SLNR-Based Joint RIS-UE Association and Beamforming Design for Multi-RIS Aided Wireless Communications

Abstract

The flexible deployment of multiple reconfigurable intelligent surfaces (RISs) can effectively overcome the coverage limitations of a single RIS and significantly enhance the capacity of massive multiple-input multiple-output (MIMO) systems. However, beamforming design and RIS-user equipment (UE) association in multi-RIS-aided massive MIMO systems under the signal-to-interference-plus-noise-ratio (SINR) maximum criterion is infeasible due to the high computational complexity. To reduce the complexity of the beamforming design, signal-to-leakage-and-noise ratio (SLNR) was adopted as a novel criterion. In this paper, we jointly consider the RIS-UE association, active beamforming design, and passive beamforming optimization for maximizing the sum-SLNR of the considered system. We firstly construct the SLNR-based bipartite graph and solve the RIS-UE association problem through the classical Kuhn-Munkres algorithm. Then we present an active beamforming design based on a generalized Rayleigh quotient to further maximize the SLNR. Moreover, we leverage the semidefinite relaxation method and alternating optimization techniques to solve the passive beamforming optimization problem. Simulation results show that the proposed scheme can achieve a larger achievable sum rate (ASR) compared to the benchmark schemes.