JPH07226961A - Exchange having loudspeaking communication system and echo canceller - Google Patents

Abstract

PURPOSE:To provide the exchange having loudspeaking communication system and echo canceller in which the cost is reduced without use of the same number of echo cancellers as that of loudspeaking terminal equipments. CONSTITUTION:An echo cancel request is publicated to an exchange 24 by a terminal equipment 25 between the exchange 24 and plural terminal equipments 25, the exchange 24 cancels an echo signal resulting from a transmission signal from the terminal equipments 25 passing through an echo path and sends the signal whose echo signal is cancelled to the terminal equipments 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exchange system having a loudspeaker communication system and an echo canceller, and more particularly, to an echo signal which is a cause of howling and is an auditory obstacle in a two-wire to four-wire conversion system and a loudspeaker communication system. The present invention relates to a loudspeaker communication system using an echo canceller that cancels or suppresses noise, and a switchboard having the echo canceller.

Unlike the conventional telephone call system, the above-mentioned loudspeaking call system does not require a handset to be held in the hand, so that it is possible to make a call while working or to realize a natural face-to-face call. Widely used in teleconferences, videophones, and public telephones.

[0003]

2. Description of the Related Art FIG. 6 shows a conventional system configuration. The system shown in FIG.
The speaker 2, the amplifiers 5 and 6, the exchange 12A and the communication network 9, the exchange 12B on the receiving side 11, the amplifiers 7 and 8, the speaker 4, and the microphone 3.

[0004] The transmitted voice produced by the transmitter 10 from the transmitting microphone 1 is amplified by a transmitted signal amplifier 5,
The data is transmitted to the receiving side via the exchange 12A, the transmission line 9, and the exchange 12B. The reception signal amplifier 8 amplifies the received signal and inputs it to the reception speaker 4 for reproduction.

When the transmitter 10 makes a call connection request to the receiver 11, the exchange 12A is connected to the receiver 11 from the receiver side exchange 12B via the communication network 9. The talker is
A voice signal is sent to the exchange 12A via the microphone 1. The exchange 12A inputs a voice signal to the exchange 12B via the communication network 9. The exchange 12B is the receiver 11
A voice signal from the talker is transmitted to. Here, when the listener 11 receives the voice signal from the speaker 10, the voice from the speaker 10 echoes through the echo path 13b and is sent to the speaker 10 together with the voice of the listener 11. . Also,
Even if the listener 11 does not speak, the voice of the sender 10 reverberates through the echo path 13b and is input to the microphone 3 on the listener 11 side. This echo signal is passed through the amplifier 7
Through the exchange 12B, the communication network 9, the exchange 12A, and the amplifier 6, the speaker 2 on the side of the talker 10 is used to transmit the talker 10
Hears the voice uttered by the speaker as echo.

As described above, in the voice call system, there is a problem in that the voice transmitted from the transmitting side to the receiving side is re-input from the receiving side microphone 3 and reverberates to the transmitting side. For the speaker 10, this reverberation phenomenon is called an acoustic echo or the like because the voice generated by the speaker 10 is reproduced from the speaker 2, and causes adverse effects such as a call disturbance and discomfort. Furthermore, the sound reproduced from the speaker 2 is the microphone 1
Is received by and forms a closed loop of the signal. When the loop gain is larger than 1, the howling phenomenon occurs and the call becomes impossible.

An echo canceller is used to solve the above-mentioned problems of the voice communication system.

FIG. 7 shows the structure of a conventional echo canceller. The echo canceller 21 shown in FIG.
The echo path estimation circuit 23 and the subtractor 24 are included. The reception signal x (n) is input to the speaker 4, the echo signal y (n) is input to the microphone 3 from the speaker 4, and the echo path transfer characteristic (impulse response) between the speaker 4 and the microphone 3 is h (n). ).

