Regime analysis of rainfall drop-size distribution models for microwave terrestrial networks

In this study, parameters of statistical models for estimating the rainfall specific attenuation in Durban, South Africa are derived. The rainfall data in this work are based on 2-year measurements obtained via the Joss-Waldvogel RD-80 disdrometer between January 2009 and December 2010. Four rainfall regimes are applied: drizzle, widespread, shower and thunderstorm types. Using the third, fourth and sixth moments of the measured data, estimators for four rainfall drop-size distribution (DSD) models - 3-parameter lognormal model, negative exponential model, 3-parameter Weibull model and the modified gamma model - are computed. The specific attenuation estimates from our model are compared with the values from predicted measurements alongside the International Telecommunication Union (ITU) estimates for frequencies between 2 and 100-GHz. The results from the specific attenuation estimation are compared with the semi-empirical measurements for their respective regimes using root-mean-square and X² error tests. From the results, the best models for the various regimes are: Weibull model for drizzle regime, modified gamma model for widespread and shower regimes and lognormal model for the thunderstorm regime.