JPH07131545A - Modem control method for facsimile - Google Patents

Abstract

PURPOSE:To prevent the error of the demodulated data due to the level change of a received signal by interrupting the switching of gains while the data signal of the picture information is received. CONSTITUTION:A modem 4 detects the level of a received signal and reports this detected level to a system control part 7. The part 7 calculates the proper gain value based on the reported signal level and when this level is stabilized. Then the part 7 sets this gain at the modem 4. A prescribed receiving action is carried out and the data signal of the picture information is received from the opposite party. Under such conditions, the modem 4 amplifies the received signal based on a set fixed gain and demodulates the data signal into the compressed data. The part 7 sends the compressed data to conding/decoding part 3 for decoding and transfers the reproduced picture information to a plotter 2 to record the received images. Thus, it is possible to prevent the error of the demodulated data caused by the level change of the received signal in a reception mode of the data signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a facsimile modem control method suitable for a CCITT G3 (group 3) standard facsimile apparatus.

[0002]

2. Description of the Related Art FIG. 8 shows a conventional example of a receiving circuit of a G3 facsimile modem.

When the facsimile machine executes a receiving operation, the filter section a of the receiving circuit removes unnecessary band components of the received signal. The variable gain amplifier b amplifies the received signal. The A / D converter c converts the amplified received signal into a digital signal with. The AGC unit d adjusts the reception signal converted into a digital signal to a constant signal level.

When the received signal is a transmission control procedure signal, the low-speed modem e demodulates the procedure signal. The high-speed modem f, when the received signal is a data signal such as image information,
The data signal is demodulated. Then, the system control unit (not shown) executes a predetermined operation according to each demodulated information.

As shown in FIG. 9, the variable gain amplifier b has a function of stepwise switching the gains A1, A2, ... At fixed wide intervals. on the other hand,
The AGC unit d has a function of continuously changing the gain within a fixed range.

At the time of the receiving operation as described above, the variable gain amplifier 2 and the AGC 4 are operated according to the signal level of the received signal.
An appropriate gain is set for each of and. As a result, the received signal is adjusted by the variable gain amplifier 2 to a signal level within a certain range, and is further finely adjusted by the AGC unit 4 to a certain level suitable for input to the low speed modem demodulation unit 5 and the high speed modem demodulation unit 6. It

As described above, the gain of the receiving circuit is adjusted in two steps by the variable gain amplifier b and the AGC circuit d to adjust the level of the received signal.

Further, conventionally, such level adjustment of the received signal has been continuously executed during the operation of receiving the data signal. As a result, even if the received signal level fluctuates during communication, the gain of the receiving circuit is adjusted according to the change to maintain a proper receiving state.

When adjusting the gain of the receiving circuit, if the adjustment range of the AGC section d is exceeded, the gain of the variable gain amplifier b will be switched. Even if the level fluctuation of the received signal is small, such a state occurs depending on the initial gain setting state.

[0010]

By the way, when the gain of the variable gain amplifier 2 is switched, the level of the reception signal passing through the reception circuit changes temporarily, and thereafter,
The AGC unit d operates so as to finely adjust to an appropriate gain.
In this case, it takes some time for the gain to be finely adjusted to stabilize the circuit operation.

Conventionally, even while receiving a data signal of image information,
When the level of the received signal fluctuates, the gain of the variable gain amplifier 2 is switched. Therefore, at the time of this gain switching, there is a problem that the operation of the high-speed modem demodulation unit f becomes temporarily unstable and a data error is likely to occur in the demodulated image information.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a control method of a facsimile modem capable of preventing an error in demodulated data due to a change in received signal level.

[0013]

To this end, according to the present invention, when an image is received, an appropriate gain is provided to an amplifier for stepwise adjusting the received signal level before starting to receive a data signal of image information. The gain is set so that the gain is not switched while the image information data signal is being received.

[0014]

As a result, it is possible to prevent the occurrence of an error in the demodulated data due to a change in the received signal level during reception of the data signal.

[0015]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a facsimile apparatus according to the first embodiment of the present invention. In the figure, a scanner 1 reads a document image, and a plotter 2 records and outputs a received image. The encoding / decoding unit 3 compresses the image information to be transmitted, while
The received data is restored to the original image information.

The modem 4 transmits a procedure signal for transmission control and modulates and demodulates image information and transmits it. The communication procedure in this case is CCITT recommendation T.264. Thirty
Comply with. Further, the procedure signal is based on Recommendation V. 21 according to the specifications of V.21. 29 or V.I. 27te
It transmits with the specification of r.

The network control device 5 executes predetermined line control when making and receiving a telephone line. Operation display section 5
Indicates that the operator performs various operations and the device displays an operating state and the like. The system control unit 7 is a microphone computer that monitors and controls the above units.

