JP4699814B2 - 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, Patent Document 3 and Patent Document 4 disclose a technique of a diversity antenna in order to reduce multipath fading not only indoors but also by long delay interference waves.
“Diversity” means “diversity” in English, and a diversity antenna means that a plurality of antenna elements for transmitting and receiving radio waves are prepared instead of one. Since wireless communication has the disadvantage that the state of radio wave propagation changes greatly, it solves the instability of communication. Diversity antennas are well-known for receiving diversity antennas (examples of Patent Document 3) for selecting and using a plurality of antennas having good reception sensitivity. There is also a transmission diversity antenna (example of Patent Document 4) that uses a transmission antenna by switching the transmission antenna as appropriate.
In addition, “spatial diversity” is a method of arranging multiple antenna elements with the same performance and changing physical positions, “angular diversity” is a method of changing the direction of receiving radio waves, and “frequency diversity” and “time diversity” are other. There is something called.
However, even if using such a diversity antenna itself is a trivial matter, it is necessary to specifically explain how to apply diversity antenna technology to efficiently realize mesh net communication in a building. Currently, no means have been established yet.
JP-A-10-107778 Japanese Patent Laid-Open No. 10-256964

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. Furthermore, the transmission power required for communication is proportional to the power 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 such problems, the present invention employs a combination of a floor reflection type communication antenna and a mesh net technology. When this floor reflection type antenna is used, the radio wave of a fixture or the like on the floor is used. Due to the presence of reflectors, radio waves may reach the receiver from the transmitter in multiple communication paths (this is called multipath), and the quality of the original communication radio wave is hindered by the collision of the multiple radio waves (multipath fading and Call it) You can't overlook the problem.
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 relates to a combination of a communication node equipped with a floor reflection type antenna and a mesh net configuration. The antenna is used as a diversity antenna, and a plurality of transmission antennas having predetermined directivity and used are provided. The transmit diversity antenna is selected as appropriate. The reception diversity technique merely selects the signal having the highest reception sensitivity from a plurality of antenna reception signals, but the gist is that the transmission diversity technique is focused. That is, in a wireless communication system in which a mesh net is formed by a plurality of floor reflection antennas installed on the ceiling of a room,
The antenna is a spatial diversity antenna comprising a plurality of antenna elements;
The antenna is for both transmission and reception;
The antenna is horizontal omnidirectional and has a vertical directivity of a predetermined angle obliquely downward in the floor direction;
The antenna elements in the antenna have the same vertical directivity and are installed with a predetermined separation distance in the horizontal direction between the antenna elements, and one of the antenna elements is used by switching for transmission. The radio waves reach the other adjacent antennas by floor reflection,
It is in the system characterized by.

With respect to the first invention described above, transmission to a specific communication node-second invention related to transmission diversity by Ack (acknowledge) reception, on the other hand, broadcast transmission without specifying a reception node-from any reception node There is a third invention related to transmission diversity by Ack reception.
The second and third inventions realize the transmission diversity by selecting the optimum transmitting antenna by performing the reception confirmation by such an Ack signal, and realize the wireless communication system of the in-building mesh net according to the first invention. There is a feature in the antenna to do.

Even if the state of wireless communication changes due to the movement of people, the movement of furniture, etc., as in the room, the transmission antenna with the best transmission state is selected from the plurality of antenna elements. That is, suppression of multipath fading can be realized automatically and easily by switching the transmitting antenna element.

FIG. 2 shows a side sectional view of the interior of the building (the symbols in the figure match those of FIG. 1 of the conventional example), where 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.
In the following explanation, for simplification, each communication node has two antennas (A, B) as diversity antennas. However, it is not always necessary that there are two antennas (A, B). .

Assuming that the directivity of the antenna elements constituting the diversity antenna of the node 111 is oblique to the floor surface like the directivity directions 111D-A and 111D-B, the shortest distance from the transmission antenna 111D-A or 111D-B The one launched by the radio wave propagation route 30 (arrow in the figure) arrives in the directivity direction 110D-A or 110D-B of the receiving antenna of the node 110. (The bold line in the figure indicates a state in which 111D-A is selected.)
Other propagation routes are generated radially due to the characteristics of the directivity of the node 111, but most of them are attenuated through reflection, diffusion, etc. on the floor and the ceiling, and most of them end without reaching the node 110. However, when the furniture 20 is present in the room, it is reflected twice like the propagation route 32 and reaches the effective area of the directivity direction 110D-A or 110D-B of the node 110 or both. In this case, since the strength of the radio wave is not so attenuated, a multipath is generated overlapping the original radio wave (route 30). Since radio waves collide with each other, they inherently become radio noise and cause multipath fading.

