WO2023120138A1

WO2023120138A1 - Wireless transfer system and electromagnetic wave reflection device

Info

Publication number: WO2023120138A1
Application number: PCT/JP2022/044752
Authority: WO
Inventors: 久美子神原; 渉石田; 貴洋北爪
Original assignee: Ａｇｃ株式会社
Priority date: 2021-12-20
Filing date: 2022-12-05
Publication date: 2023-06-29
Also published as: JPWO2023120138A1

Abstract

Provided is a wireless transfer system which communicates in a gigahertz band, wherein the wireless transfer system reduces a dead zone and improves a radio wave propagation environment. In the wireless transfer system in which a base station located in a facility and a target apparatus transmit and receive radio waves at frequencies selected from a frequency band that is equal to or higher than 3 GHz and is lower than 6 GHz, the maximum gain of an antenna of the base station is from 5 dBi to 30 dBi, and when there is a dead zone in which the reception intensity is lower by at least 10 dB than the periphery in the facility, an electromagnetic wave reflection device, which includes one or more panels with reflection surfaces each having a size from 10 cm×10 cm to 3.0 m×3.0 m, is placed between the base station and the dead zone so that the center of reflection is at the height of 0.5 m or higher from the bottom of the facility. The sum of the straight-line distance between the antenna of the base station and the electromagnetic wave reflection device, and the straight-line distance between the electromagnetic wave reflection device and the dead zone is from 5.0 m to 300 m.

Description

Wireless transmission system and electromagnetic wave reflector

The present invention relates to a wireless transmission system and an electromagnetic wave reflector.

Due to the automation of manufacturing processes and office work, and the introduction of control and management using AI (Artificial Intelligence), indoor base stations have been introduced in factories, plants, offices, commercial facilities, etc. The 5G mobile communication standard provides a frequency band below 6 GHz called “sub-6” and a 28 GHz band classified as a millimeter wave band. The next-generation 6G mobile communication standard is expected to extend to the sub-terahertz band. By using such a high-frequency band, the communication bandwidth can be greatly expanded, and a large amount of data can be communicated with low delay.

A configuration has been proposed in which an electromagnetic wave reflector is arranged along at least a portion of the process line (see Patent Document 1, for example).

WO2021/199504

Radio waves in the "sub-6" frequency band are highly straight because of the high frequency of the gigahertz band, the propagation distance is short, and the propagation loss is large. Indoor facilities such as factories, plants, and commercial facilities, and outdoor facilities such as railways and highways, have obstacles such as various devices and structures, making it difficult to maintain high communication quality. Although the radio wave propagation environment can be improved by using the electromagnetic wave reflector, the position, size, number, etc. of obstacles differ from facility to facility, and the efficient placement of the electromagnetic wave reflector cannot be determined unconditionally.

In one aspect, the object of the present invention is to reduce the dead zone and improve the radio wave propagation environment in a radio transmission system that communicates in the gigahertz band.

In one embodiment, in a wireless transmission system in which a base station located in a facility and a target device transmit and receive radio waves at a frequency selected from a frequency band of 3 GHz or more and less than 6 GHz,
The maximum gain of the antenna of the base station is 5dBi or more and 30dBi or less,
When there is a dead zone in the facility where the reception intensity is 10 dB or more lower than the surroundings, the size of the reflecting surface between the base station and the dead zone is 10 cm x 10 cm or more and 3.0 m x 3.0 m. An electromagnetic wave reflector comprising one or more of the following panels is arranged so that the reflection center is at a height of 0.5 m or more from the floor of the facility;
A total distance of a straight line connecting the antenna of the base station and the electromagnetic wave reflecting device and a straight line distance connecting the electromagnetic wave reflecting device and the dead zone is 5.0 m or more and 300 m or less.

In wireless transmission systems that communicate in the gigahertz band, dead zones are reduced and the radio wave propagation environment is improved.

1 is a schematic plan view of a facility to which the wireless transmission system of the embodiment is applied; FIG. 1 is a schematic plan view of a facility to which the wireless transmission system of the embodiment is applied; FIG. FIG. 4 is a diagram showing the positional relationship among a base station, an electromagnetic wave reflector, and a dead zone; FIG. 2 is a diagram showing an arrangement configuration and received power distribution before installing an electromagnetic wave reflection device in the wireless transmission system of Example 1; FIG. 4 is a diagram showing an arrangement configuration and received power distribution when an electromagnetic wave reflection device is installed in the wireless transmission system of Example 1; It is a schematic diagram of the electromagnetic wave reflection apparatus used for calculation. It is a horizontal cross-sectional view of the panel of the electromagnetic wave reflector. FIG. 10 is a diagram showing the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device in the wireless transmission system of the second embodiment; FIG. 10 is a diagram showing the arrangement configuration and received power distribution when the electromagnetic wave reflection device is installed in the wireless transmission system of Example 2; FIG. 10 is a diagram showing the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device in the wireless transmission system of Example 3; FIG. 10 is a diagram showing the arrangement configuration and received power distribution when an electromagnetic wave reflection device is installed in the wireless transmission system of Example 3; FIG. 10 is a diagram showing the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device in the wireless transmission system of Example 4; FIG. 11 is a diagram showing the arrangement configuration and received power distribution when an electromagnetic wave reflection device is installed in the wireless transmission system of Example 4; FIG. 12 is a diagram showing the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device in the wireless transmission system of Example 5; FIG. 12 is a diagram showing the arrangement configuration and received power distribution when an electromagnetic wave reflection device is installed in the wireless transmission system of Example 5; It is a figure which shows the modification of the panel of an electromagnetic wave reflection apparatus. FIG. 4 is a perspective view of an electromagnetic wave reflector using a hollow panel; FIG. 10 is a perspective view of another electromagnetic wave reflector using a hollow panel; FIG. 4 is a diagram showing an analysis space of reflection characteristics; FIG. 4 is a diagram showing an analysis space of reflection characteristics; This is a model of a hollow panel used for analysis of reflection characteristics. FIG. 12 is a diagram showing reflection properties of the hollow panel of Example 11; FIG. 12 is a diagram showing reflection properties of the hollow panel of Example 12;

FIG. 1 is a schematic plan view of the interior of a facility to which the wireless transmission system 1 of the embodiment is applied. FIG. 1A shows the state before the electromagnetic wave reflecting device 20 is installed, and FIG. 1B shows the state after the electromagnetic wave reflecting device 20 is installed. Although production facilities such as factories and plants are assumed in FIG. 1, the facilities are not limited to indoor facilities, and include outdoor facilities such as railways and highways.

