When a team of firefighters, first responders, or soldiers operates inside a building, in urban canyons, underground, in foliage, or under the forest canopy, the GPS-denied environment presents unique navigation challenges. An enhanced personal inertial navigation system (ePINS), based on a strapdown navigation solution using a mid-grade IMU and wavelet-based motion-classification algorithms, can track positions with errors of less than 2 percent of distance traveled in both indoor and outdoor environments.

By Yunqian Ma, Wayne Soehren, Wes Hawkinson, and Justin Syrstad

Numerous pedestrian navigation applications are currently available or proposed for development. Some of them include localization for coordinating firefighters, first responders, or soldiers. In these applications, the safety and efficiency of the entire team relies directly on the location and orientation of each team member. Operations in high signal interference areas such as cities, rugged terrain, forest, or indoor spaces deliver intermittent or no GPS signal. An alternative to GPS-based location is required.

In this article, we introduce an enhanced personal inertial navigation system (ePINS) solution specifically designed for environments where GPS is unavailable. ePINS combines an array of state-of-the-art sensors and fusion algorithms into a personal navigation system that provides accurate location information for pedestrian applications.

The ePINS concept.

The ePINS solution has the following benefits:

• Accurate positioning in GPS-denied environments;
• Small, lightweight unit can be easily carried by first responders, rescue workers, or soldiers;
• Ruggedized packaging to withstand difficult first responder and military environments.

Features of  the ePINS unit include:

• State-of-the-art micro-electromechanical systems (MEMS) gyros and accelerometers, barometric altitude sensor, and advanced navigation software;
• Advanced motion classification algorithms that accurately identify and measure user activity;
• Immunity to magnetic disturbances.

Related Work

In the field of personal navigation, it is common to find systems that rely on sensors that need infrastructure (for example, Wi-Fi positioning) or sensors that actively emit electro-magnetic radiation (such as Doppler radar). These requirements are major drawbacks for communities such as dismounted soldiers in hostile environments.

Other approaches exploit the so-called Zero-velocity update (ZUPT) mechanism, which resets the inertial measurement unit (IMU) velocity errors during the stationary phase of motion. However, implementation of such schemes relies on sensors embedded in footwear, which is not readily accepted in many user communities.

To address these drawbacks, Honeywell has been developing advanced aiding techniques for personal navigation that do not rely on infrastructure and compute a self-contained, relative-navigation solution based only on passive sensors. One technique that Honeywell has developed uses displacement estimation from human-motion models. This technology has been implemented in the ePINS prototype and shows promising performance.

The human-motion model uses IMU measurements as inputs and was developed to infer distance traveled. It generates a displacement estimate that is used as a measurement in the navigation filtering process. The first version of this model was matured under the DARPA individual Precision Inertial Navigation System (iPINS) program. The iPINS system used an IMU, GPS, barometer, and motion classification to estimate a person’s position in both indoor and outdoor environments. In this system, IMU signal characteristics (e.g., peaks and valleys in the accelerations induced by walking) were exploited to differentiate between walking and running. Honeywell recently expanded the human-motion model to identify more specific motion types using a new wavelet motion classification method.

System Description

Figure 1 displays the hardware architecture of the ePINS, a small battery-powered, highly integrated electronic system. The ePINS processing platform is an ARM11-based, i.MX31 system-on-module, paired with support electronics. In addition to the processing platform, the ePINS assembly includes a MEMS IMU, a barometric pressure sensor, a digital magnetometer, and a GPS receiver.

Figure 1. ePINS hardware architecture.

The MEMS IMU provides inertial measurements for strapdown navigation. The IMU’s small package size, light weight, low power consumption, and impressive performance make it attractive for use in the ePINS system. The device is less than 5 cubic inches and weighs less than 0.35 pounds. It consumes about 3 watts of power with a typical current draw of 600mA at 5V.

The ePINS software system is shown in Figure 2. The navigation software runs within Honeywell’s Embedded Computing Toolbox and Operating System (ECTOS IIc), which provides a layered, customizable, and reusable software architecture for implementing navigation, guidance, and control software. A Honeywell-developed simulation tool for offline analysis and development of ECTOS-based software was also used in ePINS development and testing.

Figure 2. ECTOS IIc hierarchical software structure.

The ePINS demonstration device can achieve path performance of less 2 percent distance traveled for walking motion after 1 hour of operation, independent of the magnetic environment. Current performance, packaging characteristics, and interfaces are summarized in Table 1.

Table 1. ePINS performance objectives and physical specifications.

Algorithm Description

Figure 3 depicts the overall sensor integration and data processing scheme used in the ePINS device.

Figure 3. Sensor integration using the ECTOS extended Kalman filter.

Extended Kalman Filter (EKF).  The EKF estimates the navigation and sensor errors and computes the resets applied to the strapdown navigation solution to increase its accuracy. Error models for the navigation sensors (IMU, barometric altimeter, magnetometer, GPS, and motion classification) are contained in the EKF. For the ePINS device, the virtual measurements from the step-length model and the strapdown navigation solution are fused by the EKF to assist in bounding the time dependent error growth of the strapdown navigator, which in turn helps maintain calibration of the inertial sensors. A key output of the EKF is the navigation confidence, which is an estimate of the accuracy of the navigation solution.

An important aspect of the EKF and step-length modeling is the residual test that the EKF supports. This test provides a reasonableness comparison between the step-length model estimate and the distance predicted by the strapdown navigation system. This capability significantly increases the robustness of the navigation solution, especially when the user is engaged in motions not recognized during motion classification.

Human-Motion Model. The human-motion model includes two components: wavelet motion classification and step-length model estimation. The wavelet motion classification identifies the type of motion the user is performing, and the step-length model acts as a virtual sensor that quantifies the motion as a distance-traveled estimate.

Wavelet Motion Classification. Human motions are very diverse and highly irregular. Determining what motion is being performed is a challenging problem of classification. Honeywell’s solution is based on wavelet transformation of IMU data. Predefined, or known, characteristics of a variety of motions (such as walking, running, crawling, etc.) are cataloged and stored to a device’s memory. Estimates of those same characteristics for a user are then computed in real time and compared to the catalog of stored information to find the best match.

Generating the catalog of stored information is an offline task that begins by “segmenting” recorded IMU time domain data into individual steps. An example of the output of the segmentation process is shown in Figure 4.

Figure 4. Segmentation of the IMU data using the y-axis accelerometer signal.

Figure 5 displays the segmentation results for two different walking styles (in red and blue) across approximately 15 example steps. As is evident from the graph, walking has characteristics that are common across users, for example, the sharp peaks in the z-axis acceleration caused by foot-ground impacts. Once the data has been segmented, a wavelet transformation on each data channel is performed. Wavelet transformation for many users over many different motion types takes place offline. Subsequently, a wavelet descriptor is built for each motion type based on the transformations into the wavelet domain. With this method, a wide variety of information (that is, descriptors) suitable for input to a classifier is captured about each motion. These descriptors are then cataloged and stored in memory on the ePINS device.

Figure 5. Sample steps for two subjects (red) and (blue).

Finally, for the online phase, the wavelet descriptor of the incoming IMU data is calculated by performing a wavelet transformation on each data channel. This descriptor is then compared to the pre-computed and stored descriptors to classify the motion. FIGURE 7 shows an example of the motion classifier output, where a running motion was used as an input. The classifier successfully determined the motion type (blue field), frequency and phase of the input motion, depicted by the tallest rectangle in the figure.

Figure 7. Classification results from a query of running at a certain frequency and phase (depicted by the dark sphere).

Step-Length Modeling. Once the current motion is identified, a step-length model specific to that motion is used to aid the navigation algorithms. The model for each motion type is obtained by first collecting data that measures step length and step frequency. From this data, the step-length models can be computed by performing a regression analysis of the step-length vs. step-frequency data. Since the step-length models act as a virtual sensor, the models must be as accurate as possible to achieve better system performance. To attain model accuracy, an accurate data collection method is needed.

For ePINS development, step-length models for multiple users have been identified from step-length and timing information using a precise GPS truth reference system. Step-length regression calculations then determine the step length as a function of step frequency (that is, inverse of the step time period).  An example of GPS truth data and the corresponding regression model are shown in FIGURE 6 for walking motions.

Figure 6. Step length versus frequency for the walking of subject.

Although basic step-length models are created offline, online calibration of the step-length model can be performed by the EKF if GPS is available during operation. Online calibration tends to increase the overall position accuracy, as variations in the step-length models are likely due to slight variations in biometric differences across humans, terrain features, and even mission plans and duration.

Heading Determination. Heading initialization is one of the key concerns during system start up. In its current operational use, the ePINS device may perform a dynamic or a static initialization of heading. The static method requires the user to survey the system’s initial heading to an accuracy value that is usually specified by mission performance objectives; the absolute position accuracy is dependent upon the accuracy of the initial heading.

The dynamic method is a general method for heading initialization; it is performed without input from the user, but is possible only when GPS is available. This method of heading initialization does not use any a priori information about heading and requires an EKF implementation with a large-azimuth error model. This method requires an additional period of time in which the heading error uncertainty converges.

User Interface. During a mission, the user can interact with the navigation system and monitor its output on a display. The current ePINS prototype offers two-way communication via a serial connection. The serial communication is made wireless by the addition of a Bluetooth interface. Users can use this link to monitor the status of the navigation solution and to send commands to the device.

Honeywell has developed an application for the Android platform for this purpose. One of the key features of the interface design is that the navigation system outputs data in a standard NEMA format. Thus, publically available Android applications, not just proprietary applications, can also receive and display the navigation solution output by the ePINS device.

Honeywell’s personal navigation application displays the user’s traveled trajectory in real-time. The application can be adapted to include building floor plans as well as other navigation information.

Results

The ePINS prototype has been evaluated both in simulations and indoor/outdoor experiments. The navigation results presented here were obtained in February 2012 at a Honeywell facility (FIGURE 8). First, the user completed the heading calibration, and then online step parameter estimation in the presence of GPS was performed. Once calibration and training was completed, the GPS was disabled to simulate a GPS-denied environment outdoors. The user than transitioned to indoors (with GPS still disabled), and walked a course inside that included walking up and down stairs (FIGURE 9) and ended in a conference room (FIGURE 10).

Figure 8. Course for the Honeywell facility demonstration.

Figure 9. The user walking up stairs.

Figure 10. The user at the end of the demo.

Over these conditions, the ePINS system performed robustly and within performance specifications. Live demonstrations and testing showing similar levels of performance were performed at the 2012 Joint Navigation Conference (JNC) and at military test sites in California and Indiana.

Summary

The technical approach of the ePINS solution to the problem of personnel navigation in GPS-denied environments is based on a strapdown navigation solution maintained using a mid-grade IMU and advanced motion-classification algorithms. We integrated an array of sensors and software into a system that provides accurate position information and is suitable for use by first responders, soldiers, and other personnel where GPS is unavailable. ePINS works well for a variety of pedestrian motion types, including walking, running, crawling, walking upstairs, walking downstairs, sidestepping, and walking backwards. The motion classification and modeling method is extensible to other motion types.

We tested the ePINS system in indoor and outdoor environments. FIGURE 11 depicts the future ePINS concept, and TABLE 2 presents its future physical characteristics.

Figure 11. Future ePINS concept and mounting position.

Table 2. Packaging characteristics of the future ePINS.

Acknowledgments

This article is based on a presentation made at ION GNSS 2012.

Manufacturers

The ePINS processing platform uses Honeywell Agile Navigation and Guidance Integrated Electronics support electronics. It includes a Honeywell HG1930 MEMS IMU, a Bosch Sensortec BMP085 barometric pressure sensor, a Honeywell HMC6343 digital magnetometer, and a NovAtel OEMStar GPS receiver.

Yunqian Ma is a principal scientist at Honeywell Aerospace. He received his Ph.D. degree in electrical engineering from the University of Minnesota, Twin Cities. He is currently the program manager of the GPS-denied navigation program and the next-generation personal navigation program.

Wayne Soehren is a senior technical manager at Honeywell Aerospace. He was the program manager for the development of Honeywell’s first MEMS-based GPS/INS, which developed the core capability now used in Honeywell’s IGS-2XX family of MEMS-based GPS/INS products. He holds an MSEE from the University of Minnesota.

