JPH03259629A - Echo canceller - Google Patents

Abstract

PURPOSE:To improve the echo suppression quantity by cancelling an echo linear component with a 1st echo replica generated by a linear component generating means and cancelling an echo nonlinear component with a 2nd echo replica generated by a nonlinear component generating means. CONSTITUTION:A linear component generating means 111 of an echo canceller cancelling the echo component caused by bypassing part of a transmission signal of a multi-value code to a receiver side generates and outputs a 1st echo replica having the linearity corresponding to various multi-value codes to cancel the echo component. A nonlinear component generating means 121 generates and outputs a 2nd echo replica corresponding to the difference between the echo component and the 1st echo replica. A cancellation means 131 subtracts the 1st and 2nd echo replicas from a reception signal to cancel the echo component. Thus, as a whole, both the linear component and the nonlinear component of the echo corresponding to the transmission signal of the multi-value code are constructed so as to cancel each other.

Description

[Detailed Description of the Invention] [Summary] In a transmission device that transmits data using a multilevel code, two
Regarding echo cancellers that eliminate echoes caused by mismatching in hybrid circuits that perform wire/four-wire conversion, we aim to improve the amount of echo suppression by eliminating echoes that occur when part of the multilevel code transmission signal wraps around to the receiving side. In an echo canceller that cancels an echo component, linear component generating means generates and outputs a first echo replica having linearity corresponding to the multi-values of a multi-level code, and a linear component generating means for canceling the echo component. nonlinear component generating means for generating and outputting a second echo replica corresponding to the difference from the first echo replica;
and canceling means for canceling the echo component by subtracting the second echo replica.

[Industrial application field]

The present invention relates to an echo canceller that cancels echoes caused by mismatching of a hybrid circuit that performs 2-line and 74-line conversion in a transmission device that transmits data using multilevel codes.

When bidirectional data transmission is performed via a hybrid circuit, a portion of the transmitted signal goes around as an echo to the receiving side via the hybrid circuit, thereby deteriorating the quality of the received signal. Therefore, it is necessary to cancel the echo of a part of the transmitted signal that has gone around to the receiving side.

[Conventional technology]

FIG. 5 shows the configuration of a conventional example that uses an echo canceller to cancel echoes. In FIG. 5, 411 is an echo canceller, 421 is a multilevel code transmission circuit, and 4
31 is a hybrid circuit (HYB), 441 is an adder, 451 is a multilevel code receiving circuit, and 461 is a digital-to-analog (D/A) converter.

The transmission signal transmitted from the multilevel code transmission circuit 421 is sent out to the two-wire line via the hybrid circuit 431, and at the same time, a part of it goes around to the receiving side as an echo. The echo canceller 411 is for generating an echo replica to cancel this wraparound echo.
The generated echo replica is converted into an analog signal by a D/A converter 461 and then input to an adder 441.

The adder 441 converts the received signal into an echo replica (D/A
(output of converter 461) to output a received signal with echo components canceled. Multilevel code receiving circuit 451 receives this received signal.

Further, in the echo canceller 411 shown in FIG.
21 to 525 and 551 to 555 are multipliers; 541 to 555 are multipliers;
545 and 561 indicate adders, respectively.

Four taps 511 to 514 are for sequentially delaying and capturing transmission symbols, and these captured symbols and tap coefficients C1 to C9 are applied to multipliers 521 to 521, respectively.
An echo replica is generated by multiplying by 525 and adding all the multiplication results by an adder 561. Equation (1) shows an equation for calculating an echo replica in the echo canceller 411.

rEcRJ is an echo replica, rC, (n=1 to 5)
” indicates a tap coefficient, and “a, ” indicates a symbol value, respectively.

Multipliers 551 to 555 multiply the input residual echo component ε by a tap coefficient update coefficient α to obtain a tap coefficient update value δ, and add the obtained tap coefficient update value δ. The tap coefficients C1 to C are updated by adding them in the units 541 to 545.

