TABLE OF CONTENTS Multiantenna transceivers may bring considerable performance gains in multiuser systems with respect to single antenna systems [1]. The availability of multiantenna receivers allows in fact for interference cancelation. Given a system with N users, each with one transmit antenna, it was proved in [2] that, in a Rayleigh flat-fading environment, a linear receiver with K + N antennas is capable of nulling N - 1 interferers and, at the time, yielding diversity gain K + 1 for every remaining user. In other words, the cancelation of N - 1 interferers, through linear combining, involves the use of N - 1 degrees of freedom out of the overall N + K available degrees. These degrees of freedom are then lost from the point of view of diversity gain. This is why the diversity gain on each user passes from the potential maximum value of N + K to K + 1. The remarkable property is that, after linear cancelation, every user is seen free of interference and with diversity gain K + 1. It is important to remark that this trade-off between interference cancelation and diversity gain is valid under the assumption of using a linear canceler. Using joint ML decoding, this trade-off is no longer valid. But joint ML detection can be quite complex to implement.
In this chapter we consider the situation where each user has multiple transmit antennas and uses space-time coding. In the previous chapter,...
