Network (BRAN A, BRAN B, and BRAN D, normalized for MC-CDMA systems. In the part of MC-CDMA, we use the zero forcing (ZF and the minimum mean square error (MMSE equalizers to perform our algorithms. The simulation results show that the bit error rate (BER performances of the downlink MC-CDMA systems, using proposed algorithm (AlgoZ is more accurate compared with the results obtained with the Safi et al. (Alg-CUM algorithm.
Performance of MC-MC CDMA Systems With Nonlinear Models of HPA
Labib Francis Gergis
2011-02-01
Full Text Available A new wireless communication system denoted as Multi-Code Multi-Carrier CDMA (MC-MCCDMA, which is the combination of Multi-Code CDMA and Multi-Carrier CDMA, is analyzed in thispaper. This system can satisfy multi-rate services using multi-code schemes and muti-carrier servicesused for high rate transmission. The system is evaluated using Traveling Wave Tube Amplifier (TWTA.This type of amplifiers continue to offer the best microwave high power amplifiers (HPA performance interms of power efficiency, size and cost, but lag behind Solid State Power Amplifiers (SSPA's in linearity.This paper presents a technique for improving TWTA linearity. The use of pre-distorter (PDlinearization technique is described to provide TWTA performance comparable or superior toconventional SSPA's. The characteristics of the PD scheme is derived based on the extension of Saleh'smodel for HPA
A Two-Level Spreading-despreading CDMA System and Its Performance Evaluation
无
2003-01-01
A new two-level spreading-despreading scheme is presented in this paper. By adopting the two-level scheme, the Generalized Orthogonal (GO) zone of GO codes can be utilized. In this paper, the forward link of a multi-cell CDMA system employing the two-level scheme is presented and analyzed. The BER performance obtained by Gaussian Approximation is compared with that of the conventional single-level spreading-despreading system. The results reveal that the two*$-level CDMA system introduced in this paper exhibits larger performance gain when time delay can be restricted within a given zone.
Bit Error Rate Analysis for MC-CDMA Systems in Nakagami-m Fading Channels
Zexian Li
2004-09-01
Full Text Available Multicarrier code division multiple access (MC-CDMA is a promising technique that combines orthogonal frequency division multiplexing (OFDM with CDMA. In this paper, based on an alternative expression for the Q-function, characteristic function and Gaussian approximation, we present a new practical technique for determining the bit error rate (BER of multiuser MC-CDMA systems in frequency-selective Nakagami-m fading channels. The results are applicable to systems employing coherent demodulation with maximal ratio combining (MRC or equal gain combining (EGC. The analysis assumes that different subcarriers experience independent fading channels, which are not necessarily identically distributed. The final average BER is expressed in the form of a single finite range integral and an integrand composed of tabulated functions which can be easily computed numerically. The accuracy of the proposed approach is demonstrated with computer simulations.
Dynamic interactions between asynchronous grids interconnected through an MTDC system
Endegnanew, Atsede Gualu; Beerten, Jef; Uhlen, Kjetil
2015-01-01
The large-scale integration of renewable energy sources in the power system, combined with the need for an increased transmission capacity has led to a growing interest in multi-terminal high voltage dc (MTDC) grids. In the future, these grids will be integrated with different existing asynchronous ac grids, eventually resulting in hybrid AC/DC power systems. This paper investigates interactions between asynchronous ac grids in a hybrid AC/DC power system. In the study, a symmetrical monopola...
Solving SAT and Hamiltonian Cycle Problem Using Asynchronous P Systems
Tagawa, Hirofumi; Fujiwara, Akihiro
In the present paper, we consider fully asynchronous parallelism in membrane computing, and propose two asynchronous P systems for the satisfiability (SAT) and Hamiltonian cycle problem. We first propose an asynchronous P system that solves SAT with n variables and m clauses, and show that the proposed P system computes SAT in O(mn2n) sequential steps or O(mn) parallel steps using O(mn) kinds of objects. We next propose an asynchronous P system that solves the Hamiltonian cycle problem with n nodes, and show that the proposed P system computes the problem in O(n!) sequential steps or O(n2) parallel steps using O(n2) kinds of objects.
Code division multiple access (CDMA)
Buehrer, R Michael
2006-01-01
This book covers the basic aspects of Code Division Multiple Access or CDMA. It begins with an introduction to the basic ideas behind fixed and random access systems in order to demonstrate the difference between CDMA and the more widely understood TDMA, FDMA or CSMA. Secondly, a review of basic spread spectrum techniques are presented which are used in CDMA systems including direct sequence, frequency-hopping and time-hopping approaches. The basic concept of CDMA is presented, followed by the four basic principles of CDMA systems that impact their performance: interference averaging, universa
Monte-Carlo Simulation for PDC-Based Optical CDMA System
FAHIM AZIZ UMRANI
2010-10-01
Full Text Available This paper presents the Monte-Carlo simulation of Optical CDMA (Code Division Multiple Access systems, and analyse its performance in terms of the BER (Bit Error Rate. The spreading sequence chosen for CDMA is Perfect Difference Codes. Furthermore, this paper derives the expressions of noise variances from first principles to calibrate the noise for both bipolar (electrical domain and unipolar (optical domain signalling required for Monte-Carlo simulation. The simulated results conform to the theory and show that the receiver gain mismatch and splitter loss at the transceiver degrades the system performance.
A CDMA architecture for a Ka-band Personal Access Satellite System
Motamedi, Masoud; Sue, Miles K.
1990-01-01
A Code Division Multiple Access (CDMA) architecture is currently being studied for use in a Ka-band Personal Access Satellite System (PASS). The complete architecture consisting of block diagrams of the user terminal, the supplier station, the network management center, and the satellite is described along with the access methods and frequency/time plans. The complexity of developing this system using the CDMA architecture is compared to that of a Frequency Division Multiple Access (FDMA) architecture. The inherent advantages and disadvantages of the two architectures are compared and their respective capacities are discussed.
COMPUTER SIMULATION OF RAYLEIGH FADING CHANNELS IN MC-CDMA SYSTEMS
无
2007-01-01
For Multi-Carrier-Code Division Multiple Access (MC-CDMA) systems, it is usually assumed that the fading of the subcarriers is frequency non-selective and independent of each other.This paper shows that the two assumptions are incompatible. In fact, the MC-CDMA signals at each subcarrier undergo fading that are highly correlated. Based on this observation, this paper develops a simulation algorithm for Rayleigh fading channels via frequency-domain correlation function, which incorporates the Doppler effect simultaneously. Numerical examples are presented to demonstrate the effectiveness of the new algorithm, with the conclusion that the independence assumption of subcarrier fading overrates the system performance.
Interference Analysis of TD-SCDMA System and CDMA2000 System
Hao Chen
2012-01-01
Full Text Available Abstract—In this paper, the feasibility of co-channel coexistence of Time Division- Synchronous Code Division Multiple Access（TD-SCDMA）and Code Division Multiple Access 2000（CDMA2000）systems operating in a macro cell environment is investigated. The deterministic analysis and simulation method are used to evaluate the performance compromising of both systems. Based on a more efficient calculation scheme, a novel deterministic equation is proposed and used to provide a better interpretation of the relationship between aggressor and victim in the interference system. The evaluation and simulation results show consistency with the corresponding experiment results. Furthermore, the interference characteristics of Omni-antenna and smart antenna in TD-SCDMA and CDMA2000 are compared, providing an important guideline to reduce the interference of two systems.
Interference Analysis of TD-SCDMA System and CDMA2000 System
Hao Chen; Tong Yang; Jianfu Teng; Hong He
2012-01-01
Abstract—In this paper, the feasibility of co-channel coexistence of Time Division- Synchronous Code Division Multiple Access（TD-SCDMA）and Code Division Multiple Access 2000（CDMA2000）systems operating in a macro cell environment is investigated. The deterministic analysis and simulation method are used to evaluate the performance compromising of both systems. Based on a more efficient calculation scheme, a novel deterministic equation is proposed and used to provide a better inter...
Multi User Detection For Cdma-Ofdm/Oqam System Combined With Space Time Coding
Radhia GHARSALLAH
2012-09-01
Full Text Available In this paper, we propose the combination of Multi Carrier (MC OFDM/OQAM modulation and CDMAcalled MC-CDMA-OQAM system with Space Time (ST coding in a multi user context. This combination takes advantages from multicarrier modulation, spread spectrum and spatial time diversity. Indeed, theuse of OFDM has proved its ability to fight against frequency selective channels but the insertion of guard interval yields spectral efficiency loss and sensitivity to frequency dispersion due to the use of rectangular pulse shape. Thus, cyclic prefix OFDM is replaced by an advanced ﬁlterbank-based multicarrier system OFDM/OQAM that operates without guard interval. However, OFDM/OQAM provides orthogonality only on the real domain, so transmitted symbols must be real valued. In the other hand, the CDMA component has two advantages: multiple access interference cancellation and providing orthogonality in the complex domain. From the orthogonality property provided, the Alamouti ST code can be combined with MC-CDMA-OQAM system. The resulting MIMO-MC-CDMA-OQAM system improves the spectral efficiency of wireless system, combat channel fading and reduce narrowband interference. Numerical results show the utility of this new wireless communication system; a significant BER versus Signal to Noise Ratio (SNR was achieved thus Multiple access interference (MAI is suppressed and so supporting a large number of users.
Fok, Mable P; Deng, Yanhua; Prucnal, Paul R
2010-04-01
We experimentally demonstrate what we believe to be a novel detection scheme for interfacing asynchronous optical code division multiple access (CDMA) signals with an electronic clock and data recovery system that operates only at the baseband bandwidth. This allows using a large optical bandwidth expansion factor in which the optical chip rate is much larger than the bandwidth of the optoelectronic receiver. The received optical CDMA signal is launched into a four-wave-mixing-based wavelength-aware all-optical front end that rejects multiaccess interference, followed by an amplitude-noise suppression stage comprised of a semiconductor optical amplifier. The clean signal is then converted into a non-return-to-zero-like signal by a baseband receiver. Using the proposed detection scheme, asynchronous transmission and detection of optical CDMA signals is implemented. With the novel detection scheme, the classic CDMA near-far problem is mitigated, and error-free detection is easily obtained. PMID:20364229
Song Rongfang; Bi Guangguo
2001-01-01
Quadratic programming models for integrated space-time interference suppression in CDMA systems are proposed in this paper. The models integrate the advantages of smart antenna and RAKE receiver, mitigate multiuser access interference (MAI) and interchip interference (ICI),and combine multipath components. The zero-forcing conditions are derived. Neural network implementation of the models is also studied.
Manmohan chandoliya
2015-02-01
Full Text Available Recently conventional Multi-carrier Code Division Multiple Access (MC-CDMA, techniques attract more attention of researcher’s due to its high frequency spectrum efficiency and high data rate transmission. The aim of this work is to investigate the performance of multicarrier code division multiple access (MC-CDMA technique, which is a key technology for efficient and reliable communication due to its high frequency spectrum efficiency and high data rate transmission. This paper presents the performance of conventional MC-CDMA system, orthogonal wavelet packet based MC-CDMA system (WP-MC-CDMA, and Huang, Hilbert Transformation (HHT based MC-CDMA system. This scheme outperforms other two techniques, because this scheme is based on the knowledge of the instantaneous channel stateinformation, or based on instantaneous imperfect channel estimates. Thus, by the knowledge of their channel gains or channel information, it can analyze the data more accurately. Hence, it is a more spectral efficient and high data rate transmission scheme compared to the conventional MC-CDMAand WP-MC-CDMA..
Differential Space-Time Block Code Modulation for DS-CDMA Systems
Liu Jianhua
2002-01-01
Full Text Available A differential space-time block code (DSTBC modulation scheme is used to improve the performance of DS-CDMA systems in fast time-dispersive fading channels. The resulting scheme is referred to as the differential space-time block code modulation for DS-CDMA (DSTBC-CDMA systems. The new modulation and demodulation schemes are especially studied for the down-link transmission of DS-CDMA systems. We present three demodulation schemes, referred to as the differential space-time block code Rake (D-Rake receiver, differential space-time block code deterministic (D-Det receiver, and differential space-time block code deterministic de-prefix (D-Det-DP receiver, respectively. The D-Det receiver exploits the known information of the spreading sequences and their delayed paths deterministically besides the Rake type combination; consequently, it can outperform the D-Rake receiver, which employs the Rake type combination only. The D-Det-DP receiver avoids the effect of intersymbol interference and hence can offer better performance than the D-Det receiver.
A comparison study of CDMA versus TDMA/FDMA LEO satellite systems
Ciocco, Timothy Michael
1996-01-01
In this thesis, two LEO satellite systems with different multiple access schemes are analyzed. The first system, GLOBALSTAR, uses CDMA. Equations are developed to calculate the maximum capacity of one satellite, of one satellite's user beam, and of the entire GLOBALSTAR system over CONUS. A detailed description of GLOBALSTAR's outage probability, the probability that a call will be dropped from the system or blocked from connection with the system, is given and graphed against varying average...
DOA Estimation in the Uplink of Multicarrier CDMA Systems
Antonio A. D'Amico; Michele Morelli; Luca Sanguinetti
2008-01-01
We consider the uplink of a multicarrier code-division multiple-access (MC-CDMA) network and assume that the base station is endowed with a uniform linear array. Transmission takes place over a multipath channel and the goal is the estimation of the directions of arrival (DOAs) of the signal from the active users. In a multiuser scenario, difficulties are primarily due to the large number of parameters involved in the estimation of the DOAs which makes this problem much more challenging than...
CUCKOO SEARCH-AIDED LMS ALGORITHM FOR CHANNEL ESTIMATION IN MC-CDMA SYSTEMS
Balaji, S.; N. Vasudevan
2014-01-01
In the progress of transmission systems that uses the diversity in various domains, the execution of competent baseband receivers categorized by affordable computational load is an essential thing. This would be an imperative point in the future expansion of 4G systems in which the space, time and frequency diversity will be merged together to enhance the system throughput. Here, we develop a channel estimation technique for MC-CDMA system for the minimization of BER and the maximization of t...
WAVELET-BASED OFDM-CDMA HIGH SPEED POWER LINE COMMUNICATION SYSTEMS
Zhou Lerong; Guo Jinghong; Wei Gang
2004-01-01
This letter derives the Equivalent M-band Discrete Wavelet(EMDW) transmission mode of Orthogonal Frequency Division Multiplexing(OFDM) transmission systems, and presents a new Quadrature M-band Discrete Wavelet(QMDW) based OFDM-CDMA(Code Division Multiple Access) communication systems for high speed Power Line Communication (PLC) channels.This system gives much better robustness to Inter-Channel Interference (ICI), Multi-User Interference (MUI) and noise interference, which is verified by simulation.
Madhukumar A. S.
2004-01-01
Full Text Available Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.
