Space-time partially adaptive pre-equalizer for high rate CDMA systems using conjugate gradient technique

Abstract

A novel space-time (ST) pre-equalizer is proposed for the downlink of high data rate CDMA systems over frequency-selective multipath channels. We consider the scenario in which multiple transmit antennas are used at the base station (BS) for downlink transmission, followed by a set of adaptive FIR filters to suppress the multiple access interference (MAI) and possible intersymbol interference (ISI). With the MAI and ISI effectively suppressed, each mobile station (MS) would require only a simple matched filter (MF), leading to a "thin" handsets design suitable for next-generation wireless communications. The tap weights of each adaptive FIR filter are determined based on the generalized sidelobe canceller (GSC) technique, and partial adaptivity is incorporated via the conjugate gradient (CG) algorithm for reduced complexity implementation. The proposed ST pre-equalizer is evaluated through simulations, and the results show that it can achieve better performance compared to the pre-RAKE maximum ratio combining (MRC) method.