JP2013017153A - 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 which dispense with communication between master terminals and centralized control of a server, etc. and suppressing interference of a wireless packet by leakage power from another communication cell.SOLUTION: One master terminal 1 and a plurality of slave terminals 2 construct communication cells C1, C2... for performing multi-hop communication. When the level of interference in the communication between a communication cell which the master terminal belongs to and other communication cells of the same inner-cell channel exceeds a specified threshold value, the master terminal 1 selects a wireless channel with minimum interference level, out of one or more wireless channels that are not serving as inner-cell channels in the communication cell which the master terminal belongs to and the neighboring communication cells thereof. Then, the master terminal sets the selected wireless channel as the inner-cell channel of the communication cell which the master terminal belongs to. The interference level is based on the frequency distance between each inner-channel of the communication cell which the master terminal belongs to and the neighboring communication cells.

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.

  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 A communication route between them can be established.

  In recent years, for example, there is a communication system in which a plurality of parent terminals are installed for each predetermined range and each parent terminal communicates with a plurality of child terminals existing in the vicinity, like an automatic remote meter reading system. Also in this type of communication system, it has been proposed to construct a communication network using the multi-hop communication for communication between a parent terminal and a child terminal.

  In the communication network using the parent terminal and the child terminal, the parent terminal provided for each predetermined range is directly from each of a plurality of surrounding child terminals or indirectly using another child terminal as a relay terminal. , Obtain predetermined information. That is, a communication cell by multi-hop communication is formed by one parent terminal and a plurality of child terminals from which the parent terminal obtains predetermined information, and a plurality of communication cells are provided to construct a plurality of communication networks. Has been.

  In such a communication network using a parent terminal and a child terminal, wireless packets are transmitted and received by selectively selecting one of a plurality of wireless channels provided in a predetermined frequency band. . Therefore, when a plurality of communication cells are provided, if communication is performed between adjacent communication networks using the same wireless channel, wireless packets may interfere with each other and communication quality may deteriorate. Therefore, in order to suppress interference between communication cells, a method of assigning a radio channel to each communication cell has been proposed (see, for example, Patent Documents 3 to 6).

  For example, when a parent terminal is connected to a higher-level network composed of an optical fiber network or the like, radio channels used by the parent terminal are concentrated on the server side of the higher-level network based on position information from the GPS provided in each parent terminal. It is conceivable to manage it. In this case, when the distance between the parent terminals is short, a different radio channel is assigned to each communication cell.

  There is also a method of setting so that adjacent parent terminals communicate with each other and use different wireless channels.

  Such dynamic allocation of radio channels is a multi-coloring problem of graph theory and is also an NP complete problem, so that it is difficult to derive a complete solution. Has been studied extensively in the field of mathematical graphs.

JP 2006-67557 A JP 2008-244679 A JP 2007-158485 A JP 2004-96148 A JP 2001-128224 A Japanese Patent Laid-Open No. 10-31476

  However, in a communication network using multi-hop communication as described above, each child terminal performs communication by relaying radio packets of different child terminals, so communication is performed in comparison with the case where the parent terminal and child terminals communicate directly. The physical spatial distance formed by the network increases. For this reason, even if the parent terminals are far from each other, the child terminals connected to each parent terminal are often close to each other, and the wireless packet may interfere only with the position information of the parent terminal. Cannot be reduced sufficiently. Further, when the parent terminals are located far from each other, the parent terminals cannot communicate with each other, and thus there is a problem that the possibility of radio packet interference cannot be sufficiently reduced.

  Furthermore, even when different radio channels are used between adjacent communication cells, there is a possibility that radio packets may interfere due to leakage power from adjacent radio channels when the frequency distance between the radio channels is short. .

  The present invention has been made in view of the above-described reasons, and its purpose is to eliminate the interference of radio packets due to leakage power from other communication cells without requiring communication between parent terminals or intensive management of a server or the like. Is to provide a multi-hop communication method, a multi-hop communication system, and a communication terminal.

  The multi-hop communication method of the present invention is a communication cell in which one parent terminal and one to a plurality of child terminals perform multi-hop communication using one wireless channel selected from a plurality of wireless channels as an intra-cell channel. The child terminal detects the channel in the cell in each of the communication cells adjacent to the communication cell to which the own terminal belongs, and notifies the parent terminal of the communication cell to which the own terminal belongs, and When the degree of interference in communication between the communication cell to which the own terminal belongs and another communication cell having the same intra-cell channel exceeds a predetermined threshold, the communication cell to which the own terminal belongs and the adjacent communication cell From one or a plurality of radio channels that are not used for the intra-cell channel, the communication cell to which the terminal belongs and each of the adjacent communication cells Interference level based on the frequency distance between the Le in the channel selects a radio channel to be minimized, and sets the selected radio channel in the cell channel communication cell to which the own terminal belongs.

  The multi-hop communication system of the present invention is a communication cell in which one parent terminal and one to a plurality of child terminals perform multi-hop communication using one wireless channel selected from a plurality of wireless channels as an intra-cell channel. The parent terminal and the child terminal include communication cell information for identifying a communication cell to which the own terminal belongs, and transmit a hello packet that notifies the existence of the own terminal using the intra-cell channel. When the communication cell indicated by the communication cell information of the hello packet received using the intra-cell channel is different from the first communication cell to which the terminal belongs, the child terminal receives the hello packet Detection information notifying that the second communication cell that includes the communication cell information and uses the same intra-cell channel is detected is the first communication set. When the hello packet is received by sequentially switching the plurality of radio channels, the communication cell information of the received hello packet and the channel related to the radio channel that has received the hello packet And channel usage information for notifying the intra-cell channel used by the third communication cell existing around the first communication cell, to the parent terminal belonging to the first communication cell, The parent terminal belonging to the first communication cell derives the degree of interference in communication between the first communication cell and the second communication cell based on the received detection information, and the degree of interference. Exceeds the predetermined threshold value, the first and third communication cells are not used for the intra-cell channel based on the channel usage information. The unused channel that is the channel is selected from the unused channels that have the lowest interference level based on the frequency distance between the first and third communication cells and the used channel that is the intra-channel channel. An unused channel is set as the intra-cell channel of the first communication cell.

  In this invention, it is preferable that the said parent terminal weights the said interference level according to the number of the communication cells using each of the said use channel based on the said channel utilization information.

  In this invention, it is preferable that the parent terminal removes adjacent channels, which are radio channels adjacent to the used channels, from the unused channels.

  In the present invention, the parent terminal and the child terminal transmit the hello packet including the channel usage information created in the communication cell to which the terminal belongs, using the intra-cell channel, and the first communication cell The child terminal belonging to the mobile station sequentially switches the plurality of radio channels and uses the channel use information included in the hello packet received from the third communication cell as the parent terminal belonging to the first communication cell. The parent terminal belonging to the first communication cell uses the fourth communication cell existing around the third communication cell based on the channel usage information included in the hello packet. Preferably, the intra-cell channel is detected, and the intra-cell channel used by the fourth communication cell is excluded from the unused channel.

  In the present invention, when there is no unused channel, the parent terminal belonging to the first communication cell uses N as the number of the third communication cells using each radio channel and uses each radio channel. The number of the fourth communication cells is M, the weighting factor of 0 to 1 is β, the evaluation function for each radio channel is derived as N + βM, and the radio channel that minimizes the evaluation function is set as the intra-cell channel. It is preferable.

  In this invention, the master terminal belonging to the first communication cell sets the used channel as the intra-cell channel in the first, third, and fourth communication cells, and the fourth channel for the unused channel. The interference level of the intra-cell channel of the communication cell is preferably weighted lighter than the interference level of the intra-cell channel of the third communication cell for the unused channel.

