JP4699806B2 - In-building wireless communication system - Google Patents

Description

The present invention provides a wireless communication system in which information such as the indoor environment is propagated by radio waves from a transmitter installed in the same room of a building (including the ceiling and the interior space of the ceiling) to a receiver. The present invention relates to a mesh net that can integrate large-scale indoor information by sequentially transmitting to another receiver.

A room of a building such as an office or factory is composed of an interior space (living room) and a ceiling interior space, which are partitioned by a ceiling material. While environmental information such as room temperature is measured by a sensor in an indoor space, an air conditioner, a controller, and the like are usually installed in the ceiling space. In order to construct such a temperature control loop, a one-to-one wireless communication system in which a temperature sensor is a transmitter and a controller is a receiver is used. This is because of the cost of indoor wiring work, the ease of responding to changes in the room layout and other maintenance requirements, and the reason for improving comfort by measuring the environment near people.

In this case, it is necessary to arrange the transmitter and the receiver so that they can see each other, that is, in a position where there is no obstruction of radio waves. However, there are many obstacles for wireless communication, such as pillars, beams, and air conditioning ducts in the room. Therefore, as disclosed in Patent Document 1, there is provided a communication system in which a transmitter and a receiver are installed in a ceiling internal space in a building to reflect radio waves on the floor.
As shown in FIG. 1 quoted from Patent Document 1, there is known a configuration in which a transmitter including a sensor is installed in a ceiling internal space for indoor aesthetics. There, the indoor interior space 1-1 and the ceiling interior space 1-2 are partitioned by a ceiling material 1-3, H steel 10 in the ceiling beam, rebar 12 in the floor 11, and also in the upper floor. Similarly, since there are radio wave obstacles such as the reinforcing bar 12, a floor reflection type communication antenna is employed.
JP-A-10-107711

Further, in order to construct not only one-to-one communication but also a larger indoor communication system in a building, a technology of a wireless mesh network (hereinafter referred to as “mesh net”) has been put into practical use. A mesh net is generally called a multi-hop network, and is a flexible architecture that can efficiently move data between nodes (collectively, a receiver and a transmitter are hereinafter referred to as a “node”).
In a conventional typical wireless LAN, a plurality of nodes are directly connected to one access destination node to form a network. This is referred to as a “single-hop” network, but in a multi-hop network, any node with a wireless communication function can serve as both a receiver and a transmitter, so the nearest access destination is If it is busy, the data is then routed to the next nearby low traffic node. Data is a technology that continues hopping from one node to another and arrives at the final destination. Even if it is not the closest node, when there is congestion or a failure in the propagation path, detour relaying is performed.
A technique such as a method of using a directional antenna in a mesh net is introduced in Patent Document 2 and the like, and is configured with an antenna having strong directivity. However, the technique and the configuration are different from the technique using the floor reflection type antenna as in the present invention.
JP 2004-364287 A

Further, in Patent Document 3, there is a technique for generating a null point in a substantially horizontal direction of the vertical in-plane radiation pattern of an antenna in order to reduce multipath fading due to long delay interference waves from walls, floors, and ceilings indoors. It is disclosed. A technique for adjusting the directivity of an antenna by tilting the beam of the antenna is also shown. However, even if such tilt adjustment is effective in one-to-one inter-node communication, the mesh net as described above is not very effective because the antenna sensitivity cannot be made uniform in all horizontal directions. .
JP 2001-196985 A

When air conditioning equipment, disaster prevention equipment, lighting equipment, etc. are arranged on the surface at regular intervals on the ceiling of the building, it is common to wire the signal transmission between the equipment, but the wiring work is reduced. In order to cope with the movement of the device by changing the layout, wireless signal transmission is desired. However, there are several problems with wireless. It is desirable that the equipment at the ceiling is installed on the back of the ceiling in terms of appearance, but there are various obstacles such as beams, pillars, air conditioning ducts, etc. on the back of the ceiling, and it is often impossible to see between the equipment. For this reason, when a radio wave having a straight traveling property is used, the radio wave does not reach directly, and wireless signal transmission cannot be performed stably. In addition, the transmission power required for communication is proportional to the cube of the distance, but considerable transmission power is required in a large building, and there are problems of energy saving, allowable transmission power restrictions of legal standards, etc. If the transmission power is considerable, there is a risk of interference with other networks or nodes due to the expansion of the transmission range.

