Wireless power transferable from unmanned aerial vehicle

Unmanned aerial vehicle (UAV) could wirelessly transfer power to the devices on ground, thus recharging their batteries conveniently. Nevertheless, the efficiency of this wireless power transfer from UAV to ground remains unclear. This paper aims to answer this question from the theoretical perspective. We need two models for this purpose: an energy harnessing model and a UAV-to-ground wireless channel model. In the literature, a model of harnessing radio frequency (RF) energy and turning it into DC power is available. Our goal is to quantify the theoretical efficiency of RF-to-DC power conversion, and the amount of DC power gained as a result. Following this nonlinear energy harvesting circuit model, the signal level fluctuations caused by channel fading actually enhance the power conversion. To model the wireless channel gain from the UAV to the ground, we use the modified Loo’s channel model. Connecting it to the RF-to-DC power conversion model, we can determine the theoretical amount of DC power attainable from UAV’s transmission, in addition to its power conversion efficiency. Our finding shows that a heavy shadowing condition can enhance the RF-to-DC power conversion of a nonlinear energy harvesting circuit. For example, certain heavy shadowing condition may yield a conversion efficiency that is 7 dB higher than when shadowing is absent. This concurs with the previous finding that signal attenuation and fluctuation actually made the energy easier to be captured and harnessed by the nonlinear rectenna circuitry. Our finding confirms that high RF-to-DC conversion efficiency is attainable even under shadowing conditions.