  In the present invention, each of the parent terminals is set with a priority, and when the degree of interference exceeds a predetermined threshold, whether to set the unused channel as the intra-cell channel based on the priority. It is preferable to determine whether or not.

  In the present invention, each radio channel is set with a probability according to a predetermined probability density function, and the parent terminal sets the unused channel to the intra-cell channel based on the probability of the unused channel. It is preferable to determine whether or not to set.

  In the present invention, it is preferable that the probability density function is a function having a radio channel identification number and a priority set for each of the parent terminals as variables.

  In this invention, the parent terminal, the probability of the unused channel that the degree of interference in the communication between the first communication cell and the second communication cell has exceeded a predetermined threshold in the past, It is preferable to change the unused channel in a direction not to be set as the intra-cell channel.

  The communication terminal according to the present invention includes a plurality of communication cells in which one parent terminal and one to a plurality of child terminals perform multi-hop communication using one wireless channel selected from a plurality of wireless channels as an intra-cell channel. A communication terminal used for the parent terminal of the constructed multi-hop communication system, wherein the detection result of the intra-cell channel in each of the communication cells adjacent to the communication cell to which the terminal belongs belongs to the communication cell to which the terminal belongs. When acquired from the child terminal, based on the acquired detection result, when the degree of interference in communication between the communication cell to which the own terminal belongs and the other communication cell having the same channel in the cell exceeds a predetermined threshold, From one or a plurality of radio channels not used for the intra-cell channel in the communication cell to which the terminal belongs and the adjacent communication cell. A radio channel that minimizes an interference level based on a frequency distance between each of the communication cell to which the terminal belongs and the adjacent intra-cell channel is selected, and the communication cell to which the terminal belongs belongs to the selected radio channel The channel is set to the intra-cell channel.

  The communication terminal according to the present invention includes a plurality of communication cells in which one parent terminal and one to a plurality of child terminals perform multi-hop communication using one wireless channel selected from a plurality of wireless channels as an intra-cell channel. A communication terminal used as the child terminal of the constructed multi-hop communication system, detecting the intra-cell channel in each of the communication cells adjacent to the communication cell to which the own terminal belongs, and the communication cell to which the own terminal belongs It is characterized by notifying the parent terminal.

  As described above, the present invention does not require communication between parent terminals or intensive management of servers and the like, and has the effect of suppressing radio packet interference due to leakage power from other communication cells. is there.

1 is a configuration diagram illustrating an outline of a system according to a first embodiment. 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 an adjacent 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 detection information management table same as the above. (A) (b) (c) It is a figure which shows the format of a communication packet same as the above. It is a sequence diagram which shows a communication sequence same as the above. It is a flowchart figure which shows the channel change process in a cell same as the above. 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 a channel information management table same as the above. It is a channel block diagram which shows the use condition of a radio channel same as the above. It is a table figure which shows a response | compatibility of a frequency distance-separation index | exponent same as the above. FIG. 6 is a channel configuration diagram illustrating a usage state of a wireless channel according to the second embodiment. FIG. 10 is a channel configuration diagram illustrating a usage state of a wireless channel according to the fourth 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 K. 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. Furthermore, when individually identifying the parent terminal 1, the parent terminals 1-1, 1-2, 1-3, 1-4,. . . When the child terminals 2 are individually identified using the codes of the child terminals 2-1, 2-2, 2-3,. . . Is used.

  The child terminal 2 has a function of wirelessly transmitting predetermined information about each dwelling unit K to one parent terminal 1. The parent terminal 1 has a function of acquiring predetermined information about each dwelling unit K wirelessly from the plurality of child terminals 2 and transmitting the acquired predetermined information to an upper management apparatus (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 at each dwelling unit K from the child terminal 2. Moreover, the remote monitoring system which monitors the state of the apparatus in each dwelling unit K, when the parent terminal 1 transmits / receives the preset predetermined information between the child terminals 2, and the state of the apparatus in each dwelling unit K 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.

  Further, this multi-hop communication system is a small-scale wireless network including one parent terminal 1 and one to a plurality of child terminals 2 that transmit predetermined information directly or indirectly to the parent terminal 1. A communication cell has been constructed. That is, in this embodiment, a plurality of communication cells C1, C2, C3, C4,. . . Is attached. The parent terminal 1 in each communication cell alternatively selects a communication channel used for transmission / reception of communication packets from a plurality of radio channels having different frequencies. The child terminal 2 transmits and receives communication packets using the communication channel selected by the parent terminal 1 to which the own terminal belongs. That is, the parent terminal 1 and the child terminal 2 belonging to the same communication cell transmit and receive wireless packets using the same frequency wireless channel. This one radio channel used for communication between the parent terminal 1 and the child terminal 2 in each communication cell is referred to as an intra-cell channel. In this embodiment, radio channels Ch1, Ch2,... Having different frequencies are set as radio channels that can be used by each communication terminal A.

  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 (parent terminal 1 or child terminal 2 which can communicate 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 the present embodiment, the parent terminals 1-1, 1-2, 1-3,. . . . Terminal IDs “M1”, “M2”, “M3”. . . Are pre-allocated. 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.

  Each communication cell is assigned a unique communication cell ID, and the communication terminal A transmits the communication packet including the communication cell ID of the communication cell to which the terminal belongs. In the present embodiment, the terminal ID of the parent terminal 1 belonging to the communication cell is used as the communication cell ID, and the communication cells C1, C2, C3,. . . . The communication cell IDs of “M1”, “M2”, “M3”,. . . . Is used. This communication ID corresponds to the communication cell information of the present invention.

  The table storage unit 101 of the parent terminal 1 and the child terminal 2 stores the adjacent terminal management table TB11 shown in FIG. 3, and the table storage unit 101 of the parent terminal 1 stores the detection information management table TB12 shown in FIG. Is done. Further, 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. Is stored.

  As shown in FIG. 3, the adjacent terminal management table TB11 relates to a communication terminal A (hereinafter referred to as the adjacent terminal A) that can directly communicate with the communication terminal A without being relayed by another communication terminal A. Information (neighboring terminal information) is stored in a table format. Specifically, the adjacent terminal management table TB11 includes fields of adjacent terminal ID, terminal type, reception link communication quality, transmission link communication quality, and link communication quality.

  In the adjacent terminal management table TB11, the adjacent terminal ID is a terminal ID assigned to the communication 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.

  When the noise level and interference level at the place where the communication packet is received are different, the bidirectional communication quality in the communication link is different from each other, and the bidirectional communication quality in the communication link is determined by the reception link communication quality and the transmission link communication quality. Composed. 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 adjacent terminal management table TB11, fields of reception link communication quality and transmission link communication quality in the communication terminal A are provided. From the viewpoint of guaranteeing the reliability (reliability) of communication when communication is performed between the communication terminals A and A, one of the reception link communication quality and the transmission communication quality having the worse communication state (link communication quality) The larger communication 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, information (detection information) indicating a communication cell (interference cell) using the same communication channel detected by each child terminal 2 belonging to the same communication cell as the parent terminal 1 is detected in the detection information management table TB12. Stored in table format. Specifically, the detection information management table TB12 is provided with fields of a terminal ID (child terminal ID) of a child terminal that has detected an interference cell, a communication cell ID (interference cell ID) of the detected interference cell, and a detection time. ing. This interference cell corresponds to the second communication cell of the present invention. The detection information management table TB12 is set so that detection information that has passed a certain time from the detection time is periodically deleted.

  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.