Wes Hawkinson is an engineering fellow at Honeywell Aerospace. He holds a BSEE/CE from the University of Wisconsin–Madison.
Justin Syrstad is a guidance and navigation scientist. He received a master’s degree in aerospace engineering from the University of Minnesota.

Presentation to the 11^th Meeting of the PNT Advisory Board

The following is an abbreviated transcript of Don Jewell’s briefing to the PNT Advisory Board at its meeting on Tuesday, May 7. The slides from Jewell’s briefing and the other briefings to the board are available at pnt.gov under the heading 11th PNTAB meeting.

First, a prefatory note from Don Jewell:

Author Sets the Scene

The old adage “A picture is worth a thousand words” certainly applies to the atmosphere of a PNT Advisory Board meeting. And in this case, so does the oft repeated and entirely inadequate phrase “You had to be there.”

The atmosphere of an Advisory Board meeting is extremely dynamic. You have a very distinguished board of PNT subject-matter experts who are very passionate about their areas of expertise. Some, like Drs. Parkinson and Schlesinger, the co-chairs, have been involved with PNT and GPS matters for 45 years or more. Therefore, the danger of an abbreviated transcript of an emotion-filled briefing is always unsatisfactory at best, because you miss the give and take, the repartee of experts that have invested much of their lives in this arena. So it is important that the reader understand the context of the questions and answers and sidebar conversations that took place before, during, and after the briefing, to put it in context.

It would be easy after reading this transcript and others during the meeting to put the blame for antiquated PNT equipment on the manufacturers. But nothing could be farther from the truth. The truth is, the culprits here are numerous but identifiable. They are:

1.     Outdated government regulations, directives and procurement/acquisition procedures that seriously hamper equipment manufacturers from doing their best and updating equipment as necessary.

2.     Timelines that totally ignore the dynamics of Murphy’s Law — a law of ever-shrinking timelines battling a glacial process of ever-increasing requirements bounded by antiquated procurement procedures and fiscal indecision.

In the case of military user equipment (MUE), the warfighters, first responders, and government users are the unfortunate recipients of this morass of near-pandemonium and downright confusion. Dynamic and critical user requirements are sacrificed upon the altar of “the program of record” and an agonizingly glacial government bureaucracy. Be assured that the “program of record” delivered exactly what was asked for by the original RFP and subsequent contract award.

Take Rockwell Collins for instance. Rockwell is a great company,  building rugged, reliable, precision instruments. I have flown with Rockwell communications and aviation equipment in various aircraft cockpits for the last 40 years, and they are indeed the gold standard in that arena. Rockwell has been delivering GPS military user equipment since 1978 and the company has always delivered exactly what was asked for. The problem is that the operational and refresh cycle for government user equipment needs is inside the acquisition cycle, and unfortunately exceeds it by a factor of ten — hence Murphy’s Law.

The Defense Advanced GPS Receiver (DAGR) was an excellent device when conceived and was the only game in town as regards jamming and spoofing environments. I am confident that Rockwell would have continuously updated the DAGR and made it relevant today, given the opportunity, which they were not.

In my opinion, government regulations in the area of user equipment, especially electronics and highly dynamic technological areas, need to be drastically altered to follow the aircraft procurement cycle. For example, there are probably 50 or more different block versions of the F-16 aircraft, that in truth are radically different. In some respects the “Block 1″ F-16 resembles the capabilities of the “Block 50″ version only in that it is an airborne vehicle with wings, engine, and a fuselage. Electronically and technically, it is a totally different aircraft. But the contracts for General Dynamics and now Lockheed Martin were not recompeted every time the user requirements, and hence the capabilities of the F-16 changed. I hope you all agree that would be ludicrous — and yet that is exactly the situation with MUE. When the scope changes, the contracts are painfully and laboriously recompeted, with lag times that make the process laughable — if indeed it were not so sad.

Then there is the government’s serious lack of information and training concerning MUE devices. I have been around GPS user equipment for 35 years and yet I am sure I still do not understand all the capabilities of the Precision Lightweight GPS Receiver (PLGR) and DAGR. Imagine how befuddled a young warfighter becomes when  given the devices and only a cursory amount of training, that is not only inadequate but sadly many times misleading or just flat wrong.

In our interviews we founds trainers — those that taught warfighters how to use the PLGR and DAGR — who were not aware the unit could be “keyed” or encrypted for greater accuracy. Of course we also found excellent trainers, but they were the exception to the rule. Who trains the trainers?

Although it sounds trite and seems to be a copout, don’t blame the equipment manufacturers for the current state of MUE. Blame the system and then get involved and help us change it to what it should be.

Good morning, everyone.

A special thanks to Jim Miller, Dr. James Schlesinger and Dr. Bradford Parkinson for inviting me to speak this morning on the future trends of PNT user equipment, particularly as it pertains to warfighters and first responders — certainly a subject I have been passionate about for only…oh, let’s say about 35 years.

Why GPS World?

Ever since the agenda for the PNT Advisory Board meeting appeared online, I have been receiving emails and phone calls asking why I was speaking not as one of the IDA (Institute for Defense Analyses) subject-matter experts on GPS but as the Contributing Editor for Defense for GPS World. Frankly, the answer is simple. Wearing the GPS World hat gives me the freedom to say what needs to be said today, whereas the IDA think tank attribution and publication rules, which are absolutely necessary for an FFRDC (Federally Funded Research and Development Center) to operate effectively and efficiently, would unduly restrict my comments.

Plus, for 21 years GPS World magazine has been the publisher of the definitive GPS user equipment survey for global users. It’s free for everyone to use, and it covers PNT receiver information from 55 global manufacturers with data on all aspects of 502 PNT receivers. And it is a great boon for me personally, as I only receive on average about 50+ emails or letters per month from users simply wanting to know what GPS/PNT receiver they should purchase. It is wonderful to be able to point them to the GPS World Receiver Survey.

Also wearing my GPS World hat, I can easily refer to the several thousand warfighter and first responder inputs we have received over the last 10 years — generally expressing what they would like to see in a GPS/PNT receiver or sometimes specifically the Perfect Handheld PNT Transceiver (PHPNTT), which I first wrote about six years ago (and most recently in December) in GPS World magazine.

Top 10 Warfighter – First Responder Requirements for the PHPNTT

Adhering strictly to the latest fad in government briefing formats, it is now time for me to BLUF, or give you the Bottom Line Up Front. However, being a journalist, I also have to hold something back for the end. So here are the top 10 PHPNTT requirements, in order of preference, as submitted over the last 10 years by thousands of warfighters and first responders:

• Mil-Spec rugged – solid state drive – no moving parts
• Friendly, intuitive, familiar interface – easy to use
• Multi-GNSS – All signals available – space and terrestrial
  • Wi-Fi, eLORAN, space/terrestrial augmentations, networks, communications
• Wireless, portable, seamlessly networkable
• SWAP friendly, long battery life, with solar charger
• Real-time 3D map data, NGA, Google, satellite imagery
• Not a stand-alone PNT device
  • Embedded in a computer with multiple communication capabilities – one must be secure
• Must be able to download, store and utilize new applications
• Software-defined and expandable
• Act as a sensor with automatic reporting

All these “user requirements” are closely related to what our warfighters and first responders don’t like about the current GPS MUE or Global Positioning System Military User Equipment. I state that specifically because, make no mistake about it, the current MUE is strictly GPS-based. However, the current MUE only receives two of the many signals available today on the GPS SVs, and certainly not any of the other numerous PNT (position, navigation and timing) signals also available, which of course is the crux of the issue for user equipment of the future.

Most of the top 10 requirements, and there were more than 50 requirements identifiable in all, are self-explanatory, and time does not permit me to cover them all in detail. But bear with me for a couple of quick explanations. Certainly the rugged requirement is readily understandable, and there are numerous manufacturers around the globe today that make excellent Mil-Spec rugged devices. However, the one I am most familiar with and have been extremely happy with are the rugged units from Trimble Navigation produced in Corvallis, Oregon. Trimble also happen to be a certified SAASM (Selective Availability and Anti-Spoofing Module) supplier as well.  More on those units later.

The second bullet concerns the human-machine interface on the current MUE, which is so poor that a Marine three-star wrote me a few years ago to say that in his opinion, “If anyone wants an example of how not to design an operational equipment interface then they should refer to the PLGR or DAGR. Both are consistently and sufficiently horrendous, in my opinion.”  I could not have said it better. The PLGR and DAGR use the gold standard for PNT as a signal, but the human-machine interface (HMI) is, in my opinion and in the opinion of thousands of warfighters, so antiquated and non-user friendly as to be almost unuseable. However, the units do work well and provide outstanding signals when embedded with other equipment. They just do not work well as a handheld device. The other items on the list we will cover as we proceed through the briefing.

GPS MUE Historical Perspective

I have been involved with GPS user equipment for the last 35 years, and this behemoth of a receiver was my first unforgettable encounter.

First GPS MUE receiver developed under government contract by Rockwell Collins, circa 1977.

Yes, this huge device is GPS user equipment. Can you imagine? It weighs more than 300 pounds, without the two operators, and was the very first workable GPS receiver produced for the U.S. military by Rockwell Collins, who has been producing GPS MUEs ever since. Which is an example of the prodigious acquisition issues that also need to be addressed, or corrected, if you will. Our antiquated acquisition practices are to blame for many of the failings in MUE equipment today. While I feel it is critical to mention this as a major contributing factor to the state of MUE today, it is also a story for another time.

Other than being the first GPS MUE, the significance of this huge receiver is that in my estimation it is the first and last time the U.S. military possessed a purpose-built military GPS receiver clearly superior to the products being produced by commercial and civil manufacturers for global users.

First Significant Usable and Transportable GPS Civilian Receiver

Fortunately, a good friend and colleague, both at IDA and ION (Institute of Navigation), Philip Ward, came to the rescue of all GPS users in 1981 when he delivered the TI 4100 NAVSTAR Navigator Multiplex Receiver.

TI 4100 NAVSTAR Navigator Multiplex Receiver designed by Phil Ward for Texas Instruments.

The TI 4100 was indeed the first commercially viable receiver that could be considered a transportable by anything other than an aircraft. To be historically correct, there were some backpack models that were very short-lived and not as significant as the TI 4100. The main unit and two antennas weighed approximately 50 pounds and showed promise in station wagons and helicopters. I can see a few folks in the audience smiling, so I will reiterate that the TI 4100 was a significant milestone, both in SWAP (size, weight and power), accuracy and TTFF (time to first fix). TTFF was 15-20 minutes in search mode, however; after the four SVs were located and the unit was initialized, it could consistently present a fix location in just a couple of minutes. Plus, the TI 4100 was immune from most jamming signals of the day — an impressive receiver and accomplishment for 1981.

Evolution of Commercial GPS/PNT UE

Fast-forward several years and the following picture presents a view of how quickly GPS UE developed.

Trimble units from the mid 1980s until today.

The first unit on the right in the above photo is a Trimble unit that was about the same size as the TI 4100, but considerably more capable. As you follow the units around counter clockwise, you will see that they decrease in size and weight, but what you can’t see is that they also increase incredibly where acquisition and processing speed (TTFF), accuracy and capability are concerned. Note also that you start to see stand-alone units that appear to be antennas with separate handheld display units. This is a feature the commercial manufacturers incorporated over 20 years ago, and in some respects a feature the MUE manufacturers and services are just now considering.

The defacto Garmin standby device.

Note also the Garmin GPS wrist receiver (right), which until 2005 was the most prevalent civil receiver in both of the wartime AORs (Area of Responsibility). Compare this Garmin wrist unit to the 300-pound Rockwell Collins unit I first showed you and consider that where SWAP and performance are concerned, the wrist unit is hundreds of times more capable and portable.

Current MUE – Program of Record and the Future

The pictures below depict the current MUE – Program of Record equipment, again both manufactured by, you guessed it, Rockwell Collins. First is the PLGR or the Precision Lightweight GPS Receiver. Second is the DAGR or Defense Advanced GPS Receiver. The third unit, known simply as the “Puck,” is what the U.S. Army would like to field in the next couple of years along with that separate display unit I spoke of earlier. Starting to sound very commercial, right? By the way, the Puck measures only 2 x 2 x 1/2 inches and weighs just a few ounces.

