Apparatus and methods for estimating an unknown frequency error of a tone signal

• US 8,576,743 B2
• Filed: 12/21/2011
• Issued: 11/05/2013
• Est. Priority Date: 12/28/2010
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sikri, Divaydeep, Rafique, Hassan, Altan, Cetin
• Primary Examiner(s): Rinehart, Mark
• Assistant Examiner(s): Cheng, Peter
• Application Number:
  US13/333,550
• Publication Number:
  US 20120327793A1
• Time in Patent Office: 685 Days
• Field of Search: 370/252, 370/254, 370/350, 370/484, 370/503, 370/516, 370/509, 375/260, 375/343, 375/346, 375/348, 375354-359
• US Class Current: 370/252
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 2027/0065 Frequency error detectors H04L2027/0067 takes precedence
• CPC Class Codes: H04L 2027/0091 Continuous signals
• CPC Class Codes: H04L 2027/0095 in a preamble or similar structure
• CPC Class Codes: H04L 27/22 Demodulator circuits; Receiver circuits

Abstract

Estimating an unknown frequency error of a tone signal may comprise sampling, within an error bandwidth, wireless signals including the tone signal that occupy the error bandwidth to generate signal samples, and repeatedly, for different frequency offsets: applying a frequency offset to the signal samples to produce offset values that represent the signals occupying an offset bandwidth equal to the error bandwidth offset by an offset frequency; estimating, within a frequency estimation range less than the error bandwidth, a tone frequency error using the offset values; and measuring a signal-to-noise ratio of the tone signal using the signal samples and the estimated tone frequency error. Other aspects, embodiments, and features are also claimed and discussed.

Claims

1. A method of estimating an unknown frequency error of a tone signal, the method comprising:

sampling, within an error bandwidth, wireless signals including the tone signal that occupy the error bandwidth to generate signal samples;

applying a frequency offset to the signal samples to produce offset values that represent the signals occupying an offset bandwidth equal to the error bandwidth offset by an offset frequency, wherein applying the frequency offset to produce the offset values comprises;

auto-correlating the signal samples to produce correlation values; and

rotating the phase of each correlation value by a phase representing the frequency offset;

estimating, within a frequency estimation range less than the error bandwidth, a tone frequency error using the offset values;

measuring a signal-to-noise ratio of the tone signal using the signal samples and the estimated tone frequency error;

upon determining that the measured signal-to-noise ratio does not satisfy a threshold, repeating the applying, estimating, and measuring for different frequency offsets; and

upon determining that the measured signal-to-noise ratio satisfies the threshold, determining, that the unknown frequency error of the tone signal is equal to the particular estimated tone frequency error.

2. The method of claim 1, further comprising adjusting operation of a local oscillator in accordance with the determined unknown frequency error of the tone signal.

3. The method of claim 1, wherein the different frequency offsets are spaced apart by approximately the frequency estimation range.

4. The method of claim 1, wherein the different frequency offsets have associated frequency ranges centered at the offset bandwidths and associated widths equal to the frequency estimation range that together substantially cover the error bandwidth.

5. The method of claim 1, wherein the tone frequency error is estimated by summing the offset values to produce a complex sum, calculating the phase of the complex sum and de-rotating the phase of the complex sum by the phase representing the frequency offset to produce a phase representing the estimated tone frequency error.

6. The method of claim 5, wherein the summing comprises summing only odd-numbered offset values to produce the complex sum.

7. The method of claim 6, wherein the summing comprises:

summing real and imaginary values of the largest positive odd-numbered offset value among the odd-numbered offset values; and

summing only the real values for the remaining odd-numbered offset values among the odd-numbered offset values.

8. The method of claim 6, wherein the summing comprises:

multiplying the real parts of all positive odd-numbered offset values among the odd-numbered offset values by two, except for the largest positive odd-numbered offset value, to produce doubled values;

adding the doubled values together to produce a smart sum; and

adding the largest positive odd-numbered offset value to the smart sum to produce the complex sum.

9. The method of claim 6, wherein the odd-numbered offset values comprise less than seven offset values.

10. The method of claim 9, wherein the odd-numbered offset values comprise only offset values numbered 1, 3, and 5.

11. The method of claim 1, wherein measuring the signal-to-noise ratio of the tone signal comprises:

measuring the total power of the signal samples;

measuring a noise power of the signal samples; and

subtracting the measured noise power from the measured total power to obtain a signal power of the tone signal.

