JPH03283824A - Echo canceller - Google Patents

Abstract

PURPOSE:To prevent the stop of correcting operation due to an echo path model by providing a second control circuit which controls the stop of operation of a first control circuit based on the output of a discriminating circuit which discriminates whether the level of a reception signal is higher than a preliminarily determined threshold level. CONSTITUTION:The level of the reception signal inputted to a reception-side input terminal 1 is measured by a reception signal level measuring circuit 11, and it is discriminated whether the measured level of the reception signal is higher than the preliminarily determined threshold level or not by a discriminating circuit 12 to discriminate whether the reception signal is clipped or not, and the result is sent to a second control circuit 13. If it is discriminated by the discriminating circuit 12 that the reception signal is clipped, the second control circuit 13 controls a first control circuit 8 to set the output of a comparator 6 to the absence of a transmission signal. Thus, the stop of correcting operation of an echo path model 9 at the time of clip of the reception signal is prevented.

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, the rapid increase in long-distance lines, especially satellite communications, has caused echoes in communication lines, resulting in large delays in the lines.
This is a big problem in terms of call quality. Conventionally, an echo compressor has been used to control such echoes. However, this method is based on a switching operation, and has problems such as disconnections at the beginning of speech, click noises, and other problems. Echo cancellers were developed to solve this problem. The echo canceller has an echo path model inside, and uses an echo path characteristic measuring circuit to measure the echo path characteristic from the receiving output to the transmitting output based on the receiving side signal and its echo, and converts the echo path model into the measured echo hash characteristic. By passing the received signal through this echo path model, a pseudo echo that approximates the echo signal is created, and the echo is canceled by subtracting it from the actual echo signal using a subtracter.

FIG. 2 shows a specific configuration of a conventional echo canceller. In the figure, 1 is a reception signal input terminal into which a reception signal is input, 2 is a reception signal output terminal which outputs a reception signal, 3 is a transmission signal input terminal into which a transmission signal is input, and 4
is a transmitting signal output terminal to which a transmitting signal is output, and an echo path 5 is provided between the received signal output terminal 2 and the transmitting signal input terminal 3. The received signal input to the received signal input terminal 1 is outputted from the received signal output terminal 2, and is also transmitted to one input terminal of the comparator 6, one input terminal of the echo path characteristic measuring circuit 7, and the input terminal of the echo path model 9. It is also output to . The transmit signal input to the transmit signal input terminal 3 is input to the other input terminal of the comparator 6, and the output signal of the comparator 6 is input to one input terminal of the first control circuit 8. It has become. A subtracter 10 is provided between the transmit signal input terminal 3 and the transmit signal output terminal 4, and the transmit signal input to the transmit signal input terminal 3 is input to one input terminal of the subtracter IO. Further, the output signal from the echo path model 9 is input to the other input terminal. The output signal of the subtracter 10 is output from the transmitting signal output terminal 4 and is also input to the other input terminal of the echo path characteristic measuring circuit 7. The echo path characteristic measuring circuit 7 measures the characteristics of the echo path 5 from when the received signal is output to when the transmitted signal is input, and this measurement result is output to the other input terminal of the first control circuit 8. It is now possible to do so. The first control circuit 8 receives this result and controls the echo path model 9 to stop its correction operation.

In such a configuration, the received signal input to the received signal input terminal l is sent to the echo path 5 via the received signal output terminal 2, and is also sent to the comparator 6, the echo path characteristic measurement circuit 7, and the echo path model 9. . The signal sent to the echo path 5 passes through this echo path 5 and is input to the transmitting signal input terminal 3 as an echo signal. On the other hand, the received signal input to the echo path model 9 is
By passing through the echo path model 9 having the same characteristics as the above, it becomes a pseudo echo signal that is the same as the echo signal input manually to the transmitting signal input terminal 3. This pseudo echo signal is subtracted by the subtracter 10 from the actual echo signal input from the transmit signal input terminal 3.

Therefore, the subtracter lO outputs a signal with the echo canceled, and this signal is output from the transmit signal output terminal 4.

By the way, the echo path model 9 is generally composed of an adaptive filter, and its characteristics are echo path characteristics Jl
It is controlled by a constant circuit 7 to have the same characteristics as the echo path 5. As a control method for this echo path model 9, a learning identification method is generally used. In the learning identification method, the characteristics of the echo path are estimated from the input and output signals of the echo path 5, but since the algorithm is configured on the assumption that no signals occur within the echo path 5, when the speaker on the echo path side speaks If a signal (noise signal) occurs in the echo path characteristic, the estimation of the echo path characteristic will be incorrect. Therefore, it is necessary to determine whether a signal is generated within the echo path 5.

