METHOD AND SYSTEM FOR DETERMINING CARRIER FREQUENCY OFFSETS FOR POSITIONG SINGALS

• US 20030016169A1
• Filed: 07/18/2001
• Published: 01/23/2003
• Est. Priority Date: 07/18/2001
• Status: Active Grant

• Current Assignee: Fast Location.Net, LLC
• Original Assignee: Fast Location.Net, LLC
• Inventors: Jandrell, Louis H.
• Granted Patent: US 6,529,160 B2
• Time in Patent Office: Days
• US Class Current: 342/357.12
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/17 Emergency applications
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/254 relating to Doppler shift of satellite signals
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• 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 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/34 Power consumption
• CPC Class Codes: G01S 19/35 Constructional details or hardware or software details of the signal processing chain
• CPC Class Codes: G01S 2205/008 using a mobile telephone network
• CPC Class Codes: G01S 5/0018 Transmission from mobile station to base station
• CPC Class Codes: G01S 5/0063 of measured values, i.e. measurement on base station and position calculation on mobile

Abstract

A method for directly extracting carrier frequency offsets (CFOs) from positioning signals received at a ranging receiver is provided. The positioning signals comprise a plurality of samples. The method includes, for each of a previously determined number of decimated samples, accumulating a specified number of samples into the decimated sample. A determination is made regarding whether to apply rate correction to the decimated samples. A particular number of rate corrections are applied to each decimated sample to generate a set of results when rate correction is to be applied. Each set of results is stored. A determination is made regarding whether a minimum number of significant carriers exists in the sets of stored results. The CFOs are determined based on the significant carriers when the minimum number of significant carriers exists in the sets of stored results.

Claims

1. A method for directly extracting carrier frequency offsets (CFOs) from positioning signals received at a ranging receiver, the positioning signals comprising a plurality of samples, the method comprising:

for each of a previously determined number of decimated samples, accumulating a specified number of samples into the decimated sample;

determining whether to apply rate correction to the decimated samples;

applying a particular number of rate corrections to each decimated sample to generate a set of results when rate correction is to be applied;

storing each set of results;

determining whether a minimum number of significant carriers exists in the sets of stored results; and

determining the CFOs based on the significant carriers when the minimum number of significant carriers exists in the sets of stored results.

2. The method of claim 1, the previously determined number of decimated samples corresponding to a sampled duration of approximately one second.

3. The method of claim 1, the particular number of rate corrections selected based on a desired error range between rate corrections.

4. The method of claim 3, the particular number of rate corrections selected as a rate range divided by the desired error range between rate corrections.

5. The method of claim 1, the specified number of samples selected to yield a decimated sample with at least a 20 kHz bandwidth.

6. The method of claim 1, accumulating a specified number of samples into the decimated sample comprising squaring each sample before accumulation.

7. The method of claim 6, accumulating a specified number of samples into the decimated sample further comprising multiplying each squared sample by a filtering coefficient before accumulation.

8. The method of claim 1, applying a particular number of rate corrections to each decimated sample comprising complex multiplying each decimated sample by the rate corrections.

9. The method of claim 1, determining whether a minimum number of significant carriers exists in the sets of stored results comprising Fourier-transforming each set of stored results into a frequency domain, and searching a spectrum for each Fourier-transformed set of stored results for significant carriers.

10. The method of claim 1, significant carriers comprising carriers sufficiently above a noise-background threshold.

11. The method of claim 10, significant carriers comprising carriers at least 6 dB above the noise-background threshold.

12. The method of claim 1, the minimum number of significant carriers comprising four significant carriers.

13. The method of claim 1, further comprising, when the minimum number of significant carriers does not exist in the sets of stored results, accumulating the specified number of samples into additional decimated samples up to a maximum number of decimated samples until the minimum number of significant carriers exists in the sets of stored results.

14. The method of claim 13, the maximum number of decimated samples corresponding to a sampled duration between approximately 5 and 100 seconds.

15. The method of claim 13, further comprising setting a flag to indicate that the positioning signals received at the ranging receiver are too weak for CFO extraction when the maximum number of decimated samples is formed.

17. The system of claim 16, the previously determined number of decimated samples corresponding to a sampled duration of approximately one second.

18. The system of claim 16, the particular number of rate corrections selected based on a desired error range between rate corrections.

19. The system of claim 18, the particular number of rate corrections selected as a rate range divided by the desired error range between rate corrections.

20. The system of claim 16, the specified number of samples selected to yield a decimated sample with at least a 20 kHz bandwidth.

21. The system of claim 16, the logic operable to accumulate a specified number of samples into the decimated sample by squaring each sample before accumulation.

22. The system of claim 21, the logic further operable to accumulate a specified number of samples into the decimated sample by multiplying each squared sample by a filtering coefficient before accumulation.

23. The system of claim 16, the logic operable to apply a particular number of rate corrections to each decimated sample by complex multiplying each decimated sample by the rate corrections.

24. The system of claim 16, the logic operable to determine whether a minimum number of significant carriers exists in the sets of stored results by Fourier-transforming each set of stored results into a frequency domain, and searching a spectrum for each Fourier-transformed set of stored results for significant carriers.

