TRACER 5045 System Manual | Section 2 Microwave Path Engineering Basics |
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7.OTHER CONSIDERATIONS
Path Availability
The path availability of a wireless link is a metric that expresses the fractional amount of time a link is available over some fixed amount of time, and depends on several factors. Path availability is expressed as
A = [1 – (2.5 ⋅ | (%) |
where the parameters are
aterrain factor
bclimate factor
fcarrier 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 over that terrain will have, primarily due to multipath reflections. In contrast, secondary microwave signals will be randomly dispersed over rough terrain, and will not interfere with the main signal lobe as badly as in the smooth terrain case. The terrain factor values normally used are listed below:
Terrain | Terrain Factor | Description |
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Smooth | 4 | water, flat desert |
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Average | 1 | moderate roughness |
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Mountainous | 1/4 | very rough, mountainous |
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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 availability than those in arid areas, primarily because water is a dispersive mechanism to microwave energy, and causes the main signal lobe to refract and disperse away from the receiver location. The climate factor values normally used are listed below:
Climate | Climate Factor | Description |
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Very Dry | 1/8 | desert regions |
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Temperate | 1/4 | mainland, interior region |
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Humid | 1/2 | humid and coastal regions |
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© 2003 ADTRAN, Inc. | 23 |
