JPH09232997A - Data transmission system and data transmitting method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend the range of data transmission. SOLUTION: Transmitter-receivers 1', 3' and a repeater system 2' have the same table in which plural sets of transmitting and receiving frequencies are set, and the transmitter-receiver 1' transmits a signal by the transmitting frequency, and the repeater system 2' receives the signal by that frequency, and amplifies it, and transmits it by the receiving frequency corresponding on the table, and the transmitter-receiver 3' receives the signal by that receiving frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system by a spread spectrum method using frequency hopping and a data transmission method in the same, and more particularly, to data transmission by performing transmission through a highly reliable relay device. And a data transmission method in the same.

[0002]

2. Description of the Related Art A conventional data transmission system is shown in FIG.
I will explain using. FIG. 8 is a configuration block diagram showing the configuration of a conventional data transmission system. The conventional data transmission system, as shown in FIG.
The relay device 2 is basically configured. Normally, more transmission / reception devices are normally provided, but FIG. 8 shows a case where transmission / reception is performed on a one-to-one basis for the sake of simplicity. The transmitter / receiver 1 and the transmitter / receiver 3 have the same functions, but the reference numerals are different for the sake of explanation.

Next, the function of each part will be specifically described.
The transceivers 1 and 3 perform data transmission by a spread spectrum method using frequency hopping. Specifically, the transmitter / receiver 1 shown in FIG.
(Frequency Shift Keying) or PSK (Phase Shif
data transmitted by a carrier wave having a frequency f (t) that changes with time, and the transmitting / receiving apparatus 3 receives at a frequency f ′ (t) that changes with time, It demodulates and receives data.

The relay device 2 relays data by transmitting data received at the frequency f (t) at the frequency f '(t).

Next, the operation of the conventional data transmission system and the data transmission method will be described. First, the transmission / reception device 1 performs, for example, FSK modulation on the data to be transmitted, transmits the data on a carrier wave of frequency f (t). Then, the relay device 2 receives the signal and sends the signal to the frequency f ′ (t).
It is transmitted on the carrier wave of. The transmitter / receiver 3 receives the signal, FSK demodulates and takes out the data.

At the time of this relay, depending on the settings of f (t) and f '(t), the transmission data may overlap as shown in FIG. FIG. 9 is an explanatory diagram showing an example of overlapping transmission data.

[0007]

However, in the above-mentioned conventional data transmission system and the data transmission method in the conventional data transmission system, the reception data and the transmission data in the relay device may overlap with each other depending on the change in the frequency band, resulting in a transmission error. Therefore, there is a problem that the distance of data transmission cannot be extended.

The present invention has been made in view of the above circumstances, and extends the distance of data transmission by performing transmission via a relay device capable of changing the frequency band so that a transmission error does not occur. It is an object of the present invention to provide a data transmission system and a data transmission method therefor.

[0009]

The invention according to claim 1 for solving the above-mentioned problems of the prior art is a data transmission system in which a frequency hopping is performed to transmit a signal by spread spectrum. , It is characterized by performing a relay that converts the frequency transmitted from the transmitting side to another predetermined frequency and transmits it to the receiving side, so that the frequency bands of the frequencies converted by the relay do not overlap in advance. By setting it, relay can be performed reliably.

The invention according to claim 2 for solving the problem of the above-mentioned conventional example has a table in which a plurality of pairs of frequencies for transmission and reception are set in the data transmission system, The transmission / reception apparatus includes a first transmission / reception apparatus that performs frequency hopping according to a transmission frequency to transmit a signal by spread spectrum, and the table. The signal is received and amplified at the transmission frequency, and the transmission is performed according to the table. A relay device for converting and transmitting to a reception frequency corresponding to a trust frequency and the table, and performing frequency hopping according to the reception frequency of the table to receive a signal by spread spectrum; It is characterized in that it has a transmitter / receiver device and is set in advance so that the frequency bands of the frequencies converted by relay do not overlap. In, it is possible to reliably relay.

According to a third aspect of the present invention for solving the above-mentioned problems of the conventional example, in the data transmission method in the data transmission system according to the second aspect, the first transmission / reception device acquires the transmission right at the start of the transmission. Make the requested transmission, second
When the transmitter / receiver of 1 transmits a positive response to the request, the first transmitter / receiver acquires the transmission right and performs only the transmission until the end of the transmission, and the second transmitter / receiver of the second until the end of the transmission. The feature is that only reception is performed, and data transmission can be reliably performed.

