GPS World

Tag: Loran-C

  • eLoran: Part of the solution to GNSS vulnerability

    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.

    Photo:

    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)
    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)
    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.”

     

  • South Korea partners with broadcaster on eLoran and 10-cm GPS

    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
    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.”

  • Precise time for all: Paper calls for resilient national timing

    Precise time for all: Paper calls for resilient national timing

    Image: RNT Foundation
    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.”

  • China expanding Loran as GNSS backup

    China expanding Loran as GNSS backup

    An August 2020 paper published by the journal Sensors revealed China’s plans to expand coverage of its terrestrial Loran positioning, navigation and timing (PNT) system with three new transmitter sites in the western part of the country. The article indicates that this is a part of providing a backup system for GNSS.

    According to the paper, “…the vulnerability of GNSS to unintentional and intentional interference signals can be found frequently nowadays. For national security and economic effectiveness, a reliable and complementary navigation system is needed desperately. The suitability of the Loran for a backup navigation system has been evaluated and reported.”

    China has operated a Loran system for decades. While the system is capable of operating independently, its signals are also compatible with systems operated by South Korea and Russia. These are coordinated through the Far East Radio Navigation Service (FERNS) to ensure the systems are complementary and reinforce each other where coverage overlaps. The United States and Japan were also members of FERNS until they terminated Loran transmissions in 2010 and 2015, respectively.

    Image: RNT Foundation
    Image: RNT Foundation

    Little public information about China’s Loran system has been available and our queries have gone unanswered. One of the few documents available in the west is a 2014 paper about Loran-C from the Chinese Academy of Sciences in Shaanxi, China which can be accessed through the RNT Foundation website. It shows substantial Loran coverage in the eastern part of the nation, but only a broken circle indicating “projected coverage” in the west.

    Graphic from 2014 Chinese Academy of Sciences paper on Loran showing projected coverage in the western part of the country with a dotted circle. (Image: RNT Foundation)
    Graphic from 2014 Chinese Academy of Sciences paper on Loran showing projected coverage in the western part of the country with a dotted circle. (Image: RNT Foundation)

    The single transmitter in that area projected by the 2014 paper could provide a strong, difficult to disrupt timing signal for fixed receivers with known locations.

    Three new transmitters will be installed according to the August 2020 paper titled “High-Accuracy Positioning Based on Pseudo-Ranges: Integrated Difference and Performance Analysis of the Loran System.” The increased service in the western part of the country will provide “full coverage” positioning, navigation and timing usable by both fixed and mobile receivers.
    The August 2020 paper is the first known documentation in over a decade of specific Chinese intentions regarding its Loran system.

    Still, it is not a surprise to many observers. At 2019’s Stanford PNT Symposium, Xiaochun Lu of China’s National Time Service Center described the nation’s plan for a “comprehensive” PNT system. This system will include a wide variety of PNT sources including low earth orbit satellites, inertial systems, local positioning systems, and Loran.

    Like Ms Lu, the authors of the August 2020 paper are employed at China’s National Time Service Center, which is part of the Chinese Academy of Sciences.

  • UrsaNav installs eLoran testbed in South Korea

    UrsaNav installs eLoran testbed in South Korea

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

  • 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)
    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.”

  • Alt-PNT receivers emphasize low-power requirements

    Alt-PNT receivers emphasize low-power requirements

    LORAD++ CORE, an alternative PNT source to combat GNSS denial: 60 x 30 x 8 millimeters
    LORAD++ CORE, an alternative PNT source to combat GNSS denial: 60 x 30 x 8 millimeters

    A new series of integrated eLoran/Chayka/GNSS receivers emphasize low-power requirements and small size for alternative positioning, navigation and timing (PNT) to reduce risks of GNSS denial.

    Loradd++, from Netherlands-based firm Reelektronika, consists of a receiver board of 60 x 30 x 8 millimeters, consuming less than 500 milliwatts (3.3 volts) in continuous operation. The Loradd++ can be used with either E-field or H-field antennas, features dual serial interface for integrated systems, and is connectable to certain miniature GNSS receiver modules.

    eLoran and Chayka are recognized as alternative PNT systems, but current receivers on the market are large in comparison to miniature GNSS devices. Chayka is a Russian terrestrial radio navigation system, similar to Loran-C. It operates on similar frequencies around 100 kHz, and uses the same techniques of comparing both the envelope and the signal phase to accurately determine location.