12. The method of claim 11, wherein measuring the noise power of the signal samples comprises:

generating sine wave samples representing a regenerated tone using the signal samples and a phase representing the estimated tone frequency error;

subtracting the sine wave samples from the signal samples to produce noise samples; and

measuring the power of the noise samples.

13. The method of claim 12, wherein generating the sine wave samples comprises:

rotating the phase of the signal samples by the phase representing the estimated tone frequency error to produce rotated signal samples;

computing and summing the powers of the rotated signal samples to produce a power sum; and

generating sine wave samples based on a specified tone frequency and the power sum.

14. The method of claim 1, further comprising:

detecting the tone signal by dividing the signal samples into blocks of three samples and coherently summing the blocks of three samples to produce plural coherent sums;

correlating the plural coherent sums; and

performing tone detection based on the plural coherent sums.

15. An apparatus for estimating an unknown frequency error of a tone signal, the apparatus comprising:

a sampler for sampling, within an error bandwidth, wireless signals including the tone signal that occupy the error bandwidth to generate signal samples; and

signal processing circuitry configured to;

apply a frequency offset to the signal samples to produce offset values that represent the signals occupying an offset bandwidth equal to the error bandwidth offset by an offset frequency, wherein applying the frequency offset to produce the offset values comprises the signal processing circuitry being configured to;

auto-correlate the signal samples to produce correlation values; and

rotate the phase of each correlation value by a phase representing the frequency offset;

estimate, within a frequency estimation range less than the error bandwidth, a tone frequency error using the offset values;

measure a signal-to-noise ratio of the tone signal using the signal samples and the estimated tone frequency error;

repeat the applying, estimating, and measuring for different frequency offsets upon determining that the measured signal-to-noise ratio does not satisfy a threshold; and

determine that the unknown frequency error of the tone signal is equal to the particular estimated tone frequency error upon determining that the measured signal-to-noise ratio satisfies the threshold.

16. The apparatus of claim 15, further comprising an adjustment module configured to adjust operation of a local oscillator in accordance with the determined unknown frequency error of the tone signal.

17. The apparatus of claim 15, wherein the different frequency offsets are spaced apart by approximately the frequency estimation range.

18. The apparatus of claim 15, wherein the different frequency offsets have associated frequency ranges centered at the offset bandwidths and associated widths equal to the frequency estimation range that together substantially cover the error bandwidth.

19. The apparatus of claim 15, wherein the tone frequency error is estimated by summing the offset values to produce a complex sum, calculating the phase of the complex sum and de-rotating the phase of the complex sum by the phase representing the frequency offset to produce a phase representing the estimated tone frequency error.

20. The apparatus of claim 19, wherein the summing comprises summing only odd-numbered offset values to produce the complex sum.

21. The apparatus of claim 20, wherein the summing comprises:

summing real and imaginary values of the largest positive odd-numbered offset value among the odd-numbered offset values; and

summing only the real values for the remaining odd-numbered offset values among the odd-numbered offset values.

22. The apparatus of claim 21, wherein the summing comprises:

multiplying the real parts of all positive odd-numbered offset values among the odd-numbered offset values by two, except for the largest positive odd-numbered offset value, to produce doubled values;

adding the doubled values together to produce a smart sum; and

adding the largest positive odd-numbered offset value to the smart sum to produce the complex sum.

23. The apparatus of claim 21, wherein the odd-numbered offset values comprise less than seven offset values.

24. The apparatus of claim 21, wherein the odd-numbered offset values comprise only offset values numbered 1, 3, and 5.

25. The apparatus of claim 15, wherein measuring the signal-to-noise ratio of the tone signal comprises:

measuring the total power of the signal samples;

measuring a noise power of the signal samples; and

subtracting the measured noise power from the measured total power to obtain a signal power of the tone.

26. The apparatus of claim 25, wherein measuring the noise power of the signal samples comprises:

generating sine wave samples representing a regenerated tone using the signal samples and a phase representing the estimated tone frequency error;

subtracting the sine wave samples from the signal samples to produce noise samples; and

measuring the power of the noise samples.

27. The apparatus of claim 26, wherein generating the sine wave samples comprises:

rotating the phase of the signal samples by the phase representing the estimated tone frequency error to produce rotated signal samples;

computing and summing the powers of the rotated signal samples to produce a power sum; and

generating the sine wave samples based on a specified tone frequency and the power sum.

