Wireless transmission system

Abstract

Provided is a wireless transmission system that achieves both improvement in radio-wave propagation environment and suppression of radio-wave leakage to the outside of a desired area.　This wireless transmission system comprises: a plurality of electromagnetic wave reflecting devices that are provided on opposite sides of a passage along the direction of travel on the passage and reflect radio waves in a predetermined band selected from between 1 MHz and 300 GHz; a master unit that is connected to a base station; slave units that are disposed along an area surrounded by the plurality of electromagnetic wave reflecting devices provided on the opposite sides of the passage and the floor surface of the passage; cables that connect the master unit and the slave units so as to enable communication therebetween; and antennas that are connected to the slave units and radiate radio waves based on a signal transmitted from the master unit toward the inside of the area.

Description

Wireless Transmission System

[0001] The present disclosure relates to wireless transmission systems.

[0002] Conventionally, there has been a wireless transmission system that includes a base station that transmits and receives radio waves in a desired band selected from a frequency band of 1 GHz to 300 GHz, and an electromagnetic wave reflection device that is arranged along at least a part of a production line where production equipment that transmits and receives the radio waves is arranged, and has a reflective surface that reflects the radio waves (see, for example, Patent Document 1).

[0003] International Publication No. 2021 / 199504

[0004] However, depending on the environment in which a wireless transmission system is installed, the location of the base station may be limited, making it difficult to ensure a good positional relationship between the base station and the electromagnetic wave reflector. In such cases, it may be difficult to reduce dead zones, and the radio wave propagation situation may not be improved sufficiently. In addition, there is a need to suppress leakage of radio waves outside the desired area to avoid interference with other commercial radio waves.

[0005] Therefore, an object of the present invention is to provide a wireless transmission system that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0006] A wireless transmission system according to an embodiment of the present disclosure includes a plurality of electromagnetic wave reflection devices provided on both sides of a passageway along the direction of travel of the passageway and reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz, a base unit connected to a base station, a sub-unit arranged along an area surrounded by the plurality of electromagnetic wave reflection devices provided on both sides of the passageway and the floor of the passageway, a cable connecting the base unit and the sub-unit so that they can communicate with each other, and an antenna connected to the sub-unit and radiating radio waves based on a signal transmitted from the base unit into the area.

[0007] It is possible to provide a wireless transmission system that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0008] FIG. 1 is a diagram showing an example of a road 32 on which the wireless transmission system 1 of the embodiment is arranged. FIG. 2 is a diagram showing an example of the configuration of an electromagnetic wave reflective fence 100A. FIG. 3 is a diagram showing an example of a manufacturing line 35 of a factory on which the wireless transmission system 1 of the embodiment is arranged. FIG. 4 is a diagram showing an example of the layer structure of a reflective panel 10. FIG. 5 is a diagram showing an example of the configuration of a unit cell 20 of a conductive pattern 15 composed of a hollow pattern 151.

[0009] Hereinafter, an embodiment to which the wireless transmission system of the present disclosure is applied will be described. In the following, the same elements will be denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] In the following description, the XYZ coordinate system is defined. The direction parallel to the X axis (X direction), the direction parallel to the Y axis (Y direction), and the direction parallel to the Z axis (Z direction) are perpendicular to one another. For ease of explanation, the -Z direction may be referred to as the lower side or bottom, and the +Z direction may be referred to as the upper side or top. Planar view refers to viewing from the XY plane. In the following description, the length, width, thickness, etc. of each part may be exaggerated to make the configuration easier to understand. Terms such as parallel, right angle, orthogonal, horizontal, vertical, and up and down may be misaligned to the extent that they do not impair the effects of the embodiments.

[0011] In this embodiment, a wireless transmission system for indoor and outdoor use uses an electromagnetic wave reflector and a distributed antenna system (DAS) to reduce blind spots. In this specification, a "blind spot" refers to an area where the reception power is reduced by 10 dB or more due to the influence of an obstruction compared to the surrounding reception environment without obstructions. Generally, electromagnetic waves below 3 THz are called radio waves, but in this specification, communication waves transmitted from a base station are called "radio waves," and electromagnetic waves in general are called "electromagnetic waves."

[0012] Blind zones include not only two-dimensional areas but also three-dimensional spaces. When production equipment, sensors, or mobile communication terminals with wireless communication capabilities are located in a blind zone, it becomes difficult to send and receive signals between them and base stations. Therefore, by introducing an electromagnetic wave reflector and DAS, the blind zones can be reduced and the radio wave environment can be improved.

[0013] <Embodiment> <Wireless transmission system 1 installed outdoors> Fig. 1 is a diagram showing an example of a road 32 on which a wireless transmission system 1 according to an embodiment is installed. Fig. 1 shows, as an example, the wireless transmission system 1 installed outdoors. The road 32 is an example of a passageway, and an example of which is a highway. Here, as an example, a form in which the wireless transmission system 1 is installed on the road 32 will be described. However, in addition to the road 32, the wireless transmission system 1 can also be installed in outdoor facilities such as medical facilities, event venues, and railroad tracks, and indoor facilities such as factories, plants, offices, and commercial facilities.

[0014] A base station (BS) 33 is provided near the road 32. The base station 33 has an antenna 33A and an input / output terminal. The input / output terminal is a terminal that can input and output transmission / reception signals similar to those input and output to and from the antenna 33A.

[0015] Additionally, a plurality of poles 34 are provided on both sides of the road 32 along the direction of travel of the road 32. As an example, the poles 34 are provided inside the electromagnetic wave reflecting devices 60 when viewed from the road 32, but they may also be provided outside the electromagnetic wave reflecting devices 60. The poles 34 may be poles for installing lighting, signs, etc., or may be utility poles, etc.

[0016] For example, the base station 33 performs wireless communication via the antenna 33A at a frequency included in the frequency band of 1 MHz to 300 GHz, and also performs communication with the master unit 110 connected via the optical fiber cable 110A at a frequency included in the frequency band of 1 MHz to 300 GHz. For example, the electromagnetic wave reflecting device 60 has a reflecting panel that reflects radio waves at the frequency of the base station 33.

[0017] FIG. 1 shows a wireless environment in which a road 32 is used as a communication area as an example of an outdoor environment. In the coordinate system of FIG. 1 , the length direction of the road 32 is the X direction, the width direction is the Y direction, and the direction perpendicular to the road surface is the Z direction. A large number of vehicles 31 travel on the road 32. The vehicles 31 may be vehicles with automatic or semi-automatic driving functions, or may not have automatic driving functions. In either case, the vehicles 31 themselves have wireless communication functions installed, not just mobile devices carried by the drivers and passengers, and large amounts of data are transmitted and received between the vehicles 31 and a control and management system.

