GNSS

Signal Structures for
Satellite-Based Navigation:
Past, Present, and Future*
John W. Betz
23 April 2013

*Approved for Public Release; Distribution Unlimited. 13-0908. The contents of this material reflect the views of the author. Neither the Global Positioning Systems Directorate nor the U.S. Air Force makes any warranty or guarantee, or promise, expressed or implied, concerning the content or accuracy of the views expressed herein.

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Early Satnav Signal Design

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Project 621B Contributions to Structure of Original
GPS Signals and Receiver Processing

 Direct sequence spread spectrum/code division multiple access  “Clear/Acquisition” signal
 Techniques for Selective Availability (SA)
 …and differential techniques to remove SA
 Poor crosscorrelation performance of short spreading codes used for GPS C/A code signal
 Carrier-aided code tracking
 DLL tracking error model for wideband processing of
BPSK-R signals in white noise
 6 dB lower tracking threshold of coherent phase locked loop carrier tracking over Costas loop tracking
 “Pseudocoherent carrier tracking” and data wiping
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Project 621B Contributions Not Included in
Structure of Original GPS Signals

 Powerful error correction codes, both block and

convolutional
 Separate pilot (“unmodulated carrier component’) and data components
 Phase-multiplexing and time-multiplexing of different signals or components onto the same carrier

© 2012 The MITRE Corporation. All rights reserved.

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Satnav Circa 10 Years Ago

 Two global systems: GPS and GLONASS
– Fewer than 40 total operational satellites
– Each satellite transmitted three signals, only one for civil use
 SBAS emerging; none fully operational

© 2012 The MITRE Corporation. All rights reserved.

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Satnav Today

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