JPS6057730B2 - 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 that occurs in a transmission path having a carrier line in, for example, 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 MODE) that transmits binary data.
It has developed together with M.

Here, the amount of distortion occurring in the transmission path is detected, for example, in the following manner. When an impulse is transmitted at a known time from the transmitting side, it is distorted on the transmission path and the received waveform g()
is as shown in Figure 1.

Here, time = 0 is the time at which the impulse should be received, and =T or -T is the time at which adjacent data exists. That is, T corresponds to the period of data. g(nT)
(n=±1, ±2, . . . ) should originally be a value of 0, but due to distortion in the transmission path, it becomes a wired value, causing intersymbol interference. Here, considering the worst value of intersymbol interference, 1 and D
,■ Σ (Ig(nT)1+1g(-nT)1)n■
1 or D, ■n30 (g'(nT)+Ff(-nT)) may be considered as the amount corresponding to the transmission line distortion.

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

In the above conventional technology, specific time t=nτ(n=±1
, ±2, . . . complex operations are required, such as detecting and storing the received impulse waveform values, and further performing calculations corresponding to D1 or D2.

In addition, to determine whether D1 or D2 has become the minimum, change the parameters before and after, and
1 or D2 must be examined, and the determination method itself is complicated. Therefore, there were drawbacks such as an increase in the scale of the equipment for realizing this. (3) Object of the Invention An object of the present invention is to provide a transmission line distortion correction device having means for easily detecting an amount corresponding to the group delay of a transmission line having a carrier circuit.

(4) General description of the invention In the present invention, an impulse signal is transmitted at a known time, all time values of adjacent clocks before and after the impulse in the received waveform are detected, and the difference between these is brought closer to a predetermined value. A correction means having variable frequency characteristics is controlled as shown in FIG.

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

The transmitting side sends an impulse signal at a known time. Then, the received waveform g(t) becomes as shown in FIG. 1 above.

Here, it is assumed that only g(τ) and g(−τ) are detected from the received waveform.

In the present invention, the difference between g(.tau.) and g(-.tau.) is detected, and the correction means having variable frequency characteristics is controlled so that this value approaches a predetermined value. 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 line,
Most of the distortion in amplitude and group delay occurs when the telephone line passes through the 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, and a plurality of links are formed from the transmitting section to the receiving section because the signal passes through a plurality of carrier relay stations. The larger the number of links, the larger the group delay distortion.) When g(τ)-g(-τ) is expressed as a variable, the result is as shown in FIG. It was assumed that the received impulse signal was band-limited by an ideal low-pass filter with a band of 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 line) and the amount corrected by the correction means, that is, the residual distortion, corresponds to the number of links in Figure 2, and this is positive if the correction is insufficient.
A negative value indicates a case where the correction is excessive. In Figure 2, g(τ) - g(-τ) converges to about 01 if the correction is insufficient, and -0.2 if the correction is excessive, so g
If the characteristics of the correction means are controlled so that (τ)-g(-τ) approaches 0, the residual distortion becomes 0 and proper correction is performed.

As mentioned above, the difference between g(τ) and g(-τ) in the impulse reception waveform corresponds to the magnitude of the residual distortion after correcting the transmission line distortion, so this is detected and this becomes close to a predetermined value. The correction means may be controlled in such a manner. FIG. 3 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. g(.tau.) and g(-.tau.) in the impulse signal in the demodulated signal are detected by the level detection means 4 and converted into a difference by the linear combination means 5. Reference numeral 6 denotes a control means that uses the output of 5 to change the frequency characteristics of the correction means 2a.

For example, as is clear from FIG. 2, the polarity of the difference signal is checked, and if it is positive, the correction is insufficient, so the correction amount of the correction means 2a is increased. On the other hand, if the polarity is negative, the correction is excessive, so the correction amount of the correction means 2a is decreased. In this way, the correction means 2
The correction amount (ie, frequency characteristic) of a is changed, and finally a corrected signal is obtained at the output terminal 7. FIG. 4 shows another configuration example in which the received signal is first demodulated by the demodulating means 3 and then its distortion is corrected by the correcting means 2b.

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. 5 shows an embodiment of the level detecting means 4. Switches 9 and 10 lead the demodulated signal applied to the terminal 8 to capacitors 11 and 12 via switches 9 and 10 at times t=-τ and τ, respectively. Short circuit.

Since we thought that the time at which the impulse is received is known in advance, the above time is also known. In this way, after receiving the impulse signal, the terminal 13 will be connected to g(-
τ), and g(τ) is obtained at the terminal 14. correction means 2,
Although various configurations of 2a and 2b are possible, 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. These have frequency characteristics with opposite distortion characteristics.

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

Reference numeral 20 denotes a switch which outputs the optimum one of each correction element through an output terminal 21.

Which one is determined to be optimal is determined by determining the difference between g(τ) and g(−τ) of the received impulse signal according to the method described above. In the above explanation, it is assumed that impulse signals are transmitted, but step signals may also be transmitted.

In other words, if the step signal is f(t), the impulse signal can be expressed as g(t) = f(t) - f(t - τ), so using the received step signal, g(τ) can be expressed according to the above formula.
, g(-τ) can also be calculated on the receiving side. (6) Summary As explained above, in the present invention, the difference between the time values of adjacent clocks before and after the impulse of the received impulse signal is detected, and the frequency characteristics of the correction means are changed so that this detected value approaches 0. .

Therefore, there is no need to find the minimum value as in the prior art, and the operation is stable. Further, since there are two types of values to be detected, there is no need for complex arithmetic processing using many detected values as in the prior art, and the device can be easily realized.

[Brief explanation of the drawing]

Figure 1 shows the impulse received waveform, Figure 2 shows g(T)-g
Figures 3, 4, 5, and 6 showing changes in (-τ) with respect to transmission line distortion are diagrams showing embodiments 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;
A selection means for selecting one of the plurality of group delay distortion correction means and connecting it to the transmission line, and adjacent clocks before and after the impulse of the received impulse signal obtained through the selected one of the group delay distortion correction means. and means for driving the selection means so that the detected value of the detection means approaches the value obtained when the number of links is zero. Transmission line group delay distortion correction device.