Energy Maximization for Ground Nodes in UAV-Enabled Wireless Power Transfer Systems

In UAV-enabled wireless power transfer (WPT) systems, the UAV is usually planned to fly and charge the ground nodes (GNs), so as to prolong the lifetime of wireless sensor networks. But in fact, the long charging distance between the UAV and the GNs makes the GNs receive less energy. In order to maximize the received energy of GNs, this article focuses on the charging process and proposes a V-shaped WPT scheme, where the UAV descends to the optimal hover position and charges the GNs, so as to transfer more energy to the GNs. Moreover, considering that the GNs far from the hover position receive little energy in the V-shaped WPT scheme, we further develop an Inverted Trapezoidal WPT scheme to improve the fairness of the energy received by the GNs, in which the UAV continuously charges the GNs whether it is hovering or flying horizontally after lowering its altitude. Because the UAV's flight and maneuvering are strictly constrained by its loading energy, we establish the UAV's propulsion power consumption model in different flight attitudes and formulate the optimization problems of the GNs' received energy in two schemes, and then develop two algorithms to solve them. The simulation results show that the performance metrics of UAV's energy consumption, the efficiency, and fairness of GNs' received energy are better than the compared schemes.