JP2008085890A - Radio transmission system and mobile station therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio transmission system based on a close coupling radio transmission method with which high-quality data transmission can be performed without complicating circuit configuration or communication scheme. <P>SOLUTION: The present invention relates to a mobile station 3 for a radio transmission system comprising a plurality of data transmission couplers 24, 25 for wirelessly transmitting a data signal f3 containing a video image to a fixed station 5 via paired stranding cables 4 connected to the fixed station 5, wherein the plurality of couplers 24, 25 are disposed so that phases of level variations in reception signals f1 received from the paired stranding cables 4 become different from each other, and a switching means 26 is provided for switching a transmission source of the data signal f3 to the coupler 24, 25 with a highest level of the reception signal f3, among the plurality of couplers 24, 25. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio transmission system suitable for use as an inspection device by remote control and a mobile station thereof, and more particularly to a radio transmission system that performs signal transmission by a tightly coupled radio transmission system and the mobile station.

  Conventionally, inspection devices with inspection robots that automatically run remotely have been developed in order to inspect dangerous locations such as highways, bridge decks, and the upper half of tunnels. Yes. In such an inspection device, it is common to use a wireless transmission system that can be miniaturized without a cable as signal transmission between a controller that is a fixed station and an inspection robot that is a mobile station having a camera (Patent Literature). 1).

  In the case of such a wireless transmission system without a cable, a specific low-power radio that has a small transmission output and does not require a license to use radio waves may be adopted. Has the disadvantage of being limited. Therefore, the present applicant has already developed an inspection device that employs a tightly coupled wireless transmission system without such drawbacks (see Patent Document 2).

  In this inspection device, a cable is laid along the traveling direction of the inspection robot, which is a mobile station, and the cable is connected to a controller, which is a fixed station. By transmitting and receiving wireless signals in close contact with or close to each other, video signals captured by the mobile station camera are transmitted and received wirelessly between the fixed station and the mobile station via a cable. By adopting such a tightly coupled wireless transmission system, it is possible to extend the transmittable distance while complying with the electric field strength defined by law.

When transmitting a video signal between a fixed station and a mobile station using such a tightly coupled wireless transmission method, the image may be analog-transmitted using an induction wireless method using a twisted cable. However, it is difficult to transmit the video signal, and the video quality varies significantly depending on the condition of the transmission path.
In particular, with recent advances in image processing technology, it is possible to quickly and accurately inspect the captured video by digital image processing. To achieve this, high-quality video is added to the controller, which is a fixed station. A signal needs to be transmitted.

For this reason, the inspection robot apparatus described in Patent Document 2 employs a multilevel digital modulation method such as the QPSK method in order to improve the image quality, and digitally transmits the modulated image signal through the cable. ing.
JP-A-8-128015 JP 2006-42020

  By the way, since a large frequency band is required to transmit a large-capacity video signal by the digital modulation method, the video signal is modulated and transmitted to a radio signal having a high carrier frequency. However, since the transmission path in the cable is a distributed constant circuit in the high frequency region, the signal transmission characteristics greatly vary depending on the positional relationship between the inspection robot, which is a mobile station, and the cable.

For this reason, when the inspection robot moves on the rail while photographing, a change in the signal transmission characteristics occurs due to a change in the relative position with respect to the cable, and thus the level of the radio signal received by the controller also changes.
Therefore, in the inspection device described in Patent Document 2, a plurality of transmission frequencies are set to stabilize a digital image, and a video signal is transmitted by selecting a frequency with a good reception state in a controller on the reception side. ing.

  However, in such a transmission system, it is necessary not only for the inspection robot on the transmission side of the video signal but also for the controller on the reception side to be able to receive in multiple frequency bands, so the circuit configuration of the fixed station is complicated. become. Further, in this case, since it is necessary to perform control communication for frequency switching between the inspection robot and the controller, there is also a drawback that the communication method between the two becomes complicated.

