Tag: eLoran

10 questions on eLoran

Photo: UrsaNav

A PNT expert suggested that my piece titled “Opposite and Complementary: eLoran is part of the solution to GNSS vulnerability” in our November 2021 issue could be augmented with information not currently available on the proposed eLoran capability. This expert also questioned my statement that eLoran “does not have any common failure modes with GNSS” and pointed to potential common threats such as from cyberattacks, physical attacks, and space weather.

Matteo Luccio

I welcome such feedback on the contents of these pages — and agree that in this case some hard questions are warranted. So, in the interest of further exploring the use of eLoran, I pose some questions, hoping that its advocates will provide answers. I know that at least some of them will not shy away from this challenge.

Please note that I wish to keep the discussion on positioning, not the easier question of timing, because that was the primary focus of my article. I also wish to address long-term outages (weeks or months), which would have a greater impact on the United States.

Some of these questions have been addressed, at least in part, in various studies and proposals, most of them now more than a decade old. So, it would be helpful to update those answers and consolidate them in the pages of this magazine.

1. Accuracy specifics. While my November article stated that eLoran would have a two-dimensional accuracy of “better than 20 meters, and in many cases, better than 10 meters,” is that RMS, 95%, or some other statistic?

2. Performance standard. GPS provides a commitment to users in a published performance standard. What specific measures of positioning accuracy, integrity and continuity would you recommend the proposed eLoran system be committed to provide (using the architecture described in the answer to Question 6)?

3. Coverage. Would you recommend this eLoran positioning performance hold for the entire United States (including Alaska, Hawaii, Puerto Rico and other territories), only for the “lower 48” states, or only parts of these 48 states?

4. Current users. By number of users, the predominant common current civil uses of GNSS for positioning are consumer devices (mostly cellphones). By contribution to the U.S. economy, the predominant uses are high-precision applications. For what fraction of these uses would eLoran positioning be adequate? Could an eLoran receiver and antenna fit in today’s consumer devices?

5. Future uses. Emerging civil uses of GPS for positioning include autonomous ground and air vehicles, navigation to space and in space, and lane-accurate car navigation. Which of these could be served by eLoran?

6. Architecture. To maintain accuracy during a prolonged GPS outage, eLoran would require reference stations to calibrate time-varying propagation errors, as well as a certain number of transmitters for good nationwide geometry and for redundancy, ensuring service even if a transmitter is attacked or is taken off-line for maintenance. What architecture would you recommend to achieve this?

7. Infrastructure cost. What would be the cost of installing the required transmitters, power supplies, reference stations, communication links and control system for the architecture described in the answer to Question 6? Can you reference a recent and independent estimate? To a ballpark figure, what cost fixed-price contract would you accept to implement it? Similarly, what would be the annual costs for operating and maintaining this infrastructure?

8. Impact. eLoran transmitters are large and high-power. Providing positioning across the United States could require building some of them from scratch or significantly reconstructing old Loran sites. What issues — such as environmental, aviation safety and security — would this raise, and how would you recommend they be addressed?

9. Receivers. Assuming all the above were achieved, it would accomplish nothing unless eLoran receivers were widely purchased, installed and used. How much would that cost? Who would pay? Should we assume that “if we build it, they will come”?

10. Alternatives. Given the widespread development of other positioning technologies over the past decade, much has changed since the earlier recommendations for eLoran. How do we know that eLoran is the right investment — or even a needed part of the solution or needed system in a system of systems — for the future of U.S. PNT?

Common threats to GNSS and eLoran could include the following:

1. Cyber attacks. Given that GPS’s OCX is said to be the most cybersecure system built by the U.S. Department of Defense, how would eLoran’s control system be even more cybersecure than OCX, to avoid a common cyber-vulnerability?

2. Physical attacks. Given concerns about possible physical attacks on GPS satellites, which move at multiple km/sec 20,000 km from Earth, would it not be easier to physically attack eLoran transmitters, which are stationary, terrestrial, in remote locations, and hundreds of feet tall and require massive power sources?

3. Space weather. GPS is potentially vulnerable to severe space weather that could damage satellites or temporarily hinder signal propagation from space to Earth. However, severe space weather could also damage the power grid upon which megawatt eLoran transmitters rely. How would eLoran service be protected from the effects of severe space weather, such as a Carrington Event?

Send me your thoughts at the e-mail address below, with “eLoran” in the subject line.

Matteo Lucio | Editor-in-Chief
[email protected]

January 21, 2022
eLoran: Part of the solution to GNSS vulnerability

Opposite and complementary

Though marvelous, GNSS are also highly vulnerable. eLoran, which has no common failure modes with GNSS, could provide continuity of essential timing and navigation services in a crisis.

GPS fits Arthur C. Clarke’s famous third law: “Any sufficiently advanced technology is indistinguishable from magic.” Yet, it also has several well-known vulnerabilities — including unintentional and intentional RF interference (the latter known as jamming), spoofing, solar flares, the accidental destruction of satellites by space debris and their intentional destruction in an act of war, system anomalies and failures, and problems with satellite launches and the ground segment.

Over the past two decades, many reports have been written on these vulnerabilities, and calls have been made to fund and develop complementary positioning, navigation and timing (PNT) systems. In recent years, as vast sectors of our economy and many of our daily activities have become dependent on GNSS, these calls have intensified.

