JPH0865213A - Echo canceler - Google Patents

Abstract

PURPOSE: To provide an echo canceler in which a nonlinear concordant area is made variable so as to conduct optimum nonlinear concordant processing in response to a state of an echo path. CONSTITUTION: The echo canceler 606 in which a nonlinear echo canceler generating a nonlinear pseudo echo component and a linear echo canceler generating a linear pseudo echo component are combined is provided with a nonlinear concordant range decision processing section 101 to obtain a concordant area of the nonlinear echo canceler maximizing the integral value of impulse response under the operation of the linear echo canceler in the converging state and with a switch 102 activating the nonlinear echo canceler at its concordant area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller used in a transceiver that bidirectionally transmits data using, for example, a metallic two-wire cable.

[0002]

2. Description of the Related Art An echo canceller system is one of the systems for performing bidirectional digital data transmission using an existing metallic two-wire cable (subscriber line). FIG. 6 is a diagram showing the configuration of the echo canceller system. As shown in the figure, the transmission data includes an encoder 601 and a D / A converter 60.
2 and the driver circuit 603, and then the hybrid circuit 6
It is input to 04. The hybrid circuit 604 transmits the transmission signal to the transmission line 605, and blocks a wraparound echo of the transmission signal to the receiving circuit side.

By the way, the characteristics of the transmission line 605 vary over a wide range depending on the use conditions such as the length of the transmission line, the branch line, and the line diameter. However, it is not possible to realize a hybrid circuit that can completely eliminate the wraparound echo under use conditions that vary over a wide range. Therefore, a part of the transmission signal sneak into the reception circuit and is superimposed on the reception signal to deteriorate the reception signal.

The echo canceller 606 shown in FIG. 6 suppresses an echo by generating a pseudo echo signal equivalent to a sneak echo from the transmission signal and subtracting the pseudo echo from the sneak echo to the reception circuit side of the transmission signal.
The received signal is transmitted from the transmission line 605 to the hybrid circuit 60.
The reception filter 607 that performs processing such as band limitation after 4
Is input to Then, the echo is removed by the adder 609 through the A / D converter 608, and the original signal is restored through the line equalizer 610 and the decoder 611. The echo canceller 606 generally uses a transversal type filter as shown in FIG. The echo canceller 606 of the transversal type filter shown in FIG.
A plurality of delay lines 701 for inputting and sequentially delaying a transmission signal, a multiplier 702 for weighting the output of each delay line 701, and an adder 7 for adding the output of each multiplier 702.
And 03. The weighting coefficient of each multiplier 702 is obtained by the LMS algorithm based on an error signal which is a difference signal between the echo and the output of the echo canceller, for example. Coefficient obtained in this way (tap coefficient)
Becomes the sampling value of the impulse response of the echo path, and the equivalent of the echo path can be equivalently realized by the transversal type filter, and thus the pseudo echo component can be generated.

However, in the case of an echo canceller consisting of a transversal type filter, since the pseudo echo is generated by linear addition of each tap coefficient, the nonlinear characteristics of the D / A converter, the hybrid circuit, etc. included in the echo path cause. It is not possible to cancel the echo with the resulting non-linear component.

Therefore, a RAM map type echo canceller is known as an echo canceller for suppressing such a non-linear component. FIG. 8 is a diagram showing a general configuration of a RAM map type echo canceller. RA shown in FIG.
The M-map type echo canceller is a multiplier 702 and an adder 70 in the transversal type filter shown in FIG.
3 is replaced with the RAM 801, and the addition result of each tap is written in the contents of the RAM 801. In this RAM map type echo canceller, since the pseudo echo component is generated for each input waveform, it is possible to suppress the non-linear component.

However, when the number of taps (the number of delay lines) increases, the RAM capacity increases sharply. Therefore, for example, 2B1Q
In the case of a code (which means a code of 2 bits per symbol), if it exceeds 8 taps, it becomes unrealistic.

