Method and apparatus for detecting control signals

• US 5,442,696 A
• Filed: 12/31/1991
• Issued: 08/15/1995
• Est. Priority Date: 12/31/1991
• Status: Expired due to Fees

• Current Assignee: AT&T IPM Corp. (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Lindberg, Craig R., Thomson, David J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Shehata, M.
• Application Number:
  US07/816,332
• Time in Patent Office: 1,323 Days
• Field of Search: 379/386, 379/282, 379/283, 370/110.3, 340/825.39, 340/825.73, 340/825.74, 340/825.76
• US Class Current: 379/386
• CPC Class Codes: H04L 27/30 wherein each code element is represented by a combination of frequencies
• CPC Class Codes: H04Q 1/4575 which are transmitted in digital form

Abstract

The present invention provides a method and apparatus for detecting control signal information for an element of a communication system. The control signal information is included in one or more segments of a signal communicated over a communication system channel. The invention provides for the application of a plurality of tapers to a segment of a communicated signal; the transformation of a tapered segment; the determination of a similarity score based on a transform of a tapered segment and a model of a control signal; the identification of control signal information based on a similarity score; and the creation of an indicator signal representative of the identified control signal information to the communication system element. The control signal information may comprise a dual-tone multi-frequency signal. The tapers may comprise a discrete prolate spheroidal sequence. A similarity score may be determined based on a ratio of energy distributions. The numerator of the ratio may comprise an energy distribution based on a control signal model, and the denominator of the ratio may comprise an energy distribution based on a difference between a transformed tapered segment and the control signal model.

Claims

1. A method of discriminating control signal information from non-control signal information, the control signal information for use by a communication system element, the control signal information and the non-control signal information included in one or more segments of a signal communicated over a communication system channel, the control signal information comprising signal components at one or more predetermined control signal frequencies, the non-control signal information comprising signal components at one or more information signal frequencies, the method comprising the steps of:

applying a plurality of tapers to a segment of a communicated signal;

performing a transform of a tapered segment;

determining a similarity score based on a transform of a tapered segment and a model of a control signal, the similarity score reflecting a comparison of signal components of the communicated signal at the predetermined control signal frequencies with signal components of the communicated signal at other information signal frequencies;

classifying one or more segments of the communicated signal as representing either control signal information or non-control signal information based on a similarity score; and

providing an indicator signal representative of control signal information to the communication system element when the communicated signal has been classified as representing control signal information.

2. The method of claim 1 further comprising the step of receiving a communicated signal and producing one or more segments thereof.

3. The method of claim 2 wherein the step of producing one or more segments comprises the step of producing overlapping segments.

4. The method of claim 1 wherein the control signal information comprises DTMF signal information.

5. The method of claim 1 wherein the control signal information comprises call progress signal information.

6. The method of claim 1 wherein the control signal information comprises supervisory audio tone signal information.

7. The method of claim 1 wherein the step of applying a plurality of tapers comprises the step of applying a taper which comprises a discrete prolate spheroidal sequence.

8. The method of claim 1 wherein the step of applying a plurality of tapers comprises the step of forming a product of a taper value and an input signal segment value.

9. The method of claim 1 wherein the step of applying a plurality of tapers comprises the step of applying a taper value to a possible communicated signal value.

10. The method of claim 9 further comprising the step of storing in memory information which comprises a taper value applied to a possible communicated signal value.

11. The method of claim 1 wherein the step of performing a transform comprises the step of performing a Fourier transform.

12. The method of claim 1 wherein the model of a control signal comprises a sinusoidal model.

13. The method of claim 12 wherein the sinusoidal model comprises an amplitude modulated sinusoidal model.

14. The method of claim 12 wherein the sinusoidal model comprises a frequency modulated sinusoidal model.

15. The method of claim 12 wherein the sinusoidal model comprises a first sinusoidal model and a second sinusoidal model.

16. The method of claim 15 wherein the first sinusoidal model comprises a first control signal information frequency and the second sinusoidal model comprises a second control signal information frequency.

17. The method of claim 16 wherein the step of determining a similarity score comprises the step of estimating amplitude information based on a transformed tapered segment and wherein each of the first and second sinusoidal models comprises estimated amplitude information.