Rockwell- Collins PLGR.

Rockwell Collins DAGR.

Army’s Future PUCK.

Between the PLGR, which was decertified by the Marine Corps in 2010, and the DAGR, there are approximately 500,000 of these MUE devices fielded today, and yet almost none of them are utilized as handhelds. Our research shows that indeed only 1 in 40 is used as a true stand-alone handheld. Most DAGRs are primarily used to interface with legacy communications equipment, primarily U.S. Army, that calls for fire support, read ordnance, and all the others are either stored or embedded with other equipment, which means the “horrendous user interface,” a common warfighter description, is not a major issue. The bottom line is the DAGR is very good at what it does, it is just that what it does (warfighter quote) “…stopped being functional, when compared with other more capable PNT equipment, almost the day is was delivered to the AOR in 2005.”

While the Puck is certainly a major improvement in SWAP and concept, it essentially provides the same two GPS signals and SAASM capability as provided by the DAGR, just in a smaller form factor, and it does away with the continuously vilified user interface. The Puck technology totally ignores current-day PNT, multi-GNSS platforms and the other 160 PNT signals available today. Review the GPS World 2013 Receiver Survey and you will only find a handful of receivers that are so incredibly limited, and they are invariably produced, you guessed it, for the U.S. government as part of a GPS program or alternate program of record.

MUE: How Not to Build a PNT Device, or Why Warfighters Use Garmins and iPhones

The list you are looking at now is comprised of the first 15 minutes of conversation with thousands of warfighters interviewed over the last 10 years — they just had to tell us what was wrong with the current MUE before they finally got around to telling us what, if they were king or queen for a day, they wanted to see in the PHPNTT. This is not my opinion but the actual words of the warfighters. First of all, understand that the PLGR is a single-frequency GPS-only receiver with a security module (PPS-SM) to access encrypted P(Y)-code for anti-jam purposes. It was initially fielded 1990-2004, replaced by the DAGR in 2005. There are approximately 165,000 PLGRs and 450,000 DAGRs fielded at a cost of more than $1 billion. Now the warfighter comments:

• Both the PLGR and DAGR have an antiquated, proprietary OS and “extremely unfriendly — non-intuitive” user interface.
• PLGR and DAGR are not functional as handheld units but function well as embedded devices — although typically not networked, and we are not even sure they can be networked.
  • Example: One STRYKER vehicle variant has nine separate DAGRs incorporated, each with its own antenna and operating totally independently of the others.
• PLGR was decertified by U.S. Marine Corps in 2010 due to friendly-fire incidents.
• DAGR used today primarily as embedded device only with a “ horrible user interface”:
  • Monochrome screen, no active maps, navigation direct waypoint only.  Provides user with PNT information as coordinates — requires paper map to be an effective tool.
  • For other than straight-line navigation — time, distance and ETA are incorrect.
  • Programming/mission planning require special cables, software and a laptop computer.
  • Additional cables, radios and hardware are required for PLGR or DAGR to communicate.
  • Proprietary OS — no capability for additional programs to be added or utilize.
  • SWAP issues — large, heavy, limited battery life (multiple batteries) for typical missions.
  • TTFF — warm, approximately 2 minutes; cold with almanac download, 30+ minutes.
  • Position accuracy expressed as PDOP (1-6) on separate screen from PNT data. Nominal accuracy of a coded DAGR is typically about 1 meter or more.
• Advantages: Anti-jam and legacy interface capabilities.

So, the bottom line as far as the warfighters are concerned is that if you want to operate legacy equipment that requires a GPS input, such as calling in “fires” or artillery or if you are in a jamming environment, then you need the DAGR or its capability. Our survey shows, however, that only 1 in 40 use the DAGR as a handheld, and yet every single one of our respondents — that’s 100 percent, a rarity in statistics — stated they had a backup unit, primarily a Garmin, until 2005, and then popular backup units were more than likely an iPhone, iPad or Trimble unit.

One of the Most Popular PNT Devices in Theater Today – More than 365M Sold to Date

Today there is no question concerning the most prevalent PNT unit in both AORs. It is, you guessed it, the Apple iPhone and/or the Apple iPad. Let’s take a brief look at the capabilities of this non-ruggedized but still amazing device, which can easily be made Mil-Spec rugged with aftermarket cases and enclosures such as those produced by Otterbox, which I have personally tested and reviewed numerous times.

The Apple iPhone 5.

The attributes you see listed here are for the iPhone and iPad, and are those that assist in some aspect of PNT and/or integrity and accuracy.

• Assisted GPS SBAS — WAAS (PNT)
• Assisted GLONASS — (SBAS) (PNT)
• Digital compass (PN)
• Wi-Fi (Communications-Data + PNT)
• Cellular (Communications-Data + PNT)
• Bluetooth (Communications-Data + PNT)
• Skyhook Wireless (PNT)
• Three-axis gyro (PN)
• Accelerometer (PN)
• Pedometer (PN) – Application
• Internet (Communications-Data) Skype application (PNT)
• Real-time accuracy and integrity representation (PN)
• 361+ navigation applications in the App Store ready for instant download and designed for iPhone and iPad. The majority of these applications are available at no cost to the user.
• Real-time 3-D maps — Google maps — satellite imagery — updated continuously
• Automatic location-based services (LBS) — warfighter support
• BFT (Blue Force Tracking) + other .mil App Store apps including multiple mil-GRID systems.
• Warfighter discounts and mil-spec hardened cases (http://www.apple.com/r/store/government/).
• One-button combat application.

All this capability available in just four ounces — truly a SWAP and capability revolution.

Of course, what really makes the list of iPhone and iPad capabilities revealing is that the first two attributes alone more than double the number of PNT signals received and utilized by the iPhone versus the DAGR, and that number does not account for the GPS L2C (second civilian signal) and L5 (DOT safety of life signal) with CNAV, which when activated will be the strongest GPS signal broadcast to date. The CNAV data is an upgraded version of the original NAV or navigation message. It contains higher precision representation and nominally more accurate data than the nominal NAV data. There are 26 more PNT satellite signals available today in the iPhone and iPad, and they are comprised of multi-GNSS signals and augmentations. The kicker for me is that in addition to all the additional space signals are terrestrial signals, and almost any map or grid system the user desires. Plus there are apps (software applications) that translate between grid systems. And if you don’t like the interface of the navigation program you are using, then there are literally 360+ other choices. I also find the pedometer function interesting, in that firefighters now use this capability along with the Blue Force Tracking app in buildings when they are momentarily without GPS, GLONASS (Russian GNSS), WAAS (U.S. Wide Area Augmentation System), EGNOS (European Geostationary Navigation Overlay Service) or other SBAS (Satellite Based Augmentation System) signals.

Realistically, to defeat the current unencrypted MUE today, an adversary only has to jam one GPS signal, but to defeat the iPhone or iPad an adversary has to jam all the GPS signals, all the GLONASS signals, all the Wi-Fi signals, all the mobile 3G and 4G CDMA and GSM (read as different mobile telephone systems) signals and still the iPhone or iPad will use the accelerometer, gyro, compass and pedometer functions to determine position. Indeed, it will continue to function as a PNT device. All this in just four ounces at a cost about one-sixth of the DAGR displayed on a screen that has 100 times greater resolution and is in color. Remember, the DAGR has a monochrome screen. No contest. Plus try saying, “Take me home, Siri” to a DAGR and see what happens.

Garmin

What about Garmin, you ask? At the beginning of the current conflicts, Garmins were the prevailing additional PNT device. There are still thousands of them in theater, and they have saved many lives, as we will see. However, just look at this sales chart for smart PNT devices.

Products                                                             Total Units Sold (approximate)

iPhone (since 2005)                                            250,600,000 (M)

iPad (since 2010)                                                115,000,000 (M)

Garmin Sales                                                     ~100,000,000 (M)

iPhone/iPad App Store (since 2008)

Downloads of the 361+ navigation apps         2,200,000,000+ (B)

(Note: Total App Store downloads will exceed 50 billion by the time this is published.)

The Future

The future of PNT devices globally, especially for warfighters and first responders, is clearly with rugged mobile devices capable of downloading, storing, updating and utilizing applications. The Garmin cannot do that, although it can be updated, and just look at the numbers. Garmin started business as a GPS device provider in 1989. In that time, while branching out into marine and aviation devices, some of the best in the world for those purposes, they are still primarily GPS only (with SBAS). They have sold approximately 100M devices in 24 years compared to Apple’s iPhone and iPad numbers, which total more than 365M devices in less than eight years. The iPad alone outsold all Garmin products in just three years. I confess that I happily own several Garmins, think that are fantastic PNT devices, and it is really tough to beat the $99 wrist Garmin. When all is said and done, the Garmin gives you better information in a non-jamming environment than the DAGR. And Garmin units are still saving lives. Take this vignette from SSG Kyle Dorsch:

“My name is SSG Kyle Dorsch…a Reconnaissance team leader in the 2-30 Infantry Battalion, 10th Mountain Division, deployed to the Logar province, Afghanistan. I have used my Garmin eTrex Vista H throughout my deployment…it has been a lifesaver in more than a literal sense. In fact, there isn’t a leader in our establishment without a Garmin product…my Garmin guided me and my four-man team seamlessly through some of the toughest areas of Afghanistan…it also literally saved my life.”

SSG Dorsch goes on to explain that the eTREX, which was placed strategically on his combat vest, actually stopped an enemy bullet meant for him, and just like Timex the eTREX kept on ticking.

My Obligatory Caveat

Note that SSG Dorsch has always had a Garmin with him in theater and indicates that his leadership has as well. There is no doubt the eTrex saved his life, literally. However, I would never tell a warfighter to not use their government-issued MUE. In a severe jamming environment, it may prove to be a lifesaver, and it may be the only equipment that interfaces with legacy communications and fire support equipment. Take that advice for what it is worth today, because hopefully this will not be the case much longer.

DARPA and Smart COTS Devices on the Battlefield Now

DARPA (the Defense Advanced Research Projects Agency, the real inventors of the Arpanet and the Internet), a much-storied DoD research arm, launched an effort recently called “Transformative Apps.” It developed a few dozen smart applications that work on a number of mobile devices. In addition to mapping, navigation and smart routes, the apps identify explosives and various weapons, and help navigate and locate parachute drops.

A screenshot of the DARPA Smart Routes application. The green routes are safe routes and the red are routes that have been traveled too many times or indicate where problems may exist.

DARPA builds prototypes that are transferred to the Services and become official applications used by hundreds of thousands of warfighters. The challenge is to rapidly adapt COTS (commercial off-the-shelf) technology to the unique circumstances of the military, which often operates over large, hostile areas with little to no formal communications infrastructure.

DARPA reports that more than 1,000 war fighters in Afghanistan now use the DARPA Transformative Apps technology as it continues to be rolled out to the Services.

The most interesting aspect of DARPA’s participation in PNT software is that it will definitely accelerate the multi-GNSS and all-signals-available scenario, because it is not constrained by woefully out-of-date DoD regulations. DARPA does what is smart, what cutting-edge technology will support, what makes sense, and ultimately what saves lives.

This good bit of news from DARPA combined with the following statement from the DoD in the Wall Street Journal earlier this month should give us all some hope for the future of PNT and MUE.

Pentagon Expects to Enlist Apple, Samsung Devices

The U.S. Department of Defense expects in coming weeks to grant two separate security approvals for Samsung’s Galaxy smartphones, along with iPhones and iPads running Apple’s latest operating system — moves that would boost the number of U.S. government agencies [ed. legally] allowed to use those devices.

–  Wall Street Journal, May 2, 2013

In my humble opinion, this announcement is simply outstanding…albeit about 10 years late to need. Indeed, Ms. Teri Takai, the current DoD CIO (Chief Information Officer) gest it and is trying hard, but she can’t do all the heavy lifting alone.

