Global Positioning System Reference
In-Depth Information
acquisition, carrier tracking, and data demodulation deteriorate as the (
C
S
/
N
0
)
eff
is
reduced until these receiver functions are lost. Chapter 5 shows that the effect of
interference on code tracking is not described by (
C
S
/
N
0
)
eff
, so a separate assessment
must be performed to evaluate the effect on code tracking and loss of lock.
Equation (6.21) can be rearranged to solve for (
C
ι
/
C
s
)
dB
as follows:
(
)
CN
(
)
CN
S
0
eff
,
dB
S
0
dB
−
−
(
)
CC
=
10
log
QR
10
−
10
(6.22)
10
10
ι
c
S
10
dB
Computing the unjammed (
C
S
/
N
0
)
dB
in (6.21) and (6.22) in units of dB-Hz
involves numerous parameters and is presented piecewise as follows:
(
)
(
)
(
)
(
)
CN
=
C
−
N
dB-Hz
dBW
S
0
S
0
dB
dB
dB
() ( ) ( )
(
)
C
=
C
+
G
−
L
S
Ri
SVi
dB
dB
dB
dB
[
]
(
)
()
(
)
N
=
10
log
kT
+
T
dBW
(6.23)
0
10
ant
amp
dB
()
N
f
dB
()
T
=
290 10
−
1
K
10
amp
where:
(
C
S
)
dB
=
recovered signal power received from SV
i
(
dBW)
(
N
0
)
dB
=
thermal noise power component in a 1-Hz bandwidth (dBW)
(
C
Ri
)
dB
=
received signal power from SV
i
at antenna input (dBW)
(
G
Svi
)
dB
=
antenna gain toward SV
i
(dBic)
L
dB
=
receiver implementation loss, including A/D converter loss (dB)
k
= Boltzmann's constant = 1.38
×
10
−23
(J/K)
T
ant
=
antenna noise temperature (K)
T
amp
=
amplifier temperature (K)
Q
=
jamming resistance quality factor (dimensionless)
R
c
=
spreading code rate (chips/s)
(
N
f
)
dB
=
amplifier noise figure at 290K (dB)
158.5 dBW (i.e., the
IS-GPS-200 minimum specified received signal power level for L1 C/A code) (see
Section 4.3.2 for details). Further assume that a fixed reception pattern antenna
(FRPA) is used with a typical gain roll off to about -3 dBic at the elevation mask
angle of 5º above the horizon. This is the elevation angle where the minimum GPS
received power specification is met. It is also typical for the antenna gain to increase
to 1.5 dBic or more at zenith, where the GPS minimum received power specification
is also met. In between these two elevation angles, the received signal power tends to
As a computation example of (6.23), assume (
C
Ri
)
dB
=−
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