JPH03254564A - Data terminal equipment - Google Patents

Abstract

PURPOSE:To attain proper data transmission through the use of a V.29 MODEM by calculating the energy of a frequency component of a 2900Hz band of a reception signal and discriminating the deterioration in the signal of a high frequency band of the reception signal based on the calculated energy. CONSTITUTION:A band pass filter 26 extracts a component of 2900Hz band of a normalized digital reception signal RNd, an energy arithmetic processing section 27 calculates the signal energy of 2900Hz band based on an output signal of a band pass filter 26 and sequentially outputs the result of calculation to a register 28 as an energy signal EG. When the locking of the operation of an automatic gain adjustment circuit 24 is finished and the energy signal EG outputted from the arithmetic processing section 27 represents the high frequency band characteristic of a line at that time properly, a signal P2 is outputted from a demodulation processing section 25 and the energy signal EG at that point of time is stored in the register 28.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data terminal device that receives a signal modulated by a 29 digital modem and demodulates it into received data.

[Prior Art] For example, in a data terminal device such as a Group 3 facsimile device that uses an analog line network such as a public telephone line as a transmission path, a digital modem for transmitting data at high speed has a data transmission speed of 9600 bps ( Fall pack speed is 7200 bps) CCITT Recommendation V
．． The recommended data transmission speed is 4800bps (
The fall pack speed is 2400 bps) CCITT Recommendation V, 27ter modem, etc. are used.

Here, when performing data transmission using the 29 modem, if the condition of the transmission path is poor, the receiving device cannot properly demodulate the received data.

Therefore, for example, in Group 3 facsimile equipment, in order to check whether the high-speed modem function set at the sending terminal can be used, a modem training procedure for the set high-speed modem function is performed before transmitting image information. .

As a result, the high-speed modem function used for image information transmission is set, so that image information can be transmitted at high speed and without data errors.

[Problems to be solved by the invention] However, in such conventional devices, for example,
Even if modem training using the 29 modem function is successful, the data transmission status may be extremely unstable depending on the line condition at the time, and reception errors may occur frequently when image information is actually transmitted. Therefore, there have been cases where an inconvenience has arisen in that appropriate image information cannot be transmitted.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a data terminal device which eliminates the disadvantages of the conventional device and allows data transmission to be carried out appropriately.

[Means for Solving the Problems] The present invention provides an automatic gain adjustment circuit that adjusts the gain of a received signal, and an automatic gain adjustment circuit that adjusts the gain of a received signal.
A band-pass filter circuit extracts a frequency component in the 0Hz band, an energy calculating means calculates the energy of the output signal of the band-pass filter circuit, and a high-frequency band signal of the received signal is calculated based on the output signal of the energy calculating means. It is equipped with a judgment means for judging deterioration.

[Effect] Therefore, since it has been determined that the characteristics of the high frequency band necessary for the 29 modem have deteriorated, it is necessary to determine whether data transmission by the 29 modem can be performed stably. (2) Data can be transmitted appropriately using a 29 modem.

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

First, the principle of the present invention will be explained.

Figure 1 shows CCITT Recommendation ■, Recommendation Upper Dem (16-level QA
16 types of signal elements transmitted in M) are shown.

After the transmission data is scrambled, it is divided into consecutive groups of four bits (quad bits), and the temporally first one of each quad bit is
The th bit sets the relative amplitude of the signal element to be transmitted, and the 2nd to 4th bit pattern sets the relative amplitude of the signal element to be transmitted.
A phase change relative to the phase of the previous signal element is set.

In this way, the signal elements corresponding to the quad bits of the transmission data string are determined.

Also, V. Prior to data transmission by the X.29 modem, the transmitting terminal performs phase synchronization, amplitude adjustment, and
Sends a synchronization signal to initialize the descrambler.

As shown in FIG.
Segment S in which the symbol interval number TS2 is 128, which alternately repeats B (at 9600 bps; see Figure 1).
G2, V. The segment SG3 has a symbol interval number TS3 of 384 and is composed of an equalizer adjustment pattern for adjusting the continuous automatic equalizer built in the X.29 modem, and the segment SG3 has a symbol interval number TS4 of 48 and consists of scrambled data rlJ. Consists of segment SG4.

