JPH02146826A - Echo canceler - Google Patents

Abstract

PURPOSE:To always obtain a sufficient echo canceling characteristic by interrupting the supply of an echo path characteristic to an echo path model when a reception signal level is a reference value or over. CONSTITUTION:A reception signal is fed to a subtractor 7 via an echo path 5. A pseudo echo outputted from an echo path model 6 is outputted to the subtractor 7 in response to the echo path characteristic from an echo path characteristic measuring circuit 8 and a transmission signal from which an echo is canceled is outputted from a transmission signal output terminal 4. On the other hand, a reception signal from an input terminal 1 is inputted also to a reception signal level measuring circuit 9, and when the level reaches a reference value or over, a control circuit 11 is controlled by a decided output of a deciding circuit 10, a disturbed characteristic outputted from the circuit 8 is interrupted and not supplied to the model 6. As a result, a sufficient echo canceling characteristic is always obtained.

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, a received signal inputted from a received signal input terminal 1 is sent to a received signal output terminal 2 and simultaneously to an echo path model 6 and an echo path characteristic measuring circuit 8. The signals sent to the echo paths pass through the echo paths and are converted into echoes and input to the transmission signal input terminal 3 of the echo canceller.

The echo path characteristic measuring circuit 8 measures the characteristics of the echo path from the output of the received signal to the input of the transmitted signal and outputs it to the echo path model 6.

The echo path model 6 generates a pseudo echo having characteristics similar to an echo busular by inputting the characteristics of the echo path from the input reception signal.

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 canceller. The echo canceller assumes that the echo path characteristic is a linear system and has an internal linear filter to cancel the echo. Therefore, when nonlinear distortion occurs, the echo path behaves as if noise were input to the echo path, which disrupts the operation of the echo path characteristic measurement circuit. Satisfactory echo path characteristics cannot be measured. As a result, the characteristics of the echo path model are disturbed, making it impossible to sufficiently cancel the echo.

[Means to solve the problem]

The echo canceller of the present invention includes: an echo path characteristic measuring circuit that measures from the output of a received signal to the input of a transmitted signal and outputs an echo path characteristic; an echo path model that inputs the echo path characteristic and generates a pseudo echo; and the transmitted signal. and a subtracter that subtracts the pseudo echo from the subtracter and outputs the result, the echo path characteristic being input to the echo path model is supplied when the received signal level exceeds a set reference value. It has a control means for shutting off.

〔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.

The received signal from the received signal input terminal 1 is input to an echo path model 6, an echo path characteristic measuring circuit 8, and a received signal level measuring circuit 9.

The echo path characteristic measuring circuit 8 measures and outputs the characteristics of the echo path from the received signal output to the transmitted signal input.

The received signal level measuring circuit 9 constantly measures the level of the received signal and outputs it to the determination circuit 10. The determination circuit 10 compares the output from the reception signal level measuring circuit 9 with a predetermined threshold level (a value above this threshold level that may cause overload distortion in the echo path). When the received signal level is input to the echo path and no waveform distortion occurs in the echo path, it is determined whether there is a possibility of exceeding the overload level of the echo path. If this determination circuit determines that there is a possibility of causing overload distortion when the received signal causes waveform distortion in the echo path, it outputs a signal to the control circuit 11.

When the control circuit 11 receives the signal from the determination circuit 10, it stops supplying the characteristic data from the echo path characteristic measuring circuit 8, controls the echo path model 6 to stop correcting the generated pseudo echo, and controls the echo path By setting the model to the value of the echo path model before overload distortion occurs,
Eliminates the effects of disturbances after overload distortion occurs.

On the other hand, the received signal input to the echo path model 6 is:I
- Near - By passing through an echo path model 6 having the same characteristics as the HAS 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 subtracter 7 is a signal in which the echo has been canceled out from the transmitting signal output terminal 4.

In this way, when there is a possibility of exceeding the overload level of the echo bus when the received signal level is input to the echo path and causes waveform distortion in the echo bus, modification of the echo bus model is stopped, thereby preventing disturbance of the echo bus model. Even if an excessive signal is input, the echo can be sufficiently canceled.

〔Effect of the invention〕

As explained above, the present invention utilizes an echo bus model consisting of an adaptive filter that generates a pseudo echo with the same characteristics as the echo bus from the output of the received signal to the input of the transmitted signal, and an echo bus model that generates a pseudo echo from the actual echo. The effect is that sufficient echo cancellation characteristics can always be obtained by the subtracter, the filter circuit connected to the receiver's power, and the signal limiting circuit.

3... Sending signal input terminal, 4... Sending signal output terminal, 5... Echo bus, 6... Echo bus model, 7... Subtractor, 8... Echo bus characteristic measurement circuit,
9... Receiving signal level measuring circuit, 10... Judgment circuit, 11... Control circuit.

Claims (1)

[Claims] An echo path characteristic measurement circuit that measures from the output of a received signal to the input of a transmitted signal and outputs an echo path characteristic; an echo path model that inputs the echo path characteristic and generates a pseudo echo; and a circuit that subtracts the pseudo echo from the transmitted signal. and a subtracter for outputting an echo signal, the echo canceller further comprising a control means for cutting off the supply of the echo path characteristic input to the echo path model when the received signal level exceeds a preset reference value. Features an echo canceller.