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Chaos-based multi-user time division multiplexing communication system

IET COMMUNICATIONS 2007年第4期1卷 549-555页

作者： Jovic, B. Unsworth, C. P. Univ Auckland Dept Elect & Comp Engn Auckland 1 New Zealand Univ Auckland Dept Elect Engn Auckland 1 New Zealand

A chaos-based multi-user time division multiplexing (TDM) communication system has been proposed and its benchmark performance compared to that of the chaos-based direct sequence code division multiple access (DS-CDMA) system in the noisy and Rayleigh fading channels. The benchmark performance of the systems is investigated in terms of the bit error rate (BER) under the assumption of perfect synchronisation. The chaotic spreading signals, used to encrypt the binary messages, are generated using the logistic map. The degradation in performance of the systems in the Rayleigh fading channel when compared with the noisy channel is demonstrated. Furthermore, it is shown that in both noisy and Rayleigh fading channels, the chaos-based multi-user TDM system outperforms the chaos-based DS-CDMA system for a large number of users in the system, whereas the chaos-based DS-CDMA system yields better performance for low user numbers. The overall BER performance degradation for the chaos-based DS-CDMA multi-user system in noisy and Rayleigh fading channels is characterised by the flattening of the BER curves at low levels of noise due to the prevailing effects of the inter-user interferences.

关键词： Raleigh fading channels System performance direct-sequence code-division multiple access noisy channel Rayleigh fading degradation of performance Noise levels time division multiplexing CDMA mobile communications

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Ant colony optimisation-based multiuser detection for direct-sequence CDMA systems with diversity reception

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IET COMMUNICATIONS 2007年第4期1卷 556-561页

作者： Lain, J.-K. Lai, J.-J. Natl Yunlin Univ Sci & Technol Dept Elect Engn Touliu Yunlin Taiwan

An ant colony optimisation (ACO)-based multiuser detector assisted by spatial diversity reception using direct-sequence CDMA is proposed. By taking advantage of heuristic values and the collective intelligence of ACO, the proposed detector offers almost the same bit error rate (BER) performance as the full-search-based optimum multiuser detector does, while greatly reducing the computational complexity. The near-far resistance of the ACO-based multiuser detector is also examined. The BER performance for a ten-user system deteriorates scarcely when the interfering users' energy is 12 dB higher than that of the desired user.

关键词： Ants direct-sequence code-division multiple access bit error rate performance Collective intelligence Multiuser detection diversity reception CDMA mobile communications

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Error-resilient pattern classification using a combination of spreading and coding gains

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IET IMAGE PROCESSING 2007年第3期1卷 278-286页

作者： El-Helw, A. M. Moniri, M. Chibelushi, C. C. Staffordshire Univ Fac Comp Engn & Technol Stafford ST16 9DG Staffs England

An approach that aims to enhance error resilience in pattern classification problems is proposed. The new approach combines the spread spectrum technique, specifically its selectivity and sensitivity, with error-correcting output codes (ECOC) for pattern classification. This approach combines both the coding gain of ECOC and the spreading gain of the spread spectrum technique to improve error resilience. ECOC is a well-established technique for general purpose pattern classification, which reduces the multi-class learning problem to an ensemble of two-class problems and uses special codewords to improve the error resilience of pattern classification. The direct sequence code division multiple access (DS-CDMA) technique is a spread spectrum technique that provides high user selectivity and high signal detection sensitivity, resulting in a reliable connection through a noisy radio communication channel shared by multiple users. Using DS-CDMA to spread the codeword, assigned to each pattern class by the ECOC technique, gives codes with coding properties that enable better correction of classification errors than ECOC alone. Results of performance assessment experiments show that the use of DS-CDMA alongside ECOC boosts error-resilience significantly, by yielding better classification accuracy than ECOC by itself.

