Adtran TRC4205 Manual Do Utilizador
TRACER 4205 System Manual
Section 2, Microwave Path Engineering Basics
612804205L1-1A
© 2002 ADTRAN, Inc.
21
7.
RECEIVER SENSITIVITY
Receiver sensitivity is a value expressed in decibels referenced to one milliwatt (dBm) that corresponds to
the minimum amount of signal power needed at the receiver to achieve a given bit error rate (BER).
Receiver sensitivity is usually a negative number of decibels, and as such smaller receiver sensitivity is
better for a given BER. Several factors affect receiver sensitivity, including the data bandwidth of the
wireless link, and the amount of additional signal degradation introduced in the receiver electronics. The
receiver sensitivity of the TRACER 4205 is -78 dBm at 10
the minimum amount of signal power needed at the receiver to achieve a given bit error rate (BER).
Receiver sensitivity is usually a negative number of decibels, and as such smaller receiver sensitivity is
better for a given BER. Several factors affect receiver sensitivity, including the data bandwidth of the
wireless link, and the amount of additional signal degradation introduced in the receiver electronics. The
receiver sensitivity of the TRACER 4205 is -78 dBm at 10
-6
BER.
8.
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:
9.
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)