Envisioning a Future: GNSS System of Systems, Part 3

A Role for C-Band?

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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.

The radio frequency spectrum is finite. Crowding in the L-band occupied — or planned for use — by the world’s global navigation satellite systems is only going to get worse, as more systems and more signals come on line. Several gigahertz up the RF spectrum from L-band, however, lies a wide swath of bandwidth that is comparatively untapped: the C-band. In fact, early in its development the Galileo program received an allocation of C-band from the World Radiocommunications Conference. Although Galileo system designers decided quite early not to use the allocation for a variety of practical reasons, C-band remains an enticing subject because of certain characteristics that seem to complement or compensate for technical limitations of L-band, particularly the need for better indoor positioning capability. This column examines C-band as a candidate for a future GNSS signal or signals and evaluates its advantages and disadvantages compared with L-band signals.

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

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The radionavigation satellite service (RNSS) portion of the RF spectrum is overcrowded, especially on L1 where GPS, Galileo, Compass overlap portions of one another’s signal frequencies and GLONASS signals occupy more than 11 MHz of nearby bandwidth. Indeed, even those bands that have not been used so far will certainly be shared by many systems in the near future. Therefore, the search of alternative frequency resources is something that must inevitably occur with a high probability in the coming years.

During the World Radio Conference 2000 (WRC-2000), the Galileo program obtained authorization to use C-band frequencies. At the time, a dedicated portion of the C-band had been assigned for radionavigation, but technical complexities made it impossible for the first generation of Galileo to make use of it. Phase noise problems, increased signal transmit power requirements, and signal attenuation issues — to name only a few — knocked down all the proposed solutions. We will refer to these aspects in detail in the following discussion.

As happens with any kind of technology, however, many ideas that have been abandoned in the past due to excessive technical challenges or demanding drawbacks often become objects of interest some years or decades later. As technology evolves, constraints alter, and the environment of possibilities changes.

Against this background, the question emerges as to whether the use of C-band frequencies could represent a real alternative for a future GNSS. In this column, we will try to shed some light on this interesting possibility. Before that, let us first look at what we understand about C-band and how the regulatory RF spectrum situation affecting its use varies in different countries.

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

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. Contact Prof. Hein at Guenter.Hein@unibw-muenchen.de.

Markus Irsigler received his diploma in geodesy and geomatics from the University of Stuttgart, Germany. He then joined the Institute of Geodesy and Navigation at the University of the Federal Armed Forces Munich where he worked as a research associate. During this time, his scientific research work focused on GNSS receiver design and performance with special focus on multipath propagation and mitigation. In 2001, he was principal investigator and project manager of a study that examined the use of C-band frequencies for satellite navigation. Since 2007, he has been working for IFEN GmbH, Poing, Germany, as a product manager and system engineer.

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.