An F/A-18F Super Hornet assigned to Strike Fighter Squadron (VFA) 102 launches from the flight deck of the aircraft carrier USS Ronald Reagan on July 10, 2018. (Photo: U.S. Navy/ Mass Communication Specialist 2nd Class Kenneth Abbate/Released)
Along with partner L3 Technologies, the Enhanced Link Navigation System (ELNS) offers new solution to defeat enemy countermeasures to detect and disrupt allied signals.
CTSi and partner L3 Technologies this month completed flight-testing of a newly developed integrated communication and navigation system for use in highly contested and GPS-denied environments.
Designated the Enhanced Link Navigation System (ELNS), the prototype was built under a U.S. Navy $8.7 million Small Business Innovative Research (SBIR) Phase III contract and flight tested at the St. Mary’s County Regional Airport near Patuxent River, Maryland.
“Our team put ELNS in the air in less than 18 months. It worked the first time and every time during 15 flights, which included 152 approaches,” said Ian Gallimore, CTSi chief technology officer. He went on to say that ELNS provided area navigation to replace GPS at ranges in excess of 50 nautical miles all the way through landing.
Pilots from Airtec, who provided turn-key flight test support, said during test events, “These needles are… money,” and “ELNS is as good as any instrument landing system I’ve flown, I’d fly it in the weather.”
“ELNS is scalable for unmanned aircraft in all groups, from those needing high integrity like MQ-25, to small unmanned aircraft on tight weight budgets,” said Martin King, Navy project manager. “ELNS is the first system to bring GPS-denied navigation capability to small UAS. By combining significant investments in related fields to create a whole new capability like this, ELNS takes position, navigation and timing (PNT) for air vehicles in a compelling new direction.”
ELNS utilizes L3 Technologies’ waveforms that defeat adversary strategies to detect and disrupt allied signals, using waveforms that are essential in communications-denied and GPS-denied environments.
“There is a strong fit between what ELNS brings and the threats that our forces are facing today,” said Tom Sanders, CTSi chief executive officer.
Honeywell has produced a new inertial navigation unit that provides accurate navigation for customers across a broad range of industries including agriculture, robotics and autonomous vehicles, without compromising on size, cost or performance.
The HGuideN580 inertial navigation technology improves accuracy in urban and rural environments. (Photo: Honeywell)
The HGuide n580 is the first Honeywell-produced, industrial-focused navigation solution that uses both precision inertial measurement unit technology and GNSS to improve location accuracy even when facing natural and manmade obstacles.
“The blend of inertial and satellite navigation capabilities provided by the HGuide n580 is especially important where precision is required in demanding environments — for example, autonomous cars traveling in cities, where our technology can extend the accuracy and performance of navigational systems while keeping passengers safe,” said Chris Lund, senior director, Navigation and Sensors, Honeywell Aerospace. “Honeywell’s history and expertise in navigation technology enables customers to implement this new wave of advanced technology into their own applications and operations.”
Roughly the size of a deck of cards, the HGuide n580 gives Honeywell’s industrial customers the capabilities needed to navigate accurately in areas with limited satellite coverage, such as densely populated cities where tall buildings, underground tunnels, and multi-layer freeway stacks or bridges often create challenges to traditional GPS navigation.
For a GPS unit to function properly, it requires a strong signal connection between the unit on the ground and multiple satellites in the sky to accurately orient its position. City infrastructure such as buildings and tunnels can temporarily block the signal between GPS unit receivers and satellites, creating urban canyons.
With the HGuide n580 integrated system, Honeywell’s inertial measurement unit technology combines with GPS to act as a backup solution, which means the loss of GPS signal caused by an urban canyon does not result in a complete loss of navigation.
To learn more about the new HGuide n580 solution and Honeywell’s other commercially available navigation technologies, visit the Honeywell Aerospace website.
The U.S. Army is soliciting proposals for research, development, design and testing that directly supports battlefield technologies in the area of positioning, navigation and timing (PNT).
Broad Agency Announcement (BAA W56KGU-18-R-PN22) was issued by the U.S. Army’s Communications-Electronics Research, Development and Engineering Center (CERDEC) on Nov. 24 through FedBizOpps.gov.
CERDEC — based at the Aberdeen Proving Ground in Maryland — aims to discover technical approaches to improve and enhance current and future land warrior capabilities, flexibility and responsiveness in line with its strategic vision for enhancing warfighter capabilities to operate in both symmetric and unsymmetrical environments.
GPS-denied environments. “The goal is to support CERDECs Strategic Thrust for PNT by providing technical and operational capabilities that enables the soldier to continue their operations in hostile RF and GPS-denied environments,” reads the BAA. “Proposed technical approaches may apply to operations both before and after the cessation of hostilities.
“This announcement emphasizes approaches that address the very different challenges presented by urban fighting and dramatically enhance warfighter capabilities, for example, the ability to interact, maneuver and operate under a time constrained environment. These changes should generally result in lower casualties, lower collateral damage, and the effective use of combat power.
“The specific topics of interest revolve around the research and development of technologies may provide revolutionary improvements to the entire spectrum of PNT.”
Soldiers with 18th Military Police Brigade, assault opposing enemy threats during an Urban Operations training at the 7th Army Training Command’s Grafenwoehr Training Area, Germany, Oct. 20, 2017. (U.S. Army photo by Spc. Javon Spence)
CERDEC’s plan is to support multiple and potentially multiphase efforts that pursue the design, development, integration and demonstration of critical and enabling technology and system attributes pertaining to PNT. Proposed efforts will primarily be of service and material with aims at resolving technical barriers.
Proposals. Proposals submitted should range in scope from study and analysis type work with limited data and deliverables, to larger efforts for component developments, techniques and demonstrations with breadboard or prototype-style deliverables.
The contracts are expected to be cost-plus-fixed-fee, but can be negotiated.
Orolia, through its Spectracom brand, has launched VersaPNT. VersaPNT provides virtually failsafe battlefield navigation, even in GPS-denied environments, to protect critical networks with Assured PNT technology, the company said.
The new, ground, air or sea vehicle-mounted solution is designed for military environments, with a ruggedized, compact, low-power and lightweight form factor.
Today, military vehicles are portable networks, providing seamless connections with U.S. headquarters, regional command posts and individual soldiers. Remote areas are challenging environments for military networks, and enemy forces are jamming, spoofing and disrupting operations.