The invention according to claim 4 for solving the above-mentioned problems of the conventional example is the data transmission method according to claim 3, wherein a table for storing a pair of frequencies for transmission and reception is used for transmission. The frequency and the frequency for reception are stored as a specific frequency, and the second transmitting / receiving device that only performs reception resets the signal to the specific frequency when no signal is received for a certain period of time. Even if a transmission error occurs during data transmission, the data transmission distance can be extended by using the specific frequency as a reset so that the data transmission can be restored.

[0013]

Embodiments of the present invention will be described with reference to the drawings. The data transmission system (present system) according to the present invention selects frequencies so as not to cause overlap by using a preset frequency table.

This system will be described with reference to FIGS. 1 is a configuration block diagram of a transmitter / receiver of a data transmission system according to an embodiment of the present invention, and FIG. 2 is a configuration block diagram of a relay device of a data transmission system according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing an example of a hopping pattern table, and FIG. 4 is an explanatory diagram showing the configuration of a message transmitted by the transmission / reception device of the data transmission system according to the embodiment of the present invention.

Here, the frequency values stored in the corresponding positions in FIGS. 3A and 3B, for example, f1 and f8, are set so that signals do not overlap each other. It is assumed that the frequency bands are sufficiently separated. Also,
The message is a signal transmitted and received when a control process (hereinafter, referred to as a preliminary process) such as preparation for data transmission or suspension of data transmission is performed between transmitting and receiving devices.

Like the conventional data transmission system, this system is basically composed of transmitting / receiving devices 1'and 3'and a relay device 2 '. Further, similarly to the conventional case, the overall configuration is that a larger number of transmission / reception devices are originally arranged, but here, for the sake of explanation, an example in the case of performing one-to-one data transmission is shown. I have to. Here, the transmitter / receiver 1'and the transmitter / receiver 3'have the same function, but the reference numerals are different for the sake of explanation.

In this system, 21 from f0 to f20
, But f0 is used only for the transmission of preprocessing messages. That is, the frequency band f
At 0, no data is transmitted.

The transmitter / receivers 1'and 3'have a table in which a pair of frequencies, a transmission frequency and a reception frequency, are registered, data is transmitted at the transmission frequency, and the corresponding positions on the table are stored. The reception frequency is registered with the reception frequency.

Further, the transmitting / receiving devices 1'and 3'perform periodical transmission / reception of messages in the frequency band f0 to perform preliminary processing, and when a NULL (blank) command is received at that time, the command is ignored. The message is then discarded.

Further, one of the transmitter / receivers 1'and 3'requests the transmission right in the preparatory process, and the side which has transmitted the request for the transmission right first obtains the transmission right and unilaterally transmits the data. Is. In the following, particularly, the preliminary processing in which a request for a transmission right and an affirmative response or a negative response thereto are used as a message,
This is called preparation processing.

The relay device 2'has a table in which a pair of frequencies of a transmission frequency and a reception frequency are registered, and the transmission frequency of the table is the reception frequency of the transmission / reception devices 1 ', 3'. The frequency is the same as the frequency, and the reception frequency is the same as the transmission frequency of the transceivers 1'and 3 '.

Then, the relay device 2'includes the transmitting / receiving device 1 '.
The signal received at the receiving frequency is amplified, converted into a transmitting frequency corresponding to the receiving frequency, and transmitted to the transmitting / receiving device 3 '.

Here, regarding the transmitting / receiving devices 1'and 3 ',
More specifically, the transceivers 1'and 3'are the same as those shown in FIG.
As shown in FIG. 3, the input unit 4, the transmission unit 5, and the reception unit 6
And an output means 7 and a control means 8,
The transmitter 5 includes a modulator 51, a spread code generator 52,
It is composed of a diffusion means 53 and a transmission means 54,
The receiving unit 6 includes a receiving means 61 and a despreading code generator 62.
And despreading means 63 and demodulating means 64.