In the production facility shown in FIG. 1, there are structures 12 such as storage racks, racks, and manufacturing machines, and production equipment 14 such as automatic transport devices, robot arms, and assembly devices. A structure involved in production, such as a large manufacturing machine, can be both the structure 12 and the production equipment 14 . In this specification and claims, production equipment 14 also includes structures 12 that participate in production and transmit and receive radio waves to and from the base station 10 .

The base station 10 is located within the facility and transmits and receives radio waves to and from the production equipment 14 in a predetermined frequency band. The production equipment 14 is an example of a target equipment that transmits and receives radio waves to and from the base station 10 . The number of base stations 10 provided in the facility is not limited to one, but from the viewpoint of installation work and cost, it is desirable that a single base station 10 can cover a certain extent of service area.

The base station 10 and the production equipment 14 transmit and receive radio waves at a desired frequency selected from a frequency band of 3 GHz or more and less than 6 GHz. The maximum gain of the antenna of base station 10 is, for example, 5dBi or more and 30dBi or less. The maximum gain of the antenna of the base station 10 is expressed as an absolute gain with reference to a virtual isotropic antenna.

Depending on the transmission/reception angle between the base station 10 and the production equipment 14, the structure 12 becomes an obstacle to radio wave propagation. Metal structures such as ducts and pipes also exist at the production site, and radio waves are reflected and scattered by these structures 12 as well. Therefore, a dead zone 30 is generated in which the reception intensity of radio waves radiated from the antenna of the base station 10 is below a predetermined level. In particular, in the high frequency band of 3 GHz or more and less than 6 GHz, the radio wave has strong straightness and little diffraction, so the radio wave from the base station 10 is difficult to reach.

In this specification and the scope of claims, the term "dead zone" refers to a zone where the reception strength is reduced by 10 dB or more compared to the surrounding unshielded reception environment due to the influence of a shield such as the structure 12. . The dead zone 30 includes not only a two-dimensional area but also a three-dimensional space. When the production equipment 14 is in the dead zone 30, it becomes difficult to receive signals from the base station 10, which may reduce production efficiency. Therefore, as shown in FIG. 1B, an electromagnetic wave reflector 20 is introduced.

By arranging the electromagnetic wave reflector 20, the radio waves from the base station 10 can be delivered to the dead zone 30. The reflecting surface 21 of the electromagnetic wave reflecting device 20 is made of any material that can maintain the electric field intensity of the incident radio wave as much as possible and reflect the radio wave toward the dead zone 30 . For example, it may be formed of a conductor film, a conductor mesh, a periodic pattern of conductors, etc. formed on or inside a dielectric. The density of the conductor mesh and the period of the periodic pattern are designed to reflect radio waves of 3 GHz or more and less than 6 GHz, and have a pitch or period of 1/5 or less of the free space wavelength in this band.

The reflecting surface 21 of the electromagnetic wave reflecting device 20 may be a specular reflecting surface that reflects the radio wave at the same angle as the incident angle, or an artificial surface that reflects the radio wave in a desired direction at an angle different from the incident angle. good. In particular, when it is difficult to transmit radio waves to the production equipment 14 by specular reflection from the position of the base station 10 and the dead zone 30 and the spatial position where the electromagnetic wave reflector 20 can be installed, an artificial A smooth surface is preferred. A specular reflection surface and an artificial surface may be mixed in the reflection surface 21 . The arrangement configuration of FIG. 1B reduces the dead zone in the facility and improves the communication environment.

FIG. 2 is a schematic plan view of another facility to which the wireless transmission system 1 is applied. FIG. 2A shows the state before the electromagnetic wave reflecting device 20 is installed, and FIG. 2B shows the state after the electromagnetic wave reflecting device 20 is installed. As in FIG. 1, the frequency of radio waves emitted from the base station 10 is 3 GHz or more and less than 6 GHz, and the maximum gain of the antenna of the base station 10 is 5 dBi or more and 30 dBi or less.

In a process line for assembling automobiles, home appliances, etc., production equipment 14 such as a plurality of robot arms may be arranged in the line, and structures 12 such as fences and pillars 13 may be arranged outside. A dead zone 30 can occur in the central portion along the longitudinal direction of the process line due to reflections and scattering from pillars, fences, and robot arms. In this case, as shown in FIG. 2B, by providing the electromagnetic wave reflector 20 along the process line, the radio waves from the base station 10 can reach the dead zone 30. FIG.

The location where the dead zone 30 occurs differs from facility to facility, and the optimal arrangement position of the electromagnetic wave reflector 20 also differs from facility to facility. By arranging the electromagnetic wave reflection device 20 so as to satisfy a predetermined condition in relation to the base station 10 and the dead zone 30, the inventors have found that, regardless of the arrangement of the structures 12 in the facility, the efficiency can be improved to some extent. We examined and confirmed that the dead zone can be reduced.

