Long-term rain attenuation statistics and variations in Ku band satellite communications

Long-term rain attenuation statistics and variations are discussed using Ku band satellite signal observations conducted at Osaka Electro-Communication University in Neyagawa, Japan, from 1988 to 2015. The yearly cumulative time percentages of Ku band attenuation indicate fairly large variations which amount to about 20% around the mean values. Besides the yearly rainfall rate statistics, these variations seem to be caused by difference in the equivalent path length in each year, which becomes longer as the average ground temperature at the rain time from May to October becomes higher. However, the increase of the equivalent path length is not sufficiently explained by that of rain height, but rather related to the rain types which frequently appear in summer time and have much larger cloud sizes. Also, the equivalent path length tends to increase further for the last 10 years since 2006, and this tendency seems to be related to the overall increase of the average ground temperature in rain time of each year.

1. Introduction

It is well known that rain attenuation effects become significant in satellite communications using frequency of higher than 10 GHz. Rain attenuation statistics are usually predicted by rainfall rate statistics observed on the ground for a long period. Typical statistical values used in the predictions, such as the ITU-R recommendations, are rainfall rate with a yearly time percentage of 0.01% and average 0°C height [1], [2].