JP2965225B2 - Car carrier communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier communication system for controlling the travel of a carrier by exchanging data between management means such as a central control device and a plurality of carriers. .

[0002]

2. Description of the Related Art Conventionally, data communication is performed between management means including central control and the like and a plurality of transport vehicles (for example, unmanned transport vehicles) on a floor so that travel control of each transport vehicle is performed. A communication system for a transport vehicle is known.
In this communication system, the management means has a plurality of transmission / reception devices such as an optical spatial data transmission device, and these transmission / reception devices are arranged on a ceiling, and each carrier has a transmission / reception device such as an optical spatial data transmission device. Are arranged to transmit and receive data via these transmitting and receiving devices.

[0003]

However, in the communication system of the carrier, when a plurality of carriers exist in the transmission area of the one transceiver on the ceiling, transmission from the transceiver on the ceiling is performed. The carrier could not identify to which of these carriers the transmitted data was transmitted. Therefore, data is returned from the plurality of carriers at the same time, and as a result, these data interfere with each other and accurate data communication cannot be performed.

As a countermeasure for this, conventionally, it has been set so that only one carrier can enter the transmission area of the transmitting / receiving device on the ceiling. However, in this case, it is necessary to set the transmission area to be narrow. Therefore, when performing data communication, it is necessary to temporarily stop the traveling carrier in the transmission area, thus deteriorating work efficiency.

As a network between the central control device (master station) and the transmitting / receiving device (slave station), a network using a LAN is generally used. In this case, the central controlling device is provided for each transmitting / receiving device. To send the data. For this reason, data communication takes time as the number of transmitting / receiving devices increases, and communication with all carriers requires a long time.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a communication system of a carrier capable of reliably performing data communication without interference while traveling.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention controls the traveling of a carrier by exchanging transmission data and response data between a management means and a plurality of carriers. in the communication system of the transport vehicle, it said management means, a central control unit for outputting the transmission data of each transport vehicle, which is added identification data unique to each transport vehicle periodically respectively each of the said central control unit While outputting transmission data for each carrier, a plurality of slave stations for guiding the received response data to the central control unit are connected to each of the plurality of slave stations in a state of being distributed and arranged, and a plurality of types of transports are connected. It is either frequency <br/>, a plurality of fixed transmitter for transmitting the transmission data to each transmission area at different carrier frequencies from the carrier frequency <br/> transmission areas adjacent the fixed For transmitter And a plurality of fixed receivers for receiving response data from the carrier at the same carrier frequency as the corresponding fixed transmitter, wherein the carrier transmits transmission data from the fixed transmitter. A mobile receiver enabled to receive the plurality of types of carrier frequencies , and response data for creating response data corresponding to the received data when identification data in the received data matches identification data of the vehicle. and creating means, and carrier frequency determination means for the carrier frequency of the received signal to determine from the plurality types, transport to switch the carrier frequency of the mobile transmitter to the carrier frequency and the judgment
Frequency switching means, having a plurality of types of carrier frequencies ,
A mobile transmitter for transmitting response data in synchronization with the reception of the transmission data at the carrier frequency switched by the carrier frequency switching means.

[0008]

According to the present invention, the transmission data for each carrier outputted from the central control unit of the management means is sequentially transmitted to a plurality of slave stations, and is periodically (polled) while sequentially switched from the slave stations. The signal is guided to all the fixed transmitters, and is transmitted to each transmission area on any one of a plurality of types of carrier frequencies. The fixed transmitters are provided in a larger number than the number of slave stations, and are distributed so that the carrier frequencies of adjacent transmission areas are different carrier frequencies from each other. The data communication with the server is effectively performed without interference. On the other hand, each carrier extracts data having the identification code of the own vehicle from the transmission area periodically received by the mobile receiver, and treats the data as reception data of the own vehicle. And
Response data corresponding to the content of the received data is generated, and the response data switched to the same carrier frequency as the received carrier frequency by the carrier frequency switching means is used as the fixed transmitter having the carrier frequency corresponding to the fixed transmitter. Is received reliably.

[0009]

FIG. 1 is a block diagram showing an example of a carrier communication system according to the present invention.

This communication system is used for exchanging data between a plurality of transport vehicles 5 traveling on the floor and management means for instructing the transport vehicles 5 to travel or stop. is there.

