The sixth generation networks envision the deployment of terahertz (THz) band as one of the key enabling property thanks to its abundant bandwidth. However, the ultra-wide bandwidth in THz causes beam-split phenomenon due to the use of a single analog beamformer (AB). Specifically, beam-split makes different subcarriers to observe distinct directions since the same AB is adopted for all subcarriers. Previous works mostly employ additional hardware components, e.g., time-delayer networks to mitigate beam-split by realizing virtual subcarrier-dependent ABs. This paper introduces an efficient and unified approach, called beam-split-aware (BSA) hybrid beamforming. In particular, instead of virtually generating subcarrier-dependent ABs, a single AB is used and the effect of beam-split is computed and passed into the digital beamformers, which are subcarrier-dependent while maximizing spectral efficiency. Hence, the proposed BSA approach effectively mitigates the impact of beam-split and it can be applied to any hybrid beamforming architecture. Manifold optimization and orthogonal matching pursuit techniques are considered for the evaluation of the proposed approach in multi-user scenario. Numerical simulations show that significant performance improvement can be achieved as compared to the conventional techniques.

翻译：第六代网络将太赫兹（THz）频段的部署视为关键使能特性之一，得益于其丰富的带宽资源。然而，太赫兹超宽带宽因使用单个模拟波束赋形器（AB）而引发波束分裂现象。具体而言，由于所有子载波共用同一模拟波束赋形器，波束分裂导致不同子载波观测到不同的方向。以往的研究大多采用额外硬件组件（例如时延网络）通过实现虚拟子载波依赖的模拟波束赋形器来缓解波束分裂。本文提出一种高效且统一的方法，称为波束分裂感知（BSA）混合波束赋形。具体而言，并非虚拟生成子载波依赖的模拟波束赋形器，而是使用单个模拟波束赋形器，计算波束分裂的影响并将其传递至数字波束赋形器，后者在最大化频谱效率的同时具备子载波依赖性。因此，所提出的BSA方法能有效缓解波束分裂的影响，并适用于任何混合波束赋形架构。采用流形优化和正交匹配追踪技术，在多用户场景下对所提方法进行评估。数值仿真表明，与传统技术相比，该方法可实现显著的性能提升。