Rate Optimization and Power Allocation in RIS-assisted Multi-user OFDM Communication

The research investigates the data rates of a wide-band multi-user system by optimizing the phases of the reconfigurable intelligent surfaces (RISs) elements and performing fair power allocation for subcarriers. A practical beamforming codebook is developed to select the RIS configuration that maximizes the signal-to-noise ratio (SNR). This guides the iterative power and semidefinite relaxation (SDR) algorithms for finding the optimal RIS configuration. The iterative power method is validated by comparing the achievable data rate and the computational complexity with the existing techniques in the literature. Simulation results revealed that the data rate performance of our proposed iterative power method is comparatively close to the known approaches such as the SDR and the strongest tap maximization (STM). Notably, our method exhibits superior performance to STM in non-line-of-sight (NLoS) channels, while also maintaining lower computational complexity compared to SDR.