Joint Beamforming Design for Cooperative Double-RIS Aided mmWave Multi-User MIMO Communications

Abstract

To alleviate the blockage effect and explore the potential of reconfigurable intelligent surface (RIS) assisted communication, we investigate the cooperative double-RIS assisted multi-user millimeter wave (mmWave) multiple-input multiple-output (MIMO) communications. To improve system performance, we jointly optimize the transmit beamforming matrix at the base station and the phase shift matrices at RISs to maximize the system sum rate, which is an intractable non-convex problem. To solve the problem, we propose an efficient alternating optimization algorithm based on the techniques of weighted minimum mean square error (WMMSE), Lagrange multiplier and majorization-minimization (MM). Simulation results validate the effectiveness of the proposed algorithm, as well as the superiority of double-RIS in improving system performance.