JP2012070368A - Multi-hop communication method, multi-hop communication system, and communication terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-hop communication method, a multi-hop communication system, and a communication terminal that can prevent a slave terminal which cannot communicate with a master terminal from occurring by preventing slave terminals from concentrating under a particular master terminal.SOLUTION: In a multi-hop communication method, each of multiple master terminals 1 and each of multiple slave terminals 2 perform multi-hop communication with each other, and a slave terminal 2 constructs a communication route with a single master terminal 1. A slave terminal 2-1 constructing a communication route with a master terminal 1-1, if the remaining number of communication routes the master terminal 1-1 can construct with slave terminals 2 is equal to or less than a threshold value K1, constructs a communication route with a master terminal 1-2 which has the remaining number of communication routes it can construct with slave terminals 2 larger than a threshold value K2.

Description

  The present invention relates to a multihop communication method, a multihop communication system, and a communication terminal.

  Conventionally, when communicating between communication terminals existing on a communication network, when communication cannot be performed directly between communication terminals that are trying to transmit information, other communication terminals are used for relaying communication. Multi-hop communication that enables communication is known. Such multi-hop communication is used particularly in a wireless network which is one of communication networks. Furthermore, multi-hop communication is also used in a PLC network, which is a communication network constructed using a technology of power line carrier communication (hereinafter abbreviated as “PLC” (Power Line Communication)).

  In such a communication network, communication terminals that can communicate with each other may become unable to communicate due to connection / disconnection of communication terminals, fluctuations in the communication environment, and the like, and the network topology of the communication network may change. Therefore, in order to perform good communication between the communication terminals, it is necessary to construct a communication route between the communication terminals when the network topology of the communication network changes (see, for example, Patent Documents 1 and 2). ).

  As a method of constructing a communication route, for example, by exchanging route information between communication terminals, searching for a usable communication route and selecting a route with good communication quality from among the usable communication routes, the communication terminal There is a way to build a communication route between.

  There is also a method for constructing a communication route between communication terminals by selecting a communication route in consideration of not only the communication quality but also the number of hops of the communication route.

JP 2006-67557 A JP 2008-244679 A

  Recently, there are communication networks in which a plurality of parent terminals are installed for each predetermined range, and each parent terminal communicates with a plurality of child terminals in the vicinity. In such a communication network, It has been proposed to use the multi-hop communication for communication with a child terminal. Then, a parent terminal provided for each predetermined range acquires predetermined information from each of a plurality of peripheral child terminals directly or indirectly using another child terminal as a relay terminal.

  In a communication network using the above parent terminal and child terminals, a single parent terminal establishes a communication route with a plurality of child terminals, thereby setting a plurality of child terminals under the control of one parent terminal. The And the parent terminal needs to hold | maintain each information (route information) of the communication route constructed | assembled between several subordinate subordinates on a memory as a route table, for example. However, depending on the capacity of the memory for storing the route table, there is an upper limit to the number of route information (number of records) that can be stored in this memory. That is, there is an upper limit on the number of child terminals that can establish a communication route with one parent terminal.

  Therefore, when a child terminal is concentrated under a certain parent terminal and the number of records stored in the parent terminal reaches the upper limit, a child terminal that can establish a communication route only with this parent terminal A situation occurs where a communication route cannot be established.

  As described above, the conventional communication network using multi-hop communication has a problem in that the child terminals are concentrated under the specific parent terminal, and the child terminals that cannot communicate with the parent terminal are generated.

  The present invention has been made in view of the above reasons, and its purpose is to suppress the generation of child terminals that cannot communicate with the parent terminal without the child terminals being concentrated under the control of the specific parent terminal. An object is to provide a multihop communication method, a multihop communication system, and a communication terminal.

  In the multi-hop communication method of the present invention, each of the plurality of parent terminals and each of the plurality of child terminals perform multi-hop communication with each other, and the child terminal establishes a communication route with the one parent terminal. In the multi-hop communication method, the child terminal that has established a communication route with the first parent terminal has a remaining number of communication routes that the first parent terminal can establish with the child terminal. When the value is equal to or lower than the first threshold, a communication route is established with the second parent terminal whose remaining number of communication routes that can be established with the child terminal exceeds the second threshold. It is characterized by that.

  In the multi-hop communication system of the present invention, each of a plurality of parent terminals and each of a plurality of child terminals perform multi-hop communication with each other, and the child terminal establishes a communication route with one parent terminal. In the hop communication system, the parent terminal includes information on the number of remaining records indicating the remaining number of communication routes that can be established with the child terminal, and transmits a hello packet for notifying the existence of the own terminal, The child terminal that establishes a communication route with the terminal transmits a hello packet that includes the remaining record number information of the parent terminal that establishes a communication route with the own terminal and notifies the existence of the own terminal. The child terminal that has not established a communication route with the parent terminal receives the plurality of hello packets within a predetermined time, the parent terminal that is the transmission source of the hello packet; and For each of the parent terminals for which the child terminal that is the source of the low packet is building a communication route, a communication cost is calculated based on at least the communication quality of the communication route existing with the parent terminal, The child terminal constructing a communication route with the parent terminal having the lowest communication cost and constructing a communication route with the first parent terminal is the first parent terminal or the first When the number of remaining records of the first parent terminal based on the hello packet received from the child terminal constructing a communication route with one parent terminal is equal to or less than a first threshold, The number of remaining records of the second parent terminal based on the hello packet received from the child terminal that has established a communication route with the parent terminal or the second parent terminal is a second threshold value. If it exceeds Characterized by constructing a communication route between said second main terminal.

  In this invention, the child terminal that is building a communication route with the first parent terminal, when the own terminal is a relay terminal between the other child terminal and the parent terminal, Even if the number of remaining records of the first parent terminal becomes equal to or less than the first threshold value, it is preferable that a communication route is continuously established with the first parent terminal.

  In this invention, the child terminal that is building a communication route with the first parent terminal, when the own terminal is a relay terminal between the other child terminal and the parent terminal, It is preferable that the first threshold value be increased as the number of the other child terminals using the own terminal as the relay terminal decreases.

  In this invention, the child terminal that is building a communication route with the first parent terminal, when the own terminal is a relay terminal between the other child terminal and the parent terminal, It is preferable that the second threshold value is lowered as the number of the other child terminals using the own terminal as the relay terminal decreases.

  In this invention, the child terminal constructing a communication route with the first parent terminal, when the number of remaining records of the first parent terminal is less than or equal to the first threshold, If the number of remaining records of the second parent terminal exceeds the second threshold value, a parent terminal change notification packet is transmitted to the first parent terminal and communication is performed with the second parent terminal. The first parent terminal that has constructed the route and received the parent terminal change notification packet preferably increments the number of remaining records of the terminal itself.

  In this invention, the child terminal constructing a communication route with the first parent terminal, when the number of remaining records of the first parent terminal is less than or equal to the first threshold, If the number of remaining records of the second parent terminal exceeds the second threshold value, the first parent terminal changeable packet is transmitted to the first parent terminal, and the first parent terminal changeable packet is received. If the number of remaining records of the terminal is equal to or less than the first threshold, the parent terminal transmits a parent terminal change permission packet to the child terminal that is the transmission source of the parent terminal changeable packet, The child terminal that increments the number of remaining records and receives the parent terminal change permission packet preferably establishes a communication route with the second parent terminal.

  In the communication terminal of the present invention, the parent terminal and the child terminal establish a communication route with each other to perform multi-hop communication, and the child terminal that establishes a communication route with the first parent terminal includes: When the remaining number of communication routes that can be established between the first parent terminal and the child terminal falls below the first threshold, the remaining number of communication routes that can be established with the child terminal is the second. A communication terminal used for the parent terminal of a multi-hop communication system that establishes a communication route with the second parent terminal that exceeds the threshold value of the communication terminal, and is a communication route that can be established with the child terminal It is characterized by transmitting a hello packet that includes information on the number of remaining records indicating the number of remaining terminals and that reports the existence of the terminal itself.

  The communication terminal of the present invention is a communication terminal used for a child terminal that performs multi-hop communication by establishing a communication route with a parent terminal, and establishes a communication route with the first parent terminal. If the remaining number of communication routes that can be established between the first parent terminal and the child terminal falls below a first threshold, the remaining communication routes that can be established with the child terminal A communication route is established with the second parent terminal whose number exceeds the second threshold.

  As described above, according to the present invention, there is an effect that it is possible to suppress the generation of child terminals that cannot communicate with the parent terminal without the child terminals being concentrated under the control of the specific parent terminal.

It is the schematic which shows the radio | wireless network which the multihop communication system of this invention comprises. It is a block diagram which shows the structure of a communication terminal same as the above. It is a table figure which shows the structure of a communicable terminal management table same as the above. (A) (b) It is a table figure which shows the structure of a communication route table same as the above. It is a table figure which shows the structure of a record cost table same as the above. It is a sequence diagram which shows a communication sequence same as the above. (A) (b) It is a figure which shows the format of a communication packet same as the above. It is a table figure which shows the structure of the subordinate terminal table of Embodiment 3. FIG. 10 is a sequence diagram illustrating a communication sequence according to the fifth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic diagram of a wireless network configured by the multi-hop communication system of the present embodiment. This wireless network is used in a dwelling unit group composed of a plurality of dwelling units X. Within the dwelling unit group, a parent communication terminal 1 is installed for each predetermined range (for example, every radius of 500 m). The communication terminal 2 as a child is installed. Hereinafter, the parent communication terminal 1 is referred to as a parent terminal 1 and the child communication terminal 2 is referred to as a child terminal 2. Further, when the parent terminals 1 are individually identified, the parent terminals 1-1, 1-2, 1-3,. . . When the child terminal 2 is individually identified using the code of the child terminal 2-1, 2-2, 2-3,. . . Is used.

