“We’ll be ready to launch the first GPS III in 2015, but it now appears the next generation GPS Operational Control System, or OCX, won’t be ready for about a year or two after that,” General William L. Shelton, commander of Air Force Space Command (AFSPC) told attendees at the 28th Annual National Space Symposium.

Launch of the first GPS III satellite has slipped to 2015 and completion of the ground control system is now delayed by up to two years, according to the chief of the Air Force’s space operations

“We’ll be ready to launch the first GPS III in 2015, but it now appears the next generation GPS Operational Control System, or OCX, won’t be ready for about a year or two after that,” General William L. Shelton, commander of Air Force Space Command (AFSPC) told attendees at the 28th Annual National Space Symposium.

The first GPS III satellite had been expected to launch sometime in 2014. The slip in the satellite’s launch date, however, is not due to development problems with the spacecraft, according to the program’s primary contractor.

“Production is proceeding well and we are on schedule to deliver the first GPS III satellite for launch availability in 2014,” said Michael Friedman, a spokesman for Lockheed Martin. “The Air Force will make a launch date decision based on booster availability, ground system readiness and DoD priorities.”

Capt. Chris Sukach, an AFSPC spokesperson at Peterson Air Force Base, Colorado, explained, “The GPS program launches at a rate required to sustain the constellation; so, satellite Available for Launch (AFL) dates and projected range dates may differ. As planned, GPS III SV-01 will be available for launch no earlier than spring of 2014 and is in the process of planning for launch in 2015, given the current health of the constellation.”

Several sources familiar with the program suggested that the launch delay might be due to a shortage of launch capacity.

Military officials have, however, been anticipating a shortfall of launch capability and studying ways to ease the crunch and keep down escalating costs and effort that could be particularly important to maintaining the capability of the GPS system. The early satellites were launched in rapid succession to fill out the constellation and are now aging — and potentially failing — in rapid succession as well.

To keep the constellation healthy the military is looking at launching more than one GPS satellite at a time. The Air Force and industry are also considering other kinds of launch vehicles for military payloads.

“We’re working hard with United Launch Alliance to get costs under control,” Shelton told the meeting attendees in April, “and we’re simultaneously planning for new entrants to complete the certification process required to fly national security payloads.”

While the delay of the first satellite launch should be a year or less, the slippage on the ground control segment could be as long as two years. This has triggered some changes to the way the work is being handled.

Re-Engineering the OCX Contract
Completion of the Next Generation Operational Control System or OCX, which was expected to be delivered in 2015, has been delayed to 2016 or 2017. However, an expert familiar with the issue who spoke on condition of anonymity, said that the schedule had some padding for contingencies.

The source said that the delay is the result of modifications to the technical baseline of the contract and formal recognition of shifts in the contract’s requirements.

“Over the last six months, there have been a number of significant contractual changes to the OCX program,” confirmed Jared Adams, a spokesman for OCX prime contractor Raytheon, including “updates to the technical baseline and scope reductions to address affordability challenges.”

Those affordability challenges had led the Air Force to ask Raytheon to find some savings, said the source. After working closely with defense officials, the company proposed deferring or deleting some capabilities, implementing some changes in the near term and delaying others until later in the sustainment part of the program, said the source.

Although the person declined to cite specific details changes because they were still under consideration, the modifications could save more than $100 million. Some of those changes, however, would come at the expense of the program’s schedule, according to the source.

But Air Force Has a Plan
To reduce the impact of the OCX delay, said Shelton, the Air Force has “developed a mitigation plan that will at least allow launch and some navigation payload control.”

That plan includes several new contracts, including two awarded to Raytheon and Lockheed at the beginning of the year. The Air Force says that an early version of OCX software (Block 0) will be capable of supporting all mission operations necessary to launch and check out the first GPS III spacecraft.

Raytheon won the Launch and Checkout System (LCS) contract that supports the GPS III satellites up to the point of launch. Under LCS the firm “will provide for the early identification and mitigation of any GPS III enterprise risks, support ground checkout and launch operations and resolve any anomalies prior to the first GPS III satellite launch,” said Ray Kolibaba, GPS OCX program manager for Raytheon’s intelligence and information systems business, in a January statement.

