JPH0779285B2 - Subscriber line transmission system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a subscriber line transmission system for transmitting data via a subscriber line.

[Conventional technology]

Conventionally, AMI (Alternat
ive Mark Inversion) method is used. Data is,
It is converted into three values of 0, +1 and -1, and +1 and -1 appear alternately. On the receiving side, a line equalizer is used to restore the data.

[Problems to be solved by the invention]

However, in the above-mentioned conventional AMI method, since the AMI becomes a ternary signal, if a mismatch in the characteristics on the frequency axis occurs between the line and the equalizer, the characteristics of the output signal of the equalizer suddenly increase. Deteriorates. Therefore, the equalizer has a drawback that a very precise one is required.

An object of the present invention is to provide a subscriber line transmission system which does not require a highly accurate equalizer on the receiving side and which requires an equalizer having a simple structure.

[Means for solving problems]

According to the present invention, in the subscriber line transmission system in which data to be transmitted is transmitted from the transmission side to the reception side via the subscriber line, the baud rate (baud) of the data is transmitted to the transmission side.
rate) the carrier having a frequency equal to the reciprocal of the above is quadrature-phase modulated with the data and provided with a modulator for sending to the subscriber line, and the receiving side receives the quadrature-phase modulated wave from the subscriber line, A subscriber line transmission system is provided which is provided with a demodulator for demodulating a baseband signal and an equalizer for compensating for distortion of the baseband signal due to the subscriber line and outputting the data. To be

〔Example〕

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

FIG. 1 is a block diagram of an embodiment of the present invention. 1 is a transmission data input terminal, 2 is an encoder, 3 is a modulator, 4 is a subscriber line, 5
Is a demodulator, 6 is an automatic equalizer, and 7 is an output terminal.

Serial data is given to the transmission data input terminal 1 as transmission data. The serial data is input to the encoder 2. The encoder 2 is a serial-parallel converter including a differential encoding that is normally used. Therefore, when the modulator 3 performs 4-phase phase modulation, the encoder 2 outputs 2 bits, and when it performs 8-phase phase modulation, it outputs 3 bits. The modulator 3 modulates with a phase determined by the output of the encoder 2. At this time, the major feature is that the data conversion point and the phase of the modulation signal are in phase synchronization. That is, the modulator 3 is
A carrier having a frequency equal to the reciprocal of the baud rate of data is quadrature-phase modulated with the data, and the subscriber line 4
Send to.

Thus, by orthogonally modulating the carrier wave having the frequency equal to the reciprocal of the data modulation rate (baud rate) with the data, the phase synchronization between the data and the carrier wave is obtained as described later with reference to FIG. , The data conversion point and the phase of the modulation signal can be synchronized. The modulator 3 usually requires a multiplier, but in the present invention,
Since the carrier wave having a frequency equal to the reciprocal of the modulation rate (baud rate) of the data is quadrature-modulated with the data, the data and the carrier wave are in phase synchronization. It can be composed only of gates,
The structure is simple. Similarly, the demodulator 5 can have a simple structure.

The modulation process for quadrature phase modulation is shown in FIG. In FIG. 2, A indicates input serial data, and B and C indicate 2-bit parallel data. D and E are carrier waves for modulation, D is COS type, E is SI
It is N type. A modulation signal F is obtained by modulating D and E with B and C. Input data and carrier wave are in phase synchronization,
Also, the modulation process is greatly simplified because each carrier is a square wave.

In FIG. 1, the demodulator 5 and the equalizer 6 constitute a receiver, and the details thereof are shown in FIG. In FIG. 3, the demodulator 5 is a timing recovery circuit 5-3 for outputting a COS wave and a SIN wave, and a multiplication for multiplying the COS wave and the SIN wave by the quadrature phase modulated wave from the subscriber line 4, respectively. Units 5-1 and 5-2
And have. The transmission loss of the subscriber line 4 increases in the high frequency region, but the phase modulated wave is distorted from such a line.