A key component of any continent-wide complementary PNT would be a low-frequency, very high power, ground-based system, because it does not have any common failure modes with GNSS, which are high-frequency, very low power and space-based. Such a system already exists, in principle: it is Loran, which was the international PNT gold standard for almost 50 years prior to GPS becoming operational in 1995. At that point, Loran-C was scheduled for termination at the end of 2000.

However, beginning in 1997, Congress provided more than $160M to convert the U.S. portion of the North American Loran-C service to enhanced Loran (eLoran). In 2010, when the U.S. Loran-C service ended, its modernized and upgraded successor was almost completely built out in the continental United States and Alaska. During the following five years, Canada, Japan, and European countries followed the United States’ lead in terminating their Loran-C programs.

Today, however, eLoran is one of several PNT systems proposed as a backup for GPS.

The National Timing Resilience and Security Act of 2018 required the Secretary of the U.S. Department of Transportation (DOT) to “provide for the establishment, sustainment, and operation of a land-based, resilient, and reliable alternative timing system” as a backup to GPS. In January 2020, the DOT awarded contracts to 11 companies to demonstrate their technologies’ ability to act as a backup for GPS. Of these companies, two were working on eLoran projects.

Technical advisers to the federal PNT Executive Committee have been advocating and recommending that the government implement eLoran for the past 11 years. Yet, while the U.S. government announced in 2008, and again in 2015, its intention to build an eLoran system, it has not done so yet.

Not Your Grandfather’s Loran

In the 1980s, I used Loran-C to navigate on sailing trips off the U.S. East Coast. It had an accuracy of a few hundred feet and required interpreting blue, magenta, black and green lines that were overprinted on nautical charts. The system was a modernized version, launched in 1958, of a radio navigation system first deployed for U.S. ship convoys crossing the Atlantic during World War II. Its repeatability was greater than its accuracy: lobster trappers could rely on it to return to the same spots where they had been successful before, though they may have had some offset from the actual latitude and longitude.

By contrast, eLoran has an accuracy of better than 20 meters, and in many cases, better than 10 meters. It was developed by the U.S. and British governments, in collaboration with various industry and academic groups, to provide coverage over extremely wide areas using a part of the RF spectrum protected worldwide. Unlike GNSS, eLoran can penetrate to some degree indoors, under very thick canopy, underwater and underground, and it is exceptionally hard to disrupt, jam or spoof.

Unlike Loran-C, eLoran is synchronized to UTC and includes one or more data channels for low-rate data messaging, added integrity, differential corrections, navigation messages, and other communications. Additionally, modern Loran receivers allow users to mix and match signals from all eLoran transmitters and GNSS satellites in view.

Finally, eLoran can be used for integrity monitoring of GPS — and vice versa. “Think of a resiliency triad, consisting of GNSS (global), eLoran (continental), and an inertial measurement unit, a precise clock, or a fiber connection,” said Charles A. Schue, CEO of UrsaNav. “It is extremely difficult to jam or spoof all three sources at the same time, in the same direction, and to the same amount.”

For the eLoran system to cover the contiguous United States, between four and six transmission sites could provide overlapping timing coverage, and 18 transmission sites could provide overlapping positioning and navigation.
U.S. Developments

The INVEST in America Act authorizes $157 million for the Department of Homeland Security to conduct research in five separate areas, one of which is positioning, navigation and timing resiliency; however, none of this money is for eLoran per se. The regular DOT appropriation for next year has $17 million for PNT-related research, $10 million of which is for “GPS Backup/Complementary PNT Technologies Research.” However, neither of these bills has yet been finalized, let alone passed into law, so they may change.

“These are very complex systems, with five- to seven-year sales cycles,” pointed out Schue, “and the process is even slower now due to the pandemic. With adequate funding, eLoran signals could start becoming available in the contiguous United States within a year of a service contract being signed. We should recall that GPS — as, indeed all of the GNSS — was brought online gradually as satellites were developed and launched into space. There should be no expectation that any other nationwide system would be available at the flip of a switch instead of through gradual implementation.”

the former Loran-C transmission antenna at Værlandet, Norway. (Photo: UrsaNav)

International Developments

Loran-C and eLoran operate internationally. Saudi Arabia, China and Russia continue to operate Loran-C or Chayka systems. In October 2020, a Chinese paper described how the nation is expanding Loran to its west to cover the whole country to protect itself from disruptions of space-based services. A previously published report made it clear that they are upgrading or have upgraded from Loran-C to eLoran. South Korea has an ongoing project to upgrade its Loran-C to eLoran. It also seems the project will ensure that the South Korean system will be useable on its own, even if the Russian and Chinese systems with which it normally cooperates are not available for some reason, according to Dana Goward, president of the Resilient Navigation and Timing Foundation.

The United Kingdom is still committed to eLoran, and operates one station that has been used as an alternative time reference to GNSS. “However, as the sole station still transmitting in that area of Europe it’s of no use for positioning,” said Nunzio Gambale, CEO of Locata Corporation. “Unfortunately, the EU’s shutdown of their old Loran sites seems to have been completed, and no EU-based Loran sites remain operational. Their actions leave scant hope for Loran’s resurrection any time soon as an alternative to GNSS positioning in Europe. That’s a shame, because eLoran has beneficial PNT characteristics that other alternate technologies will struggle to replicate.”

A deck officer on a ship takes a relative bearing using a pelorus. Loran-C was developed in large part for maritime navigation. (Photo: aytugaskin/iStock/Getty Images Plus/Getty Images)

Advocacy

“There is fairly good agreement across the PNT community that there is no sole solution [to GPS vulnerabilities],” Schue said. “It needs to be a system of systems.”

