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The Need for a Robust, Precise Time and Frequency Alternative to GNSS



Michael A. Lombardi, Mitch Narins, Per Enge, Ben Peterson, Sherman Lo, Yu-Hsuan Chen, Dennis Akos


Positioning, Navigation, and Timing (PNT) services are key enablers of both essential safety and security applications and economically beneficial capacity and efficiency applications worldwide. Whether users are ground-based, sea-based or in the air, their primary/go-to source of PNT has become a Global Navigation Satellites System (GNSS), with the US Global Positioning System (GPS) being the most widely used. Starting in 2001, with the publishing of the landmark Volpe Transportation Systems Center's GPS Vulnerability Report and leading up to the Department of Homeland Security sponsored GPS Interference Testing in 2012, the world has became much more aware of the vulnerability of GNSS-based services - especially in 2011, as the result of significant interest in using the spectrum directly adjacent to GPS for mobile communications services. This was an important wake up call to the world. But while users of GNSS positioning and navigation services are usually at least cognizant of the source of their services, many users of GPS precise time and frequency are oblivious to both the source of these services and their inherent vulnerability. In fact many time and frequency users are not even aware of how GNSS-provided time is crucial to their operations. The Federal Aviation Administration (FAA) has initiated an Alternate Position, Navigation, and Timing (APNT) program to research various alternative strategies. These strategies are necessary to ensure a safe, secure, and effective transition of the US National Airspace System (NAS) to the Next Generation Air Transportation System (NextGen). While discussing some of the position and navigation aspects of this program, this paper concentrates on the need for a robust time and frequency alternative to GNSS that will support aviation and have the potential to provide robust precise time and frequency services to other user communities. Alternatives strategies to be explored include use of existing NAS ground-based navigat
GPS World


critical infrastructure, GPS, PNT, time accuracy


Lombardi, M. , Narins, M. , Enge, P. , Peterson, B. , Lo, S. , Chen, Y. and Akos, D. (2012), The Need for a Robust, Precise Time and Frequency Alternative to GNSS, GPS World (Accessed June 12, 2024)


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Created November 1, 2012, Updated February 19, 2017