Determining position without current broadcast ephemeris
View Patent ↗Devices and methods are described for determining position information without broadcast ephemeris data for extended time periods. A client device is disclosed that stores satellite states determined from broadcast ephemeris and numerically integrates equations of motion with regard to the stored satellite states to determine current satellites states. The client device uses the current satellite states in conjunction with received satellite signals to determine where the satellite signals were received.
1. A device, comprising:
a satellite state predictor operable to calculate current satellite states using broadcast ephemeris previously received from a plurality of satellites, wherein a validity time for the previously-received broadcast ephemeris has expired, and
a location determination system adapted to use the current satellite states in a determination of a location for the device if current broadcast ephemeris is unavailable.
2. The device of claim 1 , wherein the plurality of satellites are GPS satellites and the location determination system is a GPS location determination system.
3. The device of claim 2 , wherein the GPS satellite state predictor is adapted to calculate current satellite states by numerically integrating equations of motion for the GPS satellites.
4. The device of claim 3 , wherein the GPS satellite state predictor is adapted to calculate at least one parameter selected from the group consisting of a current lunar parameter, a current solar parameter, a current Earth orientation parameter, a solar radiation pressure parameter, and a y-bias parameter, the GPS satellite state predictor being further adapted to adjust the equations of motion according to the at least one parameter before the numerical integrations.
5. The device of claim 4 , wherein the GPS satellite state predictor is adapted to calculate the at least one parameter using a series expression.
6. The device of claim 5 , wherein the series expression is a series expression of powers and sinuosoids.
7. The device of claim 6 , wherein the series expression in the form of A+Bt+Ct 2 +D cos(wt)+E sin(wt), where A, B, C, D, E, and w are constants and t represents a current time.
8. The device of claim 1 , wherein the location determination system is further adapted to use current broadcast ephemeris to determine the current satellite states if the current broadcast ephemeris is available.
9. The device of claim 1 , wherein the satellite state predictor comprises a processor.
10. A method, comprising:
receiving broadcast ephemeris from a plurality of satellites to determine satellite states for the plurality of satellites;
storing the satellite states;
after a validity time for the received broadcast ephemeris has expired, numerically integrating equations of motions for plurality of satellites using the stored satellite states to determine current satellite states;
in a receiver, receiving satellite signals from the plurality of satellites to provide a plurality of pseudo-range measurements; and
calculating a first position for the receiver using the pseudo-range measurements and the current satellite states.
11. The method of claim 10 , further comprising: calculating a second position for the receiver using current broadcast ephemeris and the received satellite signals.
12. The method of claim 10 , further comprising:
calculating at least one parameter selected from the group consisting of a current lunar parameter, a current solar parameter, a current Earth orientation parameter, a solar radiation pressure parameter, and a y-bias parameter; and
adjusting the equations of motion according to the at least one parameter before numerically integrating.
13. The method of claim 12 , wherein calculating the at least one parameter comprises calculating the current lunar parameter, the current solar parameter, the current Earth orientation parameter, the solar radiation pressure parameter, and the y-bias parameter.
14. The method of claim 13 , wherein calculating the current lunar parameter, the current solar parameter, the current Earth orientation parameter, the solar radiation pressure parameter, and the y-bias parameter comprises determining values for a plurality of series expressions.
15. The method of claim 14 , wherein each series expression is a series expression of powers and sinusoids.
16. The method of claim 15 , wherein each series expression is in the form of A+Bt+Ct 2 +D cos(wt)+E sin(wt), where A, B, C, D, E and w are constants and t represents a current time.
17. The method of claim 16 , further comprising: processing historical satellite states to determine the constants A, B, C, D, E and w.
18. The method of claim 17 , further comprising: storing the constants A, B, C, D, E and w in non-volatile memory.
19. The method of claim 17 , further comprising: determining whether a valid period for the constants has expired.
20. The method of claim 19 , further comprising: if the valid period has expired, re-calculating the constants.