Robust Transceiver Design for RIS-Aided Spatially Correlated MIMO Channels With Uncertainty

We study the design of statistically robust transceiver for a reconfigurable intelligent surface (RIS) assisted single-user multiple-input multiple-output (MIMO) downlink system. Unlike existing works, we aim to minimize the maximal per-stream mean square error (MSE) with imperfect channel state information (CSI). To tackle the resulting non-convex optimization, we propose a low-complexity alternating optimization algorithm. Specifically, by fixing RIS phase shifts, we reformulate the original problem as a sum MSE minimization problem. Leveraging Karush-Kuhn-Tucker (KKT) conditions, we derive a closed-form solution for the joint precoder and linear receiver design. Numerical simulations illustrate the robustness and significant performance gain over non-robust schemes with low computational complexity.