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Downlink Specific Linear Equalization for Frequency Selective CDMA Cellular Systems

Authors:

Thomas P. Krauss,

William J. Hillery,

Michael D. ZoltowskiAuthors Info & Claims

Journal of VLSI Signal Processing Systems, Volume 30, Issue 1-3

Pages 143 - 161

Published: 04 February 2002 Publication History

Abstract

We derive and compare several linear equalizers for the CDMA downlink under frequency selective multipath conditions: minimum mean-square error (MMSE), zero-forcing (ZF), and RAKE. MMSE and ZF equalizers are designed based on perfect knowledge of the channel. The downlink specific structure involves first inverting the multipath channel to restore the synchronous multi-user signal transmitted from the base-station at the chip-rate, and then correlating with the product of the desired user's channel code times the base-station specific scrambling code once per symbol to decode the symbols. ZF equalization restores orthogonality of the Walsh-Hadamard channel codes on the downlink but often suffers from noise gain because certain channel conditions (no common zeros) are not met; MMSE restores orthogonality only approximately but avoids excessive noise gain. We compare MMSE and ZF to the traditional matched filter (also known as the RAKE receiver). Our formulation generalizes for the multi-channel case as might be derived from multiple antennas and/or over-sampling with respect to the chip-rate. The optimal symbol-level MMSE equalizer is derived and slightly out-performs the chip-level but at greater computational cost. An MMSE soft hand-off receiver is derived and simulated. Average BER for a class of multi-path channels is presented under varying operating conditions of single-cell and edge-of-cell, coded and un-coded BPSK data symbols, and uncoded 16-QAM. These simulations indicate large performance gains compared to the RAKE receiver, especially when the cell is fully loaded with users. Bit error rate (BER) performance for the chip-level equalizers is well predicted by approximate SINR expressions and a Gaussian interference assumption.

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Cited By

Yue LWeerasinghe NHan CHashimoto T(2010)Partial multiuser detection for CS-CDMA/CP over multipath channelsIEEE Transactions on Communications10.1109/TCOMM.2010.062510.08065058:8(2305-2313)Online publication date: 1-Aug-2010
https://dl.acm.org/doi/10.1109/TCOMM.2010.062510.080650
Yue LWeerasinghe NHan CHashimoto T(2009)Partial multiuser detection for CS-CDMA/CP over multipath channels and its comparison with DS-CDMAProceedings of the 2009 IEEE international conference on Communications10.5555/1817770.1817967(3728-3732)Online publication date: 14-Jun-2009
https://dl.acm.org/doi/10.5555/1817770.1817967
Fulghum TCairns DCozzo CWang YBottomley G(2009)Adaptive generalized rake reception in DS-CDMA systemsIEEE Transactions on Wireless Communications10.1109/TWC.2009.0603308:7(3464-3474)Online publication date: 1-Jul-2009
https://dl.acm.org/doi/10.1109/TWC.2009.060330
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Downlink Specific Linear Equalization for Frequency Selective CDMA Cellular Systems

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Published In

cover image Journal of VLSI Signal Processing Systems

Journal of VLSI Signal Processing Systems Volume 30, Issue 1-3

February 2002

312 pages

ISSN:0922-5773

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Copyright © Copyright © 2002 Kluwer Academic Publishers.

Publisher

Kluwer Academic Publishers

United States

Publication History

Published: 04 February 2002

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Cited By

Yue LWeerasinghe NHan CHashimoto T(2010)Partial multiuser detection for CS-CDMA/CP over multipath channelsIEEE Transactions on Communications10.1109/TCOMM.2010.062510.08065058:8(2305-2313)Online publication date: 1-Aug-2010
https://dl.acm.org/doi/10.1109/TCOMM.2010.062510.080650
Yue LWeerasinghe NHan CHashimoto T(2009)Partial multiuser detection for CS-CDMA/CP over multipath channels and its comparison with DS-CDMAProceedings of the 2009 IEEE international conference on Communications10.5555/1817770.1817967(3728-3732)Online publication date: 14-Jun-2009
https://dl.acm.org/doi/10.5555/1817770.1817967
Fulghum TCairns DCozzo CWang YBottomley G(2009)Adaptive generalized rake reception in DS-CDMA systemsIEEE Transactions on Wireless Communications10.1109/TWC.2009.0603308:7(3464-3474)Online publication date: 1-Jul-2009
https://dl.acm.org/doi/10.1109/TWC.2009.060330
Li TLiang WDing ZTugnait J(2005)Blind multiuser detection for long-code CDMA systems with transmission-induced cyclostationarityEURASIP Journal on Wireless Communications and Networking10.1155/WCN.2005.2062005:2(206-215)Online publication date: 1-Apr-2005
https://dl.acm.org/doi/10.1155/WCN.2005.206
Liu PXu Z(2004)Joint performance study of channel estimation and multiuser detection for uplink long-code CDMA systemsEURASIP Journal on Wireless Communications and Networking10.1155/S16871472044040582004:1(98-112)Online publication date: 1-Aug-2004
https://dl.acm.org/doi/10.1155/S1687147204404058
Petré FLeus GMoonen MDe Man H(2004)Multicarrier block-spread CDMA for broadband cellular downlinkEURASIP Journal on Advances in Signal Processing10.1155/S11108657044010482004(1568-1584)Online publication date: 1-Jan-2004
https://dl.acm.org/doi/10.1155/S1110865704401048
Leus GPetré FMoonen M(2004)Space-time chip equalization for maximum diversity space-time block coded DS-CDMA downlink transmissionEURASIP Journal on Advances in Signal Processing10.1155/S11108657043092972004(740-750)Online publication date: 1-Jan-2004
https://dl.acm.org/doi/10.1155/S1110865704309297

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