关键词： direct-sequence code-division multiple access error-resilience pattern class spread-spectrum technique coding gain Pattern recognition

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Joint data detection and estimation of time-varying multipath rayleigh fading channels in asynchronous DS-CDMA systems with long spreading sequences

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EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS 2007年第2期18卷 115-132页

作者： Xiao, Pei Strom, Erik G. Newcastle Univ Sch Elect Elect & Comp Engn Newcastle Upon Tyne NE1 7RU Tyne & Wear England Chalmers Univ Technol Dept Signals & Syst Commun Syst Grp SE-41296 Gothenburg Sweden

In this paper, we present a joint approach to data detection and channel estimation for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signaling formats and long scrambling codes. Our emphasis is placed on different channel estimation algorithms since the performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigate channel estimation algorithms under different conditions. The estimated channel information is used to enable coherent data detection to combat the detrimental effect of the multiuser interference and the multipath propagation of the transmitted signal. In the considered multiuser detector, we mainly use interference cancellation techniques, which are suitable for long-code CDMA systems. Interference cancellation and channel estimation using soft estimates of the transmitted signal is also proposed in this paper. Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of channel estimation and bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems. Copyright (C) 2006 AEIT.

关键词： Raleigh fading channels direct-sequence code-division multiple access Multi-user Interference Interference cancellation channel estimation data detection Asynchronous Mean square error spreading sequence Multipath propagation

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V2V Channels and Performance of Multiuser Spread Spectrum Modulation

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IEEE VEHICULAR TECHNOLOGY MAGAZINE 2007年第4期2卷 19-25页

作者： Sen, Indranil Matolak, David W. Ohio Univ Athens OH 45701 USA

Vehicle-to-vehicle (V2V) communications have drawn much attention in recent years. In this article, we discuss tradeoffs between implementation complexity and accuracy of several stochastic channel models for the V2V environment, and then address spread-spectrum system performance attained using these channel models. Two different propagation environments are considered: urban and open areas (highways). The necessity of employing nonstationary channel models to accurately represent the channel is substantiated by comparing stationary and nonstationary empirical model outputs with measured data. A framework to compare single-carrier direct sequence code division multiple access (SC-DS-CDMA) and multicarrier DS-CDMA (MC-DS-CDMA) performance in V2V channels is presented, and bit error ratio (BER) performance of the schemes is provided for the two channels. Our comparison of single-and multi-user performance shows that MC-DS-CDMA performs better than SC-DS-CDMA in both V2V environments.

关键词： Spread spectrum communication System performance Multiaccess communication AWGN Intelligent transportation systems Communication standards direct-sequence code-division multiple access Frequency Rayleigh channels Power system modeling

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Performance Analysis of SC DS-CDMA and MC DS-CDMA Systems over Nakagami-m Fading Channel

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IETE TECHNICAL REVIEW 2007年第4期24卷 323-330页

作者： Anuradha, S. Srigowri, S. Krishna, K. S. Rama Reddy, K. V. V. S. VRS Engn Coll Dept ECE Vijayawada 520007 India Andhra Univ Coll Engn Dept ECE Vishakhapatnam 530003 Andhra Pradesh India

This paper deals with simulation of Nakagami-m fading in wireless channels using generalized SC DS-CDMA and MC DS-CDMA schemes using binary phase shift keying modulation scheme. The paper proposes for deriving Bit Error Rate (BER) in BPSK-SC DS-CDMA and MC DS-CDMA systems over Nakagami-m fading channels. The numerical results are plotted as BER vs SNR for various values of Nakagami factor m, number of users K and jamming interference (JSR) using MAT LAB software. The performance of Nakagami-m channel using BPSK-SC DS-CDMA and MC DS-CDMA techniques are compared. It is observed that there is a decrease in Bit Error Rate for increase in m for SC DS-CDMA and MC DS-CDMA. The number of users k, JSR increases as Bit Error Rate increases for MC DS-CDMA. For the same values of m BER for MC DS-CDMA is smaller when compared with SC DS-CDMA using Maximal Ratio Combining (MRC) diversity technique.

关键词： direct-sequence code-division multiple access Scandium Fading channels CDMA mobile communications

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Wideband impulse modulation and receiver algorithms for multiuser power line communications

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EURASIP JOURNAL ON ADVANCES IN SIGNAL PROCESSING 2007年第1期2007卷 096747-096747页

作者： Tonello, Andrea M. Univ Udine Dipartimento Ingn Elettr Gest & Meccan I-33100 Udine Italy

We consider a bit-interleaved coded wideband impulse-modulated system for power line communications. Impulse modulation is combined with direct-sequence code-division multiple access (DS-CDMA) to obtain a form of orthogonal modulation and to multiplex the users. We focus on the receiver signal processing algorithms and derive a maximum likelihood frequency-domain detector that takes into account the presence of impulse noise as well as the intercode interference (ICI) and the multiple-access interference (MAI) that are generated by the frequency- selective power line channel. To reduce complexity, we propose several simplified frequency-domain receiver algorithms with different complexity and performance. We address the problem of the practical estimation of the channel frequency response as well as the estimation of the correlation of the ICI-MAI-plus-noise that is needed in the detection metric. To improve the estimators performance, a simple hard feedback from the channel decoder is also used. Simulation results show that the scheme provides robust performance as a result of spreading the symbol energy both in frequency (through the wideband pulse) and in time (through the spreading code and the bit-interleaved convolutional code). Copyright (c) 2007.