The PNT community, he said, is working with Congress and the administration “to move ahead with actual RFPs to start the contracting process — instead of continuing to admire the problem.” UrsaNav, NextNav, OPNT and other companies and organizations “are working together as best as we can to tell the federal government that we all believe in a system-of-systems approach and that there ought to be some tangible forward motion.”

While DOT has the lead on providing PNT resiliency, it and the departments of Defense and Homeland Security need to cooperate on this, Schue argued. “Many, if not all, of the other departments — such as Commerce, Energy, State, Interior and Agriculture — also have a stake.”

GNSS will remain for a reason. “Unless a new national terrestrial PNT system moves the game forward for many markets, it’s just far too easy to remain with the GNSS system, which is fundamentally free,” Gambale said. “That’s a really difficult price point to compete with, unless you’re delivering significant new value to the market.”

The time to act is now. “This issue has been studied to death for more than 20 years,” Goward said. “There are technologies ready to deploy. It is time for action. A failure of national PNT will be catastrophic.”

November 3, 2021
UrsaNav trials eLoran as GNSS backup with ADVA grandmaster clock

Successful eLoran field trial using ADVA’s OSA 5420 Series demonstrates same accuracy and stability as GPS with much-improved resilience

UrsaNav and ADVA have conducted an enhanced long-range navigation (eLoran) field trial using UrsaNav’s eLoran receiver and ADVA’s Oscilloquartz grandmaster clock technology. The successful demonstration shows that eLoran offers a robust and reliable backup for GPS and other GNSS, and could be used to provide an assured position, navigation and timing (PNT) service.

The trial follows U.S. PNT Executive Order 13905 aimed at strengthening national resilience through PNT services, including protecting critical infrastructure such as electrical power grid and communication networks from rising cyber threats. By harnessing ADVA’s flexible OSA 5420 series, designed with assured PNT (A-PNT) technology, UrsaNav has shown that eLoran can provide a new layer of protection and significantly boost timing resilience and security.

“The success of this field trial demonstrates how eLoran, as part of ADVA’s assured PNT solution, can serve as a crucial backup for GPS,” said Charles Schue, CEO, UrsaNav. “We have shown how our technology enables ADVA’s grandmaster clock to receive UTC timing from the eLoran system for a period of several days with the same accuracy and stability as GPS. Of course, this capability is extensible to other GNSS as well. eLoran is far less vulnerable to unintentional jamming and spoofing disruptions or intentional attacks, thereby delivering nanosecond precision with even more resilience.”

“By partnering with ADVA, we’ve been able to show that our eLoran receiver interoperates with the best network timing toolkit available,” Schue said. “The OSA 5420 Series is a great product — highly efficient and easy to operate. Together with ADVA, we’re paving the way for tomorrow’s more robust assured PNT synchronization architecture. Now that UrsaNav has demonstrated the power of our OSA 5420 Series to utilize eLoran in the event of outages, we have another very important tool to ensure the quality and availability of time-sensitive services.”

UrsaNav’s latest trial used the OSA 5420 series grandmaster clock with built-in GNSS receiver. Timing stability from GPS was measured for several days. This was then replaced with eLoran for the same period with no loss of stability.

The test was conducted indoors where GNSS signals are not usually available, potentially extending the availability of precise UTC timing to many more environments.

“Commercially available GNSS jammers and spoofers are easy and cheap for attackers to acquire,” explained Nir Laufer, VP, product line management, Oscilloquartz, ADVA. “That’s part of the reason why we’re seeing a growing number of incidents across the world of blocked or misleading signals. If power utilities, enterprises, service providers and governments continue to rely on GNSS alone, it’s only a matter of time before the consequences become very serious. That’s why we’re committed to tackling GNSS vulnerabilities with advanced technologies like our ePRTC offering, cesium atomic clocks and our optical timing channel solution. Now that UrsaNav has demonstrated the power of our OSA 5420 series to utilize eLoran in the event of outages, we have another very important tool to ensure the quality and availability of time-sensitive services.”

The demo showed how ADVA’s synchronization technology enables protection for critical infrastructure that needs ultra-reliable aPNT solutions. (Photo: Business Wire)

July 27, 2021
Prince Philip championed GPS as Master of Trinity House

The official portrait of HRH The Duke of Edinburgh as Master of Trinity House. (Image: Trinity House)

Prince Philip, technology advocate, championed both GPS and alternative navigation methods during his lifetime.

Prince Philip — the Duke of Edinburgh and husband of Queen Elizabeth II of the United Kingdom — died on April 9 at Windsor Castle in England. He was 99. His funeral will take place April 17.

As the Master of Trinity House, Prince Philip was the U.K.’s authority for lighthouses in England, Wales, the Channel Islands and Gibraltar. Trinity House is also responsible for the provision and maintenance of other navigational aids, such as light vessels, buoys and maritime radio/satellite communication systems.

In its extensive coverage of his death, the BBC aired a radio program in its World Service that mentioned the prince’s knowledge and concern about GPS. “As Master of Trinity House, he was infuriated that people didn’t understand what would happen if GPS were shut down,” said the narrator.

Real Admiral Sir Jeremy de Halpert was Prince Philip’s deputy master at Trinity House. “ Prince Philip from the very beginning understood that it was a single point of failure,” de Halpert told the BBC. “GPS can be jammed very easily… He encouraged us to move ahead and make sure the country has a failsafe backup, which we have done, and it is now operational,” he said.

