Today’s headlines frame my thoughts about securing GNSS assets, which one expert has characterized as our “least visible and most vulnerable infrastructure.”

In the Columbia River Gorge, a National Scenic Area spanning the Washington-Oregon border, a 15-year-old boy has been accused of intentionally tossing fireworks into tinder-dry grass thereby starting a (thus far) 33,000-acre forest fire that has devastated a natural treasure. Meanwhile, in the latest incident of large-scale identity theft, credit-rating agency Equifax has belatedly acknowledged a months-long breach of its database in which 143 million personal records were reportedly accessed.

In one case, an individual — obliviously or purposefully — creates outsized havoc, in the other, a skilled team of professional thieves disrupt a global enterprise and endanger the financial well-being of millions.

Of course, we have headlines closer to the point, such as “Reports of Mass GPS Spoofing Attack in the Black Sea,” or “South Korea developing eLoran Network to Protect Ships” from North Korean GPS jamming.

These latter incidents, of course, arise from state-sponsored or –enabled actions. But, as with the Columbia gorge fire, personal behaviors — often harder to detect and prevent — can similarly afflict GNSS capabilities. In recent years, considerable attention has focused on the use of small GNSS jammers, also known as “personal privacy devices.” Perhaps the best-known case is that of a trucker trying to jam his vehicle’s own receiver who interrupted GPS-aided landing operations at Newark International Airport.

As the articles on jamming and spoofing mitigation in this issue of Inside GNSS reflect, the motives and methods of perpetrators vary. But, given the natural progression of information-sharing and widening expertise in GNSS — along with our cultural soft spot for making heroes out of rebels and outlaws — we can probably assume that the trend toward disruption will only get worse.

Some GNSS user groups have struck out on their own to ensure the security of their constituencies and their particular needs. Military users benefit from a variety of alternative PNT technologies such as geomagnetic mapping, vision- and image-based navigation, and chip-scale atomic clocks and inertial measurement units. The U.S. Federal Aviation Administration has decided to retain, for the time being, a minimum operational network of VHF omnidirectional range (VOR) facilities originally planned to be phased out with the introduction of GNSS.

Over time, some of these alternatives may migrate into the commercial and professional space — then again, they may not. And the vast majority of individual GNSS consumers have no organizations to advocate for their needs.

So, what is to be done? How can we ensure that the positioning, navigation, and timing (PNT) utility is available to all users, and not just those sectors with the resources to develop solutions for themselves? The future of location-based applications and enterprise — and the associated economic benefits — depend on a satisfactory answer to that question.

Multi-level threats clearly require multi-tiered responses that fit the corresponding scope and scale of different domains. At the system level, GNSS providers are exploring such measures as encryption, signal authentication, stronger signal power, and advanced signal designs.

National and international legal/initiatives include such efforts as regulating the sale and use of GNSS jammers and spoofers. Alternative PNT systems — for example, enhanced Loran (eLoran) — represent a potential multinational approach to the problem.

At the level of user equipment, several GNSS manufacturers are incorporating interference detection and mitigation (IDM) and antispoofing capabilities into proprietary products.

The variety of these initiatives and their advocates illustrates the breadth of concern about assured PNT, but also reflect the fractured nature of responses to the threats to GNSS. The situation calls for leadership with the expertise and stature to bring comprehensive solutions before the wider GNSS community.

The International Committee on GNSS has the membership and forum, if not yet the clear mandate, to impose such solutions globally. At the national level, the U.S. Space-Based PNT Executive Committee assisted by its expert advisory panel seems the most likely candidate for this role.

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Like many massive infrastructure projects, the NextGen program has suffered numerous setbacks, many self-inflicted. An August 2016 report from the Office of the Inspector General (OIG) of FAA’s parent, the Department of Transportation, noted, “FAA’s plans have proven to be unrealistic, lacking stable investment priorities and requirements for NextGen systems.”

With more than $7 billion in modernization funds already expended, the FAA is currently projecting costs of $14.8 billion from Fiscal Year (FY) 2015 to 2030, according to the OIG report. Despite the characterization of NextGen as being wildly over budget, however, total cost estimates for the program “have evolved, but not increased markedly since FY 2004,” the OIG says. The president’s proposed FY18 budget requests $988 million for continued NextGen development, down from $1.055 billion in FY17.

As other infrastructure modernization efforts involving GNSS have shown, getting the technology right is the easy part. The Global Positioning System has a 22-year operational history to bolster expectations about its performance, which has continued to improve steadily. The arrival of other GNSS systems has only strengthened this technological resource.

Instead, the sticking points arise from such issues as enterprise architecture, systems integration with other technologies such as data communications and weather forecasting, interagency cooperation, human factors, cybersecurity, operational procedures, and regulatory updates to accommodate modernization.

Like America’s healthcare insurance system, modernization of the National Air Space is more complicated than casual observers might think.

NextGen needs to happen, first, because it will pay off in improved aviation operations, greater capacity, and better use of the crowded National Air Space (NAS). FAA modernization has already provided $2.7 billion in savings from such things as less usage of fuel and is expected to provide another $160 billion in benefits through NextGen’s targeted 2025 completion date.

