Telephonic communications – Subscriber line or transmission line interface – Network interface device
Reexamination Certificate
1998-03-02
2001-02-06
Hudspeth, David R. (Department: 2741)
Telephonic communications
Subscriber line or transmission line interface
Network interface device
C370S290000
Reexamination Certificate
active
06185301
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an echo canceler for eliminating the echoes generated at a proximal end of a transmission line of a telecommunication system through which speakers at the opposite ends of the line can talk to each other.
2. Description of the Related Art
In a prior art echo canceler, a single adaptive filter circuit and a single subtractor are provided. That is, in this adaptive filter circuit, tap coefficients are calculated in accordance with an error signal and a received signal, and a pseudo echo signal is generated in accordance with the tap coefficients and the received signal. Also, the subtracter subtracts the pseudo echo signal from a transmitting signal, thus cancelling echoes in the transmitting signal. In the prior art echo canceler, however, when the background noise is large at the proximal end of a line or when it is impossible to determine whether the line is for a 2-wire system or a 4-wire system, the characteristics of detecting double-talk are degraded, and the characteristics of tap coefficients are not stable. This will be explained later in detail.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an echo canceler that can stably provide excellent characteristics of tap coefficients without degrading the characteristics of detecting double-talk, even when the background noise is large at the proximal end of the line or when it is impossible to determine if the line is for a 2-wire system or a 4-wire system.
According to the present invention, in an echo canceler, a first adaptive filter circuit calculates first tap coefficients using a first convergence coefficient, and generates a first pseudo echo signal, and a first subtracter subtracts the first pseudo echo signal from a transmitting signal to generate a first error signal. A second adaptive filter circuit calculates second tap coefficients using a second convergence coefficient, and generates a second pseudo echo signal, and a second subtracter subtracts the second pseudo echo signal from the transmitting signal to generate a second error signal. A control circuit selects one set of the first tap coefficients and the second tap coefficients in accordance with a received signal, the transmitting signal, and the first and second error signals. A third adaptive filter circuit generates a third pseudo echo signal in accordance with the set of tap coefficients selected by the control circuit and the received signal, and a third subtracter subtracts the third pseudo echo signal from the transmitting signal to generate a third error signal serving as an actual transmitting signal.
In this echo canceler, the first and second filter circuits are constantly operating for tap estimation regardless of the operation of the control circuit.
REFERENCES:
patent: 4554417 (1985-11-01), Boyer
patent: 5263020 (1993-11-01), Yatsuzuka et al.
patent: 5313498 (1994-05-01), Sano
patent: 5463618 (1995-10-01), Furukawa et al.
patent: 5535149 (1996-07-01), Mori et al.
patent: 5610909 (1997-03-01), Shaw
patent: 5644596 (1997-07-01), Sih
patent: 5748725 (1998-05-01), Kubo
patent: 5828589 (1998-10-01), Degenhardt
patent: 5859914 (1999-01-01), Ono et al.
patent: 5867486 (1999-02-01), Sugiyama
patent: 5937060 (1999-08-01), Oh
patent: 5960077 (1999-09-01), Ishii et al.
patent: 5978473 (1999-11-01), Rasmusson
patent: 5999828 (1999-12-01), Sih et al.
patent: 6009083 (1999-12-01), Flanagan et al.
patent: 195 06 324 (1995-10-01), None
patent: 0 508 847 (1992-10-01), None
Patent Abstracts of Japan, “Control System For Voice Switch Used Jointly With Echo Canceler”, 0534210 (Dec. 14, 1993), Abstract of Igai Kazunori, 07170337, (Jul. 4, 1995).
Foley & Lardner
Hudspeth David R.
Lerner Martin
NEC Corporation
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