“The new LightSquared business plan and the new FCC rules significantly expand the terrestrial transmission increasing the potential for interference to GPS receivers,” the U.S. departments of Defense and Transportation (DOD and DOT) wrote to the Federal Communications Commission in 2011 after the FCC granted the company permission to offer broadband via its satellite and base station networks to a wide variety of mobile broadband partners. The move — heralded by supporters as hastening the advent of 4G services across the country, especially in underserved communities — sent shockwaves across the GNSS/PNT community, which opposed the plan forcefully for the threat it posed to GPS.
Reborn in December 2015 as Ligado Networks, the company obtained the FCC’s unanimous approval in April 2020 for the use of spectrum near the L-bands used by GPS for its 5G network. It is scheduled to launch its first deployment at the end of September.
Nearly all the federal government, including DOD and DOT, as well as most manufacturers of GNSS receivers, are very strongly opposed. On September 9, the National Academies of Science, Engineering and Medicine’s Committee to Review FCC Order 20-48 will release its independent evaluation of the issue, as mandated by the 2021 National Defense Authorization Act.
The study, begun in May 2021, considered three issues:
1. Which of two prevailing proposed approaches for evaluating harmful interference is most effective to mitigate the risk of harm.
2. The potential for harmful interference from Ligado to mobile satellite services — such as Iridium.
3. The feasibility and practicality of the remedies proposed by the FCC.
I am very pleased to announce that Prof. Penina “Penny” Axelrad has joined GPS World’s Editorial Advisory Board.
Penny is a University of Colorado (CU) Distinguished Professor in the Ann and HJ Smead Department of Aerospace Engineering Sciences. She received her B.S. and M.S. degrees in Aeronautical and Astronautical Engineering from MIT and her Ph.D. in Aeronautics and Astronautics from Stanford University. She has been a member of the faculty at CU since 1992, serving as primary advisor for 25 Ph.D. graduates and many M.S. and undergraduate research students.
Penny has been active in research on GPS and PNT technology and applications for aircraft, spacecraft and remote sensing, as well as estimation of satellite orbits and attitude, since 1985, co-authoring more than 60 journal papers and 130 conference papers. She has served as principal investigator or co-investigator on grants and contracts totaling $17 million. She is a Fellow of the Institute of Navigation and the American Institute of Aeronautics and Astronautics, and a member of the National Academy of Engineering. Since 2013 she has served as a member of the National Space-Based Positioning, Navigation and Timing (PNT) Advisory Board.
I overlapped with Penny at MIT in the mid-1980s. Now, nearly 40 years later, I look forward to her contributions to this magazine.
The average age of surveyors in the United States is nearly that of retirement. Can new technology attract a new generation to the profession?
“We do not fully understand the trend in the United States,” said Simon Peng, ComNav Technology, “but in China we find that modern survey technology — such as UAV/lidar mapping and total stations — make field work simple. New trends such as computer imaging, point clouds and building information models (BIM) attract young surveying engineers.”
Using the equipment in the field is becoming increasingly easier, said Bernhard Richter, Leica Geosystems. “Our goal is that operating the field equipment should not be more difficult than playing with your smartphone. That means that you don’t need the super expert in the field so much anymore.” However, he argued, “someone who studied surveying should now be more the data manager, have the expertise to put the data in geospatial relation, and know in which reference frame he is operating.”
For example, that person needs to know about orthometric and ellipsoidal heights, especially for engineering projects between countries that might have different height codes. “Anybody who has an interest to geolocate an object can capture the data and upload it to the cloud environment,” Richter said. “Then there are the data managers. Certainly, they need to know the physical limits of surveying technology, and they need to manage the complexity of modeling Earth. They need to become data managers to really put data to work.”
“The anticipated number of new professionals is not necessarily replacing all the surveyors who are expected to retire over the next 10 years,” said Boris Skopljak, Trimble. To tackle this challenge Trimble is using a two-pronged approach: attracting younger workers by raising awareness of surveying as a future career and modernization of the profession. For the first prong, Skopljak cited “phenomenal programs out there, such as Get Kids into Survey.” He pointed out that many Trimble employees are part of those education programs, “promoting inclusion of not just a younger generation, but also of women and minority groups that are heavily underrepresented in our industry today.”
For the second prong, “Digital data capture workflows present opportunities. A very common interview question we ask these days is ‘Do you play video games?’ Generally, those young professionals who are gamers thrive in the 3D environment. The technology aligns well with the interests of younger folks.”
Additionally, a growing number of educational institutions are evolving their curriculums to meet these needs, said Skopljak. Trimble is establishing Trimble Technology Labs in selected academic institutions around the world that are helping students access the latest technology and the best modern engineering practices. Boosting productivity also helps compensate for the declining number of surveyors, because it reduces the number of people needed to get the job done. “As the technology becomes easier to digest and operate and more focused on the workflows, it also becomes easier for companies to standardize it and attract talent,” Skopljak said.
One of the biggest threats to the survey profession, according to Huff, is that it “let bits and pieces of traditional surveys fall off to the wayside.” Geographic information systems (GIS) use the same positioning technology, he pointed out. “Fifty years ago, that was more of a function of the surveyor than it was necessarily the GIS profession. In many ways, while the surveyor is aging — the licensed cadastral surveyors certainly are aging — there is a new generation of folks coming through who are leveraging the new technology, such as drones and mobile mapping systems.”
This new generation, Huff argued, will achieve the same accuracies as the previous one partly because it’s getting easier to do so. “We definitely have more of a generation of digital users that can leverage the technology to do things where even my mentors performed many calculations by hand, on the fly, from plain tables in their logbooks with sine, cosine and tangent in them. Now, I think that technology and 3D immersive technology, which hinges on GPS location, attracts a younger crowd to certain facets of the profession.”
