Robust and fast convergent blind multi-user detectors for DS-CDMA systems in nonstationary multipath environments

A set of adaptive receivers is proposed in this paper for direct-sequence code division multiple access (DS/CDMA) systems. Specifically we develop adaptive step-size blind algorithms which are based on constant modulus (CMA), constrained minimum output energy (CMOE) and multiuser constant modulus (MU-CMA) criteria. The applications of these algorithms to a nonstationary multipath environment were analyzed and simulation studies of the proposed algorithms were carried out. These studies show that the proposed adaptive step-size CMA, adaptive step-size CMOE and the adaptive step-size MU-CMA yield superior performance to most of the existing standard blind algorithms under severe nonstationary multipath fading channels. This is particularly the case when the number of interferers are nonstationary in the statistical sense. The robust nature of the proposed receivers is analysed also with respect to the initial step-size settings. In our simulations, both deterministic and Markovian time-varying interference statistics were considered. Specially, the Markovian time-varying case is of interest in mobile wireless systems where the number of users arrive according to a Poisson process, and hence, the interference statistics switch rapidly with time.