The echo path estimation circuit 23 of the echo canceller 21 estimates the impulse response of the echo path (between the speaker 4 and the microphone 3), and the estimated value h ^ (n) is used as the pseudo echo path 2
Transfer to 2. Next, in the pseudo echo path 22, the estimated value h ^ (n) output from the echo path estimation circuit 23 and the received signal x
The convolution operation with (n) is executed and the pseudo echo signal y ^
(N) is output to the subtractor 24. The subtractor 24 subtracts y ^ (n) from the output signal z (n) of the microphone 3. In the echo path estimation circuit 23, if the echo path impulse response is well estimated, the echo signal y (n) and the pseudo echo signal y ^ (n) are substantially equal.
As a result of this subtraction, if the error signal e (n) is “0”,
The echo signal y included in the output z (n) of the microphone 3.
(N) has been deleted. Here, the pseudo echo path 22 is
It is necessary to follow the temporal change of the echo path characteristic h (n).
Therefore, the echo path estimation circuit 23 uses an adaptive algorithm to estimate the echo path impulse response. The adaptive algorithm is to use the received signal x (n) and the error signal e (n) so that the power of the error signal e (n) is minimized.
This is an algorithm that determines the estimated value h ^ (n) of the impulse response, and the LMS method, learning identification method, ES method, etc. are known.

FIG. 8 shows a case where a conventional loudspeaker equipped with an echo canceller is connected to a local exchange. The loudspeaker terminal device 22 installed in a certain premises 23 shown in the figure has the echo canceller 21 shown in FIG. 7. In the echo canceller 21 shown in FIG. 7, when the terminal device 22 receives the reception signal via the exchange 12, the reception signal x (n) changes the reception signal x (n).
The audio signal is input to the speaker 4 via 1 and reproduced. This audio signal is input to the microphone 3 via the echo path. The echo estimation circuit 23 estimates the impulse response h (n) of the echo path, and inputs the estimated value h ^ (n) to the pseudo echo path 22. The pseudo echo path 22 receives the received signal x
(N) and the estimated value h ^ (n), the pseudo echo signal y ^
(N) is output to the subtractor 24. The subtractor 24 uses the output signal z (n) from the microphone 3 to generate the pseudo echo signal y ^.
Subtract (n). Here, if the impulse response of the echo path is performed correctly, the echo signal y (n) and the pseudo echo signal y ^ (n) are substantially equal to each other, and the echo signal y (n) is output from the output signal z (n) from the microphone 3. (N) is deleted. Therefore, the reception signal input to the loudspeaker terminal device 22 is reproduced by the speaker 4, and even if the reception signal is echoed to the microphone 3, the echo cancellation device 21 is provided so that the reception signal is transmitted from the terminal device 22 through the exchange 12B. From the speaker 2 of the terminal device, the echo sound is reproduced without being included.

[0011]

However, in the loudspeaker terminal device having the above-mentioned conventional echo canceller, although all the connected terminals are rarely used at the same time,
Since a costly echo canceller is provided in each of the loudspeaker terminal devices, the cost will increase when a system including an exchange is considered.

The present invention has been made in view of the above points, solves the above-mentioned conventional problems, and can reduce costs without degrading the communication quality with a small number of echo cancellers. Another object of the present invention is to provide an exchange having an echo canceller.

A further object of the present invention is to provide an echo canceller on the exchange side without providing the echo canceller on the loudspeaker terminal device, thereby enabling echo canceling without using many echo cancellers. It is an object of the present invention to provide a switchboard having a special public address communication system and an echo canceller.

[0014]

FIG. 1 is a block diagram showing the principle of the present invention.

According to the present invention, the exchange 24 and the plurality of terminal devices 2 are provided.
5, the transmission side terminal device 25 issues a call connection request to the exchange 24, the exchange 24 makes a call connection with the reception side terminal device, and the signal sent from the transmission side terminal device 25 is reflected by the reception side terminal device. The echo signal after passing through the path is erased by the exchange, and the signal from which the echo signal is erased is transmitted to the terminal device 25.

Further, according to the present invention, when a call connection request is issued from the terminal device on the transmitting side to the exchange, a voice amplification request is issued at the same time, and when the voice amplification request is issued, the exchange 24
Eliminate the echo signal.

Further, the exchange 24 of the present invention has at least one echo canceller 21 for canceling the echo signal passing through the echo path of the receiving side terminal device 25.

Further, in the exchange of the present invention, when the call connection request is issued from the transmission side terminal device, the echo canceller 21 of the exchange receives the signal via the echo path of the reception side terminal device.

Further, the echo device installed in the exchange of the present invention comprises a sending signal input to the echo path and a pseudo echo path generated from the echo signal after the sending signal passes through the echo path.
Eliminating means for eliminating the echo signal by subtracting the pseudo echo signal obtained by inputting the transmission signal into the pseudo echo path from the echo signal.