“VersaPNT provides continuous mission assurance and C4ISR support, even in hostile environments,” said Rohit Braggs, Orolia vice president, PNT networks and sources. “This innovative technology solution protects critical networks for complex military and homeland security land, air and sea operations.”
Every minute counts on the battlefield, and VersaPNT provides critical decision support with real-time situational awareness to facilitate a rapid response, according to the company. This lifesaving technology can also help keep soldiers and civilians out of harm’s way, while ensuring continuous tracking of friendly and enemy forces.
VersaPNT provides essential command and control, navigation, communication and electronic intelligence support for U.S. and allied military, homeland security, first responder, civilian agency, special operations and intelligence missions.
Demonstrations are available at the AUSA Annual Meeting, Orolia Booth #2944.
In the battle for reliable positioning and timing, the U.S. Army is engaged in a multitude of activities, including mounted and dismounted A-PNT (assured position, navigation and timing) systems, anti-jam technology and pseudolites.
The idea is simple: Take some GPS satellites, and put them on or near the ground. Now you have a navigation system where you have full control over the locations and power of the transmissions. You can ensure that the transmissions reach places that GPS normally struggles with, such as deep urban canyons, forests and valleys.
You can turn up the transmit power, so they are much harder to jam than spaceborne GPS signals. These pseudo-satellites, commonly referred to as pseudolites, have seen steady interest over the years for a variety of applications.
Now the U.S. Army is pursuing the use of pseudolites as part of its initiative to maintain operation in GPS-denied environments.
Pseudolite Basics
There are various types, and use-cases, of pseudolites. In this column we’ll consider the direct-ranging pseudolite, which can be simply considered as a ground-based GPS satellite. If we deploy several pseudolites on the ground, we can imagine that a normal GPS receiver would be able to receive the GPS-standard transmissions and derive a position, just as we would from the space-based satellite transmissions.
The fact that the pseudolites are ground-based introduces us to the first consideration: The locations of the transmitters are no longer described by orbital parameters. Instead of calculating the position of satellites, we need to describe the location of the pseudolites in geographical terms, perhaps with a fixed position described in Earth-centered, Earth-fixed (ECEF) coordinates.
The transmitted navigation data message, which would normally contain almanac and ephemeris information, may now need to contain the geographical position of the pseudolite. Not a problem, but our GPS receivers will need a software upgrade to be able to handle this situation.
The deployment of the pseudolites themselves poses an interesting problem. Imagine a military scenario, where the army is deployed to a region of interest. Navigation warfare is taking place, and GPS is frequently jammed in the region.
High-power pseudolites are deployed to allow the army to navigate despite the jamming, using the same standard-issue GPS receivers that soldiers are familiar with.
The first problem is, having placed your pseudolites in position, how do you know where they are?
You might choose to place your pseudolites at locations that have previously been surveyed, so you know where they are in advance. But this isn’t likely, particularly if you’ve just moved your troops into an unfamiliar area. You might also want to move the pseudolites regularly, as the army moves to new ground. So the pseudolites need to determine their own position, and the easiest way for at pseudolite to determine its own position is with GPS, of course.
Isn’t this a bit incestuous? If we’re using pseudolites because GPS is jammed, how does the pseudolite get its position? This is why military pseudolites will typically be fitted with some form of anti-jam technology, such as a controlled radiation pattern antenna. This allows the pseudolite to receive GPS satellite signals in the presence of jamming, determine its own position, and transmit that as part of its own navigation message.
So, now that we can get pseudolite locations, the next consideration is: Where should pseudolites be placed?
A-DOP-ting a Good Layout
If you know about GNSS, you’ll be familiar with the concept of dilution of precision (DOP). This is essentially a measure of how accurate your position estimate is likely to be, due to the geometry of the satellites: a good wide spread of satellite positions gives us better accuracy.
Figure 1. Poor satellite geometry, resulting in high DOP. (Image: Michael Jones)Figure 2. Good satellite geometry, resulting in low DOP. (Image: Michael Jones)
The DOP can be easily calculated by forming a covariance matrix of the geometry, expressed in an appropriate coordinate frame. If (xn, yn, zn) denotes the position of the nth pseudolite, and (x, y, z) the position of the receiver, we can express the unit vectors from the receiver location to the pseudolite location:
We then form a matrix of these unit vectors:
Finally, we form the covariance matrix from which we can extract the DOP values:
From the elements of this matrix we can determine the various DOP metrics. Let’s concentrate on horizontal DOP (HDOP), given by:
When positioning using GPS satellites, we are blessed with a Walker constellation that generally gives us a nice spread of satellite locations (unless we’re in an urban canyon). On the battlefield, using pseudolites, we do not have the same luxury.
Let’s consider a scenario: a conflict in Helmand province, Afghanistan. An operating base is established at Camp Shorabak, where a pseudolite is operating, and three further pseudolites are deployed in the field. This is shown in figure Figure 3.
Figure 3. Scenario with four pseudolites. (Image: Michael Jones)
Taking a look at Figure 4, we can see what this means for HDOP. The regions shaded green represent locations where our HDOP is less than 2.5, and the red areas represent an HDOP greater than 50.
Soldier #1 is surrounded by the four pseudolites, which is a pretty nice arrangement: We get an HDOP of around 2.4. But if we now consider soldier #2, located a bit further out, we get a very different picture.
Here we have an HDOP of 64, which is fairly terrible. It’s not really that surprising looking at the geometry — to soldier #2 the pseudolites all appear in a similar direction. Soldier #2 cannot expect to achieve good positional accuracy in this arrangement.
Figure 4. HDOP for the Afghanistan scenario. (Image: Michael Jones)
So getting a good geometric spread of ground-based pseudolite locations could be a bit of a challenge, especially if the operating area is constantly moving and changing. The next thing to think about is getting enough height.
Getting the Height Right
When we perform positioning using GPS, we typically track several satellites, which have a range of elevations. Many GPS receivers will choose to ignore the satellites at low elevations, such as those within 5 degrees of horizontal, because those satellites are generally the least reliable. They may be partially obscured, and subject to more noise and fading.
Ground-based pseudolites all have very low elevations by definition. Unless the terrain is perfectly flat and smooth, pseudolites quickly become obscured. Even with flat ground, pseudolite signals will disappear behind the horizon after a few kilometers.
Let’s go back to our Afghanistan scenario again. This time, instead of looking at DOP, let’s look at the geographical coverage of our four pseudolites. Here we’ll assume that our user, the soldier, is 2 meters (m) high, and the pseudolite antennas are mounted at a height of 20m above the ground. That’s pretty high — the army will need to erect some masts.
