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October 5, 2008

EUPOS GNSS, DGNSS and Applications Symposium 2008

The International Symposium on Global Navigation Satellite Systems, Space-based and Ground-based Augmentation Systems and Applications 2008 will take place in Berlin at the EnergieForum, located in the middle of Berlin’s growing media centre between the “Ostbahnhof“ (East Train Station) and the Spree River.

Representatives from Europe, Japan, Africa and the United States will report on world-wide activities in civil use of satellite navigation, including:

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By Inside GNSS
August 24, 2008

Agricultural and Energy Prices Driving GNSS Products and Services

From the perspective of consumers, the yearlong rise in commodity prices — from oil and natural gas to corn and wheat — has clouded the economic outlook. But for producers, including many GNSS manufacturers and service providers, those clouds have silver linings.

Recent financial reports from companies active in agricultural and natural resource markets bear this out. GNSS products used to guide and control equipment are in heavy demand as are real-time differential correction services, particularly those using global satellite-based systems.

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By Glen Gibbons
August 14, 2008

Follow the Sun: GNSS and Solar Car Racing

Continuum, the University of Michigan’s solar car that raced 2,400 miles propelled by the amount of power used by a hair dryer, started out in Texas and never surrendered the lead until they reached their goal in Alberta, Canada, on July 22.

Continuum, the University of Michigan’s solar car that raced 2,400 miles propelled by the amount of power used by a hair dryer, started out in Texas and never surrendered the lead until they reached their goal in Alberta, Canada, on July 22.

But when did the five-time winners of the North American Solar Challenge 2008 (NASC 2008) decide it was a sure thing?
“I knew we had won when we crossed the finish line,” said Alex Dowling, head strategist for the space-age car built and driven by engineering students through the hot middle of North America. “Until then, I worried about an unforeseeable problem, such as a vehicle system failing. I didn’t count it as a victory until we crossed the finish line.”

Maintaining an average speed of about 46 miles per hour, the ultra-modern Continuum covered the distance from Plano, Texas, to Calgary, Alberta, in 51 hours, 41 minutes and 53 seconds. (See the sidebar, “The Race,” for more about NASC 2008.)

Solar Power

What does it take to propel a 650-pound car and driver on such a serious road trip? Well, the more sun the better for the car’s solar cells, which convert the small amount of solar energy that makes it through the atmosphere directly into electrical energy.

Located on the vehicle’s upper surface, the car’s solar array consists of 2,700 triple-junction gallium-arsenide solar cells — the same type found on satellite solar panels. Any energy generated by the solar array that is not used to drive the vehicle is stored in Continuum’s lithium-polymer batteries.

But it took more than sunlight to make a winner out of Continuum. It took planning, strategy, and close coordination among the race car driver, escort vehicles, and the University of Michigan support team — assisted in all three task by GPS positioning.

The Cloud Strategy

The Michigan team emphasized the importance of accurate GPS and route information to their success. “This helped us plan ahead and save extra energy in the battery for those nasty hills,” they said on their 2008 race blog.

About two months before the race, the Michigan students drove the route and surveyed it at a 10 Hz sampling rate using two donated, 20-channel L1 survey GPS receivers and a commercial satellite-based differential GPS (DGPS) service. Along the route, data such as latitude, longitude, quality of the GPS signal and heading were collected and stored on a laptop computer. The team also marked locations of hills, for later use in planning vehicle speeds.

The GPS receiver was not integrated with the computer used to record the route information. Instead, the GPS receiver output route data over an RS-232 (serial) connection to the laptop. The team developed software that records the GPS data onto its hard drive.

The DGPS service provider specifies a 10-centimeter real-time accuracy using its corrections, but the Michigan team didn’t need to verify these for the survey. “We care more about precision than accuracy for our application,” said Dowling. “If everything is off by one meter in the same direction, it doesn’t matter. We care about the differences in elevation.”

After the route survey, the GPS information was postprocessed using the team-developed software. The team overlapped the data from the route survey, which included coordinates of stop signs, speed limit changes, and so forth, into a digital mapbase. To help navigation during the race, a team member wrote a custom program inside of the mapping software to show the upcoming hazards on the race route, along with turn-by-turn directions and the location of other caravan vehicles.

The postprocessed data was also stored and used by the computer to run simulations during the race. Indeed, no fewer than three strategists, including Dowling, were running route simulations during the race.

These people rode in a “chase” car, the support vehicle following about 20 feet behind Continuum. Variables that the simulations took into account included radiation levels, cross-winds, grade of the road, current state of the vehicle’s battery, and weight of the vehicle. Sometimes multiple simulations were run using the same program, but with different weather patterns as inputs.

Dowling primarily used two simulation/optimization programs, each with different optimization algorithms that took into account various factors (one had more detail than the other) and took different amounts of time to run.

“I knew the advantages and shortcomings of each simulation technique and was able to make an educated guess about which simulation was closest to reality,” he said. With that information and other undisclosed inputs, Dowling was able to recommend a vehicle speed conducive to making the most efficient use of the available sunlight and stored energy in the battery.

The simulation and optimization software took into account the exact location of the vehicle.

Traveling the right speed at all times was a key to winning the race. Continuum couldn’t produce enough energy to run the entire distance at the speed limit, and the team faced a hard choice. If the car traveled fast under clouds, it risked drawing down too much battery power. On the other hand, running under clouds at the speed limit could help win the race and would move the car into sunny weather sooner, where it could gather more energy.

During the race, the GPS survey receiver was installed on the chase cars, but not on Continuum because it would have been extra weight on the vehicle. (It’s a race car, after all.)

The receiver was configured to output at 10 Hz and used a one-meter DGPS correction service during the race. The motor on Continuum contains a Hall Effect sensor that measured the speed of the vehicle.

Other support vehicles had simpler GPS navigation units on them. These units were used in conjunction with the navigation software described earlier to share the location of support vehicles with each other. This position data was transferred over the Internet using cellular Internet cards.

With the benefit of the GPS route survey, at any point in the race the team knew what terrain lay ahead of the race car and could budget Continuum’s energy better.

Dowling believes the Michigan strategy was superior to the other teams. “Lots of times we drove fast to get out of the clouds and were able to spend more time driving in the sun. Most of the other teams drove slowly in the clouds and were stuck under them for a longer period of time.”

Lead, Scout, Weather, and Chase

During the race, Continuum enjoyed the support of four escort vehicles. Running about a half-hour in front of the Michigan team, meteorology student Brad Charboneau transmitted weather forecasts from “Weather.” About 10 miles in front of Continuum, ”Scout” carried two relief solar car drivers and cleared the road of any foreign objects, including road kill, which might slow down or disable the ground-hugging solar car.

“Lead,” the vehicle carrying support engineering students, ran just in front of Continuum. Directly behind the solar car, “Chase” carried the three strategists, Michigan’s race manager Jeff Ferman, crew chief Doug Lambert, and an additional engineer as driver.

The team used two main modes of communication: radio or text-style messaging. The solar car driver had a radio for communications with the Lead and Chase vehicles. Lead and Chase could send text messages that appeared on a driver display. The driver then answered questions using “yes” and “no” buttons on the steering wheel.

Ferman said the Chase and Lead cars shared the same telemetry information, including speed of the solar vehicle, voltages and currents, and the battery pack reading. “Any power consumptions that we can read, we do read,” he said.

Under the Hood

Continuum runs on three wheels, like a large tricycle. The front wheel steers and drives the car.

The driver adjusts the vehicle’s speed using a throttle paddle (potentiometer) on the steering wheel — a small lever that can be depressed with the thumb. The vehicle’s electrical system processes this signal and adjusts the output of the vehicle’s motor according, which causes the vehicle to either accelerate, decelerate or maintain speed.

The team’s strategists also have the ability of sending a cruise-control command to the vehicle. If the driver accepts the new cruise control speed, the vehicle automatically adjusts. Continuum’s motor is also capable of regenerative braking. In addition, the vehicle has custom disk brakes.

During the race, teams drove from 8 a.m. until 6 p.m. each day over a 10-day period. In the morning and evening, they were permitted to charge their main battery using only their solar array. Continuum was very competitive in almost every area, said Dowling, with an efficient battery pack and electric motor, a powerful solar array, and an aerodynamic body.

The car had already competed in the World Solar Challenge held during the summer of 2007 in Australia. It had finished seventh, despite a serious accident on the first day.

“Our team spent the past year perfecting the car while other teams were still building their vehicles,“ Dowling said, “So, Continuum was very reliable, and we spent only minimal time on the side of the road during the race.”

About the Race

Fifteen solar cars from universities in the U.S., Canada, and Germany completed in North American Solar Challenge (NASC) 2008, sponsored this year by Toyota, the DNA Group, and Crowder College Missouri Alternative and Renewable Energy Technology (MARET) Center.

The 18-year-old event is designed to inspire young people to pursue careers in science and engineering. And with each race, the solar cars travel faster and further with greater reliability.

NASC’s predecessors, the American Solar Challenge and Sunrayce, were underwritten by the U.S. Department of Energy until funding was cut in 2005. The race generally has been held every two years since 1990.

This year, the race was run in five stages over the course of 10 days. The University of Michigan, whose team is profiled here, is a seasoned veteran of the competition. The 2008 winner, Continuum, is their ninth solar-powered vehicle. It beat the second-place entry — Ra 7 from Principia College in Illinois — by 10 hours.

