Envisioning a Future: GNSS System of Systems, Part 1

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“Working Papers” explore the technical and scientific themes that underpin GNSS programs and applications. This regular column is coordinated by Prof. Dr.-Ing. Günter Hein.

Seven years ago, the U.S. Global Positioning System was the only real GNSS around. The GLONASS constellation had dwindled to seven satellites. Final approval and funding of Europe’s Galileo program was yet to be achieved. Since then, Russia has gone a long way toward rebuilding and modernizing GLONASS. Galileo has put its first experimental GNSS satellite, GIOVE-A, into space. And China has announced plans to build a full-fledged GNSS of its own — Compass — building on three Beidou satellites that it has launched in recent years. With those activities under way, it’s not too early to begin thinking about what a multisystem GNSS might look like and mean for users, receiver manufacturers, and service providers.

Günter W. Hein, José-Ángel Ávila-Rodríguez, Stefan Wallner, Thomas Pany, Bernd Eissfeller, and Philipp Hartl

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We have just made the transition into the new year of 2007. Most of us probably already have our eyes focused onto the next 12 months along with some wishes and perspectives that we would like to have fulfilled in the coming 365 days.

In the same spirit, over the next two issues of Inside GNSS this column will take a look into the near future and — what is even more exciting — into the further future of satellite navigation. But what that future will look like depends to an enormous extent on what the past was; so, we should have first a look back into the roots of GNSS.

Long ago the Americans entered the global navigation satellite system (GNSS) era with the Global Positioning System (GPS) as the result of efforts that began in the late 1960s. The Russians followed soon afterwards (or did they do it in parallel?) with GLONASS. Both of these systems are now undergoing extensive modernization. Moreover, the European Galileo system is joining the GNSS club, and China is now planning its own version called Compass.

In the meantime lots of augmentation and regional systems have been developed or are currently under consideration. From military to civil signals, from medium Earth orbit (MEO) to geostationary Earth orbit (GEO) and inclined geosynchronous orbits (IGSO), the palette of systems and offered services is as wide as imagination allows.

Is it not time, therefore, to pause and think for a moment about where we want GNSS to move? Is it not already time to really “think global” and to coordinate and harmonize all the existing and projected navigation satellite systems? If so, then the question naturally arises: what should the “Global Navigation Satellite System of Systems” look like?

This column will try to shed some light on the fascinating new world of GNSS in which we will live around the year 2020 if all the currently modernizing and planned new systems come into reality. It will be a complex world where the word “coordination” will be the key and from which, if we do it right, users will be the ones that will profit the most. After all, why should a GNSS user really care about whether one of his or her signals comes from GPS, the other from Galileo, the third from GLONASS and the fourth from Compass as long as the GNSS receiver works well?

Scenes from the Present

Today only GPS is fully operational. Nevertheless, Russia hopes to return GLONASS to full operation capability (FOC) with a completed constellation by 2009, and Galileo’s FOC is now expected in 2012. Compass is already knocking on the door, and in spite of the fact that China has still a long way to go and lengthy negotiations will be needed, a scenario of four global coverage satellite systems seems to be very likely in a future not so far away from today.

From the experience with Galileo, we know how important the roles of interoperability and compatibility with GPS were from the very beginning. Unfortunately, major differences between those two systems and GLONASS still exist.

However, also on the GPS/GLONASS side, work on attaining real interoperability is continuing. Just recently during the GPS/GLONASS Working Group 1 meeting in December 2006, both sides emphasized the benefit to the user community that a common approach concerning FDMA/CDMA would bring in terms of interoperability. The Russian side announced that they will come to a decision on adding or converting to a CDMA format by the end of 2007. The formal U.S.-Russia statement can be viewed at
<http://www.glonass-ianc.rsa.ru/i/glonass/joint_statement_eng.pdf>.

The direction in which COMPASS will go remains a large unknown. In fact, if the need of standardization was always there, it seems that the concept is gaining in interest the more systems come into play.

But before dreaming with our ideal GNSS, let us first look more closely into what the current reality is and what the plans for new GNSS systems are.

(For the rest of this story, please download the complete article using the PDF link above)

Manufacturers

Figures 5 and 7 were generated using the Satellite Tool Kit (STK) from Analytical Graphics, Inc. (AGI), Exton, Pennsylvania, USA.

Author Profiles

Prof. Dr.-Ing. Günter Hein is a member of the European Commission’s Galileo Signal Task Force and organizer of the annual Munich Satellite Navigation Summit. He has been a full professor and director of the Institute of Geodesy and Navigation at the University of the Federal Armed Forces Munich (University FAF Munich) since 1983. In 2002, he received the United States Institute of Navigation Johannes Kepler Award for sustained and significant contributions to the development of satellite navigation. Hein received his Dipl.-Ing and Dr.-Ing. degrees in geodesy from the University of Darmstadt, Germany.

José-Ángel Ávila-Rodríguez is a research associate at the Institute of Geodesy and Navigation at the University FAF Munich. He is responsible for research activities on GNSS signals, including BOC, BCS, and MBCS modulations. Ávila-Rodríguez is involved in the Galileo program, in which he supports the European Space Agency, the European Commission, and the Galileo Joint Undertaking, through the Galileo Signal Task Force. He studied at the Technical Universities of Madrid, Spain, and Vienna, Austria, and has an M.S. in electrical engineering. His major areas of interest include the Galileo signal structure, GNSS receiver design and performance, and Galileo codes.

Bernd Eissfeller is a full professor of navigation and vice-director of the Institute of Geodesy and Navigation at the University FAF Munich. He is responsible for teaching and research in navigation and signal processing. Till the end of 1993 he worked in industry as a project manager on the development of GPS/INS navigation systems. He received the Habilitation (venia legendi) in Navigation and Physical Geodesy in 1996 and from 1994-2000 he was head of the GNSS Laboratory of the Institute of Geodesy and Navigation.

Thomas Pany has a Ph.D. in geodesy from the Graz University of Technology and a M.S. in physics from the Karl-Franzens University of Graz. Currently he is working at the Institute of Geodesy and Navigation at the University of Federal Armed Forces Munich. His major areas of interest include GPS/Galileo software receiver design, Galileo signal structure and GPS science.

Stefan Wallner studied at the Technical University of Munich and graduated with a diploma in techno-mathematics. He is now research associate at the Institute of Geodesy and Navigation at the University FAF Munich. Wallner’s main topics of interests are the spreading codes and the signal structure of Galileo and also interference and interoperability issues involving GNSS systems.

Phil Hartl has an M.S. in electrical engineering and a Ph.D. Habil. in space technology from the Technical University of Munich, a Ph.D. in aeronautics and astronautics from the University of Stuttgart. He has served as the head of the DLR Space Research Centre Oberpfaffenhofen, director of the Institute of Satellite Technology of the Technical University of Berlin, and director of the Institute of Navigation of the University Stuttgart. He was principal scientists for many satellite experiments and numerous national and international projects. Since his retirement as full professor in 1995, Dr. Hartl has been active as scientific consultant to various research and industrial organizations in various fields of aerospace.