Once a GPS III satellite is ready for launch, the support function is handed off to Lockheed Martin. Under its new Launch and Checkout Capability (LCC) contract, Lockheed will support the actual launches, early orbit operations and checkout of all GPS III satellites before they are turned over to Air Force Space Command for operation. The contract includes trained satellite operators and an operations center at Lockheed Martin’s Newtown, Pennsylvania, facility.

The LCC team should be ready for the first scheduled readiness exercise in August, said Friedman.

“The two pieces [LCS and LCC] work hand in hand,” said Keoki Jackson, vice-president of Lockheed Martin’s navigation systems mission area. He said that the LCC work moves the overall ground control capability forward by bringing online some GPS III–specific capabilities before the full OCX system is in place.

“We start with the LCC and then transition at some point in time to full OCX operations,” he said. Full OCX operations will encompass the IIF satellites, the IIR and IIRM satellites, and the full on-orbit operational maintenance of the GPS III after the early-orbit checkout.

According to the AFSPC’s Sukach, LCS brings integrated capabilities not available with the existing Architecture Evolution Plan (AEP) and the Launch, Anomaly, and Disposal Operations (LADO) system. The were both introduced in September 2007 and are currently used for command and control of GPS satellites.

“An advantage of LCS is that it can perform on-orbit checkout exclusively, thus omitting the need to de-conflict schedules with the 50th Space Wing in order to conduct the operation,” Sukach told Inside GNSS. “More importantly, LADO is not capable of launching a GPS III. Part of the OCX acquisition strategy was to ensure the government had one integrated system to launch, checkout, command and control GPS. OCX does that, as AEP and LADO are two stand alone systems.”

The LCC/LCS is scheduled to be available to support the first GPS III SV-01 launch, according to the Air Force.

Because the earlier generation of high-performing GPS Block IIAs had not been expected to last until the modernized control segment came on-line, AFSPC proposes to fund the current LADO operator, Braxton Technologies, to add command and control capability to OCX for them as well.

A Larger Part for LCC to Play
Jackson said that the Air Force is now considering an expanded role for LCC.

“The planned Launch and Checkout Capability only allows the check out and testing of the payloads, but currently doesn’t support the full operation in setting the vehicle healthy as part of the constellation,” he said. The Air Force is studying ways to extend the capability for full operations of the satellite downstream, Jackson added

Lockheed will likely gain some useful experience for such a downstream mission under a new contract announced May 4.

“Under the contract, Lockheed Martin will provide technical support to the Air Force’s 2nd Space Operations Squadron (2SOPS) to monitor the health and performance of the first two GPS III satellites from launch through their 15 year operational design lives,” said Friedman in a statement. The contract will also support the LCC operations at the company’s Newtown facility.

Before the implementation of the LCC a lot of the GPS III work would have been done out of Schriever Air Force Base, Colorado, by Air Force personnel, said Jackson. Tapping the facility in Newtown will enable the Air Force to move faster.

The government has a fairly lengthy lead-time to staff and train personnel for these positions, Jackson said. “In general, a contractor operation is more streamlined in terms of the schedule to make that happen.”

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Return to main article: "Demystifying GLONASS Inter-Frequency Carrier Phase Biases"

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1996 soccer game in the Midwest, (Rick Dikeman image)

Nouméa ground station after the flood

A pencil and a coffee cup show the size of NASA’s teeny tiny PhoneSat

Bonus Hotspot: Naro Tartaruga AUV

Pacific lamprey spawning (photo by Jeremy Monroe, Fresh Waters Illustrated)

“Return of the Bucentaurn to the Molo on Ascension Day”, by (Giovanni Antonio Canal) Canaletto

The U.S. Naval Observatory Alternate Master Clock at 2nd Space Operations Squadron, Schriever AFB in Colorado. This photo was taken in January, 2006 during the addition of a leap second. The USNO master clocks control GPS timing. They are accurate to within one second every 20 million years (Satellites are so picky! Humans, on the other hand, just want to know if we’re too late for lunch) USAF photo by A1C Jason Ridder.

Detail of Compass/ BeiDou2 system diagram

Hotspot 6: Beluga A300 600ST

1. GROWTH SPURT
California/Nevada, USA
√ The age of the Sierra Nevada mountains — home of Yosemite Valley and Lake Tahoe — is puzzling to geodesists. Integrating GPS and inSAR, Universities of Nevada and Glasgow teams studied the area’s uplift and found that it is growing by 1 to 2 millimeters per year. The verdict? The entire range could have arisen in less than 3 million years.

