Millimeter Wave Energy Harvesting
Millimeter wave (mmWave) communications is a key candidate technology for future 5G cellular networks. This is mainly due to the availability of large spectrum resources at higher frequencies, which leads to much higher data rates. Recent research suggests that mmWave systems will typically feature (i) large-dimensional antenna arrays with directional beamforming at the transmitter/receiver—which is motivated by the small wavelength that allows packing a large number of antenna elements into small form-factors; and (ii) a dense deployment of base stations (BSs) to ensure comparable coverage to ultra high frequency (UHF) networks. These mmWave features also seem attractive for transferring wireless energy to an energy harvesting node that can extract energy from the incident RF signals. This could potentially power the massive number of low-power wireless devices in future paradigms such as as the Internet of Things. The signal propagation at mmWave frequencies, however, suffers from poor penetration and diffraction characteristics, making it sensitive to blockage by buildings. It is, therefore, unclear if mmWave cellular networks will be more favorable for RF energy harvesting compared to the conventional (below 6 GHz) frequencies. Further, the network level design principles for mmWave energy harvesting systems are not well understood.
Our recent research considers a scenario where low-power energy harvesting devices extract energy and/or information from the transmission of a mmWave cellular network. We provide an analytical framework to characterize the performance of wireless energy and information transfer using metrics such as energy coverage probability. Our analysis accounts for the key distinguishing features of mmWave systems, namely the sensitivity to blockage and the use of potentially large antenna arrays at the transmitter/receiver. We consider two operating scenarios, one where devices have their beams aligned to that of a mmWave BS, and the other where no such beam alignment is assumed. For the former, we show that the energy coverage improves with narrower beams. For the latter, wider beams provide better energy coverage. This trade-off is evident in the more general scenario having both types of devices, where there typically exists an optimal beamforming beamwidth that maximizes the network-wide energy coverage. Our results also reveal that mmWave cellular networks could potentially provide better energy coverage than lower frequency solutions.
T. A. Khan, R. W. Heath, Jr. and P. Popovski, “On Wirelessly Powered Communications with Short Packets“, accepted in 2016 IEEE GLOBECOM Workshops, Washington DC.
T. A. Khan, A. Alkhateeb, and R. W. Heath, Jr., “Energy Coverage in Millimeter Wave Energy Harvesting Networks“, in Proc. 2015 IEEE GLOBECOM Workshops, San Diego.
This work was funded in part by the Army Research Office under Grant No. W911NF-12-R-0011, and gifts from Nokia and Mitsubishi Electric Research Labs (MERL), Cambridge.