  The child terminal 2 has a function of wirelessly transmitting predetermined information about each dwelling unit X to one parent terminal 1. The parent terminal 1 has a function of acquiring predetermined information related to each dwelling unit X wirelessly from the plurality of child terminals 2 and transmitting the acquired predetermined information to an upper management device (not shown) using an optical fiber line or the like. For example, a remote meter reading system can be configured by the master terminal 1 acquiring meter reading information such as power usage, gas usage, and water usage in each dwelling unit X from the child terminal 2. Moreover, the remote monitoring system which monitors the state of the apparatus in each dwelling unit X, when the parent terminal 1 transmits / receives the preset predetermined information between the child terminals 2, The state of the apparatus in each dwelling unit X It is also possible to configure a remote control system or the like that controls

  In this wireless network, the parent terminal 1 and the child terminal 2 transmit and receive wireless signals to each other by multi-hop communication. That is, in this wireless network, communication is performed directly or indirectly between the parent terminal 1 and each child terminal 2, and the child terminal 2 that cannot directly communicate with the parent terminal 1 is connected to another child terminal within a communicable distance. 2 communicates with the parent terminal 1 by sequentially relaying communication packets. In communication between the parent terminal 1 and the child terminal 2, another child terminal 2 that relays communication packets is referred to as a relay terminal.

  FIG. 2 is a block diagram of the communication terminal A. In the present embodiment, the same communication terminal A is used for the parent terminal 1 and the child terminal 2. For example, the communication terminal A is set to “parent” using setting means such as a jumper switch or a changeover switch. It functions as the parent terminal 1 and functions as the child terminal 2 by being set to “child”. Further, hereinafter, when the parent terminal 1 and the child terminal 2 are not distinguished, they are referred to as communication terminals A.

  The communication terminal A includes a storage unit 10, a control unit 20, and a wireless communication interface unit 30.

  The storage unit 10 includes a nonvolatile memory such as a ROM, a rewritable nonvolatile memory such as an EEPROM, and a volatile memory such as a RAM. And the memory | storage part 10 is provided with the table memory | storage part 101 which memorize | stores the link information etc. regarding the communication route and the communicable adjacent terminal (the parent terminal 1 or the child terminal 2 which can be communicated directly). Further, the storage unit 10 stores each program such as a control program for operating the communication terminal A, information necessary for executing each program, and the like.

  In this embodiment, a unique terminal ID is assigned to each of the parent terminal 1 and the child terminal 2, and the terminal ID assigned to the own terminal is also stored in the storage unit 10 of each communication terminal A. In this embodiment, the parent terminals 1-1, 1-2, 1-3,. . . . Terminal IDs “M1”, “M2”, “M3”. . . Are pre-allocated. Also, the child terminals 2-1, 2-2, 2-3,. . . . Includes a terminal ID “T1”, “T2”, “T3”, etc. by the parent terminal 1 when a communication route to be described later is established. . . Is assigned.

  Further, each communication terminal A is pre-assigned with a device ID such as a serial number (manufacturing number) or a MAC address, and the storage unit 10 of each communication terminal A stores this device ID in advance. . The communication packet transmitted and received by the communication terminal A is subjected to communication control by adding this device ID.

  The table storage unit 101 of the parent terminal 1 and the child terminal 2 stores a communicable terminal management table TB1 shown in FIG. The table storage unit 101 of the parent terminal 1 stores the communication route table TB21 shown in FIG. 4A, and the table storage unit 101 of the child terminal 2 stores the communication route table TB22 shown in FIG. The record cost table TB3 shown in FIG. 5 is stored.

  As shown in FIG. 3, the communicable terminal management table TB1 is information (communication is possible) regarding the communication terminal A (adjacent terminal) that can directly communicate with the communication terminal A without being relayed by another communication terminal A. Terminal information) is stored in a table format. Specifically, the communicable terminal management table TB1 includes fields of adjacent terminal ID, terminal type, reception link communication quality, transmission link communication quality, and link communication quality.

  In the communicable terminal management table TB1, the adjacent terminal ID is a terminal ID assigned to the communication terminal A (hereinafter referred to as the adjacent terminal A) that can directly communicate with the own terminal. The terminal type indicates the type of the adjacent terminal A (parent terminal 1 “parent” or child terminal 2 “child”). The reception link communication quality indicates the communication quality of the communication link from the adjacent terminal A to the own terminal. The transmission link communication quality indicates the communication quality of the communication link from the own terminal to the adjacent terminal A. The link communication quality indicates the communication quality in the communication link between the adjacent terminal A and the own terminal.

  For example, the communication quality value SQ is used as the link communication quality in the communication link between the two communication terminals A-A capable of direct communication. The communication quality value SQ is represented by an integer value such as 10 steps or 20 steps that becomes smaller as the received signal strength between the two communication terminals A-A capable of direct communication becomes larger. That is, as the communication quality value SQ is smaller, the communication packet is less attenuated and the communication state is better.

  And since the noise level at the place where the communication packet is received is different, the bidirectional communication quality in the communication link is different from each other, and the bidirectional communication quality in the communication link is composed of the reception link communication quality and the transmission link communication quality. The The received link communication quality is a received signal strength when the own terminal A receives a communication packet from another communication terminal A in a link between two communication terminals A-A capable of direct communication. As for the transmission link communication quality, in the link between two communication terminals A-A capable of direct communication, the own terminal A transmits a communication packet to the other communication terminal A, and the other communication terminal A receives the communication packet. Is the received signal strength.

  Also in the communicable terminal management table TB1, fields of reception link communication quality and transmission link communication quality in the communication terminal A are provided. Then, from the viewpoint of guaranteeing communication reliability (reliability) when communication is performed between the communication terminals A and A, one of the reception link communication quality and the transmission link communication quality having the worse communication state (link communication). The higher quality value) is adopted as the link communication quality between the two communication terminals A-A.

  The route communication quality, which will be described later, which is an evaluation of the communication quality of the communication route between the parent terminal 1 and the child terminal 2, is the link of each communication link constituting the communication route between the parent terminal 1 and the child terminal 2. The sum of communication quality is adopted.

  The communication quality value SQ described above is associated with the received signal strength. However, instead of the received signal strength, the communication quality value SQ is associated with other elements such as an SN ratio, an EVM (Error Vector Magnitude), a bit error rate, and a packet error rate. May be calculated.

  Next, a communication route between the parent terminal 1 and the child terminal 2 is formed by one or more communication links. Then, the communication route table TB21 (see FIG. 4A) held by the parent terminal 1 includes information (communication route information) regarding the communication route between the parent terminal 1 and the child terminals 2 subordinate to the parent terminal 1. Stored in table format. Specifically, the communication route table TB21 is provided with terminal ID, route communication quality, hop count, and hop destination fields.

  In the communication route table TB21 held by the parent terminal 1, the terminal ID is a terminal ID assigned to the subordinate child terminal 2 in which the communication route is constructed. The route communication quality indicates the communication quality in the communication route to the child terminal 2 registered in the terminal ID field. The number of hops indicates the number of hops in the communication route to the child terminal 2 registered in the terminal ID field. The hop destination indicates the communication terminal A of the transmission destination at each hop in the communication route to the child terminal 2 registered in the terminal ID field.

  Here, in the communication route table TB21, the unit of line composed of the plurality of fields is a record, and the number of lines is referred to as the number of records (that is, the number of lines in the communication route table TB21 is the number of records). The upper limit of the number of records is determined by the memory capacity of the table storage unit 101, and there is also an upper limit on the number of child terminals 2 that can construct a communication route with one parent terminal 1.

  Hereinafter, a value obtained by subtracting the number of currently registered records from the upper limit of the number of records that can be registered in the communication route table TB21 of the parent terminal 1 is referred to as a remaining record number. The number of remaining records corresponds to the remaining number of communication routes that can be established between the parent terminal 1 and the child terminal 2. That is, the larger the number of remaining records, the larger the remaining number of child terminals 2 that can construct a communication route with the parent terminal 1, and the smaller the number of remaining records, the more the communication route with the parent terminal 1 becomes. The remaining number of child terminals 2 that can be constructed is reduced.

  Next, the communication route table TB22 (see FIG. 4B) held by the child terminal 2 includes information (communication route information) regarding the communication route between the child terminal 2 and the parent terminal 1 that can communicate with the child terminal 2. , Stored in table format. Specifically, the communication route table TB22 includes fields for terminal ID, route communication quality, hop count, and hop destination.

  In the communication route table TB22 held by the child terminal 2, the terminal ID is a terminal ID assigned to the parent terminal 1 that can communicate with the child terminal 2. The route communication quality indicates the communication quality in the communication route to the parent terminal 1 registered in the terminal ID field. The number of hops indicates the number of hops in the communication route to the parent terminal 1 registered in the terminal ID field. The hop destination indicates the destination communication terminal A at each hop in the communication route to the parent terminal 1 registered in the terminal ID field.

  In the communication route tables TB21 and TB22, the number of hops is the number of communication terminals A in the communication route from the own terminal to the communication destination terminal. For example, in the case of a communication route in which the child terminal 2-4 communicates with the parent terminal 1 via the child terminal 2-3 and the child terminal 2-1, the number of hops is “3”. As the hop destination, the terminal IDs of the communication terminals A that are routed from the own terminal to the communication destination terminal are registered in order of passage, and finally, the terminal IDs of the communication terminals A registered in the terminal ID field are registered.

  Next, the record cost table TB3 (see FIG. 5) held by the child terminal 2 stores information on the number of remaining records of the parent terminal 1 and information on the communication cost with the parent terminal 1 in a table format. ing. Specifically, the record cost table TB3 includes fields for terminal ID, number of remaining records, and communication cost.

  In the record cost table TB3 held by the child terminal 2, the terminal ID is a terminal ID assigned to the parent terminal 1. The number of remaining records indicates the number of remaining records of the parent terminal 1 registered in the terminal ID field. The communication cost indicates the communication cost of the communication route existing between the parent terminal 1 registered in the terminal ID field.

