Two dimensional MMSE-DFE for space-time coded wideband CDMA

In this paper, two single-antenna receiver structures for multiuser space-time coded wideband CDMA downlink are studied in frequency selective fading channels. The first structure is the standard space-time coded RAKE receiver, while in the second structure, we have proposed a two dimensional decision feedback equalizer (2D-DFE), whose filters are optimized to jointly cancel noise, ISI, and MUI based on the MMSE criterion. For this receiver, by modeling the spreading sequences of the interfering users as random sequences, system bit error probability has been calculated using the Gaussian approximation. Our numerical results show that the 2D-DFE exhibits significant performance improvement over the space-time coded RAKE structure, especially in the interference-limited conditions.