- 30 Maj 2016
Satellites of a satellite positioning system broadcast within the navigation signals ephemeris data having a certain period of validity. The period of validity may, for instance, be defined as the time interval in which the accuracy of a position fix derived from these ephemeris data meets the specifications, respectively the end user's expectations. At a mobile station, e.g. a mobile phone, a digital camera, a portable computer, a handheld computer or any like device equipped with a satellite-positioning receiver, 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. A server station, e.g. an AGNSS server or any like assistance data provider receives the ephemeris data broadcast by the satellites, e.g. by means of a reference receiver connected to it. A request for assistance data from the mobile station is received at the server station, which then transmits ephemeris data as part of the assistance data to the mobile station in response to the request. According to an important aspect of the invention, upon receiving the request for assistance data issued by said 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, i.e. if the specified position fix accuracy can be achieved with the broadcast ephemeris data, the server station transmits the broadcast ephemeris data to the mobile station. In the negative, i.e. only if the specified position fix accuracy cannot be achieved with the broadcast ephemeris data, 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.
THE MAIN APPLICATION AREAS
- Global Navigation Satellite Systems (GNSS)
- location-based services (lbs)
- timing & synchronisation
THE MAIN INNOVATIVE ASPECTS AND ADVANTAGES
The advantage of such a solution is that the applicative layers have a much higher data rate than the control plane layers. Nevertheless, the user can access to this layer only if he has subscribed, which raises the issue of position-fixing related to emergency calls. One would therefore prefer conveying assistance data to the mobile station and retrieving position information from the mobile station over the control plane of the communication network. The protocol is standardised in the TS44.031 (RRLP) for GSM and the TS23.371 (RRC) for UMTS. An important advantage of the control plane implementation is that data exchange with regard to position is possible, even without a SIM (Subscriber Identity Module) card. As a consequence, emergency calls can be located, even if the user has not subscribed. Another advantage is that the operator is completely in control of the process and can vouch for the service. The main drawback is that the signalling layers have a low data rate, which leads to problems if many mobile stations request for assistance data. One therefore seeks for methods for exchanging GNSS assistance data with reduced data rate.