GPS receiver using stored navigation data bits for a fast determination of GPS clock time

• US 7,348,921 B2
• Filed: 09/19/2005
• Issued: 03/25/2008
• Est. Priority Date: 09/19/2005
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Yu, Yiming
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Mull; Fred H.
• Application Number:
  US11/229,948
• Publication Number:
  US 20070063894A1
• Time in Patent Office: 918 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.15
• US Class Current: 342/357.63
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073

Abstract

A GPS receiver having a fast method for determining GPS clock time. The GPS receiver includes a signal processor for receiving GPS signals from GPS satellites and detecting current GPS data bits carried by the respective GPS signals, a chapter memory for storing a block of expected GPS data bits for the respective GPS satellites, and a GPS time detector for detecting a successful match when a chunk of the expected data bits within a selected search range within the block matches a chunk of the current data bits, and using the successful match for determining the GPS clock time. In an anytime embodiment the GPS receiver enters an operation mode at any time in order to minimize user request latency. In a focused embodiment the GPS receiver enters the operation mode at a prescribed time-of-entry in order to minimize power consumption for cycles of standby and operation modes.

Claims

1. A method for determining global navigation satellite system (GNSS) clock time, comprising:

storing expected GNSS data bits for a GNSS signal source;

maintaining a clock time estimate while in a standby mode;

receiving a GNSS signal from said GNSS signal source;

detecting a chunk of current GNSS data bits from said GNSS signal;

using said time estimate for selecting a search range of said expected data bits;

detecting a successful match when one of a plurality of chunks of said expected data bits within said search range matches said chunk of current data bits; and

using said successful match for determining a GNSS clock time, wherein;

detecting said successful match includes;

verifying that said current data bit chunk matches no more than one of said expected data bit chunks.

2. The method of claim 1, further comprising:

using said time estimate for computing time-variant GNSS data bits and augmenting said stored expected data bits with said time-variant expected data bits for providing said chunks of said expected data bits.

3. The method of claim 1, wherein:

said search range is centered according to said time estimate.

4. The method of claim 1, wherein:

said search range has a length more than a length of said expected data bit chunk and less than a length of a global positioning system (GPS) frame.

5. The method of claim 1, further comprising:

designating a time-of-entry within global positioning system (GPS) subframes one though three; and

wherein;

receiving said GNSS signal includes using said time estimate for entering an operation mode from said standby mode according to said time-of-entry.

6. The method of claim 1, wherein:

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

7. A method for determining global navigation satellite system (GNSS) clock time, comprising:

storing expected GNSS data bits for a GNSS signal source;

maintaining a clock time estimate while in a standby mode;

receiving a GNSS signal from said GNSS signal source;

detecting a chunk of current GNSS data bits from said GNSS signal;

using said time estimate for selecting a search range of said expected data bits;

detecting a successful match when one of a plurality of chunks of said expected data bits within said search range matches said chunk of current data bits; and

using said successful match for determining a GNSS clock time;

wherein;

detecting said successful match includes;

comparing bits of said current data bit chunk to corresponding bits of one of said expected data bit chunks;

noting signs of said bit comparisons;

counting inversions between consecutive said signs for determining an inversion count; and

determining said inversion count is not greater than a selected inversion limit.

8. The method of claim 7, wherein:

said inversion limit is at least two.

9. A method for determining global navigation satellite system (GNSS) clock time, comprising:

storing expected GNSS data bits for a GNSS signal source;

maintaining a clock time estimate while in a standby mode;

receiving a GNSS signal from said GNSS signal source;

detecting a chunk of current GNSS data bits from said GNSS signal;

using said time estimate for selecting a search range of said expected data bits;

detecting a successful match when one of a plurality of chunks of said expected data bits within said search range matches said chunk of current data bits; and

using said successful match for determining a GNSS clock time;

wherein;

receiving said GNSS signal includes;

entering an operation mode from said standby mode;

determining an update age since said expected data bits were updated; and

updating said expected data bits with said current data bits when said update age is greater than a selected update age threshold.

10. The method of claim 9, wherein:

updating said expected data bits includes updating said expected data bits for global positioning system (GPS) subframes one through three when said update age is greater than about one hour.

