JPS6129225A - Demodulating device - Google Patents

Abstract

PURPOSE:To obtain a demodulating device with simple constitution by providing plural BPFs corresponding to one of plural demodulation speed and deciding a demodulation speed of demodulation signals in comparing with the output of these BPFs. CONSTITUTION:In a facsimile receiving set, when a training check field signal is received, a training sequence receiver 14 sends out a preparation for receiving confirmation signal to a transmitter and sets center frequency of variable pass band BPF18 according to transmission speed designated by a digital instruction signal. Out of received signals, signals that passed BPF16 or BPF18 of center frequency 600Hz are monitored in a monitoring section 24, and transmission speed of received signal is detected. When the monitoring section 24 reports the result of detection to the receiving section, the receiving section 14 can discriminate signal of what communication speed came in, that is, can identify whether it is a protocol signal or picture signal. Accordingly, it is not necessary to provided two kinds of modems, a modem for protocol and a modem for receiving picture signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulator, more specifically, a demodulator that complies with the C0-ITT Recommendation 7.311 (7) G3 standard and < 2,400 bps.
The present invention relates to a demodulator suitable for facsimile reception using a protocol.

Previously, the modem for G3 facsimile was a 300bps modem for implementing the protocol, and a 300bps modem for communicating image information! +, G0
Two modems were used: 0/7, 200/4, and 800/2.400 bps modems, and both modems were on standby so that they could receive signals.

As an option for implementing the protocol in the G3 standard, the use of a 2.4 oobps modem instead of a 300 bps modem is also allowed. For this reason, many regions, such as Europe, recommend a 2,400 bps protocol.

In general, a 63 facsimile must be equipped with both a CCITT Recommendation T, 30 protocol standard-hi protocol modem and an image information modem. In the case of 300bps protocol, the 300bps modem uses FSK method,
This is because the modulation method is different from pS or QAM image information modems, and 300bps modems can be configured much more inexpensively than image information modems, so two types of modems, a protocol modem and an image information modem, can be used in the 03 facsimile device. It was equipped.

However, in the case of a 2,400 bps protocol, installing two types of modems, a protocol modem and an image information modem, in a facsimile machine is wasteful in terms of system configuration and is not a good idea. This is 2.400bp for a single screen information modem.
This is because when operating as a 2,400bps protocol modem, it is exactly the same as a 2,400bps protocol modem, and a 2.4QObps protocol modem can be realized at almost the same price as an image information modem.

1-'' An object of the present invention is to eliminate such drawbacks of the prior art and provide a demodulator having a simple device configuration.

The configuration of the present invention will be described below based on one embodiment.

Prior to describing the embodiment, a case where simultaneous reception by a protocol modem and an image information modem is required will be described with reference to FIG. In the same figure, the signals shown in parentheses are ・2・4
This shows the output signal transmitted by QObp.

First, the transmitting station TI transmits a digital command signal DO8 to the receiving station Rx, and subsequently transmits a training check field TCP. When receiving preparation is completed, receiving station Rx returns a receiving preparation confirmation CFR to transmitting station Tx. Then, as shown on the left side of the figure, the transmitting station Txt± confirms the signal CFR and starts transmitting the image information PI.

Signals TCF and AX are 9,600/7,20
It is selected from either 0/4,800/2.400 bps, and which one is used is defined by signal DC8.

However, as shown on the right side of the figure, if the signal CFR is not correctly received at the transmitting station Tx for some reason, the procedure for transmitting the signals DGS and TCF is repeated again. Therefore, the receiving station Rx is in a state where it has finished transmitting the signal CFR,
That is, in the state shown by the dotted line 100 in the figure, it is uncertain whether the next signal expected to be received is PIX or DO9. In other words, either receive the 2.400bps OC8 signal and reconfigure the protocol, or
? , 20G/4,800/2.400bps signal P! There are two possibilities of receiving K.

As shown in FIG. 1, the embodiment of the present invention includes a training sequence receiving section 14 connected between a receiving line 10 of a transmission line and an output terminal 12 to a host machine. The training sequence receiving unit 14 complies with CCTTT Recommendation V, 2fll, as shown in FIG. 4, for example.

Run a training sequence consisting of segments 1.3.4 and 5 in V, 27ter, etc. The length of segment) l is 200 ms. Also, the length of segment 3 varies depending on the transmission speed.9. B00/
7. 53 milliseconds at 200 bps, a, eoobp
s is 31 milliseconds, 2,400 bps is 42
It is millisecond. Training sequence receiving unit [4 is
These segments are used to perform adaptive convergence of various parameters such as automatic line equalization, automatic gain control, carrier extraction, and timing extraction of the demodulator.

In this embodiment, the reception line 10 includes two bandpass filters (BP
F) 1B and 18, and their respective outputs 20 and 22 are supplied to the monitor section 24. The bandpass filter 1G has a passband with a center frequency of 800 Hz in order to detect a signal with a modulation rate of 1.200 po. In response to the output 2o of the bandpass filter 16, the monitor unit 24
It is identified that a signal with a transmission rate of 2,400 bps is received on the reception line IO.

The bandpass filter 18 has its center frequency and its passband selectively switched in order to detect signals other than those having a modulation rate of 1.200 po. For example, if the transmission speed is Ia, 60
At 0/7,200 bps, the modulation rate is 2.400 po, so the center frequency is 1.200 Hz, 4.8
At 00 bps, the modulation rate is t, 6oo po, so the center frequency is selected to be 800 Hz. Note that when the one-stroke information is transmitted at 2,400 bPS, the above-mentioned problem does not occur because the transmission speed is the same as the protocol transmission speed.

