On the performance of adaptive MMSE detectors for a MC-CDMA system in fast fading Rayleigh channels

Multi-carrier CDMA (MC-CDMA) is a hybrid multiple access scheme combining multi-carrier modulation (MCM or OFDM) with direct sequence spread spectrum (DS-SS). Although a common assumption in the analysis of the performance of the various MC-CDMA detectors is that they have perfect knowledge of the fading channel, this assumption is no longer valid as the fading rate (Doppler spread) of the channel increases. We examine the performance of various forms of the minimum mean square error (MMSE) detector operating in a fast fading Rayleigh channel described by a Gauss-Markov state-space model. We show that, although adaptive detection based on the LMS and RLS algorithms is possible without explicit channel estimation, a low complexity detector, termed MMSE per carrier, combined with an RLS channel estimator can achieve better performance as well as increased robustness to the selection of the adaptation parameters