JPH03280725A - Echo canceller - Google Patents

Abstract

PURPOSE:To cancel an echo sufficiently even for a line having large surrounding noise by stopping the correction of an adaptive filter when the output of a reception signal level measuring circuit is discriminated to be larger than the output of an adder circuit. CONSTITUTION:A comparator circuit 14 compares a threshold level in the presence of surrounding noise with a reception signal level to decide whether or not a signal larger than the surrounding noise is inputted to a reception signal input. Moreover, a comparator circuit 11 compares a predetermined threshold level with a reception signal level to decide whether or not the reception signal level is enough to be larger to ensure required S/N. Noise larger than the surrounding noise is inputted based on the output of both comparators 11, 14 and only when the signal ensuring the required S/N is inputted, a control circuit 15 applies control to a correction control circuit 8 to control an echo path model 6 by an echo path characteristic measuring circuit 7.

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 a switching operation, they have had problems such as interruptions at the beginning of speech and clicking noises.

Echo cancellers were developed to solve this problem. The echo canceller has an internal adaptive filter (
Based on the call signal, the characteristics from the receiver's output to the transmitter's power are measured using an echo path characteristic measurement circuit, and the echo path model is modified to match the measured echo path characteristics. A pseudo echo similar to an echo signal is created by passing the received signal through, and the echo is canceled by subtracting it from the actual echo signal using a subtracter.

Here, a conventional echo canceller will be explained with reference to FIG. The received signal inputted from the received signal input terminal 1 is sent to the received signal output terminal 2, and at the same time is sent to the echo path model 6, the echo path characteristic measuring circuit 7, and the received signal level measuring circuit 10. 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 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 9 from the actual echo signal input from the transmitting signal input terminal 3.

Therefore, the echo is canceled in the output of the subtracter 9 and the signal is output from the transmitting signal output terminal 4. The echo path characteristic measuring circuit 7 controls the echo path model 6 so that the output of the subtracter 9 becomes small based on the received signal and the output of the subtracter 9, and controls the echo path 5 and the echo path model 6 so that they have the same characteristics. ing. The reception signal level measuring circuit 10 measures the magnitude of the reception signal, and the comparison circuit 11 determines whether or not the measured reception signal is greater than a predetermined threshold level. If it is smaller than the level, the S/N of the signal returning to the transmitting signal input terminal will deteriorate, and the echo path 5 may not be measured accurately. Therefore, the echo path model 6 should be corrected by the echo path characteristic measuring circuit 7. The correction control circuit 8 controls it to stop.

As described above, in an echo canceller, when the receiver's human power signal of the echo canceller becomes smaller, the signal returned to the transmitter's human power becomes smaller, making it impossible to obtain a sufficient S/N ratio and increasing errors in measuring echo path characteristics. For this reason, conventionally, echo cancellers measure the level of the human input signal of the receiver of the echo canceller, and stop measuring the echo path characteristics when the signal level drops and it is considered that a sufficient S/N ratio cannot be obtained. At this time, the threshold level for determining whether or not to measure the echo path characteristics is generally set to a level that is not affected by line noise. If this threshold level is set high, the echo path characteristics can be measured in a portion where the S/N ratio is sufficient, but there is a problem in that the measurement time becomes shorter and the time until the echo disappears becomes longer.

For this reason, conventionally, this threshold level was
Since a bad level of /N passes through in a short time, it is set lower than the level that generates the actually necessary S/N to the extent that the amount of cancellation does not decrease significantly.

[Problem to be solved by the invention]

However, in a call with large ambient noise, the ambient noise exceeds this threshold level, and this ambient noise is regarded as a signal and the echo path characteristics are measured, and the characteristics of the long-term adaptive filter are determined at the portion with poor S/N. For this reason, a sufficient amount of echo cancellation cannot be obtained.

An object of the present invention is to provide an echo canceller that performs correction in a short time while ensuring a sufficient amount of cancellation.

