Power Control and Trajectory Optimization for a THz-Enabled UAV-Relay in Cognitive Radio Network

Unmanned aerial vehicles (UAVs) and Terahertz (THz) are vital parts of next-generation wireless communications due to their promising features. However, THz communication links suffer from severe path loss caused by vapor loss and molecular absorption, which cannot be neglectable in the optimization problem for the UAV relay in the sub-THz band system. This paper presents a secure UAV-relay mobile system operating at sub-THz bands for a cognitive network. We considered the path loss effect and investigated the performance of a UAV relay that receives information from a base station (SBS) and transmits it to a secondary user (SU) while avoiding interference from primary users (PUs) and eavesdroppers. An optimization problem is proposed to achieve our objective of maximizing the secrecy rate of UAV communication. We considered several constraints in our proposed optimization problem, such as velocity, UAV elevation, maximum transmitted power, information causality, and interference temperature (IT) constraints. The main problem has been divided into two subproblems. Additionally, we solved our proposed problem efficiently by proposing an alternative algorithm. The extensive analysis and performance results show that our proposed algorithm effectively impacts the physical layer security added to theUAV-relay communication at sub-THz communication.