Worldwide techniques for predicting the multipath fading distribution on terrestrial LOS links: background and results of tests

In 1988, the International Telecommunication Union (ITU) adopted new methods for predicting the deep-fading distribution due to multipath propagation for the average worst month on ultra high-frequency (UHF)-super high frequency (SHF) terrestrial line-of-sight (LOS) links. Employing refractivity gradient statistics available from world maps, the methods were recommended for application in all regions of the world. One method for the deep-fading range did not utilize detailed path profile information and was designed for preliminary planning or licensing purposes. A second method, which did employ the path profile was intended for more detailed design purposes. A multipath fading data base comprising some 246 links (including 34 over water) in 23 countries of the world has now been assembled for testing and revising these methods. Revisions to the geoclimatic model used in both methods and an associated method for predicting the shallow-fading distribution have been adopted by Study Group 3 of the new radiocommunications sector of the ITU (ITU-R). This paper summarizes the basis of the original and revised versions of the deep-fading prediction methods and presents the results of the most extensive tests to date. Some discussion of potential future revisions is also provided.