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May 27, 2008

Topcon Draws on GNSS Expertise to Build Leadership

Recent leadership appointments at Topcon Positioning Systems (TPS) reflect the company’s efforts to expand its focus from being a vendor of equipment for surveying, civil engineering, and construction to a broad-spectrum provider of positioning solutions drawing heavily on GNSS-based technologies.

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By Glen Gibbons
May 1, 2008

Hemisphere GPS Reports Record Revenues, Profits in First Quarter

Hemisphere GPS has reported US$25.9 million in revenues for the first quarter of 2008, an increase of 56 percent from the year-earlier period (US$16.7 million) and a record for the company.

The company also reported record first quarter net income of $5.8 million, or $0.11, an increase of 169 percent compared to $2.2 million, or $0.05 per share, in the first quarter of 2007.

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By Glen Gibbons
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October 21, 2007

Pat Fenton: GNSS from the Outside In

Patrick Fenton’s career as the guiding mind behind the design of six generations of breakthrough GNSS receiver technologies began the moment he realized his hobby — computer programming — might end the need for surveyors to spend long evenings reducing and verifying the data they collected each day.

Patrick Fenton’s career as the guiding mind behind the design of six generations of breakthrough GNSS receiver technologies began the moment he realized his hobby — computer programming — might end the need for surveyors to spend long evenings reducing and verifying the data they collected each day.

It was the summer of 1981. Fresh out of the University of Calgary’s survey engineering program, Fenton was enjoying a taste of what he’d envisioned would be a “professional outdoor career” as a rookie land surveyor for ShellTech Surveys, a now defunct division of Shell Canada.

“We would spend all day turning the angles and measuring for a road project,” he said. “Then, evenings we would spend hours reducing the data and making sure it was all correct. I was able to hop on the computer and get that done for the crew very quickly.”

Fenton’s inspired effort ended his work outdoors. “They told me to stay in the office and develop the software,” he recalled. “From then on I worked on processing the data and developing equipment that would make their jobs easier.”

When the oil crunch hit, ShellTech was sold in January 1982 and became Nortech Surveys Ltd. Fenton worked on a number of high-tech survey systems for the oil exploration industry, including INS, microwave ranging, and GPS. He became software manager of a Nortech subsidiary, Norstar Instruments.

“At the time, there wasn’t a suitable GNSS instrument on the market that met the needs of Nortech; so, the management decided that we had the talent to jump into the survey instrument business,” Fenton said. “We did create a very nice product; however, we lacked knowledge in high quality manufacturing. Each one we built was a little bit different.”

A Better Mouse Trap

NovAtel, then a giant in Canada’s cell phone industry, acquired the NorStar division in 1989.

“The combination of skills at NovAtel was exactly what was needed for our GPS products, that is RF, software and production engineers, DSP chip designers, and marketing experience,” Fenton said. “At NovAtel, we completely redesigned the receiver from the antenna down.”

At about the same time, Fenton hit upon an insight that led to an industry first: true sub-meter pseudorange positioning capability.

“I realized that the signal processing design and tracking loops within the GNSS receivers of that day were optimized for maximal signal power to signal processing complexity ratio,” he explained. “They were not optimized for range or carrier phase tracking accuracy — the elements driving position accuracy. It was during this period that I came up with the Narrow Correlator concept.”

His invention, commercialized into the GPS1001 receiver in 1991, was five times more precise than the previous technology. It received the Better Mouse Trap Award that year from the Institute of Navigation (ION).

Today Fenton is vice-president and chief technology officer (CTO) for NovAtel, which has become a leading provider of GPS and augmentation components and subsystems designed for rapid integration into an endless variety of high precision, commercial applications.

At the tender age of 49, he holds 15 patents and has authored more than 20 technical articles for the ION. So significant are his contributions to the evolution of GNSS that his peers have recognized him with the ION Satellite Division’s highest honor: the Johannes Kepler Award.

Fenton is also known for projects that have significantly improved receiver capability to allow reliable positioning and precise navigation even in obstructed environments where GPS alone doesn’t work. Marine, mining, precision agriculture, and surveying and mapping are among the applications benefiting from such advancements.

On the Fast Track

For example, he has spent several years leading a small team that is integrating inertial measurement units with NovAtel’s GNSS receivers. The results of their success using digital terrain modeling (DTM) techniques to improve precise position output availability are showcased during telecasts of NASCAR and IndyCar races.

“Our challenge was to provide Sportvision a continuous stream of time-tagged position and velocity measurements from each race car,” Fenton said. “Sportvision uses this information to annotate the TV camera image stream with details such as the driver’s name, speed, and lap time while the race is underway.”

Sounds simple enough. But NASCAR tracks presented formidable challenges for radio frequency coverage, the lifeblood of GNSS technology.

“In addition to lots of steep bleachers there are cat walks around and over the track,” Fenton explained. “Probably the worst obstacle was the steel mesh catch fence that completely surrounds and overhangs the track. When the cars are up against the wall, more than half the sky is blocked by the catch fence.”

No sky, no satellite coverage. Not only that, but the tracks are very short. Laps can take as little as 15 seconds. “When a car is halfway around the track, it has blocked the other half of the sky. In this case, as a result, we could never lock in a satellite for more than 10 seconds.”

Using a DTM of the NASCAR track, Fenton’s team was able to constrain a car’s position. “This algorithm acted like an additional satellite and improved the availability substantially,” he explained. “But it wasn’t until we added integrated IMUs [inertial measurements units] that we were able to deliver 100 percent position and velocity availability.”

Fenton’s hallmark is a knack for finding and integrating technologies that drive powerful new applications. During the mid-1990s, as he rose from chief engineer to director of research and development, he was instrumental in NovAtel’s acquisition and commercialization of the MEDLL (Multipath Estimation Delay Lock Loop) technology, licensed from Delft University. WAAS, the U.S. Federal Aviation Administration’s Wide Area Augmentation System, and the European Geostationary Navigation Overlay Service (EGNOS) use it.

This powerful combination of scientific chops and market acumen earned Fenton a vice presidency in 1997 and the additional title of CTO in 2003. He was appointed to NovAtel’s board of directors in 2005.

The company’s latest generation OEMV series of GNSS receivers, released last year, illustrates the exponential changes in core technology that occur between versions. NovAtel’s “system on a chip” now has more than four million gates, almost eight times as many as its predecessor.

Fenton, who grew up in Canada’s capitol (Ottawa) has retained his zest for the outdoors including a passion for photography. He met his wife Tanis through her brother, a skiing buddy. They have three children; two in college and one in high school, and the entire family takes full advantage of Alberta’s rich recreational opportunities.

But even in the remotest glacier field, Fenton never completely loses touch with GNSS. Each winter he and a group of friends rent a backcountry hut and helicopter in for a week of alpine skiing. “Four times in our lives we’ve been up in a whiteout,” Fenton said. “We were able to navigate back to the hut with GPS.”

Fenton’s coordinates:
N51 06’ 59” W114 02’ 18”


Engineering Specialties
System conceptualization, GNSS receiver design and signal processing, multipath mitigation techniques, and firmware development.

His Compass Points
• Home and family: wife Tanis and three children, household activities, weekend trips, summer vacations, extended family, and friends
• Career: applied technology, mentoring, teamwork, business relationships, learning, and change
• Hobbies: photography, and outdoor activities

Favorite Equation
This formula is a derivative of the Central Limits Theorem. It’s a simple formula but I use it all the time to estimate expected signal-to-noise ratio levels at the output of hardware correlators at various stages of designing GNSS receivers.

GNSS “Aha” Moment
In the summer of 1985, I started developing position processing software from data Nortech had collected from their various survey operations. I realized that I could make a significant contribution.

First Significant GNSS Achievement
I came up with the Narrow Correlator concept. This technique made for a five-fold improvement in pseudo range accuracy, leading the way to reliable sub-meter positions.

GNSS Mentor
Probably the single person that I’ve learned the most from in GNSS over the years is Dr. A.J. Van Dierendonck. He was the chief scientist with Stanford Telecommunications Inc. where we were sourcing GPS receiver channels for the first GPS product I was involved with in 1986. He has been a technical consultant with us, periodically, for nearly 20 years.

GNSS Event that Most Signifies That GNSS had “Arrived”
I think the first Gulf war with all the publicity and TV images of the smart weapons provided a huge boost to the popularity and awareness of GNSS. Before that time, I always had to explain what GPS was. After that time, everyone seemed to have a good appreciation for what GNSS was.

Influences of Engineering on His Daily Non-Work Life
My engineering mind is always churning. For example, over the last couple of years my wife and I built an energy-efficient house. I was heavily involved with all the engineering aspects of that; producing all the CAD construction drawings, design of all the mechanical systems including the in-floor geo-thermal heating system, and the networks for phone and internet connectivity to all the rooms.

Popular Notions about GNSS That Most Annoy
The notion that GNSS will work deep indoors, under ground, or under water – perhaps for oil exploration at the bottom of a drill tip or for diving. If you can’t pick up FM radio, then most likely your GPS won’t work.

Favorite Non-GNSS Activities
Winter: skiing, snowboarding, alpine touring
Spring/Summer/Fall: cycling, canoeing, camping, sailing, fly fishing
All seasons: photography

What’s Next
There are several possibilities. The first would be multi-constellation, multi-frequency GNSS. This is where a single receiver tracks multiple satellite constellations (GPS, Galileo, GLONASS, etc.) and provides a blended robust position solution. The second may come from time of arrival (TOA) positioning of cellular phone tower signals. The density of cell phone towers is continuing to increase. At a certain point, the use of TOA processing of cell signals will rival consumer GPS for the large urban and indoor markets.


