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Multiuser detection for DS-CDMA UWB in the home environment

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 2002年第9期20卷 1701-1711页

作者： Li, QH Rusch, LA Intel Corp Intel Labs Santa Clara CA 95052 USA Univ Laval Dept Elect & Comp Engn St Foy PQ G1K 7P4 Canada

We demonstrate the effectiveness of multiuser detection for an ultra-wideband (UWB) pulse based direct sequence spread spectrum system using code division multiple access. Extensive simulations were run using channel soundings of the 2-8 GHz band collected in a residential setting and characterized by a high level of multipath fragmentation. We show that the adaptive minimum mean square error (MMSE) multiuser detection (MUD), receivers are able to gather multipath energy and reject intersymbol and interchip interferernce for these channels to a much greater extent than RAKE receivers with 4 and 8 arms. We also demonstrate the adaptive MMSE is able to reject a narrowband IEEE 802.11a OFDM interferer, even for signal-to-interference ratio as severe as -30 dB. We show the adaptive MMSE exhibits only a 6 dB penalty relative to the single user case for the heavy multi-access interference (number of asynchronous users equal to spreading code length). The practical RAKE receivers were incapable of effectively rejecting either the strong narrowband interference or the heavily loaded wideband interference. Even more moderate levels of interference caused significant degradation in the performance of the practical RAKE receivers.

关键词： adaptive signal detection broadband networks code division multiple access indoor radio interference suppression intersymbol interference least mean squares methods multipath channels multiuser channels multiuser detection radio networks radio receivers suppression of interference Broadband networks radio receivers Radio networks indoor radio RAKE receivers code division multiple access Multiuser detection direct-sequence code-division multiple access multiuser channels adaptive signal detection direct sequence spread spectrum systems home environment Multipath channels intersymbolic interference

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Resolving subchip-spaced multipath components in CDMA communication systems

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 1999年第6期48卷 1803-1808页

作者： Kostic, Z Pavlovic, G AT&T Labs Res Red Bank NJ 07701 USA Lucent Bell Labs Holmdel NJ 07733 USA

A method is developed for resolving channel multipath components for direct-sequence code-division multiple-access (DS-CDMA) communication systems, Components which are spaced closer than a chip interval of the DS signature sequence are separable by the presented technique, The method is based on the constrained iterative deconvolution which uses the method of projection onto convex sets (POCS), A novel POCS constraint is derived which takes advantage of the noise covariance modified by a matched filter at the front end of the receiver, Simulation results for m-sequences and BPSK modulation are presented.

关键词： closer direct-sequence code-division multiple access Binary phase shift keying Convexity code division multiple access front-ends COMMUNICATION SYSTEMS projection method

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Multiuser Decorrelator Detectors in MIMO CDMA Systems over Nakagami Fading Channels

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2009年第4期8卷 1944-1952页

作者： Sacramento, Ariel Lionel Hamouda, Walaa Concordia Univ Dept Elect & Comp Engn Montreal PQ H3G 1M8 Canada

Space-time spreading has been employed to exploit the spatial diversity in multiple-input multiple-output (MIMO) code-division multiple-access (DS-CDMA) systems. In the presence of multiuser interference, resulting from the cross-correlation between users' code sequences, the full system diversity cannot be achieved when using the conventional matched receiver. In this paper we investigate the performance of space-time spreading (STS) and transmit diversity in the uplink of a MIMO DS-CDMA system over Nakagami-m fast-fading channels. The space-time system employs N = 2 transmit antennas and L receive antennas at the user side and base-station, respectively. We analyze the performance of the system when a linear decorrelator detector is employed to mitigate the effect of multiuser interference. In our analysis, we start by finding the probability density function (pdf) of the signal-to-interference ratio (SINR) at the output of the space-time combiner. Using this pdf, we derive a closed form expression for the bit-error rate (BER) for binary phase-shift keying (BPSK) transmission. The accuracy of the derived pdf and BER expression are verified using simulations, for different values of fading figure in and number of users.

