JPH01291562A - Signal transmission system for telephone line - Google Patents

Abstract

PURPOSE:To compensate missed data by preparing plural tables with different push-button dial signals corresponding to data desired to transmit, respectively, and transmitting the data for plural times based on respective table. CONSTITUTION:When the data (575E0), for example, is transmitted, a DTMF signal is sent in sequence (1) (2) (3) (4) (5) based on the table 1, and the DTMF signal in sequence (6) (7) (8) (9) (10) based on the table 2. Assuming that a signal having the highest frequency 1633Hz out of the frequencies of the DTMF signal is missed due to the frequency characteristic of a line, it results that no signals of (4) and (7) are detected, however, the signal of (4) is compensated by the signal of (9), and since the signal of (7) is already compensated by the signal of (2), received data can be reproduced correctly as the (575E0). When data length is variable, it is necessary to prevent erroneous data from being reproduced by attaching sum check and parity check, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal transmission system over a telephone line, and in particular, to data transmission via a telephone line using a push button dial signal (hereinafter referred to as DTMF signal). This invention relates to a signal transmission method on a telephone line that performs the following.

[Prior art] Transmission using DTMF signals has been carried out for a long time, and the method is
Hz, 1633Hz) and low group (697Hz, 770H
By combining and transmitting the two frequencies of
It sends out bi-soto signals. The high group and low group each have a frequency of 4PJt class, and there are frequency differences even within the same group, so when transmission is carried out over a telephone line, the line loss becomes large and the line characteristics have frequency characteristics.

[Problem to be solved by the invention] As mentioned above, since line characteristics have frequency characteristics, generally the higher the frequency, the greater the degree of attenuation.
If the level at which the signal reaches the other party changes depending on the frequency, part of the transmitted data may be lost.

In such cases, even if the data is retransmitted,
There is a high possibility that the same data will be missing again, and it is difficult to fill in the missing data.

Furthermore, if the four-wire loss is particularly large, or if the line is heavily noisy, data transmission may become completely impossible. Even in such cases, data transmission may be possible by lengthening the signal transmission time or increasing the signal transmission level, but this cannot be done if the transmission time and transmission level are fixed. The upper limit of the average value of the transmission level to the telephone line is determined by technical standards, and in order to increase the transmission level, it is necessary to maintain the so-called pause time when no signal is being transmitted so that the average level does not rise. It is necessary to do so.

After all, if you try to ensure data transmission by lengthening the transmission time or raising the transmission level, the time required for data transmission will become longer.

An example of transmitting data using a telephone line is water,
There is a system in which automatic meter reading for gas, electricity, etc. is performed between a terminal device installed in each home and an information receiving device installed at a sales center, etc., but in such a system, the communication time per meter is The shorter the time, the greater the number of meter readings per certain period of time, leading to more efficient meter reading operations.

Furthermore, the shorter the communication time, the cheaper the telephone charges, so it is desirable to shorten the communication time (transmission time) as much as possible.

Therefore, the main object of the present invention is to provide a signal transmission system over a telephone line that can compensate for some missing data due to the frequency characteristics of the line.

[Means for Solving the Problems] The present invention is a signal transmission system in a telephone line that transmits data via a telephone line using a push button dial signal, in which a push button dial signal is pressed in response to each piece of data to be transmitted. A plurality of tables with different button dial signals are prepared, and each data is transmitted a plurality of times based on each table.

[Function] In the signal transmission system on a telephone line according to the present invention, by transmitting data multiple times based on each table with different push button dial signals for one data, the signals transmitted using the tables consisting of Even if data is missing, it is possible to supplement the missing data with data transmitted in other tables.

[Embodiment of the Invention] First, in explaining this embodiment, an example of a terminal device that performs transmission and reception based on the present invention will be explained. A terminal device is installed in each home in an automatic meter reading system, and the terminal device transmits the usage amount of gas, water, electricity, etc. to the management center via telephone line, and the transmission to the management center is by DTMF signal. Reception from the management center is performed using a single frequency tone signal. The reason why reception is performed using a single frequency tone signal is because the amount of information regarding reception is small. In other words, only a confirmation signal for the transmitted meter reading data is required, and the circuit configuration within the terminal device can be simplified. Further, the frequency of the tone signal is set to 2100 Hz in order to distinguish it from each frequency of the DTMF signal to be transmitted.