  Next, the wireless communication interface unit 30 is a communication interface circuit for performing communication with another communication terminal A using a wireless signal.

  The control unit 20 is a device that controls the operation of the entire communication terminal A by controlling each unit of the communication terminal A, and includes, for example, a microprocessor and its peripheral circuits. And the control part 20 is provided with the table process part 201, the communication process part 202, and the transmission timer part 203, and constructs | assembles the communication route between the child terminal 2 and the parent terminal 1 directly or indirectly. A communication route construction process, which is a process, is executed.

  The table processing unit 201 manages the registration contents of each table stored in the table storage unit 101 of the storage unit 10. The communication processing unit 202 transmits / receives communication packets to / from another communication terminal A using the wireless communication interface unit 30 and performs an operation described later, thereby performing communication between the parent terminal 1 and the child terminal 2. A communication route construction process for constructing a route is performed. The transmission timer unit 203 is a time measuring unit that measures the elapse of a predetermined time, and notifies the communication processing unit 202 of arrival of transmission timings of various communication packets at predetermined time intervals.

  Next, the construction of a communication route in this wireless network will be described using the sequence of FIG.

  First, when the communication terminal A is activated, the transmission timer unit 203 in the control unit 20 of each communication terminal A starts timing to transmit a hello packet (hereinafter referred to as “H packet”). When the time is up, the transmission timer unit 203 notifies the communication processing unit 202 that it is the transmission timing of the H packet. Upon receiving this notification, the communication processing unit 202 transmits the H packet to the wireless network by broadcast communication.

  The H packet is a communication packet in which each communication terminal A notifies the other communication terminals A of the existence of its own terminal. FIG. 7 (a) shows the format of the H packet, which includes a source terminal ID part, a destination terminal ID part, an operation code part, a terminal type part, a communication route part, and a remaining record number part. Configured.

  The transmission packet terminal ID part of the H packet accommodates the terminal ID of the communication terminal A that has transmitted the H packet. The transmission destination terminal ID portion accommodates the terminal ID of the communication terminal A that is the transmission destination of the H packet. In the case of the H packet, the transmission destination code ID “BC” is accommodated. The operation code portion stores the code of the H packet. The terminal type section stores information for identifying whether the communication terminal A that has transmitted the H packet is the parent terminal 1 or the child terminal 2.

  Further, the communication route part of the H packet accommodates communication route information indicating the communication route from the child terminal 2 to the parent terminal 1 and route quality information indicating the communication quality of this communication route. The communication route information is expressed by sequentially arranging the terminal IDs of the communication terminals A that pass through the communication route from the child terminal 2 to the parent terminal 1. The route quality information is represented by the sum of link communication qualities in the communication route, and this sum of link communication qualities is referred to as route communication quality.

  For example, it is assumed that the child terminal 2-4 establishes a communication route with the parent terminal 1 via the child terminal 2-3 and the child terminal 2-1, and the route communication quality is 17. In this case, “T4 → T3 → T1 → M1; 17” is accommodated in the communication route part of the H packet transmitted by the child terminal 2-4. The number of hops of this communication route is “3”. Further, the communication route part of the H packet transmitted by the parent terminal 1 is “null” (or empty data), which corresponds to the hop number “0” and the route communication quality “0”.

  When the communication terminal A that has transmitted the H packet is the parent terminal 1, the remaining record number portion of the H packet contains the number of remaining records of the parent terminal 1 that is the transmission source of the H packet. When the communication terminal A that has transmitted the H packet is the child terminal 2, the remaining record number portion of the H packet is the number of remaining records of the parent terminal 1 in which the child terminal 2 that is the transmission source of the H packet constructs a communication route. Is housed.

  The H packet is a child in which the communication terminal A is set as the parent terminal 1 and the communication terminal A has established a communication route to the parent terminal 1 in order to suppress communication traffic of the wireless network. When it is the terminal 2, it is transmitted from each communication terminal A. The H packet transmission processing is performed at regular time intervals after activation.

  For communication packets other than the H packet, when the communication processing unit 202 of the communication terminal A receives the communication packet, it calculates the received link communication quality and refers to the operation code of the received communication packet. Determine the type.

  Specifically, in FIG. 6, the parent terminals 1-1 and 1-2 transmit H packets (S1, S2). In the child terminal 2-1 that has received the H packet transmitted by the parent terminal 1-1, the communication processing unit 202 refers to the terminal type part of the received H packet, and thereby the communication terminal A that has transmitted this H packet. Determine the type. When it is determined that the communication terminal A that has transmitted the H packet is the parent terminal 1, the child terminal 2-1 determines that it can communicate directly with the parent terminal 1-1, and determines that “the child terminal 2-1 → the parent terminal”. It is determined that the communication route of “1-1” exists. Then, the table processing unit 201 of the child terminal 2-1 extracts the terminal ID and the terminal type by referring to the transmission source terminal ID part and the terminal type part of the received H packet. Then, a new record is provided in the communicable terminal management table TB1 of the table storage unit 101, and the extracted terminal ID, terminal type, and calculated received link communication quality are changed to the adjacent terminal ID, terminal type, and received link communication quality. Register each. Then, the table processing unit 201 of the child terminal 2-1 registers the received link communication quality of the parent terminal 1-1 as the temporary link communication quality in the link communication quality of the communicable terminal management table TB1.

  Here, the reception link communication quality is assumed to be the provisional link communication quality, as described above, where the link communication quality is the worse of the reception link communication quality and the transmission link communication quality (the one with the larger numerical value). This is because the transmission link communication quality is not known at the present time.

  Further, in the child terminal 2-1, which has received the H packet transmitted by the parent terminal 1-1, the communication processing unit 202 transmits the H packet by referring to the remaining record number part of the received H packet. The number of remaining records of the parent terminal 1-1 is acquired. Then, the table processing unit 201 of the child terminal 2-1 registers the number of remaining records of the parent terminal 1-1 in the record / cost table TB3 of the table storage unit 101 corresponding to the terminal ID of the parent terminal 1-1. To do.

  When the child terminal 2-1 receives the H packet from the parent terminal 1-2 within a certain time after receiving the H packet from the parent terminal 1-1, similarly to the above, the communicable terminal management A new record is provided in the table TB1. Then, the terminal ID extracted from the H packet of the parent terminal 1-2, the terminal type, and the calculated reception link communication quality are registered in the adjacent terminal ID, terminal type, and reception link communication quality of the communicable terminal management table TB1, respectively. . Then, the table processing unit 201 of the child terminal 2-1 registers the received link communication quality of the parent terminal 1-2 as the temporary link communication quality in the link communication quality of the communicable terminal management table TB1.

  Further, in the child terminal 2-1, which has received the H packet transmitted by the parent terminal 1-2, the communication processing unit 202 transmits the H packet by referring to the remaining record number portion of the received H packet. The number of remaining records of the parent terminal 1-2 is acquired. Then, the table processing unit 201 of the child terminal 2-1 registers the number of remaining records of the parent terminal 1-2 in the record / cost table TB3 of the table storage unit 101 corresponding to the terminal ID of the parent terminal 1-2. To do.

  In the child terminal 2-1, which directly receives the H packet from the plurality of parent terminals 1-1 and 1-2, the communication processing unit 202 refers to the storage unit 10 and assigns a terminal ID to the own terminal. Determine whether or not. When the terminal ID is not assigned to the own terminal, the child terminal 2-1 determines the parent terminal 1 that requests the assignment of the terminal ID (that is, the parent terminal 1 that constructs the communication route) as follows. I do.

  First, in the child terminal 2-1, which directly receives H packets from the plurality of parent terminals 1-1, 1-2, the communication processing unit 202 communicates with each communication existing between the parent terminals 1-1, 1-2. Calculate the communication cost of the route.

  In the child terminal 2, the communication cost of the communication route between the child terminal 2 and the parent terminal 1 is calculated based on the route communication quality (sum of link communication quality) of the communication route and the number of hops of the communication route.

The communication cost formula is:
Communication cost = Ka × [Route communication quality included in communication route portion of H packet + Link communication quality of communication enable terminal management table TB1] + Kb × [Number of hops based on communication route information included in communication route portion of H packet + 1 ]
It is represented by Ka is a weighting factor of route communication quality (sum of link communication quality) of the communication route. Kb is a weighting factor of the number of hops of the communication route.

  The communication cost calculated as described above is the communication quality level in the communication route between the parent terminal 1 and the child terminal 2, and the communication quality level in the communication route becomes higher as the value of the communication cost is lower.

Here, the communication route part of the H packet transmitted by the parent terminal 1 is “null” (or empty data), which corresponds to the number of hops “0” and the route communication quality “0”. Therefore, the communication cost between the child terminal 2 and the parent terminal 1 that directly received the H packet from the parent terminal 1 is
Communication cost = Ka × [Link communication quality of communicable terminal management table TB1] + Kb × [1]
It is represented by

  Then, the communication processing unit 202 of the child terminal 2-1 calculates the communication cost for the parent terminals 1-1 and 1-2 that are H packet transmission sources. Then, the table processing unit 201 of the child terminal 2-1 corresponds to each terminal ID of the parent terminals 1-1 and 1-2 in the record / cost table TB3 of the table storage unit 101. Each communication cost of 1-2 is registered.

  Then, the communication processing unit 202 of the child terminal 2-1 transmits an address request packet for requesting terminal ID allocation to the lower one of the parent terminals 1-1 and 1-2 (S3). Here, it is assumed that the communication cost of the parent terminal 1-1 is lower than the communication cost of the parent terminal 1-2, and the child terminal 2-1 transmits an address request packet to the parent terminal 1-1. When the child terminal 2-1 receives the H packet from only one parent terminal 1, the child terminal 2-1 requests the parent terminal 1 to assign a terminal ID.

