  Terahertz (THz) wireless communications have the potential to realize
ultra-high-speed and secure data transfer with miniaturized devices for
unmanned aerial vehicle (UAV) communications. The atmospheric turbulence due to
random airflow leads to spatial inhomogeneity of the communication medium,
which is yet missing in most existing studies, leading to additional
propagation loss and even loss of spatial coherence (LoSC) in MIMO systems. In
this paper, the attenuation and loss of spatial coherence for atmospheric
turbulence are modeled in THz UAV MIMO channels. Specifically, the frequency-
and altitude-dependency of the refractive index structure constant (RISC), as a
critical statistical parameter characterizing the intensity of turbulence, is
first investigated. Then, the LoSC, fading, and attenuation caused by
atmospheric turbulence are modeled, where the turbulence-induced fading is
modeled by a Gamma-Gamma distribution, and the turbulence attenuation as a
function of altitude and frequency is derived. Numerical results show that the
turbulence leads to at most 10 dB attenuation with frequency less than 1 THz
and distance less than 10 km. Furthermore, when the distance is 10 km and the
RISC is 10^-9m^(-2/3), the loss of spatial coherence effect leads to 10 dB
additional loss for a 1024*1024 ultra-massive MIMO system.

Systems and Control;Systems and Control