  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 2-2 communicates with the parent terminal 1 via the child terminal 2-1, the number of hops is “2”. 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 wireless communication interface unit 30 is a communication interface circuit for performing communication with another communication terminal A using a wireless signal. Then, the wireless communication interface unit 30 uses a wireless channel that is alternatively selected from a plurality of wireless channels having different frequencies as an intra-cell channel, and uses it for transmission / reception of communication packets in the communication cell to which the terminal itself belongs.

  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 management 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 control unit 20 includes a channel switching processing unit 204, an interference detection unit 205, and a change timer unit 206, and determines an intra-cell channel used for transmission / reception of communication packets between the child terminal 2 and the parent terminal 1. -The in-cell channel determination process, which is a process for changing, is executed.

  The table management 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.

  The channel switching processing unit 204 selectively selects an intra-cell channel from a plurality of radio channels based on the interference state of communication between communication cells detected by the interference detection unit 205, and the radio communication interface unit 30 Set to. The interference detection unit 205 detects an interference state between communication cells from the communication packet transmitted from the other communication terminal A received by the communication processing unit 202 and outputs the detected interference state to the channel switching processing unit 204. The change timer unit 206 is a time measuring unit that detects that a predetermined time has come, and notifies the channel switching processing unit 204 of the arrival of the communication channel change timing.

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

  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. 6A shows the format of an H packet, which includes a source terminal ID part, a destination terminal ID part, a cell ID part, an operation code part, a terminal type part, and a communication route part. Composed.

  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 cell ID section accommodates a communication cell ID assigned to the communication cell to which the communication terminal A that has transmitted the H packet belongs. In this embodiment, the parent terminal 1 accommodates the terminal ID of the own terminal, and the child terminal 2 accommodates the terminal ID of the parent terminal 1 of the communication cell to which the own terminal belongs. 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, assume that the child terminal 2-2 establishes a communication route with the parent terminal 1 via the child terminal 2-1, and the route communication quality is 17. In this case, “T2 → T1 → M1; 17” is accommodated in the communication route portion of the H packet transmitted by the child terminal 2-2. The number of hops of this communication route is “2”. 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”.

  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.

  The child terminal 2 for which the communication route to the parent terminal 1 is not established receives this H packet, and obtains the communication cost between the child terminal 2 and the parent terminal 1 based on the route communication quality information of the H packet. The communication route to the parent terminal 1 and the parent terminal 1 with the lowest communication cost is constructed. Since a method for constructing a communication route between the parent terminal 1 and the child terminal 2 is a known technique, a detailed description thereof is omitted.

  Next, a method for determining a communication channel in this wireless network will be described using the sequence of FIG.

  First, when the parent terminal 1 is activated, the channel switching processing unit 204 of the parent terminal 1 sets a predetermined wireless channel in the communication interface unit 30 as a temporary intra-cell channel (step S1). Here, the provisional intra-cell channel is used because it is unclear which radio channel is used as an intra-cell channel in surrounding communication cells, so the intra-cell channel is changed by performing the following operations. It is because it assumed that. When determining the temporary intra-cell channel, for example, the wireless signal strength may be measured for each available wireless channel, and the lowest signal strength may be selected. You may make it select at random from a radio channel.

  Here, when the child terminal 2 arranged around the parent terminal 1 receives the H packet transmitted using the temporary intra-cell channel and the communication quality is higher than the communication cell to which the own terminal belongs. A communication route is established with the parent terminal 1. Thereby, the child terminal 2 arranged around the parent terminal 1 performs direct / indirect communication using the same intra-cell channel as the parent terminal 1, and includes the parent terminal 1 and the child terminal 2. A communication cell is formed. The child terminal 2 stores the terminal ID assigned to the parent terminal 1 of the communication cell to which the own terminal belongs in the storage unit 10 as the communication cell ID.

  In the present embodiment, as shown in FIG. 1, the communication cell C1 includes a parent terminal 1-1 and child terminals 2-1, 2-2, 2-3, and the communication cell C2 includes a parent terminal 1 -2 and child terminals 2-4 and 2-5, and the communication cell C3 includes a parent terminal 1-3 and a child terminal 2-6. Then, the child terminal 2-2 relays the child terminal 2-1, and indirectly communicates with the parent terminal 1-1, and the child terminal 2-1 and the child terminal 2-3 directly communicate with the parent terminal 1-1. Communicate. Further, the child terminal 2-5 relays the child terminal 2-4 to communicate indirectly with the parent terminal 1-2, and the child terminal 2-4 directly communicates with the parent terminal 1-2. The child terminal 2-6 communicates directly with the parent terminal 1-3.

  Here, in each of the parent terminals 1-1, 1-2, and 1-3, a channel Ch1 is set as an intra-cell channel used for transmission and reception of communication packets. Further, there are child terminals 2-1 and 2-5 in a range in which direct communication with the child terminal 2-2 is possible. That is, although the child terminal 2-2 and the child terminal 2-5 are included in different communication cells, wireless packet communication is performed in each communication cell using the same intra-cell channel. Further, a parent terminal 1-1 and a child terminal 2-6 exist in a range where direct communication with the child terminal 2-3 is possible. That is, although the child terminal 2-3 and the child terminal 2-6 are included in different communication cells, wireless packet communication is performed in each communication cell using the same intra-cell channel.

  Here, each child terminal 2 periodically transmits H packets as described above, and receives H packets transmitted from surrounding communication terminals A. In the present embodiment, the H packet transmitted using the intra-cell channel of the communication cell to which the own terminal belongs is received.

  When the child terminal 2 receives the H packet, the child terminal 2 compares the communication cell ID included in the H packet with the communication cell ID of the communication cell (first communication cell) to which the own terminal belongs. In this embodiment, since the terminal ID of the parent terminal 1 is used as the communication cell ID, the communication cell ID included in the H packet and the terminal ID of the parent terminal 1 of the communication cell to which the own terminal belongs are actually used. Compare. As a result of this comparison, if both communication cell IDs are different, a channel indicating that an interference cell (second communication cell) which is another communication cell using the same intra-cell channel as the communication cell to which the terminal belongs is detected. A detection information packet (hereinafter referred to as a D packet) is transmitted directly or indirectly to the parent terminal 1 of the communication cell to which the own terminal belongs. The D packet corresponds to the detection information of the present invention.

  FIG. 6B shows the format of this D packet. The D packet includes a transmission source terminal ID part, a transmission destination terminal ID part, a cell ID part, an operation code part, and a detection information part.

  The transmission packet terminal ID part of the D packet contains the terminal ID of the communication terminal A that has transmitted the D packet. The transmission destination terminal ID section accommodates the terminal ID of the communication terminal A that is the transmission destination of the D packet, and in the case of the D packet, the terminal ID of the parent terminal 1 of the communication cell to which the communication terminal A belongs is accommodated. The cell ID portion accommodates a communication cell ID assigned to a communication cell to which the communication terminal A that transmits the D packet belongs. In this embodiment, the parent terminal 1 accommodates the terminal ID of the own terminal, and the child terminal 2 accommodates the terminal ID of the parent terminal 1 of the communication cell to which the own terminal belongs. The operation code portion accommodates a D packet code. In the detection information part, for example, an interference cell ID that is the same value as the cell ID part included in the received H packet and indicates the communication cell ID of the detected interference cell is accommodated.

  Specifically, in FIG. 7, when the child terminal 2-5 belonging to the communication cell C2 transmits an H packet to the surrounding terminals (step S2), the child terminals 2-2 and 2-4 are respectively connected from the child terminal 2-5. H packets are received. Since the child terminal 2-4 that has received the H packet is included in the same communication cell C2 as the child terminal 2-5, it does not transmit the D packet.