FIG. 2 shows a block diagram of the receiving circuit in the modem 4. In the figure, a filter section a removes unnecessary band components from the received signal. The variable gain amplifier b has a function of switching the gain stepwise at wide constant intervals. This gain is set by the system controller 7. The A / D conversion c converts the received signal into a digital signal. The variable gain amplifier b and the A / D conversion c are configured in the AFE (analog front end) section of the modem 4. The AFE unit is a circuit unit that processes an analog signal.

The AGC section d detects the level of the received signal and continuously adjusts the received signal to a constant signal level. The detected signal level is notified to the system control unit 7. Low speed modem e
Is for demodulating the procedure signal. High speed modem f
Is for demodulating a data signal of image information. AGC
The section d, the low-speed modem e and the high-speed modem f are configured in the DSP (digital signal processor) section of the modem 4. The DSP unit is a circuit unit that processes digital signals.

Next, a first embodiment of the receiving operation of the facsimile apparatus having the above configuration will be described.

Now, assume that an incoming call is made from another facsimile machine. Then, as shown in FIG. 3, this facsimile machine first connects the line in response to the incoming call (process 10).
1) First, a predetermined constant gain is set in the variable gain amplifier b as an initial value (process 102). And
A known transmission control with the other party is started (process 103).

That is, as shown in FIG.
The D signal is transmitted and the DCS signal is received from the other party.
After this, the modem training signal and the TCF (training check) signal are received. In this case, in the modem 4, the received signal passes through the filter unit a and the unnecessary band component is removed. Then, it is amplified by the variable gain amplifier b and converted into a digital signal by the A / D conversion c. Then, the signal level is adjusted by the AGC section d and input to the low speed modem e and the high speed modem f. The low speed modem e is D
Demodulate procedure signals such as CS signals. The high speed modem f
It receives a modem training signal to perform a predetermined training operation or demodulates a TCF signal.

In this embodiment, after the transmission control is started, the reception of the modem training signal is monitored (N loop of the process 104). Then, when the reception of the modem training signal starts (Y in process 104), the AGC unit d detects the reception signal level at that time and notifies the system control unit 7 of the detection result. The system control unit 7 calculates the value of the proper gain to be set in the variable gain amplifier b based on the notified signal level (process 105).

Thereafter, it is monitored whether the received signal level is stable for a certain period of time (process 106). If the received signal level is unstable and fluctuates (N in process 106), the appropriate gain is recalculated (to process 105).

When the received signal level is stable (Y in step 106), the system controller 7 sets the calculated appropriate gain in the variable gain amplifier b (step 10).
7).

After that, a predetermined receiving operation is executed. That is, the bit error of the demodulated data obtained by demodulating the TCF signal is checked. Here, if the bit error is equal to or less than the specified value, the CFR signal is transmitted to notify the other party of the successful training.

As a result, the data signal of the image information is transmitted from the other party. In this case, the variable gain amplifier b amplifies the received signal with the set constant gain. If the transmission image has multiple pages, repeat the transmission control
Although the data signal of each page is received multiple times, it is received with a constant gain until the end without switching the gain in the middle. The high speed modem f demodulates the data signal into compressed data. The system control unit 7 transfers the compressed data to the encoding / decoding unit 3 for decoding and reproduces the original image information. Then, the reproduced image information is transferred to the plotter 2 and the received image is recorded. In this way, the image to be transmitted is received.

As described above, in this embodiment, an appropriate gain is set in the variable gain amplifier b before starting to receive the image information data signal, and thereafter the set gain is not switched.

In the high speed modem f, if the gain of the variable gain amplifier b is switched during the reception of the data signal, the operation may become temporarily unstable and an error may occur in the demodulated data. Then, since the gain is not switched during the reception of the image information, it is possible to prevent the occurrence of the data error of the image information due to the level fluctuation of the received signal.

Further, the gain setting of the variable gain amplifier b is executed during the reception of the modem training signal. Like the image information data signal, the modem training signal is a signal for the high-speed modem f to perform a demodulation operation, so that an appropriate gain required when receiving the image information data signal can be easily set. .

In the above embodiment, the gain of the variable gain amplifier b is set during the reception of the modem training signal, but it may be set during the reception of the TCF signal. Even in that case, the occurrence of a data error while receiving image information can be similarly prevented.

Next, the second receiving operation of the facsimile apparatus will be described.
An example will be described.

The operation of this embodiment is a training check operation executed when a TCF signal is received.

FIG. 5 shows this training check operation. That is, in this embodiment, during the receiving operation,
As described with reference to FIG. 3, an appropriate gain is set in the variable gain amplifier b based on the reception level of the modem training signal (process 201). Then, after waiting until a predetermined time point (process 202), a check operation of data demodulated from the TCF signal is started (process 203).

The time when the data check is started is shown in FIG.
As shown in (a), when the gain is set in the variable gain amplifier b during reception of the modem training signal, T
This is the time when a certain time T has elapsed from the start of receiving the CF signal. Further, as shown in (b) of the figure, when the gain is set in the variable gain amplifier b after the TCF signal reception is started, it is a time point when a predetermined time T has elapsed from the gain setting time point.

