GPS-aided geo-augmented navigation

The GPS-aided GEO augmented navigation (GAGAN) is an implementation of a regional satellite-based augmentation system (SBAS) by the Indian government. It is a system to improve the accuracy of a GNSS receiver by providing reference signals. The AAI's efforts towards implementation of operational SBAS can be viewed as the first step towards introduction of modern Communication, navigation and surveillance/Air Traffic Management system over Indian airspace. The project has established 15 Indian reference stations, 3 Indian navigation land uplink stations, 3 Indian mission control centers, and installation of all associated software and communication links. It will be able to help pilots to navigate in the Indian airspace by an accuracy of 3 m. This will be helpful for landing aircraft in marginal weather and difficult approaches like Mangalore and Leh airports. The ₹7.74 billion (US$112 million) project was created in three phases through 2008 by the Airport Authority of India with the help of the Indian Space Research Organisation's (ISRO) technology and space support. The goal is to provide navigation system for all phases of flight over the Indian airspace and in the adjoining area. It is applicable to safety-to-life operations, and meets the performance requirements of international civil aviation regulatory bodies. The space component became available after the launch of the GAGAN payload on the GSAT-8 communication satellite, which was successfully launched. This payload was also part of the GSAT-4 satellite that was lost when the geosynchronous satellite launch vehicle (GSLV) failed during launch in April 2010. A final system acceptance test was conducted during June 2012 followed by system certification during July 2013. To begin implementing a satellite-based augmentation system over the Indian airspace, Wide Area Augmentation System (WAAS) codes for L1 frequency and L5 frequency were obtained from the United States Air Force and U.S Department of Defense on November 2001 and March 2005. The system will use eight reference stations located in Delhi, Guwahati, Kolkata, Ahmedabad, Thiruvananthapuram, Bangalore, Jammu and Port Blair, and a master control center at Bangalore. US defense contractor Raytheon has stated they will bid to build the system. A national plan for satellite navigation including implementation of technology demonstration system (TDS) over the Indian air space as a proof of concept had been prepared jointly by Airports Authority of India (AAI) and ISRO. TDS was successfully completed during 2007 by installing eight Indian Reference Stations (INRESs) at eight Indian airports and linked to the Master Control Center (MCC) located near Bangalore. Preliminary system acceptance testing has been successfully completed in December 2010. The ground segment for GAGAN, which has been put up by the Raytheon, has 15 reference stations scattered across the country. Two mission control centres, along with associated uplink stations, have been set up at Kundalahalli in Bangalore. One more control centre and uplink station are to come up at Delhi. As a part of the programme, a network of 18 total electron content (TEC) monitoring stations were installed at various locations in India to study and analyse the behaviour of the ionosphere over the Indian region. GAGAN's TDS signal in space provides a three-metre accuracy as against the requirement of 7.6 metres. Flight inspection of GAGAN signal is being carried out at Kozhikode, Hyderabad, Nagpur and Bangalore airports and the results have been satisfactory so far.