Rate-Fairness-Aware Low Resolution RIS-Aided Multi-User OFDM Beamforming

This article investigates reconfigurable intelligent surface (RIS)-aided OFDM network, where a multiple-antenna aided base station (BS) transmits its downlink (DL) signals to multiple single-antenna users via an RIS, which consists of a considerable amount of low-resolution programmable reflecting elements (PREs). Explicitly, we propose the joint design of the multi-user (MU) beamformers and the RIS's PREs for quality-of-service target in terms of the individual users' rates. In the face of dispersive channels, we demonstrate that this poses a large-scale mixed discrete continuous optimization problem of intractable nature. We then tackle this challenge by developing low-complexity iterative procedures, which invoke light-weight closed-form expressions at each iteration, are developed for its computational solution. The simulations demonstrate their computational efficiency and additionally, reveal the deficiencies of the conventional MU OFDM beamforming design based on sum-rate maximization.