Radio positioning system for providing position and time for assisting GPS signal acquisition in mobile unit

• US 7,283,091 B1
• Filed: 08/08/2005
• Issued: 10/16/2007
• Est. Priority Date: 08/08/2005
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Loomis, Peter Van Wyck
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Chen; Shelley
• Application Number:
  US11/199,507
• Publication Number:
  US 20070252758A1
• Time in Patent Office: 799 Days
• Field of Search: 34235701-35717, 342450-465, 4554561-457
• US Class Current: 342/357.43
• CPC Class Codes: G01S 19/06 employing an initial estimate of the location of the receiver as aiding data or in generating aiding data
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• CPC Class Codes: G01S 19/48 by combining or switching between position solutions derived from the satellite radio beacon positioning system and position solutions derived from a further system

Abstract

A mobile location system. The GPS location system includes a radio positioning system (RPS) for determining times-of-arrival at several locations for a radio positioning signal transmitted from a mobile unit and then using the times-of-arrival for determining an RPS-based position and time for the mobile unit. The mobile unit uses the RPS-based position and time for focusing a code phase search to a narrow range for rapidly acquiring a GPS signal.

Claims

1. A radio positioning system, comprising:

at least three system units for determining a plurality of radio signal times-of-arrival (TOA)s, respectively, for a radio positioning signal received from a mobile unit;

a server for using said radio signal TOAs for computing jointly a radio positioning system (RPS)-based time for a time-of-transmission (TOT) of said radio positioning signal and an RPS-based position of said mobile unit; and

a system transceiver for transmitting a radio system signal having said RPS-based time and said RPS-based position to said mobile unit for use by said mobile unit for acquiring a global navigation satellite system (GNSS) signal; and

wherein;

the code range selector includes a bootstrap clock for determining a local elapsed time from a time-of-transmission (TOT) of said radio positioning signal and a GNSS time estimator for combining said local elapsed time with said RPS-based time for providing an RPS-based GNSS time estimate;

the code range selector using said RPS-based GNSS time estimate for selecting said code search range.

2. The system of claim 1, wherein:

said radio signal TOAs are determined in the system units according to a global navigation satellite system (GNSS) transfer time standard.

3. The system of claim 2, wherein:

said GNSS transfer time standard is global positioning system (GPS) time.

4. The system of claim 1, wherein:

said RPS-based time and said RPS-based position are resolved from a plurality of equations in the form of;

TOA_j−

TOT=[(X_j−

X)²+(Y_j−

Y)²]^1/2/C

where the TOT is the RPS-based time;

the (X, Y) is the RPS-based position;

the (X_j, Y_j) is a location of a jth one of said system units;

the TOA_j is the TOA at said jth system unit; and

the C is the speed of light.

5. The system of claim 1, wherein:

said RPS-based time and said RPS-based position are resolved from a plurality of equations in the form of;

TOA_j−

TOT=[(X_j−

X)²+(Y_j−

Y)²+(Z_j−

Z)²]^1/2/C

where the TOT is the RPS-based time;

the (X, Y, Z) is the RPS-based position;

the (X_j, Y_j, Z_j) is a location of a jth one of said system units;

the TOA_j is the TOA at said jth system unit; and

the C is the speed of light.

6. The system of claim 1, wherein:

said mobile unit includes a mobile global navigation satellite system (GNSS) receiver for receiving a global navigation satellite system (GNSS) signal having a spreading code, the GNSS receiver having a code range selector using said RPS-based time and said RPS-based position for selecting a code search range narrower than said code; and

a code recovery circuit using said code search range for acquiring said GNSS signal.

7. The system of claim 6, wherein:

said GNSS receiver is a global positioning system (GPS) receiver; and

said GNSS signal is a GPS signal.

8. The system of claim 1, wherein:

the code range selector further includes a satellite locator for using said RPS-based GNSS time estimate with GNSS orbital parameters for determining a location-in-space for a GNSS signal source transmitting said GNSS signal;

a transit time calculator for using said RPS-based position with said location-in-space for determining a transit time of said GNSS signal; and

a chip pointer for combining said RPS-based GNSS time estimate with said transit time for providing a predicted code phase for said code search range.

