Parameter estimator configured to distinguish between peaks and sidelobes of correlation function

• US 20030081662A1
• Filed: 01/29/2002
• Published: 05/01/2003
• Est. Priority Date: 11/01/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Amerga, Messay, Stein, Jeremy M., Fernandez-Corbaton, Ivan, Rick, Roland R.
• Granted Patent: US 7,308,022 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/0221 Receivers
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers

Abstract

A parameter estimator for estimating one or more parameter(s) from a signal is described. A correlation function is derived from the signal, and the correlation function analyzed to determine if one or more first peak(s) are present, and, if so, distinguishable from the sidelobe(s) of a second peak. If the one or more first peak(s) are present and distinguishable from the sidelobe(s) of the second peak, the one or more parameter(s) are estimated from the one or more first peak(s). If the one or more first peak(s) are not present, or, if present, are not distinguishable from the sidelobe(s) of the second peak, the one or more parameter(s) are estimated from the second peak. The parameter estimator may be employed in a subscriber station to estimate a parameter such as the time of arrival of one or more base station or sector pilot signals in a wireless communication system. This information may be utilized in an overall advanced forward link trilateration (AFLT) process for estimating the location of the subscriber station.

Claims

1. A parameter estimator comprising:

correlation logic for determining a correlation function representing the correlation between a signal and one or more shifted versions of an identification code; and

analysis logic for analyzing the correlation function, determining whether one or more first peak(s) are present, and, if so, whether they are distinguishable from one or more sidelobe(s) of a second peak, and, if one or more first peak(s) are present and are distinguishable from the sidelobe(s) of the second peak, estimating one or more parameter(s) relating to the signal responsive to the one or more first peak(s), and, if one or more first peak(s) are not present, or, if present, are not distinguishable from the sidelobe(s) of the second peak, estimating the one or more parameter(s) responsive to the second peak.

2. The parameter estimator of claim 1 wherein the second peak is the strongest peak.

3. The parameter estimator of claim 2 wherein the one or more first peaks(s), if any, are earlier in time than the strongest peak.

4. The parameter estimator of claim 1 wherein the identification code is a PN code.

5. The parameter estimator of claim 1 configured to distinguish a first peak from the sidelobe(s) of the second peak using a priori information regarding the correlation function.

6. The parameter estimator of claim 5 wherein the a priori information relates to the shape, amplitude, phase, or any combination thereof, of a component pulse of the correlation function representing an independent arrival.

7. The parameter estimator of claim 1 configured to distinguish a first peak from sidelobe(s) of the second peak using a threshold.

8. The parameter estimator of claim 7 wherein the threshold is a variable dependent on one or more of the energy of the first peak, the energy of the second peak, the shape, amplitude, phase, or any combination thereof, of a component pulse of the correlation function representing an independent arrival at the time of the candidate peak, the time difference between the first and second peaks, and the integration time.

9. The parameter estimator of claim 7 wherein the threshold is dependent on a noise floor.

10. The parameter estimator of claim 9 wherein the noise floor is dependent on integration time.

11. The parameter estimator of claim 9 wherein the noise floor is set to limit the false alarm probability.

12. The parameter estimator of claim 9 wherein the threshold is also dependent on the difference between the energy of the second peak and the energy of the first peak.

13. The parameter estimator of claim 9 wherein the threshold is also dependent on the ratio of the energy of the first peak to the energy of the second peak.

14. The parameter estimator of claim 9 where the threshold is derived from the maximum of the noise floor and the difference between the energy of the second peak and a predefined range.

15. The parameter estimator of claim 9 wherein the threshold is derived from the maximum of the noise floor and a predetermined fraction of the energy of the second peak.

16. The parameter estimator of claim 10 wherein the noise floor is also dependent on the difference between the energy of the second peak and the energy of the first peak.

17. The parameter estimator of claim 10 wherein the noise floor is also dependent on the ratio of the energy of the first peak to the energy of the second peak.

18. The parameter estimator of claim 1 configured to distinguish a first peak from sidelobe(s) of the second peak using multiple thresholds.

19. The parameter estimator of claim 18 wherein a first threshold is applicable if the energy of the first peak is within a first predefined range of the energy of the second peak, and a second threshold is applicable if the energy of the first peak is within a second predefined range of the energy of the second peak.

20. The parameter estimator of claim 19 wherein the second threshold is stricter than the first threshold, and the second predefined range is more relaxed in relation to the first predefined range.

21. The parameter estimator of claim 18 wherein a first threshold is applicable if the ratio of the energy of the first peak to the energy of the second peak equals or exceeds a first fraction, and a second threshold is applicable if the ratio of the energy of the first peak to the energy of the second peak equals or exceeds a second fraction.

22. The parameter estimator of claim 21 wherein the second threshold is stricter than the first threshold, and the second fraction is smaller than the first.

