Correction data for Navstar Global Positioning System transmitted in the RDS channel. Technical verification and implement in Sweden

GPS is a satellite based positioning service that is free to use by any user. The system is owned by the US government and is operated by the US Defence Department. The positioning service is distributed via 24 satellites that orbits the globe in six inclined orbits 20 thousand kilometres above the Earth surface. All satellites have their own atomic clock which is transmitted to the GPS receiver on Earth. Each satellite also transmits data of all other satellites orbits, i.e, the exact position of every satellite for a given time. This data is called the satellite almanac. Differential Corrections Incorporated in USA has developed a system that uses a 12 channel GPS reference receiver. A computer compress and encrypts the Radio Technical Commission for Maritime Services (RTCM) data in a way that makes it possible to transmit the data in the RDS channel with a very small impact on the radio broadcasting data. DCI has also developed DGPS receivers that decrypts the encrypted data back to RTCM format. This is a subscription based service