FIG. 3 is a diagram showing the positional relationship among the base station 10, the electromagnetic wave reflector 20, and the dead zone 30. FIG. A base station 10, an electromagnetic wave reflector 20, and a dead zone 30 are located in a plane parallel to the XY plane. "In a plane parallel to the XY plane" means that the base station 10 and the electromagnetic wave reflector 20 are not necessarily installed on the floor of the facility, and the dead zone 30 is not always generated on the floor of the facility. It is from. The Z direction orthogonal to the XY plane is the height direction.

Let D1 be the straight line distance connecting the reflection center R of the radio waves incident on the electromagnetic wave reflector 20 and the boundary line of the dead zone 30 . Let D2 be the straight line distance connecting the antenna of the base station 10 and the reflection center R of the electromagnetic wave reflector 20 . Given the frequency of radio waves emitted by the antenna of the base station 10 and the maximum gain of the antenna, the total length of D1 and D2 (D1+D2) satisfies a predetermined condition.

The electromagnetic wave reflector 20 is placed at a position other than the straight line connecting the base station 10 and the dead zone 30 . This is because, if the electromagnetic wave reflector 20 is on a straight line connecting the base station 10 and the dead zone 30, the electromagnetic wave reflector 20 becomes an obstacle. The angle formed by the straight line connecting the antenna of the base station 10, the center of reflection R on the electromagnetic wave reflector 20, and the dead zone 30 is any angle that can reflect the radio waves radiated from the antenna of the base station 10 to the dead zone 30. is an angle, for example, greater than or equal to 5° and less than 180°. If the angle of incidence of radio waves on the electromagnetic wave reflector 20 is less than 5°, radio wave interference may occur.

Since the configurations of the electromagnetic wave reflecting device and the electromagnetic wave shield are basically the same, the electromagnetic wave reflecting device 20 also has an electromagnetic wave shielding effect. The electromagnetic wave shielding effect of the electromagnetic wave reflector prevents electromagnetic waves of frequencies other than the radio waves of the base station 10 from entering the propagation path between the base station 10 and the dead zone 30 (and the production equipment 14 existing in the dead zone 30). can.

The center position of the reflecting surface 21 of the electromagnetic wave reflector is at least 0.5 m above the floor of the facility, considering the size and position of the production equipment 14 and the position and height of the antenna of the base station 10. is desirable. The base station 10 may be located 1.0 m to 3.0 m from the floor in order to ensure the widest possible service area within the facility. The inclination of the reflecting surface 21 of the electromagnetic wave reflector 20 with respect to the floor surface and the angle with respect to the LOS (Line of Sight) of the base station 10 depend on the shape and direction of the beam formed by the antenna of the base station 10 and the direction of the production equipment 14. It is determined as appropriate according to the position of the reception point. Specific examples of indoor placement are described below, and conditions that can contribute to the reduction of the dead zone are examined based on the examples.

FIG. 4 shows the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device 20 in the wireless transmission system 1A of the first embodiment. FIG. 5 shows the arrangement configuration and received power distribution when the electromagnetic wave reflector 20 is installed in the wireless transmission system 1A of the first embodiment.

(A) of FIG. 4 is a schematic plan view showing the positional relationship between the base station 10 and the dead zone 30 . FIG. 4B is a reception power map of radio waves radiated from the base station 10. FIG. A base station 10 is placed at a height of 2 m near a corner of an area of length 11.0 m×width 7.5 m. The base station 10 is equipped with an omnidirectional antenna with a maximum gain of 15dBi.

The base station 10 emits radio waves in the 4.8 GHz band with a vertical beam width of 10° and a horizontal beam width of 50°. The floors, ceilings and walls of an area of 11.0 m x 7.5 m shall comply with ITU-R (International Telecommunication Union-Radiocommunication sector) Recommendation P. It is made of a material conforming to 2040. The height of the omni antenna placed at the receiving point is 0.7m.

Within the area, metal structures 12-1 and 12-2 with a length of 2.1m, a width of 0.7m and a height of 2.0m are placed. The rear side of the structure 12-1 as viewed from the base station 10 is a dead zone 30 in which the received power is 10 to 30 dB lower than the surrounding area. The presence of the dead zone 30 is also confirmed from the received power map of FIG. 4(B). When the base station 10 and the production equipment 14 (see FIG. 1) that transmits and receives signals are present in the dead zone 30, the problem is how to efficiently deliver radio waves to the production equipment 14. FIG.

In FIG. 5, the electromagnetic wave reflector 20 is arranged to reduce the dead zone 30. FIG. 5A is a schematic plan view of the electromagnetic wave reflecting device 20 arranged in an area, and FIG. 5B is a received power map when the electromagnetic wave reflecting device 20 is used. In this layout, the reflective surface 21 of the electromagnetic wave reflector 20 is arranged at an angle of 45° with respect to the LOS of the base station 10 .

FIG. 6A shows an example of the electromagnetic wave reflector 20 used in the wireless transmission system of the embodiment. In Example 1, two electromagnetic wave reflection devices 20-1 and 20-2 each having a length of 2.0 m and a width of 1.0 m are horizontally connected to form a reflecting surface of 2.0 m×2.0 m. Each of the electromagnetic wave reflectors 20-1 and 20-2 includes a panel 200 and a frame 201 holding the panel 200. FIG. When the electromagnetic wave reflecting devices 20-1 and 20-2 are installed on the floor, the frame 201 may be provided with legs 202. FIG. The panel 200 is supported at a predetermined height from the floor P by the frame 201 and legs 202 . The height h1 from the floor P to the lower end of the panel 200 of the electromagnetic wave reflectors 20-1 and 20-2 is 13.5 cm, and the height from the floor P to the center of the reflecting surface 21 is 113.5 cm. .