Karen Van Dyke: Re-Engineering the Airways

Karen Van Dyke at Glacier Bay National Park near Juneau, Alaska

Karen Van Dyke probably isn’t someone you’d expect to see driving around Virginia with one hand piloting the steering wheel and the other gripping a map. But for Van Dyke, an electrical engineer who wryly describes herself as “geographically challenged,” the maps piled on her passenger seat remain a lifeline even though two years have passed since she moved from her native Boston to Washington D.C.

“It’s my GPS secret,” she admits. “When I get lost, I tell my husband that’s why I work in this field.”

Karen Van Dyke probably isn’t someone you’d expect to see driving around Virginia with one hand piloting the steering wheel and the other gripping a map. But for Van Dyke, an electrical engineer who wryly describes herself as “geographically challenged,” the maps piled on her passenger seat remain a lifeline even though two years have passed since she moved from her native Boston to Washington D.C.

“It’s my GPS secret,” she admits. “When I get lost, I tell my husband that’s why I work in this field.”

Why doesn’t one of the profession’s leading innovators have GPS in her car? The answer reveals just how recently GPS has come into its own. “When I bought my car in 2001, adding a navigation system wasn’t an option,” she explains. “I’d gladly have paid extra for it.”

Since then, GPS has vaulted the divide between geek speak and consumer chic. “Legislation has brought it into our cell phones. The world’s banks rely on it to time stamp their transactions,” says Van Dyke. “Eventually, coordinates will be part of every product and process in our lives – but first GPS must be improved and integrated with other technologies in order to achieve accurate positioning, navigation, and timing (PNT) information anytime and anywhere.”

That challenge keeps Van Dyke on her toes in her work for the U.S. Department of Transportation (DOT). Her specialty: incorporating GPS into the transportation infrastructure for various applications.

Little did she know, when she accepted a summer research job following her graduation from the University of Lowell in 1988, that she was sealing her professional fate. Her professor, Dr. James Rome, was doing a project for the John A. Volpe Transportation Systems Center looking at whether a new system, GPS, might reduce aircraft separation on the North Atlantic routes by providing position information where there was no radar coverage.

“That summer gave me an opportunity to learn about GPS, which I found to be a fascinating technology with tremendous future applications,” Van Dyke says. By summer’s end, she was hired by Volpe, part of the DOT Research and Innovative Technology Administration (RITA).

She says her engineering mentor, Frank Tung, modeled a well-rounded approach toward the profession. Tung was director of aviation programs when she joined Volpe and has since retired. “He always emphasized enjoying what you work on and ensuring that your work contributed to making a positive difference for the organization and transportation community,” she says.

For Van Dyke, one of the most enjoyable aspects of her work is its global nature.

“Many countries have approached the Volpe Center for assistance with development of similar satellite outage reporting systems for air navigation – especially third world countries that do not have the sophisticated ground-based infrastructure that the U.S. has,” she says. “The cost-effective and innovative benefits that GNSS technology can provide to them are tremendous.”

Van Dyke is a Fellow and past president of the Institute of Navigation (ION) whose many publications include collaborating on the first and second editions of the book, Understanding GPS: Principles and Applications. She has received the Meritorious Achievement Award (Silver Medal) from the Secretary of Transportation, the Superior Achievement Award (Bronze Medal) from the Research and Special Programs Administrator, and the ION Early Achievement Award.

She has helped spearhead many innovations – including these personal favorites:

GPS RAIM Outage Reporting Systems

Van Dyke led the Volpe Center team that designed, developed, and implemented GPS RAIM satellite outage reporting systems for both the U.S. Air Force and the FAA. These receiver autonomous integrity monitoring systems brief GPS availability to pilots during pre-flight planning to support use of TSO C129a receivers.

“Subsequently, similar work was performed for Australian, German, and Chilean aviation authorities on the implementation of systems for use by pilots and air traffic control in those countries,” she says.

Prior to commissioning the GPS Wide Area Augmentation System (WAAS) in 2003, she led a team that supported the FAA in development of the WAAS prediction model and integration into the air traffic control system to supply Notice to Airmen (NOTAM) information for all phases of flight, including precision approaches.

Reducing Vulnerability

In 2001, she participated in a Volpe Center project that produced sixteen recommendations for reducing the vulnerability of the transportation infrastructure that relies on GPS. The project was done in response to the President’s Commission on Critical Infrastructure Protection.

The team’s study of GPS civilian aviation, maritime, and surface uses assessed the effects of GPS outages and recommended steps to minimize the safety and operational impacts of both short and long term disruptions.


Van Dyke headed the Volpe Center team that developed the prototype traceability requirements tool for the GPS Joint Program Office. That led to the creation of an internal website whose acronym is GPS STARWEB, or GPS Specifications Traceability and Analysis of Requirements. STARWEB uses DOORS software – Dynamic Object Oriented Requirements — for its integrated database that establishes relationships and traceability of requirements within the GPS system.

“This equips the civil GPS community with the information necessary for informed decision making,” she says.

Currently, Van Dyke has several projects going at once. Recently, she has been supporting development of GPS III, evaluating the specifications for the future space and control segment.

She’s also working with the Federal Railroad Administration and Ohio University on the High Performance Nationwide Differential GPS initiative to evaluate whether it can be designed to meet requirements for Positive Train Control and other high accuracy applications.

Another collaboration addresses the potential use of WAAS for maritime applications. She heads a Volpe Center team that is working with Innovative Solutions International (ISI) to develop a GNSS Performance Monitoring System (GPMS) for the Brazil Aviation Authority. This system is responsible for ensuring that satellite-based systems provide a continuous, safe, and reliable signal-in-space (SIS) for navigation users.

And, with all that, she still finds time to volunteer. She has been the air navigation technical representative for the Institute of Navigation (ION) since 1992 and served as ION’s eastern region representative and president (2000-2001).

Lisa Beaty, ION’s director of operations, says “Karen’s international technical reputation precedes her, but many people may not know about her countless hours of volunteer service within the navigation community, including fostering the development of programs for the next generation of navigation professionals.”

Van Dyke’s coordinates:
39° 38.921 N 077° 08.231 W



Engineering Specialties
Identifying positioning, navigation, and timing (PNT) requirements for transportation applications, as well as development and deployment of GPS monitoring and service prediction tools.


Favorite Equation
The Keplerian parameters describing orbital motion. Most of the applications we have developed for GPS prediction systems and the analysis begins with modeling the GPS constellation performance based on Keplerian motion, Van Dyke points out.


First Significant GNSS Achievement
Back when there wasn’t a full constellation of satellites, Van Dyke was part of the Volpe Center project team that helped develop Receiver Autonomous Integrity Monitoring (RAIM) algorithms to predict the availability of GPS integrity for oceanic through non-precision approach phases of flight. The limitation was availability of service, which then led to development of the augmentation systems.


Her Compass Points
Engineer husband Ken Kepchar is, “one of those people who was born with a built-in navigation sensor.” They met at the GPS Joint Program Office at the Los Angeles Air Force Base.

Rather than follow the herd into high tech computer firms when she finished engineering school, Van Dyke’s fascination with early GPS technology led her to take a position with the John A. Volpe Transportation Systems Center.

The University of Lowell (Massachusetts) where she earned her bachelor’s and master’s degrees in electrical engineering (1988 and 1991).

Knew GNSS had Arrived When . . .
“When I first began working on GPS, my friends and family had never heard of it. I would have to explain what the acronym GPS stood for, what the system was, and the various applications of the technology. Over time, my friends and family began telling me about GPS applications they had read about in the paper or seen on the news. Now that the term GPS is commonly used in the media – it has arrived!

Popular Notion about GNSS That Most Annoys
“It is disappointing when I hear someone in the international community say that the U.S. Department of Defense can turn off GPS anytime they want. It is simply not true. The U.S. government has worked very hard to establish national space-based positioning, navigation, and timing (PNT) policy with a coordination office, headed by a civilian, with civil and military representation. The national space-based PNT Executive Committee is co-chaired by the Deputy Secretaries of Transportation and Defense.”

Consumer Engineering Wish List
“My own on-board navigation system with voice is number one on my Christmas list.”

What’s Next
Integration of GPS with other navigation sensor technology and development of a net-centric approach for reliable distribution of PNT information.

July 1, 2006


Europe and the United States are on the verge of a very important decision about their plans to implement a common civil signal waveform at the L1 frequency: Should that waveform be pure binary offset carrier — BOC(1,1) — or a mixture of 90.9 percent BOC(1,1) and 9.09 percent BOC(6,1), a combination called multiplexed BOC (MBOC). The desire for a common civil L1 signal is enshrined in a 2004 agreement on GNSS cooperation between the United States and the European Union (EU).

Europe and the United States are on the verge of a very important decision about their plans to implement a common civil signal waveform at the L1 frequency: Should that waveform be pure binary offset carrier — BOC(1,1) — or a mixture of 90.9 percent BOC(1,1) and 9.09 percent BOC(6,1), a combination called multiplexed BOC (MBOC). The desire for a common civil L1 signal is enshrined in a 2004 agreement on GNSS cooperation between the United States and the European Union (EU).

