Conjugate gradient based MMSE equalization for DS-CDMA forward link in time-varying frequency selective channels

This paper deals with synchronous direct-sequence CDMA transmission using orthogonal channel codes in time-varying, frequency selective multipath channels, motivated by the forward link in 3G CDMA systems. In recent years, receivers based on channel equalization on the chip-level prior to despreading have been proposed for the 3G wideband CDMA downlink. We evaluate the efficacy of adaptive chip-level MMSE estimation of the (multiuser) synchronous sum signal transmitted by the base-station, followed by a correlate and sum. We use the conjugate gradient (CG) algorithm for MMSE estimation and the pilot channel for training. Our simulations show that the training-based CG-MMSE equalizer can achieve much better error rates compared to RAKE reception, over a wide range of SNRs and system loads