Initial results from observations of the Galileo GIOVE-B satellite conducted by researchers at the European Space Agency (ESA) and Septentrio Satellite Navigation indicate that the multiplex binary offset carrier (MBOC) modulation outperforms the BOC(1,1) modulation on the L1 (data + pilot channels) frequency in mitigating the effects of multipath or reflected signals.

Initial results from observations of the Galileo GIOVE-B satellite conducted by researchers at the European Space Agency (ESA) and Septentrio Satellite Navigation indicate that the multiplex binary offset carrier (MBOC) modulation outperforms the BOC(1,1) modulation on the L1 (data + pilot channels) frequency in mitigating the effects of multipath or reflected signals.

Analysis of data gather in May at the GNSS receiver manufacturer’s facilities in Leuven, Belgium, show a 20–25 percent advantage for MBOC in multipath mitigation, with the largest improvement occurring in signals from lower-elevation satellites. The results are in line with the predicted benefits for MBOC versus BOC(1,1).

According to the researchers, this improvement is mainly due to the reduction of the high-frequency part of the receiver correlation error (characteristic time less than 10 seconds), which consists of tracking noise and long-range multipath.

(NOTE: More detailed information about this research will be available in a technical article in the September-October 2008 issue of Inside GNSS.) 

MBOC is the common waveform agreed upon by the United States and the European Union for use on the Galileo Open Service signal and the future GPS L1 civil signal (L1C), which will be broadcast on the Block III satellites due to begin launching in 2014.

MBOC is implemented either as — in the case of Galileo — a composite BOC or CBOC, with a superposition of BOC(1,1) and BOC(6,1), or as TMBOC, a time-division-multiplex of BOC(1,1) and BOC(6,1), as is planned for the GPS L1C signal.

The observations were collected using a Septentrio GSTB‐V2 Experimental Test Receiver (GETR) developed under contract for the Galileo program. The GETR can be configured to track the CBOC signal in both modes simultaneously on two different channels in order to make a direct simultaneous comparison of BOC(1,1) and CBOC.

An article describing the tests and results in detail will appear in the September/October issue of Inside GNSS magazine.

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UPDATED OCTOBER 19 2008: Organizers of the third meeting of the International Committee on GNSS (ICG) scheduled for December 8–12 in Pasadena, California, are actively seeking the participation of industry and interested members of the GNSS community.

UPDATED OCTOBER 19 2008: Organizers of the third meeting of the International Committee on GNSS (ICG) scheduled for December 8–12 in Pasadena, California, are actively seeking the participation of industry and interested members of the GNSS community.

For the first time, commercial providers of GNSS equipment and services
are being invited to exhibit and sponsor events at the ICG meeting,
which will take place at the Westin Pasadena hotel.

Hosted by the United States government, the gathering of representatives of the world’s GNSS system operators, augmentation and regional system providers, and organizations of important user communities follows an inaugural 2006 meeting in Vienna, Austria, and last September’s conference in Bangalore, India.

The Russian Federation will host the next ICG meeting in St. Petersburg September 14-18 2009. China has offered to host the fifth meeting.

With the encouragement of the United Nations Office for Outer Space Affairs (UN OOSA), ICG was established as an informal body to promote cooperation on matters of mutual interest related to civilian satellite-based positioning, navigation, and timing, as well as the compatibility and interoperability of GNSS systems. UN OOSA’s office in Vienna, Austria, serves as the ICG secretariat.

Within the ICG is the Providers Forum, consisting of those countries operating GNSS systems or with plans to develop one: the United States (GPS, WAAS), European Community/European Space Agency (Galileo, EGNOS), the Russian Federation (GLONASS), and China (Compass/Beidou). ICG members with regional augmentation systems are India (GAGAN, IRNSS), Japan (MSAS, QZSS), and Nigeria (NIGCOMSAT).

An ICG Experts Meeting took place July 15 in Montreal, Canada, with a variety of updates on system developments that will probably reappear in Pasadena presentations. A Chinese representative provided further details on Compass (Beidou II) signals (See related story, “China Offers More Insight into Compass Signals.”)

Mark Schmulevich, of the Russian Space Agency’s Institute of Space Device Engineering, described the GLONASS System of Differential Correction and Monitoring (SDCM) under development. SDCM, the first phase of which underwent operational testing last year, will broadcast real-time GLONASS and GPS differential corrections and integrity alerts, with a goal of 1–1.5 meters horizontal accuracy and 2-3 meters vertical accuracy Eventually, SDCM, which has a similar design as other satellite-based augmentation systems (WAAS, EGNOS, MSAS, GAGAN) will include 19 reference stations, a central processing facility, and a GEO satellite.

Four ICG working groups (WGs) deal with compatibility and interoperability (WGA), enhancement of performance of GNSS services (WGB), information dissemination (WGC), and interactions with national, regional authorities, and international organizations (WGD).

