Advanced three way call detection system and method using spread spectrum techniques

• US 6,763,099 B1
• Filed: 11/05/1999
• Issued: 07/13/2004
• Est. Priority Date: 11/05/1999
• Status: Expired due to Term

• Current Assignee: Securus Technologies Incorporated (Securus Special Investments LLC)
• Original Assignee: T-Netix, Inc. (Cognizant Technology Solutions Corp.)
• Inventors: Blink, Russell
• Primary Examiner(s): Isen, F. W.
• Assistant Examiner(s): HAROLD, JEFFEREY F
• Application Number:
  US09/435,013
• Time in Patent Office: 1,712 Days
• Field of Search: 379/189, 379/406.01, 379/406.08
• US Class Current: 379/189
• CPC Class Codes: H04M 3/002 Applications of echo suppressors or cancellers in telephonic connections in two-way loud-speaking telephone systems H04M9/08, echo suppressors or cancellers per se H04B3/20
• 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
• CPC Class Codes: H04M 3/568 audio processing specific to telephonic conferencing, e.g. spatial distribution, mixing of participants echo suppression in two-way loud-speaking telephone systems H04M9/02; sound field processing per se H04S7/30

Abstract

An advanced three way call detection system which measures delay times associated with multiple echoes of a reference signal transmitted over a two way call. A reference signal is initially transmitted over a two way call when a two way connection is first established between a local telephone and a remote telephone. The echo characteristics of the two way connection are measured and recorded in an initial echo profile. The initial echo profile represents the number of and timing of each detected echo of the reference signal after transmission of the reference signal over the two way call when the two way connection is first established. The reference signal is then continuously transmitted at various timing intervals during the telephone conversation and the incoming line is sampled in order to detect echoed versions of the reference signal in order to create subsequent echo profiles. Whether a three way calling event has occurred is determined by virtue of changes in the delay times and number of echoes in each subsequent echo profile when compared with the initial echo profile.

Claims

1. A method for detecting a three way calling event during a telephone call, the method comprising:

detecting an initial set of echo characteristics using a spread spectrum reference signal, the echo characteristics for a telephone connection over which the telephone call is made, and storing the initial set of echo characteristics in an initial echo profile;

continuously measuring the echo characteristics using the spread spectrum reference signal of the telephone connection at various times during the telephone call; and

comparing the continuously measured echo characteristics with the initial set of echo characteristics stored in the initial echo profile in order to detect a three way calling event.

2. The method of claim 1 further comprising:

reporting a three way call event if the continuously measured echo characteristics are determined to be significantly different from the initial set of echo characteristics stored in the initial echo profile as a result of the comparing step.

3. The method of claim 1, wherein detecting an initial set of echo characteristics further comprises:

transmitting the reference signal over the telephone connection when the telephone call first begins; and

detecting echoed versions of the reference signal and recording a delay time associated with each echoed version of the reference signal, thereby generating an initial echo profile describing each echoed version of the reference signal and its associated delay time.

4. The method of claim 3, wherein continuously measuring the echo characteristics of the telephone connection at various times further comprises:

successively re-transmitting the reference signal at pre-selected intervals throughout the duration of the telephone call; and

detecting echoed versions of the reference signal after each successive transmission and recording a subsequent delay time associated with each of the detected echoes.

5. The method of claim 4, wherein comparing the measured echo characteristics with those stored in the initial echo profile in order to detect a three way calling event further comprises:

comparing the subsequent delay times associated with each of the detected echoes of the reference signal with the delay times recorded in the initial echo profile in order to determine whether any of the echoed versions of the reference signal occur at subsequent delay times which differ from the initial delay times recorded in the initial echo profile.

6. The method of claim 1 wherein the reference signal is a spread spectrum pseudo-random noise signal.

7. The method of claim 1 wherein echoed versions of the reference signal are detected using auto-correlation techniques in order to accurately detect faint echoed versions of the reference signal.

8. A method for detecting three way calling event comprising:

transmitting a first analog spread spectrum signal over a telephone line from a local telephone;

detecting echoed versions of the first analog spread spectrum signal;

generating a first echo profile which records a delay time associated with each detected echoed version of the first analog spread spectrum signal;

transmitting a second analog spread spectrum signal over the telephone line from the local telephone;

detecting echoed versions of the second analog spread spectrum signal;

generating a second echo profile which records a delay time associated with each detected echoed version of the second analog spread spectrum signal; and

comparing the first echo profile with the second echo profile in order to determine whether a three way calling even has occurred.

9. The method of claim 8, further comprising generating a signal indicating that a three way calling event has occurred if the second echo profile is substantially different from the first echo profile.

10. The method of claim 8, further comprising:

generating a first digital pseudo random noise sequence;

converting the first digital pseudo random noise sequence into the first analog spread spectrum signal before transmitting the first analog spread spectrum signal over the telephone line from the local telephone.

11. The method of claim 8, further comprising:

generating a second digital pseudo random noise sequence;

converting the second digital pseudo random noise sequence into the second analog spread spectrum signal before transmitting the second analog spread spectrum signal over the telephone line from the local telephone.

