JPH1098419A - Echo canceller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deterioration in the characteristic of the echo canceller on the occurrence of a burst error and at changeover of echo paths. SOLUTION: In this echo canceller 2 that uses an adaptive FIR filter 12 to estimate an echo path, generates a pseudo echo signal from a received input signal, subtracts the pseudo echo signal from a transmitter side input signal, generates a transmitter side output signal, a uses a tap coefficient update section 14 to update a tap coefficient of the adaptive FIR filter 12 so as to conduct the adaptive control to reduce an echo component in the transmitter side output signal, when the echo canceller 2 detects a characteristic deterioration within a prescribed time, the update of a tap coefficient in the adaptive FIR filter 12 is stopped to reduce the characteristic deterioration on the occurrence of a burst error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller and, more particularly, to an echo canceller which reduces characteristic deterioration when a burst error occurs or when an echo path is switched.

[0002] An echo canceller is used for the purpose of preventing the deterioration of communication quality due to a two-wire / four-wire conversion hybrid of a transmission line and an echo caused by sound contact between a handset and the like.

In an echo canceller, it is necessary to reduce the occurrence of a burst error and the characteristic deterioration that occurs when the echo path is switched so as not to adversely affect the hearing.

[0004]

2. Description of the Related Art Conventionally, an echo canceller is used to suppress echoes that have an adverse effect on speech due to a long transmission path and a large transmission delay, such as a satellite line. Often used. However, in recent years, in order to reduce the transmission capacity, when performing band compression by audio CODEC, CODEC is used.
It is also widely applied to the case where the echo caused by the delay of the system is removed, and is actually widely used in wireless networks such as mobile terminals and base station systems. .

FIG. 16 shows an application position of an echo canceller in a communication system, and exemplifies an application position of an echo canceller for suppressing an echo generated in a two-wire / four-wire conversion hybrid.

In FIG. 16, reference numerals 1 ₁ and 1 ₂ denote echoes based on the voice of speaker A, and reference numerals 2 ₁ and 2 denote two-wire / four-wire conversion hybrids (Hybrid) for connecting speakers A and B respectively. speaker a echo canceller for, 2 ₂ are talker echo canceller for B to cancel echoes based on the sound of the speaker B.

For example, the echo of speaker A is the voice of speaker A
Is part of speaker 1's hybrid 1_Two By the speaker
A signal leaked into the receiving path of A. Speaker A's Eco
ー is the echo canceller 2 on the speaker B side₁ To suppress. Talk
Canceller 2 on the user B side ₁ From, hive of speaker B side
Lid 1_Two Echo canceller 2 via₁ Until returning to
Path of echo canceller 2₁ Called the echo path.
Also echo canceller 2₁ For, speaker A side far end
Side, speaker B side is called the near end side. For the echo of speaker B
The same applies to the case where

FIG. 17 shows an outline of the configuration of an echo canceller, wherein 1 is a hybrid, and 2 is an echo canceller. In the echo canceller 2, reference numeral 11 denotes a tap memory for accumulating tap coefficient values generated by performing a predetermined operation for each sampling period, and reference numeral 12 denotes a pseudo memory from a receiving-side input signal in accordance with tap coefficients held in a plurality of taps. An FIR type adaptive filter (adaptive FIR filter) for generating an echo signal, 13 is a subtraction section for subtracting a pseudo echo from a transmission side input signal to generate a transmission side output signal, and 14 is an adaptive FIR according to the transmission side output signal. A tap coefficient updating unit that performs a process of updating the tap coefficient of the filter 11.

[0009] The tap coefficient updating unit 14 includes a tap memory 1
Adaptive control for sequentially updating the tap coefficients of the adaptive FIR filter 12 is performed based on the tap coefficient values accumulated in 1;
As a result, the adaptive FIR filter 12 generates a pseudo echo signal in the subtraction unit 13 such that the echo component in the input signal on the transmission side is canceled.

As described above, the echo canceller generally uses the FIR type adaptive filter to estimate the echo path based on the input signal on the reception side, generates a pseudo echo signal, and generates the pseudo-echo signal on the transmission side. The echo is suppressed by subtracting the pseudo echo signal, which is the output of the adaptive FIR filter, from the (echo signal + near end input signal).

[0011]

As described above, in the echo canceller, the echo is suppressed by performing the adaptive control based on the input signal on the transmitting and receiving side and the output signal on the transmitting side. Corresponds to the input signal for transmission and reception. That is, it is assumed that an echo signal corresponding to the input signal on the receiving side is input to the transmitting side.

Here, a problem is an error that occurs in the transmission path. In particular, there is a high possibility that a burst error occurring in the echo path affects the quality of the echo canceller. As a case where a burst error occurs in the echo path, for example, a case where the echo path is multiplexed, an error occurs in the frame synchronization bit, and the synchronization is lost, and the like can be considered.

The echo generated in this case becomes a burst error of the input signal on the transmission side for the echo canceller. In this case, since the reception side of the adaptive FIR filter in the echo canceller receives the normal input signal on the reception side, the pseudo echo signal output from the filter becomes a signal corresponding to the original echo signal.

