Preliminary Investigation of Raindrop Size Distribution Modelling for Microwave Applications in Rwanda

-The choice of rain drop size distribution(RDSD) model is essential for adequate estimation and prediction of attenuation due to rain in any geographical location or region. Measurements of drop size distributions at Butare (2.6S, 29.74E); Rwanda is carried out using the Joss-WaldvogelRD-80 disdrometer installed at the National University of Rwanda. Different established distributions are fitted to the measured disdrometer data to model the RDSD for a number of rainfall events. The method of moments (MoM) is adopted for the estimation of theRDSD parameters, while the scattering functions are estimated using the Mie scattering approximation at a temperature of 20C for spherical raindrops.A comparative analysis of the proposed model is made with models from other tropical and equatorial regions. Theproposed models are used to estimate the specific rain attenuation over Rwandaand at 2.5 -150 GHz using the estimated R0.01 value for Rwanda.Between 10 ≤ f ≤ 60 GHz window, the specific rain attenuation increases with corresponding increase in the frequency. The performance above 60 GHz relative to increase in frequency shows no significant change in the specific rain attenuation.The estimated attenuation statistics presented in this study will be useful for the proper design and allocation of adequate fade margins to achieve the expected quality of service (QoS) in a radio communication system operating in this region.