The respective parts of the transmitter / receivers 1'and 3'will be specifically described below. The input means 4 has a built-in buffer, receives data input from outside the apparatus, accumulates the data in the buffer, and outputs a signal indicating that the data has been input to the control means 8. . Also, the input means 4
When a signal indicating that the data can be transmitted is input from the control means 8, outputs the data accumulated in the transmission unit 5.

The transmission unit 5 modulates the data input from the input unit 4 and the message input from the control unit 8 by using a method such as FSK, and the signal obtained by modulating the message is transmitted in the frequency band f.
0, the data modulated signal is converted into the frequency band f1 to f20.
Either of them is sent. Details will be described later.
The transmitter 5 receives a signal from the control means 8 to set the transmission frequency to f0 and sets the transmission frequency to f0.

The receiving section 6 demodulates a signal received in any one of the frequency bands f1 to f20 by a method such as FSK and outputs it to the output means 7. The signal received in the frequency band f0 is FSK or the like. It is demodulated by the above method and output to the control means 8. Details will be described later. Further, the receiving unit 6 receives a signal from the control means 8 to set the reception frequency to f0 and sets the reception frequency to f0.

The output unit 7 receives the data input from the receiving unit 6, refers to the destination code of the data, and determines whether or not it is addressed to itself. If it is addressed to itself, the data is output to the outside of the device, and the control means 8 outputs a signal indicating that the data has been received. If it is not addressed to itself, the data is discarded.

The control means 8 receives a signal indicating that the data has been input from the input means 4, generates a message requesting a transmission right, and outputs the message to the transmission section 5.
Then, when a message of an affirmative response indicating that transmission is possible is input from the receiving unit 6, the destination code of the message is referred to, it is determined whether or not it is addressed to itself, and If not addressed, discard the data. If it is addressed to itself, it is determined that the transmission right has been obtained, and a signal indicating that data can be transmitted is output to the input means 4.

Further, the control means 8 has a timer, and after outputting the message requesting the transmission right, if the response is not received for a certain period of time, the control means 8 outputs the message requesting the transmission right again. It has become. Note that this re-output may be repeated a preset number of times, and then the output of the message may be canceled.

Further, while the control means 8 does not have the transmission right, the control means 8 must count the time by the above timer and receive a signal indicating that the data has been received from the output means 7 for a certain period of time. , A signal for setting the transmission frequency and the reception frequency to f0 is output to the transmission unit 5 and the reception unit 6.

As shown in FIG. 4, the message specifies a command indicating a request or a response, a transmission right code for securing the transmission right, a transmission destination code for specifying the transmission destination, and the transmission source. And a transmission source code. The specific contents of these will be described later.

Next, each section of the transmitting section 5 will be described. The modulation means 51 modulates the input data by a method such as FSK and outputs it as a modulated signal to the spreading means 53. The spreading code generator 52 has a table of hopping patterns shown in FIG. 3A, and outputs a carrier wave of frequency f0 to the spreading means 53 in the preparation process.
After that, the frequency is hopped in the order shown in the table of FIG. 3A at regular time intervals, and the carrier of the frequency is output to the spreading means 53. Specifically, the frequency of the carrier wave after the preparation process is changed as f1 → f3 → f5 → f7.

Further, the spread code generator 52 has a control means 8
In response to the input of a signal from which the transmission frequency should be f0, the carrier of frequency f0 is output to the spreading means 53. After that, when transmitting data, the frequency of the output carrier wave returns to the beginning of the hopping pattern table shown in FIG. Specifically, it changes like f1 → f3 → f5 → f7.

The spreading means 53 modulates the inputted signal with the carrier wave inputted from the spreading code generator 52 and outputs the modulated signal to the transmitting means 54. The transmitting means 54 is for transmitting data via an antenna.

The receiving means 61 receives the signal transmitted through the antenna and outputs it to the despreading means 63. The despreading code generator 62 has a table of hopping patterns shown in FIG. 3B, hops the frequency at the same timing as the spreading code generator 52, and outputs the frequency signal of that frequency to the despreading means 63. To do.

Further, the despreading code generator 62 receives an input of a signal whose reception frequency should be f0 from the control means 8,
The carrier of frequency f0 is output to the despreading means 63. After this, when sending data,
The frequency of the output carrier wave returns to the beginning of the hopping pattern table shown in FIG. Specifically, it changes as f8 → f10 → f12 → f14.

