JPH0140536B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an echo control device for eliminating echoes in a communication circuit.

Conventionally, echo blocking devices, voice switches, echo canceling devices, etc. have been used to control echoes from long-distance lines, loudspeaker telephones, two-way repeaters, etc. The first two of these have problems such as disconnection at the beginning of the line and clicking noise when turning the line on and off. It was developed to compensate for the shortcomings of the switch. This device measures the echo path, synthesizes the echo signal and an approximate echo signal based on the measured echo path characteristics, and
This eliminates the actual echo signal, and does not have a mechanism that causes disturbances such as cutting off the beginning of speech or clicking noise.

However, in the case of this echo cancellation device, in its basic configuration, when the echo signal is superimposed with the transmission signal, noise, etc. and input to the transmission side input, the measurement accuracy of the echo path decreases, and the amount of echo cancellation decreases. It has a predisposition to decrease to a value determined by the ratio of the echo signal level of the transmitting side input to the other signal level. Therefore, in order to prevent the amount of echo cancellation from decreasing in this superimposed state, a superimposed speech detection circuit has been used in practice. However, since this superimposed call detection is performed by comparing the receiving side signal level and the sending side signal level, it is possible to detect when the superimposed signal level is small compared to the echo signal level, or to detect superimposed calls when the echo signal level is small. It had the disadvantage of being impossible to detect.

Therefore, an object of the present invention is to enable the detection of a superimposed call even when the superimposed signal level is smaller than the echo signal level and when the echo signal level is small;
An object of the present invention is to provide an echo canceling device capable of preventing a decrease in the amount of echo canceling.

In order to achieve the above object, the present invention detects the level of the transmitter signal at the output level rather than at the input level, and accordingly adds necessary circuitry.

According to the present invention, there is provided an echo cancellation device that measures the characteristics of an echo path from the input/output signals of the echo path and cancels an actual echo signal by synthesizing an approximate echo path signal based on the obtained echo path characteristics. , a received signal level measurement circuit that measures a remaining received signal level, a received signal level estimator that estimates a received signal level, and a comparison unit that compares output levels of the received signal level measurement circuit and the received signal level estimator. The echo canceling device is characterized in that the output of the comparing section controls the operation of measuring the characteristics of the echo path.

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

The figure is a block diagram showing the circuit configuration of an embodiment of the present invention, and in this case shows that it is suitable for use in long-distance lines. In Figure 1, 1,
Reference numerals 2, 3, and 4 represent terminals for receiving input, receiving output, transmitting input, and transmitting output, respectively. Since the echo canceller 5 is also used in conventional echo cancelers, it is comprised of a subtraction circuit 6 and an approximate echo signal synthesis circuit 7. The level of the signal on the receiving side is measured by the signal level measuring circuit 9 on the receiving side as before, but the level of the signal on the sending side is measured by the canceled residual echo on the sending output side of the subtraction circuit 6, which is different from the conventional method. The level is measured by the device 8.

The attenuation measuring circuit 10 calculates the signal level from the terminal 2 based on the received signal level (referred to as R) measured by the receiving side signal level measuring circuit 9 and the erased residual signal level (referred to as e) measured by the erased residual signal level measuring circuit 8. Find the loss characteristics up to the erased residual signal level measurement circuit 8,
A value with a good loss characteristic (large loss) is output by comparing it with the retained loss characteristic obtained previously.

This loss characteristic is similar to that of a hybrid circuit (not shown).
The echo path loss from L A to the terminal 3 is L _A , and the signal loss from the terminal 3 to the cancellation residual signal level measuring circuit 8 is subtracted by the subtraction circuit 6 .
If the amount of echo cancellation by the approximate echo signal is L _B , it can be expressed as e/R from the relationship e=L _A ·L _B ·R. Therefore, the attenuation measurement circuit 10 can be realized by means for calculating the ratio of two input signals, means for holding the previously calculated value, and comparison means. Generally, when there is no superimposed signal, the loss characteristic e/R decreases, but when there is a superimposed signal, it becomes the sum of the superimposed signal and the cancellation residual signal, and it appears as if the cancellation residual echo has increased, resulting in This can be mistakenly interpreted as a decrease in the sum of echo path loss and echo cancellation. In order to prevent malfunctions due to this superimposed signal, the attenuation measurement circuit 10
compares the value used last time and the value measured this time as the value of the loss characteristic (attenuation), and outputs the value indicating the larger loss (lower e/R).

The received signal level estimated value calculation circuit 11 calculates the estimated value of the received signal level (referred to as R') from the attenuation level measured by the attenuation measurement circuit 10 and the erased residual signal level from the erased residual level measuring circuit 8. demand.
This level estimated value R' can be obtained by dividing the erased residual signal level e by the loss characteristic value e/R.
1 may be a division means.

