Systematic development of new multivariable techniques for predicting the distribution of multipath fading on terrestrial microwave links

Multipath fading data obtained from 47 terrestrial microwave line-of-sight links in France and the United Kingdom are analyzed to derive narrowband prediction equations for the deep fading range of the cumulative distribution for the average worst month. A large number of possible predictor variables based on typical radio link parameters are investigated, and equations which reduce the standard error of prediction to less than half that of previous techniques for this part of Europe are developed. The improvement is achieved by increasing the number of prediction variables, using the most statistically significant variables, introducing a zonally varying geoclimatic factor, and employing more accurate analysis techniques. A reasonable choice of variables for system design includes path length, radio frequency, path inclination, and the grazing angle of specular reflection from the average terrain profile. A physical interpretation of the results suggests that a large amount of multipath fading is caused by ground reflection in combination with fading of the direct wave through the atmosphere