  The child terminal 2-2 that has received the H packet belongs to the communication cell C1, and the communication cell ID included in the H packet is different from the communication cell ID of the communication cell to which the own terminal belongs. It relays 2-1 and transmits it indirectly to the parent terminal 1-1 (step S3).

  Next, the communication processing unit 202 of the parent terminal 1-1 receives the D packet transmitted from the child terminal 2-2 belonging to the communication cell C1 (step S4), and notifies the channel switching processing unit 204 of the D packet. . The channel switching processing unit 204 stores the terminal ID of the child terminal 2-2 that transmitted the D packet, the time when the D packet was received, and the interference cell ID included in the D packet in the detection information management table TB12.

  Specifically, in FIG. 7, when the parent terminal 1-1 receives the D packet transmitted from the child terminal 2-2, the child terminal ID of the child terminal 2-2 and the D packet The interference cell ID and the detection time are stored in the detection information management table TB12 (step S5).

  Next, the channel switching processing unit 204 of the parent terminal 1-1 determines whether it is necessary to switch the channel in the cell to another wireless channel based on each information included in the detection information management table TB12. If there is, switch the channel in the cell. In the present embodiment, the intra-cell channel switching process is started with the reception of the D packet as a trigger. However, the intra-cell channel switching process may be started every predetermined time period. Good.

  First, the interference detection unit 205 of the parent terminal 1-1 refers to each record of the detection information management table TB12 and derives the degree of interference in the intra-channel channel Ch1 for each communication cell. In the present embodiment, the interference detection unit 205 always sets the interference degree of the communication cell whose interference cell ID is stored in the detection information management table TB12 to “1”.

  Then, the parent terminal 1-1 compares the interference degree derived for each communication cell (that is, the number of interfering cells using the intra-cell channel Ch1 of the parent terminal 1-1) with a predetermined threshold, and performs interference. If the number of cells is larger than this threshold value, the intra-cell channel changing process described later is performed. In the present embodiment, “1” is stored in the storage unit 10 in advance as a threshold value.

  Specifically, in FIG. 7, the master terminal 1-1 detects interference after storing various information in the detection information management table TB12 based on the D packet transmitted from the slave terminal 2-2 via the slave terminal 2-1. The unit 205 obtains the number of interference cells. Here, since only the information from the child terminal 2-2 is stored in the detection information management table TB12, and the number of interfering cells is “1”, the intra-cell channel changing process is not performed.

  Next, when the child terminal 2-6 belonging to the communication cell C3 transmits an H packet (step S6), the child terminal 2-3 receives the H packet. The child terminal 2-3 that has received the H packet belongs to the communication cell C1, and the communication cell ID included in the H packet is different from the communication cell ID of the communication cell to which the own terminal belongs. Directly transmit to 1-1 (step S7). At this time, “M3” indicating the communication cell ID (interference cell ID) of the communication cell (interference cell) to which the child terminal 2-6 belongs is included in the detection information portion of the D packet transmitted to the parent terminal 1-1. Contained.

  When the parent terminal 1-1 receives the D packet transmitted from the child terminal 2-3, the child terminal ID of the child terminal 2-3, the interference cell ID in the D packet, and the detection time are detected in the detection information management table TB12. (Step S8). Thereafter, the parent terminal 1-1 obtains the number of the interference cells described above. Here, in the detection information management table TB12, information transmitted from each of the child terminals 2-2 and 2-3 is stored, and the number of interfering cells is “2”, which is lower than the threshold value “1”. Since it is large, the process of changing the channel in the cell is started.

  FIG. 8 is a flowchart showing the intra-cell channel change process.

  First, when performing the process of changing the channel in the cell, the child terminal 2 for which the communication route with the parent terminal 1 is constructed periodically performs a process of sequentially scanning all wireless channels with a predetermined time interval. Always going to. Here, the time for scanning each wireless channel is set to a time longer than the transmission interval of the H packet, and if there is another terminal device A that uses the wireless channel to be scanned, the H packet is surely received. Can be received. Next, when receiving the H packet on each scanned radio channel, the child terminal 2 transmits a channel usage status notification packet indicating the usage status of the radio channel to the parent terminal 1 of the communication cell to which the terminal itself belongs. The channel usage status notification packet corresponds to the channel usage information of the present invention.

  FIG. 9 shows the format of this channel usage status notification packet. The channel usage status notification packet includes a transmission source terminal ID portion, a transmission destination terminal ID portion, a cell ID portion, an operation code portion, and a channel usage information portion.

  The transmission source terminal ID portion of the channel usage status notification packet accommodates the terminal ID of the communication terminal A that has transmitted the channel usage status notification packet. The transmission destination terminal ID section accommodates the terminal ID of the communication terminal A that is the transmission destination of the channel usage status notification packet, and in the case of the channel usage status notification packet, the terminal ID of the parent terminal 1 of the communication cell to which the communication terminal A belongs. Is housed. The cell ID portion accommodates a communication cell ID assigned to a communication cell to which a communication terminal A that transmits a channel usage status notification packet belongs. In this embodiment, the parent terminal 1 accommodates the terminal ID of the own terminal, and the child terminal 2 accommodates the terminal ID of the parent terminal 1 of the communication cell to which the own terminal belongs. The operation code portion contains the code of the channel usage status notification packet. The channel usage information part is a pair of channel information indicating the wireless channel that has received the H packet and a communication cell ID (communication cell information) based on the cell ID part of the H packet received using the wireless channel indicated by the channel information. Is housed. That is, the channel usage status notification packet is an adjacent cell (third communication cell) that is another communication cell existing around the communication cell (first communication cell) to which the parent terminal 1 that has received the channel usage status notification packet belongs. ) And the intra-cell channel used by this neighboring cell. In the present embodiment, the channel information includes a channel number such as “1” in the case of the wireless channel Ch1 and “2” in the case of the wireless channel Ch2. This channel number corresponds to the identification number of the wireless channel of the present invention.

  The table storage unit 101 of the parent terminal 1 further stores a channel information management table TB13 shown in FIG. In the channel information management table TB13, information (channel usage information) indicating the usage status of the channel in the cell in the adjacent cell detected by each child terminal 2 belonging to the communication cell to which the parent terminal 1 belongs is stored in a table format. Yes. Specifically, the channel information management table TB13 includes fields for a child terminal ID, an adjacent cell communication ID (adjacent cell ID), a detection time, and an intra-cell channel (used channel) in the adjacent cell.

  As described above, when the parent terminal 1 receives the channel use state notification packet transmitted from the child terminal 2 belonging to the communication cell to which the own terminal belongs, the parent terminal 1 stores each information included in the packet in the channel information management table TB13.

  Then, in the parent terminal 1 configured as described above, the interference detection unit 205 refers to each record in the channel information management table TB13 and derives the interference level of the switching destination radio channel.

  For example, the interference detection unit 205 of the parent terminal 1-1 refers to the used channel field of the channel information management table TB13 and extracts the used channel. FIG. 11 shows an example of using channel extraction when all the radio channels Ch1 to Ch10 are used, and the channels are used channels Ch1, Ch6, Ch7, and Ch10 (horizontal line area in FIG. 11). The channel used is composed of an intra-cell channel Ch1 of the parent terminal 1-1 and an intra-cell channel in an adjacent cell of the parent terminal 1-1.

  Next, the interference detection unit 205 of the parent terminal 1-1 determines whether or not an unused channel other than the used channel exists from all the wireless channels (step S101). In FIG. 11, unused channels Ch2 to Ch5, Ch8, and Ch9 exist (outlined areas in FIG. 11).

  Then, the interference detection unit 205 of the parent terminal 1-1 narrows down the intra-cell channel candidates from the unused channels based on the separation indexes of the unused channels (step S102).

