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：第六代网络将部署太赫兹频段视为关键使能特性之一，这得益于其丰富的带宽资源。然而，太赫兹频段的超宽带宽因采用单一模拟波束赋形器而引发波束分裂现象。具体而言，由于所有子载波共享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方向。现有研究多通过增加硬件组件（如时延网络）实现虚拟子载波依赖的模拟波束赋形器以缓解波束分裂。本文提出一种高效统一的方案，称为波束分裂感知混合波束赋形。该方法并非虚拟生成子载波依赖的模拟波束赋形器，而是采用单一模拟波束赋形器，计算波束分裂效应并将其传递至数字波束赋形器——后者具有子载波依赖性，同时最大化频谱效率。因此，所提出的波束分裂感知方案能有效缓解波束分裂的影响，且适用于任意混合波束赋形架构。在多用户场景下，采用流形优化与正交匹配追踪技术对该方案进行评估。数值仿真表明，相较于传统方法，该方案可实现显著的性能提升。