GNSS post positioning with selected precision

• US 20090102714A1
• Filed: 11/18/2008
• Published: 04/23/2009
• Est. Priority Date: 05/26/2005
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Bird, David G., Talbot, Nicholas Charles, Weisenburger, Shawn
• Granted Patent: US 8,199,049 B2
• Time in Patent Office: Days
• US Class Current: 342/357.310
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/22 Multipath-related issues

Abstract

A computer apparatus for post positioning with a selected precision. The apparatus includes a GNSS post processor to post process reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver to compute a secure position for the rover receiver not available to a user. The apparatus includes a vector offset generator to use the selected precision to compute a dither level for offset vectors to degrade an intrinsic precision of the secure position to provide a user-available position for the rover receiver at the selected precision.

Claims

1. A computer apparatus for post positioning with a selected precision, comprising:

a global navigation satellite system (GNSS) post processor to post process reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver to compute a secure position, not available to a user, for said rover receiver; and

a vector offset generator to use a selected precision to compute a dither level for a sequence of offset vectors to degrade an intrinsic precision of said secure position to provide a user-available position for said rover receiver at said selected precision.

2. The apparatus of claim 1, wherein:

the post processor is constructed to perform said post process in a different geographical place and at a later time than said rover GNSS carrier phases are observed.

3. The apparatus of claim 1, wherein:

the post processor includes an intrinsic precision estimator to compute said intrinsic precision based on covariance matrix components of a position fix for said secure position.

4. The apparatus of claim 1, wherein:

the vector offset generator includes an accuracy leveler to compensate said selected precision for a variation in said intrinsic precision by computing a smaller said dither level when said intrinsic precision is less precise.

5. The apparatus of claim 4, wherein:

said selected precision includes a selected horizontal precision and a selected vertical precision; and

said accuracy leveler includes a horizontal precision compensator to compensate said selected horizontal precision for a horizontal component of said intrinsic precision to provide a horizontal component of said dither level, and a vertical precision compensator to compensate said selected vertical precision for a vertical component of said intrinsic precision to provide a vertical component of said dither level.

6. The apparatus of claim 5, wherein:

said accuracy leveler further includes an east horizontal scaler to use an east part of said horizontal intrinsic precision component to scale said horizontal dither level to provide an east dither level; and

a north horizontal scaler to use a north part of said horizontal intrinsic precision component to scale said horizontal dither level to provide a north dither level.

7. The apparatus of claim 1, further comprising:

a DOP scaler to compute said selected precision by using a selected DOP scale factor and a selected DOP offset for processing a dilution of precision (DOP) of a constellation of satellites used for determining said secure position.

8. The apparatus of claim 7, wherein:

the DOP scaler includes a horizontal precision selector to calculate a horizontal component of said selected precision by multiplying a horizontal component of said DOP (HDOP) by a selected HDOP scale factor and adding a selected HDOP offset.

9. The apparatus of claim 1, further comprising:

a random process generator having east, north and up random processors constructed to use said east, north and vertical components of said dither level to provide east, north and up sequences, respectively, for said offset vectors; and

a position dither processor to add said east, north and up sequences to east, north and up components, respectively, of said secure position to provide said user-available position.

10. The apparatus of claim 9, wherein:

the random process generator includes a bias generator to generate east, north and up biases corresponding to a particular data set of said rover carrier phases to bias mean levels of said east, north and up sequences, respectively.

11. A post processing method for providing a selected precision for a position, comprising:

post processing reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver for computing a secure position, not available to a user, for said rover receiver; and

computing a dither level for a sequence of offset vectors for degrading an intrinsic precision of said secure precision for providing a user-available position at said selected precision for said rover receiver.

12. The method of claim 11, wherein:

post processing is performed in a different geographical place and at a later time than said rover GNSS carrier phases are observed.

13. The method of claim 11, wherein:

post processing includes computing said intrinsic precision based on covariance matrix components of a position fix for said secure position.

14. The method of claim 11, wherein:

computing said dither level includes compensating said selected precision for a variation in said intrinsic precision by computing a smaller said dither level when said intrinsic precision is less precise.

15. The method of claim 14, wherein:

said selected precision includes a selected horizontal precision and a selected vertical precision; and

compensating said selected precision includes compensating said selected horizontal precision for a horizontal component of said intrinsic precision to provide a horizontal component of said dither level; and

compensating said selected vertical precision for a vertical component of said intrinsic precision to provide a vertical component of said dither level.

16. The method of claim 15, wherein:

computing said dither level further includes using an east part of said horizontal intrinsic precision component for scaling said horizontal dither level for providing an east dither level; and

using a north part of said horizontal intrinsic precision component for scaling said horizontal dither level for providing a north dither level.

17. The method of claim 11, further comprising:

computing said selected precision by using a selected DOP scale factor and a selected DOP offset for processing a dilution of precision (DOP) of a constellation of satellites used for determining said secure position.

18. The method of claim 17, wherein:

computing said selected precision includes calculating a horizontal component of said selected precision by multiplying a horizontal component of said DOP (HDOP) by a selected HDOP scale factor and adding a selected HDOP offset.

19. The method of claim 11, further comprising:

generating east, north and up pseudorandom sequences having said east, north and vertical components of said dither level, respectively for said offset vectors; and

adding said east, north and up sequences to east, north and up components of said secure position to provide said user-available position.

20. The method of claim 19, further comprising:

generating east, north and up biases corresponding to a particular data set of said rover carrier phases; and

biasing mean levels of said east, north and up sequences with said east, north and up biases, respectively.

21. A computer-readable medium having computer-executable instructions stored or carried thereby that when executed by a processor, perform a method comprising steps of:

post processing reference GNSS carrier phases from a reference system and rover GNSS carrier phases from a rover receiver for computing a secure position, not available to a user, for said rover receiver; and

computing a dither level for a sequence of offset vectors for degrading an intrinsic precision of said secure precision for providing a user-available position at said selected precision for said rover receiver.

22. The medium of claim 21, wherein:

computing said dither level includes compensating said selected precision for a variation in said intrinsic precision by computing a smaller said dither level when said intrinsic precision is less precise.

23. The medium of claim 22, wherein:

said selected precision includes a selected horizontal precision and a selected vertical precision; and

compensating said selected precision includes compensating said selected horizontal precision for a horizontal component of said intrinsic precision to provide a horizontal component of said dither level; and

compensating said selected vertical precision for a vertical component of said intrinsic precision to provide a vertical component of said dither level.

24. The medium of claim 23, wherein:

computing said dither level further includes using an east part of said horizontal intrinsic precision component for scaling said horizontal dither level for providing an east dither level; and

using a north part of said horizontal intrinsic precision components for scaling said horizontal dither level for providing a north dither level.

25. The medium of claim 24, further comprising:

computing said selected precision by using a selected DOP scale factor and a selected DOP offset for processing a dilution of precision (DOP) of a constellation of satellites used for determining said secure position; and

computing said selected precision further includes calculating a horizontal component of said selected precision by multiplying a horizontal component of said DOP (HDOP) by a selected HDOP scale factor and adding a selected HDOP offset.