51. The parameter estimator of any of claims 1 or 23 in a subscriber station.

52. The subscriber station of claim 51 which is a mobile station.

23. A parameter estimator comprising:

correlation means for determining a correlation function representing the correlation between a signal and one or more shifted versions of an identification code; and

analysis means for analyzing the correlation function, determining whether one or more first peak(s) are present, and, if so, whether they are distinguishable from one or more sidelobe(s) of a second peak, and, if one or more first peak(s) are present and are distinguishable from the sidelobe(s) of the second peak, estimating one or more parameter(s) relating to the signal responsive to the one or more first peak(s), and, if one or more first peak(s) are not present, or, if present, are not distinguishable from the sidelobe(s) of the second peak, estimating the one or more parameter(s) responsive to the second peak.

24. A method of estimating one or more parameter(s) of a signal comprising:

determining a correlation function representing the correlation between a signal and one or more shifted versions of an identification code;

analyzing the correlation function to determine whether one or more first peak(s) are present, and, if so, whether they are distinguishable from one or more sidelobe(s) of a second peak;

if one or more first peak(s) are present and are distinguishable from the sidelobe(s) of the second peak, estimating one or more parameter(s) relating to the signal responsive to the one or more first peak(s); and

if one or more first peak(s) are not present, or, if present, are not distinguishable from the sidelobe(s) of the second peak, estimating the one or more parameter(s) responsive to the second peak.

25. The method of claim 24 wherein the signal is a pilot signal.

26. The method of claim 24 wherein the identification code is a PN code.

27. The method of claim 24 wherein the second peak is the strongest peak.

28. The method of claim 27 wherein the one or more first peak(s) are earlier in time than the strongest peak.

29. The method of claim 24 wherein the one or more parameter(s) relating to the signal include a time of arrival (TOA) parameter.

30. The method of claim 29 wherein the one or more parameter(s) for the signal include a root mean squared error (RMSE) for the TOA parameter.

31. The method of claim 24 wherein the one or more parameter(s) for the signal include an E_c/I₀ parameter.

32. The method of claim 24 further comprising determining if the one or more first peak(s) are distinguishable from the second peak using a priori information regarding the correlation function.

33. The method of claim 32 wherein the a priori information is knowledge regarding the shape, amplitude, phase, or any combination thereof, of a component pulse of the correlation function representing an independent arrival.

34. The method of claim 24 further comprising determining if the one or more first peak(s) are distinguishable from the second peak using a threshold.

35. The method of claim 34 wherein the threshold is a variable dependent on one or more of the energy of the second peak, the energy of a first peak, the shape, amplitude, phase, or any combination thereof, of the component pulse of the correlation function corresponding to the second peak at the time of the first peak, the time difference between the first and second peaks, and the integration time used to derive the correlation function.

36. The method of claim 34 wherein the threshold is a variable dependent on a noise floor.

37. The method of claim 36 wherein the noise floor is dependent on the integration time.

38. The method of claim 36 wherein the noise floor is set to limit the false alarm probability.

39. The method of claim 36 wherein the threshold is also dependent on the difference between the energy of the second peak and the energy of the first peak.

40. The method of claim 36 wherein the threshold is also dependent on the ratio of the energy of the first peak to the energy of the second peak.

41. The method of claim 36 wherein the threshold is derived from a maximum of noise floor and a predetermined fraction of the energy of the second peak.

42. The method of claim 37 wherein the noise floor is also dependent on the difference between the energy of the second peak and the energy of the first peak.

43. The method of claim 37 wherein the noise floor is also dependent on the ratio of the energy of the first peak to the energy of the second peak.

44. The method of claim 24 further comprising distinguishing one or more peak(s) from sidelobe(s) of the second peak using multiple thresholds.

45. The method of claim 44 wherein a first threshold is applicable if the energy of a first peak is within a first predefined range of the energy of the second peak, and a second threshold is applicable if the energy of a first peak is within a second predefined range of the energy of the second peak.

46. The method of claim 45 wherein the second threshold is stricter than the first threshold, and the second predefined range is relaxed in relation to the first predefined range.

47. The method of claim 44 wherein a first threshold is applicable if the ratio of the energy of a first peak to the energy of the second peak equals or exceeds a first fraction, and a second threshold is applicable if the ratio of the energy of a first peak to the energy of the second peak equals or exceeds a second fraction.

48. The method of claim 47 wherein the second threshold is stricter than the first threshold, and the second fraction is smaller than the first.

49. The method of claim 34 wherein the threshold is dependent on the difference between the time of a first peak and the time of the second peak.

53. The methods of any of claims 24 or 50 tangibly embodied as a series of instructions stored in a processor readable medium.

54. The methods of any of claims 24 or 50 tangibly embodied as a series of instructions stored on a server.

55. The methods of any of claims 24 or 50 tangibly embodied as logic.

50. A method of estimating one or more parameter(s) of a signal comprising:

a step for determining a correlation function representing the correlation between a signal and one or more shifted versions of an identification code;

a step for analyzing the correlation function to determine whether one or more first peak(s) are present, and, if so, whether they are distinguishable from one or more sidelobe(s) of a second peak;

a step for estimating one or more parameter(s) relating to the signal responsive to the one or more first peak(s) if one or more first peak(s) are present and are distinguishable from the sidelobe(s) of the second peak; and

a step for estimating the one or more parameter(s) responsive to the second peak if one or more first peak(s) are not present, or, if present, are not distinguishable from the sidelobe(s) of the second peak.