Kumaravel, Rasadurai; Narayanaswamy, Kumaratharan
2015-01-01
Multi carrier code division multiple access (MC-CDMA) system is a promising multi carrier modulation (MCM) technique for high data rate wireless communication over frequency selective fading channels. MC-CDMA system is a combination of code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM). The OFDM parts reduce multipath fading and inter symbol interference (ISI) and the CDMA part increases spectrum utilization. Advantages of this technique are its robustness in case of multipath propagation and improve security with the minimize ISI. Nevertheless, due to the loss of orthogonality at the receiver in a mobile environment, the multiple access interference (MAI) appears. The MAI is one of the factors that degrade the bit error rate (BER) performance of MC-CDMA system. The multiuser detection (MUD) and turbo coding are the two dominant techniques for enhancing the performance of the MC-CDMA systems in terms of BER as a solution of overcome to MAI effects. In this paper a low complexity iterative soft sensitive bits algorithm (SBA) aided logarithmic-Maximum a-Posteriori algorithm (Log MAP) based turbo MUD is proposed. Simulation results show that the proposed method provides better BER performance with low complexity decoding, by mitigating the detrimental effects of MAI. PMID:25714917
Detailed Mathematical Analysis and Performance Evaluation of MIMO-OFDM-CDMA System Using ZF Receiver
Ekta Charaya
2013-07-01
Full Text Available In this paper, we have presented the detailed mathematical analysis of the output signal to interference noise ratio (SINR for MIMO-OFDM-CDMA system using joint space-time frequency (STF spreading with ZF receiver. A 2x2 and 4x4 MIMO system is used for performance evaluation in terms of BER. The analysis shows that output SINR decreases, as the number of users increases. The average bit error probability of the system using ZF receiver is derived for different number of users. We also present exponential bound of the complementary error function (erfc for probability of error. Simulation results of MIMO-OFDM-CDMA system are in line with the results obtained through mathematical analysis
Impact of Different Spreading Codes Using FEC on DWT Based MC-CDMA System
Masum, Saleh; Kabir, M. Hasnat; Islam, Md. Matiqul; Shams, Rifat Ara; Ullah, Shaikh Enayet
2012-01-01
The effect of different spreading codes in DWT based MC-CDMA wireless communication system is investigated. In this paper, we present the Bit Error Rate (BER) performance of different spreading codes (Walsh-Hadamard code, Orthogonal gold code and Golay complementary sequences) using Forward Error Correction (FEC) of the proposed system. The data is analyzed and is compared among different spreading codes in both coded and uncoded cases. It is found via computer simulation that the performance...
Successive Interference Cancellation for DS-CDMA Systems with Transmit Diversity
Li Wei
2004-01-01
Full Text Available We introduce a new successive interference cancellation (SIC technique for direct sequence code division multiple access (DS-CDMA systems with transmit diversity. The transmit diversity is achieved with a space-time block code (STBC. In our work we first consider hard decision SIC with an STBC, and then investigate the performance of soft decision SIC with an STBC. System performance over a Rayleigh fading channel is investigated and the analysis is confirmed by simulation.
Analysis of a Priority Stack Random Access Protocol In W-CDMA Systems
Al Agha, Khaldoun; Jacquet, Philippe; Vvedenskay, Nikita
2000-01-01
The stack protocol (called also tree protocol) can be used in order to introduce a priority mechanism on the random access stage in W-CDMA. Indeed, after second generation networks supporting voice service only, the third generation systems (UMTS) should offer more services with quality and priority. However, all priorities in the UMTS system are based on the dedicated channel and after the random access mechanism that use the weak access protocol: slotted aloha. In this paper, we analyze the...
Performance of Power Decentralized Detection in Wireless Sensor System With DS-CDMA
Ali M. Fadhil
2012-08-01
Full Text Available Wireless sensor networks take great importance in recent years according to their potential applications in different areas like health monitoring, military applications, tactile system and industrial applications. In this paper the decentralized sensing with noise and band limited channel between the sensor nodes and merging stations (fusion center for different levels of power is analyzed. The evolution of the system performance is based on the considering the wireless sensor network with direct sequence-code divisionmultiple access (DS-CDMA for varying levels of power. The achieved results indicate the performance is improved with employing the direct sequence-code division multiple accesses (DS-CDMA. In the situation of large sensor systems and random spreading, the decentralized detection execution is derived supposition independent and identically distributed sensor observation via random matrix theory.
On the Performance of Synchronous DS—CDMA Systems with Generalized Orthogonal Spreading Codes
HAOLi; FANPingzhi
2003-01-01
A new synchronous DS-CDMA system em-ploying generalized orthogonal (GO) spreading codes and maximum ratio combining (MRC) scheme is presented in this paper. In particular, the forward link of the system is discussed in detail. The GO codes are used to combat the interference caused by multipath components. The aver-age correlation properties of GO codes are evaluated andthe signal interference ratio (SIR) expressions based on the Rayleigh and Racian fading multipath channel models are derived respectively. The link performance in terms of bit error rate (BER) is obtained for GO codes with different orthogonal zones by Gaussian Approximation and Monte-Carlo simulation respectively. The results reveal that the GO codes appear better BER performance than traditional orthogonal codes in synchronous CDMA systems, and the GO code with larger orthogonal zone exhibits larger per-formance gain.
Time of Arrival Estimation in Probability-Controlled Generalized CDMA Systems
Hagit Messer
2007-11-01
Full Text Available In recent years, more and more wireless communications systems are required to provide also a positioning measurement. In code division multiple access (CDMA communication systems, the positioning accuracy is significantly degraded by the multiple access interference (MAI caused by other users in the system. This MAI is commonly managed by a power control mechanism, and yet, MAI has a major effect on positioning accuracy. Probability control is a recently introduced interference management mechanism. In this mechanism, a user with excess power chooses not to transmit some of its symbols. The information in the nontransmitted symbols is recovered by an error-correcting code (ECC, while all other users receive a more reliable data during these quiet periods. Previous research had shown that the implementation of a probability control mechanism can significantly reduce the MAI. In this paper, we show that probability control also improves the positioning accuracy. We focus on time-of-arrival (TOA based positioning systems. We analyze the TOA estimation performance in a generalized CDMA system, in which the probability control mechanism is employed, where the transmitted signal is noncontinuous with a symbol transmission probability smaller than 1. The accuracy of the TOA estimation is determined using appropriate modifications of the Cramer-Rao bound on the delay estimation. Keeping the average transmission power constant, we show that the TOA accuracy of each user does not depend on its transmission probability, while being a nondecreasing function of the transmission probability of any other user. Therefore, a generalized, noncontinuous CDMA system with a probability control mechanism can always achieve better positioning performance, for all users in the network, than a conventional, continuous, CDMA system.
Spreading Code Assignment Strategies for MIMO-CDMA Systems Operating in Frequency-Selective Channels
Claude D'Amours
2009-01-01
Full Text Available Code Division Multiple Access (CDMA and multiple input multiple output- (MIMO- CDMA systems suffer from multiple access interference (MAI which limits the spectral efficiency of these systems. By making these systems more power efficient, we can increase the overall spectral efficiency. This can be achieved through the use of improved modulation and coding techniques. Conventional MIMO-CDMA systems use fixed spreading code assignments. By strategically selecting the spreading codes as a function of the data to be transmitted, we can achieve coding gain and introduce additional degrees of freedom in the decision variables at the output of the matched filters. In this paper, we examine the bit error rate performance of parity bit-selected spreading and permutation spreading under different wireless channel conditions. A suboptimal detection technique based on maximum likelihood detection is proposed for these systems operating in frequency selective channels. Simulation results demonstrate that these code assignment techniques provide an improvement in performance in terms of bit error rate (BER while providing increased spectral efficiency compared to the conventional system. Moreover, the proposed strategies are more robust to channel estimation errors as well as spatial correlation.
Spreading Code Assignment Strategies for MIMO-CDMA Systems Operating in Frequency-Selective Channels
Dahmane AdelOmar
2009-01-01
Full Text Available Abstract Code Division Multiple Access (CDMA and multiple input multiple output- (MIMO- CDMA systems suffer from multiple access interference (MAI which limits the spectral efficiency of these systems. By making these systems more power efficient, we can increase the overall spectral efficiency. This can be achieved through the use of improved modulation and coding techniques. Conventional MIMO-CDMA systems use fixed spreading code assignments. By strategically selecting the spreading codes as a function of the data to be transmitted, we can achieve coding gain and introduce additional degrees of freedom in the decision variables at the output of the matched filters. In this paper, we examine the bit error rate performance of parity bit-selected spreading and permutation spreading under different wireless channel conditions. A suboptimal detection technique based on maximum likelihood detection is proposed for these systems operating in frequency selective channels. Simulation results demonstrate that these code assignment techniques provide an improvement in performance in terms of bit error rate (BER while providing increased spectral efficiency compared to the conventional system. Moreover, the proposed strategies are more robust to channel estimation errors as well as spatial correlation.
Chain simulation of DS-CDMA communication systems
Armisén Morell, Albert
2010-01-01
Català: En aquest projecte s'ha analitzat e implementat un sistema basat amb DSSS-CDMA amb un receptor comú y diversos transmissors sobre una plataforma modular en Matlab, essent aquesta una eina de validació teòrica. S'ha primat aquesta per sobre d'una implementació en DSP principalment pel cost ecònomic de les plaques DSP. Així, s'ha decidit fer una implementació en Matlab amb les restriccions pròpies d'una placa DSP. El principal objectiu del projecte es la validació del sistema mitjançant...
Bounds for the Sum Capacity of Binary CDMA Systems in Presence of Near-Far Effect
Pad, P; Mansouri, S M; Kabir, P; Marvasti, F
2010-01-01
In this paper we are going to estimate the sum capacity of a binary CDMA system in presence of the near-far effect. We model the near-far effect as a random variable that is multiplied by the users binary data before entering the noisy channel. We will find a lower bound and a conjectured upper bound for the sum capacity in this situation. All the derivations are in the asymptotic case. Simulations show that especially the lower bound is very tight for typical values Eb/N0 and near-far effect. Also, we exploit our idea in conjunction with the Tanaka's formula [6] which also estimates the sum capacity of binary CDMA systems with perfect power control.
Performance of Turbo Interference Cancellation Receivers in Space-Time Block Coded DS-CDMA Systems
Emmanuel Oluremi Bejide
2008-07-01
Full Text Available We investigate the performance of turbo interference cancellation receivers in the space time block coded (STBC direct-sequence code division multiple access (DS-CDMA system. Depending on the concatenation scheme used, we divide these receivers into the partitioned approach (PA and the iterative approach (IA receivers. The performance of both the PA and IA receivers is evaluated in Rayleigh fading channels for the uplink scenario. Numerical results show that the MMSE front-end turbo space-time iterative approach receiver (IA effectively combats the mixture of MAI and intersymbol interference (ISI. To further investigate the possible achievable data rates in the turbo interference cancellation receivers, we introduce the puncturing of the turbo code through the use of rate compatible punctured turbo codes (RCPTCs. Simulation results suggest that combining interference cancellation, turbo decoding, STBC, and RCPTC can significantly improve the achievable data rates for a synchronous DS-CDMA system for the uplink in Rayleigh flat fading channels.
Coding Across Multicodes and Time in CDMA Systems Employing MMSE Multiuser Detector
Park Jeongsoon
2004-01-01
Full Text Available When combining a multicode CDMA system with convolutional coding, two methods have been considered in the literature. In one method, coding is across time in each multicode channel while in the other the coding is across both multicodes and time. In this paper, a performance/complexity analysis of decoding metrics and trellis structures for the two schemes is carried out. It is shown that the latter scheme can exploit the multicode diversity inherent in convolutionally coded direct sequence code division multiple access (DS-CDMA systems which employ minimum mean squared error (MMSE multiuser detectors. In particular, when the MMSE detector provides sufficiently different signal-to-interference ratios (SIRs for the multicode channels, coding across multicodes and time can obtain significant performance gain over coding across time, with nearly the same decoding complexity.
Blind ICA detection based on second-order cone programming for MC-CDMA systems
Jen, Chih-Wei; Jou, Shyh-Jye
2014-12-01
The multicarrier code division multiple access (MC-CDMA) technique has received considerable interest for its potential application to future wireless communication systems due to its high data rate. A common problem regarding the blind multiuser detectors used in MC-CDMA systems is that they are extremely sensitive to the complex channel environment. Besides, the perturbation of colored noise may negatively affect the performance of the system. In this paper, a new coherent detection method will be proposed, which utilizes the modified fast independent component analysis (FastICA) algorithm, based on approximate negentropy maximization that is subject to the second-order cone programming (SOCP) constraint. The aim of the proposed coherent detection is to provide robustness against small-to-medium channel estimation mismatch (CEM) that may arise from channel frequency response estimation error in the MC-CDMA system, which is modulated by downlink binary phase-shift keying (BPSK) under colored noise. Noncoherent demodulation schemes are preferable to coherent demodulation schemes, as the latter are difficult to implement over time-varying fading channels. Differential phase-shift keying (DPSK) is therefore the natural choice for an alternative modulation scheme. Furthermore, the new blind differential SOCP-based ICA (SOCP-ICA) detection without channel estimation and compensation will be proposed to combat Doppler spread caused by time-varying fading channels in the DPSK-modulated MC-CDMA system under colored noise. In this paper, numerical simulations are used to illustrate the robustness of the proposed blind coherent SOCP-ICA detector against small-to-medium CEM and to emphasize the advantage of the blind differential SOCP-ICA detector in overcoming Doppler spread.
Semi-hard interference cancellation for uncoded DS-CDMA systems
Kasparis, C; Piechocki, RJ; Nix, AR; Fletcher, PN
2004-01-01
A new iterative technique for suppressing multiuser interference in uncoded DS-CDMA systems is proposed. In the new approach semi-hard decisions are taken at the output of the linear MMSE detector. This involves taking hard decisions only for symbols which satisfy a reliability criterion, while the rest are left unaltered in their soft form. The semi-hard estimate is subsequently used for parallel interference cancellation, which is then followed by additional linear MMSE filtering. This proc...
Performance of Adaptive Multiuser Detectors in Space-Time Coded CDMA Systems
Alam, MM; Chockalingam, A
2003-01-01
In this paper, we present a comparative performance evaluation of adaptive multiuser detectors, including stochastic gradient (SG) and recursive least squares (RLS) algorithms (which require training data), and minimum output energy (MOE) and subspace-based MMSE (S-MMSE) algorithms (which do not require training data), under near-far conditions in a space-time coded CDMA system. VVe show that, in a near-far multiuser scenario, increasing the number of transmit antennas degrade the near-far re...
SINR evaluation of OFDM-CDMA systems with constant timing offset: asymptotic analysis
Nasser, Youssef; des Noes, Mathieu; Ros, Laurent; Jourdain, Geneviève
2005-01-01
This article presents the impact of a constant timing error on the performance of a downlink 2 dimensional spreading OFDM-CDMA system. This impact is measured by the Signal to Interference plus Noise Ratio (SINR) degradation after equalization and despreading. Using random matrix theory, an asymptotic evaluation of the SINR is obtained. It is independent of the value of users' spreading code while taking into account their orthogonality. Simulation results are provided to evaluate and discuss...
Coherent Code Tracking for Spatial Transmit Diversity DS-CDMA Systems
Stewart, R. W.; Iain G. Stirling; Garrey W. Rice
2005-01-01
Spatial transmit diversity schemes are now well integrated into third-generation cellular mobile communication system specifications. When DS-CDMA-based technology is deployed in typical macro- and microcell environments, multipath diversity and spatial diversity may be exploited simultaneously by a 2D RAKE receiver. The work presented in this paper focuses on taking advantage of spatial transmit diversity in synchronising the 2D RAKE structure. We investigate the use of coherent and noncoher...
基于CDMA的移动学系统%Mobile Learning System Over CDMA
郑明秀
2003-01-01
本文构建的以CDMA为承载基础的基于连接的移动学习系统MLSC(Mobile Learning System over CDMA),采取若干策略将现有的固定远程学习系统转换到移动环境中而形成移动学习系统.
Two Schemes of Blind MMSE Multiuser Receiver for Space-Time Coded CDMA Systems
LU Min; XU Chang-jiang; FENG Guang-zeng
2004-01-01
Minimum Mean Square Error (MMSE) multiuser detection yields the highest output SINR among all linear detectors. The blind MMSE linear detector can be implemented with batch processes or sequential processes. In this paper, according to the different implementations of blind detectors, the authors analyze two schemes of the blind MMSE multiuser receiver for space-time coded CDMA Systems and make a comparison between both schemes by the theoretical analysis and numerical simulations.
