JPS5961234A - Adaptive type echo erasing device - Google Patents

Abstract

PURPOSE:To suppress the disturbance of a false echo path at its minimum, by measuring a characteristic value corresponding to the delay time value of the false echo path, and when detecting the variation of the characteristic value, stopping the operation of a corrected value. CONSTITUTION:When receiving circuit connecting information from a terminal 5, a test signal generating circuit 11 turnes a switch 12 and applies a test signal to a line on the receiving side. The test signal is outputted from a terminal 2, delayed by the echo path and inputted from a terminal 3 as an echo signal. The time until the test signal is inputted as the echo signal is measured from the input signal and a signal outputted from a test signal generating circuit 11 to measure the absolute delay of the echo path. The tap factor of a transversal filter 19 of the false echo path is squared during the delay time measured by a delay time measuring circuit 14 and the sum of the squares is found out to measure the characteristic value. After detecting the variation of the characteristic value, the operation of the corrected amount of a correcting circuit 20 is stopped to suppress the disturbance of the false echo path 19 at its minimum by regarding the corrected variable as ''0''.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an echo canceling device inserted into a telephone line having echoes.

Echoes are caused by the impedance mismatch of the hybrid coil installed in the 2-wire 4-wire conversion section of the telephone line, and especially in long-distance telephone lines using satellite lines etc., the call quality is affected due to the large delay time. This significantly reduces the In order to control this kind of echo, two echo cancellation devices are used, but the former is a method that controls the echo path ON-OFF, and the latter is a method that gives large attenuation to the echo signal. As a result, there were problems such as the beginning of the first episode being cut off or clicking noise.

The adaptive echo cancellation device was developed to compensate for the above drawbacks.This device estimates the characteristics of the echo path using telephone speech, creates a pseudo echo path, and synthesizes the pseudo echo signal from the received signal. , the echo signal is canceled by subtracting the pseudo echo signal from the actual echo signal. Therefore, in principle, the failures seen in the above-mentioned ``echo prevention device'' do not occur, and even if there is a fluctuation in one line, it is possible to follow the fluctuation and sequentially correctly determine the echo path characteristics.

However, in this conventional adaptive echo canceler, 1
If the line is in a state where calls are being made in both directions simultaneously, if you try to continue modifying the pseudo echo path, the near-end speaker's voice will have characteristics different from the actual echo path characteristics. There was a problem that echo cancellation was not performed. That is, in the adaptive echo canceling device, simultaneous calls are detected mainly based on the magnitude relationship between the input signal level on the receiving side and the input signal level on the transmitting side.

If the near-end speaker's voice level is low compared to the far-end speaker's voice level, the near-end speaker's voice signal is regarded as an echo of the far-end speaker's voice signal, and a simultaneous call in both directions cannot be detected. Even if this is possible, and even if the detection is correct, there is a time delay between the time the true simultaneous call begins and the time it is detected and the correction of the spurious echo path is stopped. Therefore, during the time corresponding to the time delay, the pseudo echo path is disturbed by the voice of the near-end speaker, posing the problem that correct detection cannot be performed.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an adaptive echo canceling device that instantly and accurately detects two-way simultaneous calls.

According to the present invention, a pseudo-reverberation path is formed while being successively corrected by the echo signal from the echo path and the received signal, and the actual echo is formed by the pseudo-reverberation signal generated from this pseudo-reverberation path and the received signal. means for applying a test signal to a receiving side line upon receiving two-line connection information in an adaptive echo canceling device for canceling a signal; a means for measuring a delay time of the echo path based on the test signal; An adaptive echo canceling device is obtained, comprising means for determining a characteristic value corresponding to the delay time amount of the pseudo echo path and controlling the modification based on the measured characteristic value.

Next, it will be explained in detail using the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of an adaptive echo canceling device according to the present invention. This embodiment is an example of a type in which a transversal filter is used as a pseudo echo path to store the impulse response of the echo path.

FIG. 2 is a diagram showing the in/out response of the above-mentioned echo path. The following explanation will be made using Figures 1 and 2.
The directions of receiving and transmitting signals in this device are as follows: sub terminal is the receiving side input terminal, 2 is the receiving side output terminal, 3 is the transmitting side input terminal, and 4 is the receiving side input terminal.
is connected to the transmitting side output terminal. Note that this is a terminal for manually inputting line connection information from an external switching trunk or the like. Now, the test signal generation circuit 11 is connected to terminal 5.
When line connection information is received from , the switch circuit 12 is switched to apply a test signal to the receiving line. Assuming that the delay circuit 13 enclosed by the chain line does not exist, this test signal is output from the terminal 2 and is transmitted through a reverberation path (not shown) of, for example, 15 m.
The signal is delayed by approximately s and is input from terminal 3 as a reverberation signal. The delay time timing circuit 14 uses this input signal and the signal from the test signal generation circuit 11 to measure the time from when the test signal is applied to the receiving line to when the echo signal is input. This allows the absolute delay of the echo path to be measured.

