JPH03220841A - Low frequency interrupt distortion equalizer - Google Patents

Abstract

PURPOSE:To reduce the processing quantity and to converge the distortion in a short time by estimating a cut-off frequency of a low frequency cut-off of a transmission line from an electric distortion of a reception signal subjected from the transmission line and equalizing the low frequency cut-off distortion of the reception signal based on the estimated cut-off frequency. CONSTITUTION:Since the attenuation of a reception signal is increased as the transmission line is longer and the resistance of the transmission line is higher, the amplification factor of a gain control circuit 12 compensating the attenuation of the reception signal is proportional to the resistance of the transmission line. On the other hand, the cut-off frequency of the transmission line is proportional to the resistance of the transmission line. Then a coefficient correction circuit 16 estimates the cut-off frequency of the transmission line based on the amplification factor of the gain control circuit 12 to select a coefficient most suitable for the estimated cut-off frequency among a coefficient table 17 in which plural different coefficients for the cut-off frequencies of a filter 14 are prepared. Thus, since the coefficient of the filter 14 suitable for the cut-off frequency of the transmission line is selected with a simple processing based on the amplification factor of the gain control circuit 12, the distortion is converged in a short time.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention provides a low-frequency cutoff method that equalizes low-frequency cutoff distortion caused in a received signal by a transmission path using a so-called metallic cable. This invention relates to a distortion equalization device.

(Prior art) Generally, in transmission lines that use metallic cables,
A pulse transformer for blocking DC components or a power separation filter for separating the power supplied to the terminal from the signal via the transmission path may be inserted between the transmission path and the transceiver.

When such an element that blocks direct current components is inserted into a transmission path, the low frequency components of the transmitted signal are also blocked, resulting in low frequency cutoff distortion in the received signal.

In particular, if the transmission line code used for transmission is not DC balanced, the spectrum of the transmitted signal is concentrated near the DC, resulting in significant low-frequency cut-off distortion in the received signal.

for example! SDN (Integrated 5ervi)
In the CE Digital Network (Service Integrated Digital Network), a power separation filter is inserted into the transmission path in order to supply power from the transmission path to the I5DN terminal.

Furthermore, ANSI (American Nation
A 2BIQ code is adopted as the transmission path code of the 15DN basic rate subscriber line interface standardized by the American National Standards Institute.

This 2BIQ'R signal is a four-value signal with no redundancy, and the signal spectrum is concentrated in the low range.

Therefore, in the 15DN basic speed subscriber line interface, significant low-frequency cutoff distortion occurs in the signal received by the transformer and DC cutoff filter, and it is essential to equalize the low-frequency cutoff distortion or to prevent transmission errors. It is a condition.

Here, if an attempt is made to equalize the low-frequency cut-off distortion by using a filter whose cut-off characteristic is inverse to that of the transmission line, there will be a problem in terms of performance, since the gain P> of this filter at direct current will be unimpeded.

Therefore, a so-called quantization feedback equalizer is generally used to equalize the low-frequency cutoff distortion.

The operation of this quantization feedback type equalizer will be explained with reference to FIG.

FIG. 3 is a block diagram showing the configuration of a 2BIQ code transceiver using a quantization feedback type equalizer.

In the figure, a signal (No. 8) received from a transmission path (not shown) is input to a D/D converter 1 and converted into a digital signal at a predetermined sampling timing.

The received signal converted into a digital signal is sent to the gain control circuit 2.
and is amplified to a predetermined amplitude.

The received signal output from the gain control circuit 2 is sent to the determination circuit 3, where vI+constant circuit 3 determines 4fi! ! quantized to

The quantized received signal is input to the filter 4, and the received signal that has passed through the filter 4 is subtracted from the quantized received signal and added to the output of the gain control circuit 2.

Further, input/output signals of the determination circuit 3 are inputted to the minimum error detection circuit 5, and output signals thereof are inputted to the coefficient correction circuit 6.

Note that 7 is a coefficient table prepared with coefficients of a plurality of cutoff frequencies of the filter 4, and 8a, 8b, and 8c are adders.

