JPS59151545A - Adaptive type echo cancellor - Google Patents

Abstract

PURPOSE:To obtain a prescribed canceling characteristic to any receiving signal by controlling at least one of a correcting coefficient, receiving signal and a residual echo signal depending on a tap coefficient, the receiving signal and the residual echo signal stored in a storage circuit. CONSTITUTION:A pseudo echo line comprising a receiving signal storage circuit 105, a tap coefficient storage circuit 107, and an integration circuit 110 forms a pseudo echo signal from a receiving signal Xj-i. A subtraction circuit 109 subtracts an echo signal from an output of the pseudo echo line and outputs a residual echo signal ej. A correcting amount arithmetic circuit 108 calculates a correcting amount DELTAhi<j> of the tap coefficient hi<j> of a transversal filter constituting the pseudo echo line based on the receiving signal, the residual echo signal and a correcting coefficient alpha according to Equation. Further, a control circuit 601 controls at least one of the correcting coefficient alpha, the receiving signal Xj-i and the residual echo signal ej.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adaptive echo canceler for eliminating echo signals in a communication line.

2. Description of the Related Art Conventionally, echo prevention devices have been used as means for preventing communication interference caused by echo signals generated in long-distance communication lines. However, this device only has one line on.

Since the off-state operation is performed, there are drawbacks such as cutting off at the beginning of speech and generation of crackling noise.

Echo canceling devices have been put into practical use to solve the drawbacks of such echo blocking devices. This device measures the echo path characteristics, synthesizes a pseudo echo signal that approximates the echo signal based on the measured characteristics, and cancels the actual echo signal using the pseudo echo signal. Such an echo canceling device does not have to turn on and off two lines, so it does not have the drawbacks of an echo blocking device.

As is well known, the adaptive echo cancellation device can be regarded as a type of system identification device. That is, a received signal is used as a signal for system identification, and a pseudo echo path that is almost the same as the echo path of the unknown system is formed (identified).

Here, the received signal needs to have a frequency band that is the same as and larger than the echo path to be identified. That is, identification cannot be performed for bands other than the band of the received signal used, and the identification becomes so-called undefined.

In an actual echo cancellation device, when a normal voice signal or white noise is used as an identification signal, sufficiently stable identification is possible because it includes a wave tram of the same band as one echo path. However, when applied to a communication line, a signal with a very narrow band compared to the band of one echo path may be applied as an identification signal for a long time. That is, continuous sine waves, modem signals, etc. may be transmitted. If such a narrowband signal is used as a reception signal, the band of the narrowband signal is identified, but the other bands are undefined.

A correction loop is formed for the band of the narrowband signal and identification is possible, but a correction loop is not formed for other bands and identification is not possible.

On the other hand, in an actual echo canceller, there are limitations due to its hardware configuration, and noise (disturbance) is mixed into the echo signal in the echo path, so calculations are required in the process of identifying the pseudo echo path. An error will occur. This calculation error does not cause a major problem as long as the identification signal includes the overlap tram of the entire band of the echo path. but.

When the narrowband signal is applied, the following problems occur.

That is, in a frequency band outside the narrow band where there is no signal, a correct transfer function cannot be estimated, and it becomes undefined. For this reason, if estimation is continued for a long time, calculation errors will gradually accumulate, and may exceed the magnitude of the memory circuit that stores the tag coefficients of the transversal filters that make up the pseudo-echo path. The inno and russ models generated in this manner differ from the actual echo path characteristics even in the narrow band, making it impossible to cancel out the echoes.

SUMMARY OF THE INVENTION An object of the present invention is to provide an adaptive echo cancellation device that ensures predetermined cancellation characteristics for all received human input signals and at the same time provides stable operation.

This will be explained below with reference to two drawings.

FIG. 1 shows a conventional adaptive echo canceler in block diagram form.

A reception signal Xj of one time manually input from the reception signal input terminal 101 is input to the reception signal storage circuit 105 and simultaneously sent to the echo path through the reception signal output terminal 102. The transmission signal Yj at time j inputted to the transmission signal input terminal 103 along the echo path is sent to the subtraction circuit 109, and
The difference from the pseudo echo signal Yj created in step 06 is taken.

The output signal ej of the subtraction circuit 109- is sent to the transmission signal output terminal 104 and sent out to the transmission line, and at the same time is sent to the correction amount calculation circuit 108, which will be described later.

A pseudo echo path 106 consisting of a transversal filter includes a received signal storage circuit 105 that stores a received signal, a storage circuit 107 that stores tag coefficients of the transversal filter, and a convolution operation of the contents of these storage circuits 105 and 107. and an integral calculation circuit 110. The output signal of the integral calculation circuit 110 is the pseudo echo signal YJ.
become.

The output signal ej of the subtraction circuit 109 and the reception signal from the storage circuit 105 are applied to a correction amount calculation circuit 108, and the correction amount of the tap coefficient of the transversal filter is calculated. Further, the output of the correction amount calculation circuit 108 is applied to an addition correction circuit 204 for correcting the tap coefficient.

FIG. 2 is a block diagram of the adaptive echo canceler shown in FIG. 1, in which the learning identification method is used as a modification algorithm.

In FIG. 2, the correction amount calculation circuit 108 is a multiplier 201
, 203. Divider 202. It is constituted by a square accumulation circuit 205 and calculates the following equation (1).

Further, the tag coefficient is modified by the addition modification circuit 204 based on equation (2).

Here, 1 represents the first evening, 0, α is the correction coefficient,
N indicates the number of taps of the transversal filter.

If we follow the above learning identification correction algorithm.

When a normal voice signal, white noise, etc. is used as the identification signal, sufficiently stable identification can be performed because it includes a sloshing tram in the same band as one echo path. However, when a signal having a very narrow band compared to the echo path band, such as a continuous sine wave or a modem signal, is transmitted as an identification signal, calculation errors may cause unstable operation.

On the other hand, one major feature of the present invention is that the correction amount calculation circuit 1
Note that the calculation error that occurred in 08 is very small at the initial stage, and even when a narrowband signal is input, the residual signal is forced so that a modified roof 0 is formed in a frequency band outside that band. The reason is that a minute error signal is added to the .

The present invention comprises: a pseudo echo path that creates a pseudo echo signal from received signals Xj, , i; and a subtraction circuit that takes the difference between the echo signal and the output of the pseudo echo path and outputs a residual echo signal ej;
Based on the received signal, the residual echo signal, and the modification coefficient α, the modification amount ΔhJ of the tag coefficient hj of the transversal filter constituting the pseudo echo path is calculated using the following formula (1).
and a correction amount calculation circuit that calculates and outputs according to the following.

In the transversal filter, an adaptive type comprising: an addition circuit that corrects the tap coefficients stored in the storage circuit by adding the output of the tap coefficients stored in the storage circuit that stores the tap coefficients and the output of the correction amount calculation circuit. In the echo cancellation device, the correction coefficient α in the equation (1), the received signal X·i, and the residual echo signal are determined depending on the tap coefficients stored in the storage circuit, the received signal, and the residual echo signal. The present invention is characterized in that it includes a circuit that controls at least one of the echo signals ej.

The present invention will be explained in detail below.

FIG. 3 shows a first embodiment of the invention.

This device includes a residual echo signal control circuit 601. In this control circuit 601,
and the output signal X of the receiving signal storage circuit 105, and the polarity signal 5gnX- of are input to the first exclusive OR J-1:l-1 dart 504. Also, the first gate 504
output signal and residual echo signal e, -4 polar signal 8 gn
e j-1 is input to the second exclusive OR gate 1-505. Furthermore, it becomes a constant depending on the output of the second gate 505! or 2, and a constant selected by this selection circuit 502 as the residual echo signal ej
A multiplier 501 that multiplies by -1 is provided.

Here 2:>klo and these selections follow Table 1 below. Of course, the effect is exactly the same as in the previous embodiment.

Table 1 With such a configuration, 1, for example, Δ in the above equation (1)
When hj-1 is 10, the constant is selected and =1. When Δh lamp 1 is -, 2 is selected as the constant. This constant is multiplied by the residual echo signal ej-1 and added to the correction amount calculation circuit 108 by 1, thus controlling to reduce ΔhJ□1.

FIG. 4 shows a second embodiment of the invention. This device is designed to vary the correction coefficient α in equation (1).

The polarity signal s of the storage signal hj of the coefficient storage circuit 107
gnh: and the polarity signal sgnXj-1 of the output signal X1 of the reception signal storage circuit 105 are applied to the first exclusive logic-sum gate 506. Also the first
The output signal of the gate 506 and the polarity signal sgnej of the residual echo signal ej are combined into a second exclusive OR gate 507.
I am trying to input it into . And the second case) 50
7, the correction coefficient α of the first correction coefficient setter 802 and the correction coefficient α2 of the second correction coefficient setter 803 are adjusted.
A selection circuit 508 is provided for selecting one of the two.

