A novel spatial tracking loop for laser communication over turbulent unguided optical channels

A spatial tracking strategy for unguided optical communications is proposed. The proposed model assumes an optical link where the major impairment is due to optical turbulence and that the spatial tracking errors due to platform movements have been successfully tracked and compensated. The optical turbulence, which results in large fades, results in a gamma-gamma-distributed signal intensity level at the receiver. Further, it is assumed that the intensity fluctuations have been estimated using estimation strategies proposed recently. In the proposed ST model, the onset of fading is used to maintain the current state of the ST system in order to circumvent the impact of noise on the signal-level-compromised tracking loop under large signal fade condition. Through analytical analysis, it is demonstrated that the proposed loop reduces the standard deviation of the spatial tracking error by a sizable margin as compared with the standard tracking loop (STL).