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Differentially coherent combining for double-dwell code acquisition in DS-CDMA systems

IEEE TRANSACTIONS ON COMMUNICATIONS 2003年第7期51卷 1046-1050页

作者： Shin, OS Lee, KB Seoul Natl Univ Sch Elect Engn & Comp Sci Seoul 151742 South Korea

The use of differentially coherent combining is proposed to improve the performance. of a double-dwell acquisition system by increasing the reliability of a decision in the verification stage. The detection and mean acquisition time performance of the acquisition scheme with the proposed combining, scheme is analyzed in frequency-selective Rayleigh fading channels, and compared with that of two previously published double-dwell acquisition schemes based on long correlation intervals and noncoherent combining. It is shown that the proposed acquisition scheme outperforms the previous ones, and that the performance improvement increases as the frequency offset increases.

关键词： acquisition differentially coherent combining double-dwell search direct-sequence code-division multiple access (DS-CDMA) frequency offset

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PERFORMANCE ANALYSIS OF A HYBRID CDMA ISMA PROTOCOL FOR INDOOR WIRELESS COMPUTER COMMUNICATIONS

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1994年第5期12卷 909-916页

作者： VANROOSMALEN, H NIJHOF, J PRASAD, R Faculty of Electrical Engineering Telecommunications and Traffic-Control Systems Group Delft University of Technnology Delft Netherlands

A combination of direct sequence code division multiple access (DS-CDMA) and p-persistent Inhibit Sense multiple access (ISMA) protocols is proposed for Indoor Wireless Communications (IWC). The combination of these two protocols is called the hybrid CDMA/ISMA protocol. The performance of the hybrid CDMA/ISMA protocol is analyzed with a Markov model considering Differential Phase Shift Keying (DPSK) modulation. The performance is measured in terms of throughput and delay. The performance is also evaluated using computer simulation of which the results are in close agreement with the Markov model results. The study of indoor wireless communications using a hybrid CDMA/ISMA protocol can be useful for various applications in research and design offices, medical data communication in hospitals, etc.

关键词： Performance analysis Multiaccess communication access protocols Wireless application protocol Wireless communication direct-sequence code-division multiple access Differential phase shift keying Differential quadrature phase shift keying Phase modulation Throughput

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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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On the accuracy of Gaussian approximations in the error analysis of DS-CDMA with OQPSK modulation

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IEEE TRANSACTIONS ON COMMUNICATIONS 2002年第12期50卷 2064-2071页

作者： Landolsi, MA Stark, WE King Fahd Univ Petr & Minerals Dept Elect Engn Dhahran 31261 Saudi Arabia Univ Michigan Dept Elect Engn & Comp Sci Ann Arbor MI 48109 USA

This paper considers the bit error probability analysis of direct-sequence code-division multiple access with offset quadrature phase-shift keying (OQPSK) modulation and random signature sequences. A statistical characterization of the decision variable at the output of the correlation receiver is obtained. and several techniques for evaluating the error performance, previously derived for binary phase-shift keying (BPSK)-modulated systems, are then extended to the case of OQPSK. This includes exact bit error evaluation, as wen as various approximation methods based on Gaussian modeling of the multiple-access interference terms. These techniques known as the standard and improved Gaussian approximations, have increasing complexity depending on the level of accuracy required. For BPSK the standard approximation is typically found to be inaccurate, unless the number of users becomes large, and only the improved approximation yields sufficient accuracy in general. But for the case of OQPSK, the relative performance comparison developed in this paper shows that, for all practical purposes, the simple standard approximation is surprisingly very accurate even with a small number of users.

关键词： direct-sequence code-division multiple access (DS-CDMA) Gaussian approximation methods offset quadrature phase-shift keying (OQPSK)

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RAPID-sequence ACQUISITION FOR DS/CDMA SYSTEMS EMPLOYING KASAMI sequenceS

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IEEE TRANSACTIONS ON COMMUNICATIONS 1994年第2-4期42卷 1957-1968页

作者： BARGHOUTHI, RT STUBER, GL School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta GA USA

A sequence acquisition scheme based on sequential estimation and soft-decision combining methods is proposed and analyzed for direct-sequence CDMA systems employing Kasami sequences. The proposed technique is effective for Kasami sequences having very long periods. The algebraic properties of Kasami sequences are exploited to provide a very reliable estimate of the correct phase of the local shift register before tracking is attempted. This estimate is obtained by generating and combining multiple statistics for each chip that comprises the initial phase estimate. Expressions 'are derived for the mean and variance of the acquisition time, and the probabilities of acquisition, false dismissal, and false alarm. The proposed scheme compares well with the performance of alternative parallel acquisition schemes.