Therefore, for example, when a long tap number such that the impulse response length of the echo path reaches several tens of taps is required, the RAM map type and the transversal type are conventionally used together. That is, since the nonlinear distortion sharply decreases as the amplitude decreases, it is not necessary to consider the influence of the nonlinear component in the region where the amplitude response is relatively small, and the transversal type that removes the linear echo component can be used. . RA like this
9 and 10 show configuration examples of an echo canceller that uses both the M map type and the transversal type. Figure 9 shows R
The AM map type and the transversal type are connected in parallel. FIG. 10 shows a RAM map type and a transversal type connected in series.

[0009]

However, a non-linear echo canceller such as a RAM map type echo canceller which produces a non-linear pseudo echo component and a transversal echo canceller which produces a linear pseudo echo component are used together. In this case, considering a general and realistic RAM capacity, the RAM map type is, for example, 1 symbol 2
If expressed in bits, it will be about 8 taps, and RAM
The map type non-linear correspondence area is fixed. In this case, depending on the state of the echo path, the area near the main tap of the echo path impulse response (the area having a relatively large impulse response value) deviates from the RAM map type non-linear type corresponding area, and the echo suppression component for the non-linear component deteriorates. There is a case. Further, in order to maximize the cancellation performance of the nonlinear echo component in the limited non-linear response region, it is desired to make the non-linear response region variable.

The present invention has been made in order to solve such a problem, and provides an echo canceller capable of varying the non-linear correspondence region and performing the optimum non-linear correspondence processing according to the situation of the echo path. The purpose is to do.

[0011]

In order to solve such a problem, an echo canceller of the present invention is an echo canceller for removing a wraparound echo from a transmission signal to a receiving circuit, which is a non-linear type which produces a non-linear pseudo echo component. An echo canceller, a linear echo canceller that generates a linear pseudo echo component, a determining unit that determines an optimum corresponding region of the nonlinear echo canceller according to characteristics of an echo path, and the nonlinear echo canceller. And means for operating in the corresponding area determined by the determining means. As an aspect of the echo canceller of the present invention, a non-linear echo canceller that generates a non-linear pseudo echo component and a linear pseudo echo component are generated in an echo canceller that removes a wraparound echo from a transmission signal to a reception circuit. Under the operation of the linear echo canceller and the linear echo canceller in the converged state, the range of the tap length of the nonlinear echo canceller that maximizes the integral value of the impulse response is obtained, and this range is set to the nonlinear echo. Some include a determining unit that determines the corresponding region of the canceller, and a unit that operates the non-linear echo canceller in the corresponding region determined by the determining unit.

Further, as another aspect of the echo canceller of the present invention, in an echo canceller for removing a wraparound echo from a transmission signal to a reception circuit, a non-linear echo canceller for generating a non-linear pseudo echo component and a linear pseudo canceller. A linear echo canceller that produces an eco-component,
Under the operation of the non-linear echo canceller and the non-linear echo canceller in the converged state, the application range of the non-linear echo canceller in which the average value of the eco-residual component is minimum is obtained, and this range is set to the non-linear echo. Some include a determining unit that determines the corresponding region of the canceller, and a unit that operates the non-linear echo canceller in the corresponding region determined by the determining unit.

[0013]

In the present invention, since the corresponding area of the non-linear echo canceller is changed to be optimum according to the characteristics of the echo path, the optimum nonlinear correspondence processing can be performed in the limited corresponding area. It is possible to maximize the cancellation performance of the nonlinear echo component by the nonlinear echo canceller.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a transceiver according to an embodiment of the present invention. As shown in the figure, the transmission signal is sent to the transmission line 605 via the D / A converter 602, the driver 603 and the hybrid circuit 604.
At this time, due to the incompleteness of the hybrid circuit 604,
Part of the transmitted signal wraps around to the receiving circuit side as an echo.
The echo canceller 606 suppresses this wraparound echo. The echo canceller 606 in this embodiment is
This is a configuration in which a RAM map type echo canceller and a transversal type echo canceller are used together. In the echo canceller 606, the delay line 701 and the RAM 801 constitute a RAM map type echo canceller. Also,
The delay line 701, the multiplier 702, and the adder 703 form a transversal echo canceller. Further, reference numeral 101 is a non-linear corresponding range determination processing unit according to the present invention, and reference numeral 102 is a switch according to the present invention.

