Reduced-rank adaptive chip-level MMSE equalization for the forward link of long-code DS-CDMA systems

In this paper, we discuss the recently proposed downlink mobile receiver structure for long code DS-CDMA consisting of a chip level MMSE channel equalizer followed by descrambling and despreading. We show that the known pilot sequence can be exploited to estimate the chip-observation cross-correlation vector (needed to train the equalizer), and propose to use two low complexity reduced rank adaptive filtering algorithms for equalization: the stochastic gradient multistage Wiener filter (SG-MSWF), and the adaptive conjugate gradient reduced rank filter (ACGRRF). Simulations show that both algorithms attain close to optimal performance with reasonable complexity.