1. GROWTH SPURT
California/Nevada, USA
√ The age of the Sierra Nevada mountains — home of Yosemite Valley and Lake Tahoe — is puzzling to geodesists. Integrating GPS and inSAR, Universities of Nevada and Glasgow teams studied the area’s uplift and found that it is growing by 1 to 2 millimeters per year. The verdict? The entire range could have arisen in less than 3 million years.

• (University of Nevada, Reno, news May 3, 2012) Geodetic Lab uses GPS and radar for most precise measurements over entire Sierra Nevada mountain range
• (Geology journal pre-issue publication page, April 27, 2012) Sierra Nevada Uplift

2. TESTING 1 . . . 2. . . . K
Moscow, Russia
√ Russia will test its second GLONASS-K satellite in 2013, instead of this year. The modernized K class is unpressurized, lighter, more accurate and longer-lived than previous models. It transmits four civil and military signals. Grigory Stupak, deputy head of Russian Space Systems, announced the news at the 6th International Satellite Navigation Forum in Moscow.

(Ria Novosti April 17, 2012) Russia to test second Glonass-K satellite in 2013

3. TRAFFIC UPDATES
Tiruchirappalli, Tamil Nadu, India
√ Speaking at Trichy Airport, the first in India to use satellite-based air traffic management, officials said GAGAN — GPS Augmented Navigation System — will be in all airports by June 2013. The ISRO website shows a second GAGAN satellite will launch in 2012 and the third in 2013-14. The Indian SBAS will cover longitudes from South Africa to Australia.

• Indian Space Research Organization (ISRO) Future Programs
• The Economic Times of India, May 13 GAGAN navigation system to be set up in all airports by next year

4. JAM SESSION
Kaesong, North Korea; Seoul, South Korea; Beijing, China
√ South Korean president Lee Myung-bak visited Chinese President Hu Jintao and, magically, North Korea stopped jamming GPS signals. From April 28 until May 14, the peninsula’s bad boys disrupted more than 300 commercial flights, 10 ships, and untold automobiles in South Korea with coordinated signals originating in Kaesong.

• (Dong-A May 17, 2012)  NK stops jamming satellite signals in South Korea

5. ALL THE SHIPS AT SEA
Guangzhou, China
√ 70,000 Chinese fishers use Beidou’s short message service (SMS) to send 700,000 messages a month, said official Ran Chengqi at the Chinese Satellite Navigation Conference in May. Although 80% of Chinese fishing boats lack modern navigation equipment, coastal provinces have been underwriting installation of receivers partly to facilitate warnings in case of maritime border conflicts.

• (Xinhua, May 15, 2012) Beidou navigation system installed on more Chinese fishing boats

ONLINE EXTRAS!

6. Turn Left at the Pub
Newcastle, England
√ Based on research that shows giving up driving is closely related to a decline in health in older people, Newcastle scientists built a mobile driving simulator to investigate new technologies that could help keep elderly drivers safely behind the wheel as long as possible.

With test subjects in their 80s, the Intelligent Transport team at Newcastle University is investigating in-vehicle tools, including GPS, that can do the trick. They developed a satellite navigation device that uses local landmarks as turning cues: a local pub, a library, or a post office.

In a country that drives on the left, the GPS planned routes that avoided right-hand turns in order to help less confident drivers who were wary of oncoming traffic. The researchers are also experimenting with night visions systems and intelligent speed adaptations.

• (Newcastle University April 23, 2012) Keeping older drivers on the road

7. Che Catastrofe! Venice Still Sinking
Venice, Italy
√ Concerned citizens started precise measurements of the sea surrounding Venice 140 years ago. Before that, art supplied the information.

Canaletto, the popular 18th century landscape painter and printmaker of Venetian scenes (see inset photo, above right), was so meticulous and accurate in his paintings that scientists could later determine the city had sunk more than two feet since 1727. But they thought the city was stabilized after a series of flood control and restoration projects.

However, Venice could be 3.2 inches lower by 2032, according to a 10-year study that used GPS and inSAR, a radar tool for measuring Earth’s deformation.

