Near-field codebook design for extremely large-scale MIMO systems based on cellular coverage

In the 6G extremely large-scale MIMO systems, the transmission range between base stations and users falls within the near-field region, traditional far-field channel estimation codebooks would no longer be applicable. To address this issue, a near-field codebook design scheme based on cellular coverage was proposed. Firstly, the scheme transformed the near-field angular and distance domain, demonstrated that the coverage area of codeword in this transformed domain approximated an ellipse. Then, the ellipse in the transformed domain was compressed into a circle, and the near-field domain, after being transformed, was covered with a honeycomb pattern using a regular hexagon distribution. Finally, the center positions of the honeycombs were adjusted and mapped back to the original domain to obtain suitable angle and distance sampling points, and accordingly, the codebook was generated. The simulation results indicate that the codebook designed achieves higher channel estimation accuracy compared to existing near-field codebooks under the same codebook dimension.