JPH02146825A - Echo canceler - Google Patents

Abstract

PURPOSE:To always obtain a sufficient echo canceling characteristic by using a prescribed filter and a signal limiter so as to provide a required distortion to a reception signal and applying echo canceling processing. CONSTITUTION:A reception signal from a reception signal input terminal 1 receives a waveform distortion approximated to the characteristic of an echo path 5 by a filter 8 and a signal limit device 9 limits a level of a signal in excess of an overload level of the path 5. Then the signal is supplied to a subtractor 7 via the echo path 5 and a transmission signal input terminal 3, and also fed to an echo path model 6, in which the signal comes to a pseudo echo approximated to the characteristic of the echo path and the result is fed to a subtractor 7. As a result, a transmission signal sufficient in echo canceling characteristic is outputted at all times from a transmission signal output terminal 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an echo canceller used in communication lines.

[Conventional technology]

In recent years, due to the rapid increase in long-distance lines, especially satellite communications, the presence of echoes occurring in communication lines has become a serious problem in terms of speech quality due to the large line delay. Conventionally, echo suppressors have been used to control echoes, but since they are based on switching operations, they have had problems such as interruptions at the beginning of speech and click noises.

The echo canceller developed to solve this problem has an internal adaptive filter (echo path model) that measures the characteristics from the receiving output to the human power of the speaker based on the call signal, and then creates an echo path model based on this measurement. A pseudo echo that approximates the echo signal is created by passing the received signal through this echo path model in accordance with the echo path characteristics, and the echo is canceled by subtracting it from the actual echo signal using a subtractor.

FIG. 2 is a block diagram of an example of a conventional echo canceller.

In FIG. 2, the received signal input from the received signal input terminal 1 is sent to the received signal output terminal 2 and simultaneously to the echo path model 6. The signal sent to the echo path 5 passes through the echo path 5 and is input as an echo to the transmission signal input terminal 3 of the echo canceller.

On the other hand, the received signal input to the echo path model 6 passes through the echo path model 6 having the same characteristics as the echo path 5, thereby generating a pseudo echo 3 that is the same as the echo input to the transmit signal input terminal 3.

This pseudo echo is subtracted by the subtracter 7 from the actual echo signal input from the human power transmitting terminal 3. Therefore, the echo is canceled in the output of the subtracter 7, and the signal is output from the transmit signal output terminal 4.

[Problem to be solved by the invention]

In the conventional echo canceller described above, when an excessive reception signal is input from the reception terminal 1 and there is a device with a small overload margin in the echo path, nonlinear distortion is generated in the echo path, and the internal characteristics of the echo path 5 and the echo canceller are affected. As a result, the subtracter 7 cannot cancel the echo sufficiently.

[Means to solve the problem]

The echo canceller of the present invention includes an echo path model that synthesizes and outputs a condensed echo that approximates the characteristics of an echo path from the output of a received voice signal to the input of a transmit signal, and a subtracter that subtracts and outputs the signal, a filter that applies waveform distortion approximating the characteristics of the echo path to the received signal input from the received signal terminal and outputs the resultant signal, and a signal limiter that controls the output level from the filter. It has

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In FIG. 1, a received signal from a received signal terminal 1 is input to a filter 8. As shown in FIG. The filter 8 applies waveform distortion approximating the echo path to the passed received signal and outputs it.

The signal limiter 9 limits the magnitude of the signal that may exceed the overload level of the echo path 5 among the waveform distortion generated by the filter 8, and prevents the waveform distortion generated in the echo path 5 from exceeding the overload level. The received signal thus obtained is also supplied to the echo path model 6.

The reception signal from the signal limiter 9 passes through the echo path 5 and is input as an echo to the transmission signal input terminal 3 of the echo canceller. On the other hand, the received signal input to the echo path model 6 is transmitted to the echo path model 6 which has the same characteristics as the echo path model 5.
, a pseudo echo identical to the echo input to the transmitting signal input terminal 3 is generated. This pseudo echo is subtracted by the subtracter 7 from the actual echo signal input from the human power transmitting terminal 3. Therefore, the output of the subtractor 7 is a signal in which the echo has been canceled out from the transmitting signal output terminal 4.

Note that in this embodiment, the filter circuit 8 and the signal limiter 9
Although the combination is shown as being used in one stage, using multiple stages can more reliably suppress the signal level within the overload range of the echo path.

In this way, the received signal that has passed through the filter 8 and the signal limiter 9 will not exceed the overload level of the echo path even if waveform distortion occurs in the echo path, and the echo path will always exhibit linear characteristics. Therefore, the amount of echo cancellation does not decrease, and sufficient echo cancellation characteristics can always be obtained.

〔Effect of the invention〕

As explained above, the present invention utilizes an echo path model consisting of an adaptive filter that generates a condensed echo that approximates the characteristics of the echo path from the output of the received signal to the input of the transmitted signal, and an echo path model that generates a simulated echo from the actual echo. The subtracter that subtracts the echo, the filter circuit connected to the receiver's power, and the signal limiting circuit have the advantage that sufficient echo cancellation characteristics can always be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an example of a conventional echo canceller. 1... Receiving signal input terminal, 2... Receiving signal output terminal, 3... Transmitting signal input terminal, 4... Transmitting signal output terminal, 5... Echo path, 6... Echo path model ,7
...Subtractor, 8...Filter, 9...Signal limiter.

Claims (1)

[Claims] an echo path model that synthesizes and outputs a condensed echo that approximates the characteristics of an echo path from the output of a received voice signal to the input of a transmitted voice signal; and a subtracter that subtracts the condensed echo from the inputted voice signal and outputs the result. and a filter that applies waveform distortion approximating the characteristics of the echo path to the reception signal input from the reception signal terminal and outputs the resultant signal, and a signal limiter that controls the output level from the filter. echo canceller.