  On the other hand, as described later in the embodiment, when the transmission medium is a twisted cable, the transmission characteristics of the coupler greatly change depending on the directions of the two electric wires constituting the cable. For this reason, when the inspection robot moves on the rail while photographing, the transmission characteristics of the coupler change at a smaller pitch than the change based on the cable distributed constant circuit. However, in the inspection device described in Patent Document 2, No measures are taken for countermeasures against such a change in transmission characteristics due to the twisted structure of the cable.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a wireless transmission system using a tightly coupled wireless transmission method capable of high-quality data transmission without incurring a complicated circuit configuration or communication method. .
Another object of the present invention is to provide a wireless transmission system based on a tightly coupled wireless transmission system capable of high-quality data transmission even when a twisted cable is employed.

  The present invention relates to a movement of a wireless transmission system including a plurality of data transmission couplers for wirelessly transmitting a data signal including video to the fixed station via a twisted cable connected to the fixed station. The plurality of couplers are arranged such that the phase of the level fluctuation of the received signal received from the twisted cable is different from each other, and the transmission source of the data signal is selected from among the plurality of couplers And a switching means for switching to a coupler having the highest received signal level.

  According to the mobile station of the present invention described above, the plurality of couplers for data transmission are arranged so that the phases of the level fluctuations of the received signals received from the twisted cable are different from each other. Since the data signal transmission source is switched by the switching means to the coupler having the highest received signal level, the deterioration of the data signal transmitted from the selected coupler to the twisted cable can be minimized. The data signal from the mobile station can be transmitted to the fixed station without deteriorating.

Further, according to the mobile station of the present invention, the data signal is transmitted to the fixed station by the coupler having the better transmission characteristics among the plurality of couplers for data transmission provided in the mobile station. Thus, there is no need to employ a circuit configuration for receiving a plurality of frequency bands in the fixed station, and there is no need to perform control communication for frequency switching between the mobile station and the fixed station. This simplifies the circuit configuration and communication method of the entire system.
In the present invention, the received signals received from the twisted cable by the plurality of couplers on the mobile station side are specifically transmitted from the fixed station via the twisted cable, and the mobile station is remotely operated. A control signal can be used.

  In the present invention, the switching means may be provided in the fixed station. In this case, the level comparison of received signals received by each coupler on the mobile station side and switching control of the coupler are performed on the fixed station side. However, it is difficult to accurately perform such control between the mobile station and the fixed station. For this reason, there arises a disadvantage that the control signal for switching the coupler from the fixed station interferes with the data signal, and the transmission of the data signal to the fixed station can be hindered.

Therefore, it is recommended that the switching means be mounted on the mobile station side together with each coupler for data transmission.
In this case, since the level comparison of the received signals received by each coupler and the coupler switching control are performed in the mobile station, for example, a timing adjusting means for operating the switching means in the guard bit of the data signal is further provided. By providing the mobile station, the switching timing of the coupler can be adjusted so as not to interfere with the transmission of the data signal, and the data signal can be appropriately transmitted to the fixed station.

In the present invention, the distance between the couplers for data transmission is not limited to a specific distance as long as the phase of fluctuation of the control signal in each coupler is not uniform, The coupler is preferably arranged at a position where the phase of the level fluctuation of the received signal is inverted. More specifically, such a coupler is arranged at a position separated by an odd multiple of 1/4 of the twisting pitch of the twisted cable in the cable length direction, which is the moving direction of the mobile station. Can be realized.
In this case, when the transmission loss in one coupler is the maximum, the transmission loss in the other coupler is minimized, so either one of these couplers is selectively adopted by the switching means. In this case, the transmission loss of the data signal with respect to the twisted cable can be minimized.