FIG. 6B shows a configuration example of the panel 200 used in the electromagnetic wave reflector 20 in horizontal cross section. Panel 200 has a conductive layer 215 sandwiched between dielectric layers 208 . The conductive layer 215 may be held adhesively between the two dielectric layers 208 by an adhesive layer 216 . The conductive layer 215 forms the reflecting surface 21 (see FIG. 5) of the electromagnetic wave reflector and has a predetermined conductive pattern that reflects radio waves in the range of 24 GHz to 32 GHz. When a plurality of electromagnetic wave reflectors 20 are connected as shown in FIG. 6A, the conductive layers 215 are electrically connected inside the frame 201 between adjacent panels 200 . By making the conductive layer 215 electrically continuous, it is possible to form the reflective surface 21 in which the reflection potential is continuous between the plurality of panels 200 . In the simulation, two polycarbonate plates are used as the dielectric layer 208 with a conductive layer 215 in between. In actual operation, other resin transparent to electromagnetic waves of 28 GHz may be used, and the conductive layer 215 may be formed on the surface of one dielectric layer 208 .

Returning to FIG. 5, as shown in FIG. 5B, by placing the electromagnetic wave reflector 20, the reception intensity behind the structure 12-1 is improved by 10 to 30 dB, and the dead zone 30 is reduced. It can be seen that The reception strength is expressed as a relative strength with the omni-antenna as a reference. At this time, the linear distance D2 from the antenna of the base station 10 to the reflection center R of the electromagnetic wave reflector 20 is 7.0 m, and the linear distance D1 from the boundary of the dead zone 30 to the reflection center R of the electromagnetic wave reflector 20 is 3.0 m. 9m. The total distance of D1 and D2 (D1+D2) is 10.9m. It is confirmed that under the conditions of Example 1, the dead zone 30 is reduced and the radio wave propagation environment is improved.

FIG. 7 shows the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device 20 in the wireless transmission system 1B of the second embodiment. FIG. 8 shows the arrangement configuration and received power distribution when the electromagnetic wave reflector 20 is installed in the wireless transmission system 1B of the second embodiment.

(A) of FIG. 7 is a schematic plan view showing the positional relationship between the base station 10 and the dead zone 30, and (B) of FIG. 7 is a received power map of radio waves emitted from the base station 10. FIG. A base station 10 is arranged at a position of 2 m in height by the wall along the long side of an area of 11.0 m in length and 7.5 m in width. The base station 10 is equipped with an omnidirectional antenna with a maximum gain of 15dBi.

The base station 10 emits radio waves in the 4.8 GHz band with a vertical beam width of 10° and a horizontal beam width of 50°. Floors, ceilings and walls in an area of 11.0m x 7.5m shall comply with ITU-R Recommendation P. It is made of a material conforming to 2040. The height of the receiving point is 0.7 m.

Within the area, metal structures 12-1 and 12-2 with a length of 2.1m, a width of 0.7m and a height of 2.0m are placed. Compared to implementation advantage 1, structures 12-1 and 12-2 have different positional relationships with respect to the base station 10. FIG. Behind the structures 12-1 and 12-2 is a dead zone 30 in which the received power is 10 to 30 dB lower than the surrounding area. The presence of the dead zone 30 is also confirmed from the received power map in FIG. 7B.

In (A) of FIG. 8, the electromagnetic wave reflection device 20 is placed in the area. As shown in FIG. 6A, the electromagnetic wave reflecting device 20 has a configuration in which two electromagnetic wave reflecting devices 20-1 and 20-2 each having a width of 2.0 m and a width of 1.0 m are connected horizontally. It has a reflecting surface 21 of 0 m. The height h1 of the reflecting surface 21, that is, the lower end of the panel 200 from the floor surface P is 13.5 cm, and the height from the floor surface P to the center of the reflecting surface 21 is 113.5 cm.

In the layout of the second embodiment, when viewed from the base station 10, the production equipment 14 (see FIG. 1) exists behind the structure 12-2, and the production equipment 14 does not exist behind the structure 12-1. It is assumed that An electromagnetic wave reflector 20 is introduced to reduce the dead zone 30 behind the structure 12-2. The electromagnetic wave reflecting device 20 is arranged parallel to the structures 12-1 and 12-2, and arranged closer to the structure 12-2 than the center of the two structures 12-1 and 12-2. Radio waves from the base station 10 are incident on the reflecting surface 21 of the electromagnetic wave reflector 20 at an angle of incidence greater than 45°, and are reflected toward the dead zone 30 behind the structure 12-2.

From (B) of FIG. 8, it can be seen that the reception strength is improved by 10 to 50 dB in the dead zone 30 on the rear side of the structure 12-2. At this time, the straight-line distance D2 from the antenna of the base station 10 to the reflection center R of the electromagnetic wave reflector 20 is 13.5 m. A straight line distance D1 from the boundary within the dead zone 30 to the reflection center R of the electromagnetic wave reflector 20 is 1.5 m. The total distance (D1+D2) of D1 and D2 is 15.0 m.

It is confirmed that under the conditions of Example 2, the dead zone 30 is reduced in the area where the production equipment 14 exists, and the radio wave propagation environment is improved.

FIG. 9 shows the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device 20 in the wireless transmission system 1C of the third embodiment. FIG. 10 shows the arrangement configuration and received power distribution when the electromagnetic wave reflector 20 is installed in the wireless transmission system 1C of the third embodiment.

(A) of FIG. 9 is a schematic plan view showing the positional relationship between the base station 10 and the dead zone 30, and (B) of FIG. 9 is a received power map of radio waves emitted from the base station 10. FIG. A base station 10 is arranged at a position of 2 m in height by the wall along the long side of an area of 11.0 m in length and 7.5 m in width. The base station 10 is equipped with an omnidirectional antenna with a maximum gain of 10dBi.

