Method for reducing noise from an asymmetric digital subscriber line modem

• US 6,721,394 B1
• Filed: 12/09/1999
• Issued: 04/13/2004
• Est. Priority Date: 12/09/1999
• Status: Expired due to Fees

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Sarsoza, Lloyd, Murphy, Tim, Staszak, Martin
• Primary Examiner(s): BARNIE, REXFORD N
• Application Number:
  US09/458,568
• Time in Patent Office: 1,587 Days
• Field of Search: 379/387, 379/399.01, 379/413.02, 379/413, 379/413.04, 379/1.01, 379/1.03, 379/27.01, 379/27.02, 379/27.03, 379/27.04, 379/28, 379/29.07, 379/30, 379/22, 379/22.02, 379/22.03, 379/22.04, 379/22.08, 379/24, 375/222
• US Class Current: 379/22.08
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data
• CPC Class Codes: H04M 3/18 with means for reducing interference or noise; with means for reducing effects due to line faults with means for protecting lines
• CPC Class Codes: H04M 3/30 for subscriber's lines , for the local loop

Abstract

A method for reducing audible noise in a telephone from a splitterless asymmetric digital subscriber line modem. The modem examines the shape of the power spectrum of fast retrain signals both when the telephone is on-hook and off-hook. By comparing the spectra, in particular the slopes of the spectra, the modem may determine the quality of the telephone that shares the telephone loop with the modem. The modem cuts back its transmitted power depending on the quality of the telephone by an amount that suppresses the audible noise in the telephone. In this manner, a customer may simultaneously use the telephone and the modem on the same telephone loop.

Claims

1. A method for reducing audible noise in a telephone from a splitterless Asymmetric Digital Subscriber Line modem, where the telephone and the modem share a telephone loop, to enable simultaneous use of the telephone and the modem, the method comprising the steps of:

measuring a first spectral characteristic for the telephone loop when the telephone is on-hook, wherein the first spectral characteristic is measured by the modem, and wherein measuring the first spectral characteristic comprises;

detecting a first plurality of tones in the modem, wherein the first plurality of tones is transmitted from a central office to the modem over the telephone loop while the telephone is on-hook; and

calculating an on-hook power slope value in response to detecting the first plurality of tones, wherein the first spectral characteristic is the on-hook power slope value, and wherein the on-hook power slope value is a measure of change of power with rising frequency for the first plurality of tones;

measuring a second spectral characteristic for the telephone loop when the telephone is off-hook, wherein the second spectral characteristic is measured by the modem, and wherein measuring the second spectral characteristic comprises;

initiating transmission of a second plurality of tones from the central office to the modem over the telephone loop in response to the telephone going off-hook;

detecting the second plurality of tones in the modem, wherein the second plurality of tones is transmitted from the central office to the modem over the telephone loop while the telephone is off-hook; and

calculating an off-hook power slope value in response to detecting the second plurality of tones, wherein the second spectral characteristic is the off-hook power slope value, and wherein the off-hook slope value is a measure of change of power with rising frequency for the second plurality of tones;

computing a power cutback value for the modem, wherein the power cutback value is determined from the first spectral characteristic and the second spectral characteristic; and

limiting transmitted power from the modem by an amount equal to the power cutback value.

2. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 1.

3. The method of claim 1 wherein the step of calculating the on-hook power slope value comprises the steps of:

obtaining a first logarithmic power value in a first bin, wherein the first bin corresponds to one of the first plurality of tones having a first frequency, and wherein the first logarithmic power value corresponds to average power in the first bin;

obtaining a second logarithmic power value in a second bin, wherein the second bin corresponds to another of the first plurality of tones having a second frequency, and wherein the second logarithmic power value corresponds to average power in the second bin; and

computing the on-hook power slope value proportional to the first logarithmic power value minus the second logarithmic power value.

4. The method of claim 1 wherein the step of calculating the off-hook power slope value comprises the steps of:

obtaining a third logarithmic power value in a third bin, wherein the third bin corresponds to one of the second plurality of tones having a third frequency, and wherein the third logarithmic power value corresponds to average power in the third bin;

obtaining a fourth logarithmic power value in a fourth bin, wherein the fourth bin corresponds to another of the second plurality of tones having a fourth frequency, and wherein the fourth logarithmic power value corresponds to average power in the fourth bin; and

computing the off-hook power slope value proportional to the third logarithmic power value minus the fourth logarithmic power value.

5. The method of claim 1 wherein the first plurality of tones and the second plurality of tones are Fast Retrain tones.

6. The method of claim 1, wherein the computing step comprises the steps of:

computing a difference between the first spectral characteristic and the second spectral characteristic;

determining whether the difference is less than a threshold value; and

when the difference is less than the threshold value, setting the power cutback value equal to a first value, wherein the first value is associated with power cutback for a good quality telephone.

7. The method of claim 6, wherein the transmitted power from the modem is measured with respect to a nominal transmitted power for the modem.

8. The method of claim 6, wherein the first value is approximately 12 decibels.

9. The method of claim 6, wherein the computing step further comprises the steps of:

setting the power cutback value equal to a second value, wherein the second value is associated with power cutback for a noisy telephone, when the difference exceeds the threshold value.

10. The method of claim 9, wherein the transmitted power from the modem is measured with respect to a nominal transmitted power for the modem.

11. The method of claim 9, wherein the second value is approximately 24 decibels.

12. The method of claims 6, wherein the threshold value is approximately 8.4×

10<sup>−

3</sup> deciBels per kiloHertz.

13. A method for reducing audible noise in a telephone from a splitterless Asymmetric Digital Subscriber Line modem, where the telephone and the modem share a telephone loop, to enable simultaneous use of the telephone and the modem, the method comprising the steps of:

detecting a first plurality of Fast Retrain tones in the modem, wherein the first plurality of Fast Retrain tones is transmitted from a central office to the modem over the telephone loop while the telephone is on-hook;

calculating an on-hook power slope value in response to detecting the first plurality of Fast Retrain tones, wherein the on-hook power slope value is a measure of change of power with rising frequency for the first plurality of Fast Retrain tones;

initiating transmission of a second plurality of Fast Retrain tones from the central office to the modem over the telephone loop in response to the telephone going off-hook;

detecting the second plurality of Fast Retrain tones in the modem, wherein the second plurality of Fast Retrain tones is transmitted from the central office to the modem over the telephone loop while the telephone is off-hook;

calculating an off-hook power slope value in response to detecting the second plurality of Fast Retrain tones, wherein the off-hook power slope value is a measure of change of power with rising frequency for the second plurality of Fast Retrain tones;

computing a difference between the on-hook power slope value and the off-hook power slope value;

determining whether the difference is less than a threshold value;

when the difference is less than the threshold value, setting the power cutback value equal to approximately 12 deciBels;

when the difference exceeds the threshold value, setting the power cutback value equal to approximately 24 deciBels; and

limiting transmitted power from the modem by an amount equal to the power cutback value, wherein the transmitted power from the modem is measured with respect to a nominal transmitted power for the modem.

14. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 13.

15. The method of claim 13, wherein the threshold value is approximately 8.4×

10<sup>−

3</sup> deciBels per kiloHertz.