Wireless transmission system

Abstract

Provided is a wireless transmission system in which a radio wave propagation environment is improved. This wireless transmission system is provided with: a base station that performs wireless communication in a frequency band included in the range of 1 GHz to 300 GHz (inclusive); a first reflector that reflects a direct wave from the base station; and a second reflector that reflects the electromagnetic wave reflected by the first reflector, and that reflects the electromagnetic wave when the maximum gain of the transmission antenna of the base station is 5-30 dBi. The sum of a first linear distance (D1) from the base station to the first reflector and a second linear distance (D2) from the first reflector to the second reflector is 2.5 m or more and 250.0 m or less.

Description

Technical Field

[0001] The present invention relates to a wireless transmission system. Background Art

[0002] The introduction of wireless base stations to indoor and outdoor areas is progressing for the purpose of realizing automation of manufacturing processes and office work, remote operation, control and management based on AI (Artificial Intelligence), and autonomous driving. In addition to indoor areas such as factories, workshops, offices, and commercial facilities, and outdoor areas such as highways and railway lines, wireless base stations are also being introduced in scenes that have nothing to do with indoors or outdoors, such as medical sites and event venues. In the fifth-generation mobile communication standard (hereinafter referred to as "5G"), a frequency band below 6 GHz, called "sub-6", and a 28 GHz band classified as a millimeter wave band are provided. In the next-generation 6G mobile communication standard, it is expected to expand to the sub-terahertz band. By using such a high-frequency band, the communication bandwidth is greatly expanded, and a large amount of data communication can be carried out with low latency.

[0003] In 5G, since radio waves with strong linear propagation performance are used, places where radio waves are difficult to reach will occur. In particular, in places where points where base station antennas cannot be seen (NLOS: Non-Line-Of-Sight) are likely to occur, means are needed to send radio waves radiated from the base station to the desired area. A structure in which an electromagnetic reflection device is arranged along at least a portion of the production line is proposed (for example, refer to patent document 1). In addition, in order to allow freedom in the reflection direction and beam width, the development of a reflecting surface with an artificial surface called a "metasurface" is being promoted. The metasurface is formed by a periodic structure or pattern that is thinner than the wavelength and is designed to reflect radio waves in the desired direction (for example, refer to non-patent document 1). Since the metasurface can achieve the desired reflection angle while maintaining a planar configuration structure, the metasurface can effectively function as a reflector even in an environment where there is no space to set up multiple electromagnetic wave reflection panels.

[0004] Patent Document 1: International Publication No. 2021 / 199504

[0005] Non-patent literature 1: Diaz-Rubio et al., Sci. Adv. 2017: 3: e1602714 1 Summary of the Invention

[0006] Depending on the environment in which base stations are deployed, blind spots can occur in various locations. By placing reflectors in appropriate locations, wireless communication with base stations can be achieved even in NLOS environments, where direct waves from the base stations are invisible. However, using reflectors solely to reflect direct waves from the base stations is difficult to effectively reduce blind spots and fully improve radio quality. One object of the present invention is to provide a wireless transmission system that improves the radio wave propagation environment.

[0007] In one embodiment, the wireless transmission system includes:

[0008] A base station for performing wireless communication in a frequency band included in a range of 1 GHz or higher and 300 GHz or lower;

[0009] a first reflector that reflects direct waves from the base station; and

[0010] The second reflector reflects the electromagnetic wave reflected by the first reflector.

[0011] When the maximum gain of the transmitting antenna of the above-mentioned base station is greater than or equal to 5dBi and less than or equal to 30dBi, the sum of the first straight-line distance from the above-mentioned base station to the above-mentioned first reflector and the second straight-line distance from the above-mentioned first reflector to the above-mentioned second reflector is greater than or equal to 2.5m and less than or equal to 250.0m.

[0012] The use of wireless communication systems improves the radio wave propagation environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic plan view of a wireless transmission system according to an embodiment.

[0014] Figure 2 This is a schematic diagram of an electromagnetic wave reflecting device using the reflector according to the embodiment.

[0015] Figure 3 This is a schematic diagram of an electromagnetic wave reflecting fence formed by combining multiple electromagnetic wave reflecting devices.

[0016] Figure 4 This is a diagram showing an example of a layer structure in the thickness direction of a reflector.

[0017] Figure 5 This is a schematic plan view of the environment used for measuring received power.

[0018] Figure 6 It is a schematic plan view showing the arrangement structure of a reference example using a single reflector.

[0019] Figure 7 is a planar schematic diagram of a reflector with a metasurface.

[0020] Figure 8This is a diagram showing an example of a unit pattern constituting a metasurface.

[0021] Figure 9 It is a plan view schematically showing the configuration structure of a wireless transmission system using a reflector having a metasurface. DETAILED DESCRIPTION

[0022] In an embodiment, a wireless transmission system is provided for use in indoor and outdoor environments where blind spots occur. Radio waves in the millimeter wave band and the sub-terahertz band are high frequencies, and therefore have high linear propagation performance, short propagation distances, and large propagation losses. Various structures and obstructions exist in factories, workshops, roads, commercial facilities, and other equipment, making it difficult to maintain high communication quality. The use of reflectors can improve the radio wave propagation environment, but the position, size, and number of obstructions vary for each device, and the effective configuration of reflectors cannot be generalized. In addition, there are limits to the improvement of the radio wave propagation environment using a single reflector.

[0023] In an embodiment, a wireless transmission system is provided for expanding an area in which the radio wave propagation environment is improved. The structure of the wireless transmission system of the embodiment is described below with reference to the accompanying drawings. The method shown below is an example for concretizing the technical idea of the present invention and does not limit the present invention. In order to facilitate understanding of the invention, the size, positional relationship, etc. of each component shown in the drawings are sometimes exaggerated. In the following description, the same components or functions are sometimes marked with the same name or figure mark, and repeated descriptions are omitted.