The base station 10 emits radio waves in the 4.8 GHz band with a vertical beam width of 10° and a horizontal beam width of 50°. Floors, ceilings and walls in an area of 11.0m x 7.5m shall comply with ITU-R Recommendation P. It is made of a material conforming to 2040. The height of the omni antenna placed at the receiving point is 0.7 m.

Within the area, metal structures 12-1 and 12-2 with a length of 2.1m, a width of 0.7m and a height of 2.0m are placed. As seen from the base station 10, the rear side of the structures 12-1 and 12-2 is a dead zone 30 in which the received power is 10 to 30 dB lower than the surroundings. The presence of the dead zone 30 is also confirmed from the received power map in FIG. 9B.

In (A) of FIG. 10, the electromagnetic wave reflection device 20 is placed within the area. As shown in FIG. 6A, the electromagnetic wave reflecting device 20 has a configuration in which two electromagnetic wave reflecting devices 20-1 and 20-2 each having a height of 2.0 m and a width of 1.0 m are connected horizontally. It has a reflecting surface 21 of 2.0 m. The height h1 of the lower end of the reflecting surface 21 from the floor surface P is 13.5 cm, and the height from the floor surface P to the center of the reflecting surface 21 is 113.5 cm.

In the layout of the third embodiment, when viewed from the base station 10, the production equipment 14 (see FIG. 1) exists behind the structure 12-2, and the production equipment 14 does not exist behind the structure 12-1. It is assumed that An electromagnetic wave reflector 20 is introduced to reduce the dead zone 30 behind the structure 12-2. The electromagnetic wave reflector 20 is arranged parallel to the structures 12-1 and 12-2, and is arranged closer to the structure 12-2 than to the center of the two structures 12-1 and 12-2. Radio waves from the base station 10 are incident on the reflecting surface 21 of the electromagnetic wave reflector 20 at an angle of incidence greater than 45°, and are reflected toward the dead zone 30 behind the structure 12-2.

From (B) of FIG. 10, it can be seen that the reception strength is improved by 10 to 30 dB in the dead zone 30 on the rear side of the structure 12-2. At this time, the straight line distance D2 from the antenna of the base station 10 to the reflection center R of the electromagnetic wave reflector 20 is 13.5. A straight line distance D1 from the boundary of the dead zone 30 to the reflection center R of the electromagnetic wave reflector 20 is 1.5 m. The total distance (D1+D2) of D1 and D2 is 15.0 m.

It is confirmed that under the conditions of Example 3, the dead zone 30 is reduced in the area where the production equipment 14 exists, and the radio wave propagation environment is improved. From Example 2 and Example 3, it can be seen that even if there is a difference of 5 dBi in the maximum gain of the antenna of the base station 10, the dead zone can be reduced to the same degree. In the layout of Example 1, even when the maximum gain of the antenna of the base station 10 is 10 dBi, which is 5 dBi lower than 15 dBi, the same degree of dead zone reduction effect as in FIG. 5B is expected. Also, in Examples 1 and 2, when the maximum gain of the antenna of the base station 10 is increased by 5dBi from 15dBi, a dead zone reduction effect greater than that shown in FIGS. 5B and 8B is expected. be.

FIG. 11 shows the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device 20 in the wireless transmission system 1D of the fourth embodiment. FIG. 12 shows the arrangement configuration and received power distribution when the electromagnetic wave reflector 20 is installed in the wireless transmission system 1D of the fourth embodiment. In the arrangement of FIG. 11A, wireless transmission system 1D includes a process line in which part 125, robot arm 123, etc. reside. Along the process line, a polycarbonate safety fence 121 is provided over a length of 50m. In FIG. 12, instead of the safety fence 121, the electromagnetic wave reflection device 20 is arranged over the same length of 45 m.

A base station 10 is placed on one end side of a process line provided on a floor of 70m x 35m. The base station 10 has an omnidirectional antenna with a height position of 3.0 m and a maximum gain of 15 dBi. The base station 10 radiates radio waves in the 4.7 GHz band with a vertical beam width of 28° and a horizontal beam width of 28°. The floor, ceiling, walls and pillars of the floor are made of concrete. The height of the receiving point is 0.8 m, and the receiving antenna is an omnidirectional antenna. From the received power distribution in FIG. 11B, the back of the structure away from the base station 10 is a dead zone where the received power is 10 to 60 dB lower than the surroundings.

In (A) of FIG. 12, the electromagnetic wave reflector 20 is used instead of the safety fence 121. Fifty electromagnetic wave reflection devices 20 each having a width of 1.0 m and a height of 2.0 m are connected and installed. The lower edge of the panel 200 is 0.15m above the floor and the center of reflection is above 0.15m above the floor. From the received power map of FIG. 12B, it can be seen that the received power is improved by about 10 dB to 20 dB inside the process line including the dead zone. The linear distance D1 from the dead zone to the reflection center of the electromagnetic wave reflector 20 at this time is 5.0 m. A straight line distance D2 from the antenna of the base station 10 to the reflection center R of the electromagnetic wave reflector 20 is 60.0 m. The total distance (D1+D2) of D1 and D2 is 65.0 m.

FIG. 13 shows the arrangement configuration and received power distribution before installing the electromagnetic wave reflection device 20 in the wireless transmission system 1E of the fifth embodiment. FIG. 14 shows the arrangement configuration and received power distribution when the electromagnetic wave reflecting device 20 is installed in the wireless transmission system 1B of the fourth embodiment. In the arrangement configuration of FIG. 13A, the base station 10 is arranged at the end of the floor of length 300.0 m×width 100.0 m. The base station 10 has an omnidirectional antenna with a height of 3.0 m from the floor and a maximum gain of 15 dBi.

The base station 10 emits radio waves in the 4.7 GHz band with a vertical beam width of 28° and a horizontal beam width of 90°. The floor, ceiling, walls and columns of the floor are concrete. The height of the receiving point is 1.0 m, and the receiving antenna is an omnidirectional antenna.