The despreading means 63 demodulates the signal input from the receiving means 61 at the frequency output by the despreading code generator 62 and outputs it to the demodulating means 64. The despreading means 63 outputs to the demodulation means 64 a signal indicating that preliminary processing is being performed when the frequency input from the despreading code generator 62 is f0. If not, this signal is not output.

The demodulation means 64 demodulates the signal input from the despreading means 63 by a method such as FSK. Further, the demodulation means 64 receives an input of a signal indicating that preparatory processing is being performed from the despreading means 63 and outputs the demodulated signal to the control means 8 as a message. When the signal is not input, the demodulated signal is output to the output means 7 as data.

Next, the relay device 2'will be described more specifically. The relay device 2'has a control means 25 as shown in FIG. 2 and the receiving means 2 controlled by the control means 25.
1, the amplifying means 22, the frequency shifting means 23, and the transmitting means 24.

The respective parts of the relay device 2'will be specifically described below. The receiving means 21 has a table of hopping patterns shown in FIG. 3 (a) and a first pointer pointing to one of the frequencies stored therein, and the transmitting / receiving device 1'transmits while referring to the table. The first pointer is incremented at regular time intervals according to the frequency hopping, and the signal received and demodulated at the received frequency is output to the amplification means 22.

The amplification means 22 amplifies the signal input from the reception means 21 and outputs it to the frequency shift means 23. The frequency shift means 23 has a hopping pattern table shown in FIG. 3B and a second pointer that points to one of the frequencies stored in the table.
Referring to the table, the transmission frequency is hopped by incrementing the second pointer and shifting to the frequency according to the table of FIG. 3B in accordance with the hopping timing of the reception frequency, and the transmission frequency is hopped. It modulates the signal input by (4) and outputs it to the transmission means 24.

Further, the frequency shift means 23 counts the time when there is no input from the amplifying means 22 by a timer, and when a preset time has elapsed, the reception frequency and the transmission frequency are reset to f0. , And the first and second pointers are reset to “0”. When the first and second pointers are "0", the frequency shift means 23 considers that the transceivers 1'and 3'are preparing for transmission and reception, and increments the pointer only once. Give up. That is, the pointer is
It changes in the order of “0” → “0” → “1” → “2”, the reception frequency changes as f0 → f0 → f1 → f3, and the transmission frequency f0 → f0 → f8. → f1
It changes like 0.

Further, the frequency shift means 23 includes the first,
When there is no frequency to be pointed to by the value of the second pointer,
The values of the first and second pointers are reset to "1". Specifically, in the example of FIG. 3, the value of the pointer is
When it is "11", it is incremented, and when it is "12", there is no value to be instructed, so it is reset to "1". The pointer value and the frequency correspond to each other as shown in FIG. The transmitting means 24 transmits the input signal to the air via the antenna.

Next, the operation of the present system will be described, firstly, when the transmission is normally performed, and secondly, when the transmission error occurs.

First, the case where transmission is normally performed will be described with reference to FIG. FIG. 5 is an explanatory diagram showing a flow of transmission in the transmission system according to the embodiment of the present invention. As a preparation process, the transmitter / receiver 1'uses the reception request (request for transmission right) as a command, the destination code as the transmitter / receiver 3 ', and the source code as the transmitter / receiver 1', and transmits at the transmission frequency f0 ( In step S1), the relay device 2'receives the signal, amplifies it, and similarly transmits it at the transmission frequency f0 (S2). At this time, in the frequency shift means 23 of the relay device 2 ', the values of the first and second pointers are not incremented.

This radio wave is received by the transmission / reception device 1'and the transmission / reception device 3 '. Since the transmission / reception device 1'has a different transmission destination code from itself, the data is discarded and the transmission / reception device 3'is.
Then, since the destination code is mine, it is received. When the transmitter / receiver 3'is in a receivable state, the transmitter / receiver 1'is used as the destination code and the transmitter / receiver 3'is used as the destination code and transmitted at the transmission frequency f0 (S3).

Then, the relay device 2'receives and amplifies this radio wave, and similarly transmits it at the transmission frequency f0 (S
4). The data transmitted by this radio wave is received by both the transmitter / receivers 1'and 3 ', but is discarded by the transmitter / receiver 3'and received by the transmitter / receiver 1', as before. In the process S4, the frequency shift means 23 of the relay device 2'increments the values of the first and second pointers to "1".