François Freulon, Septentrio, agreed that new technologies now available “can be easily adopted by new generations in the profession,” yet added that “quality surveying requires a good formation and experience in the field.” Therefore, he argued, “surveying education systems will need to adapt their programs and incorporate newer techniques such as new positioning modes and corrections.
Surely RTK remains as the main accuracy technique, but this could change quickly in the coming years as correction services bring better performance and regional coverage.”
Advances in GNSS technology constantly expand the range of projects that benefit from them.
ComNav Technology
A telecom company adopted its CORS station to build China’s national CORS service for public companies. It is increasingly used for field robotics, including the development of self-driving cars.
Leica Geosystems
Bernhard Richter, vice president of Geomatics, Leica Geosystems AG, pointed to one of the biggest infrastructure projects in Europe, which aims to connect London to Birmingham, Manchester and Leeds with a high-speed railway system, avoiding the need to fly between those cities. This will have great environmental benefits because high-speed trains are much more efficient than planes.
However, high-speed rail requires tremendous precision. “First comes the prep work, moving dirt,” said Richter. “Then you must install the railroad ties with tenths of a millimeter precision relative to each other to avoid side accelerations. For a surveyor, it really has everything in one project. You need to constantly work with civil engineers. You then try to build as much as possible with machine-control-guided systems to make the leveling as automated as possible.” The project will include building bridges over whole valleys and monitoring them, particularly during the construction phase, to ensure that they are not moving.
“Even the factory they are building is huge, so just to build the factory you need a lot of surveying,” Richter said. The project is generating 25,000 jobs at 300 construction sites, all of which must be managed on very tight schedules. In this context, the quality of the survey gear is critical. “On a construction site, the surveyor should be an invisible person,” Richter said. “When they come with the big machines and want to get stuff done, they don’t want a surveyor on the site. So, he has to work off hours, then remain on alert and trust that what comes out of an instrument is correct.” Leica Geosystems is one of the main suppliers for this project. “They chose us because of our focus on reliability, trust and quality.”
Trimble
Software is increasingly driving sales, pointed out Boris Skopljak, vice president, Surveying & Mapping Strategy and Product Marketing at Trimble Inc. As an example, he cited Trimble’s SX12 scanning total station, which uses Trimble Access software to leverage scanning, imaging and traditional total station capabilities in the field. “We have provided more inspection tools to enable people to decide whether something is meeting the tolerance.” The Trimble Connect cloud-based collaboration platform, coupled with the continuous field and office connectivity, has driven productivity increases and moved customers toward choosing the company’s solutions, he said.
As an example of Trimble solutions, Skopljak cited City Rail Link, New Zealand’s first underground rail network and the largest transportation infrastructure project ever undertaken there. “The Trimble R10 was integral to acquiring static observations above the work site, while the Trimble S9, DiNi and Trimble Business Center network adjustment were game changers for the survey control network,” he said. To expedite mine tunneling the surveyors used the SX12’s combined total station and scanning functionality with Trimble Access field software infield inspection tools. “Fewer customers are choosing solutions on a spec. It’s not about how many satellites you can track, for how many days, or how many points you can scan. They are choosing solutions based on the ecosystem and productivity.”
“Nothing can remain immense if it can be measured,” Hannah Arendt wrote in 1958 in The Human Condition. This could be the guiding inspiration for any geodesist or surveyor throughout history. In about 240 B.C., Eratosthenes became the father of geodesy by ingeniously measuring Earth’s circumference using the Sun, a well, a vertical column, the distance a camel caravan traveled from Syene to Alexandria and some basic mathematics. His estimate of 46,000 kilometers was 16% too large but remarkably close considering that he lacked any modern measuring tool. (For a great account of this epic feat, see John Noble Wilford’s The Mapmakers.)
Geodesy, a branch of applied mathematics, is concerned with accurately measuring and understanding three of Earth’s fundamental properties: its geometric shape, its orientation in space, and its gravity field. Earth’s true shape varies from the mathematically smooth surface of an ellipsoid due to local differences in its density that cause variations in the strength of the gravitational pull, in turn causing regions to dip below or bulge above a reference ellipsoid.
This undulating shape is the geoid, which geodesists have defined as the three-dimensional surface along which the pull of gravity is a specific constant. It serves as the zero-level surface for height measurements globally, and all GNSS are pegged to it. It is a hypothetical surface that essentially represents an extension of the idealized mean sea level over (actually, mostly under) Earth’s land surface. Unlike the surface of the oceans, however, it is unaffected by wind, waves, the Moon, or forces other than Earth’s gravity.
Surveyors are content with measuring much smaller portions of Earth’s surface, from single lots to national boundaries. Unlike Eratosthenes, they work with the latest fruit of modern science and technology — including GNSS receivers, robotic total stations, inertial measurement units, lidar, other sensors and unmanned aerial vehicles — and can measure distances with millimeter precision.
When I started in this business a little more than 20 years ago, we used to group GPS receivers by accuracy into three buckets: consumer grade, resource/mapping grade and survey grade. As accuracy has increased for all GNSS receivers, the boundaries between those categories, especially between mapping and surveying, have blurred. Additionally, we now have way more GNSS satellites — in some parts of the world, as many as 70 are in view at one time — and a panoply of public and private, ground-based and satellite-based corrections services.
So, surveyors have a growing set of tools, and they are constantly getting more accurate and more user-friendly.
Now, let me throw another number in the mix: 66. That is the average age of surveyors in the United States. In the short run, employment for surveyors hinges in part on the vagaries of the economy. In the long run, however, population growth and climate change will force large investments in infrastructure. On most construction sites, the first to arrive and the last to leave are the surveyors. We know what their tools are, but who will they be?
Land surveying is an ancient practice, dating back at least 5,000 years to when Egyptian rulers used it to tax land plots. Over the centuries, it has been repeatedly transformed by new technologies — the compass (about 200 B.C), the theodolite (1550s), Gunter’s chain (1620), the sextant (1757), electronic distance measurement (1950s), and total stations (1970s). Then came GPS, followed by the other GNSS and corrections services.
