Frequency-Domain Multi-Stage Soft Interference Cancellation for DS-CDMA Uplink Signal Transmission

Koichi ISHIHARA  Kazuaki TAKEDA  Fumiyuki ADACHI  

IEICE TRANSACTIONS on Communications   Vol.E90-B   No.5   pp.1152-1161
Publication Date: 2007/05/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.5.1152
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
DS-CDMA,  frequency-domain equalization (FDE),  MUI cancellation,  multi-user detection (MUD),  

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It is well-known that, in DS-CDMA downlink signal transmission, frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion can replace rake combining to achieve much improved bit error rate (BER) performance in severe frequency-selective fading channel. However, in uplink signal transmission, as each user's signal goes through a different channel, a severe multi-user interference (MUI) is produced and the uplink BER performance severely degrades compared to the downlink. When a small spreading factor is used, the uplink BER performance further degrades due to inter-chip interference (ICI). In this paper, we propose a frequency-domain multi-stage soft interference cancellation scheme for the DS-CDMA uplink and the achievable BER performance is evaluated by computer simulation. The BER performance comparison of the proposed cancellation technique and the multi-user detection (MUD) is also presented.