Energy Optimization of a Laser-Powered Hovering-UAV Relay in Optical Wireless Backhaul

Abstract

Due to their flexibility and low cost deployment, unmanned aerial vehicles (UAV) will most likely act as base stations and backhaul relays in the next generation of wireless communication systems. However, these UAVs-in the untethered mode-can only operate for a finite time due to limited energy they carry in their batteries. In free-space optical communications, one solution is to transport both the data and the energy from the source to the UAV through the laser beam-a concept known as simultaneous lightwave information and power transfer (SLIPT).In this study, we have analyzed the SLIPT scheme for laser-powered decode-and-forward UAV relays in an optical wireless backhaul. The major goal of this study is to optimally allocate the received beam energy between the decoding circuit, the transmitting circuit and the rotor block of the relay in order to maximize a quality-of-service metric such as maximum achievable rate, outage or error probabilities. As expected, we note that the optimal power allocation depends heavily on the source-relay and relay-destination channel conditions. In the final part of this study, we have maximized the operational time of the UAV relay given that the maximum achievable rate stays above a certain threshold in order to meet a minimum quality-of-service requirement.

Optical Wireless Communications: Illuminating the Path for Cooper's Law

“…Laser-powered UAVs (operating on the SLIPT principle) have significant potential to integrate with the conventional terrestrial network made up of tethered and untethered UAVs to expand the coverage area of a wireless cellular network [247], [248]. Moreover, by optimizing how the power is split between the decoding and forwarding blocks of a laser-powered UAV relay, significant performance gains can be achieved in terms of coverage probability and channel capacity [247], [249]. Recently, low latency FSO communications with laser-powered UAVs were proposed based on optimal blocklength allocation, power control, trajectory planning, and energy harvesting techniques [250].…”

Optimal Power Allocation Between Beam Tracking and Symbol Detection Channels in a Free-Space Optical Communications Receiver

“…Assuming that the pointing error (due to angle-of-arrival fluctuations) is distributed as a Rayleigh random variable [15], [28], [29], the received signal power-denoted by P s -captured by the detector is furnished by the relationship:…”

“…This condition is almost always satisfied since the beam footprint is made large enough to accommodate any deviations due to misalignment or pointing error. In most scenarios, a suboptimal value of beam radius ρ (in relation to σ p ) is given by ρ = √ 2σ p [29].…”

“…The authors in [24], [25] consider generalized models of pointing error for capacity calculations, whereas [26], [27] consider pointing error modeling along with turbulence induced fading in FSO links. The authors in [28], [29] exclusively consider Rayleigh distribution-based pointing error model for dual and multihop relaying FSO channels that involve hovering unmanned aerial (UAV) based relays. The study…”