TRACER 5045 System Manual

Section 2 Microwave Path Engineering Basics

 

 

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 – (2.5 106)abfd3(10F10)] ⋅ 100%

(%)

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

 

 

 

 

 

 

Smooth

4

water, flat desert

 

 

 

Average

1

moderate roughness

 

 

 

Mountainous

1/4

very rough, mountainous

 

 

 

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

 

 

 

 

 

 

Very Dry

1/8

desert regions

 

 

 

Temperate

1/4

mainland, interior region

 

 

 

Humid

1/2

humid and coastal regions

 

 

 

612805045L1-1A

© 2003 ADTRAN, Inc.

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ADTRAN 5045 system manual Other Considerations, Path Availability, Terrain Terrain Factor Description