[0024] Wireless Transmission System

[0025] Figure 1 The figure is a schematic plan view of a wireless transmission system 1 according to an embodiment. The wireless transmission system 1 includes: a base station 31, which is installed indoors or outdoors and performs wireless communications using frequencies within a frequency band between 1 GHz and 300 GHz, for example, between 1 GHz and 170 GHz; a first reflector 10-1, which reflects direct waves from the base station 31; and a second reflector 10-2, which reflects electromagnetic waves reflected by the first reflector 10-1. In the environment where the base station 31 is located, there is a structure 40 that blocks the direct waves from the base station 31. In factories and workshops, the structure 40 is a metal pipe, tube, rack, production machinery, etc. Outdoors, the structure 40 is a building, billboard, roadside tree, etc. As viewed from the base station 31, the area behind the structure 40 becomes a blind spot 30.

[0026] In this specification and claims, "blind spot" refers to an area where the received power is reduced by 10dB or more compared to the surrounding receiving environment without obstruction due to the influence of obstructions such as structures 40. Blind spot 30 includes not only two-dimensional areas but also three-dimensional spaces. Figure 1In the coordinate system, the plane on which structure 40 is placed is defined as the XY plane, and the height direction perpendicular to the XY plane is defined as the Z direction. If user devices such as production equipment, sensors, and mobile terminals with wireless communication capabilities are located in blind spot 30, it becomes difficult for them to transmit and receive signals with base station 31. Therefore, reflectors are introduced into wireless transmission system 1 to expand the radio wave propagation area.

[0027] The embodiment assumes an environment where it is difficult to eliminate the blind zone 30 using a single reflector. In the case where the reflector has a mirror reflective surface, Figure 1 In this configuration, it is difficult to transmit radio waves from the base station 31 to the blind spot 30 using a single reflector. Therefore, the first reflector 10-1 is positioned at a location where the direct wave from the base station 31 reaches with a certain intensity or higher, and the second reflector 10-2 is positioned to reflect the reflected wave from the first reflector 10-1 toward the blind spot 30. As long as the second reflector 10-2 can receive the reflected wave from the first reflector 10-1, it can be located in an NLOS environment where it is not visible from the base station 31.

[0028] The straight-line distance from base station 31 to first reflector 10-1 is D1 (first straight-line distance), and the straight-line distance from first reflector 10-1 to second reflector 10-2 is D2 (second straight-line distance). When the maximum gain of base station 31's transmitting antenna (denoted as "Tx" in the figure) is between 5 dBi and 30 dBi, the sum of D1 and D2 is between 2.5 m and 250 m. If the combined distance of D1 and D2 is less than 2.5 m, it is difficult to effectively transmit the radio waves radiated from base station 31 via first reflector 10-1 to second reflector 10-2. If the combined distance of D1 and D2 exceeds 250 m, it is difficult to transmit the radio waves with sufficient reflection intensity via first reflector 10-1 to second reflector 10-2, due to the maximum gain of the transmitting antenna and the linear propagation performance of the radio waves.

[0029] When the straight-line distance from the second reflector 10-2 to the boundary of the blind spot 30 is D3 (the third straight-line distance), and the maximum gain of the transmitting antenna of the base station 31 is 5 dBi or more and 30 dBi or less, the sum of D1, D2, and D3 is 5.0 m or more and 300.0 m or less. If the total distance of D1, D2, and D3 is less than 5.0 m, it is difficult to transmit the radio waves from the base station 31 to the blind spot 30 via the first reflector 10-1 and the second reflector 10-2, making it difficult to effectively expand the area of improvement in the radio wave propagation environment. If the total distance of D1, D2, and D3 exceeds 300.0 m, it is difficult to transmit the radio waves to the blind spot 30 with sufficient strength via the first reflector 10-1 and the second reflector 10-2, considering the maximum gain of the transmitting antenna and the linear propagation performance of the radio waves.

[0030] To satisfy the aforementioned distance relationship, the first reflector 10-1 is positioned to reflect direct waves from the base station 31, and the second reflector 10-2 is positioned to reflect the reflected waves from the first reflector 10-1 toward the blind spot 30. This allows the radio waves from the base station 31 to be transmitted to the blind spot 30 at a reception power sufficient for wireless communication, thereby improving the radio wave propagation environment.

[0031] The reflecting surface 17-1 of the first reflector 10-1 and the reflecting surface 17-2 of the second reflector 10-2 are formed of a material that can maintain the electric field strength of the incident radio wave as much as possible and reflect it in the designed direction. When the reflecting surfaces 17-1 and 17-2 are mirror-reflecting surfaces, for example, solid films of aluminum, copper, silver, gold, platinum, rhodium, chromium, nickel, stainless steel, etc. can be used. When the reflecting surfaces 17-1 and 17-2 have an artificial metasurface that reflects at an angle different from the incident angle, the above-mentioned conductive material is used to form a mesh, a periodic pattern, etc. The density of the conductive mesh and the period of the periodic pattern can also be designed to selectively reflect radio waves (e.g., 28 GHz ± 4 GHz) from the base station 31.

[0032] The reflecting surface 17-1 of the first reflector 10-1 and the reflecting surface 17-1 of the second reflector 10-2 need only be large enough to cover at least the area determined by the radius r of the first Fresnel zone. The radius r1 of the first Fresnel zone when the radio wave radiated from the transmitting antenna of the base station 31 and reflected by the first reflector 10-1 reaches the second reflector 10-2 in phase is defined by the following equation.

[0033] r1=[λ×D1×D2 / (D1+D2)] 1 / 2

[0034] Here, λ is the operating wavelength of the base station 31. Similarly, when the radio wave reflected by the second reflector 10-2 reaches the blind zone 30 in phase, the radius r2 of the first Fresnel zone is defined by the following equation.