    The first of a new series of receivers is Reelelektronika’s Loradd++/E, which is an integration of the Loradd++ with an E-field antenna housed in a small single radome that can be connected via a data cable (up to 150 meters) and a dongle to a USB port on a PC. The radome contains a u-blox M8T GNSS receiver with antenna and measures 135 millimeters in height and 85 millimeters in diameter. The Loradd++/E needs less than 700 milliwatts at 4-16 volts.

    Reelektronika manufactures eLoran equipment for users, service providers and surveyors. The company developed the eDLoran system. eDLoran works with existing Loran transmitter stations and yields differential Loran position and navigation accuracies comparable to GPS; see the cover story of the July 2014 issue of GPS World. The system can thus be considered as a robust backup for GPS.

  • PNT Roundup: Taviga collaboration, leap second reconsidered and drone rules

    eLoran

    New joint venture to ensure, assure secure PNT

    The founders of Chronos and UrsaNav have formed a new collaboration, named Taviga, that will focus on preserving and establishing low-frequency (LF) positioning, navigation and timing (PNT) networks in the United Kingdom, Europe and the U.S., using repurposed Loran-C or purpose-built eLoran technology.

    Taviga aims to ensure timing and navigation for critical infrastructure, protecting it from cyber and other threats, and addressing the concern that over-dependence on single systems for PNT increases vulnerability.

    According to a joint press release, “Taviga combines the founders’ decades of experience specializing in low-frequency (LF) PNT technology and industrial timing applications at national and international levels. Its objective is to provide a commercially operated assured LF PNT service.”

    Partner with Government. Charles Curry of Chronos Technology Ltd. in the UK and Charles Schue of UrsaNav Inc. in the U.S. joined forces to launch Taviga Ltd. and Taviga LLC. Taviga anticipates working in partnership with government agencies and other entities that have a vested interest in reducing the vulnerability and improving the resilience of critical national infrastructure with a dependency on the GPS and other GNSS sources of PNT.

    “We have been researching the precise timing capability of eLoran transmissions for over 10 years,” Curry said. “During that time, the system has never failed, and most impressively it has continued to deliver sub-microsecond time accuracy traceable to UTC in very challenging locations, including deep inside buildings.

    “Our research program was supported by the UK’s Innovation Agency — Innovate UK through two flagship projects, GAARDIAN and SENTINEL,” Curry continued. “These two projects highlighted the vulnerabilities that threaten GPS signals (and in the future, Galileo) such as jamming, interference and spoofing. They also demonstrated how eLoran is a technically dissimilar source of PNT and not vulnerable to the same types of interference. eLoran is a truly complementary source of PNT, ideal for use in critical infrastructure applications such as telecoms, broadcasting, financial services and power utilities.

    “Every government, academic and industrial study has resulted in the selection of the LF technology known as Enhanced Loran, or eLoran, as the best wide-area complement to GNSS,” UrsaNav’s Schue added. “There is no doubt that the combination of GNSS and eLoran provides the PNT resilience that most users require.

    “Integrated GNSS-eLoran solutions can provide the proof-of-time and proof-of-position necessary to safeguard national infrastructure and for business continuity of operations,” Schue said. “Adding eLoran to the PNT mix enables or enhances capabilities of regional and purpose-built solutions. Overreliance on a single solution is neither prudent nor safe.”

    Tests led by Chronos and using UrsaNav’s eLoran receiver engine have consistently demonstrated positioning accuracies of better than 10 m and timing accuracies of less than 100 nanoseconds in the area of differential eLoran reference sites.

    Taviga’s goal is the long-term operation of an eLoran system for at least 10 years, a period that provides the necessary service assurance continuity to enable industrial users to invest with confidence in an eLoran-based timing and navigation service that complements their GNSS solutions. As users become accustomed to the capabilities and resilience of a combined GNSS-eLoran solution, Taviga expects to expand the service footprint worldwide.

    Timing

    Leap second lives on

    The International Telecommunication Union (ITU) World Radiocommunication Conference (WRC-15) decided that further studies are required on the impact and application of a future reference time-scale, including the modification of Coordinated Universal Time (UTC) and suppressing the so-called “leap second.”