Figure 5 shows what we get. The green areas are locations where our soldier can see all four pseudolites; yellow three, orange two, and red one. At all other locations, no pseudolite signals can be seen at all. You can quickly see that the range isn’t great — terrain, even small undulations in the ground, is a line-of-sight killer. Add some buildings and trees and the situation gets worse. Reduce the height of our pseudolites below 20m, and the situation gets worse. Soldier #1 can receive three pseudolite signals, but soldier #2 has no hope in this case.
Figure 5. Pseudolite visibility at 20m antenna height. (Image: Michael Jones)
Let’s raise the height of the antennas to a fairly crazy 100m above ground (Figure 6). As expected, we get much better coverage, but soldier #2 still has a problem. To get good signal coverage over any sizable area, you really do need to get those antennas as high as possible.
Figure 6. Pseudolite visibility at 100-m antenna height. (Image: Michael Jones)
Augmenting GPS
Often, we don’t want to rely on pseudolite signals alone. If GPS is available, we clearly want to make use of it, and so we want to use a mixture of both GPS satellites and pseudolites. Consider working in a region of sporadic GPS reception, such as an urban environment or forest. We can usually receive a couple of good GPS satellites, but we also need a couple of pseudolites to help us get a complete navigation solution.
Coming back to one of our original objectives, which is to avoid redesigning the GPS receiver hardware, we need to make sure that our receivers can receive and process both GPS satellite signals and pseudolite signals simultaneously. To achieve this, we can decide to make our pseudolites transmit GPS-standard signals, and make use of unassigned spreading codes to essentially create new satellites in the constellation.
But we quickly run into a problem. GPS satellites are always a distance of around 20,000 kilometers away, and the received signal strength is also fairly constant: around –158.5 dBW. This is a very small signal, as we all know, sitting well below the noise floor. When we suddenly bring high-power pseudolites into the mix, we have quite a nasty problem to deal with.
Near, Far, Wherever You Are
Let’s say, for argument’s sake, we have a pseudolite transmitting with a power of 1 watt. Conducting a basic link budget analysis gives us the plot below and suggests that, at a distance of 10 km from the pseudolite, we can expect to receive the signal at around –112 dBW. This is way above our GPS satellite signal level, but might be manageable by a receiver. Now consider a receiver at a distance of 100 m from the transmitter: we receive a power of –72 dBW, which is huge.
In our quest to augment GPS and make it more robust, we have in fact created a GPS jammer, and achieved exactly the opposite. As with any radio communications link, the received power is extremely sensitive to the distance (varying with the square of distance). In pseudolite terminology, this is known as the near/far problem.
Figure 7. Theoretical received power for a 1-W pseudolite, under ideal conditions. (Figure: Michael Jones)
The near/far problem has given engineers headaches for quite some time. Essentially, the problem comes down to: How can our GPS receivers handle such a massive dynamic range of expected signals? Especially if our objective is to avoid modifying the GPS receiver hardware, if at all possible.
How can a receiver handle the high power of a close-up pseudolite, which is to all intents a jammer, whilst simultaneously receiving the tiny GPS satellite signals from space? Various solutions have been proposed over the years, but one of the current favorite techniques involves pulsing the pseudolite signal.
The idea, then, is to only turn on the pseudolite periodically, essentially applying a duty cycle to the transmission. If a pseudolite isn’t transmitting, it can’t interfere with the normal GPS signals. There are a couple of things to take into consideration here:
What should the pulse duty cycle be, to enable both satellites and pseudolites to be tracked?
How does the GPS receiver behave when presented with alternating large and small signals?
A mathematical analysis of duty cycle effects is beyond the scope of this column, but consider Figure 8 for a qualitative view. Here we have two pseudolites operating alongside GPS satellites. The duty cycle chosen here is for the pseudolite to be operational for 10% of a 1 millisecond integration period. This gives enough time, when the pseudolite is not transmitting, for the low-level GPS satellites to be tracked.
The second pseudolite, which is closer and therefore higher power, transmits for a further 10% slot after the first pseudolite. You can see that each additional pseudolite eats into the time available for tracking GPS satellites, and degrades the signal-to-noise ratio. There are some tricks you can play, such as transmitting multiple pseudolites at the same time if you know they will be similar power levels, but it can get complicated.
Figure 8. Received power versus time, for a pulsed pseudolite scenario. (Figure: Michael Jones)
The Importance of Gain Control
How the receiver copes with the large differences in received power level depends largely on the design of the RF front-end in the receiver. Most GPS receivers will have a certain amount of automatic gain control (AGC), which is a feedback loop designed to keep power levels constant. Many GPS receivers, though, simply aren’t designed with enough AGC to handle pseudolite-level signals (think GPS jammers again).
Military receivers, though, tend to have greater RF handling capabilities, and more bits in the ADC, so are better-suited to the situation. It is then a question of making sure the AGC loop responds in an appropriate time, compared to the duty cycle of pulses.
Figure 9 illustrates a slow AGC response, which is not particularly suitable. Compare this with Figure 10, where we have a fast AGC response, quickly adapting to the switches in power level. A receiver with this characteristic will be better able to track both pseudolite and satellite signals.
Figure 9. Pulsed pseudolites with slow AGC response (in red). (Figure: Michael Jones)Figure 10. Pulsed pseudolites with fast AGC response (in red). (Figure: Michael Jones)
Airborne Pseudolites
If you’ve read this far, you’ll now know that the main problems with ground-based pseudolites are lack of good geometry, signal blocking by terrain, and the horrendous near/far issues. Wouldn’t it be nice if we could raise the pseudolites to a really high altitude, and all these problems would go away? Wait, that’s the GPS satellite constellation!
Ok, let’s not put them that far up. But how about carrying pseudolites on high-altitude airborne platforms instead? Great idea, and that’s why this is a current thread of defense activity in various countries. High-altitude long-endurance (HALE) or HAPS (high-altitude pseudo-satellite; the clue is in the name) unmanned platforms can be used to carry pseudolites at high altitude.
This solution can provide excellent coverage, the pseudolites can be repositioned as necessary, and the near/far problem is also far less pronounced.
I leave you once again with our Afghanistan scenario, from the point of view of a high-altitude airship at 18,000 meters.