For the EU and the European Space Agency (ESA), that decision — and its consequences — will come sooner: with the Galileo L1 Open Service (OS) that will be transmitted from satellites to be launched beginning in the next few years. For the United States, the waveform decision will shape the design of the L1 civil signal (L1C) planned for the GPS III satellites scheduled to launch in 2013. For a background on the process that led to design of the GPS L1 civil signal and its relevance to the BOC/MBOC discussion, see the sidebar L1C, BOC, and MBOC.

The May/June issue of Inside GNSS contained a “Working Papers” column titled, “MBOC: The New Optimized Spreading Modulation Recommended for Galileo L1 OS and GPS L1C”. Authored by members of a technical working group set up under the U.S./EU agreement, the article discussed the anticipated MBOC benefits, primarily improved code tracking performance in multipath. The column also noted that, while lower-cost BOC(1,1) receivers would be able to use MBOC, it would come at the cost of a reduction in received signal power.

An article in the “360 Degrees” news section of the same issue of Inside GNSS noted that some GNSS receiver manufacturers believe MBOC is not best for their applications and perhaps should not have been recommended. (This point was noted on page 17 of the May/June issue under the subtitle “MBOC Doubters.”) See the sidebar “Other Observers” (below) for additional comments from companies with concerns about MBOC recommendation.

This article, therefore, continues the discussion of a common signal waveform by asking several companies with different product perspectives whether they consider the proposed MBOC waveform to be more or less desirable for their applications than the BOC(1,1). Currently, BOC (1,1) is the baseline defined in the June 26, 2004, document signed by the U.S. Secretary of State and the vice-president of the European Commission (the EU’s executive branch): “Agreement on the Promotion, Provision and Use of Galileo and GPS Satellite-Based Navigation Systems and Related Applications.”

Maximum benefit from MBOC will be obtained by receivers using recently invented technology that employs computationally intensive algorithms. Although such receivers clearly will provide benefits to their users because of the BOC(6,1) component of MBOC, the practical value of the benefits have not been quantified, which is one purpose of the questions raised in this article. For the moment, let’s call all these prospective MBOC users “Paul”.

Meanwhile, patents on the most widely used multipath mitigation technologies today, such as the “narrow correlator” and the more effective “double-delta” techniques, will expire about the time the new signals are fully available, making these techniques more widely available. Unfortunately, the double-delta technology cannot use the BOC(6,1) component of MBOC. In addition, narrowband receivers, which today dominate consumer products, also cannot use the BOC(6,1). Let’s call all these users “Peter”.

Therefore, the fundamental question raised by this article is whether we should rob Peter to pay Paul. If the amount taken is quite small and the benefits are large, then the answer should be “yes.” If the amount taken creates a burden to Peter, now and for decades to come, with little benefit to Paul, then the answer should be “no.” The in-between cases are more difficult. The purpose of this article is to explore the tradeoffs.

To address this issue, we invited engineers from companies building a range of GNSS receivers to take part in the discussion. We’ll introduce these participants a little later. But first, let’s take a look at the technical issues underlying the discussion.

BOC/MBOC Background

The RF spectrum of a GPS signal is primarily defined by the pseudorandom code that modulates its carrier and associated data. A pseudorandom code appears to be a completely random sequence of binary values, although the sequence actually repeats identically, over and over.

For the C/A code on the L1 frequency (1,575.42 MHz), the state of the code (either +1 or –1) may change at a clock rate of 1.023 MHz. We call this binary phase shift keying, or BPSK(1), meaning BPSK modulation with a pseudorandom code clocked at 1.023 MHz. Note that the bits of a pseudorandom code often are referred to as “chips,” and four BPSK chips are illustrated at the top of Figure 1. (To view any figures, tables or graphs for this story, please download the PDF version using the link at the top of this article.)

Among many other topics, the 2004 U.S./EU agreement settled on a common baseline modulation for the Galileo L1 OS and the GPS L1C signals: BOC(1,1). (The BOC(n,m) notation means a binary offset carrier with n being a 1.023 MHz square wave and m being a 1.023 MHz pseudorandom code.) Like BPSK(1), the BOC(1,1) waveform also is a BPSK modulation, meaning there are only two states, either a +1 or a –1. The timing relationships of the code and the square wave are illustrated by Figure 1.

Although the agreement defined BOC(1,1) as the baseline for both Galileo L1 OS and GPS L1C, it left the door open for a possible signal “optimization” within the overall framework of the agreement. As documented in the paper by G.W. Hein et al., “A candidate for the GALILEO L1 OS Optimized Signal” (cited in the “Additional Resources” section at the end of this article) and many other papers, the EC Signal Task Force (STF) after much study initially recommended a composite binary coded symbols (CBCS) waveform.

Because the agreement made it desirable for GPS L1C and Galileo L1 OS to have an identical signal spectrum and because GPS III implementation of CBCS would be difficult, a search was made by a joint EC/US working group to find an optimized signal that was acceptable for both GPS and Galileo. The result is MBOC (discussed in the May/June “Working Papers” column and the like-named IEEE/ION PLANS 2006 paper by G. W. Hein et al. cited in “Additional Resources.”).

Like all modernized GPS signals — including M-code, L2C, and L5 — L1C will have two components. One carries the message data and the other, with no message, serves as a pilot carrier. Whereas all prior modernized GPS signals have a 50/50 power split between the data component and the pilot carrier, L1C has 25 percent of its power in the data component and 75 percent in the pilot carrier.

The L1C MBOC implementation would modulate the entire data component and 29 of every 33 code chips of the pilot carrier with BOC(1,1). However, 4 of every 33 pilot carrier chips would be modulated with a BOC(6,1) waveform, as illustrated in Figure 2. The upper part of the figure shows 33 pilot carrier chips. Four of these are filled to show the ones with the BOC(6,1) modulation. Below the 33 chips is a magnified view of one BOC(1,1) chip and one BOC(6,1) chip.

The BOC(1,1) chip is exactly as illustrated in Figure 1 while the BOC(6,1) chip contains six cycles of a 6.138 MHz square wave. With this image in mind, we can easily calculate that the pilot carrier has 29/33 of its power in BOC(1,1) and 4/33 of its power in BOC(6,1). Because the pilot carrier contains 75 percent of the total L1C signal power, then the percent of total BOC(6,1) power is 75 × (4/33) or 9.0909+percent. Conversely, the data signal has 25 percent of the total L1C signal power; so, the calculation of BOC(1,1) power is 25 + 75 × (29/33) or 90.9090+ percent.

Because the Galileo OS signal has a 50/50 power split between data and pilot carrier, the implementation is somewhat different in order to achieve the same percentages of BOC(1,1) and BOC(6,1) power. For the most likely time division version of MBOC for Galileo, 2 of 11 chips in the pilot carrier would be BOC(6,1) with none in the data component. Thus, the percent of total BOC(6,1) power is 50 × (2/11) or 9.0909+ percent. Similarly, the percent of total BOC(1,1) power is 50 + 50 × (9/11) or 90.9090+ percent. This makes the spectrum of Galileo L1 OS the same as GPS L1C.

Code Transitions. The fundamental purpose of MBOC is to provide more code transitions than BOC(1,1) alone, as is evident in Figure 2. (A code loop tracks only the code transitions.) However, these extra transitions come on top of the increased number in BOC(1,1) compared to the L1 C/A signal.

Taking into account that the pilot carrier has either 75 percent of the signal power with GPS or 50 percent with Galileo, GPS with BOC(1,1) has 2.25 times more “power weighted code transitions” than C/A-code (a 3.5-dB increase). Galileo with BOC(1,1) has 1.5 times more (a 1.8-dB increase). MBOC on GPS would further increase the net transitions by another factor of 1.8 (2.6-dB increase), and the most aggressive version of MBOC on Galileo would increase the net transitions by a factor of 2.2 (3.4-dB increase).

Therefore, given the improvement of BOC(1,1) over C/A code, the question raised by this article is whether a further improvement in number of transitions is worth subtracting a small amount of signal power during all signal acquisitions, for all narrowband receivers, and for all receivers using the double-delta form of multipath mitigation.

A portion of Table 1 from the May/June “Working Papers” column is reproduced here, also as Table 1. Of the eight possible waveforms in the original table, only three are included here. These are representative of all the options, and they include the two versions of MBOC considered most likely for implementation in Galileo and the only version GPS would use.

Two new columns have been added in our abbreviated version of the table. The first is an index to identify the particular option, and the last identifies whether GPS or Galileo would use that option.

Receiver Implementations

Most GNSS receivers will acquire the signal and track the carrier and code using only the pilot carrier. For GPS L1C this decision is driven because 75 percent of the signal power is in the pilot carrier. Little added benefit comes from using the data component during acquisition and no benefit for code or carrier tracking, especially with weak signals.

For Galileo, the decision is driven by the data rate of 125 bits per second (bps) and the resulting symbol rate of 250 symbols per second (sps). This allows only 4 milliseconds of coherent integration on the Galileo data component (compared with 10 milliseconds on the GPS data component). Because coherent integration of the pilot carrier is not limited by data rate, it predominantly will be the signal used for acquisition as well as for carrier and code tracking.

Reflecting the reasons just stated, Figure 3 compares the spectral power density in the pilot carrier for each of the three signal options listed in Table 1. In each case the relevant BOC(1,1) spectrum is shown along with one of the three MBOC options. These plots show power spectral density on a linear scale rather than a logarithmic dB scale, which renders small differences more prominent.