Efforts so far have barely scratched the surface of what GNSS and other NextGen technologies can provide.

However, the need to get NextGen back on track has gained heightened urgency with the renewed push to privatize U.S. air traffic control (ATC). On June 27, the House Transportation and Infrastructure Committee approved a measure that would turn the nation’s taxpayer-funded ATC infrastructure and operations (carried out by 30,000 public employees) over to a nonprofit organization controlled by aviation industry representatives.

The measure, previously backed unsuccessfully by House Transportation Committee chairman Bill Shuster, has gained important support from President Donald Trump.

NAS modernization is a perhaps uniquely complicated undertaking with many elements subject to inevitable changes as technologies and operational environments (including the political and economic context) evolve. NextGen is a moving target being shot at from a moving platform.

Attempting to privatize air traffic control at this point in the process would throw a very large monkey wrench into some very delicate works in progress. As Senate Appropriations Committee Chairman Thad Cochran (R-Miss.) and committee Vice Chairman Sen. Patrick Leahy (D-Vt.) said in a February 28 letter to Senate Commerce, Science and Transportation Committee Chairman Sen. John Thune, “If air traffic control were separated during this critical period of technological advancement, the progress already being made to synchronize investment from government and industry related to safety, equipage, training, operational changes, and overall integration would be lost.”

And the FAA, not some newly convened group dominated by stakeholders with their own interests in mind, should continue to lead this project. As a special National Research Council committee concluded in a congressionally mandated analysis of NextGen in 2015, “Replacing or upgrading systems while continuously and safely operating the whole system is an intricate undertaking, a process that the FAA seems to have mastered.”

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With the Australian government’s announcement earlier this month that it would invest $12 million in a two-year program looking into the future of positioning technology in Australia, comes plans for testing of satellite based augmentation systems (SBAS) to be undertaken, and for future applications for all four major modes of transport in Australia, as well as for potential safety, productivity, efficiency and environmental benefits.

With the Australian government’s announcement earlier this month that it would invest $12 million in a two-year program looking into the future of positioning technology in Australia, comes plans for testing of satellite based augmentation systems (SBAS) to be undertaken, and for future applications for all four major modes of transport in Australia, as well as for potential safety, productivity, efficiency and environmental benefits.

The SBAS test-bed is Australia’s first step toward developing the positioning technology and expertise needed to be competitive globally and could impact the country’s place as an industry leader in the Asia Pacific region. An SBAS would overcome current gaps Australia has in mobile and radio communications and, when combined with on-ground operational infrastructure and services, could ensure that accurate positioning information can be received anytime and anywhere within Australia.

The two-year project will test two new satellite positioning technologies including next generation SBAS and Precise Point Positioning, which will provide positioning accuracies of several decimeters and five centimeters, respectively. Currently, positioning in Australia is usually accurate to five to 10 meters.

“SBAS utilizes space-based and ground-based infrastructure to improve and augment the accuracy, integrity and availability of basic Global Navigation Satellite System (GNSS) signals, such as those currently provided by the USA Global Positioning System (GPS),” stated Federal Minister for Infrastructure and Transport Darren Chester, who added the program could test the potential of SBAS technology in the four transport sectors—aviation, maritime, rail and road.

“The future use of SBAS technology was strongly supported by the aviation industry to assist in high accuracy GPS-dependent aircraft navigation. Positioning data can also be used in a range of other transport applications including maritime navigation, automated train management systems and in the future, driverless and connected cars.”

From using Google Maps on smartphone to emergency management and farming, many people use and benefit from positioning technology every day without even realizing it.

The funding will be used to test instant, accurate and reliable positioning technology that could provide future safety, productivity, efficiency and environmental benefits across many industries in Australia, including transport, agriculture, construction, and resources.
According to the Australian Government, research has shown that the wide-spread adoption of improved positioning technology has the potential to generate upwards of $73 billion of value to Australia by 2030.

The benefits to this improved technology can be widespread. Minister for Resources and Northern Australia Matt Canavan said access to more accurate data about the Australian landscape would also help unlock the potential of the North.

“This technology has potential uses in a range of sectors, including agriculture and mining, which have always played an important role in our economy, and will also be at the heart of future growth in Northern Australia,” Senator Canavan said.
“Access to this type of technology can help industry and Government make informed decisions about future investments.”

The SBAS test-bed is Australia’s first step towards joining countries such as the United States, Russia, India, Japan and many across Europe in investing in SBAS technology and capitalizing on the link between precise positioning, productivity and innovation.

Early this year, Geoscience Australia with the Collaborative Research Centre for Spatial Information (CRCSI) will call for organizations from numerous industries including agriculture, aviation, construction, mining, maritime, rail, road, spatial, and utilities to participate in the test-bed.

GNSS Infrastructure
The SBAS test-bed will utilize existing national GNSS infrastructure developed by AuScope as part of the National Collaborative Research Infrastructure Strategy.

It will test two new satellite positioning technologies — next generation SBAS and Precise Point Positioning, which provide positioning accuracies of several decimeters and five centimeters, respectively.

Highly accurate positioning technologies are already available in Australia, but they can be cost-prohibitive and not readily available in many areas.