[0035] r2=[λ×D2×D3 / (D2+D3)] 1 / 2

[0036] If the distance D1 from the antenna of the base station 31 operating in the 28 GHz band (wavelength of approximately 10.7 mm) to the first reflector 10-1 is 10.0 m, and the distance D2 from the first reflector 10-1 to the second reflector 10-2 is 10.0 m, the reflecting surface 17-1 of the first reflector 10-1 only needs to be approximately 20 cm on a side. Similarly, if the distance D2 from the first reflector 10-1 to the second reflector 10-2 is 10.0 m, and the distance D3 from the second reflector 10-2 to the farthest edge of the blind spot 30 in the reflection direction is 10.0 m, the reflecting surface 17-2 of the second reflector 10-2 only needs to be approximately 20 cm on a side. In the 4.7 GHz band, at the same distance, a side of more than 50 cm between the first reflector 10-1 and the second reflector 10-2 can be sufficient. For closer distances, a side of 20 cm or less can be sufficient. On the other hand, to cover as large a reflection area as possible with a smaller number of reflectors 10, the reflecting surface of at least one of the first reflector 10-1 and the second reflector 10-2 can be expanded to approximately 3.0 m x 3.0 m. In this embodiment, two or more reflectors with sizes ranging from 0.1 m x 0.1 m to 3.0 m x 3.0 m are deployed to reduce the blind spot 30 and expand the radio wave propagation area.

[0037] In addition to considering the location, height, and maximum gain of the base station 31's transmitting antenna, the position of the reflection center R of the reflecting surface 17-1 of the first reflector 10-1 and the reflecting surface 17-2 of the second reflector 10-2 is determined by taking into account the location and spatial extent of the blind spot 30. The reflection center R is preferably located at a height of at least 0.5 m from the ground or road surface where the reflector 10 is installed. The inclination of the first reflector 10-1 or the second reflector 10-2 relative to the ground or road surface and the line of sight (LOS) angle relative to the base station 31 are appropriately determined based on the shape of the beam formed by the base station 31's antenna, the horizontal and vertical radiation angles, the location of the blind spot 30, and other factors.

[0038] At least one of the first reflector 10-1 and the second reflector 10-2 may have a metasurface on at least a portion of its reflective surface that reflects the incident electromagnetic wave at an angle different from the incident angle. Alternatively, at least one of the first reflector 10-1 and the second reflector 10-2 may have a specular reflective surface on at least a portion of its reflective surface that reflects the incident electromagnetic wave at the same angle as the incident angle.

[0039] <Electromagnetic wave reflecting device and electromagnetic wave reflecting fence using a reflector>

[0040] Figure 2This is a schematic diagram of an electromagnetic wave reflecting device 60 including a reflector 10 according to an embodiment. The plane in which the electromagnetic wave reflecting device 60 is installed is defined as the XY plane, and the height direction perpendicular to the XY plane is defined as the Z direction. The electromagnetic wave reflecting device 60 includes the reflector 10, which reflects electromagnetic waves at the operating frequency of the base station 31, and is located at a desired location within the communication area of the base station 31.

[0041] The electromagnetic wave reflecting device 60 may also include a frame 50 that holds both ends of the reflector 10, a top frame 57 that holds the upper end, and a bottom frame 58 that holds the lower end. The frame 50, top frame 57, and bottom frame 58 hold the entire circumference of the reflector 10. The frame 50 may also be referred to as a "side frame" due to its position relative to the top frame 57 and bottom frame 58. While the top frame 57 and bottom frame 58 are not required, their presence ensures the mechanical strength and safety of the reflector 10 during transportation, assembly, and installation.

[0042] When the electromagnetic wave reflecting device 60 is made to stand on its own indoors or outdoors, the legs 56 may be provided. Figure 2 In the example shown, the legs 56 support the lower end of the frame 50. However, the legs 56 may also be connected to the base frame 58. Alternatively, the legs 56 can be fixed to the ground or road surface using screws or other similar means. The legs 56 may also be provided with movable components such as casters to enable movement at the installation location. Alternatively, the legs 56 may be omitted and the reflector 10 may be completely surrounded by a frame and installed parallel to or at an angle relative to a wall, ceiling, or the ground.

[0043] Figure 3 This is a schematic diagram of an electromagnetic wave reflecting fence 100 formed by connecting electromagnetic wave reflecting devices 60-1 and 60-2 with a frame 50. The reflectors 10 of electromagnetic wave reflecting device 60-1 and 60-2 are held by frame 50. Each reflector 10 may also have a non-specular reflecting surface, at least in part, where the incident angle and reflection angle of the electromagnetic wave differ. In addition to diffusing and scattering surfaces, non-specular reflecting surfaces also include artificial reflecting surfaces, or metasurfaces, designed to reflect radio waves in a desired direction. To maintain continuity of the reflected potential, the reflecting surfaces 17 of adjacent reflectors 10 are sometimes preferably electrically connected to each other. However, when using metasurfaces, the reflecting surfaces 17 of adjacent reflectors 10 do not need to be electrically connected. By holding adjacent reflectors 10 with frame 50, an electromagnetic wave reflecting fence 100 connected in the X direction is obtained. The connected electromagnetic wave reflecting fence 100 can also be used as the first reflector 10-1 or the second reflector 10-2. Thereby, the area where the radio quality is improved can be expanded.

[0044] Figure 4: represents the layer structure in the thickness direction (Y direction) of the reflector 10. The reflector 10 includes a conductive layer 11 and a dielectric layer 14 or 15 bonded to at least one surface of the conductive layer 11 via an adhesive layer 12 or 13. Figure 4 In the example shown, the conductive layer 11 is sandwiched between the dielectric layers 14 and 15 via the adhesive layers 12 and 13. For outdoor use, a protective layer such as an anti-ultraviolet film may be provided on at least one of the dielectric layers 14 and 15. Generally, when the reflector 10 is placed outdoors, the surface substrate of the reflector 10 is susceptible to deformation, discoloration, and degradation due to the influence of visible light contained in sunlight, ultraviolet rays, and temperature fluctuations. If the dielectric layers 14 and 15 on the surface of the reflector 10 are resin substrates, they are susceptible to temperature fluctuations and other effects. If the dielectric layer 14 or 15 is deformed to approximately 1 / 100 of its original size, the reflection direction or reflection efficiency may change. Furthermore, ultraviolet radiation can change the relative dielectric constant of the resin material or dielectric material, potentially deviating from the designed reflection direction and reflection efficiency. From this perspective, depending on the location of the reflector 10, it is preferable to provide a protective layer on the surface of the dielectric layer 14 and / or 15.

