Evaluation of Distributed Multi-User MIMO-OFDM With Limited Feedback

In this article, we investigate the performance of cellular networks employing remote radio units to enable distributed multi-user MIMO transmission using block-diagonalization precoding. We consider the downlink of an OFDM-based LTE compliant multi-carrier system in which the users provide channel state information (CSI) to the base station via limited capacity feedback links. With limited feedback, residual interference between the spatially multiplexed users cannot be avoided, causing an interference-limitation of the achievable downlink throughput. Efficient CSI quantization is therefore central in such systems to achieve a performance gain over single-user MIMO. Building on Grassmannian CSI quantization concepts, we propose an effective CSI feedback clustering approach in this work to exploit the correlation of the wireless channel in the frequency domain. We furthermore derive the corresponding channel quality feedback and propose a practical greedy multi-user scheduler.