Warning sirens about the vulnerabilities of GPS to jamming, spoofing, solar activity and other disruptions have been blaring for many years. Now the U.S. Department of Transportation (DOT), which represents other federal civil departments and agencies on all GPS-related matters within the federal government, might finally be moving from study to action. On September 12, at the annual meeting of the Civil GPS Service Interface Committee held in conjunction with ION GNSS+ in Denver, Robert Hampshire, DOT’s Deputy Assistant Secretary for Research and Technology and Chief Science Officer, announced the release of DOT’s Complementary Positioning Navigation and Timing Action Plan. It aims to drive CPNT adoption across the United States transportation system and within other critical infrastructure areas. You can read more here and download the planhere.
Which GPS vulnerabilities does DOT aim to address and how quickly can it “drive adoption” of CPNT? Attempting to answer these questions requires pushing through a dense thicket of bureaucratic jargon. I asked Karen Van Dyke, Director for Positioning, Navigation, and Timing (PNT) and Spectrum Management in Hampshire’s office four questions. What follows are excerpts from her answers. You can read her full response here.
What is your office’s charter within the federal government to advance the development and deployment of complementary PNT?
Her office’s efforts, Van Dyke told me, “support federal policy governing PNT programs and activities for national and homeland security, civil, commercial, and scientific purposes. These include Executive Order 13905, Strengthening National Resilience Through Responsible Use of Positioning, Navigation, and Timing Services (EO 13905) and Space Policy Directive 7, The United States Space-Based Positioning, Navigation, and Timing Policy (SPD-7).”
Which GPS vulnerabilities and at what scale is this plan addressing?
The action plan, Van Dyke told me, “addresses disruption, denial, and manipulation of GPS for critical infrastructure sectors” on “both a widespread and local scale.”
How and when will this action plan move the federal government’s posture on CPNT from study to action?
Van Dyke cited field demonstrations conducted in 2020 by the Volpe Center of candidate PNT technologies that could offer complementary service in the event of GPS disruptions and a 2021 report to Congress that distilled the PNT resiliency recommendations. DOT, she said, should develop “system requirements for PNT functions that support safety-critical services” and “standards, test procedures, and monitoring capabilities to ensure that PNT services, and the equipage that utilize them, meet the necessary levels of safety and resilience”.
How does DOT intend to engage PNT stakeholders?
Van Dyke pointed to a PNT Industry roundtable that DOT held in August 2022 that included representatives from CPNT technology vendors and critical infrastructure sectors and “informed the development” of the action plan. She also pointed out that on September 11, DOT issued a request for information “as one of the steps to drive adoption” of CPNT services “to augment GPS for the nation’s transportation system, and through the executive branch interagency process, for other critical infrastructure sectors.”
The United Kingdom’s Minister for Science, Research, Innovation announced in Parliament today a 10 point “policy framework” for advancing positioning, navigation, and timing (PNT).
The announcement addressed improvements to both PNT technology and policy.
Six technology efforts were listed:
“National Timing Centre: develop a proposal for a National Timing Centre (NTC) to provide resilient, terrestrial, sovereign, and high-quality timing for the UK (UTC(NPL)), including sovereign components and optical clocks.” This project has been underway for some time and is being executed by the UK’s National Physical Laboratory. The announcement said another £14 million had been identified and was being allocated to the project.
“MOD Time: develop a proposal for ‘MOD Time’ creating deeper resilience through a system of last resort and use NTC provided timing to support MOD.”
“eLORAN: develop a proposal for a resilient, terrestrial, and sovereign Enhanced Long-Range Navigation (eLORAN) system to provide backup position and navigation.” In May, the UK’s spectrum office, Ofcom, sought interest from industry in obtaining eLoran broadcast licenses. The U.S. Department of Transportation issued a similar request for information this month.
“UK SBAS: develop a proposal for a UK Precise Point Positioning Satellite-Based Augmentation System (SBAS-PPP) to replace the UK’s use of the European Geostationary Navigation Overlay Service (EGNOS), monitor GNSS and enable GNSS-dependent high accuracy position for autonomous and precision uses.” Since Brexit, the UK has not been a part of the EU’s Galileo enterprise. This SBAS decision comes after the UK government researched and rejected the idea of establishing its own GNSS.
“Next Generation PNT: deploy existing R&D funding into a UK Quantum Navigator and investigate possible options for a UK sovereign regional satellite system.” Britain has made development of quantum capabilities, including PNT, a particular national focus.
“Infrastructure Resilience: rollout resilient GNSS receiver chips, develop holdover clocks, and consider options for legislation on CNI sectors to require minimum resilient PNT.” The U.S. Executive Order 13905 points in a similar direction as this idea for legislation, which is a good segway to the announcement’s policy provisions.
Four organizational and policy initiatives included in today’s statement in Parliament:
“National PNT Office: establish a National PNT Office in the Department of Science, Innovation and Technology to improve resilience and drive growth with responsibility for PNT policy, coordination, and delivery.” Last year the Resilient Navigation and Timing Foundation reported a cross-government office had been established by the UK that included representation from the Ministry of Defence. That office was within the Department for Business, Energy & Industrial Strategy (BEIS). Since then, BEIS has been split into two departments, one of which is Science, Innovation, and Technology.
“PNT Crisis Plan: retain and update a cross-government PNT crisis plan to be activated if GNSS-provided PNT is lost and identify and implement short term mitigations.” Similar plans exist in the United States. The absence of an interference detection and monitoring system, though, has helped stymie U.S. government efforts to respond quickly and effectively.
“PNT Skills: explore options for centers for doctoral training in timing and PNT and review PNT skills, education, and training for longterm sovereign PNT capability.” A similar need has been identified by the U.S. President’s National Space-based PNT Advisory Board.
“Growth Policy: develop a PNT growth policy, including R&D programs, standards and testing, to drive innovation for PNT based productivity.” The U.S. PNT R&D Plan is a similar effort.
Also mentioned in the statement to parliament are two new PNT documents published today by the UK Space Agency. The first is a summary of technical concepts developed under the Space Based PNT Programme. The second is an updated report on the economic impact to the UK of a disruption to GNSS.
ION GNSS+ 2023 is underway at the Hyatt Regency Denver at Colorado Convention Center. On the second day, industry leaders and show attendees gathered for the 63rd meeting of the Civil GPS Service Interface Committee. During a break, a cake was wheeled out to celebrate 50 years of GPS. GPS World staff wanted to highlight some key parts of the event.
(From left to right) Rick Hamilton, GPS Info Analysis Team Lead, U.S. Coast Guard; Harold “Stormy” Martin, Director,National Coordination Office for Space-Based Positioning, Navigation, and Timing; Dr. Bradford Parkinson, Edward Wells Professor, Emeritus, Aeronautics and Astronautics (Recalled), Co-Director, Center for Position, Navigation and Time, Stanford University; Capt. Scott Calhoun, Commanding Officer, U.S. Coast Guard Navigation Center (NAVCEN) and Karen Van Dyke Director, PNT and Spectrum Management, U.S. Department of Transportation, gathered around a cake to celebrate the 50th anniversary of GPS.
Image: Matteo LuccioImage: Matteo Luccio
A closer look at the 50 years of GPS cake. Learn more about the history of GPS here.
Image: Matteo Luccio
Lt. Colonel Robert Wray, Commander, Second Space Operations Squadron, U.S. Space Force (second from left), who was featured on the May cover of GPS World. Click here to read our May cover story, featuring an exclusive interview with Lt. Colonel Wray about the training and duties of his team, the challenges they face, and more.
Image: Matteo Luccio
Dr. Bradford Parkinson(left) and Dr. Robert Hampshire, Deputy Assistant Secretary of Research and Technology and Chief Science Officer, U.S. Department of Transportation (right). Click here to learn more about Dr. Bradford Parkinson, who is nicknamed “The father of GPS.”
Image: Matteo Luccio
Col. Andy Menshner, GPS Space and Ground (SML), Space Systems Command, U.S. Space Force, speaking about GPS acquisitions and development updates during the Civil GPS Service Interface Committee.