Old Adages Die Hard

I remember an old GPS adage that portentously proclaimed, “If it is not supported on the GPS satellite, it cannot be supported in the user equipment.” Unfortunately, there are those still holding to this totally fallacious belief. Today in the current budget environment, amazing capabilities are being implemented with user equipment that multiply the capabilities of the PNT satellite, other satellites and space signals, terrestrial signals and synergistic augmentations. Indeed, the total price of the PLGR and DAGR program combined would barely pay for some NRE (non-recurring engineering) costs and two launches of the GPS III satellites that should be ready for launch in 2014. Today we need to look even harder at what is doable with user equipment, especially in the military, because it is all we can afford. As Winston Churchill was once quoted as saying, “Gentlemen, we have run out of money; now we have to think.” However, having said that, let’s not forget that the multi-GNSS environment has multiplied many fold the number and capabilities of PNT signals on orbit today.

PNT User Equipment TRENDS — Space SIGNALS available

Jim Doherty, USCG Captain retired, and I are friends and colleagues at the Institute for Defense Analyses (IDA). We are both old retired navigators as well. We both still have the skills to successfully navigate an aircraft or ship, for that matter, from San Francisco to Tokyo using only a sextant. While we are proud of that talent or ability, one that very few possess today, we would much rather accomplish the feat with an exceptional multi-GNSS device, and they exist today like never before. These next lists show all the signals that are available today compared to what the GPS MUE can receive and use for PNT purposes. Plus, Jim and I both share a firm belief in another old navigators’ adage: Receive Everything – Trust Nothing!

Civil-commercial multi-GNSS UE receives more space and terrestrial signals than U.S. GPS MUE.

• GPS MUE “officially” utilizes L1(CA), L2 P(Y) with SAASM.
  
• There are NO commercially viable M-code receivers available today and there will not be for several years to come.

PNT civil UE philosophy: Track and use all PNT signals available.

• GPS L1-CA/L2-codeless and ready for L2C, L5, L1C (GPS III & QZSS)
• SBAS (WAAS, EGNOS, MSAS, GAGAN, SDCM) + NDGPS & many other augmentations
• GLONASS L1/L2/L5
• Galileo E1/E5 (CBOC & Alt BOC)
• Compass B1/B2/B3 (carrier signals only- no full signal specifications)                           
• QZSS (Japanese GEO – highly elliptical) broadcasting L1 CA/C/SAIF, L2C, L5, LEX Pilot
• Wi-Fi, 3G-4G, Skyhook, eLORAN (UK), networks, CORS, VRS, GVRS

And do not be deceived: there are plenty of PNT receivers available today to receive all these signals and they have existed for some time. Equipment manufacturers have been ready to receive, process and utilize all the GPS and multi-GNSS signals for years. For example, Trimble built and shipped an L2C receiver in 2003, and that signal has still not been activated on any U.S. GPS payloads although, as we heard from Major General Marty Whelan (USAF – AFSPC/A5) earlier today, General Shelton (USAF), the four-star commander at AFSPC (Air Force Space Command) has announced a six-week test of the L2C signal and full CNAV message in June of this year. A great step forward.

One of these days we might even catch-up with the Japanese – more on that in a moment.

Trimble built and shipped receivers for GLONASS signals in 2006, even though GLONASS did not reach FOC or Full Operational Capability until late in 2010. A designation it is having serious problems maintaining. Trimble also ships L5 receivers as well as commercial SBAS receivers that result in extremely accurate and reliable positions. Lest you think all these signals have gone to waste, remember that Japan’s QZSS-1 broadcasts both L2C and L5 with a full CNAV message today, and the Trimble receivers and others with the multi-GNSS capability work well with those signals, as we shall see.

Global Virtual Reference Stations

Trimble (VRS) and John Deere (StarFire) PNT receivers have the capability Trimble has designated as Global Virtual Reference Stations, which — along with real-time kinematic (RTK) processing — provide users with an unprecedented number of signals and a real-time processed signal with corrections. This results in centimeter-level accuracy for any of their receivers that have the capability to receive and process the signals. For both manufacturers, that will soon be almost all of their receivers. Sure, there will probably be a small monthly fee involved, but the accuracy difference between 1 meter (~3 feet) and 3 centimeters can mean life and death if you are unlucky enough to be in the collateral damage zone or in the sights of a Hellfire missile during war time.

Multi-GNSS SVs and Signals in View

To highlight this point, just glance at the following graphical log file generated by software in the latest Trimble Multi-GNSS PNT receiver. The chart depicts a log file from a receiver located in Singapore. The location is significant only because in that location the receiver is in full view of the Japanese QZSS-1 PNT SV and all its extra U.S. originated PNT signals (L2C & L5) mentioned earlier. This particular Trimble receiver is networked and reports results automatically and continuously to a web page, while receiving GVRS updates and corrections plus other PNT information, such as an updated almanac, over the same network. The question becomes, is it a PNT device with a computer and embedded communications? Or is it a computer with communications and an embedded PNT function? You be the judge. Regardless of which you choose, this is the future of PNT and MUE.

This civil receiver reports 40+ SVs with 169 separate signals in view and usable. This does not count the number of Wi-Fi and/or GVRS signals it is capable of receiving. Meanwhile, a GPS MUE receiver in the same location only observes a total of 10 SVs it can process for a total signal count of 20. However, one of the key points on this log depiction has to do with integrity. Notice the orange and red lines. They indicate that the receiver has labeled these signals as “suspect” and has automatically dropped them from the solution for any of a host of reasons — a failed integrity check, jamming, spoofing, wrong way path, a runaway clock, etc. You name it, and if it is suspicious, the receiver will drop that SV and its signals from its PNT calculations. Built-in integrity.

The obvious question becomes just how accurate is this Trimble receiver over a 24-hour period? The next graphical log file denotes that it is accurate within 3 centimeters.

Trimble multi-GNSS receiver web page log file denotes continuous availability of PNT signals with an average accuracy of 3 cms.

Assured PNT

When we asked warfighters what was more important to them in a combat zone — availability or accuracy of the PNT signals, the answer was, not surprisingly, both. But, of course, they need to receive the signal first, and then they can worry about accuracy.

So, if you were Ms. Teri Takai and you were worried about “assured PNT,” would you rather do that with 20 signals from 10 SVs or 169 signals from 49 SVs and some very strong, difficult to jam, terrestrial signals as well — adding up to, on average, 33 times more accuracy than the GPS-only signal? To me, the answer is obvious. And of course, all that is on the line with every mission the DoD performs, as is the safety of our critical national infrastructure as this next chart depicts.

• Assured PNT or lack thereof impacts all missions, across all platforms and domains
• Assured GPS MUE PNT today depends on:
  • L1(C/A), L2 P(Y), SAASM (Future M-Code)
  • Accuracy ~ 1m

• Assured Multi-GNSS MUE PNT with all signals available depends on:
  • GPS L1/L2/L5/L1C/L2C/M-Code/SAASM
  • SBAS (WAAS, EGNOS, MSAS, GAGAN, SDCM+)
  • GLONASS L1/L2/L5
  • Galileo E1/E5 (CBOC & Alt BOC)
  • Compass B1/B2/B3
  • QZSS GEO – L1 CA/C/SAIF, L2C, L5, LEX Pilot
  • Two-way communications, Networking, PNT servers, each PNT device with unique IP address and each PNT device serves as a sensor
  • Software definable devices
  • Multiple software applications (Apps)
  • Accuracy ~ 3 cm

Army Making Strides

I spoke above about DARPA getting into the PNT business, and that is a good thing. But how about the largest military user of PNT, the United States Army? The U.S. Army is making some interesting changes as well. The Army announced a few months ago that there would be no more purchases of DAGRs, and that it was pursuing smartphones as a communications and small computing platform as well as an alternate PNT tool and display device. This is where the Puck comes into play.

Inside the Puck.

While it is a wonderful idea I fully endorse, the problem with the Puck is that under the current design scheme it will still only transmit the current two GPS signals to a smartphone or other PNT display device. And warfighters lament that it is another device run by batteries for which our warfighters need to carry spares. Why not make the Puck a multi-GNSS device? we asked. The answer we received is that it would make it too power hungry and just require more batteries. So to misquote Shakespeare “…for want of a battery, the war was lost?” The Army is definitely on the right track, but they need to figure out how to make the Puck a multi-GNSS device. Can you say Lithium ION and solar charger – Hoorah!?

The Army Hub

The Puck is moving in the right direction. However, with the addition of another device, the Army is definitely on the right track. This device is designated the “Hub,” and while it is again GPS-oriented, it contains multiple terrestrial and internal signal augmentations and backups, as the image depicts.

Inside the U.S. Army’s Hub.

With apologies to the U.S. Army, I unabashedly modified the chart, and I made it very obvious. The red text depicts my addition of a multi-GNSS card or module versus or in addition to the CGM (Common GPS Module) and GB-GRAM or Ground-Based GPS Receiver Application Module. The multi-GNSS card/module already exists today. Several PNT receiver manufacturers manufacture it with 28-nm technology versus the 95-nm technology — for the as-yet-unavailable for about four more years if the rumors are correct — GPS-only CGM. For me, the addition seems to be an easy fix, as there is lots of room in the Hub. But this fix or module (CGM) is years and millions of dollars down the road, versus a solution that exist today.

YUMA 2 or Hub or Both

The solution, frankly, is one of the smart tablets available today from numerous manufacturers — seven, actually, that have the wherewithal to produce a secure multi-GNSS device with a SAASM module.

The Trimble Yuma 2.

The Army Hub.

This is an example of the solution in the form of a Yuma 2 tablet computer from Trimble, which I am in the processing of reviewing for GPS World. The Yuma 2 has all the multi-GNSS features we have been discussing and more, plus it can in time accommodate all the modules scheduled to be incorporated into the Hub. Why build a whole new display device when the core already exists with many more capabilities than were imagined or real estate would ever allow for the Hub? Plus, it is available today as a rugged Mil-Spec device with a full color, high-resolution touch screen. And in the end it will provide a 3-cm solution versus a 1-meter solution. What more could you want? And it is available today with an outstanding and intuitive interface.

Conclusion – Services PNT UE Trends

I have been focusing on the Army today not simply because they are the biggest U.S. military user of PNT devices, but because they are moving in the right direction for the future of PNT and MUE devices. Of course, all the services and many agencies need a well-thought-out and secure PNT solution, and if we have learned anything it is that one size does not fit all. Indeed, our national security and our national infrastructure depend upon future PNT devices. For security purposes alone, they should have a certain degree of application and signal diversity.

Now let’s review:

• Army has a way ahead with an assured PNT program.
  • Includes end of PLGR and DAGR and adding new networkable devices.
  • Plans for fourth-generation multi-GNSS and multi-function handheld devices and embedded PNT devices as sensors to include the Puck and Hub.
• Marine Corps: Decertified PLGRs in 2009 and attempts to limit the use of DAGRs.
  • DAGRs used primarily as embedded devices.
  • Purchasing approved SAASM devices from commercial vendors.
• USAF: Outfitted 70% of aircraft with modern, integrated, networkable and upgradeable PNT devices.
• Navy: More than 60% of the fleet outfitted with modern PNT networked devices.
• The Bottom Line is – One size does not fit all but one conclusion is clear – while GPS may and will always hopefully be the Gold Standard – multi-GNSS solutions are the future.

The Future of PNT Devices

This last list depicts the future of PNT as best as I can define it; indeed, as it has already been defined for us by our warfighters and first responders or, as Kirk Lewis would have me say, government users. The users are not waiting around, nor have they bothered to adhere to woefully out-of-date regulations. It is what they desire, and since their lives depend on it, it is what they should have.

• Multi-GNSS — Utilize all PNT signals available.
  • Space and Terrestrial (GPS, GLONASS, eLORAN).
  • Traditional and non-traditional (Wi-Fi, GVRS, carrier signals).
• Multi-function COTS devices with non-proprietary OS (operating System), intuitive interfaces and Mil-Spec ruggedized.
  • Multiple methods of communications: Wi-Fi, Skype, 4G, text, auto-text, satellite.
• Software Downloads – Applications
  • COTS applications plus .mil apps store.
• Networked devices for SA, updates and PNT,
  • Real-time satellite imagery and mission data injects.
  • Defense and intelligence LBS.
• Each device will be a sensor on a network,
  • Automatically report jamming, interference and location data.
• Utilize SAASM and anti-jam military signals only as required.

Thanks you for your time and kind attention today. And remember, Happy Navigating!