  First, the interference detection unit 205 of the parent terminal 1-1 obtains interference levels of unused channels Ch2 to Ch5, Ch8, and Ch9. This interference level is derived based on the frequency distance between the unused channel and the used channel. Specifically, as shown in FIG. 11, first, the frequency distance X1 between the unused channel closest to the unused channel on the low frequency side and the unused channel, and the nearest used channel and unused channel on the high frequency side of the unused channel. Is obtained for each unused channel. The frequency distance X1 on the low frequency side and the frequency distance X2 on the high frequency side are represented by the difference in channel numbers of the radio channels.

  For example, in the case of the unused channel Ch2 and the used channels Ch1 and Ch6, the frequency distance X1 = 1 on the low frequency side and the frequency distance X2 = 4 on the high frequency side. In the case of the unused channel Ch3 and the used channels Ch1 and Ch6, the frequency distance X1 = 2 on the low frequency side and the frequency distance X2 = 3 on the high frequency side are obtained. In the case of the unused channel Ch4 and the used channels Ch1 and Ch6, the frequency distance X1 = 3 on the low frequency side and the frequency distance X2 = 2 on the high frequency side. In the case of the unused channel Ch5 and the used channels Ch1 and Ch6, the frequency distance X1 = 4 on the low frequency side and the frequency distance X2 = 1 on the high frequency side. In the case of the unused channel Ch8 and the used channels Ch7 and Ch10, the frequency distance X1 = 1 on the low frequency side and the frequency distance X2 = 2 on the high frequency side are obtained. In the case of the unused channel Ch9 and the used channels Ch7 and Ch10, the frequency distance X1 = 2 on the low frequency side and the frequency distance X2 = 1 on the high frequency side are obtained.

  Next, as shown in FIG. 12, the separation index corresponding to the frequency distance is set in advance, and the frequency distances X1 and X2 are converted into the separation index. Here, the frequency distance “1” corresponds to the separation index “10”, the frequency distance “2” corresponds to the separation index “3”, and the frequency distance “3 or more” corresponds to the separation index “1”. The separation index decreases as the frequency distance increases. For example, when the frequency distance X1 = 1 on the low frequency side and the frequency distance X2 = 4 on the high frequency side, the separation indexes corresponding to the frequency distances X1 and X2 are the separation index “10” on the low frequency side and the separation index on the high frequency side. The index becomes “1”.

  Next, the sum of the separation indices corresponding to the frequency distances X1 and X2 is derived as an interference level. That is, the interference level = the separation index on the low frequency side + the separation index on the high frequency side.

  For example, when the separation indexes corresponding to the frequency distance X1 on the high frequency side and the frequency distance X2 on the low frequency side are “10” and “1”, the interference level = 10 + 1 = 11. This interference level indicates the interference level between the unused channel and the used channel. The lower the interference level, the more difficult the unused channel and the used channel interfere with each other.

  Therefore, in FIG. 11, the interference level of the unused channel Ch2 = 11 (= 10 + 1), the interference level of the unused channel Ch3 = 4 (= 3 + 1), and the interference level of the unused channel Ch4 = 4 (= 1 + 3). Further, the interference level of the unused channel Ch5 = 11 (= 1 + 10), the interference level of the unused channel Ch8 = 13 (= 10 + 3), and the interference level of the unused channel Ch9 = 13 (= 3 + 10).

  That is, the interference levels of the unused channels Ch2, Ch3, Ch4, Ch5, Ch8, and Ch9 shown in FIG. 11 are “11”, “4”, “4”, “11”, “13”, and “13”. Become. In this case, the unused channels Ch3 and Ch4 having the minimum interference level “4” are candidates for the intra-cell channel.

  Next, the interference detection unit 205 of the parent terminal 1-1 refers to the interference cell ID in the detection information management table TB12. This interference cell ID is the communication ID of the parent terminal 1 belonging to the interference cell that uses the same intra-cell channel as the own terminal. The priority n is set for each of the own terminal and the parent terminal 1 belonging to the interference cell using the same intra-cell channel depending on the size of the communication ID. Therefore, the interference detection unit 205 of the parent terminal 1 obtains the calculation result of the function f (n) by applying the priority n of the own terminal to the function f (n) (step S103). The interference detection unit 205 of the parent terminal 1 has random number generation means, and changes the channel in the cell in the own terminal according to the magnitude relationship between the calculation result of the function f (n) and the generation result of the random number. It is determined whether or not to perform (step S104). For example, when the constant a is set, the function f (n) = exp {−a (n−1)} is expressed. If the priority n is set higher as the communication ID of the parent terminal 1 is smaller, the communication ID is smaller. The parent terminal 1 has a higher channel change probability.

  When all the communication cells to which the terminal belongs and the interference cell change the intra-cell channel equally, the possibility of re-interference after the change increases. However, as described above, since the change probability of the intra-cell channel is set based on the respective priorities of the own terminal and the parent terminal 1 belonging to the interference cell, there is a possibility of re-interference after the change of the intra-cell channel. Can be suppressed.

When the interference detection unit 205 of the parent terminal 1-1 determines to change the channel in the cell, the channel number j is set as a parameter for each of the unused channels Ch3 and Ch4 that are candidates for the channel in the cell. A probability density function p (j) is calculated (step S105). For example, when the constants b and c and the interference level R _j of the radio channel Chj are represented by the probability density function p (j) = b / (R _j + cj), the smaller the channel number j of the radio channel, the probability density The function p (j) becomes high. The constant b is set so that Σp (j) = 1. On the other hand, if it is determined in step S104 that the intra-cell channel change is not to be executed, this process is terminated.

  Then, the interference detection unit 205 of the parent terminal 1-1 selects an unused channel Ch3 having a high probability density function p (j) among the unused channels Ch3 and Ch4 as a switching destination intra-cell channel. The channel switching processing unit 204 of the parent terminal 1-1 sets an unused channel Ch3 as a new intra-cell channel of the communication cell C1 (step S106).

  For example, when the unused channels Ch3 and Ch4 that are candidates for the intra-cell channel are selected at random, the number of intra-cell channels used in the entire system increases after the intra-cell channel reset process in the system converges. However, as described above, the smaller the channel number j of the radio channel, the easier the system can be operated with a smaller number of radio channels by facilitating selection of a new intra-cell channel.

Further, the probability density function p (j, n) = b / (R _j + c | j−n |) may be used. In this case, for the parent terminal 1 with priority n, there is a high probability that an unused channel with channel number j is selected as a new intra-cell channel. Therefore, the probability of setting the same intra-cell channel for a plurality of communication cells decreases, and re-interference after changing the intra-cell channel can be suppressed.

  Furthermore, when the interference detection unit 205 of the parent terminal 1-1 has used the wireless channel of channel number j1 as the intra-cell wireless channel in the past, the history of changing to another wireless channel due to interference with the interfering cell. Suppose that In this case, if there is a radio channel with channel number j1 in an unused channel that is a candidate for a channel in a cell, the probability density function p (j) or probability density function p in the direction in which the probability density function with channel number j1 decreases. (J, n) may be changed to reduce the selection probability of channel number j1. In this case, it is possible to suppress the repeated occurrence of returning the intra-cell channel to the original radio channel after setting the radio channel having an interference history in the past to the intra-cell channel.

  Further, when there is no unused channel in step S101, the interference detection unit 205 of the parent terminal 1-1 determines that the wireless channel with the smallest number of interfering cells among all the wireless channels is the current intra-channel channel Ch1. It is determined whether or not there is (step S107). Specifically, the interference detection unit 205 of the parent terminal 1-1 refers to the channel information management table TB13 stored in the table storage unit 101, and derives the number of adjacent cells using the same radio channel. Then, the interference detection unit 205 of the parent terminal 1-1 compares the number of interference cells in the current intra-cell channel Ch1 with the number of interference cells in other radio channels.

