JPS6282711A - Adaptive transversal filter - Google Patents

Abstract

PURPOSE:To revise a stable tap coefficient even when a signal with a high peak level is inputted by continuing the correction control corrected by a correction coefficient in response to the level of the peak by a sample time of tap number of a tap delay line. CONSTITUTION:An instantaneous power obtained by a multiplier 10 and an output of a power calculator 4 are multiplied with CNP/N at a multiplier 11, a peak factor CPK being a ratio of the result to the mean power multiplied with the peak factor CNP of a normal signal is obtained by a divider 13 and the result is inputted to a discrimination/timer section 15 and a storage device 14. When CPK>1, the discrimination/timer section 15 discriminates it as a signal with a high peak, a multiplier 12 multiplies the peak factor CPK stored in the storage device 14 and the total sum of the power of the signals in a tap delay line 1 and outputs the result. The output of the total sum of the corrected power is given by a timer of the discrimination/timer section 15 during the hang-over time of the sample time of the tap number of the tap delay line 1. Thus, even when a signal having a high peak is inputted, the tape coefficient is revised stably.

Description

[Detailed Description of the Invention] [Summary] In an adaptive transversal filter that processes with a finite word length, the input of a signal with a strong peak property is detected, and the power used for modifying the tap coefficient is adjusted according to the size of the peak. By correcting with a correction coefficient and continuing this correction control for the sample time of the number of taps in the tap delay line, it is possible to stably update the tap coefficients even when a signal with strong peaks is input. This is what I did.

[Industrial application field]

The present invention relates to an improvement in an adaptive transversal filter that processes with a finite word length and is used in an echo canceller or the like.

In the above-mentioned adaptive transversal filter, it is desirable to be able to stably update the tap coefficients even when a signal with a strong peak is input, such as when a person clears their throat or starts speaking.

An example in which an adaptive transversal filter is used as an echo canceller will be explained below.

[Conventional technology]

FIG. 2 is a block diagram when a conventional adaptive transversal filter is used as an echo canceller.

In the figure, 1 is a tap delay line, 2 is a tap coefficient sender, 3 is a tap coefficient updater, 4 is a power calculator, 5゜6 is an adder,
7 to 9 indicate multipliers.

In FIG. 2, when a signal x7 is input from the receiving line, this signal passes through an echo path and becomes an echo y7, which appears on the transmitting line.

In the echo canceller, in order to cancel this echo, a pseudo echo yn (generation will be explained later) is generated, and by taking the difference from VnVh-en in an adder 5, a residual echo e is generated on the transmitting line. , l.

In order to create this pseudo echo yn, the sampled input signal is sequentially input to a tap delay line 1 with N taps,
From each tap Xn IX1% -In...X n
-N*1 signal is outputted and input to the multiplier 7.8.9 and the tap coefficient updater 3, as well as to the power calculator 4.

The power calculator 4 calculates the total power of the signals in the tap delay line 1 Σ X′+s−j and inputs this value to the Tabb coefficient updater 3 .

The residual echo en is also input to the tap coefficient updater 3, and the tap coefficients h0 to h sent out from the tap coefficient transmitter 2
The successive updates for setting N-1 to the optimal value are performed using an optimal algorithm of the learning identification method that converts the residual echo en into a signal, as shown in the following equation (1).

(ntri (n) h6=hl +en −x, −, / ΣJ
x,, -j ・ ・ ・ (1) The tap coefficients obtained in this way and the signal χn-4 from the tap of the tap delay line l are combined into a multiplier as shown in the following equation (2). 7～
9 to obtain the pseudo echo yn.

[Problem that the invention seeks to solve]

However, in the above method, when a signal with a strong peak is input, such as when someone clears their throat or starts a conversation, an instantaneous residual echo en and signal X7-! The correlation value (e n −x
Even though n-4) increases, the total power of the signals in tap delay line 1, Σ However, there is a problem that sometimes an overflow occurs in calculations for updating the tap coefficients, and stable updating of the tap coefficients is not performed.

[Means for solving problems]

The above problem is solved by detecting the input of a signal with strong peak characteristics, correcting the power used to correct the tap coefficient using a correction coefficient according to the size of the peak, and performing correction control for this correction.
This is achieved by the adaptive transversal filter of the present invention, which lasts as many sample times as the number of taps in the tap delay line.

[Effect]

According to the present invention, when a signal with a strong peak property is input, it is detected, and at this time, the power used for correcting the tap coefficient is corrected by a correction coefficient according to the size of the peak,
Since this correction control is continued for a sample time equal to the number of taps of the tap delay line, overflow of calculations for updating tap coefficients will not occur.

〔Example〕

FIG. 1 is a block diagram when an adaptive transversal filter according to an embodiment of the present invention is used as an echo canceller.

In the figure, 10 to 12 are multipliers, 13 is a divider, 14 is a holder, 15 is a judgment/timer section, and 16 is a selector, and the same reference numerals indicate the same functions throughout the figures.

The difference between FIG. 1 and FIG. 2 is that a portion surrounded by a dotted line has been added.

This added part will be explained below.

The following (3 ) As shown in the formula, the peak factor CH of the normal signal is added to the average power.
A peak factor (correction coefficient) Cpg, which is a ratio of the value multiplied by P (usually about ten-odd db), is determined by the divider 13 and input to the judgment/timer section 15 and the holder 14.

Crx=xA/CHP ・(1/N) ・Σx27−
j... (3) In the judgment/timer section 15, if CPK≦1, it is judged to be a normal signal, if CPK>1, it is judged to be a signal with a strong peak property, and when it is judged to be a normal signal, , selector 16 is controlled, and the sum of the powers of the signals in the tap delay line 1 Σ
When it is determined that the signal has a strong peak property -s#, the multiplier 12 outputs the peak factor (correction coefficient) CFK held in the holder 14 and the signal knob delay.

The output of the corrected power sum is outputted by the timer of the determination/timer section 15 after a hangover time corresponding to the sample time of the number of taps of the tap delay line 1.

In other words, when it is determined that the signal has a strong peak, a correction coefficient is added to the total power of the signal in tap delay line 1 to prevent overflow from occurring due to normalization, and this correction is performed. Since the control is continued until the signal x passes through the tap delay line 1, the tap coefficients can be stably updated even if a signal with a strong peak property is input.

Although the above description has been made regarding the case where the filter is used as an echo canceller, it goes without saying that this can also be applied to an adaptive transversal filter used in other applications.

〔Effect of the invention〕

As described in detail above, according to the present invention, even if a signal with a strong peak property is input, tap coefficients can be stably updated.

[Brief explanation of drawings]

FIG. 1 is a block diagram when an adaptive transversal filter according to an embodiment of the present invention is used as an echo canceller. FIG. 2 is a block diagram when a conventional adaptive transversal filter is used as an echo canceller. . In the figure, 1 is a tap delay line, 12
is a tap coefficient transmitter, 13 is a tap coefficient updater, 1■ 4 is a power calculator, 15
．． 6 is an adder, 17~
9. 10 to 12 are multipliers, 13 is a divider, 14 is a holder, 15 is a judgment/timer section, and 16 is a selector. `` 覦にい〈 ME＝１ ■ 禾 ２ fig.

Claims (1)

[Claims] In an adaptive transversal filter that processes with a finite word length, the input of a signal with strong peak characteristics is detected, and the power used to modify the tap coefficient is corrected by a correction coefficient according to the size of the peak. and the adaptive transversal filter is characterized in that the correction control continues for a sample time equal to the number of taps of the tap delay line.