JP2011244194A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system which allows for communication only within limited space in the vicinity of a leaky transmission line and which is easy to manufacture and inexpensive.SOLUTION: A communication system comprises a leaky transmission line 2 which is built into a structure 1 or placed on the structure 1. The communication device allows for communication via the leaky transmission line 2 within a region where distance from the leaky transmission 2 is equal to or less than three times a wavelength of electromagnetic wave transmitted over the leaky transmission line 2.

Description

  The present invention relates to a communication system using a leaky transmission line, and more particularly to a communication system using a structure in which a leaky transmission line capable of communicating only in the vicinity of the leaky transmission line is incorporated.

  Conventionally, as a leaky transmission line, for example, a leaky coaxial cable (LCX: Leaky Coaxial Cable) has been proposed and used as a transmission / reception antenna in a wireless communication system. LCX, for example, is laid along the train track for the purpose of wireless communication between the train and the ground, and for the purpose of communication by fire radio and police radio between the subway premises and the underground shopping center. And will be laid in the underground mall. In addition, wireless communication systems represented by mobile phones and wireless LANs are rapidly expanding because anyone can use a communication network anytime, anywhere.

  In addition, with the large-capacity transmission of wireless communication systems, the shift to the high frequency band of the operating frequency is progressing, and electromagnetic waves are not only applied to underground areas and buildings where terrestrial waves are not reachable, but also to insensitive areas such as shadows of buildings. It is surely delivered. The leaky transmission line can be used as an antenna for an electromagnetic wave insensitive zone because a part of an electric signal to be transmitted propagates in a space outside the leaky transmission line and forms an electromagnetic field around it.

  As a typical example of such a leaky transmission line, a transmission line type LCX (leaky coaxial cable) is used. As described in Non-Patent Document 1, LCX includes a center conductor 101, an insulator 102 covering the center conductor 101, and a periphery of the insulator 102, as shown in FIG. And an outer conductor 103 disposed on the outer conductor 103 and an outer sheath 104 covering the outer conductor 103. The material forming the center conductor 101 and the outer conductor 103 of LCX is generally copper, but aluminum may be used in some cases. As a material forming the insulator 102, polyethylene or the like is mainly used.

  The LCX outer conductor 103 is periodically provided with openings 105 in the cable length direction as an electromagnetic wave leakage mechanism, as shown in FIG. The radiation principle of LCX is that a part of the electric signal energy transmitted inside the cable is radiated to the outside through the opening 105 as an electromagnetic wave. LCX is similar to a general antenna, and transmission (radiation) and reception (incidence) are reversible, and if electromagnetic waves can be transmitted far away, weak electromagnetic waves from far away can be received.

  By the way, when a wireless LAN is used in a conference room or the like, a communication system is demanded from the viewpoint of information security so that radio waves of the wireless LAN remain only in the conference room or the like and do not leak outside. The above-described conventional LCX is intended to actively radiate electromagnetic waves far away, and thus has not been used as a communication application only in a limited space for ensuring information security.

  In the leaky transmission line for the purpose of communication only in a limited space, it is not the communication that allows “anywhere, anyone” as described above, but in the vicinity of the leaky transmission line as described in Patent Document 1. Only need to allow wireless communication.

  The signal transmission device described in Patent Document 1 enables communication only in the vicinity of the device. As shown in FIGS. 17A and 17B, this signal transmission device includes a mesh-like first conductor portion 201 and a flat plate-like second conductor portion 202 parallel thereto. Electromagnetic wave energy is supplied to the region 203 sandwiched between the first conductor portion 201 and the second conductor portion 202 from the outside. Since a region 204 in which electromagnetic energy oozes out from the mesh-shaped first conductor portion 201 is generated, the antenna portion of the wireless communication device is brought close to the oozing region 204 on the upper surface of the sheet-like signal transmission device on the first conductor portion 201 side. Then, communication can be performed between the signal transmission device and the wireless communication device.

JP 2007-82178 A

"LCX communication system" (written by Toshihiko Kishimoto and Shin Sasaki) Corona first edition

  By the way, in the signal transmission device as described above, the first conductor 201 having a complicated mesh shape, the second conductor 202 having a flat plate shape, a flat plate in which the first conductor and the second conductor are opposed to each other in parallel, and the entirety thereof. The manufacturing process and the material cost are high, and the production is complicated. Also, the connector installation processing cost is high.

