JP4500330B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system including a parent node that collects information and a plurality of child nodes that are wirelessly connected to the parent node directly or via other child nodes.

  In recent years, research and development related to ubiquitous network technology and applications using the technology have been active. For example, the Ministry of Internal Affairs and Communications' “Survey Study Group on Ubiquitous Sensor Network Technology” proposes the use of the ubiquitous sensor network in the field of disaster prevention and disaster countermeasures as one of the future use images. This use in the field of disaster prevention / disaster countermeasures assumes a ubiquitous network system (hereinafter referred to as “disaster prevention network system”) that can quickly grasp the situation of the stricken area where a major earthquake or the like has occurred (Non-patent Document 1). ).

  As a specific example of the “disaster prevention network system” described above, a plurality of child nodes having sensors for collecting various information (temperature, gas, chemical substances, etc.) of the disaster area are scattered from the air to the disaster area. Each child node and the parent node that collects the sensor data of each child node autonomously constructs a wireless network, and the parent node sequentially transmits the sensor data of each child node to the monitoring center that monitors the status of the disaster area. A system is conceivable.

  Since the child node in the “disaster prevention network system” is small and needs to be battery-powered, a short-range wireless system with reduced transmission power is used, and the child node is a small microcomputer and a small amount of RAM and ROM. It is necessary to consist of. On the other hand, each child node sequentially transmits sensor data to the parent node. However, if the sensor data cannot be transmitted directly to the parent node, the other child node is used as a relay node and the sensor data is transmitted through an efficient relay route. Need to send. Furthermore, in order to protect human lives and property, and to quickly recover the disaster area, communication reliability is required, and even if a relay node fails, other child nodes do not interrupt communication and bypass relay It is necessary to configure a so-called autonomous wireless network that transmits sensor data to a parent node using a route.

  There is ZigBee (registered trademark) as a wireless method capable of reducing current consumption that can be used in the above-mentioned “disaster prevention network system”. The communication distance of ZigBee (registered trademark) is usually about 10 m to 70 m, and the communication speed is 250 kbps. ZigBee (registered trademark) employs a communication protocol called AODV as an autonomous wireless network system, and enables a wide range of data transfer (Non-Patent Document 2).

“Survey Study Group on Ubiquitous Sensor Network Technology” Final Report, http://www.soumu.go.jp/s-news/2004/pdf/040806_4_b1.pdf AODV (Ad-hoc On-Demand Distance Vector Routing): RFC3561

  In AODV, when a transmission source node searches for a communication path to a transmission destination node, first, the transmission source node broadcasts an RREQ packet toward an adjacent node (this is called “flatting”). The adjacent node that has received the RREQ packet further transfers the RREQ packet by flatting, and thereafter, the transfer of the RREQ packet is repeated until a transmission destination node is found.

  When the destination node receives the RREQ packet, it returns the RREP packet to the source node. At this time, each relay node forms a routing table in the transmission / reception of this series of packets. Thereafter, if there is no change in the operation status of the relay node, each node transmits and receives data packets between the transmission source node and the transmission destination node using the routing table of the local node. Here, if the operating status of the relay node changes and a specific node moves or breaks down, the source node or the relay node again flattens the packet for route search and sends the destination route. Will search.

  On the other hand, there is a specific low-power radio as a radio system that can reduce the current consumption and can be used for the “disaster prevention network system” as in ZigBee (registered trademark). The communication distance of the specific low-power radio is about 300 m and the communication speed is 1200 bps to 4800 bps. There is an advantage that the communication distance can be longer than ZigBee (registered trademark), but the communication speed is low.

  In addition, it is inefficient to use a communication protocol based on a high-speed network such as AODV for a specific low-power radio. More specifically, in a low-speed network, (1) the occupied time of a frequency band due to flatting becomes long, congestion occurs on the wireless network, and the utilization efficiency of the wireless network decreases. (2) When an abnormality occurs in the relay node, transmission of sensor data is interrupted until a new route can be searched. (3) If a protocol such as AODV is used, problems such as an increase in the memory capacity of the RAM or ROM occur, which is inefficient. (4) Furthermore, it is desirable that it can be economically realized at a low cost in order to disperse a plurality of child nodes and parent nodes in a large amount in the affected area. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and wireless communication that can be made into an autonomous wireless network even with low-speed wireless communication and that has ensured communication reliability with a simpler protocol than before. To realize the system.