GPS took absolute readings of the city and its surrounding lagoons. inSAR detected the change elevation relative to other sites.

The new study also indicated that the lagoon area was tilting eastward, a millimeter or two each year, leaving Venice in the west somewhat higher. Prior satellite analyses didn’t pick up on the tilt, possibly because the scientists were using inSAR alone.

The scientific study was published on March 28 in the American Geophysical Union journal G-Cubed (Geochemistry, Geophysics, Geosystems).

Canaletto’s art survives in museums, private collections and college dorm walls all over the world.

The post GNSS Hotspots | May 2012 appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Return to main article: "How do GNSS-derived heights differ from other height systems?"

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The diversity and redundancy provided by multiple, independent, compatible, and in some respects, interoperable GNSS systems must be a good thing, right?

Well, almost certainly. But as with many things in life and technology, the devil’s in the details. And, as the varied characteristics and design specifications of new GNSSes and regional systems become clearer, it may not be too early to sort out those details.

The diversity and redundancy provided by multiple, independent, compatible, and in some respects, interoperable GNSS systems must be a good thing, right?

Well, almost certainly. But as with many things in life and technology, the devil’s in the details. And, as the varied characteristics and design specifications of new GNSSes and regional systems become clearer, it may not be too early to sort out those details.

Poll a representative cross-section of experts, and a consensus forms around the top three benefits of using signals from more than one GNSS: increased accuracy, integrity, and service availability — with continuity of service running a close fourth.

In challenging environments, such as urban areas, many signals are contaminated by non-line-of-sight reception or multipath interference. With multi-constellation GNSS, the best signals may be selected for a navigation solution and the worst ones discarded.

Moreover, multi-constellation GNSS brings a significant improvement in the proportion of space and time over which sufficient signals are available without interruption to compute a position solution.

Signal diversity and redundant measurements, together with better geometry from multiple GNSS satellites, allows improved receiver-based integrity monitoring to be carried out, including the detection of multiple satellite/signal failures.

These terms are equally applicable across all domains. For example, when sensing the atmosphere in order to estimate tropospheric delays (which feed into weather forecasting and climate-change studies), the increased number of signal rays through the atmosphere greatly improves the ability to refine the temporal and spatial density of the derived parameters and models.

Beyond this terra cognita, however, more systems bring more variables and more choices, and the way ahead is not always clear.

To help illuminate the unknowns, we called on not one expert, but rather a gallery of them from the iNsight Project — “Innovative Navigation using new GNSS SIGnals with Hybridised Technologies.” Four leading British academic GNSS research centers comprise iNsight.

Participants in this virtual roundtable included the following (with the initials by which they are identified in the answers to our questions): Professor Terry Moore (TM), Director of the Nottingham Geospatial Institute at the University of Nottingham; Professor Marek Ziebart (MZ), Head of the Space Geodesy and Navigation Research Group at University College London (UCL); Dr. Paul Groves (PG), a lecturer in the same group at UCL; Professor Washington Ochieng (WO), Director of the Imperial College London (ICL) Engineering Geomatics Group; Dr. Shaojun Feng (SF), an ICL research fellow; Professor Izzet Kale (IK), Director of the Applied DSP and VLSI Group at University of Westminster.

IGM: What are the practical benefits for product designers and system integrators of having common frequencies and signal designs for GNSS signals?

iNsight: This significantly simplifies RF front-end design at the expense of a slight increase in susceptibility to inter-system interference. The antenna, front-end, and correlator design can be much simpler compared to components designed to operate with multiple systems, and in particular the filtering within the front end of a receiver can also be tighter. A receiver processing signals from different constellations sharing the carrier frequency does not require multiple RF and IF stage filters. The digital front-end, delivering the signals to the baseband processor, would also be simplified. The similarity of the different systems means that signals can be processed in a similar way. Obviously, the positioning algorithms will need extension to cope with the diversities of multiple systems. Beyond this, common signal designs only reduce software development costs. (IZ, TM, PG, WO, SF)

iNsight: Clarity in performance metrics and in standardization. At present we have a plethora of potential coordinate systems/datums from which to choose. For the manufacturer this is not an issue since as long as a reliable transformation exists from one frame to another then a positioning solution can be provided. However, the user does care about coordinate systems and the quality of service delivered. Trends in aviation and the maritime industry show a steady dawning of awareness, followed inevitably by a movement towards a single global datum for positioning and mapping products.

