The European Space Agency (ESA) has named Paul Verhoef its new Director of Galileo Programme and Navigation-Related Activities. Verhoef, former coordinator for Galileo activities with the European Commission, was named as one member of a new senior leadership team after a special meeting of the ESA Council in Paris on Nov. 21.
At the weekend meeting, the agency selected several new managers for key positions. The new leadership team is expected to start work in early 2016.
Space Applications
Director of Telecommunications and Integrated Applications (D/TIA), Magali Vaissiere
Director of Galileo Programme and Navigation-Related Activities (D/NAV), Paul Verhoef
Science and Exploration
Director of Science (D/SCI), Alvaro Giménez Cañete
Director of Human Spaceflight and Robotic Exploration Programmes (D/HRE), David Parker
Space Technology and Operations
Director of Technical and Quality Management (D/TEC), Franco Ongaro
Director of Operations (D/OPS), Rolf Densing
Administration
Director of Internal Services: Human Resources, Facility Management, Finance and Controlling, Information Technology (D/HIF), Jean Max Puech
Director of Industry, Procurement and Legal Services (D/IPL), Eric Morel de Westgaver
A Wide-Area Multi-Application PNT Resiliency Solution
By Stephen Bartlett, Gerard Offermans and Charles Schue
INNOVATION INSIGHTS with Richard Langley
WHERE HAVE ALL THE SYSTEMS GONE, long time passing?
Radionavigation systems, that is (and apologies to Pete Seeger). If we look at the 1990 Federal Radionavigation Plan (FRP), published by the U.S. Departments of Transportation and Defense, as I did in this column in March 1992, we see that there were 10 radionavigation systems in use by different user segments: Loran-C, Omega, very high frequency (VHF) Omnidirectional Range/Distance Measuring Equipment, Tactical Air Navigation, the Instrument Landing System, the Microwave Landing System, Transit, aviation radiobeacons, marine radiobeacons and GPS.
The latest FRP, issued in 2014, includes only seven or six and a half when you consider that marine radiobeacons were mostly phased out in the intervening years. Systems were shut down because with the advent of GPS, they were considered to be redundant. While there were attendant cost savings, the closure of the various systems has resulted in a dangerous virtual sole dependence on GPS for navigation without any backup.
Transit, was the first to go. It consisted of a constellation of six or seven active satellites in circular, polar orbits at altitudes of roughly 1,100 kilometers. The satellites transmitted signals on 150 and 400 MHz, and receivers measured the integrated Doppler frequency shift of the received signals. Transit was terminated at the end of 1996.
Transit was followed by the Omega hyperbolic navigation system. Omega consisted of eight stations around the globe transmitting time-shared carrier-wave signals on four frequencies between 10.2 and 13.6 kHz. The Omega system was closed down in September 1997.
The marine radiobeacons have been mostly shut down in recent years, although aeronautical beacons continue to operate. Radiobeacons are nondirectional transmitters that operate in the low- and medium-frequency bands. Some marine radiobeacons became Differential GPS stations and subsequently part of the Nationwide DGPS network. That network is being scaled back to provide only coastal and Great Lakes coverage.
And that brings us to Loran-C. Like Omega, it was also a hyperbolic navigation system. A receiver measured the difference in times of arrival of pulses transmitted at 100 kHz by a chain of three to five synchronized stations separated by hundreds of kilometers. At one time, the operation of Loran-C was the responsibility of the U.S. Coast Guard. Together with a number of host nations, the Coast Guard operated 17 chains of stations around the world, including one jointly operated with Russia. These stations provided coverage of the coastal areas of North America and the U.S. interior, northern Europe, the Mediterranean Sea, the Far East and the Hawaiian Islands. Additionally, several other countries operated Loran-C stations. Although moves were already underway to update the Loran technology, the Obama administration decided to terminate Loran-C in the U.S., considering it to be an unnecessary antiquated system. The Coast Guard terminated the transmission of all U.S. Loran-C signals in February 2010 and began dismantling stations.
So, is there no longer a viable non-GNSS alternative or backup system for GPS navigation? While there are other possibilities for time transfer, one of GPS’s other applications, there is no widely available substitute navigation system. Currently. However, as we will see in this month’s column, a new version of Loran — Enhanced Loran or eLoran — has been developed and is being tested on the U.S. east coast. Not your father’s Loran, eLoran seems to be the perfect solution for PNT resiliency.
Telecommunications, energy, finance and transportation are just four among the many critical infrastructure / key resource sectors that have come to rely solely on GPS for positioning, navigation and timing (PNT). In fact, the U.S. Department of Homeland Security (DHS) has determined that 11 of the 16 critical infrastructure sectors in the U.S. are critically dependent on GPS for timing. While we can start to imagine what a day without GPS might be like, we’d really rather not — it would be somewhat depressing and really quite dangerous. We would rather imagine a day when there is a wide-area complementary solution available that protects and augments GPS. In this article, we will delve into such a solution: Enhanced Loran, or eLoran for short. We will explain how it works, debunk some myths, speculate on how it could be used in the U.S. (and abroad), highlight the state of current technology and discuss the state of the possible. We will also summarize the state of eLoran in the world and where things might go from here.
What Is eLoran?
eLoran is the latest in the longstanding and proven series of low-frequency, LOng-RAnge Navigation (LORAN) systems, one that takes full advantage of 21st-century technology. It meets the accuracy, availability, integrity and continuity performance requirements for maritime harbor entrance and approach maneuvers, aviation non-precision instrument approaches, land-mobile vehicle navigation and location-based services. It’s a precise source of time (phase) and frequency. Additionally, eLoran provides user bearing (azimuth) and has built-in integrity. In full disclosure, however, eLoran is only a 2D positioning solution unless integrated with a simple altimeter.
eLoran is a low-frequency radionavigation system that operates in the frequency band of 90 to 110 kHz. eLoran is built on internationally standardized Loran-C, and provides a high-power PNT service for use by all modes of transport and in other applications. eLoran is an independent dissimilar complement to GNSS. It allows GNSS users to retain the safety, security and economic benefits of GNSS even when their satellite services are disrupted.
eLoran uses pulsed signals at a center frequency of 100 kHz. The pulses are designed to allow receivers to distinguish between the groundwave and skywave components in the received composite signal. This way, the eLoran signals can be used over very long ranges without fading or uncertainty in the time-of-arrival (TOA) measurement related to skywaves.