The management means comprises a central control unit 1, a master station 2, a plurality of slave stations 3, and a plurality of transmission / reception devices 4. The transport vehicle 5 has a transmission / reception device 6, and performs travel control and the like in accordance with data from the management unit.

As shown in FIG. 2, the central control unit 1
PU11, ROM12, RAM13, SIO14, PI
O15, CRT terminal 16, operation unit 17, and display unit 1
8 to output control data for controlling the traveling of each carrier 5 to the master station 2 and to receive data (RD signal) from each carrier 5 input through the master station 2 Each carrier 5 is managed based on this. The circuits 11 to 15 of the central control device 1 are connected by a bus line.

The CPU 11 outputs predetermined control data to the master station 2 based on the operation contents of the operation unit 17 and the like, the control programs stored in the ROM 12 and the RAM 13 and the data from the carrier 5. The CPU 11
Is configured to cause the CRT terminal 16 and the display unit 18 to perform a predetermined display based on data or the like from each carrier 5.

The ROM 12 and the RAM 13 store a control program, various data, and the like. SIO
Reference numeral 14 connects the CPU 11 and the like to the CRT terminal 16. The PIO 15 includes the CPU 11 and the operation unit 17.
And the display unit 18. The CRT terminal 16 performs various displays such as the position of the carrier 5 and control contents. The operation unit 17 performs various settings. The display unit 18 includes an LED or the like, and performs an error display or the like when a failure occurs in the carrier 5 or the like.

As shown in FIG. 2, the master station 2
, A ROM 22, a RAM 23, an SIO 24, a PIO 25, and an interface 26 for controlling communication with the slave station 3. Then, the master station 2 performs a process (polling) of sequentially switching transmission data to each carrier 5 at predetermined time intervals and outputting the data to the slave station 3. The circuits 21 to 25 of the master station 2 are connected by a bus line.

The CPU 21 transmits a transmission request signal (RS signal) to the slave station 3 prior to the transmission of the transmission data from the central control unit 1 to the slave station 3, and the slave station 3 transmits the RS request signal to the slave station 3. When the transmission enable signal (CS signal) is responded, the transmission data is transmitted to the slave station 3. Also, CP
When the carrier detection signal (CD signal) is input from the slave station 3, the U21 stores the data input from the slave station 3 at this time as reception data (RD signal) in the master station 2. Further, as shown in FIG. 6, the CPU 21 adds identification data A for identifying to which carrier 5 the data is to be transmitted before the control data B, and these data A,
B is output to the slave station 3 as transmission data (SD signal). Further, the CPU 21 extracts identification data from the data received from the slave station 3 and determines from which of the vehicles 5 the data is from the extracted identification data.

The ROM 22 and the RAM 23 store each transport vehicle 5.
The storage unit stores identification data, control programs, various types of data, and the like corresponding to. The SIO 24 converts the transmission data (parallel data) into serial data and transmits the serial data to the interface 26. PIO25
Transmits the transmission data from the central control device 1 to the CPU 21 and the like, and transmits the reception data from the slave station 3 to the central control device 1. Note that a dual port RAM may be used instead of the PIO 25. When a well-known personal computer is used as the central control device 1, the master station 2 can be accommodated in an expansion slot of the personal computer. In this case, the central controller 1 and the master station 2
25 (or dual port RAM), so that data transmission can be performed at an arbitrary timing.

As shown in FIG. 1, each of the slave stations 3 is connected to each other.
Alternatively, a plurality of transmission / reception devices 4 are connected. And
The slave station 3 transmits data received from the transmission / reception device 4 to the master station 2 and also transmits transmission data from the master station 2 to the transmission / reception device 4 and another slave station 3.

Here, an example of the configuration of the slave station 3 will be described with reference to the circuit diagram of FIG. Note that FIG.
2 shows a case where two transmitting / receiving apparatuses 4a and 4b are connected.

