Differential global positioning system using almanac data for a fast time to first fix

• US 6,211,817 B1
• Filed: 07/27/1999
• Issued: 04/03/2001
• Est. Priority Date: 07/27/1999
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Eschenbach, Ralph F
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H.
• Application Number:
  US09/361,916
• Time in Patent Office: 616 Days
• Field of Search: 342/357.03, 342/358, 342/357.02, 701/215
• US Class Current: 342/357.31
• CPC Class Codes: G01S 19/071 DGPS corrections
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]

Abstract

A DGPS system using GPS almanac data for determining the locations-in-space and the DGPS corrections for GPS satellites for providing a differentially corrected location of a remote GPS user receiver. A GPS reference receiver determines almanac-based DGPS corrections from the differences between ranges that are measured to GPS satellites and ranges that are calculated to the GPS almanac-based locations-in-space of the GPS satellites from the known location of the GPS reference receiver. The GPS user receiver measures pseudoranges to the GPS satellites. Then, in a first embodiment, the GPS reference receiver radios the DGPS corrections to the GPS user receiver. The GPS user receiver uses almanac-based locations-in-space for the GPS satellites and the almanac-based DGPS corrections for differentially correcting the measured user pseudoranges for providing a differentially corrected user location. In a second embodiment, the GPS user receiver radios the measured user pseudoranges to the GPS reference receiver. The GPS reference receiver uses the measured user pseudoranges, the almanac-based locations-in-space for the GPS satellites, and the almanac-based DGPS corrections for providing the differentially corrected user location.

Claims

1. A method in a differential global positioning system (DGPS) system, comprising steps of:

computing an almanac-based location-in-space of a GPS signal source from GPS almanac data pertaining to said GPS signal source;

at a GPS user receiver, determining a user pseudorange between said GPS signal source and said GPS user receiver; and

using said almanac-based location-in-space, said user pseudorange, and an almanac based DGPS range correction for calculating a differentially corrected user location of said GPS user receiver, said almanac-based DGPS range correction based upon said GPS almanac data pertaining en said GPS signal source.

2. The method of claim 1, further comprising a step of:

receiving said almanac-based DGPS range correction at said GPS user receiver; and

wherein;

the step of computing said almanac-based locationin-space includes computing said almanac-based location-inspace at said GPS user receiver; and

the step of calculating said differentially corrected user location includes a step of calculating said differentially corrected user location at said GPS user receiver.

3. The method of claim 1, further comprising a step of:

receiving said user pseudorange at a GPS reference receiver; and

wherein;

the step of computing said almanac-based location-in-space includes computing said almanac-based location-in-space at said GPS reference receiver; and

the step of calculating said differentially corrected user location includes a step of calculating said differentially corrected user location at said GPS reference receiver.

4. The method of claim 1, further comprising steps of:

calculating an almanac-based reference range between a reference location of a GPS reference receiver and said almanac-based location-in-space;

measuring a reference range between said GPS reference receiver and said GPS signal source; and

calculating said almanac-based DGPS range correction from a difference between said calculated almanac-based reference range and said measured reference range.

5. The method of claim 1, wherein:

the step of calculating said differentially corrected user location includes steps of;

calculating said differentially corrected user location by calculating an almanac-based user range between an assumed user location of said GPS user receiver and said almanac-based location-in-space;

differencing said user pseudorange and said calculated almanac-based user range for providing an almanac-based linearized pseudorange;

forming a location equation with said almanac-based linearized pseudorange and said almanac-based DGPS range corrections; and

using said location equation for calculating said differentially corrected user location.

6. A global positioning system (GPS) user receiver, comprising:

a user processor;

a user GPS source location code for execution by the user processor for computing an almanac-based location-in-space of a GPS signal source from GPS almanac data pertaining to said GPS signal source;

a user range code for execution by the user processor for measuring a user pseudorange between the GPS user receiver and said GPS signal source; and

an almanac-based DGPS location code for execution by the user processor for using said almanac-based location-in-space, said user pseudorange, and an almanac based DGPS range correction for calculating a differentially corrected user location of said GPS user receiver, said almanac-based DGPS range correction based upon said GPS almanac data pertaining to said GPS signal source.

7. The GPS user receiver of claim 6, further comprising:

a receiver for receiving said almanac-based DGPS range correction.

8. The GPS user receiver of claim 6, wherein:

the almanac-based DGPS location code is further for calculating said differentially corrected user location by calculating an almanac-based user range between an assumed user location of said GPS user receiver and said almanac-based location-in-space, differencing said user pseudorange and said calculated almanac-based user range for providing an almanac-based linearized pseudorange, forming a location equation with said almanac-based linearized pseudorange and said almanac-based DGPS range corrections, and using said location equation for calculating said differentially corrected user location.

9. A global positioning system (GPS) reference receiver, comprising:

a reference processor;

a reference GPS source location code for execution by the reference processor for computing an almanac-based location-in-space of a GPS signal source from GPS almanac data pertaining to said GPS signal source;

a reference range measurement code for execution by the reference processor for measuring a measured reference range from said GPS signal source to the GPS reference receiver;

a reference range calculation code for execution by the reference processor for calculating an almanac-based calculated reference range from almanac-based location-in-space to a pre-determined reference location of the GPS reference receiver; and

a reference differential correction code for determining an almanac-based DGPS range correction from a difference between said measured reference range and said almanac-based calculated reference range.

10. The GPS reference receiver of claim 9, further comprising:

a transmitter for transmitting said almanac-based DGPS range correction.

11. The GPS reference receiver of claim 9, further comprising:

a receiver for receiving a measured user pseudorange between a GPS user receiver and said GPS signal source;

an almanac-based DGPS correction code for execution by the reference processor for using said almanac-based location-in-space, said measured user pseudorange, and said almanac based DGPS range correction for calculating a differentially corrected user location of said GPS user receiver.

12. The GPS reference receiver of claim 11, wherein:

the almanac-based DGPS location code is further for calculating said differentially corrected user location by calculating an almanac-based user range between an assumed user location of said GPS user receiver and said almanac-based location-in-space, differencing said user pseudorange and said calculated almanac-based user range for providing an almanac-based linearized pseudorange, forming a location equation with said almanac-based linearized pseudorange and said almanac-based DGPS range corrections, and using said location equation for calculating said differentially corrected user location.