Global Positioning System Reference
In-Depth Information
parenthesis for reference. Note that this produces nine different values of
J
/
S
perfor-
mance for the same receiver tracking threshold.
Figure 6.4 depicts the (
J
/
S
)
dB
performance as a function of the (
C
S
/
N
0
)
eff,dB
(receiver tracking threshold) for L1 C/A, L1 P(Y), and M code receivers for
null-to-null jammers customized to each signal. The same assumptions were made
as in the earlier examples to determine the unjammed (
C
S
/
N
0
)
dB
.
Tolerable jamming (tolerable
J
) is a better way than
J
/
S
of comparing receiver
jamming performance when there are multiple levels of signal power involved. Since
the values of (
J/S
)
dB
in Table 6.4 are based on the receiver tracking threshold, the tol-
erable
J
dB
(dBW) is (
J
/
S
)
dB
(dB) plus the specified minimum received signal power
level, (
C
Ri
)
dB
(dBW). Table 6.5 compares the receiver tolerable
J
performance for L1
C/A code, L1 P(Y) code, and M code for BLWN null-to-null(s) jammer assuming
that all three receivers have the same 28-dB-Hz tracking threshold. (Actually, the
M-code signal should have an even lower tracking threshold because of TDDM, as
discussed in Chapter 5.) This comparison example reveals that the M code receiver
outperforms the P(Y) code receiver by 4.5 dB and the P(Y) code receiver outper-
forms the C/A code receiver by 6.8 dB when all three receivers have the same track-
ing threshold (28 dB-Hz). With the 3-dB reduction in threshold from TDDM in M
code, M code would outperform P(Y) code by 7.5 dB in tolerable jamming.
Figure 6.5 depicts the tolerable
J
dB
performance as a function of the (
C
S
/
N
0
)
eff,dB
(receiver tracking threshold) for L1 C/A, L1 P(Y), and M code receivers for BLWN
null-to-null(s) jammers customized to each signal. The same assumptions were
made as in the previous examples to determine the unjammed
C
S
/
N
0
.
Computing RF Interference Signal Levels
Even though the
J
/
S
performance of a GNSS receiver sounds impressive when the
ratio is reported in decibels, it becomes less impressive when the actual jammer sig-
M code
P(Y) code
C/A code
90
Frequency: L1 = 1575.42 MHz
Received GPS signal power (C ) (dBW):
M = 158, P(Y) = 161, C/A = 158.5
Receiver implementation loss: L = 2 dB
Receiver amplifier noise figure: (N )
85
Ri dB
−
−
−
80
dB
75
= 4.3 dB
fdB
Antenna temperature: Tant = 100 K
Antenna gain toward SVs: (G
70
)
= 1.5 dB
SVi dB
JdB
Antenna gain toward jammer: (G )
=
−
3 dB
65
Jammer type: band limited white noise
Jamming resistance Q factors:
M = 5.3, P(Y) = 2.22, C/A = 2.22
60
55
50
45
40
35
30
−
5
0
5
10
15
20
25
30
35
Tracking threshold (C/N )
(dB-Hz)
0 eff,dB
Figure 6.4
J
/
S
performance as a function of receiver tracking threshold.
Search WWH ::
Custom Search