A structure 12 with a length of 50.0 m, a width of 30.0 m, and a height of 3.0 m is placed on the floor. From the received power map in FIG. 13B, it can be seen that the rear side of the structure 12 as viewed from the base station 10 is a dead zone in which the received power is 10 to 10 to 40 dB lower than the surrounding area.

In (A) of FIG. 14, the electromagnetic wave reflector 20 is arranged at an oblique angle with respect to the structure 12 . The electromagnetic wave reflecting device 20 is used by horizontally connecting 28 electromagnetic wave reflecting devices 20 having a length of 2.0 m and a width of 1.0 m shown in FIG. 6A. The height of the lower end of the reflecting surface 21 (panel 200) from the floor surface P is 0.135 m. From FIG. 14B, it can be seen that the reception strength is improved by about 10 dB to 20 dB in the dead zone behind the structure 12 . At this time, the straight line distance D1 from the dead zone to the reflection center of the electromagnetic wave reflector 20 is 50.0 m. A straight line distance D2 from the antenna of the base station 10 to the reflection center of the electromagnetic wave reflector 20 is 250.0 m. The total distance (D1+D2) of D1 and D2 is 300.0 m.

In Examples 1 to 5, when the positional relationship among the base station 10, the electromagnetic wave reflector 20, and the dead zone 30 to be eliminated satisfies a predetermined condition, the dead zone 30 in which the target equipment such as the production equipment 14 exists is can be reduced. Depending on the frequency band of radio waves radiated from the base station 10, the conditions to be met by the positional relationship between the base station 10, the electromagnetic wave reflector 20, and the dead zone 30 vary. That is, in the frequency band of 3 GHz or more and less than 6 GHz, the conditions do not change significantly, and the conditions of Examples 1 to 5 apply within the range of 3 GHz or more and less than 6 GHz.

The electromagnetic wave reflector 20 does not have to have a configuration in which two electromagnetic wave reflectors 20-1 and 20-2 are combined as shown in FIG. 6A. Moreover, it does not necessarily have to be supported by the legs 202 . If the radio waves from the base station 10 can be reflected toward the dead zone 30, the electromagnetic wave reflecting device 20 without the legs 202 may be leaned on a desk, shelf, stand, or the like. The manner in which the electromagnetic wave reflector 20 is supported is not critical. Therefore, the legs 202 may be used as shown in FIG. 6A, or only the frame 201 surrounding the panel 200 of the electromagnetic wave reflector 20 may be used. As in the fourth and fifth embodiments, a required number of electromagnetic wave reflecting devices 20 may be connected and used. A configuration in which a plurality of electromagnetic wave reflectors 20 are connected is effective in reducing dead zones in the process lines shown in FIGS.

The size of the electromagnetic wave reflector 20 may be any size that allows the radio waves radiated from the base station 10 to reach the dead zone 30, and is a size that satisfies at least the first Fresnel zone of the radio wave propagation path. The radius r of the first Fresnel zone is obtained using the linear distances D1 and D2 and the wavelength λ as
r=[λ×D1×D2/(D1+D2)] ^1/2
is represented by The wavelength of radio waves in the 4.8 GHz band is about 62 mm, and the radius r is about 5 cm to 40 cm, where D1 and D2 are the distances obtained in Examples 1-5. The area of the reflecting surface 21 per panel of the electromagnetic wave reflector 20 is desirably at least 10 cm×10 cm. By increasing the size of the reflective surface 21 per panel, radio waves can be transmitted over a wide area with one panel. may be The size of the panel 200 of the electromagnetic wave reflector 20 is desirably 3 m×3 m or less. Therefore, the size of the panel 200 is 15 cm x 15 cm or more and 2.5 m x 2.5 m or less, or 20 cm x 20 cm or more and 2.0 m x 2.0 m or less. You can make an appropriate decision by taking into consideration the

The height of the central position of the reflecting surface 21 is determined by the height of the antenna of the base station 10 and the height of the receiving point. In Examples 1 to 5, the antenna of the base station 10 is arranged at a height of 2 to 3 m above the floor surface. The antenna of station 10 may be placed at a position 1.5 m or more and 10 m or less from the floor. The base station 10 can be installed near the ceiling, suspended from the ceiling, or installed on a pole installed on the floor. Assuming that the receiving antenna of the production equipment 14 is located at a position of 0.7 m or more and 2.0 m or less from the floor surface, the center of the reflection surface 21 of the electromagnetic wave reflector 20 is considered to ensure sufficient reception strength at the production equipment 14. , or the height of the reflection center R (see FIG. 3) is preferably 0.5 m or more. In this case, depending on the position of the base station 10, the height of the center of reflection R may be lower than the height of the reception point of the production equipment 14 or higher than the height of the reception point. In the former case, radio waves from the base station 10 installed at a high position can be effectively delivered to the production equipment 14 located in the dead zone 30 .

Based on the simulation results of Examples 1-5, the following conditions are derived.
(1) The frequency band of radio waves emitted from the base station 10 placed in the facility is 3 GHz or more and 6 GHz or less.
(2) The maximum gain of the antenna of the base station 10 is 5dBi or more and 30dBi or less, and may be 10dBi or more and 30dBi or less from the viewpoint of the reach of radio waves.
(3) The dead zone 30 is a zone where the reception strength is 10 dB or more lower than the surrounding propagation environment.
(4) The size of the reflective surface per panel of the electromagnetic wave reflector 20 is 10 cm x 10 cm or more and 3.0 m x 3.0 m or less, and from the viewpoint of panel weight, strength, ease of handling, etc. , 15 cm x 15 cm or more, 2.5 m x 2.5 m or less, 20 cm x 20 cm or more, 2.0 m x 2.0 m or more. The height of the reflection center from the floor surface P can be set to 0.135 m or more, 0.15 m or more, or 0.5 m or more.
(5) The total length of D1 and D2 is 5.0 m or more and 300 m or less.
(6) The height of the reflection center of the electromagnetic wave reflector 20 may be equal to or lower than the height of the receiving point of the production equipment 14 (target equipment).