In order to overcome these problems, the floor reflection type communication antenna and mesh net technology are used in combination. However, when this floor reflection type antenna is used, the presence of radio wave reflectors such as furniture on the floor. May cause radio waves to reach the receiver from the transmitter via multiple channels (this is called multipath), and the original radio wave quality is hindered (called multipath fading) due to the collision caused by the multiple radio waves. It can not be overlooked.
Accordingly, an object of the present invention is to suppress multipath fading in wireless communication between nodes in a mesh net using a floor reflection type antenna.

The gist of the present invention lies in the combination of a communication node equipped with a floor reflection type antenna and a mesh net configuration, and the antenna is provided with directivity to adjust the mounting position of the antenna. That is, in a wireless communication system in which a mesh net is formed by a plurality of nodes having floor reflection antennas installed on the ceiling of a room, the antenna is used for both transmission and reception, and the antenna is not horizontal. It has directivity and has a vertical directivity of a predetermined angle obliquely downward from the horizontal direction to the floor direction, and the antenna can be adjusted in the mounting position, and the ceiling height of the room is H, adjacent When the plane distance between nodes to be performed is L and the predetermined angle is a, the predetermined angle is a
In the wireless communication system, the mounting position of the antenna is adjusted so that = ArcTan (2H / L) .

About the said invention, it shall be set as the radio | wireless communications system which is an antenna which can move the attachment position of this antenna horizontally or perpendicularly with respect to a floor surface as a subordinate concept invention.
Further, the antenna may select a collinear or MSA type antenna.

By making the antenna with directivity of a predetermined angle from the horizontal direction to the floor obliquely, floor reflection type inter-node wireless communication becomes possible, and omnidirectional (
In other words, by using an antenna having 3 60 ° directivity), a mesh network for wireless communication can be formed between adjacent nodes, and an efficient communication network in a multi-hop format can be obtained.
Further, since the wireless communication distance can be shortened, energy saving of the node can be achieved.

FIG. 2 shows a side sectional view of the interior of the building (the symbols in the figure are consistent with FIG. 1 of the conventional example), in which communication nodes 110 and 111 are arranged in the ceiling internal space 1-2. These nodes may be temperature sensors and controllers, or may be controllers (hereinafter collectively referred to as “nodes”).
In this example, a situation is shown in which the node 111 plays the role of a transmitter and the node 110 plays the role of a receiver.

Node 1
Assuming that the antenna directivity of 1 1 is oblique from the horizontal direction to the floor as in the directivity direction 1 1 1 D, the radio wave propagation route 3 0 is the shortest.
The one indicated by (arrow in the figure) arrives in the directivity direction 1 1 0 D of the receiving antenna of the node 1 1 0. Other propagation routes are generated radially due to the characteristics of the directivity direction 1 1 1D, but they are attenuated through reflection, diffusion, etc. on the floor and ceiling, and so on.
Most of them end without reaching 1 0. However, when the fixture 2 0 exists in the room, it is reflected twice like the propagation route 3 2 and the directivity 1 of the node 1 1 0
The effective area of 10 D is reached. In this case, since the intensity of the radio wave is not so attenuated, a multipath is generated overlapping with the original radio wave (route 3 0). Since radio waves collide with each other, they inherently become radio noise and cause multipath fading.

In FIG. 3, paying attention to the antenna 3-1, its horizontal directivity is 3 60.
° Unidirectional directivity in all directions (omnidirectional), while the vertical directivity is oblique to the floor from the horizontal direction , and the predetermined directivity angle a is determined as follows: To do. Note that the inter-node plane distance is L and the indoor ceiling height is H (see FIG. 2 for H and L).
a = ArcT an (
2H / L) (1)
In the above example, the route 3 is maintained while maintaining the setting of the expression (1).
The occurrence of multipath can be prevented by placing the radio wave 2 outside the area of the directivity azimuth 1 1 0 D of the receiving antenna or entering the null point at the center of the directivity azimuth.
Therefore, as shown in FIG.
It is only necessary to provide means that can be moved in −1 h or in the vertical adjustment direction 3-1 v.
In addition, as another effect on this, FIG.
In the case where an obstacle occurs on the route 3 0, it is possible to adjust so that the radio wave of the route 3 2 is preferentially used.

Next, FIG. 4 shows a layout of the antenna of the mesh net system as a plan view of the interior of the building. Wireless communication nodes 100 to 134 are arranged in the wireless communication area 180 in a mesh configuration. There is a parent node 190 in a wired communication area 181 which is a peripheral part such as a perimeter, and the parent node 190 is connected to a parent node on the upper and lower floors by a wired communication line 190B, and also connected to a parent node in another room by a wired 190C. Is done.