Image: Matteo Luccio
(Second from left)Karen Van Dyke, Director, PNT and Spectrum Manager, U.S. Department of Transportation Deputy Chair, serves as chair of the 63rd Civil GPS Service Interface Committee. Read more from the Department of Transportation here.
Image: Matteo Luccio
Attendees gathered to hear speakers from the U.S. Department of Transportation, the U.S. Space Force, and other departments and agencies.
Click hereto stay up to date with our show coverage!
In May the President’s PNT Advisory Board heard a presentation about a National Guard project called NITRO. RNT Foundation President, Dana Goward, recently spoke with the project’s leader, Maj. Gen. Richard R. Neely, Adjutant General, Illinois National Guard, to find out more.
Mr. Goward: Thanks for speaking with us, General. Could you start by telling us what NITRO is and why it’s important?
Maj. Gen. Neely: Of course. NITRO is a project to ensure that the National Guard and our state’s first-responder partners can maintain communications and other critical functions even if we lose GPS timing signals.
NITRO is an acronym for Nationwide Integration of Timing Resiliency for Operations. ]You know how we in the military love our acronyms.
Telecoms and most of the rest of America’s critical infrastructure are dependent on timing from GPS. However, GPS signals are weak, highly vulnerable and under threat.
In addition to bad actors who can and do jam and spoof signals, accidental interference happens all the time. Operations at the Dallas and Denver airports were each interrupted by accident for more than a day last year, for example. A couple of years ago, a passenger airliner almost hit a mountain because of interference with GPS.
Q: It sounds like this is a safety of life issue.
A: It is. Right now, if we lost GPS signals and had to respond to a domestic attack, natural disaster, or other contingency, I am confident there would be additional unnecessary casualties. We are building NITRO so that we can save those lives and keep America safe.
Q: So how does NITRO work?
A: In addition to GPS, it gets multiple sources of space-based and terrestrial time from government and commercial providers. NITRO can use any trusted source. It is not provider- or vendor-specific.
Inputs are combined and compared, matched to the nation’s atomic clocks keeping Coordinated Universal Time, and users are sent the best accurate time multiple ways including over fiber, terrestrial broadcast, and resilient wireless networks.
Another great way in which I think it will be useful: NITRO gives us a common operating picture that can help detect and terminate GPS disruptions and anomalies around the country.
Q: Is the National Guard the only user?
A: Absolutely not! This is a state/federal partnership. The states’ Adjutant Generals are working with their Homeland Security Advisors to make it available to state, local, and tribal first responders. In some instances, also to critical infrastructure.
Even though we are in the early stages of implementation, NITRO is being used by seven states and 256 organizations and it is protecting more than 33 million people, including citizens here in Illinois.
Q: Is NITRO a tasking from the President or Congress? Who told you to do this?
A: NITRO helps execute long standing presidential policy and orders, as well as the recently released National Cybersecurity Implementation Plan. It also meets congressional mandates for backups and alternatives to GPS timing.
However, we created NITRO because we identified a serious threat to the National Guard’s mission execution. It closes 11 operational gaps for us, all without changes to end-user equipment.
Q: With what groups are the NITRO team working?
A: All the states are involved through their adjutant generals, homeland security advisors, and emergency managers. The NITRO board I chair is made up of the adjutant generals from six states.
We are also coordinating across the federal government, especially with the Departments of Homeland Security, Transportation, Commerce, and Energy.
As part of this we are partnering with the Department of Transportation to establish a NITRO engineering and operational site at Joint Base Cape Cod. This will allow engineers from different organizations to see more easily what we are doing and contribute their expertise.
Q: NITRO is going to provide timing signals in places and at times when GPS is not available. Won’t the National Guard also need navigation information?
A: Positioning and navigation are very important, but not quite as critical as timing. So, we are addressing that problem first. And since wireless location and navigation are often based on timing signals, NITRO will provide a good foundation for services and systems that can augment GPS-based navigation.
Q: So, how is the project going?
A: From a technical and operational standpoint, it’s going great. We have very high satisfaction ratings from NITRO users, and states are eager to be connected as soon as possible.
The technologies used are all mature, reasonably low cost, and most components are commercially available. So, engineering-wise it is low risk.
And our team is doing a great job helping folks move from full dependency on GPS to resilient positioning, navigation and timing (PNT) operations.
Q: Do you have any concerns going forward to full deployment?
A: The only thing I worry about is continued funding. Over the next five years we need something less than the cost of one GPS satellite. You would think that would be easy to find for an important effort like this, but it is a state/federal partnership, not a Department of Defense project. So, it falls into a kind of bureaucratic and budgetary no man’s land.
Q: What’s the solution for funding?
A: That’s not our call. The folks at the White House are exploring several alternatives, and I know several members of Congress are also concerned. We see a possibility of this fitting nicely with the recent infrastructure funding bill.
Q: It sounds like NITRO is something America really needs. Let’s hope they find a solution to the funding challenge, and quickly, to keep you on track. Thank you very much for your time!
Advanced industrial societies are increasingly reliant on the fantastic capabilities of global navigation satellite systems (GNSS) — GPS, GLONASS, BeiDou and Galileo — and, therefore, increasingly vulnerable to their weaknesses. From providing our position on a map on our smartphone to timing financial transactions, cell phone base stations, and the internet; from steering tractors in the field to guiding first responders; from giving surveyors sub-centimeter accuracy to monitoring continental drift; from providing navigation to ship captains and airplane pilots, to enabling automated control of earth moving machinery, GNSS have become a critical infrastructure. Yet their well-known vulnerabilities — such as jamming, spoofing, multipath and occultation — continue to fuel the development of complementary sources of positioning, navigation and timing (PNT) data, especially for new and rapidly expanding user segments such as autonomous vehicles.
In a January 2021 report, the U.S. Department of Transportation pointed out that “suitable and mature technologies are available to owners and operators of critical infrastructure to access complementary PNT services as a backup to GPS.”1
Several new PNT systems are being developed and deployed that are partially or entirely independent of the four existing GNSS constellations. This cover story focuses on the following companies, products and services:
Safran Federal Systems (formerly Orolia Defense & Security) makes the VersaPNT, which fuses every available PNT source — including GNSS, inertial, and vision-based sensors and odometry. I spoke with Garrett Payne, Navigation Engineer.
Xona Space Systems is developing a PNT constellation consisting of 300 low-Earth orbit (LEO) satellites. It expects its service, called PULSAR, to provide all the services that legacy GNSS provide and more. I spoke with Jaime Jaramillo, Director of Commercial Services.
Spirent Federal Systems and Spirent Communications are helping Xona develop its system by providing simulation and testing. I spoke to Paul Crampton, Senior Solutions Architect, Spirent Federal Systems as well as Jan Ackermann, Director, Product Line Management and Adam Price, Vice President – PNT Simulation at Spirent Communications.
Satelles has developed Satellite Time and Location (STL), a PNT system that piggybacks on the Iridium low-Earth orbit (LEO) satellites. It can be used as a standalone solution where GNSS signals will not reach, such as indoors, or are otherwise unavailable. I spoke with Dr. Michael O’Connor, CEO.
Locata has developed an alternative PNT (A-PNT) system that is completely independent from GNSS and is based on a network of local ground‐based transmitters called LocataLites. I spoke with Nunzio Gambale, founder, chairman, and CEO.
Due to the limited space available in print, this article only uses a small portion of these interviews. For full transcripts of them (totaling more than 10,000 words) click here.
1 Andrew Hansen et al., Complementary PNT and GPS Backup Technologies Demonstration Report, prepared for the Office of the Assistant Secretary for Research and Technology, Department of Transportation, January 2021, p. 195.
Locata dish antenna pointed to the European Union’s Joint Research Center in Ispra, Italy, 44 km away, just under the setting sun. The Yagi antenna above is pointed to a cell tower in Como and used to connect the system for remote control and data logging. (Image: Locata)
Complementary PNT
“Traditionally, augmentation to GNSS has been done through inertial navigation systems (INS),” Price said. “More recently, ground- and space-based augmentation systems have increased in usage. However, both technologies depend on the absolute positioning information provided by GNSS. They do not represent a true alternative PNT.”
