Decision Feedback Chip-Level Maximum Likelihood Detection for DS-CDMA in a Frequency-Selective Fading Channel

Akihiro SAITO
Shinsuke TAKAOKA
Fumiyuki ADACHI

Publication
IEICE TRANSACTIONS on Communications   Vol.E89-B    No.9    pp.2564-2571
Publication Date: 2006/09/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.9.2564
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
Keyword: 
DS-CDMA,  frequency-selective fading channel,  maximum likelihood detection,  rake combining,  

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Summary: 
In direct sequence code division multiple access (DS-CDMA), variable rate transmission can be realized by simply changing the spreading factor SF for the given chip rate. In a frequency-selective fading channel, the transmission performance can be improved by using rake combining. However, when a very low SF is used for achieving a high transmission rate, error floor is produced due to insufficient suppression of inter-chip interference (ICI). In this paper, decision feedback chip-level maximum likelihood detection (DF-CMLD) is proposed that can suppress the ICI. An upper-bound for the conditional bit error rate (BER) is theoretically derived for the given spreading sequence and path gains. The theoretical average BER performance is numerically evaluated by Monte-Carlo numerical computation using the derived conditional BER. The numerical computation results are confirmed by computer simulation of DS-CDMA signal transmission with DF-CMLD.