UAV Trajectory Design on Completion Time Minimization of WPT Task in UAV-Enabled Multi-User Network

In this paper, we study a UAV-enabled wireless sensor network (WSN), where a UAV is dispatched to charge multiple sensors deployed on the ground floor via the wireless power transfer (WPT) technique. A probabilistic line-of-sight (PLoS) channel model and a practical nonlinear energy harvesting (EH) model are considered in the characterization of the harvested energy by sensors. Focusing on a WPT task where a minimum energy budget is required by each sensor, we formulate a UAV trajectory optimization problem minimizing the corresponding completion time. To simplify the analysis, we reformulate the completion time minimization problem via inserting a successive-hover-and-fly (SHF) structure into UAV trajectory without loss of optimality. Afterwards, we proved the convexity in the LoS probability and nonlinear harvested power with respect to a higher-order power of a horizontal distance. Based on the proved convexity, we construct a convex approximation for the harvested energy at each sensor and propose an iterative solution for iteratively reducing the completion time until a convergence to a suboptimal point. At last, the simulation results are presented to confirm the convergence of the proposed algorithm and reveal the benefits in adopting the more practical PLoS model.