JPH05304493A - Echo canceler circuit - Google Patents

Abstract

PURPOSE:To provide an echo canceler circuit with the improved stability of echo eliminating operation by preventing the misjudgement of a double talking state due to the change of echo paths, thereby enabling the detection of the more stabilized double talk. CONSTITUTION:Whether a subtracted value for which the level of a residual echo signal Es is subtracted from the level of a near end speaker signal Ts with a subtracter 153 is positive or negative is decided with a deciding part 154, a counter 155 is counted up when the subtracted value is negative and the counted value of the counter 155 is cleared when it is positive. When the counted value of the counter 155 reaches the prescribed value, even when the double talking state is decided by a double talk detection circuit 103, a filter factor updating part 123 is controlled and the inhibition of the learning of the tap factor of an adaptive filter 101 is canceled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller circuit for canceling an acoustic echo generated in a communication system such as a mobile communication system, and more particularly, to eliminate an unstable operation due to an erroneous double talk determination due to a sudden change in echo path. The present invention relates to an improved echo canceller circuit.

[0002]

2. Description of the Related Art As a conventional echo canceller circuit, the one shown in FIG. 2 is known. The echo canceller circuit 100 receives the far-end talker reception signal Rs, and transmits the far-end talker reception signal Rs via a digital-analog converter (D / A) 11.
2 and outputs the far-end talker received signal Rs through the adaptive filter 101, thereby forming a pseudo echo signal EES corresponding to the echo path EC between the transmitter 12 and the receiver 13, and the receiver 13 The pseudo echo signal EES is subtracted from the near-end talker reception signal Ts input from the analog-to-digital converter (A / D) 14 to obtain a residual echo signal Es from which an echo is canceled. Is configured.

The adaptive filter 101 first receives the far-end talker reception signal Rs from the input signal register (X-RE).
G) 125 and takes this input signal register (X-R
EG) 125 receives the far-end talker received signal Rs and the tap coefficient stored in the tap coefficient register (TAP-REG) 126. The convolution operation unit 127 performs a convolution operation to form a pseudo echo signal EES. ..

Here, the tap coefficient register (TAP-R
The tap coefficient stored in the EG) 126 is adaptively updated and controlled by the filter coefficient updating unit 123 based on the far-end talker reception signal Rs and the residual echo signal Es. Identification method is used,
The update formula of the tap coefficient is shown below. Here, hi (j + 1) h is a tap coefficient value after updating, hi (j) is a coefficient value before updating, μ is a step size, e is a level value of the residual echo signal Es, and x (ji) is Far-end talker reception signal Rs
, N is the order of the tap coefficient.

Further, in this adaptive algorithm of the tap coefficient, the far-end talker reception signal Rs is received and the near-end talker reception signal Ts is generated from the analog-digital converter (A / D) 14. In the double talk state, the adaptive update control of the appropriate tap coefficient cannot be performed, so
This double-talk state is detected by the double-talk detection circuit (DT
D) 103, and in the double talk state, the adaptive filter 10 by the filter coefficient updating unit 123.
It is configured to prohibit adaptive update control of a tap coefficient of 1.

Here, a double talk detection circuit (DTD)
The determination of the double talk state by 103 obtains the ratio R of the level value x of the far-end talker reception signal Rs to the level value e of the residual echo signal Es by the calculation of R = log (x / e) (2) When the level ratio R becomes smaller than a preset threshold value Dth, the double talk state is determined.

Further, this threshold Dth is a variable threshold D
In the single-talk state, this variable threshold Dth (k) is set to Dth (k + 1) = Dth (k) + δ2 ( 3), on the other hand, in the double-talk state, this variable threshold value Dth (k) is set to Dth (k + 1) = Dth (k) −δ2 ( Set to 4).

The upper limit of the variable threshold Dth (k) is set in order to easily return to the single talk state when the double talk state continues for a long time, and conversely, the single talk state continues for a long time. The lower limit value is set in order to make it easier to determine the next double-talk state.

[0009]

In the conventional echo canceller circuit as described above, the determination of the double-talk state is performed by the level value x of the far-end talker reception signal Rs with respect to the level value e of the residual echo signal Es. Since it is performed by using the ratio R of R, the echo path EC between the transmitter 12 and the receiver 13 changes abruptly, and the residual echo signal E
Even when the level value e of s suddenly increases, it may be erroneously determined to be the double talk state. In this case, the adaptive update control of the tap coefficient of the adaptive filter 101 is prohibited. , It is impossible to get out of the double talk state forever, and it becomes impossible to perform echo cancellation.

In view of this, the present invention provides an echo canceller circuit which prevents erroneous determination of the double talk state due to changes in the echo path, thereby enabling stable double talk detection, and improving the stability of the echo canceling operation. The purpose is to provide.

[0011]

In order to achieve the above object, the present invention obtains a pseudo echo signal by passing a far-end talker received signal through an adaptive filter, and the pseudo echo signal is obtained from the near-end talker received signal. Echo cancellation is performed by subtracting a signal, and the ratio of the level of the far-end talker reception signal to the level of the residual echo signal obtained by subtracting the pseudo echo signal from the near-end talker reception signal is a predetermined value. When it becomes smaller than the threshold value, it is determined as a double-talk state, and in the echo canceller circuit for inhibiting learning of the tap coefficient of the adaptive filter, the residual echo from the level of the near-end talker signal is detected. When the subtraction value obtained by subtracting the signal level is observed and the negative ratio of the subtraction value increases, the tap coefficient of the adaptive filter is determined even if the double talk state is determined. Characterized in that it cancels the prohibition of learning.

[0012]

Operation: A sudden change in the echo path occurs, where h
Σh ² (n) <Δh ² (n) where (n) is the impulse response in the adaptive filter after the echo path is changed and Δh (n) is the difference between the impulse responses in the adaptive filter before and after the echo path is changed. When the above condition is satisfied, the residual echo signal Es becomes larger than the near-end talker receiving signal Ts. In this case, in the double-talk state determination by the conventional double-talk detection circuit, this may be erroneously determined as the double-talk state.

In the present invention, paying attention to this point, the subtraction value obtained by subtracting the level of the residual echo signal from the level of the near-end speaker signal is observed, and when the negative ratio of the subtraction value becomes large, , Even if the double-talk state is determined, by preventing the learning of the tap coefficient of the adaptive filter, it is possible to prevent the situation where the echo cannot be canceled for a long time due to the change of the echo path, and the stable echo is stable. Achieve the erase operation.

Although the echo path has changed, Σh
^{In the case of 2} (n)> Δh ² (n), the residual echo signal is smaller than the near-end talker received signal, so that the single talk state can be restored by the double talk determination by the conventional bulltalk detection circuit.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the echo canceller circuit of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the echo canceller circuit of the present invention. In FIG. 1, the echo canceller circuit 10 of this embodiment includes an adaptive filter 101, a subtractor 102, a double talk detection circuit (DTD) 103, a filter coefficient updating unit 123, and an echo path change detecting unit 150. Here, the adaptive filter 101, the subtractor 102, the double-talk detection circuit (DTD) 103, and the filter coefficient updating unit 123 perform almost the same operations as the conventional circuit shown in FIG.
For convenience of description, the same reference numerals as those used in FIG. 2 are used in FIG.

The adaptive filter 101 has the same configuration as that shown in FIG. 2. As shown in FIG. 2, the far-end talker received signal Rs is first input to the input signal register (X-RE).
G) 125 and takes this input signal register (X-R
EG) 125 the far-end talker received signal Rs and the tap coefficient stored in the tap coefficient register (TAP-REG) 126, the convolution operation unit 127 performs the convolution operation, and the transmitter 12 and the receiver. The pseudo echo signal EES corresponding to the echo path EC between the signal 13 and 13 is formed.

The pseudo echo signal EES formed by the adaptive filter 101 is applied to the subtractor 102, which is input from the handset 13 and converted into a digital signal by the analog-digital converter (A / D) 14. By subtracting the pseudo echo signal EES from the near-end talker reception signal Ts, the residual echo signal E with the echo canceled
form s.