Geoscience Australia is working with the CRCSI on the project, which is designed to evaluate the effectiveness of an SBAS for Australia, and build expertise within government and industry on its transformative benefits. The project is funded through the Department of Industry, Innovation and Science, and Department of Infrastructure and Regional Development.

Positioning data has become fundamental to a range of applications and businesses worldwide. It increases productivity, secures safety and propels innovation; enables GPS on smartphones, provides safety-of-life navigation on aircraft, increases water efficiency on farms, helps to locate vessels in distress at sea, and supports intelligent navigation tools and advanced transport management systems that connect cities and regions.

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As described in the November-December issue of Inside GNSS, “Interference Localization from Space,” radio frequency interference causes the satellite industry to lose millions of dollars per year due to detrimental effects, ranging from a degradation in the quality of service to the complete loss of service.

As described in the November-December issue of Inside GNSS, “Interference Localization from Space,” radio frequency interference causes the satellite industry to lose millions of dollars per year due to detrimental effects, ranging from a degradation in the quality of service to the complete loss of service.

In an effort to combat this, Vienna, Austria-based Siemens Convergence Creators has announced its new Satellite Geolocation Service, designed to enable satellite and service operators to localize satellite signal interference worldwide.

For satellite operators and users, including the GNSS community, the ability to rapidly identify and mitigate interference — intentional or not — is crucial to protecting the core functionality of their assets and service operations.

According to a statement by the European Space Agency (ESA), which supported the development of the geolocation system, SIECAMS ILS ONE works by analyzing the signal distortions primarily caused by satellite movement, atmospheric, or weather influences and other environmental factors. By comparing such signal distortions of the interference signal with known signals, ILS ONE is able to identify the precise location of the interference source.  

Up to now, interference geolocation systems required having two geostationary satellites in close proximity to each other in order to obtain sufficient crosstalk for reliable geolocation signal processing. According Siemans Convergence Creators, SIECAMS results in a significant improvement in the resolution of interference issues compared with traditional satellite-interference localization systems.

“The SIECAMS single-satellite solution is a real game-changer for the satellite industry,” says Stephane Pirio, ESA Technical Officer for the activity. “It is much cheaper than traditional geolocation systems and this makes it particularly attractive for small- and medium-size satellite operators.”

SIECAMS ILS ONE has been very successfully used by Eutelsat since early 2016.

Siemens Convergence Creators has made substantial investments towards the development of tools for satellite interference mitigation in the last decade within the framework of its SIECAMS product line. SIECAMS currently comprises the carrier-monitoring and interference-detection tool SIECAMS CMS, the carrier-ID detection tool SIECAMS CID, the geolocation system SIECAMS ILS, and the single-satellite geolocation system, SIECAMS ILS ONE.

Until now, the company says, satellite operators had to invest in high-quality geolocation tools and personnel training to enable their own staff to identify, locate, and reduce or eliminate sources of interference in order to avoid potential damage claims and the risk of losing customers. Even so, locating the origin of interference may take days, weeks, or even months.

The localization of satellite interference works worldwide because Siemens Convergence Creators’ Satellite Geolocation Service offers coverage of practically the entire inhabited landmass on Earth.

The Satellite Geolocation Service went into operation on January 9 and can be ordered on demand for individual interference events, or via yearly subscription that includes a contingent of interference localization instances.

Part 2 of the Working Papers on satellite-based geolocation of interference can be found in the January-February issue of Inside GNSS.

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The U.S. Air Force has approved Lockheed Martin’s current GPS satellite ground control system upgrade to enable it to operate with more powerful and accurate GPS III satellites, the company said.

The Air Force’s Critical Design Review (CDR) for the Contingency Operations (COps) contract, completed on November 17, allows Lockheed Martin to proceed with the modification of the existing Architecture Evolution Plan (AEP) Operational Control Segment. The AEP, maintained by Lockheed Martin, controls the 31 GPS IIR, IIR-M and IIF satellites in orbit.

The U.S. Air Force has approved Lockheed Martin’s current GPS satellite ground control system upgrade to enable it to operate with more powerful and accurate GPS III satellites, the company said.

The Air Force’s Critical Design Review (CDR) for the Contingency Operations (COps) contract, completed on November 17, allows Lockheed Martin to proceed with the modification of the existing Architecture Evolution Plan (AEP) Operational Control Segment. The AEP, maintained by Lockheed Martin, controls the 31 GPS IIR, IIR-M and IIF satellites in orbit.

Lockheed Martin said that the COps modifications allow the AEP to support the new GPS Block III satellites by enabling them to perform their positioning, navigation and timing mission, once they are launched. COps is envisioned as a temporary gap filler prior to the GPS constellation’s transition to the next generation Operational Control System (OCX) Block 1, the company said.

"The GPS constellation is a valuable asset to our warfighters, our nation and the world. This risk-reduction effort ensures the Air Force has the ability to maintain the constellation at full strength," said Mark Stewart, vice president of Lockheed Martin’s Navigation Systems mission area. "We are here to support the Air Force and the GPS III program any way we can."

In February, the Air Force awarded Lockheed Martin the $96 million COps services and supplies contract. The government approved the company’s proposed ground system modification during a Preliminary Design Review on May 11, the company said.