Now comes sensor fusion, which aims to compensate for the limitations of GNSS — orbit and satellite clock errors, ionospheric and tropospheric delays, multipath, dilution of precision, urban canyons, jamming, extremely weak received signal, etc. — by integrating it with other sources of positioning data, including inertial measurement units (IMUs), lidar sensors and cameras. Even crowdsourced geolocation data collected with cell phones help expedite surveys by guiding surveyors to landmarks.
In the following article, representatives of five companies share their perspectives on recent advances in surveying and the remaining challenges.
Many More Satellites
City Rail Link is New Zealand’s first underground rail network and the largest transportation project ever undertaken there. In this photo, taken at Karangahape Station, the Mined Tunnel Team installs a lattice girder secondary support structure using a Trimble SX12. (Photo: Link Alliance)
Compared to just a few years ago, there are many more GNSS satellites, signals and options for correction services. Over the past decade, the average number of satellites in view has more than doubled to more than 40 today. Some parts of the world have more than 70 satellites in view, said Boris Skopljak, vice president, Surveying & Mapping Strategy and Product Marketing at Trimble Inc.
“The developments in GNSS field systems have always been geared toward simplifying workflows, improving accuracies and increasing productivity,” Skopljak said. “In the last few years, we’ve seen that on a massive scale. In some of our materials, we no longer even quote how many signals our GNSS receivers are tracking.”
The vast increase in the number of satellites has extended high-precision applications to the robotics and automotive markets. The challenge now is “position solution,” not just GNSS, said Simon Peng, director of the Overseas Department at ComNav Technology. The improvements in the satellite constellations, antenna technologies and algorithms also enable surveyors and other users to obtain results faster and to operate in environments previously impervious to GNSS, such as under heavy canopy and very close to buildings.
“Our customers can now operate in environments where there is no virtual reference station (VRS) infrastructure or real-time kinematic (RTK), by leveraging precise point positioning (PPP) solutions, such as the Trimble RTX corrections service,” Skopljak said.
“Additional satellite signals and constellations (like Beidou),” Skopljak said, “improved antenna technology and continuously evolving algorithms are contributing to improving the RTX accuracy while bringing the convergence times to almost instantaneous in normal conditions and making technology available in more regions.”
“When I first started surveying, if we had a 12-channel receiver, that was doing very well,” recalled Jesse Huff, head of Sales and Marketing, JAVAD GNSS. “Now, we’re tracking 36 birds in the sky at one time with an 874-channel receiver. That’s phenomenal.”
Huff described a patent-pending feature called real-time post-processed kinematic (RTPK). “It combines RTK, PPK and PP techniques, with multiple core processing engines and a single solution coming out of that. It is impressive standing underneath a giant oak tree and surveying that monument with GPS and knowing what your accuracies are. We’re not even chasing RMS values; we can report the actual positional uncertainties, which is amazing.”
Pole tilt compensation enables surveyors to precisely and easily localize points that are difficult or dangerous to access. (Photo: ComNav Technology Ltd.)
“With so many signals and the new ways of how we compute positions based on PPP technology, we can almost globally get to centimeter-level positioning within a couple of minutes from just one global correction link,” said Bernhard Richter, vice president of Geomatics at Leica Geosystems AG, part of Hexagon. “Under optimum conditions, you can have almost an instantaneous global accuracy of a couple of centimeters.” In mature areas, he added, a local RTK network infrastructure enables achieving centimeter accuracy within a couple of seconds.
Galileo, Richter pointed out, will be fully operational in 2023 with great signals, though he’s “a bit skeptical” about the system’s target date for its high-accuracy service. “So, we will basically get global constellation corrections that allow us also centimeter-level positioning.” BeiDou has been fully operational since 2020. “GLONASS is more unpredictable,” Richter said. “It looks like modernization is slowing down a bit, in particular the CDMA developments.” Additionally, he pointed out, it is possible that one or more governments may decide not to use those signals, for military or political reasons. “It’s not the manufacturers who decide which signals to take.”
“In open-sky conditions, additional satellites have added redundancy — which is always good for position integrity — but it’s only when obstacles start to appear on the horizon, blocking out parts of the sky, that all-in-view RTK really comes into its own,” said François Freulon, Head of Product Management at Septentrio. When they did not have a full view of the sky, he recalled, GNSS users used to have to carefully schedule their work to coincide with times of high satellite visibility. “Nowadays, by using multiple constellations and signals, RTK can reach the parts that receivers in the past could not tread. More signals and constellations have also helped in easing the collection workflow for surveyors, making the capture of data in difficult conditions much quicker and more efficient.” New correction services are further simplifying the workflow “thanks to new positioning techniques, pricing business models and simplified network density.” However, corrections companies still face challenges in ensuring that centimeter accuracy can be uniformly achievable at a global scale.
Sensor Fusion
The ongoing evolution in computing power and communication technology “leads to many more sensor combinations,” Skopljak said. “We are not talking about GNSS alone anymore. We are talking about integrating a GNSS antenna, a receiver, an IMU, power and communications into a single compact housing.” The integration of inertial sensors makes it possible to localize the instrument rod tip when the pole instrument is tilted. “That allows our customers to measure more safely in dangerous environments.”
“We are reaching a maturity stage of what we can do only with GNSS,” said Richter. “It’s all about sensor fusion. The problem when signals are obstructed, that’s not solved, even though we can do positioning from Wi-Fi hotspots or from local pseudolites.” So, fusing data from cameras, lidar, GNSS and IMUs in better ways is the way to go and presents “a huge open research ground.”
