Efficient Path and Charge (P&C) Scheduling for a Mobile Charger to Improve Survivability and Throughput of Sensors with Adaptive Sensing Rates

Wireless sensor networks (WSNs) provide long-term monitoring of the environment but sensors are powered by small batteries. To extend WSN lifetime, using a mobile charger (MC) to visit sensors and charge their batteries is a promising solution. Though many approaches are developed to find the MC's visiting path, they usually assume that sensors have a fixed sensing rate (SR) and prefer fully charging sensors. In practice, SRs can be adaptive, as sensors may adjust their SRs due to application needs or energy saving. Moreover, with the fully charging policy, some low-energy sensors take long to wait for the MC's service. Thus, the paper formulates a path and charge (P&C) problem, which asks how to dispatch the MC to visit sensors with adaptive SRs and decide the time to charge them, such that their survivability and throughput can be maximized. An efficient P&C scheduling (EPCS) scheme is proposed to solve the P&C problem by building a shortest path to visit each sensor. Afterward, some energy-rich sensors may be excluded from the path to help the MC fast move to charge those near death. EPCS also adopts a floating charging strategy based on the ratio of workable sensors and their energy depletion. Simulation results show that EPCS can significantly improve both survivability and throughput of sensors.