System integrators have come to rely on the centimeter-level positioning accuracy made possible with real-time kinematic (RTK) commercial GPS receivers. Many authorized defense customers rely on access to the Precise Positioning Service (PPS) for single-point positioning. The OEM625S will combine a commercial dual-frequency NovAtel GNSS receiver with an L-3 IEC XFACTOR SAASM in a single card solution, reducing overall size and power requirements for end customer applications.

The OEM625S will maintain NovAtel’s OEMV-2 form factor, ensuring a successful drop-in replacement and backward compatibility for existing customers. Integrators can continue to use their existing user interface, which will be enhanced with OEM625S logs and commands for SAASM functionality.

NovAtel’s well-established, comprehensive set of software commands facilitates system integration, NovAtel said. The SAASM position is provided via a dedicated communication port, as well as through NovAtel’s software command protocol, allowing for maximum flexibility.

“For the past 17 years NovAtel’s customers have enjoyed great success in integrating our OEM family of high-precision receivers into a wide array of defense applications,” stated Graham Purves, executive vice president of NovAtel. “Adding the L-3 XFACTOR SAASM to our receiver card will allow defense customers to continue to use our products in the most demanding military environments.”

Ric Pozo, general manager of L-3 IEC’s Navigation Systems business unit, commented, “We are pleased to collaborate with NovAtel and provide the warfighter this highly flexible and capable GPS SAASM product. Our combined teams are looking forward to bringing this one-of-a-kind solution to market.”

NovAtel will accept orders for the OEM625S from authorized customers starting in the third quarter of 2012.

A new hardware assessment tool automates testing and mission replay, managing military GPS receiver input and output data, with an operational implementation and with a better control of initialization conditions, especially direct P(Y) acquisition. The test bench drives a GPS/Galileo simulator, a digital jammer, and software programs for visibility computation based on terrain modeling, and for multipath generation on 3D renderings.

Comprehensive assessment of military GPS receivers becomes more complex as they are integrated into advanced systems. To limit testing on systems under live conditions, laboratory evaluations with real elements are essential.

A new hybrid test bench called Statistical INERtial Gnss HYbrid in Simulation (SINERGHYS) is designed for governmental use to validate the integration of GPS/Galileo receivers within the navigation system for different platforms. As system-level requirements become more stringent, this bench has been designed to assess the behavior of the complete system in an operational context.

This new assessment hardware-in-the-loop tool is designed to automate testing and to replay missions with an operational implementation and with a better control of initialization conditions, especially direct P(Y) acquisition. This test bench drives many simulation tools: a GPS/Galileo simulator, a digital miniaturized jammer, and different softwares such as one enabling the computation of visibility depending on the terrain modeling, or one dedicated to the generation of multipaths on surfaces of realistic 3D scenes.

Figure 1. Depiction of SINERGHYS.

Figure 2. Focus on the bench.

A Common Bench. Since 2000, with the arrival of the new cryptographic generation (the selective availability anti-spoofing module, or SAASM), the French government defence procurement agency (DGA) GPS laboratory decided to buy off-the-shelf GPS SAASM receivers that cover different form factors and applications. To test performance, it was necessary to acquire a test bench suitable for each GPS receiver. Testing procedures became more and more complex, and most of the manufacturer-provided benches could not perform every test required, such as direct P(Y) acquisition. To improve French expertise concerning GPS receivers, the DGA GPS laboratory decided to develop a common, generic test bench taking into account the integration constraints of each receiver. The perimeter of the hybrid test bench consists of a PC and a generic GPS test bench.

Figures 3 and 4 show examples of military GPS receivers integrated into the bench.

Figure 3. MPE-S (Ground-based application, Rockwell Collins).

Figure 4. 1000S (Avionics,Thales).

Figure 5. Embedded jammer.

Figure 6. Jamming environment for a fighter aircraft. (Click to enlarge.)

Bench management is centralized, so test conditions are generic, and all simulation parameters are fully controlled. This enables users to display a unique view of the complete information and to be able to replay specific scenarios.

The bench manages military GPS receivers’ input and output data as described in the respective receivers’ interface control document (ICD) or interface specification: this enables, for example, the initialization of GPS receivers by sending precise time to facilitate direct P(Y) acquisition. This new bench is compatible with many GPS receivers with different form factors and applications.

Several receivers can be tested at the same time with the same software, so that the behavior of the GPS receivers can be compared in real time. Data from the different receivers can be observed on the same window of the graphic user interface (GUI). Specific data from ICDs can be displayed on the GUI. The user can visualize three different windows: the first is related to integrity, the second to alarms, and the third to cryptography. All the data output by the receivers can be recorded and replayed.

To facilitate and enhance trials on GPS receivers, the bench can use a Monte Carlo method, enabling sequentially and automatically chained scenarios, up to 10,000 test sequences, primarily for characterization of time-to-first-fix (TTFF).

Inertial navigation system (INS)/GPS hybridization in real time can be simulated via processing based on a Kalman filter of the information delivered by simulated INS and GPS. Loose and tight coupling can be selected through the GUI as well as filter parameters. The Kalman filter design is independent from the receiver and from the type of trajectory simulated. The user can decide whether the GPS receiver does receive aiding either from the simulated INS, or from the optimal navigation (output of Kalman filter).

Interfaces

The bench can interface with various external means and drive some tools and materials involved in the functioning of the bench.

With GPS Simulator. In the interface with the simulator, an intuitive GUI facilitates scenario preparation. When ready, SINERGHYS begins to drive the GPS simulator in remote-control mode. Any type of trajectory can be simulated with its operational environment modeled. The simulator outputs an RF signal to the receiver, and representative aiding, if required, by ethernet protocol to SINERGHYS.

With Jammer. Two types of interference signal generators can be used with the bench. Any available waveform can be generated. The bandwidth can go up to 20 Mhz for one generator and up to 80 Mhz for the other.

SINERGHYS is also compatible with a specific jammer called Embedded Jammer, designed to test vulnerability of GNSS systems (Figure 5).

The GPS receiver under test tracks the real GPS satellites combined with the simulated jamming signal. Thanks to the position and attitudes provided by the aircraft and to a modelized antenna diagram, the jammer computes in real time representative jamming that would be generated by real jammers.

This jammer works in two modes: localized mode (coordinates, jammer power, and waveform) and power profile mode. It was initially designed to be used inside an aircraft but can be used for laboratory testing as well.

The simulated environment is defined in the configuration software: waveform, emitter, scenario definitions (bands, number of emitters), and antenna diagram.

Four GNSS bands can be selected: GPS L1 and L2 (40 MHz) and Galileo E6 (40 MHz) and E5 (90 MHz). The embedded jammer can generate up to 14 simultaneous jammers per band, each with different waveforms. Therefore, up to 56 simultaneous jammers can be simulated.

The center frequency of the jamming signals can be chosen anywhere in the bandwidth. Modulation examples: continuous wave, broadband noise, binary phase shift keying), binary offset carrier (x,y), and so on.

Figure 7. Modulation examples.

External software interfaces fall under three categories.

Warfare. Electronic warfare software, which provides jamming coverage, performs a precise assessment of propagation (reflection and diffraction) of the interfering signals (depending on terrain modeling). Interference levels are transmitted to SINERGHYS during pre-processing.

Figure 8. Warfare GUI.

Satellite Tool Kit (STK). This software is designed to provide sophisticated modeling and visualization capabilities and  performs functions critical to all mission types, including propagation of vehicles, and determination of visibility areas and times. STK generates paths for space and ground-based objects, such as satellites, ships, aircraft, and land vehicles. STK also provides animation capabilities and a two-dimensional map background for visualizing the path of these vehicles. Within SINERGHYS, STK is used for real-time visualization.

Figure 9. STK GUI.

Ergospace. This software is designed to generate multipaths, enabling the modeling of reflected paths of different satellite signals on surfaces of realistic 3D scenes. Pre-processed multipaths are sent to SINERGHYS and generated by the GPS simulator. The software is also used for real-time visualization.

Figure 10. Ergospace GUI.

Figure 11. Example of the window showing the general state of the GPS receiver (c/n, svid, gram receiver and channel states, code and frequency tracked).

Operational Mission Characterization

The bench can evaluate and characterize receiver performance in most possible representative conditions.

Management of GPS Inputs/Outputs. Both black and red keys can be loaded inside the GPS receivers in both DS101 and DS102 protocols. This loading can be performed manually through key loaders such as KYK13 or DTD/ANCYZ10, but also through the host application with hexadecimal keys.

The bench can send commands to GPS receivers such as non-volatile memory erasure command, INS, precise time source, precise time and time interval (PTTI) activation commands, or choices between “mixed mode” and “all Y,” between “L1 primary” and “L2 primary,” and so on. Depending on user requirements, the bench can provide time, position, speed, almanac, ephemeris, or specific navigation sub-frames.

To test the jamming resistance of GPS receivers, it is essential to be able to provide INS aiding. SINERGHYS uses perfect or degraded aiding and adapts the format or the frequency for the considered GPS receiver.

Direct P(Y) acquisition functionality is an important case that needs to be evaluated. The GPS receiver needs a precise time to perform direct P(Y) acquisition. The time accuracy, from a few nanoseconds to several milliseconds, has a strong impact on the GPS behavior. A special delay box applied to the pulse-per-second signal of the GPS simulator in accordance with PTTI message (that is, time figure of merit), enables such a simulated accuracy.

A standard IS 153-like interface was developed to display GPS data on a convenient GUI in order to have a common software to visualize output data from the GPS receivers. The user can also visualize some specific data from GPS ICDs concerning integrity, alarms, and cryptography.

All receiver output data are recorded for later analysis.

Table 1. Example of Direct P(Y) acquisitions in accordance with time uncertainty (with times to get “GRAM state 5” and “protected status”).

Monte Carlo Trials

The bench enables sequentially and automatically chaining scenarios (up to 10 000 test sequences) to perform statistics on acquisition times. Indeed, it is primarily used for the characterization of TTFF. GPS signal acquisition is dependent on many different parameters, as described in Figure 12. To properly characterize receiver acquisition times requires a large number of tests. The comparison with GPS Receiver Applications Module requirements can be easily performed.

Figure 12. Setup parameters to study GPS signal acquisition.

Figure 13. Example of a random selection for the position error.

One Monte Carlo trial consists of a repetition of unitary test: powering the receiver, then sending to the GPS receiver random errors of position, speed, time, levels of jamming, and finally stopping the test sequence on trigger. At the end of Monte Carlo trials, statistical computing enables accurate analysis and expertises.

The random selections are optimized to reduce the number of cases. The bench can replay a particular case: as the seeds are deterministic, a special case of Monte Carlo method can be selected and replayed.

Real-Time INS/GPS Data Fusion

The information delivered by INS and GPS are processed by a Kalman filter. The INS trajectory is provided by the simulator or by an external file.

Two types of coupling are considered: loose coupling with position and velocity information, and tight coupling with pseudoranges and delta ranges to estimate errors. In both cases, the GPS receiver receives aiding from either the simulated INS or the optimal navigation (Kalman filter output).

Figure 14. Example of an optimal navigation along a specified trajectory in a jamming environment.

Figure 15. Position and velocity errors and navigation corridor.

The purpose of the Kalman filter is to estimate the navigation errors (position, velocity, and attitudes) and sensor errors (INS, GPS).

The filter design is original because it is independent from the receiver under test and from the type of application (hardiness privileged with reference to jamming). It is also able to estimate the time offset between position and velocity measurement on any GPS receiver under test.

Conclusion

SINERGHYS combines several resources into a single test bench. A complex mode can simulate an operational implementation with different interfaces and by chaining test sequences: receiver initialization, management of the switching of antenna patterns during a simulation, masking of GPS signals, management of jamming, INS/GPS data fusion, and so on. In this mode, missions can be replayed in a realistic environment. This bench is a complementary resource for flight trials and digital models because it can characterize the initialization phases with a good control of initial conditions. SINERGHYS enables users to know, as precisely as possible, the capabilities and limitations of a specific global navigation chain.