28. The apparatus of claim 15, wherein the signal processing circuitry is further configured to:

detect the tone signal by dividing the signal samples into blocks of three samples and coherently summing the blocks of three samples to produce plural coherent sums;

correlate the plural coherent sums; and

perform tone detection based on the plural coherent sums.

29. The apparatus of claim 15, further comprising:

a receiver unit for processing radiated signals including a carrier signal having an unknown frequency error and noise signals, the carrier signal being frequency-modulated by a tone signal, and for providing baseband signals including the tone signal and baseband noise signals to the signal processing circuitry.

30. An apparatus for estimating an unknown frequency error of a tone signal, the apparatus comprising:

means for sampling, within an error bandwidth, wireless signals including the tone signal that occupy the error bandwidth to generate signal samples;

means for applying a frequency offset to the signal samples to produce offset values that represent the signals occupying an offset bandwidth equal to the error bandwidth offset by an offset frequency, wherein the means for applying the frequency offset to produce the offset values comprises;

means for auto- correlating the signal samples to produce correlation values; and

means for rotating the phase of each correlation value by a phase representing the frequency offset;

means for estimating, within a frequency estimation range less than the error bandwidth, a tone frequency error using the offset values;

means for measuring a signal-to-noise ratio of the tone signal using the signal samples and the estimated tone frequency error;

means for repeating the applying, estimating, and measuring for different frequency offsets upon determining that the measured signal-to-noise ratio does not satisfy a threshold; and

means for determining that the unknown frequency error of the tone signal is equal to the particular estimated tone frequency error upon determining that the measured signal-to-noise ratio satisfies the threshold.

31. The apparatus of claim 30, further comprising means for adjusting operation of a local oscillator in accordance with the determined unknown frequency error of the tone signal.

32. The apparatus of claim 30, wherein the different frequency offsets are spaced apart by approximately the frequency estimation range.

33. The apparatus of claim 30, wherein the different frequency offsets have associated frequency ranges centered at the offset bandwidths and associated widths equal to the frequency estimation range that together substantially cover the error bandwidth.

34. The apparatus of claim 30, wherein the tone frequency error is estimated by means for summing the offset values to produce a complex sum, means for calculating the phase of the complex sum and means for de-rotating the phase of the complex sum by the phase representing the frequency offset to produce a phase representing the estimated tone frequency error.

35. The apparatus of claim 34, wherein the means for summing comprises means for summing only odd-numbered offset values to produce the complex sum.

36. The apparatus of claim 35, wherein the means for summing comprises:

means for summing real and imaginary values of the largest positive odd-numbered offset value among the odd-numbered offset values; and

means for summing only the real values for the remaining odd-numbered offset values among the odd-numbered offset values.

37. The apparatus of claim 35, wherein the means for summing comprises:

means for multiplying the real parts of all positive odd-numbered offset values among the odd-numbered offset values by two, except for the largest positive odd-numbered offset value, to produce doubled values;

means for adding the doubled values together to produce a smart sum; and

means for adding the largest positive odd-numbered offset value to the smart sum to produce the complex sum.

38. The apparatus of claim 35, wherein the odd-numbered offset values comprise less than seven offset values.

39. The apparatus of claim 38, wherein the odd-numbered offset values comprise only offset values numbered 1, 3, and 5.

40. The apparatus of claim 30, wherein means for measuring the signal-to-noise ratio of the tone signal comprises:

means for measuring the total power of the signal samples;

means for measuring a noise power of the signal samples; and

means for subtracting the measured noise power from the measured total power to obtain a signal power of the tone.

41. The apparatus of claim 40, wherein means for measuring the noise power of the signal samples comprises:

means for generating sine wave samples representing a regenerated tone using the signal samples and a phase representing the estimated tone frequency error;

means for subtracting the sine wave samples from the signal samples to produce noise samples; and

means for measuring the power of the noise samples.

42. The apparatus of claim 41, wherein means for generating the sine wave samples comprises:

means for rotating the phase of the signal samples by the phase representing the estimated tone frequency error to produce rotated signal samples;

means for computing and summing the powers of the rotated signal samples to produce a power sum; and

means for generating sine wave samples based on a specified tone frequency and the power sum.