Below is the section of the documentary where the prince’s support for GPS and a GPS backup is discussed.

GPS World thanks Innovation editor Richard Langley for sharing the material.

April 15, 2021
University revises PNT backgrounder In response to concerns

Beyond GPS report. Check out the report here. (Cover: NSI)

George Mason University has revised a briefing paper on positioning, navigation and timing (PNT) in response to concerns about its accuracy.

The university’s National Security Institute “NSI Backgrounder — Beyond GPS: The Frontier of Positioning, Navigation, and Timing Services” was first issued on Dec. 2. Some staff on Capitol Hill and members of industry soon had concerns about several of its assertions.

Responding to letters from industry, National Security Institute (NSI) Executive Director and Professor Jamil Jaffer said he determined that three of the issues raised, while not fatal to the document, warranted clarification.

ELoran callout. The first was a statement in the backgrounder that the National Timing Resilience and Security Act (NTRSA) “specifies 13 technical requirements for a GPS backup, which essentially define the eLoran system.”

This was a concern to some on the hill as Congress is generally reluctant to specify solutions. Legislators prefer to specify outcomes and then defer to the executive branch on how to make them happen.

Members of industry pointed out that government systems like WWVB and the low-frequency portion of DARPA’s STOIC program, as well as commercial systems like NextNav and Locata, could meet or be adapted to meet the NTRSA requirement.

The revised backgrounder says the NTRSA “specifies 13 mainly technical requirements for a GPS back-up, which align closely with the capabilities of the eLoran system. Other systems may meet the Act’s requirements to varying degrees.”

Multiple technologies. The revised backgrounder also corrects a statement that the NTRSA requires the Department of Transportation to establish an eLoran system. It now says “a system that complies with the Act, and DOT may pursue multiple technologies in implementing the Act.”

Department officials had previously said they were taking a system-of-systems approach and expected to employ multiple technologies. Subsequently, a DOT report was released that documents the need for several diverse systems. It lists transmissions using low frequency (eLoran, STOIC), ultra high frequency (NextNav, Locata) and L-band from space (GPS, Satelles). It also says the terrestrial transmitters should be interconnected by fiber.

Public-private partnership. A third correction was made in the document to reflect how the Congressional Budget Office regarded the possibility of using a public-private partnership in previously proposed legislation.

Members of industry also expressed concern that one of the authors of the document serves on the advisory board for Satelles Inc. and that this was not disclosed in the paper. The backgrounder appeared on the Satelles website the same day it was published.

The university concluded that such disclosure was not necessary as the paper said the author “provides advisory services to industry, including in the PNT area.” At the author’s request, though, his profile on NSI’s webpage will be updated to show his relationship with Satelles.

January 26, 2021
First Fix: National timing architecture needed now

Dana Goward, President, Resilient PNT Foundation

The Empire State Building sits atop a massive and solid foundation that hardly anyone ever sees. Above ground it has 2.8 million square feet of offices and hundreds of businesses. It houses 15,000 workers. Yet it would all come crashing down if the underlying and unseen foundation weren’t incredibly strong and dependable.

Timing is the unseen foundation of every networked technology, digital broadcast, financial transaction, electrical grid management and of most navigation systems, just to name a few applications. Yet, as GPS World readers know, signals from our dominant source of timing — GPS — are very faint and easily disrupted.

Short term, localized disruptions happen all the time, and many systems have adapted. A delivery driver using a jammer to hide from his boss is unlikely to disrupt a cell base station as he passes by, for example.

Photo: Georgijevic/E+/Getty Images

But more serious threats are out there. More and more hobbyists are finding ways to spoof receivers. Every few decades the sun flares strongly enough to fry satellites or charge the ionosphere. And because there are so few alternatives, GPS and other GNSS have become huge, tempting targets for adversary nations, terrorists, and sophisticated hackers.
Instead of Manhattan bedrock, our timing foundation is sometimes more like shifting sands.

Systems engineering tells us that, if something is essential, there ought to be two, three or more independent ways of receiving it. Most aircraft, for example, have two or three systems powering the flight controls — because controlled flight is important!
The white paper “A Resilient National Timing Architecture” outlines how the United States can leverage existing infrastructure and provide all citizens two, and many of them three, independent paths to coordinated universal time (UTC).

It proposes a national timing back- bone of mature technologies with very different failure modes — GNSS, eLoran and fiber. This combination will provide rock-solid timing at the 500 ns or better level of accuracy relative to UTC everywhere across the nation, and at 100 ns or better in major metro areas. Users accessing two or more systems would be nearly bulletproof to timing service disruptions.

The National Timing Resilience and Security Act of 2018 mandated a terrestrial system to back up GPS timing. Our white paper provides a path forward.

Complying with the law while benefiting current and future technologies should be sufficient motivation. If it isn’t, we must also realize that not acting on this will continue to place us behind other nations such as the United Kingdom, South Korea, Russia and China — all of whom are actively reinforcing their national timing systems.

The task will not be a simple one. Yet America was able to overcome the expense and difficulties of building GPS, at the time the world’s most refined and complex technology, and put it in space. By comparison, establishing a resilient national timing architecture using existing technology in our homeland would be child’s play.

Timing is essential. It is infrastructure for our infrastructure. If our national timing is weak, so is everything that is built upon it.

We will profit from ensuring our timing is as strong, resilient, and easily accessed as possible.

And we will suffer if it is neglected.

