Theoretical Analysis of Decision Feedback Chip-level Maximum Likelihood Detection in DS-CDMA Mobile Radio

Abstract In direct sequence code division multiple access (DS-CDMA), when small spreading factor (SF) is used to achieve high speed transmissions an average bit error rate (BER) performance severely deteriorates due to severe inter-path interference (IPI) in a frequency-selective fading channel. The authors proposed a decision feedback chip-level maximum likelihood detection (DF-CMLD) that can effectively suppress the IPI in low SF. In this paper, theoretical conditional upper-bounded BER is derived for the given set of channel gains in a frequency-selective fading channel and spreading code sequence. The theoretical average BER performance is numerically evaluated using the derived conditional upper-bounded BER.and is confirmed by computer simulation. Keyword frequency-selective fading, DS-CDMA, rake combining, DF-CMLD