Time is often the elephant in the error budget for GNSS integration. For the mass market, this is largely unimportant. However, for the system developer the issue is becoming more complex. With a choice of frequencies, we have a choice of timescales based on multiple possibilities for ionosphere-free clock solutions. Discontinuities in one timescale become observable against another. Service providers themselves may find they question their approaches. Even at this early stage of GPS/GLONASS integration the optimal solution is not apparent. Class! More work required! (MZ)

IGM: From a technical as well as practical perspective, what are the most promising non-GNSS technologies for integration with GNSS?

iNsight: The time is probably right for a change of positioning and navigation philosophy. The question should no longer be which technologies should integrate GNSS. This may seem heresy in this publication, but perhaps we should now consider the inertial measurement unit (IMU) to be the primary positioning and navigation sensor, and the real question is what do we integrate with the IMU to bound the growth on the INS errors; GNSS, of course, being a prime candidate in most, but not all environments. (TM)

The benefits of integrating GNSS with dead-reckoning technologies are well known. As time progresses, the mix of technologies used for positioning will expand. Three new approaches currently emerging are signals of opportunity (SOOP), 3D mapping, and vision. SOOP comprises signals designed for purposes other than positioning, such as phone signals, GSM, WCDMA, Bluetooth, WiFi, WiMAX, and television. City models (3D mapping) enable new positioning techniques, such as shadow matching that offer improved accuracy in poor-geometry environments, such as urban canyons. It can also be used to identify reflected signals and for conventional map matching and height aiding. Digital cameras are cheap and becoming increasingly ubiquitous. They can be used to aid positioning in many different ways: measuring the distance travelled, position fixing through landmark identification, and aiding GNSS signal selection by detecting obstructions. SOOP should also include signals from low-earth-orbiting (LEO) communication satellites, because in remote mountain area where the GNSS reception is poor, the only SOOP maybe the signal from LEOs. (IZ, PG, WO, SF)

One in a series of articles sponsored by NovAtel Inc.

The post Multi-GNSS Integration appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

I refer, of course, to the untoward and unexpected initiative by the British Ministry of Defense (MoD) to patent the technical innovations that underlie the planned next generation of civil GNSS signals.

As Desi Arnaz often said to Lucille Ball during an “I Love Lucy” episode on TV, “You’ve got some ’splaining to do.”

I refer, of course, to the untoward and unexpected initiative by the British Ministry of Defense (MoD) to patent the technical innovations that underlie the planned next generation of civil GNSS signals.

As outlined in this issue’s Washington View column, the endeavor has caught up the MoD’s technology branch, the Defense Science & Technology Laboratory (DSTL), its commercial licensing arm, Ploughshare Innovations Ltd., and a couple of DSTL innovators, Tony Pratt and John Owen.

Yes, this crew has been busy, busy, busy in recent years — filing applications at patent offices around the world that would put two families of signals intended for global exploitation — including the GPS L1C and Galileo Open Service — into the pocket of national commerce.

Very interesting . . . since everyone knows that a technical working group comprised of experts from Europe and the United States had crafted and agreed upon the key elements of the signal design.

With patents published in the United Kingdom, Australia, and Europe, and another nearing approval in the United States, Ploughshare has begun making the circuits of GNSS companies with the prospect of royalties hanging over the conversations.

This appears to be more than the oft-repeated observation that America and Britain are two nations divided by a common language. During this bicentennial of the War of 1812, one can’t be too careful.

I mean, what kind of “special relationship” is this, anyway?

Perhaps we have been Pollyannaish, lulled by the too-good-to-be-true aura that surrounds that U.S. gift to the world: the Global Positioning System. Because while the stewards of GPS assert the principles of free and open GNSS services playing on a level field, they appear at risk from someone stealing the ball behind their backs.

Many people have tried to reinvent the wheel, but no one has gotten into a patent fight over it.

Of course, provocative intrusions are not unknown in the world of GNSS technology. Russia’s import duties on GNSS receivers lacking GLONASS, China’s dilatory approach to BeiDou ICDs and its overlay on Galileo’s public regulated service (PRS), the earlier European footprint (now withdrawn) of PRS on GPS M-code.