[0018] Base stations 33 and wireless transmission systems 1 are installed along roads 32 to realize wireless communication between mobile objects such as vehicles 31 and the network.

[0019] The wireless transmission system 1 includes an electromagnetic wave reflecting device 60, a master unit 110, an optical fiber cable 110A, a repeater 120, a slave unit 130, optical fiber cables 140 (140A, 140B), and an antenna 150. The optical fiber cable 140 has optical fiber cables 140A and 140B. The optical fiber cable 140 is an example of a cable, the optical fiber cable 140A is an example of a first cable, and the optical fiber cable 140B is an example of a second cable. Note that a low-loss coaxial cable or the like may be used instead of the optical fiber cables 140 (140A, 140B).

[0020] FIG. 1 shows, as an example, a configuration in which the handset 130 and the antenna 150 are mounted on a pole 34. As an example, the antenna 150 is fixed to the handset 130, and the handset 130 is fixed to the pole 34 using a jig or the like. While FIG. 1 shows, as an example, a configuration in which the handset 130 and the antenna 150 are mounted on a plurality of poles 34 that are adjacent to each other in the direction of travel of the road 32, this configuration is not limiting. The handset 130 and the antenna 150 may be positioned at an appropriate interval in the direction of travel of the road 32, such as every third or every fourth pole 34, for example. Furthermore, the handset 130 and the antenna 150 may be positioned randomly, rather than regularly, such as every third or every fifth pole 34. The interval between the handset 130 and the antenna 150 in the direction of travel of the road 32 may be, for example, approximately 100 m.

[0021] 1 also shows, as an example, a configuration in which a master unit 110 is connected to an input / output terminal of one base station 33 via an optical fiber cable 110A, one repeater 120 is connected to the master unit 110 via an optical fiber cable 140A, and multiple slave units 130 are connected to one repeater 120 via multiple optical fiber cables 140B. The connection of multiple slave units 130 to one repeater 120 is, as an example, a star connection.

[0022] Although Figure 1 shows a star connection configuration as an example, the connection of multiple slave units 130 to one repeater 120 may also be a cascade connection in which multiple slave units 130 are connected in series to one repeater 120 via optical fiber cable 140B.

[0023] Further, while FIG. 1 shows an example of a configuration in which one repeater 120 is connected to the master device 110, a configuration in which multiple repeaters 120 are connected to one master device 110 may also be used.

[0024] Also, Figure 1 shows, as an example, a configuration in which a slave device 130 is connected to a master device 110 via a repeater device 120, but the wireless transmission system 1 may also be configured in such a way that multiple slave devices 130 are connected to one master device 110 without including a repeater device 120.

[0025] The slave device 130 of the wireless transmission system 1 is connected to the base station 33 via the repeater 120 and the master device 110, and radiates radio waves supplied from the base station 33 from an antenna 150 attached to the slave device 130. Here, a configuration in which the antenna 150 is attached to the slave device 130 will be described, but the antenna 150 may also be attached to the repeater 120 in addition to the slave device 130. In this case, radio waves may be radiated from the antenna 150 of the slave device 130 and the antenna 150 of the repeater 120.

[0026] The antenna 150 transmits and receives signals or data to and from the vehicles 31 at a predetermined frequency within a frequency band of, for example, 1 MHz to 300 GHz. Furthermore, in order to ensure that high-frequency radio waves, which have poor linearity due to the topography of the road 32, the surrounding environment, and the presence of many vehicles 31, can reach each vehicle 31 from the antenna 150, a plurality of electromagnetic wave reflecting devices 60 are arranged on both sides of the road 32 (on both sides in the width direction of the road 32) along the traveling direction of the vehicles 31 on the road 32. A plurality of electromagnetic wave reflecting devices 60 may be connected together to form an electromagnetic wave reflecting fence, which is installed on the shoulder of the road 32. Electromagnetic wave reflecting fences will be described later with reference to FIG. 2A .

[0027] The radio waves transmitted and received by the wireless transmission system 1 through the antenna 150 are preferably, for example, radio waves in the 1 GHz to 300 GHz frequency band, which includes the Sub-6 frequency band and millimeter wave bands of fifth-generation mobile communication systems (5G). Currently, the Sub-6 frequency band and the 28 GHz band, which is included in the millimeter wave band, are used, and the next-generation 6G mobile communication standard is expected to expand to the sub-terahertz band. Using such high-frequency bands significantly expands the communication bandwidth, enabling large-volume data communication with low latency.

[0028] The radio waves transmitted and received by the wireless transmission system 1 may be Long Term Evolution (LTE), LTE-Advanced (LTE-A), Ultra Mobile Broadband (UMB), or Citizens Broadband Radio Service (CBRS). The radio waves transmitted and received by the wireless transmission system 1 may be IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20, Ultra Wideband (UWB), Bluetooth (registered trademark), Low Power Wide Area (LPWA), or the like.

[0029] The radio waves transmitted and received by the base station 33 through the antenna 33A are, as an example, radio waves in the frequency band of 1 GHz to 300 GHz, including frequency bands such as those of the fifth generation mobile communication system (5G) and millimeter wave bands, similar to the radio waves transmitted and received by the handset 130 through the antenna 150 as described above, and may be LTE, etc. as described above.

[0030] The base station 33 may be provided along the road 32, similar to the slave unit 130, or may be provided at a location away from the road 32. When the base station 33 is provided along the road 32, the antenna 33A may be capable of emitting radio waves toward the road 32, similar to the antenna 150. The optical fiber cable 110A connecting the base station 33 and the master unit 110 may be fixed to a structure or the like between the base station 33 and the master unit 110, for example.

[0031] Furthermore, repeater 120 may be provided along road 32, similar to slave unit 130, or may be provided at a location away from road 32. Optical fiber cable 140A connecting master unit 110 and repeater 120 may be fixed to a structure or the like between master unit 110 and repeater 120, for example. Similarly, optical fiber cable 140B connecting repeater 120 and slave unit 130 may be fixed to a structure or the like between repeater 120 and slave unit 130, for example.

[0032] As an example, the top (upper end) of the electromagnetic wave reflecting device 60 is installed at a position higher than the slave unit 130 and the antenna 150. The antenna 150 is preferably a directional antenna that forms a beam toward the inside of the road 32, at a position sandwiched between the electromagnetic wave reflecting devices 60 on both sides of the road 32.

[0033] If the antenna 150 is placed too high, it becomes difficult to obtain sufficient strength of the radio waves radiated downward. Furthermore, if the antenna 150 is placed too high, more radio waves will leak outside the electromagnetic wave reflecting devices 60 on both sides of the road 32. For this reason, it is advantageous to install the antenna 150 at a position lower than the top (upper end) of the electromagnetic wave reflecting devices 60, which are 2 to 3 meters high. This configuration allows radio waves to be efficiently supplied to the area surrounded by the multiple electromagnetic wave reflecting devices 60 on both sides of the road 32 and the floor of the road 32. Note that, if radio wave leakage is not an issue, the antenna 150 may be placed at a position higher than the top (upper end) of the electromagnetic wave reflecting devices 60. Furthermore, the slave unit 130 and the antenna 150 may be spaced apart.

