JPH03278742A - Digital transmission system - Google Patents

Abstract

PURPOSE:To integrate a same function as a dummy line as a large scale and to avoid disturbance due to a far-end crosstalk (FFXT) by generating digitally a deformed pulse waveform due to waveform distortion caused by the frequency dependency of a transmission loss of a dummy line when the dummy line is inserted to the system. CONSTITUTION:Line control sections 1, 2 each consists of a connection terminal T10 to a transmission line, a digital memory DM 11, a D/A converter DA 12, a drive circuit DR 13, a switch SW 14, an equalizer EQ 15 and a discrimination section DS 16. Digital waveform information is predetermined and stored in the DM 11 for each distance step of the transmission line and the DS 16 selects digital waveform information corresponding to a fundamental waveform in the DM 11 depending on the level of level detection information 18 of a reception signal detected by the EQ 10. Thus, the output level of a line termination section 2 is decreased, the disturbance due to FEXT1 is reduced, the line termination section 6 receives a signal with better quality, the level adjustment is automated and the system is suitable for large scale circuit integration.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a digital transmission system, and in particular to a digital transmission system that avoids far-end crosstalk in a digital transmission system using a transmission medium in which transmission loss depends on frequency. Regarding the method.

[Conventional technology]

In order to transmit digital information to a long distance via a transmission medium, the digital information is converted into a code suitable for the transmission medium and transmission means, and then sent out as a pulse waveform to the transmission medium and transmitted to the destination point by far. It is customary to use a method. In addition, the transmission loss characteristics of transmission media generally depend on the frequency, and the receiving side that receives the pulse waveform transmitted via the transmission medium corrects the pulse waveform distortion to create a waveform that is convenient for the receiving side. Equalizers and amplifiers are often required to equalize the Furthermore, when transmitting digital information to multiple destination points with different transmission distances using a transmission medium that is prone to far-end crosstalk (hereinafter referred to as FEXT), it is necessary to Since it is desirable to have the same reception level, level adjustment means is often used to adjust the transmission level to the other party depending on the length of the transmission distance.

The transmission loss characteristics of the transmission medium are frequency dependent and the FE
An example of a transmission medium susceptible to XT is stranded copper cable, which is commonly used for digital transmission.

In this digital transmission method using stranded copper cables, in order to avoid deterioration in communication quality caused by FEXT,
It is necessary to pay close attention to the design of the level diagram on the cable so that there are no extreme differences in the received level.

In particular, since multiple copper cables installed for general telephone lines are bundled together, crosstalk between lines is likely to occur.

In recent years, as the amount of information has increased, digital transmission systems using copper cables for general telephone lines have become popular. When digital transmission systems are applied to copper cables for general telephone lines, cables with uneven line lengths are often bundled together, and reception level differences with adjacent lines are likely to occur, so avoid mutual interference due to FEXT. It is necessary to take measures to Conventionally, in order to avoid such reception level differences, a pseudo line is often inserted on the transmitting side for level difference correction so that the reception level from any point on the cable is the same level diagram. This pseudo-line is constructed with passive elements such as LCR so that its transmission loss characteristics approximate those of the transmission medium, and from the receiving side, the length of the transmission medium is equivalent to the pseudo-line loss. Since it only appears to be extended by , it does not have any effect on the equalizer on the receiving side.

[Problem to be solved by the invention]

In the conventional digital transmission system that performs level adjustment using the pseudo-line described above, LCR
Pseudo-lines made up of passive elements such as the above are difficult to integrate into LSIs, and therefore have the drawback of being a factor that discourages designs aimed at miniaturization and economicalization. Additionally, it is desirable to automate the selection of pseudolines in order to save costs when installing communication lines, but it is necessary to prepare many types of pseudolines in order to select the most appropriate pseudoline. There are drawbacks.

An object of the present invention is to automate level adjustment and avoid FEXT interference when applying a time-division two-way multiplex transmission system (ping-pong transmission system) to copper cables installed for general telephone lines. Another object of the present invention is to provide a digital transmission system suitable for LSI implementation.