On the other hand, since the transmission-side input signal input to the echo canceller has a burst error, the output signal of the echo canceller, which is the subtraction result between the two, becomes an error. Since the echo canceller performs adaptive control using its own output result, the error path is estimated in an erroneous direction during a period in which a burst error occurs.

In this case, since the correct echo path is estimated again with the signal after the error has disappeared, adaptive control of the echo canceller can recover after the disappearance of the burst error. During this period, the characteristics of the echo canceller will be degraded.

As described above, when the error of the input signal on the transmission side is a burst error, the degree of characteristic deterioration is much larger than that of the case of a random error.
There was a problem that it would affect hearing characteristics.

The cause of the temporary deterioration of the characteristics may be caused by a change in the echo path, in addition to the above-mentioned burst error in the echo path. For example, in an echo canceller when applied to a base station of a mobile communication terminal, switching of the echo path may occur as the terminal moves.

In this case, for a new echo path,
It is necessary to reconverge the echo canceller quickly, but after the echo canceller converges, the update amount of the tap coefficient is often reduced to improve the amount of echo suppression. This takes time, which may have a significant effect on hearing characteristics.

The present invention is intended to solve such problems of the prior art, and a first object of the present invention is to
As described above, the characteristic degradation caused in the echo canceller due to the burst error generated in the echo path is detected quickly, and the updating of the tap coefficients of the adaptive FIR filter is stopped, thereby preventing the estimation of the echo path from being largely disturbed. It is to keep the deterioration to be instantaneous.

Further, a second object of the present invention is to re-converge when the echo path is switched by detecting the switching of the echo path, updating the tap coefficient after increasing the tap coefficient update amount, and updating the tap coefficient. It is to shorten the time to reduce the characteristic deterioration.

Further, a third object of the present invention is to distinguish between a temporary characteristic deterioration state caused by a burst error occurring in an echo path and a characteristic deterioration caused by switching of an echo path, and to temporarily reduce the temporary characteristic deterioration. It is to realize both of the above, and reducing the characteristic deterioration at the time of switching of the echo path.

[0022]

SUMMARY OF THE INVENTION A first object of the present invention is to detect a temporary characteristic deterioration occurring in an echo canceller due to a burst error occurring in an echo path, and to perform adaptive F
Stopping the update of the tap coefficient of the IR filter to prevent a large disturbance in the estimation of the echo path and suppress the characteristic deterioration to an instantaneous one can be realized as follows.

As a method for detecting the characteristic deterioration of the echo canceller, the amplitude value of the output signal on the transmission side, the output signal level on the transmission side, or the pseudo echo signal level is compared with the input signal level on the reception side or the input signal level on the transmission side. Expression
When (1) to (6) hold, it can be regarded as a deteriorated state.

Transmission-side output signal amplitude value> Reception-side input signal level × threshold 1 Expression (1) Transmission-side output signal level> Reception-side input signal level × Threshold value 2 Expression (2) Transmission-side output signal amplitude value> Transmission Side input signal level × threshold 3 Equation (3) Transmission side output signal level> Transmission side input signal level × Threshold 4 Equation (4) Pseudo echo signal level> Receiver input signal level × Threshold 5 Equation (5) Pseudo Echo signal level> transmission side input signal level × threshold value 6 ... Equation (6)

In any of the detection methods, when the characteristic deterioration is temporarily detected, the updating of the tap coefficients is stopped. As a result, it is possible to instantaneously detect the characteristic deterioration of the echo canceller, and it is possible to prevent continuation of erroneous adaptive control by stopping updating of the tap coefficient. As a result, it is possible to keep the characteristic deterioration instantaneous.

In general, the input signal level on the transmitting side is
It is often calculated using data of all taps of the echo canceller. This is because the echo canceller can operate without knowing the simple delay time that occurs in the echo path.
This is because it does not recognize which position in the tap is stored. However, when the calculated values of all taps are used as the input signals on the receiving side when comparing transmitted and received signals as in Equations (1), (2), and (5), accurate comparison should be performed. Can not.

In order to solve this problem, a mechanism for obtaining delay time information of the echo path is provided, and based on the information, the data stored in the tap is used to generate the echo signal. Then, the receiving-side input signal is selected, and the receiving-side input signal level may be calculated based on the selected signal.

In this case, as the level calculator, one having the same configuration can be applied to input / output signals to be transmitted and received. By comparing the levels calculated by the detectors having the same configuration, the detection accuracy can be improved. It is possible. As a method of obtaining the delay time information of the echo path, a method of internally providing a delay time detector, a method of inputting delay time information from the outside, and the like are conceivable.

Hereinafter, specific means and actions for solving the problem in this case will be described.

(1) An echo path is estimated using the adaptive FIR filter 12, a pseudo echo signal is generated from the received input signal, and the pseudo echo signal is subtracted from the input signal on the transmission side to generate an output signal on the transmission side. At the same time, in the echo canceller 2, the tap coefficient updating unit 14 updates the tap coefficients of the adaptive FIR filter 12 based on the transmission-side output signal to perform adaptive control to reduce the echo component in the transmission-side output signal. When the characteristic deterioration is detected within a predetermined time in step 2, the update of the tap coefficients in the adaptive FIR filter 12 is stopped.