[0034] The antenna 150 is disposed closer to the center of the width of the road 32 than the electromagnetic wave reflecting devices 60 on both sides of the road 32. In other words, the antenna 150 is disposed within an area surrounded by the multiple electromagnetic wave reflecting devices 60 provided on both sides of the road 32 and the road surface (floor surface) of the road 32.

[0035] The area surrounded by the multiple electromagnetic wave reflecting devices 60 provided on both sides of the road 32 and the road surface (floor surface) of the road 32 includes a position in the height direction that is higher than the top (upper end) of the electromagnetic wave reflecting devices 60. The antenna 150 only needs to be placed within this area, so it may be provided at a position higher than the top (upper end) of the electromagnetic wave reflecting devices 60.

[0036] Also, for example, if the pole 34 is located outside the electromagnetic wave reflecting device 60 relative to the road 32, the sub-unit 130 and the antenna 150 can be connected by a cable, and the antenna 150 can be positioned closer to the center of the width of the road 32 than the electromagnetic wave reflecting devices 60 on both sides of the road 32, similar to the antenna 150 shown in Figure 1.

[0037] Also, for example, if the pole 34 is located outside the electromagnetic wave reflecting device 60 relative to the road 32, the sub-unit 130 and the antenna 150 may be positioned outside the width of the road 32 beyond the electromagnetic wave reflecting devices 60 on both sides of the road 32, and the antenna 150 may be positioned facing into the area so that the radio waves emitted by the antenna 150 are radiated within the area surrounded by the electromagnetic wave reflecting device 60 and the road surface (floor) of the road 32.

[0038] Furthermore, the area surrounded by the multiple electromagnetic wave reflecting devices 60 provided on both sides of the road 32 and the road surface (floor surface) of the road 32 also includes the area directly above the electromagnetic wave reflecting devices 60. That is, the antenna 150 may be located directly above the electromagnetic wave reflecting devices 60. For example, the antenna 150 may be provided along the top (upper edge) of the electromagnetic wave reflecting devices 60, or may be located directly above the electromagnetic wave reflecting devices 60 via a fixing member or the like attached to the top (upper edge) of the electromagnetic wave reflecting devices 60. The term "the antenna 150 is located directly above the electromagnetic wave reflecting devices 60" means that there is a portion where the antenna 150 and the electromagnetic wave reflecting devices 60 overlap in the width direction of the road 32 when viewed from directly above. Furthermore, when the antenna 150 is located directly above the electromagnetic wave reflecting devices 60, it is preferable that the antenna 150 faces toward the center of the road 32 in the width direction. This is because radio waves emitted from the antenna 150 can be emitted toward the road 32.

[0039] By arranging a plurality of antennas 150 on both sides of the road 32 along the direction of travel of the road 32, radio waves radiated from the antennas 150 are efficiently concentrated on the road 32 and radio waves are suppressed from leaking outside the road 32. As a result, the received power outside the electromagnetic wave reflection devices 60 on both sides of the road 32 becomes lower than the average or median value of the received power on the road 32 sandwiched between the electromagnetic wave reflection devices 60 on both sides.

[0040] Even if radio waves are emitted from the antenna 150, other vehicles 31 may obstruct the LOS (Line of Sight). In such cases, radio waves are emitted from the antennas 150 installed along the road 32 on both sides thereof, and can therefore reach the vehicle 31. Furthermore, the radio waves emitted from the antennas 150 can be reflected by the electromagnetic wave reflecting devices 60 and delivered to the vehicle 31.

[0041] The size of the reflecting surface of the electromagnetic wave reflecting device 60 needs to be large enough to cover at least the area determined by the radius R of the first Fresnel zone. The radius R of the first Fresnel zone when radio waves radiated from the antenna of the base station 33 and reflected by the electromagnetic wave reflecting device 60 reach the vehicle 31 in phase is defined by the following equation:

[0042] R=[λd1d2 / (d1+d2)] １ / ２ Here, λ is the wavelength used, d1 is the distance from the antenna of the base station 33 to the electromagnetic wave reflecting device 60, and d2 is the distance from the electromagnetic wave reflecting device 60 to the antenna of the vehicle 31.

[0043] In the 28 GHz band (wavelength approximately 10.7 mm), assuming that the distance d1 from the antenna of the base station 33 to the electromagnetic wave reflecting device 60 is 20.0 mm and the distance d2 from the electromagnetic wave reflecting device 60 to the vehicle 31 is 10.0 m, the size of the reflecting surface of the electromagnetic wave reflecting device 60 only needs to be several tens of centimeters on one side. On the other hand, from the viewpoint of forming an electromagnetic wave reflecting fence that covers a wide reflection area with a small number of electromagnetic wave reflecting devices 60, the width and length of the reflecting surface of the electromagnetic wave reflecting device 60 may be approximately 2.0 m x 4.0 m. In the embodiment, the electromagnetic wave reflecting device 60 is arranged along the road 32 so that the received power on the back side of the reflecting surface of the electromagnetic wave reflecting device 60, i.e., in the area outside the road 32, is lower than the average or median of the received power on the road 32.

[0044] When the handset 130 and antenna 150 are installed on the road 32, they may be attached to a pole 34 installed on the road shoulder as required by the Road Structure Act. In this case, the electromagnetic wave reflecting device 60 may be installed along the road edge located on the outside of the road on one side close to the road shoulder, and along the road edge on the opposite side. Alternatively, a pole or the like may be installed near the center of the road, and the handset 130 and antenna 150 may be attached to the pole 34.

[0045] The width of the road 32 may be 5 m to 30 m. Although it depends on the strength of the radio waves, for example, when the strength is approximately 10 dBi to 30 dBi at most, this is a realistic distance at which the vehicle 31 can receive the radio waves radiated from the antennas 150 arranged on both sides of the road 32 and acquire data.

[0046] 1 shows a wireless transmission system 1 having a configuration in which a plurality of electromagnetic wave reflecting devices 60 are arranged along the road 32, but in some sections, a member that does not reflect electromagnetic waves may be arranged instead of the electromagnetic wave reflecting devices 60. In this case, the member that does not reflect electromagnetic waves may have a configuration that does not leak radio waves outside the road 32.

