JPH03272267A - Receiver using modem of facsimile equipment - Google Patents

Abstract

PURPOSE:To receive a high speed picture signal correctly starting from a succeeding short training by starting a timer for time count through the reception of a reception signal and correcting a line distortion correction coefficient as required corresponding to the time count for a prescribed time of the timer when it is detected that the reception signal is not a training signal. CONSTITUTION:When a signal at a low speed is received while the mode is set to be the fast speed mode, a reception signal detection section 16 of a receiver side MODEM discriminates the presence of the reception signal to start a timer 17, the signal is demodulated by a demodulation section 9 and a training detection section 15 detects whether or not the demodulated signal is a training signal. When it is detected that the signal is not the training signal, the correction of a line distortion correction coefficient is stopped while the started timer 17 counts a prescribed time. When a prescribed time elapses, since the timer 17 is stopped, a line distortion correction section 18 corrects the correction coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to facsimile modem receivers, and more particularly to low-speed procedural signal reception in a high-speed data transmission mode.

(Prior Art) Facsimile transmission in a public network is performed using a modem, and some modems are equipped with a mode that shortens training time.

In this short training, normal training is performed in advance to store correction coefficients for line conditions, and in the second training, training time can be shortened by omitting setting up of these correction coefficients.

Incidentally, the facsimile communication procedure is defined in the CCITT facsimile recommendations, and as shown in FIG. 4, it consists of a low-speed mode for the procedure and a high-speed mode for image signal transmission. Here, the transmission of a plurality of original documents will be explained assuming that negotiation of the transmission speed, etc. between the transmitting and receiving modems has been completed.

As shown in Figure 4, the modem of the receiving facsimile first receives a high-speed mode TCF (training signal) from the transmitting facsimile, and if it is received in good condition, it switches to the low-speed mode for control. sends a CFR (reception readiness confirmation signal) back to the sending facsimile. Thereafter, the receiving facsimile receives the image signal in the high speed mode, and then receives the MPS (signal for notifying transmission of the next image signal) in the low speed mode. When the receiving facsimile confirms this MPS, it switches to low-speed mode MCF (message confirmation signal).
is sent to the sender. When the sending facsimile receives this MCF, it sends the next image signal to the receiving facsimile in high speed mode. In this way, the above sequence is repeated to transmit a plurality of original documents.

If the above-mentioned short training that shortens the training time is adopted in the above sequence, the result will be as follows.

The first high-speed TCP starts with normal modem training, and at this time, the receiving modem sets up a line distortion correction coefficient and maintains it even after high-speed reception ends. As a result, when receiving a high-speed image signal again after transmitting the CFR, the receiving modem uses the line distortion correction coefficient held above to omit part of the training time and shorten the time. You can do some training.

An example of this short training will be explained with reference to FIGS. 5 and 6.

FIG. 5 is a continuous reception timing chart of the modem in the high speed mode.

FIG. 6 is a reception timing chart when a momentary signal interruption occurs in the middle of data.

As shown in FIG. 5, during training in the normal high-speed mode, the modem receiver performs timing synchronization by the second short training signal. Also, as shown in Figure 6, if a non-training signal comes after a signal interruption (instantaneous interruption), it is determined that the data signal has been interrupted, and the already formed line distortion correction coefficient and timing are used as they are. and resume reception.

However, the following problems have occurred in conventional facsimile reception modems that perform this type of short training.

When the receiving facsimile is ready to receive high-speed image signals starting with the second short training, it sends out the MCF as shown in Figure 4, but depending on line conditions, the transmitting facsimile may not be able to detect the MCF. . In this case, as shown by the dotted line in FIG. 4, the sending facsimile sends a low-speed MPS again. Therefore, the receiving facsimile machine performs low-speed reception in high-speed mode.

This will be explained with reference to FIGS. 7, 8, and 9. FIG. 7 is a timing chart when a low speed flag (for example, the above-mentioned MPS, etc.) is received while the high speed mode is still set after receiving the high speed mode. Further, FIG. 8 shows a block diagram of the receiving side of the facsimile modem, and FIG. 9 shows a flowchart relating to this facsimile modem.

