Energy harvesting communications: Part III [Guest Editorial]

as a promising approach to enable self-sufficient and self-sustaining operation for devices in energy-constrained networks by scavenging energy from the ambient environment to power up devices. In particular, for wireless sensor networks, if the sensors, which spread throughout homes or factories, in buildings or even outdoors, are powered by energy harvesting, there are no batteries to replace and no labor costs associated with replacing them. For a cellular network, energy harvesting can be used to provide power in many elements of a telecom network, saving considerable costs in electricity supply, and providing low-maintenance monitoring. As another important focus, RF energy is currently broadcast from billions of radio transmitters around the world. The ability to harvest RF energy, from ambient or dedicated sources, enables wireless charging of low-power devices and has significant benefits to product design, usability, and reliability. This Feature Topic focuses on energy harvesting related issues in communications, through presenting a holistic view of research challenges and opportunities in the emerging area of energy harvesting communications. We hope this Feature Topic is able to help readers to obtain better understanding of some key issues in energy harvesting, and drive more research interest. This is Part III of this Feature Topic, starting with “A Hierarchical Packet Forwarding Mechanism for an Energy Harvesting Wireless Sensor Network” by Dapeng Wu et al., which investigates a dynamic gradient-aware hierarchical packet forwarding mechanism based on the relative positions of the sensor nodes. The article “Wireless Information and Power Transfer: From Scientific Hypothesis to Engineering Practice,” by Rong Zhang et al., surveys the state-of-the-art findings on simultaneous wireless information and power transfer (SWIPT), including design challenges, potential solutions, and research ideas. The article “Delay-Sensitive Dynamic Resource Control for Energy Harvesting Wireless Systems with Finite Energy Storage,” written by Fan Zhang et al., studies optimization of the delay performance of energy harvesting wireless systems with finite energy storage, covering the resource allocation to the channel fading information, data queue length, and energy queue. The article “Toward Secure Energy Harvesting Cooperative Networks,” by Jiawen Kang et al., addresses the security issues and solutions in energy harvesting cooperative networks, where the vulnerability of energy cooperation models in energy attacks is analyzed, and several energy defense solutions are proposed.