Decision feedback equalization and transmit diversity for wideband CDMA

Abstract

A single-user receiver structure for space-time coded CDMA downlink is studied in a multiuser frequency selective channel. The proposed scheme is a two dimensional Decision Feedback Equalizer (2D-DFE), whose filters are optimized based on the MMSE criterion to cancel noise, ISI, and MUI with a reasonable complexity. By modeling the spreading codes of the interfering users as random sequences, system performance has been evaluated using the Gaussian approximation. Two models for the desired user's spreading sequence have been considered and compared. Our numerical results show that in both cases the 2D-DFE exhibits significant performance improvement and capacity enhancement over the standard space-time coded RAKE structure, especially in interference-limited conditions.