Energy-Efficient UAV-Enabled Wireless Power Transfer for Real-Time Charging Requirements

Due to the varying energy capacities and power consumption rates of Sensor Nodes (SNs), their charging needs may not coincide. Traditional Wireless Power Transfer (WPT) systems cannot handle the additional charging requirements from energy-deficient SNs after determining trajectories for UAVs. This paper investigates a multi-UAV-enabled WPT system for SNs with real-time charging needs. Fixed-wing UAVs are utilized to transfer power to SNs. An optimization problem is formulated to maximize the energy efficiency of UAVs, defined as the ratio of the energy received by SNs to the total energy consumed by UAV flights. The whole flight process can be divided into two phases, i.e., Straight Flight (SF) and Circle Flight (CF). A Target Selection Algorithm (TSA) is proposed to help UAVs select appropriate SNs, reducing total SF distance. The optimal flight velocity is also calculated to minimize each UAV’s flight energy consumption. In the CF stage, UAVs should follow the trajectories optimized by Successive Convex Approximation (SCA) to achieve energy efficiency maximization of UAVs. Numerical results are given to evaluate the performance of the proposed algorithm.