Figure 11. High-altitude platform, potentially carrying a pseudolite at 18,000 m. (Image: Michael Jones)
A team from Draper and the Massachusetts Institute of Technology (MIT) has developed advanced vision-aided navigation techniques for UAVs that do not rely on external infrastructure, such as GPS, detailed maps of the environment or motion capture systems.
When a firefighter, first responder or soldier operates a small, lightweight flight vehicle inside a building, in urban canyons, underground or under the forest canopy, the GPS-denied environment presents unique navigation challenges.
In many cases, loss of GPS signals can cause these vehicles to become inoperable and, in the worst case, unstable, potentially putting operators, bystanders and property in danger.
Attempts have been made to close this information gap and give UAVs alternative ways to navigate their environments without GPS. But those attempts have resulted in further information gaps, especially on UAVs whose speeds can outpace the capabilities of their onboard technologies.
For instance, scanning lidar routinely fails to achieve its location-matching with accuracy when the UAV is flying through environments that lack buildings, trees and other orienting structures.
Finding a Solution
DARPA awarded contracts to Draper and two other industry teams to create UAVs that autonomously sense and maneuver through unknown environments without external communications or GPS under the Fast Lightweight Autonomy (FLA) program. (Photo: Draper)
Working together under a contract with the Defense Advanced Research Projects Agency (DARPA), Draper and MIT created a UAV that can autonomously sense and maneuver through unknown environments without external communications or GPS under the Fast Lightweight Autonomy (FLA) program.
The team developed and implemented unique sensor and algorithm configurations, and has conducted time-trials and performance evaluations in indoor and outdoor venues.
“The biggest challenge with unmanned aerial vehicles is balancing power, flight time and capability due to the weight of the technology required to power the UAVs,” said Robert Truax, senior member of technical staff at Draper. “What makes the Draper and MIT team’s approach so valuable is finding the sweet spot of a small size, weight and power for an air vehicle with limited onboard computing power to perform a complex mission completely autonomously.”
Draper and MIT’s sensor- and camera-loaded UAV was tested in a number of environments ranging between cluttered warehouses and mixed open and tree filled outdoor environments with speeds up to 10 m/s in cluttered areas and 20 m/s in open areas.
The UAV’s missions were composed of many challenging elements, including tree dodging followed by building entry and exit and long traverses to find a building entry point, all while maintaining precise position estimates.
“A faster, more agile and autonomous UAV means that you’re able to quickly navigate a labyrinth of rooms, stairways and corridors or other obstacle-filled environments without a remote pilot,” said Ted Steiner, senior member of Draper’s technical staff. “Our sensing and algorithm configurations and unique monocular camera with IMU-centric navigation gives the vehicle agile maneuvering and improved reliability and safety — the capabilities most in demand by first responders, commercial users, military personnel and anyone designing and building UAVs.”
Draper’s contribution to the DARPA FLA program — documented in a recent research paper for the 2017 IEE Aerospace Conference — was a novel approach to state estimation (the vehicle’s position, orientation and velocity) called SAMWISE — Smoothing And Mapping With Inertial State Estimation.
SAMWISE is a fused vision and inertial navigation system that combines the advantages of both sensing approaches and accumulates error more slowly over time than either technique on its own, producing a full position, attitude and velocity state estimate throughout the vehicle trajectory.
The result is a navigation solution that enables a UAV to retain all six degrees of freedom and allows it to fly autonomously without the use of GPS or any communication with vehicle speeds of up to 45 miles per hour.
The team’s focus on the FLA program has been on UAVs, but advances made through the program could potentially be applied to ground, marine and underwater systems, which could be especially useful in GPS-degraded or denied environments.
Northrop Grumman Corporation has been awarded a contract from the U.S. Air Force for technology maturation and risk reduction in support of next-generation navigation systems.
Under the $49 million contract from the Air Force Life Cycle Management Center, Northrop Grumman will provide the preliminary hardware and software architecture design for the Embedded GPS/Inertial Navigation System (INS)-Modernization, or EGI-M, technology. The modernized system is expected to be available for platform integration starting in 2019.
Northrop Grumman’s EGI-M will be based upon modular, open systems architecture to support the rapid insertion of new capabilities and adaptability based on unique platform requirements. Additionally, EGI-M will incorporate M-code-capable GPS receivers, which will help to ensure the secure transmission of accurate military signals.
“We are dedicated to ensuring mission success and the safety of warfighters by providing an EGI-M solution that offers robust, accurate and reliable positioning, navigation and timing [PNT] information, even in GPS-denied conditions,” said Dean Ebert, vice president, navigation and positioning systems business unit, Northrop Grumman Mission Systems.
EGI-M technology is designed for compatibility with current systems on legacy aircraft, allowing ease of integration and rapid adoption of new capabilities.
EGI-M will also comply with the Federal Aviation Administration’s NextGen air traffic control requirements that aircraft flying at higher altitudes be equipped with Automatic Dependence Surveillance-Broadcast (ADS‑B) Out by January 2020.
ADS-B Out transmits information about an aircraft’s altitude, speed and location to ground stations and to other equipped aircraft in the vicinity.
Aerial refueling requires highly precise relative navigation. (ILLUSTRATION: Charles Park)
Future UAVs will require relative navigation capability to fulfill a broad range of assisted manned and unmanned missions. A new approach, demonstrated in application to aerial refueling, provides access to accurate relative time-space positioning information (R-TSPI) between platforms.
By Shahram Moafipoor, Jeffrey A. Fayman, Lydia Bock and David Honcik
The advent of unmanned aerial vehicles (UAVs) highlights the importance of precise relative navigation information for safe use of UAVs in many application areas. Future military and civilian UAV applications will increasingly require capabilities such as
sense and avoid
swarming
vehicle-to-vehicle (V2V) platooning
docking
autonomous landing and
autonomous aerial-refueling,
all of which require access to accurate relative time-space positioning information (R-TSPI) between platforms.
In this article, we present the foundation for a generic approach to relative navigation capable of meeting the full range of relative assisted manned and unmanned operations. We present a relative extended Kalman filter (R-EKF) that integrates line-of-sight relative observations from GPS as well as non GPS-based onboard sensors measuring relative bearing and/or relative distance. Multi-sensor fusion provides enhanced system integrity and robustness to partial or total lack of GPS-satellite navigation (GPS-denied). The relative navigation system described here uses these technologies, providing up to 100 Hz R-TSPI with an accuracy of up to ±1.0 m (a function of relative distance), ±0.1 m/s velocity and ±0.5º attitude. The system can be applied to a variety of relative navigation applications; here we focus on its use in aerial refueling.
