The spatial distribution of rain and its implications for wide area communications systems

Rain is a major source of attenuation or radio paths operating above 10 GHz, one that is unlikely to be compensated for by available fade margin alone. A number of fade mitigation techniques have been proposed to increase the potential availability of a system; one of which, site diversity, was investigated by the RCRU during the STENTOR experiment. Site diversity relies on the spatial and temporal inhomogeneity of rain fields. As it can be expensive to implement, it is advisable to study the spatial and temporal variation of rain using other methods such as rain gauge networks and radar. These studies provide valuable information on structures inside the rain fields, such as the size, shape and orientation of rain cells. This information is needed to accurately model and simulate the spatial variation of 2-D rain fields. This paper discusses the implications of the results of one such analysis, completed using the data recorded from CAMRa (the Chilbolton Advanced Meteorological Radar), which is located in the South of England. Using these results and other fractal techniques a model can be devised to simulate the spatial variation in rain rate fields. The use of this model for design and optimum use of communications systems (both slant path and terrestrial) are outlined.