JPS6057729B2 - Transmission line distortion correction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention corrects group delay distortion occurring in a transmission path having a carrier line, for example in a telemetry system that transmits measured data at a remote location over a telephone line. The present invention relates to a transmission line distortion correction device.

(2) Prior art A transmission path distortion correction device called an automatic equalization device is a modem device (usually called MODEM) that transmits binary data.
has developed together.

Here, the amount of distortion occurring in the transmission path is detected, for example, in the following manner. When an impulse is transmitted from the transmitting side at a known time, the received waveform g(), which is distorted on the transmission path, becomes as shown in FIG.

Here, time = 0 is the time at which the impulse should be received, and =T0 or -To is the time at which adjacent data exists. That is, To corresponds to the period of data. g(
Although nT0) (n■±1, ±2, . . . ) should originally be 0, it becomes a finite value due to distortion in the transmission path, causing intersymbol interference. Here, considering the worst value of intersymbol interference, \ can be considered as the amount corresponding to transmission i distortion.

Conventionally, a technique has been used in which the received signal is supplied to a correction means such as a transversal filter whose frequency characteristics are variable, and the characteristics are controlled so that the above-mentioned D1 or D2 is minimized at the output thereof. .

In the above conventional technology, the specific time t=nτ.

(N = ±1, ±2, ...) Complex operations are required, such as detecting and storing a large number of values of the received impulse waveform, and further performing calculations corresponding to D1 or D2. (3) Purpose of the Invention The present invention provides means for easily detecting the amount corresponding to the group delay distortion of a transmission line having a carrier line. The purpose of the present invention is to provide a transmission line distortion correction device.

(4) General description of the invention In the present invention, a step signal is transmitted at a known time and two values at times equidistant from the time when the intermediate value of the received waveform is taken, or a value obtained by a linear combination of these. A correction means having variable frequency characteristics is controlled so that the value approaches a predetermined value.

(5) Examples Hereinafter, the present invention will be explained in detail with reference to Examples. Ru.

When a step signal is transmitted from the transmitting side at a known time, the received waveform f(t) becomes as shown in FIG.

Here, the time at which the reception level reaches an intermediate value (0.5 in the figure) is set as the reference t=o, and from this point, etc.! Attention is paid to the received signals f(I) and f(-I) at times separated by a new time τ/2. Here, τ is an arbitrary time. In the present invention, f(
I), f (No. 1) or the sum or difference of both,
The correction means having variable frequency characteristics is controlled so that these values approach predetermined values. It will be shown below that the above value corresponds to the distortion of the transmission path. Considering the telephone line, which is the most commonly used transmission path, most of the distortion in amplitude and group delay occurs when the telephone line passes through a carrier line.

Therefore, the number of links in the carrier line (link refers to the section in which a signal modulated on the carrier line is demodulated; from the transmitting section to the receiving section, multiple links are formed because it passes through multiple carrier relay stations. The larger the number of links in j, the larger the group delay distortion) is used as a variable to show f(I) and f(-I) as shown in FIG. In each figure, it is assumed that even if the step signal has no transmission path distortion, the band is limited by an ideal low-pass filter with a band of approximately 112τ. As will be described in detail later, a case will be considered in which the above value is detected from the received waveform after the distortion generated in the transmission path is corrected by the correction means.
Therefore, the difference between the distortion generated in the transmission path and the amount corrected by the correction means, that is, the residual distortion, corresponds to the number of links in Figure 3, and this will be positive, but if the correction is insufficient, it will be negative. indicates a case where the correction is excessive. In Figure 3, f(I) converges to 0.7 regardless of whether the correction is insufficient or excessive, so the characteristics of the correction means are such that f(snow) approaches the maximum value of 0.9. If this is controlled, the residual distortion will be reduced to 0 and appropriate correction will be performed.

Similarly, if we focus on f(-I), this is the minimum value 0
．． It should be controlled so that it approaches 1. In Figure 4, f
(I)+f(-I) is shown.

From this, it can be seen that control should be performed so that f(I)+f(-I) approaches 1.0. In Figure 5, f(I)
-f (No. 1) is shown.

From this, it can be seen that control should be performed so that f(I)-f (one snow) approaches the maximum value of 0.8. As mentioned above, the two values at times equidistant from the time when the intermediate value of the step reception waveform is taken, or their sum or difference, correspond to the magnitude of the residual distortion after correcting the transmission line distortion. It is sufficient to detect this and control the correction means so that the detected value approaches a predetermined value. FIG. 6 shows an example of the overall configuration of the correction device.

