JPH01826A - echo canceller device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Summary) An echo canceller device for a two-wire full-duplex modem can be easily achieved by using a delay time that is an integral multiple of the round-trip delay time as the delay time of multiple far-end echoes. This configuration realizes the cancellation of multiple echoes.

[Industrial application field]

The present invention relates to an echo canceller device, and more particularly to an echo canceller device for a two-wire full-duplex modem.

Figure 3 shows a schematic configuration of a two-wire full-duplex communication system using a two-wire telephone line. High print circuits (IYB) are used to separate non-transmitting and receiving channels at the input and output sides of the section.

In this way, if the impedance of the two-wire line connected by the high-print circuit and the impedance of the balanced network (not shown) used in combination with the hybrid coil are not the same, complete signal separation will not be possible. , an echo will occur.

Therefore, there is a need to cancel echo in such two-wire full-duplex communication systems.

[Conventional technology]

In such a two-wire full-duplex communication system, as shown in FIG. 3, the transmission signal from the transmitter a1 of the modem A goes through the hybrid circuit a2 and goes around to the receiver a3, causing a near-end echo that leaks into the received signal. , create a pseudo-echo signal from the transmitted signal in each modem C in order to cancel the far-end echo returning around the hybrid circuits C1 and C2,
For example, a CCITT Recommendation V, 32 (9600 b/s) full-duplex modem is used as a modem including an echo canceller device that extracts only the signal from the other modem side by subtracting this pseudo echo signal from the received signal.

In this case, the near-end echo loops around inside the modem, so the delay time is small, but the far-end echo comes around the 4-wire section at the same time, causing a delay. The journey time reaches 600m5.

Therefore, in the echo canceller device, in order to cancel far-end echoes whose delay times vary depending on the line to be connected, it is necessary to know the echo delay time prior to communication.

Therefore, in conventional echo canceller devices, regarding the far-end echoes that go around the hybrid circuits cl and C2 and return, By measuring the round trip delay with the modem and using this round trip delay as the delay time of the far end echo, this delay time is given to the transmitted signal and the far end echo is canceled.

[Problem that the invention seeks to solve]

The far-end echo includes multiple echoes in which an echo that first goes around the hybrid circuit C2 goes around the hybrid circuit C1, goes around the hybrid circuit C2 again, and comes back.

Some of these multiple echoes include 3 laps around the 4-line section,
It also includes those that return after 4 laps, etc. in this case,
The echo that goes around the 4-line section once and returns is called the first far-end echo, the echo that goes around twice and returns as the second far-end echo, and the echo that goes around three times and returns as the third far-end echo. , the echo path has an impulse response as shown in FIG.

・Conventional echo canceller devices only cancel the first far-end echo, which corresponds to the round-trip delay, among these multiple echoes, and the delay time of multiple echoes after the second far-end echo is unknown. There was a problem in that the echo sound could not be erased completely and an unpleasant echo sound was generated on the receiving side.

Therefore, an object of the present invention is to realize an echo canceller device that can eliminate all multiple echoes.

[Means for solving problems]

It can also be seen from the measured data shown in FIG. 5 that multiple echoes have a delay time that is an integral multiple of the delay time of the first far-end echo, if the delay time occurring in the two-line section is excluded from the generation process. That is, for example, the second and third far-end echoes have delay times approximately twice and three times that of the first far-end echo, respectively.

Therefore, in this case, a delay time twice or three times the round-trip delay time measured in the training sequence can be used as the delay time of the second and third far-end echoes.

FIG. 1 shows 2 according to the present invention, which was made with attention to this point.
This is a schematic diagram conceptually showing an echo canceller device for a wired full-duplex modem, where 1 is a near-end echo canceller for the received signal, and 21 to 2n are the number of multiple far-end echoes to be canceled in the received signal. The provided far-end echo canceller groups 31 to 31 correspond to the respective far-end echoes, and send transmission signals delayed by a delay time that is an integral multiple of a delay time equal to a predetermined round-trip delay time to each far-end echo canceller group. a group of delay circuits provided to 21 to 27, and 4
is an adder that adds the outputs of the far-end echo canceller groups 2I to 2 to generate a pseudo echo signal.