To facilitate the development of advanced and autonomous applications, Price suggested incorporating terrestrial sources of PNT as well as ones based on LEO, medium-Earth orbit (MEO) and geostationary equatorial orbit (GEO) satellites. This, he added, would also keep costs from becoming prohibitive. “LEO brings many benefits in comparison to MEO in just about every industry to which it can be applied,” Jaramillo said.
While mass reliance on GNSS facilitates access to GNSS data and makes devices that use it increasingly cost-effective, over-reliance on a single sensor is risky, Austin pointed out.
“That’s where complementary PNT comes in: if you can put your eggs in other baskets, so you have that resilience or redundancy, then you can continue your operation — be it survey, automotive or industrial — even if GNSS falls or is intermittently unavailable or unavailable for a long time,” Austin said.
It has been said that “the only replacement for GNSS is another GNSS.” Inertial navigation, dead reckoning, lidar, and referencing local infrastructure that, in turn, has been globally referenced using GNSS, enable mobile platforms to maintain relative positioning during GNSS outages. However, absolute positioning will continue to require GNSS. “If you claim to be breaking free from GNSS you’re really saying, ‘I can navigate in this building, but I don’t know where this building is,’” Austin said.
GNSS-INS Integration
GNSS and INS have always been natural allies because they complement each other. The recent completion of the BeiDou and Galileo constellations, which has greatly increased the number of satellites in view, has made the requirement for six satellites at any one time for real-time kinematic (RTK) “a much more reasonable proposition,” Austin said. Coupled with the drop in the price of inertial measurement units (IMU), this has made it possible to “make a more cost-effective IMU than ever or spend the same and get a much better sensor than you ever could before,” he said. “Your period between the GNSS updates is also less noisy and you have less random walk and more stability.”
It used to be that the performance of an accelerometer might far outweigh that of a gyroscope, resulting in excellent velocity but poor heading. “Now,” Austin said, “we can pick a much more complementary combination of sensors and manufacture and calibrate an IMU ourselves while using off-the-shelf gyroscopes and accelerometers. That allows us to make an IMU that is effectively not bottlenecked in any one major area.”
Autonomous vehicles require decimeter accuracy to keep to their lane, while their absolute position is irrelevant to that task. It is, however, essential for map navigation and to know about infrastructure such as traffic signs and stoplights that may not be in a vehicle’s line of sight.
“That’s where the global georeferencing comes in and where GNSS remains critical,” Austin said. “One of the key things we’re examining is GNSS-denied navigation: how we can improve our inertial navigation system via other aiding sources and what other aiding sensors can complement the IMU or inertial measurement unit to give you good navigation in all environments. Use GNSS when it’s good, don’t rely on it when it’s bad or completely absent.”
Nowadays, car makers are increasingly moving their research and development tests from indoor, controlled environments to open roads. Therefore, “they are looking for a technology that allows them to keep doing those tests that they did on the proving ground, but in real world scenarios,” Austin said. “So, they rely on the INS data to be accurate all the time. In autonomy and survey, on the other hand, the INS is used actively to feed another sensor to either georeference or, in the case of autonomy, actively navigate the vehicle. So, that data being accurate is critical because an autonomous vehicle without accurate navigation cannot move effectively and would have to revert to manual operation.”
Image: Xona Space Systems
New vs. Old
Complementary PNT systems differ from legacy GNSS along several variables. One is coverage. For example, Satelles and Xona will provide global coverage, while Versa PNT and Locata are local. Another is encryption. Unlike GPS, which encrypts only its military SAASM/M-code signal, Xona’s PULSAR system will encrypt all its signals, Jaramillo said. “For autonomous applications, security is very important. If you’re riding in an autonomous car, you certainly don’t want somebody to be able to spoof the GNSS signal and veer it off course.”
Additionally, the design of Xona’s constellation includes a combination of polar and inclined orbits, which will greatly improve coverage in the polar regions compared to current GNSS coverage. This is particularly important as climate change makes the arctic more accessible. “The idea of having a LEO-based constellation is to take advantage of what can be done in LEO for GNSS,” Jaramillo said. “If you want the most resilient time and position, you need to use a combination of everything.”
Based on its architecture, Jaramillo said, Xona will provide better timing accuracy than GNSS does today. “Our satellites are designed to use GPS and Galileo signals, as well as inputs from ground stations, for timing reference and will share their time amongst themselves. We will average all these timing inputs and build a clock ensemble on the satellites. That enables much higher accuracies than just having a few single inputs.”
Satelles’ STL service can either substitute for GNSS where the latter is unavailable or supplement it where it is available. When used as a supplement, “the goal is having a solution that is resilient to an outage, interference, jamming, spoofing, those sorts of things,” O’Connor said. “In that case, the receiver card that might be provided by one of our partner companies would have both GNSS and STL capabilities and would take the best of both worlds.” Depending on the product configuration, its locational accuracy is generally in the 10- to 20-meter range, O’Connor said.
Orolia Defense & Security’s Versa PNT “is an all-in-one PNT solution that provides positioning, navigation, and very accurate timing,” Payne said. “Every type of sensor that you’re using for PNT has its strengths and weaknesses. That’s why we have a very accurate navigation filter solution that dynamically evaluates the sensor inputs.” In GNSS-degraded environments, the Versa’s software alerts users that GNSS signals are not reliable, automatically filters out those measurements, and navigates on the basis of the other sensors, such as an IMU, a speedometer, an odometer, or a camera.
Locata’s system is completely independent of GNSS because it does not require atomic clocks. At its heart is the company’s TimeLoc technology, which generates network synchronization of less than a nanosecond, Gambale said. “TimeLoc,” Locata literature states, “synchronizes the co-located signals with other LocataLites as the signals are slewed until the single difference range between it and the other LocataLites is the geometric range. This internal correction process is accurate to millimeter level.” Applications of this system include indoor positioning for consumer devices such as mobile phones, industrial machine automation for warehousing and logistics, positioning first responders within buildings, and military applications in GPS-jammed environments.
Constellations and Timelines
How long will it take to develop and/or complete these complementary PNT systems?
Xona is a start-up, and its timeline will depend on its success with investors.“We have basically locked down our signal and system architecture. Now, it’s a matter of building out the ground segment and launching satellites,” Jaramillo said.
Xona’s current target is to launch its first satellites into operation by the beginning of 2025 and to achieve full operational capability by 2027. The company will roll out PULSAR in phases. “In our first phase, we’re going to offer timing services and GNSS augmentation that only require one satellite in view,” Jaramillo said. “Then, as we roll out to phase two, we’ll be able to start to offer positioning services in mid-latitudes with multiple satellites in view. Phase three will include high-performance PNT and enhancements globally.”
Satelles’ STL is already on Iridium’s 66 active satellites, which are all relatively new, having been launched between 2016 and 2018, and cover the entire globe constantly. STL’s signal and capability are flexible, O’Connor said.
Orolia Defense & Security is now evaluating UWB computer technology from different vendors and integrating it in the Versa’s software. “We will probably begin performing full field tests in the first quarter of 2024,” Payne said.
Locata’s mission, Gambale said, “is to deliver technology advances which enable complete, independent sovereign control over PNT for companies, critical infrastructure systems, and in the future – entire nations. It’s designed for the many entities and nations which do not have – and can never afford – their own constellations”.
“Our business model,” Gambale added, “is based on enabling others – from companies through to nations – to develop their systems and products based upon our core technology developments. We do not dictate how our technology will be deployed. Locata’s technology can be available to any suitably qualified partner, to fashion our core developments for their own use.”
The Launch of a Falcon 9 rocket carrying Xona satellites. (Image: Xona Space Systems)
Business Model
It is challenging for any new commercial entrant in the PNT field to challenge a free global service, such as GPS. While all these new services are the opposite of GPS, which is a gift from U.S. taxpayers to the world, their business models vary somewhat.
“We are targeting both mass market applications and high-performance ones,” Jaramillo said. “For the mass market applications, our business model includes a lifetime fee: a customer pays a fee one time, and the service works for the life of the device. For higher performance applications that have more capabilities associated with them, there will be different tiers, each with different services.”
These will include an integrity service that will verify that the signal has a certain level of performance thresholds, for use in critical applications. “If it drops below certain performance thresholds,” Jaramillo said, “we will flag that to the device so that it knows that, even though it is receiving a signal, it should not continue to use it due to signal degradation.”