[Means to solve the problem]

The echo canceller of the present invention uses an echo path model consisting of an adaptive filter having the same characteristics as the echo path characteristic measured by an echo path characteristic measuring circuit that measures the characteristics of the echo path from the receiving signal output end to the transmitting signal input end. The echo canceller cancels the echo by combining the signals and subtracting them from the actual echo using a subtracter, which includes a received signal level measuring circuit that measures the received signal level, and an output of the received signal level measuring circuit and a predetermined threshold level. a first comparison circuit for comparison, a minimum signal level measuring circuit for determining the lowest value of the receiving signal level, an adding circuit for adding a constant value to the output of the lowest signal level measuring circuit, and an output of the adding circuit and the receiving signal. a second comparison circuit that compares the output of the signal level measurement circuit; a control circuit that corrects the correction control circuit based on the output of the first comparison circuit and the output of the second comparison circuit; A first comparison circuit determines that the output of the received signal level measurement circuit is greater than a predetermined threshold level, and a second comparison circuit determines that the output of the received signal level measurement circuit is greater than the output of the adder circuit. and the correction control circuit that controls to stop the correction of the adaptive filter of the echo path model based on the output of the echo path characteristic measurement circuit when it is determined that

In addition, the echo canceller of the present invention uses a pseudo echo path model consisting of an adaptive filter having the same characteristics as the echo path characteristic measured by an echo path characteristic measuring circuit that measures the characteristics of the echo path from the receiving signal output end to the transmitting signal input end. An echo canceller that cancels echoes by synthesizing the echoes and subtracting them from the actual echoes using a subtracter, comprising: a received signal level measuring circuit for measuring a received signal level; a minimum signal level measuring circuit for determining the lowest value of the received signal level; an addition circuit that adds a constant value to the output of the lowest signal level measurement circuit; a selection circuit that selects the larger of the output of the addition circuit and a predetermined threshold level; and a measurement value of the reception signal level measurement circuit. A comparison circuit that compares the output value of the selection circuit with the output value of the selection circuit; and a modification control circuit that controls the output of the comparison circuit to stop modification of the adaptive filter of the echo path model by the output of the echo path characteristic measurement circuit. .

〔Example〕

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

Conventionally, by comparing the receiving signal level and a preset threshold level, the S/N when the signal returns to the transmitting signal input terminal as an echo has been estimated. In order to increase the length, the actually required S
The threshold level is set lower than the receiving signal level that ensures /N. This value is set to such an extent that the amount of cancellation does not drop significantly, with the expectation that a bad level of S/H will pass in a short time since the signal changes. However, in a call with large ambient noise, the ambient noise exceeds this threshold level, and this ambient noise is regarded as a signal and the echo path characteristics are measured. Since the signal level of this ambient noise hardly changes, the characteristics of the long-term adaptive filter are determined by the portion with poor S/N ratio.

On the other hand, the echo canceller according to the first embodiment of the present invention, as shown in FIG. This is because ambient noise is always present, so when measuring the received signal input, when the person at the game is not speaking, only the ambient noise enters the received signal input and the signal level becomes the lowest. Ambient noise can be estimated by measuring the value. To the ambient noise level determined by the lowest signal measuring circuit 12, a certain value is added to the adding circuit 13 to prevent malfunction, and this value is used as a threshold level when ambient noise is present. A comparison circuit 14 compares the threshold level when there is ambient noise with the reception signal level, and determines whether a signal larger than the ambient noise is input to the reception signal input. In addition, the comparator circuit 11 compares a predetermined threshold level and the received signal level, and determines the required S/S signal level.
Based on the output of the zero comparator, which determines whether the signal is large enough to ensure the required S/N, the control circuit 15, the modification control circuit 8 is controlled to modify the echo path model 6 by the echo path characteristic measuring circuit 7. With this control, the echo path characteristics are measured only when the signal level is sufficiently large compared to the surrounding noise and the necessary S/N can be secured, so the S/N of the signal returned to the transmitter is always sufficient. Moreover, sufficient convergence time is provided, and echoes can be sufficiently canceled.

