Fast Distance Sampling for Uniform Circular Array in Near-Field 3D Beam-Focusing

Extremely large-scale array (XL-array) and Terahertz (THz) band have emerged as key research areas in the sixth generation (6G) network. As such, the near-field communication becomes more important since users are more likely to be located in the near-field. Different from their far-field counterparts, the near-field focusing beams utilize additional distance information to focus beam energy at specific spatial-locations. In this letter, we consider a uniform circular array (UCA) system and propose a fast distance sampling method for UCA and design its codebook. Specifically, we propose the non-uniform distance sampling and codebook for UCA by utilizing the zero-order Bessel function, and taking into account the effect of the distance information on the correlation between the near-field beam vectors of UCA. Based on the proposed non-uniform distance sampling and codebook, a two-stage searching scheme for three-dimensional (3D) beam focusing is designed. Simulation results verify that the designed beam focusing scheme can achieve comparable accuracy and rate performance as compared to the 3D exhaustive search.