Receivers and Chipsets
Predictably, these new ventures have spawned a web of alliances.
The success of both Xona and Satelles will hinge in part on the availability of receivers for their signals. To manufacture them, Xona is “in discussions with just about every tier one manufacturer out there,” Jaramillo said. “We have a strong relationship with Hexagon | NovAtel. They have been supportive of us for a long time now and are very advanced in their development and support for our signals.” Additionally, Xona designed its signals “so that most receivers can support them with just a firmware upgrade.”
Satelles is also working with partners, including Adtran (through their Oscilloquartz product line), Jackson Labs (now VIAVI Solutions), and Orolia (now Safran Trusted 4D). “Companies like that provide the solutions that are favored by critical infrastructure providers today,” O’Connor said. “They ultimately integrate our STL capability into their solutions. They can use our reference designs or create their own custom designs based on our reference designs.”
Satelles uses a different process to take measurements of the STL satellite signals than legacy GNSS. “It’s not a single chip that’s measuring both satellites, it’s ultimately two chips that are making those measurements,” O’Connor explained. “Then, we leave it to our partners to determine how to perform the position calculation and the integration of those signals. It can be integrated loosely or tightly.”
Markets and Applications
The target markets and applications for these new PNT services also vary.
The markets in which Satelles has the highest adoption rates are data centers, stock exchanges and 5G networks, said O’Connor. He pointed out that 5G networks need about five to 10 times more nodes to cover a geographic area than 4G networks.
“GNSS has been used for years to time 4G networks, but most 5G network sites — such as femtocells and picocells — are indoors or in places where GNSS is challenged. We deliver that timing service indoors, outdoors, everywhere.” Generally, an STL-only solution is best suited for timing, O’Connor said. “It will do timing at about 100 ns, depending on what kind of oscillator is being used and the exact configuration of the product.”
Orolia provides precise position, timing, and situational awareness for different applications. “Our systems can be used for ground, air and sea-based applications,” Payne said. “At Orolia Defense and Security we market to the U.S. government, defense organizations and contractors.” Beyond those arenas, however, its systems can be used “anywhere accurate position and/or timing is needed.”
Versa PNT. (Image: Safran Federal Systems)
The Role of Simulation
Simulation plays an important role in the development of new PNT systems. “Before the Xona constellation or any other emerging constellation has deployed any satellites, simulation is the only way for any potential end-user or receiver OEM to assess its benefits,” Ackermann said. “Before you can do live sky testing, a key part of enabling investment decisions — both for the end users as well as the receiver manufacturers, and everybody else — is to establish the benefits of an additional signal through simulation.”
Then, new receivers must be validated to ensure they perform as intended. “The best way to do that is with a simulator,” Jaramillo said. “Spirent works with two levels of customers: first, the receiver manufacturers, then all the application vendors that use those receivers.”
Spirent Communications did that for Xona’s system using its new SimXona simulator. “First, we did in-depth validation ourselves,” Ackermann said. “Then, we worked in a close partnership with Xona for them to certify that against their own developments. So, we followed a proven development approach. It’s just that, in this case, the signal comes out of a LEO.” Spirent Communications’ sister company Spirent Federal Systems also provided support to Xona, said Crampton.
Validation and Adoption
The European Commission’s Joint Research Centre in Ispra, Italy, recently conducted an eight-month test campaign to assess the performance of alternative PNT (A-PNT) demonstration platforms, including Satelles and Locata. According to the final report, released in March 2023, the demonstrations “showcased precise and robust timing and positioning services, in indoor and outdoor environments. [T]ime transfer technologies over different means were demonstrated, including over the air (OTA), fiber, and wired channels. The results … showed that all A-PNT platforms under evaluation demonstrated performances in compliance with the requirements set.”
Satelles has also been working with the U.S. National Institute of Standards and Technology (NIST) to evaluate its system. “They have subjected STL to rigorous third-party, hands-off technology evaluations,” O’Connor said. “They confirmed the timing accuracy specifications to UTC and validated the operational characteristics of STL, such as the resilience in the absence of GNSS, the ability to receive the signal indoors, and having global availability.”
The industry is now focused on adoption. “All the providers of these capabilities ultimately need adoption in industry to remain active and viable,” O’Connor said.
With the recent completion of two new GNSS constellations, the growth in the number and variety of augmentation services, and the development and deployment of complementary PNT products and services, the geospatial industry is at an inflection point.
Due to the limited space available in print, I was able to use only used a small portion of the interviews I conducted for our July cover story. For full transcripts of them (totaling more than 12,000 words) see below:
Safran Federal Systems (formerly Orolia Defense & Security) makes the VersaPNT, which fuses every available PNT source — including GNSS, inertial, and vision-based sensors and odometry. I spoke with spoke with Garrett Payne, Navigation Engineer.
Xona Space Systems is developing a PNT constellation consisting of 300 low-Earth orbit (LEO) satellites. It expects its service, called PULSAR, to provide all the services that legacy GNSS provide and more. I spoke with Jaime Jaramillo, Director of Commercial Services.
Spirent Federal Systems and Spirent Communications are helping Xona develop its system by providing simulation and testing. I spoke with Paul Crampton, Senior Solutions Architect, Spirent Federal Systems as well as Jan Ackermann, Director, Product Line Management and Adam Price, Vice President – PNT Simulation at Spirent Communications.
Oxford Technical Solutions develops navigation using inertial systems. I spoke with Paris Austin, Head of Product – New Technology.
Satelles has developed Satellite Time and Location (STL), a PNT system that piggybacks on the Iridium low-Earth orbit (LEO) satellites. It can be used as a standalone solution where GNSS signals will not reach, such as indoors, or are otherwise unavailable. I spoke with Dr. Michael O’Connor, CEO.
Locata has developed an alternative PNT (A-PNT) system that is completely independent from GNSS and is based on a network of local ground‐based transmitters called LocataLites. I spoke with Nunzio Gambale, founder, chairman, and CEO.
Transportation Secretary Pete Buttigieg made a surprise appearance at the DOT roundtable on complementary PNT. (Screenshot: DOT)
“If this is a problem, the government should act like it.”
Citing more than 10 years of government studies, warnings and promises, representatives from a wide variety of industries criticized the government recently for doing little to address an important national security problem.
At issue was the need for national backup capabilities for GPS and the essential positioning, navigation, and timing (PNT) signals it provides.
GPS signals are weak and easy to block or imitate. At the same time the signals are used by most technologies including networks, telecommunications, electrical grids, broadcast, mobile radios, transportation, and other critical infrastructures.
After Russia threatened to destroy all GPS satellites in 2021 in its run-up to invading Ukraine, a member of the White House National Security Council told a public meeting “GPS is still a single point of failure” for the nation.
The government was criticized for inaction at a “Complementary PNT Roundtable” hosted by the Department of Transportation (DOT) in early August. The department is the federal lead for civil GPS and PNT issues.
Eight attendees interviewed after the event reported a surprising unanimity of comments and concerns expressed by industry reps at the meeting.
Enough with the studies
A repeated theme was that the government has done enough studies to understand the problem and available technologies.
“They have been studying this for over twenty years,” one attendee observed. “The Volpe [Transportation Systems Center] report came out in 2001. And there have been lots of studies since then. All have just been refinements of those original findings.”
Another consistent theme was disdain for the idea that industry and the free market will solve the problem without government leadership and active support.
“GPS is free,” said one attendee from a company that provides PNT services. “We can and do sell to meet niche demands, but it is laughable to suggest we can ever sell enough subscriptions to be enough of a backup for GPS.”
A major telecommunications company rep echoed the sentiment. Wireless telecom is especially reliant on PNT. “We use GPS and would use Loran and low Earth orbit satellites if they were available, but we are not going to build it on our own. There is just no business case.”
“We have a big list of things we could do that would increase our resilience and/or cut costs,” said another telecom provider. “There is no big driver for most, though. No competitive pressure, no government mandates.”
Government must walk the walk
“The government has been telling us for over a decade that this is a problem,” said one attendee. “If that’s true, why aren’t they acting like it? Transportation is critical infrastructure and needs a GPS backup, for example. So why hasn’t DOT done something?” Of all the criticisms expressed, this was predominant, according to interviewees.