When a low-speed mode signal is received while the high-speed mode is still in the high-speed mode, as shown in the flow chart of FIG. The signal is demodulated by the demodulator 9 (step 202), and the training detector 15 detects whether the demodulated signal is a training signal (203). If a training signal is detected in step 203, the process proceeds to step 206, and if the short training mode is not set in step 206, the line distortion correction coefficient is raised again (step 207). If the short training mode is set in step 2.7, reception is restarted using the already held line distortion correction coefficient and timing as they are (step 208).

However, if it is not determined to be a training signal in step 203, for example if the beginning of the low-speed signal is a flag as shown in FIG. The line distortion correction unit 18 then corrects the correction coefficient (step 204) and generates received data (step 205). For this reason, the correction coefficient of the line correction section 18 of the modem shown in FIG. 2 deviates from the optimum value for the modem signal in the high speed mode. In this case, since the correction coefficient is not the optimum value, the high-speed image signal starting with the next short training cannot be received correctly.

In addition, if low-speed mode reception is detected separately from high-speed mode, is it possible to immediately switch the modem to low-speed mode? In this case, the problem is that a detector to detect low-speed mode signals will be added. occurs.

(Problems to be Solved by the Invention) As mentioned above, in the conventional facsimile modem receiver,
When a low-speed procedure signal is received in the high-speed mode due to a momentary interruption or the like, there is a problem in that the correction coefficient of the line distortion correction section deviates from the optimum value for the modem signal in the high-speed mode.

Therefore, the present invention was made in view of the above-mentioned problems.
Even if a low-speed procedure signal is received in a high-speed mode, the correction coefficient for the high-speed mode is retained and the lever correction coefficient is used to start receiving a high-speed image signal starting with the short training that will be sent later. The purpose is to provide a facsimile modem receiver that can.

[Structure of the Invention] (Means for Solving the Problem) A facsimile modem that retains a line distortion correction coefficient formed at the time of starting training and uses the held line distortion correction coefficient to shorten the time for starting the next training. In the receiver, a received signal detection section that detects a received signal, a timer that measures a predetermined time after detecting the received signal, and a detection means that detects whether the received signal is a training signal; The present invention is characterized by comprising means for making a predetermined correction of the line distortion correction coefficient in response to the measurement of a predetermined time by the timer when the detection means detects that the signal is not a training signal.

(Function) In the facsimile modem receiver of the present invention, the timer starts timing upon reception of the received signal, and further detects whether or not the received signal is a training signal. A predetermined correction of the line distortion correction coefficient is performed in response to the measurement of a predetermined time by the timer.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a basic block diagram of a facsimile modem receiver according to the present invention, which is the same as that shown in FIG. 8 with a timer 17 added thereto.

FIG. 2 is a flowchart related to FIG. 1.

Hereinafter, the configuration and operation of the present invention will be explained with reference to FIGS. 1 and 2.

When receiving a low-speed signal while in high-speed mode, the receiving modem first determines that there is a multiplied signal by the received signal detection section 16 shown in FIG. 1, as shown in the flowchart of FIG.
The timer 17 is started (step 101). Then, this signal is demodulated by the demodulator 9 in step 10.
2) The training detection unit 15 detects whether or not this demodulated signal is a training signal (step 103). If it is detected that the signal is a training signal, the process moves to step 108, and it is determined whether the short training mode is set (step 1).
07). If the settings have been made in step 107, reception is resumed using the line distortion correction coefficient and timing formed during modem training and already held (step 109). If it is detected in step 103 that it is not a training signal (step 1o3), correction of the line distortion correction coefficient is stopped while the timer 17 started in step 101 measures a predetermined time (step 1o4). Then, when the predetermined period of time has elapsed, the timer 17 stops, and at this time the line distortion correction section 18 corrects the correction coefficient (step 1.05) and generates received data (step 106). Therefore, the line distortion correction coefficient of the line distortion correction unit 18 of the facsimile modem receiving unit is necessary for high-speed training because the high-speed correction coefficient is not corrected during the time when low-speed signals (for example, MPS, etc.) are being received. Therefore, the high-speed image signal starting with the subsequent short training can be correctly received.

