Free-Space Optical Communication Impaired by Angular Fluctuations

In this paper, the impairments of free-space optical (FSO) communication systems caused by angular fluctuations including beam misalignment and angle-of-arrival (AOA) fluctuations are modeled 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 considered. Furthermore, the issue of imperfect phasefront tracking in practical coherent receivers is investigated.