JPH0222566B2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention]

The present invention relates to a transmission line distortion correction device for correcting group delay distortion of a transmission line having a carrier line in, for example, a telemetry system that transmits measured data at a remote location over a telephone line.

[Prior art]

There are 2 transmission line distortion correction devices called automatic equalizers.
A modem (usually MODEM) that transmits value data
) has developed together with Conventionally, the received signal is supplied to a correction means with variable frequency characteristics, such as a transversal filter, and the tap coefficient is changed to minimize intersymbol interference at the output, thereby eliminating distortion occurring in the transmission path. A corrective technique was used. In the above conventional technology, specific time t=nτ(n
It requires complex operations such as detecting and storing the values of the received impulse waveform (=±1, ±2, ...), and performing calculations to measure the amount of intersymbol interference. There were drawbacks such as the large scale of the equipment to achieve this.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a transmission line distortion correction device having means for easily detecting an amount corresponding to group delay distortion of a transmission line having a carrier line.

[General explanation of the invention]

In the present invention, a step signal is transmitted at a known time, the maximum value and minimum value of the received waveform are detected,
A correction means having variable frequency characteristics is controlled so that the value obtained by linear combination of these approaches a predetermined value.

【Example】

Hereinafter, the present invention will be explained in detail with reference to Examples. When a step signal corresponding to a synchronizing signal is transmitted from the transmitting side together with data at a known time, the received waveform f(t) generally accompanies vibration as shown in FIG. This vibration is the sum of vibrations caused by the fact that the band of the transmitted step signal is inherently finite and vibrations caused by distortion in the transmission path. Assuming a transmission line with large distortions that require automatic equalization, it can be said that the vibrations generated in the transmission line are much larger than those that originally exist in the received waveform. Here, the maximum value of the received waveform including vibration is f(t)
max, and the minimum value is f(t)min. In the present invention, this f(t)max, f(t)min, or the sum or difference between the two is detected, and a correction means having variable frequency characteristics is controlled so that these values approach a predetermined value. be. It will be shown below that the above value corresponds to the group delay 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 transport line (the number of links is
It refers to the number of sections in which a signal modulated on a carrier line is demodulated, and multiple links are formed when the signal passes through multiple carrier relay stations from the transmitter to the receiver. The larger the number of links, the larger the group delay distortion) is used as a variable to show f(t)max and f(t)min as shown in FIG. Note that when a signal that has passed through an m-link carrier line is corrected by a correction means that corrects the distortion of n links, it is equivalently (m-n)
The result is a signal with link distortion. This (m-n)
Links are defined as the number of residual links. Here, the number of residual links is 0 (i.e., when no distortion is added to the transmission path)
But these values are 1.09 or -0.09, 1
Otherwise, the reason why it does not become 0 is due to vibrations caused by band-limiting of the step signal. In addition,
The band limit in the calculations in the figure assumes ideal reduction filter characteristics. Now, let us consider the case where the above value is detected from the received waveform after the distortion generated in the transmission path is corrected by the correction means. As mentioned above, the difference between the distortion generated in the transmission path and the amount corrected by the correction means, that is, the number of residual links, is positive when the correction is insufficient, as shown in Figure 2. It becomes negative when the correction is excessive. In Figure 2, f(t)max converges to about 1.2 if the correction is insufficient, and converges to 1.0 if the correction is excessive, so the correction means should be adjusted so that f(t)max approaches 1.09. If the characteristics are controlled, the residual distortion will be reduced to 0 and appropriate correction will be performed. Similarly f(t)
If we focus on min, we can control it so that it approaches -0.09. FIG. 3 shows f(t)max-f(t)min.
From this, it can be seen that control should be performed so that f(t) max - f(t) min becomes the minimum, in this case approaching 1.18 (1.09 + 0.09). FIG. 4 shows f(t)max+f(t)min.
From this, f(t)max+f(t)min is 1.0(1.09−
0.09). Note that the above numerical values are just examples, and may vary depending on the characteristics of the filter used for band limitation. As mentioned above, the maximum value, minimum value, sum, difference, etc. of the step reception waveform correspond to the magnitude of residual distortion after correction of transmission line distortion, so this is detected and this value approaches a predetermined value. The correction means may be controlled in such a manner. FIG. 5 shows an example of the overall configuration of the transmission line distortion correction device of the present invention. 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 by the demodulating means 3 into a baseband signal from the carrier signal. The maximum value and minimum value of the step signal in the demodulated signal are determined by maximum value/minimum value detection means 4.
and is converted into the sum or difference of the maximum value and minimum value by the linear combination means 5. If the maximum or minimum value is used directly, the linear combination means 5
is omitted. Reference numeral 6 denotes a control means that uses the output of 5 to change the frequency characteristics of the correction means 2a. Next, the specific configuration of the correction means 2a shown in FIG. 5 will be explained. A distorted signal is applied to the input terminal 1. 19 to 22 are correction elements having various correction amounts; for example, 19 corresponds to 1 link, and 20 corresponds to 2 links.
21 corresponds to a link, 21 corresponds to a 3 link, etc., and has a frequency characteristic that is the opposite of the distortion characteristic. 19 to 22 can be realized using a normal active filter, transversal filter, etc. 23 is a switch which is controlled by the control means 6, and outputs the optimum correction element to the output terminal 24. A specific example of the maximum value/minimum value detection means 4 is as shown in the figure.
Lead to 12. Capacitors 11 and 12 are brought to the same potential as reference potential 15 by shorting switches 13 and 14 immediately before the step signal is applied. The value of reference potential 15 is the intermediate level of the step signal, for example the value of 0.5 in FIG. In this way, after receiving the step signal, the maximum value can be obtained at terminal 16 and the minimum value can be obtained at terminal 17. For example, when using the sum of the maximum value and the minimum value, the linear combination means 5 is constituted by an addition circuit 25 and a level comparison/judgment circuit 26, as shown in the figure.
The level comparison/judgment circuit 26 compares the reference level signal with a value of 1.0 with the output signal of the adder circuit 25. If this output signal is larger than 1.0, as is clear from FIG. 4, the correction is insufficient. Therefore, a signal is generated from the terminal 27 to increase the correction amount of the correction means 2a. On the other hand, if this output signal is smaller than 1.0, the correction is excessive, and therefore a signal is generated from the terminal 27 to reduce the amount of correction by the correction means 2a. Then, according to this signal, the control means 6 performs control to change the correction amount (that is, the frequency characteristic) of the correction means 2a so that this output signal approaches 1.0, and finally outputs the corrected signal to the output terminal 7. obtain. Furthermore, even when the maximum value or the minimum value is used alone, the excess or deficiency of correction can be determined by determining the magnitude with respect to a predetermined value as described above. In addition, when using the difference between the maximum value and the minimum value, as is clear from Figure 3, if the above difference becomes smaller by increasing the correction amount, the correction amount is insufficient, and if the above difference becomes large, the correction amount is excessive. I understand that there is something. The control means 6 consists of a switch selection determination circuit 28, and for example, as an initial setting, a control signal such that the switch 23 is connected to the correction element 19 is sent to the terminal 2.
Occurs on 9th. When a signal for increasing the amount of correction is input from the linear combination means 5 to the terminal 27, a control signal is generated to the terminal 29 to connect a switch to the correction element 20. Thereafter, when a signal that increases the correction amount is similarly input, the terminal 2
9 to generate a control signal for the switch to realize the desired operation. FIG. 6 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. The correction means 2b has the same structure as the correction means 2a in FIG.
One of a and 2b corrects the carrier signal, and the other corrects the baseband signal, and although the specific characteristics for correction are different, both of them must realize frequency characteristics that are opposite to the distortion generated in the transmission path. Bye.

