Design and Performance of a Low Frequency Time and Frequency Dissemination Service

A. Helwig, G. Offermans, C. Stout, C. Schue

Abstract:	Synchronization in time and frequency between various geographically separated locations is critically important to a number of industries and applications. Examples include the wired and wireless telecommunication industry, transportation and shipping, banking and financial transactions, utilities and power delivery systems, computer networks, emergency services, and military and homeland security systems. Timing is also a critical component of the U.S. National Position, Navigation, and Timing (PNT) Architecture, the National Airspace System (NAS), and the Intelligent Transportation System (ITS). The Global Positioning System (GPS) has become the sole means in many instances for obtaining these crucial timing signals. GPS provides the necessary timing performance levels and there are a myriad of low-cost, single-purpose GPS receivers on the market. However, GPS, and in fact any Global Navigation Satellite System (GNSS) or Regional Navigation Satellite System (RNSS), is vulnerable to both intentional and unintentional interference, jamming, and spoofing resulting in a range of service degradation from complete outages to sporadic and unpredictable unavailability to incorrect information. To maintain accurate timing in a GPS-denied environment using radio signals, we focus on providing high-power, Low Frequency (LF) solutions. Because of its long propagation range, the ability to measure the arrival time of a pulsed signal with great accuracy, and a well-defined ground wave signal propagation path, an LF solution makes for an attractive terrestrial-based alternative to a low-power, high-frequency, satellite-based signal. Our paper discusses LF system concepts for providing an alternative precise time and frequency source. A pre-production transmitter has been developed and was installed and tested on-air using an existing LF transmission site. The accuracy of the transmitted signal was measured and evaluated. We outline our plans for setting up an R&D test bed for additional on-air testing and present estimated coverage predictions. We also discuss the development and production of our first generation LF timing receiver, which has been undergoing testing and evaluation using on-air signals since March 2011. A timing research and development company is providing independent testing and analysis. Available results demonstrate that our receiver performs to Stratum-1 levels and meets the International Telecommunication Union (ITU) requirements for Primary Reference Clocks (PRC) in telecommunication networks. We present test and measurement setup, results, and conclusions based on our work.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	462 - 508
Cite this article:	Helwig, A., Offermans, G., Stout, C., Schue, C., "Design and Performance of a Low Frequency Time and Frequency Dissemination Service," Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, Newport Beach, CA, January 2012, pp. 462-508.
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