Decision feedback equalization and transmit diversity for wideband CDMA

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.