An adaptive multistage parallel interference canceller for CDMA systems over Rayleigh fading channels

In direct-sequence code-division multiple-access (DS-CDMA) communication systems, the partial cancellation weight (PCW) in the partial parallel interference cancellation (PPIC) multiuser detection scheme does not give us any idea about the correctness of the bit-decision in the previous stage. Therefore, in this study, we investigate the statistical behavior of the adaptation PCW based on the least mean square (LMS) algorithm in which the adaptation PCW of the last chip in a symbol period reveals the information of the correctness of the bit-decision. Then, an adaptive decision-threshold obtained by maximum a posteriori probability (MAP) detection criterion is proposed to judge the correctness of the bit-decision in the previous stage and the bit-inversion (BI) procedure is proposed to invert the incorrect bit-decision. Furthermore, after BI procedure, a full PIC is performed to cancel the multiple access interference (MAI). Simulation results show that the proposed three-stage BI-based full PIC (BI-FPIC) multiuser detector can reach the performance of single-user-bound over flat fading channels under perfect channel estimation.