3-D Position Optimization of Solar-Powered Hovering UAV Relay in Optical Wireless Backhaul

A major hurdle in widespread deployment of UAVs (unmanned aerial vehicle) in existing communications infrastructure is the limited UAV onboard energy. Therefore, this study considers solar energy harvesting UAVs for wireless communications. In this context, we consider three dimensional position optimization of a solar-powered UAV relay that connects a distant sensor field to an optical ground station (OGS) for data processing. The integrated sensor-UAV-OGS network utilizes radio frequency band for sensor-to-UAV links and the optical band for the UAV-to-OGS feeder link. Since atmospheric conditions affect both the harvested solar energy as well as the optical wireless signal, this study tackles UAV position optimization problems under various channel conditions such as clouds, atmospheric turbulence and dirt. From this study, we discover that the optimum position of the UAV—that maximizes the end-to-end channel capacity—is heavily dependent on the atmospheric channel conditions.