Terahertz Communications Between Unstable Transceivers With Pointing Errors Over FTR Fading

Terahertz (THz) wireless communication has emerged as a promising technology for high-speed, ultra-broadband, and low-latency data transmission. However, the performance of THz systems is significantly affected by various channel and system parameters. Existing literature often models THz transmission links using $\alpha -\mu $ fading with pointing error, which is suitable for optical communication systems or a specific type of THz antennas. A new pointing error model designed for THz antennas has recently been proposed. The fluctuating two-ray (FTR) fading model emerges as a very suitable choice for THz transmission, as it considers the line-of-sight components and their random phase distributions, in addition to multipath and non-linearity of the propagation medium. In this paper, we model a THz transmission link considering FTR short-term fading, channel path loss, and the recently proposed pointing error, with two standard uniform $N \times N$ THz antenna arrays, one mounted at the unstable transmitter and one at the unstable receiver (instability accounts for the dynamic nature of drone-to-drone communication scenarios, particularly, dynamic drones fluctuating in yaw, roll, and pitch directions). Novel exact analytical closed-form expressions for the probability density function, the cumulative distribution function, and moment generating function of the received instantaneous signal-to-noise ratio are derived for the aforementioned system using standard mathematical functions. Next, closed-form expressions for performance metrics, namely, the outage probability, the average bit error rate, and the average channel capacity, are derived. Furthermore, the $n$ th moment of the received instantaneous signal-to-noise ratio and diversity order of the system are derived. The effects of various channel and system parameters on the system performance are studied, and the accuracy of the derived analytical expressions is confirmed by simulation results.