The present invention includes a parent node that collects information, and a plurality of child nodes that are wirelessly connected to the parent node directly or via other child nodes, the child node including a sensor that collects information A storage device that stores a table in which identification codes of other child nodes in a wirelessly connectable range and the number of relays to the parent node of the child node are associated with each other. In the wireless communication system that transmits information collected by its own sensor or information received from another child node directly or via another child node having the smallest number of relays to the parent node, the child node further includes: The relay node identification codes are stored in the storage device in ascending order of the number of relays to the parent node, and the child node stores information on other child nodes with the smallest number of relays to the parent node. The predetermined time after the transmission, to see if the information from the other child node is a relay destination has been sent to the other child nodes or parent nodes is the next relay destination, from another child node becomes the relay destination When the information is not transmitted, the information is switched to another child node having the next smallest number of relays from the candidate child node as a relay destination to the parent node based on the table, and the information is retransmitted. And

In addition, when there are a plurality of relay destination child nodes that have the same number of relays to the parent node , the child node that transmits the information transmits the information to a child node that can ensure better wireless communication. It is desirable to do.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a low-speed radio | wireless communication, an autonomous radio network is possible, and the radio | wireless communications system which ensured the reliability of communication with a simpler protocol than before can be implement | achieved.

  Hereinafter, the communication system 1 according to the present embodiment will be described in detail with reference to FIGS. The communication system 1 according to the present embodiment will be described assuming a “disaster prevention network system”. First, the configuration of the communication system 1 according to the present embodiment will be described.

  FIG. 1 is a diagram showing an overall configuration of a communication system 1 according to the present embodiment. A communication system 1 shown in FIG. 1 includes child nodes 100-1 to 100-15 and a parent node 300, and is connected to a monitoring center 700 via a public line network 500. Here, a dotted line connecting the child nodes 100-1 to 100-15, the parent node 300, and the public network 500 is a wireless line, and a solid line connecting the public network 500 and the monitoring center 700 is a wired line. (Note that the section of the public line network 500 and the monitoring center 700 may be a wireless line).

  FIG. 2 shows the child node 100. The child node 100 illustrated in FIG. 2 includes a communication unit 100a for communicating with other child nodes 100 and the parent node 300, and a sensor unit 100b that collects various types of information.

  The communication unit 100a includes a transmission / reception antenna 11, a transmission unit 12, a reception unit 13, a control unit 14, a display unit 15, and a storage unit 16. Here, the communication unit 100a complies with, for example, a specific low power wireless standard (“ARIB STD-T67”, as an example, a transmission / reception frequency of 429 MHz band, an antenna power of 10 mW, a communication speed of 4800 bps, and a radio area radius of about 100 to 300 m). Shall.

  The transmission / reception antenna 11 is an antenna for performing wireless communication with other child nodes 100. The transmission unit 12 modulates and amplifies a transmission packet (transmission signal). The receiving unit 13 performs amplification and demodulation of the received packet (received signal). The receiving unit 13 includes a detection circuit (not shown) that detects the received electric field strength of the received packet. The received electric field strength detected by the detection circuit is used for generating a routing table, selecting a relay node at the time of packet transfer, and the like, as will be described later.

  The control unit 14 performs signal processing such as transmission packet generation and reception packet decoding. The display unit 15 is configured by an LED lamp that indicates whether or not the device is in operation or indicates information transfer or the like. The storage unit 16 stores a routing table required when transferring information (the routing table will be described in detail later).

  The sensor 18 is a sensor for collecting various types of information (for example, information on temperature, humidity, atmospheric pressure, sound, gas, chemical substances, etc.) of the disaster area. The A / D converter 17 digitizes the analog information so that the controller 14 can process it.

  Next, the configuration of the parent node 300 shown in FIG. 3 will be described. The parent node 300 shown in FIG. 3 includes a child node communication unit 300a for communicating with the child nodes 100-1 to 100-15 and a public line communication unit for communicating with the public line network 500 (base station thereof). 300b.

  Similar to the communication unit 100a described above, the child node communication unit 300a includes a transmission / reception antenna 31, a transmission unit 32, a reception unit 33, a control unit 34, a display unit 35, and a storage unit 36, and a specific low power wireless standard. ("ARIB STD-T67").