As Inside GNSS reported, under a separate contract in October, Lockheed Martin completed the Commercial Off-the-Shelf (COTS) Upgrade no. 2 (CUP2) project, which is part of a multi-year plan to refresh the AEP’s technology and enhance the system’s ability to protect data and infrastructure, the company said. Lockheed Martin said CUP2 is now fully operational and managing the current GPS constellation.

In September, Lockheed Martin received a $395 million U.S. Air Force Space and Missile Systems Center contract option to build two additional GPS III satellites. The contract option calls for long-lead and production hardware to manufacture GPS III space vehicles (SVs) 9 and 10.

The government plans to compete future purchases of GPS III satellites beginning with the GPS III SV 11. This future competition will maintain the current technical GPS III baseline, and will add additional hosted payloads to increase system accuracy, search and rescue capability, and universal S-Band compatibility, the Air Force said.

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Lockheed Martin has announced a major upgrade to modernize the GPS ground control system, the company said. The commercial-off-the-shelf (COTS) upgrade no. 2 (CUP2) project, which became operational in mid-October to manage the 31 GPS satellites, is the latest step in the U.S. Air Force’s plan to refresh technology and transform the legacy operational control segment, also known as the Architecture Evolution Plan (AEP), the company said.

Lockheed Martin has announced a major upgrade to modernize the GPS ground control system, the company said. The commercial-off-the-shelf (COTS) upgrade no. 2 (CUP2) project, which became operational in mid-October to manage the 31 GPS satellites, is the latest step in the U.S. Air Force’s plan to refresh technology and transform the legacy operational control segment, also known as the Architecture Evolution Plan (AEP), the company said.

"Under CUP2, Lockheed Martin and the Air Force installed modern commercial hardware and a major software upgrade that enhances the system’s ability to protect data and infrastructure from cyber threats, as well as improves its overall sustainability and operability," said Vinny Sica, Lockheed Martin vice president and general manager of mission solutions. "Continued modernization and cyber-hardening of the GPS control system is vitally important to the sustainment of navigation services for our military and all global GPS users."

The Air Force awarded Lockheed Martin the CUP2 project in November 2013 through its GPS Control Segment contract. The system, a part of a GPS Control Segment contract, is deployed into the AEP’s GPS Master Control Station and the Alternate Master Control Station.

This is the third major technology upgrade of the GPS command and control system since the GCS contract began in January 2013, the company said.

In May, as part of Contingency Operations (COps) through the GPS III contract, Lockheed Martin demonstrated a preliminary design to build off CUP2 and further upgrade the AEP, the company said. This supports the next generation GPS III satellites to perform their positioning, navigation and timing mission.

Lockheed Martin said COps is a temporary gap filler prior to the entire GPS constellation’s transition to the next-generation Operational Control System (OCX) Block 1, which is currently in development.

The Air Force’s Space and Missile Systems Center, Global Positioning Systems Directorate, contracted the CUP2 upgrade. The Air Force Space Command’s 2nd Space Operations Squadron (2SOPS), based at Schriever Air Force Base, Colorado, manages and operates the GPS constellation.

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In September NOAA, through the government’s Commercial Weather Data Pilot program, awarded contracts to San Francisco, California-based Spire Global ($370,000) and GeoOptics ($695,000), of Pasadena, California, to provide RO data. This data will be used to assess whether commercially provided information can be incorporated into the agency’s weather models.

The National Oceanic and Atmospheric Administration (NOAA) will purchase data from small commercial satellites to expand its GNSS radio occultation (RO) efforts to better predict weather.

In September NOAA, through the government’s Commercial Weather Data Pilot program, awarded contracts to San Francisco, California-based Spire Global ($370,000) and GeoOptics ($695,000), of Pasadena, California, to provide RO data. This data will be used to assess whether commercially provided information can be incorporated into the agency’s weather models.

The RO technique has been around for a long time, taking advantage of the effects of electrical energy and moisture in the atmosphere on GNSS signal propagation. The GPS signals bend a bit as they skim through the atmosphere; a deflection that is a function of the density of the atmosphere. The time it takes for the signal to travel the now-longer path around the curve of the planet can be used to calculate atmospheric properties, such as temperature, pressure, humidity and electron density.

With its Stratos product, Spire gathers RO data from 10 low Earth orbit (LEO) small, or microsatellites with multiple sensors, tracking GPS signals providing 3.65 atmospheric profiles per year, according to the company. GeoOptics will begin launching its LEO cubesat constellation, CICERO, in early 2017. When RO data is combined with that from polar-orbiting weather satellites, NOAA believes it can make better weather forecasts.

Both Spire and GeoOptics will begin providing GNSS RO data to NOAA by April 30, 2017, the agency said. NOAA’s National Environmental Satellite, Data, and Information Service (NESDIS) will analyze the data and issue a report in early 2018.

"[NOAA’s] models take data from a number of sources including radiosondes, land-based stations, and satellites," said Sandy MacDonald, Spire’s director for numerical weather prediction. "GPS RO data delivers a very accurate and detailed sounding of temperature and moisture from the upper atmosphere into the lower atmosphere. About 40 percent of the soundings make it to the lowest layer of the atmosphere, the boundary layer. GPS RO data is exceptionally useful for making bias corrections in the full atmosphere."

