JPH02146846A - Data transmission system - Google Patents

Abstract

PURPOSE:To improve the efficiency of data transmission by using a control signal from a terminal equipment and varying data transmission speed depending on the length of the transmission data. CONSTITUTION:A transmission data A is inputted to a modulation section 14 via a multi-value coding section 11 and a switching device 13 to obtain a transmission output. On the other hand, a training signal to apply the synchronization establishment of a control system built in a demodulation section 21 at the receiver side is outputted from a generating section 12 via the switching device 13 and the modulation section 14. Most of the training signal is used for establishing the synchronization of the control system of the demodulation section 21, and the data of modulation frequency is switched by using a control signal B to send the data transmission speed to the receiver side. In this case, the control signal B is inputted from the terminal equipment and is turned ON/OFF depending on the length of the transmission message.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data transmission method for a modem and, more particularly, to a data transmission method for a modulator and demodulator that performs carrier control in a multipoint line.

[Conventional technology]

A conventional data transmission method will be explained with reference to the drawings.

FIG. 4 is a block diagram showing an example of a multipoint line.

In FIG. 4, by using a polling method or a selecting method communication method on a multipoint line, each slave station's modem device (hereinafter referred to as a modem) 101 to
Control is performed from the master station modem 100 so that transmission carriers from the ION do not collide. FIG. 5 is a sequence diagram showing an example of communication when using the polling method in FIG. 4.

Next, Figure 4 shows the data transmission method of conventional modems.
This will be explained with reference to FIG.

From the master station modem 100 to each slave station modem 101 to 1ON,
Access is made sequentially according to the addresses M and -Mn. Slave station modem 1 accessed from master station modem 100
01 sends only the message "@EOT" to the master station modem 100 when there is no message to be sent back to the master station modem 100. Upon receiving the "EOT" message, the master station modem 100 accesses the next slave station modem 102. Access each slave station modem in sequence and turn on the slave station modem ION.
Upon receiving a response from the slave station modem 101, the slave station modem 101 is accessed again. When the accessed slave station modem has a message to be sent to the master station modem 100, it transmits the message to the master station modem lOO when accessed.

As explained above, in the case of data transmission from the slave station modems 101 to ION of a multipoint line to the master station modem 100, a transmission request signal is sent from a terminal (not shown) connected to each slave station modem 101 to 1ON. It is necessary to control the transmission carrier by turning on/off the (S).

On the other hand, in a modem with a data transmission rate of 4800 bps or higher, for example, when carrier control is performed using the R8 signal, the synchronization of the control system of the reception section of the modem of the other station is performed when the R8 signal is turned on from off. In order to establish synchronization, a training signal is sent out, and data transmission is executed after synchronization is established.

-For example, in a 9600 bps modem, CCIT
T Recommendation ■, 29, training time is 2
53m5ec is compulsory.

[Problem to be solved by the invention]

In the conventional data transmission system described above, the length of the message to be transmitted is unrelated to the data transmission rate, so that both short messages and long messages are transmitted at the same transmission rate.

Generally, when the data transmission rate is low, it is possible to reduce the training time compared to when the data transmission rate is high. Additionally, when the data transmission speed is high, error correction coding (trellis coding) is sometimes used to reduce the ratio of bit errors to line noise, and in this case soft decisions are made on the demodulation side. execution and traceback, the receive take will be delayed by the time it traces back. Therefore, for short messages, it is possible to increase the data transmission efficiency by lowering the data transmission speed.

That is, in the conventional data transmission system described above, since the data transmission rate is fixed, there is a drawback that the transmission efficiency is low when the message is short.

[Means to solve the problem]

The data transmission system of the present invention is a data transmission system using a modem, in which the modulator receives a control signal containing information on the bit length of transmission data to be transmitted from a terminal connected to the modulator, and synchronizes the modulation and demodulation. a transmission means for transmitting the transmission data by changing the data transmission rate or modulation method according to the control signal after a training signal for establishing the transmission data; and a second buffer memory for storing data received from the line, and the data rate between the modem and the terminal is kept almost constant regardless of the data transmission rate between the modem and the modem. do.

〔Example〕

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

FIG. 1 is a block diagram of a modulation/demodulation device showing one embodiment of the present invention, FIG. 2 is a diagram showing a signal point arrangement of the modulation/demodulation device of this embodiment, and FIGS. It is a figure which shows an example of the format of the transmission signal in an example.

In FIG. 1, the modulation/demodulation device of this embodiment generates a training signal using a buffer memory IJIO for temporarily storing transmission data and a control signal B from a terminal (not shown) connected to the modulation/demodulation device of this embodiment. A training signal generation unit 12 that generates a training signal, a multi-level encoding unit 11 that multi-level encodes the transmission take A from the buffer memory 10 using a control signal B, and a multi-level encoded transmission from the multi-level encoder 11. A switch 13 that switches and outputs data and a training signal from the training signal generator 12, and a switch l.
a modulation unit 14 that modulates the signal from 3 and sends it to the line;
A demodulation section 21 that receives and demodulates a signal from a line, a training signal detection section 23 that detects a training signal from the output signal of the demodulation section 21, and a training signal detection section 2
The data determining section 22 determines the received data C from the output signal of the demodulating section 21 by detecting the synchronization signal of No. 3, and a buffer memory 24 temporarily accumulates the received data C.

