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Design and Performance of Code Tracking for the GPS M Code Signal
September 2000
John W. Betz, The MITRE Corporation
ABSTRACT
The binary offset carrier (BOC) modulation of the new GPS
military ranging signal, the M code signal, provides essential
benefits in many respects. Because of this signal's differences
from conventional ranging signals, M code receiver performance
also benefits from some changes to conventional designs.
Extensive analysis, simulation, and hardware experimentation
have yielded useful insights in receiver design; some of the key
insights are provided in this paper. A discriminator design
approach is described based on theoretically developed S curves
and predictions of code tracking accuracy, and used to configure
the experimental hardware. It is seen that the design approach
must be somewhat different from that used for receivers of C/A
code and Y code signals, in order to take advantage of the
unique characteristics of BOC modulations. Theoretical
expressions are presented that describe performance of
despreading and code tracking the M code signal's BOC(10,5)
modulation using a delay-locked loop with noncoherent early-late
discriminator. Simple algebraic approximations are also provided.
Theoretical predictions of signal-to-noise ratio and code tracking
accuracy in white noise are compared with measured results,
demonstrating the utility of the design approach and close
comparison between theoretical predictions and measurements.
Finally, the effect of front-end bandwidth on receiver performance
is assessed.
Additional Search Keywords
GPS, M Code Signal, Code Tracking, Pseudorange, Delay-Locked Loop
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