  In the above configuration, the child terminal 2 selects the parent terminal 1 that is the destination of the address request packet based on the provisional link communication quality. However, the following method may be used as a method of determining the parent terminal 1 that is the transmission destination of the address request packet. First, when the child terminal 2 receives H packets from a plurality of parent terminals 1, the child terminal 2 selects two or more parent terminals 1 with high provisional link communication quality, and each of the selected two or more parent terminals 1 and Investigate the bidirectional route communication quality between. Then, the address request packet is transmitted to the parent terminal 1 having the lowest communication cost obtained from the bidirectional route communication quality.

  Thus, when the child terminal 2 receives H packets from a plurality of parent terminals 1, the communication cost between each parent terminal 1 is reduced based on the route communication quality of the communication route and the number of hops of the communication route. calculate. Then, a communication route is established with the parent terminal 1 having the lowest communication cost (that is, the parent terminal 1 having the highest communication quality level of the communication route) among the plurality of parent terminals 1.

  For example, as shown in FIG. 7B, the address request packet transmitted by the child terminal 2 includes a transmission source terminal ID portion, a transmission destination terminal ID portion, a transmission communication route portion, an operation code portion, a distribution address. Unit, an adjacent terminal unit, and a link communication quality unit.

  The transmission source terminal ID portion of the address request packet accommodates the terminal ID of the communication terminal A that has transmitted the address request packet. The transmission destination terminal ID portion accommodates the terminal ID of the communication terminal A that is the transmission destination of the address request packet. In the case of the child terminal 2 in which the terminal ID is not set, “reserved terminal ID” is set in the transmission source terminal ID portion.

  The transmission communication route unit accommodates information related to a communication route when transmitting an address request packet. The information is represented by arranging terminal IDs according to the communication route from the child terminal 2 as the transmission source to the parent terminal 1 as the transmission destination. The communication terminal A that has received the address request packet determines the communication terminal A as the transmission destination (forwarding destination, relay destination) of the address request packet based on the transmission communication route part of the received address request packet, and determines the address request packet. Transfer (relay) to this destination communication terminal A.

  The operation code part accommodates an address request code.

  In the case of an address request packet, the distribution address portion contains “null” (or empty data).

  In the case of an address request packet, the adjacent terminal unit accommodates the terminal ID of the communication terminal A that is the transmission source of the H packet received by the child terminal 2.

  The link communication quality unit accommodates the link communication quality with the communication terminal A that is the transmission source of the H packet received by the child terminal 2. The child terminal 2 for which the terminal ID is not set accommodates the received link communication quality as a temporary link communication quality in the link communication quality part of the address request packet.

  More specifically, the address request packet transmitted from the child terminal 2-1 to the parent terminal 1-1 is illustrated as “reserved terminal ID” in the transmission source terminal ID portion and “M1 in the transmission destination terminal ID portion. "Is accommodated, and" reserved terminal ID → M1 "is accommodated in the transmission communication route part. Furthermore, the operation code part contains “address request code”, the distribution address part contains “null”, the adjacent terminal part contains “M1”, and the link communication quality part contains “ 4 "is accommodated.

  In the parent terminal 1-1 that has received the address request packet transmitted from the child terminal 2-1, the communication processing unit 202 assigns a terminal ID to the child terminal 2-1 that has transmitted the address request packet. Here, it is assumed that the terminal ID “T1” is assigned to the child terminal 2-1.

  The communication processing unit 202 of the parent terminal 1-1 extracts the adjacent terminal ID “M1” and the link communication quality “4” included in the received address request packet. Since the terminal ID “M1” is accommodated in the adjacent terminal part of the address request packet, the communication terminal unit 202 of the parent terminal 1-1 determines that the child terminal 2-1 to which the terminal ID “T1” is assigned is the parent terminal 1 -1 can be directly communicated, and it is determined that a communication route of “M1 → T1” is established between the parent terminal 1-1 and the child terminal 2-1. The link communication quality “4” accommodated in the address request packet is the transmission link communication quality of the parent terminal 1-1 → the child terminal 2-1, in the parent terminal 1-1.

  In addition, the communication processing unit 202 of the parent terminal 1-1 compares the received link communication quality calculated when the address request packet is received with the transmitted link communication quality. Then, the link communication quality (the larger numerical value) having a poor communication state is set as the link communication quality between the parent terminal 1-1 and the child terminal 2-1. For example, when the reception link communication quality calculated when the address request packet is received is “5”, the transmission link communication quality “4” is compared with the reception link communication quality “5”, and the link communication quality “5” is compared. " Since the parent terminal 1-1 can directly communicate with the child terminal 2-1 having the terminal ID “T1”, the link communication quality “5” is determined between the parent terminal 1-1 and the child terminal 2-1. It becomes route communication quality.

  In the parent terminal 1-1, the table processing unit 201, the adjacent terminal ID “T1” assigned to the child terminal 2-1, the terminal type “child”, the reception link communication quality “5”, and the transmission link communication quality “ 4 ”and link communication quality“ 5 ”are registered in the communicable terminal management table TB1. The reception link communication quality “5” is the communication quality in the link of the child terminal 2-1 → the parent terminal 1-1, and the transmission link communication quality “4” is the link of the parent terminal 1-1 → the child terminal 2-1. Is the communication quality.

  Further, in the parent terminal 1-1, the table processing unit 201 uses the terminal ID “T1” assigned to the child terminal 2-1, the route communication quality “5”, the number of hops “1”, and the first hop “T1”. Is registered in the communication route table TB21.

  Then, the parent terminal 1-1 transmits an address response packet to the child terminal 2-1 that has transmitted the address request packet (S4).

  For example, as shown in FIG. 7B, the address response packet includes a transmission source terminal ID unit, a transmission destination terminal ID unit, a transmission communication route unit, an operation code unit, a distribution address unit, and an adjacent terminal. And a link communication quality unit. That is, the address response packet has a format similar to that of the above-described address request packet.

  The transmission source terminal ID portion of the address response packet accommodates the terminal ID of the communication terminal A that has transmitted the address response packet. The transmission destination terminal ID portion accommodates the terminal ID of the communication terminal A that is the transmission destination of the address response packet. When an address response packet is transmitted to the child terminal 2 whose terminal ID has not been set, a broadcast communication code “BC” such as broadcast is accommodated in the transmission destination terminal ID portion.

  The transmission communication route unit accommodates information related to a communication route when transmitting an address response packet. The information is represented by arranging terminal IDs in accordance with a communication route from the transmission source parent terminal 1 to the transmission destination child terminal 2. The communication terminal A that has received the address response packet determines the communication terminal A as the transmission destination (forwarding destination, relay destination) of the address response packet based on the transmission communication route part of the received address response packet, and determines the address response packet. Transfer (relay) to this destination communication terminal A. In the case of an address response packet, since the terminal ID of the child terminal 2 as the transmission destination has not yet been set, the last (end) of the transmission communication route part is a code for broadcast communication such as broadcast communication, for example. “BC” is registered.

  The operation code part accommodates an address response code.

  In the case of an address response packet, the distribution address part accommodates a terminal ID assigned to the child terminal 2 that is the transmission source of the address request packet.

  The adjacent terminal unit accommodates the terminal ID of the communication terminal A that is the transmission source of the H packet received by the child terminal 2.

  The link communication quality unit accommodates the link communication quality with the communication terminal A that is the transmission source of the H packet received by the child terminal 2.

  More specifically, an example of the address response packet created by the parent terminal 1-1 includes “M1” in the transmission source terminal ID portion, “BC” in the transmission destination terminal ID portion, and a transmission communication route. The section contains “M1 → BC”. Furthermore, the operation code part contains “address response code”, the distribution address part contains “T1”, the adjacent terminal part contains “M1”, and the link communication quality part contains “5”. Is contained.

  In the child terminal 2-1 that has received the address response packet transmitted by the parent terminal 1-1, the communication processing unit 202 has the distribution address “T1” and the adjacent terminal ID “ M1 ”and link communication cost“ 5 ”are extracted.

  Then, the child terminal 2-1 sets “T1” as the terminal ID of the own terminal. Further, in the child terminal 2-1, the table processing unit 201 registers the transmission link communication cost “5” corresponding to the adjacent terminal ID “M1” in the communicable terminal management table TB1.

  Further, the communication processing unit 202 of the child terminal 2-1 compares the received link communication quality “4” corresponding to the adjacent terminal ID “M1” with the transmitted link communication quality “5” in the communicable terminal management table TB1. To do. Then, the link communication quality (the larger numerical value) having a poor communication state is set as the link communication quality between the parent terminal 1-1 and the child terminal 2-1. In this case, the link communication quality is updated to “5”.

  Then, as described above, since the child terminal 2-1 is determined that the communication route of “child terminal 2-1 → parent terminal 1-1” can be established, the link communication quality “5” The route communication quality between the parent terminal 1-1 and the child terminal 2-1. That is, the child terminal 2-1 has a communication route with the number of hops “1” and the route communication quality “5” established with the parent terminal 1-1. Therefore, the table processing unit 201 of the child terminal 2-1 adds the terminal ID “M1”, the route communication quality “5”, the number of hops “1”, and the first hop “M1” of the parent terminal 1 to the communication route table TB22. sign up.

  Thus, when the parent terminal 1 (parent terminal 1-1) and the child terminal 2 (child terminal 2-1) can communicate directly, the H packet transmission process of the parent terminal 1, the address request packet transmission of the child terminal 2 The three steps of the step and the address response packet transmission step of the parent terminal 1 are executed. Then, by executing these steps, the terminal ID (communication address) of the child terminal 2 is set, and a communication route between the parent terminal 1 and the child terminal 2 that can directly communicate with each other is established on both sides. .

  Next, the child terminal 2-1 for which the communication route to the parent terminal 1-1 has been established receives notification from the transmission timer unit 203 and transmits the H packet to the wireless network by broadcast communication when the H packet transmission timing comes. (S5).

