Optimization of Beam Divergence Angle in Free-Space-Optical Communications With Pointing Error

Free-space optical (FSO) communication has been implemented in unmanned aerial vehicles (UAVs) using steerable laser beams, with advantages in spectrum resources and security. However, in mobile scenarios, the misalignment between transceivers and mechanical vibrations are inevitable. These may cause non-zero boresight pointing errors, resulting in channel fading. To mitigate the impacts of the issues, we optimize the beam divergence angle to improve the reliability of UAV-assisted FSO communication systems. In this paper, we optimize the beam divergence angle to maximize the average receiving power of the receiver. We also formulate an optimization problem for the beam divergence angle to minimize the outage probability in optical mobile links. Besides, an optical wireless communication (OWC) prototype is built to compare the bit error rates (BERs) of the collimated beam and the optimized beam, respectively.