JPS63318822A - Echo canceler type 2-wire/4-wire canceler - Google Patents

Abstract

PURPOSE:To judge a trouble of an echo canceler or the disconnection of a line in a communication unable state by detecting only a pseudo echo in a look-back mode to confirm the normal working of an echo canceler. CONSTITUTION:In a loop-back mode a switch 3 is set at a ground level with a switch 7 connected to a bit inverting circuit 6 and an estimated coefficient is fixed by means of a switch 13. Under such conditions, a pseudo echo signal produced by an echo canceler is supplied to a subtraction circuit 4 and an inverted pseudo echo signal is supplied to a wave detecting circuit 5. The pseudo echo signal undergone the wave detection and binary coding through the circuit 5 is supplied to an interface part 8 after the bit inverted by the circuit 6. The part 8 compares the transmission signal with the received pseudo signal. Then the normal working of the echo canceler is decided when the coincidence is obtained between said both signals. Thus the loop-back mode is through and a normal working state is reset.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an echo canceller method 2 in data communication.
The present invention relates to a four-wire conversion circuit, and particularly to a method for checking an echo canceller function using loopback.

[Conventional technology]

A block diagram of a conventional echo canceller is shown in FIG.

1 is a hybrid circuit for 2-wire/4-wire conversion, 2 is an echo canceller, 4 is a subtraction circuit for subtracting a pseudo echo signal from the received signal, 5 is a detection circuit, 8 is an interface section, 9
is a transmission signal path, 10 is a two-wire signal path, 11 is a reception signal path,
12 is a convergence signal indicating convergence of the echo canceller.

A signal sent from the interface section 8 is input to the hybrid circuit 1 through a transmission signal path 9.

In the hybrid circuit 1, due to impedance mismatch, a part of the transmitting signal is converted into an echo signal to the receiving signal path 1.
Go around to 1. On the other hand, the echo canceller 2 creates a pseudo echo signal using the transmission signal and the prediction coefficient, and the subtraction circuit 4
Enter. The output of the subtraction circuit 4 is the difference between the echo signal and the pseudo echo signal, which is called a residual echo, and is input to the echo canceller 2 and the detection circuit 5. The echo canceller increases or decreases the prediction coefficient so that the residual echo signal becomes smaller, and when the residual echo becomes smaller than a preset value, it is considered that convergence has occurred and outputs a convergence signal 12. therefore,
Based on the convergence signal 12, it is assumed that the echo canceller 2 is operating normally.

Further, in another conventional circuit shown in FIG. 4, loopback of the digital circuit section is executed by connecting a switch 15 for selecting either the transmitting signal or the output of the detection circuit 5 as the input of the interface section 80 to the transmitting signal side. are doing.

[Apex while the invention is trying to solve]

In the conventional echo canceller function check method described above, convergence of the echo canceller is determined only by the convergence signal of the adaptive operation, so it is not known whether the echo canceller is actually operating normally until communication is performed. Therefore, when communication is impossible, there is a drawback that it is impossible to determine whether the echo canceller is malfunctioning, whether there is a break in the line, or whether there is a failure on the transmitting side.

Furthermore, loopback of only the digital circuit section has the disadvantage that although it is possible to diagnose whether or not there is a failure on the transmitting side, it is not possible to diagnose failures in the echo canceller or the transmission line.

[Means for solving problems]

The purpose of the present invention is to determine whether the failure occurred in the digital circuit or the echo canceller circuit when a communication failure occurs.
To obtain an echo canceller type two-line and four-line conversion circuit capable of identifying whether an echo has occurred on a line.

According to the present invention, an echo canceller system 2-wire 4
The line conversion circuit includes a hybrid circuit for 2-wire and 4-wire conversion, an echo canceller circuit, a detection circuit for detecting a received signal, a subtraction circuit, and an interface section, and after the echo canceling operation of the echo canceller circuit converges,
By inputting only the pseudo echo signal to the subtraction circuit that takes the difference between the received signal and the pseudo echo signal, only the inverted signal of the pseudo echo is output from the subtraction circuit, and the inverted signal is detected, bit inverted, and then compared with the transmitted signal. Thus, an echo canceller type 2-wire 4-wire conversion circuit is obtained.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. 1
is a hybrid circuit for 2-wire/4-wire conversion, 2 is an echo canceller, 3 is a switch that switches the input of subtraction circuit 4 to either the received signal or the ground level, and 5 is a switch that switches the input of the received signal to 2(i
6 is a bit inversion circuit that inverts the binary data obtained in step 5; 7 is a detection circuit that converts the input signal of the interface section 8 into the output of the detection circuit 5 and the bit inversion circuit 6; 9 is a transmission signal path, 10 is a two-wire signal path, 11 is a reception signal path, and 12 is a convergence signal indicating that the echo canceller has converged.