A received signal (usually a carrier wave signal) applied to the input terminal 1 is given an inverse characteristic of transmission line distortion by a correction means 2a whose amplitude and group delay characteristics with respect to frequency are variable. The corrected signal is demodulated from a carrier signal to a baseband signal by demodulation means 3. The above two values of the step signal in the demodulated signal are detected by the level detection means 4,
The linear combination means 5 converts it into a sum or a difference. If f(dark) or f(-I) is used directly, 5 is omitted. However, in the following, f(I) and f(-I) alone and their sum and difference will be considered as linear combination values of f(I) and f(-I). Control means 6 uses the output of 5 to change the frequency characteristics of the correction means 2a.

For example, when using the sum of f(I) and f(-I),
As is clear from FIG. 4, this value is compared with a value of 1.0, and if the sum is greater than 1.0, the correction is insufficient, so the correction amount of the correction means 2a is increased. On the other hand, the sum is 1.
If it is smaller than 0, the correction is excessive, so the correction means 2a
Decrease the amount of correction. In this way, the correction amount (that is, the frequency characteristic) of the correction means 2a is adjusted so that the sum approaches 1.0.
Finally, a corrected signal is obtained at the output terminal 7. In addition, when using f(I) alone or the difference between f(I) and f(-snow), as is clear from Figures 3 and 5, if the above value becomes larger by increasing the correction amount, the correction amount is insufficient. It can be seen that if the above value becomes small, the amount of correction is excessive, and if the above value becomes small, the amount of correction is excessive.

Further, when f(-I) alone is used, although the characteristics are opposite to those described above, it is still possible to determine whether the amount of correction is too much or too little.

FIG. 7 shows another configuration example, in which the received signal is first demodulated by the demodulating means 3.
After demodulating the signal, the correction means 2b corrects the distortion. One of the correcting means 2a and 2b corrects the carrier wave signal, and the other corrects the baseband signal, and although the specific characteristics for correction are different, both correct the frequency characteristic opposite to the distortion generated in the transmission path. Just make it happen. FIG. 8 shows an embodiment of the level detecting means 4, in which the demodulated signal applied to the terminal 8 is guided to the capacitors 11, 12 via the switches 9, 10. Short-circuited at - time.

Since we believe that the time at which the Step 22 knob signal is received is known in advance, these times should also be known.

In this way, after receiving the step signal, f
(-I), and f(I) is obtained at the terminal 14. Although various configurations of the correction means 2 can be considered, a simple example is shown in FIG.

A distorted signal is applied to the input terminal 15. 16-1
9 is a correction element having various correction amounts; for example, 1
6 corresponds to 1 link, 17 corresponds to 2 links, 18 corresponds to 3 links, etc., and have frequency characteristics with opposite distortion characteristics.

16 to 19 can be realized using active filters, transversal filters, etc.

Reference numeral 20 is a switch that takes out the optimum one of each correction element to an output terminal 21.

Which one is determined to be optimal is determined by determining the linear combination value of f (snow) and f (-I) of the received step signal according to the method described above. , (6) Summary As explained above, in the present invention, the value at a time equidistant from the time when the intermediate value of the received step signal is taken, or the sum or difference thereof, is detected, and this detected value approaches a predetermined value. The frequency characteristics of the correction means are changed accordingly.

Therefore, there are only one or two types of values to be detected, and there is an advantage that the apparatus can be easily implemented without the need for complicated arithmetic processing using many detected values as in the prior art.

[Brief explanation of the drawing]

Figure 1 shows the impulse received waveform, Figure 2 shows the step received waveform, and Figures 3, 4, and 5 show f(I), f(-I) in the received step signal, and their linear combination values. 6, 7, 8, and 9 are diagrams showing examples of the present invention.

Claims (1)

[Claims] 1. A plurality of group delay distortion correcting means each corresponding to a different number of links for correcting group delay distortion occurring in a transmission path having a carrier line and corresponding to the number of links of the carrier line;
The time at which one of the plurality of group delay distortion correction means is selected and the intermediate level of the reception step signal obtained through the selection means connected to the transmission line and the selected one of the group delay distortion correction means is taken. a detection means for detecting a value at a time equidistant from , or a sum or difference of the above values; and a selection means for detecting a value detected by the detection means to be close to a value obtained when the number of links is zero. 1. A transmission line group delay distortion correction device, comprising driving means.