Rain Attenuation at mmWave and Optical Bands from Visibility and Rainfall Intensity Measurements

Wireless communications at very high frequencies, from mmWave to Free-Space Optics (FSO), dramatically increase link capacity, but their performance decreases significantly under adverse weather. Existing global models for rain attenuation, such as the one in Rec. ITU-R P.838-3, are straightforward as they rely on rainfall intensity only, but they do not capture the complexity of rain microphysics. This study investigates the potentiality of visibility measurements to enhance the understanding of rain attenuation. Specifically, we show the preliminary results of an experimental study in Milan started in late 2022 involving colocated E-band (83 GHz), FSO links (1.550 µm), and visibility and rainfall sensors on both sides of the links. The correlation between rainfall intensity and visibility decreases during heavy rain, probably due to the microphysical effects. Moreover, the accuracy in estimating rainfall attenuation at mmWave and FSO from visibility and rainfall is comparable.