JOINT SPACE-FREQUENCY MULTIUSER SYMBOL DETECTOR FOR MC-CDMA SYSTEM WITH UNIFORM LINEAR ARRAY
Wu Xiaojun; Yin Qinye; Feng Aigang; Zhao Zheng; Zhang Jianguo
2002-01-01
The MultiCarrier Code Division Multiple Access (MC-CDMA) scheme is promising for relieving capacity limit problems of Direct Sequence (DS-) CDMA systems due to serious InterChip Interference (ICI) and MultiUser Interference (MUI) in high-data-rate wireless communication systems. In this paper, the Uniform Linear Array (ULA) is applied to the base station of macrocellular MC-CDMA systems in a frequency-selective fading channel environment. A joint space-frequency multiuser symbol sequence detector is developed for all active users within one macrocell without space-frequency channel estimation. Simultaneously, Directions-Of-Arrivals (DOAs) of all active users can also be estimated. By dividing the ULA into two identical overlapping subarrays, a specific auxiliary matrix is constructed, which includes both symbol sequence and DOA information of all active users. Then, based on the subspace method, performing the eigen decomposition on such auxiliary matrix, the closed-form solution of symbol sequences and DOAs for all active users can be obtained. In comparison with schemes based on channel estimation, our algorithm need not explicitly estimate the space-frequency channel for each active user,so it has lower computation complexity. Extensive computer simulations demonstrate the overall performance of this novel scheme.
JOINT SPACE－FREQUENCY MULTIUSER SYMBOL DETECTOR FOR MC－CDMA SYSTEM WITH UNIFORM LINEAR ARRAY
无
2002-01-01
The MultiCarrier COde Division Multiple Access (MC-CDMA) scheme is promising for relieving capacity limit problems of Direct Sequence(DS-CDMA systems due to serious InterCip Interference(ICI) and MultiUser Interference(MUI)in high-data-rate wireless communication systems.In this paper the Uniform Linear Array(ULA) is applied to the base station of macrocellular MC-CDMA systems in a frequency-selective fading channel environment.A joint space-frequency multiuser symblo sequence detector is developed for all active users within one macrocell without space-frequency channel estimation.Simultaneously,Directions-of -Arrivals (ODAs)of all active users can also be estimated.By dividing the ULA into two identical overlapping subarrays,a specific auxiliary matrix is constructed,which includes both symbol sequence and DOA information of all active users,Then,based on the subspace method,performing the eigen decomposition on such auxiliary matrix,the closed-form solution of symbol sequences and DOAs for all active users can be obtained.In comparison with schemes based on channel estimation,our algorithm need not explicitly estimate the space-frequency channel for each active user,so it has lower computation complexity,Extensive computer simulations demonstrate the overall performance of this novel scheme.
Asynchronous Cooperative e-Learning System and Its Evaluation
Eto, Kazuhiro; Miyoshi, Takumi
Much attention has been attracted to collaborative learning on an e-learning system. However, it is difficult to implement the collaborative environment to an asynchronous e-learning system since collaboration would be realized only when learners join the system at the same time. On the other hand, cooperative learning has been proposed. In this method, learners can study on their own pace without making mutual agreement but with receiving cognitive information from others. In this paper, the authors have developed the asynchronous cooperative e-learning system that provides learners' attendance and studying progress as the cognitive information. The subjective evaluation experiments show that our system is slightly inferior to the synchronous collaborative e-learning system, but it can motivate the learners more than the conventional system.
Time Delay Tracking for Multiuser Synchronization in CDMA Networks
Zahid Ali
2013-09-01
Full Text Available Multipath propagation, multiple access interference and non-line of sight propagation, etc. have impeded the accuracy in mobile data measurements. Multiuser receivers in asynchronous Code Division Multiple Access (CDMA systems require the knowledge of several parameters such as timing delay between users. In this paper, the problem of time delay estimation for CDMA systems is examined by proposing an approach based on blind nonlinear least mean squares (LMS based early-late delay tracker. A system model is developed and a delay tracking algorithm is presented. The simulation results of the proposed delay tracker are compared with the classical delay-locked loop (DLL approach in a multipath scenario and these show that the proposed delay tracker provides very good performance in challenging cases of closely spaced multipath delays.
Adaptive digital beamforming for a CDMA mobile communications payload
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
Improvement of BER performance in MIMO-CDMA systems by using initial-phase optimized gold codes
Develi, Ibrahim; Filiz, Meryem
2013-01-01
This paper describes a new approach to improve the bit error rate (BER) performance of a multiple-input multiple-output code-division multiple-access (MIMO-CDMA) system over quasi-static Rayleigh fading channels. The system considered employs robust space-time successive interference cancellation detectors and initial-phase optimized Gold codes for the improvement. The results clearly indicate that the use of initial-phase optimized Gold codes can significantly improve the BER performance of the system compared to the performance of a multiuser MIMO-CDMA system with conventional nonoptimized Gold codes. Furthermore, this performance improvement is achieved without any increase in system complexity.
RF and ELF Exposures from Cellular Phone Handsets: TDMA and CDMA Systems (invited paper)
The future digital systems for personal communications have now been partially standardised, so it is possible to get a good idea of the exposure power levels and time variation of the power, which may be assumed to be the two biologically relevant parameters. Using GSM and the coming UMTS system the relevant details are discussed, where the main difference is between the highly periodic TDMA (Time Division Multiple Access) power variation and the more smooth, slowly varying CDMA signal (Code Division Multiple Access). Epidemiological and biological studies must reflect the intricate details of the various systems. (author)
Detailed Mathematical Analysis and Performance Evaluation of MIMO-OFDM-CDMA System Using ZF Receiver
Ekta Charaya; Deepak Kedia
2013-01-01
In this paper, we have presented the detailed mathematical analysis of the output signal to interference noise ratio (SINR) for MIMO-OFDM-CDMA system using joint space-time frequency (STF) spreading with ZF receiver. A 2x2 and 4x4 MIMO system is used for performance evaluation in terms of BER. The analysis shows that output SINR decreases, as the number of users increases. The average bit error probability of the system using ZF receiver is derived for different number of users. We also prese...
Proposal Of DQRAP/CDMA MAC protocol optimization
Giovanini, G; Alonso Zárate, Luis Gonzaga; Agustí Comes, Ramon
2001-01-01
Future third-generation mobile communication systems will need MAC protocols suitable for multimedia CDMA radio communications. DQRAP/CDMA (distributed queueing random access protocol/CDMA) is a general purpose MAC protocol oriented to the CDMA environment. Analytical model expressions and computer simulations have shown its capacity to achieve near-optimum performance under certain traffic scenarios. Starting from the DQRAP/CDMA specification presented in Alonso et al. (2000), we propose som...
An information theory criteria based blind method for enumerating active users in DS-CDMA system
Samsami Khodadad, Farid; Abed Hodtani, Ghosheh
2014-11-01
In this paper, a new and blind algorithm for active user enumeration in asynchronous direct sequence code division multiple access (DS-CDMA) in multipath channel scenario is proposed. The proposed method is based on information theory criteria. There are two main categories of information criteria which are widely used in active user enumeration, Akaike Information Criterion (AIC) and Minimum Description Length (MDL) information theory criteria. The main difference between these two criteria is their penalty functions. Due to this difference, MDL is a consistent enumerator which has better performance in higher signal-to-noise ratios (SNR) but AIC is preferred in lower SNRs. In sequel, we propose a SNR compliance method based on subspace and training genetic algorithm to have the performance of both of them. Moreover, our method uses only a single antenna, in difference to the previous methods which decrease hardware complexity. Simulation results show that the proposed method is capable of estimating the number of active users without any prior knowledge and the efficiency of the method.
PV-solar / Wind Hybrid Energy System for GSM/CDMA Type Mobile Telephony Base
Station Md. Ibrahim; Mohammad Tayyab
2015-01-01
This paper presents the design of optimized PV-Solar and Wind Hybrid Energy System for GSM/CDMA type mobile base station over conventional diesel generator for a particular site in south India (Chennai). For this hybrid system ,the meteorological data of Solar Insolation, hourly wind speed, are taken for Chennai (Longitude 80ο .16’and Latitude 13ο .5’ ) and the pattern of load consumption of mobile base station are studied and suitably modeled for optimization of the hybrid ...
PV-solar / wind hybrid energy system for GSM/CDMA type mobile telephony base station
Pragya Nema, R.K. Nema, Saroj Rangnekar
2010-01-01
This paper gives the design idea of optimized PV-Solar and Wind Hybrid Energy System for GSM/CDMA type mobile base station over conventional diesel generator for a particular site in central India (Bhopal) . For this hybrid system ,the meteorological data of Solar Insolation, hourly wind speed, are taken for Bhopal-Central India (Longitude 77o.23'and Latitude 23o.21' ) and the pattern of load consumption of mobile base station are studied and suitably modeled for optimization of the hybrid en...
High spectral efficiency optical CDMA system based on guard-time and optical hard-limiting (OHL)
Gagliardi, R M; Bennett, C V; Mendez, A J; Hernandez, V J; Lennon, W J
2003-12-02
Optical code-division multiple access (OCDMA) is an interesting subject of research because of its potential to support asynchronous, bursty communications. OCDMA has been investigated for local area networks, access networks, and, more recently, as a packet label for emerging networks. Two-dimensional (2-D) OCDMA codes are preferred in current research because of the flexibility of designing the codes and their higher cardinality and spectral efficiency (SE) compared with direct sequence codes based on on-off keying and intensity modulation/direct detection, and because they lend themselves to being implemented with devices developed for wavelength-division-multiplexed (WDM) transmission (the 2-D codes typically combine wavelength and time as the two dimensions of the codes). This paper shows rigorously that 2-D wavelength/time codes have better SE than one-dimensional (1-D) CDMA/WDM combinations (of the same cardinality). Then, the paper describes a specific set of wavelength/time (W/T) codes and their implementation. These 2-D codes are high performance because they simultaneously have high cardinality (/spl Gt/10), per-user high bandwidth (>1 Gb/s), and high SE (>0.10 b/s/Hz). The physical implementation of these W/T codes is described and their performance evaluated by system simulations and measurements on an OCDMA technology demonstrator. This research shows that OCDMA implementation complexity (e.g., incorporating double hard-limiting and interference estimation) can be avoided by using a guard time in the codes and an optical hard limiter in the receiver.
On the analysis of peak-to-average ratio (PAR) for IS95 and CDMA2000 systems
Lau, VKN
2000-01-01
Peak-to-average ratio (PAR) of a signal is an important parameter to a linear amplifier because it determines the backoff factor needed to be applied to the amplifier in order to avoid clipping and hence spectral regrowth. In this paper, we analyzed the PAR of the downlink direct code-division multiple-access (DS-CDMA) signal for the IS-95 (2G) and the CDMA2000 (3G) systems. Both the single-carrier (SC) and the multi-carrier (MC) situations are considered. For MC systems, an analytical model ...
Arithmetic Operations and Factorization using Asynchronous P Systems
Takayuki Murakawa
2012-07-01
Full Text Available
In the present paper, we consider the asynchronous parallelism in membrane computing, and propose asynchronous P systems that perform two basic arithmetic operations and factorization. Since there is no restrictive assumption for application of rules, sequential and maximal parallel executions are allowed on the asynchronous P system.
We first propose a P system that computes addition of two binary numbers of m bits. The P system works in O(m sequential and parallel steps using O(m types of objects. We next propose a P system for multiplication of the two binary numbers of m bits, and show that the P system works in O(m log m parallel steps or O(m^{3} sequential steps using O(m^{2} types of objects. Finally, we propose a P system for factorization of a positive integer of $m$ bits using the above P system as a sub-system. The P system computes the factorization in O(m log m parallel steps or O(4^{m}
Improved DOA Estimation Algorithm with Sensor Array Perturbations for CDMA System
杨维; 程时昕
2003-01-01
An improved direction of arrival (DOA) estimation algorithm with sensor gain and phase uncertainties for synchronous code division multiple access(CDMA) system with decorrelator is presented. Through decorrelating processing DOAs of the desired users can be estimated independently and all other resolved signal interferences are eliminated. Emphasis is directed to applications in which sensor gain and phase are perturbed that often happen actually. It is shown that improved DOA estimation can be achieved for decoupled signals by gain and phase pre-estimation procedures.
PV-solar / Wind Hybrid Energy System for GSM/CDMA Type Mobile Telephony Base
Station Md. Ibrahim
2015-05-01
Full Text Available This paper presents the design of optimized PV-Solar and Wind Hybrid Energy System for GSM/CDMA type mobile base station over conventional diesel generator for a particular site in south India (Chennai. For this hybrid system ,the meteorological data of Solar Insolation, hourly wind speed, are taken for Chennai (Longitude 80ο .16’and Latitude 13ο .5’ and the pattern of load consumption of mobile base station are studied and suitably modeled for optimization of the hybrid energy system using HOMER software. The simulation and optimization result gives the best optimized sizing of wind turbine and solar array with diesel generator for particular GSM/CDMA type mobile telephony base station. This system is more cost effective and environmental friendly over the conventional diesel generator. The presented system reduce approximate 70%-80% fuel cost over conventional diesel generator and also reduced the emission of CO2 and other harmful gasses in environments. It is expected that the proposed developed and installed system will provide very good opportunities for telecom sector in near future.
Average of peak-to-average ratio (PAR) of IS95 and CDMA2000 systems-single carrier
Lau, VKN
2001-01-01
Peak-to-average ratio (PAR) of a signal is an important parameter. It determines the input backoff factor of the amplifier to avoid clipping and spectral regrowth. We analyze and compose the PAR of the downlink signal for IS95 and the CDMA2000 single-carrier systems. It is found that the PAR of the transmitted signal depends on the Walsh code assignment. Furthermore, we found that the PAR of CDMA2000 signal is always lower than the IS95 signal. Finally, PAR control by Walsh code selection is ...
Experience with synchronous and asynchronous digital control systems
Regenie, V. A.; Chacon, C. V.; Lock, W. P.
1986-01-01
Flight control systems have undergone a revolution since the days of simple mechanical linkages; presently the most advanced systems are full-authority, full-time digital systems controlling unstable aircraft. With the use of advanced control systems, the aerodynamic design can incorporate features that allow greater performance and fuel savings, as can be seen on the new Airbus design and advanced tactical fighter concepts. These advanced aircraft will be and are relying on the flight control system to provide the stability and handling qualities required for safe flight and to allow the pilot to control the aircraft. Various design philosophies have been proposed and followed to investigate system architectures for these advanced flight control systems. One major area of discussion is whether a multichannel digital control system should be synchronous or asynchronous. This paper addressed the flight experience at the Dryden Flight Research Facility of NASA's Ames Research Center with both synchronous and asynchronous digital flight control systems. Four different flight control systems are evaluated against criteria such as software reliability, cost increases, and schedule delays.
PV-solar / wind hybrid energy system for GSM/CDMA type mobile telephony base station
Nema, Pragya; Rangnekar, Saroj [Energy Engineering Department, Maulana Azad National Institute of Technology , Bhopal-462007 M.P. (India); Nema, R.K. [Electrical Engineering Department, Maulana Azad National Institute of Technology, Bhopal-462007 M.P. (India)
2010-07-01
This paper gives the design idea of optimized PV-Solar and Wind Hybrid Energy System for GSM/CDMA type mobile base station over conventional diesel generator for a particular site in central India (Bhopal). For this hybrid system ,the meteorological data of Solar Insolation, hourly wind speed, are taken for Bhopal-Central India (Longitude 77 deg.23'and Latitude 23 deg.21' ) and the pattern of load consumption of mobile base station are studied and suitably modeled for optimization of the hybrid energy system using HOMER software. The simulation and optimization result gives the best optimized sizing of wind turbine and solar array with diesel generator for particular GSM/CDMA type mobile telephony base station. This system is more cost effective and environmental friendly over the conventional diesel generator. It should reduced approximate 70%-80% fuel cost over conventional diesel generator and also reduced the emission of CO2 and other harmful gasses in environments. It is expected that the newly developed and installed system will provide very good opportunities for telecom sector in near future.