132d Air Refueling Squadron. A Boeing KC-135R Stratotanker refuels an F-22A Raptor. (Photo: USAF)
AERIAL REFUEL CHALLENGES
Automated aerial refueling for manned and unmanned platforms is a challenging problem requiring accurate R-TSPI. The Geo-RelNAV system provides a key measurement for aerial refueling: the vector closure rate, the differential velocity between the tanker and refueling aircraft. The closure rate is monitored in real time onboard the tanker. The measurement can be used to:
maintain safety-of-flight by ensuring refueling aircraft do not exceed a certain velocity,
determine whether or not a refueling aircraft is approaching the tanker with sufficient velocity, and
provide data to drogue-control engineers to improve control law design.
As a GPS/INS system, Geo-RelNAV can produce a relative navigation solution at a faster sample rate than GPS alone. Solutions are available via serial and/or Ethernet (both TCP and UDP) providing input to external systems as well as the tools for analysis engineers to monitor the data in real time using standard monitoring and recording tools. The system provides R-TSPI in different frames, including the body frame of the platforms, local navigation frame (wander-azimuth) and Earth-fixed frame, as well as transferring the solution to arbitrary points of interest on the aircraft such as the refueling aircraft’s refueling probe.
RELATIVE INERTIAL NAVIGATION
We use the terms primary and secondary in this article to identify the platforms for which R-TSPI data is being generated. R-TSPI is always provided for the primary with respect to the secondary. Referring to Figure 1, the tanker is considered the primary and the refueling aircraft, the secondary (or vice versa, depending on the location of the control segment). Data is always transmitted through the data link from the secondary to the primary. Figure 1 summarizes the geometric relations, where the primary body frame is labeled p-frame and the secondary body frame is labeled s-frame. The body frame fixed to the primary (P) is shown by (xPp,yPp,zPp), and body frame fixed to the secondary (S) is shown by (xSs,ySs,zSs).
Fgure 1. Primary/secondary geometry and corresponding body frames fixed to the vehicle body.
The relative navigation equation is set up for the state of the secondary with respect to the state of the primary in the center of the body frame of the primary, p-frame:
(1)
where xPp is the primary position vector established in the p-frame, and xSp is the secondary position vector defined in the p-frame. Note that these vectors can also be obtained from the primary/secondary strapdown inertial navigation solutions after transferring to the reference (eccentric) point. Equation (1) represents the fundamental equation, from which the relative navigation equations are derived. Once the relative kinematic model of the position and velocity are established, the next step is to develop the relative attitude kinematic model. The relative attitude, denoted by the quaternion qpS, is used to map vectors in the s-frame to vectors in the p-frame:
(2)
where qp and qs are the quaternion attitudes of the primary and secondary with respect to the i-frame, qp* is the conjugate of qp, and is the quaternion multiplication operator.
Hardware for the relative navigation system.
RELATIVE EXTENDED KALMAN FILTER
To establish the R-EKF, we must derive the relative inertial error equations. The R-EKF has 21 basic states including nine for relative position, δΔxpPS , relative velocity, δΔvpPS , and relative attitude, Ψpps, and 12 to model the primary’s gyro and accelerometer bias (non-constant) and non-linear scale factors. Since the relative distance between the secondary and primary is small compared to the radius of the Earth, the gravity terms are negligible. Thus, in the linearized terms, the relative gravitational terms are ignored. It should be noted that the secondary states are assumed to be known for retrieving the absolute primary TSPI information. Since Equations (1) and (2) can only provide the general dynamic model for a nonlinear state model, all these equations must be linearized using Taylor series about nominal values (neglecting the higher-order terms). After perturbation state equations are established, they should be discretized from a continuous-time to a discrete-time sequence. The final solution to the state equation can be expressed as:
(3)
with:
(4)
FPpS is the Jacobian matrix, and the perturbation elements are all related to the primary:
(5)
RELATIVE GPS MEASUREMENT MODEL
When GPS is available, high-accuracy relative positions are derived from the use of carrier-phase differential GPS, a technique commonly used in static positioning applications such as surveying. However, unlike those applications, in this case the reference receiver is not stationary; it is located on a moving platform (secondary) creating a moving baseline. The relative GPS measurement in our system is provided by epoch-by-epoch (EBE) differential carrier-phase processing, which measures accurate relative position between the secondary and primary systems. The EBE relative position has a typical accuracy better than 3 cm (1-sigma horizontal) and 6 cm (1-sigma vertical). Testing of the relative measurement was conducted using two ground vehicles configured with 10-Hz dual-frequency GPS sensors. The mean difference was less than 5 cm. As a conclusion, the GPS relative mode was shown to provide accurate relative positions between the platforms. Once the relative position is measured, the R-EKF observation model can be established as:
(6)
The (ΔxpPS )GPS term is the relative position measured by using GPS data, and the term (ΔxpPS)INS is the relative position, which is predicted by using the last updated inertial solutions. Note that in order to use this relative observation, the lever-arm vector between the GPS and IMU of both the primary and the secondary must be accurately measured and applied (see Figure 2).
Figure 2. Relative observation model.
Here, the observation model is represented on the condition that the vector of observations has yielded certain values based on an assumed linear relationship to:
(7)
Equations (3) and (7) are the fundamental equations of the R-EKF.
SYSTEM ARCHITECTURE
Relative navigation is computed and provided at one of the units, designated the primary unit. This requires data from the secondary unit to be transferred to the primary unit over a data link. The primary unit uses this transmitted data to calculate its position, velocity and attitude relative to the secondary unit. Figure 3 summarizes the architecture and data-flow. Mathematically, the data from the secondary unit used in the relative calculations are assumed to be errorless.
Figure 3. Geo-RelNAV architecture.
OPERATIONAL ENVIRONMENT
We distinguish the following three relative navigation stages, illustrated in Figure 4, where each phase utilizes a unique processing mode.
Fgure 4. Relative navigation phases.
In the Approach phase, the data link between primary and secondary units is not closed. An autonomous navigation solution for both the primary and secondary units is computed on each platform independently. This information will be later used when the system transitions to the Engagement phase to initialize the R-EKF.
In the Engagement phase, the data link between primary and secondary units is closed, and the R-TSPI solution is computed between the platforms. Sensor observations are transmitted across the data link from the secondary unit to the primary unit. The primary unit implements the R‑EKF to produce the R-TSPI solution.
