JPS6156659B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a facsimile device that is capable of transmitting and receiving good facsimile information even when the line condition deteriorates and the error rate becomes high, and particularly a facsimile device that can send and receive good facsimile information on both domestic lines and international lines. The present invention relates to a facsimile device that can send and receive information.

When sending and receiving facsimile information, if the line condition deteriorates, distortion will occur in the transmission characteristics such as amplitude characteristics, phase characteristics, and delay characteristics of the transmission line, and the error rate will increase, making it difficult to send and receive good data. Reception becomes difficult. This becomes a particular problem when facsimile information is sent and received over an international line, where the line condition is more degraded than that of a domestic line.

Conventionally, when the line condition deteriorates while sending or receiving facsimile information, for example,
As disclosed in Japanese Patent Publication No. 131610 and Japanese Patent Publication No. 45-24249, a transmission method has been proposed in which the modulation method is switched to a transmission rate that provides a predetermined error rate.

This conventional method shifts down the transmission speed from 9600 bits/sec to 4800 bits/sec and from 4800 bits/sec to 2400 bits/sec when the line error rate increases. Because of this, there was a drawback that the transmission time was long.

The present invention is a facsimile system that improves the shortcomings of conventional systems, and allows facsimile information to be sent and received as well as on domestic lines, without downshifting the transmission speed, even on international lines where transmission characteristics deteriorate. The purpose is to provide equipment.

Hereinafter, the present invention will be explained in detail based on FIGS. 1 to 6.

FIG. 1 shows the range (δ ₁ ) in which the amplitude distortion characteristics of the transmission characteristics of a MODEM (modulator/demodulator) of a facsimile apparatus can be corrected.

That is, normally MODEM is ±
2KC can correct amplitude distortion in a range of approximately 4dB. Since the amplitude distortion characteristic of a domestic line is within this range, when transmitting facsimile information over a domestic line, the transmission characteristic distortion can be corrected by MODEM.

Figure 2 shows typical amplitude characteristic distortion (δ
₂ ). In other words, in the circuit line,
It shows approximately 6dB attenuation at ±2KC. Therefore, the distortion caused by the international line cannot be corrected by MODEM, resulting in a deficit of about 2 dB, so an appropriate compensation circuit, ie, an equalizer, is required.

Figure 3 shows the amplitude characteristics (δ ₃ ) of the equalizer required to compensate for _the amplitude characteristic distortion of international lines. Between the characteristic δ ₂ δ ₃ ≧ δ ₂ −
If there is a relationship of δ ₁ , the amplitude distortion caused by the international line will be compensated.

Transmission distortion includes phase distortion and delay distortion in addition to amplitude distortion, but phase distortion and delay distortion that cannot be compensated by MODEM can also be compensated for by inserting an equalizer in the same way as amplitude distortion. can.

However, if facsimile information is transmitted and received via a domestic line with this equalizer inserted, overcompensation will occur and transmission distortion will occur.

Therefore, in order to send and receive facsimile information successfully when using both domestic and international lines, it is necessary to identify whether the line is a domestic line or an international line, and only when an international line is being used. All you have to do is insert an equalizer into the line.

Next, a method for identifying domestic lines and international lines will be explained with reference to FIGS. 4 and 5.

Figure 4 shows a facsimile communication sequence based on CCITT that is common to both domestic and international lines.The receiving side sends a command signal containing receiving function information such as paper size and line density of the receiving device.
When a DIS (Digital Information Signal) is sent to the sending side, the sending side selects a receiving function that matches the sending function and sends a response signal DCS (Digital Common Signal).
specifies the function of the receiving device on the receiving side. Next, do training. In other words, a reference signal is transmitted from the transmitting side to the receiving side, and when the receiving side confirms that the reference signal can be received in a satisfactory state, it informs the transmitting side that it can be received using CFR (Con firmation to Receive). Inform. this
After receiving the CFR, the sender begins transmitting facsimile information.

Normally, a facsimile communication sequence is performed according to the above procedure. On the other hand, the timing of the communication sequence at this time is as shown in FIG.

That is, FIG. 5 shows a timing chart of the typical communication sequence shown in FIG. 4 for a domestic line and an international line.

The timing T ₁ at which the sending side sends the DCS after receiving the DIS differs depending on the distance between the sending and receiving stations in the case of domestic lines, but is generally 0 to 200ms, that is, 0 < T ₁ < 200ms. Yes (waveform diagrams a and b).

