Signals of Opportunity as an Augmentation or Alternative to GNSS for Critical Timing Applications

Lisa Perdue, John Fischer, Ronald Dries

Abstract:	Though GNSS signals provide very precise timing to UTC, they all have two major drawbacks – a very weak signal that is easily jammed and cannot be received well indoors, as well as no authentication mechanism, which allows it to be easily spoofed. In this paper we explore using alternative signals as either a standalone timing reference or as an augmentation to GNSS as a reference. Two possible alternative signals are the eLoran signal and the new Iridium STL signal. Though both provide a less accurate timing signal than GNSS, their higher power and diverse nature offer a robust alternative or supplement to GNSS. Depending on the signal availability, we will analyze and test them for use with a time and frequency server to provide timing signals such as 1PPS, NTP, and PTP. The GNSS and alternative references are monitored and compared to the holdover oscillator to perform real time analysis on both references, even if the primary reference is lost. Two configurations are tested; GNSS used as a primary reference and the alternative is used as a backup; and the alternative is used as the primary reference. Various effects that would degrade GNSS based timing such as GNSS L1 Band interference, GPS NAV data UTC timing errors, and GPS spoofing are applied to both setups (where applicable). Results on the 1PPS accuracy generated by the time and frequency server will be presented.
Published in:	Proceedings of the 48th Annual Precise Time and Time Interval Systems and Applications Meeting January 30 - 2, 2017 Hyatt Regency Monterey Monterey, California
Pages:	171 - 176
Cite this article:	Perdue, Lisa, Fischer, John, Dries, Ronald, "Signals of Opportunity as an Augmentation or Alternative to GNSS for Critical Timing Applications," Proceedings of the 48th Annual Precise Time and Time Interval Systems and Applications Meeting, Monterey, California, January 2017, pp. 171-176. https://doi.org/10.33012/2017.14988
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