In FIG. 3, paying attention to the antenna 4-1, its horizontal directivity is 360 ° omnidirectional homogeneous directivity (non-directional), while its vertical directivity is oblique to the floor surface. The predetermined directivity angle “a” is determined as follows. Note that the inter-node plane distance is L, and the indoor ceiling height is H (see FIG. 2 for H and L).
a = ArcTan (2H / L) (1)
In the above example, while maintaining the setting of the expression (1), the radio wave of the route 32 is set outside the area of the directivity directions 110D-A and 110D-B of the receiving antenna or at the null point in the center of the directivity direction. If so, the occurrence of multipath can be prevented.
More specifically, multipath fading is caused by combining two waves (or three or more waves) whose phases are different by 180 degrees due to a difference in delay time and canceling each other. Utilizing the property that the propagation path length differs depending on the antenna position and the transmission-reception delay time is different, the propagation path length is changed by changing the antenna position equivalently by the diversity antenna, that is, the delay time of each path is changed. Adopt a mechanism.
Therefore, as shown in FIG. 2, a means for realizing transmission diversity at the node 111 is provided. For example, multipath fading due to the propagation route 32 is prevented by switching the transmission antenna at the transmission node and using 111D-A rather than the directivity 111D-B. That is, when the antenna A or B in the node 111 as the transmission source is appropriately switched and a reception completion notification (hereinafter referred to as “Ack”) is received from the node 110 as the reception destination, the transmission is completed. In the following communication, in this example, the node 111 preferentially uses the antenna A for the node 110, but if it is not A, it is repeated a predetermined number of times by switching to B as appropriate (hereinafter referred to as "retry"). Take the configuration.

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, the wireless arrival areas on the horizontal plane of the node 111 are indicated by 111A-A and 111A-B. This indicates the range where radio waves reach other nodes by floor reflection. 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. Nodes 112 and 121 determine that they are downstream nodes. Basically, even if communication is received from node 111, retransmission is not performed, and upper nodes 101 and 110 move in the parent node direction (upward direction). An example of a basic protocol of a mesh net is to relay and propagate a communication message. In that case, as a result of the relay communication 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 further used by a central monitoring device (not shown).

In the installation of a plurality of antennas for transmission diversity, as long as each transmission antenna of the transmission diversity antenna shown in FIG. 3 and Expression (1) is equivalent to a predetermined directivity performance, the plurality of antennas are adjacent to each other. Since the transmission radio wave can reach the matching node (the wireless reachable area on the horizontal plane as the transmitting antenna in FIG. The performance of the mesh net is maintained.

(1) Antenna structure FIG. 5 shows an embodiment of an antenna mounting means in the present invention.
In the ceiling internal space 1-2, a cage 4-8 is provided so as to hold the ceiling suspension bolt 8 provided between the upper floor (the ceiling of the main floor) 11 and the ceiling material 1-3, thereby The antenna body is held in the ceiling interior space. This antenna is used for both transmission and reception, and the antenna may be symbol 4 or 3 in the figure. However, if attention is now paid to the transmission antenna element, for example, two antennas are formed from the transmission antenna body 4 toward the indoor interior space 1-1. Two antenna elements (4-1A, 4-1B) are set up.
It is known that it is sufficient to shift the separation distance between antenna elements by about one wavelength in order to realize space diversity, 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 separation of about 12 cm is sufficient.

Here, examples of the antenna element itself having horizontal omnidirectionality and vertical oblique angle directivity are illustrated.
-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.

(2) Functional block structure of antenna In the first place, the antenna is used for both transmission and reception, the antenna element itself is also used for transmission and reception, and the diversity function is provided not only on the transmission side but also on the reception side.
FIG. 6 shows a block diagram of the antenna 4 for both transmission and reception.
Located at the center is the MPU 40, which controls various functions, and is constituted by a microprocessor, a memory, and the like.
First, the receiving side will be described. In this case, the receiving diversity function is realized. The radio wave signals received from the antenna elements 4-1A and 4-1B pass through the transmission / reception splitters 46 and 47, undergo waveform shaping and the like by the reception receivers 42 and 43, and enter the reception level comparator 44. Here, the one with better reception sensitivity is selected and a signal is passed to the MPU. The MPU not only uses signal data but also obtains information (A / B) of the selected antenna from the reception level comparator and may use it for the subsequent transmission diversity function. It can also be used to update an inter-node antenna map (Table 1) described later.
Next, the transmission side will be described. The MPU passes data to be transmitted to the transmission driver 41 when an event occurs (communication request event, transmission of periodic environment information, information propagation from other nodes, etc.). At the same time, the one to be used as the transmission antenna (A or B channel) is determined as transmission diversity, and the switch 45 is switched. As a result, transmission data is transmitted from the selected antenna (4-1A or 4-1B) via the transmission / reception splitter.