NOAA already uses GNSS RO data through the six-satellite COSMIC constellation, which is a joint satellite program with Taiwan. The agency has requested more federal funding for COSMIC-2 follow-on satellites.

Currently, Spire’s satellites collect RO data in a pre-production capacity, said MacDonald, a 40-year NOAA veteran who leads Spire’s RO efforts in Boulder, Colorado. "Unlike some forms of data, GPS-RO requires processing for it to be useful in forecasting. This September, at the International Radio Occultation Working Group, we revealed the first commercially collected and processed GPS-RO profiles," he said. "The biggest hurdles to getting the data is access to on-time rocket launches. We have the single most aggressive launch schedule in the industry with over 70 satellites manifested over the next year but delays on the launch pad affect how quickly we get access to this data."

Congressional Push for Commercial Data
While Congress approved $3 million for Commercial Weather Data Pilot program, the effort was initiated through the Weather Research and Forecasting Innovation Act. The measure, sponsored by two Oklahoma representatives, Frank Lucas and Jim Bridenstine, both Republicans, calls for commercial data for weather monitoring purposes.

U.S. Representative Lamar Smith, R-Texas, who is chairman of the House Committee on Science, Space, and Technology, said it was a good thing that NOAA is acquiring private sector weather data. "In the face of looming data gaps and continual delays with our governmental satellite systems, the private sector can provide data to better predict weather and protect American lives and property," he said. "In the face of real threats, NOAA needs to address its shortfalls and think beyond government weather systems by making further awards under the [Commercial Weather Data Pilot program].

"We see a future with small satellites delivering data of the same quality that required large satellites and much greater cost in the past," MacDonald said. "We’ve already demonstrated that small satellites are most effective when collecting large amounts of data through Spire’s ship tracking product. Similar to ship tracking where frequent updates are important, spatial density is an important factor in the usefulness of GPS RO data. By launching many small satellites, they’re able to capture an exceptional number of occultations in comparison to smaller number of traditional satellites."

Small satellites have the attention of the White House Office of Science and Technology Policy (OSTP). A new OSTP initiative, "Harnessing the Small Satellite Revolution," calls for NASA, the Defense Department (DoD), Commerce Department, and other agencies to promote government and private small satellite use.

In addition to NOAA’s weather efforts, small satellites will be used for remote sensing, communications, science, and space exploration, the White House said. NASA will fund as much as $30 million in small satellite data purchases, including $25 million for nongovernment spacecraft constellations. NASA also intends to purchase such Earth science observation data as moderate-resolution land imaging and RO data.

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The 22nd World Congress and Exhibition on Intelligent Transport Systems and Services will be held at the Convention Centre Bordeaux and Exhibition Centre Bordeaux in Bordeaux, France on October 5 – 9, 2015. It will focus on how achieving intelligent mobility will change our lives, and the benefits space can bring to ITS applications.

The theme for this year’s event is “Towards Intelligent Mobility – Better Use of Space”, and will offer Plenary, Executive, Technical/Scientific, Special Interest and Interactive Sessions.

The 22nd World Congress and Exhibition on Intelligent Transport Systems and Services will be held at the Convention Centre Bordeaux and Exhibition Centre Bordeaux in Bordeaux, France on October 5 – 9, 2015. It will focus on how achieving intelligent mobility will change our lives, and the benefits space can bring to ITS applications.

The theme for this year’s event is “Towards Intelligent Mobility – Better Use of Space”, and will offer Plenary, Executive, Technical/Scientific, Special Interest and Interactive Sessions.

A Congress topic of note for the GNSS community is "Space Technologies and Services For ITS", and will include discussion of GNSS positioning and timing services used by all modes of transport, and how, when combined with vehicle sensors and with vehicle-to-infrastructure (V2X) communication, future multi-constellation and multi-frequency receivers will dramatically improve positioning performance and contribute to the development of a wide range of innovative ITS applications, including:

• Hybridization of GNSS receivers with other sensors (eg video, lidar).
• Collaborative cloud-based mapping.
• Reliable positioning for critical ITS services.
• Solutions for regulated services (eg eCall, digital tachograph, dangerous goods)
• New services from multi-constellation receivers.
• Monitoring transport infrastructures using Earth observation satellites.
• Traffic monitoring with infra-red cameras from satellites.

This year’s event will also include a special session on "GNSS Services
and Performance Standardization Workshop" with discussion of GNSS
positioning and timing services used by all modes of intelligent
transport. The workshop is organized by ERTICO and the Satellite
Positioning Performance Assessment for Road Transport (SaPPART) European
Cooperation in Science and Technology (COST) Action.

Other congress topics include:

• Cooperative ITS Deployment Challenges
• Multimodal Transport for People and Goods
• Urban Trends Driving ITS Changes
• Solutions for Sustainable Mobility
• Automated Roads, Automated Management, Automated Driving
• Are Big Data and Open Data Transport’s “Silver Bullets”?