PV-solar / wind hybrid energy system for GSM/CDMA type mobile telephony base station
Pragya Nema, R.K. Nema, Saroj Rangnekar
2010-03-01
Full Text Available This paper gives the design idea of optimized PV-Solar and Wind Hybrid Energy System for GSM/CDMA type mobile base station over conventional diesel generator for a particular site in central India (Bhopal . For this hybrid system ,the meteorological data of Solar Insolation, hourly wind speed, are taken for Bhopal-Central India (Longitude 77o.23'and Latitude 23o.21' and the pattern of load consumption of mobile base station are studied and suitably modeled for optimization of the hybrid energy system using HOMER software. The simulation and optimization result gives the best optimized sizing of wind turbine and solar array with diesel generator for particular GSM/CDMA type mobile telephony base station. This system is more cost effective and environmental friendly over the conventional diesel generator. It should reduced approximate 70%-80% fuel cost over conventional diesel generator and also reduced the emission of CO2 and other harmful gasses in environments. It is expected that the newly developed and installed system will provide very good opportunities for telecom sector in near future.
Blind Multiuser Detection for Long-Code CDMA Systems with Transmission-Induced Cyclostationarity
Ding Zhi
2005-01-01
Full Text Available We consider blind channel identification and signal separation in long-code CDMA systems. First, by modeling the received signals as cyclostationary processes with modulation-induced cyclostationarity, long-code CDMA system is characterized using a time-invariant system model. Secondly, based on the time-invariant model, multistep linear prediction method is used to reduce the intersymbol interference introduced by multipath propagation, and channel estimation then follows by utilizing the nonconstant modulus precoding technique with or without the matrix-pencil approach. The channel estimation algorithm without the matrix-pencil approach relies on the Fourier transform, and requires additional constraint on the code sequences other than being nonconstant modulus. It is found that by introducing a random linear transform, the matrix-pencil approach can remove (with probability one the extra constraint on the code sequences. Thirdly, after channel estimation, equalization is carried out using a cyclic Wiener filter. Finally, since chip-level equalization is performed, the proposed approach can readily be extended to multirate cases, either with multicode or variable spreading factor. Simulation results show that compared with the approach using the Fourier transform, the matrix-pencil-based approach can significantly improve the accuracy of channel estimation, therefore the overall system performance.
Weyl Spreading Sequence Optimizing CDMA
Tsuda, Hirofumi; Umeno, Ken
2016-01-01
Recently, the new spreading sequence obtained by the Weyl sequence is proposed for CDMA systems. Its cross-correlation function follows $O(\\frac{1}{N})$, where $N$ is the code length of the spreading sequence. In this paper, we optimize the Weyl sequence code design to assign to each user for CDMA systems and we analytically calculate its theoretical SIR (Signal to Interference Noise Ratio). It is theoretically proven that the CDMA systems with spreading sequence has about 2.5 times larger ca...
A Novel Method of SIR Measurement for Power Control in CDMA Systems
CDMA is interference limited multiple access system. Power control is an effective way to reduce co-channel interference and solve the near-far problem. Consequently, it can improve the system capacity, and make higher data rate possible. CDMA2000 employs fast closed-loop power control in reverse link to combat channel fading, and the estimation of signal to interference ratio (SIR) is required for closed-loop power control. Transmitting power is adjusted by comparing the SIR estimation with SIR target. So, it is crucial to measure the SIR of received signal accurately. Traditional measurement methods mostly depend on pilot signal strongly, when the pilots are few, there is a greater error brought to the measurement of SIR. In this paper, we discuss the SIR measurement of the received signal under the fewer pilots condition (especially only one pilot symbol) and present a novel SIR measurement method. According to the simulation, the numerical results indicate that the SIR measured by the proposed method is more accurate than the SIR measured by conventional method under fewer pilots condition
Singh, Jaswinder
2010-03-10
A novel family of three-dimensional (3-D) wavelength/time/space codes for asynchronous optical code-division-multiple-access (CDMA) systems with "zero" off-peak autocorrelation and "unity" cross correlation is reported. Antipodal signaling and differential detection is employed in the system. A maximum of [(W x T+1) x W] codes are generated for unity cross correlation, where W and T are the number of wavelengths and time chips used in the code and are prime. The conditions for violation of the cross-correlation constraint are discussed. The expressions for number of generated codes are determined for various code dimensions. It is found that the maximum number of codes are generated for S codes is compared to the earlier reported two-dimensional (2-D)/3-D codes for asynchronous systems. The codes have a code-set-size to code-size ratio greater than W/S. For instance, with a code size of 2065 (59 x 7 x 5), a total of 12,213 users can be supported, and 130 simultaneous users at a bit-error rate (BER) of 10(-9). An arrayed-waveguide-grating-based reconfigurable encoder/decoder design for 2-D implementation for the 3-D codes is presented so that the need for multiple star couplers and fiber ribbons is eliminated. The hardware requirements of the coders used for various modulation/detection schemes are given. The effect of insertion loss in the coders is shown to be significantly reduced with loss compensation by using an amplifier after encoding. An optical CDMA system for four users is simulated and the results presented show the improvement in performance with the use of loss compensation. PMID:20220892
New theoretical framework for OFDM/CDMA systems with peak-limited nonlinearities
无
2007-01-01
A new theoretical framework for the evaluation of the in-band nonlinear distortion effects on the performance of OFDM systems is presented. In contrast to previous works that approximate the nonlinear noise as a Gaussian additive random process, the new framework is based on the properties of the large deviations of a stationary Gaussian process and shot noise theories, which can evaluate the performance of the OFDM system with high accuracy, especially at realistic scenarios where the Gaussian approximation of the nonlinear noise is no longer valid. The approach can be used to evaluate many communication systems with peak-limited nonlinearities and high PAPR, such as the downlink performance analysis of large capacity DS-CDMA systems.
Asynchronous compressed beamformer for portable diagnostic ultrasound systems.
Zhou, Jun; Hoyos, Sebastian; Sadler, Brian
2014-11-01
State-of-the-art portable ultrasound imaging systems employ a small transducer array and a low carrier frequency to fit stringent constraints on power and form factor, and this tends to compromise the ultrasound imaging quality. In this paper, we present a low-complexity low-power asynchronous compressed beamformer (ACB) for portable diagnostic ultrasound. The proposed ACB integrates asynchronous sampling and compressive sensing (CS), and is capable of reducing data conversion power and handling a large data volume at the mixed-signal interface. A high-rate continuoustime ternary encoding (CT-TE) scheme eliminates the need for interpolation filters and coordinate rotation digital computer (CORDIC) units typically used in a conventional architecture. A split-projection least squares (SPLS) signal reconstruction algorithm is applied that replaces high-cost nonlinear signal recovery with a series of low-complexity and independent linear problems. Experiments with measured ultrasound data demonstrate the proposed ACB architecture, and the SPLS reconstruction algorithm achieves 9-fold data compression compared with Nyquist sampling. PMID:25389158
A Unified Approach to Energy-Efficient Power Control in Large CDMA Systems
Meshkati, Farhad; Poor, H Vincent; Schwartz, Stuart C
2007-01-01
A unified approach to energy-efficient power control is proposed for code-division multiple access (CDMA) networks. The approach is applicable to a large family of multiuser receivers including the matched filter, the decorrelator, the linear minimum mean-square error (MMSE) receiver, and the (nonlinear) optimal detectors. It exploits the linear relationship that has been shown to exist between the transmit power and the output signal-to-interference-plus-noise ratio (SIR) in the large-system limit. It is shown that, for this family of receivers, when users seek to selfishly maximize their own energy efficiency, the Nash equilibrium is SIR-balanced. In addition, a unified power control (UPC) algorithm for reaching the Nash equilibrium is proposed. The algorithm adjusts the user's transmit powers by iteratively computing the large-system multiuser efficiency, which is independent of instantaneous spreading sequences. The convergence of the algorithm is proved for the matched filter, the decorrelator, and the M...
Cross-Layer Design and Analysis of Downlink Communications in Cellular CDMA Systems
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.
Performance Analysis of CDMA WLL Systems with Imperfect Power Control and Imperfect Sectorization
Sami A. El-Dolil
2008-01-01
Full Text Available Wireless local loop (WLL provides reliable, flexible, and economical access to the local telephone service using radio technology in the place of traditional wireline. In this paper, an analytical model is derived to evaluate the effect of both imperfect power control and imperfect sectorization on the performance of code division multiple access (CDMA WLL systems. The results show that the capacity degradation, due to imperfect power control, is about 25.8% and 11.5% for single cell and multiple cell systems, respectively. Increasing the overlapping angle from 0∘ to 5∘ causes the capacity gain to decrease from 6 to 5.53, while the corresponding sectorization efficiency drops from 100% to 92.3%.
WUXiaojun; YINQinye; ZENGMing; LIXing; WANGJilong
2004-01-01
In very high data-rate wireless application scenarios, Multicarrier code-division multiple access (MC-CDMA) systems including Serial-to-parallel (S/P) converting operation are more applicable. We name them as modified MC-CDMA systems. In this paper, we focus on the blind channel estimation problem of these modified MC-CDMA systems on uplink. Because we can regard each subcarrier in multicarrier communications as a channel, the modified MC-CDMA system accordingly can become a multichannel system. Upon this understanding, we model the multiuser modified MC-CDMA system as a Multiple-input multiple-output (MIMO) system. Successively, based on subspace decomposition technique, we derive a novel blind estimation scheme of uplink channels for multiuser modified MC-CDMA systems. Furthermore, based on perturbation techniques, we derive the analytical approximation of the Mean-squared error (MSE) of this blind channel estimation scheme. Extensive computer simulations illustrate the performance of the proposed algorithm, and simulation results also verify the tightness of the MSE approximation.
Dr. Sandip Nemade
2013-09-01
Full Text Available The main goal is to access the appropriateness of OFDM as a modulation technique for a fixed wireless phone system. Several of the main factors affecting the performance of a OFDM system, were measured including multipath delay spread, channel noise, distortion of the signal (clipping, and timing requirements. This paper focuses on how MIMO OFDM-CDMA systems are capable of achieving diversity gains significantly larger than that of the day to day system
BER Performance for Downlink MC-CDMA Systems over Rician Fading Channels
Vimal K. Dubey
2005-04-01
Full Text Available We consider downlink multicarrier code-division multiple-access (MC-CDMA systems using binary phase-shift keying (BPSK modulation scheme and maximal ratio combining (MRC in frequency-selective Rician fading channels. A time-domain method to obtain bit error rate (BER by calculating moment generating function (MGF of the decision variable for a tapped-delay-line channel model is proposed. This method does not require any assumption regarding the statistical or spectral distribution of multiple access interference (MAI, and it is also not necessary to assume that the fading encountered by the subcarriers is independent of each other. The analytical formula is also verified by simulations.
Coherent Code Tracking for Spatial Transmit Diversity DS-CDMA Systems
R. W. Stewart
2005-09-01
Full Text Available Spatial transmit diversity schemes are now well integrated into third-generation cellular mobile communication system specifications. When DS-CDMA-based technology is deployed in typical macro- and microcell environments, multipath diversity and spatial diversity may be exploited simultaneously by a 2D RAKE receiver. The work presented in this paper focuses on taking advantage of spatial transmit diversity in synchronising the 2D RAKE structure. We investigate the use of coherent and noncoherent techniques for tracking the timing parameters of each multipath component. It is shown that both noncoherent and coherent techniques benefit from transmit diversity. Additionally the performance gap between these two techniques increases with the number of antennas.
CP decomposition approach to blind separation for DS-CDMA system using a new performance index
Rouijel, Awatif; Minaoui, Khalid; Comon, Pierre; Aboutajdine, Driss
2014-12-01
In this paper, we present a canonical polyadic (CP) tensor decomposition isolating the scaling matrix. This has two major implications: (i) the problem conditioning shows up explicitly and could be controlled through a constraint on the so-called coherences and (ii) a performance criterion concerning the factor matrices can be exactly calculated and is more realistic than performance metrics used in the literature. Two new algorithms optimizing the CP decomposition based on gradient descent are proposed. This decomposition is illustrated by an application to direct-sequence code division multiplexing access (DS-CDMA) systems; computer simulations are provided and demonstrate the good behavior of these algorithms, compared to others in the literature.
Joint Angle and Delay Estimation (JADE) in Antenna Array CDMA Systems
无
2002-01-01
The estimate of signals parameters is very important in wireless communications. In this paper, we combine subspace-based blind channel estimation algorithm with the extension of the JADE-WSF algorithm to jointly estimate the Angles-of-Arrival (AOAs) and delays of multipath signals arriving at an antenna array in Code Division Multiple Access (CDMA) systems. Our approach uses a collection of estimates of a consistent chip-sample of space-time vector channel. The channel estimates are assumed to have constant path AOA and delay over a finite number of symbols. Unlike the traditional MUltiple SIgnal Classification (MUSIC) and Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT) algorithms for the estimation of signals parameters, the proposed method can work when the number of paths exceeds the number of antennas. The Cramer-Rao Bound (CRB) and simulations are provided.
ADAPTIVE STEP-SIZE CONSTANT MODULUS ALGORITHM FOR BLIND MULTIUSER DETECTION IN DS-CDMA SYSTEMS
Sun Liping; Hu Guangrui
2004-01-01
Blind Adaptive Step-size Constant Modulus Algorithm (AS-CMA) for multiuser detection in DS-CDMA systems is presented. It combines the CMA and the concept of variable step-size, uses a second LMS algorithm for the step size. It adjusts the step-size according to the minimum output-energy principle within a specified range, thus overcomes the problems of bad effect of fixed step-size LMS algorithm. Compared with Adaptive Step-size LMS (AS-LMS) algorithm, through simulations, this algorithm can adapt the changes of the environment, suppress multiple access interference in the dynamic environment and the stability of Signal to Interference Ratio (SIR) is superior to that of AS-LMS.
UNIVERSAL REGULAR AUTONOMOUS ASYNCHRONOUS SYSTEMS: ω-LIMIT SETS, INVARIANCE AND BASINS OF ATTRACTION
Serban Vlad
2011-07-01
Full Text Available The asynchronous systems are the non-deterministic real timebinarymodels of the asynchronous circuits from electrical engineering.Autonomy means that the circuits and their models have no input.Regularity means analogies with the dynamical systems, thus such systems may be considered to be real time dynamical systems with a’vector field’, Universality refers to the case when the state space of the system is the greatest possible in the sense of theinclusion. The purpose of this paper is that of defining, by analogy with the dynamical systems theory, the omega-limit sets, the invariance and the basins of attraction of the universal regular autonomous asynchronous systems.
Efficient Smart Antenna Systems (4G) For CDMA Wireless Communication
Singla, Brahm Mohinder; Kumar, Ashish
2012-01-01
Today, mobile communications play a central role in the voice/data network arena. With the deployment of mass scale 3G just around the corner, new directions are already being researched. In this paper we address about the 4TH G mobile communications.The Fourth Generation (4G) Mobile Communications should not focus only on the data-rate increase and new air interface.4G Mobile should instead con-verge the advanced wireless mobile communications and high-speed wireless access systems into an O...
Sodagari, Shabnam
2014-01-01
This article presents a distributed solution to autonomous quality of service provision in cognitive radio networks. Specifically, cognitive STDMA and CDMA communication networks are studied. Based on asynchronous weak commitment search the task of QoS provision is distributed among different network nodes. Simulation results verify this scheme converges very fast to optimal solution, which makes it suitable for practical real time systems. This application of artificial intelligence in wirel...
Uplink Capacity Investigations of TDD/CDMA
Wu, X; L. L Yang; Hanzo, L
2002-01-01
In this contribution we analyze the uplink capacity of a TDD/CDMA system. In TDD/CDMA the mobiles suffer from interferences inflicted by the other mobile stations (MSs) both in the reference cell the MS is roaming in (intracell interference) as we as due to those in the neighbouring cells (intercell interference). Furthermore, in contrast to FDD/CDMA, where the Base Stations (BSs) transmit in an orthogonal frequency band, in TDD/CDMA there is additional interference imposed by other BSs of th...
Chitra, S.; Kumaratharan, N.
2015-01-01
Multi-carrier code division multiple access (MC-CDMA) technique is one of the strong candidates for next generation wireless mobile communication systems. Multi-carrier systems are very much sensitive to carrier frequency offset (CFO) results in intercarrier interference (ICI). To mitigate ICI without any spectral loss, a second order duobinary coded phase rotated conjugate cancellation algorithm is proposed in this paper. In the conventional phase rotated conjugate cancellation (PRCC) techni...
