JPH08251079A - Echo canceler - Google Patents

Abstract

PURPOSE: To reduce arithmetic process quantity, reduce the power consumption, and increase the stabilizing speed and echo suppression quantity. CONSTITUTION: The echo canceler 1 which holds a tap and a tap coefficient corresponding to the time including the sum of the maximum simple delay part and real response part of an echo path is equipped with a means 2 which detects a simple delay time. Canceling operation does not use a tap and a tap coefficient corresponding to the simple delay time, but uses only an effective tap corresponding to the real response part and a tap coefficient corresponding to the effective tap.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller for suppressing echo generated in a transmission line.

The echo canceller is used for preventing deterioration of speech quality due to echo generated in a 2-wire 4-wire converter or the like. Conventionally, echo cancellers are often used to suppress echo when anxious about echo due to long transmission path such as two-way repeater for call transfer service and repeater for conference call. It was

However, in recent years, applications in which band compression is performed by a voice CODEC in order to reduce the transmission capacity have been widely put into practical use, and in order to remove an echo caused by a delay of the CODEC. Is also widely applied. In reality, it is also widely used in wireless networks such as mobile terminals and their base station systems.

[0004]

2. Description of the Related Art FIG. 7 shows an application position of a conventional echo canceller. In the case of FIG. 7, analog telephone terminals a and b are connected via a communication network to make a call.
2 is a hybrid for 2-wire / 4-wire conversion. When the signal sent from the telephone terminal b is branched to the telephone terminal a in the hybrid 1, an echo component'is generated due to impedance mismatch or the like and is sent to the telephone terminal b.

An echo canceller EC1 is provided because a delay in a transmission path such as the above-mentioned relay or the like, or a delay of a certain time or more due to the use of a satellite line or the like affects the call quality due to echo. The cancel process is performed in the echo canceller EC1. Also,
The echo canceller EC2 has a function of canceling the echo component generated in the hybrid H2 by the transmission signal from the telephone terminal a.

FIG. 9 shows the principle of a conventional echo canceller. This echo canceller (EC) is assumed to correspond to EC1 in FIG. This echo canceller (EC) 8
2 is an FIR filter (Finite Impulse Response Filt)
er), the signal sent from the far-end caller is input from the receiving side input A point) and is input to the tap memory 824, and the pseudo echo generator 823 outputs the echo path (hybrid H from point A). Via the transmission side input point D) via the tap coefficient memory 822 corresponding to the estimated value of the impulse response and the data in the tap memory 824 are calculated and a pseudo echo y _t 'is generated and transmitted by the adder 820. The echo is canceled by subtracting the pseudo echo y _t 'from the side input echo signal y _t . Adder 8
The residual echo (y _t −y _t ′) generated from 20 is transmitted from the output of the transmission side, and at the same time, the tap coefficient updating unit 821.
And the data in the tap memory 824 is used to update each coefficient in the tap coefficient memory 822.

The echo canceller estimates the echo path characteristic based on the input signal on the receiving side. Since the transfer characteristic of the echo path depends on the line to which the echo canceller is connected,
For the echo canceller, transfer characteristics are provided only when a call is made and a call is connected. Therefore, the estimation of the echo path (update of the tap coefficient) is started immediately after the call is connected.

The position where the echo canceller is placed is not necessarily close to the echo generation source such as the 2-line to 4-line converter,
The distance also depends on the connected line. Generally, the echo canceller needs to hold the taps and tap coefficients of the FIR adaptive filter according to the time corresponding to the sum of the simple delay time portion generated between the echo canceller and the echo generation source and the true response portion of the echo path. The cancel operation is performed using all the taps and tap coefficients.

FIG. 8 shows a standard example of the impulse response of the echo path. As shown in FIG. 8, it consists of a simple delay time part, a true response part, and a remainder part. Considering Japan
For example, in Tokyo, the maximum transmission delay is about 40 milliseconds. On the other hand, the impulse response of the 2-wire to 4-wire converter is said to be about 20 milliseconds. Therefore, generally in Japan, the echo canceller needs to have the taps and tap coefficients of the FIR filter corresponding to about 60 milliseconds, which is equivalent to the total of both.

[0010]

As described above, in the prior art, processing is performed to cancel all taps and tap coefficients other than the true response section (about 20 milliseconds in FIG. 8). There was a problem in that the amount of calculation and power consumption were large and the convergence speed was slow.

