JPH03285446A - Data transmitter - Google Patents

Abstract

PURPOSE:To execute data transmission without fail while correctly deciding the OFF of a procedure signal at all times by deciding a threshold value based on the signal level of one procedure signal to be received first and deciding the OFF of the procedure signal according to the threshold value. CONSTITUTION:When an operator executes a prescribed call originating operation, a call is originated to a called party and the reception of a CED signal is monitored. When the reception of the CED signal is detected, the level of the received signal detected by an absolute level detection circuit 422h is set to a reference value memory 422j. When the frame data is outputted from a demodulation circuit 422e, the reception of the procedure signal is decided and next, the OFF of the procedure signal is monitored. When the signal level detected by the absolute level detection circuit 422h is reduced only for a fixed level such as 3dB, for example, in respect to the signal level set to the reference value memory 422j, a signal OFF decision circuit 422i decides the OFF of the procedure signal under reception and a prescribed signal is transmitted according to already known transmission control procedures.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data transmission apparatus, such as a facsimile machine, which transmits data according to a fixed transmission control procedure.

[Prior Art] A commonly used G3 facsimile machine, for example,
Image information is transmitted using a transmission control procedure that complies with CCITT Recommendation T.30.

In this transmission control procedure, the transmitting side and the receiving side are, for example, C
The transmitting side transmits image information at a predetermined time point while exchanging various procedural signals such as ED, DIS, and DC5 in a fixed procedure.

In order to execute such a transmission control procedure, the transmitter and receiver must correctly determine whether the procedure signal is off (signal disconnection) when receiving various procedure signals from the other party, and then The specified transmission operation must be executed at

Conventionally, when determining whether a procedure signal is off after receiving it, the energy level of the procedure signal being received is detected, and when the energy level drops below a certain threshold, the procedure signal is determined to be off. I was judging.

In this case, the threshold value, which is a signal level, is fixedly set in advance by hardware or a switch operation by a service person.

[Problems to be Solved by the Invention] By the way, a certain amount of noise occurs in transmission lines such as telephone lines. If the energy level of this noise exceeds the threshold value, the noise will be detected as a signal, making it impossible to determine whether the procedure signal is off.

That is, now, as shown in FIG.
Bu+).

In this case, the noise level is the above threshold L (dBil
), for example, in dBm, it is possible to correctly determine whether the procedure signal is off. In this case, S/
The N ratio is X (dB).

By the way, in general, in a telephone line, the reception level of the signal transmitted from the other party changes depending on the area of one communication destination and the detour state of the connection ring.

Therefore, for example, when the received signal level becomes high as shown in FIG. 82, the S/N ratio becomes X(
dB), the noise level exceeds the threshold L (dBm) such as N2, making it impossible to determine whether the procedural signal is off.

In this way, conventionally, even if the S/N ratio is constant, when the noise level is high, it has not been possible to determine whether the procedural signal is off. Therefore, there is a problem in that a predetermined transmission control procedure is interrupted and data transmission cannot be executed.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a data transmission device that can always correctly determine whether a procedure signal is off and reliably execute data transmission if a certain S/N ratio is obtained. shall be.

[Means for Solving the Problems] To this end, the present invention includes means for detecting the signal levels of various received procedure signals, and after communication starts, the first step signal is detected based on the signal level of the first received procedure signal. When the signal level of each received procedure signal falls below the threshold, it is determined that the procedure signal is off, and predetermined various signals are transmitted to execute the transmission control procedure. It is characterized by the following.

[Function] Since the threshold value for determining whether the 1-procedure signal is off is changed according to the actual reception level of the procedure signal after communication starts, if a certain S/N ratio is obtained, noise can be detected as a received signal. This can be prevented. 1 by this number
It becomes possible to always correctly determine whether the procedure signal is off and to reliably execute data transmission.

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

FIG. 1 shows a block diagram of a facsimile machine according to an embodiment of the present invention. In the figure, a scanner 1 reads an original image and extracts image information, and a plotter 2 records the image on recording paper. The encoding/decoding unit 3 encodes image information to be transmitted for data compression, and decodes received image information to reproduce the original image information.

The modem 4 transmits image information and procedure signals for transmission control. The high-speed modem 41 transmits and receives image information using various modulation methods in accordance with CCITT Recommendations 1/27ter and V29, and the low-speed modem 4
2 transmits and receives the above procedure signal in accordance with Recommendation V.21. The network control device 5 is connected to the @call line and controls the line when a call is made or received.

The operation display section 6 includes a display and operation keys, and displays the operating status of the device, and is used by the operator to perform various operations.

The CPU 7 controls each part mentioned above, and the ROM 8
It stores the control program and various fixed data. Further, the RAM 9 temporarily stores various data, and the system bus 10 is a signal line through which the above-mentioned units exchange various data and control signals between each other.

FIG. 2 shows the configuration of the receiving side circuit of the low-speed modem 42. In FIG. 1, the received signal from the network control device 5 is input to a tone detection circuit 422a and a filter 422b. The tone detection circuit 422a detects tone signals such as CHD signals.

Filter 422b removes unnecessary signals, and its output is input to variable gain amplifier 422c. The output of the variable gain amplifier 422C is input to an A/D (analog/digital) conversion port J1422d.

The A/D conversion circuit 422d converts the input signal into a PCM signal, and its output is input to a demodulation circuit 422e that reproduces received data, an AGC control circuit 422f, and an energy detection circuit 422g.

The AGC control circuit 422f is a variable gain amplifier 422c.
It automatically controls the gain of the variable gain amplifier 422c and absolute level detection times! 4422h is input. The energy detection circuit 422g is A/
It detects the energy level of the output signal of the D conversion circuit 422d, and its output is sent to the absolute level detection circuit 422h.
has been entered.

The absolute level detection circuit 422h detects the absolute level of the received signal, and its output is sent to the signal off determination circuit 42.
21 and the reference value memory 422j. The reference value memory 422j holds the signal value of the input signal, and its output is input to the signal off determination circuit 4221.

The signal off determination circuit 4221 determines whether the 1-procedure signal is off. The signal off determination circuit 422i.

Each output of the tone detection circuit @422a and the demodulation circuit 422e is input to the CPU 7. Further, a control signal is input from the CPU 7 to the reference value memory 422j.

With the above configuration, the transmission side operation of the facsimile apparatus of this embodiment will be explained first.

This facsimile machine makes a call to the other party when a predetermined call operation is performed by an operator.

When the other party responds, the C
Monitor reception of HD signals (N loop of process 101)
.

The receiving facsimile machine first transmits a CED signal and a DIS signal, as shown in FIG.

On the transmitting side, these signals are received by a low speed modem 42. Within the low speed modem 42, a tone detection circuit 422a detects the CED signal. Further, the filter 422b removes unnecessary band components of the received signal, and the variable gain amplifier 422c amplifies the signal. A/D conversion circuit 4
22d converts the amplified signal into a PCM signal.

The demodulation circuit 422e demodulates this PCM signal and reproduces it as received data.

The AGC control circuit 422f also controls the variable gain amplifier 4 to keep the energy level of the PCM signal constant.
Adjust the gain of 22c. Energy detection circuit 422
g detects the energy level of the PCM signal.

The absolute level detection circuit 422h detects the absolute value of the energy level of the received signal based on the detected energy level and the output of the AGC control circuit 422f.

In the above, when reception of a CHD signal is detected (Y in process 101), the level of the received signal detected by the absolute level detection circuit 422h is set in the reference value memory 422j (process 102). Then, reception of the next procedure signal is monitored (N loop of process 103).

When various procedure signals are received, predetermined frame data is output from the demodulation circuit 422e. Demodulation circuit 422
When the frame data is output from e, it is determined that the procedure signal has been received (Y in process 103), and then the off state of the procedure signal is monitored (loop N in process 104). That is, the signal off determination circuit 4221 determines whether the signal level detected by the absolute level detection circuit 422h is the same as the signal level detected by the absolute level detection circuit 422h.

