JP2662032B2 - Communication method using modem - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem device, in particular, to perform an optimum equalization process according to the state of a line at the time of data communication when receiving a signal, and to receive a signal at the other end when transmitting a signal. The present invention relates to a communication method using a modem capable of easily determining a signal level.

2. Description of the Related Art In recent years, various types of data communication devices such as facsimile devices have become widespread. The receiver receives delay time distortion and amplitude distortion due to a line or the like, which causes distortion or an error in the demodulated signal on the receiver side. The line may pass through the carrier line many times depending on the distance or route to the partner device, and the length of the subscriber line is not constant, and the delay time distortion and the amplitude distortion change corresponding to the partner difference.

Therefore, conventionally, this type of device has been equipped with an automatic equalizer in a modem device to automatically correct various types of distortion occurring on a line. As a conventional example of such a modem device, there is, for example, one shown in Japanese Patent Application Laid-Open No. 58-151172 or one shown in FIG. This fifth
A modem device 1 shown in FIG. 1 includes an analog unit 3 connected to a line 2 for receiving an analog image signal input from the line, and a cable equalizer for receiving a signal from the analog unit 3 and performing an equalization process on the signal. 4 and a signal processing unit 5 that performs modulation or demodulation processing on the signal equalized by the cable equalizer 4 and outputs data of the modulated or demodulated image signal to the control line 6 and the data line 7, respectively. And a modem control unit 8 for transmitting and receiving data to and from the signal processing unit 5 via the signal line 6 and the data line 7. The cable equalizer 4 has fixed constants such as an equalization rate, and corrects the distortion of the received signal.

However, in such a conventional modem device, since the constant in the cable equalizer 4 is fixedly set, when an image signal is received from the transmitting terminal, the image signal is transmitted. It is sufficient that the deterioration corresponds to the equalization rate, but otherwise, the equalization processing in the modem device is not properly performed, and the image quality of the received and recorded image may be seriously deteriorated.

Also, in the technique shown in the above-mentioned document, a point that a plurality of equalizers (equalizers) are provided to change a correction method according to the degree of various distortions is new, but a plurality of equalizers are used. Therefore, there is a problem in that the apparatus itself becomes expensive because of the necessity of providing.

Also, when transmitting a signal, a signal for determination having two spectrums, usually called training, is added before the image signal, and this signal is made to be determined by the partner apparatus. As is clear from FIG. 6, since each is a signal in an extremely narrow frequency band, there is a problem that it is difficult for the receiving apparatus to make a difference in level.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to use a modem for reliably correcting signal deterioration when communication is performed from a transmission device to a reception device and performing reliable communication. It is to realize the communication method used.

Means for Solving the Problems In order to achieve the above object, the present invention provides a communication method using a transmitting device and a receiving device, wherein a training signal and a data signal are transmitted from the transmitting device in a predetermined frequency band. A spectrum signal having a constant gain amount is output at the receiving device, and a correction value for correcting the attenuation is determined based on the attenuation of the spectrum signal, and is communicated after the spectrum signal based on the correction value. The training signal and the data signal are corrected.

When a signal is transmitted, a spectrum signal having a constant gain in a predetermined frequency band is generated prior to the transmission of the data signal, and this signal is added before the training signal and output from the transmitting device. Before receiving the training signal, it receives a spectrum signal having a constant gain amount in a predetermined frequency band, sets a correction value for correcting the attenuated spectrum signal, and sets a correction value of a data signal to be communicated thereafter based on the correction value. The correction is performed.

Embodiment FIGS. 1 to 4 are diagrams showing an embodiment of a modem device according to the present invention and a circuit for detecting a cable equalizer level used in the embodiment.

A modem device 11 according to this embodiment includes an analog unit 13 connected to a line 12 for receiving an analog image signal input from the line 12, and a cable for receiving a signal from the analog unit 13 and performing an equalization process on the signal. With equalizer 14,
A signal processing unit 15 that performs modulation or demodulation processing on the signal that has been equalized by the cable equalizer 14, and outputs the data of the modulated or demodulated image signal to the control line 16 and the data line 17, respectively. Signal line 16 and data line
It comprises a modem control device 18 for transmitting and receiving data to and from the signal processing unit 15 via the signal processing unit 17, a level detection circuit 19, and a signal generation circuit 20 as signal generation means.

