UAV-Assisted Communications With RF Energy Harvesting: A Comprehensive Survey

Unmanned aerial vehicles (UAVs) have recently achieved sky-rocketed prominence in assisting various wireless communication scenarios due to their implicit characteristics like line-of-sight connectivity, three-dimensional mobility, on-demand deployment, and payload abilities. For realizing UAV-assisted communications in practical scenarios, one of the key challenges is the onboard power limitation of UAVs, which can affect their flight duration, maneuverability, and network lifetime. Exploiting energy harvesting (EH) techniques with UAV networks can improve operational time by addressing the UAV’s power constraints. In addition, UAVs can facilitate seamless connectivity for energy-constrained low-power devices in remote locations, disaster-struck areas, emergencies, and areas where human intervention is challenging and recharging or replacing batteries is problematic. In such scenarios, a low-altitude UAV, which flies flexibly, can serve as a radio-frequency (RF) energy transmitter to charge the nearby low-power devices efficiently and help enable their communications. Focusing on these aspects, this paper comprehensively surveys the current state-of-the-art EH techniques that can be utilized with UAV communications in various practical scenarios. Then, we highlight crucial challenges in integrating UAVs with prevailing wireless infrastructure and discuss different RF-EH receiver architectures that can be viable solutions for power-constrained UAV networks. Further, we show the channel modeling of UAV-assisted communications with EH and provide critical insights into the system performance. Besides, we offer an exhaustive review of recent works on RF-EH in UAV networks with next-generation paradigms and different problem-solving techniques/optimization methods. Finally, we suggest forthcoming trends and highlight open issues and future research directions.