JPH0531862B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a communication system, and more particularly to a frequency signal identification circuit for identifying frequency signals received from a line in a communication system.

Prior Art Such frequency signal identification circuits are often used in modulation and demodulation devices that transmit facsimile signals and data signals over analog communication lines, for example.

As is well known, these lines use many types of frequency signals for transmission control or communication control, and the receiving side detects a specific frequency signal among them as the communication control procedure progresses. There is a need to.

Therefore, conventional modulation/demodulation devices are provided with frequency identification circuits corresponding to the type of frequency of the signal to be identified, and each frequency identification circuit generates a signal indicating detection only when a signal of a specific frequency that can be identified arrives. was configured to print. The types of frequency signals actually used in communication lines are diversifying, and therefore, such a conventional configuration has the disadvantage that the overall scale of the device increases.

As an improvement over this, there is a method in which such a frequency identification function is realized by a signal processing operation in a processing system, that is, a digital signal processing device.

For example, Yukio Ichikawa et al.
In the system described in "LSI Modem", National Technical Report, Vol. 28, No. 5 (October 1982), pp. 98-99,
Eight frequency signal detection circuits are realized by digital signal processing operations. These eight detection circuits are always operating in parallel. Therefore, the processing time required for the digital signal processing apparatus as a whole to identify frequency signals is eight times the signal processing time required for identifying one frequency signal.

Digital signal processing devices, of course, perform many tasks besides identifying frequency signals, such as receiving other modulated signals. On the other hand, the processing capacity of a digital signal processing device is limited by its processing speed, so if the time required to identify a frequency signal is large,
The time allocated to other tasks will be relatively reduced. In general, for applications of digital signal processing equipment such as modem equipment, there are many important tasks other than frequency signal identification, and the system as a whole is configured to minimize the time required for frequency identification. It is advantageous to do so.

Purpose The present invention solves the drawbacks of the prior art,
It is an object of the present invention to provide a frequency signal identification circuit for a communication system in which frequency identification in signal processing is efficiently performed.

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

Referring to FIG. 1, in an embodiment in which the frequency signal identification circuit of the communication system according to the present invention is applied to facsimile communication, a modem device 100 is connected between an analog communication line 10 and a facsimile control section 12 including a facsimile main body. ing.

In this embodiment, the modem 100 is G3, G2 and
It complies with the G1 facsimile standard. As shown in the figure, the modem 100 includes a processing unit (CPU) 102 that realizes various functions of the modem and controls the entire device, and a digital signal processor (DSP) 104 that realizes the digital signal processing function.
and has. The CPU 102 and DSP 104 are interconnected via a system bus 104. bus 1
In 04, as the system memory of the CPU 102,
A memory 130 is connected in which programs and data for transmission control and operation control of the entire device are stored.

The DSP 104 has a central processing unit (not shown), of course, and advantageously has a RAM 108 and a ROM 110 as storage devices therefor, as shown. Output port 112 of DSP 104 is a digital-to-analog converter (DAC).
114 to the uplink 14 of the line 10. Further, the down line 16 of the line 10 is connected to an analog-to-digital converter (ADC) 116, and the output 118 of the latter is inputted to the DSP 104.

System bus 106 also includes I/O port 1
20 is also connected, via which the modem 100
is the facsimile control unit 12 and the multiline 18-1 to 18
-m and 20-1 to 20-n.
Multi-wires 18-1 to 18-m are transmission lines for signals indicating tonal signal detection or binary signal detection from the modem 100 to the facsimile control unit 12.
0-1 to 20-n are connection lines for transferring control signals from the facsimile control section 12 to the modulation/demodulation device 100.

The DSP 104 performs digital signal processing operations such as reception identification of tonal signals and binary signals and reception of other modulated signals. However, these functions other than those for each signal receiver are not directly related to the present invention, and therefore will not be described in detail.

In this embodiment, the frequency signal identification function is realized by a biquad filter 200 as shown in FIG. This filter 200 includes addition functions 202 and 204, delay functions 206 and 208,
multiplication functions 210, 212, 214 and 216. As is well known, the tonal signal used for G2 and G1 facsimile control is 1100Hz,
There are six types (f1 to f6): 1300Hz, 1650Hz, 1850Hz, 2100Hz and 462Hz. The G36 facsimile also uses a binary procedure using a V21 modem.

