GAGAN is the acronym for GPS Aided GEO Augmented Navigation. The GAGAN uses a system of ground stations to provide necessary augmentations to the GPS standard positioning service(SPS) navigation signal. A network of precisely surveyed ground reference stations (INdian REference Stations : INRES) is strategically positioned across the country to collect GPS satellite data. Using this information, the master control centre (INdian Master Control Centre : INMCC) generates messages to correct any signal errors. These correction messages are then up linked through (INdian Land Uplink Station : INLUS) and broadcast through communication satellites (Geostationary) to receivers on board aircraft using the same frequency as GPS. The GAGAN is designed to provide the additional accuracy, availability, and integrity necessary to enable users to rely on GPS for all phases of flight, from en route through approach for all qualified airports within the GAGAN service volume. GAGAN will also provide the capability for increased accuracy in position reporting, allowing for more uniform and high-quality Air Traffic Management (ATM). In addition, GAGAN will provide benefits beyond aviation to all modes of transportation, including maritime, highways, and railways.