First, as a training, the transversal type echo canceller is operated, and the tap coefficient is corrected by using, for example, the algorithm of the successive correction type steepest descent method to sufficiently suppress the echo. At this time, the tap coefficients C0 to CN are sample values of the echo path impulse response as shown in FIG.

The non-linear correspondence range determination section 101 determines the non-linear correspondence range using the tap coefficients C0 to CN.

FIG. 3 is a diagram showing the configuration of the non-linear corresponding range determination processing unit 101. As shown in the figure, first of all,
The selector unit 301 causes the continuous tap coefficients C0 to Cn- of the tap coefficients C0 to CN obtained by the above-described processing.
Select 1 (n is the number of nonlinear echo canceller taps). These tap coefficients C0 to Cn-1 are input to A of the maximum value detection unit 302 after the sum of squares is calculated. The output control signal generator 303 causes the selector 301 to have a tap coefficient C.
The selector output control data as tap range information for selecting 0 to Cn-1 is output, and this selector output control data is input to Ac of the maximum value detection unit 302. The maximum value detection unit 302 compares the sum of squares of the tap coefficients input to A with the input of B, which is the value of the maximum value storage RAM 304, and if A> B, gives Z = A and Zc = Ac as outputs, If A <B, Z = B and Zc = Bc are output.
The Z output of the maximum value detection unit 302 is the maximum value storage RAM 3
It is stored in 04. Further, selector output control data as tap range information giving the maximum value is output from Zc of the maximum value detection unit 302 and tap range information storage RAM.
In addition to being stored in 305, the input control signal generation unit 306
Is output to Next, the output control signal generator 303 changes the selector unit output control data so as to select consecutive tap coefficients C1 to Cn, and these tap coefficients C1 to Cn are selected.
The sum of squares of n is obtained and input to A of the maximum value detection unit 302, the same processing as described above is performed, and the maximum value and tap range information are updated.

A series of these processes are sequentially performed by changing the corresponding range starting point taps as C0 → C1 → C2 → C3 → .... Then, in the linear echo canceller tap range, the tap coefficient 2 in the non-linear corresponding tap section
The range that gives the maximum value of the sum of multiplications is found, and the range that gives this maximum value is determined as the non-linear processing adaptive region.

After that, based on the value of the tap information storage RAM 305 which gives this non-linear processing adaptive area, the switch 102 shown in FIG.
A control signal for switching connection / disconnection is generated, and the input signal of the RAM map type echo canceller is switched.

By the above processing, the adaptive range of the RAM map type echo canceller is determined and the training is performed again, and the transversal type echo canceller and the RAM map type echo canceller are simultaneously learned to suppress the echo.

Next, an embodiment in which the adaptive area is determined from the residual echo amount will be described.

FIG. 4 is a diagram showing the configuration of the transceiver according to the embodiment. The echo canceller 606 in the transceiver shown in the figure has the functions of the nonlinear corresponding range determination processing unit 101 and the switch 102 in the echo canceller 606 shown in FIG.
However, it is different from the above-described embodiment in that the adaptive region is determined from the residual echo amount.

