Rain Attenuation Prediction for Terrestrial Links at Microwave and Millimeter Bands over Rwanda

The equatorial region are often characterised with voluminous levels of rainfall, which is often detrimental to service links operating at microwave and millimetre wave bands. The rainfall being a natural and time-varying phenomenon, its induced attenuation increases with frequency and varies from year to year and from region to region. In this paper, a comprehensive analysis of rainfall attenuation are estimated for eight major cities namely Butare, Ruhengeri, Gisenyi, Byumba, Kamembe, Kibungo, Kagitumba and Kigali in equatorial Rwanda between 1 degrees 04' and 2 degrees 51' latitude South and 28 degrees 45' and 30 degrees 15' longitude East. Rainfall rate exceeded for 0.01% of the time is obtained using long term rainfall measurements obtained from Rwanda Meteorology Agency (Meteo Rwanda) for a period of twenty nine years and above. The specific attenuation due to rain is predicted at vertical and horizontal polarization for frequency from 1-200 GHz. By using International Telecommunication Union Recommendation (ITU-R), it is found from predictions that the rain attenuation is higher in Kamembe (lat. 02 degrees 28'S and long. 28 degrees 55'E) to the West and low in Kagitumba (lat. 02 degrees 03'S and long. 30 degrees 27'E) to the East irrespective of the proposed transmission frequencies. It is also seen that a horizontal polarized signal is more attenuated than vertical polarised signal. Conclusively, the Western Province of Rwanda will suffer more from rain-induced network outages compared to other parts of the country. This study will provide useful inputs in the deployment of terrestrial and satellite services across the entire Rwanda.