Method of converging an echo canceller

• US 5,381,474 A
• Filed: 06/23/1993
• Issued: 01/10/1995
• Est. Priority Date: 11/04/1991
• Status: Expired due to Term

• Current Assignee: Intellectual Ventures I LLC (Intellectual Ventures LLC)
• Original Assignee: Nokia Telecommunications Oy (Nokia Corporation)
• Inventors: Sippola, Jaakko, Lahdemaki, Heimo
• Primary Examiner(s): Dwyer, James L.
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US08/081,323
• Time in Patent Office: 566 Days
• Field of Search: 379/410, 379/406, 379/402, 379/411, 379/407, 379/3, 379/6, 370/32, 370/32.1, 370/24
• US Class Current: 379/406.08
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• 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

Abstract

Converging of an echo canceller (4A-D) integrated into a telephone exchange (1, 2) is initiated at the start of a telephone call by an internal command of the telephone exchange given by a call control (2) of the telephone exchange as soon as the call control (2) has observed an off-hook state of a called subscriber connection. The command causes the echo canceller (4A-D) to transmit a test signal to the echo path for converging the echo canceller before appearance of the speech signal.

Claims

1. A method for converging an adaptive echo canceller at the beginning of a telephone call between a calling subscriber and a called subscriber during which the called subscriber will transmit a speech signal to the calling subscriber, said method comprising:

(a) establishing a transmission connection through a telephone exchange between a calling subscriber and a called subscriber over a telephone system which includes said telephone exchange, which telephone exchange has an adaptive echo canceller integrated thereinto;

(b) at said telephone exchange detecting an off-hook state of the called subscriber, using a call control;

(c) in response to said detecting of said off-hook state, outputting an internal command of said telephone interchange to said echo canceller from said call control, for initiating convergence of said echo canceller; and

(d) in response to receipt by said echo canceller of said internal command, transmitting a test signal from said echo canceller along said transmission connection towards said calling subscriber, and using reception by said echo canceller of a return of said test signal along an echo path of said transmission connection to said echo canceller to converge said echo canceller before appearance of said speech signal on said transmission connection; and

(e) utilizing said echo canceller, as thereby converged, to suppress echo in transmission of said speech signal on said transmission connection.

2. The method of claim 1, wherein:

said test signal is a pulse.

3. The method of claim 1, wherein:

said called subscriber is a subscriber of said telephone exchange and said calling subscriber is calling in from outside of said telephone exchange.

4. A method for converging an adaptive echo canceller at the beginning of a telephone call between a calling subscriber and a called subscriber during which the called subscriber will transmit a speech signal to the calling subscriber, said method comprising:

(a) establishing a transmission connection through a telephone exchange between a calling subscriber and a called subscriber over a telephone system which includes said telephone exchange, which telephone exchange has an adaptive echo canceller integrated thereinto;

(b) transmitting a series of ring-back tones along said transmission connection to said calling subscriber, indicating that an off-hook state does not yet exist in regard to said called subscriber;

(c) at said telephone exchange using a call control to cause said echo canceller to transmit a test signal interspersed with said ring-back tones, towards the calling subscriber, for initiating convergence of said echo canceller;

(d) using a return of said test signal along an echo path of said transmission connection to said echo canceller to converge said echo canceller before said called subscriber creates an off-hook state; and

(e) utilizing said echo canceller, as thereby converged, to suppress echo in transmission of said speech signal on said transmission connection.

5. The method of claim 4, wherein:

said test signal is a pulse.

6. The method of claim 4, wherein:

said calling subscriber is a subscriber of said telephone exchange and said transmission connection connects said called subscriber to said telephone exchange via an intervening telephone exchange.

7. The method of claim 4, wherein:

said test signal is an outgoing ringing tone.

8. The method of claim 4, wherein:

said test signal is transmitted along said echo path towards said calling subscriber immediately after a ring-back tone, for reducing likelihood that the test signal will be observed by the calling subscriber.