  Furthermore, if the communication area is flat, it may be spread as it is. However, if the communication area is a curved area, the first conductor 201 and the second conductor 202 having a shape matching the shape of the communication area. Had to be made, and it was cumbersome.

  Therefore, the present invention is proposed in view of the above-described circumstances, and is easy to manufacture and inexpensive, and enables communication only in a limited space near the leaky transmission line. An object of the present invention is to provide a communication system capable of

  In order to solve the above-described problems and achieve the object, a communication system according to the present invention has any one of the following configurations.

[Configuration 1]
The leakage transmission line is installed in the structure or installed on the structure, and the leakage is within a region of less than three times the wavelength of the electromagnetic wave transmitted by the leakage transmission line. Communication via a transmission line is possible.

[Configuration 2]
In the communication system having the configuration 1, the leaky transmission line includes a central conductor, an insulator covering the central conductor, and a plurality of apertures periodically formed in the longitudinal direction of the cable wound around the insulator. A leaky coaxial cable having an outer conductor and a jacket covering the outer conductor.

[Configuration 3]
In the communication system having the configuration 1 or the configuration 2, the structure is one of a desk, a function beam, a desktop panel, a partition, or a sofa.

[Configuration 4]
In the communication system having any one of Configurations 1 to 3, the leakage transmission line is installed in a groove provided on the top, inside, or bottom of the desk top plate, or on the top plate. It is a feature.

  Since the communication system according to the present invention has the configuration 1, the leakage communication line is connected to the leakage transmission line via the leakage transmission line in a region that is less than three times the wavelength of the electromagnetic wave transmitted by the leakage transmission line. Since communication is possible, communication within a limited space is possible, and security can be protected.

  That is, the present invention can provide a communication system that is easy to manufacture and inexpensive, and that enables communication only in a limited space near the leaky transmission line.

It is a figure explaining the radiation | emission from the electric dipole described in the nonpatent literature 2. FIG. It is a side view which shows the experimental system for confirming the change state of the electromagnetic field intensity in the vicinity of LCX. It is a graph which shows the measurement result obtained by the experimental system shown in FIG. 1 is a perspective view showing a configuration of a communication system according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the principal part of the communication system which concerns on the 1st Embodiment of this invention. It is a graph which shows the measurement result of the coupling loss Lc in the communication system shown in FIG. It is sectional drawing which shows the other example of the installation state of LCX in 1st Embodiment. It is a perspective view which shows the structure of the communication system which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the other example of a structure of the communication system which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the further another example of a structure of the communication system which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the structure of the communication system which concerns on the 3rd Embodiment of this invention. It is the perspective view and side view which show the structure of the communication system (function beam, desktop panel) which concerns on other embodiment of this invention. It is a perspective view which shows the structure of the communication system (booth workstation) which concerns on other embodiment of this invention. It is a perspective view which shows the structure of the communication system (conference room) which concerns on other embodiment of this invention. It is a perspective view which shows the structure of the communication system (sofa) which concerns on other embodiment of this invention. It is sectional drawing and the side view which show the structure of the conventional leaky coaxial cable. It is sectional drawing and the side view which show the structure of the conventional signal transmission apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  The communication system according to the present invention is a communication system intended to perform communication within a range of about 2.5λ from a leaky transmission line (LCX: leaky coaxial cable) which is a kind of antenna.

  The electromagnetic field is radiated from an antenna or the like. The strength of the radiated electromagnetic field is strong in the vicinity of the antenna, and it is sharply weakened as the distance from the antenna increases. The range of sharp weakening is about 2.5λ, where λ is the wavelength used.

  FIG. 1 is a diagram illustrating radiation from an electric dipole described in Non-Patent Document 2.

As shown in FIG. 1, the radiated electric fields E _r , E _θ , and the magnetic field H _φ from the electric dipole are respectively obtained from the coordinate system shown in FIG. It is done.

  Here, k represents a wave number (k = 2πf / λ) (f is a frequency (Hz) and λ is a wavelength (m)). p is the total charge on the electric dipole (p = Ql) (Q is the charge per unit length and l is the length of the electric dipole). j is an imaginary number symbol representing the imaginary part.

As can be seen from these equations, the electromagnetic field components E _r , E _θ and H _φ are divided into terms proportional to 1 / R ³ , 1 / R ² and 1 / R. Where R is the distance from the electric dipole. In general, these terms are 1 / R ³ as an electrostatic field (Static field), 1 / R ^{2 as} an induction field, and 1 / R as a radiation field. being called.