Following this synchronization signal, user data is transmitted.

Now, as shown in Fig. 3, the transmission energy spectrum of the synchronization signal segment SG2 is as follows:
500t (z and 2
Each has a peak at 900Hz.

On the other hand, if the characteristics of the high frequency band of the transmission line deteriorate,
/N decreases, and when the characteristics of the high frequency band deteriorate and the S/N deteriorates, the transmission energy spectrum of segment SG2 of the synchronization signal becomes 4th.
It changes as shown in Figures (a), (b), and (C).

As described above, if the high frequency band characteristics of the transmission line deteriorate, or if the S/N characteristics deteriorate, the transmission energy in the 2900 Hz band decreases when the synchronization signal segment SG2 is transmitted.

Therefore, when the receiving side detects transmission energy in the 2900Hz band while receiving segment SG2 of the synchronization signal, the proportion of the detected transmission energy in the total transmission energy of all frequency bands of the transmission signal is less than a certain value. If also large + V, 29 modem transmission speed 96
It can be determined that 00 bps can be used.

Furthermore, if the ratio of the detected transmission energy in the 2900Hz band to the total transmission energy in all frequency bands of the transmission signal is less than a certain value, the V. It can be determined that it is difficult to use the transmission speed of 9600 bps of the V.29 modem. In this case, for example, you can switch to the fall pack speed of 7200 bps, or
Take measures such as inserting an equalization amount between the line and the modem to compensate for line characteristics.

FIG. 5 shows a Group 3 facsimile machine according to a first embodiment of the present invention.

In the figure, a CPU (Central Processing Unit) 1 is for controlling the operations of each part of this Group 3 facsimile machine and processing transmission procedures, and a ROM (Read Only Memory) 2 is for controlling the operations of each part of this Group 3 facsimile machine and for processing the transmission procedures. The RAM (Random Access Memory) 3 stores control programs and data such as various constants necessary for executing the control programs, and constitutes the work area of the CPU.

The scanner 4 is for reading a document image at a predetermined resolution, and the plotter 5 is for recording and outputting an image at a predetermined resolution.

The operation display section 6 is made up of various keys and displays necessary for operating this Group 3 facsimile machine.

The encoding/decoding unit 7 encodes and compresses the image signal obtained by reading with the scanner 4, and decodes the encoded and compressed image information into the original image signal.

The image storage device 8 is for storing a large amount of encoded and compressed image information, and is composed of a large-capacity storage device and the like.

The modem 9 performs processing to modulate and demodulate digital data, and has a low-speed modem function for exchanging transmission procedure signals and a high-speed modem function for transmitting image information. As for the low speed modem function, CCI
Equipped with TT Recommendation V, Recommendation Dem function (300 bps),
High-speed modem functions include CCITT recommendation ■, recommendation modem function (9600bps, 7200bps) and V
, 27ter modem function (4800bps, 2400bps
bps).

The network control device 10 is for connecting this Group 3 facsimile device to the public telephone line network, and is equipped with an automatic call/receive function.

These CPUI, ROM2, RAM3, scanner 4,
The plotter 5, operation display section 6, encoding/decoding section 7, image storage device [8, modem 9, and network control device 10 are connected to the system path 11, and data exchange between these elements is , this system bus 11 is opened.

Also, from the modem 9, the transmission signal TXd is transmitted to the network! 1
0, and from the network control device 210, the received signal RX
d is being output to modem 9.

FIG. 6 shows V in the high-speed modem function of the modem 9.

3 shows an example of a V.29 modem receiving section.

In the figure, the received signal RXd applied from the network control device 10 is applied to the common contact 20c of the switching circuit 20, and the normally closed contact 20b of the switching circuit 20 is connected to the switching circuit 20.
The normally open contact 20a of the switching circuit 20 is added to an equalizer 22 for improving the high frequency band characteristics of the @ line.