[0045] The conductive layer 11 is the surface that forms the reflective surface 17 of the reflector 10 and can be formed of a metal mesh, a periodic pattern, a geometric pattern, a transparent conductive film, or the like. As an example, the conductive layer 11 includes a metal mesh formed of a good conductor such as Cu, Ni, SUS, or Ag. In the case where a portion of the reflective surface 17 includes a metasurface, the conductive layer 11 may also include a pattern comprising a periodic arrangement of multiple metal elements. The conductive layer 11 has a thickness of not less than 10 μm and not more than 200 μm, preferably not less than 50 μm and not more than 150 μm, so as to fully function as a reflective surface that reflects electromagnetic waves of the target frequency in the designed direction.

[0046] The adhesive layers 12 and 13 have a transmittance of 60% or more, preferably 70% or more, and more preferably 80% or more relative to the operating frequency, so as to guide the incident electromagnetic waves to the conductive layer 11. The adhesive layers 12 and 13 can be formed of vinyl acetate resin, acrylic resin, cellulose resin, aniline resin, ethylene resin, silicone resin, or other resin materials. In order to make the adhesive layers 12 and 13 durable and moisture-resistant for outdoor use, ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP) can also be used. The thickness of the adhesive layers 12 and 13 is a thickness that can reliably bond and maintain the dielectric layers 14 and 15 to the conductive layer 11, for example, 10 μm or more and 400 μm or less. The adhesive layers 12 and 13 have a relative dielectric constant and dielectric loss tangent suitable for achieving the target reflection characteristics of the conductive layer 11.

[0047] The dielectric layers 14 and 15 are insulating polymer films such as polycarbonate, cycloolefin polymer (COP), polyethylene terephthalate (PET), or fluororesin. To maintain the strength of the reflector 10 and minimize the overall weight of the reflector 10, the thickness of the dielectric layers 14 and 15 is selected within a range of greater than 1.0 mm and less than 10.0 mm. When the thickness of the conductive layer 11 is set to 100.0 μm, the ratio of the thickness of the dielectric layers 14 and 15 to the thickness of the conductive layer 11 is greater than 10 and less than 80. By setting the ratio of the thickness of the dielectric layers 14 and 15 to the thickness of the conductive layer 11 within this range, the reflector 10 has mechanical strength that can withstand outdoor use and can achieve the desired reflective characteristics. When mechanical strength is prioritized, the ratio of the thickness of the dielectric material to the thickness of the conductive layer 11 becomes larger. In this case, when the reflector 10 includes a metasurface, it is preferable to appropriately design the relative dielectric constant and dielectric loss tangent of the entire dielectric portion including the adhesive layer 12 and the dielectric layer 14 or the adhesive layer 13 and the dielectric layer 15 .

[0048] Evaluation of reflectors and wireless transmission systems

[0049] Using two or more of the reflectors 10 described above, the distribution of received power in an environment with an obstruction is measured. Figure 5 This is a schematic plan view of the environment used for measuring received power. Figure 6 This is a schematic diagram of a configuration using a single reflector as a reference example. Figure 5 and Figure 6In the example, a passage 45 including a portion with a poor field of view is provided between the walls of the structure 40. The base station 31 is provided at position P0 of the passage 45. The transmitting antenna Tx of the base station 31 is provided at a height of 1.0 m, and a Sub6 (4.7 GHz) beam having directivity in the X direction is radiated at an angle parallel to the XY plane. The half-value width of the beam is approximately 10°. After extending a predetermined distance in the X direction from position P0 of the base station 31, the passage 45 is bent 90 degrees and extended in the Y direction for a predetermined distance. It is then bent in the X direction and extended for a predetermined distance. In this planar configuration, the received power is measured using a measuring device having a receiving antenna at a height of 1.0 m before and after the reflector is set, and changes in the received power are observed.

[0050] <Example 1>

[0051] Example 1 is Example 1. A passage 45 with a width of 7.0 m extends 30.0 m in the X direction from position P0, bends 90° in the Y direction, and extends 30.0 m in the Y direction. It then bends 90° in the X direction and extends 30.0 m in the X direction. At position P1, 30.0 m away from the transmitting antenna Tx of base station 31 in the X direction, a first reflector 10-1 with a height of 2.0 m and a width of 1.0 m is positioned at a 45° angle with respect to the line of sight of base station 31. At position P2, 30.0 m away from position P1 in the Y direction, a second reflector 10-2 with a height of 2.0 m and a width of 1.0 m is positioned parallel to first reflector 10-1. Position P3 is 30.0 m away from second reflector 10-2 in the X direction. As viewed from the first reflector 10-1, the area from position P2 to position P3 is a blind spot. The farthest edge of the blind spot in the reflection direction of the second reflector 10-2 is position P3. Received power was measured every 1.0 m in both the X and Y directions from position P0 to P3. The sum of the distances L1 + L2 + L3 from position P0 to P3 is 90 m. The first reflector 10-1 and the second reflector 10-2 have reflective surfaces 17-1 and 17-2 that perform specular reflection. The maximum gain of the base station 31 antenna is 20 dBi.

[0052] In the path between positions P1 and P2 (L2 = 30.0 m), the average received power before the installation of the first reflector 10-1 was -90.0 dBm. By installing the first reflector 10-1 at position P1, the average received power in this path became -70.0 dBm, a 20.0 dB improvement was confirmed. Furthermore, in the path between positions P2 and P3 (L3 = 30.0 m), the average received power before the installation of the first reflector 10-1 and the second reflector 10-2 was -100.0 dBm. By installing the first reflector 10-1 at position P1 and the second reflector 10-2 at position P2, the average received power in the path between P2 and P3 became -75.0 dBm, a 25.0 dB improvement was confirmed.

