Turbo multiuser receiver for space-time turbo coded downlink CDMA

In this paper, we consider multiple-input multiple-output (MIMO) downlink CDMA systems employing BLAST space-time turbo codes (STTuC) over the frequency-selective fading channel. In this case, there is a mixture of multiple access interference (MAI), inter-antenna interference (IAI) and inter-symbol interference (ISI) which needs to be suppressed. Here, we develop an iterative receiver structure that can combat the different species of interferences at the same time. The proposed receiver is designed following the "turbo principle" and based on parallel interference cancellation (PIC). In every iteration, the soft output of the space-time turbo decoder is fed back to improve the PIC's performance. The simulation results suggest that the proposed iterative receiver can reject the interference for STTuC CDMA systems effectively. An improved STTuC CDMA system with antenna specific scrambling is also introduced, in which the proposed receiver can avoid excessive performance degradation in slow fading rural environment.