Joint Channel Estimation and Passive Beamforming for Reconfigurable Intelligent Surface Aided Multi-user Massive MIMO System

In this paper, we propose a fast channel estimation method for the reconfigurable intelligent surface (RIS) enabled multi-user transmissions, exploiting the sparsity in the UEs-RIS-BS cascaded channel model. Further, benefiting from the channel estimation, we design the data transmission protocol with limited feedback channel information. Finally, based on the estimated channel, the RIS phase shifters are optimized with the principle of maximal ratio combining. Simulation results show that the proposed channel estimator achieves high accuracy and the system performance is significantly enhanced by the accordingly selected beamformers and combiners, as well as the optimized phase shifters.