  In the vicinity of this dipole (R <λ / 2π), the electromagnetic field and the induction field component are dominant, and in the far field (R> λ / 2π), the radiation field component occupies most of the electromagnetic field. Become. In addition, at R = λ / 2π, the electrostatic field, the induction electromagnetic field, and the radiation electromagnetic field component are equal. Therefore, it can be understood that the electromagnetic field component rapidly decreases in the vicinity as the distance from the electric dipole increases. The rapidly decreasing range is generally about 2.5λ, and the present invention is characterized by communication within this range. The specific distance of 2.5λ is about 300 mm at 2.4 GHz which is the frequency of the wireless LAN.

  FIG. 2 is a side view showing an experimental system for confirming a change state of the electromagnetic field strength in the vicinity of the LCX.

  As shown in (a) and (b) of FIG. 2, an experiment was conducted to confirm the state of change in the electromagnetic field strength in the vicinity of LCX2. The measurement frequency is 2.4 GHz. A 1 meter long LCX 2 was placed horizontally on a wooden desk 1. A half-wavelength standard dipole antenna 7 was placed above the LCX2, the distance from the LCX2 was changed, and the output power Pout (mW) from the standard dipole antenna 7 was measured.

  The line that moves the dipole antenna 7 is a line on the center of the LCX 2, a line that is 250 mm away from the center to the input side, and a line that is 250 mm away from the center to the terminal side. Note that Pin (mW) power was input to LCX2. A terminal resistor is connected to the end of LCX2 so that unnecessary reflected waves are not generated inside LCX2. The intensity of the radiated electromagnetic field was evaluated by a coupling loss Lc shown in Formula 1 that is generally used in LCX evaluation.

  FIG. 3 is a graph showing the measurement results obtained by the experimental system shown in FIG.

  In FIG. 3, the horizontal axis indicates the distance between the LCX and the antenna, and the vertical axis indicates the coupling loss Lc. The measured value at the center line of LCX is indicated by ◯, the measured value at a line 250 mm away from the input side is indicated by Δ, and the measured value at a line 250 mm away from the terminal side is indicated by □.

  FIG. 3 shows that the coupling loss Lc in the vicinity of the LCX is small, that is, the radiation is strong, and the coupling loss Lc increases rapidly as the distance from the LCX increases. The broken line in FIG. 3 is an approximate curve for the measured value. The hatched portion indicates the measurement limit of the measurement system.

  From FIG. 3, it can be seen that the intensity of the radiated wave from the LCX suddenly decreases at about 300 mm and then gradually decreases. It is considered that the electrostatic field and the induction electromagnetic field are dominant in the region where the radiation intensity is rapidly weakened, and the radiation electromagnetic field is dominant in the region where the radiation intensity is gradually weakened in the distance. The range in which the radiant intensity sharply decreases is in the range of 300 mm from LCX, which corresponds to about 2.5 times the use wavelength (2.5λ). That is, by setting the communication conditions of the communication device so that communication is possible within this range, it is possible to prevent information leakage due to electromagnetic waves outside this range.

  In the present invention, it is preferable to use LCX as the leaky transmission line. LCX is basically a coaxial cable structure, and is a simple structure consisting of a central conductor, an insulator, an outer conductor with a hole, and a sheath, so it can be mass-produced, is inexpensive, and is easily available. be able to. In addition, a connector is required to connect to a device. However, a large number of coaxial cable connectors are sold, can be easily obtained at low cost, and can be easily attached to the LCX. Although the general market price of LCX depends on the dimensions and materials of LCX, it can be obtained at a low price of about several hundred yen to several thousand yen per meter.

  In the signal transmission device described in Patent Literature 1, a mesh-shaped complex first conductor, a plate-like second conductor, a plate-like material that makes the first conductor and the second conductor face each other in parallel, and these A protective sheet surrounding the whole is required. A coaxial cable is used for connection between the transmission device and an external device. The flat sheet and the coaxial cable are very different in shape between a flat surface and a circle, and a dedicated connection part is required. Therefore, since a general connector cannot be used, in this signal transmission device, the price of the connector mounting portion becomes expensive.

  And since LCX is a cable structure and is a flexible linear body, even if the required communication area is bent in the vertical direction or in the horizontal direction, it can be freely bent and used. That is, any part of the LCX can be used by being bent in any direction, both vertically and horizontally. Therefore, it can be used freely regardless of the shape of the communication area, for example, in a hooked or circular desk, or in a situation where an obstacle must be avoided.

