Multistage multiuser decision feedback detection for DS-CDMA

Multiuser decision-feedback detectors (DFDs) for DS-CDMA are presented using the minimum mean squared error (MMSE) criterion. Both successive and parallel feedback (interference cancellation) are considered. Short spreading codes are assumed, eliminating the need for remodulation. A multi-stage DFD is presented which consists of cascaded DFDs each performing successive cancellation. In the absence of error propagation, a two-stage structure achieves the single-user bound for all users, and is shown to be equivalent to an MMSE DFD with parallel feedback. The effect of error propagation is illustrated through simulation. Both uncoded and coded performance results are presented. These results show that the DFDs can offer a significant performance gain relative to linear MMSE detection.