Method and apparatus for detection of a telephone CPE alerting signal

• US 6,940,966 B2
• Filed: 02/21/2002
• Issued: 09/06/2005
• Est. Priority Date: 02/21/2002
• Status: Expired due to Fees

• Current Assignee: VTech Telecommunications Limited (VTech Holdings Ltd.)
• Original Assignee: VTech Telecommunications Limited (VTech Holdings Ltd.)
• Inventors: Lee, Julian, Louie, Gary
• Primary Examiner(s): Tran, Sinh
• Assistant Examiner(s): Briney, III, Walter F
• Application Number:
  US10/079,969
• Publication Number:
  US 20030156709A1
• Time in Patent Office: 1,293 Days
• Field of Search: 379/377, 379/386, 379/357, 379/142.01
• US Class Current: 379/386
• CPC Class Codes: H04M 1/573 Line monitoring circuits for detecting caller identification
• CPC Class Codes: H04M 15/06 Recording class or number of calling , i.e. A-party or called party , i.e. B-party

Abstract

A method and apparatus for detecting a signaling tone within a communications channel, such as a telephone line, is presented. The energy level of the communications channel signal is measured at the frequency of the signaling tone and at one or more frequencies that are integer divisors of the signaling tone (i.e. at one or more subharmonics). The subharmonic energies are evaluated in determining whether the signaling tone is present. The technique can be implemented using a plurality of resonators and a comparator.

Claims

1. A method for detecting a predetermined signaling tone within a signal conveyed by a communications channel, the method comprising:

performing a first measurement of the energy of the communications channel signal at the frequency of the predetermined signaling tone;

performing a second measurement of the energy of the communications channel signal at a frequency that is an integer divisor of the predetermined signaling tone frequency;

performing one or more guard band measurements of the energy of the signals conveyed by the communications channel at respective one or more guard band frequencies, the guard band frequencies chosen to lie just above or just below a corresponding signaling tone frequency; and

determining that the signaling tone is present when the result of the first measurement exceeds a first threshold, where the first threshold is derived from the result of the second measurement, and when the results of the guard band measurements do not exceed a second threshold, where the second threshold is derived from the result of the first measurement.

2. The method of claim 1, in which the first threshold is approximately six decibels greater than the second measurement.

3. The method of claim 1, in which the step of performing a first measurement is further comprised of the substeps of applying the communications channel signal to a first resonator tuned to the frequency of the predetermined signaling tone;

and measuring the output of the first resonator

and in which the step of performing a second measurement is further comprised of the substeps of applying the communications channel signal to a second resonator tuned to an integer divisor of the signaling tone frequency; and

measuring the output of the second resonator.

4. The method of claim 1, wherein a plurality of guard band measurements are performed, and wherein each guard band measurement does not exceed the second threshold.

5. The method of claim 4, in which the second threshold is equal to one fourth of the first measurement.

6. The method of claim 1, in which the step of determining that the signaling tone is present is further comprised of the substep of determining that the result of the first measurement exceeds a third threshold, where the third threshold is predetermined to be indicative of a minimum acceptable energy level for a valid signaling tone.

7. The method of claim 1, in which the step of determining that the signaling tone is present is further comprised of the substep of determining that the result of the first measurement does not exceed a fourth threshold, where the fourth threshold is predetermined to be indicative of the maximum acceptable energy level for a valid signaling tone.

8. The method of claim 6, in which the step of determining that the signaling tone is present is further comprised of the substep of determining that the result of the first measurement does not exceed a fourth threshold, where the fourth threshold is predetermined to be indicative of the maximum acceptable energy level for a valid signaling tone.

9. The method of claim 1, which method further includes the step of performing one or more further measurements of the energy of the communications channel signal, each further measurement being at a frequency that is an integer divisor of the predetermined signaling tone frequency;

and

in which the step of determining that the signaling tone is present further includes the substep of determining that the result of the first measurement exceeds one or more further thresholds, where the further thresholds are derived from the results of the further measurements.

10. The method of claim 9, in which step of performing one or more further measurements is comprised of the substeps of applying the communications channel signal to one or more further resonators, each further resonator being tuned to a frequency that is an integer divisor of the predetermined signaling tone frequency;

and measuring the outputs of each of the further resonators.

11. A method for detecting a customer premises equipment alerting signal comprised of one or more signaling tones received on a telephone line by a telephone while voice or other audible communications are occurring on the telephone line, which method is comprised of:

measuring the signal energies present on the telephone line at the frequencies of the one or more signaling tones;

measuring the signal energies present at one or more sub-harmonic frequencies of each of the one or more signaling tones;

measuring the signal energies present at one or more guard band frequencies, the guard band frequencies chosen to lie just above or just below a corresponding signaling tone frequency; and

determining that the alerting signal is present when the energy of each signaling tone frequency exceeds a threshold derived from the energies measured at the one or more sub-harmonic frequencies for each signaling tone, and when the energy of each signaling tone frequency exceeds a threshold derived from the energy measured at the one or more guard band frequencies of that signaling tone.

12. The method of claim 11, in which the step of determining that the alerting signal is present is further comprised of the substep of determining that the energy of each signaling tone exceeds a predetermined minimum signaling tone energy level.

13. The method of claim 12, in which the step of determining that the alerting signal is present is further comprised of the substep of determining that the energy of each signaling tone does not exceed a predetermined maximum signaling tone energy level.

14. A telephone alerting signal detector for detecting the presence of a signaling tone on a communications channel, the detector comprising:

a signaling tone resonator tuned to the frequency of the signaling tone;

one or more sub-harmonic resonators, each sub-harmonic resonator being tuned to a frequency that is an integer divisor of the signaling tone frequency;

one or more guard band resonators, each guard band resonator being tuned to a frequency that is slightly greater than or less than the signaling tone frequency;

a comparator including inputs that are derived from the outputs of the signaling tone and sub-harmonic resonators and from the guard band resonator outputs, whereby the output of the comparator is indicative of the presence of the signaling tone if the signaling tone resonator output exceeds a first threshold derived from the sub-harmonic resonator outputs, and if the signaling tone resonator output exceeds a second threshold, where the second threshold is derived from the guard band resonator levels.

15. The telephone alerting signal detector of claim 14, in which the comparator further includes an input corresponding to a predetermined minimum signaling tone level, such that the comparator output is indicative of the presence of the signaling tone if the signaling tone resonator output exceeds the first threshold and the predetermined minimum signaling tone level.

16. The telephone alerting signal detector of claim 15, in which the comparator further includes an input corresponding to a predetermined maximum signaling tone level, such that the comparator output is indicative of the presence of the signaling tone if the signaling tone resonator output exceeds the first threshold and the predetermined minimum signaling tone level, and the predetermined maximum signaling tone level exceeds the signaling tone resonator output.

17. The telephone alerting signal detector of claim 14, in which the first threshold is approximately six decibels greater than the greatest of the one or more sub-harmonic resonator outputs.

18. The telephone alerting signal detector of claim 14, in which the second threshold is approximately four times the level of the greatest guard band resonator output.