Spatio-temporal array processing for CDMA/SDMA downlink transmission

We address the problem of performing optimum spatio-temporal processing when using adaptive antenna arrays at the base stations for multiuser downlink transmission in CDMA systems, using periodic spreading sequences and assuming a knowledge of the channel of all the users. This assumption typically holds in TDD based mobile communication systems. We consider the SDMA strategy for using antenna arrays to gain system capacity. In that case the number of interfering users located in the same cell, namely d, can be higher than the spreading factor. The goal is to design FIR transmission filters at the base station in order to maximize the minimum matched filter bound among the d users. Several approaches, namely the zero-forcing, linear minimum mean square error, minimum output energy and the pre-RAKE are considered to solve the problem.