VCEC: Velocity Control of Energy-Constrained RF-Based Wireless Charger in Sensor Networks with Multi-Depots Deployment

Abstract

RF energy transfer, as the main far-field wireless energy transfer technology in wireless sensor networks, allows the relatively long charging distance from wireless charger to sensor nodes. Existing charging schemes based on a mobile RF energy charger neglect the energy consumption of the charger and its limited battery capacity. Motivated by this, we consider the practical charging scenario where energy-constrained mobile charger (MC) travels along a constrained long trajectory in the network area to wirelessly power the sensors, with multiple depots (for the energy provision of MC) deployed on the trajectory to achieve high energy efficiency. In this paper, we introduce VCEC, a Velocity-Control scheme of Energy-constrained mobile Charger to maximize the minimum charged energy in nodes after MC passes through the whole trajectory. Specifically, we first simplify the initial velocity-control problem to a tractable one by discretizing the trajectory into segments and propose a distributed algorithm to solve it. Then, we present a segment merging algorithm for the real-world applications. Our VCEC scheme achieves an approximation ratio of (1-Θ)(1+ e)^-1. Simulations and test-bed experiments are conducted to show that VCEC promotes the bottleneck node's charged energy by at least 20% as compared to the baseline scheme where MC moves at a constant speed.