SYSTEM AND METHOD FOR APPLYING CODE CORRECTIONS FOR GNSS POSITIONING

• US 20100156709A1
• Filed: 12/19/2008
• Published: 06/24/2010
• Est. Priority Date: 12/19/2008
• Status: Active Grant

• Current Assignee: Hemisphere GNSS(USA) Incorporated
• Original Assignee: Nexteq Navigation Corporation
• Inventors: ZHANG, Yufeng, LEE, Suen, GAO, Yang
• Granted Patent: US 7,911,378 B2
• Time in Patent Office: Days
• US Class Current: 342/357.230
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry

Abstract

A method and system for approximating a position using a Global Navigational Satellite System (GNSS) having a plurality of GNSS satellites and an augmentation system, the method including the steps of obtaining an initial code pseudorange measurement and an initial carrier phase measurement from a signal transmitted by a GNSS satellite in the GNSS system, receiving a code correction from the augmentation system, using the code correction to correct the initial code pseudorange measurement and the initial carrier phase measurement to mitigate for errors in the signal, to result in a corrected code pseudorange measurement and a corrected carrier phase measurement, and using a code dominated measurement in a filter which outputs apposition and ambiguity estimate.

Claims

1. A method for approximating a position using a GNSS system having a plurality of GNSS satellites and an augmentation system, the method comprising:

(a) obtaining an initial code pseudorange measurement and an initial carrier phase measurement from a signal transmitted by a GNSS satellite in the GNSS system;

(b) receiving at least one code correction from the augmentation system;

(c) using the at least one code correction to correct the initial code pseudorange measurement and the initial carrier phase measurement to mitigate for errors in the signal, to result in a corrected code pseudorange measurement and a corrected carrier phase measurement; and

(d) using a code dominated measurement in a filter which outputs a position and ambiguity estimate.

2. The method of claim 1 wherein in step (d), a carrier phase dominated measurement is used in the filter which outputs a position and ambiguity estimate.

3. The method of claim 1 comprising the further step (e) of using a carrier phase dominated measurement in the filter after a stable filter output is achieved by repeating steps (a) to (d).

4. The method of claim 1 wherein if no corrections are received from the augmentation system, the method directly goes from step (a) to step (c) where the code corrections are treated as zeros.

5. The method of claim 1 wherein code pseudorange dominated measurement comprises a combination of the corrected code pseudorange measurement and at least one other measurement comprising or derived from a corrected carrier phase measurement.

6. The method of claim 1 wherein the carrier phase dominated measurement can comprise of only the corrected carrier phase measurement or a combination of the corrected carrier phase measurement and at least one other measurement.

7. The method of claim 1 using a single frequency GNSS system wherein the code pseudorange dominated measurement comprises one of:

(a) a code pseudorange measurement plus a carrier phase measurement combination;

(b) a code pseudorange plus IFCP combination;

or

(c) a code pseudorange, carrier phase plus IFCP combination.

8. The method of claim 7 wherein the carrier phase dominated measurement comprises one of:

(a) the corrected carrier phase measurement only;

(b) the IFCP only;

(c) carrier phase plus IFCP combination.

9. The method of claim 1 using a multiple frequency GNSS system wherein the code pseudorange dominated measurement comprises one of:

(a) a code pseudorange measurement plus φ

_{IonosphereFree} combination;

(b) a code pseudorange measurement, P_{IonosphereFree}, plus φ

_{IonosphereFree};

(c) a code pseudorange measurement, P_{IonosphereFree}, φ

_{IonosphereFree} plus IFCP combination;

or

(d) a code pseudorange measurement, φ

_{IonosphereFree} plus IFCP combination.

10. The method of claim 9 wherein the carrier phase dominated measurement comprises one of:

(a) P_{IonosphereFree} plus the φ

_{IonosphereFree} measurement;

(b) the φ

_{IonosphereFree} measurement only;

(c) P_{IonosphereFree}, φ

_{IonosphereFree} plus IFCP; and

(d) φ

_{IonosphereFree} plus IFCP.

11. The method of claim 1 wherein the modeled errors comprise one or more of:

the Sagnac effect, the relativity effect, the troposphere delay, earth tide compensation, and phase windup for carrier phase measurements.

12. The method of claim 1 wherein the code corrections received from the augmentation system are used to mitigate a satellite orbit error or a clock error, or both a satellite orbit error and a clock error.

13. The method of claim 1 wherein the code corrections received from the augmentation system are used to mitigate ionosphere delay errors.

14. The method of claim 1 wherein the GNSS system is a GPS, GLONASS, GALILEO, Beidou or a future Global Navigation Satellite System.

15. The method of claim 1 wherein the augmentation system is a satellite based augmentation system, ground based augmentation system or other augmentation systems providing code corrections.

16. The method of claim 15 wherein the satellite based augmentation system comprises the US Wide Area Augmentation System, the Japanese Multi functional Satellite Augmentation system, the European Geostationary Navigation Overlay Service or a future augmentation system providing code correction.

17. A computer readable memory having recorded thereon statements and instructions for execution by a data processing system to carry out a method as claimed above.

18. A device for approximating a position using a GNSS system having a plurality of satellites and an augmentation system, the apparatus comprising:

(a) at least one memory, the memory containing a set of program instructions;

(b) at least one processor operatively connected to the memory, the at least one processor responsive to the program instructions to;

(i) obtain an initial code pseudorange measurement and an initial carrier phase measurement from a signal transmitted by one of the plurality of satellites in the GNSS system;

(ii) receive at least one code correction from the augmentation system;

(iii) use the at least one code correction to correct the initial code pseudorange measurement and the initial carrier phase measurement to mitigate for errors in the signal, resulting in a corrected code pseudorange measurement and a corrected carrier phase measurement; and

(iv) use a code pseudorange dominated measurement in a filter which outputs a position and ambiguity estimate;

(v) repeating steps (i) to (iv) until a stable filter output is achieved; and

(vi) using a carrier phase dominated measurement in the filter.

19. The device of claim 18 wherein the at least one processor is responsive to the program instructions to implement a method as claimed above.