Adtran TRC4106 Manual Do Utilizador
TRACER 4206 System Manual
Section 2, Microwave Path Engineering Basics
612804206L1-1B
© 2002 ADTRAN, Inc.
21
9.
FADE MARGIN
Fade margin is a value indicating the amount of extra signal power available to the receiver to operate at a
maximum bit error rate (BER). Higher levels of fade margin are better, and will protect the viability of the
microwave link against signal fading. For most applications, 20 to 30 dB of fade margin should ensure a
reliable link. Fade margin is simply the difference between the available signal power at the receiver and
the receiver sensitivity, discussed previously:
maximum bit error rate (BER). Higher levels of fade margin are better, and will protect the viability of the
microwave link against signal fading. For most applications, 20 to 30 dB of fade margin should ensure a
reliable link. Fade margin is simply the difference between the available signal power at the receiver and
the receiver sensitivity, discussed previously:
10. 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
available over some fixed amount of time, and depends on several factors. Path availability is expressed as
where the parameters are
a
terrain factor
b
climate factor
f
carrier frequency (GHz)
d
path length (miles)
F
fade margin (dB)
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:
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
F
P
R
P
sens
P
R
G
T
G
R
L
L
P
P
sens
(dB)
A
1
2.5 10
6
×
(
)abfd
3
10
F 10
⁄
(
)
[
] 100%
×
(dB)