Although eLoran is based upon Loran-C, it has key differences:
All transmissions are synchronized to UTC (like GPS)
Time-of-transmission control
The ability to use differential corrections (similar to DGPS)
Receivers use “all-in-view” signals
Includes one or more Loran data channels that provide: Low-rate data messaging, added integrity, differential corrections (dLoran and/or DGPS) and other communications including navigation messages.
An eLoran receiver measures the TOA of the eLoran signal:
TOA = TOR – TOT = PF + SF + ASF + ∆Rx
where TOR is time of reception, TOT is time of transmission, PF is the primary factor (propagation delay through air), SF is the secondary factor (propagation delay over sea), ASF is the additional secondary factor (propagation delay over terrain) and ∆Rx is the delay due to receiver electronics and cables.
The primary and secondary factors are well-defined delays and can be calculated as a function of distance. The additional secondary factor delay is mostly unknown at the time of installation. Fortunately, the ASFs remain very stable over time. Any fine changes in ASF over time may be compensated for by one or more differential eLoran reference station sites providing corrections over the Loran data channel.
When eLoran is used for positioning, a minimum of three eLoran transmitting sites are needed to calculate a two-dimensional position fix and time. Time (phase) and frequency can be derived from a single transmitting site as well. With three sites, timing can be derived while a receiver is in motion. An integrated eLoran/GPS receiver can take advantage of combinations of eLoran and GPS transmissions to develop a PNT solution. Any additional measurements provide a means to improve the solution’s accuracy (using weighted least squares) or to protect the solution’s integrity (by receiver-autonomous integrity monitoring).
To achieve the highest accuracy levels, the user receiver corrects its TOA measurements with the published ASF values for the area and differential eLoran corrections received through the Loran data channel. ASF maps for specific geographic areas are distributed to users in a receiver-independent data format that is currently being standardized by the Radio Technical Committee for Maritime Services’ (RTCM’s) Special Committee (SC) 127 on eLoran. The ASF map data would be published by the service provider responsible for aids to navigation.
As described before, the measured ASF values remain stable over long periods of time. Any small changes in the published ASFs due to changes in propagation path characteristics or transmitter-related delays will be compensated for by differential corrections. For this, a differential eLoran reference station site is deployed within 20 to 30 miles (32 to 48 kilometers) of the area of interest. The reference station compares its measured ASFs against the published values and broadcasts corrections to the users through the Loran data channel. Figure 1 shows the principle of differential eLoran positioning in a maritime environment and is representative of its use in other modalities as well.
Figure 1. Overview of a representative eLoran system.
eLoran meets the application requirements shown in Table 1. While unaided, Loran-C does not meet the requirements for a multi-modal, redundant PNT system, specifically the position accuracy requirement. The U.S. first developed eLoran to reduce the positioning error and to enable the system to meet modal performance requirements.
Table 1. eLoran system performance requirements.
eLoran Applications
We are staunch advocates of GPS and believe it should be fully funded, kept technically advanced, protected, toughened and augmented. When GPS is available and trustworthy, it should be used. However, no technology is failsafe, and prudent users should not rely on a sole source for their PNT needs. GPS has been called “a single point of failure” for much of the U.S. economy and critical infrastructure. Applications and requirements vary widely from wireless network communications of ± 1.5 microseconds, to maritime harbor entrance and approach requirements of ± 20 meters, to phasor measurement unit requirements in the electric power grid of ± 500 nanoseconds.
It is important to recognize the challenge of providing assured PNT while also taking advantage of the efficiencies gained by implementing a common solution across all sectors, industries and users. Point solutions can provide complementary PNT for specific individual or modal needs, and any resilient PNT ecosystem includes multiple levels of redundancy.
Some key application areas in which eLoran can provide complementary PNT are telecommunications, energy, finance and transportation. We believe these will be some of the first sectors to adopt and exploit eLoran as a component of their critical infrastructure protection and possibly as a co-primary PNT solution alongside GPS.
Telecommunications Sector. A March 2014 letter from the Alliance for Telecommunications Industry Solutions (ATIS) to the National Security Telecommunications Advisory Committee contained an attached document, Recommended Updates to Telecom Vulnerability to Loss of GPS Signals Documentation, that outlined three areas of concern that ATIS has identified relating to the exposure of commercial communications systems to a loss of the GPS signal. Included in the documentation was the statement: “With the Loran systems decommissioned, GPS is currently the only technology that can meet synchronization requirements for E911 as there is no other widely available access to UTC time of day in the United States.” eLoran’s Loran data channel provides the UTC time-of-day information that the telecommunications industry seeks, as well as providing complementary timing (phase) and/or frequency solutions that would mitigate ATIS’s concerns about: (1) the size of the area and duration effects of a GPS outage, (2) the effects of spoofing, (3) the inability of oven-controlled crystal oscillators (OCXOs) to maintain phase alignment for 24 hours at 1.5 microseconds, and (4) the phase performance of OCXOs in varying temperature environments.
The European Telecommunications Standards Institute Primary Reference Clock mask is one tool used by the telecommunications industry to determine the quality of timing signals in telecommunication applications. Figure 2 shows that eLoran is able to meet maximum time interval error (a measurement of wander or time stability) requirements, often outperforming GPS. Testing was performed independently in a cooperative effort between the United Kingdom National Physical Laboratory and Chronos Technology Ltd., UrsaNav’s reseller in England.
