Multi-Attention Mechanism for Beam Training in RIS-Assisted Near-Field Communications

The large number of antennas in extremely large aperture array (ELAA) systems shifts the propagation regime of signals in wireless communication systems towards near-field spherical wave propagation, from beamforming to beamfocusing. The design of the two-dimensional beam codebook that contains both the angular and distance domains is challenging. To address this issue, we propose a reconfigurable intelligent surface (RIS)-assisted near-field beam training based on a novel multi-attention algorithm, which provides a fine-grained codebook with enhanced spatial resolution. Specifically, we transform the beam selection task into a location detection process, enabling more effective beam search. Experimental results unveil that the proposed method achieves beam selection accuracy up to 97% at signal-to-noise ratio (SNR) of 20 dB, and improves 10% over the baseline method at different SNRs.