    Leap seconds are added periodically to adjust to irregularities in the Earth’s rotation in relation to UTC, the current reference for measuring time, in order to remain close to mean solar time (UT1). A leap second was added most recently on June 30 at 23:59:60 UTC. The proposal to suppress the leap second would have made continuous reference timescale available for all modern electronic navigation and computerized systems to operate while eliminating the need for specialized ad hoc time systems.

    A report will be considered by the World Radiocommunication Conference in 2023. Until then, UTC shall continue to be applied as described in Recommendation ITU‑R TF.460‑6.

    Disconnect from the Sun? As a representative of the Lick Observatory of the University of California stated, “a problem is that simply omitting leap seconds would redefine the meaning of the word “day” so that it is not related to the sun in the sky, nor connected with the rotation of the Earth.”

    “Modern society is increasingly dependent on accurate timekeeping,” said ITU Secretary-General Houlin Zhao.“ITU is responsible for disseminating time signals by both wired communications and by different radiocommunication services, both space and terrestrial, which are critical for all areas of human activity.”

    Further studies will be coordinated by ITU along with several other international organizations.

    Inertial/GNSS

    Drone rules, registry

    The Federal Aviation Administration announced in December an official rule and registration process for hobbyists who own small unmanned aircraft weighing more than 0.55 pounds and less than 55 pounds, including payloads such as on-board cameras.

    The online registration system does not yet support registration of small UAS used for any purpose other than hobby or recreation — for example, using an unmanned aircraft in connection with a business. The FAA is developing enhancements that will allow such online registrations by spring of 2016.

    The registration procedure is a statutory requirement that applies to all hobby aircraft. Under this rule, any owner of a small UAS who has previously operated an unmanned aircraft exclusively as a model aircraft prior to Dec. 21, 2015, must register no later than Feb. 19, 2016. Owners of any other UAS purchased for use as a model aircraft after Dec. 21, 2015, must register before the first flight outdoors.

    Owners may register through a web-based system or paper-based process. There is a $5 registration fee, but the FAA is offering a full rebate for those who register before Jan. 20, 2016.

    Under the rule, each aircraft must be marked with a unique number, although not necessarily the serial number. The goal is to help authorities track down an owner if a drone collides with another aircraft, flies too high or encroaches on an airport.

    Owners using the model aircraft for hobby or recreation will only have to register once and may use the same identification number for all of their model UAS. The registration is valid for three years.

    “We expect hundreds of thousands of model unmanned aircraft will be purchased this holiday season,” FAA Administrator Michael Huerta said. “Registration gives us the opportunity to educate these new airspace users before they fly so they know the airspace rules and understand they are accountable to the public for flying responsibly.”

  • Chronos and UrsaNav partner on Loran PNT networks

    Chronos and UrsaNav partner on Loran PNT networks

    Taviga-logoThe founders of Chronos and UrsaNav have formed a new collaboration, named Taviga, that will focus on preserving and establishing low-frequency (LF) positioning, navigation and timing (PNT) networks the United Kingdom, Europe and the United States, using repurposed Loran-C or purpose-built eLoran technology.

    Taviga — named for timing and navigation — aims to ensure timing and navigation for critical infrastructure from cyber and other threats, and address the concern that over-dependence on single systems for PNT increases vulnerability.

    According to a joint press release, “Taviga combines the founders’ decades of experience specializing in low-frequency (LF) PNT technology and industrial timing applications at national and international levels. Its objective is to provide a commercially operated assured LF PNT service.”

    Charles Curry, founder of Chronos Technology Ltd. in the UK, and Charles Schue, founder of UrsaNav Inc. in the United States, joined forces to launch Taviga Ltd. and Taviga LLC. Taviga anticipates working in partnership with government agencies and other entities that have a vested interest in reducing the vulnerability and improving the resilience of critical national infrastructure with a dependency on the GPS and other GNSS sources of PNT.

    “We have been researching the precise timing capability of eLoran transmissions for over 10 years,” Curry said. “During that time, the system has never failed and most impressively it has continued to deliver sub-microsecond time accuracy traceable to UTC in some very challenging locations including deep inside buildings.