In the Departure phase, the activity requiring R-TSPI (that is, refueling) is complete, and the secondary platform pulls away from the primary platform. In this phase, we transition from the R-EKF back to the autonomous independent navigation system.
The Approach phase is as important as the Engagement phase in attenuating the initialization error in terms of position, velocity and attitude. To initialize the R-EKF, the autonomous TSPI solution from the secondary unit is transferred to the primary unit, where the initial relative position, velocity and attitude are estimated.
There are three conditions under which this initialization must occur:
upon transition from the Approach phase to the Engagement phase,
when in the Engagement phase and the system experiences a data link dropout, and
when there is a large latency in the data link. If the data link latency is too large, the data arriving at the primary can no longer be used.
VALIDATION TESTING
Several system tests were conducted including static bench testing, dynamic ground vehicle testing and flight testing. We discuss the results for the static and bench testing here.
For static bench testing, the system was set up on two points with a measured fixed displacement. The sensor configuration included dual-frequency GPS receivers, ring laser gyro-based IMUs, and a data link operating in the 900-MHz frequency band.
The results show that relative position held to the fixed offset with a standard deviation of less than 0.1 m in North, East and Up. Relative velocity held to zero with a standard deviation less than 0.01 m/s, and relative attitude was also maintained with the accuracy up to the gyro bias stability of the ring laser gyro IMU (1°/hr for a stationary platform).
The overall performance of the system in static bench test confirms the stability of the hardware and software of the system, when it is not exposed to any dynamics, and the sensors are in close proximity (no data link latency or data dropouts).
Dynamic Drive Test. In a more realistic test to simulate the operational phases described in Figure 4, the drive test followed a scripted path. As shown in Figure 5, the two platforms left Geodetics’ facility and drove separately (simulated Approach) until they met each other at the Fiesta Island test site, where the data link was closed for the Engagement phase. The primary and secondary navigation systems operated independently during the Approach phase.
Figure 5. Drive test ground trajectory of the primary (blue) and secondary (red).
Once the data link was closed at the test site, the R-EKF engaged, using initialization information transmitted from the secondary to the primary platform. To provide a “truth source” for evaluating the performance of the relative navigation solution, both autonomous GPS/IMU systems were fed data from an external reference receiver. Table 1 shows the statistical data analysis in the form of mean and standard deviation for the collected data.
Average RMS of fit in the relative position, velocity and attitude of approximately 1.0 m, 0.1 m/s and 0.3º, respectively, were computed for the entire relative navigation period. In this dynamic test, we encountered frequent data link dropouts, data link latency, as well as GPS outages, causing discontinuity in the R-EKF measurement updates until GPS was reacquired. During these periods, the R-EKF prediction model, updated with the last calibrated IMU data, provided the R-TSPI. This test help confirm that system performance is at the expected levels, even in the presence of real-world data link and GPS problems.
Table 1. Statistical analysis of the R-TSPI solution.
GPS-DENIED OPERATIONS
Over-reliance on GPS has exposed vulnerabilities associated with this technology. For example, GPS is easily jammed and spoofed. While spoofing can be addressed with Selective Availability Anti-Spoofing (SAASM) technology, and advances such as M-code will mitigate other vulnerabilities, systems of the future must be robust to partial or total lack of GPS. Advanced sensor-fusion technologies are necessary to provide capabilities in conjunction with, and in the absence of, GPS.
In the context of aerial refueling, sensors such as active and passive vision systems can be used as complimentary observations by the system, providing a GPS-free relative distance observation in situations where GPS is blocked due to airframe masking, jamming, and so on.
Data from both active (lidar) and passive (camera) vision sensors were added to the system, providing significant advantages in the process flow. The use of vision sensors provides the relative distance observation in GPS-denied conditions for continuity in R-EKF updating. In addition, vision-based relative distance allows for the detection of outliers by evaluating the redundancy contribution of the measured GPS-based relative distance, and enables the transfer of the R-TSPI solution from the secondary refueling center to the on-the-fly probe-drogue system, as shown in Figure 6.
Figure 6. Vision sensor aiding increasing the integrity
For the active vision system, we leveraged a fully integrated lidar mapping payload as shown in Figure 7 (left). For the passive sensor, we utilize a stereo camera. Figure 7 (right) shows the test area and the simulated drogue. Imagery observations from the passive camera and the lidar system were processed with independent algorithms appropriate to each data type and the relative distance between each of the two sensors, and the simulated drogue was measured with an RMS error of less than 10 cm.
Figure 7. Geo-MMS (left) and its application (right) for measuring relative distance.
INTEGRITY
While outside the scope of this article, in addition to supplying a GPS-free relative distance observation, the use of vision sensors was applied to the task of increasing system integrity. This includes, in general, the capability to indicate when the system should not be used for the intended operation. We focused on two aspects: outlier detection (inner reliability), and the effect of undetected outliers (outer reliability).
To properly address the reliability and integrity requirements, a quality testing mechanism was designed to assess the estimated/predicted relative distance observations before passing them in to the R-EKF module.
CONCLUSIONS
An autonomous relative navigation, in its application for the aerial refueling problem, places special attention on system architecture so that it can handle most possible real-world scenarios, including frequent data link dropouts, data link latency and GPS outages. The core of the system is a relative extended Kalman filter, which uses GPS and IMU measurements of the primary and secondary platforms to estimate the relative inertial navigation states. The system is able to provide relative TSPI at the IMU sample rate with an accuracy of ±1.0 m position, 0.1 m/s velocity and ±0.5º attitude.
An added benefit of the system architecture is the ability to add observation models that do not rely on GPS. Thus, redundancy can be introduced using sensors such as vision systems.
SHAHRAM MOAFIPOOR is a senior navigation scientist at Geodetics, focusing on new sensor technologies, sensor-fusion architectures, application software, embedded firmware and sensor interoperability in GPS and GPS-denied environments. He holds a Ph.D. in geodetic science from The Ohio State University.
JEFFREY A. FAYMAN serves as Geodetics’ CTO. He holds a Ph.D. in computer science from the Technion Israel Institute of Technology and has published more than 40 papers in robotics, computer vision, computer graphics and navigation systems.
LYDIA BOCK serves as Geodetics’ president and CEO. She has more than 35 years of industry experience spanning a variety of high-tech industries including electronics, semiconductors and telecommunications. She has a Ph.D. from the Massachusetts Institute of Technology.
