XL-MIMO promises to provide ultrahigh data rates in Terahertz (THz) spectrum. However, the spherical-wavefront wireless transmission caused by large aperture array presents huge challenges for channel state information (CSI) acquisition. Two independent parameters (physical angles and transmission distance) should be simultaneously considered in XL-MIMO beamforming, which brings severe overhead consumption and beamforming degradation. To address this problem, we exploit the near-field channel characteristic and propose one low-overhead hierarchical beam training scheme for near-field XL-MIMO system. Firstly, we project near-field channel into spatial-angular domain and slope-intercept domain to capture detailed representations. Secondly, a novel spatial-chirp beam-aided codebook and corresponding hierarchical update policy are proposed. Theoretical analyses and numerical simulations are also displayed to verify the superior performances on beamforming and training overhead.
翻译:XL-MIMO承诺在Terahertz(Thz)频谱中提供超高数据率,然而,大型孔径阵造成的球波前沿无线传输对获取频道状态信息提出了巨大挑战,XL-MIMO波束应同时考虑两个独立参数(物理角度和传输距离),这会造成严重的间接消耗和波束退化。为解决这一问题,我们利用近场通道特征,并为近场XL-MIMO系统提出一个低管级波束训练计划。首先,我们将近场通道投射到空间角域和斜度间域,以获取详细的表达方式。第二,提出了一部新的空间-正准波波束辅助代码和相应的等级更新政策。还进行了理论分析和数字模拟,以核实波形成和培训间接费用的优异性表现。