Differential GPS corrections using virtual stations

• US 7,711,480 B2
• Filed: 06/27/2005
• Issued: 05/04/2010
• Est. Priority Date: 01/03/1994
• Status: Expired due to Fees

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Robbins, James E.
• Primary Examiner(s): Tran; Khoi H.
• Assistant Examiner(s): MANCHO, RONNIE M
• Application Number:
  US11/169,054
• Publication Number:
  US 20060064244A1
• Time in Patent Office: 1,772 Days
• Field of Search: 701/214, 701/301, 701/215, 701/213, 701/207, 340/991, 340/993, 340/990, 342/357.03, 342/352, 342/358, 342/357.02, 342/357.06, 342/357.08, 342/357.11, 342/357.01
• US Class Current: 701/213
• CPC Class Codes: G01C 15/00 Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
• CPC Class Codes: G01C 21/28 with correlation of data from several navigational instruments
• CPC Class Codes: G01S 19/071 DGPS corrections
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• 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

Method and apparatus for providing GPS pseudorange correction and carrier phase correction information for navigation or surveying activities over a selected geographic region S of arbitrary size. In a navigation mode, a virtual reference station (VRS), positioned near a selected location L, receives differential GPS (DGPS) correction signals, translates these signals into a selected format, and broadcasts this DGPS information in this format for use by a local user. In a survey mode, the VRS receives corrected GPS information, translates this information into a selected format and broadcasts this translated and corrected GPS information and the VRS location, for use by a mobile station in forming a baseline vector from the GPS mobile station to the VRS location.

Claims

1. A method of providing GPS pseudorange correction information for navigation over a selected geographic region of arbitrary size, the method comprising:

receiving GPS signals from at least three GPS satellites at each of three or more spaced apart GPS reference stations whose location coordinates in a selected coordinate system are known, within the selected geographic region, where each reference station transmits GPS information signals, including information obtained from the GPS signals received;

receiving the GPS information signals transmitted by each reference station at a central station, obtaining ephemeris information for each of the satellites, estimating a satellite location error vector for each satellite from the information obtained from the GPS signals and from the ephemeris information, determining for each satellite a component of range error at a selected location due to satellite location error, and

making available the component of range error for each satellite to compensate for satellite location error when computing a position estimate from GPS signals received at a mobile station location.

2. The method of claim 1, wherein determining a component of range error comprises, for each satellite:

determining a calculated range from the selected location to the satellites; and

combining the calculated range with the satellite location error vector.

3. The method of claim 2, wherein estimating a satellite location error vector for each satellite comprises:

determining from the GPS signals a measured location of the satellite;

determining from satellite ephemeris information a calculated location of the satellite; and

comparing the measured location with the calculated location to determine the satellite location vector.

4. The method of claim 3, further comprising, at a mobile station location:

receiving GPS signals from the satellites; and

applying the component of range error for each satellite to compute from the GPS signals received at the mobile station location a compensated estimate of the mobile station location.

5. The method of claim 4, wherein the component of range error is determined for each satellite at a central station and transmitted to the mobile station location.

6. The method of claim 2, further comprising, at a mobile station location:

receiving GPS signals from the satellites; and

applying the component of range error for each satellite to compute from the GPS signals received at the mobile station location a compensated estimate of the mobile station location.

7. The method of claim 3, wherein the component of range error is transmitted with an issue of data ephemeris label.

8. The method of claim 1, wherein estimating a satellite location error vector for each satellite comprises:

determining from the GPS signals a measured location of the satellite;

determining from satellite ephemeris information a calculated location of the satellite; and

comparing the measured location with the calculated location to determine the satellite location vector.

9. The method of claim 8, further comprising, at a mobile station location:

receiving GPS signals from the satellites; and

applying the component of range error for each satellite to compute from the GPS signals received at the mobile station location a compensated estimate of the mobile station location.

10. The method of claim 9, further comprising determining for each satellite a pseudorange correction at the selected location by combining the component of range error for the satellite with an estimated clock error for the satellite and with a tropospheric delay correction and with an ionospheric delay correction.

11. The method of claim 1, further comprising calculating for the selected location an azimuth angle and an elevation angle for each satellite, and making the azimuth angle and the elevation angle for each satellite available to compensate at the mobile station location for at least one of ionospheric delay correction and tropospheric delay correction.

12. The method of claim 1, wherein the selected location corresponds approximately to the mobile station location.

13. The method of claim 1, wherein determining a component of range error comprises running a Kalman filter having, for each satellite, states for satellite clock error and for components of a satellite location error vector.

14. The method of claim 1, wherein making available the component of range error for each satellite comprises synthesizing a virtual-reference-station correction message which simulates a correction message that would be produced by a real reference station receiving GPS signals at the selected location.

15. The method of claim 14, wherein the information obtained from the GPS signals is derived from carrier phase measurements of GPS signals received at the reference stations, and wherein the method further comprises:

for each satellite, estimating from the signal information a satellite velocity error.

16. The method of claim 1, wherein the information obtained from the GPS signals is derived from carrier phase measurements of GPS signals received at the reference stations, and wherein the method further comprises:

for each satellite, estimating from the signal information a satellite velocity error.

17. The method of claim 1, wherein the signal information is derived from GPS signals obtained at an observation time during which at least one satellite is visible from at least three reference stations.