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The American Global Positioning System (GPS) and the Russian Global Orbiting Navigation Satellite System (GLONASS) are the two navigation satellite systems currently in operation. Both were designed in the 70s for military purposes: to provide positioning information to their respective armies anywhere on the planet where they were located.

Both the GPS and the GLONASS include a civil service (Standard Positioning Service) which is accessible to the whole world. Since many of the GLONASS satellites have surpassed their useful life without being replaced, for all intents and purposes GPS holds a true monopoly on the navigation satellite systems.

The civilian side of GPS does not satisfy the needs of some sectors -above all for civil aviation-, as it does not completely satisfy the four basic requirements set out by the ICAO for GNSS systems. These are: accuracy (position information error, speed and time provided by the system); integrity (guarantees the reliability of the position); continuity (guarantees to constantly receive the accuracy and integrity services without interruptions) and availability (absolute confirmation that the precision, integrity and continuity services will be available whenever they are needed.)