Employing Ambient RF Energy in Connected Devices

Abstract

Pervasive connectivity is stunted by the requirement for batteries. RF energy harvesting is a compelling solution to this problem. However, the fundamental energy requirements of wireless communication limit the means for connectivity in these highly energy constrained RF harvesting devices. Further, variation in power availability for conventional RF harvesters, which target single fixed spectral bands, severely limits the area in which they can be applied. Ambient backscatter addresses communication energy requirements by employing ambient RF energy in another way: devices perform modulated scattering of ambient RF to transmit information. This allows RF harvesting ambient backscatter devices to communicate with far less power than those using conventional radio, partially closing the gap between the power requirements of a connected device and the power harvesting capabilities of an ambient harvester. Multiband RF harvesting addresses single-source energy availability issues by allowing an ambient harvesting node to gather energy on multiple bands at once, summing power efficiently from multiple ambient sources. A parallel method for resolving single-source fading issues in ambient backscatter is wideband ambient backscatter, in which a transmitter backscatters energy across an extremely wide bandwidth, allowing any signal in that entire band to be a host for backscatter communication. The overall motivation of this work is to explore ways in which ambient RF can be practically employed in connected devices to prolong operating life, or even to allow batteryless operation.