  The terminal ID “T1” of the communication terminal 2-1 that has transmitted the H packet is accommodated in the transmission source terminal ID portion of the H packet transmitted by the child terminal 2-1. The transmission destination terminal ID portion accommodates the terminal ID of the communication terminal A that is the transmission destination of the communication packet. In the case of the H packet, the transmission destination code ID “BC” is accommodated. The operation code portion stores the code of the H packet. The terminal type section stores information for identifying whether the communication terminal A that has transmitted the H packet is the parent terminal 1 or the child terminal 2.

  Further, the communication route part of the H packet transmitted from the child terminal 2-1 includes communication route information representing the communication route from the child terminal 2-1 to the parent terminal 1-1 and route quality information representing the communication quality of this communication route. Is housed. Here, the terminal ID “T1” of the child terminal 2-1, the terminal ID “M1” of the parent terminal 1-1, and route communication of the communication route established between the child terminal 2-1 and the parent terminal 1-1. From the quality “5”, “T1 → M1; 5” is accommodated in the communication route part.

  Further, the remaining record number portion of the H packet transmitted by the child terminal 2-1 contains the number of remaining records of the parent terminal 1-1 in which the child terminal 2-1 constructs a communication route.

  In the child terminal 2 that has received the H packet transmitted by the child terminal 2-1 for which the communication route to the parent terminal 1-1 has been constructed, for example, the child terminal 2-2, the communication processing unit 202 transmits the received H packet. The communication terminal A that has transmitted the H packet is determined by referring to the terminal type section. When it is determined that the communication terminal A that has transmitted the H packet is the child terminal 2, the communication route part of the received H packet is referred to. The communication route part of the H packet transmitted from the child terminal 2-1 includes the communication route “T1 → M1; 5” to the parent terminal 1-1. 1 is determined to be communicable. That is, it is determined that a communication route of “child terminal 2-2 → child terminal 2-1 → parent terminal 1-1” can be constructed.

  Then, the table processing unit 201 of the child terminal 2-2 extracts the terminal ID and the terminal type by referring to the transmission source terminal ID part and the terminal type part of the H packet received from the child terminal 2-1. Then, a new record is provided in the communicable terminal management table TB1 of the table storage unit 101, and the extracted terminal ID, terminal type, and calculated received link communication quality are changed to the adjacent terminal ID, terminal type, and received link communication quality. Register each. Then, the table processing unit 201 of the child terminal 2-2 registers the received link communication quality as the temporary link communication quality in the link communication quality of the communicable terminal management table TB1.

  Further, in the child terminal 2-2 that has received the H packet transmitted by the child terminal 2-1, the communication processing unit 202 refers to the remaining record number part of the received H packet, so that the child terminal 2-1 The number of remaining records of the parent terminal 1-1 constructing the communication route is acquired. The table processing unit 201 of the child terminal 2-2 registers the number of remaining records of the parent terminal 1-1 in the record / cost table TB3 of the table storage unit 101 corresponding to the terminal ID of the parent terminal 1-1. To do.

  Furthermore, it is assumed that the child terminal 2-3 has already established a communication link with the parent terminal 1-2. Then, it is assumed that the child terminal 2-2 also receives the H packet from the child terminal 2-3 within a predetermined time after receiving the H packet from the child terminal 2-1 (S6). In the child terminal 2-2 that has received the H packet transmitted by the child terminal 2-3, the communication processing unit 202 refers to the terminal type part of the received H packet, thereby determining the communication terminal A that has transmitted the H packet. to decide. When it is determined that the communication terminal A that has transmitted the H packet is the child terminal 2, the communication route part of the received H packet is referred to. The communication route part of the H packet transmitted by the child terminal 2-3 includes the communication route to the parent terminal 1-2, and the child terminal 2-2 can communicate with the parent terminal 1-2. to decide. That is, it is determined that a communication route of “child terminal 2-2 → child terminal 2-3 → parent terminal 1-2” can be constructed.

  Then, similarly to the above, the table processing unit 201 of the child terminal 2-2 uses the terminal ID extracted from the H packet of the child terminal 2-3, the terminal type, and the calculated received link communication quality as the communicable terminal management table TB1. Are registered in the adjacent terminal ID, terminal type, and received link communication quality. Then, the table processing unit 201 of the child terminal 2-2 registers the received link communication quality as the temporary link communication quality in the link communication quality of the communicable terminal management table TB1.

  Further, in the child terminal 2-2 that has received the H packet transmitted by the child terminal 2-3, the communication processing unit 202 refers to the remaining record number part of the received H packet, so that the child terminal 2-3 The number of remaining records of the parent terminal 1-2 constructing the communication route is acquired. Then, the table processing unit 201 of the child terminal 2-2 registers the number of remaining records of the parent terminal 1-2 corresponding to the terminal ID of the parent terminal 1-2 in the record / cost table TB3 of the table storage unit 101. To do.

  Thus, in the child terminal 2-2 that directly receives the H packet from the plurality of communication terminals A (here, the child terminals 2-1 and 2-3), the communication processing unit 202 refers to the storage unit 10, It is determined whether or not a terminal ID is assigned to the own terminal. When the terminal ID is not assigned to the own terminal, the child terminal 2-2 performs the following process to determine the parent terminal 1 that requests the assignment of the terminal ID.

  First, in the child terminal 2-2 that directly receives the H packet from the plurality of child terminals 2-1, 2-2, the communication processing unit 202 transmits each communication route via each of the child terminals 2-1, 2-3. The communication cost is calculated.

  In the child terminal 2, the communication cost of the communication route between the child terminal 2 and the parent terminal 1 is calculated based on the route communication quality (sum of link communication quality) of the communication route and the number of hops of the communication route.

The communication cost formula is:
Communication cost = Ka × [Route communication quality included in communication route portion of H packet + Link communication quality of communication enable terminal management table TB1] + Kb × [Number of hops based on communication route information included in communication route portion of H packet + 1 ]
It is represented by Ka is a weighting factor of route communication quality (sum of link communication quality) of the communication route. Kb is a weighting factor of the number of hops of the communication route.

  The communication cost calculated as described above is the communication quality level in the communication route between the parent terminal 1 and the child terminal 2, and the communication quality level in the communication route becomes higher as the value of the communication cost is lower.

  Then, the communication processing unit 202 of the child terminal 2-2 transmits each communication route (that is, the parent terminal 1-1, the parent terminal 1) via each of the child terminals 2-1 and 2-3 that are transmission sources of the H packet. The communication cost is calculated for each communication route up to -2. Then, the table processing unit 201 of the child terminal 2-2 corresponds to each terminal ID of the parent terminals 1-1 and 1-2 in the record / cost table TB 3 of the table storage unit 101. Each communication cost of 1-2 is registered.

  Then, among the parent terminals 1-1 and 1-2, an address request packet for requesting allocation of terminal IDs is transmitted to the lower communication cost (that is, the higher communication quality level) (S7). Here, the communication cost of the communication route of the parent terminal 1-1 via the child terminal 2-1 is lower than the communication cost of the communication route of the parent terminal 1-2 via the child terminal 2-3. 2 transmits an address request packet via the child terminal 2-1. When the child terminal 2-2 receives the H packet from only one communication terminal A, it requests the terminal ID assignment using the communication route via the communication terminal A.

  In this way, when the child terminal 2 receives H packets from a plurality of terminal devices A, it is sent to the parent terminal 1 via each terminal device A based on the route communication quality of the communication route and the number of hops of the communication route. The communication cost of the communication route to reach is calculated. Then, a communication route is established with the parent terminal 1 via the terminal device A that forms the communication route with the lowest communication cost among the plurality of terminal devices A.

  More specifically, an example of an address request packet transmitted from the child terminal 2-2 via the child terminal 2-1, "reserved terminal ID" is accommodated in the transmission source terminal ID portion, and the transmission destination terminal ID portion includes “T1” is accommodated, and “reservation terminal ID → T1 → M1” is accommodated in the transmission communication route part. Furthermore, the operation code part contains “address request code”, the distribution address part contains “null”, the adjacent terminal part contains “T1”, and the link communication quality part contains “ 3 "is accommodated.

  In the child terminal 2-1 that has received the address request packet transmitted by the child terminal 2-2, the communication processing unit 202 refers to the transmission communication route part of the address request packet, so that the next transmission destination of the address request packet is It is determined that the terminal is the parent terminal 1-1. Then, the communication processing unit 202 rewrites the destination terminal ID part to the terminal ID “M1” of the parent terminal 1-1 that is the next destination, and then transmits the address request packet (S8).

  More specifically, the address request packet 80b transmitted by the child terminal 2-1 is exemplified by “T1” being accommodated in the transmission source terminal ID portion and “M1” being accommodated in the transmission destination terminal ID portion. “Reservation terminal ID → T1 → M1” is accommodated in the route portion. Furthermore, the operation code part contains “address request code”, the distribution address part contains “null”, its adjacent terminal part contains “T1”, and its link communication quality part contains “3”. Is contained.

  In the parent terminal 1-1 that has received the address request packet relayed by the child terminal 2-1, the communication processing unit 202 assigns a terminal ID to the child terminal 2-2 that has transmitted the address request packet. Here, the terminal ID “T2” is assigned to the child terminal 2-2.

  The communication processing unit 202 of the parent terminal 1-1 extracts the adjacent terminal ID “T1” and the link communication quality “3” included in the received address request packet. Since the communication processing unit 202 of the parent terminal 1-1 has the terminal ID “T1” accommodated in the adjacent terminal part of the address request packet, the child terminal 2-2 to which the terminal ID “T2” is assigned is the parent terminal 1 −1, it is determined that communication is possible through a communication route to the child terminal 2-1 corresponding to the terminal ID “T1”. Then, the communication processing unit 202 determines that a communication route (M1 → T1 → T2) from the parent terminal 1-1 to the child terminal 2-2 via the child terminal 2-1 has been established.