[Problem to be solved by the invention]

By the way, in the conventional method mentioned above, one tap per tap
The tap coefficients correspond to each other, and an echo replica is calculated by multiplying each symbol value a7 by each tap coefficient C7.

Therefore, there is no problem if the loop echo maintains linearity with respect to the multi-value (symbol value) of the multi-value code, but
There is a problem in that a sufficient amount of echo suppression cannot be obtained when a nonlinear component of the echo is present.

For example, the 2BIQ code is the 2-bit “10°” of the binary symbol.
"11""01'""oo" +3°+1.-1.-
Transmission is performed in accordance with the four-value level of 3, but if the echo component lacks linearity, a difference will occur between the actual echo component B and the echo replica A used for calculation, as shown in Figure 6. Therefore, residual echo components exist and the amount of echo suppression deteriorates.

Such nonlinearity of the echo component is mainly due to the signal sending ability of the multilevel code transmitting circuit 421, which functions as a line driver.

The present invention was created in view of these points, and an object of the present invention is to provide an echo canceller that improves the amount of echo suppression.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the echo canceller of the present invention.

In the figure, a linear component generating means 111 in an echo canceler that cancels an echo component generated when a part of a transmission signal of a multi-level code goes around to the receiving side is a linear component generating means 111 of a multi-level code. A first echo replica having linearity corresponding to is generated and output.

The nonlinear component generation means 121 generates and outputs a second echo replica corresponding to the difference between the echo component and the first echo replica.

The canceling means 131 cancels the seven eco precepts by subtracting the first and second echo replicas from the received signal.

Therefore, as a whole, it is configured to cancel both the linear component and the nonlinear component of the echo corresponding to the multilevel code transmission signal.

[For production]

When the transmission signal of the multilevel code is input to each of the linear component generation means 111 and the nonlinear component generation means 121, the linear component generation means 111 generates a first echo having linearity corresponding to the multivalues of the multilevel code. Generate and output a replica.

On the other hand, the nonlinear component generating means 121 generates and outputs a second echo replica corresponding to the difference between the echo and the above-mentioned first echo replica, that is, the nonlinear portion of the echo. The canceling means 131 cancels the echo component contained in the received signal by subtracting these two echo replicas from the received signal.

In the present invention, the linear component of the echo is canceled by the first echo replica generated by the linear component generating means 111, and the nonlinear component of the echo is canceled by the second echo replica generated by the nonlinear component generating means 121. , it becomes possible to reduce residual echo components.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 2 shows the configuration of a transmission device in an embodiment to which the echo canceller of the present invention is applied.

In FIG. 2, 211 is an echo canceller, 221 is an echo canceller, and 221 is an echo canceller.
is the subtap echo canceller, 231 is the adder,
Reference numeral 241 indicates a hybrid circuit (HYB), 251 a multilevel code transmitting circuit, and 261 a multilevel code receiving circuit.

The linear component generating means 111 shown in FIG.

The multi-level code transmission circuit 251 converts manually input transmission data (transmission symbols) into a multi-level transmission signal and outputs the signal. Further, the multi-level code receiving circuit 261 converts the input multi-level received signal into a multi-level code and outputs the multi-level code. The hybrid circuit 241 sends out the transmission signal output from the multi-level code transmitting circuit 251 to a two-wire line, and separates the received signal sent via this two-wire line to the multi-level code receiving circuit. 261.

The echo canceller 211 has one tap coefficient for each tap, and multiplies the input symbol value by the tap coefficient to generate and output a first echo replica having linearity. The subtap echo canceller 221 has tap coefficients corresponding to the number of symbol values (for example, 4 in the case of a 2BIQ code) corresponding to one tap, and has a second echo replica for canceling the nonlinear component of the echo. Generate and output. The adder 231 is
The two echo replicas described above are subtracted from the received signal input from the hybrid circuit 241 to cancel the echo, and the received signal from which the echo has been removed is input to the multilevel code receiving circuit 261 .