[0053] <Example 2>

[0054] Example 2 is embodiment 2. The specifications of the passage 45 are the same as those of Example 1. At a position P1 30.0 m away from the transmitting antenna Tx of the base station 31 in the X direction, two reflectors 10 with a height of 2.0 m and a width of 1.0 m are arranged at an angle of 45° with respect to the line of sight of the base station 31. Figure 3 As shown, two reflectors 10 are connected in the width direction by a frame 50 to form a first reflector 10-1 with a height x width of 2.0 m x 2.0 m. The two connected reflectors 10 have mirror reflective surfaces and are electrically connected by the frame 50 so that the reflection potential is continuous.

[0055] At position P2, 30.0 m away from position P1 in the Y direction, a second reflector 10-2 with a height of 2.0 m and a width of 1.0 m is placed parallel to the first reflector 10-1 (2.0 m x 2.0 m). Second reflector 10-2 has a mirror-like reflective surface. Position P3 is 30.0 m away from second reflector 10-2 in the X direction. Received power is measured every 1.0 m in both the X and Y directions from position P0 to P3. The sum of the distances from position P0 to P3 (L1 + L2 + L3) is 90 m. The maximum antenna gain of base station 31 is 20 dBi.

[0056] In the path between positions P1 and P2 (L2 = 30.0 m), the average received power before the installation of the first reflector 10-1 was -90.0 dBm. However, by installing the 2.0 m × 2.0 m first reflector 10-1 at position P1, the average received power in this path section decreased to -65.0 dBm, a 25.0 dB improvement was confirmed. In the path between positions P2 and P3 (L3 = 30.0 m), the average received power before the installation of the first reflector 10-1 and the second reflector 10-2 was -100.0 dBm. By installing the 2.0 m × 2.0 m first reflector 10-1 at position P1 and the 2.0 m × 1.0 m second reflector 10-2 at position P2, the average received power in the path section between P2 and P3 decreased to -75.0 dBm, a 25.0 dB improvement was confirmed.

[0057] <Example 3>

[0058] Example 3 is a comparative example 1 relative to Example 1. Figure 6 As shown, the specifications of the passage 45 are the same as those in Example 1. Figure 6 In this configuration, a first reflector 10-1 with a height of 2.0 m and a width of 1.0 m is positioned at position P1, 30.0 m away from the transmitting antenna Tx of base station 31 in the X direction, at a 45° angle with respect to the line of sight of base station 31. Only first reflector 10-1 is used; no reflector is placed at position P2. A position 30.0 m away from position P2 in the X direction is designated as position P3. Received power is measured at 1.0 m intervals in both the X and Y directions from position P0 to position P3. The sum of the distances L1 + L2 + L3 from position P0 to position P3 is 90 m. The first reflector 10-1 has a reflective surface 17-1 that performs specular reflection. The maximum gain of the antenna of base station 31 is 20 dBi.

[0059] In the path between positions P1 and P2 (L2 = 30.0 m), the average received power was -90.0 dBm before the installation of first reflector 10-1. However, by installing first reflector 10-1 at position P1, the average received power in this path section decreased to -70.0 dBm, demonstrating a 20.0 dB improvement. In the path between positions P2 and P3 (L3 = 30.0 m), the average received power was -100.0 dBm before the installation of first reflector 10-1. After the installation of first reflector 10-1 at position P1, the average received power between P2 and P3 decreased to -100.0 dBm. The first reflector 10-1 alone does not improve the radio wave propagation environment in this path section. This is because the radio waves reflected by first reflector 10-1 continue to propagate straightly at position P2 and are scattered by structure 40, which forms a wall.

[0060] <Example 4>

[0061] Example 4 is a comparative example 2 with respect to Example 2. At a position P1 30.0 m away from the transmitting antenna Tx of the base station 31 in the X direction, two reflectors 10 with a height of 2.0 m and a width of 1.0 m are arranged at an angle of 45° with respect to the line of sight of the base station 31. Figure 3 As shown, two reflectors 10 are connected in the width direction by a frame 50 to form a first reflector 10-1 with a height x width of 2.0 m x 2.0 m. The two connected reflectors 10 have mirror reflective surfaces and are electrically connected by the frame 50 so that the reflection potential is continuous.

[0062] Only the 2.0 m × 2.0 m first reflector 10-1 at position P1 was used; no reflector was placed at position P2. Position P3, 30 m away from position P2 in the X direction, was designated as position P3. Received power was measured every 1.0 m in both the X and Y directions from position P0 to P3. The sum of the distances from position P0 to P3 (L1 + L2 + L3) was 90 m. The maximum gain of the antenna of base station 31 was 20 dBi.

[0063] In the path between positions P1 and P2 (L2 = 30.0 m), the average received power was -90.0 dBm before the installation of the first reflector 10-1. However, by installing the 2.0 m x 2.0 m first reflector 10-1 at position P1, the average received power in this path section decreased to -65.0 dBm, demonstrating a 25.0 dB improvement. In the path between positions P2 and P3 (L3 = 30.0 m), the average received power was -100.0 dBm before the installation of the first reflector 10-1. After installing the 2.0 m x 2.0 m first reflector 10-1 at position P1, the average received power between P2 and P3 decreased to -100.0 dBm. Simply connecting two reflectors 10 using the first reflector 10-1 does not improve the radio wave propagation environment in this path section.

[0064] <Example 5>

[0065] Example 5 is Example 3. In Example 3, the radio wave propagation environment is improved in a relatively narrow closed space such as a warehouse. Figure 5 The distance L1 between positions P0 and P1 of the configuration structure is set to 2.0 m, the distance L2 between positions P1 and P2 is set to 3.0 m, and the distance L3 between positions P2 and P3 is set to 5.0 m. The width of passage 45 is 3.0 m. A base station is installed at position P0. The maximum gain of the antenna of base station 31 is 10 dBi.

