JPS6337738A - Digital transmission system for pair cable - Google Patents

Abstract

PURPOSE:To perform correct decoding regardless of whether or not pulse polarity inversion is caused on a transmission medium by generating a control signal indicating whether or not the polarity inversion is caused on a transmission line according to which of a 1st and a 2nd frame synchronizing circuit performs frame. CONSTITUTION:A switching controller 9 detects whether or not the pulse polarity is inverted on the transmission line including a cable 10 after the convergence of an equalizer 2 according to which of the frame synchronizing circuits 7 and 8 a pulse indicating synchronization attainment arrives from. The connection state of a polarity switch is so set that when the inversion is not cause (or caused), the sent pulse train of the discriminator 3 (or 4) is led to the positive polarity pulse input terminal of a decoder 6 and the sent pulse train of the discriminator 4 (or 3) is led to the negative pulse input terminal of the decoder 6. Then, the training and frame synchronization of the equalizer 2 are performed in a training period and the pulse polarity inversion on the transmission line is detected; when there is the inversion, the polarity is inverted again by the polarity switch 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital transmission system for pair cables, and particularly to a digital transmission system for pair cables for transmitting digital signals in a ternary code format using pair cables.

[Conventional technology]

BACKGROUND OF THE INVENTION With the progress of digitization of transmission systems in public communication networks and the like, digital transmission systems for pair cables, in which digital signals are transmitted using pair cables, are being put into practical use. The conventional bare cable digital transmission system mainly consists of forming a pulse code change (PCM) signal into a frame structure having a predetermined format, and transmitting positive and negative polarity pulses. During communication, first, a frame containing a training signal for training the equalizer for waveform distortion equalization provided in the receiving section of the termination device of the pair cable is transferred, and the equalizer training and frame synchronization are performed. After the establishment is completed, communication between the end devices begins.

[Problem that the invention seeks to solve]

On the other hand, in a pair of cables constituting a communication line, the so-called tip-side and ring-side wire pairs are not necessarily connected tightly between both ends without reversal. Therefore, the pulse polarity of the digital signal transmitted from one of the two terminal devices connected via the pair cable during communication may be reversed when the other terminal receives it. The conventional transmission method described above uses the AMI code format, and the pulse polarity itself can be completely ignored during decoding, and communication is possible regardless of whether or not the pulse polarity is inverted as described above.

However, in order to improve transmission efficiency, 3B2T and 483
When using a ternary code format such as T, if the pulse polarity of a digital signal obtained by ternary encoding of a binary word is reversed, it becomes impossible to decode the original binary word. Therefore, in this case, decoding that ignores the pulse polarity is impossible, and it is difficult to decode a communication line that has a pair of cables in which the chip side and the ring side are connected without being reversed at both ends.
However, there is a problem in that it is impossible to apply conventional transmission methods as they are.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a digital transmission system for pair cables that allows correct decoding regardless of the presence or absence of pulse polarity reversal in the transmission medium.

[Means for solving problems]

The transmission method of the present invention receives a ternary digital signal, which has a frame configuration in which a predetermined frame pattern is inserted and includes positive and negative pulses, arriving via a transmitter with a pair of cables. first and second discriminators that respectively identify the presence or absence of the positive polarity pulse and the negative polarity pulse; The first and second frame synchronization circuits establish frame synchronization by detecting the timing at which a pattern with inverted pulse polarity appears, and which of the first and second frame synchronization circuits established synchronization for the previous two frames. a switching controller that generates a control signal indicating the presence or absence of polarity reversal in the transmission line in response to the polarity reversal; When the control signal indicates the polarity inversion, the first
and a polarity switcher that switches the connection state so that the signals transmitted from the second discriminator are exchanged with each other and then guided to the decoder.

〔Example〕

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

FIG. 1 is a block diagram showing one embodiment of the present invention. This embodiment includes a polarity switching device 5 for switching one pulse polarity in a receiving section of a terminal device that transmits and receives a digital signal in the form of a three-value signal, and a switching controller 9 for making this switching ΔU. It has a new configuration. cable 1
oii: Hefgarn Luteashi, the end of the device &! Road interface 1! /c is connected. , the line interface 1 is a circuit for preventing the digital signal transmitted from the transmission section to the cable] 0 from being routed to the reception section, for example, a time division switch or a high 2 line with an echo canceller.
The lid circuit is A^. A receiving signal arriving from the other party's terminal device via the cable 10 passes through the line interface l and is then sent to the receiving section Vc4. The equalizer 2 in the receiving section is provided to equalize waveform distortion occurring in the transmission path, and operates adaptively in response to a training signal in a training frame sent from the other party at the start of communication. When the training operation converges, a convergence display signal 1g is generated and sent to the switching 'i&iJ controller 9, and a waveform-equalized signal is sent to the discriminators 3 and 4. The discriminators 3 and 4 respectively discriminate the positive polarity pulse and the negative polarity pulse in the received signal given from the equalizer 2, generate pulses having a predetermined pulse width at the time of discrimination, and switch the polarity switch 5,
It is sent to frame synchronization circuits 7 and 8.