Figure 2. Maximum time interval error plot of eLoran and GPS.
Energy Sector. At present, GPS is the only time source for phasor measurement unit (PMU) (also known as synchrophasor) and frequency data recorder (FDR) sensors used to collect data that measures the state of an electrical system and manages power quality. PMUs/FDRs are a necessary component of the movement to a smart-grid approach to improve energy efficiency on the electrical grid and in businesses and homes. PMUs and FDRs cease to work if the GPS signal is lost or unstable. In 2013, UrsaNav began working with the University of Tennessee at Knoxville (UTK) to demonstrate the capability of eLoran, alongside GPS, to provide the necessary timing accuracy for UTK’s high-precision FDRs to collect synchrophasor data from the U.S. power grid. The required accuracy of the timing reference source is ± 500 nanoseconds, needed by each device performing synchrophasor measurements.
The laboratory setup in Bedford, Mass., used side-by-side FDRs: one using a GPS receiver and one using an eLoran receiver. Other than replacing the GPS receiver with an eLoran receiver in one of the FDRs, no other changes were made. The eLoran signals were being transmitted from a former U.S. Coast Guard (USCG) Loran Support Unit in Wildwood, N.J., more than 300 miles (483 kilometers) from our Bedford laboratory.
“Raw” eLoran was used for the test, that is, with no differential corrections nor continuous receiver antenna calibration. Figure 3 shows the resultant frequency and phase angle comparisons between GPS and eLoran. Green is eLoran; black is GPS. Frequency comparisons are on the left, top and bottom. Phase angle comparisons are on the right, top and bottom. The bottom left graph is a blow-up of the area encircled in red in the top left graph. The bottom right graph is a blow-up of the area encircled in red in the top right graph. In both cases, eLoran performs on par with GPS.
Figure 3. Frequency data recorder outputs from GPS and eLoran.
Financial Sector. A European Securities and Markets Authority (ESMA) report, dated May 22, 2014, indicates that the majority of trading venues are already coordinated with GPS time, and further states that the deployment of these systems might be costly and technically challenging. ESMA’s view is that each trading venue and market participant should rely on an atomic clock to issue timestamps. An eLoran timing alternative would be less costly, less technically challenging, and, when used in concert with other solutions (such as GPS, atomic clocks or Network Time Protocol / Precision Time Protocol) would also provide trusted time. eLoran would provide absolute time over very wide areas, thereby allowing dispersed markets and users to take advantage of this synchronized time solution. Additionally, eLoran can often provide time indoors, using a magnetic field (H-field) antenna, thereby precluding the permits and expense required for a rooftop antenna installation. ESMA has asked for industry comment on its proposed requirement to synchronize clocks to the microsecond level, and invited industry responses to its preliminary view that business clocks be accurate at least up to the microsecond level.
Transportation Sector – Aviation. PNT use in air traffic management is illustrative. In accord with U.S. Federal Aviation Administration (FAA) planning, a principal surveillance source in the U.S. national air space (NAS) by 2020 will be Automatic Dependent Surveillance-Broadcast (ADS-B), where the required positional accuracy of aircraft relies on GPS position. Moreover, the independent validation and backup of GPS-derived positions relies on accurate time-of-arrival measurements at a network of 650 radio stations in the NAS that currently use GPS-disciplined clocks with accuracy down to 30 nanoseconds. These radio stations are critical infrastructure of the Surveillance and Broadcast Services (SBS) system, which provides ADS-B surveillance to FAA air traffic management (ATM).
The FAA recognizes the need for a backup to surveillance and navigation in the event of local, regional and wide-scale GPS outages, and is examining both near-term and long-term strategies for continuity of operations during those outages. Because of the long lead times for ATM technology insertion, near-term mitigation strategies out to at least 10 years are constrained by existing ATM ground infrastructure and current avionics capabilities. Long-term solutions are not so constrained, and may be based on new signals in space, new ground infrastructure and new avionics capabilities.
Surveillance. Beginning in 2020, ADS-B will be a principal surveillance technology. In recognition of the need for a backup if GPS fails, the FAA is planning to maintain a mix of beacon-interrogation radar and wide-area multilateration (WAM) in the near term. The long-term strategy is still very much in the evolutionary stage.
Navigation. Near-term strategies involve a mix of approaches based upon existing infrastructure and the current capability of avionics. A leading approach, referred to as DME/DME/IRU, uses two-way ranging to multiple Distance Measuring Equipment (DME) facilities augmented by the avionics inertial reference unit (IRU). This approach is practical and applicable more to air carrier aircraft than regional jets or general aviation. Other approaches rely to some extent on the use of very high frequency Omni-Directional Range (VOR) facilities. As with surveillance, the long-term strategy is very much evolutionary.
It is instructive to note that near-term solutions rely on existing radar, DME and VOR infrastructure because it is in place and is compatible with existing avionics. In the long-term view, new technologies with less costly infrastructure are likely to be more cost-effective, especially if they provide benefits beyond ATM applications. eLoran is such a technology.
Transportation Sector – Maritime. There is an increasing awareness in the maritime world that no single system can provide PNT resiliently under all circumstances. At this moment, GPS (with augmentations) is used on most commercial vessels, and in many cases integrated into systems we did not expect would need or use GPS-derived position or time. Even though the introduction of GLONASS, Galileo, BeiDou and other GNSS systems will provide some resilience, the underlying (satellite) technology remains the same, only providing relatively weak signals from space at mostly the same or close-by frequencies for compatibility and inter-operability.
The International Maritime Organization (IMO) recognizes the need for multiple PNT systems on board maritime vessels. The organization developed the e-Navigation concept to increase maritime safety and security via means of electronic navigation, which calls for at least two independent dissimilar sources of positioning and time in a navigation system to make it robust and fail safe. As a follow on, IMO’s Navigation, Communications and Search and Rescue Committee is considering performance standards for multi-system shipborne navigation receivers, which includes placeholders for satellite, augmentation and terrestrial systems.