43. The apparatus of claim 30, further comprising:

means for detecting the tone signal by dividing the signal samples into blocks of three samples and coherently summing the blocks of three samples to produce plural coherent sums;

means for correlating the plural coherent sums; and

means for performing tone detection based on the plural coherent sums.

44. A computer-readable storage device comprising code, which, when executed by a processor, cause the processor to perform operations for estimating an unknown frequency error of a tone signal, the computer-readable storage device comprising:

code for sampling, within an error bandwidth, wireless signals including the tone signal that occupy the error bandwidth to generate signal samples;

code for applying a frequency offset to the signal samples to produce offset values that represent the signals occupying an offset bandwidth equal to the error bandwidth offset by an offset frequency, wherein the code for applying the frequency offset to produce the offset values comprises;

code for auto-correlating the signal samples to produce correlation values; and

code for rotating the phase of each correlation value by a phase representing the frequency offset;

code for estimating, within a frequency estimation range less than the error bandwidth, a tone frequency error using the offset values;

code for measuring a signal-to-noise ratio of the tone signal using the signal samples and the estimated tone frequency error;

code for repeating the applying, estimating, and measuring for different frequency offsets upon determining that the measured signal-to-noise ratio does not satisfy a threshold; and

code for determining that the unknown frequency error of the tone signal is equal to the particular estimated tone frequency error upon determining that the measured signal-to-noise ratio satisfies the threshold.

45. The computer-readable storage device of claim 44, further comprising code for adjusting operation of a local oscillator in accordance with the determined unknown frequency error of the tone signal.

46. The computer-readable storage device of claim 44, wherein the different frequency offsets are spaced apart by approximately the frequency estimation range.

47. The computer-readable storage device of claim 44, wherein the different frequency offsets have associated frequency ranges centered at the offset bandwidths and associated widths equal to the frequency estimation range that together substantially cover the error bandwidth.

48. The computer-readable storage device of claim 44, wherein the tone frequency error is estimated by code for summing the offset values to produce a complex sum, code for calculating the phase of the complex sum and code for de-rotating the phase of the complex sum by the phase representing the frequency offset to produce a phase representing the estimated tone frequency error.

49. The computer-readable storage device of claim 48, wherein the code for summing comprises code for summing only odd-numbered offset values to produce the complex sum.

50. The computer-readable storage device of claim 49, wherein the code for summing comprises:

code for summing real and imaginary values of the largest positive odd-numbered offset value among the odd-numbered offset values; and

code for summing only the real values for the remaining odd-numbered offset values among the odd-numbered offset values.

51. The computer-readable storage device of claim 49, wherein the code for summing comprises:

code for multiplying the real parts of all positive odd-numbered offset values among the odd-numbered offset values by two, except for the largest positive odd-numbered offset value, to produce doubled values;

code for adding the doubled values together to produce a smart sum; and

code for adding the largest positive odd-numbered offset value to the smart sum to produce the complex sum.

52. The computer-readable storage device of claim 49, wherein the odd-numbered offset values comprise less than seven offset values.

53. The computer-readable storage device of claim 52, wherein the odd-numbered offset values comprise only offset values numbered 1, 3, and 5.

54. The computer-readable storage device of claim 44, wherein code for measuring the signal-to-noise ratio of the tone signal comprises:

code for measuring the total power of the signal samples;

code for measuring a noise power of the signal samples; and

code for subtracting the measured noise power from the measured total power to obtain a signal power of the tone.

55. The computer-readable storage device of claim 54, wherein code for measuring the noise power of the signal samples comprises:

code for generating sine wave samples representing a regenerated tone using the signal samples and a phase representing the estimated tone frequency error;

code for subtracting the sine wave samples from the signal samples to produce noise samples; and

code for measuring the power of the noise samples.

56. The computer-readable storage device of claim 55, wherein code for generating the sine wave samples comprises:

code for rotating the phase of the signal samples by the phase representing the estimated tone frequency error to produce rotated signal samples;

code for computing and summing the powers of the rotated signal samples to produce a power sum; and

code for generating the sine wave samples based on a specified tone frequency and the power sum.

57. The computer-readable storage device of claim 44, further comprising:

code for detecting the tone signal by dividing the signal samples into blocks of three samples and coherently summing the blocks of three samples to produce plural coherent sums;

code for correlating the plural coherent sums; and

code for performing tone detection based on the plural coherent sums.