  The transmission / reception antenna 31 is an antenna for performing wireless communication with other child nodes 100. The transmission unit 32 modulates and amplifies the transmission packet. The receiving unit 33 performs amplification and demodulation of the received packet. The control unit 34 performs signal processing such as transmission packet generation and reception packet decoding. The display unit 35 is configured by an LED lamp that indicates whether or not the device is in operation or indicates the transfer of information. The storage unit 36 stores a routing table necessary for transferring information to the other child nodes 100-1 to 100-15.

  The public line communication unit 300b includes a transmission / reception antenna 37, a transmission unit 38, a reception unit 39, and an external network control unit 41. The public line communication unit 300b is configured by the same communication standard (for example, W-CDMA) as the public line network 500 in order to communicate with the public line network 500 (its base station).

  The transmission / reception antenna 37 is an antenna for performing wireless communication with the public network 500 (the base station). The transmission unit 38 modulates and amplifies the transmission packet. The receiving unit 39 performs amplification and demodulation of the received packet. The external network control unit 41 performs signal processing such as transmission packet generation and reception packet decoding, and exchanges information with the control unit 34.

  The public line network 500 is a cellular network conforming to the W-CDMA described above, and each base station can perform wireless communication with the parent node 300 described above. In addition, the monitoring center 700 receives information transmitted from the parent node 300 via the public line network 500.

  As will be described later, in the communication system 1 according to the present invention, when a child node on the relay path cannot communicate, the relay child node detects that no packet is transmitted from the relay destination child node. Then, the packet is transferred by switching to another child node as a relay destination. Thereby, in the communication system 1 which concerns on this embodiment, the radio | wireless communications system which ensured the reliability of communication is realizable. In addition, since it is only necessary to detect a packet, which will be described later, even if the relay destination child node cannot communicate, a communication system can be constructed with a simpler protocol.

  FIG. 4 is an example of a wireless packet format in the present embodiment. The header portion 43 is a portion that represents a route for relay transmission of the packet. The data unit 45 is a part that stores actual information (data such as temperature and the number of relays to the parent node 300) necessary for the packet. The error detection code 47 is a code for detecting whether or not an error has occurred in the data due to radio wave interference or the like when data from the system identification code of the header section 43 to the end of the data section 45 is wirelessly transmitted.

  The header part 43 includes some information. The bit synchronization 431 is a signal for synchronizing the bit timing on the transmission side on the reception side. The frame synchronization 432 is a signal for recognizing the packet format position on the receiving side. The system identification code 433 is an identification code for specifying the parent node 300 and the child nodes 100-1 to 100-15 that perform transmission and reception of the wireless packet (in addition, each node is set in advance in its own node). Even if a packet with a system identification code different from the identification code is received, the packet is not processed).

  The relay source identification code 434 represents the identification code of the parent node 300 or the child nodes 100-1 to 100-15 that actually transmitted the packet. The relay destination identification code 435 is an identification code of the parent node 300 and the child nodes 100-1 to 100-15 that should receive the packet (in addition, each node identifies its own node set in advance in its own node). Even if a packet with a relay destination identification code different from the code is received, the packet is not processed).

  The transmission source identification code 436 represents the identification code of the parent node 300 or the children 100-1 to 100-15 that is the origin of transmitting the packet. The transmission destination identification code 437 represents the identification code of the parent node 300 or the child nodes 100-1 to 100-15 at the final end that should finally receive the packet. If the transmission destination identification code 437 is a special code called a broadcast code, the packet is to be received by any node. Note that the child nodes 100-1 to 100-15 do not relay even if a packet having the transmission destination identification code 437 of the broadcast code is received.

  The packet type 438 indicates what kind of content the packet has (the details of the packet type 438 will be described later). The data length 439 represents the number of bytes of the data part 45. The length of the data part 45 is variable for each packet type.

  FIG. 5 shows the configuration of the data unit 45 for each packet type 438. The packet type 438 “1” indicates “event notification packet”. At this time, sensor data such as temperature is inserted into the data section 45. The transmission source is any one of the child nodes 100-1 to 100-15.

  The packet type 438 “3” indicates “relay node information packet”. At this time, the minimum number of relays from the own node to the parent node 300 is inserted in the data section 45. The transmission source is either the child node 100-1 to 100-15 or the parent node 300.

  Next, operation | movement of the communication system 1 is demonstrated using FIGS. The communication system 1 performs “table formation processing” and “information transfer processing”. Hereinafter, each process will be described in detail.

