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A method of predicting a location of a satellite is provided wherein the GPS device, based on previously received information about the position of a satellite, such as an ephemeris, generates a correction acceleration of the satellite that can be used to predict the position of the satellite outsid

A method of predicting a location of a satellite is provided wherein the GPS device, based on previously received information about the position of a satellite, such as an ephemeris, generates a correction acceleration of the satellite that can be used to predict the position of the satellite outside of the time frame in which the previously received information was valid. The calculations can be performed entirely on the GPS device, and do not require assistance from a server. However, if assistance from a server is available to the GPS device, the assistance information can be used to increase the accuracy of the predicted position.

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1. A method of predicting a location of a satellite, comprising: receiving, at an RF antenna of a GNSS device, an ephemeris associated with a satellite, the ephemeris valid for an effective time period;using the ephemeris, the GNSS device calculating position data and velocities of the satellite for

1. A method of predicting a location of a satellite, comprising: receiving, at an RF antenna of a GNSS device, an ephemeris associated with a satellite, the ephemeris valid for an effective time period;using the ephemeris, the GNSS device calculating position data and velocities of the satellite for a plurality of time intervals over the effective time period;the GNSS device calculating, at a time during the effective time period, a plurality of correction acceleration terms for reducing errors between predicted position data and predicted velocities of the satellite and ephemeris-derived position data and velocities of the satellite at each of the plurality of time intervals over the effective time period, the predicted position data and predicted velocities being determined using a plurality of previously calculated orbit state vectors stored in memory of the GNSS device;the GNSS device calculating a current orbit state vector using force model coefficients adjusted based on the plurality of correction acceleration terms and storing the current orbit state vector in the memory, the current orbit state vector being used as initial state for propagating an orbit of the satellite within a predicted time period, at least a portion of the predicted time period occurring after the effective time period; andthe GNSS device determining the location of the satellite using the orbit. 2. A method as claimed in claim 1, wherein the GNSS device is a GPS device. 3. A method as claimed in claim 2, wherein when the effective time period has expired, the GPS device determines the location of the satellite using the propagated orbit. 4. A method as claimed in claim 2, wherein during the effective time period, the GPS device determines the location of the satellite using the position data and velocity. 5. A method as claimed in claim 4, wherein the ephemeris is a broadcast ephemeris. 6. A method as claimed in claim 4, wherein the ephemeris is a synthetic ephemeris. 7. A method as claimed in claim 2, wherein the errors between the plurality of predicted position data and the plurality of predicted velocities of the satellite and the plurality of ephemeris-derived position data and velocities of the satellite comprise radial errors and along track errors. 8. A method as claimed in claim 2, wherein the current orbit state vector and orbit state vectors for previous time periods are stored in the memory as polynomials. 9. A method as claimed in claim 8, wherein the polynomial is converted into a synthetic ephemeris by the GPS device in order to determine the location of the satellite. 10. A method as claimed in claim 2, wherein when a network interface of the GPS device is in communication with an AGPS server, the AGPS server providing a synthetic ephemeris to the GPS device when the effective time period has expired. 11. A method as claimed in claim 2, wherein the force model coefficients are calculated iteratively. 12. A method as claimed in claim 2, wherein the GPS device uses a plurality of force models, each force model based on a different set of force model coefficients selected to achieve selected performance characteristics. 13. A method as claimed in claim 12, wherein the selected performance characteristics comprise: computational load, memory requirements, orbital prediction duration and accuracy. 14. A method as claimed in claim 12, wherein the GPS device selects one of the plurality of force models to use when propagating the orbit of the satellite after the effective time period in response to the selected performance characteristics. 15. A method as claimed in claim 12, wherein the GPS device receives the force model correction acceleration terms from a remote server. 16. A method of predicting a location of a satellite, comprising: a GNSS device propagating an orbit of the satellite using an orbit state vector calculated using a force model, coefficients of the force model being calculated at a time during an effective time period of a broadcast ephemeris received by an RF antenna of the GNSS device, the coefficients being calculated to reduce errors, for a plurality of time intervals over the effective time period of the broadcast ephemeris, between a plurality of ephemeris-derived position data and velocities and a plurality of predicted position data and predicted velocities calculated using a plurality of previously calculated orbit state vectors; andwhen the effective time period has expired, determining the location of the satellite using the orbit. 17. A method as claimed in claim 16, wherein the GNSS device is a GPS device. 18. A method as claimed in claim 16, wherein the errors comprises radial errors and along track errors. 19. A GNSS device comprising: an RF receiver for receiving an ephemeris comprising position data and velocities associated with a satellite, the position data and the velocities valid for an effective time period;a processor for calculating, at a time during the effective time period, ephemeris-derived position data and velocities of the satellite for a plurality of time intervals over the effective time period, calculating a plurality of correction acceleration terms for reducing error between predicted position data and predicted velocities of the satellite and the ephemeris-derived position data and velocities of the satellite at each time interval over the effective time period, the predicted position data and predicted velocities being determined using a plurality of previously calculated orbit state vectors, and calculating a current orbit state vector using force model coefficients adjusted based on the plurality of correction acceleration terms; anda memory for storing the current orbit state vector and previously calculated orbit state vectors;wherein the current orbit state vector is for propagating an orbit of the satellite within a predicted time period, at least a portion of the predicted time period occurring after the effective time period. 20. A GPS device as claimed in claim 19, wherein the error between the predicted position data and the predicted velocity of the satellite and the position data and the velocity of the satellite comprises radial errors and along track errors.