In this case, however, our British colleagues appear to be plowing someone else’s field — many other persons’ fields, actually, because aside from the U.S./EU agreement on common civil signals, GNSS systems in general are converging on the de facto standard.

Are we seeing, once again, the “tragedy of the commons” at work, where the quick and clever privatize the endeavors of many?

The situation has become something of an enigma wrapped inside a conundrum since the parties to the patents, when confronted in their endeavors, have fallen publicly silent.

Within this void of explanation we can sense a furious intensity of reflection among the perpetrators. One that matches the often furious exclamations of program managers and officials — both in the United States and around the world — discovering the signal patents.

And yet caution and an assumption of benign intent should guide the expanding dialog taking place privately about this issue among GNSS providers.

Pratt and Owen are men of good repute; DSTL, a bastion of innovation. In this instance, they may have overreached, nay, encroached upon the commonwealth of GNSS.

But it is a trespass that can still be put right.

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Return to main Washington View article: "USPTO Nears Approval of Troubling British Patent on New GPS Civil Signal"

During the course of discussing the patent issue with Inside GNSS, Dr. Ingo Baumann of the space industry law firm BHO Legal and Dr. Ingolf Bode of patent law firm Bode Meitinger, provided a written response to some questions. Those questions and their answers are produced below in their entirety. Neither Baumman nor Bode, whose firms are both located in Germany, are involved in the ongoing dispute.

Inside GNSS: This is a case where a single country in the EU has filed a patent on a technology used in an EU-wide project. Is that unusual?

Baumann/Bode: It is not unusual that a governmental body is filing a patent application. There is no exclusion in the European Patent Convention (EPC) for such a case. A patent application may also affect technologies, systems, or services used on a European or even global level. What is unusual here is that a patent claim raises sensitive political issues between the US, the EU and UK as an EU Member State with potential effects on cooperation in global GNSS systems and services.

Inside GNSS: Is there a process for such situations? Would the European Commission, for example, negotiate an EU-wide deal on royalties or does each country and company deal with the patent separately?

Baumann/Bode: In principle anybody could negotiate with the patent holder, the British Secretary of State for Defence, about licenses and associated royalties. However, this cannot be in the interest of Galileo as a system with global coverage and service area. Remember that the creation of a competitive European GNSS industry is among the key goals of the European GNSS programmes. We are not aware of the European Commission position on the matter, but a reliable and comprehensive agreement with the British Government must be found rapidly in order to prevent further political tensions and uncertainties in the GNSS industry, namely the receiver manufacturers.

Inside GNSS: The U.S. appears likely to challenge the patent. Does the U.S. challenge it at the EU level or in the UK or both?

Baumann/Bode:We are not informed about the U.S. plans to react against the patent filings. However, the European Patent No. 1830199 has meanwhile been granted. Any interested party now would have to make use of the opposition procedure before the European Patent Office (EPO). The time limit generally ends within nine months from the publication of the grant of the European Patent. Here this would be on November 2, 2012. The decision of the EPO on the opposition procedure has effect for all 28 contracting states, including UK, and would be the easiest way to challenge the European Patent.

Inside GNSS: What does it mean if the EU denies a patent that was granted in the UK?

Baumann/Bode: It is not possible for any third party, even not for the European Union, to ignore a valid patent without committing an infringement. But the EU itself has no authority to deny the patent. Only the EPO can revoke a European Patent for all Member States at once. After the time limit for the opposition procedure has run out, national patent courts then can only revoke the respective national part of a European Patent for the national territory it has competence. Any interested party must then submit claims in all 28 EPC member states.

Inside GNSS: How long does the U.S. have to challenge the patent at the World Intellectual Property Organization (WIPO)?

Baumann/Bode: The time limit for third-party observations against the WIPO application relating to Patent 1830199, the so called PCT-Application, expires for the international phase after a period of maximum 31 months. However, the application is split into a bundle of national or regional patent applications or already granted patents. After the international phase, a third party can only challenge one or more of these national or regional patents.

Inside GNSS: Does the fact that the signal was developed jointly by the U.S. and the EU have any bearing when it comes to the U.S. challenging the patent in the EU and in the UK?

