11-GHz Radio: Application of Rain Attenuation Data to 11-GHz Radio Path Engineering

Abstract

This paper describes the procedures adopted at Bell Laboratories for using rain attenuation data to engineer 11‐GHz microwave radio hops and routes. Rain outage time charts, which show the rain outage time as a function of rain attenuation and hop length, are the basic tools in engineering the hops. The charts, their formulation, and the procedures for using the charts are described and illustrated with several examples. The procedures are used to demonstrate and quantify the sensitivity of allowable hop lengths to the available rain attenuation margin, the effects of a limited rain attenuation margin, and the effects of the variation in the outage in a single year from the 20‐year average outage. Guidelines for judging if a hop or route is performing as engineered are developed.

Improvements in fixed point-to-point microwave radio path design

“…Engineering paths based on worst-case statistics would lead to very uneconomical radio systems (and that data is not available). As Osborne [17] noted, at the present time there is no definitive proven solution to this problem. There is no practical method to limit the worst case outage time of radio paths with path loss dominated by rain attenuation.…”

“…In addition, many areas of interest have no rain data. As Osborne [17] observed, "… there are still areas [in the United States] a few hundred miles on a side for which no rain data exists …" This further complicates rain-fading estimation.…”

“…The actual rain rate measured over any one specific year will be different than the average value. Osborne [17] observed that the worst-case one-year rain rates can exceed long-term averages by a multiplicative factor of 2 to 20. Worst-case month or hour rates can exceed long-term averages by extremely large factors.…”