On the basins of attraction of the regular autonomous asynchronous systems
Vlad, Serban E.
2012-01-01
The Boolean autonomous dynamical systems, also called regular autonomous asynchronous systems are systems whose 'vector field' is a function {\\Phi}:{0,1}^{n}{\\to}{0,1}^{n} and time is discrete or continuous. While the synchronous systems have their coordinate functions {\\Phi}_{1},...,{\\Phi}_{n} computed at the same time: {\\Phi},{\\Phi}{\\circ}{\\Phi},{\\Phi}{\\circ}{\\Phi}{\\circ}{\\Phi},... the asynchronous systems have {\\Phi}_{1},...,{\\Phi}_{n} computed independently on each other. The purpose of t...
Multiple-access interference in 2-D wavelength/time optical CDMA system with optical hard-limiters
Chovan, Jozef; Uherek, František
2005-08-01
In this paper we present the proposed modification of 2-D wavelength/time (WIT) decoder1 by placing the second optical hard-limiter (0-HL) after decoder"s last optical coupler. The MA1 improvement of the 2-D W/T Optical Code Division Multiple Access (0-CDMA) system for the cases of 2D WIT decoder with one and with two 0-HLs is analyzed. Average value of signal-to-interference difference (SID) is used as the MA1 merit. The model of such 2D W/T 0-CDMA system for numerical calculation of the SID is proposed and presented in this paper. In the analyzed system, 2-D WIT Generalized Multiwavelength Prime Codewords (GMWPC), which are generated by algorithm reported in2 are used for achieving multiple-access. We assume the implemented 0-HL proposed in 3. The properties of such 0-HL were approximated [4] and its two ideality parameters, which characterize the measure of its ideality, were defined. The input and output time optical pulses sequence of W/T 0-CDMA decoder is numerical simulated. Dependencies of SID versus the weight of codeword and the number of active users in the system are presented. The influence of the properties used 0-HLs is evaluated.
Code-Division Multiple-Access (CDMA)
Justesen, Jørn
1999-01-01
A simplified CDMA system is presented. A single-user approach and a multi-user approach to demodulation of transmitted bits is presented.......A simplified CDMA system is presented. A single-user approach and a multi-user approach to demodulation of transmitted bits is presented....
THE STUDY OF AN M-ARY MC-CDMA SYSTEM BASED ON CYCLIC SPREADING CODES & PRE-EQUALIZATION
Chu Zhenyong; Ying Xiaofan; Yi Kechu; Tian Hongxin
2005-01-01
A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MCCDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.
杨维; 程时昕
2003-01-01
The conventional 2D-Rake receivers for code-division multiple access (CDMA) system over frequency-selective fading channels are generally based on the second-order statistics while assuming perfect array conditions. However, the sensor response, location uncertainty, and the use of sample statistics can severely degrade the performance of second-order statistics processing. And in practical application, it is impossible to calibrate the array frequently. In this paper a cumulant-based 2D-Rake receiver for synchronous CDMA system with decorrelator is presented. Decorrelating is a multi-user detection approach that not only provides a fundamental solution to the mutual interference problem in CDMA communications but also makes it convenient for the decoupled signal to be processed spatially and temporally. High-order signal processing has some inherent advantages over that of second-order. Employing second-order statistics it is impossible to estimate source steering vector blindly, while employing higher than second-order cumulants, this purpose can be achieved. The performance analysis shows that employing cumulant-based signal processing technique the proposed 2D-Rake receiver is blind and demonstrates excellent performance.
A. M. Muha
2009-04-01
Full Text Available In the article the structural reliability of different variants of structured schemes of the steady-state converter for traction drive of promising multi-system electric locomotives with asynchronous traction engines is compared.
CUCKOO SEARCH-AIDED LMS ALGORITHM FOR CHANNEL ESTIMATION IN MC-CDMA SYSTEMS
S. Balaji
2014-01-01
Full Text Available In the progress of transmission systems that uses the diversity in various domains, the execution of competent baseband receivers categorized by affordable computational load is an essential thing. This would be an imperative point in the future expansion of 4G systems in which the space, time and frequency diversity will be merged together to enhance the system throughput. Here, we develop a channel estimation technique for MC-CDMA system for the minimization of BER and the maximization of throughput. The maximization of throughput is an essential thing for the successful reception of signal. At the receiver side, the original data is obtained based on the channel estimation algorithm and the inverse process of the transmitter side is performed in the receiver side. The major contribution of our work is to estimate the channel information in an adaptive way. We estimate the channel using the cuckoo search algorithm based on the best solution we obtain from the cuckoo search algorithm. After estimating the channel, we calculate the Bit Error Rate (BER performance and throughput based on the acknowledgement send by the receiver. Experimental results show that our technique is better in terms of BER and throughput compared to the existing technique.
Simulation of the Double-closed Loop Three-phase Asynchronous Variable Voltage Control System
Shuhua Jiang
2011-01-01
When controlling the voltage and speed of the asynchronous motor, to expand the speed control range and reduce the speed fluctuation, the speed control system adopts two feedback control loops, i.e. the speed feedback control loop and the current feedback control loop. The principle and components of the double-closed loop three-phase asynchronous variable voltage control system are studied, and the simulation model and the test result based on MATLAB/Simulink are provided in this article thr...
LIJunqiangI; K.B.Ltaief; CAOZhigang
2003-01-01
The capacity of MC-CDMA communica-tion systems can be significantly enhanced by employing multiuser detection (MUD) techniques. In this paper, a group oriented MUD based on the combination of smart antennas and multiuser detection is presented. The pro-posed method is featured as a novel technique for further improving the system capacity and performance. In this method, all the users are first divided into several groups according to their impinging Direction of arrivals (DOA).All users with similar DOAs are classified into the same group and then MUD is employed in each group in parallel.Because spatial filtering cannot suppress all the interfer-ence between the groups, interference cancellation among groups is used prior to MUD within the groups. It is shown that the proposed group oriented MUD algorithm can sig-nificantly reduce the computational complexity and pro-cessing time delay compared with the conventional MUDschemes. Furthermore, it is demonstrated that significant performance improvement can be achieved.
On Intercell Interference and Its Cancellation in Cellular Multicarrier CDMA Systems
Plass Simon
2008-01-01
Full Text Available Abstract The handling of intercell interference at the cell border area is a strong demand in future communication systems to guarantee efficient use of the available bandwidth. Therefore, this paper focuses on the application of iterative intercell interference cancellation schemes in cellular multicarrier code division multiple access (MC-CDMA systems at the receiver side for the downlink. First, the influence of the interfering base stations to the total intercell interference is investigated. Then, different concepts for intercell interference cancellation are described and investigated for scenarios with several interfering cells. The first approach is based on the use of the hard decision of the demodulator to reconstruct the received signals. This does not require the higher amount of complexity compared to the second approach which is based on the use of the more reliable soft values from the decoding process. Furthermore, the extrinsic information as a reliability measure of this soft iterative cancellation process is investigated in more detail based on the geographical position of the mobile terminal. Both approaches show significant performance gains in the severe cell border area. With the soft intercell interference cancellation scheme, it is possible to reach the single-user bound. Therefore, the intercell interference can be almost eliminated.
Performance Evaluation of Hybrid ARQ with Code Combining in Packet-Oriented CDMA System
CHENQingchun; FANPingzhi
2004-01-01
In this paper, an extended SNR (signal to noise ratio) concept is proposed to explicate the contribution of code combining to the performance improvement of hybrid ARQ (Automatic repeat request) over the additive white Gaussian noise channel. By extending the Pursley's SNR analysis to hybrid ARQ with code combining in packet-oriented CDMA (Code division multiple access)system, the extended SNR formula is derived, which describes explicitly the SNR variation of the code symbol involved in code combining. It is revealed that the extended SNR formula includes Pursley's SNR formula as a specialcase. Moreover, it is shown that the effective SNR of the combined symbol is increased by a coefficient, which is proportional to the number of repeated replicas involved in the code combining. Based on the extended SNR formula and the resultant SNR variation, a quasi-analytical approximation method is proposed for the performance evaluation of hybrid ARQ with code combining. The residual error rates, average transmission number together with throughput performance are presented by means of numerical analysis and through simulations. It is validated that the extended SNR formula and the resultant quasi-analytical approximations offer a simplified routine to estimate the performance of hybrid ARQ with code combining, particularly for the applications whose reliability performance with respect to the FEC counterpart system could be numerically calculated or evaluated through simulations.
Adaptive Wavelet Neural Networks for Signal Detection in DS-CDMA System
WANGLing; JIAOLichengt; TAOHaihong; LIUFang
2004-01-01
The Multiple access interference (MAI) is the major factor that limits the performance and capacity of a nonorthogonal Direct sequence Code division multiple access (DS-CDMA) system. By using the adaptability of highly parallel structure neural networks and the excellent approximation ability of wavelets, two kinds of Adaptive wavelets neural networks (AWNN) signal detectors are proposed in the paper, in which the inputs of detectors are the received signal vector corresponding to a single interesting user sampled at the chip rate, named by AWNN single-user detector, respectively, and to all or partial active users sampled at the bit rate after passing through a matched filter, named by AWNN multiuser detector and partial users AWNN multiuser detector. The complexity of the multiuser detectors only depends on that of wavelet networks. The performance analysis of the proposed detectors compared with the matched filters under single-user and multiuser systems and the multiuser detector based on multilayer perceptrons are carried out by Monte Carlo simulations. Results show that the adaptive wavelet neural networks multiuser detectors are superior to other detectors mentioned above.
Turbo-coded CDMA-based two-way relaying
Ng, Soon Xin; Liao, Sha Sha
2012-01-01
In this contribution, we have studied the performance of a Turbo-Coded (TC) Code Division Multiple Access (CDMA) based two-way relaying scheme. More explicitly, we employ a seven-user CDMA model, where two of the CDMA users are communicating with each other with the aid of an additional relay node, while the other ¯ve CDMA users are interferers. More explicitly, two CDMA users exchange their information frames within two timeslots. Note that the conventional one-way relaying system can only t...
Algorithm of sky-ground-wave signal separation in CDMA system
Zhang Jingjuan; Chen Shiru
2008-01-01
To solve the problem of the sky-wave interference in radio positioning system operating in CDMA mode, an algorithm of sky-ground-wave separation is provided. Based on the MLE (maximum likelihood estimate),and by estimating the amplitude and the phase of the sky-wave signal, the provided algorithm for separating sky-ground-wave is implemented. The mathematics model used for signal processing is established, and the possible solutions are provided. The structure and signal processing flow implementing the presented algorithm in the receiver are presented. A multi-channels signal searching idea is adopted, some of which process the sky-wave signal, and some of which process the ground-wave signal. Numerical analysis and simulation show that the proposed algorithm has higher accuracy, more rapid processing speed, and simpler implementation for the estimation of the sky-wave signal parameter, and can separate the sky-wave signal and ground-wave signal from the arrival combination signal effectively.
Energy-Efficient Power Control in Multipath CDMA Channels via Large System Analysis
Buzzi, Stefano; Poor, H Vincent
2008-01-01
This paper is focused on the design and analysis of power control procedures for the uplink of multipath code-division-multiple-access (CDMA) channels based on the large system analysis (LSA). Using the tools of LSA, a new decentralized power control algorithm aimed at energy efficiency maximization and requiring very little prior information on the interference background is proposed; moreover, it is also shown that LSA can be used to predict with good accuracy the performance and operational conditions of a large network operating at the equilibrium over a multipath channel, i.e. the power, signal-to-interference-plus-noise ratio (SINR) and utility profiles across users, wherein the utility is defined as the number of bits reliably delivered to the receiver for each energy-unit used for transmission. Additionally, an LSA-based performance comparison among linear receivers is carried out in terms of achieved energy efficiency at the equilibrium. Finally, the problem of the choice of the utility-maximizing tr...
Performance analysis of CDMA power control system based on fuzzy prediction
杨涛; 谢剑英
2004-01-01
Power control is of paramount importance in combating the near-far problem and co-channel interference in a CDMA cellular system. Due to fast fading and ambient interference in a wireless channel, conventional fixed-step power control schemes have difficulty in compensating for the fast fading channel dynamically and in a timely manner. To acquire flexible power regulation in order to maintain required transmission capacity under the given transmission quality requirement, we propose a hybrid power control scheme which makes full use of the simple fuzzy inference rule refined by an operator in the fuzzy control and prediction property from related previous results in Generalized Prediction Control (GPC). In implementation of this strategy, we classify the fading zone into three levels according to the signal-to-noise-rate (SNR) requirement. In each level the power compensation amount varies with fading gradient and the compensation scheme varies as well. The digital results show that adoption of the fuzzy-GPC power regulation scheme has acquired a reasonable performance improvement when compared with fixed-step and fuzzy schemes. According to theoretic analysis and simulation results,we can conclude that under a variational transmission environment, a flexible power regulation scheme such as fuzzy-GPC is easy to adapt to the environment and thus overcomes the near-far effect and multi-access interference effectively.
Low-power Implementation of an Encryption/Decryption System with Asynchronous Techniques
Nikos Sklavos
2002-01-01
Full Text Available An asynchronous VLSI implementation of the International Data Encryption Algorithm (IDEA is presented in this paper. In order to evaluate the asynchronous design a synchronous version of the algorithm was also designed. VHDL hardware description language was used in order to describe the algorithm. By using Synopsys commercial available tools the VHDL code was synthesized. After placing and routing both designs were fabricated with 0.6 μm CMOS technology. With a system clock of up to 8 MHz and a power supply of 5 V the two chips were tested and evaluated comparing with the software implementation of the IDEA algorithm. This new approach proves efficiently the lowest power consumption of the asynchronous implementation compared to the existing synchronous. Therefore, the asynchronous chip performs efficiently in Wireless Encryption Protocols and high speed networks.
Raghavan, Rajesh S.; Shamma, Mohammed A.
2003-01-01
This paper will present work being done to model and simulate a CDMA based Mobile Satellite System architecture for providing all or part of the future Air Traffic Management (ATM) services. Such a system, will help in relieving the dependence on ground based networks, if not eliminate it. Additionally such an architecture can be used in parallel or as a supplementary service along with ground based links to help alleviate any capacity bottlenecks, or in areas where such services are difficult to make available such as in oceanic, remote areas outside the jet highways, or in developing countries where ground services are less available.
Claude D'Amours
2011-01-01
Full Text Available We analytically derive the upper bound for the bit error rate (BER performance of a single user multiple input multiple output code division multiple access (MIMO-CDMA system employing parity-bit-selected spreading in slowly varying, flat Rayleigh fading. The analysis is done for spatially uncorrelated links. The analysis presented demonstrates that parity-bit-selected spreading provides an asymptotic gain of 10log(Nt dB over conventional MIMO-CDMA when the receiver has perfect channel estimates. This analytical result concurs with previous works where the (BER is determined by simulation methods and provides insight into why the different techniques provide improvement over conventional MIMO-CDMA systems.
Loyko V. I.
