Trajectory design of UAV-aided energy-harvesting relay networks in the terahertz band

Unmanned aerial vehicle (UAV)-aided relaying benefits from easy deployment, strong communication channels, and mobility compared with traditional ground relaying, thereby enhancing the wireless connectivity of future industrial Internet of Things networks. In this paper, a UAV-assisted relay network capable of harvesting energy from a source is designed by exploiting the radio frequency band and transmitting information between the transmitter and corresponding receiver utilizing the terahertz (THz) band. Subsequently, the channel capacity is analytically derived using the finite blocklength theorem for THz communication. In addition, we formulate an optimization problem to determine the optimal location of the UAV to maintain the minimum channel capacity between the transmitter and receiver pair. To determine the optimal location, we employ the augmented Lagrange multiplier approach. Regarding the optimal location, we propose an algorithm for two UAV trajectories, namely forward and backward trajectories, that employs modified minimal jerk trajectories. The numerical results indicate that the backward trajectory provides better system performance in terms of channel capacity. Moreover, the simulation findings show that in urban, dense urban, and high-rise areas, the backward trajectory improves upon the forward trajectory by approximately 41.07%, 59.02%, and 76.47%, respectively, while using a blocklength of 400 bytes.