It is an object of the present invention to provide an echo canceller capable of realizing reduction of processing calculation amount, reduction of power consumption (low power), improvement of convergence speed and echo suppression amount.

[0012]

FIG. 1 is a block diagram showing the first principle of the present invention, and FIG. 2 is a block diagram showing the second principle of the present invention. In FIG. 1, reference numeral 1 denotes an echo canceller, 10 to 13 show a part of the principle of the echo canceller, 10 denotes a buffer for holding and outputting an input signal for a set delay time, 1
Reference numeral 1 is a tap memory, 12 is a tap coefficient updating unit including a tap coefficient memory, 13 is a pseudo echo generating unit, 14 is a subtracting unit, 2 is a delay time measuring unit, and H is a hybrid for 2-wire to 4-wire conversion.

In FIG. 2, 3 is an echo canceller, and 3 is
0 is a tap memory, 31 is a tap coefficient updating unit including a tap coefficient memory, 32 is a pseudo echo generating unit, 33 is an effective tap searching unit, 34 is a subtracting unit, 35 is an echo suppression amount detecting unit, and H is the same as in FIG. It is a similar hybrid.

According to the present invention, of the taps and tap coefficients possessed by the echo canceller, the cancel operation is performed only by the taps (referred to as effective taps) and tap coefficients corresponding to the time of the true response section, thereby reducing the amount of processing calculation and reducing the load. It realizes powering and improvement of convergence speed.

[0015]

In the case of FIG. 1, the external delay time measuring unit 2
The simple delay time until the receiving side output signal is received as the transmitting side input signal via the echo path is measured. The value of the simple delay time obtained by the measurement is input to the echo canceller 1. In the echo canceller 1, the buffer 10 holds only the simple delay time input to the input on the reception side, and then outputs it to the tap memory 11 for the tap (effective tap) corresponding to the true response section. Then, the pseudo echo generation (not shown) and the updating operation in the tap coefficient updating unit 12 are performed. Therefore, the tap memory 11 and the tap coefficient memory (not shown) of the tap coefficient updating unit 12 need only have a capacity corresponding to the impulse response time, and the amount of processing calculation is only the processing of valid taps. It does not take.

Next, in the case of FIG. 2, the tap memory 30 and
Tap coefficient memory of tap coefficient updating unit 31 (not shown)
Has a capacity that covers both the simple delay time part and the response part. As a search for effective taps, while the echo canceller 3 is operating, the effective tap search unit 33 searches for the tap coefficient having the maximum value among all the retained tap coefficients. When the tap coefficient with the maximum value is retrieved,
A certain number of tap coefficients before and after that tap coefficient are selected, and the taps corresponding to these tap coefficients are set as valid taps corresponding to the true response part. Here, when the tap coefficient having the maximum value is not detected, for example, any one of the tap coefficients may be selected.

In the echo canceling process, of the canceling operations, the pseudo echo is calculated using only the effective taps and the corresponding tap coefficients, and the echo path estimation (tap coefficient updating process) is performed in the following (1). It can be performed by either of (2) and. (1) Use all taps and all tap coefficients.

(2) An echo suppression amount detection unit 35 is provided, and while the echo suppression amount is less than a certain amount, the echo path is estimated using all taps and all tap coefficients. Performed using only valid taps and corresponding tap factors.

[0019]

FIG. 3 is a block diagram of the first embodiment. The first embodiment corresponds to the first principle configuration of the present invention shown in FIG.

In FIG. 3, reference numerals 1, 10 to 13, and 2 correspond to the respective symbols in FIG. 1, and 1 is an echo canceller (E
C), 10 is a buffer, 11 is a tap memory having a capacity for a true response time, 12 is a tap coefficient updating unit including a tap coefficient memory (not shown) for a true response time, and 13 is a pseudo echo generating unit. , 14 is a control unit, 15 is a subtractor, 2 is a delay time measuring unit, 3 is a hybrid for two-line to four-line conversion (indicated by H), and 4 is a switch.

