Spatio-temporal array processing for matched filter bound optimization in SDMA downlink transmission

We address the problem of performing optimum spatio-temporal processing when using adaptive antenna arrays at base stations for multiuser downlink transmission, assuming a knowledge of the channel related to each user. This assumption typically holds in the context of time division duplex (TDD), time division multiple access (TDMA) based mobile communication systems. For frequency division duplex (FDD) based systems that assumption is still valid if the base station is provided with feedback from each mobile about the downlink channel. We consider the spatial division multiple access (SDMA) strategy for using antenna arrays to gain system capacity. In that case the interfering users are located in the same cell and communicate with the same base station. The base station performs transmission through m channels resulting from an array of antennas and/or oversampling of the transmitted signals, towards d co-channel users. The goal is designing the m×d transmission FIR filters at the base station in order to maximize the minimum matched filter bound (MFB) among the d users. We address zero-forcing (ZF), minimum mean squared error (MMSE) and other approaches to solve that problem and we provide the related solutions, under specified assumptions and constraints concerning transmitter and receiver complexity