The center panel shows the GPS case with either BOC(1,1) or TMBOC-75. (The BOC(1,1) peaks are arbitrarily scaled to reach 1.0 Watt per Hertz (W/Hz). The BOC(1,1) peaks of TMBOC-75 are lower by 12% (-0.6 dB) in order to put additional power into the BOC(6,1) component of TMBOC-75, primarily at ±6 MHz.

All three panels of Figure 3 have the same relative scaling. The reason the peaks of the BOC(1,1) components in panels 1 and 3 are at 0.67 W/Hz is that GPS L1C will transmit 75 percent of its total signal power in the pilot carrier whereas Galileo will transmit 50 percent. The difference is simply 0.5/0.75 = 0.67 (-1.8 dB).

The first panel of Figure 3 also shows the Galileo TMBOC-50 option in which the BOC(1,1) component peaks are lowered by 18 percent (-0.9 dB) in order to provide power for the BOC(6,1) component, primarily at ±6 MHz.

The third panel shows the same Galileo BOC(1,1) power density but with the CBOC-50 option. In this case the BOC(6,1) component exists in the data channel as well as the pilot carrier. That is why it is half the amplitude at ±6 MHz as in panels 1 and 2. That also is why less power is taken from the BOC(1,1) component for the BOC(6,1) component; in this case the reduction is 9 percent (-0.4 dB). This is not considered an advantage by those who want to track the BOC(6,1) component, and it also reduces the data channel power for narrowband receivers by the same 9 percent or 0.4 dB.

As stated before, the fundamental question raised by this article is whether we should rob Peter to pay Paul. As with all such top-level questions, the answers lie in the details and in the perceptions of those affected. Inside GNSS posed a series of questions to industry experts in order to explore their perspectives and preferences.

The Questions and Answers

Q: What segment of the GNSS market do your answers address? Describe your market, including typical products and the size of the market.

Fenton – High precision survey and mapping, agriculture/machine control, unmanned vehicles, scientific products, and SBAS ground infrastructure where centimeter accuracy is very important. NovAtel sells at the OEM level to software developers and system integrators and calculates its present total addressable market (TAM) at $300-$400 million USD, again at the OEM level.

Garin – We are focused on consumer electronics where very low cost and very low power are of critical importance, such as personal navigation devices (PNDs), cellular phones, and in general applications where the power consumption is at a premium. These objectives should be reached with little to no impact on the user experience. The loss of performance due to design tradeoffs is mitigated by assisted GPS (A-GPS).

Hatch /Knight – NavCom supplies high-precision, multi-frequency GNSS receivers that employ advanced multipath and signal processing techniques, augmented by differential corrections from our StarFire network. These receivers are widely used in the agriculture, forestry, construction, survey, and offshore oil exploration markets. Current market size is on the order of 100,000 units per year.

Sheynblat/Rowitch – Our answers address wireless products for the consumer, enterprise, and emergency services markets. There are over 150 million Qualcomm GPS enabled wireless handsets in the market today, and this large market penetration and heavy usage is primarily driven by low cost, low power, and high sensitivity. The vast majority of other GPS enabled consumer devices worldwide are also cost driven.

Stratton – Rockwell Collins is a leading provider of GPS receivers to the U.S. military and its allies, and we are also a major supplier of GNSS avionics to the civil aviation industry. The civil aviation applications demand high integrity and compatibility with augmentation systems, while the military requirements range from low-power, large-volume production to high-dynamic and highly jam-resistant architectures (as well as civil compatible receivers). Military receivers are impacted due to civil compatibility requirements. Our company has produced over a half million GPS receivers and has a majority market share in military and high-end civil aviation (air transport, business, and regional) markets.

Studenny – Our market is commercial aviation where continuity of operation and integrity are the most important performance parameters.

Weill – I and a colleague, Dr. Ben Fisher, of Comm Sciences Corporation, are the inventors of a new multipath mitigation approach which we call Multipath Mitigation Technology (MMT), so our primary product is technology for improved multipath mitigation. MMT is currently incorporated in several GPS receivers manufactured by NovAtel, Inc. Their implementation of MMT is called the Vision Correlator.

Q: Which signal environments are important for your products: open sky, indoor, urban canyon, etc.

Fenton – In general, most of our customers operate in open sky environments. However, a significant number are operating under or near tree canopy and in urban canyons.

Garin – Ninety percent of our applications are or will be indoors and in urban canyons.

Hatch /Knight – Our receivers are mostly used in open sky and under-foliage conditions.

Stratton – Our products use civil signals mainly in open sky conditions, although civil signals may be used to assist the acquisition of military signals in a broad variety of environments.

Studenny – Aircraft environments, with particular attention to safety-of-life. Also, ground-based augmentation system (GBAS) ground stations.

Weill – Any environment in which multipath is regarded as a problem, including precision survey, indoor (911) assisted GPS, and military and commercial aviation.

Q: Which design parameters are most critical for your products: power, cost, sensitivity, accuracy, time to fix, etc.

Fenton – In general, our products service the high end “commercial” markets. Our customers in general have priorities in the following order: a) accuracy, b) robust tracking, c) cost, d) power, e) time to first fix.

Garin – The most important criteria are, from the highest to the lowest: power, cost, sensitivity, time-to-first-fix, and finally, accuracy.

Hatch /Knight – Accuracy is most important.

Sheynblat/Rowitch – We have invested substantial engineering effort to achieve market-leading sensitivities (-160 dBm) while maintaining very low receiver cost. Engineering investment, focus on sensitivity, and close attention to cost models is probably also true for other vendors focused on mass market, AGPS enabled devices that have to work indoors. All of these GPS vendors go to great lengths to improve sensitivity for difficult indoor scenarios. Every dB counts and may make the difference between a successful or a failed fix, which is of particular concern for E-911 and other emergency situations.

Stratton – The tradeoff in relative importance of these parameters varies widely depending on the particular application, though life-cycle cost (including development and certification) arguably is most significant.

Studenny – Actually, all parameters are important. However, we focus on safety-of-life and the drivers are both continuity of operation and integrity (hazardously misleading information or HMI).

Specifically, we believe cross-correlation, false self-correlation, and the ability to resist RFI, as well as improving multipath performance, are signal properties of great interest to us. A well-selected coding scheme minimizes all of these and HMI in particular. Finally, HMI may become a legal issue for non-aviation commercial applications, especially if those applications involve chargeable services, implied safety-of-life, and other such services.

Weill – MMT is most effective in receivers that have high bandwidth and are receiving high-bandwidth signals. However, it can substantially improve multipath performance at lower bandwidths.

Q: Do you really care whether GPS and Galileo implement plain BOC(1,1) or MBOC? Why?

Fenton – Yes, we expect that the MBOC signals combined with the latest code tracking techniques will provide a majority of our customers a significant performance benefit for code and carrier tracking accuracy in applications where multipath interference is a problem.

Garin – I do not believe that MBOC will significantly benefit our short-term market. The MBOC expected multipath performance improvement will be meaningless in the urban context, where the dominant multipath is Non Line of Sight and where the majority of the mass market usage is concentrated. However we believe that a carrier phase higher accuracy mass market will emerge within a 5 year timeframe, with back-office processing capabilities, and wireless connected field GPS sensors. This will be the counterpart of the A-GPS architecture in cell phone business. MBOC would have an important role to play in this perspective. We envision this new market only in benign environments, and not geared towards the surveyors or GIS professionals.

Hatch /Knight – The MBOC signal will significantly improve the minimum code tracking signal to noise ratio where future multipath mitigation techniques are effective. The expected threshold improvements will be approximately equal to the best case improvements indicated by this article. MBOC will be less beneficial to very strong signals where the noise level is already less than the remaining correlated errors, like troposphere and unmitigated multipath.

Designing a receiver to use the MBOC code will be a significant effort. The resulting coder will likely have about double the complexity of the code generator that does not support MBOC. There will be a small recurring cost in silicon area, and power consumption will increase significantly. Overall, MBOC is desirable for our high performance applications. For many applications the costs are greater than the benefits.

Sheynblat/Rowitch – Yes, we do care about the decision of BOC versus MBOC. The proposed change to the GPS L1C and Galileo L1 OS signal to include BOC(6,1) modulation will perhaps improve the performance of a very tiny segment of the GPS market (high cost, high precision) and penalize all other users with lower effective received signal power due to their limited bandwidth. We prefer that GPS and Galileo implement the BOC(1,1) signal in support of OS location services.

Stratton – This decision does not appear to have much influence on our markets when viewed in isolation, but we would like to see GPS make the best use of scarce resources (such as spacecraft power) to provide benefits that are attainable under realistic conditions.

Studenny – Yes, we do care. GPS L5 needs to be complemented by a signal with similar properties at L1, the reason being that a momentary outage during precision approach on either L1 or L5 should not affect CAT-I/II/III precision approach continuity or integrity. We understand that there are constraints in selecting a new L1 signal; however the proposed MBOC waveform better supports this. This is keeping with supporting the FAA NAS plans and transitioning to GNSS for all phases of flight including precision approach.

Weill – Yes. Comm Sciences has established that the performance of current receiver-based multipath mitigation methods is still quite far from what is theoretically possible. It is also known that GNSS signals with a wider RMS bandwidth have a smaller theoretical bound on ranging error due to thermal noise and multipath. Since multipath remains as a major source of pseudorange error in GNSS receivers, I feel that the use of an MBOC signal for GPS and Galileo is an opportunity to provide the best possible multipath performance with evolving mitigation methods that take advantage of the larger RMS bandwidth of an MBOC signal as compared to plain BOC(1,1).