Frame synchronization circuits 7 and 8 are ternary frame synchronization circuits. The frame pattern transmitted from the other party has a predetermined ternary pulse pattern, and the frame synchronization circuit 7 includes the above-mentioned frame in the positive pulse train and negative pulse train sent from the discriminators 3 and 4, respectively. Frame synchronization is established by detecting the timing at which the pattern appears. The other frame synchronization circuit 8 establishes frame synchronization by detecting the timing at which a pattern in which the pulse polarity of the above frame pattern is reversed appears in the pulse train sent from the discriminators 3 and 4. That is, if there is no pulse polarity reversal in the transmitter including the cable 10, frame synchronization is established in the frame synchronization circuit 7, and if there is pulse polarity reversal in the transmission path, the frame synchronization circuit 8 establishes frame synchronization.
Frame synchronization is established at Frame synchronization circuit 7
and 8 for which frame synchronization has been established generates a pulse to indicate the establishment of synchronization and sends it to the switching controller 9. After the equalizer 2 converges, the switching controller 9 inverts the pulse polarity in the transmission line including the cable 10 depending on which of the frame synchronization circuits 7 and 8 the pulse indicating the establishment of synchronization comes from. If there is no reversal (or if there is), K is the discriminator 3 (or 4).
The connection state of the polarity switch 5 is adjusted so that the output pulse train of the discriminator 4 (or 3) is guided to the positive polarity pulse input terminal of the decoder 6, and the output pulse train of the discriminator 4 (or 3) is guided to the negative polarity pulse input terminal of the decoder 6. Let it be set.

In this way, during the training period, training of the equalizer 2 and establishment of frame synchronization are executed, and pulse polarity reversal on the transmission path is detected, and if there is reversal, the polarity switch 5 re-inverts the pulse polarity. . Therefore, when transitioning to subsequent communication, the decoder 6 performs normal decoding and outputs received data regardless of whether or not the pulse polarity of the transmission path is reversed.

FIGS. 2(a) and 2(bl) are a block diagram showing an example of the configuration of the polarity switch 5 and the switching controller 9 in this embodiment, and a timing diagram for explaining the operation thereof. In b), the frame pattern of the transmission signal from the other party has a three-value symbol format expressed as (+1.0.0.-1.0.0), and the pulse polarity is reversed via the transmission path. An example of the case where the frame is received is shown below.Frame synchronization circuit 7
By detecting the appearance timing of the frame pattern, the frame synchronization circuit 8 inverts the pulse polarity of the frame pattern (-1, 0, O, +1).
．． By detecting the appearance timing of a pattern of 0.0 ), synchronization is established for each, and the one that is able to establish synchronization sends out a pulse. The pulse indicating synchronization establishment is
The convergence display signal K of the equalizer 2 is also guided to the data selector 90 of the switching controller 9. In addition to this, the data selector 90 is given a high level ( ) ( ) voltage and a low level peak voltage as input data. Data selector 9
0 is H when a pulse is received from the frame synchronization circuit 7 during the pulse rising period of the convergence display signal of the equalizer 2.
When receiving a pulse from the frame synchronization circuit 8, the LTj voltage is selectively transmitted. The same figure (b
) Show K? In iJ, since the received signal undergoes pulse polarity inversion on the transmission path, synchronization is established in the frame synchronization circuit 8 and pulses are sent out. In response to this,
Data selector 90 sends out Lll pressure.

If there is no pulse polarity reversal on the transmission path, the frame synchronization circuit 7 establishes synchronization and sends out a pulse, and in response, the data selector 90 sends out an H voltage.

The output signal from the data selector 90 is applied to the switch SW of the polarity switch 5, further passes through the inverter 50, and is applied to the switch SW2 after its level is inverted. The switches SW and SW2 are both turned on when an H voltage is applied, and turned off when an L voltage is applied. Therefore, when there is no pulse polarity reversal in the transmission path, switches S are turned on, switches S to ■2 are turned off, and the output signals of discriminators 3 and 4 are not switched, but each of K , are connected to the positive pulse input terminal and the negative pulse input terminal of the decoder 6.

Further, when there is a pulse polarity reversal in the transmission path, the switch SW is turned off, the switch SW2 is turned on, and the output signals of the discriminators 3 and 4 are exchanged with each other, and the decoder 6 connected to. As a result, the decoder 6
The connection state of the 1-polarity switch 5 is set so that a positive pulse train and a negative pulse train having the same pattern as the transmission signal are input to the positive pulse input terminal and the negative pulse input terminal of the transmitter, respectively, and the transition to communication begins. Sometimes the decoder 6 can perform normal decoding.

〔Effect of the invention〕

As described above, the present invention has the effect of realizing a digital transmission system for pair cables that is capable of correctly decoding ternary codes regardless of the presence or absence of pulse polarity inversion in the transmission path.

[Brief explanation of the drawing]

1 and 2 (al is a block diagram showing an embodiment of the present invention, and FIG. 2(b) is a timing diagram for explaining the operation of the embodiment of the present invention. l...・Line interface, 2...Equalizer, 3゜4...Discriminator, 5...Polarity switch, 6...Decoder, 7. 8... Frame synchronization circuit, 9... Switching controller, 10...
...Cable, swl, sw, ...Switch, 50...Inverter, 90...
data selector. -4~ No. 1 Closed

Claims (1)

[Claims] A ternary digital signal having a frame configuration in which a predetermined frame pattern is inserted and containing pulses of positive polarity and negative polarity is received via a transmission line with a pair of cables, and the pulses of the positive polarity and the pulse of the negative polarity, respectively, are received. first and second discriminators that identify the presence or absence of a pulse of negative polarity, and the frame pattern and a pattern in which the pulse polarity of the frame pattern is inverted appear in the transmission signals of the first and second discriminators, respectively. first and second frame synchronization circuits that detect timing and establish frame synchronization; and polarity reversal on the transmission path depending on which of the first and second frame synchronization circuits establishes the frame synchronization. a switching controller that generates a control signal indicating the presence or absence of a signal; The receiving section includes a polarity switcher that switches the connection state so that when the control signal indicates that the polarity is inverted, the signals output from the first and second discriminators are exchanged and then guided to the decoder. A digital transmission method for pair cables characterized by: