Other Considerations; Path Availability - ADTRAN 12804108L1A System Manual

TRACER 4108/4208 System Manual
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 –
where the parameters are
a terrain factor
b climate factor
f 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 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
Smooth
Average
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
Very Dry
Temperate
Humid
612804208L1-1B
6 – 3 –
×
( )abfd (
2.5 10 10
Terrain Factor
4
1
1/4
:
Climate Factor
1/8
1/4
1/2
© 2003 ADTRAN, Inc.
Section 2 Microwave Path Engineering Basics
⁄
F 10
×
) ] 100%
Description
water, flat desert
moderate roughness
very rough, mountainous
Description
desert regions
mainland, interior region
humid and coastal regions
(%)
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