Three-Dimensional Channel Estimation for Near-Field XL-RIS: A Polar-Domain Approach

Near-field communications present new opportunities by leveraging near-field channels, posing challenges for traditional far-field models, which this paper addresses through efficient near-field channel estimation methods for wideband MIMO mmWave systems with extremely large-scale reconfigurable intelligent surfaces (XL-RIS). Specifically, we introduce a novel three-dimensional polar-domain communication model and propose the Three-Dimensional-Polar-Domain Simultaneous Orthogonal Matching Pursuit (3D-P-SOMP) algorithm. By leveraging channel sparsity in the polar domain, the proposed method efficiently estimates near-field channels while incorporating both angular and distance information. Simulation results demonstrate the superiority of the proposed approach in terms of estimation accuracy and computational efficiency, paving the way for practical applications in next-generation wireless communication systems.