JPS6336620A - Facsimile transmission system - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of the line by deciding the signal transmission speed depending on the distortion of line for the signal reception state so as to select the optimum signal transmission speed at a short time. CONSTITUTION:A facsimile FAX transmission system consists of a sender side terminal equipment comprising a FAX transmitter 1, a MODEM 2 and a network controller 3 and a reception terminal equipment comprising a FAX receiver 4, a MODEM 5, a line circuit 6 and a connection detection circuit 7, and both the equipments are tied via an exchange 8 and the line 9. A distortion measurement signal is sent in the specific signal transmission speed from the transmitter 1. The receiver 4 measures the distortion from the received distortion measurement signal and selects the optimum speed among plural transmission speeds of the transmission picture signal based on the result of measurement. Further, the optimum means among correction control means correcting the filter tap coefficient of the automatic equalizer of the demodulator 26 to correct the distortion characteristic is selected in a secular change. The transmitter sends the picture signal at the selected signal transmission speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a facsimile transmission system for transmitting one image signal from three transmitting devices to a receiving device via a line such as a telephone switching network.

Note that devices to which the present invention can be applied include not only ordinary facsimile machines but also communication terminal devices and document creation devices equipped with a facsimile transmission function.

Option 1 Generally, in a system that performs facsimile transmission using lines such as a telephone exchange network as described above, a modem with multiple signal transmission speeds is used, and a facsimile transmitting device and a receiving device are connected to each other. The signal transmission speed that allows the fastest and least distorted image signal to be transmitted between
ii! The image signal is transmitted after the start of the I-communication.

The procedure for setting the signal transmission speed in this type of facsimile transmission system is that the calling party (sending party) calls the called party (receiving party), and the called party indicates that the called party is a facsimile terminal. 21001- as a station identification signal
1z 1■ sound signal is returned, and then the called party transmits the type of signal transmission speed of its own modem (14.4Kbps,
9.6Kbps, 7.2Kbps, 4.8bps
, 2.4 Kbps, etc.), encoding method (two-dimensional encoding method, -dimensional encoding method), etc. 1 The calling side receives these and selects the function that matches itself, Information indicating the selected function is sent to the called party as command information.

After that, the calling side sends a training signal to the called side at the signal transmission speed indicated by the command information in order to set up the called side's modem to a state where it can receive data, and the called side receives this. If the image signal cannot be received without error at the signal transmission speed after training, a training failure signal is returned to the calling party.

As a result, when the calling side receives this training failure signal, it sends command information to the called side to perform a fallback to lower the signal transmission speed by one step, and performs training at the new signal transmission speed. , when the training is successful, a reception ready signal is sent from the called party to the calling party.

Shift to image signal transmission.

However, if the optimal signal transmission speed is set in this way, the greater the degree of distortion in one line, the more training failures will occur, and the time required for training will be longer. The problem was that it was long.

Also, in such facsimile transmission systems, to correct various distortion characteristics of the line.

The demodulator of the receiving device is equipped with an automatic equalizer that equalizes the waveform of the received baseband signal.

As such an automatic equalizer, for example, a transversal type or acyclic type automatic equalizer is generally used.

Basically, as shown in FIG. 7, this consists of a tapped delay line 101 to which the received signal a from the transmission line 90 is input;
Multiplier 10 that multiplies the output of each tap by a tap coefficient
2 and an adder 103 that sums the outputs of the multipliers 102 and outputs an equalized signal Y, and the equalized signal Y is determined by an identification determination unit 110. Based on the results, the estimation control unit 1
20 estimates fluctuations in the characteristics of the transmission path SO and corrects the tap coefficients of the equalization filter unit 100 to optimize automatic equalization.

The automatic equalization algorithm of such a transversal automatic equalizer, that is, the filter tap coefficient adjustment method, is as follows:
The so-called ADA and FTA methods based on maximum slope methods are well known.

In order to further increase the convergence speed, a modification of these methods is often used in practice in which the correction coefficient is not fixed but is varied over time.

In this method, it is necessary to determine when and how much to change the correction coefficient, but this can only be decided through trial and error while checking the equalization condition for various simulated line conditions. .

Even if modems have exactly the same configuration, if the timing and amount of change in the filter tap coefficients differ, the modem performance will be completely different.

In addition, the total performance of a modem, including the automatic equalizer, is measured by the bit error rate, so once you have set the timing and amount of change, you can measure the bit error rate under various line conditions. Check the effect,
The data (time of change and amount of change) that gives the best results will be adopted.

