JPS6076825A - Adaptive echo canceller - Google Patents

Abstract

PURPOSE:To shorten the production time of an echo line model and to ensure an echo cancelling effect by comparing a transmission signal and a past reception signal to prevent the discontinuation of a correcting action due to a erroneous interruption. CONSTITUTION:A present reception signal supplied through an input terminal 11 of the reception side is sent to a telephone reception terminal from the output terminal 12 of the reception side and also supplied to the 1st memory 15. A transversal filter is provided with the 1st and 2nd memories 15 and 16 and a superposition integration circuit 17. The memory 16 stores the echo line characteristic. A bidirectional call detecting circuit 20 compares the past sample reception signal with a transmission signal and decides a bidirectional call when the transmission signal is larger than the reception signal. Then the circuit 20 stops the correcting action of a correction circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adaptive echo canceler used to eliminate echo signals in N communication lines.In recent years, with the rapid increase in long distance lines, Q-4 and satellite communications, Reverberant signals are a major problem. The echo coefficient is a signal generated by a speaker that is reflected at the end of the receiver and received by the speaker, but it does not pose much of a problem as long as the propagation time is short. However, in lines with long propagation times, such as satellite communications, the presence of echo signals significantly degrades speech quality.

In the past, echo rejection devices are commonly used to reject echoes. This uses a switch circuit that compares the levels of the transmitting and receiving lines and turns on the one with the higher level and turns off or attenuates the one with the lower level, so there are problems such as cutting off at the beginning of the line and occurrence of click noise. I don't like it.

Adaptive echo cancelers have been developed to address the above-mentioned drawbacks. This device uses a filter, that is, an echo path model, that has characteristics similar to those of the echo path.
This is a device that creates an approximate echo signal that approximates the echo signal and uses this to cancel the echo signal. Since the characteristics of the echo path are not constant, the echo path model is adaptively modified so that the cancellation residual signal after the echo signal is canceled by the approximate echo signal becomes small. However, since not only the echo signal but also the normal transmission signal is present in the transmission No. 4, the echo path model is erroneously corrected during two-way communication, and the characteristics of the echo path model are disturbed. In order to prevent this erroneous correction,
A two-way conversation is detected by comparing the levels of the received signal and the received signal No. 4, and the modification of the echo path model is stopped when a two-way conversation occurs. However, with this method,
When there is a delay in the echo path, an erroneous interrupt is generated in which the echo of the receiving signal No. 4 is mistakenly detected as a two-way conversation and correction is stopped, so there is a drawback that it takes a long time to create the echo path model. In order to alleviate this drawback, the time window for detecting the level of the receiving signal 4 is widened, and the receiving signal
There is also a device that prevents the above-mentioned erroneous interrupts and shortens the time required to create an echo path model by comparing the signal level and the transmission signal level. However, such a device has drawbacks such as increasing the size of the device to widen the time window and increasing power consumption.

An object of the present invention is to solve the above-mentioned conventional drawbacks, to accurately determine when a two-way call is being made, to prevent disturbances in the echo path model, and to prevent erroneous interruptions due to echoes of the receiving signal No. 4. An object of the present invention is to provide an adaptive echo canceling device that can prevent echoes from occurring.

The echo canceling device of the present invention includes a first memory that records the reception number 4, a second memory that stores the echo transmission path characteristics,
a convolution integrator circuit that performs convolution integration of the contents of the first memory and the second memory; a subtracter that subtracts the output signal of the convolution integrator circuit from an input oscillator from the echo transmission path; and an output of the subtracter. A correction circuit that corrects the contents of the second memory so that the value becomes smaller, and a two-way communication detection circuit that detects a two-way communication state by comparing the levels of transmitting and receiving No. 4. , wherein the adaptive echo canceling device is controlled to stop the operation of the correction circuit by the output of the two-way conversation detection circuit, wherein the two-way conversation detection circuit is configured to detect transmission numbers and the contents of the first memory. By comparison, it is assumed that the two-way internal communication μ state is determined.

The two-way communication detection circuit can make an appropriate judgment very easily by comparing the transmission signal and the maximum level of the contents of the first memory.

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

FIG. 1 is a block diagram showing one embodiment of the Kien IIJJ. That is, the currently received No. 4 X1 input from the receiving side input terminal 11 is sent from the receiving side output terminal 12 to a receiving terminal (not shown) and is also input to the first memory 15. The first memory 15, the second memory 16, and the convolution integrator circuit 17 constitute a transversal filter, and the second memory 16 has an echo path characteristic H,'()=1.2. ...)
is stored.

The convolution integrating circuit 17 receives the received signal data X, -, stored in the first memory 15 two timeslots ago.