The ITS World Congress in Bordeaux is organized by ERTICO – ITS Europe in close cooperation with the European Commission, ITS America and ITS Asia-Pacific, and is hosted by TOPOS.

Congress organizers will also offer a social program for attendees to enjoy all areas of interest in and around Bordeaux, its region, products and services. The official language of the Congress is English. A selected number of sessions will be conducted in French.

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Thousands? Millions?

Yes, back in the wreckage of the second George Bush’s second term, Barack Obama looked pretty good by comparison. Even then, though, raising the banner of “Hope” before the eyes of a desperate nation was a risky thing to do.

But now — much as I hate it — I’d have to answer Sarah Palin’s snide query, “How’s That Hopey-Changey Stuff Working Out For Ya?’’ Not so well, Mrs. Palin, really not so well.

And back in 2009, Obama’s resistance to being separated from his Blackberry by security-minded officials seemed amusing — a generational indication that smartphones might be competing for the affections of Americans toward their automobiles. Instead, it actually foreshadowed U.S. eavesdropping on the phones of world leaders.

What seemed wonkish but well-informed inclination toward new technology turned out to be mere fancy for the hipness of social media. Hence, the near-catastrophe of LightSquared driven by an impulsive search for 500 megahertz of RF spectrum to reallocate as wireless broadband.

No, once in the White House, the execution of plans fell far short of the rhetoric. Thus, the early promise to close our gulag for terrorists at Guantanamo — filled with innocent and guilty alike — appears no more likely to happen in 2014 than in 2009.

Any more than Obama’s teaching courses in constitutional law seems to have engendered a respect for the protections of the U.S. Constitution.

Or that the good intentions of universal health insurance coverage could survive its poor design and disastrous rollout. “Let it be written, let it be done,” did not work any better for the president’s health care mandate than the same mantra did for Yul Brynner as Pharaoh in “The Ten Commandments.”

What would I like to see this administration achieve in the way of space-based positioning, navigation, and timing (PNT) before last call at the polls in 2016? Well, for a starter, here’s a short list:

• Admit that the Global Positioning System — or more broadly, PNT — really is a part of the national critical infrastructure that deserves at least as much consideration and protection as the other 16 sectors identified in the National Infrastructure Protection Plan. After all, GPS has a very tangible, physical presence in its satellites and ground control segment.
• Support an international GNSS monitoring and assessment service that would benefit all system providers and users. Isn’t that a natural corollary to the administration’s 2010 amendment to National Space Policy authorizing use of foreign GNSS services to strengthen GPS?
• Acknowledge that Americans’ personal location should be considered private unless willingly made public by individuals, granting it the Fourth Amendment protections envisioned in the Supreme Court’s Katz v. United States decision. And enforce those protections against wholesale National Security Agency surveillance as well as the FBI and local police. And while we’re at it, let’s admit that Edward Snowden is closer to being a patriot in the tradition of Daniel Ellsberg with his Pentagon Papers than the traitorous spy that embarrassed officials are trying to portray him as.
• Get the unmanned aerial systems (UAS) initiative off the ground and into the air. Is it possible that we could learn from the experience of many other nations, including those in Europe, that are well ahead of the United States in this area. This may seem at odds with the previous suggestion, but with adequate legal guidelines personal privacy can remain secure while the civil benefits of UAS are revealed. The FAA’s responsibility for ensuring aviation safety are not incompatible with advancing the UAS project vigorously.
• Actually design and approve plans for — if not the completion of — a system to detect and mitigate GNSS interference as well as ensure a backup for GPS. More than nine years after a presidential directive to do so, we should either invest the resources and leadership to get it done or admit that it’s beyond our abilities.

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Ionospheric scintillations are rapid temporal fluctuations in both amplitude and phase of trans-ionospheric GNSS signals caused by the scattering of irregularities in the distribution of electrons encountered along the radio propagation path. The occurrence of scintillation has large day-to-day variability. The most severe scintillations are observed near the poles (at auroral latitudes) and near the equator (within ± 20 degrees of geomagnetic equator).

Ionospheric scintillations are rapid temporal fluctuations in both amplitude and phase of trans-ionospheric GNSS signals caused by the scattering of irregularities in the distribution of electrons encountered along the radio propagation path. The occurrence of scintillation has large day-to-day variability. The most severe scintillations are observed near the poles (at auroral latitudes) and near the equator (within ± 20 degrees of geomagnetic equator).

Equatorial amplitude scintillation affects both code and carrier tracking and degrades pseudorange and carrier phase measurements. Deep amplitude fades over sufficient duration can cause loss of lock in both code and carrier tracking within a GNSS receiver. Equatorial phase scintillation adversely affects the operation of a receiver’s phase lock loop (PLL) and leads to carrier cycle slips, navigation data bit errors, and complete loss of carrier lock.

Usually the level of scintillation can be characterized by the S₄ amplitude scintillation index; the higher the S₄ index, the more severe the scintillation. Details for computing the S₄ index can be found in the Additional Resources section at the end of this article. Carrier phase tracking is very sensitive to scintillation due to a PLL’s stringent tracking threshold. Therefore, one solution for the scintillation problem is to employ a frequency lock loop (FLL) to replace a PLL for carrier tracking, due to its better robustness to signal attenuation and signal dynamics. However, many GNSS applications require (multi-frequency) carrier phase measurements, which a FLL cannot provide.