(2) In the case of (1), the transmission side output signal amplitude value and the reception side input signal level of the echo canceller 2 or the transmission side output signal level and the reception side input signal level, or the transmission side output signal amplitude value And the transmitter input signal level, or the transmitter output signal level and the transmitter input signal level, or the pseudo echo signal level and the receiver input signal level, or the pseudo echo signal level and the transmitter input signal level for comparison. When each result exceeds a predetermined threshold, the characteristic deterioration of the echo canceller 2 is detected.

By doing so, the characteristic deterioration is instantaneously detected and the updating of the tap coefficient is stopped, so that erroneous adaptive control is prevented from being continued, and the characteristic deterioration amount can be reduced. .

(3) In the case of (2), from the data generated from the input signal on the receiving side and stored in the tap memory 11 based on the delay time information of the echo path, the The selected receiving-side input signal is selected, and the receiving-side input signal level is calculated based on the receiving-side input signal. Thereby, it is possible to improve the detection accuracy of the characteristic deterioration.

The second object of the present invention is to detect the change of the echo path, increase the tap coefficient update amount, and update the tap coefficient, thereby achieving reconvergence at the time of the change of the echo path. Reducing the required time and reducing the characteristic deterioration can be realized as follows.

As a method of detecting the switching of the echo path, a method in which the following means are combined with the determination method based on the above-described equations (1) to (6) can be considered.

A timer is provided in the echo canceller, and
If the state determined by (1) to (6) continues for a certain period of time or more and the double talk state is not detected by the double talk detector, it is not a temporary characteristic deterioration based on a burst error, but an echo. It is determined that the characteristic is deteriorated due to the switching of the route.

Here, the case where the double talk state is not detected is limited in the method of detecting the characteristic deterioration by the above-mentioned equations (1) to (6), and the case of the double talk state is also detected at the same time. This is because there is a possibility.

The update amount used for updating the tap coefficient is usually smaller after convergence of the echo canceller than when the echo canceller converges. Therefore, when reconverging at the time of switching the echo path, the update control is started after increasing the tap coefficient update amount used until immediately before, or the update control is performed by adaptively setting the tap coefficient update amount. By doing so, it is possible to promptly recover the characteristic deterioration at the time of reconvergence.

Hereinafter, specific means and actions for solving the problem in this case will be described.

(4) In the cases (1) to (3), when the continuation of the characteristic deterioration exceeding a certain time is detected, and when the double talk state is not detected, the switching of the echo path is detected and the adaptive FIR filter The update of the tap coefficient at 12 is restarted. As a result, it is possible to reconverge when the echo path is switched, while reducing the amount of characteristic degradation that occurs temporarily.

(5) In the case of (4), when the switching of the echo path is detected, the update of the tap coefficient is restarted by increasing the tap coefficient update amount. As a result, it is possible to reduce the characteristic deterioration amount due to the switching of the echo path.

(6) In the case of (4), a plurality of tap coefficient update amounts are prepared in advance, and when the switching of the echo path is detected, the tap coefficient update amount is selected according to the characteristic deterioration amount to update the tap coefficients. To resume. As a result, the amount of characteristic deterioration due to reconvergence can be further reduced.

(7) In the case of (4), when the switching of the echo path is detected, the update amount of the tap coefficient is set adaptively according to the characteristic deterioration amount, and the update of the tap coefficient is restarted. As a result, the amount of characteristic deterioration due to reconvergence can be further reduced.

The third object of the present invention is to detect the switching of the echo path and identify a temporary characteristic deterioration state caused by a burst error occurring in the echo path and a characteristic deterioration caused by the switching of the echo path. It is possible to realize both actions of suppressing the temporary characteristic degradation to be instantaneous and reducing the characteristic degradation when the echo path is switched, as follows.

The switching of the echo path is detected when the characteristic deterioration continues for a certain period of time, as described above. In this case, since the characteristic deterioration period until the detection is performed may be a temporary characteristic deterioration due to a burst error generated in the echo path, updating of the tap coefficients in the adaptive FIR filter is stopped. Therefore, the echo canceller restarts updating the tap coefficients after detecting the switching of the echo path, and starts reconvergence.

FIG. 18 is a diagram (1) for explaining the tap coefficient update processing when reconvergence is started after the detection of the change of the echo path. In the figure, the tap coefficient update suspension period indicated by (a) is necessary when the characteristic degradation is temporary, but is necessary when the characteristic degradation is caused by the switching of the echo path. The reconvergence time is delayed by this period.

On the other hand, the tap memory and tap coefficient updating unit of the echo canceller are provided with one system (hereinafter referred to as “main system”) used for canceling and one system for standby (hereinafter referred to as “standby system”). ) Is provided, and during the detection of characteristic deterioration, the present system stops the updating process of the tap coefficients, and the standby system performs the updating process. When the characteristic deterioration is temporary, the tap coefficient of this system is continuously used.
When the switching of the echo path is detected, canceling is performed using the tap coefficients of the standby system.

By doing so, it is possible to reduce the amount of characteristic deterioration associated with reconvergence upon detection of echo path switching while suppressing temporary characteristic deterioration to instantaneous deterioration.