The output signal of the equalizer 22 is applied to the normally open contact 21a of the switching circuit 21, and the common contact 21a of the switching circuit 21
1c is connected to the input end of the analog/digital converter 23.

The analog/digital converter 23 converts the received signal RXd into a corresponding digital signal, and the output signal is sent to the automatic gain adjustment circuit 2 as the digital received signal RDd.
It has been added to 4.

The automatic gain adjustment circuit 24 is for normalizing the entire band energy of the digital reception signal RDd, and its output signal is applied to the demodulation processing section 25 and the bandpass filter 26 as the normalized digital reception signal RNd. There is.

The demodulation processing unit 25 performs a predetermined demodulation process based on the normalized digital reception signal RNd, and converts the corresponding reception data R.
The received data RD is output to the system bus 11.

The bandpass filter 26 filters the normalized digital received signal R.
The signal in the 2900 Hz frequency band included in Nd is extracted, and the output signal is output to the energy calculation processing section 27.

The energy calculation processing section 27 calculates the signal energy in the 2900 Hz band, and its output signal is added to the register 28 as the energy calculation signal EG.

The register 28 receives the signal P output from the demodulation processing section 25.
When 1 is applied to the clear input terminal CLR, the stored data is cleared, and when the signal P2 output from the demodulation processing section 25 is applied to the load input terminal LD, the energy calculation signal E
G, and the stored data is output to the system bus 11.

Here, as shown in FIGS. 7(a) to 7(C), the demodulation processing unit 25 outputs the signal Pi when it detects the segment SG2 of the synchronization signal sent from the transmitting side, and also outputs the signal Pi to the automatic gain adjustment circuit. 24 operation pull-in is completed and segment S
Signal P2 is output immediately before detecting G3.

Further, when the switching signal SL output from the CPUI rises to the logic H level, the switching circuit 20.21 switches the operation from the normally closed contacts 20b, 21b to the normally open contacts 20a, 21a.

Therefore, when the switching signal SL is at the logic L level, the switching circuits 20 and 21 each switch between the normally closed contacts 2 and 2.
0b and 21b are selected, and the received signal RXd output from the network control bag [10 is applied as is to the analog/digital converter 23.

Further, when the switching signal SL is at the logic H level, the switching circuits 20 and 21 have normally open contacts 20a and 20, respectively.
21a is selected, and the received signal RXd is applied to the analog/digital converter 23 with its high frequency band characteristics improved by the equalizer 22.

This V. 29 When the modem receiving section receives the synchronization signal from the transmitting side, the received signal RXd is converted into the corresponding digital received signal RD via the analog/digital converter 23.
After being converted into d, it is applied to the automatic gain adjustment circuit 24.

First, when receiving the segment SGI of the synchronization signal, the automatic gain adjustment circuit 24 operates in a no-signal state.
The demodulation processing unit 25 then prepares to start receiving segment SG2.

When the reception of the segment SG2 is started, the automatic gain adjustment circuit 24 is pulled into operation by the segment SG2, and the demodulation processing unit 25 starts the operation of the segment SG2.
When G2 is detected, signal P1 is output. This clears the register 28.

After this, the automatic gain adjustment circuit 24 normalizes the energy of the digital reception signal RDd to form a normalized digital reception signal RDd, and based on the normalized digital reception signal, the demodulation processing unit 25
, segment SG3, and segment SG4, and when segment SG4 is finished, the process moves to the user data demodulation operation and receives the received data RD.
form. Furthermore, when segment SG2 has been received a predetermined number of symbols, signal P2 is output.

On the other hand, the bandpass filter 26 extracts the 2900Hz band component of the normalized digital reception signal RNd, and the energy calculation processing section 27 calculates the signal energy of the 2900Hz band based on the output signal of the bandpass filter 26, and calculates the signal energy of the 2900Hz band. The calculation results are sequentially output to the register 28 as an energy signal EG.

Then, the operation of the automatic gain adjustment circuit 24 is completed, and the value of the energy signal EG output from the energy calculation processing section 27 is in a state where it appropriately reflects the high frequency band characteristics of the line at that time. When the signal P2 is output from the demodulation processing unit 25, the value of the energy signal EG at that time is stored in the register 28.
is stored in the register 28 and held in the register 28.

