Double warning thresholds for preemptive charging scheduling in Wireless Rechargeable Sensor Networks

Wireless power transfer technique provides new alternatives for solving the limited power capacity problem for ubiquitous mobile wireless devices, and makes wireless rechargeable sensor networks (WRSNs) promising. However, mainly due to the underestimate of unbalanced influences of spatial and temporal constraints posed by charging requests, traditional scheduling strategies achieve rather low charging request throughput and success rate, posing as a major bottleneck for further improvement. In this paper, we propose a Double Warning thresholds with Double Preemption (DWDP) charging scheme, in which double warning thresholds are used when residual energy levels of sensor nodes fall below certain thresholds. By introducing specific comparison rules, warning thresholds can be used to adjust charging priorities of different sensors, warn the upcoming recharge deadlines, as well as support preemptive scheduling. Then DWDP is extended to where multiple Wireless Charging Vehicles (WCVs) are employed, and a Collaborative Charging DWDP, namely CCDWDP is proposed. Finally, we conduct extensive simulations to manifest the advantages of DWDP as well as CCDWDP. Simulation results reveal that DWDP can achieve better performance in guaranteeing the successful scheduling of the high-priority task and improving stability of the system. CCDWDP outperforms in terms of high charging throughput and short charging delay. (C) 2018 Elsevier B.V. All rights reserved.