Ray Tracing Meets Terahertz: Challenges and Opportunities.

It is very likely that the terahertz (THz) spectrum will be used for the operation of the upcoming 6th-generation (6G) wireless communication systems. This article presents a study for the application of ray tracing (RT) for THz channel modeling. Because of the extremely short wavelengths of THz signals, we argue that signal propagation in the THz spectrum can be precisely modeled by employing RT techniques and thus accurate channel models can be obtained in an efficient manner. We first review recent research and standardization activities related with RT-assisted channel modeling which mainly deal with millimeter-wave (mmWave) applications and to a much lesser extent have been applied the THz spectrum. Then, we present the basic THz wave propagation characteristics, including reflection, scattering, penetration, shadowing as well as signal absorption by atmospheric molecules and tiny particles under different weather conditions. The methodologies for the appropriate construction of target scenarios are presented as well as efficient computational methods for the effective RT operation. Finally, various research and development (R&D) challenges related to RT-based channels for future THz communication systems are identified and possible solutions are highlighted.