December 14, 2020
South Korea partners with broadcaster on eLoran and 10-cm GPS

“Fourth industrial revolution and advanced technology” for all sectors

The government of South Korea signed an agreement on Oct. 28 for its new eLoran system to support digital radio and television broadcasts. The Memorandum of Understanding (MOU) also provides for the government to use commercial radio and television infrastructure to transmit GNSS integrity and correction information.

Titled “Utilization of Next Generation Maritime PNT Information,” the MOU is between the Ministry of Oceans and Fisheries and the public broadcaster Munhwa Broadcasting Corporation (MBC).

Image: Ministry of Oceans and Fisheries, South Korea

Timing signals from GPS/GNSS are often used to enable digital broadcasts. These signals have been regularly blocked by jamming from North Korea in the past. MBC officials report that using eLoran timing signals will allow the company to continue operations when signals from space are not available or reliable for whatever reason.

Also in the agreement is the government’s use of MBC’s network to transmit GNSS integrity and correction information as part of a project to enable 10 cm location accuracy.

Both of these efforts appear to be part of a “maritime PNT system of systems” approach being pursued by South Korea to ensure maritime navigation, with spill-over benefits to other sectors. Core technologies will be eLoran, VEDS-R mode, and differential GNSS. This is very similar to the “hybrid system” called for by the European Space Agency-sponsored MarRINav project in the United Kingdom.

While the MOU and efforts discussed are nominally maritime focused, the South Korean government’s intent is to benefit and support all sectors. According to the press release about the MOU signing, the ministry will promote the system “so that eLoran, the core technology of the era of the fourth industrial revolution, and next-generation advanced marine PNT technology can be actively used in a wider variety of fields.”

eLoran services will be available in South Korea next year. Two existing Loran-C transmitter sites will have been upgraded to the eLoran standard, and one new eLoran transmitter site added. Two differential eLoran correction stations have already been deployed as part of the eLoran testbed.

South Korea has been studying upgrade of its Loran-C network to the more automated and accurate eLoran standard since 2016. The government describes eLoran as an “advanced terrestrial navigation system that can stably provide PNT services without radio disturbance by using a terrestrial transmission tower rather than a satellite.”

UrsaNav of Billerica, Massachusetts, was awarded a contract in July to supply and install a testbed eLoran system near Inchon, South Korea. Initial tests were completed in September, according to the government press release. “We conducted a performance demonstration experiment that actually compared the performance of the GPS receiver and the GPS-eLoran integrated receiver by transmitting jamming and spoofing signals to the ship. It was confirmed that the GPS-eLoran integrated receiver displayed the correct location while the GPS receiver did not.” Additional testing should finish within the next few months.

Current users of Loran-C signals in Korea will be unaffected by the transition from Loran-C to eLoran. Upgraded receivers will be required, though, if users want to take advantage of eLoran’s improved accuracy and other features.

Development of the system to transmit GNSS integrity and correction information to enable 10-cm accuracy is not as far along. The government has said it expects services to be available in 2023.

At the signing ceremony, Minister of Oceans and Fisheries Moon Sung-Hyuk said “eLoran in the era of the fourth industrial revolution, and next generation advanced maritime PNT technology are the nation’s core infrastructure resources that can be used throughout the industry. It is expected that the public will be able to use PNT services more stably by actively sharing the infrastructure and technology we have.”

November 23, 2020
Precise time for all: Paper calls for resilient national timing

Image: RNT Foundation

A new white paper sponsored by the Resilient Navigation and Timing Foundation (RNT Foundation) discusses the need and implementation of a reliable and resilient national timing architecture that will include space-based assets. This system-of-systems architecture — GNSS, terrestrial eLoran broadcasts and fiber — is essential to underpin today’s technology and support development of tomorrow’s systems, according to the executive summary of A Resilient National Timing Architecture.

“Everyone in the developed world needs precise time, all the time, whether they know it or not,” said Marc Weiss, one of the paper’s authors and an internationally recognized expert on timing and synchronization. “It is a foundation of every networked technology, digital broadcast, and most navigation systems, to name just a few critical uses.”

Three Paths to Precise Time

“Precise time is so important that everyone needs at least three independent methods of getting it. So, if one, or even two, fail it is not a national disaster,” said Pat Diamond, co-author of the paper. “Our proposed architecture calls for precise time via GNSS, terrestrial eLoran broadcasts and fiber.” Diamond is a long-time network designer, developer, and entrepreneur. He is also a member of the U.S. National Space-Based Positioning, Navigation, and Timing Advisory Board.

Diamond also pointed out that these three methods should be the backbone for timing distribution in the U.S., but won’t be the only methods. “What we are describing is a baseline architecture that will be added to,” he said. “It is a starting point. We envision in the paper additional distribution methods like time from other satellites, user clocks, and so on, all being part of the mix.”

Government Leadership

The U.S. federal government has a leadership interest and responsibility in all of this, according to the paper. Nations have long recognized the military and commercial advantages of determining and distributing precise time. Great Britain’s Longitude Act of 1714 was really about developing a chronometer to support safe navigation of Royal Navy and British merchant fleet. In the United States, the U.S. Naval Observatory has been keeping and distributing a national time scale time since 1845.

“Just because the feds have an important leadership role, doesn’t mean they have to build and own a bunch of systems,” said Dana A. Goward, the paper’s third co-author and executive director of the RNT Foundation. “There are a variety of ways these systems can be established. Public-private-partnerships, subscription contracts like the FAA did with their air traffic ADS-B system, and cooperative agreements are all examples. As we move forward with 5G telecommunications and perhaps even timing and navigation, it will be increasingly important to have a rock solid timing infrastructure to support it all.”

