JPH0695774B2 - 2-wire bidirectional automatic gain control system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a two-wire bidirectional automatic gain control system in a two-wire bidirectional gain control device for compensating for speech loss between subscribers.

As a part of diversified telephone exchange services, services that automatically transfer incoming calls are becoming popular.

FIG. 3 is a diagram showing an example of an automatic switching network to which the present invention is applied.

In FIG. 3, when the subscriber 2 accommodated in the calling station 1 makes a call to the subscriber 4 accommodated in the receiving station 3, the subscriber 4 transfers the incoming call to a transfer destination by a predetermined procedure in advance. If you have registered for automatic transfer to the subscriber 6 accommodated in the station 5,
The outgoing call of the subscriber 2 is connected to the subscriber 6 via the transfer device 7 provided in the receiving station 3 and the transfer destination station 5.

In such a case, the call loss between the subscribers 2 and 6 is greater than the call loss between the subscribers 2 and 4 or the call loss between the subscribers 4 and 6 and the call loss between the called station 3 and the transfer destination station 5. Or, the call loss between the originating station 1 and the terminating station 3 is additionally added, and the automatic call switching network may exceed the prescribed call loss guaranteed for the subscriber interconnection.

In order to compensate for the call loss above the specified value, the transfer device 7 is provided with a two-wire bidirectional gain control device. A two-wire bidirectional gain control device of this type is required to promptly and accurately compensate for a required call loss even when various subscribers are connected to each other.

[Conventional technology]

FIG. 4 is a diagram showing an example of a conventional two-wire gain control device.

The two-wire gain control device shown in FIG. 4 includes two-wire to four-wire conversion circuits 8 and 9, level adjusting amplifiers 10, 11, 12 and 13, code circuits 14 and 15, and decoding circuits 16 and 17.
, Variable gain circuits 18 and 19, a control circuit 20, and echo cancellers 21 and 22.

The voice transmitted from the subscriber 2 and transmitted to the two-wire / four-wire conversion circuit 8 is amplified by the variable gain circuit 18, transmitted to the subscriber 6 via the two-wire / four-wire conversion circuit 9, and similarly the subscriber. The voice transmitted from 6 to the two-wire to four-wire conversion circuit 9 is amplified by the variable gain circuit 19 and transmitted to the subscriber 2 via the two-wire to four-wire conversion circuit 8, so that the subscribers 2 and 6
The call loss during the period is compensated to the above specified value or less.

If the impedance of the balanced network provided in the two-wire to four-wire conversion circuits 8 and 9 is completely matched with the impedance of the two-wire line leading to the subscribers 2 and 6, the gain variable circuit 18 The output voice is not transmitted to the variable gain circuit 19, and the voice output from the variable gain circuit 19 is not transmitted to the variable gain circuit 18.

However, 2 which is actually connected to the two-wire / four-wire conversion circuits 8 and 9
Since the line circuit impedance changes variously depending on the connected subscriber, impedance matching in the two-wire to four-wire conversion circuits 8 and 9 becomes incomplete. As a result, part of the sound (echo) output from the variable gain circuit 18 is input to the variable gain circuit 19 via the two-wire / four-wire conversion circuit 9, and part of the sound output from the variable gain circuit 19 ( Echo) is input to the variable gain circuit 18 via the two-wire to four-wire conversion circuit 8 and the gains of the variable gain circuits 18 and 19 are changed to the two-wire to four-wire conversion circuits 8 and 9.
If the reverberation attenuation amount is exceeded, the two-wire bidirectional gain control device may be in an oscillating state.

In order to prevent such a state, echo cancellers 21 and 22 composed of response type FIR filters are inserted. The echo canceller 21 transmits the sound output from the variable gain circuit 18 to the two-wire / four-wire conversion circuit 9 via the decoding circuit 16 and the level adjusting amplifier 11, and after performing a predetermined calculation on the sound, Subtraction is performed from the echo sound returned from the two-wire / four-wire conversion circuit 9 via the level adjusting amplifier 12 and the encoding circuit 15, and the coefficient of the FIR filter is corrected so that the subtraction result (that is, the total elimination amount) becomes small. Similarly, the echo canceller 22 also performs arithmetic processing on the sound output from the variable gain circuit 19 and corrects the echo sound returned from the two-wire / four-wire conversion circuit 8 so as to be sufficiently erased.