  Then, when the number of interfering cells of the current intra-cell channel Ch1 is the smallest among all the radio channels, this process is terminated, and the communication cell C1 maintains the intra-cell channel Ch1. On the other hand, if the number of interfering cells in the current intra-cell channel Ch1 is not the minimum, one or more other radio channels with the minimum number of interfering cells are set as candidates for the intra-cell channel (step S108). And the process of said step S103-S106 is performed with respect to the candidate of the channel in a cell in which the number of this interference cell is the minimum, and any one candidate is selected as a channel in a cell of a switching destination, Communication cell C1 Set to a new in-cell channel.

  Next, the parent terminal 1-1 obtains a change time for changing the intra-cell channel from the current time, and sends a channel change notification packet including the change time and the new intra-cell channel to the same communication cell C1 as its own terminal. Is transmitted by broadcast communication to all the child terminals 2 belonging to. Here, this change time is, for example, a time five minutes after the current time, and a time at which all the child terminals 2 belonging to the same communication cell C1 as the own terminal can normally receive this channel change notification packet. As long as it is set to.

  The format of the channel change notification packet is shown in FIG. The channel change notification packet includes a transmission source terminal ID part, a transmission destination terminal ID part, a cell ID part, an operation code part, a change time part, and a communication channel part.

  The transmission source terminal ID portion of the channel change notification packet accommodates the terminal ID of the communication terminal A that has transmitted the channel change notification packet. The transmission destination terminal ID section accommodates the terminal ID of the communication terminal A that is the transmission destination of the channel change notification packet. In the case of the channel change notification packet, the transmission destination code ID “BC” is accommodated. The cell ID unit accommodates a communication cell ID assigned to the communication cell to which the communication terminal A that transmitted the channel change notification packet belongs. In this embodiment, the parent terminal 1 accommodates the terminal ID of the own terminal, and the child terminal 2 accommodates the terminal ID of the parent terminal 1 of the communication cell to which the own terminal belongs. The operation code portion contains the code of the channel change notification packet. The change time portion stores a change time for starting the change of the communication channel, and the communication channel portion stores a value capable of identifying the communication channel to be changed at the change time.

  Specifically, in FIG. 7, the parent terminal 1-1 sets the new communication channel as channel Ch3, sets the communication channel change time five minutes after the current time (step S9), and broadcasts the channel change notification packet. It transmits by communication (step S10).

  The child terminal 2 in the communication cell C1 that has received the channel change notification packet activates the change timer unit 206 included in the own terminal in order to change the communication channel at the time stored in the change time portion of the channel change notification packet ( Step S12). At this time, the child terminal 2-2 receives the channel change notification packet from the parent terminal 1-1 by the child terminal 2-1 relaying the channel change notification packet (step S11). Further, when a channel change notification packet of a communication cell different from the communication cell to which the own terminal belongs is received, these processes are not performed.

  Thereafter, when the predetermined time has elapsed and the change time is reached, the channel switching processing unit 204 of the parent terminal 1-1 and each child terminal 2 receives the notification from the change timer unit 206 and changes the communication channel to the channel Ch3. (Step S13). In this way, the communication channel used in the communication cell C1 including the parent terminal 1-1 and each child terminal 2 is changed to the channel Ch3 which is a new communication channel.

  Thereby, the child terminal 2-2 and the child terminal 2-5, and the child terminal 2-3 and the child terminal 2-6 transmit and receive communication packets in each communication cell using different communication channels. Thus, communication packet interference can be reduced.

  As described above, in this system, communication between the parent terminals 1 and intensive management of servers and the like are unnecessary, and interference of radio packets between communication cells can be reduced. Furthermore, even among unused channels, you can select a radio channel that has less interference due to leakage power from the used channel, so that interference from wireless packets due to leakage power from other communication cells is suppressed, and interference seen from the frequency axis is also suppressed. it can.

(Embodiment 2)
The multi-hop communication system of the present embodiment has the same configuration as that of the first embodiment, and the setting of unused channels is different from that of the first embodiment. Is omitted.

  FIG. 13 shows an example of extracting unused channels in the parent terminal 1-1 when all the radio channels Ch1 to Ch10 are selected.

  First, the channels used are Ch1, Ch6, and Ch10 (horizontal line region in FIG. 13). The used channels include the intra-channel channel Ch1 of the parent terminal 1-1 in addition to the radio channels (intra-cell channels used by adjacent cells) stored in the channel information management table TB13.

  Next, the interference detection unit 205 of the parent terminal 1-1 extracts radio channels (adjacent channels) adjacent to the high-frequency side and the low-frequency side of the used channels Ch1, Ch6, and Ch10. In the case of FIG. 13, adjacent channels Ch2, Ch5, Ch7, and Ch9 are formed (dot areas in FIG. 13).

  Next, the interference detection unit 205 of the parent terminal 1-1 extracts the radio channels excluding the used channels and the adjacent channels from all the radio channels Ch1 to Ch10 as unused channels. In the case of FIG. 13, the unused channels Ch3, Ch4, and Ch8 are formed (the white areas in FIG. 13).

  Then, the interference detection unit 205 of the parent terminal 1-1 uses the unused channels Ch3, Ch4, and Ch8 to change the intra-cell channel as in the first embodiment.

  Therefore, by not setting the adjacent channel adjacent to the used channel as a new intra-cell channel, it is possible to suppress interference due to spurious or the like of the adjacent channel.

(Embodiment 3)
In the multi-hop communication system of this embodiment, when the interference level is obtained in step S102 of FIG. 8, the interference level is weighted according to the number of communication cells using each of the used channels. 1 is different. In addition, the same code | symbol is attached | subjected to the structure similar to Embodiment 1, and description is abbreviate | omitted.

  In FIG. 11, the separation index on the low frequency side and the separation index on the high frequency side for each unused channel are obtained in the same manner as in the first embodiment. Then, the interference detection unit 205 of the present embodiment refers to the channel information management table TB13 and derives the number of communication cells (adjacent cell or own terminal) that use the used channel. Here, the number of communication cells using the use channel Ch1 is “2”, the number of communication cells using the use channel Ch6 is “4”, the number of communication cells using the use channel Ch7 is “1”, and the number of communication cells using the use channel Ch10. The number “1”.

  The interference detection unit 205 multiplies the low frequency side separation index by the number of communication cells using the low frequency side use channel when obtaining the interference level of each of the unused channels Ch2 to Ch5, Ch8, and Ch9. Further, the high frequency side separation index is multiplied by the number of communication cells using the high frequency side use channel. Then, the sum of the multiplication result on the high frequency side and the multiplication result on the low frequency side is used as the interference level.

  Therefore, in FIG. 11, the interference level of the unused channel Ch2 = 24 (= 10 × 2 + 1 × 4), the interference level of the unused channel Ch3 = 10 (= 3 × 2 + 1 × 4), and the interference level of the unused channel Ch4 = 14 (= 1 × 2 + 3 × 4). Further, the interference level of the unused channel Ch5 = 42 (= 1 × 2 + 10 × 4), the interference level of the unused channel Ch8 = 13 (= 10 × 1 + 3 × 1), and the interference level of the unused channel Ch9 = 13 (= 3) × 1 + 10 × 1).

