JPH0385027A - Control system for echo canceller - Google Patents

Abstract

PURPOSE:To output a control signal controlling an echo canceller from a transmission line equipment side by detecting a difference of a waveform between a signaling signal and an audio signal, and operating the echo canceller only at the time of transmitting the audio signal. CONSTITUTION:A CODEC 12 converts a sender side input signal 6 and a receiver side input signal 9 into a digital signal. A signal processor 13 receiving the signal detects a frequency component of the input signal. When a known single frequency or a known 2-frequency synthesized wave is inputted or when no input signal is obtained consecutively for a certain time, the processor 13 judges it that a signaling signal is sent or a transmission line is in an idle state for the time and outputs a control output signal 11 to turn off an echo canceller. On the other hand, when a signal including other multi-frequency component than the known single frequency or the known 2-frequency synthesized wave is obtained, the processor 13 judges it that the period is under transmission of the audio signal, and outputs the control output signal 11 to turn on the echo canceller.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an echo canceller used in long-distance lines such as satellite communications, and particularly relates to an improvement in an on/off control method for echo canceller operation.

[Prior Art] Generally, in long-distance lines such as satellite communications, echo cancellers are used to improve echoes caused by impedance mismatching between, for example, two-wire circuits and four-wire circuits. This echo canceller.

As is well known, it operates by estimating the echo and subtracting the echo estimate from the transmitted signal.

[Problems to be Solved by the Invention] Normally, an echo canceller needs to operate at all times when transmitting an audio signal. but.

In the following cases, it is necessary to forcibly stop the operation.

For example, as shown in FIG. 3, when echo cancellers 2A and 2B are installed on the signal transmission path between exchange IA and exchange IB, a signaling signal serving as connection information is transmitted between exchanges IA and 1B. This signaling signal is transmitted by various signaling methods based on one international standard.

CCITTNa 5, which is currently widely used in international lines
In this case, the data is transmitted as shown in FIG. That is, when a capture signal Sll is sent from one originating station, one terminating station receives the signal and transmits a ready signal MS12 to the originating station. When the originating station receives the signal, the exchange recognizes it as a legitimate captured signal. At the same time, the transmitting station ends sending out the acquisition signal S11. On the receiving station side.

After receiving the completion of the capture signal S11 from the originating station, the transmission of the ready signal S12 is finished.

The above signaling process includes a response signal S21 from the receiving station after sending the MF code and a confirmation signal S22 from the originating station in response to the response signal S21. Call end signal S from the receiving station when the call ends
31 and a confirmation signal S32.31 from the originating station in response to this. A similar procedure is also used to exchange the disconnection signal S41 from the originating station and the recovery confirmation signal S42 from the terminating station.

This procedure is called a converged method because the signaling processing is performed while checking each step, and is a procedure commonly used to increase the reliability of signal transmission, which is important in connections between exchanges.

Here, 1. For example, if we consider the transmission of the acquisition signal Sll and the ready signal S12, the frequencies are both in-band frequencies of 2400 Hz, and 2. The transmitting side and the receiving side will send out signals overlapping in time. . In this case, if the echo canceller is enabled, since the transmitting frequency and the receiving frequency are the same, it will adaptively operate to determine that it is the echo and suppress its own transmission. As a result, the echo canceller suppresses the signaling signal, causing a malfunction in the signaling process.

In order to prevent such malfunctions, it is usually necessary to turn off the echo canceller when transmitting a signaling signal and turn it on only when transmitting a voice signal. On the other hand, in the case of an exchange connection, it is difficult for the transmission line equipment to determine whether it is transmitting a voice signal or signaling, and conventionally the exchange side controls the on/off of the echo canceller. Ta.

This will be explained again with reference to FIG.

In Fig. 3, 6A and 6B are transmission signals from the exchange, and 7
A and 7B indicate received signals to the exchange.

Here, regarding the exchange IA side, the control signal 8A for the echo canceller 2A described above is as follows.

It is desirable to input the signal from the exchange IA to the echo canceller control input terminal of the echo canceller 2A and to control it so that it is always turned off during signaling signal transmission. However, 1 normal switching equipment is not designed to output an echo canceller control signal.

Currently, it is limited to switching equipment for satellite communications, etc.

Needless to say, if an existing switchboard is to have an echo canceller control function, it will be necessary to modify the switchboard.

