THEORETICAL STUDY OF RAIN INDUCED PROPAGATION EFFECTS ON SATELLITE TELECOMMUNICATION IN SOME TROPICAL LOCATIONS

Abstract

The study investigates the scattering effect of oblate spheroidal raindrops on Earth-space wave communication in the frequency band 1-52 GHz in three tropical locations lle-Ife, Nigeria (4.34~, 7.33'N>" Douala, Cameroon (9.70~, 4.0S'N>, and Nairobi, Kenya (36.7SoE,1.300S), Elevation angles of 23° and 55° are assumed for wave propagation in the regions. The incident waves are assumed to be linearly polarized that is, the incident waves are horizontally and vertically polarized. The tropical lognormal raindrop size distribution model has been used to estimate the raindrops number density. The specific attenuation and specific phase shift are calculated in terms of the power law relationship between attenuation and rainfall rate since measured cumulative distribution of rain rates are available from the locations. The total slant path attenuation is then computed using the International Telecommunication Union (ITV) recommended model. Rain rate measured at the locations are used. The calculation of the propagation parameters i based on the measured Mean Annual (MA) and Mean Worst Month (MWM) rain 1 rates in each location. Differential propagation parameters are also computed at th frequencies and elevation angles investigated. The results are then used to compute t Cross Polarization Discrimination (XPD) and the Co-Polarized Attenuation (CPA) at two rain rates and elevation angles for rain rates exceeded for 0.01 % of time (99.9 :-'0 time availability). The total slant path attenuation for other time percentages such a 0.001% and 0.1 % of time are calculated using the scaling formula also recommended by the ITU The total slant path attenuation, co-polarized attenuation, and cross polarization discrimination in Cameroon and Kenya are compared with that of Nigeria. The predicted slant path attenuation, CPA, and XPD for Cameroon. is closer to those obtained for Nigeria than that for Kenya. Further, at the elevation angle of 55°, and for links over the Atlantic Ocean Region (AOR), the CPA and XPD are higher in Cameroon than Nigeria by about 24% at the most. At the elevation angle of 23°, and for links over the Indian Ocean Region (lOR), the percentage difference between CPA and XPD in Cameroon is higher than in Nigeria by about 1136%. Therefore, it can be safely said that rain induced degradation of Earth-space communication will be most severe in Cameroon and least severe in Kenya.