  That is, the interference levels of the unused channels Ch2, Ch3, Ch4, Ch5, Ch8, and Ch9 shown in FIG. 11 are “24”, “10”, “14”, “42”, “13”, and “13”. Become. In this case, the unused channel Ch3 having the minimum interference level “10” is a candidate for the channel in the cell.

  Then, the interference detection unit 205 of the parent terminal 1-1 uses the unused channel Ch3 as a candidate for an intra-cell channel, and performs an intra-cell channel change process as in the first embodiment.

  A radio channel in which a plurality of communication cells are used redundantly increases traffic and increases the probability of interference over time. However, by weighting the interference level according to the number of communication cells using each of the used channels, interference can be suppressed from both the frequency axis and the time axis.

(Embodiment 4)
The communication terminal A of the multi-hop communication system according to the present embodiment uses the intra-cell channel of the communication cell to which the own terminal belongs and uses the channel information management table TB13 created by the parent terminal 1 of the communication cell to which the own terminal belongs. Are transmitted periodically. Here, the child terminal 2 periodically obtains the channel information management table TB13 created by the parent terminal 1 of the communication cell to which the own terminal belongs from the parent terminal 1, so that the H packet including the channel information management table TB13 is obtained. Transmission is possible.

  Then, for example, the child terminal 2 belonging to the communication cell C1 (first communication cell) sequentially switches all the radio channels, and adjacent cells (third communication) that are other communication cells existing around the communication cell C1. H packet is received from the cell. Then, the child terminal 2 belonging to the communication cell C1 extracts the channel information management table TB13 from the received H packet, and transmits a packet including the channel information management table TB13 to the parent terminal 1-1 of the communication cell C1.

  Here, if a communication cell existing around an adjacent cell is a quasi-adjacent cell (fourth communication cell), the channel information management table TB13 included in the H packet from the adjacent cell indicates the channel in the cell in the quasi-adjacent cell. This is information indicating the usage status.

  Thus, the interference detection unit 205 of the parent terminal 1-1 can detect the intra-cell channel used by the semi-adjacent cell (used channel viewed from the adjacent cell) based on the channel information management table TB13.

  Then, the interference detection unit 205 of the parent terminal 1-1 removes the intra-cell channel used by the quasi-adjacent cell from the unused channel, and uses this unused channel to determine the channel in the cell as in any of the first to third embodiments. Perform the change process.

  For example, when the intra-cell channel changing process is performed in the communication cell C1, the interference level increases in an adjacent cell using the intra-cell channel after the change of the communication cell C1. As a result, there is a possibility that the process of changing the channel in the cell is performed also in the adjacent cell, and it may take a long time for convergence in the entire system.

  However, in the present embodiment, not only radio channels (used channels) used by neighboring cells but also radio channels used by quasi-adjacent cells are excluded from candidates for intra-cell channels. Therefore, even when the intra-cell channel is changed in one communication cell, the possibility of changing the intra-cell channel in the adjacent cell is reduced, and the convergence time of the entire system can be shortened.

  Next, when considering adjacent cells and semi-adjacent cells, the interference detection unit 205 of the parent terminal 1-1 narrows down channel candidates in the cell from unused channels in step S102 of FIG. .

  FIG. 14 shows an example of extracting unused channels in the parent terminal 1-1 when all the radio channels Ch1 to Ch10 are used.

  First, use channels Ch1, Ch6, and Ch7 are set in the parent terminal 1-1 (vertical line region in FIG. 14). The channel used is composed of an intra-cell channel Ch1 of the parent terminal 1-1 and an intra-cell channel in an adjacent cell of the parent terminal 1-1.

  Further, radio channels used by the quasi-adjacent cells are quasi-used channels Ch4 and Ch10 (dashed lines in FIG. 14).

  In this case, in FIG. 14, there are unused channels Ch2, Ch3, Ch5, Ch8, and Ch9 (the white areas in FIG. 14).

  Then, in step S102 of FIG. 8, the interference detection unit 205 of the parent terminal 1-1 narrows down intra-cell channel candidates from the unused channels based on the separation indexes of the unused channels.

  First, the interference detection unit 205 obtains interference levels of unused channels Ch2, Ch3, Ch5, Ch8, and Ch9. This interference level is derived based on the frequency distance between the unused channel and the used and semi-used channels. Specifically, as shown in FIG. 14, in the case of the unused channel Ch2, the used channel Ch1, and the semi-used channel Ch4, the frequency distance X1 = 1 on the low frequency side and the frequency distance X2 = 2 on the high frequency side. In the case of the unused channel Ch3, the used channel Ch1, and the semi-used channel Ch4, the frequency distance X1 = 2 on the low frequency side and the frequency distance X2 = 1 on the high frequency side are obtained. In the case of the unused channel Ch5, the semi-used channel Ch4, and the used channel Ch6, the frequency distance X1 = 1 on the low frequency side and the frequency distance X2 = 1 on the high frequency side. In the case of the unused channel Ch8, the used channel Ch7, and the semi-used channel Ch10, the frequency distance X1 = 1 on the low frequency side and the frequency distance X2 = 2 on the high frequency side are obtained. In the case of the unused channel Ch9, the used channel Ch7, and the semi-used channel Ch10, the frequency distance X1 = 2 on the low frequency side and the frequency distance X2 = 1 on the high frequency side are obtained.

  Next, as in the first embodiment, the frequency distances X1 and X2 are converted into separation indices (see FIG. 12).

  Next, the sum of the separation indices corresponding to the frequency distances X1 and X2 is derived as an interference level. At this time, weighting is performed in consideration of adjacent cells and quasi-adjacent cells.

  Specifically, interference level = α × low frequency side separation index + β × high frequency side separation index. Α is set to “α = 1” when the low frequency side radio channel is the use channel, and “α = 0.3” when the low frequency side radio channel is the semi-use channel. Also, β is set to “β = 1” when the radio channel on the high frequency side is the use channel, and “β = 0.3” when the radio channel on the high frequency side is the semi-use channel. That is, when determining the interference level with the communication cell to which the terminal belongs, weighting is performed so that the interference level with the quasi-adjacent cell is lighter than the interference level with the adjacent cell. Therefore, it is possible to derive an interference level in which the influence of interference on the terminal by the quasi-neighboring cell is suppressed than the influence of interference on the terminal by the neighboring cell.

  Therefore, in FIG. 14, the interference level of the unused channel Ch2 = 10.9 (= 10 × 1 + 3 × 0.3) and the interference level of the unused channel Ch3 = 6 (= 3 × 1 + 10 × 0.3). Further, the interference level of the unused channel Ch5 = 13 (= 10 × 0.3 + 10 × 1), the interference level of the unused channel Ch8 = 10.9 (= 10 × 1 + 3 × 0.3), and the interference of the unused channel Ch9. Level = 6 (= 3 × 1 + 10 × 0.3).

  That is, the interference levels of the unused channels Ch2, Ch3, Ch5, Ch8, and Ch9 shown in FIG. 11 are “10.9”, “6”, “13”, “10.9”, and “6”. In this case, the unused channels Ch3 and Ch9 having the minimum interference level “6” are candidates for the intra-cell channel.

  Then, the interference detection unit 205 of the parent terminal 1-1 uses the unused channels Ch3 and Ch9 as candidates for the intra-cell channel, and performs the intra-cell channel change process as in the first embodiment.

  Further, similarly to the third embodiment, the low frequency side separation index is multiplied by the number of communication cells using the low frequency side use channel, and the high frequency side separation index is multiplied by the number of communication cells using the high frequency side use channel. May be multiplied. Thus, interference can be suppressed from both the frequency axis and the time axis by weighting the interference level according to the number of communication cells using each of the used channels.

