Joint Divergence Angle of Free Space Optics (FSO) Link and UAV Trajectory Design in FSO-Based UAV-Enabled Wireless Power Transfer Relay Systems

Abstract

Free Space Optics (FSO)-based UAV-enabled wireless power transfer (WPT) relay systems have emerged as a key technology for 6G networks, efficiently providing continuous power to Internet of Things (IoT) devices even in remote areas such as disaster recovery zones, maritime regions, and military networks, while addressing the limited battery capacity of UAVs through the FSO fronthaul link. However, the harvested power at the ground devices depends on the displacement and diameter of the FSO beam spot reaching the UAV, as well as the UAV trajectory, which affects both the FSO link and the radio-frequency (RF) link simultaneously. In this paper, we propose a joint design of the divergence angle in the FSO link and the UAV trajectory, in order to maximize the power transfer efficiency. Driven by the analysis of the optimal condition for the divergence angle, we develop a hybrid BS-PSO-based method to jointly optimize them while improving optimization performance. Numerical results demonstrate that the proposed method substantially increases power transfer efficiency and improves the optimization capability.