Q: Are the GNSS receivers of interest narrowband (under ±5 MHz) or wideband (over ±9 MHz)?

Fenton – Wideband. High precision GNSS receivers typically process all available bandwidth ~20 MHz (±10 MHz).

Garin – Our GNSS receivers are narrowband today, but we expect the widening of the IF bandwidth (or equivalently their effective bandwidth) to ±9 MHz, in the next 3-5 years, with the same or lower processing and power consumption.

Hatch /Knight – Our receivers are primarily wideband.

Sheynblat/Rowitch – The receivers of interest are narrowband. Low cost GPS consumer devices do not employ wideband receivers today and will most likely not employ wideband receivers in the near future. Any technology advances afforded by Moore’s law will likely be used to further reduce cost, not enable wideband receivers. In addition, further cost reductions are expected to expand the use of positioning technology in applications and markets which today do not take advantage of the technology because it is considered by the manufacturers and marketers to be too costly.

Stratton – All of our markets require wide-band receivers; however, the civil receiver/antenna RF characteristics are adapted to high-bandwidth C/A processing (where the bulk of RF energy is at band center). So the MBOC signal does raise some potential compatibility questions.

Studenny – Wideband.

Weill – I believe the trend will be toward wideband receivers for most applications. If one looks at the history of GPS receiver products, it is clear that there has always been competitive pressure to increase positioning accuracy, even at the consumer level. Not only is better accuracy a marketing advantage, but it has also opened up entirely new applications. The availability of wide bandwidth signals is a key factor in continuing to improve positioning accuracy. Although currently available receivers that can take advantage of wider bandwidth signals cost more and consume more power, the rapid rate of improving digital technology should make low-cost, low-power, wide bandwidth receivers available in the not-so-distant future. The availability of an MBOC signal would maximize the capability of such receivers.

Other Observers

Inside GNSS invited comments from a broad range of companies representative of most GNSS markets. In addition to those who fully responded to our questions, several offered abbreviated remarks:Garmin International, Inc. did not identify a spokesperson, but it submitted the following official statement: “It is Garmin’s policy not to disclose any information about future designs. However, we would like to indicate that we support the BOC(1,1) implementation over the MBOC.”Sanjai Kohli, Chief Technology Officer of SiRF Technology Inc., submitted the following official statement: “The existence of the BOC(6,1) chips in the MBOC signal won’t matter very much to SiRF. Still, to maximize the availability of weak signals, it would be preferable not to suffer any loss of signal power. Therefore, SiRF would prefer that all chips be BOC(1,1). Furthermore, it is doubtful that any advanced method of multipath reduction will be of much benefit for urban and indoor signal reception, since it is likely that the line-of-sight component of the weak signal is blocked.”

European Company – A large and well known European consumer products company could not obtain internal approval to answer the questions, but the following unofficial communication from a technical manager is of interest: “Our understanding about the pros and cons of MBOC as compared with BOC(1,1) is . . . that narrow-band receivers are not able to utilize the higher frequency components of the MBOC signal and they thus represent wasted power from their viewpoint. This is especially true for acquisition, because the acquisition bandwidth many times seems to be narrower than the tracking bandwidth, especially in those parallel acquisition receivers that are used in consumer products specified for weak signal operation. For such receivers the received signal power is critical in the acquisition phase, not so much in the tracking phase.”

L1C, BOC, and MBOC

Pertinent to the subject of this article is the remarkable way in which the L1C signal was designed. The original C/A- and P-code signals were designed by a small group of technologists under the direction of the GPS Joint Program Office (JPO). Although from the beginning GPS was understood to be a dual-use (civil and military) system, the signals were designed primarily from a military perspective.

Design of the L2C civil signal was led by a JPO deputy program manager representing the Department of Transportation (DoT) — but the process took place under extreme time pressure. The RTCA, Inc., with authorization from the Federal Aviation Administration (FAA), initially defined the L5 signal. The RTCA is a consensus-driven open forum, but its focus is almost exclusively on aviation.

In contrast, development of L1C was funded by the Interagency GPS Executive Board (IGEB), now superseded by the National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee. Representatives of the Department of Defense (DoD) and DoT co-chair the PNT Executive Committee: so, the central focus is on managing GPS as a dual-use utility. Reflecting this, the L1C project was co-chaired by a DoD representative and by a civil representative. (The civil co-chair was Dr. Ken Hudnut of the U.S. Geological Survey. A sequence of JPO officers represented the DoD: Captains Bryan Titus, Amanda Jones, and Sean Lenahan. Tom Stansell of Stansell Consulting served as project coordinator throughout.)

L1C development consisted of two key activities. The first was a study of the wide range of civil requirements and development of five signal structure options. A technical team conducted this part of the work, drawing on experts in all aspects of the signal, including spreading code, data modulation, forward error correction, and message format.

Several team members had deep experience developing civil user equipment, from consumer chipsets to high-precision survey receivers. Others were experts on aviation requirements. The second key activity is, to our knowledge, unique: a worldwide survey of GNSS experts to determine which of the five options to choose. The design process is complete, and a draft specification (IS-GPS-800) has been published.

The innovative MBOC proposal was developed quickly by a group of very competent U.S. and EU signal experts with both civil and military backgrounds. However, this team apparently had only one person with extensive experience in receiver manufacturing, and the timeline did not allow the opportunity for a broad survey to assess equipment manufacturers’ opinions about the design. Informal conversations with some industry representatives also revealed dissatisfaction with MBOC. Therefore, Inside GNSS decided to consult a number of experts from companies that build GNSS equipment to determine their thoughts about the MBOC concept.

Additional Resources

1. Agreement on the Promotion, Provision and Use of Galileo and GPS Satellite-Based Navigation Systems and Related Applications, June 26, 2004,

2. Hein, G. W., and J-A. Avila-Rodriguez, L. Ries, L. Lestarquit, Issler, J. Godet, and T. Pratt, “A candidate for the GALILEO L1 OS Optimized Signal”, Proceedings of ION GNSS 2005 – 13-16 September 2005, Long Beach, California

3. Hein, G. W., and J-A. Avila-Rodriguez, S. Wallner, J. W. Betz, C. J. Hegarty, J. J. Rushanan, A. L. Kraay, A. R. Pratt, S. Lenahan, J. Owen, JL. Issler, T.A. Stansell, “MBOC: The New Optimized Spreading Modulation Recommended for Galileo L1 OS and GPS L1C”, Inside GNSS, Volume 1, Number 4, pp 57–65, May/June 2006

4. Hein, G. W., and J-A. Avila-Rodriguez, S. Wallner, A. R. Pratt, J. Owen, J-L. Issler, J. W. Betz, C. J. Hegarty, S. Lenahan, J. J. Rushanan, A. L. Kraay, T.A. Stansell, “MBOC: The New Optimized Spreading Modulation Recommended for GALILEO L1 OS and GPS L1C”, IEEE/ION PLANS 2006, April 24-27, 2006, San Diego, California

5. IS-GPS-200: NAVSTAR GPS Space Segment / Navigation User Interfaces; IS-GPS-705: NAVSTAR GPS Space Segment / User Segment L5 Interfaces; Draft IS-GPS-800 for new L1C signal;


The L2C Study: Benefits of the New GPS Civil Signal

GPS has had enormous benefits to the economy and society that go well beyond military and civil aviation applications – that is becoming ever more widely understood. What has been more open to discussion are the civilian non-aviation benefits of further U.S. efforts at GPS modernization, particularly the introduction of additional signals.

GPS has had enormous benefits to the economy and society that go well beyond military and civil aviation applications – that is becoming ever more widely understood. What has been more open to discussion are the civilian non-aviation benefits of further U.S. efforts at GPS modernization, particularly the introduction of additional signals.

In an effort to define and measure civilian benefits, the U.S. departments of commerce and transportation commissioned some economic analyses of civil signal modernization. Particular emphasis was placed on the value of the L2C signal centered at 1227.60 MHZ, which recently began broadcasting from the first modernized GPS Block IIR-M satellite. This article is an outgrowth of that effort.

The analysis focused on the value of signals at more than one frequency for precision non-aviation use by business and government. It considered how utilization of the second civilian signal and its benefits would evolve in the coming decades as the L2C constellation expands and as additional signals become available from GPS and other GNSSes.

In the study, projections were developed under four scenarios — with the “moderate benefit”scenario seeming most likely — that reflect combinations of developments, including the strength of markets, the timing of L2C signal availability, the timing of Galileo availability, and complementary and competitive relationships with augmentations.

The main findings of the study are:

  • The projected number of U.S. high precision users of any signal nearly doubles from 39,000 to 75,000 from 2004 to 2008, and reaches 146,000 in 2012 and 333,000 in 2017.
  • Under a “moderate benefits” scenario, the number of L2C users reaches 64,000 by 2017, of which 35,000 are dual frequency users and 29,000 use three or more frequencies.
  • Civilian benefits of L2C net of user costs range from $1.4-$9.6 billion under alternative scenarios and civilian net benefits are about $5.8 billion under the moderate benefits scenario.
  • Results are robust.
  • Positive present values of benefits net of user costs are obtained in all tests.
  • The ratio of benefits to user costs ranges from 8 to 20 in all tests.

In addition to the domestic benefits examined, L2C will undoubtedly have important international benefits.
This article presents in more detail how we defined the problem, approached the study, and arrived at those conclusions.