2015-11-01
Full Text Available The goal of the study is to research time characteristics of pseudo-noise sequence acquisition method for multicarrier communication systems of MC-DSCDMA, that allows low hardware requirements and able to operate in low quality channels. The way of achieving this lies in using a mathematical model of algorithm. The achieved results show suitability of MC-DS-CDMA-signals optimization for pseudo-noise sequence acquisition efficiency increase. The achieved results can be applied in MC-DS-CDMA communication systems development
Teleoperation system using Asynchronous transfer mode, ATM network
This paper examines the application of Asynchronous Transfer Mode (ATM) in a distributed industrial environment such as in teleoperation, which performs real time control manipulation from a remote location. In our study, two models of teleoperation are proposed; the first model is a point to point connection and the second model is through an ATM network. The performance results are analysed as to determine whether the two models can support the teleoperation traffics via simulation using commercial software design tool. (Author)
Dang, Ngoc T; Pham, Anh T
2012-11-19
Previous studies show that, compared to on-off keying (OOK) signaling, pulse-position modulation (PPM) is favorable in FSO/CDMA systems thanks to its energy efficiency and simple detection. Nevertheless, when the system bit rate increases and the transmission distance is far, the FSO/CDMA systems using PPM signaling critically suffer from the impact of pulse broadening caused by dispersion, especially when the modulation level is high. In this paper, we therefore propose to use multi-wavelength PPM (MWPPM) signaling to overcome the limitation of PPM. To further improve the system performance, avalanche photodiode (APD) is also used. The performance of the proposed system is theoretically analyzed using a realistic model of Gaussian pulse propagation. To model the impact of intensity fluctuation caused by the atmospheric turbulence, the log-normal channel is used. We find that, by using MWPPM, the effects of both intensity fluctuation and pulse broadening are mitigated, the BER is therefore significantly improved. Additionally, we quantitatively show that the system performance is further improved by using APD, especially when the average APD gain is chosen properly. PMID:23187533
A Joint Optimization Criterion for Blind DS-CDMA Detection
Sergio A. Cruces-Alvarez
2007-01-01
Full Text Available This paper addresses the problem of the blind detection of a desired user in an asynchronous DS-CDMA communications system with multipath propagation channels. Starting from the inverse filter criterion introduced by Tugnait and Li in 2001, we propose to tackle the problem in the context of the blind signal extraction methods for ICA. In order to improve the performance of the detector, we present a criterion based on the joint optimization of several higher-order statistics of the outputs. An algorithm that optimizes the proposed criterion is described, and its improved performance and robustness with respect to the near-far problem are corroborated through simulations. Additionally, a simulation using measurements on a real software-radio platform at 5 GHz has also been performed.
CDMA Technique with Inter-process Communication
V. Ravichandran
2014-02-01
Full Text Available A novel implementation of Inter process communication in CDMA NOC is proposed. In this study, the orthogonality properties of a Walsh code are used to route data packets between the IP-Cores.The asynchronous circuit design with combinational logic (Gate level design is used for transmission and receiving circuits, along with ip-cores and reduces the processing time and resource utilization. The use of asynchronous pipelined core design process increases the operating frequency as well. The data transfers over IP-Core based interconnect is implemented on gate level. The latency and throughput values are obtained for variable payload size. The performance of asynchronous and synchronous communication are measured and analyzed.
Defining the Symmetry of the Universal Semi-Regular Autonomous Asynchronous Systems
Serban E. Vlad
2012-02-01
Full Text Available The regular autonomous asynchronous systems are the non-deterministic Boolean dynamical systems and universality means the greatest in the sense of the inclusion. The paper gives four definitions of symmetry of these systems in a slightly more general framework, called semi-regularity, and also many examples.
Defining the Symmetry of the Universal Semi-Regular Autonomous Asynchronous Systems
Vlad, Serban E.
2012-01-01
The regular autonomous asynchronous systems are the non-deterministic Boolean dynamical systems and universality means the greatest in the sense of the inclusion. The paper gives four definitions of symmetry of these systems in a slightly more general framework, called semi-regularity, and also many examples.
A Unified Approach to the Analysis of Multicarrier DS-CDMA over Nakagami-$M$ Fading Channels
Yang, L-L.; Hanzo, L
2001-01-01
A class of unified multicarrier DS-CDMA (MC DS-CDMA) schemes is defined and its performance is considered over multipath Nakagami-$M$ fading channels. The spacing between two adjacent subcarriers of the unified MC DS-CDMA scheme is a variable, allowing us to gain insight into the effects of the spacing on the bit error rate (BER) performance of MC DS-CDMA systems. This unified MC DS-CDMA scheme includes the subclasses of multitone DS-CDMA and orthogonal MC DS-CDMA as special cases. The optimu...
Time-Efficient Read/Write Register in Crash-prone Asynchronous Message-Passing Systems
Mostefaoui, Achour; Raynal, Michel
2016-01-01
The atomic register is certainly the most basic object of computing science. Its implementation on top of an n-process asynchronous message-passing system has received a lot of attention. It has been shown that t \\textless{} n/2 (where t is the maximal number of processes that may crash) is a necessary and sufficient requirement to build an atomic register on top of a crash-prone asynchronous message-passing system. Considering such a context, this paper visits the notion of a fast implementa...
Chitra, S; Kumaratharan, N
2015-01-01
Multi-carrier code division multiple access (MC-CDMA) technique is one of the strong candidates for next generation wireless mobile communication systems. Multi-carrier systems are very much sensitive to carrier frequency offset (CFO) results in intercarrier interference (ICI). To mitigate ICI without any spectral loss, a second order duobinary coded phase rotated conjugate cancellation algorithm is proposed in this paper. In the conventional phase rotated conjugate cancellation (PRCC) technique, one path carries the MC-CDMA signal with a phase spin of ϕ and the other path carries the conjugate of the first path signal with -ϕ phase spin. This artificial phase rotation allows the transmitter to tune the transmitted signals so that the ICI effects could be mutually cancelled at the receiver. Although the PRCC technique reduces the spectral efficiency, the limitation can be overcome by the joint second order duobinary coding scheme with PRCC technique. In the proposed method, the correlative coding between the binary symbols modulated on adjacent subcarriers is used to reduce the ICI without any spectral loss. Simulation results show that the proposed PRCC method provides better carrier to interference ratio (CIR) and bit error rate (BER) performances compared to the conventional conjugate cancellation (CC) technique. PMID:25790029
The Use of Efficient Broadcast Protocols in Asynchronous Distributed Systems. Ph.D. Thesis
Schmuck, Frank Bernhard
1988-01-01
Reliable broadcast protocols are important tools in distributed and fault-tolerant programming. They are useful for sharing information and for maintaining replicated data in a distributed system. However, a wide range of such protocols has been proposed. These protocols differ in their fault tolerance and delivery ordering characteristics. There is a tradeoff between the cost of a broadcast protocol and how much ordering it provides. It is, therefore, desirable to employ protocols that support only a low degree of ordering whenever possible. This dissertation presents techniques for deciding how strongly ordered a protocol is necessary to solve a given application problem. It is shown that there are two distinct classes of application problems: problems that can be solved with efficient, asynchronous protocols, and problems that require global ordering. The concept of a linearization function that maps partially ordered sets of events to totally ordered histories is introduced. How to construct an asynchronous implementation that solves a given problem if a linearization function for it can be found is shown. It is proved that in general the question of whether a problem has an asynchronous solution is undecidable. Hence there exists no general algorithm that would automatically construct a suitable linearization function for a given problem. Therefore, an important subclass of problems that have certain commutativity properties are considered. Techniques for constructing asynchronous implementations for this class are presented. These techniques are useful for constructing efficient asynchronous implementations for a broad range of practical problems.
A Flexible Transmit Diversity Assisted Broadband Multicarrier DS-CDMA Scheme
Yang, L-L.; Hanzo, L
2002-01-01
In this contribution we identify some of the key problems that may be encountered when designing a broadband multiple-access -systems having bandwidth on the order of tens or even hundreds MHz We commence with a comparative discussion in terms of the Characteristics of three typical code-division multiple-access- (CDMA) schemes, namely single-carrier direct-sequence CDMA (SC DS-CDMA), multicarrier CDMA (MC-CDMA) and multicarrier (MC DS-CDMA). Their benefits and deficiencies are analyzed, when...
Jakobsen, Kaj Bjarne
1999-01-01
Specifications, Direct Sequence, Frequency Hopping, Hybrid, W-CDMA, and Power Amplifier Linearisation.......Specifications, Direct Sequence, Frequency Hopping, Hybrid, W-CDMA, and Power Amplifier Linearisation....
LAS-CDMA using Various Time Domain Chip-Waveforms
Wei, H.; Hanzo, L.
2005-01-01
LAS CDMA exhibits a significantly better performance than that of classic random code based DS-CDMA, when operating in a quasi-synchronous scenario. Classic frequency-domain raised cosine Nyquist filtering is known to show the best possible performance, but its complexity may be excessive in highchip-rate systems. Hence in these systems often low-complexity time-domain waveform shaping is considered. Motivated by this fact, the achievable performance of LAS-CDMA is investigated in conjunction...
Blind Separation of DS-CDMA Signals with ICA Method
Miao Yu; Jianzhong Chen; Lei Shen; Shiju Li
2011-01-01
The estimation of pseudo noise sequence and information sequence is of great importance in the security of DS-CDMA system, which remains a hot research problem in reconnaissance and supervision of wireless communication. In DS-CDMA system, the pseudo noise sequences of different users are uncorrelated and the information sequences of different users are statistical independent, thus independent component analysis (ICA) could be introduced to separate the DS-CDMA signals with little prior know...
Wang, Xingyuan; Xu, Bing; Luo, Chao
2012-11-01
This paper proposes a novel asynchronous communication scheme. Based on this scheme, a model using the hyperchaotic system of 6th-order Cellular Neural Network (CNN) is designed. This scheme enhances the security of asynchronous communication compared to the conventional ones. It is noteworthy that the proposed communication scheme does not depend on synchronization, and almost all chaotic systems can be involved in this scheme. Numerical simulations show the effectiveness of this scheme.
Mohamad Dosaranian Moghadam
2011-01-01
Full Text Available The interference reduction capability of antenna arrays, base station assignment and the power controlalgorithms have been considered separately as means to increase the capacity in wireless communicationnetworks. In this paper, we propose base station assignment method based on minimizing the transmitterpower (BSA-MTP technique in a direct sequence-code division multiple access (DS-CDMA receiver inthe presence of frequency-selective Rayleigh fading and power control error (PCE. This receiverconsists of constrained least mean squared (CLMS algorithm, matched filter (MF, and maximal ratiocombining (MRC in three stages. Also, we present switched-beam (SB technique in the first stage of theRAKE receiver for enhancing signal to interference plus noise ratio (SINR in DS-CDMA cellularsystems. The simulation results indicate that BSA-MTP technique can significantly improve the networkbit error rate (BER in comparison with the conventional case. Finally, we discuss on three parameters ofthe PCE, number of resolvable paths, and channel propagation conditions (path-loss exponent andshadowing and their effects on capacity of the system via some computer simulations.
Jeonghun Kim
2011-10-01
Full Text Available We propose a reliable multicast MAC protocol based on the multicarrier direct-sequence code-division multiple access (MC DS-CDMA scheme to enhance spatial reuse efficiency in wireless local area networks (WLANs. Conventional multicast MAC protocols using RTS-CTS handshake exchange CTS and ACK packets consecutively for reliable transmission. Although this protocol guarantees transmission reliability by avoiding the hidden node (HN problem, multiple CTSs and ACKs degrade network efficiency and cause the well-known exposed node (EN problem, rather than the HN problem. The multicast sender must receive multiple CTSs and ACKs from all multicast receivers in its own multicastgroup for reliable multicast. The range of the EN problem is greater than that of the unicast, and spatial reuse efficiency decreases. In the proposed protocol, CTS/ACK messages of multiple receivers can be transmitted concurrently through the MC DS-CDMA mechanism to alleviate the EN problem and enhance spatial reuse efficiency. This can reduce the transmission and carrier sensing range of multiple receivers, since the protocol spreads the CTS/ACK transmission power by the spreading gain. The proposed protocol also reduces the total transmission delay due to the reduction of the overhead of consecutive CTSs and ACKs. The proposed protocol is thoroughly examined by simulation and theoretical methods. Results show that the proposed protocol significantly reduces the aforementioned overhead, and thus improves the performance of WLAN systems.
Modelling and Simulation of Asynchronous Real-Time Systems using Timed Rebeca
Aceto, Luca; Ingolfsdottir, Anna; Reynisson, Arni Hermann; Sigurdarson, Steinar Hugi; Sirjani, Marjan; 10.4204/EPTCS.58.1
2011-01-01
In this paper we propose an extension of the Rebeca language that can be used to model distributed and asynchronous systems with timing constraints. We provide the formal semantics of the language using Structural Operational Semantics, and show its expressiveness by means of examples. We developed a tool for automated translation from timed Rebeca to the Erlang language, which provides a first implementation of timed Rebeca. We can use the tool to set the parameters of timed Rebeca models, which represent the environment and component variables, and use McErlang to run multiple simulations for different settings. Timed Rebeca restricts the modeller to a pure asynchronous actor-based paradigm, where the structure of the model represents the service oriented architecture, while the computational model matches the network infrastructure. Simulation is shown to be an effective analysis support, specially where model checking faces almost immediate state explosion in an asynchronous setting.
Hanzo, Lajos
2004-01-01
"Now fully revised and updated, with more than 300 pages of new material, this new edition presents the wide range of recent developments in the field and places particular emphasis on the family of coded modulation aided OFDM and CDMA schemes. In addition, it also includes a fully revised chapter on adaptive modulation and a new chapter characterizing the design trade-offs of adaptive modulation and space-time coding." "In summary, this volume amalgamates a comprehensive textbook with a deep research monograph on the topic of QAM, ensuring it has a wide-ranging appeal for both senior undergraduate and postgraduate students as well as practicing engineers and researchers."--Jacket.
Kang, Yu; Zhai, Di-Hua; Liu, Guo-Ping; Zhao, Yun-Bo
2016-05-01
An extended asynchronous switching model is investigated for a class of switched stochastic nonlinear retarded systems in the presence of both detection delay and false alarm, where the extended asynchronous switching is described by two independent and exponentially distributed stochastic processes, and further simplified as Markovian. Based on the Razumikhin-type theorem incorporated with average dwell-time approach, the sufficient criteria for global asymptotic stability in probability and stochastic input-to-state stability are given, whose importance and effectiveness are finally verified by numerical examples. PMID:26068932
Asynchronous data-driven classification of weapon systems
This communication addresses real-time weapon classification by analysis of asynchronous acoustic data, collected from microphones on a sensor network. The weapon classification algorithm consists of two parts: (i) feature extraction from time-series data using symbolic dynamic filtering (SDF), and (ii) pattern classification based on the extracted features using the language measure (LM) and support vector machine (SVM). The proposed algorithm has been tested on field data, generated by firing of two types of rifles. The results of analysis demonstrate high accuracy and fast execution of the pattern classification algorithm with low memory requirements. Potential applications include simultaneous shooter localization and weapon classification with soldier-wearable networked sensors. (rapid communication)
Degaudenzi, R.; Elia, C.; Viola, R.
1990-01-01
Discussed here is a new approach to code division multiple access applied to a mobile system for voice (and data) services based on Band Limited Quasi Synchronous Code Division Multiple Access (BLQS-CDMA). The system requires users to be chip synchronized to reduce the contribution of self-interference and to make use of voice activation in order to increase the satellite power efficiency. In order to achieve spectral efficiency, Nyquist chip pulse shaping is used with no detection performance impairment. The synchronization problems are solved in the forward link by distributing a master code, whereas carrier forced activation and closed loop control techniques have been adopted in the return link. System performance sensitivity to nonlinear amplification and timing/frequency synchronization errors are analyzed.
Security Performance of Optical CDMA Against Eavesdropping
Shake, Thomas H.
2005-02-01
Enhanced security has often been cited as an important benefit of optical CDMA (O-CDMA) signaling. However, the quality and degree of security enhancement has not been closely examined in the literature. This paper examines the degree and types of security that may be provided by O-CDMA encoding. A quantitative analysis of data confidentiality is presented for O-CDMA encoding techniques that use both time spreading and wavelength hopping. The probability of successful data interception is calculated as a function of several parameters, including signal-to-noise ratio and fraction of total available system capacity. For reasonable choices of system and encoding parameters, it is shown that increasing code complexity can increase the signal-to-noise ratio (SNR) required for an eavesdropper to "break" the encoding by only a few dB, while the processing of fewer than 100 bits by an eavesdropper can reduce the SNR required to break the encoding by up to 12 dB. The overall degree of confidentiality obtainable through O-CDMA encoding is also compared with that obtainable through standard cryptography. time-spreading/wavelength-hopping in particular, and O-CDMA in general, are found to provide considerably less data confidentiality than cryptography, and the confidentiality provided is found to be highly dependent on system design and implementation parameters.