The most viable terrestrial system providing PNT services that meet IMO’s requirements is eLoran. With three eLoran transmitters in good geometry, eLoran can provide sub-10 meter (95 percent probability level) horizontal positioning accuracy and UTC synchronization within 50 nanoseconds, sufficient to be the co-primary PNT solution with GNSS. The General Lighthouse Authorities of the United Kingdom and Ireland (GLAs) have installed UrsaNav’s differential eLoran reference stations to provide the world’s first initial operational capability (IOC) eLoran system.
Together with Loran transmitters in England, France, Germany, Norway and Denmark, the differential eLoran reference stations provide better than 10-meter positioning accuracy at seven ports and port approaches along the English and Scottish east coast. IOC was achieved at the end of 2014, with full operational capability planned for 2018. Other nations have either begun, or are exploring, similar projects.
Figure 4 shows the accuracy of an eLoran position at the differential reference station on the Humber River in England. Figure 5 shows the position accuracy while on board a vessel transiting outbound on the river from Humber to the North Sea.
Figure 4. Zero-baseline accuracy at Humber reference station.Figure 5. Onboard, en route accuracy on the Humber River.
Current State of eLoran Technology
eLoran technology has been available since the mid-1990s and is still available today. In fact, the state-of-the-art of eLoran continues to advance along with other 21st-century technology. eLoran system technology can be broken down into a few simple components: transmitting site, control and monitor site, differential reference station site and user equipment.
Modern transmitting site equipment consists of a high-power, modular, fully redundant, hot-swappable and software configurable transmitter, and sophisticated timing and control equipment. Standard transmitter configurations are available in power ranges from 125 kilowatts to 1.5 megawatts. The timing and control equipment includes a variety of external timing inputs to a remote time scale, and a local time scale consisting of three ensembled cesium-based primary reference standards. The local time scale is not directly coupled to the remote time scale. Having a robust local time scale while still monitoring many types of external time sources provides a unique ability to provide proof-of-position and proof-of-time. Modern eLoran transmitting site equipment is smaller, lighter, requires less input power, and generates significantly less waste heat than previously used Loran-C equipment.
The core technology at a differential eLoran reference station site consists of three differential eLoran reference station or integrity monitors (RSIMs) configurable as reference station (RS) or integrity monitor (IM) or hot standby (RS or IM). The site includes electric field (E-field) antennas for each of the three RSIMs.
Modern eLoran receivers are really software-defined radios, and are backward compatible with Loran-C and forward compatible, through firmware or software changes. ASF tables are included in the receivers, and can be updated via the Loran data channel. eLoran receivers can be standalone or integrated with GNSS, inertial navigation systems, chip-scale atomic clocks, barometric altimeters, sensors for signals-of-opportunity, and so on. Basically, any technology that can be integrated with GPS can also be integrated with eLoran.
Figure 6 shows a resilient PNT receiver that includes GPS, DGPS, eLoran and a dual-band (100/300 kHz) E-field antenna. The left-hand antenna, shown installed on the P&O Ferries’ Pride of Hull, is the resilient PNT antenna. The right-hand antenna is a standard GPS antenna.
Figure 6. Resilient PNT receiver and dual-band antenna.
World View of eLoran
Nine nations are operating Loran-C or eLoran stations, including Russia and China. It is our understanding that the Republic of Korea, India and the Kingdom of Saudi Arabia are pursuing the installation of eLoran technology or upgrading their Loran-C technology to eLoran.
The modernization and upgrade of the U.S. Loran-C system to eLoran was a congressionally mandated program jointly executed by the FAA and USCG from 1997 to 2009, and funded at $160 million. During this time, eLoran was successfully tested and demonstrated in all modes: aviation, maritime, land-mobile, location-based, and timing and frequency. Further, eLoran has been successfully in operation in the U.K. for several years. Every national and international government, industry and academic report has concluded that GNSS is vulnerable and that eLoran is the best complementary solution to help negate those vulnerabilities.
The U.S. terminated its Loran-C service, and thereby its nascent eLoran program, in 2010. Canada followed suit and terminated its Loran-C service as well. Shortly thereafter, DHS/USCG began dismantling or demolishing the modernized infrastructure. However, in December 2014, Congress directed that DHS/USCG preserve the existing, unused U.S. Loran-C infrastructure, unless the Secretary of Homeland Security certifies it is not needed for a system to complement GPS.
In March 2015, U.S. House of Representatives Resolution (H.R.) 1678, a bill that would require establishment of a strong, difficult-to-disrupt terrestrial system to complement GPS, and to serve as another source of PNT when GPS isn’t available, was referred to the Committee on Armed Services. The bill seeks to amend the language that provided for the establishment and management of GPS in Title 10, the section of law that deals with the armed services. We understand that other members of Congress have expressed interest and will be co-sponsoring the bipartisan bill. H.R. 1678 was introduced by Congressman John Garamendi (Democrat, Calif.) with Congressman Duncan Hunter (Republican, Calif.), Congressman Frank LoBiondo (Republican, N.J.) and Congressman Peter DeFazio (Democrat, Ore.) as the initial co-sponsors. In August, the bill was referred to the Subcommittee on Strategic Forces.
Additionally, in May 2015, the DHS and USCG entered into a cooperative research and development agreement with UrsaNav and Exelis (now part of Harris Corp.) to research, evaluate and document at least one alternative to GPS as a means of providing PNT information in the form of eLoran.
It is our understanding that the U.S. Congress is still considerably concerned about the lack of a complementary PNT solution to safeguard U.S. critical infrastructure and key resource sectors, and to protect our economy in the event of a GPS outage. Congress continues to press the administration for a resolution, in the form of a continental U.S. eLoran system, before our nation is placed at further risk.