(No. 0, 1, 2, ...) and the contents of the second memory (tap coefficients) H; ,,make. Then, the subtracter 1B subtracts the transmission No. 4 Y, which came from the receiving terminal to the transmitting side input terminal 13 (it is an echo signal when there is no transmission) and the above-mentioned approximate echo signal Y7, and cancels it. The residual signal e4 is sent from the transmitting side output terminal 14 and is also sent to the correction circuit 19. The correction circuit 19 outputs the erased residual signal e and the received No. 4 signal X. -1, the correction amount Δ to correct the echo path characteristic I-■;' so that the cancellation residual signal e becomes small
The contents of the second memory 16 are corrected by calculating h;. In this way, the echo path characteristic H; stored in the second memory 16 is modified so as to approximate the actual echo path characteristic.

The above configuration and operation are similar to those of a conventional adaptive echo canceller. , and the decrease /lj during two-way communication
It is controlled by the two-way call detection circuit 20 to prevent erroneous correction based on the output of the T unit 18, but in this example, the two-way call period 1#20 is determined by the past J
Receiving number 4 Xn-7 and transmitting number 4 Y for J samples, which are the outputs of the memory of g81, which stores all of the receiving number 4 for samples (the number of steps corresponding to the delay time and impulse response time), , the maximum level XI of
I'm going to send it to you.

When it becomes thicker, it is determined that it is a two-way communication and the correction circuit 19
Stop the corrective action. I'm currently receiving No. 4 Xn. However, for example, at time t3, the memory 15 &: i, t, ~
It is assumed that the user owns the 4th reception for 15 minutes (section 26). On the other hand, the transmitted signal Yn is delayed by the echo path delay time 25 after the received signal X3 passes through the echo path, as shown by a curve 22. Conventionally, the section 24 in which the transmitted signal (echo signal) represented by the curve 22 was larger than the received signal represented by the curve 21 was incorrectly determined to be a two-way communication period, but this embodiment By comparing transmission No. 4 of curve 22 with curve 23, it is determined that the above-mentioned section 24 is a two-way communication period, and therefore the correction operation of the correction circuit 19 is stopped. That is, erroneous interrupts are prevented, the contents of the second memory are modified more quickly, and therefore the erased residual signal e becomes smaller quickly. In other words, the effect is that the echo cancellation effect is large. Instead of the maximum level of the contents of the memory 15, for example, an average value may be used.

As described above, in the present invention, the two-way call detection circuit is configured to detect a two-way call by comparing the transmitted number 4 and the past received number 4 held in the first memory. Therefore, it is possible to prevent the reception signal 4 from determining that it is a two-way communication due to a delayed echo signal. That is, it prevents the correction operation from stopping due to an erroneous interrupt, shortens the time required to create an echo path model, and has the effect of canceling the echo. Also, there is no need to expand the time window for this purpose.
It is possible with small size and low power consumption. Note that by comparing the maximum value of the contents of the 41 memory with the transmission number 4, two-way communication can be detected with an extremely simple configuration.

[Brief explanation of the drawing]

Figure rA31 is a block diagram showing one embodiment of the present invention;
The figure shows the Ukei J, the Kome Haku, and the J′ in the first memory.
This is a time chart illustrating an example of a fast-paced level. Figure (In the IC, 11...Receiver 1 is the Uilj input terminal,
12... Receiving side output terminal, 13... Sending 1d side input terminal, 14... Sending = tit! l output terminal, 15...
1st memory, 16...2nd memory, 17...superimposed integral circuit, 18...subtractor, I9...-(15 positive circuit, 20--bidirectional d6 detection circuit, ...Ukei Nitu, Y4...include 47-4, en,...γn Gozanpaku, YIL approximate echo signal. 14 people Ben Misakishi 1) Toshi Sou 1st cause Second cause

Claims (1)

[Claims] (1.) A first memory for storing received signals and an echo transmission path! 1) a second memory for storing the characteristics, a superposition integration circuit for performing superposition integration of the contents of the first memory and the second memory, and an output signal of the superposition integration circuit based on the input signal from the echo transmission path; A two-way communication is established by comparing the levels of the transmitter and receiver No. 4 with a subtractor that performs subtraction, a correction circuit that modifies the contents of the second memo so that the output value of the subtractor becomes smaller, and and a two-way conversation detection circuit for detecting a state, and the adaptive echo canceling device is controlled to stop the operation of the correction circuit according to the output of the two-way conversation detection circuit, wherein the two-way conversation detection circuit This is an adaptive echo canceling device whose characteristic is to determine a bidirectional communication state by comparing transmission No. 4 and the contents of the first memory. (2. The adaptive echo canceling device according to claim 1, characterized in that the two-way conversation detection circuit d, the transmission No. 4, and the maximum level of the contents of the first memory are compared. Something to do.