The echo canceller 211 and the sub-tap echo canceller 221 are pulled in during a non-transmission period when the opposing transmission device (not shown) via the two-wire line is not transmitting anything. At this time, only the wraparound echo is output to the receiving side, so the echo canceller 211 and subtap echo canceller 221 are configured to minimize the wraparound echo.
Determine each tap coefficient of .

Also, as for the order of pull-in, first the echo canceller 2
11 to determine the tap coefficient, and then, with this echo canceller 211 operating, the sub-tap echo canceller 221 is pulled in. By performing the pull-in in this order, it becomes possible for the subtap echo canceller 221 to cancel the nonlinear component of the echo that could not be canceled by the echo canceller 211 during normal data transmission.

Further, FIG. 3 shows the configuration of a transmission device according to another embodiment.

In FIG. 3, 311 is an echo canceller, 331
is an adder, 335 is a D/A converter, 341 is a hybrid circuit (HYB), 351 and 361 are 2BIQ
353 shows a scrambler, and 363 shows a descrambler.

Both the linear component generating means 111 and the nonlinear component generating means 121 shown in FIG. 1 correspond to the echo canceller 311, and the canceling means 131 corresponds to the adder 331.

Also, in the echo canceller 311, 321.3
23 and 326 are taps, 322, 328 and 329
indicates a multiplier, 324, 325, 327, and 333 indicate adders, and 371 and 372 indicate switches, respectively.

The 2BIQ code conversion circuit 351 functions as a line driver that creates and outputs a 4-level transmission signal corresponding to every 2 bits of input data, and converts the multi-level signal shown in FIG. It corresponds to the code transmission circuit 251.

The 2BIQ code conversion circuit 351 includes a scrambler 353.
In addition, the transmission signal output from the 2BIQ code conversion circuit 351 is sent to the two-wire line via the hybrid circuit 341. On the other hand, 2BIQ code conversion circuit 361
functions as a line receiver that restores 2-bit data based on the 4-level received signal separated by the hybrid circuit 341, and corresponds to the multi-level code receiving circuit 261 shown in FIG. . The restored data is further descrambled by a descrambler 363.

Further, the echo canceller 311 generates an echo replica corresponding to both the linear component and the nonlinear component of the echo, and the generated echo replica is transferred to the D/A converter 335.
After being converted into an analog signal, it is manually input to an adder 331. The adder 331 subtracts this echo replica from the received signal separated by the hybrid circuit 341 to obtain 2B
It is supplied to an IQ code conversion circuit 361.

The n-1 taps 321 are for sequentially delaying and capturing each symbol of the transmission signal, and the captured symbols a, (k=l to n) and the main and sub tap coefficients are multiplied by a multiplier. Multiply by 322 and add all multiplication results to adder 3
33 to generate an echo replica.

Tap 323. The adder 324 and the multiplier 328 are for updating and determining the main tap coefficient Ck (k-1 to n) at the time of pull-in. The residual echo component ε is input to the multiplier 328, and the residual echo component ε is multiplied by an update coefficient α (for example, α=2−”) to determine an update value. The main tap coefficients Ck are added together, and the main tap coefficients Ck are updated.

Also, tap 326. The adder 327 and the multiplier 329 add k (ak is a symbol value, and the 2BIQ code is a 4-value level +3.+1.
-1. -3 can be taken, so ak=+3. +1. -1. −
3) is used to update and determine. The residual echo component ε is input to the multiplier 329, and the residual echo component ε is multiplied by an update coefficient β (for example, β=2-16) to determine an update value, which is stored in the tap 326 with this update value. The sub-tap coefficients Co-v and are added together to update the sub-tap coefficients CO□.

The adder 325 adds v to the main tap coefficient Ck and the sub-tap coefficient Co-, and inputs the addition result to the multiplier 322.

The echo canceller 311 is pulled in during a non-transmission period when the opposing transmission device is not transmitting anything via the two-wire line. At this time, since only the wraparound echo is output to the receiving side, the main tap coefficient C1 and subtap coefficient COall+k of the echo canceller 311 are determined so that the wraparound echo is minimized.