The L2C Evolution
L2C, together with the present L1 C/A-code signal and the future modernized civil signal L1C, will provide an alternative to augmented single frequency GPS for precision users. Separate investigations have outlined the incremental benefits of L1C (See sidebar, “The L1C Studies,” at the end of this article)

L2C signals can be used for both horizontal and vertical measurement and positioning along with L1 C/A as satellites become available over more areas and in more times of the day. The first satellite can be used for improved timing. L2C also can be used in configurations of three or more frequencies in combination with the forthcoming GPS L5 signal and with signals from Galileo and GLONASS.

At various times in each signal’s deployment and development of markets, other signals will, to varying degrees, provide complements to L2C and competitors to it. L2C has its greatest potential to generate benefits for dual frequency applications until alternative signals are widely utilized, and for long-term use in applications taking advantage of three or more frequencies.

The L2 signal is currently being widely used for augmentations, and the new signals can be used in that way along with the existing constellation. However, L5’s use as a competitor to L2C and as a partner to L2C in multiple frequency implementations primarily depends on the launch timeline for satellites carrying the L5 signal since L5, centered at the 1176.45 MHz frequency, is not currently in service. Plans call for its implementation on the GPS Block IIF satellites, with the first IIF now expected to be launched in 2008.

L2C deployment requires a commitment to operational capability. Decisions will be required as to launch dates and signal activation for each successive satellite containing the signal. The L2C benefits study is intended to contribute to decisions about L2C deployment with consideration of alternative scenarios informed by quantitative and qualitative analysis. 

To explore the implications of L2C evolution, we make projections about the numbers of U.S. precision users, incremental benefits, and user costs, based on examination of applications and available evidence on value of benefits, and consider how these can unfold over the period 2006–2030.

The analysis focuses on precision users of L2C who use two or more frequencies, although we do include estimates for supplementary multiple-frequency users and single-frequency users. However, the estimates of these types of use are more conjectural and do not contribute much to the overall value of benefits.

Benefits net of user costs are measured according to the widely accepted economic productivity approach, which includes productivity gains and cost savings. This comprehensive approach is more appropriate than one that measures benefits simply by expenditures on equipment and services.

Incremental benefits and user costs are defined to include all differences in outcomes from what would be expected in the absence of L2C. 

Signal Advantages and Availability
The L2C signal, scheduled to be the first of the modernized civil GPS signals, is intended for civilian purposes other than aviation and safety-of-life. It will provide greater accuracy and robustness and faster signal acquisition than the current L1 C/A-code signal.

Higher signal power and forward error correction will improve GPS mobile, indoor, and other uses.
The L5 signal that will arrive within a few years will be in a protected aeronautical radionavigation system (ARNS) band intended for aviation and other safety-of-life uses and will have broader applications.

Multiple signals will allow many users to obtain greater precision and availability at lower cost than achievable with proprietary augmentation systems. However, signal combinations combined with public and private augmentations for even greater precision and reliability will support applications with some of the greatest potential benefits.

Combined use of L2C with L1 C/A and L5 will also enable some precision users to achieve even greater reliability and accuracy. Although available simulations differ on the size of benefits of three signals over two, many professionals expect important advantages from such “tri-laning” techniques.

The U.S. Air Force launched first satellite containing the L2C frequency on September 25, 2005, and the signal became available on December 16. Going forward, two to four Block IIR-M satellites are expected to be launched each year. With six to eight satellites anticipated to be available by about December 2007, users will be able to access at least one single satellite with L2C at almost all times. Eighteen L2C-capable satellites  (including the Block IIF generation) will be available by about 2011 and 24 L2C signals, around 2012. (These statements are based on official 2005 launch schedules and are subject to revision.)

The first L5 launch is scheduled for March 2008. L5 does not have a GPS signal in use at its frequency, so it will not be usable to any great extent until a large part of its constellation is available. In contrast, L2 is in place to transmit the military P(Y) code and the carrier signals of the satellites are currently being used along with L1 C/A for higher-accuracy applications.

Consequently, the L2C signal can be used immediately as a second frequency. The GPS signal L1C, which is being planned now for implementation on the GPS III satellites scheduled for launch beginning in 2013, will be able to be used immediately, even for single frequency use, without augmentation because it is at the same frequency as the L1 C/A-code.

Using Multiple Frequency GPS
Many private and government precision applications could potentially benefit from multiple frequency GPS.
For example:

  • Centimeter accuracy is important to many land and marine surveying applications including planning, zoning, and land management; cadastral surveying, harbor and port mapping, aids to navigation, coastal resources management, mapping, and surveys of sensitive habitats.
  • Machine control applications using high precision GPS have grown rapidly in a number of sectors, including agriculture and forestry, mining, construction, energy, transportation, structural monitoring and positioning for mapping and geographic modeling..
  • Civil applications that rely on precise timing will benefit from increased GPS signal availability and elimination of atmospheric effects possible using dual-frequency techniques.  Beneficiary industries include those operating cellular telephone, power, and financial information networks.

Scope of Benefits and Costs
Incremental benefits — those that arise because of the availability of L2C— include far more than the comparison of multiple frequency with augmented single frequency use. Companies adopting GPS in the future may even skip single-frequency options and instead choose multiple-frequency equipment (incorporating L2C) over non-GPS alternatives. Large candidate markets include construction, agriculture, and other applications where technological alternatives exist.

In some organizations, dual-frequency GPS will be the catalyst for extensive changes in systems that will occur earlier than if dual frequency GPS had not been adopted.

In the L2C study, benefits are measured according to the “economic productivity approach,” which is superior to the expenditure/economic impact approach because:

  • Productivity gains and cost savings, which this approach emphasizes, are the main purpose of much of GPS deployment and can be much larger than expenditures.
  • Benefits may accrue to a large number of customers of the purchaser, as occurs with use of GPS timing in communications, financial services, and electric power and in use of GPS positioning for mapping, structural monitoring, and weather.
  • The more common approach (economic impact) gauges benefits by added GPS spending without deducting the loss of benefits of non-GPS expenditures that are replaced.

L2C benefits can take both market and non-market forms, including increases in the productivity of business and government operations, user cost savings, benefits to the public through provision of public services and saving lives, and through improved health and environment.

Net benefits are benefits minus user costs. Incremental user costs include all additional costs that are expected with the availability of L2C, not simply the difference in costs between single- and dual-frequency receivers. These can take the forms of enhancements and accessories purchased when adding L2C capability (e.g.  better displays, controllers and software) or costs associated with users upgrading to multiple frequency GPS from less sophisticated single-frequency GPS systems or non-GPS systems.

However, incremental user cost is net of savings from use of receivers with less proprietary technology and any reduced use of private augmentation subscription services.

Expenditures to develop the GPS system infrastructure (satellites and ground segment) are not included, however, because most represent nonrecurring, sunk costs. Moreover, if we added them to our L2C analysis, we would need to include benefits to aviation and military users as well as their associated equipment costs.

The analysis takes into account alternative conditions of timing and impact of alternatives through the use of scenarios. Projections of signal use and value of benefits are developed through the year 2030 under four scenarios: High Opportunity, Moderate Benefits, Diluted Benefits, and Opportunity lost.

These scenarios reflect combinations of developments, including the strength of markets, the timing of L2C signal availability, the timing of Galileo availability, and complementary and competitive relationships with augmentations. (See the sidebar, “L2C Benefit Scenarios” at the end of this article for details of assumptions behind each.)

Probabilities are not given for the scenarios because the likelihood of alternative Galileo delays cannot be evaluated quantitatively. Moreover, the diluted benefits and opportunity lost scenarios are significantly affected by U.S. GPS policy, which is also not predicted.

Estimates of GPS Users
The L2C study projections shown in Figure 1 are based on assumed rates of decline in prices for user equipment and services and increases in the number of users in response to price changes. Projections reflect assessments of market sizes and patterns of market penetration under each scenario. Allowance also is made for effects of economic growth on market size. Table 1 (to view tables and figures, please download the PDF of this article using the link above) provides a detailed breakdown of results by scenario.

Within each scenario, projections are made for precision L2C users of three or more frequencies, dual frequency precision users, multiple frequency supplementary users, and single frequency users of L2C.

The starting point for determining the number of high precision users is a widely relied–upon estimate of 50,000 high precision users worldwide in 2000. We assumed that the United States had 40 percent of precision users in that year.

The study further assumes that the number of U.S. high-precision GPS users will grow by 18 percent per year from 2000 to 2030. This projection is based on a rate of price decline for user equipment of 15 percent per year and a corresponding a 1 percent increase in users for each 1 percent decline in price. Finally, we include an assumption of general growth in the economy (i.e., independent of GPS receiver price) that adds 3 percent per year.

These assumptions and calculations produce a projection of U.S. high precision GPS users — those using augmentations, of 38,776 in 2004. The estimated number of U.S. high precision users of any signal or combination nearly doubles to 75,177 from 2004 to 2008 and reaches 145,752 in 2012 and 333,445 in 2017.

We computed the numbers of multi-frequency GPS users by applying an estimated percentage to the number of high-precision users for each scenario. The number of multi-frequency precision users adopting dual versus three or more frequencies was then calculated using projected values for the percent of each category. Finally, the number of L2C users was calculated based on projections of the percent of multiple frequency users that use L2C, constructed to reflect the dynamics of each of the scenarios. 

