JPH03280724A - Echo canceller - Google Patents

Abstract

PURPOSE:To attain sufficient echo cancellation without causing the deterioration in echo cancellation by controlling a reception signal so as not to generate an overload distortion in an echo path even when waveform distortion takes place in the echo path. CONSTITUTION:A reception signal inputted from a reception signal input terminal 1 is fed to an echo path 5, an echo is inputted to a transmission signal input terminal 3 of an echo canceller 8 and inputted also to an echo path model 6 to generate a same pseudo echo as the echo inputted to the transmission signal input terminal 3. Since the pseudo echo is cancelled from the actual echo by a subtracter 7, the echo is cancelled at the output of the subtracter 7, the result is outputted from a transmission signal output terminal 4, and even when waveform distortion is generated in the echo path 5 by a signal level controller 9, the level of the reception signal is controlled by a signal level controller 9 so as not to cause overload distortion in the echo path 5.

Description

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

[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. Traditionally, echo suppressors have been used to control echoes, but
Since this is based on a switching operation, there are problems in that problems such as disconnection at the beginning of speech and click noise occur.

Echo cancellers were developed to solve this problem. The echo canceller has an internal adaptive filter (
It has an echo path model), measures the characteristics from the receiver's output to the transmitter's power based on the call signal, adjusts the echo path model to the measured echo path characteristics, and passes the receiver signal through this echo path model to reduce the echo. The echo is canceled by creating a pseudo echo that approximates the signal and subtracting it from the actual echo signal using a subtracter.

[Problem to be solved by the invention]

However, in an echo canceller, when an excessive signal is input to the receiver of the echo canceller, if there is a device with a small overload margin in the echo path, nonlinear distortion will occur in the echo path, the characteristics inside the echo path and the echo canceller will deviate, and the echo cannot be canceled out sufficiently.

[Means to solve the problem]

The echo canceller device of the present invention synthesizes a pseudo echo using an echo path model consisting of an adaptive filter having the same characteristics as the characteristic of the echo path from the receiving signal output end to the sending signal input end, and subtracts it from the actual echo using a subtracter. A signal level controller is provided at the reception signal input terminal of the echo canceller for canceling echoes by controlling the reception signal level.

Further, the signal level controller includes a filter that controls the band of the received signal, and a signal control circuit that is connected to this filter and controls the level of the received signal.

Furthermore, the signal level controller includes a signal level measuring circuit for measuring the received signal level, a determination circuit for determining whether the received signal level is greater than a predetermined threshold level, and a signal level controller based on the output of the determination circuit. and a control circuit that controls the received signal level.

〔Example〕

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

Referring to FIGS. 1 and 2 showing the first embodiment, a received signal input from a received signal input terminal 1 is sent to a received signal output terminal 2 and simultaneously to an echo path model 6. The signal sent to the echo path 5 passes through the echo path 5 and is input to the transmission signal input terminal 3 of the echo canceller 8 as an echo. On the other hand, the received voice 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 identical to the echo input to the transmitted voice signal input terminal 3. This pseudo echo is subtracted by the subtracter 7 from the actual echo signal inputted from the transmitting signal input terminal 3. For this reason, the subtractor 7
In the output of , the echo is canceled and the signal is output from the transmitting signal output terminal 4. Here, a signal level controller 9 is provided at the receiving side input of the echo canceller 8, and by lowering the receiving signal level to a level that does not exceed the overload level of the echo path 5 even if waveform distortion occurs in the echo path 5, the echo canceller To control so that overload distortion of an echo passler does not occur even if waveform distortion occurs.

In this way, even if the signal controlled by the signal level controller 9 undergoes waveform distortion in the echo path 5, it does not exceed the overload level of the echo path 5, and the echo path 5 always exhibits linear characteristics. Therefore, the amount of echo cancellation does not decrease, and
Always exhibits sufficient echo cancellation properties.

Referring to FIG. 3, which shows a second embodiment, a signal level controller 9 is placed at the receiver input of the echo canceller 8.

This signal level controller 9 has a filter 91 having typical echo path characteristics, and when a signal is passed through this filter 91, waveform distortion generated in the echo path is generated in this filter 91. The signal limiting circuit 92 limits the magnitude of the signal that may exceed the overload level of the echo path 5 out of the waveform distortion generated by the filter 91, and even if waveform distortion occurs in the echo path 5, the overload level of the echo path 5 is reduced. The signal level is lowered so as not to exceed the

Note that the combination of the filter 91 and the signal control circuit 92 is as follows:
It is possible to suppress the signal level within the overload range of the echo path 5 more reliably by using multiple stages than by using one stage.

Next, referring to FIG. 4 showing a third embodiment, a signal level controller 9 is provided at the receiving side input of the echo canceller 8. The signal level controller 9 has a signal level measuring circuit 93 that measures the received signal level, and constantly measures the level of the received signal. The output of this measuring circuit 93 is compared with a predetermined threshold level (this threshold level is set to a level that does not cause overload distortion even if waveform distortion occurs in the echo path 5) in a judgment circuit 94. By doing this, the received signal level is input to the echo path 5, causing waveform distortion in the echo path 5.
Determine whether there is a possibility that the overload level will be exceeded. When the judgment circuit 94 determines that there is a possibility of causing overload distortion when the received signal causes waveform distortion in the echo path 5, the control circuit 95 connected to the output of the judgment circuit 94 adjusts the level of the received signal. is lowered to a level that does not cause overload distortion even if waveform distortion occurs in the echo path 5.

〔Effect of the invention〕

As explained above, according to the present invention, even if waveform distortion occurs in the echo path, the received signal is controlled so that overload distortion does not occur in the echo path, so even if waveform distortion occurs in the echo path, the overload level of the echo path without exceeding
Echo paths always exhibit linear characteristics. As a result, the amount of echo cancellation does not decrease, and sufficient echo cancellation can always be performed.

[Brief explanation of drawings]

FIGS. 1, 2, 3, and 4 illustrate the first embodiment of the present invention. FIG. 7 is a configuration diagram showing second and third embodiments. 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...Echo canceller, 9...
Signal level controller, 91... Filter, 92... Signal limiting circuit, 93... Signal level determination circuit, 94...
- Judgment circuit, 95... control circuit.

Claims (3)

[Claims] (1) A pseudo echo is synthesized using an echo path model consisting of an adaptive filter with the same characteristics as the characteristics of the echo path from the receiving signal output end to the sending signal input end, and the echo is canceled by subtracting it from the actual echo using a subtractor. An echo canceller device comprising a signal level controller provided at a received signal input end of the echo canceller to control a received signal level. (2) The echo canceler according to claim 1, wherein the signal level controller comprises a filter that controls the band of the received signal, and a signal control circuit that is connected to the filter and controls the level of the received signal. Device. (3) The signal level controller includes a signal level measuring circuit that measures the received signal level, a determination circuit that determines whether the received signal level is greater than a predetermined threshold level, and a 2. The echo canceller device according to claim 1, further comprising: a control circuit for controlling a reception signal level;