Ten ICG associate members represent key GNSS user communities, such as International Society for Photogrammetry and Remote Sensing and the International Earth Rotation and Reference Systems Service. The Pasadena agenda includes a session in which associate members and observers will present recent developments in their organizations and associations with regard to GNSS services and applications.

A session on GNSS scientific and technology applications will introduce issues and opportunities in user applications and GNSS technology for consideration by the ICG or its working groups. Among the topics currently proposed are earthquake-related and satellite-based applications. Industry presentations are also being invited, including one by Google representatives on coordinates and mapping issues.

At an opening plenary session, GNSS providers will present the status and future plans for their systems. All presenters will identify issues for discussion in the ICG and/or its working groups.

Later in the week, the Providers Forum and working groups will meet separately, associate members and observers will provide updates on recent developments in their organizations and associations with regard to GNSS services and applications.

Draft recommendations may be exchanged among the working groups, providers, and full ICG, with a final plenary considering proposals as recommended by the Providers Forum.

Companies interested in exhibiting and/or sponsoring an event at ICG-3 may contact the following individuals for further information: Alice Wong, Office of Space & Advanced Technology, Department of State, telephone 202-663-2388, mobile 202-439-0384, fax 202-663-2402, e-mail <wo*****@***te.gov>; or Sindy Cruz, Senior Sales Manager, The Westin Pasadena, telephone 626-304-1442, fax 626-795-7669, e-mail <Si********@****in.com>.

More information about the ICG-3 can be found on-line at <http://www.geolinks.org/>

<http://www.geolinks.org/>.

The fourth meeting of the ICG will be held September 14–18, 2009, in St. Petersburg, Russia — a change of venue from Sochi, Russia, as previously reported.

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A tentative launch date of November 7 has been targeted for the Block IIR-20(M), which will carry a payload that includes an experimental L5 signal. If all goes well, the final IIR launch would take place by December 31.

UPDATED SEPTEMBER 10 2008: With replacement parts currently being manufactured for faulty components that have delayed launch plans, Air Force GPS program managers hope to get the final two modernized Block IIR satellites on orbit by the end of the year.

A tentative launch date of November 7 has been targeted for the Block IIR-20(M), which will carry a payload that includes an experimental L5 signal. If all goes well, the final IIR launch would take place by December 31.

The component in question is the 40-second timer that triggers separation of the third stage booster from the GPS space vehicle. Pre-launch inspections of the spacecraft at Cape Canaveral discovered the problem. If the replacement timers arrive as expected by late September, the IIR-20(M) launch should proceed under the new schedule.

In the meantime, with the GPS satellite constellation currently well above the level needed for full operational capability (FOC), the launch delay has not affected the availability of GPS positioning, navigation, and timing. Some 31 operational GPS space vehicles (SVs) are currently on orbit with only 24 SVs needed to provide an FOC complement for global coverage.

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The Boeing Company has received a three-year, $153.5-million cost-plus-fixed-fee contract to continue its efforts to augment GPS for military applications by exploiting the Iridium low earth orbit (LEO) communications satellite system.

The Boeing Company has received a three-year, $153.5-million cost-plus-fixed-fee contract to continue its efforts to augment GPS for military applications by exploiting the Iridium low earth orbit (LEO) communications satellite system.

Awarded by the U.S. Navy’s Naval Research Laboratory (NRL), the funding will be used for research, development, and demonstration of the High Integrity GPS Technology Concept — known more commonly as iGPS. The program is developing techniques that enable faster acquisition (time to first fix or TTFF) of GPS satellite signals in adverse operating environments, including those with RF interference or urban settings.

The i-GPS architecture involves high-precision time transfer of GPS time and its rebroadcast over the higher powered Iridium communications channels. The High Integrity GPS team includes Boeing Advanced Systems and Phantom Works, Iridium LLC, Rockwell Collins, Coherent Navigation, and experts from academia. Phantom Works is the advanced research and development unit of Boeing.

Availability of the precise time allows GPS equipment to reduce the search volume of the receiver’s DSP correlators and accelerate TTFF, potentially including direct acquisition of the military P(Y)-code signals. The stronger Iridium signals also make GPS signal tracking more robust by increasing the antijamming capability of user equipment.

Field tests conducted in June 2007 at Cedar Rapids, Iowa, home of Rockwell Collins, which is providing user equipment modified for iGPS, demonstrated the capability of iGPS to provide time transfer to improve resistance to GPS jamming.

The contract will also support Boeing’s efforts to refine narrow-band ranging techniques using the Iridium satellite broadcasts directly, as well as broadband ranging in the future. This is made possible by the highly flexible design of the Iridium satellites, which allows on-orbit reprogramming of the spacecraft, according to David Whelan, chief scientist for Boeing Integrated Defense Systems (IDS) and general manager and deputy for IDS’s Advanced Systems group, an integrated innovation team that pursues new business opportunities.

