Evaluation of Some Raindrop Size Distribution Models for Different Rain Rates

Results from the performance of the Negative exponential and Gamma function distribution model in a tropical location is presented in this work. The inputs to the drop size distribution (DSD) models have been obtained from Heipang, Nigeria (9.04˚N, 7.5˚E) using the pointing Micro Rain Radar (MRR). The effect of the raindrop diameter on the drop size distribution models (DSD) is investigated over the operating frequency range of 4 GHz to 40 GHz. The estimated rain rate for 99.99% availability for Heipang was used as input to the DSD models. From the results obtained, we observe that the highest drop size distribution for the diameter range 3.5 mm ≤ D ≤ 5.0 mm was 24.44 for a rainfall rate of 120 mm/h considering the Gamma function distribution. While that of the negative exponential distribution model was 88.87 for the range 3.0 mm ≤ D ≤ 5.0 mm. Results further suggest that a raindrop size of 0.7 mm can cause link outage for communication links operating with a frequency of 40 GHz. This is because of a wavelength large factor that ranged between 10.714 to 1.875. This study also shows that increasing rain rates of the convective rain types arise from the combined increase of the raindrop diameters across all frequencies. The results obtained from this study are useful for adequate network design and planning for achieving a higher quality of service across radio communication links.