How much RF Energy can be Harvested from V2X Communications? An Experimental Assessment

Energy Harvesting (EH) from Radio Frequency (RF) energy sources has been envisioned as a promising approach to power small sensors, actuators and transceivers in the future Smart City. While several potential energy sources have been identified (mobile phones, dedicated power beacons, cellular base stations) most of them have tight power constraints or are too sparse to provide an adequate energy level. In the next decades, however, with the widespread of connected vehicles, vehicular communications will become a feasible source of RF energy. In this paper, we present the results of an experimental campaign aimed at quantifying the amount of energy that can be actually scavenged by battery-less sensors placed alongside a road from vehicular transmissions. Both a static and a dynamic scenario have been tested, in order to assess the impact of transmit power, vehicle trajectory and speed, as well as the storage capacity. In particular, our findings shed light on the peculiar features of this scenario, which may not be fully leveraged by commonly used harvesting boards tailored to different types of energy sources. An upper bound of the available energy for the dynamic scenario is derived, confirming that up to 0.45 mJ can be stored from the passage of a single vehicle with a proper tuning of the parameters setup.