GNSS has bad days, too

April 27, 2016  - By
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(courtesy Ursanav)

(courtesy UrsaNav)

“Even the best technology has a bad day,” Charles Schue told the New York Stock Exchange (NYSE), which relies very heavily on the best technology to keep the world’s financial edifice afloat. Vulnerabilities in the stock market were pointed up during a demonstration on April 19, showcasing how one positioning, navigation and timing (PNT) system can cover the chinks in another. Respectively, eLoran and GPS in this case.

Schue is CEO of UrsaNav, a company that has been developing complementary PNT solutions, specifically the high-power, low-frequency (LF), ground-wave technology that is eLoran, which UrsaNav calls “the most reliable, scalable, and future-proof available.” Schue spoke at the NYSE along with representatives from the Department of Homeland Security (DHS), the U.S. Coast Guard, Juniper Networks and Harris Corporation.

“2014 was a very bad year for GNSS,” Schue continued, citing the GLONASS full-system outage for 11 hours and Galileo’s wrong-orbit launch of two satellites. “This year, GPS, the gold standard, had an ‘oops’ and slipped from gold to silver, when one satellite kind of wigged out, a 13.7 microsecond error that contaminated 15 other satellites.” He ran a simulation that showed how, at one point, six GPS satellites were communicating bad timing to the Eastern seaboard, where the NYSE is located.

2016 has also seen renewed GPS jamming from North Korea.

The stock exchange, along with other global financial markets, relies on microsecond timing to properly execute all transactions. The U.S. air traffic management system likewise relies on high-precision aspects of GPS that are vulnerable to interference, jamming, and even occasional system failure. Many other industries, telecommunications principally among them, are also building infrastructures and applications that rely on GPS for precise timing, thus making them vulnerable as well.

One Back-Up Transmitter in Place

An eLoran transmitter in Wildwood, New Jersey, relies on three primary reference standards, three atomic clocks, just as each GPS satellite carries three or four atomic clocks. “The signals coming from space, the signals coming from ground, they’re very similar.” ELoran also has monitoring and control sites on the ground, just like the satellite system; it has differential reference stations, and of course eLoran receivers, playing the same role as GPS receivers.

Schue asserted that the cost of launching one GPS satellite into space would fund an eLoran system for the continental United States for 20 years. Also, that a lot of industries in addition to the financial community are building infrastructures and applications that rely on GPS for precise timing, and so are equally vulnerable.

The eLoran demonstration showed how the Wildwood station sent a timing signal 130 miles to the NYSE, deep within several urban canyons and enveloped in several layers of concrete, steel and glass. A GPS receiver in the room did not pick up anything. The eLoran receiver showed precise time, to the standard of NYSE requirements.

Equipment utilized included a Spectracom SecureSync providing time to the network, once it received it from eLoran.

On a screen display showing plus or minus 500 nanoseconds relative to Coordinated Universal Time, “that red line is us receiving eLoran timing at that antenna, 130 miles away, through the urban canyons, inside this building, right now at minus 14 nanoseconds.” The eLoran equipment transmitted and received two signals, with a data channel on one of the signals. “We could put the data channel on both signals, and we could put multiple data channels on both on there as well.”

Photo: UrsaNav Photo: UrsaNav

Schue said another demo inside a downtown Boston hotel, 305 miles from the New Jersey transmitter, obtained 83-nanosecond accuracy. A 2015 test to an outdoor receiver in Bangor, Maine, 500 miles from the transmitter, logged 68-nanosecond accuracy.

Plus or minus 100 nanoseconds is the typical GPS performance. “We can do far better, and GPS often does far better than that.”

Initial operating capability for a wide-area eLoran service providing precise time for the continental United States would require four transmitter sites across the middle of the country. The corporate and government partners hope to use some repurposed Loran-C assets and turn them into eLoran stations. Wildwood is transmitting at 360 kilowatts; if transmitting at 1 million watts, or 1 megawatt, the signal could penetrate even further inside buildings. The cost difference between the two powers of transmitter is not significant.

Bringing six more continental eLoran transmitter sites online, for a total of ten, would add a back-up positioning capability in addition to timing. “This is very important, because with positioning, you get mobile time — a co-primary solution for position, navigation, and timing.”

Using a differential receiver would yield even better local-area accuracy for about 35 miles around a selected site, for high-priority locations. Such a higher-precision system for the nation’s top 50 metropolitan areas, top 50 airports, and top 50 harbors could be accomplished with 71 differential sites.

Concurrence from Government and Other Industry Partners

Spokespersons from the DHS, Coast Guard, Juniper Networks and Harris Corporation preceded Schue at the NYSE presentation, all giving similar perspectives on U.S. vulnerability in many aspects, due to reliance on GPS as a sole, unsupported source of precision PNT.  “Of the 16 critical infrastructure / key resource sectors in the United States, 15 use GPS for timing. GPS timing is deemed essential for 11 of these sectors,” stressed DHS.

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About the Author:


Alan Cameron is the former editor-at-large of GPS World magazine.

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