  Although terahertz (THz) communications can provide mobile broadband
services, it usually has a large path loss and is vulnerable to antenna
misalignment. This significantly degrades the reception reliability. To address
this issue, the hybrid automatic repeat request (HARQ) is proposed to further
enhance the reliability of THz communications. This paper provides an in-depth
investigation on the outage performance of two different types of HARQ-aided
THz communications, including Type-I HARQ and HARQ with chase combining
(HARQ-CC). Moreover, the effects of both fading and stochastic antenna
misalignment are considered in this paper. The exact outage probabilities of
HARQ-aided THz communications are derived in closed-form, with which the
asymptotic outage analysis is enabled to explore helpful insights. In
particular, it is revealed that full time diversity can be achieved by using
HARQ assisted schemes. Besides, the HARQ-CC-aided scheme performs better than
the Type-I HARQ-aided one due to its high diversity combining gain. The
analytical results are eventually validated via Monte-Carlo simulations.
