Iterative soft decision interference cancellation receivers for DS-CDMA downlink employing 4QAM and 16QAM

Three promising receiver algorithms performing iterative soft decision interference cancellation (ISDIC) for a synchronous DS-CDMA system employing random spreading sequences and BPSK or 4QAM transmission, respectively, over an AWGN channel were proposed in Muller et al. (1998) and Lampe et al. (2001). In this paper, we extend these ISDIC receivers for a DS-CDMA downlink transmission over multipath channels when employing 4QAM and 16QAM or general square QAM constellations, respectively. Additionally, modified variants including the channel decoder into the iteration loop are investigated. It can be shown that the proposed schemes clearly surpass the standard RAKE receiver and approach the respective single user bounds within 0.5 to 2 dB in a UMTS scenario.