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

First, the configuration of an embodiment of the present invention will be described with reference to FIG. A relay contact 1 and a primary coil of a coupling transformer 2 are connected in series to the telephone line. Relay contact 1
opens and closes a DC circuit to a telephone line (equivalent to lifting and hanging the handset on a telephone)
, for sending dialing pulses (in the case of a dial line). This relay contact 1 is closed by a signal from the microcomputer 4 which turns on the transistor 15 and causes current to flow through the relay coil. The coupling transformer 2 inputs and outputs signals to and from the telephone line, and the input impedance seen from the telephone line is approximately 600.
It is Ω. The secondary coil of the coupling transformer 2 is connected to the input end of the bandpass filter 8, and is connected to the DTMF transmitter 3 via a resistor 6 having a resistance value R1, and to the transistor 5 via a resistor 7 having a resistance value R2. Connected to the collector. The emitter of the transistor 5 is grounded, the base is connected to the microcomputer 4, and the DTM
The F transmitter 3 is also connected to the microcomputer 4.

When sending normal DTMF signals, the microcomputer 4
Transistor 5 is conducting in response to the command of DTM
The DTMF signal generated by the F transmitter 3 is transmitted through the resistors 6 and 7.
The voltage is divided into 12/(R1+R2) and applied to the secondary coil of the coupling transformer 2. When it is necessary to increase the sending level of the DTMF signal in accordance with a command from the microcomputer 4, the transistor 5 becomes non-conductive, and the DTMF signal generated by the DTMF transmitter 3 is transferred directly to the secondary of the coupling transformer 2. given to the coil. Further, the DTMF signal not only serves as a signal sent to the management center, but also as a dialing signal to the switching center if this terminal device is connected to a telephone line.

2100 is a confirmation signal sent from the management center
A tone signal of Hz is input from the telephone line to a bandpass filter 8 via a relay contact 1 and a coupling transformer 2. The band pass filter 8 passes the signal in the 2100 Hz band and removes unnecessary noise, and the 2100 Hz tone signal from which the noise has been removed is sent to the amplifier 9.
The signal is converted to a logic level by the microcomputer 4 and provided to the microcomputer 4. The microcomputer 4 determines the presence or absence of the confirmation signal by counting the 2100 Hz tone signals for a certain period of time.

The microcomputer 4 is connected to a battery 10 used as a power source for circuits in the terminal device, and also includes a crystal oscillation circuit for supplying a lock signal necessary for the microcomputer 4 to grasp the transmission time of meter reading data. 11 are connected. Also, microcomputer 4
FROM12 is connected to , and this FROM12
The information necessary for each terminal device is stored in advance, such as the telephone number of the destination (control center), the telephone number of the home where the terminal device is installed, and the classification of the telephone line and dial line. Furthermore, microcomputer 4
A gas meter 14 and the like are connected via an interface 13 to the gas meter 14 and the like.

Figure 2 is a diagram showing two types of data showing the relationship between data and DTMF signals, Figure 3 is a diagram showing an example of data to be transmitted and a DTMF signal, and Figure 4 is a diagram showing the relationship between data and DTMF signals. FIG. 3 is a diagram showing the relationship between level and pause time.

Next, the operation of one embodiment of the present invention will be described with reference to FIGS. 1 to 4. First, data and DTMF
Tables showing relationships with signals are provided in two types, as shown in FIGS. 2(a) and 2(b). When transmitting data, the data is first replaced with a DTMF signal according to Table 1 and then transmitted, and then the DTMF signal with the data replaced according to Table 2 is transmitted. This 2
The two tables are created by reversing the order of frequencies within the same group for both the high and low groups. In addition, in order to reverse the magnitude of the frequency difference between the high group and the low group, it is also possible to create a table in which the order of the frequencies of only the low group is reversed. For example, in data “C”, “697Hz
and 1633Hz" (frequency difference -936Hz) is '941Hz and 1633Hz" (frequency difference -6
92Hz) by table replacement. This table may be more convenient depending on the characteristics of the receiving circuit.

For example, as shown in Figure 3, the data "575EO"
Based on Table 1, if you are trying to send
The DTMF signal is sent in the order of ■→■→■→°■→■, and then based on Table 2, the D
Send TMF signal. Due to the frequency characteristics of the line, for example, 1633H, the highest frequency of the DTMF signal,
Assuming that the signal with z is missing, the signals of ■ and ■ cannot be detected, but the signal of ■ is complemented by the signal of ■, and the signal of ■ has already been detected by the signal of ■. , the data after receiving is correct “57
5EO” is reproduced.

