JPH02177642A - Data transmission system - Google Patents

Abstract

PURPOSE:To change a communication speed and to execute data transmission by changing the gain of a signal, to which phase modulation is executed, and transmitting data by plural modulation cycles. CONSTITUTION:A gain switcher 14 outputs the gain signal of two values to a multiplier 5 based on a synchronizing signal. When the signal point of the data of three bits to be transmitted by one modulation cycle is inputted, the multiplier 15 multiplies the signal point and the gain signal of one value. When the signal point of the data two bits to be transmitted by the other modulation cycle is inputted, the multiplier 15 multiplies the signal point and the gain signal of the other value. As the result of the multiplication, the gain of the signal point in the data of the three bits to be transmitted by one modulation cycle is made higher than the gain of the signal point in the data of the two bits to be transmitted by the other modulation cycle. Thus, the communication speed can be changed without changing the band of a roll-off filter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data transmission method for transmitting data using a phase modulation method using a telephone line.

[Conventional technology]

Some data transmission systems of this type transmit data using a modulation/demodulation device that performs phase modulation and demodulation. The communication speed of such a modem depends on the modulation rate and the bits sent within one modulation period. For example, CCI
The modem of TT Recommendation v.29 has a modulation rate of 2400 baud, and when transmitting 4 bits in one modulation period, the communication speed is 9600 bps, when transmitting 3 bits it is 7200 bps, and when transmitting 2 bits it is 4800 bps. becomes. Also, CCITT Recommendation v, 27
Communication speeds of 4800 bps and 2400 bps are recommended for modem equipment. In the case of 4800 bps, it is 3-bit transmission with a modulation rate of 1600 baud, and in the case of 2400 bps, it is 2-bit transmission with a modulation rate of 1200 baud. Here, consider a case where the modulation frequency is 2400)1z and the communication speed is 7200 bps. In this case, three bits are transmitted every modulation period. The signal point arrangement at this time is as shown in Figure 3 (al), and eight-phase phase modulation as shown in ~D6.When changing the communication speed, it is done by changing the number of bits transmitted per modulation cycle. For example, 4800
In the case of 2 bits of bps, signal point E as shown in Figure 3(b)
In the case of 1 bit of 2400 bps, it is a two-phase phase modulation of signal points F, , F, as shown in FIG. 3 (C1).

However, the change is due to the modulation frequency (here 240011
z) can only be done.

[Problem to be solved by the invention]

In the conventional data transmission system described above, when changing the communication speed, it is done by changing the modulation speed, so it becomes necessary to change the band of the roll-off filter as well.

Therefore, when transmitting at a slow communication speed, the band of the roll-off filter becomes narrow, and there is a drawback that the band cannot be fully utilized.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks and provide a data transmission system that allows changing the communication speed without changing the band of the roll-off filter.

[Means to solve the problem]

The present invention provides a transmission side that includes a roll-off filter that limits a phase-modulated signal to a band suitable for the line, and a modulation unit that modulates the signal from the roll-off filter and outputs it to the line. When a signal is received, the receiving side includes a demodulator that demodulates the signal, and in the data transmission system that transmits the signal, the transmitting side phase-modulates the input binary data at a plurality of modulation cycles. , a first conversion section that changes the gain of the signal of each modulation period and outputs it to the roll-off filter, and the receiving side detects a change in the gain of the signal from the demodulation section and converts the signal of each modulation period. The present invention is characterized in that it includes a second conversion section that converts a signal with a modulation period corresponding to the gain into binary data based on phase information of this signal and outputs the binary data.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

This data transmission system consists of a transmitter 10 that modulates binary data from a terminal at multiple modulation cycles and outputs a transmission signal to a telephone line 20, demodulates a transmission signal from a telephone port &120, and The receiving section 30 outputs the digital data to the terminal. Note that the transmitting section 10 and the receiving section 30 are each provided in a modulation/demodulation device.

Furthermore, the transmitter 10 receives 2 inputs from the input terminal 11.
a code converter 12 that converts binary data into a phase-modulated signal every N bits; and a synchronization signal that generates a synchronization signal at a period of a predetermined integral multiple of N bits when binary data is input from the input terminal 11. Generator 13 and synchronization signal generator 13
a gain switch 14 that outputs a gain signal of a predetermined value when a synchronization signal is input from the code converter 12; and a multiplier that multiplies the phase modulated signal from the code converter 12 by the gain signal from the gain switch 14. a roll-off filter 16 that limits the signal from the multiplier 15 to a band suitable for the telephone line 20; and a modulator 17 that modulates the signal from the roll-off filter 16 and outputs a transmission signal to the telephone line 20. It is made up of.

On the other hand, the receiving unit 30 compares the absolute value of the waveform-equalized signal with a predetermined setting value with a demodulator 31 that demodulates and waveform-equalizes the transmission signal from the telephone line 20.
A comparator 33 outputs a comparison result, and based on the comparison result from the comparator 33, N-bit binary data is output to the output terminal 3 based on the phase information of the waveform-equalized signal from the demodulator 31.
4, and a code converter 32 which is output from the 4th section.

Next, the operation of this embodiment will be explained using an example in which binary data is transmitted using two modulation periods as one unit.

