Experimental Evaluation of Simple Precoding Technique for Multi-cell Coordinated MU-MIMO

In cellular mobile communication systems, the co-channel inter-cell interference (ICI) remains as a critical barrier to achieving further improvement in spectrum efficiency. As an approach to controlling downlink ICI, multi-cell coordinated MU-MIMO has been actively discussed in many papers. In multi-cell coordinated MU-MIMO, the simultaneous transmission for multiple mobile stations is made possible by precoding control at multiple base stations. In general, the base stations need to exchange downlink channel state information (CSI) between themselves in order to generate precoding matrices applied to the downlink transmission signals. However, the delay required for CSI exchange causes a significant degradation in downlink performance because of the residual interference between the mobile stations. Given this background, this paper first proposes a novel and simple precoding method, which eliminates the need of CSI exchange between the base stations. To demonstrate the feasibility and performance of the proposed method, we also develop a prototype system and conduct an indoor experiment. This paper overviews the prototype system and the experiment results.