Energy-Efficient UAV Multicasting with Simultaneous FSO Backhaul and Power Transfer

This letter studies an unmanned aerial vehicle (UAV) aided multicasting (MC) system, which is enabled by simultaneous free space optics (FSO) backhaul and power transfer. The UAV applies the power-splitting technique to harvest wireless power and decode backhaul information simultaneously over the FSO link, while at the same time using the harvested power to multicast the backhauled information over the radio frequency (RF) links to multiple ground users (GUs). We derive the UAV's achievable MC rate under the Poisson point process (PPP) based GU distribution. By jointly designing the FSO and RF links and the UAV altitude, we maximize the system-level energy efficiency (EE), which can be equivalently expressed as the ratio of the UAV's MC rate over the optics base station (OBS) transmit power, subject to the UAV's sustainable operation and reliable backhauling constraints. Due to the non-convexity of this problem, we propose suboptimal solutions with low complexity. Numerical results show the close-to-optimal EE performance by properly balancing the power-rate tradeoff between the FSO power and the MC data transmissions.