RF Energy Harvesting and Transfer in Cognitive Radio Sensor Networks: Opportunities and Challenges

By enabling sensor nodes to opportunistically access licensed channels, CRSN can provide a spectrum-efficient networking solution in the era of the Internet of Things. On the other hand, it also consumes extra energy for spectrum sensing and switching. This is a double-edged sword posing a dilemma between spectrum efficiency and energy efficiency. Recent advances in RF energy harvesting and transfer promote RF-powered CRSN in providing a promising way to address this challenge. In RF-powered CRSNs, sensor nodes can dynamically access the vacant licensed channels for interference-free data transmission and can also utilize the strong signals over the occupied licensed channels for energy harvesting. In this article, we investigate RF energy harvesting and transfer in CRSNs. We first introduce the architecture and advantages of RF-powered CRSN, typical applications, as well as the key challenges arising from applying RF energy harvesting and transfer into CRSN. We then propose a resource allocation framework to demonstrate how to jointly control the dynamic channel access and energy management to optimize network utility while guaranteeing network stability and sustainability. Some future directions are finally envisioned for further research.