Satellite Signal Acquisition, Tracking, and Data Demodulation - Understanding GPS: Principles and Applications - page 194

( C/N 0dB ) = 24 dB-Hz ( C/N 0dB ) = 28 dB-Hz ( C/N 0dB ) = 35 dB-Hz

660

600

Frequency 1,575.42 MHz
Prediction integration time

=

5 ms =

540

480

420

360

300

240

180

120

60

0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8
Noise bandwidth (Hz)

Figure 5.27 Jerk stress thresholds for second-order FLL.

5.6.3 C/A and P(Y) Code Tracking Loop Measurement Errors
When there is no multipath or other distortion of the received signal and no interfer-
ence, the dominant sources of range error in a GPS receiver code tracking loop
(DLL) are thermal noise range error jitter and dynamic stress error. The rule-of-
thumb tracking threshold for the DLL is that the 3-sigma value of the jitter due to all
sources of loop stress must not exceed half of the linear pull-in range of the
discriminator. Therefore, the rule-of-thumb tracking threshold is:

3 σ = 3 σ +

e RD

≤ 2 (5.21)

DLL tDLL

where:

σ tDLL = 1-sigma thermal noise code tracking jitter (chips)

R e = dynamic stress error in the DLL tracking loop (chips)

D = early-to-late correlator spacing (chips)

A general expression for thermal noise code tracking jitter for a noncoherent
DLL discriminator is [11]: