Operators of the world’s four GNSS systems and regional augmentation systems have laid the foundation for a multilateral environment in which to discuss issues of compatibility and interoperability.
Operators of the world’s four GNSS systems and regional augmentation systems have laid the foundation for a multilateral environment in which to discuss issues of compatibility and interoperability.
Meeting September 4 in Bangalore, India, in advance of a session of the International Committee on GNSS (ICG), six nations established a Providers Forum that will operate in parallel with the United Nations–backed group. Ken Hodgkins, deputy director of the State Department’s Office of Space & Advanced Technology, characterized the ICG gathering as “a huge success.”
“The PF [Providers Forum] was particularly notable in that we reached a common understanding on the general concept of compatibility and interoperability in a multilateral setting,” Hodgkins told Inside GNSS.
Initial members of the forum and their current and future systems include: China, Compass/Beidou Navigation Satellite System (CNSS); the European Union, Galileo and the European Geostationary Navigation Overlay Service (EGNOS); India, the GPS Aided Geo Augmented Navigation (GAGAN) system and Indian Regional Navigation Satellite System (IRNSS); Japan, the Quasi-Zenith Satellite System (QZSS) and the MTSAT Satellite-based Augmentation System (MSAS); Russian Federation, GLONASS and Wide-area SDCM (System of Differential Corrections and Monitoring); United States, GPS and the Wide Area Augmentation System (WAAS).
As noted in a report from the session, “The forum is not a policy-making body, but provides a means to promote discussion among system providers on key technical issues and operational concepts.” Nonetheless, it represents a comprehensive membership and focus on GNSS affairs that has not previously existed.
Baseline Principles
In the course of their discussions, the Providers Forum participants agreed on the following points:
• Transparency in the provision of open services is desirable, and requires the open publication and dissemination of signal and system characteristics, in due time, to allow manufacturers to design and develop GNSS receivers on a non-discriminatory basis.
• Discussions should emphasize cooperation regarding GNSS infrastructure (space and ground control/monitoring segments).
• System providers should strive to monitor the performance of their open signals and provide timely updates to users regarding critical performance characteristics such as timing accuracy, positioning accuracy and service availability.
• The protection of RNSS [radionavigation satellite service] spectrum is vital to GNSS service provision. Therefore, adequate spectrum protection through domestic and international regulation should be pursued.
• Physical separation of operational satellite constellations and end-of-life disposal orbits should also be examined.
Compatible, Interoperable
On the key issues of GNSS system compatibility and interoperability, the forum established the following definitions and principles:
Compatibility refers to the ability of space-based positioning, navigation, and timing services to be used separately or together without interfering with each individual service or signal.
• Radiofrequency compatibility should involve thorough consideration of detailed technical factors, including effects on receiver noise floor and cross-correlation between interfering and desired signals.
• Compatibility should also involve spectral separation between each system’s authorized service signals and other systems’ signals.
• Any additional solutions to improve compatibility are encouraged
Interoperability refers to the ability of open global and regional satellite navigation and timing services to be used together to provide better capabilities at the user level than would be achieved by relying solely on one service or signal.
• Ideal interoperability allows navigation with signals from at least four different systems with no additional receiver cost or complexity.
• Common center frequencies are essential to interoperability, and commonality of other signal characteristics is desirable.
• Geodetic reference frames and system time standards should also be considered.
The Indian Space Research Organization hosted the full ICG meeting September 4-7 and cochaired the Providers Forum with the United States.
Forum participants agreed to meet again, no later than the next meeting of the ICG, in Pasadena, California, Dec 8-12, 2008. They may also meet on the margins of the next session of the Scientific & Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space in February 2008.
The UN Office for Outer Space Affairs, as the Secretariat for the ICG, will continue to act as the focal point for Providers Forum meeting preparations. The chair of the Providers Forum will rotate among the members each year.