The operation of the first embodiment shown in FIG. 3 will be described below.
First, the delay time measuring unit 2 measures the delay time of the echo path from the receiving side output point (shown by a) to the transmitting side input point (shown by b) of the echo canceller 1. Therefore, a control signal is output to the switch 4 to pull each line into the delay time measuring unit 2. Next, the time measurement unit 20 outputs a signal from the measurement signal output unit 21 according to an instruction from the time measurement unit 20, and the time until the signal returns to the delay time measurement unit 2 via the switch 4, the hybrid 3, and the switch 4 is set to the time measurement unit 20. To measure. Information on the measured delay time (t) is supplied to the buffer 10.

This delay time (t) is generally about 40 milliseconds at the maximum in Japan, which corresponds to the time of the simple delay time part shown in FIG. Although the signal sent from the end caller is input, the signal is delayed according to the delay time information input from the delay time measuring unit 2 and then output to the tap memory 11.

The control unit 14 controls the tap coefficient updating operation using the output signal from the buffer 10, the input signal on the transmission side, and the output signal from the subtracter 15. Tap memory 11
A signal on the receiving side delayed by a time corresponding to the simple delay time is input to and holds a capacity of about 20 milliseconds. At this time, the pseudo echo generation unit 13 generates a pseudo echo using the tap coefficient of the tap memory 11 and the tap coefficient update unit 12, and subtracts the pseudo echo from the echo component supplied to the subtractor 15 and input.

The result of the subtraction is sent to the far-end talker as a transmission output signal and is input to the tap coefficient updating unit 12.
The tap coefficient updating unit 12 uses the output of the subtractor 15 and the output of the tap memory 11 to generate a tap coefficient memory (not shown).
The tap coefficient is updated, and the processing result is supplied to the pseudo echo generation unit 13.

According to the first embodiment, the buffer amount for the input on the receiving side is set according to the simple delay time, and the capacity of the tap memory of the echo canceller and the tap coefficient memory of the tap coefficient updating unit is set to about 20 milliseconds. As a result, the size can be reduced, the processing delay can be reduced and the power consumption can be reduced by reducing the calculation processing amount, and the characteristics can be improved.

FIG. 4 is a block diagram of the second embodiment. The second embodiment corresponds to the second principle configuration of the present invention shown in FIG. In FIG. 4, 3 is the echo canceller of the second embodiment, 30 to 33 correspond to respective parts having the same reference numerals shown in FIG. 2, 30 is a tap memory, 31 is a tap coefficient updating part,
Reference numeral 32 is a pseudo echo generation unit, 33 is an effective tap detection unit according to the present invention, 34 is a subtraction unit, and H is a hybrid.

In the second embodiment, the tap coefficient updating unit 3 in the effective tap detecting unit 33 in the echo canceller 3 is used.
The tap coefficient having the maximum value among all the tap coefficients held in 1 is searched. As shown in the explanatory diagram of valid taps in FIG. 5, the valid tap detection unit 33 detects the tap coefficient having the maximum value, and selects a certain number of tap coefficients before and after including the tap coefficient. The taps corresponding to those tap coefficients are set as effective taps corresponding to the true response section.

The valid tap detector 33 inputs the detection information to the pseudo echo generator 32. The pseudo echo generation unit 32 performs pseudo echo calculation using only the portion of the taps and tap coefficients corresponding to valid taps. The tap coefficient updating unit 31 updates the tap coefficients for all tap coefficients as in the conventional case. In this example, since the pseudo echo calculation is performed only with the effective taps, the processing calculation amount required for the pseudo echo calculation is about 1/3 (about 20 milliseconds / second) of the conventional one.
It is possible to reduce the power consumption to about 60 milliseconds), to realize low power, and to improve the convergence speed and the echo suppression amount by not performing the calculation for unnecessary taps.

FIG. 6 is a block diagram of the third embodiment. In FIG. 6, 3 corresponds to the echo canceller of the third embodiment, 30 to 34 correspond to the respective parts of the same reference numerals shown in the second embodiment (FIG. 4),
Reference numeral 30 is a tap memory, 31 is a tap coefficient updating unit, 32 is a pseudo echo generating unit, 33 is an effective tap detecting unit, 34 is a control unit, 35 is an echo suppression amount detecting unit according to the present invention, and H is a hybrid.

In the case of the third embodiment, the echo canceller 3
The effective tap detection unit 33 inside detects the effective tap in the tap memory held therein and inputs the detection information to the pseudo echo generation unit 32. The pseudo echo generation unit 32 calculates a pseudo echo using only a portion corresponding to an effective tap among the held taps and tap coefficients.