[0020]

In the present invention, the echo canceller is provided inside the exchange,
When the caller is connected to the exchange through the terminal device and the caller desires a loud voice call, the echo canceller provided on the exchange side erases the echo on the echo path of the loud voice terminal. In this way, by eliminating the echo signal on the exchange side, it is not necessary to provide an echo elimination device for each loudspeaker terminal device, and at least one echo elimination device may be prepared for the exchange.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows the system configuration of an embodiment of the present invention. In the figure, the same components as those in FIG. 8 are designated by the same reference numerals. Loudspeaker terminal 25 installed in a certain premises 28
Is a speaker 4, a microphone 3 and a loudness request button 2
It is composed of 6. The exchange 12 connected to the plurality of terminals 25 has a plurality of echo cancellers 21. The echo canceller 21 has the same structure as that shown in FIG. 7.

FIG. 3 shows an echo canceller installed in an exchange according to an embodiment of the present invention. As shown in the figure, a plurality of echo cancellers 21 are installed in the exchange 12. The echo canceller 21 shown in the figure receives the echo signal and the reception signal directly from the loudspeaker terminal device 25. In addition to the echo canceller 21, the exchange 12 also has a function of accepting a call connection request, a connection, and the like, and a function of performing call connection control by time division.

Below, the exchange 12 and the loudspeaker terminal device 2 will be described.
The operation between 5 will be described. FIG. 5 is a sequence chart showing the operation of the embodiment of the present invention. In the sequence chart shown in the figure, the exchange 1 is connected between the terminal device A and the terminal device B.
The case where one 2 is interposed will be described. In the figure, a communication path originally exists between the terminal device A and the exchange 12, but it is omitted for simplicity.

When the terminal device A makes a call connection request to the exchange device 12 (step 101), the exchange device 12 detects and accepts a calling signal (step 102), and sends a dial tone to the terminal device A as a response. (Step 103). When the terminal device A sends the destination telephone number (terminal identification number) as a selection signal to the exchange 12 (step 104), the exchange 12 receives the selection signal (step 10).
5) Send a ringing tone to the terminal device A (step 10
6), a call signal is transmitted to the terminal device B (step 107). The terminal device B transmits a response to the exchange 12 (step 108), and when the exchange 12 detects the response signal from the terminal device B (step 109), the terminal device A
And the call of the terminal device B are connected (step 110).

The terminal device A pushes the loud sound button 26 on the housing (step 111) and makes a loud sound request to the exchange 12 (step 112). When the exchange 12 receives the voice request signal, it connects to the echo canceller 21 (step 113). When the user of the terminal device A speaks (step 114), the transmitted signal x (n) is input to the echo canceller 21 of the exchange 12 (step 115). At this time,
Since there is no echo signal because it does not pass through the microphone 3 on the receiving side, the transmission signal x (n) is transmitted to the terminal device B (step 116).

The terminal device B receives the transmission signal x (n) from the terminal device A through the speaker 4 (step 11).
7). At this time, in the terminal device B, the loudspeaker button 26 has already been
It is assumed that is pressed. When the user of the terminal device B transmits from the microphone 3, the transmission signal s (n)
Occurs (step 118). At this time, the speaker 4
From the microphone 3 to the echo path, the echo signal y
(N) occurs. Therefore, the signal z (n) output from the microphone 3 is z (n) = y (n) + s (n). The signal z (n) is sent to the exchange 12 (step 119).

The exchange 12 receives the signal z from the terminal device B.
When (n) is received, the echo path estimation circuit 23 estimates the impulse response of the echo path and outputs the estimated value h ^ (n) to the pseudo echo path 22. The pseudo echo path 22 outputs a pseudo echo signal y ^ (n) to the subtractor 24 by performing a convolution operation of the received signal x (n) and the estimated value h ^ (n). The subtractor 24 subtracts the pseudo echo signal y ^ (n) from the input signal z (n). At this time, if the estimation by the echo estimation circuit 23 is performed correctly, the echo signal y (n) and the pseudo echo signal y ^ (n) are substantially equal. If it is not performed correctly, the error e (n) becomes large. If the error signal e (n) is small, the echo signal y
It is assumed that (n) has been erased (step 120).

In this way, the signal z (n) = s (n) + e (n) from which the echo signal y (n) has been eliminated is transmitted to the terminal device A. As a result, in the terminal device A, the echo signal due to the own transmission signal is erased.