Further, in the present invention, a weak reception signal (control signal in an embodiment described later) received by each coupler is transmitted from each coupler by connecting a duplexer to each of a plurality of couplers for data transmission. The influence received from the data signal to be reduced can be reduced as much as possible, and thereby the switching control of the coupler can be more reliably performed.
Furthermore, in the present invention, if a directional coupler that can direct the direction of outgoing radio waves to the connection side between the twisted cable and the fixed station is employed as a plurality of couplers, The data signal from the mobile station can be more reliably transmitted to the fixed station as compared with a normal coupler in which interference is suppressed and the directivity with respect to the twisted cable is constant.

  As described above, according to the present invention, it is possible to transmit data signals from a mobile station to a fixed station without degrading a circuit configuration and a communication method, and thus high-quality data transmission is possible. A wireless transmission system using a tightly coupled wireless transmission system can be provided at low cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Overall configuration of inspection equipment]
FIG. 1 is a schematic configuration diagram of an inspection apparatus employing a wireless transmission system of the present invention.
The inspection device 1 of the present embodiment is for remotely inspecting inspection points at high places such as expressways and bridge slabs, as shown in FIG. An inspection robot 3 as a mobile station provided on a traveling rail 2 laid below the vehicle, a twisted cable 4 laid along the traveling rail 2, and a fixed connected to one end of the cable 4 And a controller 5 as a station.

A terminator 6 is connected to the other end of the twisted cable 4. Further, in the example shown in FIG. 1, the twisted cable 4 is directly connected to the controller 5, but the controller 5 and the cable 4 may be indirectly connected via a matching unit (not shown).
The overall configuration and operation of the inspection device 1 will be described with reference to FIGS. 1 and 2. First, the inspection robot 3 photographs the inspection object with the TV camera 27 while traveling on the traveling rail 2, and the sound collecting microphone. At 28, sound around the inspection object is acquired.

The video and audio signals (hereinafter referred to as the data signal f3) are transmitted from the data signal couplers 24 and 25 to the twisted cable 4 and transmitted to the controller 5 via the cable 4.
The inspection robot 3 is a control signal provided separately from the couplers 24 and 25 for operating state signals such as the current position, traveling speed, direction of the TV camera, and remaining battery level (hereinafter referred to as a state signal f2). The data is transmitted to the controller 5 via the coupler 19 and the twisted cable 4.

The controller 5 receives the data signal f3 and the status signal f2 from the inspection robot 3 via the cable 4, displays an image on the television monitor 14, and outputs a sound. Furthermore, the controller 5 displays the operation state of the inspection robot 3 on the television monitor 14.
The user who performs the inspection can perform the inspection work with reference to the video and audio output displayed on the television monitor 14 while confirming the operation state of the inspection robot 3 displayed on the controller 5. Further, the user can use the operation device 12 of the controller 5 to operate the inspection robot 3 to move forward, backward, stop, and turn the television camera 27 in the vertical and horizontal directions.

In response to the above-described user operation, the controller 5 generates a signal (hereinafter referred to as a control signal f1) for instructing the operation to the inspection robot 3, and the control signal f1 is inspected via the twisted cable 4. Transmit to the robot 3.
The inspection robot 3 receives the control signal f1 from the controller 5 via the control coupler 19, and operates each part in accordance with a user operation instruction.

The twisted pair cable 4 is a cable suitable for a tightly coupled wireless transmission system, and is formed of a twisted pair cable in which two electric wires are twisted at a substantially constant pitch to make a pair. The cable 4 is used without a shield. The twisted cable 4 is laid along the traveling rail 2, and a controller 5 and a terminator 6 are connected to both ends of the twisted cable 4, respectively. The terminator 6 suppresses the generation of a reflected wave at the end of the twisted cable 4.
The twisted cable 4 can also extend the transmission distance by connecting to another twisted cable 4 via a repeater (not shown) that amplifies the radio signal.