The problem here is that a certain degree of compromise must be made regarding the data used. For a certain transmission speed (for example, 9600 bps), the line condition is: no distortion, only a little distortion, strong echo,
This is because there are many miscellaneous cases, such as cases where there is a lot of noise or cases where distortion is very large.

Generally, the equalizer is adjusted to improve the bit error rate even under poor conditions, so if the distortion is small, the equalizer's power may not be fully utilized. .

This invention has been made in view of the above points, and it shortens the time required to determine the signal transmission speed for transmitting image signals to improve line utilization efficiency, and also improves the efficiency of line utilization by reducing the time required to determine the signal transmission speed for transmitting image signals. It is an object of the present invention to enable selection of the optimum tap coefficient adjustment method (tap coefficient change timing and change ff1) according to the degree of line distortion.

1. In order to achieve the above object, the facsimile transmission system according to the present invention transmits a distortion measurement signal from a transmitting device at a specific signal transmission rate, and the receiving device (3) measures the amount of distortion from the received distortion measurement signal. and, based on the side window result, determine the optimum speed among the plurality of signal transmission speeds of the image signal to be transmitted from the transmitting device.

The transmitter selects the optimum means from among a plurality of correction control means for correcting the filter tap coefficients of the automatic equalization layer over time to correct the distortion characteristics due to the line, and the transmitter selects the optimum means by the receiver. The image signal is transmitted at the signal transmission speed.

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

FIG. 1 is a procedure explanatory diagram of an embodiment of the present invention.

In the figure, FAXL and FAX2 are facsimile transmitting and receiving devices, MOD I and MOD2 are modems, and the columns 300 bps and 4800 bps indicate signal transmission speeds.

The transmission procedure will be explained below.

Facsimile transmitting device (hereinafter simply referred to as "transmitting device")
FAXI uses a telephone (not shown).

A facsimile receiving device (hereinafter simply "
Call FAX 2 (referred to as "receiving device").

■ Receiving device FAX2 communicates with 210 via modem MOD2.
It generates a single tone signal of 0 Hz and returns a called station identification signal indicating that the called terminal station is the receiving device [FAX, 2].

(2) Next, the receiving device FAX 2 identifies the functions 1 of its own device, such as the type of transmission speed of its own modem, the type of encoding method of the image signal that it can decode, the maximum receivable paper size, etc. The signal is transmitted to the transmitter FAX l side via modem MOD2.

■ The transmitter [FAX 1] confirms that the destination is a facsimile machine based on the received called station identification signal, and waits for reception of the function identification signal.

Next, based on the received function identification signal, the transmitting device F
AX I extracts the functions that match the self-device, and among them,
Select the function that can be transferred in the shortest amount of time.

However, in the method of the present invention, the signal transmission speed is not selected at this point.

Regarding each selected function, the transmitting device FAXI transmits command information to the receiving device FAX2, and notifies the receiving device FAX2 that it is a function to be used for transmission.

・The transmitting device FAXI is the modem MO on the receiving side.
1 and 2 can be set to a receivable state, and a distortion measurement signal whose degree of distortion can be determined on the receiving side is transmitted from the modem MODI as a training signal.

The signal transmission speed for transmitting this distortion measurement signal is the recommendation V29) 9.6 used for transmitting image signals.
Kbps, 7.2 Kbps, or Recommendation V 2
7 T, er 4,3 Kbps, 2,4 Kb
Use something other than ps.

For example, Recommendation V29-4 specified for data transmission
．． A signal transmission rate of 8 Kbps is used.

In general, it is known that the No. A transmission rate of 4.8 Kbps of Recommendation V29 has a large range in which noise tolerance and line quality can be recognized, and is suitable for the signal transmission rate of training signals.

Further, among the above-mentioned 1 to 10 training signals, it is desirable that the signal pattern for measuring quality such as line distortion be a random pattern so that all signal patterns of the image signal to be transmitted appear.

Receiving device FAX2 selects the receiving function on its own device side specified in receiving command No. 18 and puts it into operation.

The modem MOD2 sets up its own device based on the training signal from the modem MODI.

Furthermore, the modem MOD2 regenerates the received signal and outputs a signal indicating the degree of line distortion.

The receiving device FAX2 measures the distortion -fIt using this output signal, and based on the measurement results, determines at which signal transmission speed it is optimal to transmit the image signal and at which it can be transmitted at high speed with fewer errors. to select the signal transmission speed.

At the same time, the optimum means is selected from among the plurality of modification control means for modifying the filter type coefficients of the automatic equalizer over time based on the measurement results of the amount of distortion.

