Optimal RIS Allocation in Multi-User MIMO Communications

In this work, we consider the precoder and multiple reconfigurable intelligent surfaces (RISs) optimization problem for a downlink multi-user multiple input multiple output (MIMO) communication scenario. In the proposed approach, the complexity of the RISs optimization is reduced by partitioning the RISs into tiles and formulating the problem as a tile assignment problem. To this end, we consider the weighted sum rate minimization problem, where the weights can be evaluated with the objective of achieving a certain degree of fairness. Simulation results show that the main benefit of introducing RISs into the communication chain is fairness, i.e., users affected by severe path losses can derive large benefits from RISs, provided they are properly designed.