13 is a switch for inputting the output of the subtraction circuit 4 to the echo canceller 2;

First, the operation of the echo canceller will be explained. Switch 3 is connected to the hybrid circuit side, switch 7 is connected to the detection circuit side, and switch 13 is closed. The signal sent from the transmission signal path 9 loops around into the reception signal path 11 as an echo signal due to the mismatch between the pseudo line impedance of the hybrid circuit 1 and the actual line impedance. on the other hand,
The echo signal generator 72 generates a simulated echo signal using the transmission signal and the prediction coefficient and inputs it to the subtraction circuit 4. The output of the subtraction circuit 4 is the difference between the echo signal and the pseudo echo signal, which is called a residual echo signal, and is input to the echo canceller 2 and the detection circuit 5. The echo canceller increases or decreases the prediction coefficient so that the residual echo signal becomes smaller, and when the residual echo signal becomes smaller than a predetermined value, it is considered that convergence has occurred and outputs a convergence signal 12.

Next, set it to loopback mode. Switch 3 is connected to ground level, and switch 7 is connected to bit inversion circuit 6. Further, a switch 13 is used to fix the prediction coefficient. At this time, the pseudo echo signal produced by the echo canceller is input to the subtraction circuit 4, and the inverted pseudo echo signal is input to the detection circuit 5. Generally, the echo signal level can be detected sufficiently by itself at -10 to 20 dB of the transmitted signal level. The pseudo echo signal detected and binarized by the detection circuit is bit-inverted by a bit inversion circuit 6, and is input to an interface section 8. The interface unit compares the transmitted signal and the received pseudo-echo signal, and if they are equal, it is determined that the echo canceller is operating normally, ends the loopback, and switches each switch 3, 7, and 13 to return to the normal operating state. Return to

FIG. 2 is a block diagram showing another embodiment of the invention.

Components with the same functions as in FIG. 1 are designated by the same numbers. 14 is a switch for switching the input of the detection circuit 5 to either the echo canceller output or the subtraction circuit output.

The convergence procedure of the echo canceller is the same as the embodiment of FIG. After the echo canceller converges, the switch 14 is switched to connect the echo canceller output and the input of the detection circuit. Further, the switch 13 is opened to fix the prediction coefficient. At this time, the pseudo echo signal is directly input to the detection circuit,
After being binarized, it is input to the interface section. Therefore, the bit inverting circuit and one switch in the embodiment of FIG. 1 are not required.

〔Effect of the invention〕

As explained above, the present invention makes it possible to confirm the normal operation of the echo canceller by detecting only pseudo echoes when the echo canceller is in the loopback mode. This has the effect of making it possible to reliably determine whether the line is broken.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the invention, Fig. 3 is a block diagram showing a first conventional example, and Fig. 4 is a block diagram showing a second conventional example. FIG. 2 is a block diagram showing a conventional example. 1...2 wire 74 wire conversion hybrid circuit, 2.
...Echo canceller, 3, 7, 13, 14.
15...Switch, 4...--Subtraction circuit,
5...Detection circuit, 6...Bit inversion circuit, 8...Interface section, 9...
Transmission signal path, 10...2-wire signal path, engineering 1...
... Reception signal path, 12 ... Convergence signal.

Claims (3)

[Claims] (1) A hybrid circuit that connects a two-wire transmission path and a four-wire transmission path having transmitting and receiving signal paths, an echo canceller circuit that receives the signal of the transmitting signal path, and an output of the echo canceller circuit and the a subtraction circuit for subtracting a signal on a reception signal path; means for adjusting the output of the echo canceller circuit with the output of the subtraction circuit; and a detection circuit for detecting the output of the subtraction circuit; An echo canceller method 2 characterized in that it has a switching circuit that fixes the output of the echo canceller by adjusting the output of the echo canceller and adds only the output of the echo canceller circuit to the detection circuit directly or via a subtracter. 4-wire conversion circuit. (2) The echo canceller according to claim 1, wherein the switching circuit operates to apply only the output of the echo canceller circuit to the subtracter and to invert the output of the detection circuit. Method 2 wire 4
Line conversion circuit. (3) The echo canceller type two-line and four-line conversion circuit according to claim 1, wherein the switching circuit operates so as to directly apply only the output of the echo canceller circuit to the detection circuit.