Modeling the atmosphere as an unguided optical communications channel

The authors propose a system-level model for simulating the Earth´s atmosphere as an unguided optical communications channel. The major degradations in received optical intensity introduced by the atmosphere are scintillation, beam spreading, beam wander, and atmospheric transmissivity. The model presented considers scintillation and beam wander to impose random fading in the received signal while beam spreading is a constant loss in intensity. Atmospheric transmissivity is treated as a filterlike channel transfer function. Relationships for the parameters of the model are given in terms of parameters which characterize the optical link. Also included is a description of an implementation of the model. The implementation discussed is being integrated into an end-to-end simulator for a direct-detention laser communication system operating in the atmosphere