Then, the transmitter / receiver 1'transmits the data at the transmission frequency f1 for a certain period of time in accordance with the hopping pattern table shown in FIG. 3 (a) (S5), and the relay device 2'is shown in FIG. 3 (a). The signal is received at the reception frequency f1 indicated by the value "1" of the first pointer in and is transmitted at the transmission frequency f8 indicated by the value of the second pointer in FIG.
At the same time, the transmitter / receiver 1'has hopped in frequency, and transmission is performed at the transmission frequency f3 (S6).

Then, before the transmission is completed, f0
When it is the order in which the transmission is performed (when the preparatory processing is performed), the transmission / reception device 1 ′ sends the command part to the NU.
LL (blank) is transmitted, and the relay device 2 ′ sends it to f0.
Then, the transceiver 2'ignores the command because it is NULL and discards it.

After that, when the transmission is completed, the transmission / reception device 1'stops transmitting. Then, the relay device 2 '
If there is no transmission from the transmitter / receiver 1'for a certain period of time, the reception frequency is set to f0, and the frequency shift means 23 sets the first and second frequencies.
The pointer of is reset to "0". Then, the transmission frequency and the reception frequency of the transmitter / receiver 3'also become f0.

Next, the operation of the present system when a transmission error occurs will be described. At this time, the transmission error is
There may be a case where it occurs in the relay device 2'and a case where it occurs in the transmission / reception device 3 ', but both of them perform the same processing, and therefore will be described using FIG. FIG. 6 is an explanatory diagram showing an operation when a transmission error of a message occurs in the relay device 2 '.

Now, the transmitter / receiver 1'has the frequency f0,
When a signal in which a message is modulated is being transmitted (S10), if a transmission error occurs in the relay device 2 '(S11),
Since the relay device 2'does not transmit to the transceiver device 3 ',
No response is received. Then, since a response cannot be obtained for a certain period of time, the transmitting / receiving means 1'generates a message again and modulates it,
It transmits at frequency f0 (S12). Then, the process is repeated until transmission / reception is normally performed. Here, the maximum number of repetitions may be set in advance, and the transmission may be stopped after repeating the set number of times.

The case where a transmission error occurs in the relay device 2'during data transmission will be described with reference to FIG. FIG. 7 is an explanatory diagram showing an operation when a data transmission error occurs in the relay device 2 '.

When the transmitter / receiver 1'transmits a signal obtained by modulating data at the frequency f17 and the relay device 2'transmits the previously received data at the frequency f2 (S20), the relay device 2'has a transmission error. Occurs and the data transmitted at the frequency f17 cannot be received, the data cannot be received for a certain period of time. Therefore, the relay device 2'and the transmitting / receiving device 3 '.
Means that both the transmission frequency and the reception frequency are f0.
During that time, the transmitter / receiver 1'transmits data at the frequency f19 (S21), but this data is not received.

Then, when the transmitter / receiver 1'performs frequency hopping and transmits a signal in which the message is modulated at the transmission frequency f0 for preprocessing (S22), it is received by the relay 2 ', and The data is transmitted at f0 and is received by the transmitter / receiver 3 '(S23), and the transmission is recovered.

In the process S1, the transmitter / receiver 1 ',
When both 3's simultaneously transmit a "reception request",
The signals received by both will contain a lot of errors,
Although it cannot be accepted as a meaningful signal, at this time, the control means 8 may generate a random number, wait for a time corresponding to the random number, and then perform transmission again. Since this method has been widely known from the past, its explanation is omitted.

According to the data transmission system and the data transmission method therefor of the present embodiment, the frequency received by the relay device 2'and the frequency to be transmitted can be set so as not to be close to each other, so that the data transmission is ensured. Therefore, there is an effect that the data transmission distance can be extended.

[0058]

According to the invention described in claim 1, frequency hopping is performed to transmit a signal by spread spectrum, and the frequency transmitted from the transmitting side is converted into another predetermined frequency and received. Since it is a data transmission system that relays to the other side, by setting in advance so that the frequency bands of the frequencies converted by the relay do not overlap, relaying can be performed reliably and the distance of data transmission There is an effect that can be extended.