The National Timing Resilience and Security Act of 2018 requires the U.S. Department of Transportation to establish a terrestrial system to backup GPS timing services by December of this year. While the department does not appear to be on track to meet that goal, it completed a technology demonstration program for GPS backup technologies earlier this year. Two companies demonstrated timing distribution by fiber. Another two demonstrated eLoran.

Many Pieces Already in Place

One of the benefits of the proposed architecture is that much of what is called for is already in place, according to the paper. “We already have fiber networks, NAPs (network access points). eLoran is mature and has been deployed by the Brits. And the U.S. government owns enough former Loran-C sites to establish a nationwide eLoran network,” Diamond said. “All we need is a bit of money and some engineering work to put this all together.”

October 19, 2020
UrsaNav installs eLoran testbed in South Korea

The eLoran transmission site at Incheon, South Korea. (Photo: UrsaNav)

South Korean is in the early stages of evaluating its eLoran system, but great results are expected based on the UrsaNav-supplied station in Incheon.

In August 2018, the Korea Research Institute of Ships and Oceans Engineering (KRISO) awarded UrsaNav, through its agent Dong Kang M-Tech, a contract to supply and install an eLoran transmitter testbed system in South Korea. UrsaNav is the exclusive, worldwide distributor of Nautel’s NL Series transmitters, provided eLoran transmitter technology, as well as timing, control and differential reference station equipment for the testbed. The contract represented the first phase in a broader program to upgrade Korea’s Loran-C stations to be the foundation of a sovereign Enhanced Loran (eLoran) positioning, navigation and timing (PNT) service.

“The Republic of Korea recognizes the challenges associated with relying solely on space-based signals, the relative ease with which those signals can be jammed or spoofed, and the necessity to provide trusted time and trusted position to its citizens and critical national infrastructure,” said Charles Schue, CEO of UrsaNav.

The 35-meter eLoran transmit antenna in Incheon. (Photo: UrsaNav)

Many critical infrastructure sectors rely on accurate time and position, including maritime, aviation, electrical distribution, telecommunications, finance/banking, and digital broadcast. A complementary PNT (CPNT) service provides continuity of operations through alternative and diverse timing and positioning information. CPNT is a vital element in ensuring national security and assuring trusted time and position.

KRISO, in conjunction with the Korea Ministry of Oceans and Fisheries (MOF), is developing an Initial Operating Capability eLoran system to provide complementary PNT services as a part of its Electronic Navigation (E-Navigation) mission. KRISO selected UrsaNav Inc. as its prime eLoran systems contractor through a competitive tender offer.

UrsaNav provided, installed and tested an eLoran transmission system at a temporary location near Incheon, South Korea, in November 2019. The company also provided ancillary equipment for Additional Secondary Factor (ASF) map measurements and map-generation software, as well as differential reference station equipment to KRISO. Because of land size restrictions at the temporary site at Incheon, the eLoran transmission system was paired to a small footprint 35-meter top-loaded monopole antenna.

In addition to the equipment provided by UrsaNav, MOF separately contracted a local Korean firm to provide an interim GPS receiver set to synchronize the existing Loran-C sites at Pohang and Kwangju to UTC.

UN-1300 eLoran transmission equipment. (Photo: UrsaNav)

KRISO is in the early stages of measuring the performance of the Korea eLoran system, but results are expected to show better than 20-meter navigational accuracy within 30 kilometers of the differential reference station at the port of Pyeongtaek.

Once the eLoran performance has been proven, MOF plans to move the Incheon eLoran equipment to a permanent site, potentially on the island of Socheongdo, and pair it with a larger “Tee” antenna to increase the output power and coverage area of the system.

MOF also plans to upgrade the existing UTC synchronized Loran-C transmission sites at Pohang and Kwangju with new eLoran transmission equipment systems. The ministry will potentially add two additional transmission sites to provide complete coverage of the land and territorial waters of South Korea.

July 22, 2020
GPS backup demonstration projects explained

The U.S. Department of Transportation awarded contracts to 11 companies to demonstrate their technologies’ ability to act as a backup for GPS.

We wanted to know a bit more about what each of them were going to demonstrate, so we asked each for an explanation. Most provided just that, so much of what appears here is in their own words. A couple of companies sent us a whole lot more than 100 words and two did not respond. For those, we did our best with the materials they sent us and other publicly available materials.

Wi-Fi, Cellular, Ultra-Wideband

PhasorLab plans to demonstrate its Hyper Sync Net (HSN) technology as a backup to GPS-based PNT solutions. HSN is a self-organizing mobile mesh network capable of maintaining high-precision time (<<1 ns) and frequency (<<1 ppb) synchronization throughout the whole network as well as an instantaneous 3D locational map of the whole mesh network requiring as little as a single master reference node.

The HSN can be deployed either as a set of fixed reference nodes providing time and positioning references to other mobile UE clients, which is like a terrestrial version of GPS, or as a private ad-hoc mobile mesh network where all members are expected to be mobile.