On the other hand, since international lines use communication satellites, the transmission time is about 200 to 400 ms, so the receiving side
Timing _T2 for receiving DCS after sending DIS is 400~
800ms, that is, 400<T ₂ <800ms (waveform diagram CD). In other words, a large amount of data has confirmed that the timing of receiving DCS after sending DIS is 0 to 200 ms on domestic lines and 400 to 800 ms on international lines.

Therefore, by measuring the time T (T ₁ or T ₂ ) from when the DIS is sent to when the DCS is received, it is possible to distinguish between domestic lines and international lines. For example, T<
If it is 300ms, it can be determined that the line being used is a domestic line, and for example, if T>300ms, it can be determined that it is an international line.

From the above, the time T from sending DIS to receiving DCS is measured. For example, if T > 300 ms, an equalizer is inserted into the line, and if T < 300 ms, the equalizer is removed from the line. In this way, desired facsimile information can be obtained on the receiving side without downshifting the transmission speed.

FIG. 6 shows a specific configuration example for implementing the present invention based on the above idea.

In the figure, 1 is an NCU (network control unit) or MODEM (modulator/demodulator) for transmitting and receiving facsimile information via a telephone line, 3 is an equalizer as explained in FIG. 3, 4 is a switch, Reference numeral 5 denotes an SCU (system control unit) that controls the operation of the entire device and measures the time (T ₁ or T ₂ ) from when the DIS is sent until the DCS is received and switches the switch 4 .

In this configuration, the switch 4 is connected to the a side, and the DIS enters the telephone line via the MODEM 2, the switch 4, and the NCU 1 and is sent to the transmitting side.

The sending side (not shown) also has a similar NCU, MODEM,
It has SCU and returns DCS. SCU5 is
Measure the time T from sending the DIS to receiving the DCS. For example, if T<300ms, connect the switch 4 to the a side as it is; for example, if T>300ms.
If so, switch the contact of switch 4 to the b side and equalizer 3.
is inserted into the line to compensate for transmission characteristic distortion. The switching of the switching device 4 is performed before the start of training, as shown in FIG. 5e. When the transmission of the facsimile information is completed, the switch 4 is switched to the a side, and the equalizer 4 is disconnected from the line.

Note that the equalizer 4 compensates for transmission characteristic distortions, that is, distortions in amplitude characteristics, phase characteristics, and delay characteristics.
For example, Electronic Communication Handbook (Nos. 183-186)
It is sufficient to employ various known filters shown in page 1.

Command signals and response signals are sent to the receiving side (or sending side)
It is not limited to DIS or DCS, as it is used to measure the time it takes for a signal sent from the sender to return via the sender. Furthermore, the equalizer 4 may be inserted on the transmitting side. That is,
When transmitting facsimile information via an international line, the equalizer 4 may be inserted into the line.

The explanation so far has been about domestic lines and international lines, but if you divide domestic lines and international lines into smaller sections according to distance and select an equalizer that is suitable for each, it will be even more accurate. Transmission characteristic distortion can be compensated for.

As explained above, according to the present invention, the characteristics of the transmission line are identified in correspondence with the distance, and an equalizer corresponding to the distance is automatically selected and inserted into the line. Even in the case of international lines, it becomes possible to transmit and receive good facsimile information with a simple configuration without downshifting the transmission speed.

[Brief explanation of the drawing]

Figure 1 is a MODEM transmission characteristic diagram, Figure 2 is an international line transmission characteristic diagram, Figure 3 is an equalizer compensation characteristic diagram, Figure 4 is a diagram of a typical facsimile communication sequence, and Figure 5 The figure is a time chart of FIG. 4, and FIG. 6 is a block diagram of the main part of a facsimile machine showing an embodiment of the present invention. 1...NCU, 2...MODEM, 3...Equalizer, 4...Switcher, 5...SCU.

Claims (1)

[Scope of Claims] 1. A facsimile device that transmits and receives facsimile information via a plurality of transmission lines, including at least one equalization means for compensating for transmission characteristic distortion of these transmission lines, and a response signal after sending a command signal. 1. A facsimile apparatus comprising: means for measuring the time until the return of the facsimile; and means for operating a predetermined one of the equalizing means in accordance with the measured time. 2. The facsimile device according to claim 1, wherein the command signal and the response signal are respectively DIS and DCS defined by CCITT, or signals equivalent to these. 3. The facsimile apparatus according to claim 1, wherein the equalizing means is a fixed equalizer for equalizing amplitude distortion and phase distortion.