DAVID HONCIK, Geodetics’ director of engineering, has more than 30 years of experience in software/hardware integration and structured software design for real-time embedded systems, Windows programs, graphics, telecommunications, aerospace, flight simulation and airborne instrumentation.
The integrated lidar mapping payload referenced is Geodetics’ Geo-MMS system.
The GPS modernization funding picture cannot be called bright, yet neither can it be characterized as dim. While big money for big projects appears hard to come by, the U.S. government and military offer many smaller allocations to help fill the chinks in GPS armor. Such initiatives concern jamming, PNT solutions in GPS-denied environments and other conundrums. A run of Small Business Innovation Research (SBIR) requests for proposals have appeared recently.
A caveat: the U.S. government has some history of soliciting innovation from small firms, then awarding continuation of the work to big, established government contractors, under the rationale that these companies have capacity to carry out large-scale manufacturing.
The current batch of RFPs specify Phase I contracts that will, by statute, all go to small businesses, as will Phase II. The problem then — for these contract winners —is that follow-on work typically goes to large primes.
Jamming. The objective of a tender issued in December of last year, with a closing date of Feb. 17, is to “develop a ground-based GNSS Jammer Location capability utilizing a single GNSS receiver capable of estimating the position of a GNSS jammer within 100 meters, and estimating jammer position within 10 meters when networked with other sensors.”
The Department of Defense (DoD) continues: “Although many effective techniques exist, they primarily rely on airborne equipment, using either high demand, low density assets or dedicated aircraft such as unmanned aerial vehicles (UAVs). To enhance the future Navwar capabilities of DoD, a ground-based capability that can operate in urban canyons or mountainous terrain will provide a significant improvement to overarching Navwar capability. In some cases, jammers may be deployed on mobile ground vehicles in an urban environment, making them difficult to detect and track.”
DoD wants you to exploit opportunities offered by multipath and controlled radiation pattern antennas (CRPAs) to detect and locate 100-watt mobile jammers.
“Four alternatives should be evaluated: 1) a single GNSS receiver without a CRPA, 2) a single GNSS receiver with a CRPA, 3) two or more networked receivers without a CRPA, and 4) two or more GNSS receivers with a CRPA. For each alternative, assess the location accuracy, cost (both recurring and nonrecurring), and suitability for integrating in a ground vehicle.”
The DoD also offers stimulus funding for a range of other problems seeking a solution. The closing date is Feb. 17 for all of these, so sharpen your pencils and put on your thinking caps.
Contracts and Future Work. Concerning the follow-on work issue, Alison Brown, Co-Chair of the Government Contracting Working Group in the Small Business Administration’s (SBA’s) Regulatory Fairness Board, has written a white paper, “SBIR Regulatory Enforcement Issues,” available here. In it, she reviews the degree to which DoD complies with existing law. Congress has enacted Sec. 5108, mandating that “To the greatest extent practicable, Federal agencies and Federal prime contractors shall issue Phase III awards relating to technology, including sole source awards, to the SBIR and STTR award recipients that developed the technology.”
Brown states that “currently there is no effective recourse for small businesses or avenues for enforcement of the current SBIR Regulations within the DOD and other government agencies.” She recounts in the paper her own experience, as founder and CEO of NAVSYS Corporation.
NAVSYS developed and fielded a precision GPS navigation capability, Talon NAMATH, under a Phase III SBIR contract to Air Force Tactical Exploitation of National Capabilities (TENCAP). The systems was declared “provisionally operational” and used in theater in Operation Iraqi Freedom. Although the Talon NAMATH system was declared a huge success in theater, the follow-on contract for a fully operational system was awarded to Boeing.
Brown is also a longtime member of GPS World’s Editorial Advisory Board.
The final specification for 3GPP Release 13 will include messaging support for Terrestrial Beacon System (TBS) location technologies, including the Metropolitan Beacon System (MBS).
NextNav is deploying the MBS positioning technology across the U.S. to allow mobile phones and other devices to reliably determine their location in indoor and urban environments where GPS signals can’t be received.
NextNav has adopted MBS for its nationwide deployment, which it calls an innovative “terrestrial constellation” bringing GNSS-like positioning performance to indoor and urban environments where satellite-based positioning is either unavailable or significantly degraded. By standardizing the core network information flow in 3GPP, support for MBS will become available across any Release 13-compliant LTE network platforms globally, similar to previously standardized GNSS systems such as GPS, GLONASS, BeiDou and Galileo satellite signals.
NextNav’s system is complementary to GPS and delivers high precision latitude, longitude and “floor level” altitude in GPS-challenged areas such as indoors and urban locations across an entire metropolitan area. Unlike cellular positioning in LTE, MBS does not consume expensive wireless spectrum to do so.
“We are gratified, after an especially intensive effort, to see 3GPP add support for Terrestrial Beacon Systems generically and for supporting the NextNav implementation of it — the Metropolitan Beacon System,” said Ganesh Pattabiraman, president of NextNav. “This speaks to the urgent market requirements for ubiquitous, high-quality indoor positioning. MBS availability as an international standard ensures that our location signals can be used in widely deployed LTE (long-term evolution) networks as part of an end-to-end system. It also opens the doors for multi-vendor systems, a critical consideration for our carrier customers and users worldwide.”
The 3rd Generation Partnership Project (3GPP) unites seven telecommunications standard development organizations (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC) and provides their members with a stable environment to produce the reports and specifications that define 3GPP technologies.
At Unmanned Systems Defense, warfighters had the opportunity to learn about new technologies from government contractors and see demos in the exhibition hall. (PRNewsFoto/AUVSI)
ARLINGTON, Va. — Despite shrinking defense budgets, existing and emerging worldwide threats will make robotic and autonomous systems’ development important for decades, said officials at the Unmanned Systems Defense 2015 conference held here Oct. 27-29.
Because America has been at war for more than 14 years, unmanned technology has been developing at a rapid rate, perhaps even faster than emerging autonomous commercial systems. The replacement of even manned aircraft has some in the military establishment wary, but others know it’s only a matter of time before most vehicles, surface ships and aircraft are unmanned.
Navy Secretary Ray Mabus said that the F-35, which has been controversial because of its cost and capabilities, may be the last manned fighter aircraft.
Mabus acknowledged the rise in autonomous vehicles not only in the military, but in the civilian world. “Our grandchildren may never have to drive a car. I can’t wait for driverless cars,” he said.
The Navy is so high on unmanned systems that it recently named retired Marine Brig. Gen. Frank Kelley as deputy assistant secretary of the Navy for unmanned systems.
