Alignment and tracking of a free-space optical communications link to a UAV

This paper investigates the ability of a mechanical gimbal to perform alignment and tracking of a free-space optical communications link between a ground station and an unmanned aerial vehicle. The repeatability and accuracy of a mechanical gimbal are experimentally analyzed in order to generate probability distribution functions for the gimbal's performance. A simulation portion investigates the amount of divergence present in the laser beam of the communications link in the presence of atmospheric turbulence along with the scintillation index of the laser beam and the probability of the signal fading below a required threshold. The data from the experimental and simulation portions are further analyzed to verify the ability of a gimbal to provide acquisition and tracking functions for a ground-to-air link along with the expected geometric loss associated with such a communications link.