Quasi-MMSE/ZF Based Limited Feedback Schemes for MU-MIMO Precoding

This paper focuses on the feedback scheme for downlink Multi-User Multiple-Input Multiple-Output (MU-MIMO) transmission with linear precoding. When the maximum transmission rank per user is limited to one, the multiple-antenna receiver uses a weight vector to transform MIMO channel matrix into an equivalent Multiple-Input Single-Output (MISO) channel vector. Then a Channel Directional Index (CDI) and a Channel Quality Indicator (CQI) are calculated and fed back to the transmitter. The existing Multiuser Eigenmode Transmission (MET) method projects the MIMO channel to its maximum eigenvector. That results in mismatched CDI and CQI when the Minimum Mean-Squared Error (MMSE) filter or the Zero-Forcing (ZF) filter is actually used for detection. In order to solve this problem, new limited feedback schemes with a quasi-MMSE weight and a quasi-ZF weight are proposed in this paper. The proposed schemes can avoid such feedback information mismatch and maximize the Signal to Interference plus Noise Ratio (SINR). Simulation results verify that the proposed schemes outperform the MET method significantly in term of sum rate.