If no signal is generated in the echo path 5, the output signal of the echo path 5 input to the transmitting side is only the echo of the received signal. Due to the nature of the communication path, the echo path 5 is always a loss line, and if no signal is generated within the echo path 5, the transmitted signal will be smaller than the received signal. Conversely, when a signal is generated within the echo path 5, the signal input to the transmitting side becomes the sum of the echo signal and the transmitting signal, and is thicker than the receiving signal.

Therefore, in the conventional echo technician Yancera, the presence or absence of the transmitting signal is determined by utilizing this property and comparing the transmitting signal level and the receiving signal level using the comparator 6. With current technology, it is difficult to judge a signal that is small compared to the level of the received signal, but if the transmitted signal has the same level as the received signal, the comparator 6 compares the levels of the received signal and the transmitted signal. This makes it relatively easy to determine whether there is a transmit signal. When the comparator 6 determines that there is a transmitting signal, the first control circuit 8 determines that the transmitting side speaker is talking and causes the echo path characteristic measuring circuit 7 to stop the correction operation of the echo path model 9. It's in control. In addition, the shorter the detection time, the more disturbances in the echo path model 9 can be suppressed for the call of the transmitting side speaker.In order to shorten the detection time, conventional echo cancellers reduce the detection time of the transmitting side signal. Comparator 6 that compares the level and the level of the receiving side signal
The width of the window is kept as short as possible.

[Problem to be solved by the invention]

However, in conventional echo cancellers, when an excessive signal that clips the input signal is applied to the received signal input terminal 1, the comparator 8 compares this crimped signal with the echo signal, so that the actual received signal level is Although there is no change in the receiving signal, it is determined as if the receiving signal has become smaller, and as a result, there is a signal on the transmitting side.The first control circuit 8 causes the echo path characteristic measuring circuit 7 to correct the echo path model 9. It stops. For this reason, it takes time for the echo path model 9 to match the characteristics of the echo path 5, and the echo signal does not disappear easily. In particular, this symptom becomes more noticeable when the width of the window of the comparator 6 is shortened in order to quickly determine the presence or absence of a transmitting signal as described above, or when a hangover time is added to improve stability.

The present invention has been made in view of such problems, and can prevent the echo from being stopped and significantly shorten the time until the echo disappears, while suppressing disturbances in the echo path model. Another object of the present invention is to provide an echo canceller that can perform correction operations in a short time.

[Means to solve the problem]

The echo canceller according to the present invention includes an echo path characteristic measuring circuit that measures the characteristics of the echo path from the output of the received signal to the input of the transmitted signal, and the echo path characteristic measuring circuit that has the same configuration as the echo path characteristic measuring circuit, An echo path model that generates an approximate pseudo echo signal, a subtracter that subtracts the pseudo echo signal from the actual echo signal, a received signal level measurement circuit that measures the level of the received signal, and a method that measures the measured received signal level and the transmitted signal. a comparator that compares the level of the signal; and a first control circuit that controls the echo path model to stop operating based on the output of the comparator.
a determination circuit that determines whether the level of the reception signal measured by the reception signal level measurement circuit is greater than a predetermined threshold level; and an operation of the first control circuit based on the output of the determination circuit. and a second control circuit that controls the operation to stop.

Such a configuration: Therefore, in the echo canceller of the present invention, the level of the received signal manually inputted is measured by the received signal level measurement circuit, and the level of the received signal measured by the received signal level measurement circuit is determined in advance in the determination circuit. It is determined whether or not it is greater than a predetermined threshold level, and the result is sent to the second control circuit. Based on this result, the second control circuit controls the first control circuit to stop its control operation. That is, if the received signal is clipped and an excessive signal is added, and the level of the received signal is higher than the threshold level predetermined in the judgment circuit, the operation of the first control circuit is stopped, and the comparison is performed. This prevents the transmitter from mistakenly detecting the presence of a transmitting signal, and prevents the correction operation of the echo path model from being stopped, thereby significantly shortening the time it takes for the echo to disappear. be able to.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an echo canceller according to an embodiment of the present invention. Here, the same reference numerals are given to the same components as the second orifice, and the explanation thereof will be omitted. In this embodiment, a receiving signal level measuring circuit 11 for measuring the level of the receiving signal is provided at the receiving side input terminal l of the echo canceller, and the level of the receiving signal measured by the receiving signal level measuring circuit 11 is set in advance. A determination circuit 12 is added that determines whether the fixed rate is higher than a threshold level and determines whether the received signal level is clipped. Note that this threshold level is set based on the value that occurs when the signal clips.