  Further, the communication processing unit 202 of the parent terminal 1-1 determines that the link communication quality “3” extracted from the link communication quality unit included in the received address request packet indicates that the child terminal 2-1 and the child terminal 2-2. It is determined that the link communication quality is between. The communication processing unit 202 adds the link communication quality “3” to the route communication quality “5” of the communication route from the parent terminal 1-1 to the child terminal 2-1, so that the parent terminal 1-1 and the child terminal 1-1 are connected. The route communication quality “8” of the communication route with the terminal 2-3 is calculated.

  In the parent terminal 1-1, the table processing unit 201 assigns the terminal ID “T2”, the route communication quality “8”, the number of hops “2”, and the first hop “T1” assigned to the child terminal 2-2. The second hop “T2” is registered in the communication route table TB21.

  Then, the parent terminal 1-1 transmits an address response packet (S9).

  More specifically, an example of the address response packet created by the parent terminal 1-1 includes “M1” in the transmission source terminal ID portion and “T1” in the transmission destination terminal ID portion. The section contains “M1 → T1 → BC”. Furthermore, the operation code part contains “address response code”, the distribution address part contains “T2”, the adjacent terminal part contains “T1”, and the link communication quality part contains “3”. Is contained.

  Then, in the child terminal 2-1 that has received the address response packet transmitted by the parent terminal 1-1, the communication processing unit 202 refers to the transmission communication route part of the address response packet, so that the next transmission of the address response packet is performed. It is determined that the destination is the child terminal 2-2. Then, the communication processing unit 202 rewrites the destination terminal ID part to the broadcast communication code “BC” which is the next destination, and then transmits an address response packet (S10).

  More specifically, the address response packet transmitted by the child terminal 2-1 is exemplified. “T1” is accommodated in the transmission source terminal ID portion, “BC” is accommodated in the transmission destination terminal ID portion, and the transmission communication route The section contains “M1 → T1 → BC”. Furthermore, the operation code part contains “address response code”, the distribution address part contains “T2”, the adjacent terminal part contains “T1”, and the link communication quality part contains “3”. Is contained.

  Then, in the child terminal 2-2 that has received the address response packet relayed by the child terminal 2-1, the communication processing unit 202 has the distribution address “T 2” and the adjacent terminal ID “ T1 ”and link communication quality“ 3 ”are respectively extracted.

  Then, the child terminal 2-2 sets “T2” to the terminal ID of the own terminal. Further, in the child terminal 2-2, the table processing unit 201 registers the transmission link communication quality “3” corresponding to the adjacent terminal ID “T1” in the communicable terminal management table TB1.

  Further, the communication processing unit 202 of the child terminal 2-2 compares the reception link communication quality corresponding to the adjacent terminal ID “T1” with the transmission link communication quality in the communicable terminal management table TB1. Then, the link communication quality (the one with the larger numerical value) having a poor communication state is set as the link communication quality between the child terminal 2-1 and the child terminal 2-2. Here, the link communication quality is “3”.

  Then, as described above, the child terminal 2-2 is determined to be able to construct a communication route of “child terminal 2-2 → child terminal 2-1 → parent terminal 1-1”. Therefore, the table processing unit 201 of the child terminal 2-2 reads the link communication quality with the child terminal 2-1 from the communicable terminal management table TB1. Furthermore, the table processing unit 201 sets the route communication quality “5” between the child terminal 2-1 and the parent terminal 1-1 contained in the communication route portion of the H packet received from the child terminal 2-1 to the child communication 2-1. The link communication quality “3” with the terminal 2-1 is added. The addition result “8” is the route communication quality with the parent terminal 1-1.

  That is, a communication route of “T2 → T1 → M1” is constructed between the child terminal 2-2 and the parent terminal 1-1 with the number of hops “2” and the route communication quality “8”. Therefore, the table processing unit 201 of the child terminal 2-2 stores the terminal ID “M1”, the communication cost “8”, the number of hops “2”, and the first hop “T1” of the parent terminal 1-1 in the communication route table TB22. The second hop “M1” is registered.

  As described above, when the parent terminal 1-1 and the child terminal 2-2 can indirectly communicate with each other via the child terminal 2-1, the H packet transmission process of the child terminal 2-1, the child terminal 2-2. The address request packet transmission process and the address response packet transmission process of the parent terminal 1-1 are executed. Then, by executing these steps, the terminal ID (communication address) of the child terminal 2-2 is set, and between the parent terminal 1-1 and the child terminal 2-2 that can indirectly communicate with each other. A communication route is established on both sides.

  Thus, in the present embodiment, the route communication quality of the communication route, the hop of the communication route, in any of the child terminal 2 that can directly communicate with the parent terminal 1 and the child terminal 2 that can indirectly communicate with the parent terminal 1. The communication route is constructed considering the number. In addition, when the child terminal 2 after startup establishes a communication route with the parent terminal 1 for the first time, without considering the number of remaining records included in the H packet, Prioritize building communication routes.

  Note that the communication route established between the parent terminal 1 and the child terminal 2 is a communication route having a hop number of 3 or more when the child terminal 2 that has established a communication route with the parent terminal 1 transmits an H packet. It can be constructed in the same way as above.

  Next, processing after each child terminal 2 has established a communication route with any one of the parent terminals 1 as described above will be described.

  First, in order to suppress communication traffic of the wireless network, the H packet is a child in which the communication terminal A is set to the parent terminal 1 and the communication terminal A has a communication route to the parent terminal 1 constructed. When it is the terminal 2, it is transmitted from each communication terminal A. And the transmission process of H packet in each communication terminal A is performed for every communication terminal A at a fixed time interval.

  Therefore, the child terminal 2 can generate an H packet from the parent terminal 1 and the child terminal 2 that can communicate directly with each other even after the communication route is established with the parent terminal 1 as described above (FIG. 7A). Reference) is received. When the communication terminal A that has transmitted the H packet is the parent terminal 1, the remaining record number portion of the H packet contains the number of remaining records of the parent terminal 1 that is the transmission source of the H packet. When the communication terminal A that has transmitted the H packet is the child terminal 2, the remaining record number portion of the H packet is the number of remaining records of the parent terminal 1 in which the child terminal 2 that is the transmission source of the H packet constructs a communication route. Is housed.

  Then, in the child terminal 2 that has received the H packet after establishing a communication route with a certain parent terminal 1, the communication processing unit 202 acquires the number of remaining records included in the received H packet. That is, the communication processing unit 202 acquires not only the number of remaining records of the parent terminal 1 that is currently building a communication route with the own terminal, but also the number of remaining records of each of the other parent terminals 1 in the wireless network. it can. Then, the table processing unit 201 of the child terminal 2 calculates the remaining number of records of the parent terminal 1 in the record / cost table TB3 of the table storage unit 101 corresponding to the terminal ID of the other parent terminal 1 in the wireless network. sign up. Here, the parent terminal 1 in which the number of remaining records is registered in the record / cost table TB3 is a terminal that can establish a communication route directly or indirectly with the child terminal 2. The record cost table TB3 is updated to the latest remaining record number every time an H packet is received.

  Further, in the child terminal 2 that has received the H packet after establishing a communication route with a certain parent terminal 1, the communication processing unit 202 determines the communication route of each communication route based on the route communication quality and the number of hops as described above. Calculate communication costs. The table processing unit 201 of the child terminal 2 registers each communication cost in the record / cost table TB3 of the table storage unit 101 corresponding to each terminal ID of the other parent terminal 1 in the wireless network.

  Then, the communication processing unit 202 of the child terminal 2 that establishes a communication route with the parent terminal 1 monitors the record / cost table TB3 and switches the parent terminal 1 that establishes the communication route with the own terminal. Judging whether or not.

  For example, the communication processing unit 202 of the child terminal 2-2 that establishes a communication route with the parent terminal 1-1 monitors the number of remaining records of the parent terminal 1-1, and the remaining number of the parent terminal 1-1. The number of records is compared with a threshold value K1 (first threshold value). When the number of remaining records of the parent terminal 1-1 exceeds the threshold value K1, the communication route established with the parent terminal 1-1 is maintained.

  However, when the number of remaining records of the parent terminal 1-1 becomes equal to or less than the threshold value K1, the communication processing unit 202 of the child terminal 2-2 determines the remaining records of other parent terminals 1 registered in the record / cost table TB3. The number is compared with a threshold value K2 (second threshold value). Of the one or more other parent terminals 1 whose remaining records exceed the threshold K2, the other parent terminal 1, for example, the parent terminal 1, with the lowest communication cost registered in the record cost table TB3. -2. Note that the threshold value K1 and the threshold value K2 may be the same value or different values.

  Then, the communication processing unit 202 of the child terminal 2-2 transmits an address request packet to the parent terminal 1-2 in order to establish a new communication route with the parent terminal 1-2. Thereafter, the child terminal 2-2 receives the address response packet from the parent terminal 1-2 in the same manner as described above, and sets the new terminal ID assigned from the parent terminal 1-2 to the own terminal. That is, the child terminal 2-2 switches the parent terminal 1 that establishes a communication route with the own terminal from the parent terminal 1-1 to the parent terminal 1-2.

  In this way, the child terminal 2 whose number of remaining records of the parent terminal 1 for which the own terminal is building a communication route is reduced, is a new communication route with another parent terminal 1 that has a surplus in the number of remaining records. Build up. Therefore, the child terminals 2 that cannot communicate with the parent terminal 1 can be suppressed without the child terminals 2 being concentrated under the control of the specific parent terminal 1.

  Further, even when the number of remaining records of the parent terminal 1-1 is equal to or less than the threshold K1, if the number of remaining records of all the other parent terminals 1 registered in the record / cost table TB3 is equal to or less than the threshold K2, The child terminal 2-2 maintains a communication route established with the parent terminal 1-1.