[Configuration of controller]
As shown in FIG. 1, the controller 5 includes a duplexer 8 connected to the twisted cable 4 and a demodulator 9 based on QPSK (Quadruple Phase Shift Keying) system connected to the duplexer 8. And a control transceiver 10.
The control transceiver 10 can transmit a control signal f1 for performing remote operation of the inspection robot 3 by, for example, an FSK (Frequency Shift Keying) method, and the control signal f1 corresponds to the control signal f1. The state signal f2 to be received can be received.

A control device 11 is connected to the control transceiver 10, and an operation device 12 is connected to the control device 11. Based on the demodulated signal of the state signal f <b> 2 input from the transceiver 10, the control device 11 switches motion display such as forward or reverse on the display unit provided in the operation device 12.
Further, the control device 11 outputs an operation signal from an operation lever provided in the operation device 12 to the transceiver 10. The transceiver 10 modulates the operation signal into the control signal f1 by, for example, the FSK modulation method, and transmits the control signal f1 to the twisted cable 4 via the duplexer 8.

  The QPSK demodulator 9 demodulates the data signal f3 composed of the QPSK modulated wave from the inspection robot 3 into an MPEG signal, and outputs this signal to the digital decoder 13. The decoder 13 converts the MPEG signal received from the demodulator 9 into an analog video signal and audio signal, and outputs the analog video signal and audio signal to a display device including the television monitor 14. The television monitor 14 performs predetermined video display and audio output based on the video signal and audio signal from the digital decoder 13.

[Configuration of inspection robot]
FIG. 2 is a schematic configuration diagram of the inspection robot 3 of the present embodiment.
As shown in FIG. 2, the inspection robot 3 includes a traveling machine body 16 that is movable along the twisted cable 4, and a drive control unit 17 and a data transmission unit 18 that are mounted on the traveling machine body 16. Among these, the drive control unit 17 includes a control coupling unit 19 arranged in close contact with or close to the cable 4, a control signal modulator / demodulator 20, a control device 21, and a drive device 22. Yes.

The control coupler 19 has a loop antenna therein, and transmits a status signal f2 to the twisted cable 4 and receives a control signal f1 from the cable 4.
The control signal modulator / demodulator 20 demodulates the control signal f 1 received from the coupler 19 by, for example, the FSK modulation method, and outputs the demodulated signal to the control device 21. The control device 21 controls the drive device 22 based on the demodulated signal.
The driving device 22 includes a driving motor for the traveling machine body 16 and a turning motor for the television camera 27. The driving device 22 moves the traveling machine body 16 forward or backward or stops based on a command from the control device 21, or causes the television camera 27 to move up and down. Make the left and right swivel motion.

  The control device 21 always keeps track of the motion state of the drive device 22 (rotation direction, operation state, etc. of the drive motor and turning motor), and sends an analog signal indicating the state to the control signal modulator / demodulator 20. Output. Then, the modem 20 modulates the control signal from the control device 21 to the state signal f2 by, for example, the FSK modulation method, and this state signal f2 is transmitted to the twisted cable 4 via the coupler 19.

  The data transmission unit 18 includes a pair of data transmission couplers 24 and 25 that are arranged at two positions apart from each other in the cable length direction that is the moving direction of the inspection robot 3, and the coupling between the two. Connected to the switching device 26 to which the devices 24 and 25 are connected, a television camera 27 for photographing the inspection object, a sound collecting microphone 28 for picking up sound around the inspection object, and the camera 27 and the microphone 28. The digital encoder 29 and a QPSK modulator 30 connected to the encoder 29.

The TV camera 27 converts an image of the inspection object photographed through the camera lens into an electrical signal and outputs it to the digital encoder 29. The sound collecting microphone 28 converts the acquired sound into an electrical signal. To the encoder 29.
The digital encoder 29 converts the video signal from the television camera 27 and the audio signal from the sound collection microphone 28 into an MPEG signal which is a video / audio digital signal, and outputs this signal to the QPSK modulator 30.

The digital encoder 29 according to this embodiment adds a synchronization preamble or Reed-Solomon error correction code to video and audio signals, and adds a predetermined guard bit to generate a frame shown in FIG. 4, for example. Each of the frames is output to the QPSK modulator 30.
The QPSK modulator 30 modulates the frame of the data signal f3 made of the MPEG signal into a QPSK modulated wave by the QPSK method, and outputs this modulated wave to the switching device 26. The switching device 26 selects one of the two couplers 24, 25, and the selected coupler 24, 25 transmits the data signal f 3 made up of the QPSK modulated wave to the twisted cable 4.

FIG. 3 is a block diagram illustrating a circuit configuration of the switching device 26.
As shown in FIG. 3, each of the couplers 24 and 25 for data transmission has a loop antenna inside, and transmits a data signal f3 composed of a QPSK modulation wave to the twisted cable 4 and from the cable 4 The control signal f1 is received.
The switching device (switching means) 26 of the present embodiment includes a pair of duplexers 31 and 32 connected to the couplers 24 and 25 for data transmission, and a pair of receivers connected to the duplexers 31 and 32, respectively. 33, 34, a level comparator 35 to which the receivers 33, 34 are connected, a timing adjustment circuit 36 for adjusting the transmission timing of the data signal f3, and couplers 24, 25 according to instructions of the adjustment circuit 36. And a switch 37 for switching.

  Each of the duplexers 31 and 32 includes a transmission filter connected between the antenna terminals of the couplers 24 and 25 and a terminal of the switch 37 on the transmission side, and a branching circuit connected between the antenna terminal and the reception terminal. And a reception filter. Further, the demultiplexing circuits included in the duplexers 31 and 32 block the influence of the transmission / reception signals (in this case, the data signal f3 and the control signal f1) on the other circuit.

  For this reason, the data signal f3 which is a transmission signal from the transmission side terminal is transmitted to the antenna terminals of the couplers 24 and 25 without reaching the reception side terminal, and is a control signal which is a reception signal supplied from the antenna terminal. f1 is supplied to the receiving side terminal without reaching the transmitting side terminal, whereby a weak control signal f1 received by each coupler 24, 25 is transmitted from each coupler 24, 25. The influence received from the data signal f3 to be reduced is reduced, and the switching control of the couplers 24 and 25 can be more reliably performed.

Each of the receivers 33 and 34 always outputs the control signal f1 to the level comparison circuit 35. The level comparison circuit 35 determines whether the control signal f1 from any of the couplers 24 and 25 is large, and The result is output to the timing adjustment circuit 36.
Based on the determination result from the level comparison circuit 35, the timing adjustment circuit 36 switches the switch 37 so that the data signal f3 from the QPSK modulator 30 is sent to the couplers 24 and 25 having the larger control signal f1.

The timing adjustment circuit 36 recognizes the timing of the guard bit included in the data signal f3 based on the MPEG signal transferred from the digital encoder 29, and causes the switch 37 to perform switching operation at this interval. Yes.
By the way, the twisted cable 4 has a structure in which two electric wires are twisted at a substantially constant pitch to form a pair, so that the transmission of the couplers 24 and 25 is performed at a position Q1 where the two electric wires are horizontally arranged. The level is maximum (transmission loss is minimum), and conversely, at the position Q2 where two wires are arranged vertically, the transmission levels of the couplers 24 and 25 are minimum (transmission loss is maximum).

  For this reason, if the twist pitch of the twisted cable 4 is P, the transmission loss in each of the data transmission couplers 24 and 25 fluctuates by repeating a maximum and a minimum at a period of almost half pitch (0.5 × P). To be. Therefore, in the present embodiment, the couplers 24 and 25 are separated from the twist pitch P of the twisted cable 4 by P × (1/4) × n (where n is an odd number). Both couplers 24 and 25 are installed in the traveling machine body 16 so that the phase of fluctuation of the control signal f1 in each coupler 24 and 25 is inverted.

