JPH02202128A - Echo eliminator - Google Patents

Abstract

PURPOSE:To eliminate an echo signal corresponding to the deviation of transmission/reception timing by providing a second filter having plural coefficients and whose output can be adjusted, and a tap switching means which can perform adjustment between each coefficient and output corresponding to the deviation of the transmission/reception timing. CONSTITUTION:An appropriate echo elimination signal 201 is generated from the second filter 4 by controlling the second filter 4 by the tap switching means 5, and the echo elimination signal 201 is supplied to a subtractor 6. The subtractor 6 supplies the echo elimination signal 201 and the echo signal due to the fluctuation of sampling timing included in a sampling signal outputted from an A/D converter 1 to a subtractor 3. The subtractor 3 performs subtraction between a signal from the subtractor 6 and the echo elimination signal 101 outputted from a filter 2, and the echo signal in the case where the interval of the transmission/reception timing is equal is eliminated from the signal from the subtractor 6, and a reception signal 25 from which the echo signal is eliminated is outputted. In such a way, the echo signal can be eliminated even when the deviation occurs in the transmission/reception timing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an echo canceling device that samples and removes echo signals accompanying 2-wire 4-wire conversion, and particularly relates to an echo canceling device that samples and removes echo signals accompanying 2-wire 4-wire conversion. The present invention relates to an echo removal device that removes echo signals that occur when the signal deviates from the human eye.

[Conventional technology]

Conventionally, this type of echo canceling device has been known as a device that samples and removes echo signals associated with two-wire and four-wire conversion.

Such an echo canceling device includes a sampling means for sampling an echo signal leaking from a transmitting circuit to a receiving circuit on the 4-wire side of a 2-wire 4-wire converter together with a received signal and outputting the sampled signal as a sampling signal; and a subtracting means for subtracting the sampling signal from the sampling means and the cancellation signal from the filter to remove the sampled echo signal. .

According to such an echo canceling device, 22!411! The echo signal leaking from the transmitting circuit to the receiving circuit on the four-wire side of the converter is sampled together with the received signal by the sampling means. In addition, I<t> generates a cancellation signal for the echo signal when sampled at equal time intervals.

The sampling signal from the sampling means and the removal signal from the filter are input to the subtraction means, where they are subtracted and the sampled echo signal is removed. The echo signals sampled in this manner are removed, but in conventional echo removal devices, the removal of echo signals is based on the assumption that the echo signals are sampled at equal intervals.

[Problem to be solved by the invention]

For this reason, the conventional echo canceling device has a drawback in that when the sampling time sometimes deviates from the equidistant agent, the ability to remove echo signals decreases. Furthermore, in conventional echo canceling devices, in order to avoid deterioration in the ability to remove echo signals, it is necessary to minimize the deviation in sampling time, but there is also a problem in that there is a limit to this.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide an echo canceling device that can remove echo signals even if the transmission/reception timing is shifted.

[Means to solve the problem]

In order to achieve the above object, the echo canceling device of the present invention includes sampling means for sampling the echo signal leaking from the transmitting circuit to the receiving circuit on the 4-wire side of the 2-wire 4-wire converter together with the received signal, and A filter that generates a cancellation signal for an echo signal sampled at time intervals, and an echo signal sampled by subtracting the signal containing the echo signal sampled at equal M time intervals and the cancellation signal from the filter. a first coefficient that generates a first cancellation signal for a sampling value deviation due to a deviation between a transmission time and a sampling time; and a time period at which the transmission times are equally spaced. a second filter having a second coefficient for generating a second cancellation signal for a change in the waveform of the echo signal due to deviation from the increment and whose output value can be adjusted; tap switching means capable of capturing a signal indicating that a deviation has occurred, switching each coefficient of the second filter according to the deviation of the sampling value, and switching the output value of the second filter;
It is characterized by comprising a second subtraction means for subtracting a signal including an echo signal corresponding to the deviation of the sampling value and a removal signal from the second filter to remove the echo signal corresponding to the deviation of the sampling value. It is something to do.

The present invention includes a second filter that has a plurality of coefficients and whose output can be adjusted, and filter switching means that can adjust each coefficient and output according to the difference in transmission and reception timing, thereby eliminating echo signals. can do.

〔Example〕

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

1 to 3 are for explaining the present invention in detail.

FIG. 1 is a block diagram showing an embodiment of an echo canceling device of the present invention.

In FIG. 1, the echo removal device includes an analog-to-digital (A/D) converter 1 as a sampling means, a filter 2, a subtracter 3 as a subtracting means, a second filter 4, and a tap switching means 5. , a subtracter 6 as a second subtraction means, a digital-to-analog (D/A) converter 7,
A device transmission signal 21 composed of a 2-wire and 4-wire converter 8 is converted into an analog pulse signal 22 by a D/A converter 7 and sent to a 2-wire transmission line 9 by the 2-wire and 4-wire converter 8. . This analog pulse signal 22 is
It becomes an echo signal and is sent to the A/D as an analog reception signal 23.
input to converter 1. The A/D converter 1 is configured to sample the echo signal leaking from the D/A converter 7 on the transmitting circuit side to the receiving circuit side on the 4-wire side of the 2-wire 4-wire converter 8 together with the analog reception signal 23. has been done.