For Richter, the challenge is not just positioning, the orientation of objects is almost as important as that, especially for such tasks as machine control. “It’s also about what you do with the data that you collect. Hexagon’s vision is of an autonomous future where we put data to work in connected ecosystems to boost efficiency.” However, he pointed out, this requires large amounts of data, such as those from aerial photogrammetry, lidar and mobile mapping systems used to create city models and digital twins of buildings. “If you really want a car to drive autonomously through a city with all the things that could happen, you must rely on a perfect replication of the real world,” he said. Other examples he cited are more efficient evacuation plans and flooding simulations. “GNSS will never be enough, but it will always be a very good enabler because it works.”
Classes of Receivers
JAVAD GNSS designed its TRIUMPH-LS Plus receiver to work under heavy tree canopy. (Photo: JAVAD GNSS)
Two decades ago, we would often group GNSS receivers by accuracy into three buckets: consumer grade, resource or mapping grade, and survey grade. As accuracy has increased for all GNSS receivers, the boundaries between those categories — especially between mapping and surveying — have blurred. “The performance of GNSS has increased so much that we are not using the traditional accuracy-based differentiation between surveying and GIS,” said Skopljak. “For mapping professionals, 10 years ago it was all about points, lines and polygons; now it is all about locating assets and adding the most accurate positions as attributes to those assets. For our survey and engineering customers, what matters is still geometry and working with the models to serve the connected construction in the field.” As for the pure GNSS technology stack, “we are seeing fewer differences between mapping and surveying receivers, but we are focusing on serving the customer in terms of product-as-a-service or as a productivity tool.”
Huff made two points. First, that “survey grade” does not necessarily equal RTK. “Some education needs to happen so that people understand RTK as a technique, not an accuracy. You can get poor accuracy and poor fixes with RTK, even when you’re using good techniques. So, when I say ‘survey grade’ I’m still talking about the full frequency receivers, using all available signals.” Second, that consumer-grade receivers, such as the chipsets in our phones and computers, do not require the same robustness as professional ones. “While they may be achieving the same precision, surveyors must be able to defend their position in a court of law.”
Huff cited the “phenomenal” success of the simultaneous localization and mapping (SLAM) movement with all kinds of positioning challenges. “From a survey perspective,” he said, “we’re dealing with a much more feature-rich dataset than we were even just 10 years ago, with everybody having some type of GPS device on their phones. There are location tags on everything. That creates evidence for the surveyor to be able to go out and recreate things, reduce trips to the field, reduce rework times — all those things that make a surveyor’s life much easier.”
Surveyors now can fly aerial surveys of hundreds of acres in less than half an hour using drones with RTK, Huff said, instead of having to wait for the flying season with traditional airborne photos. If needed, they can pick a few ground-control points for ground truthing. “We’re able to do that with photogrammetry techniques, but using GNSS technology to position drones, whether it’s real time or post-processing, has definitely made surveying jobs easier.”
Correction Services
The adoption of GNSS in construction is growing and receiver manufacturers are making it easier to use their equipment in the field. (Photo: Leica Geosystems)
Correction services — such as satellite-based augmentation systems (SBAS), the ground-based Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS) — make a big difference along with PPP and similar techniques when base stations are not available. “We have the whole CORS network here in the United States,” Huff pointed out. “We also have services available from the National Geodetic Survey.”
Those who don’t want to have to fully engage in post-processing can upload their data to the Online Positioning User Service (OPUS), AUSPOS (a free online GPS data-processing facility provided by Geoscience Australia) or other corrections services that will post-process positioning data. “It has made it more accessible for all the surveyors all the way around, especially as the technology has improved and the cost barrier to entry into a survey-grade GPS receiver has come down significantly as well,” Huff said.
Growing Adoption of GNSS
The greater number of satellites in orbit significantly reduces convergence time and increases the accuracy of the solution, which makes the technology much more user-friendly for professionals and nonprofessionals alike.
For surveyors and mapping professionals, the increasing levels of GNSS performance means that “GNSS continues to be the dominant equipment and they can operate in challenging GNSS environments while still meeting the accuracy and precision requirements,” Skopljak said. GNSS usage is also growing in such industries as agriculture, construction, transportation and logistics. “Now, when farmers are on a combine, they don’t have to wait for an RTX or PPP solution to converge for 20 minutes. The solutions just work, and they can perform their task.”
Skopljak also pointed to “more flexible business models, such as pay-as-you-go or equipping seasonal workers or fleets of spatially enabled consumers to use GNSS,” that reduce the required upfront investment. “Surveyors now can go for longer and be productive in more areas where they could not use GNSS technology before. The non-surveying professionals — such as in natural resources, farming or construction — now can just turn on the machine and things work for them. They don’t have to worry about coordinate transformations and things like that.”
“Twenty years ago, when RTK and networks kicked in and then became popular, we were discussing whether it was the end of the automated total station,” Richter recalled. “Yet, the number of automated total stations has grown ever since.” To him, this is proof that GNSS alone will never solve all surveying problems. GNSS’ weak signal will always require surveyors to supplement it with other sensors, such as reflectorless total stations. “These instruments always need to work in harmony,” Richter said.
Success on both construction sites and in machine control require a very good robotic total station and a very good GNSS receiver, Richter said. “The simple problem of leveling a pole is actually solved, and we are using the technology that we developed for tilt-compensating GNSS receivers. We’re leveraging this now into the world of the total station.” This has solved one of the fundamental problems surveyors have long had, because they no longer need to level up and can measure tilted poles with a total station and with a GNSS receiver. “We have also made it very seamless for surveyors to switch between using GNSS receivers and total stations,” Richter said.
Other sources, such as lidar, can be used to aid navigation in the absence of GNSS signals. (Photo: OxTS)
We discussed complementary PNT with Peter Rylands, senior product manager at OxTS.
What are some of the most promising approaches to complementary PNT and how does simulation technology help?