(Embodiment 2)
The configuration of the multi-hop communication system of the present embodiment is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

  First, the child terminal 2 of the present embodiment that has established a communication route with the parent terminal 1 recognizes whether or not the own terminal functions as a relay terminal in the wireless network. Here, in communication between the parent terminal 1 and the child terminal 2, the child terminal 2 that relays communication packets is referred to as a relay terminal.

  Specifically, the communication packet transmitted and received by the communication terminal A includes information related to the communication route of the communication packet (the communication route portion of the H packet shown in FIG. 7A and shown in FIG. 7B). Transmission request route part of address request packet and address response packet). The information regarding the communication route is represented by the terminal IDs of the communication terminals A passing through the communication route being arranged in order, and the child terminal 2 refers to the communication packet received from the other communication terminal A, It is possible to determine whether or not the own terminal is a relay terminal. That is, in the communication route, if the terminal ID of the terminal is not at the end and is in the middle, the terminal is a relay terminal.

  As described above, when the communication terminal A relays and forwards a communication packet received from another communication terminal A, the communication terminal A determines that the terminal is a relay terminal, but does not always continue to be a relay terminal. For example, when the other child terminal 2 leaves the wireless network or changes to another communication route due to a change in transmission path condition, it may not be a relay terminal. Therefore, it is only necessary to determine that the own terminal is a relay terminal until a predetermined time Y1 elapses after the communication packet received from another communication terminal A is relay-transferred. Specifically, when the communication packet is relayed and transferred, the timing of the time Y1 is started. When a new communication packet is relayed and transferred before the time Y1 elapses, the timing of the time Y1 is restarted. On the other hand, if a new communication packet is not relayed and transferred before the time Y1 elapses, it is determined that the own terminal is not a relay terminal.

  Then, the child terminal 2 that has determined that its own terminal is a relay terminal, even if the number of remaining records of the parent terminal 1 with which the own terminal constructs a communication route becomes equal to or less than the threshold value K1, Maintain communication routes built between them.

  In the wireless network, when the child terminal 2 functioning as a relay terminal switches the parent terminal 1 for constructing a communication route, another child terminal 2 using the child terminal 2 as a relay terminal (hereinafter, There is a risk that the communication route of the subordinate terminal) will be lost. Further, when the child terminal 2 functioning as a relay terminal switches the parent terminal 1 for constructing the communication route, the communication route of the subordinate terminal is also changed, and the child terminal 2 is concentrated under the specific parent terminal 1. There is also a fear. Furthermore, there is a possibility that the subordinate terminal that has lost the communication route cannot construct the communication route when there is no new parent terminal 1 capable of communication.

  However, in the present embodiment, as described above, the child terminal 2 functioning as a relay terminal is in contact with the parent terminal 1 regardless of the number of remaining records of the parent terminal 1 constructing the communication route. Since the established communication route is maintained, the above problem does not occur. That is, the reliability of communication within the wireless network can be maintained.

(Embodiment 3)
The configuration of the multi-hop communication system of the present embodiment is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

  First, the child terminal 2 of the present embodiment that has established a communication route with the parent terminal 1 recognizes whether or not the own terminal functions as a relay terminal in the wireless network. Here, in communication between the parent terminal 1 and the child terminal 2, the child terminal 2 that relays communication packets is referred to as a relay terminal.

  Specifically, the communication packet transmitted and received by the communication terminal A includes information related to the communication route of the communication packet (the communication route portion of the H packet shown in FIG. 7A and shown in FIG. 7B). Transmission request route part of address request packet and address response packet). The information regarding the communication route is represented by the terminal IDs of the communication terminals A passing through the communication route being arranged in order, and the child terminal 2 refers to the communication packet received from the other communication terminal A, It is possible to determine whether or not the own terminal is a relay terminal. Furthermore, the child terminal 2 can grasp the number of other child terminals 2 (hereinafter referred to as subordinate terminals) using the own terminal as a relay terminal by referring to the communication packet received from the other communication terminal A. . The slave terminal 2 that is not a relay terminal has “0” slave terminals.

  The subordinate terminal may not be a subordinate terminal when another child terminal 2 leaves the wireless network or changes to another communication route due to a change in the transmission path condition. Therefore, the child terminal 2 may determine that the other child terminal 2 is a subordinate terminal until a predetermined time Y2 elapses after the communication packet received from the other child terminal 2 is relayed and transferred. Specifically, the child terminal 2 stores the subordinate terminal table TB4 shown in FIG. The subordinate terminal table TB4 registers the terminal ID of the subordinate terminal and the final time when the communication packet from the subordinate terminal is relayed and transferred. Then, the child terminal 2 determines that the child terminal 2 whose terminal ID is registered in the dependent terminal table TB4 is a dependent terminal. Then, when the time Y2 has elapsed from the last time when the communication packet was relayed and transferred, the record of the subordinate terminal may be deleted.

  Then, the child terminal 2 of the present embodiment varies the threshold values K1 and K2 according to the number of subordinate terminals using the own terminal as a relay terminal.

  For example, if the number of subordinate terminals increases, the threshold K1 is lowered and further the threshold K2 is raised, thereby reducing the probability that the child terminal 2 switches the communication route. On the other hand, if the number of dependent terminals decreases, the probability that the child terminal 2 switches the communication route is increased by increasing the threshold value K1 and further decreasing the threshold value K2. Note that the variation pattern of the threshold values K1 and K2 may be either continuous or stepwise with respect to the variation in the number of subordinate terminals.

  Here, when the child terminal 2 functioning as a relay terminal in the wireless network switches the parent terminal 1 for constructing the communication route, the communication route of the subordinate terminal may be lost. Further, when the child terminal 2 functioning as a relay terminal switches the parent terminal 1 for constructing the communication route, the communication route of the subordinate terminal is also changed, and the child terminal 2 is concentrated under the specific parent terminal 1. There is also a fear. Furthermore, there is a possibility that the subordinate terminal that has lost the communication route cannot construct the communication route when there is no new parent terminal 1 capable of communication.

  Therefore, the child terminal 2 functioning as a relay terminal can determine the communication route established with the parent terminal 1 regardless of the number of remaining records of the parent terminal 1 that has established a communication route with the own terminal. It can be considered that the above problem can be solved by maintaining the above. However, this method may not solve the problem of suppressing the occurrence of the child terminal 2 that cannot communicate with the parent terminal 1.

  However, in the present embodiment, the child terminal 2 functioning as a relay terminal has a communication route established by the own terminal according to the number of subordinate terminals using the own terminal as a relay terminal as described above. The probability of switching the parent terminal 1 is varied. Therefore, the reliability of communication in the wireless network is maintained, and the occurrence of the child terminal 2 that cannot communicate with the parent terminal 1 is suppressed without the child terminals 2 being concentrated under the specific parent terminal 1. can do.

  Note that either a configuration in which both threshold values K1 and K2 are changed or a configuration in which only one of threshold values K1 and K2 is changed in accordance with the number of subordinate terminals may be used.

(Embodiment 4)
The configuration of the multi-hop communication system of the present embodiment is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

  First, it is assumed that the child terminal 2-2 establishes a communication route with the parent terminal 1-1. Then, the communication processing unit 202 of the child terminal 2-2 monitors the number of remaining records of the parent terminal 1-1 and compares the number of remaining records of the parent terminal 1-1 with a threshold value K1 (first threshold value). When the number of remaining records of the parent terminal 1-1 exceeds the threshold value K1, the communication route established with the parent terminal 1-1 is maintained.

  However, when the number of remaining records of the parent terminal 1-1 becomes equal to or less than the threshold value K1, the communication processing unit 202 of the child terminal 2-2 determines the remaining records of other parent terminals 1 registered in the record / cost table TB3. The number is compared with a threshold value K2 (second threshold value). Of the one or more other parent terminals 1 whose remaining records exceed the threshold K2, the other parent terminal 1, for example, the parent terminal 1, with the lowest communication cost registered in the record cost table TB3. -2. Note that the threshold value K1 and the threshold value K2 may be the same value or different values.

  Then, the communication processing unit 202 of the child terminal 2-2 transmits an address request packet to the parent terminal 1-2 after transmitting the parent terminal change notification packet to the parent terminal 1-1.

  In the parent terminal 1-1 that has received the parent terminal change notification packet from the child terminal 2-2, the table processing unit 201 performs communication route information regarding the child terminal 2-2 in the communication route table TB21 (see FIG. 4A). And increment the remaining record count by one.

  In addition, the child terminal 2-2 that has transmitted the address request packet to the parent terminal 1-2 receives the address response packet from the parent terminal 1-2 in the same manner as described above, and receives the new terminal ID assigned from the parent terminal 1-2. Set to own terminal. That is, the child terminal 2-2 switches the parent terminal 1 that establishes a communication route with the own terminal from the parent terminal 1-1 to the parent terminal 1-2.

  On the other hand, when the child terminal 2-2 transmits only the address request packet to the parent terminal 1-2 without transmitting the parent terminal change notification packet to the parent terminal 1-1, the parent terminal 1-1 It takes time to detect that the child terminal 2-2 has left the subordinate. For example, the child terminal 2 transmits a routing protocol packet such as a hello packet or a route notification packet at regular intervals. The route notification packet stores communication route information established between itself and the parent terminal 1, and is transmitted to the parent terminal 1 where the own terminal constructs a communication route. Then, the parent terminal 1-1 detects that the child terminal 2-2 has left the subordinate of its own terminal because it cannot receive a routing protocol packet such as a hello packet or a route notification packet from the child terminal 2-2 for a certain period. it can. That is, the parent terminal 1-1 detects the withdrawal of the child terminal 2-2 after a certain period of time has elapsed since the child terminal 2-2 actually left the subordinate of the own terminal. Therefore, until the parent terminal 1-1 detects the withdrawal of the child terminal 2-2, the number of child terminals 2 subordinate to the parent terminal 1-1 is reduced more than necessary, or the subordinates of the parent terminal 1-2 are subordinate. It is conceivable that the number of child terminals 2 in the network increases more than necessary.