Lines of transmission data (SD signal) from the master station 2 and a transmission request signal (RS signal) for notifying that transmission is to be performed are connected to the other slave stations 3 and the transmission / reception devices 4a and 4b, respectively. The transmission data and transmission request signal are transmitted to other slave stations 3 and the transmission / reception devices 4a and 4b as they are. As a result, transmission data corresponding to each carrier 5 is simultaneously emitted from each transmitting / receiving device 4 at the same timing. Further, the reception data (RD signal) from the other slave stations 3 and the transmission / reception devices 4a and 4b and the carrier detection signal (CD signal) indicating that the carrier has been detected are:
When the high signals are input to the gate circuits (AND circuits) 31a to 31c and the high signals are input as the carrier detection signals, the reception data is output to the OR circuit 32. The OR circuit 32 includes the gate circuits 31a to 3a.
1c is output to the master station 2. In addition, since the transmission data to each carrier 5 is sequentially switched and transmitted from each transmission / reception device 4 every predetermined time, as shown in FIG. 6, the data (identification data A and The data C) is transmitted to the transmission / reception device 4 in time series corresponding to the transmission data. Therefore, data from the plurality of transport vehicles 5 is not transmitted to the transmitting / receiving device 4 at the same time.

The other slave station 3 and the transmitting / receiving device 4
The carrier detection signals from a and 4b are input to an OR circuit 34, respectively. The OR circuit 34 receives a carrier detection signal (high signal) from one of the other slave stations 3 and one of the transmission / reception devices 4a and 4b. Then, the carrier detection signal is output to the master station 2.

Transmission enable signals (CS signals) indicating that transmission is possible from the other slave stations 3 and the transmission / reception devices 4a and 4b are input to the AND circuit 33, respectively. Slave station 3 and transmission / reception devices 4a, 4b
When the above-mentioned transmission enable signal (high signal) is input from all of the above, the transmission enable signal is output to the master station 2. Then, the master station 2 sends out the transmission data to the slave station 3 only when all the transmission / reception devices 4 can transmit.

As shown in FIG. 4, the transmission / reception device 4 includes an oscillator 41, a modulator 42, a light emitting element 43, a light receiving element 44, and a demodulator 45, and responds to transmission data input via the slave station 3. The modulated light is projected toward the carrier 5 and the light from the carrier 5 is received, demodulated into reception data, and output to the slave station 3.

The oscillator 41 oscillates at a preset frequency and outputs it to the modulator 42 and the demodulator 45. The modulator 42 is, for example, an FSK (Frequency Shift Ke).
ying) modulator, which modulates transmission data from the slave station 3 using the signal from the oscillator 41 as a carrier wave and outputs the modulated data to the light emitting element 43. Also, the modulator 42
Receives the transmission request signal from the slave station 3 and outputs a carrier to the light emitting element 43, and delays the transmission request signal and outputs the signal to the slave station 3 as a transmission enable signal.
As a result, as shown in FIG. 7, transmission data is prevented from being carried on the rising edge of the output of the light emitting element 43. The light emitting element 43 has a predetermined transmission area, and emits a signal from the modulator 42 as an optical signal.

The light receiving element 44 receives the optical signal and outputs the light signal to the demodulator 4.
5 is output. The demodulator 45 is composed of, for example, a detection circuit of a heterodyne detection method, and demodulates a signal from the light receiving element 44 into reception data and outputs the data to the slave station 3. Further, the demodulator 45 outputs a carrier detection signal to the slave station 3 when detecting a carrier having the predetermined frequency from the signal from the light receiving element 44.

The carrier wave of each transmitting / receiving device 4 is selected and set so that the frequency of the carrier wave of the adjacent transmitting / receiving device 4 does not match. That is, since it is necessary to reliably communicate regardless of the position of the carrier 5 on the floor, it is necessary to overlap the transmission areas of the transmission / reception devices 4 to some extent. In this case, if the frequencies of the carrier waves of the respective transmission / reception devices 4 are equal, the carrier waves interfere with each other and accurate communication becomes difficult.

Therefore, as shown in FIG.
For example, if the transmission area is a circle having a radius r, the transmitting and receiving devices 4 are arranged vertically and horizontally at intervals of √2 · r, and the frequency of the carrier wave is adjusted so that the frequency of the carrier wave of the adjacent transmitting and receiving device 4 does not match. Set. In this case, four types of frequencies f
It is possible to prevent the frequencies of the carrier waves of the adjacent transmitting / receiving devices 4 from being identical only by 1 to f4.