There are two approaches of particular interest. The first is looking at LEO satellite systems that can provide supplementary and potentially more secure methods of navigation, with global coverage from a single system. But these will still suffer from some of the issues GNSS systems experience, namely, what happens when you can’t obtain a signal?
The second is the use of visual aiding through sensor fusion, such as lidar and cameras, that can provide relative positioning (or absolute positioning once you have a space mapped) using SLAM algorithms. While this may increase onboard hardware dependencies, it creates a localized navigation system that can be better protected from malicious actors.
In contrast, closed-loop systems can look to an infrastructure-based system, allowing free movement within the specific area in which the infrastructure is located and a potentially more reliable source of PNT, especially indoors, where GNSS is not available. Ultra-wideband is definitely the up-and-coming technology here, but systems using Wi-Fi, cameras, Bluetooth and others also are being used.
Simulation, as within many domains, allows users to test on a large scale with fewer barriers to entry than real-world testing and an ease in making iterative changes to find an optimal solution. Whether that is to benchmark performance in locations of interest or to change configuration settings to improve visibility or positioning, simulation allows you to do this without the expense of going straight into the environment itself or configuring the actual vehicle under test.
How does OxTS fit in that mix?
OxTS provides customers with the ability to navigate anywhere; whether for reference data in R&D, georeferencing for survey and mapping, or active navigation of autonomous solutions. To do this we provide an IMU-first offering that we then complement with other technologies. Traditionally, this is with GNSS, to form an INS that can provide centimeter-level accuracy. However, we are also aware of the vulnerabilities of GNSS. For us, this is when it becomes an unreliable source of PNT in denied areas, such as indoors, in urban canyons or under tree canopies.
Because of this, we are also investigating and developing complementary solutions that can enhance our offering for users who need confidence in their position even when GNSS is not available. Whether that is through sensor fusion, our Pozyx UWB solution for indoor navigation or other proprietary software and firmware capabilities.
What kinds of complementary PNT are most useful in addressing specifically the challenges posed by jamming and spoofing and how does simulation help?
We need to look at systems that cannot be impacted by, or have mitigations from, the impact of jamming and spoofing. Solutions that are independent of radio communications or satellite use are then valuable in providing this layer of protection. This is where we could look toward OxTS’s use of IMU technology and visual aiding systems. Simulation technologies would then allow you to run hardware-in-the-loop testing, where the primary GNSS solution can have simulated jamming and spoofing to understand the performance of your complementary and protected systems when GNSS cannot be trusted.
Orolia developed the Skydel GSG-8, a PNT test solution in its GSG family of simulators, to deliver GNSS signal testing and sensor simulation performance in an easy to use, upgradable and scalable platform. (Photo: Orolia)
We discussed complementary PNT with Erik Oehler, marketing director at Orolia.
What are some of the most promising approaches to complementary PNT and how does simulation technology help?
5G is the most promising for the future. I believe the benefits in infrastructure, speed, precision, reliability, and the industry incentives 5G offer are superior to GNSS. Alternative signals of opportunity and new commercial satellite-based providers are always valuable as extra layers of resilience. However, PNT from 5G is not quite ready yet. There will be a transition period during which systems use GNSS and these signals of opportunity simultaneously, so simulation enables receivers of any complementary signal to be tested in the same environments and with the same potential threats faced by primary constellation signals.
How does Orolia fit in that mix?
Orolia has the most atomic clocks in orbit, including those aboard the Galileo constellation. We integrate anti-jam antennas and build Interference Detection and Mitigation (IDM) into our products. We partner with companies that offer alternative signals, such as STL from Satelles. Our SecureSync NTP and PTP time servers live in the world’s biggest data centers and support encrypted signals, such as M and Y code for our militaries. We innovate with industry leaders such as Meta on building a better PCIe Time Card. We offer edge time servers with the ability to automatically add Hoptroff’s Traceable Time as a Service. If 5G PNT becomes a standard, we are already providing industry leaders such as Anritsu with solutions for acceptance testing on a major carrier’s backbone. With our pending acquisition by Safran and access to a world-leading portfolio of INS components, we are one of the most qualified companies in the world to solve nearly any PNT challenge.
What kinds of complementary PNT are most useful in addressing specifically the challenges posed by jamming and spoofing, and how does simulation help?
In two technical notes published by NIST, they recognize STL as one of four recommended solutions for PNT resilience and the only one being both independent of GNSS and capable of sub-microsecond accuracy. Being closer to Earth, it is a stronger signal, making it 1,000 times less susceptible to jamming. Additionally, because it is encrypted it is inherently immune to spoofing. The aforementioned Hoptroff TTaS is time delivered over VPN, removing the outside environment component completely. For positioning and navigation, the integration of an IMU provides a contiguous PNT solution even during periods of GNSS denial, analogous to how an atomic clock provides precise time holdover during these denial periods. Combined with anti-jam antenna technology and IDM software, a robust PNT solution is always available.
Simulation helps by (1) identifying the vulnerabilities your PNT system might have (or could have in the future to evolving threats) and (2) verifying the total integrated resilient system. Our GSG-8 Advanced GNSS Simulator supports hundreds of GNSS full spectrum signals, custom signals, and hardware-in-the-loop testing of integrated IMUs at up to 1000 Hz iteration rate. Our Skydel Wavefront and Anechoic simulators can verify the most complex GNSS anti-jam antenna systems.
What improvements will the Next Generation Operational Control System (OCX) bring?
