Self-sustainable Sensor Networks with Multi-source Energy Harvesting and Wireless Charging

Energy supply remains to be a major bottleneck in Wireless Sensor Networks (WSNs). A self-sustainable network operates without battery replacement. Recent efforts employ multi-source energy harvesting to power sensors with ambient energy. Meanwhile, wireless charging is considered in WSNs as a reliable energy source. It motivates us to integrate both fields of research to build a self-sustainable network and guarantee operation under any weather condition. We propose a three-step solution to optimize this new framework. We first solve the Sensor Composition Problem (SCP) to derive the percentage of different types of sensors. Then we enable self-sustainability by bringing energy harvesting storage to the field for charging the Mobile Charger (MC). Next, we propose a 3-factor approximation algorithm to schedule sensor charging and energy replenishment of MC. Our extensive simulation results demonstrate significant improvement of network lifetime and reduction of network cost. The network lifetime can be extended at least three times compared with traditional approaches and the charging capability of MC increases at least 100%.

I. Introduction

The research of energy efficiency in wireless sensor networks (WSNs) has mainly focused on energy conservation such as low-cost communication, duty cycling, adaptive control and MAC/routing protocols [1] –[3]. These studies improve energy efficiency but yet to solve the fundamental problem of energy provisioning. Sensors will deplete energy ultimately and battery replacement is necessary but infeasible for large networks. Energy harvesters can acquire energy from the environment, e.g., solar, wind, vibration, thermal, and electromagnetic radiation [4] –[6], and made commensurate to sensor size. Unfortunately, ambient source is dynamic, and constant interruption of power supply is expected (e.g., solar harvesting during cloudy/raining days). Thus, new solutions combine multiple sources together to improve system robustness (e.g., solar-wind system [7]). However, under extreme weather conditions, it may still suffer from energy shortage when none of them are available. To this end, we introduce wireless charging as a backup and reliable energy source [8], [9]. Due to limited charging range, a Mobile Charger (MC) is usually employed to approach the proximity of sensors for effective charging [10].