The method of generating this estimated value will be explained in more detail. Now, for the sake of explanation, let e' be the erased residual signal level measured this time, e' be the previous level, R be the received signal level, and R' be the estimated value of the received signal level. Here, it is assumed that the reception signal level R can be regarded as a substantially constant value in a unit time. When there is no superimposed signal, e<e', so the attenuation measuring circuit 10 always outputs a small value e/R (high attenuation of the echo path). As a result, the received signal level estimated value R' is approximately equal to R. However, if there is a superimposed signal, e>e', so the attenuation measurement circuit 10 outputs the previously used e'/R, and as a result, R'=e·R/e'>R. That is, by comparing R and R', it is possible to detect the presence or absence of a superimposed signal.

The comparison circuit 12 performs the above comparison, and if it is determined that a superimposed signal exists, outputs a control signal instructing the echo canceller 5 to modify, stop, or reduce the modification speed of the echo path model, thereby reducing the amount of echo cancellation. can prevent a decline in When compared by the comparator circuit 12, the operation can be stabilized by adding a constant to the reception signal level measuring section 9 or the reception signal estimated value. In this device, the canceled residual echo level measuring circuit 8, the attenuation amount measuring circuit 10, and the received signal level estimation value calculation circuit 11 may be collectively named the received signal level estimating section 13.

As explained above, according to the present invention, even when the superimposed signal level is small relative to the echo level or when the echo signal level is small, the superimposed speech state can be quickly detected, and a decrease in the amount of echo cancellation can be prevented. .

Furthermore, in this embodiment, the loss characteristic e/R was obtained using the attenuation measurement circuit 10, but it is clear that there is no change in the present invention even if the reciprocal R/e is obtained and the receiving signal level estimation calculation circuit 11 is used as a multiplication means. It is.

[Brief explanation of drawings]

The figure is a block diagram showing a first embodiment of the present invention. Explanation of symbols: 1 is the receiving side input terminal, 2 is the receiving side output terminal, 3 is the transmitting side input terminal, 4 is the transmitting side output terminal, 5
6 is an echo canceller, 6 is a subtraction circuit, 7 is an approximate echo signal synthesis circuit, 8 is a cancellation residual echo level measurement circuit, 9
1 is a receiving side signal level measuring circuit, 10 is an attenuation amount measuring circuit, 11 is a receiving signal level estimation value calculation circuit, 1
Reference numeral 2 represents a comparison circuit, and reference numeral 13 represents a received signal level estimator.

Claims (1)

[Scope of Claims] 1. An echo cancellation device that measures the characteristics of the echo path from the input/output signals of the echo path and cancels the actual echo signal by synthesizing an approximate echo path signal based on the obtained echo path characteristics. , a reception signal level measurement circuit that measures and outputs a reception signal level; and an erased residual signal level measurement circuit that measures the level of a transmitted signal whose echo signal has been canceled by the echo path signal and outputs it as an erased residual signal level. a circuit, a level ratio calculation means for calculating a ratio of the erased residual signal level to the received signal level and outputting it as a first level ratio; a storage means for storing it as a level ratio; and comparing the first level ratio and the minimum level ratio, outputting the smaller value as a second level ratio, and providing the comparison to the storage means as the minimum level ratio. and an estimated value calculation means for dividing the erased residual signal level by the second level ratio and outputting the result as an estimated received signal level; and the received received signal level. An echo canceling device comprising: a comparison circuit that compares a signal level with the estimated received signal level and supplies a control signal corresponding to the comparison result to the means for synthesizing the approximate echo signal. 2. In an echo cancellation device that measures the characteristics of the echo path from the input and output signals of the echo path and cancels the actual echo signal by synthesizing an approximate echo path signal based on the obtained echo path characteristics, the received signal level is a receiving signal level measuring circuit that measures and outputs the signal level; an erased residual signal level measuring circuit that measures the level of the transmitted signal from which the echo signal has been canceled by the echo path signal and outputs it as an erased residual signal level; Level ratio calculation means for calculating a ratio of the received signal level to the signal level and outputting it as a first level ratio; and a memory for storing the largest value among the first level ratios calculated in the past as a maximum level ratio. means for comparing the first level ratio and the maximum level ratio, outputting the larger value as a second level ratio, and supplying it to the storage means as the maximum level ratio; a received signal level estimated value calculation circuit comprising an estimated value calculation means for multiplying the signal level by the second level ratio and outputs the result as a received received signal level estimated value; and the received received signal level and the received received signal level. An echo canceling device comprising: a comparison circuit that compares the estimated value and applies a control signal corresponding to the result to the means for synthesizing the approximate echo signal.