Three-Dimensional End-to-End Modeling and Analysis for Graphene-Enabled Terahertz Band Communications

Terahertz (0.1–10 THz) band communication is envisioned as a key technology to satisfy the increasing demand for ultra-high-speed wireless links. In this paper, a 3-D end-to-end model in the THz band is developed that includes the graphene-based reflectarray antenna response and the 3-D multipath propagation phenomena. In particular, the architecture of a graphene-based reflectarray antenna is investigated, and the 3-D radiation pattern is modeled. Moreover, a 3-D THz channel model based on ray tracing techniques is developed as a superposition of the line-of-sight (LoS), reflected, and scattered paths. By using the developed end-to-end model, an in-depth analysis on the 3-D channel characteristics is carried out. Specifically, the gain at the main beam of the graphene-based reflectarray antenna is 18 dB, and the 3-dB beamwidths in the elevation and the azimuth planes are <inline-formula> <tex-math notation="LaTeX">$7^\circ$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX"> $10^\circ$</tex-math></inline-formula>, respectively. The use of the reflectarray leads to a decrease of the delay spread from 1.23 to 0.099 ns, which suggests that the resulting coherence bandwidth reaches 2 GHz. Moreover, the root mean square (rms) angular spread in the elevation plane is less than <inline-formula> <tex-math notation="LaTeX">$0.12^\circ$</tex-math></inline-formula>, which is one tenth of that without beamforming. Furthermore, the wideband channel capacity at THz frequencies is characterized, which can be enhanced with a larger transmit power, a lower operating frequency, a larger bandwidth, and a higher beamforming gain. Finally, the beamforming gain enabled by the reflectarray antenna is compromised at the cost of the strict beam alignment, and the deviation needs to be smaller than <inline-formula><tex-math notation="LaTeX">$11^\circ$</tex-math></inline-formula>. The provided analysis and the channel physical parameters lay out the foundation and are particularly useful for realizing reliable and efficient ultra-high-speed wireless communications in the THz band.