Comparison of exact and approximate FSO rain attenuation formulas based on actual DSD

This contribution deals with estimation of rain attenuation on free space optical (FSO) links. The approximative model recommended by ITU-R is compared with the exact solution using actual rain drop size distribution (DSD) measured in Prague by 2D video-distrometer. Results show that the error is non-negligible especially at rain rates higher than 15 mm/h due to rain spectrum variability. We produced the new power law model. However, we concluded, that another parameter representing DSD must be added when estimating the rain attenuation on FSO links.