"Table formation process"
First, processing for forming a routing table (hereinafter referred to as “table formation processing”) required when transferring information to other child nodes or parent nodes will be described. As described above, the child nodes 100-1 to 100-15 and the parent node 300 of the communication system 1 are dispersed in the air from a helicopter or the like to a disaster area where an earthquake or the like has occurred. The child nodes 100-1 to 100-15 and the parent node 300 dispersed in the air autonomously form a routing table for transferring each information as shown in FIG.

  First, the parent node 300 inserts its own identification code into the transmission source identification code 436 and the relay source identification code 434 of the header unit 43 in the control unit 34, and the relay node information packet having the transmission destination identification code 437 as a broadcast code. Is generated. In the data part 45 of this relay node information packet, the number of relays “0 (zero)” is inserted. The packet generated in this way is transmitted via the transmission unit 32 and the transmission / reception antenna 31.

  The child node 100-1 and the child node 100-2 within the communicable range of the parent node 300 receive the packet transmitted by the parent node 300 by the transmission / reception antenna 11, and detect the received electric field strength by the reception unit 13. Further, the child node 100-1 and the child node 100-2 amplify and demodulate the received packet at the reception unit 13, and then perform predetermined processing (detection of the identification code of the parent node 300, the number of relays, etc.) at the control unit 14. )I do.

  The child node 100-1 performs processing such as reading the identification code of the parent node 300 and the number of relays from the header part 43 and the data part 45 of the received relay node information packet, and the like. A routing table in which the number of relays up to 300 “0 (zero)” and the received electric field strength measured when receiving the relay node information packet from the parent node 300 is formed and stored in the storage unit 16. Similarly, the child node 100-2 receives the identification code of the parent node 300, the relay count “0 (zero)” to the parent node 300, and the received electric field measured when receiving the relay node information packet from the parent node 300. The routing table is formed in association with the strength and stored in the storage unit 16.

  Next, the child node 100-1 performs the same process on the child nodes 100-2, 100-3, 100-5, and 100-6 that are in the communicable range (adjacent). That is, the child node 100-1 inserts its own identification code into the transmission source identification code 436 and the relay source identification code 434 of the header part 43 of the packet, and transmits the relay node information packet with the transmission destination identification code 437 as a broadcast code. Generate. In the data part 45 of the relay node information packet, the number of relays “1” to the parent node 300 is inserted. Child nodes 100-2, 100-3, 100-5, and 100-6 within the communicable range of child node 100-1 receive the packet transmitted by child node 100-1. Note that the relay count is transmitted after the received relay count is counted up by one, but the routing table may be formed after counting up at the child node of the receiving destination.

  Further, the child nodes 100-2, 100-3, 100-5, and 100-6 that form the routing cable are within the communicable range of each child node (adjacent in FIG. 1) (for example, child nodes). In the case of the node 100-2, similar processing is performed on the child nodes 100-1, 100-4, 100-6, and 100-7). When the child nodes 100-1 to 100-15 sequentially perform such processing, a routing cable is formed up to the child nodes 100-1 to 100-15.

  Further, the child nodes 100-1 to 100-15 transmit the relay node information packet in which the self identification code and the number of relays to the parent node 300 are inserted at a predetermined time interval, and receive the packet. The child nodes 100-1 to 100-15 update the routing table each time. Thereby, the child nodes 100-1 to 100-15 can form a routing table as shown in FIG.

  Such packets may be transmitted only a predetermined number of times. However, in unstable places such as disaster areas, the reproducibility of the communication environment is low. Update the table from time to time, or if there are concerns about packet transmission collisions due to the large number of child nodes, the child node will trigger a communication failure due to a failure of another child node in the information transfer process. It is desirable to update the routing table of each child node (information transfer processing will be described in detail later).

"Information transfer process"
Next, processing (hereinafter referred to as “information transfer processing”) in which the child nodes 100-1 to 100-15 transmit information such as temperature to the monitoring center 700 will be described. Here, the case where information is transferred from the child node 100-13 to the parent node 300 will be described as an example. When the child nodes 100-1 to 100-15 transfer information such as temperature to the parent node 300, an event notification packet is used.