[Means to solve the problem]

The digital transmission system of the present invention is a digital transmission system in which digital information is transmitted by transmitting transmission pulses through a transmission medium whose transmission loss characteristics depend on frequency, in which a line termination section provided at one end of the transmission medium is connected to a predetermined line terminal. storage means for predetermining and storing digital waveform information corresponding to a pulse waveform including waveform distortion that occurs when a transmission pulse of a fundamental waveform is transmitted through the transmission medium of a length, for each distance interval of the transmission medium; digital-to-analog converting means for reading out the digital waveform information from the storage means and converting it into a corresponding pulse waveform based on the logic level of the digital information to be transmitted, and converting the pulse waveform output from the digital-to-analog converting means A sending means sets a level and sends it out as a transmission pulse, a switching means switches the received signal to the equalizing means based on switching control information that separates the transmission period and the reception period, and the signal inputted through the switching means is equalized. the equalizing means for reproducing the received signal, detecting the level of the reproduced received signal, and outputting level detection information for each predetermined level; The apparatus is characterized by comprising a determining means for selecting digital waveform information corresponding to a pulse waveform of a medium having a long passage distance from the storage means.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the digital transmission system of the present invention, FIG. 2 is a circuit block diagram showing an example of the line termination section in FIG. 1, and FIG. 3 is a block diagram of the output pulse waveform in FIG. FIG. 3 is a waveform diagram showing an example.

In FIG. 1, in this embodiment, the line termination units 1 and 2 are connected to the line termination units 6 and 7 of the line termination device 5 of the communication partner via a cable bundle 3 with two cables, respectively, and are connected to each other independently in a time-sharing manner. Communication is performed using a two-way multiplex transmission method (bin-bong transmission method). Note that the line termination section 1 is installed further away from the cable bundle 3 via an extension cable 4.

Since the cable bundle 3 includes two cables, communications from the line terminals 1 and 2 interfere with each other. For example, a signal sent from the line termination section 2 is superimposed on a signal from the line termination section l as far-end crosstalk (hereinafter referred to as FEXT1) and reaches the line termination section 6. If the extension cable 4 is long, the ratio (S
/N ratio) deteriorates, and the quality of the signal received at the line termination section 6 deteriorates.

In this embodiment, in order to suppress this quality deterioration, the FEX
Lowering the level of T□.

The above-mentioned time-division bidirectional multiplex transmission method (ping-pong transmission method)
Now, if the configuration is such that the transmission bursts are sent out all at once from the line termination parts 6 and 7 of the line termination device 5, the line termination parts 1 and 2 will be in the reception state at the same time, and far-end crosstalk ( Hereinafter, the line terminal section l is subjected to interference due to F E XT2 ).

However, if the transmission levels of line termination section 6 and line termination section 7 are the same, the interference caused by FEXT2 will be reduced.

On the other hand, the line termination units 1 and 2 send out signals, and the line termination unit 6.
In the mode in which 7 receives, the interference due to FEXT is reduced by the amount of the signal level arriving from the line terminal 1 corresponding to the transmission loss of the extension cable 4, so the influence of the interference increases and the S/N ratio deteriorates. .

As shown in FIG.
) 11 and digital-to-analog converter (hereinafter referred to as DA) 1
2, a drive circuit (hereinafter referred to as DR) 1B, a switch (hereinafter referred to as 5W) 14, an equal flower vase (hereinafter referred to as EQ) 15, and a determination unit (hereinafter referred to as EQ) 15.
Hereinafter, the operation of the line termination section in this embodiment will be explained.

First, digital waveform information corresponding to a mountain waveform 21 including waveform distortion caused by the transmission path as shown in FIG. I'll keep it. As this digital waveform information, a plurality of types of waveforms 21 are prepared by predicting the waveform distortion when the cable passes through a transmission line of a predetermined length at each distance step.