Acknowledgments
The authors wish to acknowledge the assistance of Dr. Ron Bruno, Harris Corp., and Dr. Paul Williams and Chris Hargreaves, GLAs.
Manufacturers
UrsaNav provided the eLoran receiver and Symmetricom, now Microsemi, provided the GPS receiver for the timing tests shown in Figure 2.
STEVE BARTLETT is vice president of operations at UrsaNav, Inc., North Billerica, Mass.
GERARD OFFERMANS is senior research scientist at UrsaNav engaged in various R&D project work and product development.
CHARLES SCHUE is co-owner and president of UrsaNav.
FURTHER READING
eLoran
“Can eLoran Deliver Resilient PNT?” by N. Ward, C. Hargreaves, P. Williams and M. Bransby in Proceedings of The Institute of Navigation 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 20–23, 2015, pp. 1051–1054.
“eLoran Initial Operational Capability in the United Kingdom – First Results” by G. Offermans, E. Johannessen, S. Bartlett, C. Schue, A. Grebnev, M. Bransby, P. Williams and C. Hargreaves in Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, Calif., January 26–28, 2015, pp. 27–39.
“Implementing a Wide Area High Accuracy UTC Service via eLoran” by G. Offermans, E. Johannessen and C. Schue in Proceedings of the 46th Annual Precise Time and Time Interval Systems and Applications Meeting, Boston, Mass., December 2014, pp. 124–133.
2014 Federal Radionavigation Plan (F, DOT-VNTSC-OST-R-15-01, U.S. Department of Defense, Department of Homeland Security and Department of Transportation, Washington, D.C., available from the National Technical Information Service, Springfield, Virginia, 2015.
1990 Federal Radionavigation Plan, DOT-VNTSC-RSPA-90-3 and DOD-4650.4, U.S. Department of Transportation and U.S. Department of Defense, Washington, D.C., available from the National Technical Information Service, Springfield, Virginia, 1990.
The ITU World Radiocommunication Conference (WRC-15), in session in Geneva Nov. 2-27, has 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 time-scale available for all modern electronic navigation and computerized systems to operate while eliminating the need for specialized ad hoc time systems.
The decision by WRC-15 calls for further studies regarding current and potential future reference time-scales, including their impact and applications. 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 and as maintained by the International Bureau of Weights and Measures (BIPM).
WRC-15 also calls for reinforcing the links between ITU and the International Bureau of Weights and Measures (BIPM). ITU would continue to be responsible for the dissemination of time signals via radiocommunication and BIPM for establishing and maintaining the second of the International System of Units (SI) and its dissemination through the reference time scale.
Studies will be coordinated by ITU along with international organizations such as the International Maritime Organization (IMO), the International Civil Aviation Organization (ICAO), the General Conference on Weights and Measures (CGPM), the International Committee for Weights and Measures (CIPM), the International Bureau of Weights and Measures (BIPM), the International Earth Rotation and Reference Systems Service (IERS), the International Union of Geodesy and Geophysics (IUGG), the International Union of Radio Science (URSI), the International Organization for Standardization (ISO), the World Meteorological Organization (WMO), and the International Astronomical Union (IAU).
“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.”
“The worldwide coordination of time signals is critical for the functioning and reliability of systems that depend on time,” said François Rancy, Director of the ITU Radiocommunication Bureau. “ITU will continue to work with international organizations, industry and user groups towards providing coherent advice on current and potential future reference time-scales.”
CLEVELAND, Ohio — November 18, 2015 — GPS World relaunched this week with a redesigned print magazine and website, GPSWorld.com. Both feature a new logo, new design and widened coverage.
The GPS World brand has expanded its technical coverage to include all GNSS and Position, Navigation & Timing (PNT) solutions, trends and applications.
“We celebrated GPS World’s 25th anniversary in 2014 by embarking on the brand’s most-comprehensive research project to date,” said Kevin Stoltman, president and CEO of Cleveland-based North Coast Media, GPS World’s parent company.
The GPS World team conducted a research project and used a rebranding/repositioning expert to help better serve its industry-leading family of readers and marketing partners for decades to come.
“After months of comprehensive focus groups and surveys, we discovered readers and advertisers across the globe are fiercely loyal to GPS World,” Stoltman adds. “They love what we do, the information we offer. They just crave more of it: They want us to cover all GNSS and PNT technologies, trends and applications — and that’s exactly what we’re doing now, across all media platforms: print, digital and events.”
GPS World November 2015
The new GPS World publication also features a six-fold increase in segment-specific technical coverage — GNSS/PNT trends, obstacles and opportunities related to: Survey, Mapping, OEM, unmanned autonomous vehicles (UAVs), Defense, Mobile, Transportation and Machine Control. Those increase in segments also are reflected on GPSWorld.com.
“GNSS — and GPS as its leading element — remains at the core of all that we and the industry do,” said Alan Cameron, editor-in-chief and publisher of GPS World. “But it has become abundantly clear that to deliver the everywhere-everytime solution, GPS/GNSS require augmentation, back-up and alternatives. This is the promise of the future for UAVs, critical infrastructure, defense, machine control, surveying, construction and countless other fields: a consistent, highly accurate PNT solution at all times. Our new brand and expanded coverage represent our commitment to the industry in pursuit of this goal.”
The new website features a mobile-responsive design as well as new opportunities for website sponsorship with the Platinum Website Sponsorship option.
About GPS World
Founded in 1990, GPS World has an independently audited total unduplicated reach of 70,650 — delivering the largest audience in the industry. The B2B media brand publishes nine e-newsletters with a combined readership of more than 113,000, and conducts monthly technical webinars for engineers. Its website, GPSWorld.com, draws an industry-dominant 650,000 visitors and 1.5 million page views annually. (Source: June 2015 Verified Audit Circulation Annual Audit Report)
For more information on advertising or sponsorship opportunities with GPS World, please contact International Account Manager Michelle Mitchell at [email protected] or 216-363-7922.
GPS World is published by North Coast Media LLC, the largest B2B publishing company headquartered in Cleveland. NCM’s flagship brands include LP Gas, Pit & Quarry, GPS World, Pest Management Professional, Landscape Management and Golfdom. Ancillary brands include Portable Plants & Equipment, Geospatial Solutions, Athletic Turf, Truman’s Scientific Guide to Pest Management Operations and a host of other leading industry reference books.
The United Launch Alliance (ULA) declined Nov. 16 to submit a bid to launch the GPS III satellite, leaving the field wide open for commercial launch service SpaceX, reports Space News.
The first GPS III satellite is expected to launch in 2018.
Every operational GPS mission has launched on a ULA or heritage rocket — the most recent being the GPS IIF-11, which launched on Oct. 31.
ULA said it did not submit a bid in part because it does not expect to have an Atlas 5 rocket available for the mission, according to Space News. Legislation passed by Congress in 2014 requires the Air force to phase out its use of the Russian-made RD-180 engine that powers the Atlas 5 rocket used by ULA.
Rover positions obtained with 2D LTE versus GPS track.
Positioning with LTE Signals
An alternative to GNSS in urban canyons can be provided by signals from cellular base stations, particularly new signals from long-term evolution (LTE) networks, since LTE coverage will be high in cities. Wide LTE downlink bandwidth provides good resolution of multipath components, which also assists positioning.
A test used a universal software radio peripheral N210 synchronized to a GPS-locked Rubidium frequency standard. A personal computer stored LTE data samples together with GNSS sentences from a u-blox LEA-6T module. A Matlab-algorithm did the complete post-processing, extracting pseudoranges for the LTE base station and calculating the position solution.
Results of a car driven on an urban route show root-mean-square value of the absolute error using LTE compared to GPS position is 43 meters.
Positioning Using LTE Signals, by Fabian Knutti, Mischa Sabathy, Marco Driusso, Heinz Mathis, and Chris Marshall. Presented at the European Navigation Conference 2015.
Seamless Indoors
Sensor Augmented Indoor Navigation and Positioning, by M. Gemelli and Keith Nicholson, Bosch Sensortec. An overview of technologies that guide us indoors in a seamless and reliable manner, highlighting key requirements for motion and pressure sensing, low-power processing, efficient code design, wireless beaconing and map matching. Fusion software needs new data sources: Bluetooth low-energy, Wi-Fi fingerprinting, magnetic fingerprinting, ultrasound. Presented at ION GNSS+ 2015.
Disturbed Ionosphere
Mitigating satellite motion in GPS monitoring of traveling ionospheric disturbances (TIDs), by R.W. Penney and N.K. Jackson-Booth. Discusses the impact of satellite motion on the use of compact arrays of GPS receivers for estimating the velocity of travelling ionospheric disturbances (TIDs). It is shown that satellite motion has subtle effects upon standard techniques of waveform cross-correlation, or time-difference of arrival (TDOA), which can easily lead to spurious TID velocity estimates. In Radio Science, an AGU journal.
The test flight of the first GLONASS-K2 satellite — a new generation GLONASS satellite with a design life of 10 years — is expected to take place from late 2017 to early 2018, RIA Novosti reports. The Russian news agency quoted Nikolai Testoyedov, CEO of Information Satellite Systems—Reshetnev, speaking at the 2015 Dubai Air Show.
According to Testoyedov, the GLONASS-K2 satellites had difficulty being equipped following international sanctions imposed on a number of electronic components. The first unit of the series has been built, he said.
Nine GLONASS-M satellites are currently in reserve, and another nine GLONASS-K1 satellites are in production, Testoyedov said. Mass production of GLONASS-K2 satellites is expected to take place following the test, so that by the end of 2018 GLONASS-K2 satellites would be subsequently mass produced, while maintaining the regular structure of the orbital group.
With a GLONASS-M lifetime of seven years, and GLONASS K-1 and GLONASS-K2 of 10 years, the GLONASS system will be updated through 2028-2030, concluded Testoyedov.
China’s new third-generation BeiDou satellites are broadcasting some new signals in space. The newest signal, which just began broadcasting from a satellite launched on Sept. 30, is similar to the future GPS L1C signal with time-division BOC(1,1) and BOC(6,1) signals. Such a type of modulation is called time-multiplexed binary offset carrier (TMBOC).
Researchers at JAVAD GNSS have been tracking the new signals, particularly those from BeiDou-3 I2S, an inclined geosynchronous orbit (IGSO) spacecraft, NORAD number 40938. I2S is transmitting on three frequency bands.
The JAVAD researchers used the decoding approach described in their February 2013 GPS World article, “Signal Decoding with Conventional Receiver and Antenna: A Case History Using the New Galileo E6-B/C Signal” by Sergei Yudanov. As a result, the signal’s structure was decoded and L1C TMBOC tracking has been successfully tested on the JAVAD GNSS TRE-3 receiver.
In addition, new signals on 1575.42+1.023*14 MHz (B1-2), 1176.45 MHz (E5A) and 1207.14 (E5B) frequencies for three satellites (PRN 32, 33, 34) also have been decoded and tested. Figures 1–4 illustrate the experiment.
Figure 1: BeiDou TMBOC: correlation intensity (l) of BOC(1,1) (red), BOC(6,1) (green) and their sum (blue) versus code chips.Figure 2: BeiDou TMBOC: Output of “early-late” correlator (dI or derivative of I) of BOC(1,1) (red), BOC(6,1) (green) and their sum (blue) versus code chips.Figure 3: BeiDou TMBOC Signal: Horizontal axis: 0 – minus one chip shift; 327 – zero shift; 655 – plus one chip shift. C/NO and iono-free “range minus phase.” Slot – BeiDou signal: C/A – B1; P1 – B1-2; P2 – E5B; L2C – B3; L5 – E5A; L1C – L1C.Figure 4 (right): BeiDou TMBOC Signal: Horizontal axis: 0 – minus one chip shift; 327 – zero shift; 655 – plus one chip shift. C/NO and iono-free “range minus phase.” Slot – BeiDou signal: C/A – B1; P1 – B1-2; P2 – E5B; L2C – B3; L5 – E5A; L1C – L1C.