关键词： soft decision shift registers Scheme direct-sequence code-division multiple access sequential estimation tracking False False-positives False alarms acquisition time CDMA mobile communications Variance

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Multiuser detection analysis in DS-CDMA channel with Nakagami fading

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EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS 2000年第5期11卷 471-474页

作者： Novakovic, DM Dukic, ML Univ Belgrade Fac Elect Engn Dept Commun YU-11001 Belgrade Yugoslavia

In this paper the multiuser detection performance analysis in synchronous direct sequence code division multiple access (DS-CDMA) system using decorrelating and decision feedback (DFB) receivers, including single path Nakagami fading channel is presented. The lower bounds of the receivers bit error probability (BER) are derived, and the comparison of these receivers' performances to the conventional CDMA receiver is made. The analytical and numerical results show that the DFB receiver performs better in the presence of the high Nakagami fading channels.

关键词： Lower bound Multiuser detection direct-sequence code-division multiple access Nakagami fading Receivers

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Estimation of spreading sequences in LC-DS-CDMA signals based on sparse auto-encoder

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EVOLUTIONARY INTELLIGENCE 2020年第2期13卷 235-246页

作者： Qiang, Fangfang Zhao, Zhijin Shang, Junna Shen, Lei Hangzhou Dianzi Univ Sch Elect & Informat Hangzhou 310018 Peoples R China Hangzhou Dianzi Univ Sch Commun Engn Hangzhou 310018 Peoples R China Zhejiang Prov Key Lab Informat Proc Commun & Netw Hangzhou 310027 Peoples R China

A method based on a sparse auto-encoder (SAE) network for the estimation of spreading sequences in long-code direct-sequence code-division multiple access (LC-DS-CDMA) signals is proposed. First, a network classification model based on SAE and softmax classifier is established. Next, the effectiveness of the proposed method is verified by estimating Walsh sequences and m sequences. To estimate the spreading sequences, the LC-DS-CDMA signal is divided into fragments. Then, each user's spreading sequence is separated by the fast independent component analysis (Fast-ICA) algorithm, and the amplitude fuzziness is eliminated by the delay-and-multiply method. Finally, the spreading sequences are estimated by the SAE model. Experimental results showed that the proposed algorithm could effectively estimate the spreading sequences of LC-DS-CDMA signals. Compared to the existing matching algorithm and Fast-ICA algorithm, the estimation time required by the proposed algorithm was shorter, and its estimation performance at low signal-to-noise ratios was superior.

关键词： direct-sequence code-division multiple access Deep learning Sparse auto-encoder Blind source separation Signal analysis

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Design and Analysis of Asynchronous Incoherent Optical-CDMA Systems Using a New code-Shifting Technique

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IEEE TRANSACTIONS ON COMMUNICATIONS 2015年第7期63卷 2619-2631页

作者： Lin, Yen-Ting Yang, Guu-Chang Chang, Cheng-Yuan Kwong, Wing C. Natl Chung Hsing Univ Dept Elect Engn Taichung 402 Taiwan Natl Chung Hsing Univ Grad Inst Commun Engn Taichung 402 Taiwan Natl United Univ Dept Elect Engn Miaoli 36003 Taiwan Hofstra Univ Dept Engn Hempstead NY 11549 USA

In this paper, a novel code-shifting technique, which can be added atop asynchronous incoherent optical code-division multiple-access systems without complex modifications, is proposed and studied. The new technique divides the time-slot (or chips), in which the optical pulses of codewords are located, into g equal-width sub-chips;every pulse is randomly and independently shifted to start at one of the g sub-chips of its own chip, where g > 1 is a positive integer. The effects of this random g-shift to the cross-correlation property and performance of asynchronous optical codes (of periodic cross-correlation functions of at most one) are formulated. Although it is found that the periodic cross-correlation functions are worsened to 3 - 2/g, our theoretical and computer-simulation results show an unconventional finding that code performance improves as g increases.

关键词： Asynchronous communications direct-sequence code-division multiple access intensity modulation optical fiber communication

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Modified CMA based blind multiuser equaliser with decision directed scheme

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ELECTRONICS LETTERS 2008年第6期44卷 428-430页

作者： Mitra, A. Indian Inst Technol Guwahati Dept Elect & Commun Engn Gauhati 781039 India

A modified constant modulus (CM) algorithm based blind multiuser equaliser with a decision directed (DD) scheme is developed that does not require any mutual decorrelation and is suitable for downlink direct sequence code division multiple access systems. The performance of the proposed time domain adaptive equaliser is evaluated with respect to usual parameters and is found to perform better than the concurrent CM algorithm and DD scheme.

关键词： TIME-DOMAIN Equalizers code division Mentoring direct-sequence code-division multiple access Scheme

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Capacity of chaos-based asynchronous DS-CDMA systems with exponentially vanishing autocorrelations

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ELECTRONICS LETTERS 2002年第25期38卷 1717-1718页

作者： Mazzini, G Rovatti, R Setti, G Univ Ferrara CEG DI I-44100 Ferrara Italy Univ Bologna CEG ARCES I-40136 Bologna Italy

A receiver for synchronous DS-CDMA systems is proposed with a decision window that is aligned to encompass two half bits of each user. Such a receiver is compared with the classical one in terms of Shannon capacity showing a definite improvement. Based on this, traditional upper bounds and optimality criteria on the capacity of synchronous DS-CDMA systems are revised.

关键词： Autocorrelation direct-sequence code-division multiple access CDMA mobile communications Asynchronous Receivers

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