Furthermore, since the energy of the digital reception signal RDd has been normalized by the automatic gain adjustment circuit 24, the energy signal EG stored in the register 28 has a ratio of the signal energy in the 2900 Hz band to the digital reception signal RDd.

In this way, when the reception of segment SG2 of the synchronization signal is completed, the value representing the line characteristics at that time is stored in the register 28, so the CPU By reading out the 28 stored data MM, the characteristics of one line can be known.

FIG. 8 shows an example of the bandpass filter 26 and the energy calculation processing section 27.

The bandpass filter 26 is configured with a digital filter that passes a band signal of 2900 Hz, and the energy calculation processing section 27 has a configuration equivalent to a so-called energy averaging calculation circuit.

However, in this case, the energy calculation processing 27 may be one that can detect the magnitude of the 2900 Hz band signal extracted by the bandpass filter 26, instead of one that performs strict energy calculation. For example, 2
A circuit that detects the envelope of a 900 Hz band signal, or a low pass filter that passes very low frequency signals, can be used.

With the above configuration, when this group 3 facsimile device receives a call from another device, as shown in FIG. 9(a),
When an incoming call is detected, the receiving device responds with a called station identification signal CED to notify that the own terminal is a non-voice terminal, and also sends a digital signal to notify the standard transmission function of the own terminal. An identification signal DIS and a non-standard function identification signal NSF for notifying the non-standard transmission function are respectively sent to the transmitting device.

As a result, the transmitting device selects the transmission function to be used at that time based on the digital identification signal DIS and non-standard function identification signal NSF received at that time, and receives the selection as a non-standard function setting signal NSS. A training check signal TC is sent to notify the device and to perform modem training at the transmission rate set at that time.
Send P. At this time, V. 29 modem 9600b
If you set ps, first set V, 9 of 29 modem.
After sending out the 600 bps synchronization signal SS1, the training check signal TCP is sent out.

In the receiving device, the CPUI connects the modem 9 with high-speed modem function and V. The synchronization signal SS1 and the training check signal TCP are received with the selection signal SL set to the logic L level and the 9600 bps of the V.29 modem set.

At this time, when the reception of the synchronization signal SS1 is completed,
As mentioned above, since the energy signal EG is stored in the register 28 of the modem 9, the register 28 is accessed before and after the reception of the training check signal TCP is started, and the stored data song is inputted. It is determined whether the value of the stored data old is larger than a specified value, and the determination result is stored.

When the reception of the training check signal CF is completed, if the reception result at that time is good, a reception preparation confirmation signal CFR is sent to the transmitter. Also, at timing T immediately after that, if a value larger than the specified value is stored as the determination result of the old stored data, the 1 selection signal SL
is held at the logic L level, and when a determination result of the stored data song is less than the specified value, the 1 selection signal SL is raised to the logic H level and the equalizer 22 is inserted.

When the transmitter receives the reception preparation confirmation signal CFR from the receiver, the transmitter transmits the synchronization signal SS2 and then transmits the image information PIX. Further, when there is only one original to be transmitted, a procedure end signal EOP is transmitted following the image information PIX.

After retraining the modem 9 using the synchronization signal SS2, the receiving device receives the image information PIX transmitted from the transmitting device and receives the 1-procedure end signal EOP.

At this time, if the reception result of the one-stroke information PIX is good, it responds with a message confirmation signal MCF to the transmitting device.

As a result, the transmitting device sends out the disconnection command signal DCN to restore the line, and upon receiving the disconnection command signal DCN, the receiving device restores the line and ends the series of image information transmission operations.

Further, if the reception result when receiving the first training check signal TCP is not good, the receiving device receives the training failure signal FTT as shown in FIG.
respond.

At the same time, in the same manner as described above, at timing TT immediately after that, if the receiving device stores a value larger than the specified value as the determination result of the stored data old, the receiving device holds the selection signal SL at the logic L level and stores the data. When the determination result of data AH is less than the specified value, the selection signal SL is raised to the logic H level.

