Abstract
The direct-sequence code-division multiple-access (DS-CDMA) suffers from the multiple-access interference (MAI) that is caused by non-zero crosscorrelations between PN sequences. The detectors that are designed to improve the performance of DS-CDMA systems can be divided into two categories: linear detectors and nonlinear detectors. In this thesis, both are involved into our schemes. In this thesis, in addition to introducing the minimum-mean-square-error (MMSE) multiuser detector for multipath fading DS-CDMA communications, we also made comments on the improved parallel interference cancellation (PPIC) and discovered the reason why the optimal weightings have to be searched with a trial-and-error method. Furthermore, we proposed a new algorithm to decide the weightings such that we can improve the performance of the adaptive partial PIC. To make a greater improvement in performance, we combine the MMSE multiuser detector with the PIC to form turbo (iterative) MMSE multiuser detectors. Due to possessing the advantages of both the linear and nonlinear detectors, the turbo (iterative) MMSE multiuser architecture will outperform both pure MMSE and PIC schemes. Finally, extensive simulation results of various detection algorithms are presented.