    “Our research program was supported by the UK’s Innovation Agency – Innovate UK through two flagship projects, GAARDIAN and SENTINEL,” Curry continued. These two projects highlighted the vulnerabilities that threaten GPS signals (and in the future, Galileo) such as jamming, interference and spoofing. They also demonstrated how eLoran is a technically dissimilar source of PNT and not vulnerable to the same types of interference. eLoran is a truly complementary source of PNT ideal for use in critical infrastructure applications that demand precise time and timing such as telecoms, broadcasting, financial services and power utilities.

    “Every government, academic and industrial study has resulted in the selection of the LF technology known as Enhanced Loran, or eLoran, as the best wide-area complement to GNSS,” Schue said. “There is no doubt that the combination of GNSS and eLoran provides the PNT resilience that most users require.

    “Whether the application is timing/frequency, aviation, maritime, land-mobile, or location based, integrated GNSS-eLoran solutions can provide the proof-of-time and proof-of-position necessary to safeguard national infrastructure and for business continuity of operations,” Schue said. “Additionally, adding eLoran into the PNT mix enables or enhances the capabilities of regional and purpose-built solutions. PNT resilience results from an eco-system made up of layered solutions. Over reliance on a single solution is neither prudent nor safe. It’s time for Taviga.”

    Tests have been conducted as part of Innovate UK supported research projects GAARDIAN and SENTINEL, which were led by Chronos Technology Ltd and included UrsaNav’s eLoran receiver engine. eLoran transmissions from the UK, Denmark, Germany, France and Norway have consistently demonstrated positioning accuracies of better than ten meters and timing accuracies of less than 100 nanoseconds in the area of differential eLoran reference sites. Taviga will now seek to engage those governments and others in discussions as to how to transition their Loran stations to commercial operation.

    Taviga’s goal is the long-term operation of an eLoran system for at least 10 years. This length of time provides the necessary service assurance continuity to enable industrial users to invest with confidence in an eLoran-based timing and navigation service that complements their GNSS solutions. As users become accustomed to the additional capabilities and resilience provided with a combined GNSS-eLoran solution, Taviga expects to expand the service footprint into other countries worldwide.

  • Exelis, UrsaNav to Demo eLoran with Homeland Security, Coast Guard

    Exelis, UrsaNav, the Department of Homeland Security’s Science and Technology Directorate (DHS S&T), and the U.S. Coast Guard have entered into a cooperative research and development agreement (CRADA) for testing and demonstration at former Loran-C sites.

    The team will evaluate eLoran as a potential complementary system to GPS. The capabilities and potential utilization methods of eLoran will be explored in depth to identify all strengths, capacities, and potential vulnerabilities of the technology.

    The sites are the legacy ground-based radio navigation infrastructure of the decommissioned Loran-C service that could be retained and upgraded to provide eLoran low frequency service.

    Under the CRADA, Exelis will use the former Loran-C assets to put eLoran signals in space for research, test and demonstration of the ability of eLoran to meet precise positioning, navigation and timing (PNT) requirements of government and privately-owned critical infrastructure. The first station Exelis will broadcast from is located in Wildwood, N.J. The broadcast will provide a usable signal at a range up to 1,000 miles.

    “eLoran is an ideal technology to complement GPS for critical, resilient and assured PNT,” said Ed Sayadian, vice president of Civil & Aerospace Systems for Exelis. “eLoran is a difficult to disrupt technology that offers PNT and wide area broadcast data capabilities indoors, in underground locations and other GPS-denied environments.”

    “A preponderance of government, academic, and industry reports have concluded that eLoran is the best independent, multi-modal solution to provide assured PNT as a complement to GPS,” said Chuck Schue, president and CEO of UrsaNav.

    Exelis and UrsaNav have entered into this CRADA because they believe that low frequency signals, such as eLORAN, operate independently of GPS signals and can provide alternative timing, either standalone, or as a component of a PNT service. Exelis also believes that as a result of its wealth of experience in its PNT portfolio, that there are many civil and defense applications that require precise time and/or position in GPS-denied environments. Examples include radio frequency interference, both intentional and unintentional; signal attenuation from heavy forest canopy, terrain or buildings; and indoor and underground locations.

  • The System: GLONASS Fumbles Forward

    The System: GLONASS Fumbles Forward

    GLONASS PLOT from the Roscosmos GLONASS Information-Analytical Centre, showing the 12-hour outage, with full service eventually restored on April 2.
    GLONASS PLOT from the Roscosmos GLONASS Information-Analytical Centre, showing the 12-hour outage, with full service eventually restored on April 2.