Insert equalizer 22.

When the transmitting device receives the training failure signal FTT, the transmitting device changes the transmission rate to V. 2
It notifies that the transmission speed will be reduced by one step to 7200 bps of the 9 modem, and sends out a training check signal TCP at that transmission speed. Also, immediately before this training check signal TCP, V. 29 modem 7200
A bps synchronization signal SS3 is sent out.

From this point on, operations similar to those in the example transmission procedure described above are performed.

In this way, in this embodiment, the line characteristics of the 2900 Hz band are determined based on the synchronization signal SS1 sent out prior to the training check signal TCP, and the insertion/non-insertion of the equalizer 22 is determined based on the determination result. Since this is determined, if the high frequency characteristics of the line are degraded, the equalizer 22 is inserted to improve the line characteristics.

Thereby, the receiving device can receive the image information PIX with improved line characteristics, and can reduce transmission errors when receiving the image information PIX.

By the way, in the embodiment described above, it is determined whether or not to insert an equalizer to improve the characteristics of the high frequency band between the line and the modem, based on the value of the signal energy in the 2900 Hz band calculated at the time of receiving the synchronization signal. However, other judgments can also be made.

Further, in the above embodiment, the present invention is applied to a group 3 facsimile device, but the present invention can be similarly applied to other data terminal devices.

[Effects of the Invention] As explained above, according to the present invention, the received signal
00) Since the energy of the frequency acid component in the 1z band is calculated and signal deterioration in the high frequency band of the received signal is determined based on the calculated value of energy, data transmission by the 29 modem can be performed stably. (2) It is possible to appropriately transmit data using a 29 modem.

[Brief explanation of drawings]

Figure 1 shows V. Fig. 2 is a schematic diagram showing the synchronization signal; Fig. 3 is a graph showing the transmission energy spectrum of segment 2 of the synchronization signal; Fig. 4(a)
is a graph showing the transmission energy spectrum of segment 2 when the high frequency band characteristics of the transmission line deteriorate,
Figure (b) is a graph showing the transmission energy spectrum of segment 2 of the synchronization signal when the S/N of the transmission line has decreased, and Figure (C) is a graph showing the transmission energy spectrum of segment 2 of the synchronization signal when the S/N of the transmission line has deteriorated. FIG. 5 is a block diagram showing a group 3 facsimile apparatus according to an embodiment of the present invention, and FIG. 6 is a graph showing the transmission energy spectrum of segment 2 when V. 7 is a waveform diagram to explain the operation of the device in FIG. 6 when receiving a synchronization signal, and FIG. 8 is a block diagram showing an example of a bandpass filter and an energy calculation processing section. The block diagram shown in FIGS. 9(a) and 9(b) is a time chart showing an example of a transmission procedure performed by the apparatus shown in FIG. 5 at the time of reception. 1...CPU (central processing unit), 2...ROM (read only memory), 3...RAM (random memory)
access memory), 9... modem, 20.21...
・Switching circuit, 22... Equalizer, 23... Analog/digital converter, 24... Automatic gain adjustment circuit,
25... Demodulation processing unit 25. 26... Band pass filter, 27... Energy calculation processing unit, 28... Register. Figure 1 Figure 4 (a) (C) Procedural amendment (method) June 6, 1991

Claims (1)

[Claims] CCITT Recommendation V. 29 In a data terminal device using a digital modem, there is an analog/digital converter that converts the received signal into a digital signal, and an automatic system that adjusts the sum of energy in the entire frequency band of the output signal of this analog/digital converter to a constant value. A gain adjustment circuit and a V.V. 29 demodulation processing means for performing demodulation processing of the digital modem to form received data; and 290 from the output signal of the automatic gain adjustment circuit.
A band-pass filter circuit extracts a frequency component in the 0Hz band, an energy calculating means calculates the energy of the output signal of the band-pass filter circuit, and a high-frequency band signal of the received signal is calculated based on the output signal of the energy calculating means. A data terminal device comprising a determining means for determining deterioration.