Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

On-Board GPS Clock Monitoring for Signal Integrity



Marc A. Weiss, Pradipta Shome, Ron Beard


Navigation signal integrity is paramount for aviation and safety of life services. Hitherto GPS signal anomaly alerting has been provided primarily by ground based augmentations. Significantly improved navigation signal integrity and quality may be accomplished by On-board detection and correction, within stringent time-to-alert limits. In this way, most GPS signal errors, of which the time keeping system anomalies are the major source, could be eliminated. It would then be possible to provide signal integrity innately from the source constellation to specified service category levels that are enhanced to meet the integrity metrics of hazardously-misleading-information, time-to-alert, availability, continuity and accuracy. The method is to continuously monitor multiple atomic frequency standards with time-difference measurements against each other on-board the satellites, using existing components present in GPS architecture in a method similar to that routinely done in timing labs throughout the world. We focus in this paper on the issue of detecting and alleviating GPS clock anomalies using actual data illustrating frequency breaks in GPS clocks. These frequency breaks are derived from data taken in ground tests of Block IIR and Block IIF clocks. We also include some frequency breaks derived from on-orbit data. Using these data we discuss how on-orbit measurements could be used to detect and mitigate them, while also meeting stringent time-to-alert limits, such as 6 s or faster.
Proceedings Title
Precise Time and Time Interval 2010
Conference Dates
November 15-18, 2010
Conference Location
Reston, VA


Navigation signal integrity, GPS signal anomalies, on-board integrity monitoring, dual-mixer measurement system


Weiss, M. , Shome, P. and Beard, R. (2010), On-Board GPS Clock Monitoring for Signal Integrity, Precise Time and Time Interval 2010, Reston, VA (Accessed April 19, 2024)
Created November 15, 2010, Updated February 19, 2017