Coordinated precoding for downlink multi-user MIMO relay network

Relay communication network has been widely studied in recent years due to their ability to provide more reliable communication through enhanced diversity. In this work, we consider a downlink multiuser multi-input-multi-output (MU-MIMO) relay network under amplify and forward (AF) protocol. Coordinated relay system can provide the additional diversity gain due to adding the relay station (RS) compared to the direct transmit system. Assuming that the channel state information (CSI) at the base station (BS) is available, we propose a precoding method considering equivalent channel between the BS, RS and user equipment (UE), named as maximum-signal-leakage-and-noise-ratio (SLNR_max) that can effectively suppress the co-channel interference (CCI) and noise at the UE. And we also analyze the influence of increasing the number of the UEs on the sum-rate in the MU-MIMO relay network. Theoretical analysis and Monte Carlo simulation results show the un-coded BER and the sum-rate performance with coordinated relay outperforms that without relay.