Hierarchical Codebook Design for Near-Field mmWave MIMO Communications Systems

Communications system with analog or hybrid analog/digital architectures usually relies on a pre-defined codebook to perform beamforming. With the increase in the size of the antenna array, the characteristics of the spherical wavefront in the near-field situation are not negligible. Therefore, it is necessary to design a codebook that is adaptive to near-field scenarios. In this letter, we investigate the hierarchical codebook design method in the near-field situation. We develop a steering beam gain approximation method and design the lower-layer codebook to provide coverage for the Fresnel region. For the upper-layer codebook, we propose beam rotation and beam relocation methods to place an arbitrary beam pattern to a target location. The simulation results show the superiority of the proposed near-field hierarchical codebook design.