关键词： Simulation results carrier transmission on power lines direct-sequence code-division multiple access broadband Receivers channel frequency response Channel Decoder Impulse noise Robust control Pulse modulation

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Single-User Receiver for Signature-Interleaved DS CDMA in Multipath Channel

Single-User Receiver for Signature-Interleaved DS CDMA in Mu...

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International Symposium on Wireless Communication Systems (ISWCS)

作者： Alexey Dudkov Turku Centre for Computer Science (TUCS) University of Turku Turku Finland

Multipath propagation can significantly impair performance of DS CDMA due to presence of the odd correlations of user signatures caused by delayed replicas of the transmitted signal. Traditionally to neutralize this effect some form of equalizing is used, which, along with receiver complication, leads to SNR loss. In the paper signature-interleaved (SI) DS CDMA is proposed and analyzed in application to a multipath channel. It is shown that with signature interleaving the output of a single user correlator contains only correlations of either non-shifted at all or just one-chip-shifted signatures. Thereby a deteriorating impact of odd correlations on the system performance is drastically reduced. As a result, SI DS CDMA provides performance improvement versus conventional DS CDMA with no need in complex equalizing.

关键词： Multiaccess communication Multipath channels multiple access interference Propagation delay Correlators Computer science Interleaved codes System performance direct-sequence code-division multiple access Matched filters

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Multi-Rate De-Spreading code

Multi-Rate De-Spreading Code

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IFIP International Conference on Wireless and Optical Communications Networks (WOCN)

作者： Jia-Chyi Wu Chi-Min Li Han-Way Chou Department of Communications and Guidance Engineering National Taiwan Ocean University Keelung Taiwan

An efficient methodology to construct direct sequence code division multiple access (DS-CDMA) de-coding scheme has been investigated. System correlation performance is provided and analyzed. Since the perfect orthogonal codes, such as Walsh code, are difficult to obtain massively in conventional DS-CDMA system. To increase the number of spreading code utilized in system, we usually adopt sub-orthogonal codes, such as Gold sequences. Although the number of codes is extensively increased, the multiple access interference (MAI) problem has to be treated more carefully. Especially while lots of users access the DS-CDMA system at the same time. In this study, we proposed a CDMA de-spreading scheme worked in receiver part The MAI can be treated efficiently in the proposed multi-rate de-spreading scheme.

关键词： Multiaccess communication multiple access interference direct-sequence code-division multiple access Gold Multicarrier code division multiple access Frequency Autocorrelation Underwater communication Oceans Performance analysis

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Genetic Algorithm Assisted Radial Basis Function Multiuser Detector for DS-CDMA

Genetic Algorithm Assisted Radial Basis Function Multiuser D...

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IEEE Signal Processing and Communications Applications (SIU)

作者： M. Ugur Torun Damla Kuntalp Elektrik ve Elektronik Mühendisliği Bölümü Dokuz Eylüi Üniversitesi Buca Izmir Turkey

The optimal receiver for detecting the direct sequence code division multiple access (DS-CDMA) signals suffers from computational complexity which increases exponentially with the increasing number of users. Thus several sub-optimal multiuser detectors (MUD) are proposed. Radial basis function (RBF) MUD is one of these sub-optimal receivers which has a very high performance but which still suffers from computational complexity since the number of center functions increases exponentially with the increasing number of users. In this contribution, we propose a new method to minimize the number of center functions of RBF MUD using genetic algorithm (GA) and least mean squares (LMS) algorithm. Simulation results showed that the proposed method immensely reduced the complexity of the RBF MUD and the MUD was capable of succesfully tracking the bit error rate of the single-user detector.

关键词： Genetic algorithms Detectors Multiaccess communication Multiuser detection Microstrip Computational complexity direct-sequence code-division multiple access Least squares approximation Computational modeling Bit error rate

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