    Two April Disruptions Furnish Fodder for Multi-GNSS Receivers and Alternative PNT

    In an unprecedented total disruption of a fully operational GNSS constellation, all satellites in the Russian GLONASS broadcast corrupt information for 11 hours, from just past midnight until noon Russian time (UTC+4) on April 2 (or 5 p.m. on April 1 to 4  a.m. April 2, U.S. Eastern time). This rendered the system completely unusable to all worldwide GLONASS receivers. Full service was subsequently restored.

    “Bad ephemerides were uploaded to satellites. Those bad ephemerides became active at 1:00 a.m. Moscow time,” reported one knowledgeable source. GLONASS navigation messages contain, as they do for every GNSS in orbit, ephemeris data used to calculate the position of each satellite in orbit, and information about the time and status of the entire satellite constellation (almanac); user receivers on the ground processed this data to compute their precise position.

    The GLONASS fix could not take effect until each satellite in turn could be reset, during its pass over control stations in Russian territory, in the Northern Hemisphere, thus taking nearly 12 hours.

    During the outage, CEO Neil Vancans of Altus Positioning Systems reported “We are currently experiencing calls from customers all over the world who are experiencing GLONASS ‘outages’ and we have advised customers to switch GLONASS tracking off on our receivers.”

    Such a — possibly human, possibly computer-generated — error could conceivably occur with GPS, Galileo, or BeiDou. “Another reason to have backups,” mused Richard Langley of the University of New Brunswick. “And not just other GNSS.”

    Trouble Chronolog. The constellation suffered a second failure two weeks later. On April 14, eight GLONASS satellites were simultaneously set unhealthy for about half an hour, meaning that most GLONASS or multi-constellation receivers would have ignored those satellites in positioning computations. In addition, one other satellite in the fleet was out of commission undergoing maintenance. This might have left too few healthy satellites to compute GLONASS-only receiver positions in some locations.

    The two blackouts followed two other high-profile disasters: the destruction-upon-launch of three new GLONASS satellites in July 2013, and the Pacific drowning-upon-launch of three satellites in December 2010.

    Internal Dialog. The semi-official Russian news daily Izvestia (“Truth”) reported that the loss of service was inconsequential for Russian users. Loose translation courtesy of Google:

    “Temporary GLONASS failure has not led to tangible consequences for consumers of services because chip manufacturing exclusively with GLONASS for the mass market is practically nil: there are chips that work only with the GPS signals, and there are those that see both GPS and GLONASS.”

    In other words, there are practically no mass-market devices, even in Russia, that use exclusively GLONASS.

    “In any case, the failure of the entire system for a long period is a serious blow to the image of GLONASS, especially in a situation where Russia has made efforts to promote domestic navigation system to external markets. Plus in 2012, the Russian government officially promised to maintain the characteristics of the international community GLONASS at the proper level for 15 years.”

    Industry View, Multi-GNSS. During the first outage, chip company Broadcom was conicidentally conducting multi-constellation receiver tests in Asia. Frank van Diggelen, the company’s chief GNSS scientist, stated, “We have definitive data to show how a multi-constellation receiver survives such an outage. Test data coincident with the GLONASS ephemeris disruption show how a GPS/GLONASS/QZSS/BeiDou receiver survives the complete disruption of one of the constellations.”

    A Broadcom 47531receiver tracking GPS/GLONASS/QZSS/BeiDou signals simultaneously and using logic to analyze redundant measurements to check the validity of all measurements successfully identified and removed the bad GLONASS ephemeris, maintaining position continuity and accuracy. Another receiver under test at the same time, tracking only GPS and GLONASS, wandered significantly in its position reports.

    Industry View, Back Up PNT. Calling it an “unprecedented and deeply worrying total disruption…[that] shook the industry,” Locata Corporation reiterated its call for redundant terrestrial systems to back up GNSS in the wake of the outage.

    Nunzio Gambale, Locata CEO, said “We have been telling the industry for years that you cannot have a critically important capability like GPS without also having a backup! What is Plan B if the satellite systems fail? What replaces the space signal when there is a problem? This event should terrify every nation, government, and company that depends on navigation satellites for their business or, in some cases, their very lives.”