[0047] 1 shows a configuration in which a plurality of electromagnetic wave reflecting devices 60 are arranged along the road 32 as the wireless transmission system 1, but in some sections, a structure installed on the road 32 may be used as a radio wave shield instead of the electromagnetic wave reflecting devices 60. The shield may be, for example, a concrete structure, and may have a configuration that does not allow radio waves to leak outside the road 32.

[0048] The provision of multiple electromagnetic wave reflection devices 60 on both sides of the road 32 (an example of a passage) along the direction of travel of the road 32 (an example of a passage) includes, as described above, the provision of components or shielding objects that do not reflect electromagnetic waves in place of the electromagnetic wave reflection devices 60 in some sections.

[0049] <Structure of Electromagnetic Wave Reflecting Device 60 and Electromagnetic Wave Reflecting Fence 100A> Figure 2A is a diagram showing an example of the configuration of the electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fence 100A is formed by connecting electromagnetic wave reflecting devices 60-1, 60-2, and 60-3 (hereinafter, sometimes collectively referred to as "electromagnetic wave reflecting device 60"), each having reflective panels 10-1, 10-2, and 10-3 (hereinafter, sometimes collectively referred to as "reflective panel 10"), via a frame 50A. In other words, the electromagnetic wave reflecting fence 100A includes a plurality of electromagnetic wave reflecting devices 60. The configuration of each electromagnetic wave reflecting device 60 is the same as the configuration of each electromagnetic wave reflecting device 60 shown in Figure 1.

[0050] 2A is consistent with the coordinate system of Fig. 1, with the width or lateral direction of the reflective panel 10 being the X direction, the thickness direction being the Y direction, and the height direction being the Z direction. In Fig. 2A, three electromagnetic wave reflecting devices 60 are connected to form the electromagnetic wave reflective fence 100A, but the number of multiple electromagnetic wave reflecting devices 60 to be connected is determined appropriately depending on the conditions of the road 32.

[0051] As an example, the electromagnetic wave reflective fence 100A shown in FIG. 2A has a reflective surface on the +Y direction side and is positioned on the right side of the road 32 in the traveling direction (+X direction). Although the antenna 150 is omitted from FIG. 2A , the antenna 150 is actually positioned on the reflective surface of the electromagnetic wave reflective fence 100A. The reflective surface of the electromagnetic wave reflective fence 100A positioned on the left side of the road 32 in the traveling direction (+X direction) is located on the -Y direction side, and therefore the antenna 150 is positioned on the -Y direction side of the electromagnetic wave reflective fence 100A. In this way, by providing the antennas 150 on the reflective surfaces of the electromagnetic wave reflective fences 100A on both sides of the road 32, a wireless communication area can be established along the road 32 even at locations far from the base station 33 in the traveling direction of the road 32.

[0052] The reflective panel 10 used in the electromagnetic wave reflecting device 60 reflects electromagnetic waves in the range of 1 MHz to 300 GHz, preferably 1 GHz to 100 GHz, and more preferably 1 GHz to 80 GHz. The reflective panel 10 has a layer containing a conductive film as a reflective film. The conductive film has a predetermined conductive pattern designed according to the desired reflection angle, frequency band, etc. The conductive pattern may include a periodic pattern, a mesh pattern, a geometric pattern, etc., and may be formed from a transparent conductive film. The reflective panel 10 has a protective layer with ultraviolet protection function as its outermost layer.

[0053] At least a portion of the reflective panel 10 may be a non-specular reflective surface in which the angle of incidence and the angle of reflection of electromagnetic waves differ. Non-specular reflective surfaces include diffusive and scattering surfaces, as well as metasurfaces, which are artificial reflective surfaces designed to reflect radio waves in a desired direction. It may be desirable for the reflective panels 10-1, 10-2, and 10-3 to be electrically connected to each other in order to maintain the continuity of the reflected potential. However, if a metasurface is included, electrical connection between adjacent reflective panels 10 is not necessary. By holding adjacent reflective panels 10 together with a frame 50A, an electromagnetic wave reflective fence 100A connected in the X direction is obtained.

[0054] In addition to the reflective panel 10 and the frame 50A, the electromagnetic wave reflecting device 60 may have legs 56 supporting the frame 50A. The legs 56 may allow the electromagnetic wave reflecting device 60 or the electromagnetic wave reflecting fence 100A to stand on the road surface. The legs 56 may be configured to be fixed to the road surface with screws, bolts, or the like. Conversely, the electromagnetic wave reflecting device 60 or the electromagnetic wave reflecting fence 100A may stand on the road surface and further include casters or other components to make it movable. In addition to the frame 50A, a top frame 57 that holds the upper end of the reflective panel 10 and a bottom frame 58 that holds the lower end may be used. In this case, the frame 50A, the top frame 57, and the bottom frame 58 form a frame that holds the entire periphery of the reflective panel 10. The frame 50A may be referred to as a "side frame" based on its position relative to the top frame 57 and the bottom frame 58. The provision of the top frame 57 and the bottom frame 58 ensures mechanical strength and safety during transportation and assembly of the reflective panel 10. The top frame 57 may be configured so that another reflective panel or a separate member such as an electromagnetic wave absorbing panel can be connected to the upper end of the reflective panel 10. This increases the flexibility in the size and function of the electromagnetic wave reflective fence 100A.

[0055] <Wireless Transmission System 1 Installed Indoors> Fig. 2B is a diagram showing an example of a factory production line 35 in which the wireless transmission system 1 of the embodiment is installed. In Fig. 2B, the wireless transmission system 1 is installed indoors. The production line 35 is a belt-shaped production site in which equipment and devices for assembly and production are arranged in a continuous flow. In the Industrial IoT (Internet of Things), industrial devices, equipment, management systems, etc. used in the production line 35 are connected to a network to improve production efficiency and ensure safety on site.

[0056] To connect devices on a production line 35 to a network, a base station 33 and a wireless transmission system 1 are arranged, similar to the road 32 shown in FIG. 1 . In FIG. 2B , as an example, multiple AGVs (Automatic Guided Vehicles) are arranged as devices used on the production line 35, and each AGV communicates with an antenna 150 of a slave unit 130 of the wireless transmission system 1 to connect to the network. The slave unit 130, to which the antenna 150 is attached, is fixed to a pillar, for example, located closer to the production line 35 than the electromagnetic wave reflecting devices 60 provided on both sides of the production line 35. The production line 35 shown in FIG. 2B produces, for example, automobile bodies and food products. While FIG. 2B shows, as an example, a configuration in which the slave units 130 and the antennas 150 are provided on multiple pillars adjacent to each other in the direction of travel of the production line 35, the configuration is not limited to this. The slave units 130 and the antennas 150 may be arranged at appropriate intervals in the direction of travel of the production line 35, for example, every third or every third pillar, relative to a plurality of consecutively adjacent pillars. Alternatively, they may be arranged randomly, rather than regularly, such as every third or every fifth pillar. The interval between the slave units 130 and the antennas 150 in the direction of travel of the production line 35 may be, for example, about 100 m.

