  Numerous studies claim that terahertz (THz) communication will be an
essential piece of sixth-generation wireless communication systems. Its
promising potential also comes with major challenges, in particular the reduced
coverage due to harsh propagation loss, hardware constraints, and blockage
vulnerability. To increase the coverage of THz communication, we revisit
cooperative communication. We propose a new type of cooperative rate-splitting
(CRS) called extraction-based CRS (eCRS). Furthermore, we explore two extreme
cases of eCRS, namely, identical eCRS and distinct eCRS. To enable the proposed
eCRS framework, we design a novel THz cooperative channel model by considering
unique characteristics of THz communication. Through mathematical derivations
and convex optimization techniques considering the THz cooperative channel
model, we derive local optimal solutions for the two cases of eCRS and a global
optimal closed form solution for a specific scenario. Finally, we propose a
novel channel estimation technique that not only specifies the channel value,
but also the time delay of the channel from each cooperating user equipment to
fully utilize the THz cooperative channel. In simulation results, we verify the
validity of the two cases of our proposed framework and channel estimation
technique.