The characteristic value measuring circuit 15 consists of an AND gate, i6, a square circuit 17, and an accumulation circuit j8.

The ta and f coefficients of the transversal filter 19, which is a pseudo echo path as shown in FIG. 2, are squared during the delay time measured by the delay time measurement circuit 14. to be determined. At this time, the characteristic value is theoretically zero when there is a one-way call between only the far-end talker, but if there is also a call from the near-end talker, the correction by the correction circuit 20 (described later) is disturbed. Therefore, changes in characteristic values are detected. This detection is carried out instantaneously, but as soon as a change in the characteristic value is detected, a signal is issued to stop the 4 positive quantity calculations of the correction circuit 2() and set the correction amount to zero, thereby reducing the disturbance in the pseudo echo path 19. can be kept to a minimum.

Next, a method for starting the modification again when the communication state is reached with only the far-end speaker after the modification has been stopped as described above will be explained. However, since it is not possible to start correction depending on the circuit configuration using the characteristic value measuring circuit 15 described above, a two-way simultaneous call detection circuit 21, which is also provided in the conventional device, is used. That is, this two-way simultaneous call detection circuit 21 compares the signal levels on the receiving side and the transmitting side to detect whether or not there is a two-way simultaneous call, and if not, the correction circuit 20
restart the operation. The correction circuit 20 calculates a correction amount based on the receiving side signal and the cancellation residual signal output from the subtraction circuit 22, and sequentially corrects the pseudo echo path 19. The pseudo-1 and subsequent echo signals are the output of the pseudo-echo v-19 and the received signal storage circuit 23.
is obtained by performing convolution integration on the output of the convolution calculation circuit 24.

The subtraction circuit 22 cancels the echo by subtracting it from the actual echo signal.

In the above, there is a slight time lag in restarting the stopped correction using the one-way simultaneous call detection circuit 21, but even if a one-way call with only the far end speaker is mistakenly detected as a two-way simultaneous call, it will be short. In practice, this would not be a fatal problem, as it would not be a fatal problem if the time was longer.On the other hand, it would be fatal if a simultaneous call in both directions was mistakenly detected as a one-way call involving only the far end speaker. It is necessary to stop the correction instantaneously to prevent this from becoming a serious hindrance, but the apparatus shown in FIG. 1 has a structure that fully satisfies this requirement.

As can be easily seen from the operation of the apparatus of the embodiment shown in FIG. 1, if the delay time of one echo path is close to zero, the operation of the apparatus as a whole becomes unstable. The delay circuit 13, which was previously explained as being absent, is added when such a situation is assumed, and if the delay time is set to, for example, 1.25 m5, the purpose can be sufficiently achieved. However, it is not preferable to increase the sweetness by 9.

The delay time measuring circuit I4 described above is not shown because it is simple, but it can be constructed from a method for correlating the test signal and the echo signal, a method for measuring the level of the echo signal, etc., and a counting circuit. It is. That is, the counting circuit can be started from the time when the test signal is applied, and the value of the counting circuit when the correlation becomes large or when the level of the echo signal becomes large can be taken as the delay time. In addition, as a test signal to be applied to the receiving line for a short period of time after one line is connected until the start of a call, a pseudo echo path should be synthesized to some extent using a white noise burst signal or the like before the start of a call. This improves the incompleteness of echo cancellation seen in conventional adaptive echo cancellation devices until the pseudo echo path is synthesized in the early stage after the start of a call.

As described above, according to the present invention, the adaptive echo cancellation device can follow line fluctuations and perform effective echo cancellation with less disturbance in the pseudo echo path even during simultaneous calls in one and both directions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a diagram showing an example of the in/out response that is stored in the pseudo echo path. Explanation of symbols: 1 is the receiving side input terminal, 2 is the receiving side output terminal, 3 is the transmitting side input terminal, 4 is the transmitting side output terminal, 5 is the line connection information input terminal, ■1 is the test signal generation circuit, 12 is the A switch circuit, 13 is a delay circuit. ■4 is a delay time measurement circuit, and 15 is a characteristic value measurement circuit. 17 is a square circuit, 18 is an accumulation circuit, 19 is a transpersal filter (pseudo echo path), 2o is a correction circuit, 21 is a bidirectional simultaneous call detection circuit, 22 is a subtraction circuit, 23 is a received signal memory, and 24 is a correction circuit. Each convolution operation circuit is shown separately.

Claims (1)

[Claims] 1. A pseudo echo path is formed by the echo signal from the echo path and the received signal while being successively modified, and the actual echo signal is generated by the pseudo echo signal generated from this pseudo echo path and the received signal. means for applying a test signal to the receiving line upon receiving one-line connection information in the adaptive echo canceling device for canceling the echo; a means for measuring the delay time of the echo path based on the test signal; an adaptive echo canceling device comprising means for measuring a characteristic value corresponding to the amount of delay time of a path, and controlling the modification based on the measured characteristic value.