(D When the signal transmission speed is selected, the receiving device FAX2 transmits the selected signal transmission speed (shown as command information),
The sending device FAX1 is notified that reception preparation is complete.

)■ Send command information and reception preparation completion signal to the sending device FAX
When 1 receives the signal, it sets the signal transmission rate indicated in the command information to the modem MODI, and transmits the image signal at that signal transmission rate.

As described above, according to this embodiment, the signal transmission speed is determined depending on the signal reception state on the receiving side, that is, the amount of distortion caused by the line, so there is no need to take the so-called fallback procedure as in the conventional method. , the optimal signal transmission speed can be selected in a short time.

In addition, multiple control means for correcting the filter tap coefficients of the automatic equalizer, which corrects line distortion characteristics on the receiving side, are available for the same transmission speed, depending on the line situation (distortion scale). Since the optimum means is selected based on the above, it is possible to always make full use of the equalizer's ability.

FIG. 2 is a block diagram showing an example of a facsimile transmission system embodying the present invention.

This facsimile transmission system is the FAXI transmission system shown in Figure 1.
and a transmitting side terminal device consisting of a facsimile transmitting device 1 and a modem 2 corresponding to MODI, and a network control unit (NCU) 3, a facsimile receiving device 4 and a modem 5 corresponding to the FAX 2 and MOD2 in FIG. 1, and a line circuit 6.
and a receiving side terminal device consisting of a connection detection circuit 7.

These transmitting terminal devices and receiving terminal devices are connected to the exchange 8.
and the NC of the transmitting terminal device.
A telephone set 10 is connected to U3.

The input unit 11 of the facsimile sending bag @1 constituting the sending terminal device has various keys such as a sending key for giving sending instructions, and inputs instruction information necessary for controlling the sending.

The reading section 12 reads a document image upon receiving a reading instruction from a main control section 17, which will be described later, and sends the read image signal to the encoding section 13. The encoding unit 13 is the reading unit 12
The encoded image signal is stored in the buffer 14. The encoded image signal stored in the buffer 14 is sent to the modem 2 via the OR circuit 15 in response to a transmission timing signal ST from the modem 2.

The line control unit 1 sends a demodulated signal obtained by demodulating the received signal given from the modem 2 to the main control unit 17, and also sends signal transmission speed information to the modem 2 based on the information given from the main control unit 17. While sending out via signal line a,
It performs controls such as sending information received from the main control unit 17 to the modem 2 via the OR circuit 15.

The main control unit 17 is in charge of overall control of this transmitting side terminal device, and when a transmission instruction is input from the input unit 11, it sends out functional information to the line control unit 5 and becomes ready to start transmission. When this happens, it gives an instruction to the reading section 12 to read the original image, and also gives an instruction to the encoding section 13 to start encoding processing.

The counter 18 counts up each time the encoded image signal from the encoder 13 is input.2. Each time the transmission timing signal ST is input from the modem 2, it counts down, and when the count value reaches a predetermined value or more, it instructs the reading section 12 and the encoding section 13 to interrupt the processing, and the buffer 14 is Control is performed so that a predetermined number or less of image signals are stored in the storage area.

Modem 2 modulator 1st is 1 line controller 1st signal line a
The function information sent via the OR circuit 15 is modulated at the signal transmission speed indicated by the signal transmission speed information received via the NCU 3, and the transmission start signal ST is sent to the buffer 14. OR circuit 15 from buffer 14
N C
Send to tJ3. The demodulator 1120 demodulates information received from the other party and sends it to the line controller 16.

On the other hand, the decoding section 22 of the facsimile receiving device 4 constituting the receiving terminal device restores the received encoded image signal sent from the modem 5 and sends it to the recording section 21 . The recording unit 21 records image information on the recording paper B based on the image signal received from the decoding unit 22.

The selection unit 23 has two ROMs each comprising a table for selecting the transmission rate and one for selecting the tap coefficient adjustment method of the automatic equalizer, and based on the distortion measurement result by the distortion measurement circuit 27 of the modem 5, The optimum signal transmission rate is selected, the selected signal transmission rate information is sent to the line control section 24, and the optimum tap coefficient adjustment method (correction control means) is selected, the details of which will be described later.

The line control section 24 receives information received from the modem 5 and the selection section 2.
The signal transmission speed information from the main control section 25 is inputted and sent to the main control section 25, and the modem 5 is controlled by instructing the signal transmission speed according to the signal transmission speed information from the main control section 25.

The main control section 25 sets up the line control section 22 and the recording section 21, and also sends various information such as signal transmission speed information to the line control section 24.