Ellen Hall
“The OCX system is a part of an enormous modernization effort to enhance the ground control segment of the current GPS. This enhancement alone increases accuracy, but coupled with modernized satellites, the next generation OCX will increase and improve coverage and security of GPS. In terms of coverage, the Next Generation OCX will be able to fly twice as many satellites, including both legacy equipment as well as GPS IIIF satellites. In terms of security, the modernized receivers host anti-jam capabilities and information assurance features.” — Ellen Hall
Spirent Federal Systems
Bernard Gruber
“The latest GPS modernization program was envisioned in the 1990s and started with the U.S. Air Force awarding the Lockheed Martin Team a $1.4 billion contract in 2008 to build the GPS III space system. As part of the modernization effort the initial OCX contract award was given to Raytheon two years later, in 2010, while a series of development contracts have been awarded, primarily Inc 1 and Inc 2, for the Modernized GPS User Equipment (MGUE) programs to L3Harris, Raytheon and then Rockwell Collins. The improvements of OCX aligned to the space and user efforts and substantially increased security protection of this world asset. Specifically, OCX controls all legacy satellites (GPS II) and civil signals (L1 C/A) and military signals (L1P(Y), L2P(Y)). It also controls the new modernized civil signal (L2C) and the aviation safety-of-flight signal (L5). Moreover, it also will have control functions for the MGUE signals (L1M and L2M (M-Code)), and the globally compatible signal (L1C). The next Block IIIF will finally upgrade capabilities to synchronize the entire system to include a worldwide network of dedicated monitoring stations, ground antennas and backup capabilities.” — Bernard Gruber
Northrop Grumman
Editor-in-Chief Matteo Luccio sat down with experts from Spirent Federal Systems to discuss how simulation technology helps improve positioning, navigation and timing (PNT) and GNSS products and systems.
Of the 60 exhibitors at the Institute of Navigation’s Joint Navigation Conference (JNC) in San Diego this year, 16 make inertial navigation systems (INS). Many of the other exhibitors integrate INS with GNSS receivers or make simulators to test those integrations. Several exhibitors make a variety of other navigation systems, using active and passive optical sensors, wheel encoders and RF systems that map beacons of opportunity. Only seven manufacturers of GNSS receivers were present.
That’s because the conference — which took place June 6-9 and focused on technical advances in positioning, navigation and timing (PNT) — was hosted by ION’s Military Division for the Departments of Defense (DOD) and Homeland Security. “From an operational perspective,” said the conference program, it focused on “advances in battlefield applications of GPS; critical strengths and weaknesses of field navigation devices; warfighter PNT requirements and solutions; and navigation warfare.” In other words, it was mostly on how to navigate in environments in which the use of GNSS is challenged or denied due to jamming.
The conference program told the story of the GNSS/PNT community’s interests and concerns. Several sessions were on complementary PNT using terrestrial RF signals of opportunity, IMUs, geophysical fields (including gravity and Earth’s magnetic field), celestial objects, ground vision and new commercial sources of space-based PNT, such as satellites in low Earth orbit (LEO).
Other environments in which reliance on GNSS is hard or impossible — such as urban canyons, deep inside buildings, underground and underwater — pose the same navigation challenges to both military and civilian applications. Likewise, jamming is a threat to both. Therefore, several sessions focused on critical infrastructure, demonstrating that the concerns about GNSS vulnerabilities are not just military ones.
Hence the presence among the exhibitors of three manufacturers of atomic clocks, which continue to shrink in size, weight, power and cost (SWaP-C) and are used to assure holdover — that is, the time period required to keep networks synchronized when their primary timing source, usually GNSS, is disrupted or temporarily unavailable. Networks affected include cellphone providers, radio and television broadcasters, financial networks, and the biggest network of all, the Internet.
The JNC “experienced record attendance in both conference participants and exhibitors, hosting more than 1,000 attendees,” Lisa Beaty, ION executive director, told me. She attributed the increase to “the importance of PNT in the nation’s critical infrastructure, current innovation, programmatic funding, and the desire by the DOD community to collaborate and reconvene.” She confidently anticipates additional growth next year.
I am equally confident that much of the cutting-edge technology on display at this conference will find its way into civilian applications in the next few years. Whether in war or in urban canyons, GNSS navigation faces some of the same challenges.
Jackson Labs Technologies PNT-6200 Series, an STL-based time and frequency reference system installed in a 5G application. Photo: Satelles
We discussed Satellite Time and Location (STL) services and complementary PNT with Michael O’Connor, CEO at Satelles.
What is the problem with GPS/GNSS that Satelles aims to solve?
GPS and GNSS are amazing. We designed Satellite Time and Location (STL), the service that we offer, to complement those capabilities. We have focused on three unique aspects in the areas where GPS could use complementary service. First, we provide a fully independent backup. We all know that things can happen, so we aim to provide an independent source of position navigation, and timing (PNT). Second, we focused the high-power aspect of STL to enable us to reach indoors and other places where GPS does not reach. Because STL comes from low Earth orbit (LEO) satellites, the signals are naturally at a higher power.
We also focused on improving the indoor penetration capability by enhancing the signal design and doing some other things. Third, we use modern cryptographic techniques to ensure the security and resilience of the system, specifically to intentional misdirection attacks. If you can ensure that the signal is coming from the satellite and not from a third party you can have a more secure and resilient solution.
To what extent can you replace GPS during an extended outage?
We have never considered LEO PNT as a replacement for MEO (medium Earth orbit) GNSS. GNSS are the primary domain of PNT but there are applications that have additional needs. The more independence you can get, the fewer the common modes of failure, if you can at least have some survivability in the absence of GNSS. That’s one of the services we can offer. It is probably not the most important thing to our customers, honestly. The service we offer is similar to GPS and GNSS in that we have a space segment (the satellites), a ground segment, and a user segment. We have space vehicles, user equipment, and ground infrastructure that supports the space infrastructure.
What’s interesting about the way we work with the Iridium satellite constellation is that the satellites themselves include inter-satellite links. That provides a lot of resilience to ground-based events. The satellites themselves have a time transfer capability between them. So, we don’t require a direct connection to every satellite to propagate a time throughout the network. That’s one unique aspect we can take advantage of with this particular network, Iridium, which is pretty amazing.
