Free-Space Optical Communication Impaired by Angular Fluctuations

In this paper, the impairments of FSO communication systems caused by angular fluctuations including beam misalignment and angle-of-arrival (AOA) fluctuations are modelled in the presence of both atmospheric turbulence and transceiver vibrations. In particular, assuming FSO receivers with a limited field-of-view (FOV), the fading caused by AOA fluctuations is studied. The outage probability expressions for both coherent and direct detections are derived in both shot-noise-limited and thermal- noise-limited regimes. For direct detection, the optimal receiver FOV that achieves the minimum outage probability is also calculated. Furthermore, the issue of imperfect phasefront tracking in practical coherent receivers is investigated.