  In the present embodiment, as described above, the child terminal 2 that switches the parent terminal 1 that constructs the communication route transmits the parent terminal change notification packet to the old parent terminal 1 that constructs the current communication route. The address request packet is transmitted to the new parent terminal 1. Therefore, the old parent terminal 1 can detect in real time that the subordinate child terminal 2 has left the subordinate of its own terminal, and can immediately transmit a hello packet in which the number of remaining records in the route table TB21 is changed to the latest value. . That is, it is possible to notify the child terminal 2 that the number of remaining records has increased, and it is possible to prevent an unnecessarily large number of child terminals 2 from leaving the subordinates of the own terminal. That is, it is possible to prevent the number of child terminals 2 subordinate to the old parent terminal 1 from being unnecessarily reduced and the number of child terminals 2 subordinate to the new parent terminal 1 from being increased more than necessary. The number of child terminals 2 under 1 can be made more uniform.

(Embodiment 5)
The configuration of the multi-hop communication system of the present embodiment is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted. Hereinafter, the construction of a communication route in the wireless network will be described using the sequence of FIG.

  First, it is assumed that the child terminal 2-2 establishes a communication route with the parent terminal 1-1. Then, the communication processing unit 202 of the child terminal 2-2 monitors the number of remaining records of the parent terminal 1-1 and compares the number of remaining records of the parent terminal 1-1 with a threshold value K1 (first threshold value). When the number of remaining records of the parent terminal 1-1 exceeds the threshold value K1, the communication route established with the parent terminal 1-1 is maintained.

  However, when the number of remaining records of the parent terminal 1-1 becomes equal to or less than the threshold value K1, the communication processing unit 202 of the child terminal 2-2 determines the remaining records of other parent terminals 1 registered in the record / cost table TB3. The number is compared with a threshold value K2 (second threshold value). Of the one or more other parent terminals 1 whose remaining records exceed the threshold K2, the other parent terminal 1, for example, the parent terminal 1, with the lowest communication cost registered in the record cost table TB3. -2. Note that the threshold value K1 and the threshold value K2 may be the same value or different values.

  Then, the communication processing unit 202 of the child terminal 2-2 transmits a parent terminal changeable packet to the parent terminal 1-1 (S21).

  In the parent terminal 1-1 that has received the parent terminal changeable packet from the child terminal 2-2, the communication processing unit 201 can change the parent terminal if the number of remaining records in the communication route table TB21 of the own terminal is equal to or less than the threshold value K1. The parent terminal change permission packet is transmitted to the child terminal 2-2 that is the transmission source of the packet (S22). Further, the table processing unit 201 of the parent terminal 1-1 deletes the communication route information regarding the child terminal 2-2 in the communication route table TB21 (see FIG. 4A), and increases the number of remaining records by one (increment). To do).

  Then, after receiving the parent terminal change permission packet from the parent terminal 1-1, the child terminal 2-2 transmits an address request packet to the parent terminal 1-2 (S23), and then, from the parent terminal 1-2, the address is the same as described above. The response packet is received, and the new terminal ID assigned by the parent terminal 1-2 is set in the own terminal (S24). That is, the child terminal 2-2 switches the parent terminal 1 that establishes a communication route with the own terminal from the parent terminal 1-1 to the parent terminal 1-2.

  In the present embodiment, as described above, the child terminal 2 that switches the parent terminal 1 that constructs the communication route transmits the parent terminal changeable packet to the old parent terminal 1 that constructs the current communication route. The old parent terminal 1 that has received the parent terminal changeable packet transmits a parent terminal change permission packet to the child terminal 2 if the number of remaining records of the own terminal is equal to or less than the threshold value K1. After receiving the parent terminal change permission packet from the old terminal 1, the child terminal 2 transmits an address request packet to the new parent terminal 1. Therefore, since the old parent terminal 1 transmits a parent terminal change permission packet based on the number of remaining records of the own terminal, it is possible to detect in real time that the subordinate child terminal 2 leaves the subordinate of the own terminal, and is unnecessary. In addition, it is possible to further prevent many child terminals 2 from leaving the subordinates of the own terminal.

  In the case of the fourth embodiment, the increase in the number of remaining records of the old parent terminal 1 can be known by the child terminal 2 receiving the hello packet from the old parent terminal 1. However, when the number of hops of the communication route established with the old parent terminal 1 is large, a certain amount of time is required for the child terminal 2 to receive information about the latest number of remaining records of the old parent terminal 1. is there.

  On the other hand, in this embodiment, the parent terminal 1 determines in real time whether or not the communication route of the child terminal 2 can be changed according to the number of remaining records of the own terminal. Therefore, it is possible to prevent the number of child terminals 2 subordinate to the old parent terminal 1 from being unnecessarily reduced and the number of child terminals 2 subordinate to the new parent terminal 1 from being increased more than necessary. The number of child terminals 2 under 1 can be made more uniform.

  In each of the above embodiments, the parent terminal 1 and the child terminal 2 may constitute a PLC network, which is a communication network constructed using the power line carrier communication technology, and in this case, the same effect as described above is obtained. be able to.

A communication terminal 1 parent terminal 2 child terminal 10 storage unit 101 table storage unit 20 control unit 201 table processing unit 202 communication processing unit

Claims (9)

  In the multi-hop communication method in which each of the plurality of parent terminals and each of the plurality of child terminals perform multi-hop communication with each other, and the child terminal establishes a communication route with one parent terminal, In the child terminal that is establishing a communication route with the parent terminal, the remaining number of communication routes that the first parent terminal can establish with the child terminal is equal to or less than a first threshold value. A communication route is established with the second parent terminal in which the remaining number of communication routes that can be established with the child terminal exceeds a second threshold value. . Each of the plurality of parent terminals and each of the plurality of child terminals perform multi-hop communication with each other, the child terminal in a multi-hop communication system that establishes a communication route with one parent terminal,
The parent terminal includes information on the number of remaining records indicating the remaining number of communication routes that can be established with the child terminal, and transmits a hello packet to notify the existence of the own terminal,
The child terminal that establishes a communication route with the parent terminal includes the remaining record number information of the parent terminal that establishes a communication route with the own terminal, and informs the survival of the own terminal Send
When the child terminal that has not established a communication route with the parent terminal receives a plurality of the hello packets within a predetermined time, the parent terminal that is the transmission source of the hello packet, and the hello packet The communication cost is calculated based on at least the communication quality of the communication route existing between the parent terminal and the parent terminal for which the child terminal as the transmission source has established the communication route. Build a communication route with the lowest parent terminal,
The child terminal constructing a communication route with the first parent terminal is the first parent terminal or the child terminal constructing a communication route with the first parent terminal. A communication route between the second parent terminal or the second parent terminal when the number of remaining records of the first parent terminal is less than or equal to a first threshold based on the hello packet received from If the number of remaining records of the second parent terminal based on the hello packet received from the child terminal constructing the network exceeds a second threshold, a communication route with the second parent terminal A multi-hop communication system characterized by constructing.   The child terminal that is establishing a communication route with the first parent terminal, when the own terminal is a relay terminal between the other child terminal and the parent terminal, 3. The multi-hop according to claim 2, wherein a communication route is continuously established with the first parent terminal even if the number of remaining records of the parent terminal becomes equal to or less than the first threshold. Communications system.   The child terminal that is establishing a communication route with the first parent terminal, when the own terminal is a relay terminal between the other child terminal and the parent terminal, The multi-hop communication system according to claim 2, wherein the first threshold is increased as the number of the other child terminals used as relay terminals decreases.   The child terminal that is establishing a communication route with the first parent terminal, when the own terminal is a relay terminal between the other child terminal and the parent terminal, 5. The multi-hop communication system according to claim 2, wherein the second threshold value is lowered as the number of the other child terminals used as relay terminals decreases. The child terminal constructing a communication route with the first parent terminal, when the number of remaining records of the first parent terminal is less than or equal to the first threshold value, If the remaining number of records of the terminal exceeds the second threshold, a parent terminal change notification packet is transmitted to the first parent terminal, and a communication route is established with the second parent terminal. ,
The multi-hop communication system according to claim 2, wherein the first parent terminal that has received the parent terminal change notification packet increments the number of remaining records of the own terminal. The child terminal constructing a communication route with the first parent terminal, when the number of remaining records of the first parent terminal is less than or equal to the first threshold value, If the number of remaining records of the terminal exceeds the second threshold, a parent terminal changeable packet is transmitted to the first parent terminal,
The first parent terminal that has received the parent terminal changeable packet transmits a parent to the child terminal that is the transmission source of the parent terminal changeable packet if the number of remaining records of the terminal is equal to or less than the first threshold. While sending a terminal change permission packet, increment the number of remaining records of its own terminal,
The multi-hop communication system according to claim 2, wherein the child terminal that has received the parent terminal change permission packet establishes a communication route with the second parent terminal. The child terminal in which a parent terminal and a child terminal establish a communication route with each other to perform multi-hop communication, and a communication route is established with the first parent terminal. When the remaining number of communication routes that can be established with the child terminal is less than or equal to the first threshold value, the remaining number of communication routes that can be established with the child terminal is greater than the second threshold value. A communication terminal used for the parent terminal of a multi-hop communication system that establishes a communication route with two of the parent terminals,
A communication terminal including a remaining record number information indicating a remaining number of communication routes that can be established with the child terminal, and transmitting a hello packet that notifies the existence of the terminal itself. A communication terminal used for a child terminal that performs multi-hop communication by establishing a communication route with a parent terminal,
When a communication route is established with the first parent terminal, the remaining number of communication routes that the first parent terminal can establish with the child terminal is equal to or less than a first threshold. A communication terminal is configured to establish a communication route with the second parent terminal in which the remaining number of communication routes that can be established with the child terminal exceeds a second threshold value.

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