A unified approach for channel modeling of terrestrial FSO links

Channel modeling for Free Space Optical (FSO) links remain an interesting research problem for the optical wireless community. Major link attenuators for FSO include fog, rain, snow, clouds, turbulence and ambient light. The article reviews the major link attenuators and proposes a novel technique for modeling fog attenuation, which by far is the most detrimental for terrestrial FSO communications. The communication system designers of FSO have mostly remained dependent on turbulence models and over looked the other attenuators including fog due to non-availability of stochastic models for fog attenuation. The current article tries to bridge this gap in knowledge and puts forth appropriate probability density function estimates for received signal strength under fog attenuation. The variations in received signal strength during foggy events recorded at Graz and Nice are thoroughly analyzed, and it is concluded that on a small time scale, the received signal strength variations can be modeled by a Gaussian or skewed Gaussian probability density function, whereas on a larger time scale, multimodal distribution function provides a better estimate.