9. The system of claim 6, wherein:

the code range selector includes a search width sizer for using an expected accuracy of said RPS-based time and an expected accuracy of said RPS-based position for determining a search width of said code search range.

10. The system of claim 9, wherein:

said search width sizer further uses an RPS line-of-sight matrix for determining said search width.

11. The system of claim 10, wherein:

said GNSS signal is a global positioning system (GPS) signal having a pseudorandom noise (PRN) code having code chips; and

said search width is between five and twenty-five of said chips for said code.

12. The system of claim 6, wherein:

said code search range is less than twenty-five microseconds.

13. A location method, comprising:

determining at least three radio signal TOAs at a plurality of system locations, respectively, for a radio positioning signal received from a mobile unit;

jointly computing a radio positioning system (RPS)-based time for a time-of-transmission (TOT) of said radio positioning signal and an RPS-based position for said mobile unit from said TOAs; and

transmitting a radio system signal having said RPS-based time and said RPS-based position to said mobile unit, said RPS-based time and position used in said mobile unit for acquiring a global navigation satellite system (GNSS) signal; and

wherein;

selecting said code search range includes determining a local elapsed time in said mobile unit from a time-of-transmission (TOT) of said radio positioning signal;

combining said local elapsed time with said RPS-based time for providing an RPS-based GNSS time estimate; and

using said RPS-based GNSS time estimate for selecting said code search range.

14. The method of claim 13, wherein:

determining said radio signal TOAs includes determining said radio signal TOAs according to a global navigation satellite system (GNSS) transfer time standard.

15. The method of claim 14, wherein:

said GNSS transfer time standard is global positioning system (GPS) time.

16. The method of claim 13, wherein:

said RPS-based time and said RPS-based position are resolved from a plurality of equations in the form of;

TOA_j−

TOT=[(X_j−

X)²+(Y_j−

Y)²]^1/2/C

where the TOT is the RPS-based time;

the (X, Y) is the RPS-based position;

the (X_j, Y_j) is a jth said system location;

the TOA_j is the TOA at said jth system location; and

the C is the speed of light.

17. The method of claim 13, wherein:

said RPS-based time and said RPS-based position are resolved from a plurality of equations in the form of;

TOA_j−

TOT=[(X_j−

X)²+(Y_j−

Y)²+(Z_j−

Z)²]^1/2/C

where the TOT is the RPS-based time;

the (X, Y, Z) is the RPS-based position;

the (X_j, Y_j, Z_j) is a jth one of said system locations;

the TOA_j is the TOA at said jth system location; and

the C is the speed of light.

18. The method of claim 13, further comprising:

receiving in said mobile unit a global navigation satellite system (GNSS) signal having a spreading code;

using said RPS-based time and said RPS-based position for selecting a code search range narrower than said code; and

using said code search range for acquiring said GNSS signal.

19. The method of claim 18, wherein:

said GNSS receiver is a global positioning system (GPS) receiver; and

said GNSS signal is a GPS signal.

20. The method of claim 13, wherein:

selecting said code search range further includes using said RPS-based GNSS time estimate with GNSS orbital parameters for determining a location-in-space for a GNSS signal source transmitting said GNSS signal;

using said RPS-based position with said location-in-space for determining a transit time of said GNSS signal; and

combining said RPS-based GNSS time estimate with said transit time for providing a predicted code phase for said code search range.

21. The method of claim 18, wherein:

selecting a code search range includes using an expected accuracy of said RPS-based time and an expected accuracy of said RPS-based position for determining a search width of said code search range.

22. The method of claim 21, wherein:

determining said search width further includes using an RPS line-of-sight matrix for determining said search width.

23. The method of claim 22, wherein:

said GNSS signal is a global positioning system (GPS) signal having a pseudorandom noise (PRN) code having code chips; and

said search width is between five and twenty-five of said chips for said code.

24. The method of claim 18, wherein:

said code search range is less than twenty-five microseconds.