Manufacturers

SINERGHYS was developed by Bertin Technologies and specified by the French Ministry of Defense (MoD)DGA Information Superiority. It drives a Spirent GPS/Galileo simulator, Agilent 4431B and MXG generators, and software programs such as Analytical Graphics, Inc. (AGI) Satellite Tool Kit and Ergospace 3D scenes. The embedded jammer was developed by Ineo Defense in 2010 to MoD-DGA specifications.

Stéphane Gallot works at the French MoD (DGA Information Superiority) as a radionavigation expert. His particular interest is the integration of military GPS receivers including SAASM modules within French platforms.

Pascal Dutot is an architect engineer at the French MoD (DGA Information Superiority). His main activity is to optimize and control GPS integration in the global navigation chain.

Christophe Sajous works at the French MoD (DGA Information Superiority) as a radionavigation expert. He is also responsible for the “navigation per satellites” laboratory within the radionavigation department.

Jules McNeff

By Jules McNeff

An old adage says, “Be careful what you wish for, you might get it.” That is particularly relevant in today’s world of GPS and the positioning, navigation, and timing (PNT) dependencies it has created. In business, it’s all about location, and in military circles, something called real-time situational awareness, driven by the ready availability of PNT from GPS. However, it has been reported (and validated by experience) that U.S. soldiers believe that the GPS equipment they are issued through official channels is too big, too heavy, uses too many batteries, and is old-looking and not sexy like the multi-color, multi-app personal electronics and smart phones they are accustomed to at home.

Furthermore, they reportedly feel encumbered by Department of Defense (DoD) policies that require the use of encrypted military GPS signals when executing combat mission command-and-control or performing combat-related actions such as synchronizing tactical networks, designating targets, and calling for fire support when in contact with an adversary force. They wish they could just use their iPhone, or iPad, or similar smart device with its integral location-based apps and ready communication capabilities, and not have to deal with what many see as obsolescent gear and antiquated policies. Unfortunately, were that wish to really come true across the joint force and mission domain, it could have disastrous and deadly consequences.

This is not intended to be a defense of the DoD requirements and acquisition processes, for there is much that could be improved within both. Adherence to those processes in the procurement of PNT equipment means that it will take longer to develop and produce the equipment than comparable commercial units, and that the equipment will probably be heavier and less user-friendly than commercial products.

However, those processes exist and are rigorously followed, first because they are required by statute, but also for practical reasons of justifying investments of taxpayer resources and ensuring as much as possible that whatever is procured will withstand the rigors of service in its intended military application. For GPS equipment, this includes not only the rigors of the physical environment but also those of the electronic environment, including threats of both unintentional and hostile interference and signal imitation. It is precisely that threat environment that presents the greatest danger to reliance on commercial GPS products in military applications.

The U.S. military and coalition forces have been fortunate from a PNT perspective over the last couple of decades in facing relatively unsophisticated adversaries with either limited access to or limited desire to routinely employ PNT countermeasure technology. Consequently, we have seemingly become complacent to the risks posed by overreliance on commercial-derivative PNT products. This complacency is apparent in the recent reporting from the Army’s forward-leaning Network Integration Evaluation (NIE) program, in which the Army assesses leading-edge commercial technologies and identifies those with great promise in order to fast-track them into operation, bypassing as much as possible the aforementioned DoD requirements and acquisition processes. 

At the same time, the Army gives a wink and a nod to the GPS security policies requiring use of encrypted military GPS signals for combat operations. It is a virtual certainty that if GPS drives the location-based applications in the commercial-derivative technologies evaluated by NIE, those applications are all powered by civilian GPS and not the encrypted military GPS. As noted, civilian GPS is frequently seen by those not thoroughly familiar with PNT technology as the cheap, expedient choice because more secure or integrated PNT sources are too expensive, too heavy, too much bother, and so on. 

It is also apparent, though not confirmed, that during NIE field testing, the opposing force toolkit does not include navigation warfare (NAVWAR) techniques for GPS jamming and spoofing. If it did, and if the test scenarios included active GPS jamming and spoofing, then the commercial location-based apps with civilian GPS as their input would not work or would derive erroneous solutions. In that case, the Army might have to reconsider its rapid deployment decisions for these vitally important devices. Clearly, it is not doing that.

The highly touted Rifleman Radio, advertised by the Army as a success, uses civilian GPS as its source of PNT information. The Army is planning to deploy tens of thousands of these radios for operational use over the next several years. While soldiers may be told or even admonished not to use the position and timing solutions derived from these radios for other than situational awareness — in other words, not to use them for direct combat or combat-support tasks — the likelihood of that policy being followed in the real world is nil. Either of necessity or for convenience, soldiers will use what is made available to them for whatever purposes they deem appropriate. That will be true whether the commercial-derivative PNT solution is in a smartphone or a Rifleman Radio. 

For the near term, that may not be a problem. However, at some point, in a contested environment against a knowledgeable adversary, mission effectiveness will be compromised and soldiers’ lives will be endangered by such devices. Further, proliferation of these devices will constrain our own commanders in their ability to employ offensive NAVWAR techniques that might be necessary to disrupt adversary use of open civilian GPS signals against our forces in the combat theater.

These statements are not mere speculation. The vulnerability of civilian GPS signals to unintentional interference and intentional jamming is well known. Reports of personal privacy devices interfering with reception of civilian GPS signals at Newark Airport provide a recent example (see “Personal Privacy Jammers,” page 28 in this issue). What is less well understood, but even more sinister in a combat environment, is civil GPS susceptibility to spoofing: the intentional creation of false, but believable, signals. 

In a recent interview with Fox News, Todd Humphreys, a well-regarded GPS researcher from the University of Texas, stated, “The civil GPS signal is completely open and vulnerable to a spoofing attack, because they have no authentication and no encryption. It’s almost trivial to mimic those signals to imitate them and fool a GPS receiver into tracking your signals instead of the authentic ones.” In a combat environment, such deception could result in mission failure or loss of life through loss of command-and-control communications in high tempo lethal actions, erroneous target designations, or misdirected fires.

All those who recommend providing soldiers in combat situations with PNT capabilities derived from civilian GPS, whether via smart phone, iPad, or Rifleman Radio, in lieu of or even in addition to their less convenient but more reliable military GPS devices, should reconsider that recommendation in light of the above. 

There is no argument to the statement that the DoD owes the warfighter more modern, integrated, compact, battery-efficient PNT devices incorporating military GPS. Those will come through the acquisition process, though not as fast as we all would like. In reality, a proliferation of civil PNT devices in military operations will likely delay further the availability of more suitable integrated military equipment. 

In the meantime, we should not be misled because of our experience in today’s war. Instead, we must plan for future actions in anti-access/area denial situations against knowledgeable adversaries. We cannot afford to undermine the warfighters’ cause in advance by advocating reliance on vulnerable and exploitable commercial GPS equipment that can get them killed.

Jules McNeff is vice president for strategy and programs for Overlook Systems Technologies. He served 20 years in the U.S. Air Force, and then was responsible for Defense Department management and oversight of the GPS program. He is a charter member of GPS World’s Editorial Advisory Board.

By Andrei M. Shkel, Defense Advanced Research Projects Agency (DARPA)

The aggregated DARPA Microtechnology for Positioning, Navigation, and Timing (micro-PNT) program is pursuing a new wave of innovation focused on bringing to life revolutionary ideas and fabrication technologies on micro/nano/pico/femto/atto scales, packaging, ultra-low-power electronics, innovative algorithms, never-before-explored architectures, and exploitation of new integration paradigms.

After about two decades of harmonic investment in developments, potential users of so-called small technology for positioning, navigation, and timing (PNT) applications increasingly ask, “Are we there yet?” Clearly, some significant advances have been made, and we see a footprint of the technology in an ever-growing consumer electronics market full of interactive products enabled by inertial and timing microtechnologies. These products include accelerometers for gaming applications, gyros for auto safety, resonators for clocks, and more.

The question remains, however: Is the technology really on the level of what we consider to be precision navigation and timing, that is, is it capable of achieving an accuracy level of at least 10 meters in position and 1 nanosecond in time throughout the entire duration of missions that may range from minutes to hours to days? In reality, small technology remains several orders of magnitude short with respect to long-term stability, dynamic range, and accuracy compared to conventional technology, which is already known to perform adequately for many military applications.

Why does making inertial instruments and clocks small necessarily lead to degradation in performance?

We don’t yet have a complete answer to this question, and we are still working hard to disprove the contention that high-performance inertial micro-instrument is a contradiction in terms. We can make things small, but we cannot yet make them sufficiently precise and uniform; the accuracy of lithography-based manufacturing is on the order of 10^–2–10^–3 (the ratio of the average defect to the smallest feature size), while the accuracy of conventional manufacturing utilizing precision machining is two to three orders of magnitude higher, on the order of 10^–5. We know we can deposit materials layer-by-layer with high precision, but we cannot make micro-devices truly 3D, as is readily achievable using conventional machining. We consistently have an excellent case for low-cost and bulk fabrication, but we cannot seriously challenge so-called boutique processes when it comes to achieving precision, structural complexity, and long-term stability.

We need new knowledge regarding the dimensional stability of materials. We also need a better understanding of material scaling, surface effects, energy-loss mechanisms, and the consequences of fabrication imperfections on the performance of micro-instruments.

PNT applications demand both unusual new fabrication technologies and new materials with special properties. To achieve the required phenomenal accuracy for precision navigation and timing, we need a new wave of innovation in design and refinement of many existing transducers. Future breakthroughs in microtechnology for PNT will likely rely on yet-to-be-exploited physics, new materials, highly specialized fabrication technologies and batch assembly techniques, selective wafer-level trimming and polishing, a combination of passive and active calibration techniques strategically implemented right on-chip, and introduction of innovative test technologies.

Need for Advanced Capabilities

PNT technology usage has doubled every five years since 1960, mostly due to GPS and the miniaturization of electromechanical components. Future PNT usage is expected to double every two years as a result of telecommunication, automobile navigation, robotics, and other commercial markets inserting micro-electromechanical systems (MEMS) technologies. The modern PNT paradigm is based on the assumption that space-based GPS is accessible most of the time to provide position, velocity, and timing information, enabling every user to operate on the same reference system and timing standard.

The size of an apple seed: The micro-PNT objective (conceptual illustration), a single-chip timing and inertial measurement unit, 8 mm³. (Click to enlarge.)

Today’s military systems increasingly rely on GPS, creating a potential vulnerability for U.S. and allied war-fighters should GPS be degraded or denied. When GPS is inaccessible, critical information with respect to position, orientation, and timing can only be gathered through self-contained onboard instruments: a local clock and two triads of inertial sensors (three accelerometers for position and three gyroscopes for orientation). The ideal solution would be a self-sufficient instrument not relying on any external information. Precision microscale clocks and inertial sensors are required to address the paradigm of self-contained PNT.

Clocks. Position and time have a relationship important to a broad spectrum of military applications, including communication systems that feature efficient spectrum utilization, resistance to jamming, high-speed signal acquisition, and an increase in the period of autonomous operation. Other important applications include surveillance, navigation, missile guidance, secure communications, identification friend-or-foe, and electronic warfare.

The emerging applications require new compact time-distribution systems technologies capable of achieving signal phase (time) common synchronization of better than 10^–9 seconds relative to the Coordinated Universal Time (UTC) standard; intersystem synchronization of less than 10^–8 seconds relative to battle group; and less than 10^–9 seconds for interoperability, surveillance, and high-speed communications. Solid-state and atomic oscillators are the key components enabling time and frequency distribution for communication, navigation, and command and control systems.

To support emerging applications, we are interested in clocks with

• signal phase (time) communication synchronization less (better) than 28 nanoseconds (ns) within 5 minutes (real time), UTC;
• intersystem synchronization less (better) than 28 ns relative to other system nodes within 5 minutes (real time); and
• local navigation/communication systems capable of time transfer less (better) than 28 ns, UTC.

The operational frequency mismatch (δf=f), where f is a nominal frequency and δf is a frequency deviation from the nominal, is a measure of oscillator quality and subsequently the quality of the frequency distribution system. Different applications can tolerate different levels of frequency mismatches. For example, for low-accuracy aircraft/land mobile platforms, the requirement for frequency mismatch is 10^–12, while for intermediate land reference sites the requirement is an order of magnitude smaller, 10^–13. For large time-division multiple-access (TDMA) systems, the tolerable frequency mismatch is on the order of 10^–11.