When the signal level set in the reference value memory 422j decreases by a certain level, for example, 3 dB, it is determined that the procedure signal being received is turned off.

In this way, when it is determined whether the procedure signal is off (processing 1
04 Y), a predetermined signal is transmitted according to a known transmission control procedure (processing 1o5).

In this example, since the DIS signal is received in the above, 1
Next, send the DC5 signal and TC5 signal.

Then, when the transmission is finished, it is determined whether the communication has ended or not (process 106), and if the communication has not ended (process 10
(N of 6), the above process is repeated (to process 103).

In this way, when a CFR signal is received from the receiving side next time, the image information is transmitted as an EOP signal, and when an MCF signal is received, a DCN signal is transmitted.

When the predetermined communication procedure is thus completed (Y in process 106), the above-described transmission operation is ended.

As described above, in this embodiment, the reception level of the first received CHD signal is stored, and when various procedure signals are received thereafter, the detected signal level is constant with respect to the stored signal level. When only the level drops,
It is determined that the procedure signal is turned off.

Generally, on a telephone line, the reception level of the procedure signal changes for each communication. However, in this embodiment, as described above, depending on the reception level at that time.

The reception level threshold for determining whether the procedure signal is off is changed. Therefore, if there is a certain S/N ratio, it is possible to prevent noise from being detected as a received signal. This makes it possible to always accurately determine whether the procedure signal is turned off and to reliably execute data transmission.

In the above embodiment, the signal level that is a certain level lower than the first detected signal level is used as the threshold to determine whether the signal is off in one step. It goes without saying that the threshold value may be calculated by performing a certain calculation.

Further, although the explanation has been given by taking the transmitting side of facsimile communication as an example, the present invention can be similarly applied to determining whether a procedure signal is off on the receiving side. Furthermore, it is also possible to apply the present invention not only to procedural signals but also to determining whether to turn off data signals that transmit image information.

Furthermore, the present invention can be widely applied not only to the transmission of procedural signals, signals, and image information of facsimile machines, but also to data transmission devices that exchange various procedural signals.

[Effect of the invention] As described above, according to the present invention, after communication starts.

The threshold value is determined based on the signal level of the first procedural signal received, and when various procedural signals are received, the off-state of the procedural signal is determined based on the threshold value. If the N ratio is obtained, it is possible to prevent noise from being detected as a received signal, so that it is possible to always correctly determine whether the procedure signal is off and to reliably execute data transmission.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a facsimile machine according to an embodiment of the present invention, Fig. 2 is a block diagram of a receiving side circuit of a low-speed modem, Fig. 3 is an operation flowchart of the transmitting side, and Fig. 4 is a transmission control diagram. FIG. 5 is an explanatory diagram illustrating an example of the procedure, and FIG. 5 is an explanatory diagram illustrating conventional problems when determining whether a received signal is turned off. DESCRIPTION OF SYMBOLS 1... Scanner, 2... Plotter, 3... Encoder/decoder, 4... Modem, 5... Network control device, 6...
...Operation display section. 7-CPU, 8-ROM, 'J-RAM, 10-'i stem bus, 41... high speed modem, 42... low speed modem, 422a... tone detection circuit, 422b...
・Filter, 422c...Variable gain amplifier, 422
d...A/D conversion circuit, 422e...Demodulation circuit, 4
22f...AGC control circuit, 422g...Energy detection circuit, 422h...Absolute level detection circuit, 4
221...Signal off determination circuit, 422j...Reference value memory.

Claims (1)

[Claims] (1) In a data transmission device that performs data transmission by receiving various procedure signals transmitted from the other party and transmitting various signals after the received procedure signals are turned off, according to a certain predetermined procedure, signal level detection means for detecting signal levels of various procedure signals received; threshold determining means for determining a signal level threshold based on the signal level of one procedure signal received first after communication starts; a procedure signal off determination means for determining that the procedure signal is off when the signal level drops below the threshold when receiving the various procedure signals; and transmitting the various signals after determining that the procedure signal is off. 1. A data transmission device comprising: transmission control procedure execution means.