A 2021 Executive Order on responsible use of PNT services encouraged critical infrastructure providers to not rely on GPS.
The government needing to be a lead customer was mentioned a number of times at the event. This would help raise awareness, set an example, and signal to users the issue is important enough to act on.
Government action was also seen by users as key to creating confidence that a technology or service will be around for the long haul. This point seemed to resonate with many of the government representatives as well.
“I am not going to go to the time and expense of adopting something unless I know it is going to be around for 20 years or more. The only way I can be assured of that is if one of the biggest users is the government.”
Adversaries not idle
Of particular concern to some was that America’s adversaries have better, more resilient PNT, and are constantly working against us.
They are building PNT “…systems of systems. Space-based, ground-based, and everything in between-based. They are doing it. We need to get out in front and lead,” said one. China has been particularly active building multiple integrated PNT systems.
“Our adversaries are not stupid” and are going to try to stay in the lead. “They will try to interfere with any frequency, system, or combination of systems selected. We must test and build something that is survivable and resilient.”
“If China, Russia, and Iran had the ability to protect themselves from nuclear attack,” said one attendee, “we would be frantically trying to get the same capability. Yet those countries have backup and complementary systems for PNT, and the United States does not. And we’re not doing anything,” said a participant reflecting upon the event.
Hopeful signs
Several attendees said there were signs the event might not have been “just another government meeting.”
As part of his opening remarks, the event host, DOT Deputy Assistant Secretary Dr. Robert Hampshire, mentioned the bipartisan infrastructure law and affirmed that PNT is infrastructure. This led some to believe funding from the infrastructure legislation could be immediately available if the government decided to act.
Others were cheered by DOT Secretary Buttigieg’s cameo appearance and comments at the event. One remarked it was the first time they had heard a DOT Secretary say “PNT” in over 20 years.
Uncertain outcome
Despite the consistent messaging and potentially hopeful signs, some attendees questioned whether anything would change because of the two-and-a-half-hour event.
“There were about 120 people from industry and a wide variety of government agencies, but what was the point?” asked one. “We all told the government the same things we’ve told them before, often in writing.”
Another was concerned that the event didn’t discuss the most important questions.
“We were talking about individual systems and critical infrastructures,” this person said. “This is a strategic national security issue. We need to get the bullseye off GPS and ensure the United States can’t be blackmailed by having GPS held hostage.”
“And what if there is a major coronal mass ejection? China will come out much better than us because they have survivable PNT. The United States will become a second-rate power to China in an instant. We keep talking about the trees and ignoring the forest!”
One attendee whose company has a very active government relations program reported they hoped the event would help sway those in government still opposed to action.
“It is pretty clear to us that almost everyone in the departments who understand the issues is in favor of doing something as soon as possible. The same with Congress. But even though the National Security Council is worried about this, there are some folks in the Office of Management and Budget who have opposed action for over a decade.”
While some came away buoyed by what they saw as an action-oriented tone to the event, others doubted much would change. “It remains to be seen whether criticism from industry and threats from China and Russia are enough to get the government to finally do something.”
Dana A. Goward is President of the Resilient Navigation and Timing Foundation and serves on the President’s National Space-based Positioning, Navigation, and Timing Advisory Board.
The U.S. Department of Transportation (DOT) and the U.S. Coast Guard Navigation Center (NAVCEN) will hold the 61st meeting of the Civil GPS Service Interface Committee (CGSIC) on Sept. 20-21.
The meeting will be conducted at the St. Louis Union Station Hotel in St. Louis, Missouri, in conjunction with the Institute of Navigation’s 2021 ION GNSS+ conference.
The 61st CGSIC meeting will also be broadcast live online to provide a virtual option. This is a unique opportunity for anyone in the world with access to a computer to attend these public meetings of the U.S. Civil GPS program. CGSIC meetings are free and open to the public.
The three subcommittees of the CGSIC will meet on Sept. 20: Timing; International Information; and Surveying, Mapping, and Geosciences.
Summaries of the subcommittee meetings will be presented to the CGSIC plenary session Sept. 21 with a keynote address by Juliana Blackwell, director of NOAA’s National Geodetic Survey (NGS).
UNMANNED SOLUTION, a South-Korean company based in Seoul, develops autonomous vehicles, including driverless shuttles, autonomous agricultural equipment, robots, and educational platforms. (Image: SBG Systems)
What is complementary / alternative positioning, navigation, and timing (PNT)? In this month’s cover story, five of our marketing partners share their perspective on this question and explain how their products address it.
The four global navigation satellite systems (GNSS), two regional navigation satellite systems and public and private augmentation services continue to provide exceptional levels of accuracy and reliability for positioning, navigation and timing (PNT). Yet their well-known vulnerabilities also continue to fuel the need for alternative/complementary sources of PNT data, especially for new and rapidly expanding user segments such as autonomous vehicles.
What constitutes a complementary service to GNSS for PNT and what constitutes a true alternative is partly a matter of definition and opinion. In a January report, the U.S. Department of Transportation stated
…suitable and mature technologies are available to owners and operators of critical infrastructure to access complementary PNT services as a backup to GPS. To achieve the parallel objective of resilience, as described in Executive Order (EO) 13905, that path should involve a plurality of diverse PNT technologies. Promoting critical infrastructure owner/operator use of those technologies that show strong performance, operational diversity, operational readiness, and cost-effectiveness is worthwhile. Based on this demonstration, those technologies are LF and UHF terrestrial and L-band satellite broadcasts for PNT functions with supporting fiber optic time services to transmitters/control segments. (Andrew Hansen et al., Complementary PNT and GPS Backup Technologies Demonstration Report, prepared for the Office of the Assistant Secretary for Research and Technology, Department of Transportation, January 2021, p. 195.)
A portion of the former USCG Loran Support Unit in Wildwood, New Jersey, with its iconic Loran antenna. (Image: UrsaNav, Inc)
For this year’s Q&A on complementary / alternative PNT, I asked five companies in the GNSS/PNT space to tell us how they define the issue, what solutions they prioritize, what markets they target, and which of their products specifically address the need to make PNT more resilient.
Roger Hart: The deep adoption of the state-sponsored, space-based global navigation satellite systems (GNSS) defines them as the primary PNT source at this time. Inertial navigation, long predating GNSS, does provide an independent navigation solution but does not provide time. In today’s conversation, alternative PNT generally refers to deriving position and timing from existing signals not purposed for navigation, to ground-based location systems, and also to emerging satellite systems that operate at higher power — or out of the GNSS band — to provide a diversity of PNT sources.
David Sohn: Simply put, alternative PNT is usually anything that is not GNSS. So, this includes PNT derived from low Earth orbit (LEO) satellites; vision, radar, lidar combined with inertial measurement units (IMUs) and map matching; positioning off cellular WiFi, digital TV signals and other signals of opportunity; legacy nav aids like VORTAC, ILS, DME and eLoran; and new dedicated infrastructure positioning systems like Locata, NextNav or RFID.
Matthieu Noko: Here at SBG Systems, for 15 years we have been developing navigation systems based on smart coupling of GNSS technology and inertial sensors. From our perspective, inertial sensors as well as sensors such as odometers or DVL, combined with high-end algorithms and RAIM, build consistent alternatives to GNSS-only systems in the vast majority of outdoor applications. Inertial sensors dramatically enhance GNSS-only navigation systems, making it possible to provide navigational data during GNSS outages in urban environments or to reject false GNSS measurements due to multipath effects.
As its entry into the driverless category of the Formula Student Germany car race, AMZ modified the car it has used in competition since 2015 to be driverless. (Image: SBG Systems)
The hybridization of several technologies makes it possible to reach a sufficient reliability level for the majority of commercial applications. However, in some indoor applications or in case of intentional jamming or spoofing, a higher resiliency is required. Using visual odometry can then complement quite effectively the navigation system, although this technology is still at a research level. Compared to infrastructure-based alternative PNTs — such as WiFi, Bluetooth or ultra wideband (UWB) ranging — visual odometry has the great advantage of not requiring any infrastructure.
