JPS6181035A - Echo cancel system - Google Patents

Abstract

PURPOSE:To prevent the degradation of the echo cancelling action, which occurs when a single tone signal is received, with simple circuit constitution by adding a noise signal having signal components in all bands with a level corresponding to the input level of the tone signal when the narrow-band tone signal is sent. CONSTITUTION:If a narrow-band or single frequency tone signal is given to an echo cancelling circuit, an echo generator 3 and a tap coefficient corrector 4 perform the echo cancelling action by the narrow-band or single frequency signal, and an echo path in signal frequency components other than tone signal components is not estimated, and therefore, the echo cancelling action is incomplete. A noise adding circuit is provided in a signal input part RIN. The noise adding circuit consists of a tone detector 6, a level detector 7, and noise generator 8. When the tone detector 6 detects that the signal from the reception input terminal RIN is a narrow-band tone signal, the noise generating circuit 8 is connected to an input circuit, and the tone level is calculated by the level detector 7, and the noise signal is added to the tone signal with such level that the S/N ratio is degraded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an echo cancellation method for eliminating echo interference, which is invented when a hybrid circuit for converting two-line wires is used in a long-distance telephone line, for example. Regarding improvements.

[Conventional technology]

Echo cancellation is performed by estimating the response of the echo bus (i), memorizing it, and calculating it with the received signal to generate an estimated echo signal similar to the echo that occurs in the echo path, and then subtracting this estimated echo 4M from the transmitted signal. Koto number τ
Therefore, it is a device that cancels echo components. The exit signal obtained after canceling the echo component is fed back and used to estimate the characteristics of the echo path, and the tap coefficient of the estimated echo generation circuit is modified. When a single tone frequency signal such as a signal or a ringback tone is input, the echo cancellation tap coefficient 16 is applied as a target for echo cancellation.

Therefore, conventionally, modem signals, etc. are
A method is adopted in which echo cancellation is disconnected at the same time as the response tone of 2100f (z) is detected to start receiving the R message.

[Problem that the invention seeks to solve]

The function of the echo cancellation method is to continuously estimate the characteristics of the echo bus and input information, so that the sediment echo generation circuit continuously adjusts the tap coefficients to be given. However, the recent news 1ge1
1r (・, ν11 for example, push button '1
1' on a 12-talk machine! Due to service requests during the call, various tones 1c and 1 are increasingly being inserted in the middle of episodes 2IIi and L.Ru. That ho? There is a problem in that the echo cancellation is degraded.

When a Japanese issue is included, an additional signal having a frequency component exceeding the entire band e of the 8th edition of d'' is supplied to the echo path together with the tone signal, and the additional signal level is adjusted according to the value of the input signal level. The problem is solved by the echo cancellation method of the present invention, which prevents the signal light noise ratio from significantly deteriorating.
・Wik the echo cancellation effect on K over the entire 13f range
You can hold it.

[Actual example]

Hereinafter, some of the advantages of non-inventiveness will be explained with reference to the illustrated embodiments.

FIG. 1 is a block circuit diagram of echo cancellation xh.

In the figure, 1 is a hybrid circuit for 2i4aKn, 2
3 is a double talk detection circuit, 3 is an echo generation circuit, 4 is a tap coefficient correction circuit for the echo generation circuit, 5 is a subtracter for compressing and subtracting the echo component from the transmitted signal, 6 is a tone signal detection circuit, and 7 is a tone signal level. The detection circuit 8 is a circuit that adds a noise signal to the input signal.

In the figure, the echo path is formed as shown below. In other words, the signal arriving from the other side to the input terminal R+s leaks to the transmitting circuit input terminal SLN of the 4-wire line due to the impedance mismatch of the hybrid circuit l, including 16 Output terminal S, l
It returns again as an echo to the other party via JT.

