Abstract
The next-generation wireless technologies, commonly referred to as the
6G, are envisioned to support extreme communications capacity and in
particular disruption in the network sensing capabilities. The THz band
is one potential enabler for those due to the enormous unused frequency
bands and the high spatial resolution enabled by both short wavelengths
and bandwidths. Different from earlier surveys, this paper presents a
comprehensive treatment and technology survey on THz communications and
sensing in terms of the advantages, applications, propagation
characterization, channel modeling, measurement campaigns, antennas,
transceiver devices, beamforming, networking, the integration of
communications and sensing, and experimental testbeds. Starting from the
motivation and use cases, we survey the development and historical
perspective of THz communications and sensing with the anticipated 6G
requirements. We explore the radio propagation, channel modeling, and
measurements for THz band. The transceiver requirements, architectures,
technological challenges, and approaches together with means to
compensate for the high propagation losses by appropriate antenna and
beamforming solutions. We survey also several system technologies
required by or beneficial for THz systems. The synergistic design of
sensing and communications is explored with depth. Practical trials,
demonstrations, and experiments are also summarized. The paper gives a
holistic view of the current state of the art and highlights the issues
and challenges that are open for further research towards 6G.