The Path Reduction Factor for the Prediction of Rain Attenuation Affecting Short EHF Terrestrial Links

The path reduction factor (PRF), a key element of semi-empirical rain attenuation statistics prediction models, is investigated to shed some light on its value for links shorter than 1 km. PRF is here calculated from simulations underpinned by the use of the Enhanced Synthetic Storm Technique (E-SST) to take into account the rain rate spatial distribution along the path. This novel approach, in contrast with the more customary one of inferring a PRF model from measurements, offers the advantage of avoiding considering any unwanted additional attenuation not due to precipitation, but typically linked to system-induced effects. Results indicate that, as expected, PRF reduces with the increase in the rain rate R and in the path length L , and they also reveal quite a marginal dependence on the operational frequency. Most importantly, the outcomes highlight that the maximum values of PRF only slightly exceeds 1 and, in addition, they provide a possible explanation as to why, on the contrary, the path reduction factor defined in the Recommendation ITU-R P.530–18 is characterized by a steep increase as L reduces.