[0066] At position P1, 2.0 m away from the transmitting antenna Tx of base station 31 in the X direction, a first reflector 10-1 with a height of 2.0 m and a width of 1.0 m is positioned at a 45° angle with respect to the line of sight of base station 31. At position P2, 3.0 m away from position P1 in the Y direction, a second reflector 10-2 with a height of 2.0 m and a width of 1.0 m is positioned parallel to first reflector 10-1. Position P3 is 5.0 m away from second reflector 10-2 in the X direction. Received power is measured every 1.0 m in both the X and Y directions from position P0 to P3. The sum of the distances L1 + L2 + L3 from position P0 to P3 is 10.0 m. The first reflector 10-1 and the second reflector 10-2 have reflective surfaces 17-1 and 17-2 that perform specular reflection.

[0067] In the path section between positions P1 and P2 (L2 = 3.0 m), the average received power was -75.0 dBm before installing first reflector 10-1. However, installing first reflector 10-1 at position P1 reduced the average received power in the same path section to -70.0 dBm, demonstrating a 5.0 dB improvement. In the path section between positions P2 and P3 (L3 = 5.0 m), the average received power was -95.0 dBm before installing first reflector 10-1 and second reflector 10-1. However, installing first reflector 10-1 and second reflector 10-2 reduced the average received power in the same path section to -70.0 dBm, demonstrating a 25.0 dB improvement. When the distance from base station 31 to first reflector 10-1 is close to 2.0 m, the received power in the path section between P1 and P2 does not decrease significantly even without first reflector 10-1, resulting in a slightly lower improvement in received power than in Examples 1 and 2.

[0068] <Example 6>

[0069] Example 6 is Example 4. In Example 4, the radio wave propagation environment is improved in a larger environment such as a station or a shopping mall. Figure 5 The distance L1 between positions P0 and P1 is set to 150.0 m, the distance L2 between positions P1 and P2 is set to 100.0 m, and the distance L3 between positions P2 and P3 is set to 50.0 m. The width of passage 45 is 12.0 m. Base station 31 is installed at position P0. The maximum gain of the antenna of base station 31 is 30 dBi.

[0070] Three reflectors 10 with a height of 2.0 m and a width of 1.0 m are placed as shown in FIG. Figure 3The first reflector 10-1 is connected as shown in FIG. 1 and is set at a position P1 150.0 m away from the transmitting antenna Tx of the base station 31 in the X direction at an angle of 45° relative to the line of sight of the base station 31. Figure 3 The second reflector 10-2 is connected in this manner and is installed parallel to the first reflector 10-1 at position P2, 100.0 m away from position P1 in the Y direction. Position P3 is 50.0 m away from the second reflector 10-2 in the X direction. From positions P0 to P3, the received power is measured every 1.0 m in both the X and Y directions. The sum of the distances L1 + L2 + L3 from position P0 to P3 is 300.0 m. The first reflector 10-1 and the second reflector 10-2 have reflective surfaces 17-1 and 17-2 that perform specular reflection.

[0071] In the path section between positions P1 and P2 (L2 = 100.0 m), the average received power was -100.0 dBm before the installation of the first reflector 10-1, a combination of three reflectors 10. However, the installation of the first reflector 10-1, a combination of three reflectors 10, at position P1 reduced the average received power in the path section between P1 and P2 to -70.0 dBm, a 30.0 dB improvement. In the path section between positions P2 and P3 (L3 = 50.0 m), the average received power was -100.0 dBm before the installation of the first reflector 10-1 and the second reflector 10-2. However, the installation of the first reflector 10-1 and the second reflector 10-2 reduced the average received power in the same path section to -75.0 dBm, a 25.0 dB improvement. This improvement in received power is higher than in Example 6.

[0072] <Example 7>

[0073] Example 7 is Comparative Example 3. In Comparative Example 3, Figure 5 The distance L1 between positions P0 and P1 is set to 200.0 m, the distance L2 between positions P1 and P2 is set to 200.0 m, and the distance L3 between positions P2 and P3 is set to 100.0 m. The width of passage 45 is 15.0 m. Base station 31 is installed at position P0. The maximum gain of the antenna of base station 31 is 30.0 dBi.

[0074] Three reflectors 10 with a height of 2.0 m and a width of 1.0 m are placed as shown in FIG. Figure 3 The first reflector 10-1 is connected as shown in FIG. 1 and is set at a position P1 200.0 m away from the transmitting antenna Tx of the base station 31 in the X direction at an angle of 45° relative to the line of sight of the base station 31. Figure 3 Connected in this manner, the second reflector 10-2 is used and positioned parallel to the first reflector 10-1 at position P2, 200.0 m away from position P1 in the Y direction. Position P3 is 100.0 m away from the second reflector 10-2 in the X direction. Received power is measured every 1.0 m in both the X and Y directions from positions P0 to P3. The sum of the distances L1 + L2 from positions P0 to P2 is 400 m, and the sum of the distances L1 + L2 + L3 from positions P0 to P3 is 500 m. The first reflector 10-1 and the second reflector 10-2 have reflective surfaces 17-1 and 17-2 that perform specular reflection.

[0075] In the path section between positions P1 and P2 (L2 = 200.0 m), the average received power was -120.0 dBm before the installation of the first reflector 10-1, which is a combination of three reflectors 10. Even when the first reflector 10-1, which is a combination of three reflectors 10, was installed at position P1, the average received power in the same path section was still -120.0 dBm, with no improvement observed. This is presumably because, due to the maximum gain of the base station 31 antenna, the direct wave did not strike the first reflector 10-1 with sufficient intensity, and thus the radio wave could not be reflected toward position P2. Furthermore, in the path section between positions P2 and P3 (L3 = 100.0 m), the average received power was -120.0 dBm before the installation of the first reflector 10-1 and the second reflector 10-2. Even with the installation of the first reflector 10-1 and the second reflector 10-2, the average received power in the path section between P2 and P3 remained -120.0 dBm, with no improvement observed.