Researchers Steffen Thoelert and Michael Meurer from the Deutsches Zentrum für Luf t- und Raumfahrt (DLR, German Aerospace Center) have also been busy tracking the newest BeiDou IGSO satellite. Figure 5 shows a spectral measurement of the complete GNSS L-band frequency range, which shows the signal transmissions on B1, B2 and B3 band. The signal was captured with DLR’s high-gain antenna in Weilheim, operated by the DLR German Space Operations Center in Oberpfaffenhofen.
Figure 5: BeiDou Signal: Complete GNSS L-band frequency range, which shows the signal transmissions on B1, B2 and B3 band.
In comparison to the two latest BeiDou-3 MEO satellites, launched on July 25, the IGSO has an additional signal on the B3 band. The MEO satellites transmit only the QPSK(10) whilethe new IGSO also transmits an additional BOC(15,2.5) signal. Figure 6 shows the B3 frequency band separately including a combined theoretical signal (QPSK(10)+BOC(15,2.5)).
Figure 6: BeiDou Signal: the B3 frequency band separately include a combined theoretical signal PSK(10)+BOC(15,2.5)).
IIF-11 up: penultimate GPS Block IIF satellite
A United Launch Alliance Atlas V 401 launched the GPS IIF-11 mission for the U.S. Air Force on Oct. 31.
GPS IIF-11 is the second to last of the Block IIF satellites, delivering a second civil signal (L2C) for dual-frequency equipment, and a new third civil signal (L5) to support commercial aviation and safety-of-life applications. The next generation of GPS satellites is GPS III.
GPS IIF-11 is the third GPS mission to rise this year. GPS IIF-9 launched in March, and GPS IIF-10 in July. The next satellite, GPS-IIF-12, the last of its generation, is destined for space in early February 2016.
Galileos chirp
Shortly after the Galileo satellite using the E24 PRN code started transmitting on Oct. 10, its sibling began transmitting using code E30. Several stations participating in the International GNSS Service Multi-GNSS Experiment are tracking the new satellites; first among those reporting was the University of Liege, Belgium, using its Septentrio PolaRx4 and PolaRxS receivers to download signals.
The two satellites were launched on Sept. 11. A team of engineers from ESA and France’s CNES space agency are preparing for the next launch, scheduled for December.
Q:Where do you see your efforts and thoseof your organization focusing primarily over the next 5–10 years?
Vidal Ashkenazi CEO, Nottingham Scientific Ltd.
A: GPS, and GNSS generally, will continue to be a big part of our work and remain at the core of our activities. We are not tied to a single technology, though. We are driven more by applications — and so we do not rule out the use of other sensors. As GNSS becomes more widely used and people expect more from it, we will make greater use of additional sensors to fulfil application requirements in more demanding environments.
A: GPS was the catalyst for a revolution in the application of precise position and time (that is, “Positime”).But it’s now 20 years old, and the developed world has become dependent on access to Positime, still mostly from GPS but with many likely complements/backups going forward. It is time to get serious and construct a layered PNT architecture to bolster GPS with regional and local/autonomous PNT sources for resiliency and precision.
Terence McGurn Consultant, U.S. Government
A: That we need alternatives to GNSS is now a given. But I see little discussion of the strategy for deploying those alternatives. Currently, we seem to emphasize detection and mitigation of the cause of a GNSS outage. To use a medical analogy, the cause of the patient’s accident is a “nice to know”, but the real issue is to keep the patient/service alive. So I’d like to see more focus on how — and how quickly — we activate the alternatives.
Emergency readiness and response company McMurdo has completed the installation of a six-antenna next-generation Medium-Earth Orbit Search and Rescue (MEOSAR) satellite ground station system in New Zealand.
The project, which is part of a joint initiative with Maritime New Zealand and the Australian Maritime Safety Authority, is expected to significantly boost search-and-rescue capability in the New Zealand and Australia search regions and marks the first implementation of MEOSAR in Asia Pacific.
MEOSAR is the next-generation version of Cospas-Sarsat, the international search-and-rescue satellite system that has helped to save 37,000 lives since 1982. Cospas-Sarsat is in the process of upgrading its satellite system by placing search-and-rescue transponders on new GPS, GLONASS and Galileo satellites. Once qualified as operational, this system augmentation will dramatically improve both the speed and location-accuracy for detecting beacons.
In a typical satellite-based search-and-rescue scenario, ships, aircraft or individuals transmit distress signals from an emergency location beacon via satellite to a fixed ground receiving station or local user terminal. The ground station receives and calculates the location of the distress signal and creates and sends an alert to the appropriate rescue authorities. Today, the beacon-to-alert process depends on a limited number of low Earth orbit (LEO) satellites and may take several hours before a position is confirmed. With MEOSAR, beacon signals will be received more quickly and beacon locations identified with greater accuracy thereby reducing this time to minutes.
“Beacons can take the ‘search’ out of search and rescue, and the MEOSAR system will dramatically increase the global search-and-rescue capability,” said Maritime New Zealand Director Keith Manch. “Emergency distress beacons are key equipment for anyone operating at sea, on land and in the air – whether commercially or recreationally — but they can’t operate without sites like this.”
“This key installation firmly establishes McMurdo as the premier MEOSAR infrastructure provider globally,” said Remi Julien, McMurdo president. “We are committed to partnering with both Maritime New Zealand and the Australia Maritime Safety Authority to ensure that they have the technology, training and long-term support in place to significantly reduce search-and-rescue times and, ultimately, save more lives today and in the future.”