When the data length is fixed (the data length to be sent from the terminal device is always fixed), interpolation is easy and there is little chance of reproducing incorrect data, but when the data length is variable, checksum, parity etc. It is necessary to add checks to prevent incorrect data from being reproduced.

In any case, if a small portion of the data is missing, it can be supplemented, but if a large amount of data is missing, it is not possible to reproduce the data by supplementing it. In such a case, data can be sent using the following procedure and reliable reception can be expected.

When the terminal device sends data and the center correctly receives the DTMF signal from the terminal device, a confirmation signal 2100 is sent.
Hz is sent back to the terminal device. However, if the center cannot correctly receive the DTMF signal, the confirmation signal of 2100 Hz will not be returned from the center. In addition,
If the terminal device cannot receive the confirmation signal of 2100 Hz, there are 2 degrees of cases. One is when the center cannot correctly receive the DTMF signal from the terminal device, and the other is when the center can correctly receive the DTMF signal from the terminal device, but the confirmation signal 210
This is a case where the terminal device cannot correctly receive 0Hz. The latter only checks for the presence of a single frequency confirmation signal of 2100 Hz, which is much easier than detecting a DTMF signal, so it is not considered. Therefore, confirmation signal 2
The case where 100 Hz cannot be received is assumed to be the case where the center cannot correctly receive the DTMF signal from the terminal device.

By the way, the signal transmission time and pause time are shown in Figure 4(a).
For example, it is determined to be 50 m5ec as shown in . In this embodiment, if the center cannot correctly receive a DTMF signal from a terminal device, the signal sending time and pause time are extended at the same rate and retransmitted, as shown in FIG. 4(b). In this case, the upper limit of the average level of the signal sent out from the terminal device is determined by the terminal equipment technical standards, and if only the signal sending time is extended, this upper limit may be exceeded, so the signal sending time It is necessary to modulate both the pause time and the pause time so that they have the same ratio. In the example shown in Figure 4(b), the signal transmission time and pause time are each 500 m5 e.
It has been extended to c.

Modulating the signal transmission time in this way has the advantage that it becomes easier to detect the signal on the receiving side when a transmission error occurs due to impulsive noise.

If a transmission error still occurs even after extending the signal sending time and pause time and retransmitting as described above, the signal sending time is returned to the original 5Qmsec as shown in FIG. 4(a).
For example, the signal transmission level is tripled (3L), only the pause time is extended, and the signal is retransmitted. In this case, if the signal transmission level is A, the signal transmission time is Ts, and the pause time is Tp, then the average transmission level P is B - ATs/ (Ts + Tp), and the average transmission level B is the upper limit of the average level specified in the technical standards. It is necessary to set it to a value that does not exceed . Such a method is effective in cases where transmission errors occur due to extremely large line losses.

Note that the above-mentioned methods of extending the signal transmission time and pause time and methods of increasing the signal transmission level are aimed at ensuring transmission by lengthening the transmission time, and the transmission time is as long as possible. In order to suppress this, there is a method of controlling the above two methods by gradually increasing the signal sending time or signal sending level, checking the confirmation signal, and then finding the optimal method. Conceivable.

In this manner, when the confirmation signal is obtained, the terminal device memorizes the transmission method, and transmits a DTMF signal using that transmission method from the beginning for subsequent transmission and reception with the center.

[Effects of the Invention] As described above, according to the present invention, a plurality of tables with different push button dial signals are prepared corresponding to each data to be transmitted, and a plurality of each data is transmitted based on each table. Since the data is transmitted twice, data transmission from all terminal devices can be ensured while minimizing the transmission time.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an embodiment of the present invention. FIG. 2 is a diagram showing two types of tables showing the relationship between data and DTMF signals. FIG. 3 is a diagram showing an example of data to be transmitted and a DTMF signal. FIG. 4 is a diagram showing the relationship between signal transmission level and pause time. In the figure, 1 is a relay, 2 is a coupling transformer, and 3 is a DT
MF transmitter, 4 is a microcomputer, 5.15 is a transistor, 6.7 is a resistor, 8 is a bandpass filter,
9 is an amplifier, 11 is a crystal oscillation circuit, 12 is FROM, 1
B indicates an interface, and 14 indicates a gas meter. Fig.

Claims (1)

[Claims] In a signal transmission system for a telephone line in which data is transmitted via a telephone line using push-button dial signals, a different table of push-button dial signals is provided for each piece of data to be transferred. A signal transmission method for telephone lines, characterized in that multiple tables are prepared and each data is transmitted multiple times based on each table.