Rapid growth is projected in the numbers of U.S. precision multiple-frequency L2C users. In the moderate benefits scenario, the number of L2C users reaches 64,000 by 2017, of which 35,000 are dual frequency users and 29,000 use three or more frequencies. The numbers of L2C users vary widely among scenarios.

Average Net Benefits per User
The study defines average incremental net value of benefits per L2C user as the incremental value of benefits per L2C user above the incremental user cost of equipment and services. Benefits largely reflect productivity gains and/or cost savings. Estimates reflect a review of available evidence ranging from formal studies to case histories and expert opinion across a wide range of applications.

Our research suggests that average annual incremental benefit per precision L2C user net of costs could reach the range of $8,000–$16,000 per year. This includes benefits across systems that are not attributable to specific numbers of users and non-market benefits, such as safety and environmental advantages, as well as market benefits associated with the value of goods and services transactions. Market benefits attributable to numbers of users are estimated at 60 percent of all incremental net benefits.

These are peak values after benefits have had an opportunity to rise with experience using the new signal. The values decline from their peaks as new users with lower benefits are attracted by declining costs and some high benefit users move to alternatives.

In considering the plausibility of these figures, consider that:

  • If a worker saved one hour a week by avoiding rescheduling due to signal unavailability, slow signal acquisition, loss of lock and additional work due to phase ambiguities, and further assuming labor costs of $80 per hour (including salary, fringe benefits, equipment, support staff and other overheads), — the saving would total $4,000 per year. Improvements in the organization’s processes with better work flow could make the savings even greater.
  • If the telecommunications, electricity generation, and financial industries together had system benefits that together were valued at $20 per customer over 20 million customers, the benefits would be $400 million per year. Market benefits of $400 million per year, if divided by 100,000 dual frequency users, for example, would amount to an average of $4,000 per user per year.
  • $400 million in non-market benefits over 100,000 precision users would equal an additional $4,000 per user per year.

(This could result, for example, from avoiding 100 deaths due to industrial accidents or environmental impacts at a value of $4 million per incident.)

The present values of incremental user costs range among scenarios from $175 million to $514 million in year 2005 purchasing power.

Costs represent one eighth or less of the total value of benefits in each scenario.

Value of Benefits
Civilian net benefits per user are incremental, net of incremental costs, and derive from prospects for major areas of application. The patterns incorporate some high-value initial use, assume that higher benefit users switch earlier to newer signals, factor in a buildup of productivity gains with experience, and project lower values for late-entry users attracted by lower equipment prices as well as later increases in higher benefit users switching to alternative signals.

We calculate the value of civilian net benefits of L2C through multiplying civilian net benefits per user by the number of L2C users for the user type and scenario. Higher net benefit scenarios result from higher benefits per user and larger numbers of users.

At a 7 percent real (above inflation) discount rate, present values of total net civilian market benefits range from $9.6 billion to $1.4 billion dollars. Benefits under the moderate benefits scenario have a present value of $5.8 billion and those under the high opportunity scenario $9.6 billion. (Values are discounted using annual data to calendar year 2006. That essentially places the values at the middle of 2006.)

Nearly all of the incremental benefits of L2C stem from precision use of two or more frequencies. That is both because of moderate numbers of other types of users in these and their low benefits per user.

The timeframe in which other signals become available after L2C plays an important role in the size of estimated benefits. In the high opportunity scenario, for example, dual-frequency net benefits appear higher than benefits from use of three or more frequencies because the latter applications start later as additional frequencies become available.

In the other scenarios, benefits from applications using three or more signals are higher than dual-frequency benefits because the benefits of dual frequency remain as strong when competing frequencies become available.

New spending can encourage greater long run economic growth, especially when it is associated with new technology for widely usable infrastructure. The spending may induce others to innovate, invest in greater capacity, take risks and/or provide financing. While direct estimates of the size of long run economic multipliers are not readily available, analyses of determinants of growth suggest that effects are modest, perhaps adding 20% to market benefits. Because of the uncertainty surrounding such estimates, no allowance is made for growth multiplier effects in the estimates shown.

Cost-Benefit Analysis
The ratio of incremental civilian benefits to user costs is calculated by dividing the present discounted value of total incremental benefits (including net benefits and costs) by the present value of incremental costs. These are shown with a 7% real (above inflation) discount rate.

The ratios of benefits to costs range from a multiple of 20 in the high opportunity scenario to 9 in the opportunity lost scenario. It would be surprising if benefit/cost ratios were not high because only direct user expenses (and not system costs) are included to get a picture of incremental costs of each set of outcomes. 

The moderate benefits scenario, which has a ratio of 20, is considered more likely than the others. Because of the interest in obtaining the greatest benefits, focusing on the present value of net benefits is appropriate for policy rather than using the benefit/cost ratio when all ratios are high.

As mentioned, changes in various factors could substantially affect the outcomes of L2C benefits and produce either an overstatement or an understatement of these. See the “Benefit Variables” sidebar at the end of this article for a listing of the most important factors.

Rapid growth is projected in the numbers of U.S. precision GPS users and in most scenarios for the numbers of high-precision multiple frequency L2C users. Substantial L2C benefits can occur along with availability of other signals and constellations, augmentations, and alternative technologies. While Galileo will compete with L2C, Galileo signals also can increase precision L2C use in multiple frequency applications, an alternative that will become increasingly affordable.

The economic productivity approach offers a means of considering benefits in a comprehensive way. Benefits and costs are incremental. They are defined to include all changes that occur as a result of the existence of L2C.

Defined comprehensively, benefits can encompass results from more extensive changes in equipment and systems and include both benefits that are attributable to specific numbers of users and those that may be incorporated in systems and spread over a broad population. They include both market and non-market benefits — those that are not bought and sold in markets, such as benefits to life, health, security and the environment.

User costs also are incremental, including all changes that occur with the availability of L2C, and are net of savings from moving to less sophisticated and less proprietary equipment.

Sidebar: The L1C Studies
Before the L2C study, important progress had already been made in understanding the benefits of additional GPS signals. These activities included the discussion of civilian applications in the report of the Defense Science Board Task Force on GPS, released last December, and the L1C Study undertaken by the Interagency GPS Executive Board in 2004. (See the “Additional Resources” section at the end of this article to find out how to obtain these studies on line.)

Upper limits of total benefits of L1C for the single year 2005 — including those obtained by single- and multiple-frequency users in private households, businesses, governments — were estimated at approximately $2 billion: $640 million for mobile and wireless location services, $62.5 million for information/data services, $990 million for “commercial GPS,” and $490 million for in-vehicle information and navigation services (telematics).

The L1C study approximated a “rough order of magnitude” dollar value of L1C applications based on 2005 spending by applying a “team consensus” for an assumed incremental benefit as a percentage of market value (revenue) for each of 13 user categories. Spending in user group categories was based on a compilation of trade estimates.

Sidebar: L2C Benefit Scenarios
The four scenarios developed to support the L2C benefits study, along with the assumptions underling each, include the following:

High Opportunity

  • Timely signal availability
  • Larger than expected markets
  • High complementarity with L5
  • Success of High-Accuracy Nationwide Differential GPS augmentation
  • Full Galileo deployment in 2012 with less than complete technical performance

Moderate Benefits

  • Timely L2C availability
  • Large potential markets
  • Benefits moderated by competition from other signals and augmentations
  • Full Galileo deployment in 2011

Diluted Benefits

  • Large potential markets
  • Gradual L2C deployment and uncertainty about schedules slows investment in innovation and market development
  • Many users wait for L5 and for Galileo, which is expected in 2010
  • Improvements in public and private augmentations make single signal use more attractive

Opportunity Lost

  • Late signal initiation and protracted pace of L2C deployment
  • Slow introduction and adoption of user equipment
  • Some users wait for Galileo
  • Moderately large potential market size, moderate effects of availability of other signals and delay in Galileo FOC to 2011
  • Attractiveness of augmentations

Sidebar: Benefit Variables
Overstatement could result from competition from other signals, from augmentations and from other technologies that is greater than anticipated. For example,

  • Greater attractiveness of other signals because of the availability of satellites from Galileo in addition to those from GPS at the L1 and L5 frequencies
  • Advances in augmentations that make single frequency use more attractive
  • Slower price declines for L2C user equipment
  • Less triple frequency use when additional satellites are available from Galileo and/or greater use of Galileo signals at frequencies that do not correspond with L1 and L5
  • More users waiting for L5 for non-aviation civilian dual frequency use than allowed for in the study.

Understatement could result from

  • More important and/or numerous applications than were allowed for in the calculations
  • Faster price declines for multiple frequency user equipment (e.g. if competition squeezes high end margins even more) and/or larger price sensitivity of demand
  • Non-market benefits greater than the 25% of market benefits assumed
  • Impacts of L2C on long run economic growth, which were not included in the calculations and perhaps could add perhaps 20% to benefits.

For figures, graphs, and images, please download the PDF of the article, above.

Steve Bayless, Tyler Duval, Jason Kim, Scott Pace, Mike Shaw, Tom Stansell, Dave Turner, Jack Wells, Rodney Weiher, and Avery Sen offered comments, guidance and assistance to the study. Many others contributed expertise through interviews.

Additional Resources
Kenneth W. Hudnut, and Bryan Titus, GPS L1 Civil Signal Modernization (L1C), Interagency GPS Executive Board, July 30, 2004, <>

U.S. Defense Science Board, The Future of the Global Positioning System, Washington, D.C.: Office of the Under Secretary of Defense For Acquisition, Technology, and Logistics, October 2005, <>

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