  In addition, since the signal transmission apparatus described in patent document 1 uses a flat conductor, it cannot be bent in the horizontal direction. Therefore, it is necessary to change the shape of the conductor according to the communication area, which is inconvenient.

[First Embodiment]
FIG. 4 is a perspective view showing the configuration of the communication system according to the first embodiment of the present invention.

  In this communication system, as shown in FIG. 4, LCX2 is attached to the wooden desk 1 used as a structure. The desk 1 has a width of 0.7 m, a length of 1 m, and a height of 0.7 m. The LCX2 has a copper wire with an outer diameter of 2 mm, a central conductor made of polyethylene with an outer diameter of 5 mm, an outer conductor made of copper, and has an opening with a width of 2 mm and a length of 3 mm. The outer diameter is 7 mm.

  FIG. 5 is a cross-sectional view showing a configuration of a main part of the communication system according to the first embodiment of the present invention.

  As shown in FIGS. 4 and 5, a groove 3 having a depth of 8 mm and a width of 7.5 mm is provided in the central portion in the width direction of the top plate 1 a of the desk 1, and the LCX 2 is fitted into the groove 3. It is. Then, the groove 3 is covered with a plastic sheet 4 having a thickness of 1 mm.

  In this state, the coupling loss Lc was measured. Connectors were attached to both ends of the LCX, and one side was connected to the transmitter 5 to input a 2.4 GHz signal. A 50Ω terminator 6 was connected to the termination. A half-wavelength standard dipole antenna 7 is positioned at a predetermined height above the LCX 2 and moved in a direction orthogonal to the LCX 2. The height from LCX2 to dipole antenna 7 was 10 mm and 500 mm.

  FIG. 6 is a graph showing the measurement result of the coupling loss Lc in the communication system shown in FIG.

  In FIG. 6, the coupling loss Lc when the dipole antenna 7 is close to the LCX 2 (height 10 mm) is indicated by a circle. When the height of the dipole antenna 7 from the LCX2 is 10 mm, the coupling loss Lc is low directly above the LCX2, that is, the radiation is strong, and the coupling loss Lc increases as the distance from the horizontal direction increases.

  The range in which security can be secured and stable communication is possible is considered to be within 300 mm in the horizontal direction from directly above LCX2.

  Further, in FIG. 6, the case where the height of the dipole antenna 7 from the LCX 2 is 500 mm is indicated by Δ. In the case of a height of 500 mm, the coupling loss Lc was large even immediately above the LCX2, that is, the radiation was weak, and the coupling loss Lc did not change much even when separated in the horizontal direction. This is because when the height is 500 mm, the radiation field has already been entered, and the change in the electromagnetic field intensity with respect to the movement in the horizontal direction is gentle.

  Using the structure (desk 1) in the first embodiment, a wireless LAN communication experiment was performed. A personal computer in which a wireless LAN access point (AP) was connected to the LCX 2 and a wireless LAN device was incorporated was used. The personal computer was placed on the top surface of the top plate 1a of the desk 1.

  As a result, when a personal computer is placed on the top board 1a, wireless LAN communication can be performed without any problem in the range of 300 mm from LCX2, but communication becomes unstable beyond 300 mm and communication is hardly possible in the vicinity of 1 m. It was in a state. Also, when I held the personal computer in my hand and lifted it right above the LCX2, I was able to communicate without problems until the height from the LCX2 was near 300 mm, but when it was higher than that, a failure appeared in the communication state. .

  As described above, in the first embodiment, it was found that communication with information security maintained within a distance of 300 mm from the LCX 2 was possible only near the surface of the top plate 1a.

  FIG. 7 is a cross-sectional view showing another example of the installation state of the LCX in the first embodiment.

  The LCX 2 may be incorporated into the groove 3 provided on the top of the top plate 1a as shown in FIG. 7A, or on the back side of the top plate 1a as shown in FIG. 7B. You may incorporate in the groove | channel 3a provided, or as shown in (c) in FIG. 7, you may incorporate in the hole 3b drilled inside the top plate 1a.

[Second Embodiment]
In the first embodiment described above, the width of the top plate 1a of the desk 1 is 0.7 m. In this case, if one LCX 2 is arranged in the center, a communication area that maintains security is secured. did it. However, when the width of the top plate is widened, the communication range from the LCX 2 is about 300 mm, so it is difficult to secure a communication area with a single straight LCX 2.