This aspect of the iGPS draws on the experience of Transit, the Navy Navigation Satellite System that operated from the 1960s until 1996, when its navigation service was superseded by GPS. Also a LEO system, the five-satellite/five-spare Transit constellation provided ranging signals based on Doppler effects with much different dynamic parameters than GPS.

“In effect, we are remapping Iridium into a modern-day Transit system and integrating it with the GPS MEO [middle earth orbiting] system,” Whelan said in an interview with Inside GNSS.

Moreover, Boeing is investigating the use of real-time carrier phase differential GPS to improve positioning accuracy to the centimeter level, as well as integration of iGPS with microelectromechanical system (MEMS) inertial measurement units (IMUs), says Whelan, who along with the iGPS engineering team has received a number of Boeing innovation awards for their work.

The initial studies that evolved into the iGPS effort began in 2002. In addition to the military-oriented iGPS development now underway, Boeing is also investigating potential civil and commercial applications, including safety-of-life uses. “High integrity is the greatest value” of iGPS, Whelan said. Whether and when those civil applications come about depends on the DoD and NRL sponsors of iGPS, he added.

Under the NRL contract, work will be performed at Boeing facilities (or companies associated with the iGPS program) in Huntington Beach, California (34.3 percent); Philadelphia, Pennsylvania (17.3 percent); St. Louis, Missouri (1.5 percent); El Segundo, California (12.6 percent); Cedar Raids, Iowa (12.3 percent); Bethesda, Maryland (15.3 percent); Washington, D.C. (5.4 percent); Ithaca, New York (.5 percent); Chicago, Illinois (.3 percent); Burlingame, California (.5 percent), with completion expected by January 2011.

The largest commercial satellite system in the world, Iridium is a 66-satellite, cross-linked LEO constellation originally developed and launched by a consortium headed by Motorola, Inc.

Service was launched on November 1, 1998, but the company went into Chapter 11 bankruptcy within a year. A new group of investors operating as Iridium Satellite LLC acquired Iridium’s assets out of bankruptcy in December 2000 bolstered by a substantial Department of Defense (DoD) contract.

Aside from Boeing’s work on iGPS, Iridium already provides enhanced mobile satellite services (EMSS) as a DoD-supported augmentation to the company’s commercial service. Unique DoD features include end-to-end encryption, interface to secure telephone equipment, and protection of sensitive user information.

The DoD established a dedicated EMSS gateway in Wahiawa, Hawaii for government use through the Defense Information Systems Network (DISN), providing a direct connection to the Defense Switched Network (DSN), Federal Telecommunications System (FTS), or Public Switched Telephone Networks (PSTN). EMSS-authorized user handsets support secure communications.

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Researchers at Delft University of Technology (TU Delft), the Netherlands, succeeded this week in simultaneously tracking the GIOVE-A and GIOVE-B L1 Open Service signals in space, producing the first reported computation of a double-difference carrier phase integer ambiguity resolution on the first two experimental Galileo satellites in orbit.

Researchers at Delft University of Technology (TU Delft), the Netherlands, succeeded this week in simultaneously tracking the GIOVE-A and GIOVE-B L1 Open Service signals in space, producing the first reported computation of a double-difference carrier phase integer ambiguity resolution on the first two experimental Galileo satellites in orbit.

Beginning at 20:12 UTC on July 6, the researchers collected simultaneous ranging measurements to 12 GPS satellites, two geostationary European Geostationary Navigation Overlay Service (EGNOS) satellites, and to two Galileo satellites, GIOVE-A and GIOVE-B.

(NOTE: More detailed information about this research will be available in a technical article in the September-October 2008 issue of Inside GNSS)

A short baseline of a few meters between two identical receivers was set up in the flat and open Delfland area, allowing for a clear reception of the various GNSS signals in space. The measurements, across two Galileo satellites and two receivers, enabled them to form a pure Galileo double-difference. Using the geometry-free approach, the GIOVE-A–GIOVE-B carrier phase cycle double difference ambiguity can be estimated using the pseudorange code measurements.

The accompanying graph shows, for the full joint visibility duration of GIOVE-A and GIOVE-B (96 minutes), the epoch-wise ambiguity estimates. The empirical standard deviation is 3.4 cycles (on L1), which reflects the double difference pseudorange code noise.

According to the researchers, the overall (averaged) ambiguity float estimate is -9.05, which is fixed with large confidence, to the integer value -9. The carrier phase measurements of both GPS and Galileo were found to have similar precision, around 1–2 millimeters (standard deviation; undifferenced).

This achievement was reached in close cooperation with Septentrio Satellite Navigation in Leuven, Belgium. Researchers included Christiaan Tiberius and Hans van der Marel, at TU Delft, and Jean-Marie Sleewaegen and Frank Boon, of Septentrio.

The measurements were collected using two AsteRx1 L1 24-channel GNSS receivers with firmware that allows tracking of the Open Service L1-BC signal of Galileo GIOVE-A and GIOVE-B.

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