(3) Software structure of transmit diversity antenna (i) Communication addressed to specific node Based on the block structure of (2) above, a detailed software flow will be described below.
FIG. 7 shows a flow for executing transmission addressed to a specific (destination or relay) node. As an example, communication from the node 111 to the node 110 described with reference to FIGS. 2 to 4 will be taken as an example.
First, the transmission destination node starts (step 200) when an event occurs. First, a receiving node (destination) is determined (201). There may be various algorithms, but as a simple example, what is selected from the inter-node antenna map of Table 1 will be described. When the source node is the node 111, there are definitions in the destination nodes 101 and 110 (see Table 1). Therefore, the receiving node is first determined as 101 by selecting from the smaller number.
Here, next, an antenna directed to the reception destination is selected (202). In this example, the antenna B side is first selected from Table 1.
Next, data is transmitted (203), and Ack from the receiving node 101 is waited (branch step 204).
If Ack is received after waiting for a predetermined time, transmission is ended in step 210 as transmission / reception completion.
Alternatively, when Ack is not received (including the case where there is no response or Nack (abnormal reception notification)), retry is performed a predetermined number of times (205). In the retry loop, the antenna is switched (207). In this example, the transmission antenna for the destination node 101 is switched from B to A. And it repeats from the transmission step 203.
If the Ack cannot be received again (204), the predetermined number of retries may be initialized and repeated based on the antenna, depending on the number of retries. Considering the case where obstacles are removed as time passes. In this example, the antenna is returned from A to B again.
As a result of repeating the retry loop for the specific receiver several times, if the Ack cannot be received as usual, a check is made to switch the receiver (206). However, this is effective when there are other candidate receiving nodes as shown in the Table 1 map. In this example, the node 110 is the next receiving node.
If all the specific nodes have been completed, there is only an error termination (209).
Otherwise, the receiving destination is switched to the node 110 (208). From Table 1, antenna A is selected for node 110, and the process starts from (202). It can be said that the example at this time shows the communication state shown in FIG.

(Ii) Communication addressed to unspecified node FIG. 8 illustrates a flow of transmission diversity in which communication is performed as a rescue means in the case of the error termination (209) of FIG. 7 or without specifying a destination node in the first place.
Here, starting from step 300, the transmitting antenna selects A as the default. Then, the data is transmitted (303). In this case, the destination address is a broadcast address that can be received at any address. However, since the radio reachable area of radio waves is limited in the first place, only a limited number of nodes will receive (in this example, within the radio reachable area of 111A-A or 111A-B in FIG. Receivable nodes are limited to neighboring nodes).
Now, after waiting for Ack after data transmission (304), if Ack is received from some arbitrary node after waiting for a certain time, the transmission / reception is completed and the process ends in step 310.
Alternatively, when no Ack is received from anywhere (including the case where there is no response or Nack (abnormal reception notification)), retry is performed a predetermined number of times (305). In the retry loop, the antenna is switched (307). In this example, the antenna is switched from A to B. Then, the transmission step 303 is repeated.
Further, when Ack cannot be received (304), the antenna can be initialized to default again and repeated as a predetermined number of retries. Considering the case where obstacles are removed as time passes. In this example, it means that the antenna is returned from B to A and re-executed.
Even if a predetermined number of retries have been executed, if there is an error, the process can only be terminated (309).
In such a case, as an error notification, an alarm process such as a buzzer sounding so as to be understood by a person in the room or lighting of a lamp will be taken.

The implementation of the present invention is not limited to the above embodiments. In particular, with respect to receive diversity, the above example illustrates a method in which a plurality of antennas simultaneously receive and compare and select according to the reception level. However, a method in which the receive antennas are sequentially switched, and a packet is being received or ended at the switching timing. There are other mechanisms, but this is the same.
Further, it is added that the destination node determination algorithm, the antenna selection priority, and the like shown in the above description depend on the design items of the mesh net system and do not affect the essence of the present invention.

(Table 1) shows the antenna map between nodes

Indoor side cross-sectional view of conventional floor reflection antenna communication An indoor side sectional view of communication between nodes and an outline of transmission and reception diversity are shown. Indicates the vertical directivity of the antenna. A mesh net plan view and an antenna radio coverage area are shown. The antenna attachment means of a communication node is shown. The functional block structure of an antenna is shown. The transmitting antenna program flow of a specific receiving node method is shown. The transmission antenna program flow of the unspecified destination node method 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 using a mesh net by a plurality of floor reflection antennas installed on the ceiling of a room,
The antenna is a spatial diversity antenna comprising a plurality of antenna elements;
The antenna element is for both transmission and reception;
The antenna element is horizontal omnidirectional and has a vertical directivity of a predetermined angle obliquely downward in the floor direction;
The antenna elements in the antenna have the same vertical directivity and are installed with a predetermined separation distance in the horizontal direction between the antenna elements, and one of the antenna elements is used by switching for transmission. The radio waves reach the other adjacent antennas by floor reflection,
A system characterized by
The system of claim 1,
The antenna is a transmit diversity antenna;
Means for repeatedly transmitting a predetermined number of times until a plurality of antenna elements are switched to a specific destination node and an Ack response from the specific reception node is obtained;
Means for repeatedly transmitting a predetermined number of times until the receiving node is switched to switch a plurality of antenna elements to another specific receiving node and an Ack response is obtained from the specific receiving node;
Diversity antenna with
The system of claim 1, wherein
The antenna is a transmit diversity antenna;
A diversity antenna having means for repeatedly transmitting a predetermined number of times until an Ack response from an arbitrary destination node is obtained by switching a plurality of antenna elements to an unspecified destination node.

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