Rain models for the prediction of fade durations at millimetre wavelengths

Current ITU-R recommendations provide algorithms for estimating the exceedance statistics of rain-induced attenuation on terrestrial links. Another factor of interest, not currently covered by ITU-R recommendations, is the distribution of the durations of rain fades. This paper presents two algorithms for estimating this distribution. The distribution of the durations of rain events at different intensities is more fundamental than distributions of link fades. An expression for the average number of events per year of rain intensity greater than a given threshold has been developed from rain duration data gathered in the South East UK over three years. A method is presented for converting the distribution of rain durations into the distribution of link rain fade durations. The predicted distribution of rain fades is compared to 3 years´ attenuation data on a 38 GHz, 9 km, terrestrial link. The second algorithm exploits features of the spatial and temporal power spectrum of rain rate predicted by models of turbulence. A method is presented for simulating rain rate, sampled in time and space, with the predicted power spectrum and the desired rain rate exceedance distribution. Rain duration distributions are derived from simulated data and compared to experimental results