According to the second aspect of the present invention, the first transmission / reception device has a table in which a pair of frequencies for transmission and reception is set, and frequency hopping is performed in accordance with the transmission frequency of the table. And the signal is transmitted by spread spectrum, the relay device has the above table, receives and amplifies the signal at the frequency for transmission, and according to the table, changes to the frequency for reception corresponding to the frequency for transmission. As a data transmission system, wherein the second transmission / reception device has the table described above, and performs frequency hopping according to the reception frequency of the table to receive a signal by spread spectrum conversion. Therefore, by setting in advance so that the frequency bands of the frequencies converted by the relay device do not overlap, relaying can be performed reliably, and There is an effect that it is possible to extend the distance of data transmission.

According to the third aspect of the present invention, the first transmitter / receiver performs a transmission requesting the transmission right at the start of the transmission, and the second transmitter / receiver transmits a positive response to the request. The data transmission method of the data transmission system according to claim 2, wherein the first transmission / reception device obtains the transmission right and performs only transmission until the end of transmission, and the second transmission / reception device performs only reception until the end of transmission. Therefore, there is an effect that data transmission can be reliably performed.

According to the invention described in claim 4, the transmission frequency and the reception frequency are stored as a specific frequency in the table storing the pair of frequencies for transmission and reception, and only reception is performed. The second transmitter / receiver is
Since the reception frequency is reset to a specific frequency when no signal is received, the data transmission method according to claim 3 is used. Therefore, even if a transmission error occurs during data transmission, the specific frequency is used as a reset to perform data transmission. By enabling restoration, there is an effect that the distance of data transmission can be extended.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a transmission / reception device of a data transmission system according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram of a relay device of the data transmission system according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating an example of a hopping pattern table.

FIG. 4 is an explanatory diagram showing a configuration of a message transmitted by the transmission / reception device of the data transmission system according to the exemplary embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a flow of transmission in the transmission system according to the exemplary embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an operation when a message transmission error occurs in the relay device.

FIG. 7 is an explanatory diagram showing an operation when a data transmission error occurs in the relay device.

FIG. 8 is a configuration block diagram showing a configuration of a conventional data transmission system.

FIG. 9 is an explanatory diagram showing an example of overlapping transmission data.

[Explanation of symbols]

1, 1 ', 3, 3' ... Transceiver device, 2, 2 '... Relay device, 4 ... Input means, 5 ... Transmitter unit, 6 ... Receive unit, 7
... output means, 8 ... control means, 21 ... receiving means, 2
2 ... Amplifying means, 23 ... Frequency shifting means, 24 ... Transmitting means, 25 ... Control means, 51 ... Modulating means, 52
... spreading code generator, 53 ... spreading means, 54 ... transmission means, 61 ... receiving means, 62 ... despreading code generator,
63 ... Despreading means, 64 ... Demodulation means

Claims (4)

[Claims] 1. A data transmission system for performing frequency hopping to transmit a signal by spread spectrum, wherein a frequency transmitted from a transmission side is converted into another predetermined frequency and relayed for transmission to a reception side. A data transmission system characterized in that 2. A first table having a table in which a plurality of pairs of frequencies for transmission and reception are set, and frequency hopping is performed in accordance with the frequencies for transmission in the table to transmit a signal by spread spectrum. A transmitter / receiver; a relay device having the table, receiving and amplifying a signal at a transmission frequency, converting the signal to a reception frequency corresponding to the transmission frequency according to the table, and transmitting the signal; And a second transmission / reception device that performs frequency hopping according to the reception frequency of the table to receive a signal by spread spectrum. 3. The first transmission / reception device, when the first transmission / reception device performs a transmission requesting a transmission right at the start of transmission, and the second transmission / reception device transmits a positive response to the request. 3. The data transmission method in a data transmission system according to claim 2, wherein the second transmission / reception apparatus only receives the transmission right until the end of transmission, and the second transmission / reception device only receives until the end of transmission. 4. A table for storing a pair of frequencies for transmission and reception, wherein a frequency for transmission and a frequency for reception are stored as specific frequencies, and only a reception is performed.
4. The data transmission method according to claim 3, wherein the transmitter / receiver device is reset to the specific frequency if no signal is received for a certain period of time.