  FIG. 8 is a perspective view showing a configuration of a communication system according to the second embodiment of the present invention.

  As shown in FIG. 8, when the width of the top plate 1a of the desk 1 as a structure is about 1.5 m, the top plate 1a has the same dimensions and cross section as in the first embodiment. The groove 3 having a shape may be provided in a rectangular shape, and the LCX 2 may be disposed in the groove 3.

  In this embodiment, on the top board 1a, communication with security was ensured in the communicable area indicated by hatching in FIG.

  FIG. 9 is a perspective view showing another example of the configuration of the communication system according to the second embodiment of the present invention.

  As shown in FIG. 9, the LCX 2 is arranged in a communicable area indicated by hatching in FIG. 9 on the top board 1 a even if the shape of the groove 3 is a U-shape without one side of the rectangle. Communication with secure security was possible.

  FIG. 10 is a perspective view showing still another example of the configuration of the communication system according to the second embodiment of the present invention.

  In addition, as shown in FIG. 10, the LCX arrangement shape may be a shape in which semicircles are staggered (meandering shape), and security is provided in the communicable area indicated by hatching in FIG. Secured communication was possible.

[Third Embodiment]
FIG. 11 is a perspective view showing a configuration of a communication system according to the third embodiment of the present invention.

  In the third embodiment, as shown in FIG. 11, in a desk or meeting table 1 that is a structure having a circular top plate 1b, the groove 3 has a circular shape centered on the center of the top plate 1b. The LCX 2 was placed in the groove 3. In this case, the LCX 2 may be provided below the top plate 1b.

  Even in this case, communication with security was ensured in the communicable area indicated by hatching in FIG. 11 on the top board 1a.

[Other Embodiments]
FIG. 12 is a perspective view and a side view showing a configuration of a communication system (function beam, desktop panel) according to another embodiment of the present invention.

  As shown in FIGS. 12A and 12B, the communication system according to the present invention is a structure installed on a desk, and a function beam on which optional members such as a desk shelf, a tray, and a display can be attached. (Product name) (Beam member (or bowl-shaped member) provided with an attachment portion such as an optional member) 8 may be configured by installing LCX 2 at the upper part or the lower part thereof.

  In addition, the communication system according to the present invention is a structure installed on a desk as shown in FIGS. 12C and 12D, and is a desktop panel 9 that divides the desk space and other spaces. You may comprise LCX2 in the upper part or the lower part.

  FIG. 13 is a perspective view showing a configuration of a communication system (booth workstation) according to another embodiment of the present invention.

  As shown in FIG. 13, the communication system according to the present invention may be configured as a booth workstation (product name) (a work space construction fixture configured by partitioning the periphery with a partition panel). In other words, the LCX may be installed in the middle in the vertical direction of a partition (product name) (partition device, partition panel, or the like) 11 serving as a structure forming the booth.

  FIG. 14 is a perspective view showing a configuration of a communication system (conference room) according to another embodiment of the present invention.

  As shown in FIG. 14, the communication system according to the present invention may be configured by installing LCX 2 in a wiring box 13 provided on a desk 12 of a conference room serving as a structure.

  FIG. 15 is a perspective view showing a configuration of a communication system (sofa) according to another embodiment of the present invention.

  As shown in FIG. 15, the communication system according to the present invention may be configured by installing an LCX 2 in a portion between the seat surface and the backrest of the sofa 14 serving as a structure.

  The present invention is applied to a communication system using a leaky transmission line, and particularly to a communication system using a structure in which a leaky transmission line capable of communicating in the vicinity is incorporated.

1 desk 1a Top plate 2 LCX
3 groove

Claims (4)

A leakage transmission line incorporated in the structure or installed on the structure,
Communication via the leaky transmission line is possible in a region having a distance of less than three times the wavelength of the electromagnetic wave transmitted by the leaky transmission line from the leaky transmission line. . The leaky transmission line includes a center conductor, an insulator covering the center conductor, an outer conductor wound around the insulator and periodically formed with a plurality of openings in the longitudinal direction of the cable, The communication system according to claim 1, wherein the communication cable is a leaky coaxial cable having a jacket coated with a conductor. The communication system according to claim 1, wherein the structure is any one of a desk, a function beam, a desktop panel, a partition, and a sofa. The leak transmission line is installed in a groove provided on an upper portion, an inner portion, or a lower portion of the top plate of the desk, or on the top plate. The communication system according to 1.

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