Novel precoding methods for Rayleigh fading Multiuser TDD-MIMO systems

In this paper, we consider the diversity order achievable in a Rayleigh fading Multi-User (MU)-MIMO system when CSI is available at the transmitter (CSIT), but not at the receiver (CSIR). Such a scenario is relevant, for example, in Time Division Duplex (TDD) communications, where, due to channel reciprocity, CSIT can be acquired directly by sending a known training sequence from the receiver to the transmitter. We propose a novel, simple-to-implement transmit precoding scheme that converts fading MU-MIMO channels (the multiple access channel, broadcast channel and interference channel) into fixed-gain parallel Gaussian channels, while satisfying an average power constraint. Hence, the proposed precoding scheme achieves an infinite diversity order, which is in contrast with schemes based on perfect CSIR, which at best achieve a finite diversity order. Monte Carlo simulations illustrate the improvement in the BER performance obtainable from the proposed precoding schemes compared to existing diversity schemes.