Thus, when the frequency band of radio waves handled by the base station 10 and the maximum gain of the antenna of the base station 10 are specified in the facility, the electromagnetic wave reflector 20 having the reflecting surface 21 of a predetermined size is used. In the electromagnetic wave reflector 20, the sum of the linear distance D2 from the antenna of the base station 10 to the reflection center R (see FIG. 3) of the electromagnetic wave reflector 20 and the linear distance D1 from the reflection center R to the dead zone 30 is 5.0 m. Above, it arranges in the position which satisfies the condition of 300m or less. As a result, the dead zone 30 can be reduced indoors where a shield such as the structure 12 exists, and the radio wave propagation environment can be improved. The sum of D1 and D2 is the distance from the transmit antenna, via the center of reflection R, to the receive antenna. The value of D1+D2 matches the flying distance of radio waves in a specific frequency band from base station 10 . Assuming use indoors including a process line, D1+D2 should be 300 m at maximum. Under the above conditions, the dead zone 30 can be reduced indoors where there is a shield such as the structure 12, and the radio wave propagation environment can be improved.

The wireless transmission system described above is not limited to production facilities such as factories, but can also be applied to facilities such as soundproof walls used for railways and highways. Many blind zones can occur in event venues where many structures and shields are arranged, and road areas where there are many vehicle bodies and shields. By using the wireless transmission system of the embodiment, the dead zone can be reduced and the radio wave propagation environment can be improved.

<Modified example of panel>
In Examples 1 to 5, a flat transparent resin plate was used as the dielectric layer 208 . This panel 200 is called a "flat panel". The dielectric layer need not necessarily be a solid plate and may have a hollow inside. The following modification provides an electromagnetic wave reflector having a hollow panel 200A using a dielectric layer 210 having a hollow 213 therein. "Hollow" literally means that a cavity exists inside the dielectric layer 210, and its shape does not matter.

FIG. 15 shows a modification of the panel of the electromagnetic wave reflector. FIG. 15A is a schematic diagram showing part of the hollow panel 200A, and FIG. 15B is a horizontal cross-sectional view along the II line of the hollow panel 200A. The hollow panel 200A has a conductive layer 215 sandwiched between two dielectric layers 210 with an adhesive layer 216 interposed therebetween. The conductive layer 215 is formed in a pattern that reflects radio waves with a frequency of 2 GHz to 15 GHz, more preferably 3 GHz to 6 GHz. Dielectric layer 210 has hollow 213 extending in a predetermined direction inside plate 211 . The cross-sectional shape of the hollow 213 is not limited to rectangular, and may be polygonal, elliptical, circular, or the like. Having the hollow 213 inside reduces the weight of the hollow panel 200A and the dielectric constant of the dielectric layer 210 approaches that of air.

FIG. 16 is a perspective view of an electromagnetic wave reflector 20A using a hollow panel 200A. The electromagnetic wave reflector 20A includes a hollow panel 200A and a frame 201 that holds the hollow panel 200A. As shown in FIG. 16, when the electromagnetic wave reflecting device 20A is installed on the floor, a frame 201 may be provided with legs 202. A plurality of electromagnetic wave reflectors 20A are connected by the frame 201, and the hollow panel 200A is supported at a predetermined height from the floor surface by the legs 202 and the frame 201. FIG. Also, inside the frame 201, the conductive layers 215 of adjacent hollow panels 200A are electrically connected and maintained at the same reflected potential. In FIG. 16, hollow panel 200A has a number of longitudinally extending hollows 213 (see FIG. 15). For convenience of illustration, the hollow 213 is indicated by a vertical line, but the hollow panel 200A is transparent to visible light and gigahertz band radio waves. The hollows 213 may run parallel to each other inside the hollow panel 200A.

In the hollow panel 200A, the extending direction of the hollow 213 is not limited to the vertical direction. As shown in FIG. 17, a plurality of hollows 213 may extend parallel to the lateral direction of hollow panel 200A. Again, the weight of the hollow panel 200A is reduced and the dielectric constant approaches that of air.

18 and 19 are diagrams showing the analysis space 31 of the reflection characteristics of the embodiment described below. The in-plane of the panel is the XY plane, and the thickness direction is the Z direction. When the analysis space is represented by (size in the X direction)×(size in the Y direction)×(size in the Z direction), the size of the analysis space 31 when the frequency is 2 to 15 GHz is 500 mm×500 mm×21.7 mm. do. As shown in FIG. 19, the boundary condition is a design in which an electromagnetic wave absorber 32 is arranged around the analysis space 31 .

FIG. 20 is a model diagram of a hollow panel used in electromagnetic field simulation. Let t1 be the thickness of the dielectric layer 210, t2 be the thickness of the plate wall, L1 be the thickness of the hollows 213, and L2 be the lateral width or pitch of the hollows 213. FIG. In the electromagnetic field simulation using this model, a plane wave of 4.7 GHz is incident on the hollow panel 200A and reflected on the panel surface. Using general-purpose three-dimensional electromagnetic field simulation software, analyze the scattering cross section (RCS: Radar Cross Section) that represents the reflectivity of the panel.