Circuits 3, 4.5 are echo cancellers U [I? It is.

x Co-Q The main circuit 3 has the estimated signal response customization of the echo path.
, the estimated echo component is subtracted from the signal applied to the subtracter 5 via the transmission input signal SIN. The signal from which the echo component has been removed is sent to the other party from the terminal 5oL115'. A part of the output of the subtracter 5 is also supplied to the tap coefficient modification section 4. The tap coefficient (5 positive part 4 changes the tap coefficient value given to the echo generator 3 so that the residual error of the echo component at the output of the subtractor 5 approaches zero. Thus, the echo component is completely canceled out. When the signal is sent from the 86uT terminal, the echo generator 3 and the tap perform an echo cancellation effect using the 54 k'l, 16, or single frequency μ signal, and the tone ( As for other signals that have the same number component, echo summation is performed with several components, so
If the echo cancellation effect is incomplete, it becomes σ].

According to the present invention, signal input sections R and NK are provided with K noise addition times. The noise adding circuit consists of a tone detector 6, a level detector 7 and a noise generator 8.

Tone detector 6 receives signal flags from reception input terminals R and N. When it detects that the signal is a chivalry band tone signal.

The noise generation circuit is connected to the input circuit and the 1tf signal is supplied together with the tone signal to the echo cancellation circuit.The level of the noise generated by the noise generation circuit must be determined according to the level of the tone signal.

First, the tone level is calculated, and a noise signal is added to the tone at a level that does not harm the S/N ratio.

The tone signal level is calculated by the circuit shown in FIG. 2 or 3. In the row 5° diagram, R and N are the signal input parts of the level detector, and the Q level calculation result is output to the output terminal LR, N
is given to the 鑵廿 generation circuit.

71, 72, 74, 76 are m multipliers, 73.77 are adders, 75, 79.78 are delay circuits, α and β are multiplier coefficients, C wide is a clock input terminal, and CLR is a clear terminal. show.

These level calculation circuits are realized by conventional techniques (Q.

FIG. 4 shows a block diagram of the configuration for adding noise. In the figure, R+N is the signal input terminal, Rou T is the output terminal, 81 is the white noise generator, 82.83 is the multiplier, 8
4 is an adder, and 85 is a selector.

The selector 8t outputs the suppression signal TD and the tone (when the signal from the signal detector is input, the adder 84 is outputted as Avi and output) to the Ryoko Root, and when no tone signal is detected, it is output to the R and N terminals. Output the input signal to R0υT without passing it through the adder.

The output from the tone signal level calculator Fig. 1 is L R
Input from the I N terminal. Multiplier 83 supplies Asahi multiplied by multiplier r to multiplier 82 . The level of the +ftB power of the white noise generator 81 is redacted by a hanger 82, and is supplied to an adder 84, where it is added to the signal at the receiving input terminal R+N, and the tone signal detector 4 selects the tone signal detector 4. 85, output to the R and UT terminals only.

[Young fruit of invention]

As described above, according to the present invention, the deterioration of the echo canceling effect that occurs when receiving single tone No. 15 can be avoided by proper circuit adjustment, and the effect is great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are block diagrams of a level detection circuit that can be used with iCk of the present invention. FIG. 4 is a block diagram of an embodiment of a noise adding circuit according to the present invention. show. In the figure, 1 is a no hybrid circuit, 2 is a double talk detection circuit, 3 is an echo generation circuit, and 4 is a tap coefficient correction i.
'F, s is a subtracter, 6 is a tone detector, 7 is a tone level detector, 8 is a distorted sound addition circuit, 71°72.74,
76.82.83 is a multiplier, ? 3, 77.84 is a sword Ω calculator, 75.79 is a retardation circuit, 81 is a white noise generator, 8
5 indicates the selector 0 Yassai 1 Illustration 2 Figure CLK CLFX Thickness 3 HiRIN 夷4

Claims (1)

[Claims] An echo cancellation method characterized in that when a tone signal is input, a broadband noise signal of a level related to the input level of the tone signal is added to the tone signal and supplied to an echo cancellation circuit.