A Novel Near-Field Channel Estimation Method for RIS-Assisted UM-MIMO Systems

Reconfigurable intelligent surface (RIS) assisted ultra-massive multiple-input multiple-output (UM-MIMO) near-field channel estimation method provides a new idea and solution for the design and optimization of near-field communication systems. Exploiting the polar-domain sparsity, we first utilize an on-grid polar-domain simultaneous orthogonal matching pursuit (P-SOMP) algorithm for RIS-assisted UM-MIMO systems to efficiently estimate the near-field channel, and we further investigate an off-grid polar-domain simultaneous iterative gridless weighting (P-SIGW) algorithm to improve the estimation accuracy. Simulation results show that the proposed channel estimation method has better performance compared with existing algorithms.