GAGAN update

Jan 2007 | Comments Off

DR ARJUN SINGH, DR SK SARASWATI, DR K RAMALINGAM,

	An insight into the steps ahead

This paper is an update of the GAGAN status presented at NSP meeting on May 8-19, 2006 held at Brussels, Belgium and also provides the future roadmap of the project. GAGAN will provide augmented information for satellite navigation to the aircraft flying within Indian Flight Information Regions (FIRs), which consists of seven boundaries. India is situated inthe vicinity of equator. In the equatorial region the ionospheric variations are very predominant which affect the GPS as well GEO signals. It has therefore been decided to go for unique regional Iono -Tropo model over Indian airspace after collecting TEC data over an extended period of time from 20 TEC stations which have been established for the purpose. After analyzing the data for twenty months, it has been observed that seven more TEC stations are needed in the equatorial anomaly region where equatorial anomaly is very high, to develop the model more accurate.

Implementation Timescale

Technology Demonstration Systems (TDS): This phase requires implementation of a minimum configuration system which would demonstrate the capability of the system to support up to precision approaches over limited region of the Indian airspace and will serve as proof of concept. The performance objective of this system is to meet the ICAO SARPs requirements. The TDS will consist of eight Indian Reference Stations (INRES), an Indian Mission Control Center (INMCC), two Indian Land Uplink System (INLUS), Space segment, required communication links and necessary software for navigation and communication during the TDS phase.

The installation of the ground segment has been completed and Preliminary Site Acceptance Test (PSAT) has been carried out with the help of satellite emulator. In the scope of this phase second frequency L5 is being incorporated in both space and ground segments. Initial Experimentation Phase (IEP) has been merged with TDS to make the system more usable and now it is called TDS -Extended.

Final Operational Phase (FOP): during this phase, the GAGAN program will be matured. Extensive tests would be carried out to establish the stability of various elements of the system as a whole. The system will be put in extensive use for its evaluation with respect to ICAO SARPs. Certification and validation of the system will be completed before declaring the system operational. The FOP will be completed by the year 2008

Current status of GAGAN

Infrastructure for installation of INRES at Delhi, Kolkatta, Guwahati, Portblair, Ahmedabad, Banglore, Jammu and Trivanthapuram is in place. All eight INRES equipment have been installed and seven stations have been linked through Optical Fiber Cable (OFC) to INMCC for connectivity test. All the station data are being recorded at INMCC, Banglore. The installation of GPS-TEC at all twenty stations has been completed. Ionospheric data from twenty TEC stations is being analyzed by number of Indian universities and R&D institutions involved in ionospheric studies for the development of an IONO-TROPO model that will be suitable for Indian airspace. Based on the results of extensive analysis, it is proposed to install seven more GPSTEC receiver in the mid region of India due to Equatorial Indian Anomaly (EIA) where ionospheric variation is very high. It is further observed that scintillation is very active upto 60° elevation based on thirty months data.

Infrastructure for INMCC and INLUS at Banglore is in place and installation of GAGAN equipment have been completed. Infrastructure for providing standby connectivity through V-sat from all INRES to INMCC is in progress, which will be completed by December 2006. A geostationary payload in C-Band and L1 and L5 frequencies will be carried by GSAT-4 (fabricated and developed by ISRO) placed at 82 ° E. GSAT-4 is scheduled for launch by July 2007.

At present GAGAN ground segment is under integration test and data collection at INMCC Banglore has begun. The possibility for hiring of INMARSAT 4F1 navigation transponder is being explored for integration of GAGAN ground system, to complete of Final Site Acceptance Test (FSAT) and conducting user level testing of GAGAN Signal-In-Space (SIS)

Technology support of development nd maintenance of GAGAN

ISRO in association with the AAI will be developing the entire system through all the stages of TDS, IEP and FOP. ISRO will continue to provide technology support, maintenance and replenishment of the space segment of the system, as and when required, to maintain the robustness of the system.

Results

The PSAT result of the GAGAN TDS-Extended as follows

At present GAGAN ground segment is under integration test and data collection at INMCC Bangalore

The TDS phase is to demonstrate the expected vertical and horizontal positional accuracies over 95% of the time with the associated Time-to-alarm (TTA) capability.

• Results were better than 7.6 meters accuracies in both vertical and horizontal over 95% of the time within the perimeter of the reference stations.

• Using type 62 (test) message, the TTA was better than 6.2 seconds

• Results were well within the exit criteria of PSAT

• Perimeters of INRES sites too exhibited good performance

The meeting is requested to take note of the PSAT result of GAGAN.