Baumann/Bode: Article 9 of the Galileo-GPS Agreement states that nothing in it is intended to affect IPR related to global satellite-based navigation and timing signals, services or goods. But if the invention on which EP 1830199 is based was made not only by inventors from the UK but from all member of the Galileo-GPS Working Group, other members of the Working Group may also claim inventorship. This must be done before a national court and later, upon a respective positive court decision, it could lead to a change in the national and also the European patent register with regard to the inventors and patent holders.

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Return to main article: "Truth on the Range"

Locata developed a network of synchronized transceivers that transmit signals in a manner similar to GPS satellites, but which are ground-based and serve an area within sight of the transceiver sites. A Locata rover receiver placed in this network of transceivers can position itself to within a handful of centimeters using carrier-phase techniques, and within less than a meter using pseudorandom code-based techniques, completely independent of GPS or any other satellite positioning system.

This synchronized network of receivers produces single-point solutions for calculating position; hence, it does not require or use any differential correction techniques whatsoever. The Locata receiver collects 10.23 MHz chipped code pseudorange and carrier-phase measurements at selectable rates of 1, 10, 20, and 25 Hz. The synchronized network operates in the 2.4 GHz industrial, scientific, and medical (ISM) frequency band, which allows the transmission of high-power signals in a band that is independent of, and hence resistant to, GPS L1 and L2 jamming.

As with GPS, this ground-based network is capable of highly precise time distribution within the network, using a proprietary method that synchronizes the transceivers to a very high precision, delivering nanosecond accurate synchronization over large areas without requiring atomic clocks.

A transceiver within the network tracks both the Master signals as well as the signals from its own internal transmitter that is broadcasting co-located signals. This sets up a measurable time-lock loop. By taking pseudorange and carrier phase measurements from both the master and co-located signals, the transceiver is able to move or slew its signals to align with the Master.

This time-lock methodology is fundamentally based on aligning the timing (range) of the signals to correspond to the surveyed geometric distances from the receive antenna to both the Master and co-located transmit antennas. These distances are easily computed from the antenna locations and broadcast as the ephemeris on the 50 bps navigation data. To synchronize the co-located signals with the Master, a transceiver slews the signals until the single-difference range between the Master and the co-located signals is the geometric range — accurate to a millimeter level.

Essentially, the synchronization method removes the clock error between ground transceivers, leaving only the clock difference between the network of transceivers and the test-bed receiver, similar to GPS.

The post Sidebar: Time for Precise Positioning appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Return to main article: "Truth on the Range"

Return to main article: "Truth on the Range"

Locata’s COTS systems are in use today for commercial, industrial applications. These COTS applications are well served by the standard Locata system, which operates at the 2.4 GHz radio frequency allocated for industrial, scientific, and medical uses. The COTS version transmits at less than one watt in compliance with relevant Federal Communications Commission regulations for that band, which permits unlicensed operations. Transceivers in commercial applications are typically spaced less than 10 kilometers apart and only have to deal with ground-based vehicle dynamics.

When Locata and the 746 TS signed a sole-source contract in 2010 to deliver NGBPS-level capabilities, the challenging USAF specification clearly would require Locata to demonstrate that its synchronized network of transceivers could deliver new levels of performance in environments that the system had not previously experienced.

Several specific NGBPS enhancements therefore drove Locata’s development efforts for this contract:

Enhancement 1 — Distance: The operational UHARS deployment calls for a NGBPS system that will cover around 2,500 square miles (6,500 square kilometers). The USAF-Locata contract specifies that a Locata receiver shall be capable of acquiring a transmitted NGBPS signal at a range of at least 30 miles (48.3 kilometers). Critically, the nanosecond-level, time-locked synchronization essential for the Locata network’s performance must be maintained at these ranges, even when the synchronization process is sequentially “cascaded” from one slave transceiver to another slave that is not in view of the Master transceiver site.

Before the critical design review (CDR) in June 2010, Locata’s analysis concluded that the NGBPS acquisition ranges required the transmitter RF power for each signal to be increased from the standard COTS level of 100 milliwatts up to a new level of 10 watts to the antenna. Tests proved that transmitting 10 watts enables acquisition and tracking out to more than 50 kilometers and maintains received signal levels at -100 dBm or better.

A number of external amplifiers were tested over a period of months, and a suitable candidate was chosen for the Tech Demo deployment. The accompanying figure shows a plot of measured data for received power versus tracking distance, using two test aircraft antennas, and recorded during the CDR wide-area trials.