In this way, when data is transmitted using two modulation periods as one unit, for example, when the modulation frequency is 24008 and the communication speed is 7200 bps, the two modulation periods are 3X2
=6 bits of transmission data is transmitted. Here, if 5 bits are transmitted in two modulation cycles, the communication speed is 7200X.
5 + 6 = 6000 bps. When transmitting binary data from a terminal connected to the input terminal 11 of the transmitter 10 at such a communication speed, this binary data is input to the code converter 12 of the transmitter 10. Code converter 1
2, in order to transmit 5 bits of input data in two modulation cycles, first convert 3 bits of the 5 bits into the corresponding 3 bits of data transmitted in one modulation cycle. Assign to the signal point. Next, the code converter 12 assigns the remaining 2-bit data to the signal point of the 2-bit data transmitted in the other modulation period corresponding to this data. The thus phase modulated signal is input to the multiplier 15. On the other hand, the synchronization signal generator 13
When the binary data signal from the terminal is input, it generates a synchronization signal and outputs this synchronization signal to the gain switch 14. Based on this synchronization signal, the gain switch 14
A gain signal of two values is output to the multiplier 15. Multiplier 1
5, when a signal point of 3-bit data transmitted in one modulation cycle is input, this signal point is multiplied by a gain signal of one value. Furthermore, when a 2-bit signal point transmitted in the other modulation cycle is input manually, the multiplier 15 multiplies this signal point by the gain signal of the other value.

As a result of this multiplication, the gain of the signal point of 3-bit data transmitted in one modulation cycle becomes higher than the gain of the signal point of 2-bit data transmitted in the other modulation cycle.

This situation is shown in the signal point arrangement diagram of FIG.

As shown in FIG. 2, 3 bits of data transmitted in one modulation period are signal points A and -A.

It is placed at a point inside. Furthermore, 2-bit data transmitted in the other modulation cycle is placed at one of the signal points 81 to B4. Furthermore, signal point A.

The gain of ~A8 is larger than the gain of signal point Bl'''B4. That is, signal point A, ~8.

The gain of signal points 81 to B4 is outside the gain shown by circle C, and the gain of signal points 81 to B4 is inside the gain shown by circle C. In this way, data transmitted in one modulation period is distinguished from data transmitted in the other modulation period. Note that the error rate is best when the interval between signal points indicated by adjacent X marks in FIG. 2 is the same as the interval between signal points indicated by adjacent O marks.

A signal corresponding to data arranged at such signal points is output from the multiplier 15. This signal is band-limited by a roll-off filter 16 and input to a modulator 17 . The modulator 17 modulates the band-limited signal and outputs the transmission signal to the telephone port '1fA20.

The demodulator 31 of the receiving section 30, which receives the transmission signal from the telephone line 20, demodulates the transmission signal and performs waveform equalization. The waveform-equalized signal is sent to a code converter 32 and a comparator 3.
3 is output. The comparator 33 compares a predetermined setting value with the absolute value of the waveform-equalized signal, and outputs the comparison result to the code converter 32. The code converter 32 converts the waveform-equalized signal into a signal based on the phase information of this signal.
Convert to 5-bit binary data and output. That is,
Based on the comparison result of the comparator 33, the code converter 32
If the absolute value of the waveform-equalized signal is greater than the set value,
The data arranged at the signal points A1 to AI1 shown in FIG. 2 is converted into 3-bit binary data and output. In addition, if the absolute value of the waveform-equalized signal is smaller than a predetermined value, it is converted to 2-bit binary data and output as data placed at signal points B, ~B4 shown in Figure 2. be done. In this way, 5-bit binary data is output from the code converter 32 and sent to the terminal connected to the output terminal 34.

In this way, this embodiment transmits 5 bits in two modulation periods. Similarly, if 8 bits are transmitted in 3 modulation periods, the result will be 7200 x 8 ÷ 9 = 6400 bps. What if we transmit 7 bits here? 200X7÷9=5600
Various communication speeds such as bps are possible.

〔Effect of the invention〕

As explained above, the present invention has the advantage of being able to transmit data at different communication speeds by changing the gain of a phase modulated signal and transmitting data in a plurality of modulation cycles.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a signal point constellation diagram of the embodiment of FIG. 1, and FIG. 3 is a signal point constellation diagram of the conventional data transmission system. . 10... Transmitter 11... Input terminal 12... Code converter 13... Synchronization signal generator 14... Gain switcher 15... Multiplier 16... Roll-off filter 17...・Modulator 20...Telephone line 30...Receiving section 31...Demodulator 32...Code converter 33...Comparator 34...Output terminal

Claims (1)

[Claims] (1) A transmission side that includes a roll-off filter that limits a phase-modulated signal to a band suitable for the line, and a modulation section that modulates the signal from the roll-off filter and outputs it to the line, transmits a signal from the line. In a data transmission system that transmits a signal, the receiving side includes a demodulator that demodulates the signal, and the transmitting side phase-modulates the input binary data at a plurality of modulation cycles, The receiving side includes a first conversion section that changes the gain of the signal of each modulation period and outputs it to the roll-off filter, and the receiving side detects a change in the gain of the signal from the demodulation section and changes the gain of each signal. 1. A data transmission system comprising: a second conversion section that converts a signal with a modulation period corresponding to , into binary data based on phase information of the signal and outputs the converted data.