The center frequency of the filter 18 is switched by an instruction sent from the training sequence receiving section 14 through a control line 26. Training sequence receiving section 14
Is the transmitting station↑! After transmitting the signal CFR to the transmitting station Tx, the center frequency of the bandpass filter 18 is set according to the transmission speed indicated by the signal DC8 previously received from the transmitting station Tx. The monitor unit 24 determines from the output 22 of the bandpass filter 18 that a signal at the expected transmission rate has been received on the reception line IO.

In this embodiment, the passband of the bandpass filter 18 is configured to be switchable. However, it goes without saying that a plurality of bandpass filters may be prepared corresponding to each transmission speed used in the transmission system. Of course, such a filter is advantageously implemented by a digital signal processing system.

The output 2B of the monitor section 24 is input to the training sequence receiving section 14, and the receiving section 14 detects which transmission speed signal is detected by the bandpass filters 16 and 18.
Report to.

An It diagram conceptually shows the functions realized by the hardware and software of a system.
In reality, it is advantageously realized by a digital signal processing system, such as a microcomputer, as shown in FIG. The reception line IO and the connection line 12 to the host machine are connected to the system bus 50 via the interface 52.
connected to.

The system bus 50 includes an arithmetic unit 58 that realizes the functions of a demodulator, a multiplier 80, a ROM 54, and a RAM.
5G and ADO/DAC: 62 are connected. With these, the functions shown in FIG. 1 are realized.

Explain the operation. When the training sequence is entered by the signal TCP, the training sequence receiving section 14
After transmitting the signal CFR to the transmitting station Tx, it sets the center frequency of the bandpass filter 18 in accordance with the transmission rate instructed by the signal DO8 previously received from the transmitting station TI. Fifth
As shown in the figure, for a while after entering segment 3,
Outputs 20 and 2 of both bandpass filters 18 and 18
2 is monitored by the monitor unit 24. by this,
At that time, it is detected which transmission rate the signal was received.

This monitoring period T2 is required to be shorter than the length of segment 3. As mentioned above, this length is at least 31
The monitoring period Tl must not exceed 31 milliseconds. In reality, time constraints are also taken into account for various operations that should be performed in segment 3, such as automatic line equalization, automatic gain control, carrier wave extraction, and timing extraction of the demodulator. A period of, for example, less than half the length of segment 3, for example of the order of 10 milliseconds, is therefore advantageous.

The determination of the transmission speed of the incoming signal is terminated when the higher output level of the bandpass filters 16 and 18 exhibits a difference greater than a predetermined significant difference from the lower one. Absolute value ILI-L of the difference between the level Ll of the output 20 of the bandpass filter 1B and the level L2 of the output 22 of the bandpass filter 18
21 is a significant difference or more, that is, when ILI-L21>L, the determination ends. However, if I Ll-L21 < L even after the monitoring period T2, ILI-L21
Extend the monitoring period until >L.

As described above, when the transmission rate is identified during the monitoring period 2 by the outputs of the bandpass filters 16 and 18, the monitor section 24 notifies the training sequence receiving section 14 of this. As a result, the training sequence receiving section 1
4, it is possible to know at which transmission rate the signal has arrived. That is, it is determined whether a protocol signal or an image information signal has arrived, and the process then proceeds to a normal signal reception sequence.

As described above, according to this embodiment, the transmission rate is 2.400 bp.
Even in a system using the S protocol, there is no need to provide two types of modems: a pro)p modem and an image information modem. Therefore, the configuration of the facsimile machine is simplified.

According to the present invention, there is no need to separately provide a demodulator for a protocol and a demodulator for a modem for image information, so the configuration of the demodulator is simplified.

[Brief explanation of drawings]

FIG. 1 is a functional diagram conceptually showing the functions of an embodiment of a demodulator according to the present invention, and FIG. 2 shows an example of a hardware configuration for realizing the embodiment shown in FIG. 1 using a digital signal processing system. Block Diagram. FIG. 3 is a flow diagram showing an example of a facsimile transmission control procedure, FIG. 4 is a timing diagram showing an example of a facsimile training sequence, and FIG. 5 is a flow diagram showing the operation of the apparatus shown in FIG. (14, , ) training sequence receiving unit lθ, 18.
, bandpass filter 24, , monitor section

Claims (1)

[Claims] 1. A demodulator connected to a transmission line capable of transmitting modulated signals of a plurality of modulation rates, the demodulator having a passband corresponding to any one of the plurality of modulation rates. , a plurality of bandpass filter means for generating outputs corresponding to the modulation speed of the modulation signal received from the transmission path, and a determination means for comparing each output of the filter means to determine the modulation speed of the modulation signal. A demodulator comprising: 2. The apparatus according to claim 1, wherein the modulation signal includes a protocol signal and an image information signal used in facsimile, and the determining means performs the determination in a facsimile training sequence. demodulator. 3. In the apparatus according to claim 2, one of the filter means has a passband corresponding to the modulation rate of the protocol signal, and the remaining filter means have a passband corresponding to the modulation rate of the image information signal. A demodulator characterized by having corresponding passbands. 4. The demodulator according to claim 3, wherein the remaining filter means can selectively set a plurality of passbands corresponding to the modulation speed of the image information signal. .