Our environment provides numerous virtually cost–free sources of energy, e.g., heat, light and wind, which have customarily been exploited to scavenge power for human activities. Recently, their exploitation in the context of wireless communication has been envisioned to power many elements of the network, as well as yielding cost reductions in terms of electricity supply, maintenance monitoring and battery management.
Energy harvesting technologies have gained prominence in the last decade as promising solutions to increase both portable devices lifetime and energy efficiency of communication networks. Remarkably, ambient sources of energy are not the only resource that could be exploited for harvesting purposes. For instance, an abundance of fully controllable sources of energy is naturally present in wireless networks; in the form of massively deployed radio transmitters, which typically broadcast a significant amount of radio frequency (RF) energy to remote devices. As a consequence, a growing interest has recently emerged by researchers in wireless communications to develop wireless energy transfer and harvesting solutions for fifth generation (5G) networks. The variety of settings in which energy harvesting and transfer technologies can be adopted, e.g., wireless sensor networks, mobile ad hoc networks, delay tolerant networks, smart cities and so on, is certainly noteworthy. The identification of novel network architectures, protocols and algorithms to integrate energy harvesting solutions in wireless communications networks is paramount to guarantee their effectiveness.