VOLTAGE REGULATORS ASYNCHRONOUS GENERATORS
Grigorash O. V.; Bogatyrev N. I.; Hitskova A. O.
2015-01-01
A promising is currently the use of asynchronous generators with capacitive excitation as a source of electricity in stand-alone power systems. Drive asynchronous generators may exercise as a thermal engine and wind wheel wind power plant or turbines of small hydropower plants. The article discusses the structural and schematics of voltage stabilizers and frequency of asynchronous generators with improved operational and technical specifications. Technical novelty of design solutions of the m...
Performance Analysis for Bit Error Rate of DS- CDMA Sensor Network Systems with Source Coding
Haider M. AlSabbagh
2012-03-01
Full Text Available The minimum energy (ME coding combined with DS-CDMA wireless sensor network is analyzed in order to reduce energy consumed and multiple access interference (MAI with related to number of user(receiver. Also, the minimum energy coding which exploits redundant bits for saving power with utilizing RF link and On-Off-Keying modulation. The relations are presented and discussed for several levels of errors expected in the employed channel via amount of bit error rates and amount of the SNR for number of users (receivers.
Joint ICA-Based Blind Detection and Parameter Assessment in DS-CDMA Systems
Mohammad Eslami
2011-09-01
Full Text Available In this study, blind code extraction of Direct Sequence Code Division Multiple Access (DS-CDMA signals is considered, based on Independent Component Analysis (ICA method. In order to distinguish between correct and incorrect extracted codes, to estimate the number of active users and also to determine the quality of detection along with the ICA based blind detection procedure, some propositions are defined. These propositions are used to improve the performance of the ICA blind detection based method. Then, in order to analyze the proposed criteria, Principle Component Analysis (PCA and Gaussian Mixture Model (GMM are employed. Experimental results illustrate that the achieved performance of the defined criteria.
de Lamare, Rodrigo C
2012-01-01
In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, parallel and iterative interference cancellation structures. A novel efficient DF structure that employs successive cancellation with parallel arbitrated branches and a near-optimal low complexity user ordering algorithm are presented. The proposed DF receiver structure and the ordering algorithm are then combined with iterative cascaded DF stages for mitigating the deleterious effects of error propagation for convolutionally encoded systems with both Viterbi and turbo decoding as well as for uncoded schemes. We mathematically study the relations between the MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback. Simulation results for an uplink scenario assess the new it...
Investigation of Closed Vector Control System for Asynchronous Motor Drive of Shipboard Tow Winch
Н. Mehdiyev; Е. Sultanov
2014-01-01
The paper considers a closed vector control system for induction motor rotation speed of a shipboard tow winch. Structural schemes and transfer functions of the system at control and disturbing influences are presented in the paper. The system with asynchronous motor drive parameters of a shipboard tow winch has been investigated in the paper. It has been revealed that transit process duration of the given system is insignificant. The fact is rather important to prevent accidents in case of v...
CDMA Transmission with Complex OFDM/OQAM
Lélé Chrislin
2008-01-01
Full Text Available Abstract We propose an alternative to the well-known multicarrier code-division multiple access (MC-CDMA technique for downlink transmission by replacing the conventional cyclic-prefix orthogonal frequency division multiplexing (OFDM modulation by an advanced filterbank-based multicarrier system (OFDM/OQAM. Indeed, on one hand, MC-CDMA has already proved its ability to fight against frequency-selective channels thanks to the use of the OFDM modulation and its high flexibility in multiple access thanks to the CDMA component. On the other hand, OFDM/OQAM modulation confers a theoretically optimal spectral efficiency as it operates without guard interval. However, its orthogonality is limited to the real field. In this paper, we propose an orthogonally multiplex quadrature amplitude modulation (OQAM- CDMA combination that permits a perfect reconstruction of the complex symbols transmitted over a distortion-free channel. The validity and efficiency of our theoretical scheme are illustrated by means of a comparison, using realistic channel models, with conventional MC-CDMA and also with an OQAM-CDMA combination conveying real symbols.
CDMA Transmission with Complex OFDM/OQAM
Chrislin Lélé
2007-12-01
Full Text Available We propose an alternative to the well-known multicarrier code-division multiple access (MC-CDMA technique for downlink transmission by replacing the conventional cyclic-prefix orthogonal frequency division multiplexing (OFDM modulation by an advanced filterbank-based multicarrier system (OFDM/OQAM. Indeed, on one hand, MC-CDMA has already proved its ability to fight against frequency-selective channels thanks to the use of the OFDM modulation and its high flexibility in multiple access thanks to the CDMA component. On the other hand, OFDM/OQAM modulation confers a theoretically optimal spectral efficiency as it operates without guard interval. However, its orthogonality is limited to the real field. In this paper, we propose an orthogonally multiplex quadrature amplitude modulation (OQAM- CDMA combination that permits a perfect reconstruction of the complex symbols transmitted over a distortion-free channel. The validity and efficiency of our theoretical scheme are illustrated by means of a comparison, using realistic channel models, with conventional MC-CDMA and also with an OQAM-CDMA combination conveying real symbols.
Adel Omar Dahmane
2008-01-01
Full Text Available Multistage parallel interference cancellation- (MPIC- based detectors allow to mitigate multiple-access interference in direct-sequence code-division multiple-access (DS-CDMA systems. They are considered serious candidates for practical implementation showing a good tradeoff between performance and complexity. Better performance is obtained when decision feedback (DF is employed. Although MPIC and DF-MPIC have the same arithmetic complexity, DF-MPIC needs much more FPGA resources when compared to MPIC without decision feedback. In this letter, FPGA implementation of block parallel DF-MPIC (BP-DF-MPIC is proposed allowing better tradeoff between performance and FPGA area occupancy. To reach an uncoded bit-error rate of 10−3, BP-DF-MPIC shows a 1.5 dB improvement over the MPIC without decision feedback with only 8% increase in FPGA resources compared to 69% for DF-MPIC.
A modular control architecture for real-time synchronous and asynchronous systems
This paper describes a control architecture for real-time control of complex robotic systems. The Modular Integrated Control Architecture (MICA), which is actually two complementary control systems, recognizes and exploits the differences between asynchronous and synchronous control. The asynchronous control system simulates shared memory on a heterogeneous network. For control information, a portable event-scheme is used. This scheme provides consistent interprocess coordination among multiple tasks on a number of distributed systems. The machines in the network can vary with respect to their native operating systems and the intemal representation of numbers they use. The synchronous control system is needed for tight real-time control of complex electromechanical systems such as robot manipulators, and the system uses multiple processors at a specified rate. Both the synchronous and asynchronous portions of MICA have been developed to be extremely modular. MICA presents a simple programming model to code developers and also considers the needs of system integrators and maintainers. MICA has been used successfully in a complex robotics project involving a mobile 7-degree-of-freedom manipulator in a heterogeneous network with a body of software totaling over 100,000 lines of code. MICA has also been used in another robotics system, controlling a commercial long-reach manipulator
Asynchronous data change notification between database server and accelerator controls system
Database data change notification (DCN) is a commonly used feature. Not all database management systems (DBMS) provide an explicit DCN mechanism. Even for those DBMS's which support DCN (such as Oracle and MS SQL server), some server side and/or client side programming may be required to make the DCN system work. This makes the setup of DCN between database server and interested clients tedious and time consuming. In accelerator control systems, there are many well established software client/server architectures (such as CDEV, EPICS, and ADO) that can be used to implement data reflection servers that transfer data asynchronously to any client using the standard SET/GET API. This paper describes a method for using such a data reflection server to set up asynchronous DCN (ADCN) between a DBMS and clients. This method works well for all DBMS systems which provide database trigger functionality. Asynchronous data change notification (ADCN) between database server and clients can be realized by combining the use of a database trigger mechanism, which is supported by major DBMS systems, with server processes that use client/server software architectures that are familiar in the accelerator controls community (such as EPICS, CDEV or ADO). This approach makes the ADCN system easy to set up and integrate into an accelerator controls system. Several ADCN systems have been set up and used in the RHIC-AGS controls system.
Extended ℋ∞ Estimation for Two-Dimensional Markov Jump Systems under Asynchronous Switching
Rui Zhang
2013-01-01
Full Text Available This paper is concerned with the problem of designing ℋ∞ filters for a class of two-dimensional (2D Markov jump systems under asynchronous switching. The problem under consideration is primarily motivated by a realistic situation that the switching of candidate filters may have a lag to the switching of system modes. Different from conventional techniques, by a suitable augmentation, the jumping process of the error system is represented by a two-component Markov chain. Then, the extended transition probabilities are provided for the error system. A stochastic Lyapunov function approach is proposed for the design of desired filters that ensure a prescribed ℋ∞ performance for admissible asynchronous switching. Finally, a numerical example is given to illustrate the effectiveness of the developed method.
Frequency support among asynchronous AC systems through VSCs emulating power plants
Papangelis, Lampros; Guillaud, Xavier; Van Cutsem, Thierry
2015-01-01
This paper proposes a new control scheme for the Voltage Source Converters (VSCs) of a High Voltage Direct Current (HVDC) grid connecting asynchronous AC systems, so that the latter can mutually support their frequencies after a disturbance. The scheme involves no communication between VSCs. It is activated upon detection of a significant frequency deviation, with the possibility to limit the support requested from other AC systems. It relies on an integral control enforcing the frequency dro...
Duan, Yingyao; Zuo, Xin; Liu, Jianwei
2016-01-01
Networked predictive control system (NPCS) has been proposed to address random delays and data dropouts in networked control systems (NCSs). A remaining challenge of this approach is that the controller has uncertain information about the actual control inputs, which leads to the predicted control input errors. The main contribution of this paper is to develop an explicit mechanism running in the distributed network nodes asynchronously, which enables the controller node to keep informed of the states of the actuator node without a priori knowledge about the network. Based on this mechanism, a novel proactive compensation strategy is proposed to develop asynchronous update based networked predictive control system (AUBNPCS). The stability criterion of AUBNPCS is derived analytically. A simulation experiment based on Truetime demonstrates the effectiveness of the scheme. PMID:26582090
New DOA Algorithms for CDMA System%适用于CDMA系统的DOA算法
吕旌阳; 高振明; 吴伟陵
2003-01-01
提出了一个直扩码分多址(DS-CDMA)通信系统的接收信号模型,并在此模型的基础上推导出一种适用于DS-CDMA系统的DOA(Directions of Arrival)算法.算法利用期望用户的扩频序列与接收信号的信号子空间的关系,来估计信号的DOA.该算法突破了在传统的DOA算法中检测的DOA数要小于阵列的天线数的限制,其性能也远远好于一般的DOA算法.
An Asynchronous Time-Division-Multiplexed Network-on-Chip for Real-Time Systems
Kasapaki, Evangelia
Multi-processor architectures using networks-on-chip (NOCs) for communication are becoming the standard approach in the development of embedded systems and general purpose platforms. Typically, multi-processor platforms follow a globally asynchronous locally synchronous (GALS) timing organization...... important part of the T-CREST paltform and used in a number of configurations. The flexible timing organization of Argo combines asynchronous routers with mesochronous NIs, which are connected to individually clocked cores, supporting a GALS system organization. The mesochronous NIs operate at the same....... This thesis focuses on the design of Argo, a NOC targeted at hard real-time multi-processor platforms with a GALS timing organization. To support real-time communication, NOCs establish end-to-end connections and provide latency and throughput guarantees for these connections. Argo uses time division...
Zhao, Yaqin; Zhong, Xin; Wu, Di; Zhang, Ye; Ren, Guanghui; Wu, Zhilu
2013-09-01
Optical code-division multiple access (OCDMA) systems usually allocate orthogonal or quasi-orthogonal codes to the active users. When transmitting through atmospheric scattering channel, the coding pulses are broadened and the orthogonality of the codes is worsened. In truly asynchronous case, namely both the chips and the bits are asynchronous among each active user, the pulse broadening affects the system performance a lot. In this paper, we evaluate the performance of a 2D asynchronous hard-limiting wireless OCDMA system through atmospheric scattering channel. The probability density function of multiple access interference in truly asynchronous case is given. The bit error rate decreases as the ratio of the chip period to the root mean square delay spread increases and the channel limits the bit rate to different levels when the chip period varies.
Performance of Generalized Multicarrier DS-CDMA over Nakagami-$m$ Fading Channels
Yang, L-L.; Hanzo, L
2002-01-01
A class of generalized multicarrier direct sequence code-division multiple-access (MC DS-CDMA) schemes is defined and its performance is considered over multipath Nakagamifading channels. The spacing between two adjacent subcarriers of the generalized MC DS-CDMA is a variable, allowing us to gain insight into the effects of the spacing on the bit error rate (BER) performance of MC DS-CDMA systems. This generalized MC DS-CDMA scheme includes the subclasses of multitone DS-CDMA and orthogonal M...
Blind Reduced-Rank MMSE Detector for DS-CDMA Systems
Xiaodong Cai
2003-01-01
Full Text Available We first develop a reduced-rank minimum mean squared error (MMSE detector for direct-sequence (DS code division multiple access (CDMA by forcing the linear MMSE detector to lie in a signal subspace of a reduced dimension. While a reduced-rank MMSE detector has lower complexity, it cannot outperform the full-rank MMSE detector. We then concentrate on the blind reduced-rank MMSE detector which is obtained from an estimated covariance matrix. Our analysis and simulation results show that when the desired userÃ¢Â€Â²s signal is in a low-dimensional subspace, there exists an optimal subspace so that the blind reduced-rank MMSE detector lying in this subspace has the best performance. By properly choosing a subsspace, we guarantee that the optimal blind reduced-rank MMSE detector is obtained. An adaptive blind reduced-rank MMSE detector, based on a subspace tracking algorithm, is developed. The adaptive blind reduced-rank MMSE detector exhibits superior steady-state performance and fast convergence speed.
Dynamic analysis methods for detecting anomalies in asynchronously interacting systems
Kumar, Akshat; Solis, John Hector; Matschke, Benjamin
2014-01-01
Detecting modifications to digital system designs, whether malicious or benign, is problematic due to the complexity of the systems being analyzed. Moreover, static analysis techniques and tools can only be used during the initial design and implementation phases to verify safety and liveness properties. It is computationally intractable to guarantee that any previously verified properties still hold after a system, or even a single component, has been produced by a third-party manufacturer. In this paper we explore new approaches for creating a robust system design by investigating highly-structured computational models that simplify verification and analysis. Our approach avoids the need to fully reconstruct the implemented system by incorporating a small verification component that dynamically detects for deviations from the design specification at run-time. The first approach encodes information extracted from the original system design algebraically into a verification component. During run-time this component randomly queries the implementation for trace information and verifies that no design-level properties have been violated. If any deviation is detected then a pre-specified fail-safe or notification behavior is triggered. Our second approach utilizes a partitioning methodology to view liveness and safety properties as a distributed decision task and the implementation as a proposed protocol that solves this task. Thus the problem of verifying safety and liveness properties is translated to that of verifying that the implementation solves the associated decision task. We develop upon results from distributed systems and algebraic topology to construct a learning mechanism for verifying safety and liveness properties from samples of run-time executions.
A Transactional Asynchronous Replication Scheme for Mobile Database Systems
丁治明; 孟小峰; 王珊
2002-01-01
In mobile database systems, mobility of users has a significant impact on data replication. As a result, the various replica control protocols that exist today in traditional distributed and multidatabase environments are no longer suitable. To solve this problem, a new mobile database replication scheme, the Transaction-Level Result-Set Propagation (TLRSP)model, is put forward in this paper. The conflict detection and resolution strategy based on TLRSP is discussed in detail, and the implementation algorithm is proposed. In order to compare the performance of the TLRSP model with that of other mobile replication schemes, we have developed a detailed simulation model. Experimental results show that the TLRSP model provides an efficient support for replicated mobile database systems by reducing reprocessing overhead and maintaining database consistency.
