ADTRAN 12804108L1A System Manual

ADTRAN 12804108L1A System Manual Manual pdf 23 page image

TRACER 4108/4208 System Manual Section 2 Microwave Path Engineering Basics612804208L1-1B © 2003 ADTRAN, Inc. 237. OTHER CONSIDERATIONSPath AvailabilityThe path availability of a wireless link is a metric that expresses the fractional amount of time a link isavailable over some fixed amount of time, and depends on several factors. Path availability is expressed aswhere the parameters area terrain factorb climate factorf carrier frequency (GHz)d path length (miles)F fade margin (dB)Terrain Factor (a)The terrain factor is a quantity that compensates the link availability for different types of terrain.Generally speaking, the more smooth an area's terrain is, the less availability a wireless link running overthat terrain will have, primarily due to multipath reflections. In contrast, secondary microwave signals willbe randomly dispersed over rough terrain, and will not interfere with the main signal lobe as badly as in thesmooth terrain case. The terrain factor values normally used are listed below:Climate Factor (b)The climate factor is a quantity that compensates the link availability for different types of climates(weather). In general, microwave links operating in areas with high humidity will have less availabilitythan those in arid areas, primarily because water is a dispersive mechanism to microwave energy, andcauses the main signal lobe to refract and disperse away from the receiver location. The climate factorvalues normally used are listed below :Terrain Terrain Factor DescriptionSmooth 4 water, flat desertAverage 1 moderate roughnessMountainous 1/4 very rough, mountainousClimate Climate Factor DescriptionVery Dry 1/8 desert regionsTemperate 1/4 mainland, interior regionHumid 1/2 humid and coastal regionsA 1 2.5 10 6–×( )abfd3 10 F 10⁄–( )–[ ] 100%×= (%)