Beam Tracking for UAV-Assisted FSO Links With a Four-Quadrant Detector

Abstract

A ground-to-air free-space optical link is studied for a hovering unmanned aerial vehicle (UAV) having multiple rotors. For this UAV, a four-quadrant array of photodetectors is used at the optical receiver to alleviate the adverse effect of hovering fluctuations by enlarging the receiver field-ofview. Extensive mathematical analysis is conducted to evaluate the beam tracking performance under the random effects of hovering fluctuations. The accuracy of the derived analytical expressions is corroborated by performing Monte-Carlo simulations. It is shown that the performance of such links depends heavily on the random fluctuations of hovering UAV, and, for each level of instability there is an optimal size for the array that minimizes the tracking error probability Index Terms FSO, four-quadrant detector, UAV. I. INTRODUCTIONRecently, unmanned aerial vehicle (UAV) communications have attracted significant interest due to many advantageous such as fast deployment, flexible configuration, and possibility of having better channel conditions. Furthermore, technological advances of UAVs along with their reduced production costs have made future cellular networks more likely to be equipped with UAVs as flying base stations (BSs) [1]. Nevertheless, existing terrestrial wireless networks may experience radio interference when UAVs are used as aerial BSs, making it challenging to implement a practical aerial RF link. UAVs and free-space optical (FSO) based communicaiton systems have been recently proposed as a promising approach for the next generation wireless network [2], where the aerial communication links are free of radio interference. FSO links offer higher bandwidth and security than the conventional RF H. Safi and A. Dargahi are with the