Here, when the 5W14 inputs the signal input from the transmission path via T10 to the EQ15 using the switching control information 17 that separates the transmission section and the reception section, the EQ15 adjusts the signal in advance according to the reception level of this input signal. Level detection information 18 is created for each determined step. The DS16 selects the digital waveform information stored in the DMll based on this level detection information 18, reproduces the waveform in the DA12, and outputs the DR.
13, the signal is sent from the TIO to the transmission line as a pulse waveform. DA12 outputs DMl for each logic “l” of transmission information 19.
It has a function of reproducing pulses whose waveforms have been converted based on the digital waveform information of l.

When the level detection information 18 of the received signal detected by EQIO is a small level, the DS 16 determines that the transmission path length is long and selects digital waveform information corresponding to the basic waveform 20 in DMII, and also detects a large level. When detecting,
It is determined that the transmission path length is short, and digital waveform information corresponding to the mountain waveform 21 including distortion in DMII is selected.

Since the line termination unit 1 configured as shown in FIG. 2 is connected to a cable with a long transmission path, the reception level is also reduced and the fundamental waveform 20 is output. - On the other hand, since the line terminal section 2 is connected to a cable with a short transmission path length, the reception level becomes high, and a waveform 21 with a peak including distortion is output.

When the output level of the line termination section 2 becomes smaller, FEXT,
Since the interference caused by the line termination section 1 is also reduced, it becomes possible for the line termination section 6 to receive the signal from the line termination section 1 with good quality.

On the other hand, the mountain waveform 21 from the line termination section 2 is equivalent to the output when a pseudo line is inserted, and can be substituted for the function of the pseudo line. Therefore, there is no influence on the reception at the line termination section 7.

〔Effect of the invention〕

As explained above, the present invention achieves the same function as a pseudo-line by digitally generating a deformed pulse waveform caused by waveform distortion caused by the frequency dependence of the transmission loss of the pseudo-line when the pseudo-line is inserted. can be realized by a line termination section with a circuit configuration suitable for LSI implementation, and the characteristics of the pseudo line can be automatically selected depending on the length of the transmission path to be applied, which has the effect of avoiding interference due to FEXT.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the digital transmission system of the present invention, FIG. 2 is a circuit block diagram showing an example of the line termination section in FIG. 1, and FIG. 3 is a block diagram of the output pulse waveform in FIG. FIG. 3 is a waveform diagram showing an example. 1.2, 6.7... Line termination section, 3... Cable bundle, 4... Extension cable, 5... Line termination device, 10
...Connection terminal (T), 11...Digital memory (
DM), 12... Digital-to-analog converter (DA
), 13...Drive circuit (DR)-14...Switch (SW), 15...Vase (EQ), 16...
Determination unit (DS), 17... switching control information, 18...
Level detection information, 19... Transmission information, 20... Basic waveform, 21... Mountain waveform.

Claims (1)

[Claims] In a digital transmission method that transmits digital information by transmitting transmission pulses through a transmission medium whose transmission loss characteristics depend on frequency, a line termination section provided at one end of the transmission medium is used to transmit basic information through a predetermined length of the transmission medium. a storage means for predetermining and storing digital waveform information corresponding to a pulse waveform including waveform distortion that occurs when a waveform transmission pulse is transmitted for each distance interval of the transmission medium; and a logical level of the digital information to be transmitted. digital-to-analog converting means for reading out the digital waveform information from the storage means and converting it into a corresponding pulse waveform based on the digital-to-analog converting means; and setting the level of the pulse waveform output from the digital-to-analog converting means and sending it out as a transmission pulse. a switching means for switching the received signal to the equalizing means based on switching control information for dividing the transmission period and the reception period; and a switching means for equalizing the signal inputted through the switching means and regenerating the received signal. The equalizing means detects the level of the reproduced received signal and outputs level detection information for each predetermined level; 1. A digital transmission system comprising: determination means for selecting digital waveform information corresponding to a waveform from the storage means.