By the way, the signal received from the line 10 to the downstream line 16 is sampled at appropriate time intervals in the ADC 116, and is sent to the input 220 of the filter 200.
is given as sample data. Delay function 2
06 and 208 each provide a delay of one sample time for signal sampling;
This represents a time delay due to storage of sample data in a data storage device such as RAM 108 of DSP 104.

The sample data delayed by one sample time is
They are multiplied by multiplication coefficients A1 and B1 in multiplication functions 210 and 214, respectively, and the multiplication results are added to sample data one sample time later in addition functions 202 and 204, respectively. Further, the sample data delayed by one sample time is multiplied by coefficients A2 and B2 in multiplication functions 212 and 216, respectively, and the multiplication results are added to the sample data two sample times later in addition functions 202 and 204, respectively. be done.

Remaining functions 210, 212, 214 and 216
By appropriately selecting the combination of coefficients A1, A2, B1, and B2, ie, the operating parameters of the frequency signal discrimination function, the desired passband of the filter 200 is set. That is, the filter 20
The frequency signal to be passed through 0 can be selected, thereby setting the frequency to be identified by this frequency signal identification function. Thus filter 2
The frequency signal passing through 00 is output to the output 222.

Multiplication functions 210, 212, 214 and 216
The combination of coefficients A1, A2, B1 and B2 is advantageously stored in system memory 130. This is done by the CPU 102 according to the progress of the call.
is read out from the memory 130 by the DSP1
04's RAM 108. Or, instead of the system memory 130, the facsimile control unit 1
2 and may be configured to be loaded directly from the facsimile control unit 12 to the DSP 104 without going through the CPU 102.

In any case, when viewed from the facsimile control unit 12, the modulation/demodulation device 100 configured as described above is as follows.
Its filter function is configured to be programmable,
In other words, it has a programmable filter configuration. Note that when the identification frequency of the frequency identification function is not made variable but fixed as described above, it is advantageous to fixedly store these multiplication coefficients in the ROM 110 of the DSP 104.

As shown in FIGS. 3A to 3C showing the transmission control flows of CCITT facsimiles G1, G2, and G3, the tonal signals and frequencies used in the facsimile transmission control procedure between the originating station Tx and the terminating station Rx are as follows: Identified from among the six types f1 to f6 mentioned above according to the call progress status (CCITT recommendation)
T.30). For example, in G1, a 1650Hz frequency signal is used for the GI1 (group identification) signal transmitted from the receiving station Rx, and in response to this, the transmitting station Tx
A frequency signal of 1300Hz is used for the GC (group command) signal sent back from the GC.

As will be clear from the explanation that follows, there are three types of frequency signals that may need to be identified simultaneously in the progress of these facsimile calls. Therefore, in this embodiment, the DSP 104 is configured to operate at most three filters 200-1 to 200-3 (FIG. 5) at the same time.

Taking the case of G2 facsimile as an example, the operation of this apparatus will be described in detail with reference to FIGS. 4A and 4B. First, a facsimile call progresses at the originating station Tx, and when the call connection is completed with the terminating station Rx, the CPU 102 sends the DSP 104 a frequency of 165Hz.
and 1850Hz frequency signals, as well as the V21 signal. The CPU 102 has RAM 1 of the DSP 104 corresponding to each filter 200.
08 are respectively loaded with combinations of multiplication coefficients A1, A2, B1 and B2 to identify these frequency signals. Therefore, the DSP 104 controls each filter 2.
00 can identify these signal frequency signals.

For example, when a frequency signal of 1850 Hz passes through one filter 200 and is output as a GI2 signal to the output 222, the DSP 104 notifies the CPU 104 of this fact. The CPU 104 is an I/
The detection signal f4DET is output to the facsimile control section 12 via the O port 120. As a result, the facsimile control unit 12 recognizes that this facsimile call is
It is determined that the vehicle is moving at G2, and a control signal IN2 is output to the control line 20-2.

Based on this signal IN2, the CPU 102 interprets that the subsequent operation will proceed in G2, and the DSP 102
1650 of the frequency signal CFR2 (receiving readiness confirmation) to be received next.
Indicates Hz identification. This instruction is for DSP104
filter 200 passes 1650 Hz by loading the corresponding combination of multiplication coefficients A1, A2, B1 and B2 into RAM 108. When the DSP 104 identifies the 1650 Hz frequency signal using the filter 200 with the multiplication coefficient set in this manner, it notifies the CPU 102 of this fact.