FIG. 5 is a graph showing an example of the relationship between the length position of the twisted cable 4 and the transmission loss of the couplers 24 and 25.
As shown in FIG. 5, in the present embodiment, the couplers 24 and 25 are arranged at an odd number multiple of ¼ of the twist pitch P of the twisted cable 4. When the transmission loss of the coupler 24 is maximum, the transmission loss in the other coupler 25 is minimized, and the transmission loss of each coupler 24, 25 changes in a state where the phase is inverted.

Therefore, when either one of the couplers 24 and 25 is selectively employed by the switching device 26, the crossing portion of the loss fluctuation line (solid line and broken line) of the couplers 24 and 25 shown in FIG. The transmission loss is maximized and the transmission loss does not increase further.
Therefore, according to the arrangement of the couplers 24 and 25 in this embodiment, the transmission loss of the data signal f3 with respect to the twisted cable 4 can be minimized.

  As described above, according to the inspection robot 3 of the present embodiment having the above-described configuration, the data transmission couplers 24 and 25 are different from each other in the phase of fluctuation of the control signal f1 for controlling the traveling machine body 16. The transmission source of the data signal f3 is switched to the couplers 24 and 25 having the higher level of the control signal f1 received at these couplers 24 and 25 and arranged at two positions separated in the length direction. Therefore, the deterioration of the data signal f3 transmitted from the selected couplers 24 and 25 to the twisted cable 4 is minimized, and the data signal f3 from the inspection robot 3 is transmitted to the controller 5 without being deteriorated. Can do.

  Further, according to the inspection robot 3 of the present embodiment, the data signal f3 is transmitted to the controller 5 by the couplers 24 and 25 having the better transmission characteristics of the two couplers 24 and 25 for data transmission provided in the controller 5. Therefore, it is not necessary for the controller 5 to employ a circuit configuration for receiving a plurality of frequency bands, and control communication for switching the frequency between the inspection robot 3 and the controller 5 is necessary. Nor. This simplifies the circuit configuration and communication method of the entire system.

  Furthermore, in this embodiment, the switching device 26 is mounted on the inspection robot 3 side together with the couplers 24 and 25 for data transmission, and the level comparison of the control signal f1 received by the couplers 24 and 25 and the couplers are combined. Switching control is performed in the inspection robot 3. In addition, since the inspection robot 3 performs the timing adjustment for switching the couplers 24 and 25 in the guard bit of the data signal f3, the switching timing of the couplers 24 and 25 is set so as not to interfere with the transmission of the data signal f3. The data signal f3 can be appropriately transmitted to the controller 5.

The present invention is not limited to the above embodiment.
For example, in the above-described embodiment, the case where the wireless transmission system of the present invention is employed in the structure inspection apparatus 1 is exemplified. However, the transmission system may be applied to other apparatuses such as a transport apparatus in the physical distribution field. it can.
In the above embodiment, the QPSK system is adopted as a digital modulation system in which MPEG signals are multivalued. However, the present invention is not limited to this, and other modulation systems such as a BPSK system and an 8PSK system are employed. You can also
In the above embodiment, two couplers 24 and 25 for data transmission are provided, but three or more couplers may be provided. In this case, the switching device 26 may switch the transmission source of the data signal f3 to a coupler having the highest level of the control signal f1 received from the twisted cable 4 among the plurality of couplers. .

Furthermore, a directional coupler 40 shown in FIG. 6 may be adopted as each of the data transmission couplers 24 and 25 provided in the inspection robot 3. This directional coupler 40 can change the directionality of the transmission radio wave (transmission wave) by turning the rotating body inside.
In this embodiment, since the controller 5 is connected to the starting end side (left side in FIG. 6) of the twisted cable 4, it is sufficient that the radio wave of the data signal f3 is sent from the coupler 40 to the starting end side. The radio wave propagating to (right side in FIG. 6) is unnecessary. If a large level radio wave is emitted to the end side, the high level radio wave is reflected at the end of the twisted cable 4 and interferes with the radio wave sent to the start end side, and the data signal f3 to be sent to the controller 5 Adversely affects.