In the above configuration, the cutoff characteristic of the transmission path is H(2), the characteristic of the filter is G(z), the transmission signal of the opposite transceiver is X, the received signal input to the judgment circuit 3 is Y, and the judgment circuit 3 Assuming that the judgment result is correct and focusing only on the low cutoff distortion, the relationship between X and Y is expressed by the following equation.

Y, -(H(z) +1-G(z))
・X-(1) In the equation, H (z) and G (z)
When they are equal, that is, when the cut-off characteristics of the transmission line and the characteristics of the filter 4 are equal, Y becomes equal to X, and the low-frequency cut-off distortion is completely equalized.

Incidentally, as the resistance value of the transmission line changes in accordance with the transmission distance, the cut-off frequency of the transmission line also changes in proportion to the resistance value of the transmission line, as shown in FIG.

Therefore, in order to obtain sufficient equalization performance, the above-mentioned transceiver circuit prepares multiple coefficients with different cut-off frequencies in the coefficient table 7 to determine the cut-off frequency of the filter, and equalizes the low-pass distortion from among them. We try to select the coefficients that are most appropriate for the purpose.

The coefficients most suitable for equalizing low-frequency cutoff distortion are selected as follows.

That is, one coefficient is selected by the coefficient correction circuit 6 from among a plurality of coefficients prepared in the coefficient table 7.

The residual error when the received signal is equalized using the selected coefficients is determined from the difference between the human power and the output of the determination circuit 3.

Similarly, the residual errors are sequentially determined for all the coefficients, and the minimum error detection circuit 5 detects the coefficient with the minimum residual error among them.

Then, the coefficient correction circuit 6 selects from the coefficient table 7 the coefficient with which this residual error is the minimum.

In this way, the conventional quantization feedback type equalizer adapts the equalization of the low-frequency cutoff distortion.

However, II
R(lnrinite Impulse Re5pon
se) The filter requires time to converge after the coefficients are selected.

Therefore, in the above-mentioned quantization feedback type equalizer, processing such as coefficient selection and residual error calculation is performed for all prepared coefficients, so the amount of processing required until the optimal coefficient is selected is large, etc. There was a problem that it took 111f for the conversion device to converge.

(Problems to be Solved by the Invention) As described above, the conventional low-frequency cutoff distortion equalizer requires a large amount of processing to reach convergence, so there is a problem that the time for convergence 914 is long.

The present invention has been made to solve such problems, and therefore, it is an object of the present invention to provide a low-frequency cutoff distortion equalization device that can reduce the amount of processing and converge within a short Dlj interval.

[Structure of the Invention] (Means for determining the load) The present invention provides an equalization method that uses a predetermined coefficient to equalize the low-frequency cut-off distortion caused in No. 21572 due to the low-frequency connection characteristics of the transmission line. an estimating means for estimating a cut-off frequency of the transmission line from the received signal or a variable received from the transmission line; and adjusting a coefficient of the equalizing means based on the cutoff frequency estimated by the estimating means. :A adjustment means.

The cutoff frequency of the transmission path can be estimated from the amount of attenuation of the amplitude voltage of the received signal, the amount of attenuation of the power of the received signal, and the like.

It is also possible to transmit signals from opposing transceivers at a plurality of frequencies, and estimate the break frequency of the transmission path from the group delay characteristics, attenuation characteristics, etc. that the transmitted signal receives from the transmission path.

(Function) In the present invention, the cutoff frequency of the low cutoff of the transmission line is estimated from the received signal or an electrical variable received from the transmission line, and the low cutoff distortion of the received signal is estimated based on the estimated cutoff frequency. Perform equalization.

Therefore, the amount of processing required to adapt to the cut-off frequency of the transmission path is reduced, and convergence can be achieved in a short time.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a 2BIQ code transceiver using a low-frequency cutoff distortion equalizer according to an embodiment of the present invention.

As shown in the figure, a received signal received from a transmission path (not shown) is input to a converter 11 (Al1) and converted into, for example, an 8-bit digital signal at a predetermined sampling timing.

The received signal converted into a digital signal is sent to the gain control circuit 1.
2, and is amplified so that the amplitude of the received signal attenuated on the transmission path reaches a predetermined value.

The received signal amplified to a predetermined amplitude by the gain control circuit 12 is sent to the determination circuit 13, where it is quantized into four values.