Skyhook Technology’s system is powered by an immense database — created and maintained by Skyhook — that contains more than five billion geolocated access points and 200 million cell base station IDs, enabling it to accurately locate phones and devices worldwide. The user is not required to be connected to a Wi-Fi network for the system to work. The scan will simply detect Wi-Fi access points in the local area based on signals sent periodically (or on demand) according to the IEEE 802.11 specifications. Many devices will acquire information on as many as 100 access points in the surrounding area. Skyhook’s Wi-Fi positioning system (WPS) will compute an estimated end-user location based on each of the signal sources independently, and compute an optimal hybrid location estimate from all sources.

Fiber/Network

OPNT’s Global Terrestrial Timing Service (GTTS) provides GPS-independent timing-as-a-service over global fiber-based networks. Trading off cost versus service-level agreement (SLA)-backed accuracy, standard network connectivity offerings and bidirectional fibers are combined to meet application needs. As will be demonstrated with simulations of National Institute of Standards and Technology (NIST) and the two U.S. Naval Observatory (USNO) clocks, OPNT’s fully redundant solution receives its core Coordinated Universal Time (UTC) timing directly from the non-maskable interrupts (NMIs).

The demonstration will include sub-nanosecond stability with fault detection and glitchless recovery. Using the precision-timed fiber base, OPNT will also demonstrate precision monitoring of wireless signals with continuous, real-time corrections to keep the wireless transmissions and its local timing source in sync.

Seven Solutions’ core technology is called White Rabbit and was born at CERN. In this demonstration, Seven Solutions plans to showcase the performance of this technology, both on local and wide-area deployments, and explain the capabilities in terms of interoperability (integrating multiple synchronization technologies, i.e. IEEE 1588 PTP, NTP, PPS, 10-MHz clocks), scalability and resiliency. The goal is to provide a reference technology that can provide very stable time references over fiber in GPS-denied scenarios as a backup source or to complement other PNT solutions that need timing distribution at their core.

eLoran

Hellen Systems’ team said it is excited by its recent contract award to perform a GPS back-up demonstration for the Department of Transportation. Its team plans to demonstrate advanced eLoran technologies and offer resilient PNT services. Its next-generation solution will include a solid-state eLoran transmitter from Continental Electronics Corp. integrated with advanced timing and frequency products from Microsemi, a Microchip company. Hellen Systems also plans to deploy its proprietary receiver and reference systems developed by Microsemi.

Hellen Systems and program integrator L3Harris will manage the demonstration, with Booz Allen Hamilton providing technical and engineering leadership.

UrsaNav supplies eLoran, LFPhoenix and low-frequency technology for very wide-area, GPS-independent, PNT data and frequency services. UrsaNav was selected by the Volpe Center to demonstrate wide-area UTC time synchronization and distribution utilizing the former Loran site in Wildwood, New Jersey. UrsaNav will provide innovative new eLoran technology at the site in Wildwood to broadcast a UTC-synchronized eLoran signal. The demonstration will be conducted at one of the Volpe Center demonstration sites at Joint Base Cape Cod in Massachusetts or the Langley Research Center in Langley, Virginia. Either site can be utilized in the demonstration as eLoran signal transmissions from the Wildwood site can easily cover 700 miles or more.

Serco recently acquired Alion’s Naval Systems Business unit. This included a group working in New London, Connecticut, that has previously worked with and published on eLoran. While we did not get a response from Serco to our inquiry, eLoran is likely the technology the company will demonstrate.

Satellite

Globalstar-Echo Ridge’s system is based on Augmented Positioning System (APS) technology that uses ordinary signals from communications satellites (not special positioning/navigation signals, such as those from GPS satellites) to produce accurate position and timing information in compatible user devices. No new infrastructure is needed; Globalstar’s constellation of 24 low-Earth-orbit (LEO) satellites and Echo Ridge software and compatible devices at the user end provide the building blocks for the APS-based system. APS technology has been successfully demonstrated in diverse environments and incorporates multiple features to assure accurate PNT information under circumstances that can challenge or disable GPS/GNSS technology.

Satelles provides unique timing and location solutions delivered over the Iridium constellation of 66 LEO satellites. These timing and location signals are available anywhere on Earth without the need for local infrastructure, making the system perfect for complementing GPS and other location-based technologies.

Unlike standard GPS, these high-power signals can reach into many building structures. Most importantly, Satelles has customized the Iridium signal-in-space to provide a location-specific signature that can reliably prove (or authenticate) the location of a mobile device or other equipment, while being virtually impervious to spoofing and other attacks.

TRX Systems’ NEON Personnel Tracker provides ubiquitous 3D location, tracking and mapping. (Screenshot: TRX Systems)

Other

TRX Systems is the developer of NEON GPS-denied location solutions, delivering 3D location and mapping for dismount personnel where GPS is not available or is unreliable — including indoors, underground, in dense urban areas, and where GPS is found to be erroneous. NEON delivers ubiquitous, low-cost, GPS-denied location by using advanced sensor fusion, ranging and patented dynamic mapping algorithms that improve safety and situational awareness for military, public safety and industrial personnel.

NextNav’s Metropolitan Beacon System (MBS) is a 3GPP-compliant, terrestrial network of long-range broadcast beacons, transmitting a “GPS-like” signal in licensed spectrum in the sub-GHz range. The combination of an on-board atomic clock and the ability to self-synchronize allows the system to operate independent of GPS and provide full PNT services in its footprint. The ability to integrate the MBS signal in mass-market GPS and LTE chipsets can provide a seamless ability to provide full PNT services in the presence and absence of GPS. Because of its terrestrial nature, MBS is able to work indoors, in urban environments and outdoors; for barometer-equipped devices, MBS also enables floor-level altitude determination.