  Therefore, the rotating body of the directional coupler 40 is operated to direct the directivity of the outgoing radio wave from the coupler 40 toward the starting end side (the left side in FIG. 6) that is the connection side between the twisted cable 4 and the controller 5. By doing so, radio wave interference in the above-described twisted cable 4 is suppressed, and the data signal f3 from the inspection robot 3 can be reliably transmitted to the controller 5.

It is a schematic block diagram of the inspection apparatus which employ | adopted the wireless transmission system of this invention. It is a schematic block diagram of an inspection robot. It is a block diagram which shows the circuit structure of a switching apparatus. It is a figure which shows the frame structure of a data signal. It is a graph which shows the relationship between the length position of a twisted cable, and the transmission loss of each coupler. It is an enlarged view which shows the function of a directional coupler.

Explanation of symbols

1 Inspection device 2 Traveling rail 3 Inspection robot (mobile station)
4 Twisted cable 5 Controller (fixed station)
6 Terminator or Repeater 8 Duplexer 9 QPSK Demodulator 11 Controller 10 Control Transmitter / Receiver 12 Operator Console 13 Digital Encoder 14 Video Monitor 16 Traveling Machine 17 Drive Controller 18 Data Transmitter 19 Combiner C for Control Signals
20 Control Signal Modulator / Demodulator 21 Control Device 22 Drive Device 24 Data Transmission Coupler A
25 Coupler B for data transmission
26 Coupler switching device (switching means)
27 TV camera 28 Sound collecting microphone 29 Digital encoder 30 QPSK modulator 31 Duplexer 32 Duplexer 33 Receiver 34 Receiver 35 Level comparison circuit 36 Timing adjustment circuit (timing adjustment means)
37 Coupler changeover switch 40 Directional coupler f1 Control signal (received signal)
f2 status signal f3 data signal

Claims (7)

A mobile station of a wireless transmission system comprising a plurality of data transmission couplers that wirelessly transmit data signals including video to the fixed station via a twisted cable connected to the fixed station. ,
The plurality of couplers are arranged so that the phase of the level fluctuation of the received signal received from the twisted cable is different from each other,
A mobile station of a wireless transmission system comprising switching means for switching a transmission source of the data signal to a coupler having the highest received signal level among the plurality of couplers.   2. The mobile station of the wireless transmission system according to claim 1, wherein the plurality of couplers are arranged at positions where phases of level fluctuations of the received signal are inverted from each other.   The plurality of couplers are arranged at positions separated by an odd multiple of ¼ of the twist pitch of the twisted cable in the cable length direction, which is the moving direction of the mobile station. A mobile station of the described radio transmission system.   The mobile station of the wireless transmission system according to any one of claims 1 to 3, wherein the combiner switching unit includes a timing adjusting unit that switches the combiner in a guard bit of the data signal.   The mobile station of the wireless transmission system according to claim 1, wherein a duplexer is connected to each of the plurality of couplers.   The radio according to any one of claims 1 to 5, wherein the plurality of couplers are directional couplers that can direct the direction of outgoing radio waves toward the connection side between the twisted cable and the fixed station. A mobile station in a transmission system. A mobile station having a twisted cable, a data transmission coupler that is movable along the cable and wirelessly transmits a data signal including video to the cable, and connected to the cable via the cable. A fixed station for receiving a data signal from the coupler, and a wireless transmission system comprising:
The mobile station includes a plurality of couplers arranged such that phases of level fluctuations of received signals received from the twisted cable are different from each other,
The wireless transmission system, wherein the mobile station or the fixed station includes switching means for switching a transmission source of the data signal to a coupler having the highest received signal level among the plurality of couplers. .

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