Diversity Added Adaptive-Fuzzy Logic Controlled Receivers for Direct Sequence Code Division Multiple Access System

Abstract — A new approach in adjusting a step size and a forgetting factor of the Least Mean Square (LMS) and Recursive Least Square (RLS) algorithms respectively using the fuzzy logic controlled technique is developed for Maximum Ratio Combining diversity added Multiuser Detection of Direct Sequence Code Division Multiple Access (DS-CDMA) system in multipath channels. DS-CDMA is a popular multiple-access technology for wireless communication. However its performance is limited by multiple-access interference (MAI) and multipath distortion. Adaptive techniques for detection of DS-CDMA signals improves the performance of the CDMA system by reducing interference among users by employing an adaptive techniques called LMS and RLS algorithms. The diversity scheme called maximum ratio combining (MRC) as pre-processor to the adaptive MMSE detector of DS-CDMA removes the use of training sequences and the step size of LMS algorithm and forgetting factor of RLS algorithm which are to be taken constant can be varied by Fuzzy Inference System. This receiver employs a fuzzy-logic control mechanism to perform the nonlinear mapping of the squared error and squared error variation, denoted by (e2, Δe2), into a step size or a forgetting factor. Simulations have proved its better performance compared with the conventional Match Filter detector, performing nearly as well as single user case for multipath channels