The radius of the transmission area varies in the range of 1r to √ (1.5) · r due to manufacturing variations of the light emitting element 43, but as shown in FIG. Are arranged at intervals of 2√2 · r, so that transmission areas of carrier waves having the same frequency do not overlap.

Next, the configurations of the transport vehicle 5 and the transmission / reception device 6 will be described with reference to FIG.

The transport vehicle 5 has a control unit 51. The control unit 51 stores the identification data corresponding to the carrier 5 and extracts the identification data from the data received from the transmission / reception device 6, and the extracted identification data matches the stored identification data. To determine if
When the extracted identification data matches the stored identification data, a start of travel, a right turn, a left turn, a stop, and the like are performed in accordance with the received data.

In addition, the control unit 51 adds identification data corresponding to the carrier 5 to data indicating that the received data has been received in response to the received data, and transmits the data to the transmitting / receiving device 6 as transmission data. I have to. The control unit 5
In some cases, the data 1 is transmitted to the transmission / reception device 6 by adding identification data corresponding to the carrier 5 to data indicating the current position of the carrier 5 or data indicating a failure or the like. The control unit 51
When the reception data is not input from the transmission / reception device 6 for a predetermined time or more, the operation of the carrier 5 is stopped to prevent the vehicle from traveling in an uncontrolled state.

The transmitting / receiving device 6 includes an oscillating unit 60 and a light receiving element 6
1, a light receiving level detecting unit 62, an oscillation controlling unit 63, a demodulating level detecting unit 64, a demodulator 65, a gate circuit (AND circuit) 66, a delay unit 67, a modulator 68, and a light emitting element 69.
The signal is demodulated at the frequency of the carrier of the received optical signal, and is modulated at the frequency to project light.

The light receiving level detector 62 detects the light receiving level of the received light signal, determines whether or not this level is higher than a predetermined reference light receiving level, and outputs the result of the determination to the oscillation controller 63. is there. Demodulator 65
Consists of, for example, a heterodyne detection type detection circuit,
A signal from the light receiving element 61 is demodulated with an oscillation signal from the oscillation control unit 63 and is converted into reception data by the gate circuit 66.
Output to The demodulation level detection unit 64
It is determined whether or not the level of the signal demodulated by the demodulator 65 is equal to or higher than a preset reference demodulation level, and the result of this determination is output to the oscillation control unit 63.

The oscillating unit 60 outputs the oscillation control unit 6 from the frequencies f1 to f4 of the carrier wave of the transmitting / receiving device 4 described above.
An oscillation signal having a frequency corresponding to the switching signal from the
5 and the modulator 68. The oscillation control unit 63 includes a determination unit 631 and a switching unit 632. When the determination unit 631 determines that the light reception level detected by the light reception level detection unit 62 is equal to or higher than the reference light reception level, the switching unit 632 controls the oscillation unit. The 60 oscillation signals are switched in the order of the frequencies f1 to f4. Further, the oscillation control unit 63 includes a determination unit 63
When the demodulation signal level detected by the demodulation level detection unit 64 is equal to or higher than the reference demodulation level, the oscillation signal of the oscillation unit 60 is locked at the frequency. Further, the oscillation control section 63 outputs a high signal as a carrier detection signal to the gate circuit 66 and the control section 51 when the level of the demodulated signal is equal to or higher than the reference demodulated level. The oscillation control unit 6
When the level of the demodulated signal becomes lower than the reference demodulated level, the oscillating signal of the oscillating unit 60 is again transmitted to the frequency f1.
To f4.

When the carrier detection signal is input, the gate circuit 66 outputs the received data at this time to the control unit 51. The modulator 68 is, for example, an FSK type modulator, and modulates transmission data from the control unit 51 using the oscillation signal from the oscillation control unit 63 as a carrier wave and outputs the modulated data to the light emitting element 69. The modulator 68 receives a transmission request signal from the control unit 51 and outputs a carrier to the light emitting element 69.

As shown in FIG. 7, the delay section 67 delays the transmission request signal from the control section 51 by a predetermined time T0 and outputs the transmission request signal to the control section 51 as a transmission enable signal. Then, the control unit 51 outputs the identification data A and the predetermined data B to the modulator 68 when the transmission enable signal is input. As a result, transmission data is prevented from being placed on the rising edge of the output of the light emitting element 69.