Next, the operation of this embodiment will be explained using FIGS. 1, 2, and 3.

This implementation is performed by inputting the transmission data 8 to the buffer memory IJ 10, inputting the output of the buffer memory 10 to the multilevel encoding unit 11, and inputting the output to the modulation unit 14 via the switch 13. Produce an example transmit output.

Taking the case of CCITT recommendation V, 29 (9600 bps) (7) as an example, the output of the buffer memory 10 is divided into 4-bit units by the multi-level encoder 11, and the 4 bits are divided into 4 bits.

The data of
The modulator 14 performs orthogonal amplitude modulation and sends it out to the line.

On the other hand, a training signal is sent from the training signal generator 12 to the switch 13 to establish synchronization of the control system (automatic equalizer, carrier phase controller, etc.) built in the post-adjuster 21 on the receiving side. The signal is output via the modulator 14.

Most of the training signal is used to establish synchronization of the control system of the demodulator 21 on the receiving side, and by switching the data of the last number T (T: modulation period) using the control signal B,
Communicate the data transmission speed to the receiving side.

This control signal B is a signal input from a terminal (not shown) and is turned on/off depending on the length of the transmitted message. - As an example, in the polling method, if control signal B is turned on when there is a message to be transmitted when there is no transmitted message (EOT), and control signal B is turned off when there is a transmitted message, then control signal B The operation of the encoding unit 11 is switched as follows.

That is, when control signal B is off, 16 as shown in FIG.
When the signal point is on, the eight signal points shown in double circles in FIG. 2 are used, and the input is also divided into three bits and encoded. That is, the data transmission rate is 9600 bps when control signal B is off, and 7200 bps when control signal B is off.
Let it be ps.

Further, the control signal B is input to the training signal generating section 12, and when it is on, the training signal is set to be short, and when it is off, it is set to be long.

FIGS. 3(a) and 3(b) show the format of the output signal of the modulator 14.

In FIGS. 3(a) and 3(b), the shaded portions are signals for transmitting transmission rate information of transmitted data to the receiving side.

Data transmission efficiency can be increased by changing the data transmission speed until the message length is the same as the time difference between the training signals due to on/off of the control signal B and the time when the transmission message is transmitted at 7200 bps.

In addition, as another embodiment, for a modem with an error correction function such as trellis coding, the multilevel encoding unit 11 executes trellis coding according to the control signal B and performs binary encoding, or there is no coding. to switch whether to perform binary encoding. In this case, the training time is set to be the same for both. When the length of the transmitted data is short, binary encoding is performed without coding.

On the receiving side, maximum likelihood decoding is performed when error correction is present, and hard decision is performed when error correction is not present, so that the delay of received data becomes thicker when error correction is present than when there is no delay. Therefore, when the delay time of the received data and the time of the transmitted message are approximately the same, the method of this embodiment can improve the data transmission efficiency.

Further, by providing the buffer memory 10.24 for transmission data A and reception data C, it is possible to keep the data transmission speed with the terminal constant.

〔Effect of the invention〕

As explained above, the present invention has the effect of improving the efficiency of data transmission by having a transmission means that changes the data transmission speed depending on the length of the transmitted data using a control signal from a terminal connected to a modulation/demodulation device. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a modulation/demodulation device showing one embodiment of the present invention, FIG. 2 is a diagram showing a signal point arrangement of the modulation/demodulation device of this embodiment, and FIGS. FIG. 4 is a diagram showing an example of the format of a transmission signal in the example, FIG. 4 is a diagram showing an example of a multipoint line, and FIG. 5 is a sequence diagram showing an example of communication when using the polling method in FIG. 4. . 10.24・°°・・・Buffer memo 'J, 11...
...Multi-level encoding unit, 12...Training signal generation unit, 13...Switcher, 14...
Modulation unit, 21...Demodulation unit, 22...Data determination unit, 23...Training signal detection unit. Figure 2 XJ3rd 1st 354th Figure 5

Claims (2)

[Claims] (1) In a data transmission system using a modem, the modem receives a control signal containing information on the bit length of transmission data to be transmitted from a terminal connected to the modem, and a training signal for establishing modulation and demodulation synchronization. 1. A data transmission method, comprising: a transmission means for changing a data transmission rate or a modulation method according to the control signal and transmitting the transmission data. (2) The modem according to claim (1) has a first buffer memory for storing data to be transmitted from a terminal and a second buffer memory for storing data received from a line, 2. The data transmission system according to claim 1, wherein the data rate between the modem and the terminal is kept substantially constant regardless of the data transmission rate between them.