The filter coefficient updating unit 123 adaptively controls the update of the tap coefficient of the adaptive filter 101 based on the far-end talker reception signal Rs and the residual echo signal Es. A learning identification method is used as the adaptive algorithm for the update control of the tap coefficient, and the update equation of the tap coefficient is represented by the above-mentioned expression (1).

Double talk detection circuit (DTD) 103
Has absolute value detectors (ABS) 111 and 115. The absolute value detector (ABS) 111 detects the absolute value of the received far-end talker reception signal Rs, and the absolute value detector (ABS)
BS) 115 detects the absolute value of the residual echo signal Es output from the subtractor 102. Here, in the absolute value detector (ABS) 111, the past N of the far-end talker receiving signal Rs is pasted.
A register (X-REG) 118 for storing the data of the times is connected, the output of this register (X-REG) 118 is also input to the absolute value detector (ABS) 111, and the absolute value detector (ABS). ) 115 is a register (E-R) for storing the past N times data of the residual echo signal Es.
EG) 119 is connected to this register (X-R
The output of the EG) 119 is also input to the absolute value detector (ABS) 115.

The absolute value of the far-end talker reception signal Rs detected by the absolute value detector (ABS) 111 is the peak detection circuit (P
EAK-DET) 112, where the peak value of each far-end talker received signal Rs is detected, and this peak value is logarithmically converted by a logarithmic converter (LOG) 113 and added to a subtractor 114.

The absolute value of the residual echo signal Es detected by the absolute value detector (ABS) 115 is added to the peak detection circuit (PEAK-DET) 116, where the peak of each residual echo signal Es is obtained. A value is detected, and this peak value is logarithmically converted by a logarithmic converter (LOG) 113 and added to a subtractor 114.

The subtractor 114 is a logarithmic converter (LOG) 1
Logarithmic converter (LOG) 11 from logarithmic value logX corresponding to the peak value of far-end talker receiving signal Rs output from 13
The logarithmic value logE corresponding to the peak value of the residual echo signal Es output from 7 is subtracted.

That is, in the subtractor 114, logX-logE = R (5) is calculated, which corresponds to the ratio of the peak value X of the far-end talker reception signal Rs to the peak value E of the residual echo signal Es. Find the value R.

The value R calculated by the subtractor 114 is added to the comparator (COMP) 120 and the comparator (COMP)
At 120, this value R is compared with the threshold value Dth output from the threshold value control unit 121, and if R ≦ Dth (6) is satisfied, the double talk state detection signal is output as the double talk state. This double talk state detection signal is added to the filter coefficient updating unit 123.

The echo path change detecting section 150 is based on the near-end talker receiving signal Ts output from the analog-digital converter (A / D) 14 and the residual echo signal Es output from the subtractor 102, and the above-mentioned condition Σh. ² (n) <Δh
^This is to detect a sudden change in the echo path for which ² (n) holds. That is, the echo path change detection unit 150
Has an absolute value detector (ABS) 151, and this absolute value detector (ABS) 151 outputs the near-end talker receiving signal T output from the analog-digital converter (A / D) 14.
Detect the absolute value of s. Here, the absolute value detector (AB
S) 151 is connected to a register (T-REG) 156 that stores the past N times data of the near-end talker reception signal Ts. The output of this register (T-REG) 156 is also an absolute value detector. (ABS) 151 is input. Near-end talker receiving signal T detected by the absolute value detector (ABS) 151
The absolute value of s is the peak detection circuit (PEAK-DET) 15
2, the peak value of the near-end talker reception signal Ts is detected, and this peak value is added to the subtractor 114.

On the other hand, the double talk detection circuit (DTD) 1
The peak value of the residual echo signal Es detected by the peak detection circuit (PEAK-DET) 116 of No. 03 is also subtracted by the subtractor 114.
Added to.

The subtractor 153 is a peak detection circuit (PEA).
K-DET) 152 near-end talker reception signal T added from
From the peak value Tp of s, the peak detection circuit (PEAK-D
A calculation for subtracting the peak value Ep of the residual echo signal Es added from (ET) 116 is performed. That is, the subtracter 15
3 calculates Tp-Ep = G (7) and adds the subtracted value G to the determiner 154.