Specifically, first, all the switches 372 are turned on, and all the switches 371 provided on the sub-tap side are turned off, and 1. That is, the pull-in is performed so that only the main tap coefficient Ck is updated. The convergence algorithm at this time is shown in (2) 2.

Ckt=Ck”+αxa,Xsign(εt)・
” (2) In formula (2), the subscript “1” and 't J
indicates that it is time t, and 'sign (
A) J indicates a function to find the sign of A.

Next, switch 371 is turned on, and switch 372 is turned on.
is turned off, that is, the main tap count Ck is fixed, and the sub-tap coefficients CO, . . . , k are pulled in to be updated. The convergence algorithm used is shown in equation (3).

CO, w, kt== COo+ kt-'+βX a
IXsign(e t) (3) At this time, in order to increase the amount of echo suppression, the relationship α>β is maintained.

The tap coefficients ck and C○□,k determined in this way
The calculation formula for obtaining an echo replica ECR using (
4) is shown in the formula (tap length n=5).

The echo canceller 311 outputs an echo replica R2 calculated according to equation (4), and the adder 331 cancels the echo.

In this way, the echo cancellers 211 and 221 shown in FIG. 2 or the echo canceller 31 shown in FIG.
1, the amount of echo suppression can be improved by generating echo replicas that correspond to both the linear and nonlinear components of the wraparound echo and canceling the echoes.

FIG. 4 shows echo suppression characteristics when the echo canceller 311 shown in FIG. 3 is used. FIG. 4(a) shows the characteristics of this embodiment, and FIG. 4(b) shows the characteristics of the conventional example shown in FIG. 5 for comparison. The conditions are that the 2BIQ code conversion circuit 351 includes a nonlinear component of ±5%, tap length n = 5, α-10-'', β = 1.
The case of 0-+6 is shown.

As shown in the figure, it can be seen that in this example, the amount of echo suppression is improved by about 3 dB compared to the conventional example.

Note that although the above-described embodiment of the present invention has been described in detail for the case of a 2BIQ code, the present invention can be similarly applied to other multilevel codes.

〔Effect of the invention〕

As described above, according to the present invention, the linear component of the echo is canceled by the first echo replica generated by the linear component generating means, and the nonlinear component of the echo is canceled by the second echo replica generated by the nonlinear component generating means. Since the amount of echo suppression can be improved by canceling, it is extremely useful in practice.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the echo canceller of the present invention, Fig. 2 is a block diagram of one embodiment of the present invention, Fig. 3 is a block diagram of another embodiment of the present invention, and Fig. 4 is a block diagram of the principle of the echo canceller of the present invention. FIG. 5 is an explanatory diagram of the suppression characteristics of the embodiment shown, FIG. 5 is a configuration diagram of a conventional example, and FIG. 6 is an explanatory diagram of nonlinear components of an echo. In the figure, 111 is a linear component generation means, 121 is a nonlinear component generation means, 131 is a cancellation means, 211.311 is an echo canceller, 221 is a subtap echo canceller, 231.331
is an adder, 241.341 is a hybrid circuit (HYB251 is a multilevel code transmitting circuit, 261 is a multilevel code receiving circuit, 351.361 is 2B), Q code conversion circuit, 3
53 is a scrambler, and 363 is a descrambler. ) Mine 41θ The principle of the moon ゛0-tq diagram Figure 1-U-) Five-pointed A row/S I nose To) Figure Figure 2 Echo/) 4rS left Ha F\, 4 G, sB1 day Figure nFigure 6

Claims (1)

[Claims] (1) In an echo canceller that cancels an echo component generated when a part of the transmission signal of a multilevel code wraps around to the receiving side, in order to cancel the echo component, a linear function corresponding to each value of the multilevel code is used. a linear component generating means (111) for generating and outputting a first echo replica having a characteristic, and generating and outputting a second echo replica corresponding to a difference between the echo component and the first echo replica; An echo comprising: nonlinear component generating means (121); and canceling means (131) for canceling the echo component by subtracting the first and second echo replicas from the received signal. canceller.