Jacob Amacker: GNSS remains the dominant method of PNT in terms of market applicability and performance, but there are many rival technologies that have great potential and will compete with GNSS going into the future. The most important changes in PNT will be methods of position localization that are able to replace GNSS, and we will likely see these technologies integrated into huge systems, making use of ubiquitous technologies such as lidar. Whereas GNSS still provides the most accurate timing, as systems get more complex, time synchronization becomes a bigger issue, so different methods of this need to be explored.
There are many ways of improving the navigation data overall. Most commonly an IMU and a Kalman filter will be employed to stabilize any errors in the position localization method. A Kalman filter is a method of processing data from a range of sources—say, GNSS, an IMU, and a wheel speed sensor—and using them in such a way as to arrive at the position with a greater accuracy and precision than either source alone would be able to achieve. This process, however, requires precise timing for each data stream. Therefore, one area in which alternative PNT has to compete with GNSS is timing precision. GNSS makes use of atomic clocks used on satellites that are as accurate as you will get. There are also several ways of synchronizing time. A timing system can only be as precise as the most precise clock on the network, but there have been developments, such as Precision Time Protocol (PTP) that can synchronize timings across a network of clocks over Ethernet connections. Traditionally, PPS has been used and whereas this is still very precise it is not able to compete with PTP on convenience or sophistication.
Charles Schue: The common definition these days for “alternative PNT” seems to be with respect to, or as compared to, GPS or GNSS. Even the U.S. DOT’s website speaks to PNT as related to GPS.
I used alternative, complementary and backup somewhat interchangeably during my entire career with the U.S. Coast Guard. In recent years, I injected “co-primary” into the conversation as well. Prior to GNSS becoming ubiquitous, alternative, complementary and backup were not technology-based terms, but were instead operationally based. For example, “the prudent mariner” or “the prudent aviator” should use all means at their disposal to safely navigate their platform. For the navigator, this would include visual, audible and electronic signals or aids. The solution of choice obviously was the one that provided the highest accuracy, availability, integrity and continuity. However, prudence required always checking the solution of choice against other readily available alternatives, preferably that complemented each other, to ensure safety and continuity of operations. At one time, shipboard navigators might have at their disposal Loran-C, OMEGA, GPS, INS, radar, sextant, visual bearings (such as lights and landmarks), beacons, and soundings. Similar alternatives were available on aircraft.
Although always in the mix, timing was often in the background until around 2000. Then it started to become as important as positioning and, in many areas, even more important than positioning. Today’s incredible dependence on technology, and interdependence between technologies, means that knowing your “when” has become as important as knowing your “where”.
Whatever the terminology, the definition of alternative PNT should include some key features. Firstly, we should accept that the solution of choice today is GNSS, and we should define it as primary or co-primary. Next, we should acknowledge that when the primary solution is available and trustworthy, it should always be used, or at least considered. Finally, the primary solution should continually be compared with alternatives to ensure safe and secure provision of PNT to the user. Thus, an alternative PNT solution is one that is readily available; provides an easy and seamless transition to/from the primary or other alternatives; allows continuity of operation at a possibly degraded, yet usable, level of accuracy, availability, integrity or continuity; and is dissimilar enough from alternatives to withstand the effects that might be affecting the primary solution.
Do you agree with the U.S. DOT’s assessment, cited above, of what it will take to make the national PNT much more resilient and reliable? If you do, how do your offerings fit into that framework?
RH: While there are intricate differences in the signals generated by the primary PNT systems, they are all quite similar in terms of frequency and power and are all vulnerable to the same types of interference. Achieving the most resilient solutions will require the use of alternative RF bands and non-RF sources. Having a variety of alternative PNT sources will allow users to integrate the method most applicable to their platform constraints. Integration across the various PNT sources will need time synchronization to take full advantage of the alternate PNT systems. Our offerings work concurrently with GNSS, providing simulation and testing of GNSS and alternative PNT as true complements, while also offering the ability to measure timing accuracy in real time.
DS: Yes, we agree with the DOT’s assessment. However, to be clear, the DOT does not require “LF and UHF terrestrial and L-band satellite broadcasts for PNT functions with supporting fiber-optic time services to transmitters/control segments.” It stated that to achieve resilience, systems “…should involve a plurality of diverse PNT technologies…that show strong performance, operational diversity, operational readiness and cost-effectiveness.” Their demonstrations showed that those technologies they called out meet these criteria. Our solutions have been leading this resilient approach by offering several diverse, alternative PNT references.
We have fielded time-server equipment that operates from both GNSS and eLoran. Our standard offering time servers are equipped with multiple references from GNSS, network-based time services from NTP, PTP and PTP WR; internal references from disciplined atomic clocks; wireline references from IRIG, 1PPS or ASCII time code; and LEO PNT reference from the STL signal.
(Image: SimonSkafar_E+_Getty Images)
L-band or more generally the use of geostationary satellites was until very recently the only communication link for PNT augmentation services, although these signals are weak and easily disturbed or masked, especially at high latitudes. Resilient navigation will clearly need to allow multiple downlinks for corrections such as terrestrial networks (4G/5G) or satellite-based internet. In the mid-term, we expect the correction delivery over IP to become the standard, and L-band corrections to be used as a backup only. All our high-performance products already include an NTRIP client able to handle the IP corrections very easily.
JA: This is certainly one option. Largely, it is borne out of a need to compensate for the disadvantages of GNSS. This larger range of frequencies would provide a range of satellite-borne signals that have different penetration characteristics and information carrying properties but the same core purpose. Therefore, somebody making use of such a system will be better able to receive these signals even when under obstructions. Of course, some obstructions will still be impenetrable to GNSS signals and there is a long way to go to developing a comprehensive solution that can deal with timing differences when the signals travel through objects. It is likely that some other source of timing information, for example through the proposed fiber-optic services, will be necessary to smooth out these issues. Although we will see this much-needed upgrade to cover the shortfalls of GNSS employed, many other alternatives will start to take prominence. It is difficult to say which solution will win out, and it is likely that an upgraded GNSS will continue to dominate for the next decade or two at least. In terms of our offerings, we are exploring all possibilities and keep our core technology open to any position localization method. Of course, we will welcome any new technology that is a viable and improved method of PNT.
CS: I have long been an advocate of a system-of-systems approach simply because there is no PNT solution available yet that works everywhere, under all conditions, for all users, all the time. Many solutions provide only a component of PNT: an INS provides position (the “PN”), and an atomic clock provides time (the “T”). However, an INS does not know “where” it is without initialization and updates, and an atomic clock does not know “when” it is without initialization and updates. Fiber is awesome but is not wireless. Many alternatives depend upon GPS/GNSS as a necessary input. Others are augmentations that depend upon GPS/GNSS as inputs and not direct alternatives, such as space-based or land-based augmentation systems. Some are mode-dependent — such as VOR, DME, ILS, and TACAN for aviators — and thus not useful to other modes: time/frequency, maritime, land-mobile or handheld.
So, yes, we agree with the government’s assessment that low-frequency (LF), generally referring to eLoran in the United States, is the best, very wide area, terrestrial, wireless alternative, and is an essential component of any resilient PNT framework. Irrespective of whether the implementation is Loran-C, eLoran or LFPhoenix, LF is the lowest cost terrestrial PNT solution per million square miles of coverage. All our offerings are focused on the LF portion of the resilience framework. Our offerings easily integrate with any existing PNT technology and have proven in real-world government testing their ability to survive heavy jamming and spoofing environments.
What markets and applications do you target?
RH: Spirent Federal provides simulation test solutions to U.S. government and affiliated organizations. Applications range from core GNSS receiver development to real-time, hardware-in-the-loop system integrations. We have a long history of supplying the U.S. government and contractors with first-to-market products, from Y-code, SAASM, inertial and M-code, to sensor fusion of the latest alternative signals and sensors. We provide test solutions to safety-critical applications that are expected to have the same level of operational performance both in GNSS-available and GNSS-denied environments. Providing a single test platform that can help validate performance in both environments has received positive responses from users in the autonomous vehicle industry.
DS: Aerospace and defense, data-center and communication networks, public safety, industrial control, search and rescue, and space.
