Bit Error Analysis of a Dual-Hop Mixed RF-THz Wireless System With AF Relaying

The transmission range and the quality of service of terahertz ($\mathbf{T H z}$) wireless communications are constrained by the significant effects of factors such as short-term fading, path loss, and alignment errors. Cooperative relaying is a viable technique that can be used to improve link reliability and transmission range. In this study, we analyze the bit error performance of a dual-hop mixed radio frequency (RF)-THz wireless system with the fixed-gain amplify-and-forward protocol. To model the RF link between the stable source and the fluctuating relay, we consider the effect of Rayleigh fading and path loss. Modeling of the THz link between the fluctuating relay and the destination (relay and destination are considered as unstable drones, equipped with uniform standard $N_{a} \times N_{a} \mathbf{T H z}$ high directional antenna arrays fluctuating uniformly in yaw and pitch directions) is done considering the combined effect of $\alpha-\mu$ fading, path loss, and alignment errors (the recently introduced alignment error model is employed). To have a better insight into the system performance, we provide an asymptotic analysis and calculate the diversity order of the system based on system and channel parameters. Furthermore, we examine the influence of various design parameters by analyzing the average bit error rate and diversity order. The analytical results are verified by computer simulations, averaged over $10^{7}$ channel realizations.