In addition, the demodulator 2 of the modem 5 demodulates the received (H signal) from the line and sends it to the decoding unit 22 and line control unit 24, and also distorts the equalization error signal when receiving the distortion measurement signal. It is sent to the measurement circuit 27.

The details will be described later together with the distortion measurement circuit 27.

The modulator 28 modulates various information such as signal transmission speed information from the line control unit 24 and sends the modulated information to the line.

Line circuit 6 is connected to line 1B by a ringing signal from exchange 8.
The connection detection circuit 7 monitors the signal line of the line circuit 6 and notifies the main control unit 25 when the line is connected.

Next, the demodulator 26 in FIG. Distortion measurement circuit 27
．． Details of the selection section 23 will be explained with reference to FIG.

First, the demodulator 26 includes a plurality of demodulation circuits 261 to 2S4 (only four circuits are shown to simplify the explanation) corresponding to each signal transmission rate, and an acyclic demodulation circuit that equalizes the waveform of the received baseband signal. type automatic equalizer 265 and the signal 8r waveform-equalized by it.

A determination unit 266 that determines the signal waveform transmitted from el, a coding unit 267 that converts the determined signal waveforms d r and d i into received data, and a signal Er that indicates the equalization error of the automatic equalizer 265. , a subtraction circuit 268 that creates Ei,
269.

Of the 5 demodulation circuits 261 to 264, only the circuit designated by the line control unit 24 in FIG. 2 via one of the terminals Ta to Td operates.

Next, the distortion measuring circuit 27 includes a power calculating section 271, an integrating circuit section 272, and a slicing section 273, and the operation of each section will be explained later.

The selection unit 23 includes a ROM 231 for selecting a transmission rate and a ROM 232 for selecting a tap coefficient adjustment method. and,
The ROM 231 has various signal transmission speeds (2.4 Kbps,
The relationship between 4.8 Kbps...l and the address corresponding to the amount of distortion is stored in a table.

The ROM 232 stores a plurality of tap coefficient adjustment methods (change timing and amount of change of the correction coefficient) as means for controlling correction of the filter tap coefficients of the automatic equalizer 265 for one transmission rate. The automatic equalizer 265 can be controlled by selecting one of them using an address corresponding to the amount of distortion.

Here, the operation of each part in FIG. 3 will be explained with reference to FIGS. 4 to 6 as well.

Upon receiving the command information from the transmitting side, the line control unit 24 in FIG. 2 first raises the signal at the terminal Ta of the demodulator 2 in order to measure the distortion characteristics, and in this example, the transmission rate is 4.8K.
The demodulation circuit 261 for bps is activated.

When a training signal for distortion measurement transmitted from the transmitting side is received, the demodulation circuit 261 demodulates it and outputs baseband signals m r and m i of signal components whose phases are 90 degrees apart from each other.

The automatic equalizer 265 equalizes the waveforms of the signals rn r and m i and outputs 1-equalized signals er and ci.

The determination unit 266 determines the amplitude and phase values that the received baseband signal should have based on the equalized signals sr and ei. Judgment output d r, d i by this judgment unit 266
is supplied to the encoding unit 267 and the subtraction circuit 268°2Ei9.

The encoding unit 267 reproduces the transmission data based on the amplitude and phase values obtained from the determination outputs dr and di.

On the other hand, the subtraction circuit 2Ei8, 269 receives the equalization signal sr.

Take the difference between ei and the judgment outputs dr and di.

Equalization error signal Er that could not be equalized by the automatic equalizer 265
, Ei are determined and applied to the distortion measurement circuit 27.

FIG. 4 is an eye pattern diagram showing the equalization error signals Er and Et on a complex plane, and the horizontal axis is the real number 1jlfl(
(corresponding to Er) the vertical axis is the imaginary axis (corresponding to E i).

When the equalization error signal is shown in an eye pattern diagram like this, it is distributed around the intersection of the real number axis and the imaginary number axis.

5 When the line characteristics are good, the eye of the equalization error signal tends to be concentrated near the intersection of both axes, and when it is poor, it is not concentrated near the intersection of both axes, but tends to be dispersed on the complex plane. have.

The distortion measurement circuit 27 operates from the rising edge of the signal from the line control unit 24 to the terminal Te, and the power calculation unit 271 adds the squares of the absolute values of the equalization error signals Er and Ei to obtain the equalization error signal. Calculate the electric power, so-called power.

FIG. 5 shows the frequency distribution of power values calculated by the power calculation unit 271. Note that since each power value is an absolute value, it is distributed only in the positive quadrant.