In addition, low-speed procedure signals such as the MPS, etc.
From the contents of the T recommendation, it will be 1.5 seconds or less, so timer 1
The setting (time measurement) time in step 7 may be set to 1.5 seconds or less. In addition, if there is a momentary interruption of the constraint data as shown in Figure 6 above, line distortion coefficient correction starts after the line distortion coefficient is maintained for 145 seconds, but the line distortion coefficient becomes large in about 1.5 seconds after the momentary interruption. There is no change in the signal, so there is no problem with reception.

FIG. 3 is a detailed block diagram of one embodiment of the facsimile modem receiver of the present invention.

In Fig. 3, high-speed transmission data is converted into an analog waveform through a scrambling section 1, a mapping section 2, a modulation section 13, and a D/A converter 4 of the transmitting modem, and a low-pass filter (LPF) 5 cuts off unnecessary bands. Send to network telephone line. In the receiving modem, the necessary band is extracted from this line signal using a band pass filter (BPF) 6, and the necessary band is extracted from the line signal, and then the necessary band is extracted from the line signal using an automatic gain control circuit (AGC).
)7, the amplitude is optimized, the A/D converter 8 converts it into a digital signal, the demodulator 9 demodulates it with a carrier carrier to make a bestband signal, and the automatic equalizer 10 corrects the group delay distortion of the line. The phase control unit 11 corrects the phase rotation,
This signal is determined by the code determination unit 12 in the signal space and a corresponding code is assigned to it as high-speed reception data. In the above process, the correction coefficient corresponding to line distortion is corrected by feeding back the error in the signal space between the judgment result of sign judgment unit 2 and the signal before judgment to the phase control unit 11 and automatic equalizer 10. ing.

In this embodiment, the output of the received signal detection unit 16 used for AGC 7 control is used as the start signal of the timer 17, and the detection signal of the training detection unit 15 and the carry of the timer 17 are sent to the phase control unit 11 and the automatic equalizer 10. By inputting the signal, if the signal is not training, the coefficients of the automatic equalizer 10 and the phase control unit 15 are held so as not to be corrected until the timer reaches a certain value after starting to receive the signal.

Note that the received signal detection section 16 that outputs the start signal of the timer 17 is not limited to a signal detection section for controlling the AGC 7.

[Effects of the Invention] As explained above, according to the facsimile modem receiver of the present invention, when a low-speed procedure signal is received in the high-speed mode, the high-speed procedure signal is not transmitted during the time when the low-speed mode signal is being received. Since the line distortion correction coefficient is not modified, the line distortion correction coefficient necessary for high-speed training is not destroyed, and therefore the high-speed image signal starting with the subsequent short training can be correctly received.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the facsimile modem receiver of the present invention, FIG. 2 is a flowchart related to FIG. 1, FIG. 3 is a detailed block diagram of the facsimile modem receiver of the present invention, and FIG. is an example of a facsimile communication procedure; FIGS. 5, 6, and 7 are reception timing charts in a facsimile modem receiver; FIG. 8 is a block diagram of a conventional facsimile modem receiver; and FIG. 9 is a block diagram of a conventional facsimile modem receiver. It is a flowchart concerning. 9... Demodulation section, 15... Training signal detection section,
16... Received signal detection section, 17... Timer 18.
...Line distortion correction section. 4

Claims (1)

[Claims] In a facsimile modem receiver that holds a line distortion correction coefficient formed at the time of training start-up and uses the held line distortion correction coefficient to shorten the next training start-up time, the received signal is a received signal detection section for detecting; a timer for measuring a predetermined time after detecting the received signal; a detection means for detecting whether the received signal is a training signal; A facsimile modem receiver comprising means for, when detected, making a predetermined correction of a line distortion correction coefficient in response to timing of a predetermined time by the timer.