The time waveform of the baseband signal after demodulation by the demodulator 5 is shown in FIG. In FIG. 4, the solid line is the in-phase component signal and the dotted line is the quadrature component signal. Now, the transmission waveform is f
(T), its Fourier transform is F (f), the spectrum of the in-phase component signal in FIG. 4 is T _x (f) · F (f), and the spectrum of the quadrature component signal is T _y (f) / F (f ), An equivalent baseband system in which the modulator 3, the subscriber line 4, and the demodulator 5 are integrated is shown in FIG. Therefore, the equalizer 6 may have the inverse characteristics of FIG. 5, and its structure is shown in FIG. Sixth
The figure shows the structure of a typical equalizer.

Next, consider T _x (f) and T _y (f) when applied to the subscriber line 4. According to the simulation result, it can be approximated by T _y (f) = a · jT _x (f). Here, a is a constant that changes with the transmission distance. Therefore, since T _x (f) and T _y (f) can be configured by a commonly used phase difference wave device, the equalizer of FIG. 6 is simplified and described in the equalizer 6 of FIG. To be done. In the equalizer 6 of FIG. 3, 6-1 and 6-2 are 90 ° phase difference wave filters, respectively. Since a ₁ and b are variable parameters and b is multiplied by the whole, it can be realized by a so-called AGC (Automatic Gain Controller) circuit. a ₁ is determined by, for example, correlating two output terminals and using the result to control a ₁ .

Particularly, in the case of four-phase modulation, the present invention is considered to be binary transmission because the X axis is binary and the Y axis is also binary. Therefore, the accuracy of the equalizer is not required as compared with the case of a ternary sequence such as AMI, and an equalizer having a simple structure is good.

Of course, in the case of multi-phase modulation, the modulation speed (ba
The ud rate is low, and the transmission distance can be extended.

The subscriber line 4 is left with an open-ended branch line, which causes distortion, but the equalizer 6 does not have the equalization capability for this distortion. In this case, after the output terminal 7, an equalizer having an equalizing ability for the above distortion can be used. Note that the equalizer in this case is also simpler than in the case of AMI.

〔The invention's effect〕

As described above, according to the present invention, the data to be transmitted is quadrature-phase modulated and transmitted to the subscriber line, and the reception side demodulates the baseband signal from the quadrature-phase modulated wave and equalizes the data. The equalizer compensates for the distortion of the baseband signal due to the subscriber line so as to obtain the data, thereby eliminating the need to use a high-precision equalizer and equalizing a simple structure at low cost. The effect is that it can be used in a container.

[Brief description of drawings]

FIG. 1 is a block diagram of a subscriber line transmission system according to an embodiment of the present invention, FIG. 2 is a time chart of the modulator 3 of FIG. 1, and FIG. 3 is a demodulator 5 and an equalizer of FIG. 6 is a block diagram of FIG. 6, FIG. 4 is a diagram showing a time waveform of a signal demodulated by the demodulator 5 of FIG. 1, and FIG. 5 is a modulator 3, a subscriber line 4, and a demodulator of FIG. 5 is a block diagram of an equivalent circuit of a baseband transmission system, and FIG. 6 is a block diagram of an equalizer circuit of a general equalizer. 1 is a transmission data input terminal, 2 is an encoder, 3 is a modulator, 4 is a subscriber line, 5 is a demodulator, 6 is an automatic equalizer, and 7 is an output terminal.

Claims (1)

[Claims] 1. A subscriber line transmission system in which data to be transmitted is transmitted from a transmission side to a reception side via a subscriber line, and in the subscriber line transmission system, a carrier having a frequency equal to the reciprocal of the baud rate of the data is transmitted to the transmission side. And a demodulator for quadrature phase modulating the data and transmitting the quadrature phase modulated wave from the subscriber line to the receiving side, and a demodulator for transmitting the quadrature phase modulated wave from the subscriber line to the receiving side. A subscriber line transmission system, comprising: an equalizer for compensating for distortion of the baseband signal due to the subscriber line and outputting the data.