GPS receiver having a fast time to first fix

• US 6,191,731 B1
• Filed: 08/25/1999
• Issued: 02/20/2001
• Est. Priority Date: 08/25/1999
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Sanders, Jeffrey D., McBurney, Paul W.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/384,086
• Time in Patent Office: 545 Days
• Field of Search: 342/357.01, 342/357.05, 342/357.06, 342/357.12, 701/213
• US Class Current: 342/357.46
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/52 Determining velocity

Abstract

A global positioning system (GPS) receiver having a fast time to first fix using the velocity of a GPS satellite and an approximate time. The GPS receiver includes a GPS antenna for receiving a GPS signal, radio frequency circuitry for downconverting and sampling the GPS signal, a reference timer for providing a reference clocking signal, a digital signal processor for receiving the sampled GPS signal, and a microprocessor for executing program codes in a memory. The digital signal processor cooperates with the microprocessor for correlating the sampled GPS signal to an internal GPS replica signal based upon the reference clocking signal. The memory includes program codes for a pseudorange detector for measuring code phase offsets, a directional cosine calculator for calculating unit vectors, a satellite velocity calculator for calculating vector velocities, a pseudorange linearizer for determining linearized pseudoranges, and a velocity-enhanced location calculator. The velocity-enhanced location calculator uses an approximate absolute time with the linearized pseudoranges, unit vectors, and velocities of five or more GPS satellites for determining a GPS-based location for the GPS receiver before receiving a Z-count in a GPS signal. The error in the approximate time may be up to at least 100 seconds.

Claims

1. A positioning receiver, comprising:

a velocity calculator for using source location data pertaining to a positioning signal source for computing a vector velocity of said positioning signal source, said positioning signal source having a different motion than the receiver; and

a velocity-enhanced location calculator for using said velocity vector and an approximate time for resolving a geographical location of the receiver.

2. The positioning receiver of claim 1, wherein:

said positioning signal source is a global positioning system (GPS) satellite.

3. The positioning receiver of claim 1, wherein:

said positioning signal source is a global orbiting navigation system (GLONASS) satellite.

4. The receiver of claim 1, further comprising:

a pseudorange detector for measuring a code phase offset pertaining to said positioning signal source;

a signal source location calculator for using said approximate time and said source location data for computing a location-in-space for said positioning signal source;

a directional cosine calculator for computing a unit vector between an assumed location of the receiver and said location-in-space; and

a pseudorange linearizer for calculating a range between said assumed location and said location-in-space, and using said code phase offset and said calculated range for determining a linearized pseudorange; and

wherein;

the velocity-enhanced location calculator is further for using said linearized pseudorange and said unit vector for resolving said location of the receiver.

5. The receiver of claim 4, wherein:

the pseudorange linearizer is further for truncating said calculated pseudorange and using said truncated calculated pseudorange for determining said linearized pseudorange.

6. The receiver of claim 4, wherein:

the pseudorange linearizer is further for re-ranging said linearized pseudorange for placing said linearized pseudorange within a window of plus and minus one-half millisecond.

7. The receiver of claim 4, wherein:

the velocity-enhanced location calculator is further for using a location equation having a product of said unit vector and said velocity vector for resolving said location of the receiver.

8. The positioning receiver of claim 1, wherein:

said approximate time differs from a true positioning signal based time in a range of about one second to about one-hundred seconds.

17. The receiver of claim 1, further comprising:

a signal source location calculator for using said approximate time and said source location data for computing a location-in-space for said positioning signal source;

a directional cosine calculator for computing a unit vector between an assumed location of the receiver and said location-in-space; and

wherein;

the velocity-enhanced location calculator uses said velocity vector and said unit vector for calculating a range rate and uses said range rate and said approximate time for resolving said geographical location.

9. A method in a positioning receiver, comprising steps of:

computing a vector velocity for a positioning signal source from source location data pertaining to said positioning signal source, said positioning signal source having a different motion than the receiver; and

resolving a geographical location of said receiver using said velocity vector and an approximate time.

10. The method of claim 9, wherein:

said positioning signal source is a global positioning system (GPS) satellite.

11. The method of claim 9, wherein:

said positioning signal source is a global orbiting navigation system (GLONASS) satellite.

12. The method of claim 9, further comprising steps of:

measuring a code phase offset pertaining to said positioning signal source;

computing a location-in-space for said positioning signal source from said approximate time and said source location data;

computing a unit vector between an assumed location of the receiver and said location-in-space;

calculating a range between said assumed location and said location-in-space for providing a calculated range; and

determining a linearized pseudorange from said calculated range and said code phase offset; and

wherein;

the step of resolving said location of said receiver further includes using said linearized pseudorange and said unit vector.

13. The method of claim 12, further comprising step of:

truncating said calculated pseudorange; and

wherein;

the step of determining said linearized pseudorange includes using said truncated calculated pseudorange.

14. The method of claim 12, wherein:

the step of determining said linearized pseudoranges further includes re-ranging said linearized pseudoranges for placing said linearized pseudoranges within a window of plus and minus one-half millisecond.

15. The method of claim 12, wherein:

the step of resolving said geographical location includes using a location equation having a product of said unit vector and said velocity vector.

16. The method of claim 9, wherein:

said approximate time differs from a true positioning signal based time in a range of about one second to about one-hundred seconds.

18. The method of claim 9, further comprising steps of:

computing a location-in-space for said positioning signal source based upon said approximate time and said source location data; and

computing a unit vector between an assumed location of the receiver and said location-in-space; and

wherein;

the step of resolving said geographical location includes steps of calculating a range rate using said velocity vector and said unit vector; and

calculating said geographical location using said range rate and said approximate time.