Therefore, α1<α2, and these selections are made according to Table 1 above.

FIG. 5 shows a third embodiment of the invention.

This device includes a reception signal control circuit 901. In this control circuit 901, the polarity signal sgnXj-1 of the output signal X of the tag person and reception signal storage circuit 105 is
is input to the first exclusive OR gate 504. Further, the output signal of the tenth digit 504 and the polarity signal sgnej of the residual echo signal ej are input to the second exclusive OR gate 5o5. A selection circuit 502 is provided which selects a constant kl or 2 from the output of the second unit 50.5, and the constant selected by this selection circuit 502 is applied to the receiving signal applied to the correction amount calculation circuit 108. A multiplier 501 is provided.

Here, 2) k, and these selections are according to Table 1 above.

The above is the first aspect of the present invention. The adaptive echo cancelers shown in the second and third embodiments all exhibit the same effect. Outside of this,
It is clear that the same effect can be obtained by controlling the output of the accumulation circuit 205.

As explained above, the adaptive echo canceling device according to the present invention is equipped with a circuit that controls at least one of the tap coefficients, the received signal, and the residual echo signal depending on the tap coefficient, the received signal, and the residual echo signal. The correction amount ΔhJ of the arithmetic circuit is controlled to be always small.

From this, according to the present invention, it is possible to realize an adaptive echo canceling device that provides sufficiently stable operation even when a narrowband signal is applied as a reception signal for a long time.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional adaptive echo canceler;
1 is a block diagram showing the details of the correction amount calculation circuit 108 in FIG. FIG. 5 is a block diagram of the adaptive echo canceling device according to the second embodiment of the present invention, and FIG. 5 is a block diagram of the adaptive echo canceling device according to the third embodiment of the present invention. , 106... Pseudo echo path, 107... Tag coefficient storage circuit, 108... Correction amount calculation circuit, 109... Subtraction circuit, 110... Integral calculation circuit, 201, 20.3... Multiplier, 202・
...Division circuit, 204... Addition correction circuit, 205 Square accumulation circuit, 501... Multiplier, 5o2, 5oF3.
...Selection circuit, 504, 505, 506, 507...
6C) 1... Residual echo signal control circuit, 901... Receiving signal control circuit.

Claims (1)

[Claims] 1) Subtraction of a pseudo echo path for creating a pseudo echo signal from the received signal Xj-i and a difference between the 1 echo signal and the output of the pseudo echo path and outputting 9 residual echo signals ej circuit, a correction amount ΔhJ of a tag coefficient hj of a transversal filter constituting the pseudo echo path is calculated and output based on the received signal, the residual echo signal, and the modification coefficient α according to the following equation (1). quantity calculation circuit. An adaptive type comprising: an addition circuit that corrects the tap coefficients stored in the storage circuit by adding the tap coefficients stored in the storage circuit that stores the tap coefficients in the transversal filter and the output of the correction amount calculation circuit. An adaptive echo canceling device, characterized in that the adaptive echo canceling device includes a control circuit that controls at least one of the correction coefficient α, the received signal Xj-i, and the residual echo signal e3. 2. In the adaptive echo cancellation device according to claim 1, the control circuit includes a polarity signal of a tag coefficient stored in the storage circuit, a polarity signal of the received signal, and a polarity signal of the residual echo signal. a selection circuit that selects one of the two constants depending on the selection circuit; and a multiplier circuit that multiplies the residual echo signal applied to the correction amount calculation circuit by the constant selected by the selection circuit. What is claimed is: 1. An adaptive echo canceller comprising: a control circuit having a control circuit; 3) In the adaptive echo canceling device according to claim 1, the control circuit is capable of setting two correction coefficients α shown in the equation (1), and the storage circuit is and a selection circuit that selects one of the two correction coefficients depending on the polarity signal of the evening coefficient, the polarity signal of the received signal, and the polarity signal of the residual echo signal to be stored. An adaptive echo canceller featuring: 4) In the adaptive echo canceling device according to claim 1, the control circuit includes a polarity signal of a tap coefficient stored in the storage circuit, a polarity signal of the received signal, and a polarity of the residual echo signal. a selection circuit that selects one of the two constants depending on the signal; and a correction amount calculation circuit that calculates the constant selected by the selection circuit according to the equation (
1) An adaptive echo canceling device comprising: a control circuit having a multiplier for multiplying the reception signal Xj i according to 1).