  Terahertz (THz) wireless communication is envisioned as a promising
technology, which is capable of providing ultra-high-rate transmission up to
Terabit per second. However, some hardware imperfections, which are generally
neglected in the existing literature concerning lower data rates and
traditional operating frequencies, cannot be overlooked in the THz systems.
Hardware imperfections usually consist of phase noise, in-phase/quadrature
imbalance, and nonlinearity of power amplifier. Due to the time-variant
characteristic of phase noise, frequent pilot insertion is required, leading to
decreased spectral efficiency. In this paper, to address this issue, a novel
pilot design strategy is proposed based on index modulation (IM), where the
positions of pilots are flexibly changed in the data frame, and additional
information bits can be conveyed by indices of pilots. Furthermore, a turbo
receiving algorithm is developed, which jointly performs the detection of pilot
indices and channel estimation in an iterative manner. It is shown that the
proposed turbo receiver works well even under the situation where the prior
knowledge of channel state information is outdated. Analytical and simulation
results validate that the proposed schemes achieve significant enhancement of
bit-error rate performance and channel estimation accuracy, whilst attaining
higher spectral efficiency in comparison with its classical counterpart.