As described above, the transmitting / receiving device 6 sets the light receiving level of the light receiving element 44 to be equal to or higher than the reference light receiving level.
The optical signal can be reliably demodulated. Also,
If the level of the demodulated signal by the demodulator 65 is equal to or higher than the reference demodulation level, the demodulated signal can be surely converted into received data. The light receiving level is set to be equal to or higher than the reference light receiving level within the transmission area of the transmitting / receiving device 4.

Next, the operation of the transmitting / receiving device 6 will be described.

When the carrier 5 is located, for example, near the center of the transmission area of the transmission / reception device 4 of the frequency f2, the light reception level from the transmission / reception device 4 detected by the light reception level detection unit 62 is equal to or higher than the reference light reception level. . Therefore, the oscillation control unit 63 sets the oscillation signal of the oscillation unit 60 to the frequency f1 and outputs the signal to the demodulator 65. In this case, the level of the demodulated signal detected by the demodulation level detection unit 64 becomes lower than the reference demodulation level, and the oscillation control unit 63 switches the oscillation signal of the oscillation unit 60 to the frequency f2 to change the oscillation signal of the frequency f2. Output to the demodulator 65.

At this time, since the level of the demodulated signal is equal to or higher than the reference demodulated level, the oscillation control section 63 locks the oscillation signal of the oscillation section 60 at the frequency f2, and
5 and the modulator 68. Therefore, the frequency f
At 2, demodulation and modulation are performed. Thereby, the transport vehicle 5
Communicates data with the transmitting / receiving device 4 at the frequency f2 using a carrier wave at the frequency f2.

Thereafter, when the carrier 5 travels and moves to, for example, the transmission area of the transmitting / receiving device 4 at the frequency f1, the level of the demodulated signal detected by the demodulation level detecting section 64 decreases in accordance with this movement, and the reference demodulation is performed. Below the level.
Therefore, the oscillation control unit 63 sequentially switches the oscillation signal of the oscillation unit 60 from the frequency f3 in order to find an oscillation signal whose demodulation signal level is equal to or higher than the reference demodulation level.

In this case, since the level of the demodulated signal becomes equal to or higher than the reference demodulation level at the frequency f1, the oscillation control unit 63 locks the oscillation signal of the oscillation unit 60 at the frequency f1 and sends the signal to the demodulator 65 and the modulator 68. Output. And
Demodulation and modulation are performed at the frequency f1. Thus, the carrier 5 communicates data with the transmitting / receiving device 4 at the frequency f1 using the carrier at the frequency f1.

On the other hand, for example, when the light emission level of the transmission / reception device 4 decreases due to the failure of the transmission / reception device 4, the light reception level of the carrier 5 below the transmission / reception device 4 decreases. Then, when the light reception level detected by the light reception level detection unit 62 becomes lower than the reference light reception level, the oscillation control unit 63 stops the oscillation of the oscillation unit 60 and stops the demodulation and modulation operations. As a result, the control unit 51 does not receive the received data, and as a result, the operation of the carrier 5 stops. Note that the control unit 51 may turn on an alarm lamp provided on the carrier 5 in response to the stop of the demodulation operation to notify that the carrier 5 is stopped.

Thus, even if the transmission / reception device 6 moves from the transmission area of one transmission / reception device 4 to the transmission area of another transmission / reception device 4, the transmission / reception device 6 sequentially switches the oscillation frequency and the level of the demodulated signal is changed to the reference demodulation level. Since the demodulation and the modulation are performed by locking at the frequencies described above, data communication with the transmission / reception device 4 can be reliably performed.

Since the transmission data is sequentially switched from the transmission / reception device 4 to each carrier 5 and transmitted, each carrier 5 is transmitted while the transmission data to the other carrier 5 is being transmitted.
It is possible to detect a frequency at which the level of the demodulated signal is equal to or higher than the second level, lock the frequency, and prepare to perform demodulation and modulation, thereby enabling efficient communication.