  The child node 100-13 performs A / D conversion on the information (for example, temperature) detected by the sensor 18, and then inserts it into the data part 45 of the event notification packet by the control unit 14. The event notification packet is a packet for the child nodes 100-1 to 100-15 to transmit sensor data to the parent node 300. Further, the control unit 14 inserts its own identification code into the transmission source identification code 436 and the relay source identification code 434 of the header part 43 of the event notification packet, and the transmission destination identification code 437 contains the identification code of the parent node 300. In the relay destination identification code 435, the identification code of the child node 100-9 with the smallest number of relays to the parent node 300 ("3") is inserted based on the routing table. The event notification packet generated in this manner is modulated and amplified by the transmission unit 12 and then transmitted from the transmission / reception antenna 11.

  Here, the child node 100-13 checks whether the event notification packet has arrived at the child node 100-9 for a predetermined time, and the child node 100-9 has the next child node (for example, child node). 100-5, 100-8, or 100-10) to receive an event notification packet. Specifically, if the packet type, the transmission source identification code, and the transmission destination identification code match with the event notification packet transmitted by the child node 100-13, the child node 100-9 receives the event notification packet. The processing is terminated assuming that it has been completed (note that, if reception is impossible, this will be described later).

  The child node 100-9 that has received the event notification packet transmitted from the child node 100-13 transfers the received event notification packet. At this time, the child node 100-9 inserts its own identification code into the relay source identification code 434 of the header part 43 of the event notification packet, and the relay destination identification code 435 includes the parent node 300 based on the routing table. The identification code of the child node 100-5 having the smallest number of relays ("2") is inserted. The transmission source identification code 436 and the transmission destination identification code 437 are not operated. The event notification packet generated in this way is transmitted from the child node 100-9. In addition, the child node 100-9 checks whether or not the event notification packet has reached the child node 100-5 in the same manner as the child node 100-13 described above.

  Here, the child node 100-9 checks whether or not the event notification packet has arrived at the child node 100-5, and the child node 100-5 receives the next child node (for example, child node) for a predetermined time. 100-1, 100-3, 100-6, 100-8, 100-10), and attempts to receive the event notification packet. That is, if the packet type 438, the transmission source identification code 436, and the transmission destination identification code 437 match with the event notification packet transmitted by the child node 100-9, the child node 100-5 receives the event notification packet. It is assumed that it has been completed and the process is terminated.

  Then, the child node 100-5 that has received the event notification packet transmitted from the child node 100-9 has the smallest number of times of relaying the received event notification packet to the parent node 300 in the same manner as the child node 100-9 described above. Transfer to the child node 100-1 ("1" times). Further, the child node 100-1 that has received the event notification packet transmitted from the child node 100-5 transfers the received event notification packet to the parent node 300 in the same manner as the child node 100-5 described above.

  The parent node 300 receives the event notification packet thus transmitted from the child node 100-1. That is, the parent node 300 receives the event notification packet transmitted from the child node 100-1 by the transmission / reception antenna 31, amplifies and demodulates it by the reception unit 33, and then performs predetermined processing by the control unit 34. The event notification packet thus processed is converted by the external network control unit 41 into the W-CDMA format described above, and transmitted through the transmission unit 38 and the transmission / reception antenna 37.

  The event notification packet transmitted from the parent node 300 in this manner is transmitted to the monitoring center 700 via the public network 500 (the base station). The parent node 300 may transmit the individual information transmitted from the child nodes 100-1 to 100-15 to the monitoring center 700, or collect a certain amount of information and then collectively monitor the monitoring center 700. May be transmitted. It is desirable to design these appropriately according to the bandwidth of the public line network.

  Next, a case where a child node on the relay path cannot communicate will be described. Here, it is assumed that the child node 100-5 has become unable to communicate due to a failure or the like. As described above, a case where information is transferred from the child node 100-13 to the parent node 300 will be described.

  The child node 100-13 inserts information (for example, temperature) detected by the sensor 18 into the data part 45 of the event notification packet and transmits it, as in the above-described processing. The child node 100-9 receives the event notification packet transmitted from the child node 100-13. The child node 100-9 that has received the event notification packet transmitted from the child node 100-13 transfers the received event notification packet to the child node 100-5.

  The child node 100-9 measures whether or not the event notification packet is transmitted from the child node 100-5 for a predetermined time in order to check whether or not the event notification packet has reached the child node 100-5. . As described above, the child node 100-5 cannot communicate. For this reason, the child node 100-9 cannot detect an event notification packet in which the packet type 438, the transmission source identification code 436, and the transmission destination identification code 437 match the event notification packet transmitted by the child node 100-9.