【Effect of the invention】

As explained above, in the present invention, the maximum value or minimum value, or the sum or difference thereof, of the received step signal is detected, and the frequency characteristics of the correction means are changed so that the detected value approaches a predetermined value. Therefore, unlike the prior art, there is no need to detect and store the value of the received waveform at a specific time, and the operation is stable. In addition, there are only one or two types of values to be detected, and the device can be easily realized without the need for complex arithmetic processing using many detected values as in the conventional technology.
It has the following effects.

[Brief explanation of drawings]

Figure 1 is a received waveform diagram of the step signal, Figure 2 is
FIGS. 3 and 4 are diagrams showing changes in the maximum value, minimum value, and linear combination value of the received step signal, respectively, with respect to transmission line distortion, and FIGS. 5 and 6 are diagrams each showing an embodiment of the present invention. It is.

Claims (1)

[Claims] 1. In a transmission line distortion correction device for correcting group delay distortion of a transmission line having a carrier line, a plurality of correction elements for correcting group delay distortion corresponding to the number of links of the carrier line, and one of each of the correction elements. a correction means having a switch for selecting the output signal; a detection means for detecting at least one of the maximum value and the minimum value of the output signal of the correction means; the maximum value, the minimum value, the sum of the maximum value and the minimum value, and the linear combination means for comparing one of the differences between the maximum value and the minimum value with a reference level signal; and correction means for adjusting the output of the linear combination means to approach a value obtained when the number of links is zero. A transmission line distortion correction device comprising a control means for outputting a signal for switching a switch.