Efficient and Economical UAV-Facilitated Wireless Charging and Data Relay Trajectory Planning for WRSNs

With the significant progress in recent decades, wireless rechargeable sensor networks (WRSNs) have been widely deployed in smart cities, lakes, forests and other intelligent scenarios to perceive physical environment. To remotely power these sensor nodes (SNs), unmanned aerial vehicle (UAV) can provide far-field wireless charging by electromagnetic waves. Designing a trajectory for the UAV to “visit” all sensors with the shortest time is an important issue to be resolved in UAV-facilitated WRSNs. Existing researches have proposed massive novel algorithms to solve this issue but cannot realize a desirable solution for charging large-scale WRSNs within a tolerable time. In this work, we leverage UAV to wirelessly power the sensors and relay their sensed data timely. We first propose the UAV moving direction model, UAV-to-SN charging model, data backhauling model and UAV flying speed model to calculate the time consumed by the UAV for charging SNs and relaying data. In order to reduce the work time (equivalent to energy consumption) of the UAV, a flying and hovering time minimization problem is formulated. As this problem is proved as an NP-hard problem, we further propose the Fly Forward (FF) algorithm to efficiently solve it. Through extensive simulations, we have validated that the FF algorithm can effectively reduce the UAV's flying and hovering time, thus realizing an efficient and economical flying trajectory.