Modeling Transmission Properties of FSO Links: Slow Fades

The paper deals with modeling of transmission properties of free space optical digital links. Laser beam used for data transmission is a subject to several atmospheric phenomena that cause fades. Long fades are caused by precipitation (fog, heavy rain, snow). Short fades of order of tens of milliseconds are due to atmospheric turbulences and birds. Long fades contribute to the digital link unavailability while short fades interfere with communication protocols used. The paper deals with statistical modeling of long fades. A model based on two exceedance distribution functions is proposed. Parameters of such model can be identified from meteorological visibility range records. Results are available for more than 200 European sites from Sicily to Baltic Sea.