The sampling signal 24 from the A/D converter 1 and the echo-removed signal 201 from the second filter 4 that captures the transmission signal 21 are connected to be supplied to the subtracter 6. The subtracter 6 is a filter 4 of the rod 2 that takes in the sampling signal 24 from the A/D converter 1 and the transmission signal 21.
The echo cancelled signal 201 is subtracted from the echo cancelled signal 201. The second filter 4 filters the first
a first coefficient for generating a cancellation signal of
It has a coefficient of , and is configured so that the output value can be adjusted. The tap switching means 5 takes in the transmission/reception timing 30 indicating that a difference has occurred between the transmission time and the sampling time, switches each coefficient of the second filter according to the difference in the sampling value, and changes the coefficients of the second filter 4. This allows the output value to be switched.

The signal containing the echo signal sampled at evenly spaced time steps from the subtractor 6 is then supplied to the subtractor 3 . The filter 2 is configured to take in the transmitted signal 21 and generate a cancellation signal 101 for the echo signal when sampled at equal time intervals. The subtracter 3 is configured to subtract the signal containing the echo signal sampled at equal time intervals and the removal signal 101 from the filter 2 to obtain a received signal 25 from which the sampled echo signal has been removed. ing.

Here, the configuration of the second filter 4 will be explained. The transmitted signal 21 is fed to a series circuit of delay elements 410, 420, 430. Registers 411, 421, and 431 hold coefficients for removing deviations in sampling values caused by changes in the echo signal itself due to deviations in transmission timing. Register 422.432
holds coefficients for removing deviations in sampling values caused by deviations in sampling timing for echo signals caused by deviations in phase relationship between transmission timing and reception timing. These registers 411.
The coefficients of 421.431 and register 422.432 are selected by selector 423.433 and multiplied by the transmission signal by multiplier 414.424.434. Each output signal from the multiplication means 414.424.434 is fed to the addition means 440 via a respective gate 415.425.435. The output signal from the addition means 440 is output as the removal signal 201.

Selection of selector 423.433 and gate 415.42
5.435 and opening/closing are performed by the tap switching means 5.

The operation of the embodiment configured in this way will be explained.

FIG. 2 is an explanatory diagram showing the relationship between transmission/reception timing, echo signal waveform, and sampling value.

In FIG. 2, the horizontal axis represents time t, and the vertical axis represents transmission/reception timing, echo signal waveforms, and sampling values. Let T be the time step of the transmission/reception timing, and let ΔT be the deviation from the equal interval. Furthermore, to simplify the explanation, the transmission and reception timings are assumed to be the same. The purpose of this embodiment is to obtain a method for generating an echo cancellation signal 201 when the transmission/reception timing may deviate from equally spaced time increments.

First, we will explain how echo signals appear.

In Figure 2, transmission timing and transmission signal (code string)
The relationship between the transmission waveform and echo waveform for “1”, “0”, “0”, etc., and the relationship between the reception timing and the sampling value of the echo fi type (corresponding to the unit pulse response waveform of the echo bus) shows.

Here, the relationship between the echo waveform and the reception timing is as follows: ■ When the transmission timing and reception timing are both at equal intervals ■ When only the reception timing deviates from the equal interval ■ When the transmission timing and reception timing are both equal There are three possible cases in which the distance deviates from the interval. The respective sampling values in the above cases are: (1): R,, R2, R3; (2): R1+ΔR+, Rz +ΔR2, R.

+ΔR5, In the case of ■, Rt +ΔWr, R2+ΔW2,
Rs+ΔW3, becomes. (2) The case where only the reception timing deviates from equal intervals seems unlikely considering that this embodiment assumes that the transmission and reception timings are the same, but the case where the transmission and reception timings deviate at the same time However, for echo signals of signals transmitted before that, the relationship is the same as in case (2).

Based on the explanation with reference to FIG. 2 above, an actual echo signal when the transmission/reception timing deviates from equal time intervals will be described using FIG. 3.

FIG. 3 shows transmission timing, echo waveforms for pulse signals transmitted at each transmission timing, and sampling values for an actual echo signal that is a superposition of these echo waveforms.

Transmission timing 1001.1002.1003.100
4.1005, and reception timing 3001.300
2.3003.3004.3005 indicates the case where the timings are at equal intervals. Also, transmission timing 101
3 right and reception timing 3013, it is shown that there is a deviation from the equal interval by ΔT. Each echo waveform and sampling value are obtained when the transmission timing 1013 and the reception timing 3013 are shifted by ΔT. If the transmission timing 1013 and the reception timing 3013 are shifted by ΔT, the echo waveform changes. Therefore, the sampling value for the changed waveform is R1+ΔW, , R,+ΔW2
, Rs +ΔW.

becomes. Also, the echo wave% before echo waveform 200.1
The sampling values from sampling timing 3013 onwards are R,+ΔR,'R2+ΔR2,
Rs + ΔR5.

