Method for providing assistance data to mobile station of a satellite positioning system

Abstract

Satellites of a satellite positioning system broadcast within the navigation signals ephemeris data having a certain period of validity. At a mobile station, ephemeris data are required for position-fixing. In assisted satellite positioning systems, acquisition of navigation signals emitted by the satellites is facilitated as assistance data are provided to the mobile station. At a server station, a request for assistance data issued by the mobile station is received, and the server station transmits ephemeris data as part of the assistance data to the mobile station in response to its request. Upon receiving the request for assistance data issued by the mobile station, the server station decides whether the mobile station could achieve a specified position fix accuracy if the mobile station was provided with the broadcast ephemeris data. In the positive, the server station transmits the broadcast ephemeris data to the mobile station. In the negative, the server station transmits, instead of broadcast ephemeris data, long-term ephemeris data to the mobile station as part of the assistance data requested. The long-term ephemeris data are derived from satellite orbit predictions and have a period of validity substantially increased with respect to the ephemeris data broadcast by the satellites.