Global Positioning System Reference
In-Depth Information
modulation,
R
c
=
1.023 Mchip/s. Assume a bandlimited white noise (BLWN) jam-
ming waveform whose spectrum is rectangular, centered at the C/A center fre-
quency, and approximately 2 MHz wide (null to null), so that
Q
2.22. If the PLL
carrier tracking threshold example from Section 5.6.1 is used, then the tolerable
(
C
S
/
N
0
)
eff,dB
=
≅
28 dB-Hz. Substituting these and the unjammed (
C
S
/
N
0
)
dB
from the pre-
vious computational example into (6.25)
[
]
(
)
()
6
−
2 8
.
−
4 19
.
JS
dB
=++
15
.
30
.
10
l g.
2 22
×
1023
.
×
10
10
−
10
10
=
3
9.dB
For L1 P(Y) code, there is BPSK-R(10) modulation with
R
c
= 10.23 Mchip/s and
(
C
Ri
)
dB
161.5 dBW. Assume the jamming waveform has a BLWN rectangular
spectrum centered on L1 with width of 20.46 MHz (null to null) so that
Q
=−
=
2.22
(and the remaining assumptions the same). The unjammed (
C
S
/
N
0
)
dB
=
38.9 dB-Hz,
so
[
]
(
)
()
6
−
2 8
.
−
3 89
.
JS
dB
=++
15
.
30
.
10
l g.
222
×
10 23
.
×
10
10
−
10
10
=
4
9.dB
Note that if the unjammed (
C
S
/
N
0
)
dB
for Y code were the same as for C/A code
above, the (
J
/
S
)
dB
would be exactly 10 dB greater, reflecting the factor of 10 increase
in spreading code chip rate.
For the normal power M code with BOC
s
(10,5) modulation and
R
c
=
5.115
Mcps, (
C
Ri
)
dB
=−
158.0 dBW. Assume that the BLWN jamming spectrum consists of
two (null to null) rectangles, centered
±
10.23 MHz away from L1, each with width
of 10.23 MHz so that
Q
≅
5.3 (and the remaining assumptions the same). The
unjammed (
C
S
/
N
0
)
dB
=
43.4 dB-Hz so
[
]
(
)
()
6
−
2 8
.
−
4 34
.
JS
dB
=++
15
.
30
.
10
l g.
5 3
×
5 115
.
×
10
10
−
10
10
=
50
.7 d B
Table 6.4 summarizes the receiver (
J
/
S
)
dB
performance for L1 C/A code, L1 P(Y)
code, and M code for all three types of jamming with the same assumptions for
antenna gain toward the satellite (1.5 dB), gain toward the jammer (
3 dB), imple-
mentation loss (2 dB), and noise figure (4.3 dB) for a receiver tracking threshold
(
C
S
/
N
0
)
eff,dB
−
=
28 dB-Hz. The applicable
Q
used to compute each entry is shown in
Table 6.4
J
/
S
Performance (with Appropriate
Q
) for 28-dB-Hz Carrier Tracking Threshold
Jammer Type
(J/S)
dB
(Q, Dimensionless)
L1 C/A Code
L1 P(Y) Code
L1 M Code (Normal)
Bandlimited white noise null to null
39.9 (2.22)
49.7 (2.22)
50.7 (5.3)
Matched spectrum
38.2 (1.5)
48.0 (1.5)
49.5 (4.0)
Narrowband at spectral peak(s)
36.4 (1)
46.2 (1)
47.1 (2.3)
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