Global Positioning System Reference
In-Depth Information
(J/S)
= 55
(J/S)
= 60
(J/S)
= 65
(J/S)
= 70
(J/S)
= 45
(J/S)
= 50
dB
dB
dB
dB
dB
dB
20
20
Frequency: L1 = 1575. 42 MHz
SV incident signal power: (S ) = 158 dBW
Antenna gain toward jammer: (G ) = 3 dB
Receiver front end jammer power loss: (L )
18
18
rdB
JdB
16
16
= 0 dB
fdB
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
2
2
4
4
6
6
8
8
10
10
12
12
14
14
16
16
18
18
20
20
EIRP (W)
(c)
Figure 6.6
(continued.)
one shown in Figure 6.1, this can provide a warning that special (time-consuming)
search measures must be taken, such as increasing the search dwell time and adjust-
ing the search detector parameters for best C/A code search operation in the pres-
ence of CW. The new L2C and L5 signals have design features that minimize this
vulnerability. The line spectra of the P(Y) code and M code have line spacing so nar-
row that they essentially take on attributes of continuous spectrum, so these signals
do not exhibit this vulnerability.
Even if an adaptive antenna array or temporal filtering are used to reduce CW
interference to the thermal noise level, there remains a vulnerability of C/A code to
CW interference. The thermal noise floor can be determined from the following
equation:
(
)
(
)
( )
N
=
N
+
10 log
B
dBW
(6.29)
ther
0
10
dB
dB
where B
receiver front-end bandwidth (Hz).
Assume that the C/A code receiver is a narrow correlator design with a 15-MHz
bandwidth. Substituting the thermal noise density, ( N 0 ) dB , value from the example in
Section 6.2.2.5 into (6.29) yields:
=
(
)
N ther
=−
2009
.
+
718
.
=−
1291
.
d W
dB
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