The New Zealand MEOSAR system, and another being installed in Western Australia, will cover one of the largest search-and-rescue areas in the world — from north of Australia/New Zealand to the Equator and south to the South Pole, east to half way across the Pacific, and west half way across the Indian Ocean. The systems will undergo rigorous testing before being officially brought online in late 2017 by Cospas-Sarsat.
There are 58,000 emergency distress beacons registered in New Zealand which, without any changes or updates, will be immediately usable by the new systems. It is estimated, however, that an additional 25,000 beacons are unregistered. Due to the high responsiveness of the MEOSAR system, search-and-rescue authorities strongly recommend beacon registration. This will help the unnecessary deployment of search-and-rescue resources due to inadvertent beacon activations. The Rescue Co-ordination Centre New Zealand, part of Maritime New Zealand, responds to 550 beacon alerts a year.
An artist’s concept of a GPS IIR-M satellite in orbit (courtesy of Lockheed Martin).
Security upgrades developed by Lockheed Martin for the GPS ground control system are now fully operational to safeguard data and ensure satellite availability.
The GPS Intrusion Protection Reinforcement (GIPR) technology refresh is part of the Air Force’s strategy to modernize the current GPS system and to ensure the availability of its services for more than one billion global military, civilian and commercial users daily. GIPR advances the Operational Control Segment’s ability to protect data and infrastructure, enhance the sustainability of the system, and meet future GPS operational requirements. Infusing advanced hardware and software solutions for information assurance provides improved protection against today’s rapidly changing cyber threats, Lockheed Martin said in a news release.
“The GPS Control Segment Sustainment (GCS) contract is vitally important to the sustainment of positioning, navigation and timing services for our military, government officials and citizens,” said Vinny Sica, vice president of Lockheed Martin’s Space Ground Solutions. “A system this large requires continued security focus and that’s where Lockheed Martin’s information security capabilities are on the cutting edge.”
Beyond data protection, GIPR resolves many equipment obsolescence issues and increases system maintainability with modern vendor-supported hardware and operating systems. This is the second major technology refresh on the GPS command and control system since the GCS Sustainment contract was awarded.
The Air Force awarded Lockheed Martin the GIPR engineering modification in 2013, and the system is now fully deployed into the GPS Master Control Station and the Alternate Master Control Station. The project included system design, hardware procurement, software development, network configuration design and technical documentation.
The Global Positioning Systems Directorate at the U.S. Air Force Space and Missile Systems Center contracted the GIPR upgrade. Air Force Space Command’s 2nd Space Operations Squadron (2SOPS), based at Schriever Air Force Base, Colo., manages and operates the GPS constellation for both civil and military users.
Europe’s fifth and sixth Galileo satellites — subject to complex salvage maneuvers following their launch in 2014 into incorrect orbits — will help to perform an ambitious year-long test of Einstein’s most famous theory.
Galileos 5 and 6 were launched together by a Soyuz rocket on August 22, 2014. But the faulty upper stage stranded them in elongated orbits that blocked their use for navigation.
ESA’s specialists moved into action and oversaw a demanding set of maneuvers to raise the low points of their orbits and make them more circular. “The satellites can now reliably operate their navigation payloads continuously, and the European Commission, with the support of ESA, is assessing their eventual operational use,” explained ESA’s senior satnav advisor Javier Ventura-Traveset. “In the meantime, the satellites have accidentally become extremely useful scientifically, as tools to test Einstein’s General Theory of Relativity by measuring more accurately than ever before the way that gravity affects the passing of time.”
The original (in red) and corrected (in blue) orbits of the fifth and sixth Galileo satellites, along with that of the first four satellites (green).
Although the satellites’ orbits have been adjusted, they remain elliptical, with each satellite climbing and falling some 8500 km twice per day. It is those regular shifts in height, and therefore gravity levels, that are valuable to researchers.
Albert Einstein predicted a century ago that time would pass more slowly close to a massive object. It has been verified experimentally, most significantly in 1976 when a hydrogen maser atomic clock on Gravity Probe A was launched 10,000 km into space, confirming the prediction to within 140 parts in a million.
Passive hydrogen maser atomic clock of the type flown on Galileo, accurate to one second in three million years. (Photo: ESA)
Atomic clocks on navigation satellites have to take into account they run faster in orbit than on the ground — a few tenths of a microsecond per day, which would give us navigation errors of around 10 km per day.
“Now, for the first time since Gravity Probe A, we have the opportunity to improve the precision and confirm Einstein’s theory to a higher degree,” comments Javier.
This new effort takes advantage of the passive hydrogen maser atomic clock aboard each Galileo, the elongated orbits creating varying time dilation, and the continuous monitoring thanks to the global network of ground stations.
The Gravity Probe A payload of 1976, flown in a highly elliptic single orbit to measure the “gravitational redshift” of Einstein’s Theory of General Relativity more accurately than ever before, seen with its designers Robert Vessot and Martin Levine of the Smithsonian Astrophysical Observatory. The experiment compared a hydrogen maser clock on Earth with its replica in space as it ascended to about 10,000 km, and confirmed theoretical expectations to an accuracy of 0.02%. (ESA file photo)
“Moreover, while the Gravity Probe A experiment involved a single orbit of Earth, we will be able to monitor hundreds of orbits over the course of a year,” explained Javier. “This opens up the prospect of gradually refining our measurements by identifying and removing systematic errors. Eliminating those errors is actually one of the big challenges. For that we count on the support of Europe’s best experts plus precise tracking from the International Global Navigation Satellite System Service, along with tracking to centimeter accuracy by laser.”
The results are expected in about one year, projected to quadruple the accuracy on the Gravity Probe A results.
ESA’s forthcoming Atomic Clock Ensemble in Space experiment, planned to fly on the International Space Station in 2017, will go on to test Einstein’s theory down to 2–3 parts per million.
