Global Positioning System Reference
In-Depth Information
B
n
C
N
(
)
2
()
2
2
π
066
.
B
−
7 7 6
.
E
fe
0
1
,
16
MHz
≤≤
B
24 5
.
MHz
fe
T
c
1
1
+
T
C
N
(
)
BE
⋅
73
.
−
8
−
096
.
fe
0
σ
≅
(chips) (5.26)
tM
B
n
C
N
(
)
2
()
2
2
π
0007
.
B
+
84 6
.
E
fe
0
1
24 5
.
MHz
<≤
B
fe
30
MHz
T
c
1
1
+
,
C
N
0837
.
T
0
1
T
c
=
where
R
c
=
5.115 Mchips/s.
To obtain the 1-sigma jitter in meters, multiply (5.26) by 58.610 m/chip. Figure
5.28(a) uses (5.26) in units of meters to compare the modernized M code accuracy
with the P(Y) and C/A codes. Note that the correlator spacing,
D
(in M chips), does
not appear in (5.26), but this approximation is restricted to an
E-L
spacing of 1/4 M
code chips or less. The rule of thumb for M code DLL tracking threshold is identical
to (5.21). M code has a provision for dataless tracking that permits extended
predetection integration times, but this mode also loses 3 dB because every other
code bit is dataless. Reduce (
C
/
N
0
)
dB
by 3 dB before converting to
C
/
N
0
both places in
(5.26) to account for this loss in signal (increase in jitter) when using the M code
time division data multiplexing (TDDM) mode.
5.7 Formation of Pseudorange, Delta Pseudorange, and Integrated
Doppler
Contrary to popular belief, the natural measurements of a GPS receiver are not
pseudorange or delta pseudorange [14]. This section describes the natural measure-
ments of a GPS receiver and describes how they may be converted into pseudorange,
delta pseudorange, and integrated carrier Doppler phase measurements. The natural
measurements are replica code phase and replica carrier Doppler phase (if the GPS
receiver is in phase lock with the satellite carrier signal) or replica carrier Doppler
frequency (if the receiver is in frequency lock with the satellite carrier signal). The
replica code phase can be converted into satellite transmit time, which can be used
to compute the pseudorange measurement. The replica carrier Doppler phase or
frequency can be converted into delta pseudorange. The replica carrier Doppler
phase measurements can also be converted into integrated carrier Doppler phase
measurements used for ultraprecise (differential) static and kinematic surveying or
positioning.
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