A joint precoding scheme for MIMO systems with distributed single antenna AF relays

We propose a joint precoding scheme for multiple-input multiple-output systems with the aid of distributed multiple single antenna amplify-and-forward relays. Unlike the existing single relay systems equipped with a complex full matrix for relay precoding, the proposed scheme uses a real diagonal matrix whose diagonal elements are the relay gains, so that it can reduce the feedback load dramatically. Based on an iterative procedure, a source precoding matrix and each relay gain are decided, and then a power allocation between source and relays is performed. In terms of BER performance, simulation results show that the proposed scheme can perform close to the conventional scheme with small feedback load.