Iterative Multi-User Detection and Decoding for DS-CDMA System with Space-Time Linear Dispersion

Artikel i vetenskaplig tidskrift, 2009

This paper considers a Q-ary orthogonal DS-CDMA system with high rate space-time linear dispersion codes (LDC) in time-varying Rayleigh fading MIMO channels. We propose a joint multi-user detection, LDC decoding, Q-ary demodulation and channel decoding algorithm and apply turbo processing principle to improve the system performance in an iterative fashion. The proposed iterative scheme demonstrates faster convergence and superior performance (especially at low SNRs) compared to the V-BLAST based DS-CDMA system, and is shown to approach the single-user performance bound. The gain is more significant when the LDC decoding and symbol demodulation is assisted by a decision-directed multi-user detection technique. We also show that the CDMA system is able to exploit the time diversity offered by the LDCs in fast fading channels.