JPH0715547A - Facsimile equipment - Google Patents

Abstract

PURPOSE:To improve the S/N and to obtain excellent reception data by measuring an incoming level of a signal with a signal arrived at first, attenuating the reception signal, including burst noise through the selection of a proper attenuation and suppressing only the noise component outside the dynamic range of a modem. CONSTITUTION:Upon the receipt of data, after a telephone line is connected, a CNG signal representing FAX transmission is received from an opposite transmitter at first. The CNG signal coming from a telephone line 6 is inputted to a level detector 3 via an attenuator 2 from a telephone line connection section 1. Upon the receipt of the CNG level, the attenuation of the attenuator 2 is set to 0dB. The detector 3 measures a reception signal incoming level by the CNG signal. An attenuator control means 5 adjusts the attenuation of the attenuator 2 so that an input level of a demodulator 4 reaches an upper limit when the input level of the demodulator 4 is more than the preset upper limit based on the result of measurement by the detector 3. In this case, burst noise (intermittent noise) is suppressed to the outside of a dynamic range of the demodulator 4 and the S/N is not deteriorated, then excellent reception data are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a facsimile machine, and more particularly to input signal processing of a demodulator (modem).

[0002]

2. Description of the Related Art Input signal processing of a conventional facsimile machine modem will be described.

In a conventional facsimile apparatus, a received signal (hereinafter, referred to as a received signal arrival level) input from a telephone line connection portion which is a connection point with a telephone line is a reception filter for limiting a signal outside the band of a modem. It is input to the modem through (the reception filter may be built in the modem).

The received signal is filtered, but basically the received signal is not amplified or attenuated. That is, the received signal arrival level becomes the modem input level built into the device. Therefore, the dynamic range of the modem input is set to 0 to -43 dBm (guaranteed value).

In the G3 recommended facsimile machine, the S / N of the line is measured in advance and communication is performed at a transmission speed corresponding to the S / N. Specifically, an optimum transmission rate is selected by transmitting a predetermined fixed pattern for a predetermined time, counting the occurrence of errors due to noise on the line on the receiving side, and measuring S / N ( Hereinafter, this operation will be referred to as short training).

Since the short training time is short, S / N measurement by standing noise is possible, but S / N measurement by burst noise (intermittent noise) is generally impossible. When burst noise that cannot be detected during short training is larger than standing noise, when burst noise occurs during image information transmission after short training,
The modem will not be able to demodulate correctly and will appear as an error in the received data.

[0007]

In the conventional facsimile apparatus, even if the received signal arrival level is sufficiently high on the line where burst noise occurs, S / N due to burst noise is generated.
There is a problem that an error occurs in the received data due to the deterioration of. This will be described with reference to FIG. FIG. 3 is a graph showing the relationship between the received signal arrival level and the modem input level.

In FIG. 3, the standing noise (N) is -40.
dBm, the modem receiver limit -45 dBm, the burst noise (N _B) is -15 dB (M relative signal level (S)
AX), that is, S / N _B = 15 dB (MIN).

Considering when the received signal arrival level is -20 dBm, the S / N at the time of short training is determined by the standing noise, and S / N = 20 dB (burst noise is not generated during the short training). In the transmission of image information after short training, burst noise occurs, and the S / N is 5 dB (S / N-S / N) in the worst case.
_(B = 20-15 = 5 dB), the modem cannot demodulate correctly and an error occurs in the received data.

It is an object of the present invention to provide a facsimile apparatus which suppresses burst noise (intermittent noise) and improves S / N deterioration due to burst noise.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a facsimile apparatus having a demodulator, the attenuator being provided at an input portion of the demodulator and attenuating an input signal by a predetermined level by external control, and the attenuator of the attenuator. A level detector provided in the output section for detecting the level of the received signal coming from the transmitter of the other side, and the attenuator when the received level is higher than a preset upper limit value by the output of the level detector. Attenuating the reception level input to the demodulator to the upper limit value, and suppressing the burst noise included in the reception signal below the reception limit of the demodulator. Characterize.

[0012]

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

FIG. 1 is a block diagram showing an embodiment of the present invention. This facsimile apparatus includes a demodulator (modem) 4 including a demodulation preprocessing filter, an attenuator 2 for attenuating an input signal to a predetermined level by an external control at an input portion of the demodulator 4, and an output of the attenuator 2. A level detector 3 for detecting the level of a received signal coming from a transmitter on the other side,
When the reception level is higher than the preset upper limit value by the output of the level detector 3, the attenuator 2 is controlled to attenuate the reception level input to the demodulator 4 to the upper limit value,
An attenuator control means 5 for suppressing the burst noise included in the received signal to be equal to or less than the reception limit of the demodulator 4. In the figure, 1 is a telephone line connection unit, and 6 is a telephone line.

Next, the operation of this embodiment will be described with reference to FIG. Note that FIG. 2 is a graph illustrating the control of this embodiment.

When receiving data, after closing the telephone line,
First, a CNG signal indicating FAX transmission arrives from the transmitter of the other party. The CNG signal coming from the telephone line 6 is input from the telephone line connection section 1 to the level detector 3 via the attenuator 2. When detecting the CNG level, the attenuation amount of the attenuator 2 is set to 0 dB.

The level detector 3 measures the received signal arrival level by the CNG signal. In the attenuator control means 5, when the input level of the demodulator 4 is equal to or higher than a preset upper limit value (−30 dBm in FIG. 2) based on the measurement result of the level detector 3, the input level of the demodulator 4 becomes the upper limit value. The attenuation amount of the attenuator 2 is adjusted so that FIG. 2 shows the control of the attenuation amount with respect to the received signal arrival level. At this time, burst noise (intermittent noise) is outside the dynamic range of the demodulator 4 (-
Since it is suppressed to 45 dBm) and the S / N does not deteriorate, good reception data can be obtained.

Although the upper limit value is -30 dBm in the embodiment, it is determined by the reception limit value of the modem and the magnitude of the burst noise signal to be suppressed, but -3.
Around 0 dBm is considered appropriate.

In the above description, by the CNG signal,
Although the received signal arrival level was measured, for example, DCS, NS
The received signal arrival level may be measured by a signal such as S.

Further, in this embodiment, the CNG level detector 3 is used.
Is described as a block independent of the demodulator 4,
Some modern modems have built-in level detectors. In this case, the CNG level detector 3 can be included in the demodulator 4.

[0020]

As described above, according to the present invention, the arrival level of the signal is measured by the signal that arrives first, the appropriate attenuation amount is selected, and the received signal including burst noise is attenuated to reduce the noise. By suppressing only the component outside the modem dynamic range, the S / N is improved, and good reception data can be obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining control of the present invention.

FIG. 3 is a diagram for explaining a conventional example.

[Explanation of symbols]

 1 telephone line connection 2 attenuator 3 level detector 4 demodulator (modem) 5 attenuator control means 6 telephone line

Claims (2)

[Claims] 1. A facsimile apparatus having a demodulator, wherein the attenuator is provided at an input section of the demodulator and attenuates an input signal to a predetermined level by external control; A level detector for detecting the level of the received signal coming from the transmitter, and controlling the attenuator to the demodulator when the received level is higher than a preset upper limit value by the output of the level detector. An attenuator control means for attenuating an input reception level to the upper limit value and suppressing burst noise included in a reception signal to a reception limit of the demodulator or less. 2. The facsimile apparatus according to claim 1, wherein the level detector is incorporated in a demodulator.