Further, the loudness request button 26 is set to the terminal device 25.
The operation when installed at is shown below. FIG. 5 shows the relationship between the public address terminal and the exchange according to one embodiment of the present invention. Same figure (A)
Shows the state before the push of the loudspeaker button, and FIG. 7B shows the state after the push of the loudspeaker button. In the same figure (A), before pressing the loudspeaker button, the echo canceller 21 is directly connected to the exchange control unit 121 without being connected. In addition, the same figure (B)
In FIG. 6, after the voice boost button is pressed, the switch 122 connects the communication path between the exchange control unit 121 and the speaker 4 and the microphone 3 of the voice boost terminal 25 to the echo canceller 21.

Further, in the above embodiment, after the call request is made from the terminal device 25 to the exchange 12, the voice request button 2 is pressed.
6 is pressed and the output signal z (n) from the terminal device 22 is input to the echo canceller 21 at the time when the loudspeaker request signal is input to the exchange 12, but the present invention is not limited to this example, and for example, The loudness request button 26 may be removed from the terminal device 22, and the output signal z (n) may be input to the echo canceller 21 at the time when a call request is issued from the terminal device 22.

In the present invention, the echo canceller 21 is installed in the exchange 1.
It is provided in 2. Since the exchange 12 is designed by utilizing the statistical properties of calls, it is not necessary to prepare the same number of facilities as the number of terminals. For example, a time division exchange of the SPC type (stored program type) exchange 12 can handle a plurality of calls at the same time by time division multiplexing control even if traffic is concentrated. At the same time, the echo cancellers 21 may be installed in the exchange 12 in the number corresponding to the number of multiplexes for accepting call connection requests.

In the present invention, the type of exchange to be used is not limited, and various types of exchanges can be used.

Although the switch 122 is provided inside the exchange in the above embodiment, it may be externally attached to the exchange 12.

[0035]

As described above, according to the present invention, a costly echo canceller is not installed in all terminal devices,
By setting a smaller number of echo cancellers than the number of terminal devices in the exchange, it is possible to significantly reduce costs.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a system configuration diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing an echo canceller installed in an exchange according to an embodiment of the present invention.

FIG. 4 is a sequence chart showing the operation of the embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between the voice-over terminal and the exchange according to the embodiment of the present invention.

FIG. 6 is a conventional system configuration diagram.

FIG. 7 is a configuration diagram of a conventional echo device.

FIG. 8 is a diagram showing an example in which an echo canceller is provided in a conventional terminal device.

[Explanation of symbols]

 1,3 Microphones 2,4 Speakers 5,6,7,8 Amplifiers 9 Communication networks 10 Talkers 11 Listeners 12 Exchangers 13 Echo paths 21 Echo cancelers 22 Pseudo echo paths 23 Estimating circuits 24 Subtractors 25 Terminal devices 26 Loudspeakers Hope button 28 Campus 121 Exchange controller 122 Switch

Claims (5)

[Claims] 1. A step of issuing a call connection request from a transmission side terminal device to the exchange, between the exchange and a plurality of terminal devices, and the exchange performing call connection between the transmission side terminal device and the reception side terminal device. A step of erasing the echo signal after the transmission signal from the transmission side terminal device has passed through the echo path of the reception side terminal device by the exchange, and transmitting the signal from which the echo signal has been deleted to the transmission side terminal device A loudspeaker communication system consisting of steps. 2. The transmission side terminal device issues a call connection request to the exchange at the same time as a voice amplification request, and when the voice amplification request is issued, the exchange erases the echo signal. The loudspeaker communication system according to claim 1. 3. An exchange having an echo canceller, comprising at least one echo canceller for canceling an echo signal passing through an echo path of the receiving side terminal device. 4. The switching system inputs a signal via the echo path of the receiving side terminal device to the echo canceling device of the switching system at the time when a call connection request is issued from the transmitting side terminal device. An exchange having the echo canceller according to 3. 5. The reverberation device inputs a transmission signal to the echo path, a pseudo echo path generated from the echo signal after the transmission signal passes through the echo path, and the transmission signal to the pseudo echo path. 4. An exchange having an echo canceller according to claim 3, further comprising: an erasing means for erasing the echo signal by subtracting the pseudo echo signal obtained by the above method from the echo signal.