Here, if attention is paid to the wireless communication area, when the communication nodes 110 and 111 are in the relationship shown in FIG. 2 described above, the wireless arrival area 111A on the horizontal plane of the node 111 is affected by the floor reflection and radio waves are transmitted to other nodes. It shows the reachable range. Then, as can be seen from FIG. 4, the communication from the node 111 reaches the adjacent nodes 101, 112, 121 in addition to the node 110. The nodes 112 and 121 determine that they are downstream nodes, do not transmit, and the upper nodes 101 and 110 propagate the communication message toward the parent node direction (upward direction). It is an example of a protocol. In that case, as a result of relay from the upper node 101 or 110 to the node 100, the information transmitted by the node 111 is transmitted to the parent node 190 and can be used in a central monitoring system (not shown).

Therefore, even if the horizontal or vertical adjustment (3-1h, v) of the receiving antenna is moved as shown in FIG. 3, the wireless coverage area on the horizontal plane as the transmitting antenna in FIG. ) Can be carried out almost without change, so the performance of the mesh net is not impaired.

FIG. 5 shows an embodiment of the antenna attaching means shown in the principle diagram of FIG.
In the ceiling internal space 1-2, a cage 3-8 is provided so as to hold a ceiling suspension bolt 8 provided between the upper floor (the ceiling of the main floor) 11 and the ceiling material 1-3, thereby The receiving antenna body 3 is structured to rotate up and down. This rotation operation (arrow 5-1) can move in the horizontal direction. Furthermore, if it is further rotated, the vertical movement (arrow 5-2) can move the receiving antenna 3-1 in the vertical direction. (Of course, from a different perspective, this is also the adjustment of the transmitting antenna.)
It is known that shifting by one wavelength is sufficient to prevent multipath fading, and one wavelength T of radio waves is obtained by the following equation. If the propagation speed of radio waves is 300,000 km / Sec and the frequency is 2.4 GHz,
T = 300,000km / 2.4GHz (2)
It can be seen that a movement of about 12 cm is sufficient.

Next, examples of the antenna itself having horizontal omnidirectionality and vertical oblique angle directivity will be described.
-Collinear antenna Two dipole antennas are arranged in series, and the directivity in the vertical direction can be controlled by relatively changing the phase fed to the upper and lower antennas.
MSA type antenna MSA is an abbreviation of microstrip antenna, and since the back surface of the antenna is grounded, there is an advantage that the antenna characteristics are not affected by the member on the back side. Directivity similar to that of a collinear antenna can be realized. In particular, the high-order mode MSA can control the directivity in the vertical direction.

The implementation of the present invention is not limited to the above embodiments.
As another example of the antenna, a diversity antenna can be used. This is composed of a plurality of antennas, and the one having a good reception state at the time of reception is automatically selected and used. Further, at the time of transmission, the antenna determined at the time of reception is used. This is different from the configuration for mechanically adjusting the mounting position of the antenna of the present invention, but it is similar to the suppression of multipath fading by electronically adjusting the performance related to the reception directivity of the node. The effect of this is achieved.

Indoor side cross-sectional view of conventional floor reflection antenna communication Indoor side cross section of inter-node communication Indicates the vertical directivity of the antenna. Mesh net top view The antenna attachment position adjustment means of a communication node is shown.

Explanation of symbols

1-1. Indoor interior space 1-2 Ceiling interior space 1-3 Ceiling material 2 VAV unit 3 Receiver (node)
3-1 ... Receiver antenna 4 ... Transmitter (node)
4-1 · · Transmitter antenna 4-2 · · Temperature sensor 5 · · Air supply hole 6 · · Ventilation hole 8 · · Ceiling suspension bolt 9 · · beam 10 · · H steel 11 · · floor 12 · · rebar 13 · · Deck plate 14 · · Mounting bracket 18 · · Air conditioning duct 20 · · Furniture (shelf)

Claims (3)

In a wireless communication system in which a mesh net is formed by a plurality of nodes having floor reflective antennas installed on the ceiling of a room,
The antenna is for both transmission and reception;
The antenna is horizontal omnidirectional and has a vertical directivity of a predetermined angle obliquely downward from the horizontal direction to the floor direction;
The antenna is characterized in that the mounting position can be adjusted ,
When the ceiling height of the room is H, the plane distance between adjacent nodes is L, and the predetermined angle is a,
The predetermined angle is
a
= ArcTan (2H / L)
The mounting position of the antenna is adjusted so that
Wireless communication system characterized by The system of claim 1, wherein
A wireless communication system, wherein the antenna is an antenna that can move an attachment position in a horizontal direction or a vertical direction with respect to a floor surface. Claim 2
In the system of
A radio communication system, wherein the antenna is a collinear or MSA type antenna.

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