关键词： direct-sequence code-division multiple access maximal-ratio combining multiuser detection transmit diversity

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Wideband DS-CDMA for next-generation mobile communications systems

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IEEE COMMUNICATIONS MAGAZINE 1998年第9期36卷 56-69页

作者： Adachi, F Sawahashi, M Suda, H NTT Mobile Commun Network Inc Yokosuka Kanagawa Japan

Wideband wireless access based on direct sequence code division multiple access aimed at third-generation mobile communications systems is reviewed. W-CDMA is designed to flexibly offer wideband services which cannot be provided by present cellular systems, with various data rates as high as 2 Mb/s. The important concept of W-CDMA is the introduction of intercell asynchronous operation and the pilot channel associated with individual data channels. Intercell asynchronous operation facilitates continuous system deployment from outdoors to indoors. Other technical features of W-CDMA include fast cell search under intercell asynchronous operation, fast transmit power control, coherent spreading code tracking, a coherent Rake receiver, orthogonal multispreading factor forward link, and variable-rate transmission with blind rate detection. The introduction of the data-channel-associated pilot channel allows W-CDMA to support interference cancellation and adaptive antenna array techniques that can significantly increase the link capacity and coverage. This article presents radio link performance evaluated by computer simulation. Field experiment radio link performance results are also presented.

关键词： Wideband Multiaccess communication Mobile communication Adaptive arrays Radio link direct-sequence code-division multiple access Continuous time systems Power control Fading Multipath channels

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Independent component analysis using successive interference cancellation for oversaturated data

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EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS 2006年第5期17卷 577-589页

作者： Huovinen, Toni Ristaniemi, Tapani Tampere Univ Technol Inst Commun Engn FIN-33101 Tampere Finland

In this paper, advanced interference cancellation strategies are considered and applied in DS-CDMA uplink receivers. Namely, we introduce a new successive interference cancellation (SIC) scheme in which blind source separation (BSS) techniques based on independent component analysis (ICA) are considered. Our main emphasis is on the oversaturated data in which situation easily arises for example in DS-CDMA systems when the number of active connections/users is high compared to number of chips per bit being used, that is, a highly loaded system. Proposed receiver structures combine the main benefits of pure BSS/ ICA and SIC methods: (i) inherent mitigation of various types of interference sources by BSS/ICA, (ii) robustness against parameter estimation errors due to BSSACA, (iii) greatly improved interference suppression capability due to novel combination of SIC ideology and ICA for oversaturated data. The last item in the list can also be seen as a way to somewhat circumvent the 'more sources than sensors'-problem, which is a challenging problem in BSS area. Numerical experiments with DS-CDMA uplink data are given to illustrate the achieved gains in capacity and bit-error-rate performance compared to conventional successive and parallel interference cancellation (PIC) schemes as well as more an advanced LMMSE-PIC receiver and variants of BSSACA techniques alone. Copyright (C) 2005 AEIT.

关键词： Blind source separation up link direct-sequence code-division multiple access Interference cancellation Receivers interference source Parameter estimation Independent component analysis islet cell antibody suppression of interference CDMA mobile communications

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Peak-to-average power ratio performance comparison of different spreading code allocation strategies for MC-CDMA and MC-DS-CDMA

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ELECTRONICS LETTERS 2002年第20期38卷 1219-1220页

作者： Hathi, N Darwazeh, I O'Reilly, J UCL Dept Elect & Elect Engn London WC1E 7JE England

The variation of peak-to-average power ratio (PAPR) for different allocations of spreading code sequences in multi-carrier code division multiple access (MC-CDMA) and multi-carrier direct-sequence code division multiple access (MC-DS-CDMA) systems is investigated. The results show that for a small number of active users, the PAPR performance of an MC-CDMA system can be improved by careful allocation of the spreading code sequences to different users.