Enhancement 2 — Antennas: In the past, Locata COTS networks provided positioning to ground-based users, transmitting signals from either a patch antenna pointing from the perimeter into the area of interest, or from a monopole antenna radiating equally in all directions from a transceiver within an area of commercial operations.

However, neither of these antennas provides an optimal radiation pattern for NGBPS signals to be used by aircraft overhead. A monopole antenna, when oriented to provide the necessary omnidirectional pattern horizontally, suffers a null in its radiation pattern to its zenith. Aircraft above the transceiver will suffer signal dropout, and the consequent loss of that site for the geometry required for accurate positioning.

This is particularly troublesome if a 3-D solution is required, since the transceivers near (or under) an aircraft provide the primary signal components for vertical positioning. Alternatively, a patch antenna, when oriented upwards, provides good signal strengths for overhead users. However, because of its flat geometry, it does not provide good gain to the sides and will therefore severely limit the operational range of a synchronized network.

Reconciling these conflicting requirements led to an intensive search for a better aviation antenna for Locata and NGBPS uses.

After months of testing it was decided that a quadrifilar helix antenna design would best deliver the required NGBPS system performance. This led to Locata’s in-house fabrication and prototyping of several quadrifilar helix antennas specifically for testing under NGBPS conditions. Once an optimal design was determined, Locata worked with a very capable and respected antenna manufacturer to produce an aircraft-certified version of this quadrifilar helix antenna.

These quadrifilar helix antennas were used in Locata’s Australian tests with excellent results and confirmed Locata’s research and analysis. The production antenna also gave excellent performance throughout the Tech Demo, and these antennas can be seen in the accompanying photo of the USAF aircraft and even more clearly in photos of the transmitter sites.

Enhancement 3 — Dynamics: Prior to the NGBPS flight trials, Locata COTS systems had only been used to position ground-based vehicles, such as cars, trucks, and drill rigs. For the NGBPS, however, the system needed to function under aircraft operating dynamics, including banking, angular and linear accelerations, airspeeds up to 300 knots (560 kph), and altitudes up to 30,000 feet above sea level. Prior to the Tech Demo at White Sands, Locata did not have access to an aircraft that could match these performance requirements; so, all dynamic testing had been simulated, using a bench-test setup to analyze Locata’s tracking loops and a hardware-in-the-loop scenario.

In these simulation scenarios, the transmitter direct digital synthesis (DDS) chip in the transmitter section of a transceiver was commanded by software to replicate the appropriate frequency plus Doppler shifts that would be seen by a receiver on board an aircraft engaged in the specified dynamics. The receiver portion of the LocataLite transceiver (which is identical to a Locata roving receiver placed on the aircraft) then tracked this synthesized, dynamically modified signal. In this way, simply using Locata test software and transceivers, the tracking loop development and performance was simulated and verified.

This simulation demonstrated that Locata’s receiver tracking loops could handle the specified aircraft dynamics, a conclusion that was borne out with real-world aircraft dynamics tracked during the Tech Demo at White Sands Missile Range.

Enhancement 4 — Tropospherics: For the NGBPS flight trials the requirement to track signals up to 30 miles means that tropospheric delay comprises the major error source for measurements used in the navigation solution. Using standard atmospheric parameters, the unmodeled tropospheric delay is approximately 280 parts per million (ppm), which equates to approximately 13.5 meters of error over 30 miles. Therefore, in order to meet the position accuracy of less than 18 centimeters 3dRMS (when PDOP < 3), a key challenge in upgrading the COTS for the NGBPS involved developing methodologies to mitigate the effects of tropospheric error.

Locata has developed new tropospheric models that make use of meteorological stations that measure temperature, pressure, and relative humidity at the ground-based LocataLite sites and data on the aircraft. The remaining “residual” tropospheric error is then estimated in the navigation Kalman filter solution.

For the NGBPS trial at White Sands, the meteorological equipment for the aircraft did not arrive in time for the tests. The launching of weather balloons at the start and end of each test assisted Locata in refining postprocessed models to estimate aircraft data from the ground-based meteorological sites. The analysis conducted thus far indicates that the modeling alone, using data input from meteorological sites, is able to mitigate the tropospheric effects to within a few part per million.

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