[0057] To achieve wireless connection between the equipment on the production line 35 and the network, the wireless transmission system 1 provides a wireless communication area that is long in the horizontal direction. The technical specification (TS22.104) of the 3rd Generation Partnership Project (3GPP), a mobile communications standardization organization, specifies a wireless communication area with a rectangular aspect ratio of 3 to 5 times in the horizontal plane as a system requirement. For example, the area size for a use case called "Motion Control" is specified as 50 m x 10 m x 10 m (length x width x height).

[0058] In order to cover the production line 35 in the wireless communication area provided by the wireless transmission system 1 and realize network connection of the devices present in the production line 35, it is effective in terms of coverage to place multiple electromagnetic wave reflecting devices 60 on both sides of the production line 35 along the direction of travel of the production line 35 (+X direction) and to place antennas 150 along the electromagnetic wave reflecting devices 60. This is similar to the road 32 shown in FIG. 1.

[0059] In the coordinate system of Figure 2B, the length direction (travel direction) of the production line 35 is the X direction, the width direction is the Y direction, and the direction perpendicular to the floor surface is the Z direction. A large number of car bodies are transported on the production line 35. Figure 2B shows the production line 35 for car bodies as an example, but it may also be a production line for products other than vehicles. The AGVs and other equipment arranged around the production line 35 have wireless communication capabilities, and large amounts of data are transmitted and received between the AGVs and other equipment and the control and management system.

[0060] 2B , an antenna 150 is provided on the electromagnetic wave reflecting device 60. As an example, the height position of the antenna 150 is lower than the height position of the upper end of the electromagnetic wave reflecting device 60. If the antenna 150 is higher than the height position of the upper end of the electromagnetic wave reflecting device 60, the distance from the antenna 150 to the electromagnetic wave reflecting device 60 may be 5.0 m or more.

[0061] As shown in FIG. 2B, the wireless transmission system 1 can be installed indoors, and radio waves emitted from the antenna 150 can realize a long wireless communication area in the direction of travel of the production line 35.

[0062] <Layer structure of reflective panel 10> Fig. 3 is a diagram showing an example of the layer structure of the reflective panel 10. The layer structure shown in Fig. 3 is a layer structure in the XY cross section of the reflective panel 10, and the stacking direction is the thickness direction (Y direction) of the reflective panel 10. Fig. 3 shows, as an example, a cross section of the reflective panel 10 of an electromagnetic wave reflection device 60 arranged on the -Y direction side of a road 32 or a production line 35, as viewed from above (the +Z direction side).

[0063] The reflective panel 10 may be a specular reflective type using a metal mesh, or may be a non-specular reflective type having a dielectric layer 11, a periodic conductive pattern 15 provided on one surface 111 of the dielectric layer 11, and a ground layer 12 provided on the other surface 112 of the dielectric layer 11. The conductive pattern 15 forms the reflective surface of the reflective panel 10 and reflects electromagnetic waves in the range of 1 MHz to 300 GHz in a predetermined direction.

[0064] The conductive pattern 15 includes a periodic arrangement of a plurality of hollow patterns 151. The specific shape of the hollow patterns 151 will be described later with reference to FIG. 4 . The hollow patterns are formed of, for example, a good conductor such as Ag, Cu, Ni, or Al, and have a thickness of, for example, 0.01 mm or more and 0.05 mm or less. If the thickness is less than 0.01 mm, the surface resistivity becomes high, making it difficult to maintain high reflection efficiency. If the thickness is greater than 0.05 mm, it becomes difficult to maintain the flatness of the reflection surface. The surface of the conductive pattern 15 may be protected with a transparent film having a dielectric constant and dielectric loss tangent equivalent to those of the dielectric layer 11.

[0065] The hollow pattern 151 is bonded to the dielectric layer 11 by, for example, an adhesive layer 13. The adhesive layer 13 is not applied to the entire surface of the dielectric layer 11, but is applied in an amount necessary to stably support the hollow pattern 151. This is to minimize the effect of the adhesive layer 13 on the dielectric constant of the dielectric layer 11. The area occupied by the adhesive layer 13 does not need to be exactly the same as the area occupied by the conductive pattern 15, and may vary slightly as long as the hollow pattern 151 can be stably bonded to the dielectric layer 11. For example, if the area occupancy of the conductive pattern 15 with respect to the dielectric layer 11 is 10.0% or more and 45.0% or less, the area occupancy of the adhesive layer 13 with respect to the dielectric layer 11 is 9.0% or more and 50.0% or less.

[0066] If the area occupation ratio of the conductive pattern 15 is less than 10.0%, it becomes difficult to achieve the desired reflection characteristics and reflection efficiency. If the area occupation ratio of the conductive pattern 15 exceeds 45.0%, it becomes difficult to maintain the transparency of the reflective panel 10. However, in applications that do not require transparency, the area occupation ratio of the conductive pattern 15 may be set to more than 45.0% to prioritize reflection efficiency.

[0067] The adhesive layer 13 is made of a material capable of bonding the conductive pattern 15 to the dielectric layer 11, and may be made of a thermoplastic resin such as vinyl acetate resin, acrylic resin, cellulose resin, or silicone resin. The thickness of the adhesive layer 13 is such that the conductive pattern 15 can be stably bonded to the dielectric layer 11, and is, for example, 0.002 mm or more and 0.050 mm or less. From the viewpoint of ensuring adhesive strength, the thickness is desirably 0.010 mm or more and 0.050 mm or less.

[0068] The dielectric layer 11 is an insulating polymer film made of polycarbonate, cycloolefin polymer (COP), polyethylene terephthalate (PET), fluororesin, or the like, and has a thickness of approximately 0.3 mm to 1.0 mm. The dielectric layer 11 may be made of any material having a relative permittivity and dielectric loss tangent suitable for achieving the target reflection characteristics.

[0069] The ground layer 12 may be made of the same material as the conductive pattern 15, or may be made of a different conductive material. The ground layer 12 forms a predetermined parasitic capacitance between the conductive pattern 15 and the ground layer 12. The amount of phase delay is determined by the parasitic capacitance formed between the conductive pattern 15 and the ground layer 12.

[0070] As an example, the reflective panel 10 may be sandwiched between two dielectric substrates. Such dielectric substrates may be transparent to electromagnetic waves in the gigahertz to terahertz bands, specifically, electromagnetic waves in the range of 1 MHz to 3 THz, for example, 1 MHz to 300 GHz. The dielectric substrate is preferably formed as the outermost layer of the reflective panel 10 from a material with excellent impact resistance, durability, and transparency. Examples of materials that can be used as the dielectric substrate include polycarbonate, acrylic resin, and PET. The thickness of each dielectric substrate can be selected appropriately depending on the installation location, for example, between 1.0 mm and 10.0 mm. The thicknesses of the two dielectric substrates may be the same or different.