Autonomous self-driving mobility solutions move people and goods at appropriate speeds in urban and campus environments. (Image: SBG Systems)
MN: SBG targets a large range of applications including from a relatively small BVLOS drone for remote operation to large hydrographic vessels or airborne survey. We divide the applications into two main categories:
Surveying and mapping, where the inertial navigation system is used to stabilize the measurements from a lidar, sonar or camera to generate high-precision maps.
Control applications, where the PNT and orientation solution is used in real time to feed autopilot or to stabilize a camera. These applications include unmanned vehicles, machine control, camera pointing and more. High resilience is then critical to ensure safe navigation.
JA: Two main applications we are targeting with alternative PNT are surveying and ADAS systems. Both of these applications often make extensive use of lidar systems. We are therefore looking at lidar-based simultaneous localization and mapping (SLAM) algorithms to aid PNT or to provide relative position localization without GNSS. In cases when GNSS is totally unavailable, it is usually possible to set up ground control points. Although these cases are limited, they give much more flexibility in options. Anticipating a future where autonomous driving is the norm and not the exception, new building projects will need to be planned with the adequate systems in place to allow for them, and this will include a system such as UWB.
CS: Our employees have been involved in the design, development, deployment or sustainment of every Loran-C and eLoran system site in the world (transmission, control or monitor) since the mid-1970s, including components of the Russian Chayka system. Our service provider and end-user technologies are operationally proven in commercial and military environments. We specifically target the maintenance and upgrade of existing systems, as well as the implementation of new systems, globally.
Which of your products directly address the need for alternative PNT?
RH: In a broad sense, Spirent offers a market-proven and innovation-driven solution portfolio for the simulation of inertial sensors through the SimINERTIAL and SimSENSOR product lines, seamlessly integrated with our GNSS simulation. Spirent is actively engaged with several alternative RF vendors to incorporate signal simulation capability and will offer an alternative RF navigation product in 2021 called SimAltNav Replay. This product will allow for concurrent GNSS and alternative RF signal simulation. Additionally, Spirent offers many other alternative PNT solutions for testing resilient systems for connected vehicles and sensor-fusion algorithms for tactical and military-grade systems. We are developing new products to incorporate an open Ethernet interface allowing for open-source Ethernet-based sensor simulation.
Remotely controlled rovers are used to test and practice complex tasks in Mars-like desert environments. (Artist’s Rendering: Stocktrek Images_Stocktrek Images_Getty Images)
DS: Our time servers are equipped with high-quality precise internal time references such as OCXOs or atomic clocks and then disciplined by external references such as GNSS. They are resilient because they can operate precisely for long periods in GNSS-denied situations as standalone devices in holdover mode or from multiple alternative references, such as:
network-based NTP, PTP and PTP WR time services
wireline references from IRIG, 1PPS or ASCII time code
LEO PNT reference from the STL signal
eLoran when available
They are also resilient because they detect and mitigate interference from the GNSS signal before it can corrupt the PNT solution.
Our GNSS simulators are adding alternative PNT features to provide a complete test and evaluation solution for resilient PNT systems. We have recently added INS/IMU test features and have integrated with Anritsu’s cellular test stations to evaluate and qualify combined GNSS/cellular location functions. Orolia GNSS simulators support generation of custom GNSS signals and playback of IQ waveforms, and provide complete toolsets for GNSS jamming and spoofing testing. This allows creation of the threat environment to allow evaluation of alternate PNT signals as backup or alternative to GNSS. Orolia offers an open-source framework allowing any end user to develop their own sensor plug-in leveraging the Skydel simulation engine.
Our Resilient PNT for Defense product line includes the VersaPNT, which uses alternate non-GNSS PNT sensors such as IMUs, barometers, wheel ticks, INS and non-GPS-based LEO satellites. Alternate RF navigation or non-GNSS sources of radio frequency (RF) are of interest in highly degraded or contested signal environments. Interest is focused on low-Earth-orbit (LEO) constellations. These systems offer high receiver signal power (relative to GNSS) and a secure and resilient link to augment GNSS.
MN: All our products are designed to answer to challenging GNSS conditions, starting with our Ellipse series, which includes an industrial-grade IMU capable of coping with short-term GNSS outages. Its miniature size allows integration in robotics and also makes it suitable for cost-sensitive applications. Our Apogee and Horizon series, with their navigation-grade IMUs, are the most resilient systems in the event of GNSS outages. These products reach very high-end performance in real time, but become exceptional when used with our post-processing software Qinertia. Tightly coupled algorithms make the solution capable of coping with long-term GNSS outages.
JA: We have previously created solutions using retroreflective strips for path following with driving robots. and we are also compatible with Locata’s system, a large infrastructure solution popular for automation in shipping ports. More recently, we have released an offering for UWB in an integration with Pozyx. This is perfect for GNSS-denied environments as a direct replacement for what GNSS can provide in terms of position information. We are also exploring alternative ways to synchronize clocks and get timing information. This year we have developed PTP functionality on all of our devices. Alternative PNT is going to be vital as we look to the future of navigation and thinking about how we can navigate flawlessly anywhere and address more complex environments, particularly urban areas.
CS: We are focused on the provision of terrestrial low-frequency equipment and systems for primary, co-primary, alternative, complementary and backup PNT. We provide all the products and services required to design, develop, install, certify, operate and maintain Loran-C, eLoran and LFPhoenix equipment and systems. We provide the technology to perform coverage diagrams and site surveys; all the equipment required at a transmission site; all the equipment required at a differential reference station or quality-of-service site; all the equipment required for a monitor and control site; ASF measurement and analysis equipment; and various models of end-user equipment (including receivers and antennas) for the timing/frequency, maritime, aviation, land-mobile and handheld markets.
In separate letters to the Office of Management and Budget (OMB) and new Secretary of Transportation Buttigieg, influential members of Congress have urged the Biden administration to take prompt action and establish a backup timing capability for GPS.
Danger and Benefits, Solution in Hand
On March 1, Republican representatives Sam Graves and Bob Gibbs wrote to the acting OMB director citing the dangers of not having a backup, and the benefits one would bring. Graves is the ranking member of the House Transportation and Infrastructure Committee.
Calling backup timing for GPS “important telecommunications infrastructure,” they said the capability is essential. Without a backup “… it is not a question of if our transportation, financial, and telecommunications infrastructure systems will fail, it is a question of when.”
After describing some of the threats to GPS, they observed that America will suffer from an outage more than many of its adversaries. Russia and China were cited as examples of nations that already have terrestrial backup systems for space-based PNT.
The letter to OMB also cited the benefits to safety, autonomous and intelligent transportation systems, along with “5G & Future Telecommunications.” GPS interference has led to a near crash of a commercial passenger aircraft, drone accidents, and allowed white-hat hackers to force cars off the road. The letter also referenced a report by the Alliance for Telecommunications Industry Solutions (ATIS) calling for a national timing solution to complement GPS. Such a solution would “…allow faster 5G implementation and enable it to reach more Americans.”
Graves and Gibbs also mentioned the Department of Transportation’s (DOT) January report to Congress on its GPS Backup Technology Demonstration. The report called for an architecture that included signals from space in the L band, terrestrial broadcasts in the Ultra High Frequency and Low Frequency spectra, and a fiber backbone to synchronize and feed precise time to terrestrial transmitters.
Studies and Broken Promises
By contrast, a letter signed by Democratic House members focused on decades of administration studies, a broken promise, and failure to follow the law.
Transportation and Infrastructure Committee Chair Peter Defazio, along with Representatives Garamendi and Carbajal, wrote to DOT Secretary Buttigieg on Feb. 25. The letter noted that the need for a GPS backup was first identified in a 2001 DOT report. Since then, “…there have been over 18 studies and recommendations by the Federal Government calling for a land-based, wireless nationwide backup system.” Also mentioned were comments in 2014 by DHS officials calling the nation’s over-dependence on GPS “a single point of failure” for critical infrastructure.
Congress was encouraged in 2015 when the Obama administration said it would establish an eLoran timing system and follow it with a broader approach to GPS vulnerability. “This well-reasoned approach gave Congress encouragement that this national security problem would finally be addressed.”