Like the other services, the Navy is experimenting with aviation systems that are inexpensive and small. It is developing swarming drones that are designed to overwhelm a target. Mabus said one of the cool drones that the Navy is developing is called Kraken, which operates underwater, then explodes past the surface to operate in the air.
A V-Bat UAV from Martin UAV. Applications include aerial mapping, border patrol, shipboard operations and others.
The Air Force also is developing small drones that can be launched and recovered by a larger aircraft after a mission is complete.
While the meeting was filled with government bureaucrats with the requisite PowerPoint slides detailing how long programs will take, they did say that the services are plowing ahead with autonomous technology that many of their civilian counterparts say are decades away.
Convoy Operations
An Army initiative called Leader Follower includes rudimentary autonomous convoy operations capability with GPS and base mapping systems, autonomous steering and braking. Army program managers say the program is in staffing, but should be approved in a few months.
The follow on to Leader Follower is a full-blown Automated Convoy Operations capability that would allow any manned system, including tanks and mobile artillery, to operate autonomously. Automated Convoy Operations are at least two-to-three years behind the Leader Follower program, Army officials said.
Other Army programs include route clearance systems to defeat underground improvised explosive devices and caches and mine rollers.
With all the new autonomous technology, at least one speaker said the first question should be why an unmanned system is needed at all, given its high cost and long lead times for rollout. “Does the technology enable a [service member] to fight better, or does it just get in the way?” said Lt. Col. Hank Lutz, U.S. Marine Corps joint staff.
Plans to Replace Aging Unmanned Systems
Lt. Gen. Michael Williamson, U.S. Army deputy to the assistant secretary of defense for acquisition, said the service is divesting its aging robotics and drone systems, which means future contracts for defense companies. “In 14 years of war, we have rode this equipment pretty hard,” he said. “We believe in modernization, but also looking to buy new systems, which is a new shift in order to gain a competitive advantage over our enemies, who are leveraging unmanned systems.”
Jeff Smith, president and CEO of Riptide Autonomous Solutions, holds an unmanned undersea vehicle that has GPS sensors and antenna.
The big mantra from the military program managers and senior officials is having an “open architecture” that includes a control segment that works with both manned and unmanned systems. Williamson also echoed the need for standardization, but went further by saying the services should have a list of standards and one place, a facility, to ensure components actually work together.
While the “we want an open architecture” theme was in virtually every speaker’s presentation, one said that there needs to be a balance between the time a product is ready and its interoperability. “The Taliban’s [Program Objective Memorandum] cycle is a lot shorter. Don’t tell me that [your product] is plug and play,” said John Coglianese, U.S. Special Operations Command director, unmanned aerial systems.
DoD Reaches Out to Smaller Businesses, Silicon Valley
Realizing a need to assess new technologies and partner with innovative companies, the Defense Department recently established the Defense Innovation Unit, which is based in the San Francisco Bay area. The office is small with only a few personnel, said George Duchak, who was recently named director.
Duchak acknowledged that some companies suffer from government fatigue in that they see the same presentations over and over. By being out in the Silicon Valley, Duchak’s personnel can be more receptive and listen, rather than talk at companies. His office is made up of people who seek out new technology and vendors, serve as a conduit to local labs and assess companies who want work with the government, among other activities.
“We are kind of in a honeymoon period [with private companies]. It has been interesting finding companies where their patriotism aligns with whether or not they are going to make money,” Duchak said. “Google has been pretty receptive, not so much with Apple.”
Another group, the National Advanced Mobility Consortium, looks to match technology to defense needs for smaller companies looking to do business with the government. “We are trying to show how to engage nontraditional companies,” said Bill Thomasmeyer, National Advanced Mobility Consortium consultant. Thomasmeyer said it’s tough for a small company or individual entrepreneur to go through the complex government procurement cycle. “They are used to Silicon Valley, which has a 90-day cycle. The Federal Acquisition Regulation is 4,000 pages,” he said.
Currently, NAMC has 274 members, a third of which are not defense companies, Thomasmeyer said.
Future of GPS and Location Technology for Unmanned Systems
Virtually all unmanned systems, from drones to autonomous vehicles, use GPS location technology and advanced mapping. As systems evolve, and enemy threats become more sophisticated, new requirements are emerging.
“All of our systems use GPS, but we need to operate in a GPS-denied environment,” said Capt. Aaron Peters, U.S. Navy program manager for expeditionary missions.
Other program managers said what’s also needed is GPS units that feature 3-D navigation for autonomous systems.
In addition to basic positioning and navigation of drones and autonomous vehicles, the Air Force is using location technology to geo-locate damage from shell holes at airfields they use in war zones.
Rockwell Collins has been selected by the Defense Advanced Research Projects Agency (DARPA) to develop technologies that could serve as a backup to GPS. The research, being conducted as part of DARPA’s Spatial, Temporal and Orientation Information in Contested Environments (STOIC) program, aims to reduce warfighter dependence on GPS for modern military operations.
Under the terms of the agreement, Rockwell Collins will develop innovative architectures and techniques to enable communication systems that will support time transfer and positioning between moving platforms independent of GPS, with no impact on primary communications functionality.
“STOIC technology could augment GPS, or it may act as a substitute for GPS in contested environments where GPS is degraded or denied,” said John Borghese, vice president of the Rockwell Collins Advanced Technology Center. “The time-transfer and ranging capabilities we are developing seek to enable distributed platforms to cooperatively locate targets, employ jamming in a surgical fashion, and serve as a backup to GPS for relative navigation.”
Borghese added that the goal of the STOIC program is to develop positioning, navigation, and timing (PNT) systems that provide GPS-independent PNT, achieving timing that far surpasses GPS levels of performance. The program is comprised of three primary elements that, when integrated, have the potential to provide global PNT independent of GPS, including long-range robust reference signals, ultra-stable tactical clocks, and multifunctional systems that provide PNT information between cooperative users in contested environments.
For this third technical element, Rockwell Collins is tasked with developing multifunction communication system solutions that yield DARPA STOIC objective picosecond-accurate time transfer and enable GPS-levels of relative positioning accuracy in contested environments.
“Future applications of STOIC technology could include a variety of precision relative navigation operations, such as autonomous aerial refueling and cooperative navigation and collision avoidance within unmanned aerial vehicle swarms,” said Borghese. “It also could support precise time transfer for networking operations in contested environments.”
