Calculating navigation system time in a satellite navigation system

• US 8,378,889 B2
• Filed: 03/31/2009
• Issued: 02/19/2013
• Est. Priority Date: 03/31/2009
• Status: Active Grant

• Current Assignee: Maishi Electronic (Shanghai) Limited
• Original Assignee: O2 Micro Incorporated
• Inventors: Yu, Xiaoguang, Du, Sterling, Huang, Haiquan
• Primary Examiner(s): Keith, Jack W
• Assistant Examiner(s): McGue, Frank J
• Application Number:
  US12/415,048
• Publication Number:
  US 20100073230A1
• Time in Patent Office: 1,421 Days
• Field of Search: 342/357.62
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/235 Calibration of receiver components

Abstract

A satellite navigation system receiver that includes a counter and a controlling unit is described. The counter may be driven by a reference clock signal having a reference clock frequency. The controlling unit can calculate a correction value indicative of a corrected reference clock frequency by comparing an increment of the counter values during a time period with an increment of the navigation system times during the time period. The controlling unit can generate a calculated navigation system time according to the correction value.

Claims

1. A satellite navigation system receiver comprising:

a counter driven by a reference clock signal having a reference clock frequency to provide counter values, wherein said counter is operable for counting from a first time point to a second time point to generate a first increment of said counter values and for counting from a third time point to a fourth time point to generate a second increment of said counter values, wherein in a first interval from said first time point to said second time point said satellite navigation system receiver remains turned on, wherein in a second interval from said third time point to said fourth time point said satellite navigation system receiver is on then turned off and turned on again; and

a controlling unit coupled to said counter and operable for calculating a correction value indicative of a corrected reference clock frequency by dividing said first increment of said counter values during a time period by an increment of navigation system time during said time period, wherein said controlling unit is also operable for generating a calculated navigation system time according to said correction value, and said second increment of said counter values, and a navigation message from a satellite.

2. The receiver of claim 1, wherein said controlling unit calculates said correction value by calculating an average refresh rate of said counter values over a particular period of said navigation system time.

3. The receiver of claim 2, wherein said controlling unit generates said calculated navigation system time according to said average refresh rate of said counter values.

4. The receiver of claim 1, wherein said receiver is operable for determining navigation bit boundaries according to said calculated navigation system time.

5. The receiver of claim 1, wherein said receiver is operable for determining visibility of satellites according to said calculated navigation system time.

6. The receiver of claim 1, further comprising a sampling clock coupled to said controlling unit and operable for digitizing a received satellite signal, wherein said reference clock signal is provided by said sampling clock.

7. The receiver of claim 1, further comprising:

a real time clock circuit coupled to said controlling unit and operable for providing a local time, wherein said controlling unit is also operable for determining that said counter values are in error if said counter values exceed a predetermined range when a predetermined time period expires according to said local time; and

a sampling clock coupled to said controlling unit and operable for digitizing a received satellite signal, wherein said real time clock circuit is driven by said sampling clock.

8. A method for positioning a satellite navigation system receiver, comprising:

obtaining navigation system time based on navigation message from a satellite;

generating a reference clock signal having a reference clock frequency;

driving a counter by said reference clock signal for providing counter values;

counting, by said counter, in a first interval from a first time point to a second time point to generate a first increment of said counter values, wherein from said first time point to said second time point said satellite navigation system receiver remains turned on;

counting, by said counter, in a second interval from a third time point to a fourth time point to generate a second increment of said counter values, wherein from said third time point to said fourth time point said satellite navigation system receiver is on then turned off and turned on again;

calculating a correction value indicative of a corrected reference clock frequency by dividing said first increment of said counter values during a time period by an increment of said navigation system time during said time period;

generating a calculated navigation system time according to said correction value and said second increment of said counter values; and

employing said calculated navigation system time during calculation of a current position result of said receiver.

9. The method of claim 8, further comprising:

determining navigation bit boundaries according to said calculated navigation system time.

10. The method of claim 8, further comprising:

determining visibility of satellites according to said calculated navigation system time.

11. The method of claim 8, further comprising:

calculating said correction value by calculating an average refresh rate of said counter values over a particular period of said navigation system time.

12. The method of claim 11, further comprising:

generating said calculated navigation system time according to said average refresh rate of said counter values.

13. The method of claim 8, further comprising:

digitizing a received satellite signal with a sampling clock; and

generating said reference clock signal by said sampling clock.

14. The method of claim 8, further comprising:

generating a local time by a real time clock circuit; and

determining that said counter values are in error if said counter values exceed a predetermined range when a predetermined time period expires according to said local time;

digitizing a received satellite signal with a sampling clock; and

driving said real time clock circuit by said sampling clock.

15. A satellite navigation system receiver, comprising:

a radio frequency (RF) front end operable for converting a frequency of a received satellite signal to a desired frequency;

a clock coupled to said RF front end and operable for generating a reference clock signal having a reference clock frequency for driving a counter to generate counter values, wherein said counter is operable for counting in a first interval from a first time point to a second time point to generate a first increment of said counter values and for counting in a second interval from a third time point to a fourth time point to generate a second increment of said counter values, wherein from said first time point to said second time point said satellite navigation system receiver remains turned on, wherein from said third time point to said fourth time point said satellite navigation system receiver is on then turned off and turned on again;

a baseband processing unit coupled to said RF front end and operable for acquiring and tracking satellite signals and for calculating position results of said receiver; and

a controlling unit coupled to said baseband processing unit and operable for calculating a correction value indicative of a corrected reference clock frequency by dividing an increment of said counter values during a time period by an increment of navigation system time during said time period, and also operable for generating a calculated navigation system time according to said correction value and based on a navigation message from a satellite;

wherein said baseband processing unit is operable for employing said calculated navigation system time during calculation of a current position result of said receiver.

16. The receiver of claim 15, wherein said controlling unit calculates said correction value according to the following equation:

17. The receiver of claim 16, wherein said controlling unit generates said calculated navigation system time according to the following equation:

18. The receiver of claim 15, wherein said baseband processing unit is operable for determining navigation bit boundaries according to said calculated navigation system time.

19. The receiver of claim 15, wherein said baseband processing unit is operable for determining visibility of satellites according to said calculated navigation system time.

20. The receiver of claim 15, wherein said received satellite signal is digitized by said clock.

21. The receiver of claim 15, further comprising a real time clock circuit coupled to said controlling unit and operable for providing a local time, wherein said controlling unit is also operable for determining that said counter values are in error if said counter values exceed a predetermined range when a predetermined time period expires according to said local time, wherein said received satellite signal is digitized by said clock, and wherein said real time clock circuit is driven by said clock.