Zero-forcing-based two-phase relaying with multiple mobile stations

It is well known that relay stations improve the link performance between the base and mobile stations and thereby improve the total system throughput. Nonetheless, the additional resource consumption to deploy the relay station reduces the system throughput significantly. The zero-forcing (ZF)-based two-phase relaying scheme that requires only two phases to communicate a frame was suggested for the system where a single mobile station is considered. The performance bottle-necks of the conventional ZF-based two-phase relaying are channel asymmetry and an ill-conditioned channel that reduces the effective channel gain. We propose a novel two-phase relaying scheme to support multiple users simultaneously for a given channel resource. The proposed relaying scheme includes the multiuser scheduling at the relay station and the additional precoding at the base station to make the effective channels from the base and mobile stations equal to each other. We evaluate the proposed relaying scheme by numerically comparing its sum rate to those of the conventional relaying schemes.