Near-Field Channel Estimation for RIS Assisted 6G Wireless Communication

Near-field channel estimation for RIS assisted 6G wireless communication is discussed in this paper. We accurately model the near-field cascaded channel firstly, and by exploiting the special row-column sparsity of near-field cascaded channel of different users in polar-domain, a polar-domain double sparsity orthogonal matching pursuit (PDS-OMP) is proposed. Specifically, the sparsity of near-field cascaded channel in polar-domain is revealed by two-dimensional sampling in angle and distance domain. Then, by leveraging the special sparsity, where channel of different users is composed by common part and specific part, the sparsity supports of polar-domain cascaded channel are estimated. Finally, the near-field cascaded channel is recovered by utilizing the least square (LS) algorithm. Experiment results show that the proposed algorithm can achieve accurate near-field cascade channel estimation with light pilot overhead.