Despite the challenge of phase tracking under strong equatorial scintillation, several signal processing techniques can be used to improve the carrier tracking robustness. The common ones are FLL-assisted-PLL, adaptive-bandwidth PLL, and data stripping/aiding.

Given its robustness, using a FLL to aid a PLL seems like a wise approach. This combined carrier-tracking loop is called FLL-assisted-PLL. In a typical implementation, a FLL and a PLL operate in parallel to jointly control the carrier numerical controlled oscillator (NCO). The overall performance of such a FLL-assisted-PLL falls between that of a standalone FLL and a standalone PLL, depending on the loop noise bandwidths.

An adaptive-bandwidth PLL is another popular option for carrier tracking under scintillation. The use of a wide PLL bandwidth can help maintain phase tracking during periods of phase scintillation by tracking a rapidly changing phase. On the other hand, a narrow PLL bandwidth is desirable to tolerate amplitude scintillation with the ability to track at low carrier-to-noise–density (C/N₀) ratios. The adaptive-bandwidth PLL is typically implemented by a Kalman filter with a time-varying Kalman gain based on the C/N₀ conditions, because the Kalman filter explicitly models the receiver clock and optimally adapts its band-width based on C/N₀.

It is well-known that a pure PLL discriminator provides an improved signal tracking threshold by up to six decibels compared to a Costas discriminator. Modernized GNSS signals provide a pilot (data-less) component and a data component. Although tracking only the pilot component can bring a three-decibel loss due to the power sharing between the data and pilot components, a net gain of three decibels still is achieved due to the pure PLL. Therefore, tracking the pilot component of modernized GNSS signals (e.g., GPS L2C and L5) is recommended in scintillation environments.

For GNSS signals that do not have a pilot component, one can still use a pure PLL discriminator with data stripping. For example, for the GPS L1 C/A signal, after storing the data bits for the entire navigation message, or with external aiding, it is possible to predict the navigation data bits until the navigation message changes. This is so-called data stripping. With the help of data stripping, one can use a pure PLL discriminator instead of a Costas discriminator in the short term for better carrier tracking under scintillation.

Multi-Satellite, Multi-Frequency Solutions
The techniques that we have discussed thus far focus on improving the carrier tracking in a single-frequency scalar-based receiver. Carrier tracking under scintillation can be improved by using multi-satellite and multi-frequency aiding. This is because scintillation rarely occurs on all visible satellites simultaneously on account of the isolated nature of electron irregularities mentioned in the introduction.

Furthermore, scintillation is carrier frequency–dependent. Both amplitude and phase scintillation levels has an inverse relation with the signal carrier frequency. The lower the carrier frequency, the stronger the scintillation is. In other words, if the same GPS signal was broadcast on L1, L2, and L5 frequencies at the same power, scintillation will most likely affect the L2 and L5 signals more than the L1 signal.

For the benefits of both frequency diversity and satellite diversity, it is important to implement the multi-satellite and multi-frequency aiding in a multi-frequency GNSS receiver. A typical implementation of such a processing architecture — herein referred to Shared-Architecture A — is shown in Figure 1 (see inset photo, above right, for all figures).

For the purpose of a better illustration, only the processing for GPS L1 C/A and L2C signals is shown in the figure. Each satellite has multiple channels for tracking signals on different frequencies. Each channel has a Doppler removal and correlation (DRC) unit, a local signal generator unit, and a PLL.

In this architecture, the key component is the multi-frequency vector delay and frequency lock loop (VDFLL). It receives the correlation from all channels and tracks the code and frequency of all signals from all satellites jointly. Regardless of the implementation variations, a VDFLL should include a local PVT (position, velocity, and time) engine that accepts multi-frequency code and Doppler measurements. The most common choice of this local PVT engine is an extended Kalman filter.

The VDFLL provides two feedback signals for each channel. One is the code phase error or the code Doppler to control the code NCO in the local signal generator, and the other is the carrier Doppler to aid the PLL in each channel. These code phase errors and the carrier Doppler values are derived from the local PVT engine.

With the carrier Doppler aiding from the VDFLL, the PLL in each channel only needs to track the residual Doppler (i.e., that induced by scintillation). The main implementation challenge for Shared-Architecture A is incorporating a reliable multi-constellation, multi-frequency PVT engine, as implementation of multi-frequency aiding and multi-satellite aiding depend upon it.

Figure 2 presents an alternative processing architecture, named Shared-Architecture B. Compared to Shared-Architecture A, this architecture employs a delay lock loop (DLL) for code tracking in each channel, and the multi-frequency VDFLL is replaced by a single-frequency VFLL and a code phase estimator.

In this architecture, DLLs are carrier-aided by PLLs to provide low-noise pseudorange measurements. As the carrier aiding from PLLs are fused by a VFLL, the multi-satellite aiding still propagates to DLLs indirectly from the PLLs in L1 C/A channels, even though a vector delay lock loop (VDLL) is not used in this case. Instead of being used to control the code NCOs, the code phase estimates derived from the single-frequency PVT engine are applied to detect loss of code lock on L1 C/A signals and to steer the DLLs when loss of code lock does occur.

