Robust Hybrid Beamforming Design for Multi-RIS Assisted MIMO System with Imperfect CSI

Reconfigurable intelligent surface (RIS) has been developed as a promising approach to enhance the performance of fifth-generation (5G) systems through intelligently reconfiguring reflection elements. However, RIS-assisted beamforming design highly depends on channel state information (CSI) and RIS’s location, which could have significant impact system performance. In this paper, robust is investigated for multiuser millimeter wave with imperfect CSI, where weighted sum-rate maximization problem (WSM) formulated jointly optimize transmit BS, RIS placement reflect RIS. The considered WSM includes CSI error, phase shifts matrices, well variables, results in complicated nonconvex problem. To handle problem, original divided into series subproblems, location RIS, transmit/reflect error are optimized iteratively. Then, multiobjective evolutionary algorithm introduced gradient projection-based alternating optimization, can alleviate loss caused by effect CSI. Simulation reveal that proposed scheme potentially existing wireless communication, especially considering desirable trade-off among gain, user priority factor.