    GNSS navigation and timing functions underpin the world’s banking systems, stock exchanges, digital TV and Internet, cell-phone networks, and, in some cases, the national electricity supply, Locata pointed out. GPS, in particular, plays a crucial role in transportation, shipping, and logistics, serving as the enabling technology for critical functions like air traffic control. Reliability is therefore not just important; it is essential across all applications.

    “We ignore the possibility of these ‘Black Swan’ events at our own peril,” added Chris Rizos of the University of New South Wales.

    eLoran Authorization in Progress

    Russia’s April 1 GLONASS blackout occurred, ironically, only hours after the U.S. House of Representatives passed legislation to preserve infrastructure that could support a backup system for GPS that could be used for critical infrastructure and applications in the event of a similar disaster occurring in the United States.

    The 2014 Coast Guard Authorization Act requires the Department of Homeland Security (DHS) to halt dismantling and disposal of infrastructure that could be used for a terrestrial system during times and in places where GPS is not available.

    DHS had announced in 2008 that it would build such a backup system, but it never did so, and actually began dismantling, destroying, and divesting itself of Loran equipment and properties. The equipment, facilities, and sites could be used to implement a new generation eLoran system for GPS backup, among other applications. Despite strong recommendations to the contrary by its own panel of experts, the Obama administration, DHS, and the Coast Guard moved in 2009 to kill the Loran program.

    Watchdogs. Congress has lately become more visibly concerned about the vulnerability of the nation’s space systems. The 2014 National Defense Authorization Act tasked the administration with reporting on how it was going to provide necessary national security capabilities when space systems were disrupted. More recently, Congressmen Duncan Hunter (Republican, California), chair of the House Coast Guard and Marine Transportation Subcommittee, held a hearing at which he expressed his concern that the nation has no backup for GPS. He also expressed his frustration with the Department of Homeland Security, reporting that “They said they need to do a study about their study.”

    Congressman John Garamendi (Democrat, California), commented “GPS will go down one day. The question is, is there a backup?”

    The legislation passed by the House authorizes DHS to partner with public or private entities to build a system that would not only back up GPS, but also work indoors, underground and underwater — all characteristics of long-wave Loran technology.

    Resilient PNT. Dana Goward, president of the Resilient Navigation and Timing Foundation, said such a project would be relatively inexpensive. “If the existing equipment and infrastructure are preserved and reused, the system could be restored and put into operation for less than half the cost to dispose of it.”

    “It isn’t an issue of money,” Goward continued. “It is a question of the government taking this problem seriously and acting on it.”

    The foundation has as offered to partner with the government to build the system.

    “Our government has known about this issue for a long time,” Goward said. “At least since 2001. And there has been a standing presidential direction to obtain backup capability since 2004. But for some reason, it hasn’t yet happened.”

    The government’s official website about GPS (www.gps.gov) has recently updated its page on eLoran and Loran-C with a tracking log for Coast Guard and Maritime Transportation Act of 2014, which now goes to the Senate.

    IRNSS’s Second of Seven

    India’s Space Research Organisation launched a navigation satellite on April 4. IRNSS-1B is the second of seven that will comprise the first-generation Indian Regional Navigation Satellite System (IRNSS). It joins IRNSS-1A, already in orbit.

    IRNSS will consist of three geostationary satellites and two pairs in inclined geosynchronous orbits. Each IRNSS satellite uses a rubidium-based atomic clock to keep time, transmitting signals on L and S-band frequencies at 1176.45 and 2492.028 megahertz respectively.

    Lag in Recent GPS IIF’s Health Status

    By Richard Langley

    The GPS Block IIF satellite, IIF-5 or SVN64 (PRN30), launched on February 21, had not as of press time been set healthy. Typically, GPS satellites are checked out and made operational within about a month after launch.

    The delay is due to an extended navigation test being performed by the GPS master control station. A navigation upload for SVN64 was performed in March with ephemeris and clock data as usual streching weeks in advance. However, unlike with operational satellites, no further updated uploads have been performed. The aging ephermis and clock data gradually becomes less and less accurate as time goes by, but should degrade gracefully.

    Some observers will have noticed that the received navigation data from SNV64 changes infrequently. Currently, the navigation data changes once per day with an epoch of 13:00 GPS Time, unlike every two hours with operational satellites. And the data fit interval is 26 hours, compared to four hours.