In addition, in this echo canceller, a second control circuit 13 is provided between the comparator 6 and the first control circuit 8, and when the level of the received signal is higher than a predetermined threshold level in the determination circuit 12, this Second control circuit 1
3, the operation of the first control circuit 8 is stopped. That is, in order to prevent the aforementioned erroneous detection by the comparator 6, the second control circuit 13 sets the output of the comparator 6 to no transmitter signal, thereby excessively stopping the correction operation of the echo path model 9. It prevents

This is because when the received signal is clipped, the level of the received signal is at the maximum, so the level of the transmitted signal does not exceed the level of the received signal, and the echo path model 9 based on the echo path characteristic measurement circuit 7 This is because there is no need for the first control circuit 8 to stop the correction operation.

With this configuration, in the echo canceller of this embodiment, the received signal input to the received signal input terminal 1 is sent to the echo path 5 via the received signal output terminal 2, and is also transmitted to the comparator 6 and the echo path characteristic measuring circuit 7. and sent to the echo path model 9. The signal sent to the echo path 5 passes through this echo path 5 and is input to the transmitting signal input terminal 3 as an echo signal. On the other hand, the received signal input to the echo path model 9 passes through the echo path model 9 having the same characteristics as the echo path 5, thereby generating a pseudo echo signal that is the same as the echo signal input to the transmit signal input terminal 3. . This pseudo echo signal is subtracted by the subtracter 10 from the actual echo signal input from the transmit signal input terminal 3. Therefore, the subtracter 10 outputs a signal with the echo canceled, and this signal is sent to the transmitting signal output terminal 4.
is output from.

On the other hand, the level of the received signal input to the receiving side input terminal 1 is measured by the received signal level measuring circuit 11', and the level of the received signal measured by the received signal level measuring circuit 11 is determined in advance by the determination circuit 12. It is determined whether or not the signal is greater than a threshold level, and it is determined whether or not the received signal is clipped. The result is then sent to the second control circuit 13. When the determination circuit 12 determines that the received signal is clipped, the second control circuit 13 controls the first control circuit 8 to set the output of the comparator 6 to no transmitted signal. . As a result, the first control circuit 8 stops outputting an operation stop signal to the echo path model 9, and prevents the echo path model 9 from excessively stopping its correction operation.

In this way, the echo canceller of this embodiment prevents the correction operation of the echo path model 9 from being stopped due to the comparator 6 erroneously detecting that there is a transmitting signal when the received signal clips. Therefore, the time it takes for the echo to disappear can be significantly shortened, and as a result, the width of the window of the comparator 6 can be shortened to quickly determine the presence or absence of a transmitting signal. Therefore, correction operations can be performed in a short time while suppressing disturbances in the echo path model.

〔Effect of the invention〕

As described above, according to the echo canceller according to the present invention,
A reception signal level measurement circuit that measures the level of a reception signal, a determination circuit that determines whether the level of the reception signal measured by the reception signal level measurement circuit is greater than a predetermined threshold level, and this determination circuit. A second control circuit is provided to control the operation of the first control circuit to be stopped based on the output of the first control circuit, so that when the level of the received signal clips, the comparator mistakenly assumes that there is a transmitting signal. It is possible to prevent the echo path model from being detected and the corrective action is stopped, thereby greatly reducing the time it takes for the echo to disappear, while suppressing disturbances in the echo path model. You can take corrective action with .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an echo canceller according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional echo canceller. 1... Receiving signal input terminal, 2... Receiving signal output terminal, 3... Transmitting signal input terminal, 1... Transmitting signal input terminal , 5...Echo path, 6...Comparator, 7...Echo path characteristic measurement circuit, 8...
1st control circuit, 9... echo path model, 10... subtracter, 11... received signal level measurement circuit, 2... judgment circuit, 3... th... 2 control circuit.

Claims (1)

[Claims] An echo path characteristic measuring circuit that measures the characteristics of an echo path from when a received signal is output to when a transmitted signal is input; An echo path model that generates a pseudo echo signal, a subtracter that subtracts the pseudo echo signal from the actual echo signal, a received signal level measurement circuit that measures the level of the received signal, and a difference between the measured received signal level and the transmitted signal. a first control circuit that controls the operation of the echo path model to be stopped by the output of the comparator; A determination circuit that determines whether or not the threshold level is greater than a predetermined threshold level, and a second control circuit that controls to stop the operation of the first control circuit based on the output of the determination circuit. Features an echo canceller.