3D Trajectory Optimization for UAV-Assisted Hybrid FSO/RF Network with Moving Obstacles

The utilization of unmanned aerial vehicles (UAVs) as relays significantly enhances the availability of aeronautical free space optical (FSO) /radio frequency (RF) communication links. In this paper, a trajectory optimized scheme that maximizes the energy efficiency of the UAV relay is proposed. The focus of our study lies in the maximization of energy efficiency for UAVs, taking into account practical constraints in aeronautical FSO/RF communication networks, particularly the obstruction caused by moving clouds and the required data rates. Based on the cloud modeling, a feasible deployment area for UAVs that ensures line-of-sight (LOS) communication is obtained. Especially, we derive a theoretical model of propulsion energy consumption for fixed-wing UAV at variable altitudes for three-dimensional (3D) trajectory optimization. Accordingly, an energy efficient Trajectory Planning Gaining-sharing Knowledge (TPGSK) is presented to address this issue, and its effectiveness is tested. Through this algorithm, the trajectories that maximum data rate, minimum energy consumption, and optimal energy efficiency are presented, taking into consideration cloud movement. Furthermore, we find optimized energy efficiency values in various atmospheric environments. The numerical results demonstrate that the proposed design achieves significantly higher energy efficiency for the UAV-assisted hybrid FSO/RF network in comparison to other benchmark schemes