18. The method of claim 17 wherein the step of determining a similarity score comprises the step of forming a ratio, the numerator of the ratio comprising an energy distribution based on the first and second sinusoidal models, and the denominator of the ratio comprising an energy distribution based on a difference between a transformed tapered segment and a sum of the first and second sinusoidal models.

19. The method of claim 1 wherein the model of a control signal comprises expected control signal information distortion.

20. The method of claim 1 wherein the step of determining a similarity score comprises the step of estimating amplitude information based on a transformed tapered segment and wherein a model of a control signal comprises estimated amplitude information.

21. The method of claim 1 wherein the step of determining a similarity score comprises the step of determining a measure of similarity between energy distributions.

22. The method of claim 21 wherein the step of determining a measure of similarity between energy distributions comprises the step of forming a ratio, the numerator of the ratio comprising an energy distribution based on a control signal model, and the denominator of the ratio comprising an energy distribution based on a difference between a transformed tapered segment and the control signal model.

23. The method of claim 1 wherein the step of determining a similarity score comprises the step of:

determining an estimate of frequency deviation between an expected control signal information frequency and a frequency component of a transformed tapered segment; and

determining whether the estimate of frequency deviation exceeds a threshold.

24. The method of claim 1 wherein the classifying step comprises the step of determining whether a similarity score exceeds a threshold.

25. The method of claim 1 wherein the classifying step comprises the step of determining whether a frequency component of a transformed tapered segment deviates from an expected control signal information frequency by an amount which exceeds a threshold.

26. The method of claim 25 wherein the step of determining whether a frequency component of a transformed tapered segment deviates from an expected control signal information frequency comprises the steps of:

determining amplitude estimates of the transformed tapered segment at a plurality of frequencies including the expected control signal information frequency; and

determining whether the amplitude at the expected control signal information frequency exceeds the other determined amplitude estimates.

27. The method of claim 1 wherein the classifying step comprises the steps of:

determining an amplitude variation parameter based on estimates of the amplitude of a frequency component present in each of a plurality of segments; and

determining when the amplitude variation parameter exceeds a threshold.

28. The method of claim 1 wherein the classifying step comprises the steps of:

determining a phase variation parameter based on estimates of the amplitude of a frequency component present in each of a plurality of segments; and

determining when the phase variation parameter exceeds a threshold.

29. The method of claim 1 wherein the classifying step comprises the steps of:

determining an amplitude and phase variation parameter based on estimates of the amplitude and phase of a frequency component present in each of a plurality of segments; and

determining when the amplitude and phase variation parameter exceeds threshold.

30. The method of claim 1 wherein the classifying step comprises the steps of:

determining a ratio of amplitudes of a transformed tapered segment, the numerator of the ratio comprising an amplitude evaluated at one frequency of expected control signal information and the denominator of the ratio comprising an amplitude evaluated at another frequency of the expected control signal information; and

determining whether the ratio is within a predetermined range of values.

31. An apparatus for discriminating control signal information from non-control signal information, the control signal information for use by a communication system element, the control signal information and the non-control signal information included in one or more segments of a signal communicated over a communication system channel, the control signal information comprising signal components at one or more predetermined control signal frequencies, the non-control signal information comprising signal components at one or more information signal frequencies, the apparatus comprising:

means for applying a plurality of tapers to a segment of a communicated signal;

means for performing a transform of a tapered segment;

means for determining a similarity score based on a transform of a tapered segment and a model of a control signal, the similarity score reflecting a comparison of signal components of the communicated signal at the predetermined control signal frequencies with signal components of the communicated signal at other information signal frequencies;

means for classifying one or more segments of the communicated signal as representing either control signal information or non-control signal information based on a similarity score; and

means for providing an indicator signal representative of control signal information to the communication system element when the communicated signal has been classified as representing control signal information.

32. The apparatus of claim 31 further comprising a means for receiving a communicated signal and producing one or more segments thereof.

33. The apparatus of claim 32 wherein the means for producing one or more segments comprises means for producing overlapping segments.

34. The apparatus of claim 31 wherein the control signal information comprises DTMF signal information.

35. The apparatus of claim 31 wherein the control signal information comprises call progress signal information.

36. The apparatus of claim 31 wherein the control signal information comprises supervisory audio tone signal information.

37. The apparatus of claim 31 wherein the means for applying a plurality of tapers comprises a means for applying a taper which comprises a discrete prolate spheroidal sequence.

