Rain Attenuation Factor in the Earth-Space Links of Tropical Regions

Abstract

Rain attenuation is an important factor to be considered in the Earth-space communication link budget, especially for regions that receive heavy rainfall, e.g. tropical regions. Inaccurate estimation of rain attenuation may result in broken or intermittent Earth-space links. The estimation of rain attenuation depends on many other factors. One of the important ones is the height from sea level within which raindrops is assumed present, i.e. rain height. International Telecommunications Union (ITU) recommends the ITU-R P.839-4 (09-2013) method for predicting rain height, and the ITU-R P.618-13 (12-2017) method for determining rain attenuation. Recently, some works claimed inaccuracy of these methods in the tropical regions, and proposed some modified methods. This paper aims to clarify the doubts. We determine the possible causes of inaccuracy, and then assess the impact of inaccurate estimation of rain height onto rain attenuation. As compared to the modified methods, we found that the rain height values calculated from ITU-R P.839-4 make more sense. It is likely that incorrectly represented formulas were used in some related works. Moreover, rain attenuation values obtained from ITU-R P.618-13 are resilient to the changes in rain heights. As a result, we advocate the use of the ITU-R P.839-4 and ITUR P.618-13 methods in the tropical regions.