Frequency control system based on power factor control of asynchronous motor
MENG Qing-chun; YANG Fei-xia; REN Zhi-ling
2005-01-01
Deduced the relationship between the power factor (PF) and the angular frequency according to the simplified equivalent circuit of asynchronous motor, forming a power factor auto-control system. An anti-interference circuit was also introduced in the middle voltage link of inverter to avoid the shift of the optimum PF point caused by the change of the load and the reliable run of the control system was assured. The experiment results show that it has a good self-adaptation in the whole scope of speed adjustment and an obvious economization on energy while it runs under load.
CDMA Based Interconnect Mechanism for SOPC
V. Rajesh
2012-03-01
Full Text Available The Network-on-chip (NoC designs consisting of large pack of Intellectual Property (IP blocks (cores on the same silicon die is becoming technically possible nowadays. But, the communication between the IP Cores is the main issue in recent years. This paper presents the design of a Code Division Multiple Access (CDMA based wrapper interconnect as a component of System on programmable chip (SOPC builder to communicate between IP cores. In the proposal, only bus lines that carry address and data signals are CDMA coded. CDMA technology has better data integrity, channel continuity, channel isolation, and also mainly it reduces the no.of lines in the bus architecture for transmitting the data from master to slave.
Soprano, C.
1993-01-01
CDMA (Code Division Multiple Access) is known to decrease inter-service interference in Satellite Communication Systems. Its performance is increased by chip quasi-synchronous operation which virtually eliminates the self-noise; however, the theory shows that the time error on the synchronization has to be kept at less than one tenth of a chip which, for 1 Mchip/sec. spreading rate, corresponds to 10(exp -7) sec. This, on the return-link, may only be achieved by means of a closed loop control system which, for mobile communication systems, has to be capable of autonomous operation. Until now some results have been reported on the feasibility of chip quasi-synchronous operation for mobile communication systems only including satellites on GEO (Geostationary Earth Orbit). In what follows, the basic principles are exposed, and results are presented showing how low chip synchronism error may be achieved by means of an autonomous control loop operating through satellites on any Earth orbit.
Xiaoyu Hu
2007-11-01
Full Text Available The outage probability of reverse link multicarrier (MC code-division multiple access (CDMA systems with beamforming in the presence of carrier frequency offset (CFO is studied. A conventional uniform linear array (ULA beamformer is utilized. An independent Nakagami fading channel is assumed for each subcarrier of all users. The outage probability is first investigated under a scenario where perfect beamforming is assumed. A closed form expression of the outage probability is derived. The impact of different types of beamforming impairments on the outage probability is then evaluated, including direction-of-arrival (DOA estimation errors, angle spreads, and mutual couplings. Numerical results show that the outage probability improves significantly as the number of antenna elements increases. The effect of CFO on the outage probability is reduced significantly when the beamforming technique is employed. Also, it is seen that small beamforming impairments (DOA estimation errors and angle spreads only affect the outage probability very slightly, and the mutual coupling between adjacent antenna elements does not affect the outage probability noticeably.
N. P. Shrivastava
2016-01-01
Full Text Available A solution to data ageing requirements in time critical ship system like fire control system is presented. In an operational sea borne platform, navigation requirements for the onboard systems are fulfilled by ring laser gyro-based inertial navigation system. For critical systems like fire control system, navigational data must be delivered in real time without any delay. However due to delay occurring in processing of raw information and transmission of data on interface bus some latency is introduced. Algorithm for an asynchronous message transmission technique from inertial navigation system to user system to meet its latency requirements is discussed. Latency requirement is achieved by sending a separate message with the time stamp for the instance the first byte of 100 Hz attitude data is received at the processing computer of navigation system.Defence Science Journal, Vol. 66, No. 1, January 2016, pp. 26-29, DOI: http://dx.doi.org/10.14429/dsj.66.8502
Asynchronous data change notification between database server and accelerator control systems
Database data change notification (DCN) is a commonly used feature, it allows to be informed when the data has been changed on the server side by another client. Not all database management systems (DBMS) provide an explicit DCN mechanism. Even for those DBMS's which support DCN (such as Oracle and MS SQL server), some server side and/or client side programming may be required to make the DCN system work. This makes the setup of DCN between database server and interested clients tedious and time consuming. In accelerator control systems, there are many well established software client/server architectures (such as CDEV, EPICS, and ADO) that can be used to implement data reflection servers that transfer data asynchronously to any client using the standard SET/GET API. This paper describes a method for using such a data reflection server to set up asynchronous DCN (ADCN) between a DBMS and clients. This method works well for all DBMS systems which provide database trigger functionality. (authors)
THE RESEARCH OF GRADATION FUSION ALGORITHM BASED ON MULTISENSOR ASYNCHRONOUS SAMPLING SYSTEM
无
2005-01-01
This letter explores the distributed multisensor dynamic system, which has uniform sampling velocity and asynchronous sampling data for different sensors, and puts forward a new gradation fusion algorithm of multisensor dynamic system. As the total forecasted increment value between the two adjacent moments is the forecasted estimate value of the corresponding state increment in the fusion center, the new algorithm models the state and the forecasted estimate value of every moment. Kalman filter and all measurements arriving sequentially in the fusion period are employed to update the evaluation of target state step by step, on the condition that the system has obtained the target state evaluation that is based on the overall information in the previous fusion period. Accordingly, in the present period, the fusion evaluation of the target state at each sampling point on the basis of the overall information can be obtained. This letter elaborates the form of this new algorithm. Computer simulation demonstrates that this new algorithm owns greater precision in estimating target state than the present asynchronous fusion algorithm calibrated in time does.
Data-Aware Retrodiction for Asynchronous Harmonic Measurement in a Cyber-Physical Energy System
Youda Liu
2016-08-01
Full Text Available Cyber-physical energy systems provide a networked solution for safety, reliability and efficiency problems in smart grids. On the demand side, the secure and trustworthy energy supply requires real-time supervising and online power quality assessing. Harmonics measurement is necessary in power quality evaluation. However, under the large-scale distributed metering architecture, harmonic measurement faces the out-of-sequence measurement (OOSM problem, which is the result of latencies in sensing or the communication process and brings deviations in data fusion. This paper depicts a distributed measurement network for large-scale asynchronous harmonic analysis and exploits a nonlinear autoregressive model with exogenous inputs (NARX network to reorder the out-of-sequence measuring data. The NARX network gets the characteristics of the electrical harmonics from practical data rather than the kinematic equations. Thus, the data-aware network approximates the behavior of the practical electrical parameter with real-time data and improves the retrodiction accuracy. Theoretical analysis demonstrates that the data-aware method maintains a reasonable consumption of computing resources. Experiments on a practical testbed of a cyber-physical system are implemented, and harmonic measurement and analysis accuracy are adopted to evaluate the measuring mechanism under a distributed metering network. Results demonstrate an improvement of the harmonics analysis precision and validate the asynchronous measuring method in cyber-physical energy systems.
Data-Aware Retrodiction for Asynchronous Harmonic Measurement in a Cyber-Physical Energy System.
Liu, Youda; Wang, Xue; Liu, Yanchi; Cui, Sujin
2016-01-01
Cyber-physical energy systems provide a networked solution for safety, reliability and efficiency problems in smart grids. On the demand side, the secure and trustworthy energy supply requires real-time supervising and online power quality assessing. Harmonics measurement is necessary in power quality evaluation. However, under the large-scale distributed metering architecture, harmonic measurement faces the out-of-sequence measurement (OOSM) problem, which is the result of latencies in sensing or the communication process and brings deviations in data fusion. This paper depicts a distributed measurement network for large-scale asynchronous harmonic analysis and exploits a nonlinear autoregressive model with exogenous inputs (NARX) network to reorder the out-of-sequence measuring data. The NARX network gets the characteristics of the electrical harmonics from practical data rather than the kinematic equations. Thus, the data-aware network approximates the behavior of the practical electrical parameter with real-time data and improves the retrodiction accuracy. Theoretical analysis demonstrates that the data-aware method maintains a reasonable consumption of computing resources. Experiments on a practical testbed of a cyber-physical system are implemented, and harmonic measurement and analysis accuracy are adopted to evaluate the measuring mechanism under a distributed metering network. Results demonstrate an improvement of the harmonics analysis precision and validate the asynchronous measuring method in cyber-physical energy systems. PMID:27548171
A multi-host front end concentrator system for asynchronous consoles
Palandri, E M
1974-01-01
Describes a front end concentrator system for asynchronous time sharing consoles which has recently been put into operation at CERN. The concentrator will control up to 36 consoles at speeds up to 9600 bits per second and has the capability of dynamically connecting these consoles to several large Host processors. Features of the system include specially designed hardware and software to connect a wide range of different types of consoles in a flexible and expandable way, and the use of special purpose microcode to optimise console handling and facilitate the implementation of the system. The system runs in an HP2100 computer initially front-ending CDC 6000 series computers using the INTERCOM time sharing system. (6 refs).
Load Pull measurements for GSM and CDMA power modules
Fennelly, Michael; Wandrei, David
1998-01-01
A load pull system that has CDMA and GSM stimulus and response capability is presented. This novel system performs fundamental and harmonic tuning using a single, solid-state, impedance tuner without a multi-plexer or harmonic loops. Measurements of power, efficiency and spectral re-growth are obtained. Special consideration is made for the burst requirements of GSM. This paper presents the measurement system, harmonic tuning, CDMA and GSM examples.
All-optical code routing in interconnected optical CDMA and WDM ring networks.
Deng, Yanhua; Fok, Mable P; Prucnal, Paul R; Wang, Ting
2010-11-01
We propose an all-optical hybrid network composed of optical code division multiple access (CDMA) rings interconnecting through a reconfigurable wavelength division multiplexing (WDM) metro area ring. This network retains the advantages of both the optical CDMA and WDM techniques, including asynchronous access and differentiated quality of service, while removing the hard limit on the number of subscribers and increasing network flexibility. The all-optical network is enabled by using nonlinear optical loop mirrors in an add/drop router (ADR) that performs code conversion, dropping, and switching asynchronously. We experimentally demonstrate the functionalities of the ADR in the proposed scheme asynchronously and obtain error-free performance. The bit-error rate measurements show acceptable power penalties for different code routes. PMID:21042372
A.M. Galynovskiy
2013-10-01
Full Text Available Designing features for valve-engine transducers of brushless synchronous and asynchronized machines are described. Global analysis of research results on the transducer models in a MicroCap circuit simulation system is made, recommendations on the simulation system application in both scientific research and educational process given.
Relay system for phasing rotating disk selector with drive from asynchronous electric motor
Regulating system is described which ensures rotation of a massive disk selector synphaseally with a rotating reactivity modulator in a pulse reactor. Unlike the proportional regulating principle and using d.c. motor commonly utilized in solving similar problems, the given system involves an asynchronous short-circuited electric motor and a relay regulation principle. Thyristor control provides sufficiently simple realization of two selector acceleration modes (strong and weak acceleration) and two retardation modes (strong and weak braking). The mode switch-over moments are due to the regulated magnitude and its product. The given system is simple in maintenance, and has low sensitivity to oscillations in circuit voltage. In an 80-200 mc range of the selector period, the mean-square value of the displacement angle between the selector and reactor is at least +-1 deg
Kim Yong-Seok
2005-01-01
Full Text Available We present the BER analysis of antenna array (AA receiver in reverse-link asynchronous multipath Rician channels and analyze the performance of an improved AA system which applies a reverse-link synchronous transmission technique (RLSTT in order to effectively make a better estimation of covariance matrices at a beamformer-RAKE receiver. In this work, we provide a comprehensive analysis of user capacity which reflects several important factors such as the ratio of the specular component power to the Rayleigh fading power, the shape of multipath intensity profile, and the number of antennas. Theoretical analysis demonstrates that for the case of a strong specular path's power or for a high decay factor, the employment of RLSTT along with AA has the potential of improving the achievable capacity by an order of magnitude.
The concept of "stability" in asynchronous distributed decision-making systems.
Lee, T S; Ghosh, S
2000-01-01
Asynchronous distributed decision-making (ADDM) systems constitute a special class of distributed problems and are characterized as large, complex systems wherein the principal elements are the geographically dispersed entities that communicate among themselves, asynchronously, through message passing and are permitted autonomy in local decision making. Such systems generally offer significant advantages over the traditional, centralized algorithms in the form of concurrency, scalability, high throughput, efficiency, low vulnerability to catastrophic failures, and robustness. A fundamental property of ADDM systems is stability that refers to their behavior under representative perturbations to their operating environments, given that such systems are intended to be real, complex, and to some extent, mission-critical, and are subject to unexpected changes in their operating conditions. This paper introduces the concept of stability in ADDM systems and proposes an intuitive yet practical and usable definition that is inspired by those used in control systems and physics. An ADDM system is defined as a stable system if it returns to a steady state in finite time, following perturbation, provided that it is initiated in a steady state. Equilibrium or steady state is defined through placing bounds on the measured error in the system. Where the final steady state is equivalent to the initial one, a system is referred to as strongly stable. If the final steady state is potentially worse then the initial one, a system is deemed marginally stable. When a system fails to return to steady state following the perturbation, it is unstable. The perturbations are classified as either changes in the input pattern or changes in one or more environmental characteristics of the system, such as hardware failures. For a given ADDM system, the definitions are based on the performance indices that must be judiciously identified by the system architect and are likely to be unique. To
MC CDMA PAPR Reduction Techniques using Discrete Transforms and Companding
Sarala, B
2011-01-01
High Peak to Average Power Ratio (PAPR) of the transmitted signal is a serious problem in multicarrier modulation systems. In this paper a new technique for reduction in PAPR of the Multicarrier Code Division Multiple Access (MC CDMA) signals based on combining the Discrete Transform either Discrete Cosine Transform (DCT) or multi-resolution Discrete Wavelet Transform (DWT) with companding is proposed. It is analyzed and implemented using MATLAB. Simulation results of reduction in PAPR and power Spectral Density (PSD) of the MC CDMA with companding and without companding are compared with the MC CDMA with DCT and companding, DWT and companding systems. The new technique proposed is to make use of multi-resolution DWT in combination with companding in order to achieve a very substantial reduction in PAPR of the MC CDMA signal
Blind Adaptive Successive Interference Cancellation for Multicarrier DS-CDMA
Shakya, Indu; Stipidis, Elias
2011-01-01
A new adaptive receiver design for the Multicarrier (MC) DS-CDMA is proposed employing successive interference cancellation (SIC) architecture. One of the main problems limiting the performance of SIC in MC DS-CDMA is the imperfect estimation of multiple access interference (MAI), and hence, the limited frequency diversity gain achieved in multipath fading channels. In this paper, we design a blind adaptive SIC with new multiple access interference suppression capability implemented within despreading process to improve both detection and cancellation processes. Furthermore, dynamic scaling factors derived from the despreader weights are used for interference cancellation process. This method applied on each subcarrier is followed by maximum ratio or equal gain combining to fully exploit the frequency diversity inherent in the multicarrier CDMA systems. It is shown that this way of MAI estimation on individual subcarrier provides significantly improved performance for a MC DS-CDMA system compared to that with...
Li, Chuan-qi; Yang, Meng-jie; Zhang, Xiu-rong; Chen, Mei-juan; He, Dong-dong; Fan, Qing-bin
2014-07-01
A construction scheme of variable-weight optical orthogonal codes (VW-OOCs) for asynchronous optical code division multiple access (OCDMA) system is proposed. According to the actual situation, the code family can be obtained by programming in Matlab with the given code weight and corresponding capacity. The formula of bit error rate (BER) is derived by taking account of the effects of shot noise, avalanche photodiode (APD) bulk, thermal noise and surface leakage currents. The OCDMA system with the VW-OOCs is designed and improved. The study shows that the VW-OOCs have excellent performance of BER. Despite of coming from the same code family or not, the codes with larger weight have lower BER compared with the other codes in the same conditions. By taking simulation, the conclusion is consistent with the analysis of BER in theory. And the ideal eye diagrams are obtained by the optical hard limiter.