GAGAN ( GPS AIDED GEO AUGMENTED NAVIGATION) - Indian SBAS System
- Paper number
IAC-07-B2.1.09
- Author
Mr. Suryanarayana Rao, Indian Space Research Organisation (ISRO), India
- Coauthor
Mr. A.S. Ganeshan, Indian Space Research Organisation (ISRO), India
- Coauthor
Mr. P. Soma, Indian Space Research Organisation (ISRO), India
- Coauthor
Dr. Surendra Pal, Indian Space Research Organisation (ISRO), India
- Year
2007
- Abstract
International Civil Aviation Organization (ICAO) Member States have endorsed Global Satellite Navigation System (GNSS) as the future navigation system for aviation. For civil aviation, the GPS does not satisfy many of the needs in terms of accuracy, integrity and availability and the constellation needs to be augmented to provide these parameters as per the ICAO standards. The US Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay System (EGNOS), the Japanese MSAS and Indian GAGAN are examples of Satellite Based Augmentation Systems (SBAS). The Indian SBAS system GAGAN is actually the fourth such system and it will fill the gap of coverage presently existing in the region. This paper deals with the implementation of the GAGAN-TDS. Substantial Programmatic content is included.
The Indian Space Research Organization (ISRO) has taken up GAGAN in cooperation with Airport Authority of India (AAI) for the implementation of the Satellite Based Augmentation System over the Indian airspace. Although primarily intended for Civil Aviation, the system can be used by a vast majority of users like personal and public vehicles, railways, shipping, surveys etc. The GAGAN System is designed to be interoperable with other SBAS Systems mentioned earlier. This ensures that Civil Aviation users can seamlessly use the system anywhere in the world.
GAGAN TDS (Technology Demonstration System) is a forerunner for the operational Satellite Based Navigational System over the Indian region. The TDS phase of the project implements minimum set of elements for demonstrating the SBAS proof of concept over the Indian region. The Minimum set includes:
- 8 Indian Reference Stations (INRES) receiving L1 & L2 frequencies for GPS as well as GEO
- 1 Indian Master Control Centre (INMCC)
- 1 Indian Land Up linking Station (INLUS)
- GEO Navigation Transponder with L1 & L5 functionality
- Associated communication links between INRES and INMCC
- Network of 18 TEC Stations for Ionospheric Studies
GAGAN TDS configuration is shown in Fig (1) Fig (1) GAGAN TDS configuration
A Geo-Stationary Satellite Component consisting of a GPS L1 and L5 compatible navigation payload on an Indian satellite (GSAT-4) will be positioned at 83 °E to support GAGAN-TDS. The payload is a bent pipe Transponder operating at L1 and L5 frequencies in the downlink. The Indigenously designed Transponder has the specifications which are presently the best in the class. The GSAT-4 Satellite is likely to be launched by the end of 2007. In the meantime, the project is hiring INMARSAT - 4F1 Navigation Transponder for going ahead with the integration of the Ground System with the GEO and to carry out the Final System Acceptance tests for the Ground System.
In the equatorial region in which India is situated the ionosphere is characterized by large variations and gradients in TEC, existence of depletion bubbles and frequent deep fades due to scintillation. These are sources of concern for the operation of an SBAS in the region and will have to be specially dealt with. In order to study this behavior, 18 TEC receivers have been installed at various locations all over India as a part of GAGAN Project. The data is being used to evolve region specific ionospheric modifications to be incorporated to the system in the next phase of implementation.
GAGAN Implementation Status: The entire Ground System infrastructure for TDS phase is in place. A new facility for the Mission Control Centre and the land uplink station inclusive of the 11 meter antenna has been established in Bangalore. The Preliminary System Acceptance Test (PSAT) for GAGAN–TDS has been completed in June 2006. In the absence of the GEO satellite, the PSAT was carried out using Satellite Emulation System. This emulation system mimics the function of the GEO satellite for testing purposes. Good results have been obtained during the PSAT. It is seen that the vertical and horizontal errors are typically less than 4 and 2 meters respectively as seen in fig(2). Fig (2) GAGAN PSAT test results
Conclusions and Roadmap for GAGAN Final Operational Phase (FOP):
The paper records the highlights of the implementation of the GAGAN-TDS project. The entire ground system is in place. The integration of the ground system and the Preliminary System Acceptance Test show good results indicating that the TDS phase objectives will be met.
Final Operational Phase will follow the TDS. The FOP involves implementation of a full-fledged operational SBAS System containing all the required redundancies in both Ground as well as Space Segment. It is proposed to add a few more Reference stations to the GAGAN system during FOP phase. A host of other activities required for the certification of the system will be taken up in parallel. Region specific ionospheric modifications will be incorporated in this phase to take care of the Indian ionospheric condition. The GAGAN Project has evolved a road map towards an early realization of the operational System which will be an important milestone not only for ISRO but also for the GNSS user community in general.
- Abstract document
- Manuscript document
IAC-07-B2.1.09.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.