The determiner 154 determines whether the subtraction value G output from the subtractor 153 is positive or negative. When the subtraction value G output from the subtractor 153 is determined to be negative, a counter (COUNT) is determined. ) 155 is counted up, and when it is determined to be positive, the count value of the counter (COUNT) 155 is cleared. And this counter (COUN
When the count value of (T) 155 reaches a preset value M, the counter (COUNT) 155 outputs an echo path change detection signal. This echo path change detection signal is added to the filter coefficient updating unit 123.

The filter coefficient updating section 123 adaptively adaptively filters the adaptive filter 10 based on the received far-end talker reception signal Rs and the residual echo signal Es output from the subtractor 102.
The tap coefficient updating operation is basically performed when the double talk state detection signal is output from the double talk detecting circuit (DTD) 103. However, when an echo path change detection signal is output from the echo path change detection unit 150, the double talk detection circuit (DT
D) The tap coefficient is updated regardless of whether or not the double talk state detection signal is output from 103.

That is, the filter coefficient updating unit 123
Only when the double talk state detection signal is output from the double talk detection circuit (DTD) 103 and the echo path change detection signal is not output from the echo path change detection unit 150, the update operation of the tap coefficient is prohibited, and other In that case, the tap coefficient is updated.

The double talk detection circuit (DTD) 1
The threshold value control unit 121 of No. 03 is configured to generate the variable threshold value Dth (k) as in the conventional example,
In the single-talk state, in order to make it easier to detect the start timing of double-talk, this variable threshold value Dth
(K) is set to Dth (k + 1) = Dth (k) + δ2. On the other hand, in the double talk state, this variable threshold Dth (k) is set to Dth (k) in order to make it easier to detect the end timing of the double talk. Control for setting (k + 1) = Dth (k) -δ2 is performed.

The variable threshold value Dth (k) has its upper limit set so as to easily return to the single talk state when the double talk state continues for a long time, and conversely, the single talk state continues for a long time. The lower limit value is set in order to make it easier to determine the next double-talk state.

[0034]

As described above, according to the present invention,
Even if a sudden echo path change occurs, it is detected to prevent erroneous double-talk determination due to this abrupt echo path change, so an echo canceller circuit that can perform stable and reliable echo cancellation is provided. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an echo canceller circuit according to the present invention.

FIG. 2 is a block diagram showing a conventional echo canceller circuit.

[Explanation of Codes] 10 Echo Canceller Circuit 11 Digital-Analog Converter (D / A) 12 Transmitter 13 Handset 14 Analog-Digital Converter (A / D) 101 Adaptive Filter 102 Subtractor 103 Double-Talk Detection Circuit (DTD) 111 Absolute value detector (ABS) 112 Peak detection circuit (PEAK-DET) 113 Logarithmic converter (LOG) 114 Subtractor 115 Absolute value detector (ABS) 116 Peak detection circuit (PEAK-DET) 117 Logarithmic converter (LOG) ) 118 register (X-REG) 119 register (X-REG) 120 comparator (COMP) 121 threshold control section 123 filter coefficient updating section 125 input signal register (X-REG) 126 tap coefficient register (TAP-REG) 127 Convolution operation part 150 Echo Scan change detecting unit 151 the absolute value detector (ABS) 152 peak detection circuit (PEAK-DET) 153 subtractor 154 determines 155 the counter (COUNT) 156 registers (T-REG)

Claims (1)

[Claims] 1. A pseudo echo signal is obtained by passing a far-end talker reception signal through an adaptive filter, and echo cancellation is performed by subtracting the pseudo-echo signal from the near-end talker reception signal. If the ratio of the level of the far-end talker-received signal to the level of the residual echo signal obtained by subtracting the pseudo echo signal from the talker-received signal becomes smaller than a predetermined threshold value, this is set to a double-talk state. Is judged,
In an echo canceller circuit that prohibits learning of tap coefficients of the adaptive filter, a subtraction value obtained by subtracting the level of the residual echo signal from the level of the near-end talker signal is observed, and the negative ratio of the subtraction value is An echo canceller circuit, in which, when the number of double-talk states is increased, the prohibition of learning of the tap coefficient of the adaptive filter is released when the number of double-talk states is increased.