Next, referring to FIG. 2 showing a second embodiment of the present invention, this echo canceller measures the received signal input level, and the lowest level is measured by the lowest signal level measuring circuit 12. To the ambient noise level determined by the lowest signal level measuring circuit 12, an adding circuit 13 adds a constant value to prevent malfunctions, and this value is used as a threshold level when ambient noise is present. A selection circuit 14 compares and selects a threshold level when there is ambient noise and a predetermined threshold level. When the threshold level when there is ambient noise is smaller than the predetermined threshold level, it is assumed that the ambient noise has no effect on the measurement of the echo path characteristics, and the predetermined threshold level is output from the selection circuit 16, and conversely, the ambient noise is When the threshold level at a certain time is higher than a predetermined threshold level, it is assumed that ambient noise affects the measurement of the echo path characteristic, and the selection circuit 16 outputs the threshold level when there is ambient noise. The comparison circuit 11 compares the output of the reception signal level measuring circuit 10 and the output of the selection circuit 16, and the reception signal level is determined by the selection circuit 16.
S of the signal that returns to the transmit signal input terminal 3 from the output of
Since there is a possibility that /N may deteriorate and the echo path 5 cannot be measured accurately, the correction control circuit 8 controls the echo path characteristic measuring circuit 7 to stop correcting the echo path model 6. In this way, since convergence is controlled depending on the presence or absence of ambient noise, the S/N ratio of the signal returned to the transmitter is always sufficient, the convergence time is sufficient, and echoes can be canceled sufficiently.

In the first and second embodiments described above, the same components as those of the conventional echo canceller shown in FIG. 3 are indicated by the same reference numerals.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to sufficiently cancel echoes even on lines with large ambient noise.

[Brief explanation of drawings]

1 and 2 are block diagrams showing first and second embodiments of the present invention, and FIG. 3 is a block diagram showing 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... Echo path characteristic measurement circuit, 8... Correction control circuit, 9... Subtractor, 10... Receiving signal level measurement circuit, 11... Comparison circuit, 12... Minimum signal level measurement circuit , 13...Addition circuit, 14...Comparison circuit, 1
5... Control circuit, 1 6... Selection circuit.

Claims (2)

[Claims] (1) Pseudo echoes are synthesized and subtracted using an echo path model consisting of an adaptive filter with the same characteristics as the echo path characteristics measured by an echo path characteristic measurement circuit that measures the characteristics of the echo path from the receive signal output end to the transmit signal input end. In an echo canceller that cancels an echo by subtracting it from an actual echo using a receiver, a received signal level measurement circuit that measures a received signal level, and a first circuit that compares the output of the received signal level measurement circuit with a predetermined threshold level. a comparison circuit, a minimum signal level measuring circuit for determining the lowest value of the received signal level, an adding circuit for adding a constant value to the output of the lowest signal level measuring circuit, and an output of the adding circuit and the receiving signal level measuring circuit. a second comparison circuit that compares the output of the first comparison circuit with the output of the second comparison circuit; a control circuit that corrects the correction control circuit based on the output of the first comparison circuit and the output of the second comparison circuit; and the first comparison circuit. determines that the output of the received signal level measurement circuit is greater than a predetermined threshold level, and the second comparison circuit determines that the output of the received signal level measurement circuit is greater than the output of the adder circuit. An echo canceller comprising: the modification control circuit that controls to stop modifying the adaptive filter of the echo path model based on the output of the echo path characteristic measuring circuit. (2) Pseudo echoes are synthesized and subtracted using an echo path model consisting of an adaptive filter with the same characteristics as the echo path characteristics measured by an echo path characteristic measurement circuit that measures the characteristics of the echo path from the receive signal output end to the transmit signal input end. In an echo canceler that cancels an echo by subtracting it from an actual echo using a receiver, a received signal level measurement circuit measures a received signal level, a minimum signal level measurement circuit that determines the lowest value of the received signal level, and the minimum signal level measurement circuit. an adding circuit that adds a constant value to the output of the adding circuit; a selecting circuit that selects the larger of the output of the adding circuit and a predetermined threshold level; and a measured value of the received signal level measuring circuit and an output of the selecting circuit. and a correction control circuit that controls to stop correction of the adaptive filter of the echo path model by the output of the echo path characteristic measuring circuit based on the output of the comparison circuit. echo canceller.