Although the above explanation concerns the case of signaling processing between exchanges, signaling transmission is also performed in the same way when this transmission line is connected between full-duplex data MODEMs and facsimile machines.

Therefore, it is necessary to control the echo canceller, but it is impossible to issue an echo canceller control signal to commercially available terminal equipment.

An object of the present invention is to provide a control method that allows the control signal for controlling the echo canceller operation during the conventional signaling signal transmission described above to be output from the transmission line equipment side, instead of being output from the exchange or the terminal equipment.

[Means to solve the problem] In the echo canceller control method according to the present invention.

A transmitting side input signal and a receiving side input signal of the echo canceller are input, and when either of the two input signals is a specified single frequency, a two-wave composite wave, or no signal, the echo canceller is turned off.

If a complex frequency other than the above is input, it is determined that the input is an audio signal, and the echo canceller is controlled to turn on.The control circuit is configured to analyze the frequency components of the input signal. Contains a signal processor.

[Function] In the present invention, the signaling signal using a normal in-band frequency is a single frequency signal or a two-frequency composite wave, while the audio signal is a multi-frequency composite wave. A control circuit detects the difference between the two waveforms and controls the echo canceller to operate only when audio signals are being transmitted.

[Example code] FIG. 1 shows the configuration of an embodiment of the present invention. In the figure.

The same parts as in FIG. 3 are given the same numbers, and the explanation is omitted.

In this example, regarding one side (A), the transmitting side input signal 6A of the echo canceller 2A and the receiving side input signal 9A
is input to the echo canceller control circuit 10A. The echo canceller control circuit 10A receives two input signals 6A,
9A is input, and the frequency components of each input signal are detected. and.

A control output signal 11A is output to the echo canceller 2A to automatically turn off the echo canceller 2A when a prescribed signaling frequency is input and when there is no input signal for a certain period of time.

On the other hand, when an audio signal is input, the signal is not a single frequency or two-wave composite wave like a signaling frequency, but a distorted waveform that includes many high frequency components. If something is detected.

A control output signal 11 that automatically turns off the operation of the echo canceller 2A is output. this is.

The same applies to the other example (B).

An embodiment of the echo canceller control circuit 10A (IOB) (7) is shown in FIG. A codec 12 converts the transmitting side input signal 6 and the receiving side input signal 9 into digital signals. The signal passed through the codec 12 is input to the signal processor 13, where the signal is subjected to software processing equivalent to passing through a digital filter consisting of a large number of narrowband filters, and the frequency components of the input signal are detected.

First, when a known single frequency or known two-frequency composite wave is input, or when no input signal is obtained continuously for a certain period of time, the signal processor 13 determines whether the signal processor 13 is transmitting a signaling signal at that time or It determines that the echo canceller is in an idle state and outputs a control output signal 11 to turn off the echo canceller. On the other hand, if a signal containing other multi-frequency components other than the known single frequency or two-frequency combined wave component is obtained other than the above, the signal processor 13 determines that the audio signal is being transmitted during that period. Then, it outputs a control output signal 11 that turns on the echo canceller.

The above processing is performed by the signal processor 13 using a high-speed D
S P (Digital Slgnal Proc
This can be realized using a relatively simple and compact circuit through software processing.

[Effects of the Invention] As explained above, the present invention allows the echo canceller to be controlled on the side of the transmission line device including the echo canceller, so that a special echo canceller control signal is not sent to the exchange or terminal equipment connected to the transmission line. This has the effect of reliably transmitting signaling signals in any case without requiring a generation function.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of the echo canceller control circuit shown in FIG. 1, FIG. 3 is a block diagram showing an example of a conventional transmission form, and FIG. The figure is CCIT
FIG. 4 is a diagram for explaining a signaling transmission procedure using TTh5. IA, IB...Exchange, 2A, 2B...Echo canceller, 3A, 3B...Sending side transmission device, 4A, 4B
. . . Receiving side transmission device, 5A, 5B . . . subscriber terminal. 10...Echo canceller control circuit, 11...Control output signal. Figure 2

Claims (1)

[Claims] 1. In a transmission device having an echo canceller, the transmitting side input signal and the receiving side input signal of the echo canceller are input, and one of the two input signals is a specified single frequency, two-wave composite wave, or no signal. The echo canceller is sometimes turned off, and when a composite frequency other than the above is input, it is determined that an audio signal is input, and the echo canceller is turned on.
An echo canceller control method, wherein the control circuit includes a signal processor for analyzing frequency components of an input signal.