The echo suppression amount detector 35 detects the echo amount input to the subtractor 34 as the input information on the transmission side and the subtractor 34.
The echo suppression amount of the echo canceller is calculated by obtaining the difference from the amount of the echo output after being suppressed, and it is detected whether or not the echo suppression amount exceeds a preset fixed amount. The detection result is supplied to the tap coefficient updating unit 31. In the state where the echo suppression amount does not exceed the fixed amount, the tap coefficient updating unit 31 performs update processing on all tap coefficients as in the conventional case, and when it is detected that the fixed amount is exceeded, it corresponds to an effective tap. Update processing is performed only on the tap coefficient to be used.

In this example, the pseudo-echo calculation is performed only with the effective tap coefficient, so that the processing calculation amount required for the pseudo-echo calculation is reduced to about 1/3 as in the case of the second embodiment, and the low power is realized and converged. Improvements in speed and echo suppression can be achieved. Further, when the echo suppression amount exceeds a certain amount, only the tap coefficient corresponding to the effective tap is updated, so that the processing calculation amount required to update the tap coefficient in this case can be reduced to 1/3 of that of the conventional one. Low power can be achieved.

[0033]

According to the present invention, of the taps and tap coefficients possessed by the echo canceller, the cancel operation is performed only with the taps and tap coefficients corresponding to the true response section, thereby reducing the size of the device and reducing the amount of processing calculation. It is possible to realize reduction, lower power consumption, and improvement in convergence speed and echo suppression amount.

[Brief description of drawings]

FIG. 1 is a first principle configuration diagram of the present invention.

FIG. 2 is a second principle configuration diagram of the present invention.

FIG. 3 is a configuration diagram of a first embodiment.

FIG. 4 is a configuration diagram of a second embodiment.

FIG. 5 is an explanatory diagram of valid taps.

FIG. 6 is a configuration diagram of a third embodiment.

FIG. 7 is a diagram showing application positions of a conventional echo canceller.

FIG. 8 is a diagram showing a standard example of an impulse response of an echo path.

FIG. 9 is a diagram showing a principle diagram of a conventional echo canceller.

[Explanation of symbols]

 1 Echo Canceller 10 Buffer 11 Tap Memory 12 Tap Coefficient Update Unit 13 Pseudo Echo Generation Unit 14 Subtraction Unit 2 Delay Time Measurement Unit H Hybrid

Claims (6)

[Claims] 1. An echo canceller for holding a tap and a tap coefficient corresponding to a time including a sum of a maximum simple delay part and a true response part in an echo path, and an echo canceling operation corresponding to the simple delay time. The echo canceller is characterized in that the cancel operation is performed by using only the effective tap corresponding to the true response section and the tap coefficient corresponding to the effective tap without using the tap coefficient. 2. The echo canceller according to claim 1, further comprising an external input for inputting a value corresponding to the simple delay time, the valid tap is identified by using a value from the external input, and the identified valid An echo canceller characterized by performing a cancel operation using only taps and tap coefficients corresponding to the effective taps. 3. The valid tap search unit for searching a valid tap corresponding to a true response unit inside the echo canceller according to claim 1, and corresponding to the valid tap detected by the valid tap search unit and the valid tap. An echo canceller characterized by performing a cancel operation using only tap coefficients. 4. The effective tap search unit according to claim 3, searches for a tap coefficient having a maximum value from all the held tap coefficients, selects a constant tap coefficient before and after including the tap coefficient, An echo canceller characterized in that a tap corresponding to a selected tap coefficient is an effective tap corresponding to a true response section. 5. In a echo canceller which holds a tap and a tap coefficient corresponding to a time including a sum of a maximum simple delay part and a true response part in an echo path, a pseudo echo used for cancellation is calculated as a true response part. An echo canceller characterized by using only effective taps and corresponding tap coefficients corresponding to, and estimating the echo path by using all taps and all tap coefficients. 6. The estimation of an echo path according to claim 5, wherein all taps and all tap coefficients are used during a period when the echo suppression amount is less than a certain amount, and when the echo suppression amount exceeds a certain amount, an effective tap and a corresponding tap are tapped. An echo canceller characterized by being performed using only coefficients.