3-Way call detection system

• US 7,123,704 B2
• Filed: 01/14/2005
• Issued: 10/17/2006
• Est. Priority Date: 11/13/2001
• Status: Expired due to Term

• Current Assignee: DSI-ITI, Inc.
• Original Assignee: Inmate Telephone, Inc.
• Inventors: Martin, Thomas
• Primary Examiner(s): Harold, Jefferey F.
• Application Number:
  US11/035,071
• Publication Number:
  US 20050111654A1
• Time in Patent Office: 641 Days
• Field of Search: 379/189, 379/406.01, 379/207.01, 379/406.14
• US Class Current: 379/189
• CPC Class Codes: H04M 1/68 Circuit arrangements for preventing eavesdropping
• CPC Class Codes: H04M 3/2281 Call monitoring, e.g. for law enforcement purposes; Call tracing; Detection or prevention of malicious calls
• CPC Class Codes: H04M 3/305 testing of physical copper line parameters, e.g. capacitance or resistance locating faults in cables G01R31/08
• CPC Class Codes: H04M 3/56 Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities video conference systems H04N7/15

Abstract

Disclosed herein is a three-way call detection system and method for detecting the addition of a third party to a pre-existing telephonic connection between a first party and a second party. The system comprises: a meter for measuring the amplitude of a line voltage of a telephonic connection between a first party and a second party, said line voltage having a frequency band F1; a first filter to remove a frequency band F2 from said line voltage and output a filtered signal, said frequency band F2 being a subset of F1; a white noise generator for generating a low level white noise signal with a frequency band that corresponds to F2 and with an amplitude that is significantly below an amplitude level of the measured line voltage for frequency band F2; a coupler for combining the low level white noise signal to the filtered signal, thereby outputting an additive line voltage; a second filter that passes only a portion of the additive line voltage, said signal that passes being referred to as the band-passed signal, said band-passed signal having a frequency range F3, said frequency band F3 being a subset of F1 and being inclusive of F2; and a processor for processing the band-passed signal and determining a baseline amplitude level associated with a two-way call. The processor monitors the band-passed signal in the time domain for a shift in baseline amplitude level, which shift is associated with the addition of a third party to the telephonic connection. The white noise being added is preferably at least 3 dB below the amplitude level of the measured line voltage, more preferably at least 10 dB, more preferably at least 20 db, and most preferably 40 db below. The frequency band F2 is selected from F1 to be significantly large enough to permit more reliable detection, and yet small enough to be barely perceptible to the listener. For example, F2 may comprise the frequencies from 1–2 KHz. An F2 of 1–1.3 KHz. also functions well.

Claims

1. A three way call detection system for detecting the addition of a third party to an pre-existing telephonic connection between a first party and a second party, said system comprising:

a meter for measuring the amplitude of a line voltage of a telephonic connection between a first party and a second party, said line voltage having a frequency band F1,

a first filter to remove a frequency band F2 from said line voltage and output a filtered signal, said frequency band F2 being a subset of F1;

a white noise generator for generating a low level white noise signal with a frequency band that corresponds to F2 and with an amplitude that is measurably less than an amplitude level of the measured line voltage for frequency band F2,

a coupler to combine the low level white noise signal with the filtered signal, thereby outputting an additive line voltage;

a second filter that passes at least a portion of the additive line voltage and substantially all of the low level white noise signal that was added, said signal that passes being referred to as the band-passed signal; and

a processor for processing the band-passed signal and determining a baseline amplitude level associated with a two-way call;

wherein said processor monitors the band-passed signal in the time domain for a measurable shift in baseline amplitude level, which shift occurs when a third party is added to the telephonic connection.

2. The three way call detection system of claim 1, wherein the coupler is selected from the group consisting of:

a voltage adder, a summer, a signal combiner, and a processor preprogrammed with a function that adds two signals to form a combined signal.

3. The three way call detection system of claim 1, wherein the coupler is a signal combiner.

4. The three way call detection system of claim 1, wherein the coupler is a processor preprogrammed with a function that adds two signals to form a combined signal.

5. The three way call detection system of claim 1, wherein the amplitude of the line voltage is measured at a location selected from the group consisting of:

the location of the first party, a telephone switching station, and a telephone central office.

6. The three way call detection system of claim 1, wherein the amplitude of the line voltage is measured at a telephone switching station.

7. The three way call detection system of claim 1, wherein the amplitude of the line voltage is measured at a telephone central office.

8. The three way call detection system of claim 1, wherein the first filter is selected from the group consisting of:

a notch filter, a band reject filter, a digital signal processor, and a circuit that subtracts signals in frequency band F2 from the amplitude of the line voltage in frequency band F1.

9. The three way call detection system of claim 1, wherein the first filter is a band reject filter.

10. The three way call detection system of claim 1, wherein the first filter is a digital signal processor that cancels signals within frequency band F2.

11. The three way call detection system of claim 1, wherein the first filter is a circuit that subtracts the amplitude signal in frequency band F2 from the amplitude of the line voltage in frequency band F1.

12. The three way call detection system of claim 1, wherein the second filter is selected from the group consisting of:

a band pass filter, a digital signal processor, and a circuit that removes a band of frequencies from the line voltage.

13. The three way call detection system of claim 1, wherein the second filter is a band pass filter.

14. The three way call detection system of claim 1, wherein the second filter is a digital signal processor that cancels a band of frequencies.

15. The three way call detection system of claim 1, wherein the second filter is a circuit that removes a band of frequencies from the line voltage.

16. The three way call detection system of claim 1, wherein the white noise generator is selected from the group consisting of:

a white noise source coupled to a bandpass filter; and

a digital signal processor that generates a noise signal with a frequency band corresponding to F2.

17. The three way call detection system of claim 1, wherein the white noise generator is a white noise source coupled to a bandpass filter.

18. The three way call detection system of claim 1, wherein the white noise generator is a digital signal processor that generates noise with a frequency band corresponding to F2.

19. The three way call detection system of claim 1, wherein the meter is selected from the group consisting of:

a voltmeter, a multimeter, and a measuring circuit.

20. A method of detecting the addition of a third party to an pre-existing telephonic connection between a first party and a second party, said method comprising:

measuring a line voltage for amplitude, said measured line voltage having a frequency band F1;

filtering the measured line voltage to remove a frequency band F2 to create a filtered signal, said frequency band F2 being a subset of frequency band F1;

generating a low level white noise signal with a frequency band that corresponds to F2 and with an amplitude that is less than an amplitude level of the measured line voltage for frequency band F2,

adding the low level white noise signal to the filtered signal to create an additive line voltage;

filtering the additive line voltage to pass at least a portion of the additive line voltage and substantially all of the low level white noise that was added, said signal that passes being referred to as the band-passed signal;

processing the band-passed signal to determine a baseline amplitude level associated with the characteristics of a two-way call;

monitoring the band-passed signal in the time domain for a shift in baseline amplitude level, that occurs when a third party is added to the previous two-party call.