APPROXIMATE METHOD TO ESTIMATE AN UPPER BOUND ON THE EFFECT OF MULTIPATH DELAY DISTORTION ON DIGITAL TRANSMISSION

Microwave transmission on line-of-sight paths occasionally experiences severe fading associated with multiple transmission paths of differing propagation delays. An expression for the envelope delay distortion caused by two such paths is presented. Assuming that envelope delay distortions comparable to the symbol length of a digital signal could be intolerable, an expression is derived for critical pair-values of fade depth and path delay for a digital signal transmitted over a two-path medium. Good agreement of the principle was obtained with laboratory measurements made on 4- and 8-level systems. Curves are given showing the relationship between critical fade depths and relative delays, and estimates are made of channel outages based on assumed distributions of fades and time delays. The outage times are extemely sensitive to hop length, and exceed a commonly used objective for hops more than 25 mi long. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.