Rain rate and rain attenuation estimation for Ku band satellite communications over Sri Lanka

Rain attenuation is the dominant propagation impairment at microwave frequencies, which varies for different countries/regions and essential to quantify correctly for satellite systems design. There was a consistent need to estimate and compare the practical rain fade margin with existing model estimations for Sri Lanka. This paper presents the rain rate and rain attenuation estimation for Ku band satellite signals by using established models as well as actual propagation measurements. Rainfall data over three years period is considered to estimate the highest rain rate distribution. Two satellite downlinks from Intelsat-12 & INSAT-4B are used for practical measurements and three rain attenuation models (ITU-R, DAH and Karasawa) are used to calculate the respective model estimations. It is found that the rain rate which exceeded 0.01% of cumulative time for an average year (R_0.01) as 105mm/h and resulted specific rain attenuation (γ_0.01) is 2.8dB/km. Ka band rain attenuation for the same links is predicted using ITU-R frequency scaling method. Among the empirical models considered, DAH model gives overestimated results for the local context while the Karasawa model gives best-fit compliance with the measured path attenuation data.