[For production]

In the echo canceller device according to the present invention shown in FIG. 1, in response to a near-end echo, the near-end echo canceller 1 generates a pseudo near-end echo signal from a transmission signal, and generates a first, second, . . . pseudo near-end echo signal. For the n-th far-end echo, a group of delay circuits 3. In .about.36, the transmitted signals are sequentially delayed by integer multiples and provided to the far-end echo canceller groups 2 and .about.211, respectively. In each far-end echo canceller, a corresponding pseudo far-end echo signal is generated from the delayed transmission signal, which is added together with the pseudo near-end echo signal in an adder 4 to generate a pseudo echo signal, which is subtracted from the received signal. This makes it possible to eliminate not only near-end echoes but also multiple echoes based on various far-end echoes.

[Embodiment] FIG. 2 shows an embodiment of the echo canceller device according to the present invention. first, second and third far-end echo cancellers 2 for canceling
1.2□ and 2□ are used, and the delay circuit 33 is
．． 3□ and 3° are provided. The echo canceller device of the present invention is used in a two-wire full-duplex modem, so after converting the baseband transmission signal X7 to the busband signal by the modulator 5,
In order to eliminate the echo from the received signal from the hybrid circuit a2) shown in the figure, the added signal from the adder 4 is modulated by the modulator 6 to create an overall pseudo-echo. Generating a signal.

Next, the operation of this embodiment will be explained.

First, the near-end echo canceller 1 inputs the transmission signal X without delay and generates the pseudo near-end echo signal yi.

Further, the transmission signal X is sequentially transmitted through the delay circuit 3. ．． 3°, 3. signals Xz*("Xn-NY'), xs, (-
X++-! NT ), X411 (-X, 1-ssy
) and echo cancellers 28.2□, 2
, and each far-end echo canceller 2+, 2
□, 2n are pseudo far-end echo signals Vx...y]
・Generate Van.

Each echo canceller 1.2n. 2;, 2n,
Well-known transversal filter (FIR filter)
can be used. Therefore, it goes without saying that each echo canceller is used to input a signal to the receiver obtained by subtracting the pseudo echo signal from the received signal to correct the multiplication coefficient in each filter.

Note that since it is thought that there is some deviation between the actual echo delay amount and the inserted delay amount, it may be better to set the inserted delay amount to be shorter than the measured value by a predetermined value.

In addition, in the above explanation, an example for canceling three far-end echoes was shown, but this is sufficient for boat fishing, but it is not limited to this. Furthermore, it is clear that far-end echoes after the fourth far-end echo can also be canceled in the same manner.

[Effects of the Invention] According to the echo canceller device according to the present invention described above, since the transmission signal is delayed by an integral multiple of the round trip delay time to generate each necessary pseudo far-end echo signal, This has the advantage that multiple far-end echoes can be canceled with a simple configuration without using a special delay time measurement circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an echo canceller device according to the present invention, FIG. 2 is a block diagram showing an embodiment of an echo canceller device according to the present invention, and FIG. 3 is a two-wire FIG. 4 is a waveform diagram showing an impulse response of an echo path having multiple echoes, and FIG. 5 is a diagram showing the amount of delay of a far-end echo. In FIG. 1, 1... Near-end echo canceller, 2, ~21... Far-end echo canceller, 31-37
...Delay circuit, 4...Adder, 5.6...Modulator. In the drawings, the same reference numerals indicate the same or corresponding parts. Non-invention [；Keep it! Principle of echo canceller device Figure 1 Example of non-invention Fig. 2

Claims (2)

[Claims] (1) In an echo canceller device for a two-wire full-duplex modem, a near-end echo canceller (1) for a received signal and a group of far-end echo cancellers provided as many as the number of multiple far-end echoes to be canceled in the received signal are provided. (2_1 to 2_n), and corresponding to each of the far-end echoes, each far-end echo canceller group (2
Delay circuit group (3_1 to 3_n) provided to _1 to 2_n)
An echo canceller device comprising: and an adder (4) that adds the outputs of the far-end echo canceller group (2_1 to 2_n) to generate a pseudo echo signal. (2) The echo canceller device according to claim 1, wherein the transmission signal is a baseband signal, and the pseudo echo signal is a modulated signal.