Low-Overhead Near-Field Channel Estimation for XL-RIS-Assisted Multiple Access Systems

The increasing number of mobile devices creates the need for large-scale and low-latency communication in the sixth-generation (6G) wireless network, while extra large-scale reconfigurable intelligent surface (XL-RIS) assisted communication is a promising technology. It exploits considerable directional beamforming gain and overcomes the problem of communication obstacles. In XL-RIS-assisted communication systems, the radiation region is typically near-field, whereas most existing channel estimation techniques are optimized for far-field scenarios. This paper proposes a low-overhead approach for near-field channel estimation in XL-RIS-enabled wideband multiple access systems, leveraging the polar-delay domain pattern. We give an efficient design of the polar-delay domain sensing matrix for XL-RIS-assisted near-field channel and introduce a method for pilot decontamination, utilizing the sparse two-dimensional (2D) pattern inherent to the polar-delay domain channel. A novel sparse signal recovery is adapted for the polar-delay domain channel estimation process. Ultimate simulation reveals that the proposed algorithm outperforms existing methods, offering improved estimation accuracy while reducing the channel estimation overhead.