In Fig. 5, a is the distribution curve when the line characteristics are good;
C is the distribution curve when line characteristics are poor.

b shows the distribution curves for the intermediate line characteristics.

In this way, each distribution curve has a substantially Gaussian distribution shape, and as the line characteristics become better, the distribution curve becomes narrower with a higher peak at the power value P=O, and conversely, as it deteriorates, the peak becomes gentler. The distribution curve changes to a gentle and wide distribution curve.

That is, as the line characteristics deteriorate, the value obtained by integrating each curve increases.

Therefore, when the power value calculated by the power calculating section 271 is integrated by the integrating circuit section 272, the integrated value has characteristics as shown by the curve in FIG. 6 depending on the quality of the line (degree of distortion characteristics).

Qa, Qb, and Qc in this FIG.
The line quality corresponding to distribution curves a, b, and e in the figure is shown. 81 to S4 are slice levels for determining the amount of distortion by the slice unit 273.

Then, the integral value outputted from the integrating circuit unit 272 is compared with each slice level S, ~S4 in the slicing unit 273, and converted into each address corresponding to between each slice level and from S1 to +54 and output. Possibly 1
The ROM 231 of the selection unit 23 selects and reads out the signal transmission speed (also shown in FIG. S) corresponding to the address.

The signal transmission speed is instructed to the line control circuit 24.

Accordingly, the signal transmission speed at which the image signal should be transmitted from the transmitting side is determined.

In addition, in the slicing unit 273, slice levels (
(not shown) and the integral value inputted from the integrating circuit 272, and for example, by making the lower address of the above-mentioned address correspond to the comparison result, the ROM 232 of the selection unit 23 can select the lower address. The tap coefficient m adjustment method (the timing and amount of change of the filter tap coefficients) corresponding to is selected and read out, and the automatic equalizer 265 is controlled by that method.

By the way, even when the same signal transmission speed is selected, there is a certain range in the integral value of the equalization error power1.For example, even if it is determined that the transmission speed is 9.6 Kbps,
There are cases where there is almost no distortion, and cases where there is some degree of distortion but it is possible to send data at 9.6 Kbps. In the latter case, it may be determined that it is 7.2 KbρS even though it is negative.

As described above, since there is a certain range even for the same signal transmission speed, there is an optimum timing and amount of modification of the tap coefficient (to speed up convergence) for each state of line distortion.

Therefore, as described above, the ROM 232 of the R-folding section 23 selects the optimal tap coefficient adjustment method by table lookup according to the measurement result of the distortion measuring section 27.

As described above, according to the present invention, the transmission speed of image signals in a facsimile transmission system can be determined to be the optimum speed in a short time, thereby improving the effectiveness of using one line.

In addition, since the optimal correction control means is selected according to the degree of distortion in a single line and the filter tap coefficients of the automatic equalizer are corrected and controlled, the bit error rate is reduced under various line conditions and the performance of the modem is improved. do.

[Brief explanation of the drawing]

FIG. 1 is a procedure explanatory diagram of an embodiment of the invention, and FIG. 2 is a block diagram showing an example of a facsimile transmission system in which the invention is implemented. FIG. 3 is a block diagram showing details of the main parts. Figure 4, srj! I and FIG. 6 are explanatory diagrams of the respective signals, and FIG. 7 is a block diagram showing the basic configuration of a general acyclic automatic equalizer. 1...Facsimile transmitter 2.5...Modulator/demodulator (modem) 3...Network control unit (NCU) 4...Facsimile receiver 8...Exchange 23...Selector 26. ... Demodulator 27 ... Distortion measuring section 231 ... ROM for transmission rate selection 232 ... ROM for selecting tap coefficient adjustment method 261 to 26
4... Demodulation circuit 265... Automatic equalizer 26th... Judgment unit 267
... Encoding section 268, 269 ... Subtraction circuit 27
1...Power calculation section 272...Integrator circuit section 273
... Slice section Figure 1 Sending side Chichi Shingo Figure 4 T Figure 5 ic i”r la @ line quality Figure 7

Claims (1)

[Claims] 1. A transmitting device transmits a distortion measurement signal at a specific signal transmission rate, a receiving device measures the amount of distortion from the received distortion measurement signal,
Based on the measurement results, the optimum speed of the multiple signal transmission speeds of the image signal to be transmitted from the transmitting device and the filter tap coefficients of the automatic equalizer for correcting the distortion characteristics due to the line are determined over time. 1. A facsimile transmission system, characterized in that: an optimal correction control means is selected from among a plurality of correction control means, and a transmitting device transmits an image signal at a signal transmission rate selected by the receiving device.