Minimum Rate Maximization With RIS Element Allocation in OFDM Systems

In this paper, we propose a reconfigurable intelligent surface (RIS) element allocation based low complexity algorithm for a multi-user multiple-input single-output orthogonal frequency division multiplexing system. First, we propose a concept called a metric that depends solely on the channel and represents the minimum rate. Through the metric, the RIS reflection coefficients can be updated without using alternating optimization. Next, we formulate and solve a metric maximization problem to verify that the metric successfully represents the desired objective, i.e., minimum rate maximization. Finally, by utilizing the concept of RIS element allocation, we propose a low complexity algorithm that maximizes the metric. Simulation results show that the proposed metric successfully represents the minimum rate and outperforms existing benchmarks. Moreover, the RIS element allocation algorithm displays remarkable performance, achieving similar performance with the existing benchmarks even with extremely low complexity.