    The test is scheduled to run until mid-May.

     

  • GNSS Backup Delivers 5-Meter Accuracy

    The North Sea fairly boils with GNSS activity recently. Trials of the eLoran back-up for GNSS, Galileo maritime trials, Brad Parkinson’s Protect, Toughen, and Augment sermon at the European Navigation Conference in Rotterdam, and also at that conference, the dramatic release of news concerning an even newer Loran system, enhanced differential Loran, that not only backs up GNSS in the event of disruption or jamming, but delivers 5-meter accuracy in the process. Imagine that — the back-up matching the first team in performance!

    Durk van Willigen, René Kellenbach, and Cees Dekker of the Dutch consulting firm Reelektronika, and Wim van Buuren of the Dutch Pilots’ Corporation authored the ENC presentation about enhanced differential Loran, with results that greatly — and pleasantly — surprised many in the audience. A full technical article by these authors, describing the equipment, methodology, and test results of eDLoran, will appear in the July issue of GPS World. This column delivers a brief summary of the highlights.

    The new Loran project arose from the need of harbor pilots responsible for bringing large and super-large freight ships into dock. These pilots require GNSS-level accuracies of 5 meters for such work, and all parties concerned — pilots, captains, ship owners, harbor management — need some form of robustness, that is, back-up for the GNSS systems in case of jamming, unintentional interference, system failure, or other disruption.

    As extensive research had established that 5-meter accuracy cannot be met by the currently tested DLoran system, which cannot get better than 10-meter accuracy. Reelektronika developed a new differential Loran system called enhanced differential Loran, or eDLoran. A full prototype eDLoran system was built and extensively tested in the Europort (Rotterdam) area. The tests achieved accuracies of 5 meters.

    For maritime applications, eLoran is considered as the most promising backup for GNSS in case the use of satellite-based navigation signals is denied. The Dutch Pilots’ Corporation askedReelektronika to investigate whether differential Loran could meet the pilots’ 5-meter accuracy requirement for a harbor navigation. This proved to be an enormous challenge as preliminary tests showed that even 10 meters was difficult to achieve with differential Loran (DLoran) as promoted by the UK’s Trinity House/General Lighthouse Authority (see item below about Harwich UK tests by GLA and ACCESS). The challenge had led to a thorough investigation of all possible error sources of a complete differential Loran system.

    Differential techniques developed and implemented for Loran are comparable with differential GPS. Although the error sources of GPS and Loran are quite different, the major common error source in both systems is the lack of accurate propagation models.

    This led to a new research project to find a more accurate differential Loran technique. All possible error sources have been investigated again where possible, which resulted in some unexpected results regarding accuracies and costs.

    Enhanced Differential Loran: eDLoran

    The new concept of differential Loran had to fulfill two important primary improvements. The first is a significant reduction in the latency of the data in the data channel; the second is that a large number of reference stations should be capable of receiving the data channel, without saturating the data channel. The simple conclusion was that Eurofix could not meet these two improvements. However, Eurofix is still the prime GNSS backup candidate for distributing accurate UTC over very large parts of Europe. Further, Eurofix has the capability to send short messages that might be encrypted for secure communication purposes which might then form a terrestrial backup, for example, Galileo PRS.

    Instead of using the Eurofix channel, eDLoran uses the public mobile GSM (Global System for Mobile) network to send the differential corrections to users. eDLoran receivers therefore contain a simple modem for connection to the GSM network. The eDLoran reference stations are also connected to the Internet which may be implemented via a cabled access or also via a GSM modem.Fortunately, today many GSM networks are robust in respect of GPS outages.

    The eDLoran infrastructure is not connected with any eLoran transmitter station and operates completely autonomously. An eDLoran reference station is connected to a central eDLoran server by its connection to the network.

    eDLoran Results

    Both static and dynamic tests have been carried out. Here, only the final result of the dynamic test is presented. For full details on both sets of tests, see the upcoming full-length technical article in the July issue of GPS World magazine.

    The results have been demonstrated to the harbor authorities in real-time on the laptop of the pilots on which the GPS-RTK and the eDLoran position were simultaneously shown. The logged GPS-RTK data is plotted on a Google Earth map shown in the accompanying figure. The track was widened to 10 metres as the accuracy requirements are 5 metres on either side of the track. The raw eLoran track is also shown, as well as the final white eDLoran track.