The quantized received signal is input to a filter 14 which is an IIR type bypass filter.

Furthermore, the received signal that has passed through the filter 14 is subtracted from the quantized received signal by the adder 18a, and the result is equivalent to (1-G(2))·X in equation (1) shown in the conventional example described above. A received signal is generated.

This received signal and the output of the gain control circuit 12 are combined into an adder 18b.
is added and the low-frequency cutoff distortion is equalized.

Note that 17 is a coefficient table in which coefficients of a plurality of cutoff frequencies of the filter 14 are prepared.

Second, the longer the transmission line is and the higher the resistance value of the transmission line is, the greater the attenuation of the received signal becomes. Therefore, the amplification factor of the gain control circuit 12 that compensates for the attenuation of the received signal is also increased along the transmission line as shown in Figure 2. is proportional to the resistance value of

On the other hand, as previously shown in FIG. 4, the cutoff frequency of the transmission line is proportional to the resistance value of the transmission line.

From this, the cutoff frequency of the transmission line can be set by the gain control circuit 12.
It can be seen that it is possible to estimate from the amplification factor of .

Therefore, in this embodiment, the cutoff frequency of the transmission line is estimated by the coefficient correction circuit 16 based on the amplification factor of the gain control circuit 12, and the coefficients of the filter 14 for a plurality of different cutoff frequencies are selected from the prepared coefficient table 17. , the coefficient most suitable for the estimated cutoff frequency is selected.

Therefore, the coefficients of the filter 14 suitable for the cut-off frequency of the transmission path are selected by simple processing based on the amplification factor of the gain control circuit 12, so that convergence can be achieved in a short time.

Note that in the above-described embodiment, a case has been described in which the received signal is digitized and processed by a digital circuit, but the received signal may be processed as an analog signal by using an analog circuit.

Further, in this embodiment, an example has been described in which the cutoff frequency of the transmission line is estimated from the amount of attenuation of the amplitude voltage of the received signal, but the present invention is not limited to this. The cutoff frequency of the transmission path may be estimated from the amount of attenuation of the signal power.

Furthermore, the cutoff frequency of the transmission line may be estimated from the transmitted signal or the group delay characteristics and attenuation characteristics received from the transmission line by transmitting signals from a transceiver facing in the direction using multiple frequencies. In some cases, a more accurate cutoff frequency can be estimated.

Furthermore, it goes without saying that the same effects can be obtained even when the present invention is applied to a transceiver for a transmission code other than the above-mentioned 2HIQ code.

Furthermore, if the present invention is combined with the conventional method of selecting filter coefficients from residual errors, it is possible to realize a low-frequency cutoff distortion equalization device that can achieve more accurate convergence in a shorter time.

[Effects of the Invention] As described above, in the present invention, the cutoff frequency of the low-frequency cutoff of the transmission path is estimated from, for example, the electrical variation that the received signal receives from the transmission path, and the received signal is adjusted based on the estimated cutoff frequency. Equalizes the low-frequency cutoff distortion.

Therefore, the amount of processing required to adapt to the cutoff frequency of the transmission path is small, and convergence can be achieved in a short time.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a 2BIQ code transceiver using a low-frequency cut-off distortion equalizer according to an embodiment of the present invention;
The figure shows the relationship between the amplification factor of the gain control amplifier and the resistance value of the transmission line, Figure 3 is a block diagram of a 2BIQ code transceiver using a conventional low cutoff distortion equalizer, and Figure 4 shows the transmission line. FIG. 3 is a diagram showing the relationship between cut-off frequency and resistance value. 11... A/D converter, 12... Gain control circuit, 1
3... Judgment circuit, 14... Filter, 16... Coefficient correction circuit, 17... Coefficient table. Fig. 8c, □ Fig. 4

Claims (1)

[Claims] (1) Equalizing means for equalizing low frequency cutoff distortion caused in the received signal due to the low frequency cutoff characteristic of the transmission line using a predetermined coefficient; and the transmission line based on the variable received by the received signal from the transmission line. 1. A low-frequency cutoff distortion equalization device, comprising: estimating means for estimating a cutoff frequency of said estimating means; and adjusting means for adjusting coefficients of said equalizing means based on the cutoff frequency estimated by said estimating means.