Joint Placement and Phase Shift Optimization for RIS-Assisted Systems With Electromagnetic Interference

This correspondence investigates multi-operator systems enhanced by reconfigurable intelligent surfaces (RIS) with electromagnetic interference (EMI) and channel uncertainties. We propose an alternating optimization scheme aimed at maximizing the sum rate of users for the operator controlling the RIS, subject to the three-dimensional (3D) RIS placement, bounded channel state information (CSI) errors, and the phase shift constraints. For the RIS placement optimization subproblem, the successive convex approximation (SCA) is employed to handle non-convex constraints introduced by the product of the base station (BS)-RIS distance and the RIS-user distance. For the RIS phase shift optimization subproblem, the penalty-convex concave procedure (P-CCP) is adopted to ensure smooth convergence. Numerical results demonstrate that the proposed algorithm outperforms the benchmark schemes by up to 30.2% and effectively suppresses EMI, particularly in scenarios with a large number of RIS reflecting elements and high transmit power.