[0076] According to Examples 1 to 7, by placing first reflector 10-1 and second reflector 10-2 within an appropriate distance from base station 31, second reflector 10-2 reflects the radio waves reflected by first reflector 10-1 toward the blind spot, effectively delivering the radio waves to the blind spot. Furthermore, by placing first reflector 10-1 at a certain distance from base station 31 within the reach of direct waves from base station 31, the area where the radio wave propagation environment is improved can be effectively expanded, compared to a case where the distance L1 from base station 31 to first reflector 10-1 and the distance L2 from first reflector 10-1 to second reflector 10-2 are shorter. The results of Examples 1 to 7 apply when the operating frequency of base station 31 is between 1 GHz and 10 GHz, and more preferably between 5 GHz ± 3 GHz.

[0077] <Configuration example using metasurface>

[0078] Figure 7 is a schematic plan view of a reflector 20 having a metasurface, Figure 82 is a diagram showing an example of a unit pattern 210 constituting a metasurface. For the metasurface of the reflector 20, the unit pattern 210 composed of a plurality of conductive elements 220 is repeatedly arranged in the a direction and the b direction. The a direction corresponds to Figure 2 The X direction of b corresponds to the Z direction. Figure 8 As shown, the unit pattern 210 includes, for example, six conductive elements 211 , 212 , 213 , 214 , 215 and 216 .

[0079] Each conductive element 211 to 216 has a long axis in the Z direction, has the same width (w) in the X direction, and has different lengths (l) in the Z direction. Each conductive element 211 to 216 has a gap G between adjacent conductive elements and is arranged at a predetermined pitch in the X direction. Figure 8 In the example shown, unit pattern 210 is designed to reflect vertically incident 28 GHz electromagnetic waves at an angle of 50°, but this is not limiting. By designing the shape, spacing G, and length (l) of each conductive element constituting unit pattern 210, the reflection phase can be designed to reflect the incident electromagnetic wave in a desired direction.

[0080] Figure 9 Schematic diagram showing the arrangement of a wireless transmission system 2 using a reflector 20 having a metasurface. Figure 5 and Figure 6 The same applies. Base station 31 is installed at position P0 on passage 45. The transmitting antenna Tx of base station 31 is located at a height of 1.0 m. It radiates a 28 GHz band beam with X-directivity at an angle parallel to the XY plane. The beam has a half-value width of approximately 10°.

[0081] At a position P1 30.0 m away from the transmitting antenna Tx of the base station 31 in the X direction, a first reflector 20-1 with a metasurface having a height of 2.0 m and a width of 1.0 m is arranged at an angle perpendicular to the line of sight of the base station 31. The direct wave from the base station 31 is perpendicularly incident on the first reflector 20-1 and is reflected at a designed reflection angle θ. By using the first reflector 20-1 with a metasurface, the direct wave from the base station 31 is perpendicularly incident on the first reflector 20-1 and is reflected at a designed reflection angle θ. Figure 5 Compared with the first reflector 10 - 1 using a mirror reflector at an angle of 45° at the same position, the arrangement space of the reflector is reduced, and the space utilization efficiency is improved.

[0082] The electromagnetic wave reflected by the first reflector 20-1 enters the second reflector 20-2 at a nearly vertical angle. Figure 5The propagation distance is slightly longer than 30.0 m. The electromagnetic wave incident on the second reflector 20-2 is reflected at a designed reflection angle θ toward position P3. In this example, the second reflector 20-2 is configured so that the electromagnetic wave, non-specularly reflected by the first reflector 20-1, strikes it at an angle of incidence close to 0°. However, to accommodate installation space, the second reflector 20-2 can also be configured so that the electromagnetic wave strikes it at a predetermined angle of incidence greater than 0°. In this case, the incident electromagnetic wave is also reflected toward P3 at a reflection angle different from the incident angle.

[0083] Without the first reflector 20-1, the area or space from position P1 to P2 becomes a blind spot, where the received power is at least 10 dB lower than in an unobstructed environment. Installing the first reflector 20-1 reduces reflector installation space while eliminating the blind spot. Without the second reflector 20-2, the area or space from position P2 to P3 becomes a blind spot, where the received power is at least 10 dB lower than in an unobstructed environment. Installing the second reflector 20-2 reduces reflector installation space while eliminating the blind spot.

[0084] The wireless transmission system of the embodiment has been described above based on a specific configuration example, but the present invention is not limited to the above configuration example. The dimensions of the reflecting surfaces of the first and second reflectors can be appropriately designed based on the application. As an example, a planar dimension of 0.1 m × 0.1 m to 3.0 m × 3.0 m can be used. Alternatively, two or more reflectors can be connected to form the first or second reflector. In this case, the planar dimensions of each connected reflector can also be selected within the range of 0.1 m × 0.1 m to 3.0 m × 3.0 m.

[0085] At least one of the first reflector and the second reflector may also have a metasurface on at least a portion of the reflecting surface that reflects the incident electromagnetic wave at an angle different from the incident angle. Alternatively, at least one of the first reflector and the second reflector may also have a mirror reflecting surface on at least a portion of the reflecting surface that performs mirror reflection on the incident electromagnetic wave. At least one of the first reflector and the second reflector may also have a protective layer for ultraviolet protection on the outermost layer. The height of the antenna of the base station 31 is not limited to 1.0m, and may also be set at a height of 0.3m to 5.0m depending on the installation location. Depending on the position of the antenna of the base station 31, the reflecting surface of one or both of the first reflector and the second reflector may also be set to an angle that reflects the incident electromagnetic wave obliquely upward. By using the second reflector to reflect the electromagnetic wave reflected by the first reflector toward the blind spot, the blind spot that cannot be eliminated by a single reflector can be reduced.

