The AAI currently uses ground based terrestrial navigation system for providing safe navigation over the Indian airspace. This system however, has site limitations and range problems.
To overcome the limitations of ground based navigation systems, the ICAO in 1993, endorsed a Global Satellite Navigation System as a future Air Navigation System for Aviation. Following this, the AAI and ISRO entered into an MoU in 2001 for the implementation of the GAGAN project for seamless navigation over Indian airspace.
The current GPS system, maintained by the US, has 29 satellites in the 20000 kms orbit. The position accuracies required for precision approach and landing for civil aviation cannot be met by core GPS constellation. The constellation needs to be augmented to provide higher accuracy, reliability and integrity. The GPS data can be augmented with the help of Space Based Augmentation System (SBAS).
The GAGAN system proposes to augment the GPS data with the help of a geo stationary satellite to be launched by ISRO and the ground based infrastructure of reference stations, uplink earth stations and master control centre created by the AAI.