Telephonic communications – Subscriber line or transmission line interface – Network interface device
Reexamination Certificate
1997-10-28
2001-07-24
Woo, Stella (Department: 2743)
Telephonic communications
Subscriber line or transmission line interface
Network interface device
C379S406010
Reexamination Certificate
active
06266408
ABSTRACT:
This application for an echo controlling apparatus and a control method using that apparatus is based on Korean Patent Application No. 1996/49340, which is incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an echo controlling apparatus for use in a video conferencing system. More particularly, the present invention relates to an echo controlling apparatus of a video conferencing system using a personal computer (PC) and a control method using the same.
2. Description of the Related Art
FIG. 1
is a block diagram illustrating a general video conferencing system.
In
FIG. 1
, an audio signal of a person in a conference room A taking part in a video conference, generated via a first microphone
10
, is transmitted to a second speaker
16
of a conference room B via a first echo controller
11
, a transceiver
14
, and a second echo controller
15
. The audio signal output from the second speaker
16
is provided to a second microphone
18
after being echoed by a wall
17
of the conference room B or being directly coupled to the second microphone
18
. If the echo controllers
11
and
15
do not operate to control echo, the audio signal output from the second speaker
16
is fed back to a first speaker
12
at the conference room A via the second microphone
18
and the transceiver
14
. The feedback audio signal output from the first speaker
12
is provided to the first microphone
10
after being echoed by a wall
13
of the conference room A or being directly coupled to the first microphone
10
. Thus, an echo phenomenon occurs in the conference room A, where the person who has spoken in the conference room A can hear his own voice after a time lag.
The function of the echo controllers will be described with reference to FIG.
2
.
Referring to
FIG. 2
, a far-end input signal Y which is an audio signal transmitted from the opposing conference room is output to the speaker
12
of the conference room A, and includes an echo signal e. The output from an adaptive filter
23
is an estimated echo signal ê. The echo signal e output from the speaker
12
is converted into an electrical signal via the microphone
10
, and then input to a subtractor
22
. Also, a voice signal of a person speaking in the conference room A to an audience in the remote conference room B, i.e., near-end input signal S
0
, is provided to the subtractor
22
via the microphone
10
.
If the amplitude of the echo signal e input to the subtractor
22
via the microphone
10
, which has been output from the speaker
12
, is the same as that of the estimated echo signal ê output via the adaptive filter
23
, the echo signal e and the estimated echo signal ê are offset, so that only the voice of the person speaking in the conference room, i.e., pure near-end input signal S
0
, is transmitted without any echoing phenomenon.
The estimated echo signal ê output from the adaptive filter
23
is expressed by the equation ê=h×Y, and an audio input signal S via the microphone
10
is expressed by the equation S=S
0
+e. In these equations, Y represents a far-end input signal, h represents a transfer characteristic (i.e., an adaptive coefficient) of the adaptive filter, S
0
represents a near-end input signal, e represents the echo signal fed back to the microphone
10
from the output of the speaker
12
.
An audio signal S
t
transmitted to the opposite conference room is expressed by the equation S
t
=S−ê=S
0
+e−ê. Echo error is defined as the difference between the estimated echo signal ê and the echo signal e. If the amplitude of the estimated echo signal ê is equal to that of the echo signal e input to the microphone
10
, the echo error becomes zero. That is, the echo signal e is not incorporated in the audio signal S
t
transmitted to the remote conference room B via a transmission line, so that the audio signal S
t
becomes equal to the near-end input signal S
0
.
During such signal processing, an adaptive filter coefficient h is continuously updated by the equation
h(n+1)=h(n)+&agr;×error(n)×Y,
where &agr; is a constant which is set depending on the system and is usually less than 1, and h(n+1) to be updated is calculated using h(n), the constant &agr;, the previous echo error (error(n)) and the far-end input signal Y.
If the initial adaptive filter coefficient h is equal to 0, the estimated echo signal ê becomes zero according to the equation ê=h×Y. As a result, the audio signal transmitted to the opposite conference room B become the sum of S
0
and e (S
t
=S
0
+e). That is, in the initial stage, an audio signal including the echo signal e is transmitted to the opposite conference room B. Then, after a predetermined lapse of time, i.e., when the adaptive filter coefficient is not equal to zero, the audio signal S
t
including less of the echo signal e is transmitted according to the equation S
t
=S
0
+e−ê.
Thus, in a video conferencing system adopting such an echo controlling apparatus, an adaptation process is required for a predetermined time since the initial adaptive filter coefficient is equal to zero, which is a characteristic of the echo controlling apparatus. That is, the echo controlling apparatus is operated by simply setting the initial adaptive filter coefficient to zero, without providing appropriate parameters in advance, which are useful to properly set the initial adaptive filter coefficient.
Therefore, the adaptive filter coefficient is set regardless of the circumstances of a video conferencing system in the conference room, so that the preferred echo control cannot be performed until the echo controlling apparatus has adapted.
SUMMARY OF THE INVENTION
To solve the above problem, it is an object of the present invention to provide an echo controlling apparatus and a control method using the same, for controlling echoing at the state when the initial adaptation has been achieved, by calculating an adaptive filter coefficient using parameters stored in advance according to the circumstances of a video conferencing system of a conference room.
According to an aspect of the object, there is provided an echo controlling apparatus in a video conferencing system which includes a memory for storing initial parameters matching the circumstance of a video conferencing system of a conference room. The apparatus has an echo controller for calculating an initial adaptive filter coefficient using the parameters stored in the memory, and for updating the adaptive filter coefficient using new parameters input during a conference, to remove an echo signal. The apparatus also includes a controller for reading the parameters stored in the memory to provide the echo controller with the read parameter, and for updating the initial parameters stored in the memory with the new parameters input to the echo controller.
Preferably, the parameters include values for a far-end input signal, a near-end input signal and an estimated echo signal.
According to another aspect of the object, an echo controlling method in a video conferencing system is provided which comprises the steps of:
(a) reading parameters from a memory which match the circumstances of the video conferencing system as to a particular conference room;
(b) calculating an initial adaptive filter coefficient using the read parameters to control echoing; and
(c) updating the initial adaptive filter coefficient with new parameters input during the conference to continuously control echoing.
Preferably, the echo controlling method further comprises the step of storing new parameters in the memory, input during the conference after a predetermined lapse of time from the start of the conference, to update the stored parameters.
REFERENCES:
patent: 4558187 (1985-12-01), Bill et al.
patent: 4972406 (1990-11-01), Dedic
patent: 5050160 (1991-09-01), Fuda
patent: 5153875 (1992-10-01), Talkatori
patent: 5410595 (1995-04-01), Park et al.
patent: 55
Samsung Electronics Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Woo Stella
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