Small size, weight, and power (SWaP) are critical metrics for portable time and frequency distribution systems. The target performance characteristic for low-power clocks and oscillators is long-term stability (aging), which need to be less than 10^–11/month, with less than 1 W power consumption. It is desirable that the oscillators have small SWaP and preserve the level of long-term stability while surviving an inertial environment with accelerations on the level 10,000 g, where g is the gravity constant.

For comparison, the one-way satellite transmission from a GPS satellite in common view at two sites allows one to do accurate time transfer to within 10 ns, with a potential to achieve accurate time transfer of the order of 1 ns. Achieving an accuracy of time transfer on the level of 1 ns is loosely defined as precision timing.

Inertial Navigation Systems. The navigation-grade performance provided by inertial sensors is defined as an INS that accumulates an uncertainty in location not greater than one nautical mile (nmi), or 1.852 km, after one hour of navigation. The error in position is historically defined by the circular error probable (CEP) of 50 percent. The ability to achieve a CEP of 1 nmi in one hour (or 1 nmi/hour) does not translate to a unique performance requirement for a gyroscope and/or an accelerometer. Rather, it presents a trade-off in the overall inertial measurement unit (IMU) error budget. The trades can be generated within a family of gyroscope errors, such as gyro angle random walk (ARW) versus bias drift, or similarly within a family of accelerometer errors. For example, an IMU with gyroscope bias drift of 0.01º/hour combined with an accelerometer bias drift of 25 μg would guarantee a CEP of less than 1 nmi/hour, if no other errors are present. To generate the trade-off space for component performance, one efficient approach is to first generate the parameter space at the linear error covariance level, taking into account the bias drift of components, and subsequently perform  more extensive modeling in a bounded trade-off space by a nonlinear Monte Carlo simulation.

The ability to navigate and keep precise timing has been an important factor in defining the military and economic power of nations for at least a millennium. For almost a century, the development of high-performance inertial instruments has been an extensive area of research. It is anticipated that the following level of performance will soon be achieved, significantly reducing navigation errors and enhancing military capabilities, within the next 5 to 10 years:

• < 0.1 nmi/hour CEP for aircraft, vehicle, or spacecraft for attitude, guidance, and control;
• < 1.0 nmi in 30 hours for ships;
• < 0.4 nmi/hour CEP for missiles.

It is critical that future-generation INS systems be capable of operating through shock levels greater than 1,000 g.

Similar to clocks, the reduction of SWaP and cost (SWaP+C), while not compromising in performance, are the critical metrics for future development of IMUs. The current performance of state-of-the-art MEMS-based IMUs is on the level of tactical grade, with CEP approaching 100 nmi/hour. There is a great potential for achieving performance improvements that will subsequently enable platforms for personal navigation, precision navigation of small unmanned aerial vehicles (UAVs), unmanned underwater vehicles (UUVs), and GPS-free navigators for missiles. It is expected that the performance levels of chip-scale inertial instruments and clocks, shown in Table 1, could be achieved within the next 5 to 10 years, thus significantly enhancing military capabilities. The conservative estimations are projected by the Department of Defense’s Science and Technology List for Positioning Navigation and Timing. The aggressive estimates presume successful completion of the micro-PNT program described here.

Table 1. Projected performance of chip-scale inertial sensors and clocks by 2015.

The military has access to a currently specified accuracy of 21 meters (95 percent probability) from the GPS Precise Positioning Service (PPS). Accuracy can be improved after calibration for some of the GPS errors, for example, by utilizing optimal estimation techniques correlating GPS and INS signals. A CEP of less than 10 meters has been routinely achieved, with a potential to achieve accurate positioning on the order of 1 meter CEP.

Navigation, guidance, and automatic control are not the only military applications that could benefit from improvements in inertial sensors. Azimuth or north-pointing determination systems include celestial devices, magnetic compasses, and inertial sensors. Utilization of gyroscopes to precisely determine orientation has a number of benefits attributed to their immunity to magnetic fields, speed of acquisition, and potentially small SWaP+C. For this purpose, a variety of inertial equipment is being explored, including IMUs, attitude-heading reference systems (AHRS), and gyro-compasses. Providing an azimuth or north-pointing accuracy of less (better) than 0.5 arc minute multiplied by secant latitude has the potential to significantly enhance military capabilities for many targeting applications, especially for anticipated mobile platforms.

Initial prototype illustrating objective of the micro-PNT program.

Current Research

This section provides an overview of the ongoing efforts funded by DARPA (Defense Advanced Research Projects Agency) under the micro-PNT program.

Clocks. The potential payoff of the precision-clock technology developed by the program will enable ultra-miniaturized and ultra-low power absolute time and frequency references for applications such as nano/pico satellite systems, UUVs, UAVs, wristwatch-size high-security UHF communicators, and jam-resistant GPS receivers.

There are currently two efforts within the micro-PNT program involving the development of clocks: Chip-Scale Atomic Clock (CSAC) and Integrated Micro Primary Atomic Clock Technology (IMPACT).

The goal of the CSAC effort is to create ultra-miniaturized, low-power, atomic time and frequency reference units that will achieve, relative to present approaches: more than 200× reduction in size (from 230 cm³ to <1 cm³); more than 300× reduction in power consumption (from 10 W to less than 30 mW); and matching performance (1 × 10^–11 accuracy and 1 ns/day stability). This work, funded by DARPA since 2002, has been supporting 11 teams. The program is currently in its final phase and supports two performers, Symmetricom and Teledyne Scientific. Symmetricom has already demonstrated pilot units that are 1 cm³ in volume, consume on the order of 100 mW of power, and perform on the level of better than 30 × 10^–11 short-term 1 sec instability (Allan Deviation) and 5 × 10^–11/day (1.4 × 10^–10/month) long-term frequency drift.

The IMPACT program seeks to improve the stability and accuracy of microscale atomic clocks by as much as two orders of magnitude. Atomic-clock performance is affected by buffer gases (nitrogen or argon), which are necessarily present in either rubidium- or cesium-based atomic clocks. Buffer gas atoms interact with alkali atoms and effectively shift the resonant frequency of atoms. Emerging atomic-clock technologies based on laser-cooled atoms and trapped ions could overcome the limitations of CSAC.

The goal of IMPACT is to create miniaturized, low-power, integrated micro primary atomic clock technology that will achieve significant reduction in size relative to conventional clocks, but slightly larger than CSAC (volume less than 5 cm³ in final package, excluding battery); significant reduction in power relative to conventional clocks, but slightly greater than CSAC (50 mW); and two orders of magnitude increase in performance relative to CSAC (frequency accuracy 1 × 10^–13, Allan deviation at one-hour integration time, and stability characterized by 5 ns/day time loss). The work, funded by DARPA since 2008, currently involves four teams: Honeywell, Symmetricom, Sandia National Laboratories, and OE Waves.

The overall approach is based on sampling of atomic transitions at extremely low temperatures, requiring vacuum on the level of 10^–9 Torr and the ability to trap atoms in a small volume. The technology has been previously demonstrated on a large scale, but transferring the technology to small scale is far from trivial, requiring major innovations. The effort has already demonstrated magneto-optical trapping in a 16 cm³ atomic cell, and chip-scale clocks implemented using cold atoms performing on the level, quality factor × signal/noise ratio ∼ 2.6 × 10¹⁰, time loss after 1 ms equal to 10^–4 ns; after 1 second, 6 × 10^–3 ns; after 1 hour, less than 10 ns; and after 24 hours, on the order of 100 ns. Frequency retrace was demonstrated at the end of the phase on the level of 10^–11.

Inertial Sensors and Systems. There are currently three efforts within the micro-PNT program involving the development of inertial sensors and systems: Navigation-Grade Integrated Micro Gyroscopes (NGIMG), Micro Inertial Navigation Technology (MINT), and Information Tethered Micro Automated Rotary Stages (IT-MARS).

The NGIMG effort seeks to develop tiny, low-power, rotation-rate sensors capable of achieving performance commensurate with requirements for GPS-denied navigation of small platforms, including individual soldiers, unmanned (micro) air vehicles, unmanned underwater vehicles, and even tiny (for example, insect-sized) robots. By harnessing the advantages of microscale miniaturization, the NGIMG effort is expected to yield tiny (if not chip-scale) gyroscopes with navigation-grade performance characteristics: overall size less than 1 cm³ (no power source), power consumption less than 5 mW, ARW less than 0.001°/√hour, bias drift less than 0.01°/hour, scale factor stability on the order of 50 parts per million (ppm), full-scale range greater than 500°/sec, and bandwidth on the order of 300 Hz.

The NGIMG effort has been funded by DARPA since 2005, and work is currently being conducted by three teams: Northrop Grumman, Boeing, and Archangel Systems. The work has demonstrated several experimental prototypes (some, but not all, independently verified by the government) performing on the level of ARW 0.01°/√hour,  and bias drift 0.05°/hour.

The MINT effort seeks to develop microscale low-power navigation sensors that allow long-term (hours to days) precision navigation in GPS-denied environments. The goal is to create high-precision, navigation-aiding sensors that directly measure intermediate inertial variables, such as velocity and distance, to mitigate the error growth encountered by integrating signals from accelerometers and gyroscopes alone. In addition to aiding sensors such as velocity sensors, the combination of microscale inertial sensors will be integrated to a form-factor of one or two integrated circuits. Such an integrated sensor suite will be incorporated into the sole of a shoe for accurate and precise velocity sensing using zero-velocity events during walking.

The final goal of MINT is to achieve an overall package and form-factor for a velocity sensor (excluding IMU) of less than 1 cm³, power consumption for the velocity sensor of less than 5 mW, 1-meter position accuracy after 36 hours of walking, and 10 µmeter/second velocity sensing bias per step. The effort has been funded by DARPA since 2008 and involves work by four teams: Carnegie Mellon University, Analog Devices, Northrop Grumman, and Case Western Reserve University/University of Utah. To date, the work has demonstrated positioning error on the order of 4 meters after 30 minutes of walking.

The goal of the IT-MARS program is to implement and demonstrate a MEMS-fabricated rotary stage providing a rotational degree of freedom to planar MEMS structures and sensors, thus enabling free rotation of micro-structures and micro-sensors relative to the package, with coupled power and signal transfer from the rotating platform to the package. The IT-MARS effort may enable highly accurate calibration of inertial sensors and serve as a micro-platform for carouseling of inertial sensors that further enable on-chip calibration and gyro compassing. The ultimate program goal is to achieve an overall volume of no more than 1 cm3, power consumption for actuation on the order of 10 mW, angle position absolute accuracy to within 1 milli-degree, maximum wobble of 10 micro-radians, a rotation rate of 360°/second, and reliability (run time of rotor) greater than 104 hours.

This effort, which has been funded by DARPA since 2009, supports three teams: UCLA, UC-Berkeley, and the Boyce Thompson Institute. The work has already demonstrated free rotated platforms, and future efforts will focus on manufacturability and precision control of the stage-rotation and reduction of wobbling.

Figure 1. Range of missions versus speed of platforms for common Department of Defense (DoD) needs. The duration of missions ranges from seconds to minutes to hours. The majority of missile missions are fast, but less than 180 seconds (3 minutes) in duration. All missions with duration greater than 10 seconds typically use GPS. The Micro-PNT program seeks to develop a single-chip solution enabling self-contained inertial navigation (without the need for external signals such as GPS) for diverse DoD scenarios. (Click to enlarge).

New Initiatives

In January 2010, DARPA launched a coordinated effort focused on the development of microtechnology specifically addressing the challenges associated with miniaturization of high-precision clocks and inertial instruments. The new program, Microtechnology for Positioning, Navigation, and Timing (micro-PNT), aggregated the existing efforts (CSAC, IMPACT, NGIMG, MINT, and IT-MARS) and initiated four complementary new developments:

• Microscale Rate Integrating Gyroscopes (MRIG),
• Chip-Scale Timing and Inertial Measurement Unit (TIMU),
• Primary and Secondary Calibration on Active  Layer (PASCAL),
• Platform for Acquisition, Logging, and Analysis of Devices for Inertial Navigation & Timing (PALADIN&T).

