Rain Outage Performance of Tendem and Path Diversity 18-GHz Short Hop Radio Systems

The problems of utilizing the frequencies above 10 GHz for radio relay communication have been discussed by L. C. Tillotson 2 ; the major technical problem is attenuation by rain. Based on results derived from a rain gauge network in Bedfordshire, England, which 59 60 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1971 showed that the joint distribution of rain rates for two laterally separated paths is significantly less than the distributions for the individual paths, D. C. Hogg 3 suggested the use of dual path diversity as a means for reducing the magnitude of the problem. However, in deciding the value of path diversity, many other factors must be considered such as variation of fade margin with hop length, merging of the diversity paths at switching points, the nature of the attenuation distributions, and the degree of independence of two laterally separated paths versus separation. L. T. Gusler 4,5 has previously calculated the reliability and maximum lengths of diversity and nondiversity systems at 11 and 17 GHz based on attenuation distributions derived from six rain gauges on a five-mile path in New Jersey, and assumptions on joint distributions, merge paths, and repeater parameters. He concluded that diversity systems with short hops and moderate fade margins are suitable for long-haul systems, but t h a t nondiversity systems are suitable only for short-haul or low-reliability systems. These results have since been used in studies of long-haul microwave pole line systems.