[0071] <Configuration Example of Hollow Pattern> Fig. 4 is a diagram showing an example of the configuration of a unit cell 20 of a conductive pattern 15 configured with a hollow pattern 151. Fig. 4 shows, as an example, the configuration of a reflection panel 10 of an electromagnetic wave reflection device 60 arranged on the -Y direction side of a road 32 or a production line 35, as viewed from the +Y direction side.

[0072] In the example shown in FIG. 4 , the unit cell 20 has six hollow patterns 151a, 151b, 151c, 151d, 151e, and 151f made of a conductor (good conductor). The width W1 and length L of the hollow patterns 151a to 151f correspond to the width (X) and height (Z) directions of the reflective panel 10 in FIG. 2A , respectively. The hollow patterns 151a to 151f have the same width W1 and different lengths L, but their central axes are aligned (the Y coordinate position of the central axis is constant). The pitch or spacing G in the X direction is constant. The shape and size of the hollow patterns 151a to 151f control the reflection phase, and the reflected waves are superimposed to form a reflected beam in the desired direction. In this example, the unit cell 20 is designed to reflect the reflected wave beam of electromagnetic waves incident perpendicularly (with an incident angle of 0°) in a direction 50° from the normal.

[0073] Hollow patterns 151a, 151b, 151c, 151d, 151e, and 151f (hereinafter sometimes collectively referred to as "hollow patterns 151") are hollowed out with a width W2. The hollow patterns have a rectangular annular shape when viewed in the XZ plane. The width of the vertical line segments is half the difference between the outer width W1 and the inner width W2 of each hollow pattern 151. Similarly, the thickness of the horizontal line segments of hollow pattern 151 is determined according to the area of ​​the hollowed out portion. The vertical and horizontal line segments of hollow pattern 151 enable reflection of both vertically polarized and horizontally polarized radio waves.

[0074] The corners of the outer edge of the hollow pattern 151 may be right angles without any curvature, or may be curved with a curvature radius R1. In the case of a right angle, the curvature radius R1 = 0.0 mm. The corners of the inner periphery of the hollow pattern 151 are curved with a curvature radius R2. The curvature radius R1 is the same as or smaller than R2. By rounding the corners of the hollow pattern 151, particularly the corners on the inner edge side, with a predetermined curvature radius, current concentration is prevented and reflection efficiency is maintained. Specifically, by rounding the corners on the inner edge side of the hollow pattern 151 with a curvature radius R2 that is between 1 / 10 and 1 / 2 of the width W1, current concentration is suppressed while enabling response to both vertically polarized waves and horizontally polarized waves.

[0075] The conductive pattern 15 is a periodic pattern in which unit cells 20 are repeatedly arranged in the X and Z directions. By providing a reflective surface formed by the conductive pattern 15 on at least a part of the reflective panel 10, it becomes possible to reflect both horizontally polarized and vertically polarized electromagnetic waves that are incident in controlled directions.

[0076] <Experimental Results> An experiment was conducted in an indoor facility where a production line for assembling automobile parts was located in the center, surrounded by multiple structures such as metal racks, autonomous traveling robots such as AGVs, and robot arms. In this indoor facility, the antenna 33A of the base station 33 radiated toward the production line, but without the wireless transmission system 1, there was a dead zone behind the structure. In the following, the width of the electromagnetic wave reflecting device 60 refers to the width in the X direction in FIG. 2B , and the height of the electromagnetic wave reflecting device 60 refers to the height in the Z direction. A specular reflection type electromagnetic wave reflecting device was used as the electromagnetic wave reflecting device 60.

[0077] Example 1: Example 1 is Example 1. In an indoor facility measuring 150.0 m in length, 50.0 m in width, and 10.0 m in height, there are a production line for assembling automobile parts, metal racks, automated guided vehicle (AGV), robotic arms, and other structures in the center. A 5.0 m-high antenna 33A with a maximum output of 20 dBi and a half-width of 15° vertically and 30° horizontally transmits and receives radio waves in a desired frequency band selected from the 4.8 GHz frequency band. The indoor facility also houses the production line and radio wave transmitting and receiving equipment. A blind zone exists behind the structures. Thirty electromagnetic wave reflecting devices 60, each 1.0 m in width and 2.0 m in height, were installed in the blind zone, and connected along the production line to form a 30.0 m-long electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 12.0 m apart and arranged parallel to the production line.

[0078] Two antennas 150 were installed along the reflective surface of the electromagnetic wave reflecting fence 100A and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -85.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +25.0 dB. Furthermore, the radio wave intensity on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -125.0 dBm.

[0079] Example 2: Example 2 is Example 2. In an indoor facility measuring 150.0 m in length, 50.0 m in width, and 10.0 m in height, there are a production line for assembling automobile parts, metal racks, automated guided vehicle (AGV) robots, robotic arms, and other structures in the center. A 3.0 m-high antenna 33A with a maximum output of 20 dBi and a half-width of 15° vertically and 30° horizontally transmits and receives radio waves in a desired frequency band selected from the 4.8 GHz frequency band. The indoor facility also houses the production line and radio wave transmitting and receiving equipment. A blind zone exists behind the structures. Thirty 1.0 m-wide, 2.0 m-high electromagnetic wave reflecting devices 60 were installed in each blind zone, and connected along the production line to form a 30.0 m-long electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 12.0 m apart and arranged parallel to the production line.

[0080] Two antennas 150 were installed along the reflective surface of the electromagnetic wave reflecting fence 100A and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -80.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +30.0 dB. Furthermore, the radio wave intensity on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -125.0 dBm.

[0081] Example 3: Example 3 is Example 3. In an indoor facility measuring 100.0 m in length, 50.0 m in width, and 10.0 m in height, there is a production line for assembling automobile parts in the center, as well as multiple structures such as metal racks, automated guided vehicle (AGV) robots, and robotic arms. An 8.0 m-high antenna 33A with a maximum output of 20 dBi and a half-width of 15° vertically and 30° horizontally transmits and receives radio waves in a desired frequency band selected from the 4.8 GHz frequency band. The indoor facility also houses the production line and radio wave transmitting and receiving equipment. A blind zone exists behind the structure. Thirty electromagnetic wave reflecting devices 60, each 1.0 m in width and 2.0 m in height, were installed in the blind zone, and connected along the production line to form a 30.0 m-long electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 20.0 m apart and arranged parallel to the production line.

[0082] Two antennas 150 were installed along the reflective surface of the electromagnetic wave reflecting fence 100A and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -90.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +20.0 dB. Furthermore, the radio wave intensity on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -125.0 dBm.