Based on the above, when calculating the timing at which the transmission/reception timing deviates from equal intervals, that is, the sampling value after reception timing 1013, we get: ■ Timing 1013... R1+R2+R3+ΔW, +ΔR2+ΔR3 ■ Timing 3014... Rt + R2+ Rs +ΔW2+ΔR3 ■Timing 3015...Rt +R2+Rz +ΔW3 ■Following reception timing...R weight + R2+R1.

Next, the operation of removing the above-mentioned echo signal will be explained.

First, the echo cancellation signal 201 is based on the deviation of the sampling value of the echo signal, that is, as explained in FIG. 3, ΔW1. ΔW3. ΔW5
．． This is a removal signal for the portions related to ΔR2 and ΔR1. Registers 411, 421 . in second filter 4.
431 respectively have ΔW1. ΔW2. ΔW
, is stored. Registers 422 and 432 in the second filter 4 contain coefficients ΔR2 and ΔR2, respectively.
R1 is stored. In the state set in this way, the tap switching means 5 adjusts the transmission/reception timing 30.
and selector 423.433 and gate 415.425.535 based on the transmission/reception timing 30.
Switching control and opening/closing control are performed as shown in Table 1.

(Margin below) Table 1 By the tap switching means 5 controlling the second filter 4 in this way, the second filter 4 generates an appropriate echo cancellation signal 201. This echo canceled signal 201 is supplied to the subtracter 6. In the subtracter 6, this echo canceled signal 201 and the A/D converter 1
The subtracter 3 receives a signal from which an echo signal caused by variation in sampling timing contained in the sampling signal output from the subtractor 3 is removed.

Next, echo cancellation signal 101 output from filter 2
is an echo cancellation signal for an echo signal when the transmission/reception timing is at equal intervals, so the sampling value of the echo signal explained in FIG. 3 is R+ + R2+ R
This is a signal corresponding to 3. Therefore, filter 2 is
It may be one that operates in the same way as the conventional one. The echo canceled signal 101 output from this filter 2 is given to a subtracter 3. The subtracter 3 subtracts the signal from the subtracter 6 and the echo cancellation signal 101 output from the filter 2,
Echo signals when the transmission and reception timings are at equal intervals are removed from the signals from the subtracter 6, and a received signal 25 from which the echo signals have been removed is output.

Note that in this embodiment, the number of taps of the second filter 4 is 3.
Although the description has been made for the case where the taps and transmission/reception timings are the same, it goes without saying that the present invention can be applied to cases other than three taps or to cases where the transmission/reception timings are different. Further, in this embodiment, the coefficients of the second filter 4 are preset and fixed, but if the coefficients are adaptively controlled using the adaptive control means, there is no need to set the coefficients in advance.

〔Effect of the invention〕

As explained above, the present invention includes a second filter that has a plurality of coefficients and whose output can be adjusted, and a tap switching means that can adjust each coefficient and output according to the shift in transmission and reception timing. This has the effect that it is possible to remove not only echo signals sampled at equal intervals but also echo signals corresponding to shifts in transmission/reception timing.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the relationship between transmission and reception timing, echo waveform, and sampling value, and Fig. 3 is a view from the equally spaced side of transmission and reception timing in an actual echo signal. FIG. 1...A/D converter, 2...Filter, 3...Subtractor, 4...Second filter, 5...・Tap switching means, 6... Subtractor (second subtraction means), 7...
...D/A converter (sampling means), 8...
・2-wire 4-wire converter, 9...2-wire transmission line.

Claims (1)

[Claims] Sampling means for sampling the echo signal leaking from the transmitting circuit to the receiving circuit on the 4-wire side of the 2-wire 4-wire converter together with the received signal, and generating a cancellation signal for the echo signal when sampled at equal time intervals. An echo canceling device comprising a filter and a subtracting means for removing the sampled echo signal by subtracting a signal including an echo signal sampled at equal time intervals and a signal removed from the filter. A first coefficient that generates a first cancellation signal for a sampling value shift due to a sampling time shift, and a second coefficient for a change in the waveform of an echo signal due to a shift of the transmission time from a uniformly spaced time step. A second filter that has a second coefficient for generating a cancellation signal and can adjust the output value, and a second filter that takes in a signal indicating that a difference has occurred between the transmission time and the sampling time, and responds to the difference in the sampling value. to switch each coefficient of the second filter, and switch the coefficients of the second filter.
a tap switching means capable of switching the output value of the filter, and subtracting a signal including an echo signal corresponding to the deviation in the sampling value from a removal signal from the second filter to remove the echo signal corresponding to the deviation in the sampling value. An echo removal device comprising: second subtraction means.