Therefore, in the two-wire bidirectional gain control device, the subscriber 2
Immediately after the connection between and is set, the variable gain circuits 18 and 19 are set to low gain, and the echo cancellers 21 and 22 are set.
The gain of the variable gain circuits 18 and 19 needs to be increased to a required value after the correction is performed so that the echo sound is sufficiently eliminated.

[Problems to be solved by the invention]

As is clear from the above description, in the conventional two-wire gain control device, after the connection between the subscribers 2 and 6 is set, the echo cancellers 21 and 22 are activated based on the voice transmitted by the subscriber 2 or 6. Variable gain circuit 18 until corrected
There was a risk that the call loss could not be compensated adequately by and 19.

[Means for solving problems]

The present invention solves the above problems by taking the following means.

That is, in the present invention, signal applying means for applying a training signal to the echo canceling circuit is provided.

Further, after a lapse of a predetermined time from the application of the training signal by the signal applying means, a total erasing amount of the echo canceling circuit, that is, a degree of erasing of the echo canceling circuit to the training signal applied by the echo canceling circuit from the signal applying means To provide.

As long as the erased amount is less than or equal to the preset specified value as a result of the measurement, the application of the training signal and the measurement of the erased amount are repeated, and when the erased amount exceeds the specified value, the application of the training signal is stopped and the gain Set the gain of the variable circuit to the initial value.

[Action]

That is, according to the present invention, the echo canceling circuit is corrected by the training signal before the call is started after the call request via the two-wire type gain control device is generated, and the correction is completed. After the confirmation, the gain of the variable gain circuit is initialized to a predetermined value so that the call via the two-wire bidirectional gain control device can be started. If the initial setting value of gain is set to a value obtained by subtracting a predetermined margin from the average value of call loss to be compensated, it becomes possible to sufficiently compensate for the call loss from the beginning of the call, and it is still a two-line four-line Reverberation due to impedance imbalance of the conversion circuit is also prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a two-wire type gain control device according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of an echo canceling process in FIG. The same reference numerals denote the same objects throughout the drawings. The target automatic exchange network is as shown in FIG.

In FIG. 1, test signal generating circuits 23 and 24 are provided as signal applying means, and total erase amount measuring circuits 25 and 26 are provided as measuring means. Further control circuit 2
0'has the function shown in FIG.

In FIG. 1 to FIG. 3, the subscriber 2 who has called the subscriber 4 and the subscriber 6 who is the transfer destination are connected to each other via a two-wire gain control device provided in the transfer device 7. When done,
The control circuit 20 'causes the test signal generating circuits 23 and 24 to generate a training signal, which is applied to the echo canceller 21 or 22 via the changeover switch 27 or 28 in the restored state. The echo cancellers 21 and 22 are test signal generation circuits.
Based on the training signal applied from 23 or 24,
Echo cancellation processing is performed in the same process as in FIG. 4 (step S1).

On the other hand, in the total erasure amount measurement circuit 25, the echo canceller 21 is applied from the test signal generation circuit 23, the training signal transmitted to the decoding circuit 16 thereof, and the echo canceller 21 returned from the two-wire / four-wire conversion circuit 9 are transmitted. A predetermined erasing process is applied to the training signal and the erasing result transmitted to the variable gain circuit 19 is compared, and the total erasing amount M obtained as a result of the comparison is transmitted to the control circuit 20 '. Similarly, the total erasure amount measuring circuit 26 also has a total erasure amount M of the training signal for the echo canceller 22.
To the control circuit 20 '(step S2).

The control circuit 20 'compares the total erase amount M transmitted from the total erase amount measuring circuits 25 and 26 with a predetermined prescribed value R after a predetermined time (for example, several hundreds of milliseconds), and the condition M ≧ R
If is not established, the training signal is continuously applied from the test signal generating circuits 23 and 24, and steps S1 and S2 are repeated (step S3). If the condition M ≧ R is satisfied as a result of the comparison, the control circuit 20 'causes the test signal generating circuits 23 and 24 to operate.
Stop the generation of the training signal, and change the gain circuit 18
After setting the initial value of gain Gi to 19 and 19, the changeover switch
27 and 28 are operated to set the communication path between the subscribers 2 and 6 (step S4). The initial value of gain Gi is
A value obtained by subtracting a predetermined margin from the average value of the call loss to be compensated by the two-wire type gain control device when the fluctuation conditions of the two-wire type circuit connected to the two-wire to four-wire conversion circuits 8 and 9 are considered. Set to put.