    The red track is based on raw eLoran data without any corrections. The transparent blue line is made by GPS-RTK and is widened to 10 metres giving the required ± 5 metre limits of eDLoran. The white line is output from the eDLoran receiver which stays within the borders of the 10-meter-wide transparent blue line.
    The red track is based on raw eLoran data without any corrections. The transparent blue line is made by GPS-RTK and is widened to 10 metres giving the required ± 5 metre limits of eDLoran. The white line is output from the eDLoran receiver which stays within the borders of the 10-meter-wide transparent blue line.

    Conclusions

    The outcome of the research opens some new and quite surprising possibilities for multiple applications. Only a few of the authors’ conclusions appear here:

    1. eDLoran offers the best possible eLoran accuracy as it does not suffer from swaying wire antennas, sub-optimal timing control of the transmitter station and differential data latency.
    2. There is no need to replace older Loran-C stations with eLoran transmitters saving large amounts of money. The existing Loran stations have a proven reliability track record. Further savings may be obtained by containerising the transmitter and operating the stations unmanned.
    3. Installing eDLoran reference stations is fast, simple and very cost effective.
    4. As there is no data channel bandwidth limitation, multiple reference stations can be installed which offers increased reliability and makes the system more robust against terrorism and lightning damage.
    5. A single or multiple eDLoran servers can be installed in a protected area. There is hardly a practical limit in the number of differential reference stations to serve.

    To round out our North Sea reporting, here is other recent news:

    Enhanced Loran

    In March, the UK General Lighthouse Authority (GLA) and Accessibility for Shipping, Efficiency Advantages and Sustainability (ACCSEA) announced that on several excursions aboard the THV Galatea out of Harwich, UK, they successfully demonstrated a prototype resilient positioning, navigation and timing (PNT) system using enhanced Loran (eLoran) technology to automatically and seamlessly step in to transmit mission-critical data in the event of GPS loss or failure. (Note that in the preceding Reelektronika section of this column, the GLA enhanced Loran is referred to as differential Loran, while the Dutch system is called enhanced differential Loran.)

    Building on two previous trials conducted by the GLA in 2008 and 2010 which investigated the impact of GPS service denial, this latest demonstration is the first time that an automatic and seamless solution has been demonstrated in a real-world scenario. The prototype system was integrated into the bridge of the vessel and monitored the performance of independent PNT sources in order to provide the ‘best’ available. As such, when GPS was deliberately jammed, the system switched automatically to eLoran and provided eLoran-derived PNT information to the connected bridge systems, allowing them to maintain operation and enabling the mariner to continue to navigate safely and efficiently.

    ACCSEAS is taking advantage of the availability of the prototype eLoran transmitter at Anthorn and eight other Loran stations around the North Sea Region, but few vessels currently have receivers. Most recently, in January 2013, a differential Loran station was installed at Dover, UK, one of the busiest shipping lanes in the world, enabling mariners to obtain port approach level accuracies using eLoran within this area; and a receiver was fitted on a P&O Ferries vessel. The successful demonstration of the prototype resilient PNT system is a significant step towards gaining traction for the technology in the shipping industry worldwide.

    By 2014, eLoran Initial Operational Capability is expected in seven major ports along the East Coast of the UK, with full operational capability covering all major ports expected by 2019.

    Galileo Maritime Trials

    Results are being processed from the first Galileo maritime trials outside of mainland Europe. The long-range, high-latitude testing spanned the North Sea aboard Belgian frigate Leopold I-F930, carrying multiple Galileo receivers for both Galileo’s public Open Service (OS) and secure Public Regulated Service (PRS).

    Protect, Toughen, Augment GNSS

    “What can we do to reduce the vulnerability [of GPS] and ensure that the expectations of the public are going to be met?” asked Dr. Bradford Parkinson as he opened his keynote presentation at the European Navigation Conference, ENC-GNSS 2014 in Rotterdam, The Netherlands.

    Parkinson went through his 61-slide, 50-minute briefing on what he called “PTA” — Protect, Toughen, and Augment — a proposal concerning not only GPS but PNT systems globally. An article by Parkinson based on this talk will highlight the special 25th Anniversary edition of GPS World, to appear in conjunction with this year’s July issue. A brief outline appears here.