The level detection circuit 19 has a role as a cable equalizer level detection unit that detects a cable equalizer level for an input signal from the analog unit 15 and outputs the detection result to the signal processing unit 15. This level detection circuit 19
As shown in FIG. 2, the band-pass filters 21 and 22 that perform a filter operation in a high-frequency band or a low-frequency band of an input signal from the analog section 13 and output signals from these band-pass filters 21 and 22 A comparison circuit 23 for comparing and detecting deterioration of the input signal. Of the band-pass filters 21 and 22, for example, the band-pass filter 21 performs a filter operation in a high-frequency band, and
Reference numeral 22 performs a filtering operation in a low frequency band.

The signal generation circuit 20 generates a random signal in a spectrum flat band as shown in FIG.

The operation of the modem device having such a configuration will be described below.

At the time of signal reception, an image data signal (including a training signal, which is an analog signal) a that has passed through the line 12 is taken into the modem device by the analog unit 13, and first, in the initial stage, the analog signal is received. The signal output from the section 13 is input to the level detection circuit 19 via the signal line f. In this level detection circuit 19, the input signal is
The signal is input from the signal line f to the band-pass filter 21 for the high-frequency band and the band-pass filter 22 for the low-frequency band. The output of the band-pass filter 21 is connected to the signal line h, and the output of the band-pass filter 22 is connected to the signal line i. Via the comparison circuit 23
Is input to In the comparison circuit 23, the signal level between the high frequency band component and the low frequency band component of the input signal is compared, the level difference between both frequency bands is detected, and the signal line g
And outputs level difference information as a comparison result. The signal processing unit 15 calculates a set value of the cable equalizer 14 based on the level difference information input through the signal line g, and outputs the value to the cable equalizer 14 via the signal line e. As a result, the cable equalizer 14 is set to the optimum equalization condition for the input signal from the line 12, and normal image signal receiving operation processing is performed under this condition. That is, during this image signal receiving operation, the image signal enters the analog section 13 from the line 12 and passes through the signal line c to the cable equalizer.
The signal is sent to the signal processing unit 15 through the signal line e.

Next, at the time of signal transmission, a spectrum flat random signal as shown in FIG. 3 is generated by the signal generation circuit 20 prior to transmission of the image signal, and is transmitted to the analog section 13 through the signal line b. . The random signal covers, for example, 300 Hz to 3400 Hz and has a gain of PdB. Then, after the random signal is transmitted from the modem device 11 (in this case, the device on the transmitting side), it is attenuated while passing through the line 12, and has a form as shown in FIG. The receiving device receives the attenuated random signal and determines the level from this signal. Although the random signal is attenuated, a signal covering 300 Hz to 3400 Hz is used, so that it is easy for the receiving apparatus to take a band pass as a whole, and the level can be determined correctly. When the receiving device has the same modem device as in the present embodiment, the setting of the cable equalizer in the receiving operation is automatically performed in the same manner as described above.

As described above, according to the present invention, a spectrum signal having a constant gain amount in a predetermined frequency band is transmitted before communication of a data signal and a training signal. By setting a correction value for correcting to restore the original value, and correcting the data signal transmitted and received thereafter with respect to this correction value, compared to detecting a determination signal having two spectra. In addition, the receiving device can easily determine the level of the input signal, and can effectively prevent the deterioration of the image quality of the recorded image when the data signal is received. Further, by sending the training signal prior to the training signal, the training signal can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a modem device according to the present invention, FIG. 2 is a block diagram showing a configuration example of a cable equalizer level detecting means used in the above embodiment, and FIG. 3 is used in the above embodiment. FIG. 4 is a diagram showing an example of a spectrum flat signal generated by a signal generating circuit, FIG. 4 is a diagram showing a state in which the signal shown in FIG. 3 is attenuated, and FIG. 5 is a configuration example of a conventional modem device. FIG. 6 is a block diagram showing a signal for level determination used in normal training. 11 ... Modem device, 12 ... Line, 13 ... Analog part, 14
…… Cable equalizer, 15 …… Signal processing unit, 16 …… Control line, 17 …… Data line, 18 …… Modem controller, 19 ……
Level detection circuit (cable equalizer level detection means), 20 ... Signal generation circuit.

Claims (1)

(57) [Claims] In a communication method using a transmitting device and a receiving device, prior to transmitting a training signal and a data signal from the transmitting device, a spectrum signal having a constant gain in a predetermined frequency band is output, A receiving device determines a correction value for correcting the attenuation based on the attenuation of the spectrum signal, and based on the correction value, a training signal communicated after the spectrum signal, and a data signal. Communication method using a modem.