MMSE Relaying Design for Multi-Antenna Two-Hop Downlinks with Finite-Rate Feedback

We consider a MIMO relay downlink system using precoding and limited feedback from two-hop channels. Since the conventional precoding matrices are directly obtained by treating the quantized channel state information (CSI) feedback as the real CSI, we propose an improved relay precoding strategy by taking the effect of channel quantization error into account. The proposed relaying technique is designed based on the minimum mean square error (MMSE) criterion and is robust to the channel uncertainties due to quantized CSI feedback. Numerical results verify the effectiveness of the proposed scheme.