Worst Month Tropospheric Attenuation Variability Analysis: ITU Model vs. Rain Gauge Data for Air-Satellite Links

An important unmanned aircraft system (UAS) application area is in rescue functions in remote areas, where ground station control may not be applicable. In such settings, an air-satellite (AS) communication link may be required. For transmissions in the millimeter wave (mmWave) frequency bands, rain attenuation can be a dominant fading component in the AS link, especially in so-called “worst month” conditions. Several models have been established by the International Telecommunications Union (ITV) to quantify rain attenuation. However, since the models are for global use, results are not always sufficiently accurate in local areas. Hence the use of local precipitation data can improve rain attenuation estimation accuracy. In this paper, we investigate attenuations in the AS channel in two frequency bands (30 and 45 GHz) for Columbia, SC. We use local rain gauge data from the National Oceanic and Atmospheric Administration (NOAA), along with the regional ITV data, as inputs to the ITV tropospheric time series attenuation model. Statistical results for attenuation distributions and time series are analyzed for the worst month. We show that use of local measured rain gauge data can yield rain fades significantly larger than those predicted by the regional ITV data-on the order of 20 dB larger, for probabilities (~ fractions of time) ranging from 0.001 to 0.04.