“However, in 2018, after no additional action was taken, Congress took responsibility to codify the commitments outlined in the 2015 letter, and on a nearly unanimous bipartisan basis in both Houses, passed the National Timing Resilience and Security Act (NTRSA) to implement the land-based timing back-up system.”
The letter also notes that Congress further nudged the administration on this issue in last year’s appropriations. The act for 2021 provided funding for six new DOT staff positions to support the project and directed the department to make the hires.
Timing and Positioning
Observers say that it is almost certain the capabilities implemented to satisfy the terrestrial timing requirement in NTRSA will also provide a positioning capability independent of GPS.
NTRSA requires DOT to “… incorporate the recommendations from any GPS back-up demonstration program” into the solution set. The combination of technologies recommended by the demonstration report will provide users one or more terrestrial services from which location can be derived.
Also, mobile devices must know their locations to use wireless timing signals. Location information independent of space-based signals is needed to provide these users resilient timing service.
A new white paper sponsored by the Resilient Navigation and Timing Foundation (RNT Foundation) discusses the need and implementation of a reliable and resilient national timing architecture that will include space-based assets. This system-of-systems architecture — GNSS, terrestrial eLoran broadcasts and fiber — is essential to underpin today’s technology and support development of tomorrow’s systems, according to the executive summary of A Resilient National Timing Architecture.
“Everyone in the developed world needs precise time, all the time, whether they know it or not,” said Marc Weiss, one of the paper’s authors and an internationally recognized expert on timing and synchronization. “It is a foundation of every networked technology, digital broadcast, and most navigation systems, to name just a few critical uses.”
Three Paths to Precise Time
“Precise time is so important that everyone needs at least three independent methods of getting it. So, if one, or even two, fail it is not a national disaster,” said Pat Diamond, co-author of the paper. “Our proposed architecture calls for precise time via GNSS, terrestrial eLoran broadcasts and fiber.” Diamond is a long-time network designer, developer, and entrepreneur. He is also a member of the U.S. National Space-Based Positioning, Navigation, and Timing Advisory Board.
Diamond also pointed out that these three methods should be the backbone for timing distribution in the U.S., but won’t be the only methods. “What we are describing is a baseline architecture that will be added to,” he said. “It is a starting point. We envision in the paper additional distribution methods like time from other satellites, user clocks, and so on, all being part of the mix.”
Government Leadership
The U.S. federal government has a leadership interest and responsibility in all of this, according to the paper. Nations have long recognized the military and commercial advantages of determining and distributing precise time. Great Britain’s Longitude Act of 1714 was really about developing a chronometer to support safe navigation of Royal Navy and British merchant fleet. In the United States, the U.S. Naval Observatory has been keeping and distributing a national time scale time since 1845.
“Just because the feds have an important leadership role, doesn’t mean they have to build and own a bunch of systems,” said Dana A. Goward, the paper’s third co-author and executive director of the RNT Foundation. “There are a variety of ways these systems can be established. Public-private-partnerships, subscription contracts like the FAA did with their air traffic ADS-B system, and cooperative agreements are all examples. As we move forward with 5G telecommunications and perhaps even timing and navigation, it will be increasingly important to have a rock solid timing infrastructure to support it all.”
The National Timing Resilience and Security Act of 2018 requires the U.S. Department of Transportation to establish a terrestrial system to backup GPS timing services by December of this year. While the department does not appear to be on track to meet that goal, it completed a technology demonstration program for GPS backup technologies earlier this year. Two companies demonstrated timing distribution by fiber. Another two demonstrated eLoran.
Many Pieces Already in Place
One of the benefits of the proposed architecture is that much of what is called for is already in place, according to the paper. “We already have fiber networks, NAPs (network access points). eLoran is mature and has been deployed by the Brits. And the U.S. government owns enough former Loran-C sites to establish a nationwide eLoran network,” Diamond said. “All we need is a bit of money and some engineering work to put this all together.”
At first it was a flurry of letters and public statements from U.S. senators and members of the house. Then there was a senate hearing on the topic, and the issue was discussed in several other hearings.
The Federal Communications Commission’s (FCC) approval of a long-standing request by Ligado Networks continues to be controversial. The request was to make terrestrial broadcasts on a frequency near that used by GPS. Broadcasts which, according to analyses by the departments of Defense and Transportation, will interfere with GPS reception for many users.
Now it looks as though Congress is ready to move beyond talk and enact one or more pieces of legislation. These would require an independent technical review of the FCC’s decision and place limits on the ability of Ligado Networks to use the license it was granted.
Congressional interest has been fueled both by member concerns and a regular drumbeat of input from constituents. The recently formed Keep GPS Working Coalition is just one example. It was created from a larger group of more than 70 companies and organizations across a broad swath of industries that has gone on record against the decision and has been supporting congressional action.
National Defense Authorization Act
A primary vehicle for congressional action looks to be the National Defense Authorization Act (NDAA) for 2021. Unlike other “annual” legislation that often gets sidetracked or delayed during election years, Congress has passed an NDAA for each of the past 59 years. As such, it is a particularly powerful tool.
This is doubly so in this case, as the member of Congress that has been the most outspoken critic of the FCC’s decision is Senator Jim Inhofe (R-OK). He chairs the Senate Armed Services Committee that has direct responsibility for the NDAA.
Responding to conflicting claims about the findings of government and private tests, the bill requires the Defense department to contract with the National Academies of Science, Engineering and Medicine for an independent technical review.
Evaluating Potential Impact on GPS
Among other things, the review will compare the different methods of evaluating the potential impact on GPS services from Ligado’s transmissions, and determine which of those was the most effective in guarding against any harm.
The bill also prohibits the Defense Secretary from spending any money to comply with the FCC’s order until the Congress has been given an estimate of the total cost to the department of coping with Ligado’s transmissions.
While the FCC order requires Ligado to modify or replace any government receivers impacted by its operations, the Defense department and others have said this is only a small fraction of the overall costs they would incur.
The bill requires the Defense Department estimate to consider a much larger scope of costs including:
To upgrade, repair, or replace potentially affected receivers
To modify, repair, or replace equipment, pares, associated ancillary equipment, software, facilities, operating manuals, training, or compliance with regulations, including with regard to the underlying platform or system in which a capability of the Global Positioning System is embedded; and,
For personnel of the department to engineer, validate, and verify that any required remediation provides the Department with the same operational capability for the affected system prior to terrestrial operation in the 1525 to 1559 megahertz or 1626.5 to 1660.5 megahertz bands of electromagnetic spectrum.
The House version of the NDAA also provides that:
“The Secretary of Defense may not enter into a contract, or extend or renew a contract, with an entity that engages in commercial terrestrial operations using the 1525–1559 megahertz band or the 1626.5–1660.5 megahertz band unless the Secretary has certified to the congressional defense committees that such operations do not cause harmful interference to a Global Positioning System device of the Department of Defense.”
RETAIN GPS and Satellite Communications Act
Senator Inhofe has also announced he will introduce stand-alone legislation when Congress returns from summer recess. His “Recognizing and Ensuring Taxpayer Access to Infrastructure Necessary for GPS and Satellite Communications Act,” or “RETAIN GPS and Satellite Communications Act,” would require Ligado to modify or replace any receiver, including those used by private citizens, that would be impacted by Ligado’s operations.
This modification would be required before the FCC’s order allowing them to transmit could come into force. Most observers opine that the number of impacted civil receivers in the U.S. is so great that this would effectively deny Ligado use of the frequency.
Introduction of the RETAIN GPS and Satellite Communications Act was planned for before the summer recess. Its delay until after was likely to provide more time to recruit co-sponsors.
GPS Interference a ‘Niche’ Issue
One observer commented that “GPS and the FCC Ligado order are really niche issues. As time goes on, more and more members of Congress will hear about it from constituents and be appalled.”
The delay will also allow time for the mammoth NDAA bill to clear Congress. RETAIN GPS would then have more chance for the spotlight.
Many industry observers have opined that regardless of congressional action, Ligado will struggle to find a successful 5G or other business model that will generate a significant revenue stream from the spectrum.
As public concern continues to grow and Congress responds with legislation, it may turn out that Ligado finally won the battle at the FCC but ended up losing the war.