FIG. 21 shows the reflection characteristics of the hollow panel 200A of Example 11. In Example 11, the dielectric layer 210 has a thickness t1 of 5.0 mm, a plate wall thickness t2 of 0.5 mm, a thickness L1 of the hollows 213 of 4.0 mm, and a pitch L2 of 3.5 mm. It is made of polycarbonate with a cross-sectional hollowness of 70.0%. A panel in which a conductive layer 215 (see FIG. 20) is sandwiched between two pieces of this polycarbonate is used. The simulation is performed by changing the incident angle from −60° to +60° in increments of 10°. The dB value of the main peak of the scattering cross section is as shown in FIG. A scattering cross section of more than 20 dB is obtained in the range of ±40°, a scattering cross section of more than 22 dB is obtained in the range of ±20°, and substantially symmetrical scattering is obtained in the minus direction and the plus direction with respect to 0°. A cross-sectional area is obtained.

FIG. 22 shows the reflection characteristics of the flat panel of Example 12. As a model, as shown in FIG. 6B, two sheets of polycarbonate having a thickness of 5 mm are pasted together with a conductive layer 215 interposed therebetween. The hollowness is 0%. The simulation is performed by changing the incident angle from −60° to +60° in increments of 10°. The dB value of the main peak of the scattering cross section is as shown in FIG. Similar to the hollow panel 200A, a scattering cross section exceeding 20 dB was obtained in the range of ±40°, and a scattering cross section exceeding 22 dB was obtained in the range of ±20°. , yielding an almost symmetrical scattering cross section.

There is no significant difference in the scattering cross section obtained between the hollow panel 200A and the flat panel 200 for incident radio waves of 3 GHz to 6 GHz. and either can be used. When using the flat panel 200, the thickness of the panel is not limited to 5.0 mm, but is set to an appropriate thickness in the range of 1.0 mm to 10.0 mm in consideration of the material, strength, transparency, etc. of the panel. may The thickness of the hollow panel 200A is also not limited to 5.0 mm, and is set to an appropriate thickness within a range in which the hollow 213 can be formed inside.

Although the present invention has been described based on specific embodiments, the present invention is not limited to the above configuration examples. The cross-sectional hollowness of the hollow panel can be appropriately set in the range of 10% to 75% in consideration of the strength, weight, dielectric constant, etc. of the panel. The panel size of the electromagnetic wave reflector used in the wireless transmission system is not limited to 2 m×1 m, and is appropriately selected within the range of 10 cm×10 cm to 3 m×3 m as described above. When a plurality of panels are connected and used, a frame 201 may be used to connect the adjacent panels so that the conductive layers are electrically connected. When hollow panel 200A is used, hollow 213 does not necessarily have to extend continuously from the top end to the bottom end of hollow panel 200A. The hollow 213 may be provided in a partial region of the hollow panel 200A, or the hollow 213 may be provided separately in the upper half and the lower half of the hollow panel 200A. The wireless transmission system of the embodiment is effectively used in a facility that includes production equipment and the like and includes process lines that tend to create dead zones. In addition to the process line, it can be effectively used for indoor and outdoor event facilities where many exhibits and people are likely to line up.

This application claims priority based on Japanese Patent Application No. 2021-206521 filed on December 20, 2021, and includes the entire contents of this Japanese Patent Application.

1, 1A to 1E wireless transmission system 10 base station 12, 12-1, 12-2 structure (shield)
14 production equipment (target equipment)
20, 20-1, 20-2, 20A, 20B Electromagnetic wave reflector 21 Reflective surface 30 Dead zone 200 Panel

200A Hollow panels

208, 210 Dielectric layer 211 Plate 213 Hollow 215 Conductive layer R Reflection center D1 From dead zone to electromagnetic wave reflector D2 Straight line distance from the base station antenna to the reflection center of the electromagnetic wave reflector

Claims

In a wireless transmission system in which a base station located in a facility and a target device transmit and receive radio waves at a frequency selected from a frequency band of 3 GHz or more and less than 6 GHz,
The maximum gain of the antenna of the base station is 5dBi or more and 30dBi or less,
When there is a dead zone in the facility where the reception intensity is 10 dB or more lower than the surroundings, the size of the reflecting surface between the base station and the dead zone is 10 cm x 10 cm or more and 3.0 m x 3.0 m. An electromagnetic wave reflector comprising one or more of the following panels is arranged so that the reflection center is at a height of 0.5 m or more from the floor of the facility;
A wireless transmission system according to claim 1, wherein a total distance of a straight line connecting the antenna of the base station and the electromagnetic wave reflector and a straight line distance connecting the electromagnetic wave reflector and the dead zone is 5.0 m or more and 300 m or less.
The horizontal beam width of the radio waves radiated from the base station is 10° or more and 180° or less.
A wireless transmission system according to claim 1.
The reflective surface of the electromagnetic wave reflecting device has at least one of a specular reflective surface that reflects the radio wave at an angle that is the same as the incident angle, and an artificial surface that reflects the radio wave at an angle different from the incident angle,
3. A wireless transmission system according to claim 1 or 2.
The height of the center of reflection of the electromagnetic wave reflector is equal to or lower than the height of the receiving point of the target device.
A wireless transmission system according to any one of claims 1-3.
the facility is a production facility, the target device is a production device, and
the dead zone exists along a process line within the production facility;
The electromagnetic wave reflector is arranged along the process line,
A wireless transmission system according to any one of claims 1-4.
The panel of the electromagnetic wave reflector has a hollow inside,
A wireless transmission system according to any one of claims 1-5.
The cross-sectional hollowness of the panel is 10% or more and 75% or less.
A wireless transmission system according to claim 6.
a dielectric layer;
and a conductive layer that reflects radio waves in a frequency band of 3 GHz or more and 6 GHz or less,
The dielectric layer has a hollow inside,
Electromagnetic wave reflector.
the hollow includes a plurality of hollows extending in parallel inside the dielectric layer;
The electromagnetic wave reflector according to claim 8.
The dielectric layer has a hollowness of 10% or more and 75% or less.
The electromagnetic wave reflector according to claim 8.