The overall goal of the new aggregated micro-PNT program is to focus all of these complementary efforts toward achieving one specific overarching goal: self-contained chip-scale inertial navigation (see opening illustration). The reduction of SWaP+C of IMUs and timing units (TUs) is the technological objective. The developments consider a number of operational scenarios, ranging from dismounted-soldier navigation to navigation, guidance, and control (NGC) of UAVs/UUVs and guided missiles. The new micro-PNT initiatives will increase the dynamic range of inertial sensors, addressed by the new MRIG effort; reduce the long-term drift in clocks and inertial sensors, addressed by the PASCAL work; develop ultra-small chips providing position, orientation, and time information, addressed by the TIMU effort; and provide a universal and flexible platform for the testing and evaluation of components developed within the comprehensive micro-PNT program, addressed by the PALADIN&T effort.

The primary goal of MRIG is to create a vibratory gyroscope that can be instrumented to measure the angle of rotation directly, thereby extending the dynamic range and eliminating the need for integrating the angular rate information; MRIG will thus eliminate the accumulation of errors due to numerical/electronic integration.

The final goals are to:

• extend the dynamic range to 15,000°/second;
• achieve drift repeatability on the level of 0.1°/hour (angle dependent) and 0.01°/hour (bias-dependent) under variable –55°C to 85°C thermal conditions;
• achieve ARW of 0.001°/√hour, an operation range of 1,000 g with acceleration sensitivity of 10^–5 degrees/hour/g, vi
  bration sensitivity angle random walk of 0.01°/√hour per g/√Hz, and drift rate of 0.01°/hour per g²/√Hz.

These performance characteristics are thought to be achievable through development of precision 3-D fabrication technologies utilizing high-Q materials; development of wafer-level balancing and trimming techniques that reduce the effects of aniso-inertia (mass misbalance), aniso- compliance (stiffness misbalance), and aniso-damping (damping misbalance); and development of active control and an active calibration architecture.

These performers have been selected for the initial phase of the MRIG effort: Draper Labs, Honeywell, Northrop Grumman, Systron Donner, UC-Irvine, UC-Davis, UCLA, Cornell, University of Michigan, and Yale University.

The TIMU effort will address challenges associated with the development of a miniature (10 mm³), low-power (200 mW), high-performance (CEP on the order of 1 nmi/hour), and self-sufficient navigation system on-a-chip. The smallest state-of-the-art IMUs perform on the level of tactical-grade instruments (CEP on the order of 100 nmi/hour) and are about the size of an apple (more than 104 mm3). This effort intends to develop a technological foundation for a navigation-grade TIMU (CEP less than 1 nmi/hour and time accuracy of 1 nanosecond/minute) with a significant reduction in SWaP, potentially miniaturizing the TIMU to the size of an apple seed (10 mm³).

PASCAL will develop self-calibration technologies intended to eliminate long-term bias drift of inertial sensor and clocks. The grand challenge of this effort is to raise long-term bias stability to the level of 1 ppm.

This level of stability represents a two-orders-of-magnitude improvement compared to state-of-the-art inertial microsensors, currently at 200 ppm. The work will investigate an approach for fabricating sensors on an active layer that may serve as a calibration layer for micro-PNT systems.

The PALADIN&T effort will develop a universal platform for test and evaluation of early prototypes developed in the micro-PNT program. The effort will also simplify the uniform evaluation of pilot prototypes within the program and provide an early field demonstration, advancing the technology readiness level.

Conclusions

Current state-of-the-art microscale clocks and inertial instruments can provide the required level of precision only for missions having a duration of no more than about one minute. The micro-PNT program at DARPA is developing small SWaP+C inertial sensors for a variety of operational scenarios for missions ranging from minutes to hours. Current projects (CSAC, IMPACT, NGIMG, MINT, IT-MARS) mainly focus on navigation, characterized as missions of prolonged durations in relatively benign environments (a few hours of operation on a platform moving at relatively low speed, less than 100 km/hour).

The new initiatives (MRIG, TIMU, PASCAL, and PALADIN&T) target the challenges of missile guidance for precision engagement scenarios, short duration missions in highly dynamic environments (10 seconds to 3 minutes of operation at speeds of 1,000 km/hour and higher). Ongoing efforts and new initiatives explore new physical phenomena, high-quality factor materials, specialized fabrication technologies, and innovative approaches to system integration.

Disclaimer. The views, opinions, and findings in this article are those of the author and should not be interpreted as representing official views or policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the Department of Defense. The document GPS0911 [DISTAR case 17952] is approved for public release, distribution unlimited.

Andrei M. Shkel received a Ph.D. in mechanical engineering from the University of Wisconsin-Madison and is a program manager in the Microsystems Technology Office at the Defense Advanced Research Project Agency (DARPA), and on-leave professor of mechanical and aerospace engineering at University of California, Irvine, where he is also the director of the UCI Microsystems Laboratory. He holds 15 U.S. and international patents (12 pending) on micromachined angle-measuring gyroscopes, wide-bandwidth rate gyroscopes, light manipulators and tunable optical filters, and hybrid micromachining processes.

Troops take part in GPS handheld training with Ed Meyer.

Operation Waypoint, a Minnesota-based, non-profit program administered by American Legion Post 621, has broadened its program from a state and regional focus to national in scope with its new website, gpsfortroops.org.

Run by volunteers, the program is committed to increasing the safety of military men and women deploying to the Middle East with the guidance of highly accurate, handheld GPS units and mapping cards for Iraq and Afghanistan. Since its inception, Operation Waypoint has relied heavily on its partnership with GPS device manufacturer Lowrance to provide GPS products and charts to soldiers preparing to serve, as well as generous donations from service and social organizations and numerous individuals to fund the effort.

Operation Waypoint was started in 2005 by retired educator Ed Meyer after a former student, preparing for deployment to Iraq, contacted him to ask what type of GPS unit would be best for his mission. As the military only provides one GPS device per unit, which is usually mounted in a vehicle, Meyer contacted a friend at Lowrance, requested three GPS handheld devices, and trained the company commander and two former students how to use them.

Close Call in Baghdad. Shortly after the soldiers arrived in Iraq, while traveling at night, their 24-vehicle convoy took a wrong into a dangerous Baghdad neighborhood following the lead truck’s Army-issued GPS unit. Realizing the mistake, the convoy commander called Sgt. Gaylen Heacock, one of the soldiers equipped with a Lowrance GPS supplied by Meyer. Heacock’s device determined the correct route and was able to guide the convoy to safety. Upon hearing of how the Lowrance units aided in safety, Meyer worked through the American Legion Auxiliary and Post 621 to broaden the idea into a full not-for-profit program.

“Our goal is to spearhead an even larger movement where communities nationwide can directly support our troops in a very meaningful way,” said Meyer. “I believe that every soldier that feels a GPS would aid them in their mission in the Middle East should have one with them.”

With the enhancement of GPS accuracy and advanced features, today’s GPS units are even better suited to the challenges often seen by the military than when the program began. Operation Waypoint provides soldiers with Lowrance Endura Safari handheld GPS units that contain a precision GPS+WAAS antenna with 42-channel receiver and 3-axis magnetic compass to ensure troops have pinpoint accuracy for proper guidance or calling in air support when needed. The combination of the touchscreen, simple menus, and the ability to control one-handed or with gloves keeps usability fast and seamless, Meyer said. However, the most important benefit is the ability to store up to 2,000 waypoints for areas of safe passage, suspected insurgent buildings, and other items that are marked and identified with any of 193 different icons and then shared between GPS units over time or added to satellite maps.

“The [GPS] unit helped ensure the safety of crews while running convoys through the worst part of Iraq,” said Sgt. Heacock. “It’s helpful in pinpointing casualty evacuation points and points of hostile action.”

To date, Operation Waypoint is responsible for delivering more than 200 handheld devices into the hands of deploying soldiers. The St. Augusta American Legion accepts donations for Operation Waypoint and purchases its Endura Safari handheld GPS units directly from Lowrance. Lowrance also provides permission for the organization to copy and encrypt its Middle East mapping onto locally sourced microSD cards. While more work, this avoids packaging and operational overhead costs that would normally be seen by a manufacturer. Once the GPS and mapping cards are prepared, each participating soldier is personally trained on the GPS device and mapping before he or she takes it overseas.

“Each Lowrance GPS and chart card costs $115 after corporate discounts are factored in,” said Meyer. “Unfortunately, there are still times when we can’t purchase enough units. I have even given my personal GPS away, because I can’t imagine turning down a brave soldier. The challenge, as with most non-profits, is maintaining enough donations to support the program effectively.”

Operation Waypoint seeks to grow nationally by working with other American Legion Posts and organizations with a goal to provide a GPS device to every deployed unit. The Operation Waypoint website was redesigned to build awareness, make it easier for visitors to donate, and encourage other organizations to become partners in the project to provide GPS devices for soldiers in their own communities.

Operation Waypoint GPS handheld recipients.

The first time I ever heard of the Magnavox Research Laboratory in Torrance, California, was in 1966, as a young engineer working at Hughes Aircraft. We were building large (46-foot diameter) ground stations for the Defense Satellite Communications System (DSCS). Magnavox was supplying the secret anti-jam modems used in the terminals.

Because of this, I also learned a little about spread-spectrum pseudo-noise (PN), something quite esoteric at the time and not taught in engineering school. I noticed a widespread respect for Magnavox from my colleagues who referred to the company and its equipment as “Magicbox.”

Within a year I had transferred to the Hughes division responsible for developing satellites. We were working on a study known as 621B, for using satellites for positioning. Our teammate for the study was Magnavox. That team was responsible for the payload signal design, for which the team chose PN as the modulation to provide for multiple access, ranging, data transmission, and anti-jam.

Before long, my boss decided to leave Hughes and go work for Magnavox. He took two of his systems engineers with him. I was one of them.

In1968, the U.S. Air Force could not yet sell the 621B concept as an Advanced Development Program, so instead opted to experiment and prove that PN modulation could be used to accurately measure a half-mile of cable. Hughes bowed out since there wasn’t any satellite procurement in the offing. Magnavox and the other 621B contractor, TRW, each took on the challenge of measuring the cable.

Where Hughes had been 10-deep in Ph.D.s in every discipline, Magnavox was 10-deep in PN experts, which I believe at that time was the world’s majority. Thus it was natural for the Air Force to ask them to continue, and develop a receiver to be used in the next phase of 621B. An inverted range was set up with four PN transmitters, and an aircraft with the receiver and a bottom antenna flew over them. The aircraft’s position was determined using the PN range measurements and the known locations of the transmitters. The data from that receiver, called the MX450, was used to help justify the Department of Defense (DoD) decision to proceed into the Advanced Development Phase of GPS. Some of the people who contributed to this were named in Dr. Brad Parkinson’s recent articles on the origins of GPS. During that time I was working on the next generation of spread-spectrum modems for the DSCS.

Magnavox went on to develop these PN satcom modems for all three services, and thus was a natural choice to develop the first military GPS receivers (known as X and Y sets and the first Manpack), as well as the first C/A receiver, the Z set, and the very first spaceborne receiver called GPSPAC.

As soon as we completed the first Manpack, I approached Col. Paul Weber, the Joint Program Office Army Deputy Program Manger, and asked if he would pose with the Manpack on his back for a brochure we wanted to produce to show to potential Army and Marine Corps users. He agreed, dressed in his combat uniform, and went with our photographer into the wild woods of San Pedro (near the Port of Los Angeles) for the picture shown in the brochure.

Magnavox also developed the military GPS Engineering Models in competition with Rockwell Collins. Magnavox lost the production contract to Rockwell Collins a year after I left to join IEC, now known as L-3 Communications.

Magnavox also pioneered commercial GPS sets for use in the marine and survey markets. Today, you will still find many of the original GPS user equipment developers still at it as consultants and engineers at Raytheon, Navcom, Trimble, IEC, and others. Perhaps our most famous alumni is Dr. Min Kao, the “min” of Garmin.

Len Jaconbson

LEN JACOBSON is a consultant to the GPS industry and has served as an expert witness in many legal proceedings involving GPS. He is the author of the book GNSS Markets and Applications, published in 2007, and is a longstanding member of this magazine’s Editorial Advisory Board.