When the call path is set up, the subscribers 2 and 6 start the call. The control circuit 20 'corrects the gains of the variable gain circuits 18 and 19 from the initial value Gi based on the voices transmitted from the subscribers 2 and 6.

As is clear from the above description, according to the present embodiment, the two-wire bidirectional gain control device in the transfer device 7 immediately receives the echo canceller by the training signal when the connection between the subscribers 2 and 6 is set. After correcting 21 and 22 in a short time, the gain of variable gain circuits 18 and 19 is set to the initial value Gi to set the speech path, so that sufficient speech loss compensation is supplied from the beginning to subscribers 2 and 6. It becomes possible to do.

It is to be noted that FIGS. 1 to 3 are merely examples of the present invention until now, and the test signal generating circuits 23 and 24 are not limited to those which generate the training signal, but generate, for example, a voice. Many other modifications can be considered, but the effect of the present invention does not change in any case. Further, the configuration of the two-wire type bidirectional gain control device is not limited to that shown in the figure, and many other modifications may be considered, but in any case, the effect of the present invention does not change. Further, it goes without saying that the automatic conversion network which is the subject of the present invention is not limited to that shown in the figure.

〔The invention's effect〕

As described above, according to the present invention, in the two-wire bidirectional gain control device, the echo canceller circuit is trained by the training signal before the call is started after the call request via the two-wire bidirectional gain control device is generated. Is corrected in a short time, and after confirming that the correction is completed, the gain of the variable gain circuit is initialized to a predetermined value, and a call via the two-wire bidirectional gain control device can be started. If you set the initial setting value of gain to the value obtained by subtracting the margin from the average value of call loss to be compensated,
From the beginning of the call, it is possible to fully compensate for the call loss,
However, the reverberation caused by the impedance imbalance of the two-wire / four-wire conversion circuit is also prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a two-wire type gain control device according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of an echo canceling process in FIG. 1, and FIG. 3 is an automatic telephone as an object of the present invention. FIG. 4 is a diagram showing an example of a network, and FIG. 4 is a diagram showing an example of a conventional two-wire type gain control device. In the figure, 1 is an originating station, 2, 4 and 6 are subscribers, 3
Is a receiving station, 5 is a transfer destination station, 7 is a transfer device, 8 and 9 are two-wire / four-wire conversion circuits, 10, 11, 12 and 13 are level adjusting amplifiers, 14 and 15 are sign circuits, and 16 and 17 are Decoding circuit, 18 and 19 variable gain circuit, 20 and 20 'control circuit, 21 and 22 echo canceller, 23 and 24 test signal generating circuit, 25 and 26 total erasure amount measuring circuit, and 27 and 28 switch Switches, S1 to S5, indicate steps.

Front Page Continuation (72) Inventor Shigeyuki Umi 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa, Fujitsu Limited Inventor Kiyohisa Wakabayashi 3-9-11 Midoricho, Musashino-shi, Tokyo Inside the Nippon Telegraph and Telephone Public Corporation Musashino Electric Communication Laboratory (72) Inventor Hitoshi Fuda 5-33-1, Shiba, Minato-ku, Tokyo Inside NEC Corporation

Claims (1)

[Claims] 1. A variable gain circuit and an echo canceller circuit are provided,
In a two-wire type bidirectional gain control device for connecting subscribers via an automatic switching network, a signal applying means for applying a training signal to the echo canceling circuit, and a predetermined time after application of the training signal. Measuring means for measuring the amount of cancellation of the echo canceling circuit is provided, and after the call request via the two-wire bidirectional gain control device is generated, the training signal is started to be applied from the signal applying means, When the measurement result of the measuring means exceeds a predetermined value, the application of the training signal is stopped, and the gain of the gain variable circuit is set to a predetermined initial value. A two-wire bidirectional automatic gain control method, which enables to start a call via a gain control device.