FIG. 19 is a diagram (2) for explaining the tap coefficient update processing when reconvergence is started after the detection of the change of the echo path, and shows the operation in the case where the present system and the standby system are provided. . In the figure, the canceling after the tap coefficient update suspension period shown in (a) reconverges using the tap coefficients of the standby system, so that the tap coefficient is one system (same as the example in FIG. 18). It has been shown that the characteristics of the echo canceller are better as compared with.

Hereinafter, specific means and actions for solving the problem in this case will be described.

(8) In the cases of (4) to (7), two systems are provided: a main system that uses the tap memory and the tap coefficient updating unit for the canceling operation of the echo canceller, and a standby system for the standby. Normally, the tap coefficients are updated in both the main system and the standby system.During detection of characteristic deterioration, the main system stops updating the tap coefficients and continues the update process in the standby system, and switches the echo path. At the time of detection, the main system and the standby system are exchanged for canceling. This makes it possible to reduce the amount of characteristic deterioration accompanying reconvergence at the time of echo path switching, while suppressing temporary characteristic deterioration to instantaneous deterioration.

(9) In the case of (8), each time the echo path switching is detected, the main system and the standby system are switched, and within a fixed time from the end of the characteristic deterioration detection and the detection of the echo path switching, A process of copying the value of the tap memory of the system to the tap memory of the standby system is performed. As a result, it is possible to reduce the maximum required processing amount within the sample time.

(10) In the case of (9), when the characteristic deterioration is detected, the update process is started after clearing the tap memory of the standby system. Thereby, early convergence can be achieved at the time of detecting characteristic deterioration.

(11) In the cases of (4) to (7), a tap memory and a tap coefficient updating unit are used for the canceling operation of the echo canceller, and a backup standby system is used.
The standby system is always operating, the standby system operates only when the characteristic deterioration is detected, and when the characteristic deterioration is detected, the value of the tap memory of the main system is copied to the tap memory of the standby system, and then the update processing is performed by the standby system. At the start, when the switching of the echo path is detected, the update processing is started in the main system after the value of the tap memory in the standby system is copied to the tap memory in the main system. As a result, it is possible to reduce the amount of processing required in normal times.

(12) In the cases of (4) to (7), there are two systems: a main system in which the tap memory and the tap coefficient updating unit are used for the canceling operation of the echo canceller, and a standby system for the standby.
System, this system always operates, the standby system operates only during the characteristic deterioration detection, and when the characteristic deterioration is detected, the standby system update process is started after clearing the standby system tap memory,
When the switching of the echo path is detected, the update process is started in the main system after the value of the tap memory in the standby system is copied to the tap memory in the main system. As a result, it is possible to reduce the amount of processing required for normal operation and to improve the convergence speed.

(13) In the cases of (4) to (7), two systems are used: a main system in which the tap memory and the tap coefficient updating unit are used for the canceling operation of the echo canceller, and a standby system for the standby.
The system is always operating, the standby system operates only when the characteristic deterioration is detected, the tap memory of the standby system is cleared within a certain time from the end of the characteristic deterioration detection and the detection of the switching of the echo path, and the echo path is cleared. Upon detection of the switching, the update process is started in the main system after the value of the backup tap memory is copied to the main system tap memory. As a result, it is possible to reduce the amount of processing required in normal times.

[0057]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment (1) of the present invention is intended to achieve the first object of the present invention, and temporarily deteriorates characteristics of an echo canceller due to a burst error generated in an echo path. Is detected and the updating of the tap coefficient of the adaptive FIR filter is stopped, thereby preventing a large disturbance in the estimation of the echo path and suppressing the characteristic deterioration to an instantaneous one.

FIG. 1 is a circuit configuration example of the embodiment (1).
7 shows (1), and shows a configuration in the case where equation (1) is used as a condition for judging characteristic deterioration. FIG.
The same numbers as those in the above case are indicated by the same numbers, 15 is a level calculator for calculating the input signal level on the receiving side from the data stored in the tap memory 11, 16 is the amplitude value of the output signal on the transmitting side and calculated by the level calculator 15. A comparator for comparing the result of multiplying the input signal level of the receiving side by a threshold value 1 is a comparator 17.
The determination unit determines whether or not to update the tap coefficients in the tap coefficient update unit 14 according to the comparison result in No. 6.

The comparator 16 compares the amplitude of the output signal on the transmitting side with the level of the input signal on the receiving side under the condition of equation (1) to generate an output indicating the characteristic deterioration caused in the echo canceller. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic deterioration is based on the burst error generated in the echo path, and updates the tap coefficient in the tap coefficient update unit 14. To stop.

As described above, according to the configuration of FIG. 1, the deterioration of the characteristics in the echo canceller 2 is instantaneously detected, and when it is temporary, the updating of the tap coefficients is stopped. It is possible to prevent the adaptive control from being continuously performed, so that the characteristic degradation of the echo canceller based on the burst error can be kept instantaneous.

FIG. 2 is a circuit configuration example of the embodiment (1).
5 shows (2), and shows a configuration in the case where equation (2) is used as a condition for judging characteristic deterioration. The same components as those in FIG. 1 are indicated by the same reference numerals, and reference numeral 18 denotes a level calculator for calculating the level of the output signal on the transmission side. Comparator 16
Compares the transmission-side output signal level calculated by the level calculation unit 18 with the result obtained by multiplying the reception-side input signal level calculated by the level calculation unit 15 by the threshold value 2.