January 9, 2020
DOT gets cracking on a new PNT concept

Congress mandated movement in December 2017.

U.S. National PNT Architecture from a 2007 Department of Transportation report, updated in 2017. (Graphic: U.S. Department of Transportation)

The U.S. Department of Transportation (DOT) says it will implement a terrestrial timing system to complement and back up GPS signals, and plans to demonstrate the new system “toward the end of the calendar year.”

The demo is anticipated to include a range of technologies, including among others local positioning systems such as Locata and NextNav, wide-area coverage by eLoran, and — though the parameters of DOT’s mandate specified terrestrial backup — space-based signals furnished by Satelles.

The statement came in response to an inquiry in March from the House of Representatives’ Transportation and Infrastructure Committee concerning progress on a GPS Backup Technology Demonstration that was mandated in December 2017. Although funds were appropriated for the project, committee chair Peter DeFazio of Oregon saw little to no evidence of work being done, and so required a status report.

DOT issued a Request for Information (RFI) on May 3, with a due date of June 3. The RFI asked for “readiness-level six” technologies (bearing demonstrated results in a relevant environment) “capable of providing backup positioning, navigation, and/or timing services to critical infrastructure in the event of a temporary disruption to GPS.

“This demonstration effort also is expected to encompass technologies capable of providing complementary PNT functions to GPS by either expanding PNT capabilities, including cross checks, or extending them to GPS or Global Navigation Satellite System (GNSS)-denied or degraded user environments.”

The DOT said it is “interested in leveraging PNT service technology initiatives.” Possibly, the agency intends to contract for a service rather than build a new system.

Congress first required DOT to establish an operational terrestrial timing system to back up GPS signals, then expanded that definition to include positioning and navigation services.

Systems or services, or combinations thereof, must now provide all three functions.

June 7, 2019
Korea institute awards UrsaNav an eLoran test bed contract

The Korea Research Institute of Ships and Oceans Engineering (KRISO) has awarded UrsaNav a contract to supply an eLoran Transmitter Test Bed System in the Republic of Korea.

UrsaNav, the exclusive, worldwide distributor of Nautel’s NL Series transmitters, will provide eLoran transmitter technology, as well as timing and control equipment.

A meeting to kick off the eLoran work. (Photo: UrsaNav)

The contract, awarded through UrsaNav’s agent Dong Kang M-Tech, represents the first phase in a broader program to upgrade Korea’s Loran-C stations to be the foundation of a sovereign Enhanced Loran (eLoran) positioning, navigation and timing (PNT) service.

The Republic of Korea recognizes the challenges associated with relying solely on space-based signals, the relative ease with which those signals can be jammed or spoofed, and the necessity to provide trusted time and position to its citizens and critical national infrastructure, UrsaNav said in a press release.

The press release also included the following description of the importance of eLoran.

Accurate time and position are necessary components upon which many critical infrastructure sectors rely, including maritime, aviation, electrical distribution, telecommunications, finance/banking, and digital broadcast. A complementary PNT (CPNT) service provides continuity of operations through alternative and diverse timing and positioning information. CPNT is a vital element in ensuring national security and assuring Trusted Time and Trusted Position.

eLoran is the latest in the longstanding series of low-frequency (LF), LOng-RAnge Navigation (LORAN) systems. It meets the accuracy, availability, integrity, and continuity performance requirements for maritime harbor entrance and approach maneuvers, aviation En Route and Non-Precision Approaches, land-mobile vehicle navigation, and location-based services. It provides bearing (azimuth) information, even when the user is not moving, and has built-in integrity. Users within the coverage area can simultaneously synchronize their timing to absolute (not relative) UTC. Of equal importance is that the eLoran signal includes one or more Loran Data Channels that are available to provide one-way, low data rate, “Short Message Service” information.

eLoran is completely independent of GPS/GNSS, operates in the internationally protected 90 to 110 kHz spectrum, is built on internationally standardized Loran-C, and provides a high-power PNT service for use by all timing and navigation users. SAE International expects to release eLoran standards this year. The RTCM also has maritime-related eLoran standards underway.

eLoran is a key vertex of a Resilience Triad that would typically include space-based, terrestrial, and at least one other PNT source. It is a very-wide area (i.e., country-wide or “continental”) source of PNT that continues providing a resilient solution even when GNSS may be unavailable or untrustworthy. eLoran delivers information comparable to that of GNSS, but with completely different phenomenology. It is a very high-power, LF, pulsed transmission, whereas GNSS are low-power, UHF, multiple modulation scheme transmissions. eLoran is literally at the other end of the spectrum from GNSS, and has completely dissimilar failure modes. That is, an issue that disrupts GNSS is unlikely to disrupt eLoran. The unique characteristics of eLoran enable its use in environments where GNSS does not work very well, or at all (e.g., indoors, underwater, underground, and in mountain or urban canyons).

eLoran is exceptionally difficult to spoof or jam, and it is nearly impossible to do so at a distance. Just as equipment required to spoof and jam GNSS must mimic relatively low powered GNSS transmissions, spoofing and jamming eLoran requires very high powered transmissions. Equipment needs alone to disrupt eLoran over a significant area would be almost prohibitive for any actor other than a nation state engaged in open conflict. This is the reason that an independent assessment by researchers at Stanford University described eLoran as “for all practical purposes, unjammable” across any significant area. A MITRE paper concluded: “The analysis shows a very low probability of successfully producing operationally significant interference.”

August 28, 2018