38. The apparatus of claim 31 wherein the means for applying a plurality of tapers comprises a means for forming a product of a taper value and an input signal segment value.

39. The apparatus of claim 31 wherein the means for applying a plurality of tapers comprises a means for applying a taper value to a possible communicated signal value.

40. The apparatus of claim 39 further comprising a memory for storing information which comprises a taper value applied to a possible communicated signal value.

41. The apparatus of claim 31 wherein the means for performing a transform comprises a means for performing a Fourier transform.

42. The apparatus of claim 31 wherein the control signal model comprises a sinusoidal model.

43. The apparatus of claim 42 wherein the sinusoidal model comprises an amplitude modulated sinusoidal model.

44. The apparatus of claim 42 wherein the sinusoidal model comprises a frequency modulated sinusoidal model.

45. The apparatus of claim 42 wherein the sinusoidal model comprises a first sinusoidal model and a second sinusoidal model.

46. The apparatus of claim 45 wherein the first sinusoidal model comprises a first control signal information frequency and the second sinusoidal model comprises a second control signal information frequency.

47. The apparatus of claim 46 wherein the means for determining a similarity score comprises means for estimating amplitude information based on a transformed tapered segment and wherein each of the first and second sinusoidal models comprises estimated amplitude information.

48. The apparatus of claim 47 wherein the means for determining a similarity score comprises means for forming a ratio, the numerator of the ratio comprising an energy distribution based on the first and second sinusoidal models, and the denominator of the ratio comprising an energy distribution based on a difference between a transformed tapered segment and a sum of the first and second sinusoidal models.

49. The apparatus of claim 31 wherein the control signal model comprises expected control signal information distortion.

50. The apparatus of claim 31 wherein the means for determining a similarity score comprises a means for estimating amplitude information based on a transformed tapered segment and wherein a control signal model comprises estimated amplitude information.

51. The apparatus of claim 31 wherein the means for determining a similarity score comprises means for determining a measure of similarity between energy distributions.

52. The apparatus of claim 51 wherein the means for determining a measure of similarity between energy distributions comprises means for forming a ratio, the numerator of the ratio comprising an energy distribution based on a control signal model, and the denominator of the ratio comprising an energy distribution based on a difference between a transformed tapered segment and the control signal model.

53. The apparatus of claim 31 wherein the means for determining a similarity score comprises:

means for determining an estimate of frequency deviation between an expected control signal information frequency and a frequency component of a transformed tapered segment; and

means for determining whether the estimate of frequency deviation exceeds a threshold.

54. The apparatus of claim 31 wherein the means for classifying comprises means for determining whether a similarity score exceeds a threshold.

55. The apparatus of claim 31 wherein the means for classifying comprises means for determining whether a frequency component of a transformed tapered segment deviates from an expected control signal information frequency by an amount which exceeds a threshold.

56. The apparatus of claim 55 wherein the means for determining whether a frequency-component of a transformed tapered segment deviates from an expected control signal information frequency comprises:

means for determining amplitude estimates of the transformed tapered segment at a plurality of frequencies including the expected control signal information frequency; and

means for determining whether the amplitude at the expected control signal information frequency exceeds the other determined amplitude estimates.

57. The apparatus of claim 31 wherein the means for classifying comprises:

means for determining an amplitude variation parameter based on estimates of the amplitude of a frequency component present in each of a plurality of segments; and

means for determining when the amplitude variation parameter exceeds a threshold.

58. The apparatus of claim 31 wherein the means for classifying comprises:

means for determining a phase variation parameter based on estimates of the amplitude of a frequency component present in each of a plurality of segments; and

means for determining when the phase variation parameter exceeds a threshold.

59. The apparatus of claim 31 wherein the means for classifying comprises:

means for determining an amplitude and phase variation parameter based on estimates of the amplitude and phase of a frequency component present in each of a plurality of segments; and

means for determining when the amplitude and phase variation parameter exceeds a threshold.

60. The apparatus of claim 31 wherein the means for classifying comprises:

means for determining a ratio of amplitudes of a transformed tapered segment, the numerator of the ratio comprising an amplitude evaluated at one frequency of expected control signal information and the denominator of the ratio comprising an amplitude evaluated at another frequency of the expected control signal information; and

means for determining whether the ratio is within a predetermined range of values.