Improving ITU-R rain attenuation model for HAPS earth-space link

Rain attenuation can have a high impact on the service availability of radio communication systems especially that operate in the Ka-band where the rain attenuation is 10 times larger than at C-band. Achieving a high availability of services in advanced HAPS link design requires an extensive knowledge about the radio channel behavior. In order to predict precisely the rain attenuation for a certain location, accurate environment characteristics estimation is required because it is geographically dependent. This paper presents an analytical model that is able to predict the earth-space rain attenuation when the signal path is either completely or partially affected by the rain. It is based on the empirical ITU-R model. The frequency of the predicted signal has been carried out in this study is 31 GHz and the specific attenuation was evaluated using power law approximation. The relationship between the rain cell size and the attenuation is compared for different times exceeded in an average year, for example, a 1 km diameter rain cell size, the attenuation is about -43 dB for 0.01% availability. Using this comparison it is deduced that the amount of attenuation will be doubled as the cell size of the rain increases.