Improved DS-CDMA Multi-stage PIC in Fading Channels using a Generalized Soft Limiter

In this paper, we examine performance of a multi-stage parallel interference cancellation (PIC) receiver using a generalized soft limiter. The generalized soft limiter (GSL) improves the accuracy of the reconstructed interference signals by making hard decisions on "reliable" signals and partial soft decisions on "unreliable" signals. The system performance degradation caused by imperfect amplitude estimation and near-far effects is also analyzed in the paper. It is also shown that GSL-PIC can achieve comparable performance to that of hyperbolic tangent decision PIC (HT-PIC), which has been shown to be the optimum decision for the single user case with Gaussian interference and noise. The advantage of the GSL is that it is much easier to implement than the HT. Both GSL-PIC and HT-PIC are shown to be able to achieve performance much better than other improved PIC techniques such as null-zone decision PIC (NZ-PIQ, soft-limiter PIC, and partial PIC (PPIC) in most scenarios.