Low-Cost Passive Beamforming for RIS-Aided Wideband OFDM Systems

Reconfigurable intelligent surface (RIS) has become a promising solution to improve the performance of future wireless systems with low energy consumptions. Concerning a RIS-aided orthogonal frequency division multiplexing (OFDM) system, we perform optimization with respect to the RIS passive beamforming such that the sum rate over all subcarriers is maximized. Different from an existing successive convex approximation (SCA) method, we propose a majorization-minimization (MM)-based iterative approach to optimize the RIS passive beamforming, where a closed-form solution is obtained in each iteration. Simulation results show that the proposed RIS passive beamforming achieves almost the same performance as the SCA-based method while with much lower computational complexity.