12. A system for detecting three way call events on a telephone line, comprising:

a transmitting module for transmitting a plurality of spread spectrum reference signals over a telephone connection during a telephone call in order to determine echo characteristics of the telephone connection; and

a receiving module for continuously receiving echoed versions of the plurality of spread spectrum reference signals in order to monitor the echo characteristics of the telephone connection over the duration of the telephone call, wherein the receiving module detects a three way call event if the echo characteristics of the telephone connection change over the duration of the telephone call.

13. The system of claim 12, wherein the receiving module:

records a plurality of time delays associated with each echoed version of an initial reference signal in the plurality of reference signals and records the plurality of time delays in an initial echo profile;

measures echo times associated with echoed versions of each of the other reference signals in the plurality of reference signals; and

compares the plurality of time delays in the initial echo profile with the measured echo times associated with the echoed versions of each of the other reference signals in the plurality of reference signals in order to determine whether a three way calling even has occurred.

14. The system of claim 13 wherein the receiving module comprises:

an auto correlator for receiving the echoed versions of the plurality of reference signals;

a sample count register for recording the plurality of time delays associated with each echoed version of the initial reference signal in an initial echo profile and measuring echo times associated with echoed versions of each of the other reference signals in the plurality of reference signals; and

a comparing module for comparing the plurality of time delays in the initial echo profile with the measured echo times associated with the echoed versions of each of the other reference signals in the plurality of reference signals in order to determine whether a three way callings even has occurred.

15. The system of claim 12, wherein the receiving module generates an alarm signal indicating that a three way calling event has occurred if the plurality of time delays in the initial echo profile do not correlate with the measured echo times associated with the echoed versions of each of the other reference signals.

16. The system of claim 12, wherein the transmitting module comprises:

a pseudo random sequence generator for generating pseudo random sequences; and

a transmit logic with a digital-to-analog converter for converting the pseudo random sequences into the plurality of reference signals which are transmitted over the telephone connection during the telephone call in order to determine echo characteristics of the telephone connection.

17. A system for detecting three way call events on a telephone line, comprising:

a digital signal processor; and

a memory, coupled to the digital signal processor, for storing a sequence of instructions which, when executed by the digital signal processor, cause the digital signal processor to perform the steps of;

successively transmitting a spread spectrum reference signal over the telephone line;

detecting echoed versions of each of the successively transmitted reference signals;

measuring an echo time delay associated with each of the detected echoed versions of each successively transmitted reference signal; and

reporting a three way call event if the echo time delay for the detected echoed versions of each successively transmitted reference signal does not remain consistent.

18. The system of claim 17, wherein the reference signal is a digital pseudo-random noise sequence.

19. The system of claim 18, wherein the digital pseudo-random signal is converted into a spread spectrum analog signal before each transmission.

20. The system of claim 18, further comprising an auto correlator for detecting the echoed versions of each of the successively transmitted digital pseudo-random noise sequence.

21. A computer program product comprising:

a computer useable medium having computer readable code embodied therein for detecting a three way calling event, the computer readable code causing a computer to;

detect an initial set of echo characteristics using a spread spectrum reference signal, the echo characteristics for a telephone connection over which a telephone call is made, and store this initial set of echo characteristics in an initial echo profile;

continuously measure the echo characteristics using the spread spectrum reference signal of the telephone connection at various times throughout the duration of the telephone call; and

compare the measured echo characteristics with those stored in the initial echo profile in order to detect a three way calling event.

22. A method for detecting a three way calling event during a telephone call, the method comprising:

detecting an initial set of echo characteristics using a FM Chirp reference signal, the echo characteristics for a telephone connection over which the telephone call is made, and storing the initial set of echo characteristics in an initial echo profile;

continuously measuring the echo characteristics using the FM Chirp reference signal of the telephone connection at various times during the telephone call; and

comparing the continuously measured echo characteristics with the initial set of echo characteristics stored in the initial echo profile in order to detect a three way calling event.

23. The method of claim 22 further comprising:

reporting a three way call event if the continuously measured echo characteristics are determined to be significantly different from the initial set of echo characteristics stored in the initial echo profile as a result of the comparing step.

24. The method of claim 22, wherein detecting an initial set of echo characteristics further comprises:

transmitting the reference signal over the telephone connection when the telephone call first begins; and

detecting echoed versions of the reference signal and recording a delay time associated with each echoed version of the reference sign, thereby generating an initial echo profile describing each echoed version of the reference signal and its associated delay time.

25. The method of claim 22, wherein continuously measuring the echo characteristics of the telephone connection at various times further comprises:

successively re-transmitting the reference signal at pre-selected intervals throughout the duration of the telephone call; and

detecting echoed versions of the reference signal after each successive transmission and recording a subsequent delay time associated with each of the detected echoes.

26. The method of claim 25, wherein comparing the measured echo characteristics with those stored in the initial echo profile in order to detect a three way calling event further comprises:

comparing the subsequent delay times associated with each of the detected echoes of the reference signal with the delay times recorded in the initial echo profile in order to determine whether any of the echoed versions of the reference signal occur at subsequent delay times which differ from the initial delay times recorded in the initial echo profile.

27. The method of claim 22, wherein echoed versions of the initial reference signal are detected using a matched FIR filter with an infinite impulse response.