When the gain is set in the variable gain amplifier b,
Although the circuit operation temporarily becomes unstable, the training check operation can be correctly executed by checking the demodulated data after the elapse of the fixed time T as described above.

Next, the third receiving operation of the facsimile apparatus will be described.
An example will be described.

FIG. 7 shows the operation of the facsimile apparatus of this embodiment. That is, when the facsimile machine receives an incoming call, the line is connected (process 3) as in the above-described embodiment.
01), an initial value is set in the variable gain amplifier b (process 3
02), transmission control is started (process 303).

In the present embodiment, thereafter, the reception of the DCS signal is monitored (N loop of processing 304), and when the reception of the DCS signal is started (Y of processing 304), the received signal level of the DCS signal is detected. The proper gain of the variable gain amplifier b is calculated (process 305). Then, it is monitored whether the received signal level is stable for a certain period of time (process 30).
6). Here, if there is a level change (N in process 306), the appropriate gain is recalculated (to process 305).

When the signal level of the DCS signal is stable (Y in process 306), the process waits until the signal turns off (N loop in process 307). Then, when the DCS signal is turned off (Y in process 307), the calculated appropriate gain is set in the variable gain amplifier b (process 308).

Thereafter, the gain of the variable gain amplifier b is not switched, and the receiving operation is executed to the end as in the above-mentioned embodiment.

As described above, even when the variable gain amplifier b is set to an appropriate gain when receiving the procedure signal for transmission control, the same effect as the above-described embodiment can be obtained.

Since the gain setting is executed when the procedure signal is turned off, the procedure signal can be stably received. Further, in this case, since the gain of the variable gain amplifier b is not switched during reception of the modem training signal or the TCF signal, those signals can also be received stably.

In the above embodiment, the basic communication procedure of transmitting and receiving the CED signal and the DCS signal at the start of the facsimile communication has been described as an example, but the NSF signal and the NS
It goes without saying that, when transmitting and receiving the S signal, the gain setting of the variable gain amplifier b may be executed when receiving the NSS signal.

Although the above embodiments have been described by taking facsimile communication as an example, the present invention may be applied to other modem communication for transmitting data while executing transmission control.

[0047]

As described above, according to the present invention, before starting the reception of the image information data signal, an appropriate gain is set in the amplifier for adjusting the received signal level stepwise, and the image information data signal is set. Since the gain is not switched during reception, it is possible to prevent an error in the demodulated data due to a change in the received signal level.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a facsimile apparatus according to a first embodiment of the present invention.

FIG. 2 is a block configuration diagram of a receiving circuit of a modem.

FIG. 3 is a flowchart of a receiving operation which is the first embodiment of the operation of the apparatus.

FIG. 4 is an explanatory diagram showing a communication procedure.

FIG. 5 is a flowchart of a training check operation that is the second embodiment of the device operation.

FIG. 6 is an explanatory diagram of a waiting time during the training check operation.

FIG. 7 is a flowchart of a receiving operation which is a third embodiment of the operation of the device.

FIG. 8 is a block diagram of a receiving circuit of a conventional modem.

FIG. 9 is an explanatory diagram showing a gain setting method by a variable gain amplifier and an AGC unit.

[Explanation of symbols]

 1 Scanner 2 Plotter 3 Encoding / Decoding Section 4 Modem 5 Network Control Device 5 Operation Display Section 7 System Control Section a Filter Section b Variable Gain Amplifier c A / D Conversion d AGC Section e Low Speed Modem f High Speed Modem

Claims (5)

[Claims] 1. A signal level stepwise adjusting means for adjusting the received signal to a signal level within a fixed range by switching the gain of an amplifier for amplifying the received signal in a stepwise manner, and the received signal within the fixed range is further fixed level. In a method of controlling a facsimile modem, which comprises a signal level continuous adjusting means for adjusting the signal level to a constant level and a demodulating means for demodulating a data signal adjusted to a constant level, the signal level stepwise adjusting means at the time of image reception. Is a method for controlling a facsimile modem, wherein an appropriate gain is set in the amplifier before starting to receive the image information data signal, and the gain is not switched while the image information data signal is being received. 2. The method for controlling a facsimile modem according to claim 1, wherein the gain setting for the amplifier is executed when a modem training signal or a training check signal is received. 3. When the training check signal is demodulated and the bit error of the demodulated data is checked, the check operation is started after a certain time or more has elapsed from the time when the gain was set. 2. A method for controlling a facsimile modem as described in 2. 4. The method for controlling a facsimile modem according to claim 1, wherein the setting of the gain for the amplifier is executed when a procedure signal for transmission control is received. 5. The gain setting for the amplifier is 1
5. The method of controlling a facsimile modem according to claim 4, wherein the method is executed at the end of reception of one procedure signal.