11. The method of claim 9, wherein:

updating said expected data bits includes updating said expected data bits for several GPS frames when said update age is greater than about two hours.

12. A global navigation satellite positioning system (GNSS) receiver for determining a global navigation satellite system (GNSS) clock time, comprising:

a chapter memory for storing expected GNSS data bits for a GNSS signal source;

a clock for maintaining a clock time estimate while the GNSS receiver is in a standby mode;

a signal processor for receiving a GNSS signal from said GNSS signal source; and

detecting a chunk of current GNSS data bits from said GNSS signal;

a GNSS time detector for using said time estimate for selecting a search range of said expected data bits, detecting a successful match when one of a plurality of chunks of said expected data bits within said search range matches said chunk of current data bits, and using said successful match for determining a GNSS clock time, wherein;

the GNSS time detector includes a match limiter for verifying that said current data bit chunk matches no more than one of said expected data bit chunks for detecting said successful match.

13. The receiver of claim 12 wherein:

the GNSS time detector includes a time variant generator for using said time estimate for computing GNSS data bits that change with time and augmenting said stored expected data bits with said time-changing expected data bits for providing said chunks of said expected data bits.

14. The receiver of claim 12, wherein:

the GNSS time detector centers said search range according said time estimate.

15. The receiver of claim 12, wherein:

the GNSS time detector selects a length said search range of more than a length of said expected data bit chunk and less than a length of a GPS frame.

16. The receiver of claim 12, wherein:

a standby time regulator for designating a time-of-entry within global positioning system (GPS) subframes one though three and causing the receiver to enter an operation mode from a standby mode according to said time-of-entry; and

a data update regulator coupled to the standby mode regulator for updating said GPS subframes one through three in said operation mode.

17. The receiver of claim 12, wherein:

the GNSS receiver is a global positioning system (GPS) receiver for receiving a GPS signal from a GPS signal source.

18. A global navigation satellite positioning system (GNSS) receiver for determining a global navigation satellite system (GNSS) clock time, comprising:

a chapter memory for storing expected GNSS data bits for a GNSS signal source;

a clock for maintaining a clock time estimate while the GNSS receiver is in a standby mode;

a signal processor for receiving a GNSS signal from said GNSS signal source; and

detecting a chunk of current GNSS data bits from said GNSS signal;

a GNSS time detector for using said time estimate for selecting a search range of said expected data bits, detecting a successful match when one of a plurality of chunks of said expected data bits within said search range matches said chunk of current data bits, and using said successful match for determining a GNSS clock time, wherein;

the GNSS time detector includes a data bit comparator for comparing bits of said current data bit chunk to corresponding bits of one of said expected data bit chunks;

a sign comparator for noting signs of said bit comparisons;

a sign inversion counter for counting inversions between consecutive said signs for providing an inversion count; and

an inversion limit detector for determining said inversion count is not greater than a selected inversion limit for detecting said successful match.

19. The receiver of claim 18, wherein:

said inversion limit is two.

20. A global navigation satellite positioning system (GNSS) receiver for determining a global navigation satellite system (GNSS) clock time, comprising:

a chapter memory for storing expected GNSS data bits for a GNSS signal source;

a clock for maintaining a clock time estimate while the GNSS receiver is in a standby mode;

a signal processor for receiving a GNSS signal from said GNSS signal source; and

detecting a chunk of current GNSS data bits from said GNSS signal;

a GNSS time detector for using said time estimate for selecting a search range of said expected data bits, detecting a successful match when one of a plurality of chunks of said expected data bits within said search range matches said chunk of current data bits, and using said successful match for determining a GNSS clock time;

a standby mode regulator for causing the receiver to enter an operation mode from said standby mode and determining an update age since said expected data bits were updated; and

a data update regulator coupled to the standby mode regulator for updating said expected data bits in said chapter memory with said current data bits when said update age is greater than a selected update age threshold.

21. The receiver of claim 20, wherein:

the data update regulator updates said expected data bits for global positioning system (GPS) subframes one through three when said update age is greater than about one hour.

22. The receiver of claim 20, wherein:

the data update regulator updates said expected data bits for several global positioning system (GPS) frames when said update age is greater than about two hours.