[0083] Example 4: Example 4 is Example 4. An indoor facility measuring 100.0 m in length, 50.0 m in width, and 10.0 m in height contained a production line for assembling automotive parts, as well as multiple structures, including metal racks, automated guided vehicle (AGV) robots, and robotic arms, in the center. A 3.0 m-high antenna 33A with a maximum output of 15 dBi and a half-width of 15° vertically and 20° horizontally transmits and receives radio waves in a desired frequency band selected from the 28.2 GHz frequency band. The indoor facility also contained the production line and radio wave transmitting and receiving equipment. A blind zone was present behind the structures. Thirty 1.0 m-wide, 2.0 m-high electromagnetic wave reflecting devices 60 were installed in each blind zone, and connected along the production line to form a 30.0 m-long electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 15.0 m apart and arranged parallel to the production line.

[0084] Two antennas 150 were installed along the reflective surface of the electromagnetic wave reflecting fence 100A and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -90.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +20.0 dB. Furthermore, the radio wave intensity on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -125.0 dBm.

[0085] Example 5: Example 5 is a fifth embodiment. An indoor facility measuring 500.0 m in length, 30.0 m in width, and 10.0 m in height contained a production line for assembling automobile parts, metal racks, automated guided vehicle (AGV) robots, robotic arms, and other structures in the center. A 6.0-m-high antenna 33A with a maximum output of 20 dBi and a half-width of 30° vertically and 10° horizontally was used to transmit and receive radio waves in a desired frequency band selected from the 4.8 GHz frequency band. The indoor facility also contained the production line and radio wave transmitting and receiving equipment. A blind zone was present behind the structures. Two thousand 1.0-m-wide, 2.0-m-high electromagnetic wave reflecting devices 60 were installed in the blind zone, arranged in groups of four (4.0 m high), and connected along the production line to form a 500.0-m-long electromagnetic wave reflecting fence 100A. The distance between the electromagnetic wave reflecting fences 100A on both sides of the production line was set to 30.0 m, and the fences were arranged parallel to the production line.

[0086] Two antennas 150 were installed along the reflective surface of the electromagnetic wave reflecting fence 100A and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -95.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +15.0 dB. Furthermore, the radio wave intensity on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -125.0 dBm.

[0087] Example 6 Example 6 is Example 6. An indoor facility measuring 500.0 m in length, 30.0 m in width, and 10.0 m in height contained a production line for assembling automobile parts, as well as multiple structures, such as metal racks, automated guided vehicle (AGV) robots, and robotic arms, in the center. A 4.0-m-high antenna 33A with a maximum output of 15 dBi and a half-width of 15° vertically and 20° horizontally was used to transmit and receive radio waves in a desired frequency band selected from the 28.2 GHz frequency band. The indoor facility also contained the production line and radio wave transmitting and receiving equipment. A blind zone was present behind the structures. Two thousand 1.0-m-wide, 2.0-m-high electromagnetic wave reflecting devices 60 were installed in the blind zone, arranged four at a time (4.0 m high) vertically. These devices were then connected along the production line to form a 500.0-m-long electromagnetic wave reflecting fence 100A. The distance between the electromagnetic wave reflecting fences 100A on both sides of the production line was set to 30.0 m, and the fences were arranged parallel to the production line.

[0088] Two antennas 150 were installed along the reflective surface of the electromagnetic wave reflecting fence 100A and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -90.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +20.0 dB. Furthermore, the radio wave intensity on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -125.0 dBm.

[0089] Example 7 Example 7 corresponds to Comparative Example 1. In an indoor facility measuring 100.0 m in length, 50.0 m in width, and 10.0 m in height, there was a production line for assembling automotive parts, as well as multiple structures, such as metal racks, automated guided vehicle (AGV) robots, and robotic arms, in the center. A 10.0 m-high antenna 33A with a maximum output of 20 dBi and a half-width of 15° vertically and 30° horizontally was installed, transmitting and receiving radio waves in a desired frequency band selected from the 4.8 GHz frequency band. The indoor facility also housed the production line and radio wave transmitting and receiving equipment. A blind zone existed behind the structure. Fifteen electromagnetic wave reflecting devices 60, each 1.0 m wide and 2.0 m high, were installed in the blind zone and connected along the production line to form a 15.0 m-long electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 12.0 m apart and arranged parallel to the production line.

[0090] The electromagnetic wave reflecting device 60 was installed, but the repeater 120, slave unit 130, and antenna 150 were not installed, and radio waves were emitted only from antenna 33A of base station 33. The blind zone changed from -110.0 dBm to -105.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +5.0 dB. Furthermore, the radio wave strength on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -85.0 dBm. Compared to when the repeater 120, slave unit 130, and antenna 150 were installed, the degree of improvement in the radio wave level in the blind zone was very low.

[0091] Example 8 Example 8 corresponds to Comparative Example 2. In an indoor facility measuring 100.0 m in length, 50.0 m in width, and 10.0 m in height, there are a production line for assembling automobile parts, metal racks, automated guided vehicle (AGV) robots, robotic arms, and other structures in the center. In the indoor facility, a 10.0 m-high antenna 33A with a maximum output of 15 dBi and a half-width of 15° vertically and 15° horizontally transmits and receives radio waves in a desired frequency band selected from the 28.2 GHz frequency band, and the production line and radio wave-transmitting and receiving equipment are located. A blind zone exists behind the structures. In Example 8, an electromagnetic wave reflective fence 100A was not installed.

[0092] Two antennas 150 were installed in the same location as the antenna 150 in Examples 1 to 6, and connected to the base station 33 via the slave unit 130, repeater 120, and master unit 110. The blind zone changed from -110.0 dBm to -102.0 dBm before and after installing the wireless transmission system 1, confirming an improvement of +8.0 dB. In addition, the radio wave strength on the back side of the electromagnetic wave reflecting device 60 (the back side as seen from the production line) changed from -115.0 dBm to -95 dBm. Compared to when the electromagnetic wave reflecting fence 100A was installed, the degree of improvement in the radio wave level in the blind zone was very low.

[0093] <Effects> The wireless transmission system 1 includes: a plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passageway along the direction of travel of the passageway and reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz; a base station 110 connected to a base station 33; a slave unit 130 placed along an area surrounded by the plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passageway and the floor of the passageway; a cable (optical fiber cable 140) connecting the base station 110 and the slave unit 130 so that they can communicate with each other; and an antenna 150 connected to the slave unit 130 and radiating radio waves based on a signal transmitted from the base station 110 toward the area. Therefore, the antenna 150 can radiate radio waves along the passageway. Furthermore, the electromagnetic wave reflecting device 60 can reflect radio waves within the area surrounded by the plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passageway and the floor of the passageway, while suppressing leakage of radio waves outside the area.