The comparator 16 compares the transmission-side output signal level with the reception-side input signal level under the condition of the equation (2) to generate an output indicating the characteristic deterioration caused in the echo canceller. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic deterioration is based on the burst error generated in the echo path, and updates the tap coefficient in the tap coefficient update unit 14. To stop.

FIG. 3 is a circuit configuration example of the embodiment (1).
5 shows (3), and shows a configuration in the case where equation (3) is used as a condition for judging characteristic deterioration. 1 are denoted by the same reference numerals, and reference numeral 19 denotes a level calculator for calculating the level of the transmission-side input signal. Comparator 16
Compares the transmission-side output signal amplitude value with the result of multiplying the transmission-side input signal level calculated by the level calculator 19 by a threshold value 3.

The comparator 16 outputs the amplitude value of the output signal on the transmission side,
By comparing the transmission-side input signal level calculated by the level calculation section 19 with the condition of the equation (3), an output indicating the characteristic deterioration caused in the echo canceller is generated. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic degradation is based on a burst error generated in the echo path, and
The update of the tap coefficient in Step 4 is stopped.

FIG. 4 is a circuit configuration example of the embodiment (1).
7 shows (4) and shows a configuration in the case where equation (4) is used as a condition for judging characteristic deterioration. 2 and 3 are denoted by the same reference numerals. The comparator 16 compares the transmission-side output signal level calculated by the level calculation unit 18 with a result obtained by multiplying the transmission-side input signal level calculated by the level calculation unit 19 by a threshold value 4.

The comparator 16 compares the transmission-side output signal level with the transmission-side input signal level under the condition of the equation (4), and generates an output indicating the characteristic deterioration occurring in the echo canceller. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic deterioration is based on the burst error generated in the echo path, and updates the tap coefficient in the tap coefficient update unit 14. To stop.

FIG. 5 is a circuit configuration example in the embodiment (1).
7 shows (5), and shows a configuration in the case where equation (5) is used as a condition for judging characteristic deterioration. 1 are denoted by the same reference numerals, and reference numeral 20 denotes a level calculation unit that calculates the level of the pseudo echo signal at the output of the adaptive FIR filter 12. The comparator 16 compares the pseudo echo signal level calculated by the level calculator 20 with a result obtained by multiplying the receiving-side input signal level calculated by the level calculator 15 by a threshold value 5.

The comparator 16 compares the level of the pseudo echo signal with the level of the input signal on the receiving side under the condition of the equation (5) to generate an output indicating the characteristic deterioration occurring in the echo canceller. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic deterioration is based on the burst error generated in the echo path, and updates the tap coefficient in the tap coefficient update unit 14. To stop.

FIG. 6 is a circuit configuration example of the embodiment (1).
6 shows (6), and shows a configuration in the case where equation (6) is used as a condition for judging characteristic deterioration. The same components as those in FIGS. 3 and 5 are denoted by the same reference numerals. The comparator 16 compares the pseudo echo signal level calculated by the level calculator 20 with a result obtained by multiplying the transmission-side input signal level calculated by the level calculator 19 by a threshold value 6.

The comparator 16 compares the level of the pseudo echo signal with the level of the input signal on the transmitting side under the condition of the equation (6) to generate an output indicating the characteristic deterioration occurring in the echo canceller. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic deterioration is based on the burst error generated in the echo path, and updates the tap coefficient in the tap coefficient update unit 14. To stop.

FIG. 7 is a circuit configuration example of the embodiment (1).
(7) is shown, based on the delay time information of the echo path, selects the input signal on the receiving side that is the source of the echo signal from the data stored in the tap memory. An example in which the input signal level of the receiving side is calculated based on the signal is shown, and a case in which the above-described equation (1) is used is illustrated. However, another equation can be applied. In the figure,
The same components as those in FIG. 1 are indicated by the same numbers, and 21 is a signal for detecting a receiving-side input signal which is a source of an echo signal.
This is a level calculation signal detection unit.

The level calculating signal detecting section 21 selects the receiving-side input signal from which the echo signal is based, based on the delay time information of the echo path from the outside.
5 calculates the level of the input signal on the receiving side. Comparator 1
6 compares the amplitude value of the output signal on the transmission side with the result of multiplying the input signal level on the reception side calculated by the level calculation unit 15 by a threshold value 1.

The comparator 16 compares the amplitude of the output signal on the transmission side with the level of the input signal on the reception side under the condition of the equation (1) to generate an output indicating the characteristic deterioration occurring in the echo canceller. When the continuation of the output is within a predetermined time, the determination unit 17 determines that the characteristic deterioration is based on the burst error generated in the echo path, and updates the tap coefficient in the tap coefficient update unit 14. To stop.

It should be noted that, under the conditions of the formula (2) or (5),
The present invention can also be applied to a case where the output signal level or the pseudo echo signal level on the transmission side is compared with the input signal level on the reception side, and in this case, the level can be compared by a level detector having the same configuration. Therefore, the detection accuracy of characteristic deterioration can be further improved.