关键词： Multicarrier code division multiple access direct-sequence code-division multiple access MC-DS-CDMA Coding sequence Peak to average power ratio code division CDMA mobile communications spreading code allocation

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Equivalence of zero-forcing detector and oblique projector

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ELECTRONICS LETTERS 2008年第6期44卷 425-427页

作者： Li, J. Zhang, X. D. Tsinghua Univ Dept Automat Beijing 100084 Peoples R China

Zero-forcing (ZF) detection is a simple linear detector which is used in multiple-input multiple-output systems and direct-sequence code-division multiple-access systems. The equivalence between the zero-forcing detector and the oblique projector is proved in a rigorous approach. Moreover, the proof gives insight into the noise enhancement effect of the ZF detector.

关键词： sequence coding direct-sequence code-division multiple access output system Insight multiple input multiple output systems linear detector zero frequency Oblique Noise effects

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Integrated space-time equaliser for DS/CDMA receiver with unequal reduced lengths

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ELECTRONICS LETTERS 1999年第1期35卷 20-22页

作者： Pham, VD Vu, TB Univ New S Wales Sch Elect Engn Sydney NSW 2052 Australia

An integrated space-time equaliser is proposed for direct sequence code division multiple access (DS/CDMA) receivers. A significant reduction in mean square error over that possible with the previous equalisers cascaded space-time reduced-length receiver is obtained with the integrated architecture. In addition, the use of unequal reduced lengths between array elements can significantly reduce the complexity without significantly reducing the performance.

关键词： Equalizers direct sequence systems code division multiple access Radio receivers Error analysis Computational complexity Integrated space-time equalizers Space-time reduced-length receivers Equalizers complexity classes HELIOS DEVICES inequalities direct-sequence code-division multiple access direct sequence spread spectrum systems radio receivers Array Element Receivers code division multiple access

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Adaptive blind multiuser DS-CDMA downlink equaliser

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ELECTRONICS LETTERS 2005年第21期41卷 1184-1186页

作者： Hadef, M Weiss, S Rupp, M Univ Southampton Dept Elect & Comp Sci Southampton SO9 5NH Hants England Tech Univ Vienna Inst Comp & RF Engn A-1060 Vienna Austria

A robust and simple adaptive blind multiuser equaliser for downlink DS-CDMA systems is presented. The adaptation is based on forcing various user symbols onto a constant modulus, whereby no additional constraints such as the mixed cross-correlation are required. The proposed algorithm has a moderate computational complexity and shows a BER performance close to the MMSE solution.

关键词： adaptive equalisers blind equalisers code division multiple access computational complexity error statistics least mean squares methods multiuser detection spread spectrum communication BER performance DS-CDMA downlink MMSE adaptive blind multiuser equal Spread spectrum communication bit error rate performance direct-sequence code-division multiple access code division multiple access Mini Mental State Examination Blind equalizers complexity classes Multiuser detection Downlink Equalizers

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Capacity enhancement of band-limited DS-CDMA system using weighted despreading function

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IEEE TRANSACTIONS ON COMMUNICATIONS 1999年第8期47卷 1218-1226页

作者： Huang, YJ Ng, TS McGill Univ Dept Elect & Comp Engn Montreal PQ H3A 2A7 Canada Univ Hong Kong Dept Elect & Elect Engn Hong Kong Peoples R China

This paper addresses capacity enhancement of a band-limited direct-sequence code-division multiple-access system by using a weighted despreading function (PVDF) in the receiver. An ideal Gaussian channel with perfect power control is assumed, The system performance is measured by the signal-to-interference-plus-noise ratio of the decision variable derived in the frequency domain, the bandwidth efficiency factor, the capacity enhancement factor, and the bit-error rate. It is shown that tuning a parameter of the WDF employed helps to partially flatten the in-band cross-spectrum of a pair of spreading and despreading functions. Numerical results show that the capacity of the proposed system improves over the conventional system using rectangular despreading function. To assess practical implications of the WDF receiver, the sensitivity to timing error is also analyzed.

关键词： band-limited systems cellular bandwidth efficiency direct-sequence code-division multiple access weighted despreading function

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