In the above description, when the light receiving level from the transmitting / receiving device 4 is equal to or higher than the reference light receiving level, the oscillation control unit 63 changes the frequency of the oscillation signal of the oscillation unit 60 sequentially from the frequency f1 to the frequency of the demodulated signal. It oscillates at a frequency where the level is higher than the reference demodulation level,
The frequency of the oscillation signal of the oscillation unit 60 is sequentially switched from the frequency f1, and the level of the demodulated signal at each frequency is stored.
The frequency having the highest level of the demodulated signal among the frequencies f1 to f4 may be detected and oscillated at the frequency. In this case, when the carrier 5 is in a portion where the transmission areas of the adjacent transmission / reception devices 4 overlap, the levels of the demodulated signals of a plurality of frequencies may be equal to the maximum. In such a case, for example, the lower frequency is prioritized. I do.

The transport vehicle 5 may be a manned transport vehicle. For example, the control unit 51 displays the instruction content from the management unit on the display unit based on the received data, and the operator transports the content in accordance with the display content. You may drive a car.

Although the transmitting / receiving device 4 of the management means and the transmitting / receiving device 6 of the carrier 5 transmit and receive optical signals respectively, these transmitting and receiving devices may transmit and receive using known radio waves. Ultrasound may be used.
Further, when radio waves are used as the transmitting and receiving device, it is possible to transmit and receive to and from a plurality of carriers 5 using one antenna as the transmitting and receiving device on the management means side.

[0049]

According to the present invention, while the number of slave stations is reduced, the number of fixed transmitters that need only be arranged is increased, so that transmission of transmission data by polling each carrier can be performed over a wide range. And can be performed over
By employing a plurality of types of carrier frequencies in a distributed manner so that the carrier frequencies of adjacent transmission areas are different carrier frequencies from each other, interference between the transmission areas is eliminated, and reliable data transmission can be performed. In addition, since the mobile transmitter of the carrier switches the received carrier frequency and returns the response data, the management means always transmits the created data from the carrier at the corresponding carrier frequency without interference. Reliable reception is possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of a communication system according to the present invention.

FIG. 2 is a block diagram illustrating an example of a central control device and a master station.

FIG. 3 is a circuit diagram illustrating an example of a slave station.

FIG. 4 is a block diagram illustrating an example of a transmission / reception device on a management unit side.

FIG. 5 is a block diagram illustrating an example of a transport vehicle.

FIG. 6 is a timing chart showing a data transmission timing.

FIG. 7 is a timing chart showing a relationship among a transmission request signal, a transmission enable signal, and transmission data.

FIG. 8 is a distribution diagram showing distribution of transmission areas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Central control apparatus 2 Master station 3 Slave station 4,6 Transceiver 5 Carrier 11 CPU 12 ROM 13 RAM 51 Control part of carrier

Continuation of front page (56) References JP-A-62-26939 (JP, A) JP-A-62-109448 (JP, A) JP-A-55-80947 (JP, A) JP-A-62-27804 (JP) JP-A-64-24529 (JP, A) JP-A-64-9508 (JP, A)

Claims (1)

(57) [Claims] 1. In a carrier communication system for controlling travel of a carrier by exchanging transmission data and response data between the managing means and a plurality of carriers, the management means includes: A central control unit that periodically outputs transmission data for each transport vehicle to which unique identification data is added, and outputs transmission data for each transport vehicle from the central control unit, and receives received response data. A plurality of slave stations leading to the central control unit, connected to each of the plurality of slave stations in a state of being distributed and arranged, and any one of a plurality of types of carrier frequencies , and adjacent transmission areas a plurality of fixed transmitters and carrier frequency <br/> transmits the transmission data at different carrier frequencies to each other in each transmission area is provided corresponding to the fixed transmitter, identical to the fixed transmitter corresponding transport frequency of In a plurality of fixed receivers for receiving the response data from the transport vehicle, the transport vehicle, mobile reception of the transmission data from the fixed transmitters are to be received with respect to the plurality of types of carrier frequencies Device, response data creating means for creating response data corresponding to the received data when the identification data in the received data matches the identification data of the vehicle, and the carrier frequency of the received signal from among the plurality of types and carrier frequency determination means for determining, conveyed to switch the carrier frequency of the mobile transmitter to the carrier frequency and the judgment
Frequency switching means, having a plurality of types of carrier frequencies ,
A mobile transmitter for transmitting response data in synchronization with the reception of the transmission data at the carrier frequency switched by the carrier frequency switching means.