Embodiment (2) of the present invention is intended to achieve the second object of the present invention, and detects a change of the echo path, increases the tap coefficient update amount, and then increases the tap coefficient. Is performed, the time required for reconvergence when the echo path is switched is reduced, and the characteristic deterioration is reduced.

FIG. 8 is a circuit configuration example in the embodiment (2).
(1) is the same as that shown in FIGS. 1 and 3, and the same reference numeral is used. Reference numeral 22 denotes a double talk detector for detecting a double talk state.

The double talk detector 22 receives the input signal level on the receiving side from the level calculator 15 and the level calculator 19.
The double talk state is detected by comparing the input signal from the transmitting side. The comparator 16 compares the amplitude value of the output signal on the transmission side with the input signal level on the reception side calculated by the level calculator 15 under the condition of the equation (1), and outputs an output indicating the characteristic deterioration caused in the echo canceller. Occur.

The determination unit 17 is in a state where the characteristics of the echo canceller continue to be degraded for a certain period of time or more by the output of the comparator 16, and the double talk state is generated by the output of the double talk detector 22. When it is detected that there is no echo path switching, it is determined that the echo path has been switched, and the tap coefficient updating unit 14 increases the tap coefficient update amount for the adaptive FIR filter 12. The adaptive FIR filter 12 performs re-convergence of the echo canceller with the increased tap coefficient, so that the time required for re-convergence when the echo path is switched can be shortened, and characteristic deterioration can be reduced.

Instead of simply increasing the tap coefficient update amount, a plurality of tap coefficient update amounts are prepared in advance,
At the time of echo path switching detection, the tap coefficient update amount may be selected according to the characteristic deterioration amount to cause reconvergence, or at the time of echo path switching detection, adaptively according to the characteristic deterioration amount. Set the tap coefficient update amount,
Reconvergence may be performed. As a result, the time required for reconvergence can be further reduced, and the characteristic deterioration can be reduced.

FIG. 9 is a circuit configuration example of the embodiment (2).
(2), which are the same as those in FIGS. 1 and 3 and are indicated by the same numbers, and 23 is a tap coefficient updating unit 14
Is a tap coefficient update amount calculation unit that calculates the update amount of the tap coefficient in.

The comparator 16 compares the transmission-side output signal amplitude value with the reception-side input signal level calculated by the level calculation section 15 under the condition of the equation (1), thereby reducing the characteristic deterioration caused in the echo canceller. Produces the output shown. The determination unit 17 determines whether the output of the comparator 16
When it is detected that the characteristics of the echo canceller continue to deteriorate and the output of the double talk detector (not shown) detects that the double talk state has not occurred, it is determined that the switching of the echo path has occurred. Thus, the tap coefficient updating unit 14 increases the tap coefficient update amount.

At this time, the tap coefficient update amount calculator 23 calculates
The tap coefficient updating unit 14 adaptively sets the tap coefficient update amount for the adaptive FIR filter 12 in accordance with the magnitude of the output indicating the characteristic degradation of the echo canceller based on the comparison result of the comparator 16. Adaptive FIR filter 12
Performs the reconvergence of the echo canceller in an optimum state by using the tap coefficient, so that the time required for the reconvergence when the echo path is switched can be reduced, and the characteristic deterioration can be reduced.

Embodiment (3) of the present invention is intended to achieve the third object of the present invention, in which a temporary characteristic deterioration state due to a burst error occurring in the echo path and a switching of the echo path are used. The present invention realizes both of suppressing the temporary characteristic deterioration to be instantaneous by distinguishing the characteristic deterioration that occurs, and reducing the characteristic deterioration at the time of switching of the echo path.

FIG. 10 shows an example of a circuit configuration in the embodiment (3), in which the same components as those in FIG. 1 are indicated by the same numbers, and 24 _{1 and} 24 ₂ denote the tap coefficient updating unit / tap, respectively. A memory 25 is a switching unit for switching the tap coefficient updating unit / tap memories 24 _{1 and} 24 ₂ to connect to the adaptive FIR filter 12. It is a characteristic degradation state / echo path switching state identification unit for distinguishing the echo path switching state.

One of the two tap coefficient update units / tap memories 24 _{1 and} 24 ₂ is a main system and the other is a standby system. The main system performs canceling. Is updated only, and the characteristic degradation state /
In the echo path switching state identification unit 26, while the characteristic deterioration is being detected, the present system stops updating the tap coefficients, and the standby system performs the tap coefficient updating process. If the characteristic deterioration is temporary, the tap coefficient of the main system is continuously used. However, when the switching of the echo path is detected, the canceling is performed using the tap coefficient of the standby system. This makes it possible to reduce the amount of characteristic deterioration due to reconvergence while suppressing temporary characteristic deterioration to instantaneous deterioration.

FIG. 11 shows a control method according to the embodiment (3).
(1) is shown. As shown in the figure, the two systems of tap coefficient update units / tap memories are always operated, and the main system and the standby system are alternately switched every time the echo path switching is detected. Then, within a certain period from the echo path switching detection point and the characteristic deterioration detection end point, the value of the main tap memory is copied to the standby tap memory,
Processing is performed to make the tap coefficient value of the standby tap memory equal to the tap coefficient of the main tap memory. By employing this method, it is possible to reduce the maximum required processing amount within the sample time.