  In the present embodiment, the interference detection unit 205 of the parent terminal 1-1 performs the following operation when there is no unused channel in step S101 of FIG.

  First, assume that the number of adjacent cells using each wireless channel is N, the number of quasi-adjacent cells using each wireless channel is M, and 0 ≦ weighting coefficient β ≦ 1. Then, when there is no unused channel, the interference detection unit 205 of the parent terminal 1-1 derives the evaluation function for each radio channel = N + βM. That is, when viewed from the communication cell C1 to which the parent terminal 1-1 belongs, the interference with the quasi-adjacent cell is relatively small compared to the interference with the adjacent cell. Good. Then, one or a plurality of radio channels that minimize this evaluation function are set as candidates for the intra-cell channel of the communication cell C1. If β = 1, the weighting for interference with adjacent cells and the weighting for interference with quasi-adjacent cells can be made equal to each other.

  In this way, even when there is no unused channel, weighting is performed so that interference with a quasi-adjacent cell is lighter than interference with an adjacent cell when determining interference with a communication cell to which the terminal belongs. Can do. Therefore, when the intra-cell channel is changed in one communication cell when there is no unused channel, the possibility of changing the intra-cell channel in the adjacent cell can be reduced while suppressing interference with the own terminal.

1 (1-1, 1-2, ...) Parent terminal 2 (2-1, 2-2, ...) Child terminals C1, C2,. . . Communication cell

Claims (13)

Using one radio channel selected from a plurality of radio channels as an intra-cell channel, constructing a plurality of communication cells in which one parent terminal and one to a plurality of child terminals perform multi-hop communication,
The child terminal detects the intra-cell channel in each of the communication cells adjacent to the communication cell to which the own terminal belongs, and notifies the parent terminal of the communication cell to which the own terminal belongs,
When the degree of interference in communication between a communication cell to which the own terminal belongs and another communication cell having the same intra-cell channel exceeds a predetermined threshold, the parent terminal and the adjacent communication cell to which the own terminal belongs The interference level based on the frequency distance between the communication cell to which the own terminal belongs and the intra-cell channel of each of the adjacent communication cells from the one or more radio channels not used for the intra-cell channel in the communication cell is minimum. A multi-hop communication method comprising: selecting a wireless channel to be set, and setting the selected wireless channel as the intra-cell channel of the communication cell to which the terminal belongs. Using one radio channel selected from a plurality of radio channels as an intra-cell channel, constructing a plurality of communication cells in which one parent terminal and one to a plurality of child terminals perform multi-hop communication,
The parent terminal and the child terminal include communication cell information for identifying a communication cell to which the own terminal belongs, and transmit a hello packet that notifies the existence of the own terminal using the intra-cell channel,
When the communication cell indicated by the communication cell information of the hello packet received using the intra-cell channel is different from the first communication cell to which the own terminal belongs, the child terminal uses the received hello packet of the hello packet. Transmitting a plurality of radio channels including detection information notifying that the second communication cell including the communication cell information and using the same intra-cell channel is detected to the parent terminal belonging to the first communication cell; When the hello packet is received by sequentially switching, the communication cell information of the received hello packet and channel information related to the radio channel that has received the hello packet are included around the first communication cell. Channel usage information for notifying the intra-cell channel used by an existing third communication cell belongs to the first communication cell. And sends it to the Kioya terminal,
The parent terminal belonging to the first communication cell derives the degree of interference in communication between the first communication cell and the second communication cell based on the received detection information, and the degree of interference. Exceeds the predetermined threshold, based on the channel usage information, the first and third communication cells start from the unused channels that are radio channels that are not used for the intra-cell channel. An unused channel that minimizes an interference level based on a frequency distance between the communication cell and the used channel that is the intra-cell channel of the communication cell is selected, and the selected unused channel is selected in the cell of the first communication cell. A multi-hop communication system characterized by being set to a channel.   The multi-hop communication system according to claim 2, wherein the parent terminal weights the interference level according to the number of communication cells using each of the used channels based on the channel usage information.   The multi-hop communication system according to claim 2 or 3, wherein the parent terminal removes an adjacent channel, which is a radio channel adjacent to each of the used channels, from the unused channel. The parent terminal and the child terminal transmit the hello packet including the channel use information created in the communication cell to which the terminal belongs, using the intra-cell channel,
The child terminal belonging to the first communication cell sequentially switches the plurality of radio channels and uses the channel use information included in the hello packet received from the third communication cell as the first communication. Transmitted to the parent terminal belonging to the cell,
The parent terminal belonging to the first communication cell uses the intra-cell channel used by a fourth communication cell existing around the third communication cell based on the channel use information included in the hello packet. The multi-hop communication system according to claim 2, wherein the intra-cell channel used by the fourth communication cell is excluded from the unused channel.   When there is no unused channel, the parent terminal belonging to the first communication cell uses N as the number of the third communication cells that use each radio channel, and the fourth uses each radio channel. The number of communication cells is M, a weighting factor of 0 to 1 is β, an evaluation function for each wireless channel is derived as N + βM, and a wireless channel that minimizes the evaluation function is set as the channel in the cell. The multi-hop communication system according to claim 5. The parent terminal belonging to the first communication cell is
The used channel is the intra-cell channel in the first, third, and fourth communication cells,
The interference level of the intra-cell channel of the fourth communication cell for the unused channel is weighted lighter than the interference level of the intra-cell channel of the third communication cell for the unused channel. The multi-hop communication system according to claim 5 or 6, characterized in that:   Each of the parent terminals determines whether or not to set the unused channel as the intra-cell channel based on the priority when priority is set and the degree of interference exceeds a predetermined threshold. The multi-hop communication system according to claim 2, wherein the multi-hop communication system is a multi-hop communication system. Each radio channel has a probability set according to a predetermined probability density function,
The multi-hop according to any one of claims 1 to 8, wherein the parent terminal determines whether to set the unused channel as the intra-cell channel based on the probability of the unused channel. Communications system.   10. The multi-hop communication system according to claim 9, wherein the probability density function is a function having a radio channel identification number and a priority set for each of the parent terminals as variables.   The parent terminal determines the probability of the unused channel that the degree of interference in the communication between the first communication cell and the second communication cell has exceeded a predetermined threshold in the past as the unused channel. The multi-hop communication system according to claim 9, wherein the multi-hop communication system is changed in a direction not to set the channel in the cell. A multi-hop communication system in which a plurality of communication cells in which one parent terminal and one to a plurality of child terminals perform multi-hop communication using one wireless channel selected from a plurality of wireless channels as an intra-cell channel A communication terminal used for the parent terminal,
The detection result of the channel in the cell in each of the communication cells adjacent to the communication cell to which the own terminal belongs is obtained from the child terminal of the communication cell to which the own terminal belongs,
Based on the acquired detection result, when the degree of interference in communication between the communication cell to which the own terminal belongs and another communication cell having the same intra-cell channel exceeds a predetermined threshold, the communication cell to which the own terminal belongs And based on the frequency distance between the communication cell to which the terminal belongs and the intra-cell channel of each of the adjacent communication cells from one or more radio channels not used as the intra-cell channel in the adjacent communication cell. A communication terminal that selects a radio channel with a minimum interference level and sets the selected radio channel as the intra-cell channel of the communication cell to which the terminal belongs. A multi-hop communication system in which a plurality of communication cells in which one parent terminal and one to a plurality of child terminals perform multi-hop communication using one wireless channel selected from a plurality of wireless channels as an intra-cell channel A communication terminal used for the child terminal,
A communication terminal that detects the intra-cell channel in each of the communication cells adjacent to the communication cell to which the own terminal belongs and notifies the parent terminal of the communication cell to which the own terminal belongs.

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