Beam Energy Spread-Based Near-Field Codebook Design for Uniform Circular Array

With the emergence of extremely large-scale antenna arrays (ELAAs), the next generation of wireless communication is likely to occur in the radiating near-field region of base stations (BS). In such regions, beam training needs to search both the angle and distance dimensions, leading to a prolonged training process and coverage hole (dead zone). To cope with those issues, we propose a novel codebook design guideline for the uniform circular array by maximizing the overlapping coverage between the beam coverage (BC) and near-field region, where the energy spread effect in the near-field region is exploited to obtain the optimal focusing point to improve the beam gain inside the dead zone. Based on this guideline, we construct the beam coverage-based codebook structure and two-stage beam training (TSBT) scheme. Numerical simulations show that the TSBT scheme with the proposed codebook can potentially reduce beam training overhead while improving the success rate and patching the dead zone.