FIG. 12 shows a control method according to the embodiment (3).
(2) is shown. As shown in the figure, the two systems of tap coefficient update units / tap memories are always operated, and the main system and the standby system are alternately switched every time the echo path switching is detected. Then, at the time of characteristic deterioration detection, after clearing the backup tap memory, within a certain period of time from the time point at which the echo path switching is detected and the time point at which the characteristic deterioration detection ends,
The value of the tap memory of the main system is copied to the tap memory of the standby system, and processing is performed to make the tap coefficient value of the tap memory of the standby system equal to the tap coefficient of the tap memory of the main system.
By adopting this method, it is possible to improve the convergence speed at the time of detecting the characteristic deterioration.

FIG. 13 shows a control method according to the embodiment (3).
(3) is shown. As shown in the drawing, the present system always operates on the two tap coefficient update units / tap memories, and the standby system is controlled so as to operate only during the characteristic deterioration detection. At the time of characteristic deterioration detection, the value of the tap memory of the main system is copied to the tap memory of the standby system, and then the update process is started at the standby system. After copying to the tap memory, the update process is started in the main system. By employing this method, it is possible to reduce the amount of processing required in normal times.

FIG. 14 shows a control method according to the embodiment (3).
(4) is shown. As shown in the drawing, the present system always operates on the two tap coefficient update units / tap memories, and the standby system is controlled so as to operate only during the characteristic deterioration detection. When the characteristic deterioration is detected, the update processing is started in the standby system after clearing the tap memory of the standby system, and when the switching of the echo path is detected, the value of the tap memory of the standby system is copied to the tap memory of the main system. Start update processing in the system. By adopting this method, it is possible to reduce the amount of processing required in normal times and to improve the convergence speed.

FIG. 15 shows a control method according to the embodiment (3).
(5) is shown. As shown in the drawing, the present system always operates on the two tap coefficient update units / tap memories, and the standby system is controlled so as to operate only during the characteristic deterioration detection. Within a certain period of time from the end of characteristic deterioration detection and the detection of echo path switching, the standby system tap memory is cleared, and when the echo path switching is detected, the value of the standby system tap memory is copied to the main system tap memory. ,
Start update processing in this system. By employing this method, it is possible to reduce the amount of processing required in normal times.

[0091]

As described above, in the echo canceller of the present invention, it is possible to detect the characteristic deterioration instantaneously, thereby stopping the updating of the tap coefficient.
Since it is possible to prevent the erroneous adaptive control from being continued, it is possible to limit the characteristic degradation to an instantaneous one.

Further, it is possible to detect the switching of the echo path, and by updating the tap coefficient after increasing the tap coefficient update amount, the time required for reconvergence at the time of the switching of the echo path is obtained. Since it is shortened, the characteristic deterioration can be significantly reduced.

Further, by distinguishing between a temporary characteristic deterioration state caused by a burst error occurring in the echo path and a characteristic deterioration caused by switching of the echo path, the temporary characteristic deterioration can be suppressed to an instantaneous one.
It is possible to realize both of the above-mentioned features, that is, to reduce characteristic deterioration when the echo path is switched.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration example (1) in an embodiment (1).

FIG. 2 is a diagram showing a circuit configuration example (2) in the embodiment (1).

FIG. 3 is a diagram showing a circuit configuration example (3) in the embodiment (1).

FIG. 4 is a diagram showing a circuit configuration example (4) in the embodiment (1).

FIG. 5 is a diagram showing a circuit configuration example (5) in the embodiment (1).

FIG. 6 is a diagram showing a circuit configuration example (6) in the embodiment (1).

FIG. 7 is a diagram showing a circuit configuration example (7) in the embodiment (1).

FIG. 8 is a diagram showing a circuit configuration example (1) in the embodiment (2).

FIG. 9 is a diagram showing a circuit configuration example (2) in the embodiment (2).

FIG. 10 is a diagram showing an example of a circuit configuration according to the embodiment (3).

FIG. 11 is a diagram showing a control method (1) in the embodiment (3).

FIG. 12 is a diagram showing a control method (2) in the embodiment (3).

FIG. 13 is a diagram showing a control method (3) in the embodiment (3).

FIG. 14 is a diagram showing a control method (4) in the embodiment (3).

FIG. 15 is a diagram showing a control method (5) in the embodiment (3).

FIG. 16 is a diagram illustrating an application position of an echo canceller in a communication system.

FIG. 17 is a diagram illustrating an outline of a configuration of an echo canceller.

FIG. 18 is a diagram (1) illustrating a tap coefficient update process when reconvergence is started after detection of a change in an echo path.