FIG. 5 is a diagram showing the configuration of the non-linear corresponding range determination processing unit 401. As shown in the figure, in the non-linear corresponding range determination processing unit 401, the selector 301 first outputs the outputs X0 to XN (each of the delay lines 701 of the linear echo canceller based on the output of the output control signal generation unit 303). N
+1 is the number of taps of the linear echo canceller) and selects continuous output signals RC0 to RCn (n + 1 is the number of taps of the nonlinear echo canceller) to the RAM map type echo canceller which is a non-linear echo canceller. After the echo canceller 606 is trained and the linear echo canceller and the non-linear echo canceller are converged, the residual echo amount ek which becomes the echo cancellation residual is input. Then, from the residual echo amount ek, the integration processing unit 501 calculates the average value of the echo cancellation residual power for a fixed time. The minimum value detecting unit 504 compares the average value of the power input to A and the minimum power value (stored in the RAM 502) input to B, and if A ≦ B, Z = A and Zc = A.
c, and if A> B, Z = B and Zc = Bc. The output of Z of the minimum value detection unit 504 is the RAM 5
Stored in 02. The output of Zc is the RAM 503.
Stored in.

The series of processes are sequentially performed by the selector 30.
1 output signal RC0 to RCn → RC1 to RCn + 1 → R
C2 to RCn + 2 → RC3 to RCn + 3 → ... Then, the range in which the echo residual power is minimized is obtained. The range obtained as a result is set as the optimum non-linear corresponding region, the input of the non-linear echo canceller is determined based on this information, and the training is performed again to suppress the echo.

[0026]

As described above, according to the present invention, the optimum nonlinear correspondence processing can be performed in a limited correspondence area, and the cancellation performance of the nonlinear echo component by the nonlinear echo canceller can be maximized. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a transceiver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a state of an echo path impulse response.

3 is a diagram showing a configuration of a non-linear corresponding range determination processing unit shown in FIG.

FIG. 4 is a diagram showing a configuration of a transceiver according to another embodiment of the present invention.

5 is a diagram showing a configuration of a non-linear corresponding range determination processing unit shown in FIG.

FIG. 6 is a diagram illustrating a general configuration example of a transceiver including an echo canceller.

FIG. 7 is a diagram showing a general configuration of a transceiver having a transversal echo canceller.

FIG. 8 is a diagram showing a general configuration of a transceiver including a RAM map type echo canceller.

FIG. 9 is a diagram showing a general configuration of a transceiver having an echo canceller that uses both a RAM map type and a transversal type.

FIG. 10 is a diagram showing a general configuration of a transceiver having an echo canceller that uses both a RAM map type and a transversal type.

[Explanation of symbols]

101 ... Non-linear correspondence range determination processing unit, 102 ... Switch, 602 ... D / A converter, 603 ... Driver, 604
Hybrid circuit 605 Transmission line 606 Echo canceller 608 A / D converter 609 Adder 701 Delay line 702 Multiplier 703 Adder 801 RAM

Claims (3)

[Claims] 1. An echo canceller for removing a wraparound echo from a transmission signal to a receiving circuit, a non-linear echo canceller for generating a non-linear pseudo echo component, and a linear echo canceller for generating a linear pseudo echo component. And a determining unit that determines an optimum corresponding region of the nonlinear echo canceller according to the characteristics of an echo path, and a unit that operates the nonlinear echo canceller in the corresponding region determined by the determining unit. Characteristic echo canceller. 2. An echo canceller for removing a wraparound echo from a transmission signal to a receiving circuit, a non-linear echo canceller for generating a non-linear pseudo echo component, and a linear echo canceller for generating a linear pseudo echo component. Under the operation of the linear echo canceller in the converged state, the range of the tap length of the nonlinear echo canceller that maximizes the integral value of the impulse response is obtained, and this range is defined as the corresponding region of the nonlinear echo canceller. An echo canceller comprising: determining means for determining; and means for operating the non-linear echo canceller in the corresponding region determined by the determining means. 3. An echo canceller for removing a wraparound echo from a transmission signal to a receiving circuit, a non-linear echo canceller for generating a non-linear pseudo echo component, and a linear echo canceller for generating a linear pseudo echo component. Under the operation of the non-linear echo canceller and the non-linear echo canceller in the converged state, the application range of the non-linear echo canceller in which the average value of the eco-residual component is minimized is obtained, and this range is set to the non-linear type An echo canceller, comprising: determining means for determining the corresponding area of the echo canceller; and means for operating the non-linear echo canceller in the corresponding area determined by the determining means.