LOW BANDWIDTH METHOD FOR EPHEMERIS RECOVERY IN OVER-THE-AIR TRANSMISSION

• US 20150301183A1
• Filed: 11/01/2013
• Published: 10/22/2015
• Est. Priority Date: 11/04/2012
• Status: Abandoned Application

• Current Assignee: Iposi, Inc.
• Original Assignee: Iposi, Inc.
• Inventors: Derbez, Eric
• Application Number:
  US14/440,508
• Publication Number:
  US 20150301183A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01S 19/05 providing aiding data

Abstract

A method and apparatus are disclosed for processing and transmitting precise orbit predictions of satellites in a Global Navigation Satellite System such as Navstar-GPS or a communication device such as Iridium which employs force models and curve fitting techniques so encode ephemerides, and particularly ephemerides of duration of a month, in order to minimize bandwidth requirements over-the-air and NVRAM storage requirements. The methods also apply to GNSS constellations such as Galileo or GLONASS.

Claims

1. A method for encoding an orbit prediction of a satellite over a period of time and having a start time T comprising:

selecting a reference ephemeris model M_eph whose validity includes T;

selecting a multi-day precise orbit prediction POP;

fitting the initial velocity and empirical accelerations A₀ of model M_eph at T to the POP using force models while holding the initial position P₀ from M_eph at T fixed;

determining a scalar along-track velocity correction v_a to the velocity of M_eph at T relative to the fitted velocity and empirical accelerations A₀; and

encoding the empirical accelerations A₀ and the scalar along-track velocity correction v_a.

2. The method of claim 1 comprising:

determining a scalar radial velocity correction v_r to velocity of M_eph at T relative to the initial elements I at T.

3. The method of claim 2 comprising:

determining a scalar cross-track velocity correction v_c to velocity of M_eph at T relative to the initial elements I at T.

4. The method of claim 1 comprising encoding the reference ephemeris model M_eph.

5. The method of claim 1 comprising selecting the reference ephemeris model M_eph to be an ICD-200 ephemeris model.

6. The method of claim 5 wherein the ICD-200 ephemeris model is obtained off-air or derived from the POP.

7. The method of claim 1 wherein the start time T is the TOE of reference ephemeris model M_eph.

8. The method of claim 1 comprising selecting the POP to he in SP3 format.

9. The method of claim 1 wherein the satellite is a GPS, GNSS, or a QZSS satellite.

10. The method of claim 1 wherein the satellite is an Iridium or a LEO satellite.

11. The method of claim 1 comprising determining an along-track model M_a and a cross-track model M_o of position errors E between the integrated force models and the POP.

12. The method of claim 11 wherein the period of time is equal to or greater than a month.

13. The method of claim 1 comprising:

omitting the initial position and velocity vector of the satellite in the encoding.

14. The method of claim 1 additionally comprising:

encoding the clock bias, drift, and drift rate.

15. The method of claim 1 comprising an additional fitting to the POP while holding P₀ and V_eff fixed and allowing A0 to vary.

16. A method of decoding an orbit prediction of a satellite comprising:

obtaining the data encoded according to the method of claim 1;

computing the satellite position from the model M_eph at time T;

computing the satellite velocity from the model M_eph at time T;

correcting the satellite velocity at time T with the obtained scalar along-track velocity correction v_a; and

integrating the satellite position, corrected satellite velocity, and obtained along-track empirical accelerations A₀ using the set of integrated force models to recover the fit to the POP.

17. A method of decoding an orbit prediction of a satellite comprising:

obtaining the data encoded according to the method of claim 2;

computing the satellite position from the model M_eph at time T;

computing the satellite velocity from the model M_eph at time T;

correcting the satellite velocity at time T with the obtained scalar along-track velocity correction v_a and the scalar radial velocity correction v_r; and

integrating the satellite position, corrected satellite velocity, and obtained along-track empirical accelerations A_o using the set of integrated force models to recover the fit to the POP.

18. A method of decoding an orbit prediction of a satellite comprising:

obtaining the data encoded according to the method of claim 3;

computing the satellite position from the model M_eph at time T;

computing the satellite velocity from the model M_eph at time T;

correcting the satellite velocity at time T with the obtained scalar along-track velocity correction v_a, the scalar radial velocity correction v_r, and the scalar cross-track velocity correction v_c; and

integrating the satellite position, corrected satellite velocity, and obtained along-track empirical accelerations A_o using the set of integrated force models to recover the fit to the POP.

19. The method of claim 16 comprising:

determining position errors E from the along-track model M_a and the cross-track model M_c;

and subtracting out the determined position errors E from the integrated satellite positions.

20. The method of claim 16 comprising:

omitting the initial position and velocity vector of the satellite in the decoding.

21. A server for encoding an orbit prediction of a satellite comprising a server which has been programmed to encode the orbit prediction according to the method of claim 1.

22. A receiver device for decoding an orbit prediction of a satellite comprising a receiver device which has been programmed to decode the orbit prediction according to the method of claim 16.