  Since the event notification packet to be transmitted from the child node 100-5 is not detected, the child node 100-9 regards that the event notification packet has not reached the child node 100-5, and based on the routing table, The event notification packet is transferred by switching to the child node having the next smallest number of relays to the parent node 300 from the candidate child nodes 100-8 and 100-10. Further, the child node 100-9 may retransmit a predetermined number of times to the child node 100-5 when the event notification packet has not arrived.

  In this routing table, the child nodes 100-8 and 100-10 have the same number of relays to the parent node 300 of “3”. In such a case, the child node 100-9 performs processing so as to transfer the event notification packet to the child node 100-8 that has a better reception environment (that is, the reception field strength is high). That is, the child node 100-9 inserts the identification code of the child node 100-8 into the relay destination identification code 435 of the header section 43 and transfers the event notification packet.

  Thus, the retransmitted event notification packet is received by the child node 100-8. Here, the child node 100-9 again transmits the child node 100-8 to the next child node for a predetermined time in order to confirm whether or not the event notification packet has reached the child node 100-8. Attempt to receive event notification packets. That is, if the packet type 438, the transmission source identification code 436, and the transmission destination identification code 437 match with the event notification packet transmitted by the child node 100-9, the child node 100-8 receives the event notification packet. It is assumed that it has been completed and the process is terminated.

  The child node 100-8 that has received the event notification packet transmitted from the child node 100-9 inserts its own identification code into the relay source identification code 434 of the header part 43 of the event notification packet, and enters the relay destination identification code 435. Inserts the identification code of the child node 100-3 having the smallest number of relays to the parent node 300 and the strongest received electric field strength based on the routing table, and transmits the event notification packet.

  Then, the event notification packet transmitted from the child node 100-8 is transferred to the parent node 300 via the child nodes 100-3 and 100-1. The parent node 300 transmits the event notification packet transferred from the child node 100-13 to the monitoring center 700 through the public network 500 in the same manner as described above.

  As described above, in the communication system 1, even if a child node (for example, the child node 100-5) on the relay path becomes unable to communicate, the relay source child node (for example, the child node 100-9) relays. It detects that the previous child node is unable to communicate, and switches to the other relay node child node to transfer the event notification packet. For this reason, the radio | wireless communications system which ensured the reliability of communication is realizable. Further, even if the child node of the relay destination cannot communicate, it is only necessary to try to receive the event notification packet for a predetermined time, so that the communication system can be constructed with a simpler protocol.

It is a figure which shows the whole structure of the communication system which concerns on this embodiment. It is a figure which shows the structure of the child node which concerns on this embodiment. It is a figure which shows the structure of the parent node which concerns on this embodiment. It is a figure which shows the radio | wireless packet format structure which concerns on this embodiment. It is a figure which shows the structure of the radio | wireless packet classification which concerns on this embodiment. It is a figure which shows the routing table memorize | stored in the child node which concerns on this embodiment.

Explanation of symbols

  11, 31, 37 Transmission / reception antenna, 12, 32, 38 Transmission unit, 13, 33, 39 Reception unit, 14, 34 Control unit, 15, 35 Display unit, 16, 36 Storage unit, 17 A / D conversion unit, 18 Sensor, 41 External network control unit, 100-1 to 100-15 Child node, 300 Parent node, 500 Public line network, 700 Monitoring center.

Claims (2)

A parent node that collects information, and a plurality of child nodes that are wirelessly connected to the parent node directly or via other child nodes;
The child node is
A sensor that collects information, and a storage device that stores a table in which identification codes of other child nodes in a wirelessly connectable range and the number of relays to the child node of the child node are associated with each other. In a wireless communication system for transmitting information collected by its own sensor or information received from another child node directly to the parent node or through another child node having the smallest number of relays to the parent node based on
The child node further stores the identification code of the relay node in the storage device in ascending order of the number of relays to the parent node,
The child node transmits information to another child node having the smallest number of relays to the parent node, and then, for a predetermined time , another child node whose information is the next relay destination from another child node that is the relay destination or confirm is sent to the parent node, when the information from the other child node serving as the relay destination has not been transmitted, to the parent node from among the candidate slave node that is a relay destination in accordance with the table A wireless communication system, wherein information is retransmitted by switching to another child node having the next smallest number of relays. The wireless communication system according to claim 1,
When there are a plurality of relay destination child nodes that have the same number of relays to the parent node , the child node that transmits the information transmits the information to the child node that can ensure better wireless communication. A wireless communication system.

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