Use of the HYCELL model for predicting rain attenuation on UAS low elevation datalinks

A new approach based on the HYCELL model for predicting the rain attenuation on low elevation links is presented. Using the Cumulative Distribution Function (CDF) of rainfall rate and the probability of rain occurrence for a specific region as an input to HYCELL, rain fields are simulated at mid-scale (i.e. 150×150 km²) for different locations in the world. From the geometrical (path length, elevation angle) and radiowave (frequency, polarization) characteristics of a link, the simulated rain fields are then converted into rain attenuation fields. Monte-Carlo technique is used to compute the long-term CDF of rain attenuation for links with elevation angles as low as 0° and for different frequencies at Ku and Ka bands. The methodology is applied on UAS datalinks operating at Ku and Ka frequency bands located at any elevation angles in a distance of less than 150 km from the transmitter. The results are compared to experimental distributions provided by the ITU-R DBSG3 database for Earth-satellite and terrestrial links. The results are also compared to Recommendations ITU-R P.618 and P.530. It is shown that the predictions of rain attenuation derived from HYCELL are close to the considered DBSG3 measurements and, in some cases, more accurate than the attenuation prediction derived from ITU Recommendations.