Ring tone detection for a telephone system

• US 5,442,694 A
• Filed: 04/12/1994
• Issued: 08/15/1995
• Est. Priority Date: 04/12/1994
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Dialogic, Inc. (Enghouse Systems Limited)
• Inventors: Dumont, Andrew, Pan, Zhibing, Juall, Chet, Chitrapu, Prabhakar
• Primary Examiner(s): Dwyer, James L.
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US08/226,678
• Time in Patent Office: 490 Days
• Field of Search: 379/386, 379/373, 379/372, 379/377
• US Class Current: 379/373.01
• CPC Class Codes: H04M 1/82 Line monitoring circuits for call progress or status discrimination for detecting caller identity H04M1/573
• CPC Class Codes: H04M 19/04 the ringing-current being generated at the substations
• CPC Class Codes: H04Q 1/50 Conversion between different kinds of signals

Abstract

A technique for software ring tone detection is disclosed utilizing, in the preferred embodiment, a recursive algorithm. The technique provides flexibility in that a digital signal processor may be reprogrammed to detect ring tone frequencies and amplitudes present in numerous different countries.

Claims

1. A method of detecting a ring tone signal in a telephone apparatus receiving an input signal from a remote caller, said telephone apparatus comprising a transformer having a first side for interfacing with a telephone network and a second side for interfacing with a voice processing apparatus the method comprising the steps of:

attenuating the input signal being received at the first side of the transformer from a telephone network while said voice processing apparatus is on-hook;

digitizing said attenuated signal;

processing said digitized signal in a processor having an input to determine whether said ring tone is present or not; and

switching the input of the processor to receive a signal from the second side of said transformer after said voice processing apparatus goes off-hook.

2. The method of claim 1 wherein said step of attenuating comprises the step of transmitting the signal through a high pass filter.

3. A method of processing signals received from a telephone network, having a voice band at a telephone apparatus said telephone apparatus having at least an on-hook state and an off-hook state comprising the steps of:

inputting, while said apparatus is on-hook, said received signals into a digital signal processor;

digitally processing said signals from a first side of a transformer to detect information transmitted outside the voice band of the telephone network while said apparatus is on-hook;

switching said apparatus to an off-hook state; and

digitally processing, in the processing means, said signals from a second side of the transformer to detect information within the voice band Of the telephone network after said step of switching.

4. A method of digitally estimating the frequency of a signal received from a telephone networks, said signal having an auto-correlation function, a frequency, and a period, and of activating a ring tone detect logic circuit, the method comprising the steps of:

digitally calculating the auto-correlation function of said received signal at multiple time lags to obtain a numerator;

digitally calculating the auto-correlation function of said received signal at a single time lag to obtain a denominator;

dividing the numerator by the denominator to obtain a result;

obtaining an estimate of said frequency, from said result, after no more than one half of said period; and

asserting a logic signal to a predetermined state if said frequency estimate is within a predetermined range to thereby activate said logic circuit.

5. The method of claim 4 wherein said numerator and said denominator are calculated respectively as the following summations:

space="preserve" listing-type="equation">Num(n)=[Σ

{x(i)+x(i-2)}x(i-1)]/2n

space="preserve" listing-type="equation">and

space="preserve" listing-type="equation">Den(n)=[Σ

x.sup.2 (i-1)]/n

both of said summations running from i=0 to n-1.

6. The method of claim 4 wherein said numerator and said denominator are calculated as the following summations:

space="preserve" listing-type="equation">Num(n)=Σ

λ

.sup.n-i-1 x(i-1) {x(i)+x(i-2)}

space="preserve" listing-type="equation">and

space="preserve" listing-type="equation">Den(n)=Σ

λ

.sup.n-1-1 x.sup.2 (i-1)

both of said summations running from i=0 to n-1.

7. The method of claim 4, wherein said numerator and said denominator are calculated as the following summations:

space="preserve" listing-type="equation">Num(n)=Σ

{x(i)+x(i-2)}x(i-1)

space="preserve" listing-type="equation">and

space="preserve" listing-type="equation">Den(n)=Σ

x.sup.2 (i-1)

both of said summations running from i=n-M+1 to n, 1≦

M≦

n.

8. The method of claim 4 further comprising the step of calculating the inverse cosine of said result.

9. Apparatus for detecting ring tone in a telephone network having a voice bandwidth said apparatus comprising:

filter means having a passband and arranged to receive said ring tone from said telephone network, said filter means being arranged such that said ring tone is outside said passband;

an analog to digital (A/D) convertor having an input and an output and being connected to the output of said filter means for digitizing said filtered ring tone signal;

a digital signal processor coupled to said output of said A/D convertor for digitally processing samples output by said A/D convertor and for detecting when ring tone is present; and

means for detecting whether said apparatus is in an on hook or off hook state, and for connecting the input of said A/D convertor to a different electrical point based upon said on hook or off hook state.

10. The apparatus of claim 9 wherein said digital signal processor also detects signals other than ring tone.

11. Apparatus of claim 10 wherein said digital signal processor includes:

means for calculating the autocorrelation function of said ring tone signal at predetermined time lags.

12. Apparatus of claim 11 wherein said digital signal processor includes:

means for detecting signals within the voiceband of the telephone network; and

means for detecting signals outside of said bandwidth of said telephone network.

13. Apparatus of claim 9 wherein said digital signal processor calculates the following summations:

space="preserve" listing-type="equation">Num(n)=[Σ

{x(i)+x(i-2)}x(i-1)]/2n

space="preserve" listing-type="equation">and

space="preserve" listing-type="equation">Den(n)=[Σ

x.sup.2 (i-1)]/n

both of said summations running from i=0 to n-1.

14. Apparatus of claim 9 wherein said digital signal processor calculates the following summations:

space="preserve" listing-type="equation">Num(n)=Σ

λ

.sup.n-i-1 x(i-1) {x(i)+x(i-2)}

and

space="preserve" listing-type="equation">Den(n)=Σ

λ

.sup.n-i-1 x.sup.2 (i-1)

both of said summations running from i=0 to n-1.

15. Apparatus of claim 9 wherein said digital signal processor calculates the following summations:

space="preserve" listing-type="equation">Num(n)=Σ

{x(i)+x(i-2)}x(i-1)

space="preserve" listing-type="equation">and

space="preserve" listing-type="equation">Den(n)=Σ

x.sup.2 (i-1)

both of said summations running from i=n-M+1 to n, 1≦

M≦

n.

16. Apparatus of claim 13 wherein said digital signal processor is programmed to calculate said summations in a recursive manner.

17. Apparatus of claim 14 Wherein said digital signal processor is programmed to calculate said summations in a recursive manner.

18. Apparatus of claim 15 wherein said digital signal processor is programmed to calculate said summations in a recursive manner.

19. Apparatus for detecting ring tones in a telephone signal being received from a remote user, said apparatus comprising:

processing means for detecting ring tone signals and for performing voice processing during a telephone call; and

switching means for switching the input to the processing means from either a first electrical point or a second electrical point.

20. Apparatus for detecting ring tone in a telephone network having a voice bandwidth said apparatus comprising:

filter means having a passband and arranged to receive said ring tone from said telephone network, said filter means being arranged such that said ring tone is outside said passband;

an analog to digital (A/D) convertor having an input and an output and being connected to the output of said filter means for digitizing said filtered ring tone signal;

a digital signal processor coupled to said output of said A/D convertor for digitally processing samples output by said A/D convertor and for detecting when ring tone is present; and

means for detecting whether said apparatus is in an on hook or off hook state, and for connecting the input of said A/D convertor to process information either inside or outside the voice bandwidth based upon said on hook or off hook state.