Opportunistic feedback of channel information in multi-user MIMO environments

In this paper, we consider opportunistic feedback of channel state information (CSI) for multi-user multi-antenna transmission. The base station utilizes channel quality information (CQI) as the CSI for closed-loop multi-antenna transmission, which is often achieved from mobile stations in a quantized format. However, only the use of quantized CQI may noticeably deteriorate the transmission performance. We first analyze the effect of CSI quantization error on the multi-user beamforming performance. Then, we propose a novel scheme for opportunistic CSI feedback and user scheduling in multi-user multi-antenna transmission environments. Simulation results show that the proposed scheme can improve the spectral efficiency using a small amount of CSI feedback signaling overhead.