Fundamentals of Multi-User MIMO Communications

In recent years, the remarkable promise of multiple-antenna techniques has motivated an intense research activity devoted to characterizing the theoretical and practical issues associated with multiple-input multiple-output wireless channels. This activity was first focused primarily on single-user communications but more recently there has been extensive work on multi-user settings. The aim of this chapter is to provide an overview of the fundamental information-theoretic results and practical implementation issues of multi-user multiple-antenna networks operating under various conditions of channel state information. The contents of this chapter are as follows. In Section 1 we introduce basic notation and describe the system model of interest. The latter includes both uplink and downlink models for a general mobile communication system operating with multiple antennas at both the base station and mobile terminals. In Section 2 we concentrate on channel capacity as a means of characterizing such systems, and review basic results under various operating conditions, including patterns of knowledge of information about the state of the channel between transmitter(s) and receiver(s). In Section 3 we address the problem of acquisition of channel state information at the transmitter and receiver, and describe the distinctive features of open-loop and closed-loop systems. In Section 4 we provide an overview of system design issues and discuss techniques that require channel state information at the transmitter, while in Section 5 we briefly review some recent work on techniques that allow