An Improved Sparse Channel Estimation in RIS-assisted mmWave MIMO Systems

Reconfigurable Intelligent Surfaces (RISs) have gained significant attention in millimeter-wave (mmWave) communication systems due to their ability to configure the wireless propagation environment. However, the presence of an RIS between the transmitter and receiver increases the number of channel coefficients that need to be estimated, resulting in huge pilot overhead. In this paper, we propose a new scheme based on a low-complexity smooth rank-approximation function to improve the quality of channel estimates of both the direct and reflected channels. Simulation results unveil the effectiveness of the proposed scheme in terms of achieving better estimation quality, spectral efficiency, and convergence compared to the benchmark schemes.