Additionally, we have multiple ground infrastructure and monitoring sites and multiple sources of time at those ground monitoring and control stations. For example, some of them rely on GNSS combined with atomic clocks as their master timing source but we also have one installed at the National Institute of Standards and Technology facility in Boulder, Colorado. So, we have multiple primary time sources that we can integrate into our filtering across the network. That, combined, with satellite links, allows us to maintain time for substantial periods independent of GNSS.
How do you define “complementary PNT” and how does Satelles fit in that mix?
Several applications have additional needs beyond what GNSS offer. There are many technologies that can come to bear on that. There’s the LEO satellite base, which is where Satelles fits in, but there are also local and wide-area terrestrial radio navigation sources, network-based time transfer, signals of opportunity, and so on. They all have something important to offer, depending on the application. Satelles’ LEO satellite solution is available today, has global coverage, and is relatively affordable. It leverages the capital investments that have been made to launch the satellites to provide this service globally. The industry is working together to make sure that an awareness of these capabilities is propagated throughout the industries that we serve.
Besides the orbit height, which requires many more satellites, how does your system differ from GNSS?
We do not consider LEO PNT as something that might replace MEO PNT. The fundamental difference is being in lower Earth orbit, which results in a higher received power. That is what allows us to penetrate, just based on the 1/r2 losses. The measurable Doppler signatures give additional observables for PNT calculations, and higher satellite dynamics that can help with multipath. This service relies on many of the same physics and geometry as GPS. We measure the time of arrival of a very similar signal. The signals from the Iridium satellites are even in the L band. Very often we’re using a GPS chip that’s been reprogrammed to track and utilize our service as well as GPS or instead of GPS.
If I explained how GPS works to, say, a high school science class, how much of that basic explanation—about trilateration, spread spectrum, etc.—would also apply to your system?
It’s fundamentally the same. It relies on a lot of the same physics and geometry. We measure the time of arrival of a very similar signal. The signals from the Iridium satellites are even in the L band. Very often we’re using a GPS chip that’s been reprogrammed to track and utilize our service as well as GPS or instead of GPS. There are subtle differences—for example, a lower Earth orbit is faster—but it is very similar.
How would GPS user equipment have to be modified to make use of your service?
We don’t think of STL as something where we are modifying GPS user equipment. Rather, we think about what must be done in an end-user application to meet their needs. For example, one of our partners, Orolia, has a GNSS + STL secure synchronization product that we have delivered to customers in data centers and major stock exchanges around the world. Those are operational and in service. They integrate through standard interfaces, such as PPS or PTP, depending on the type of equipment to which they are connecting.
Ultimately, we don’t think of it is as replacing GPS user equipment. Rather, where a user has a need for PNT, they’re opting for this GNSS + STL solution because they have an indoor need, such as a data center, or they have a need for resilience in the case of a stock exchange.
Another example is Jackson Labs. The Jackson Labs 2600 is also a GNSS + STL solution that generally is integrating with existing 5g. It has a specialized transcoder interface that can work with any existing GNSS-type equipment. In some cases, we’ve taken a chip that was originally designed for GPS and modified its firmware.
Who are the earliest adopters?
Satelles’ LEO satellite solution is available today, has global coverage, and is relatively affordable. It leverages the capital investments that have been made to launch the satellites to provide this service globally. Data centers, stock exchanges and cell phone providers are implementing these capabilities today. The major wireless operators are seeing that more and more of the 5G infrastructure they roll out is going indoors, where GPS doesn’t reach. We provide a solution that integrates with their existing solutions and can provide reliable timing capabilities.
If your solution can survive on its own, why does it need GNSS at all?
In some cases, the user is not using GNSS at all. The product itself has a GNSS capability. User equipment is very affordable and the service is taxpayer-funded. In many cases, especially for indoor installations, the equipment that is installed is capable of tracking GNSS and STL signals, but often it relies on the STL signal itself for timing.
How do you predict STL spreading through various applications and industries?
We have our hands full with the markets we’re going after now, but there are certainly going to be other markets in which the customers will recognize that they have a critical need to implement a backup solution.
In the long run, could LEO satellites replace MEO ones for GNSS?
Sometimes there have been misperceptions in the industry. I’ve never considered that LEO PNT satellites might replace MEO ones. There are excellent reasons why Brad Parkinson, Jim Spilker, Gaylord Green and others decided almost 50 years ago to put GPS in MEO. Those physics haven’t changed. You can cover a large portion of Earth with each satellite. LEO will not replace MEO, but it has unique characteristics that make it a great complement to the GNSS MEO solutions.
Do you have any additional comments about complementary PNT?
It’s good to see that the federal government is encouraging the adoption of complementary PNT, which they often call “GPS backup.” It is encouraging to see the amount of activity on this issue that’s been going in Washington over the last couple of years. Although our company is very focused on delivering a LEO-based PNT service, which has several advantages for customers that need a global capability, many technologies can play an important role in those solutions.
The U.S. Department of Transportation did a fantastic job of looking at several of those technologies across those different categories. The European Union has also had a similar activity recently. Some reports will be coming out soon about that. It is very important that the government understands that this is an important issue for our society and encourages industry to adopt these solutions and is even starting to make some investments toward that. That includes executive order 13905 and some recent funding increases by Congress.
All of that has been very important and positive, as has modifying some of the legislation to be more inclusive of multiple technologies, such as removing the words “land-based” from the National Timing, Resilience, and Security Act this year.
I am involved in an industry consortium, the Open PNT Industry Alliance, with several other companies whose CEOs are in alignment that there is no single answer. Having a thriving ecosystem of technologies and companies trying to solve this important problem is incredibly important and it’s exciting to see.
Data shows how successful baseline validation testing of Spirent’s inertial simulation model as compared to real world inertial system performance. Photo: Spirent Federal Systems
We discussed complementary PNT with Roger Hart, head of engineering and Jeff Martin, head of sales at Spirent Federal.