[0094] Therefore, it is possible to provide a wireless transmission system 1 that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0095] The cable may be an optical fiber cable, which allows signals to be transmitted between the master unit 110 and the slave unit 130 with low loss.

[0096] The wireless communication system 1 may further include a repeater 120 that transmits a signal transmitted from the master device 110 to the slave device 130, and the cable may have a first cable (optical fiber cable 140A) that connects the master device 110 and the repeater 120, and a second cable (optical fiber cable 140B) that connects the repeater 120 and the slave device 130. By transmitting a signal from the master device 110 to the slave device 130 via the repeater 120, it is possible to provide a wireless communication system 1 that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space over a wide area.

[0097] The first cable (optical fiber cable 140A) and the second cable (optical fiber cable 140B) may be optical fiber cables, which enable low-loss signal transmission between the master device 110 and the repeater 120 and between the repeater 120 and the slave device 130.

[0098] Alternatively, one or more repeaters 120 may be connected to one master device 110, and one or more slave devices 130 may be connected to one repeater 120. By transmitting signals from the master device 110 via one or more repeaters 120 and from each repeater 120 to one or more slave devices 130, it is possible to provide a wireless transmission system 1 that achieves both an improved radio wave propagation environment and suppression of radio wave leakage outside the required space over an even wider area.

[0099] Furthermore, the repeaters 120 may be arranged along the area, which makes it easier to arrange the slave units 130 and the antennas 150 along the area, and facilitates designing an area that improves the radio wave propagation environment.

[0100] Moreover, the slave unit 130 may be attached to a structure installed along a plurality of electromagnetic wave reflecting devices 60. The slave unit 130 and the antenna 150 can be arranged along a plurality of electromagnetic wave reflecting devices 60, which makes it easier to design an area that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0101] Furthermore, the height position of the antenna 150 may be equal to or lower than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices 60. Since a larger amount of radio waves radiated from the antenna 150 is reflected within the area surrounded by the plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passage and the floor of the passage, it is possible to more effectively reduce blind zones and suppress leakage of radio waves outside the area.

[0102] The width of the passage may be 5 m to 30 m. In a passage of such a practical width, it is possible to improve the radio wave propagation environment while suppressing radio wave leakage outside the required space.

[0103] While exemplary wireless transmission systems of the present disclosure have been described above, the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

[0104] The following supplementary notes are further disclosed with respect to the above embodiments. (Supplementary Note 1) A wireless transmission system including: a plurality of electromagnetic wave reflection devices provided on both sides of a passage along the direction of travel of the passage and reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz; a base station connected to a base station; a slave station placed along an area surrounded by the plurality of electromagnetic wave reflection devices provided on both sides of the passage and the floor of the passage; a cable connecting the base station and the slave station so that they can communicate with each other; and an antenna connected to the slave station and radiating radio waves based on a signal transmitted from the base station toward the area. (Supplementary Note 2) The wireless transmission system according to Supplementary Note 1, wherein the cable is an optical fiber cable. (Supplementary Note 3) The wireless transmission system according to Supplementary Note 1 or 2, further including a repeater that transmits a signal transmitted from the base station to the slave station, wherein the cable includes: a first cable connecting the base station and the repeater; and a second cable connecting the repeater and the slave station. (Supplementary Note 4) The wireless transmission system according to Supplementary Note 3, wherein the first cable and the second cable are optical fiber cables. (Supplementary Note 5) The wireless transmission system according to Supplementary Note 3, wherein a plurality of repeaters are connected to one master unit, and one or a plurality of slave units are connected to one repeater. (Supplementary Note 6) The wireless transmission system according to Supplementary Note 3, wherein the repeaters are arranged along the area. (Supplementary Note 7) The wireless transmission system according to any one of Supplements 3 to 6, wherein the slave unit is attached to a structure installed along the plurality of electromagnetic wave reflecting devices. (Supplementary Note 8) The wireless transmission system according to Supplementary Note 1 or 3, wherein the height position of the antenna is equal to or lower than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices, or, if the height position of the antenna is equal to or higher than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices, the distance from the antenna to the electromagnetic wave reflecting device is 6.0 m or more. (Supplementary Note 9) The wireless transmission system according to any one of Supplements 1 to 8, wherein the width of the passage is 5 m to 30 m.

[0105] This international application claims priority based on Japanese Patent Application No. 2024-010143, filed on January 26, 2024, the entire contents of which are incorporated herein by reference.

[0106] 1 Wireless transmission system 32 Road (an example of a passageway) 33 Base station 34 Pole 35 Production line (an example of a passageway) 60 Electromagnetic wave reflecting device 100A Electromagnetic wave reflecting fence 110 Base station 120 Repeater 130 Sub-station 140 Optical fiber cable (an example of a cable) 140A Optical fiber cable (an example of a first cable) 140B Optical fiber cable (an example of a second cable) 150 Antenna

Claims

1. A wireless transmission system, comprising: a plurality of electromagnetic wave reflection devices provided on both sides of the passage along the traveling direction of the passage, which reflect radio waves in a predetermined band selected from 1 MHz or more and 300 GHz or less; a master unit connected to a base station; a slave unit arranged along a region surrounded by the plurality of electromagnetic wave reflection devices provided on both sides of the passage and the floor surface of the passage; a cable communicably connecting the master unit and the slave unit; and an antenna connected to the slave unit and radiating radio waves based on a signal transmitted from the master unit into the region.

2. The wireless transmission system according to claim 1, wherein the cable is an optical cable.

3. The wireless transmission system according to claim 1, further comprising a repeater for transmitting a signal transmitted from the master unit to the slave unit, wherein the cable has a first cable connecting the master unit and the repeater and a second cable connecting the repeater and the slave unit.

4. The wireless transmission system according to claim 3, wherein the first cable and the second cable are optical cables.

5. The wireless transmission system according to claim 3, wherein a plurality of the repeaters are connected to one master unit, and one or a plurality of the slave units are connected to one repeater.

6. The wireless transmission system according to claim 3, wherein the repeater is arranged along the region.

7. The wireless transmission system according to any one of claims 3 to 6, wherein the slave unit is attached to a structure installed along the plurality of electromagnetic wave reflection devices.

8. The wireless transmission system according to claim 1 or 3, wherein the height position of the antenna is below the height position of the upper ends of the plurality of electromagnetic wave reflection devices, or when the height position of the antenna is above the height position of the upper ends of the plurality of electromagnetic wave reflection devices, the distance from the antenna to the electromagnetic wave reflection device is 6.0 m or more.

9. The wireless transmission system according to claim 1, wherein the width of the passage is 5 m to 30 m.

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