[0086] As mentioned above, although embodiment of this disclosure was described, this disclosure can include the following structures.

[0087] (Item 1)

[0088] A wireless transmission system, comprising:

[0089] A base station for performing wireless communication in a frequency band included in a range of 1 GHz or higher and 300 GHz or lower;

[0090] a first reflector that reflects direct waves from the base station; and

[0091] The second reflector reflects the electromagnetic wave reflected by the first reflector.

[0092] When the maximum gain of the transmitting antenna of the above-mentioned base station is greater than or equal to 5dBi and less than or equal to 30dBi, the sum of the first straight-line distance from the above-mentioned base station to the above-mentioned first reflector and the second straight-line distance from the above-mentioned first reflector to the above-mentioned second reflector is greater than or equal to 2.5m and less than or equal to 250.0m.

[0093] (Item 2)

[0094] According to the wireless transmission system described in item 1,

[0095] The total of the first straight-line distance, the second straight-line distance, and a third straight-line distance from the second reflector to the farthest boundary of the blind spot in the reflection direction of the reflector is greater than or equal to 5.0 m and less than or equal to 300.0 m.

[0096] (Item 3)

[0097] The wireless transmission system according to item 1 or 2,

[0098] The second reflector is installed in a NLOS environment that is invisible from the base station.

[0099] (Item 4)

[0100] The wireless transmission system according to any one of items 1 to 3,

[0101] At least one of the first reflector and the second reflector is formed by connecting a plurality of reflectors.

[0102] (Item 5)

[0103] The wireless transmission system according to any one of items 1 to 3,

[0104] The first reflector or the second reflector has a planar size of not less than 0.1 m×0.1 m and not more than 3.0 m×3.0 m.

[0105] (Item 6)

[0106] According to the wireless transmission system described in item 4,

[0107] The planar dimensions of each of the plurality of reflectors are selected from a range of not less than 0.1 m×0.1 m and not more than 3.0 m×3.0 m.

[0108] (Item 7)

[0109] The wireless transmission system according to any one of items 1 to 6,

[0110] At least one of the first reflector and the second reflector includes a metasurface on at least a portion of a reflecting surface that reflects an incident electromagnetic wave at an angle different from an incident angle.

[0111] (Item 8)

[0112] The wireless transmission system according to any one of items 1 to 6,

[0113] At least one of the first reflector and the second reflector has a specular reflection surface that specularly reflects incident electromagnetic waves on at least a portion of its reflection surface.

[0114] (Item 9)

[0115] The wireless transmission system according to any one of items 1 to 8,

[0116] At least one of the first reflector and the second reflector has an ultraviolet protection layer as an outermost layer.

[0117] (Item 10)

[0118] The wireless transmission system according to any one of items 1 to 9,

[0119] The transmitting antenna of the base station is installed at a height of 0.5 m to 5.0 m above the ground or road surface.

[0120] This application claims priority based on Japanese Patent Application No. 2022-198617 filed on December 13, 2022, and includes the entire contents of that Japanese patent application.

[0121] Description of Reference Numerals

[0122] 1, 2…wireless transmission system; 10, 20…reflector; 10-1, 20-1…first reflector; 10-2, 20-2…second reflector; 11…conductive layer; 12, 13…adhesive layer; 14, 15…dielectric layer; 17, 17-1, 17-2…reflecting surface; 31…base station; 40…structure; 45…passageway; 50…frame (side frame); 56…leg; 57…top frame; 58…bottom frame; 60, 60-1, 60-2…electromagnetic wave reflecting device; 100…electromagnetic wave reflecting fence; 210…unit pattern; Tx…transmitting antenna; D1…first straight-line distance; D2…second straight-line distance; D3…third straight-line distance.

Claims

1. A wireless transmission system, characterized in that: include: A base station for performing wireless communication in a frequency band included in a range of 1 GHz or higher and 300 GHz or lower; a first reflector for reflecting a direct wave from the base station; as well as a second reflector, reflecting the electromagnetic wave reflected by the first reflector; When the maximum gain of the transmitting antenna of the base station is greater than or equal to 5 dBi and less than or equal to 30 dBi, the sum of a first straight-line distance from the base station to the first reflector and a second straight-line distance from the first reflector to the second reflector is greater than or equal to 2.5 m and less than or equal to 250.0 m.

2. The wireless transmission system according to claim 1, wherein: A total of the first straight-line distance, the second straight-line distance, and a third straight-line distance from the second reflector to the farthest boundary of the blind spot in the reflection direction of the second reflector is 5.0 m or more and 300.0 m or less.

3. The wireless transmission system according to claim 1, wherein: The second reflector is arranged in a NLOS environment that is invisible from the base station.

4. The wireless transmission system according to claim 1, wherein: At least one of the first reflector and the second reflector is formed by connecting a plurality of reflectors.

5. The wireless transmission system according to claim 1, wherein: The planar size of the first reflector or the second reflector is not less than 0.1 m×0.1 m and not more than 3.0 m×3.0 m.

6. The wireless transmission system according to claim 4, wherein: The planar size of each of the plurality of reflectors is selected within a range of not less than 0.1 m×0.1 m and not more than 3.0 m×3.0 m.

7. The wireless transmission system according to claim 1, wherein: At least one of the first reflector and the second reflector includes a metasurface on at least a portion of a reflecting surface that reflects an incident electromagnetic wave at an angle different from an incident angle.

8. The wireless transmission system according to claim 1, wherein: At least one of the first reflector and the second reflector has a specular reflection surface that specularly reflects incident electromagnetic waves on at least a portion of a reflection surface.

9. The wireless transmission system according to any one of claims 1 to 8, characterized in that: At least one of the first reflector and the second reflector has an ultraviolet protection layer on its outermost layer.

10. The wireless transmission system according to any one of claims 1 to 8, characterized in that: The transmitting antenna of the base station is set at a height of not less than 0.5 m and not more than 5.0 m from the ground or road surface.

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