Thereafter, frequency signals such as the PIS signal (procedure interruption signal), EOM (end of message) signal, and MCF (message confirmation) signal are identified in the same manner. Note that 462Hz of the PIS signal may not be used.

The same applies to the receiving station Rx. Referring to FIG. 4B, when a facsimile call is received,
The CPU 102 instructs the DSP 104 to identify the 1300Hz, 2100Hz and V21 signals. For example, upon recognizing that a 2100Hx GC2 signal has been received from the transmitting station Tx, the DSP 104 will notify the CPU
102, and the CPU 102 uses I/O port 1.
A detection signal is sent to the facsimile control unit 12 via 20.
Output f5DET. Therefore, the facsimile control unit 12 outputs a control signal IN2 to the control line 20-2 to instruct the CPU 102 to operate at G2 from now on.

In this way, in the receiving station Rx, as in the case of the transmitting station Tx described above, the frequency signal identification operation is performed as follows.
Three biquad filters 200 calculate the multiplication coefficient according to the frequency signal to be identified according to the transmission control procedure.
This is done by setting .

As is clear from the above explanation, DSP104
Three filters 200-1 to 200 prepared for
-3 is used to identify various frequency signals depending on the progress of the transmission control procedure. For example, as shown in FIG. 5, the pattern is as shown in FIG.
is the frequency signal f4 in the next transmission control state following this
The filter 200-2 is configured to identify the frequency f2 and is used in a certain transmission state to identify the frequency f2.
is the frequency signal f5 in the next transmission control state following this
is set to identify the

Therefore, there is no need to provide a number of frequency signal identification circuits corresponding to the types of frequency signals to be identified as in the conventional method, and this reduces the number of frequency signal identification circuits corresponding to the types of frequency signals that may be identified simultaneously. An identification function may be provided. Therefore, compared to the conventional method, the storage area for programs and data required to realize the frequency signal identification function is reduced, and the overall time required for the processing is also shortened.

Note that the embodiments described here are for explaining the present invention, and the present invention is not necessarily limited thereto, and modifications and variations that can be made by those skilled in the art without departing from the spirit of the present invention. Modifications are within the scope of this invention. For example, although at most three frequency signal identification functions are provided in this embodiment, it may be any other number, and there are six types of frequency signals to be identified.
It is not limited to this number.

Effects According to the present invention, a number of frequency signal identification functions corresponding to the types of frequency signals that may be simultaneously identified in a transmission control procedure are provided, and the frequency signals to be identified by them are determined based on the operating parameters of the identification functions. The combination is set by appropriately selecting the combination as the transmission control procedure progresses. Therefore, compared to the conventional method, the storage area for programs and data required to realize the frequency signal identification function may be smaller. Further, the overall time required for the processing is also shortened, and the digital signal processing apparatus can allocate the shortened processing time to other signal processing. Therefore, efficient frequency signal identification can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment in which the frequency signal identification circuit of the communication system according to the present invention is applied to facsimile communication, and FIG. A functional diagram showing an example realized by a filter, Figs. 3A to 3C are flow diagrams showing an example of facsimile transmission control procedure, and Figs. 4A and 4B show an example of frequency signal identification flow in G2 facsimile transmission control. Explanatory diagram, FIG. 5 is an explanatory diagram showing an example of the flow of frequency identification operation in the embodiment shown in FIG. Explanation of symbols of main parts, 12... facsimile control unit, 100... modulation/demodulation device, 102...
CPU, 104...Digital signal processing device, 1
08...RAM, 110...ROM, 130...
System memory, 200... Bi-cut filter.

Claims (1)

[Claims] 1. In a frequency signal identification circuit of a communication system connected to a communication line and identifying a frequency signal received from the communication line, the frequency signal identification circuit is configured to have an operating parameter settable, an identification means for identifying a frequency signal corresponding to a frequency signal corresponding to an operating parameter; a storage means for storing the operating parameter necessary for identifying a frequency signal in a call connection on the communication line; and a call transmission control procedure on the communication line. control means for controlling the progress of the transmission control procedure and reading out the operating parameters from the storage means and setting them in the identification means according to the progress of the transmission control procedure; A frequency signal identification circuit for a communication system, characterized in that it is prepared to correspond to the maximum number of possible types of frequency signals.