25. The system of claim 16, significant carriers comprising carriers sufficiently above a noise-background threshold.

26. The system of claim 25, significant carriers comprising carriers at least 6 dB above the noise-background threshold.

27. The system of claim 16, the minimum number of significant carriers comprising four significant carriers.

28. The system of claim 16, the logic further operable, when the minimum number of significant carriers does not exist in the sets of stored results, to accumulate the specified number of samples into additional decimated samples up to a maximum number of decimated samples until the minimum number of significant carriers exists in the sets of stored results.

29. The system of claim 28, the maximum number of decimated samples corresponding to a sampled duration between approximately 5 and 100 seconds.

30. The system of claim 28, the logic further operable to set a flag to indicate that the positioning signals received at the ranging receiver are too weak for CFO extraction when the maximum number of decimated samples is formed.

16. A system for directly extracting carrier frequency offsets (CFOs) from positioning signals received at a ranging receiver, the positioning signals comprising a plurality of samples, the system comprising:

a computer-processable medium; and

logic stored on the computer-processable medium, the logic operable to, for each of a previously determined number of decimated samples, accumulate a specified number of samples into the decimated sample, to determine whether to apply rate correction to the decimated samples, to apply a particular number of rate corrections to each decimated sample to generate a set of results when rate correction is to be applied, to store each set of results, to determine whether a minimum number of significant carriers exists in the sets of stored results, and to determine the CFOs based on the significant carriers when the minimum number of significant carriers exists in the sets of stored results.

31. A system for directly extracting carrier frequency offsets (CFOs) from positioning signals received at a ranging receiver, the positioning signals comprising a plurality of samples, the system comprising:

means for accumulating, for each of a previously determined number of decimated samples, a specified number of samples into the decimated sample;

means for determining whether to apply rate correction to the decimated samples;

means for applying a particular number of rate corrections to each decimated sample to generate a set of results when rate correction is to be applied;

means for storing each set of results;

means for determining whether a minimum number of significant carriers exists in the sets of stored results; and

means for determining the CFOs based on the significant carriers when the minimum number of significant carriers exists in the sets of stored results.

32. The system of claim 31, the previously determined number of decimated samples corresponding to a sampled duration of approximately one second.

33. The system of claim 31, the particular number of rate corrections selected based on a desired error range between rate corrections.

34. The system of claim 33, the particular number of rate corrections selected as a rate range divided by the desired error range between rate corrections.

35. The system of claim 31, the specified number of samples selected to yield a decimated sample with at least a 20 kHz bandwidth.

36. The system of claim 31, the means for accumulating a specified number of samples into the decimated sample comprising means for squaring each sample before accumulation.

37. The system of claim 36, the means for accumulating a specified number of samples into the decimated sample further comprising means for multiplying each squared sample by a filtering coefficient before accumulation.

38. The system of claim 31, the means for applying a particular number of rate corrections to each decimated sample comprising means for complex multiplying each decimated sample by the rate corrections.

39. The system of claim 31, the means for determining whether a minimum number of significant carriers exists in the sets of stored results comprising means for Fourier-transforming each set of stored results into a frequency domain, and means for searching a spectrum for each Fourier-transformed set of stored results for significant carriers.

40. The system of claim 31, significant carriers comprising carriers sufficiently above a noise-background threshold.

41. The system of claim 40, significant carriers comprising carriers at least 6 dB above the noise-background threshold.

42. The system of claim 31, the minimum number of significant carriers comprising four significant carriers.

43. The system of claim 31, further comprising means for accumulating, when the minimum number of significant carriers does not exist in the sets of stored results, the specified number of samples into additional decimated samples up to a maximum number of decimated samples until the minimum number of significant carriers exists in the sets of stored results.

44. The system of claim 43, the maximum number of decimated samples corresponding to a sampled duration between approximately 5 and 100 seconds.

45. The system of claim 43, further comprising means for setting a flag to indicate that the positioning signals received at the ranging receiver are too weak for CFO extraction when the maximum number of decimated samples is formed.

46. A method for directly extracting carrier frequency offsets (CFOs) from positioning signals received at a ranging receiver, the positioning signals comprising a plurality of samples, the method comprising:

for each of a previously determined number of decimated samples, accumulating a specified number of samples into the decimated sample, the specified number of samples selected to yield a decimated sample with at least a 20 kHz bandwidth, the previously determined number of decimated samples corresponding to a sampled duration of approximately one second;

determining whether to apply rate correction to the decimated samples;

applying a particular number of rate corrections to each decimated sample to generate a set of results when rate correction is to be applied, the particular number of rate corrections selected based on a desired error range between rate corrections;

storing each set of results;

determining whether a minimum number of significant carriers exists in the sets of stored results by Fourier-transforming each set of stored results into a frequency domain and searching a spectrum for each Fourier-transformed set of stored results for significant carriers, the minimum number of significant carriers comprising four significant carriers, significant carriers comprising carriers at least 6 dB above a noise-background threshold;

determining the CFOs based on the significant carriers when the minimum number of significant carriers exists in the sets of stored results;

when the minimum number of significant carriers does not exist in the sets of stored results, accumulating the specified number of samples into additional decimated samples up to a maximum number of decimated samples until the minimum number of significant carriers exists in the sets of stored results, the maximum number of decimated samples corresponding to a sampled duration between approximately 5 and 100 seconds; and

setting a flag to indicate that the positioning signals received at the ranging receiver are too weak for CFO extraction when the maximum number of decimated samples is formed.