In Shared-Architecture B, because the L1 C/A signal is more resistant to equatorial scintillation than the L2C signal, the L2C PLLs are aided by the L1 C/A PLLs. Since the carrier Doppler from the L1 C/A channels is already fused by the VFLL, the L2C PLLs benefit from the satellite diversity as well. In the L2C channels, similar to the L1 C/A channels, the carrier-aided DLLs are used for code tracking. The estimated L2C code phases based on the L1 C/A timing information are only used for detecting the loss of code locks and for code steering after loss of locks.

Shared-Architecture B also has the advantage of implementing multi-satellite aiding and multi-frequency aiding separately. For example, if only the multi-frequency aiding mode is needed, the receiver can simply disable the VFLL aiding and keep the L1-to-L2 aiding, which Shared-Architecture A cannot.

For signal acquisition, both architectures only acquire the signal on a single frequency (referred to here as the master frequency signal), because the carrier Doppler and timing information of the master frequency signal can directly estimate the code phase and carrier Doppler parameters of other frequency signals. In order words, the timing information and carrier Doppler from the master frequency signal can be used to directly initialize the code and carrier tracking loops of other frequency signals. The typical choice of the master frequency signal is the GPS L1 C/A signal, due to its shorter ranging code and stronger scintillation resistance compared to others.

We implemented Shared-Architecture A and Shared-Architecture B in a multi-constellation, multi-frequency GNSS software receiver. We will only present here the results of the Shared-Architecture B with the intermediate frequency (IF) data affected by equatorial ionospheric scintillation, but results with Shared-Architecture A were similar.

Data was collected in Rio de Janeiro during a research project established between the Brazilian Institute of Geography and Statistics (IBGE), the University of the State of Rio de Janeiro (UERJ), and the Position, Location And Navigation (PLAN) Group at the University of Calgary, to investigate the effects of equatorial ionospheric scintillation on GNSS signals during the current solar maximum.

Figure 3 shows the percentile of valid L1 C/A and L2C phase observations with the Shared-Architecture B and a standard architecture (without using multi-frequency and multi-satellite aiding). Valid phase observations are defined as those where the carrier phase observations have a phase lock indicator (PLI) value larger than 0.6 (see Additional Resources) and no cycle slips are detected. The results are based on eight hours of data using two-hertz measurements.

As reflected in the figure, due to the benefits of multi-frequency/multi-satellite aiding, Shared-Architecture B provides significantly more valid measurements than a standard architecture over the entire S₄ range, especially for the L2C carrier phase. This demonstrates the importance of the multi-frequency/multi-satellite aiding for a multi-frequency GNSS receiver.

In conclusion, despite the challenge of carrier tracking under strong equatorial scintillation, the performance of carrier tracking can be improved via modern signal processing techniques. Due to the natural characteristics of scintillation, multi-frequency/multi-satellite aiding benefits multi-frequency carrier tracking under equatorial ionospheric scintillation. The improved performance of the proposed multi-frequency/multi-satellite aiding was shown with IF data collected in Brazil.

Additional Resources
For equatorial scintillation
Doherty, P. H., and S. H. Delay, C. E. Valladares, and J. A. Klobuchar, “Ionospheric Scintillation Effects in the Equatorial and Auroral Regions,” Proceeding of ION GPS-2000, Salt Lake City, Utah, USA, September 2000

For S₄ index calculation and PLI calculation
Van Dierendonck A.J., and J. Klobuchar and Q. Hua, “Ionospheric Scintillation Monitoring Using Commercial Single Frequency C/A Code Receivers,” Proceedings of the 6th International Technical Meeting of Satellite Division of the Institute of Navigation (ION GPS 1993), pp. 1333-1342, September 1993

Van Dierendonck, A. J., “GPS Receivers,” in Global Positioning System: Theory and Applications, Vol. 1, AIAA, Washington, DC, pp. 330–433, 1996

For FLL-assisted-PLL and adaptive-bandwidth PLL
Ward, P. W., “Performance Comparison between FLL, PLL and a Novel FLL-Assisted-PLL Carrier Tracking Loop Under RF Interference Conditions,” Proceedings of ION GNSS 1998, pp. 783-795, September 1998

Humphreys, T. E., and M. L. Psiaki, B. M. Ledvina, and P. M. Kintner, Jr., “GPS Carrier Tracking Loop Performance in the Presence of Ionospheric Scintillations,” Proceedings of ION GNSS 2005, Long Beach, California, USA, September 2005

For vector tracking
Lashley, M., and D. Bevly , “GNSS Solutions: How do vector delay lock loops predict the satellite signals?” Inside GNSS, September/October 2012

For GSNRx
http://plan.geomatics.ucalgary.ca/project_info.php?pid=27, including the following available on that website:

Petovello, M. G., and C. O’Driscoll, G. Lachapelle, D. Borio, and H. Murtaza, “Architecture and Benefits of an Advanced GNSS Software Receiver,” Journal of Global Positioning Systems, vol. 7, no. 2, pp. 156–168, 2008

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