  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.
