On the Maximum Achievable Sum-Rate of the RIS-Aided MIMO Broadcast Channel

Reconfigurable intelligent surfaces (RISs) represent a new technology that can shape the radio wave propagation and thus offers great variety of possible performance implementation gains. Motivated by this, we investigate achievable sum-rate optimization in broadcast channel (BC) presence RISs. We solve this problem exploiting well-known duality between Gaussian multiple-input multiple-output (MIMO) BC multiple-access (MAC), correspondingly derive three algorithms which optimize users' covariance matrices RIS phase shifts dual MAC. The are optimized decomposition method with block coordinate maximization (BCM), or gradient-based method. either sequentially using closed-form expression, computed parallel present computational complexity analysis for proposed algorithms. Simulation results show tend to converge same overall, but may produce different some specific situations, due non-convexity considered problem. Also, methods generally more time efficient. In addition, demonstrate provide significant gain RIS-assisted assisted multiple RISs depends on placement