FIG. 19 is a diagram (2) illustrating a tap coefficient update process when reconvergence is started after detection of a change in an echo path.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 hybrid 2 echo canceller 11 tap memory 12 adaptive FIR filter 13 subtractor 14 tap coefficient update unit 15 level calculation unit 16 comparator 17 determination unit 18 level calculation unit 19 level calculation unit 20 level calculation unit 21 level calculation signal Detector 22 Double talk detector 23 Tap coefficient update amount calculator 24 ₁ Tap coefficient update unit / tap memory 24 ₂ Tap coefficient update unit / tap memory 25 Switching unit 26 Characteristic deterioration state / echo path switching state identification unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Fujino 4-1-1, Kamiodanaka, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Kazunari Hirakawa 3--22, Hakata-ekimae, Hakata-ku, Fukuoka City, Fukuoka Prefecture No. 8 Inside Fujitsu Kyushu Digital Technology Co., Ltd.

Claims (13)

[Claims] An echo path is estimated using an adaptive FIR filter to generate a pseudo echo signal from a received input signal, and the pseudo echo signal is subtracted from a transmission input signal to generate a transmission output signal. A tap coefficient updating unit that updates the tap coefficients of the adaptive FIR filter based on the transmission-side output signal, thereby performing adaptive control to reduce an echo component in the transmission-side output signal. An echo canceller, which stops updating of tap coefficients in the adaptive FIR filter when characteristic deterioration is detected within a predetermined time. 2. The echo canceller according to claim 1, wherein a transmission-side output signal amplitude value and a reception-side input signal level, or a transmission-side output signal level and a reception-side input signal level, or a transmission-side output signal of the echo canceller. The amplitude value is compared with the transmission side input signal level, or the transmission side output signal level and the transmission side input signal level, or the pseudo echo signal level and the reception side input signal level, or the pseudo echo signal level and the transmission side input signal level are compared. When the comparison results exceed predetermined threshold values, respectively, the characteristic deterioration of the echo canceller is detected. 3. The echo canceller according to claim 2, wherein, based on the delay time information of the echo path, an echo signal is selected from data generated from a receiving-side input signal and stored in a tap memory. An echo canceller characterized by selecting the receiving-side input signal obtained as described above and calculating the receiving-side input signal level based on the receiving-side input signal. 4. The echo canceller according to claim 1, wherein when the continuation of the characteristic deterioration exceeding the predetermined time is detected and the double talk state is not detected, the echo path is switched. , And updating of tap coefficients in the adaptive FIR filter is restarted. 5. The echo canceller according to claim 4, wherein, when the switching of the echo path is detected, the update amount of the tap coefficient is increased and the update of the tap coefficient is restarted. 6. The echo canceller according to claim 4, wherein a plurality of tap coefficient update amounts are prepared in advance, and when the echo path switching is detected, a tap coefficient update amount is selected according to the characteristic deterioration amount to perform tapping. An echo canceller characterized by restarting coefficient updating. 7. The echo canceller according to claim 4, wherein when the switching of the echo path is detected, the tap coefficient update amount is adaptively set according to the characteristic deterioration amount, and the tap coefficient update is restarted. And echo canceller. 8. The echo canceller according to claim 4, wherein said tap memory and said tap coefficient updating unit are used for a canceling operation of said echo canceller, and said spare is used as a spare. In the normal state, the tap coefficients are updated in both the main system and the standby system. During the characteristic deterioration detection, the main system stops updating the tap coefficients and performs update processing in the standby system. An echo canceller characterized in that, when the switching of the echo path is detected continuously, the main system and the standby system are switched to perform the canceling. 9. The echo canceller according to claim 8, wherein the main system and the standby system are switched every time when the switching of the echo path is detected, and within a fixed time from the end of the characteristic deterioration detection and the time of the detection of the switching of the echo path. An echo canceller for performing a process of copying a value of a tap memory of a main system to a tap memory of a standby system. 10. The echo canceller according to claim 9, wherein an update process is started after clearing a standby tap memory when characteristic deterioration is detected. 11. The echo canceller according to claim 4, wherein said tap memory and said tap coefficient updating unit are used for a canceling operation of said echo canceller, and a backup spare is used. 2 with the system
The system is always operating, the standby system operates only when the characteristic deterioration is detected, and when the characteristic deterioration is detected, the value of the tap memory of the main system is copied to the tap memory of the standby system, and then the update processing is performed by the standby system. An echo canceller characterized by starting and updating a tap memory of a backup system to a tap memory of a main system after detecting a change of an echo path, and then starting an update process in the main system. 12. The echo canceller according to claim 4, wherein said tap memory and said tap coefficient updating unit are used for a canceling operation of said echo canceller, and said spare is used as a spare. 2 with the system
System, this system always operates, the standby system operates only during the characteristic deterioration detection, and when the characteristic deterioration is detected, the standby system update process is started after clearing the standby system tap memory,
An echo canceller characterized in that upon detection of a change of an echo path, an update process is started in the main system after copying the value of the tap memory in the standby system into the tap memory in the main system. 13. The echo canceller according to claim 4, wherein said tap memory and said tap coefficient updating unit are used for a canceling operation of said echo canceller, and a backup spare is used. 2 with the system
The system is always operating, the standby system operates only when the characteristic deterioration is detected, the tap memory of the standby system is cleared within a certain time from the end of the characteristic deterioration detection and the detection of the switching of the echo path, and the echo path is cleared. An echo canceller characterized in that upon detection of switching, the value of the standby tap memory is copied to the main tap memory and then the update processing is started in the main system.