What are some of the most promising approaches to complementary PNT sources and how does simulation technology help?
Roger Hart: The vulnerabilities of GNSS have been recognized. Legacy GNSS are all operating on pretty much the same frequencies and power levels, so, they have some significant common vulnerabilities. There is great interest in finding ways to complement or even replace those capabilities.
Dead reckoning, magnetic and inertial systems have been around for a long time. There are emerging markets to make use of alternative radio frequencies for navigation. In some cases, we are piggybacking on communications signals and deriving PNT from them. In other cases, we are using new PNT signals. A couple that we’ve been focusing on are the alternative navigation systems.
They may be using different orbits, different frequencies, different encoding schemes that set them apart from the legacy GNSS systems, so that, used together, they provide greater resiliency and even stand alone when one or the other system may be affected by interference.
Not to be forgotten is inertial navigation. It’s been around for a long time and is still a standard of navigation. Together with GNSS, it makes it a terrific navigation system. It almost defines complementarity because where GPS is vulnerable inertial can fill in the gaps and where inertial drifts GPS does not. So, paired, they make a very strong system.
At Spirent, we’ve been working with customers to provide a variety of options for both those alternative navigation systems and inertial. Both are a very active field of development and we’re keeping abreast of that.
Jeff Martin: Some good points, Roger. This is something we’ve been engaged in for quite a long time. Since we provide test equipment to the community, it’s critical that we understand what they’re worried about, what the vulnerabilities are. It keeps things exciting, it keeps us on our toes and looking ahead to what’s coming.
What are some of the remaining challenges of integrating GNSS receivers with inertial sensors and, again, how does simulation technology help with that?
Hart: Inertial works by integrating sensor measurements that come in. Therefore, any errors that are present just accumulate over time and can corrupt your navigation solution. So, there’s a strong focus on updating error models and on translating them so that everyday users can use them and get real-life-type performance out of them.
There’s a tendency to think of integrating GPS-INS as putting everything together in one box. There are packages that do that. However, the push now is to go to more distributed systems that are integrated but not packaged in the same box. One example is the all-source positioning and navigation standard that is being developed by the Department of Defense. It will allow you to swap one sensor for another as long as they adhere to the standard. That information all goes back to a sensor fusion engine.
Martin: We have known GNSS simulators well for about four decades. We have been playing in the inertial sandbox for at least a couple of decades as well. This has given us the opportunity to build relationships with the with the key manufacturers and designers of inertial systems. Those relationships have been expanding well beyond inertial to many other sensors and systems that are now coming online. It’s been exciting.
Much work is going into using low Earth orbit satellites for PNT—whether piggybacking on the Iridium satellites or launching new ones. How does simulation help with that?
Hart: It certainly helps with the development of the receivers. The groups that are using these alternative RF and LEO or MEO systems need simulation as they develop the receivers. It gives you the ability to try things certainly before you launch them. At this conference there is considerable interest in making things reprogrammable. We have the NTS-3 satellite, which will be running experiments for different waveforms that can be generated. Even M-code is a step in the direction of giving more flexibility to the signal. It has a lot more flexible cryptography and signal generation than the legacy system with the C/A and P/Y codes.
Our simulation platforms are software based, so we can generate and receive data that can be useful for developing software-defined receivers. It gives you the opportunity to try different waveforms. We have already delivered a satellite-based alternative navigation system simulator. Now, we can build on that one to help the other Leo constellations as they come forward.
Martin: Roger put it well. This is where things get fun. People are concerned with PNT vulnerabilities, so we’re seeing these alternative navigation solutions coming forward. Spirent has done a good job over its nearly 40 years of existence of manufacturing and designing its own hardware and software. It has given us the opportunity to respond quickly. These things are coming fast. People need solutions quickly. We have some solutions already and the platform that we have created gives us the flexibility to develop more. We’re seeing more and more ideas come to fruition and people need to test them. So, this is where it gets fun. We’re excited.
Much work has gone into addressing the enduring challenge of urban canyons. How does simulation technology help?
Hart: Urban canyons are the worst nightmare for GNSS signals. If you’re surrounded by tall buildings, signals are blocked. You may have few or even no satellites in a direct line of sight and many multipath reflections. So, diminished and corrupted signals are available to you. Of course, the more GNSS satellites you have, the better chance you have of getting good signals. But complementing that are radar and vision systems. Those are the ones that will stand out, particularly the vision systems that can read the street signs, see where the curb is, look for parked cars. All those kinds of things will help fill in when you have poor GNSS coverage.
You can observe what’s going on in the environment and simulate it. You can also use our forecasting tool to look ahead.
Martin: This is where things get exciting, isn’t it? In these terrible environments where GNSS is contested—whether it’s an urban environment or one with intentional jamming—there is a lot we can do to help our industry. When this happens in real life, it’s bad news. But when you create that scary situation in the controlled environment of a laboratory, it is great. You can pick things apart and see where you need to improve. I get excited about it. It’s probably the geek in me. It gives us and our partners a lot to look forward to.
How does simulation technology help with sensor fusion?
Hart: It definitely helps you put all the pieces together. You can’t know how your system will work by individually testing each piece. System is the key word here. Simulation enables you to generate the signals and bring them together into a sensor fusion engine. You can test different algorithms. It’s certainly much cheaper and quicker than trying to build this into a product and then test it. Over the decades, simulation has proved itself as a very valuable way in both basic development and integrating the final product.
Martin: That system-wide fusion is where the magic happens.
It sounds like simulation technology—and Spirent Federal in particular—are very much at the center of a lot of the current developments and discussions about complementary PNT. Do you have any final comments?
Hart: As Jeff said, it’s an exciting time. There are many things going on—new technologies, new ways of communicating. It’s a busy time and a bit of a scramble sometimes to keep up with all the new things that are coming.
Martin: People look to Spirent to be their testing resource and it puts us right in the middle of it.
