Session P4a: T&F Transfer Utilizing Existing and Emerging Communication Systems

Investigation of eLoran Timing Performance Using Multiple Transmitters
P. M. McIntosh, G. Offermans, S. Deane, D. Louviaux, C. Kuehner, and S. Bartlett, UrsaNav, LLC
Location: Seaview A/B
Alternate Number 1

The need for alternative sources of timing for critical infrastructure such as the electric grid, transportation systems, communication networks and financial institutions is clear with the growing number of disruptions to GNSS. These disruptions can lead to potentially significant outages in such infrastructure with serious safety and economic impacts. A nationwide system using eLoran has already been shown to be suitable as backup source for UTC [1] in the event GPS is unavailable. This paper presents an additional case study on timing accuracy and navigation performance using multiple eLoran transmitters in the Western USA. As noted in NIST Technical Note 2187 [2], the timing industry was being encouraged to develop a single-chip eLoran receiver due to the vulnerability of the GPS signal showing that the already well-understood system can act in this role.
UrsaNav currently operates three eLoran/Loran transmitters located in George, WA, Fallon, NV and Havre, MT. Two stations are equipped with a Loran Data Channel (LDC) capability which is used to transmit differential Loran corrections generated by a reference station(s). In this investigation a reference station will be deployed in Boise, ID and connected to each of the stations via the internet allowing the transfer of the measured differential corrections.
The objective of this study is to deploy at least two receivers that can log the timing information and corrections broadcast on the LDCs from multiple transmitters over a period of several days to demonstrate and further confirm that an eLoran timing service can meet a 1us timing requirement. Such receivers could be easily integrated into critical infrastructure using standard protocols such as IRIG-B. Additionally, since multiple transmitters will be employed in the study a navigation accuracy assessment conducted via a drive test will also be included.

Based on the prior work conducted in the USA, it is anticipated that all receivers will perform well under 1us and for those near the reference station timing is expected to be substantially better and into the sub-200 ns range. Using two receivers in close proximity to each other in a multi-day trial will provide data for external variations to be studied as well as confirming performance between units. Part of the study will also include mapping of the additional secondary factor in the surrounding area. This will be used to improve the accuracy of the navigation testing which is expected to be in the range of 50m. The drive route will be tested several times to evaluate repeatable accuracy.
The results of the investigation will confirm that a network of UTC synchronized eLoran transmitter stations can provide wide coverage and accurate timing suitable for use in critical infrastructure and serve as a resilient back-up to GPS. The eLoran network can also be used as a navigation source with an accuracy of 50m or better.
References
[1] Offermans, G., Bartlett, S., and Schue, C. (2017) Providing a Resilient Timing and UTC Service Using eLoran in the United States. J Inst Navig, 64: 339–349. doi: 10.1002/navi.197.
[2] Sherman, J. , Arissian, L. , Brown, R. , Deutch, M. , Donley, E. , Gerginov, V. , Levine, J. , Nelson, G. , Novick, A. , Patla, B. , Parker, T. , Stuhl, B. , Yao, J. , Yates, W. , Lombardi, M. , Zhang, V. and Sutton, D. (2021), A Resilient Architecture for the Realization and Distribution of Coordinated Universal Time to Critical Infrastructure Systems in the United States: Methodologies and Recommendations from the National Institute of Standards and Technology (NIST), Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.2187.