JP2020145634A - Wireless communication device and wireless communication system - Google Patents

Abstract

To improve flooding efficiency in a wireless multi-hop network.SOLUTION: A wireless communication device is used in a wireless network including a plurality of nodes, and includes an interference point node identification unit, a relay node identification unit, a grouping unit, a setting unit, and a notification unit. The interference point node identification unit identifies an interference point node to which packets arrive from the plurality of relay nodes. For each of the interference point nodes, the relay node identification unit identifies a relay node that transmits a packet that reaches the interference point node. The grouping unit groups the relay nodes such that two or more relay nodes that transmit packets to the same interference point node belong to different groups. The setting unit sets different transmission timings for each of the groups. The notification unit notifies each of the relay nodes of the transmission timing set by the setting unit.SELECTED DRAWING: Figure 4

Description

The present invention relates to a flooding technique in a wireless multi-hop network.

In a wireless network having a plurality of nodes, flooding has been put into practical use as one of the technologies for transmitting information to all the nodes by a multi-hop method. In flooding, packets are transmitted by the following procedure.
(1) The source node broadcasts the packet.
(2) Each node that receives the packet broadcasts the packet as a relay node (multi-hop transfer).
(3) However, when each node newly receives the same packet as the packet received in the past, the newly received packet is not relayed (avoidance of duplicate transmission).

Flooding can efficiently transmit information to all nodes in the wireless network by the above procedure. However, since a plurality of nodes broadcast, in a wireless network with a large number of nodes, the packet loss rate may increase due to packet collision. In addition, the transmission of redundant packets may generate unnecessary traffic, which may reduce the efficiency of the entire wireless network.

These problems can be mitigated, for example, by having only the minimum number of nodes relaying packets. For example, in a wireless multi-hop network using an OLSR (Optimized Link State Routing) protocol, a flooding method has been proposed in which only selected nodes perform broadcast transfer. The node selected to execute the broadcast transfer is called MPR (multipoint relay). Methods for selecting and flooding MPRs are described, for example, in Patent Document 1 and Non-Patent Documents 1 and 2.

Patent No. 5136434

IETF MANET RFC3626 (October 2003) OLSR (Optimized Link State Routing) Protocol, https://internet.watch.impress.co.jp/www/column/wp2p/wp2p06.htm

As described above, in flooding in which only the selected node (that is, the MPR node) executes broadcast transfer, unnecessary traffic is reduced and communication efficiency is improved. However, if the number of MPR nodes is too small, the information may not reach all the nodes in the wireless network. Therefore, in order to reliably distribute information to all the nodes in the wireless network, it is preferable to select a number of MPR nodes including a margin. However, if the MPR node is selected in such a policy, some nodes will receive radio waves from a plurality of MPR nodes. In this case, an error may occur due to the interference of radio waves, and the packet may not be transferred to the next node.

An object of one aspect of the present invention is to improve the efficiency of flooding in a wireless multi-hop network.

The wireless communication device of one aspect of the present invention is used in a wireless network including a plurality of nodes. The wireless communication device includes a storage unit that stores route information representing a node that receives a packet transmitted by the broadcast transfer for each relay node that executes the broadcast transfer among the plurality of nodes, and the route information. An interference point node identification unit that specifies an interference point node that a packet arrives from a plurality of relay nodes, and a relay node that specifies a relay node that transmits a packet that reaches the interference point node for each interference point node. The specific unit and the grouping unit that groups the relay nodes specified by the relay node specific unit so that the two or more relay nodes that send packets to the same interference point node belong to different groups, and each group. A setting unit for setting different transmission timings and a notification unit for notifying each relay node specified by the relay node identification unit of the transmission timing set by the setting unit are provided.

According to the above aspects, flooding efficiency is improved in a wireless multi-hop network.

It is a figure which shows an example of the wireless communication system which concerns on embodiment of this invention. It is a figure which shows an example of flooding. It is a figure which shows an example of flooding using an MPR node. It is a figure which shows an example of the wireless communication apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the adjacent node information and a flooding route table. It is a figure which shows an example of the mutual interference table and the flooding sequence table. It is a flowchart which shows an example of the process of creating a mutual interference table. It is a flowchart which shows an example of grouping of a source relay node. It is a figure which shows an example of the wireless terminal apparatus which concerns on embodiment of this invention. It is a flowchart which shows an example of operation of a wireless terminal apparatus. An example of the communication method which concerns on embodiment of this invention is shown.

FIG. 1 shows an example of a wireless communication system according to an embodiment of the present invention. The wireless communication system 100 includes a plurality of nodes and transmits packets in a multi-hop manner. In this embodiment, the wireless communication system 100 shall transmit packets according to the OLSR protocol.

The wireless communication system 100 includes a gateway node 1 and a plurality of nodes 2a to 2e and 2p to 2v. In the following description, any node among the nodes 2a to 2e and 2p to 2v may be referred to as "node 2".

A wireless communication device is mounted on the gateway node 1. The wireless communication device can transmit a wireless signal. In addition, the wireless communication device can receive the wireless signal transmitted from the adjacent node. Further, the wireless communication device distributes information to all the nodes 2a to 2e and 2p to 2v by flooding. In the following description, the wireless communication device mounted on the gateway node 1 may be referred to as a "gateway node".

A wireless terminal device is mounted on each node 2. The wireless terminal device can transmit a wireless signal. In addition, the wireless terminal device can receive a wireless signal transmitted from an adjacent node. Further, the wireless terminal device can transfer the signal received from the adjacent node to another node. That is, the wireless terminal device may operate as a relay node. For example, when flooding is performed by the gateway node 1, the wireless terminal device broadcasts and transfers the flooding packet received from the adjacent node. In the following description, the wireless terminal device mounted on the node 2 may be referred to as a "node".

In the wireless communication system 100 having the above configuration, each node 2 periodically broadcasts a Hello packet. The Hello packet is a control packet for notifying the neighboring node of its existence. Therefore, each node 2 can recognize the node adjacent to itself by specifying the source of the received Hello packet. Then, each node 2 creates adjacent node information representing a node adjacent to itself and stores it in the memory in its own node. Further, the adjacent node information created by each node 2 is exchanged between the nodes. Therefore, each node 2 can recognize the node two hops ahead by counting from its own node.

The adjacent node information created by each node 2 is transmitted to the gateway node 1. That is, the gateway node 1 collects the adjacent node information created in each node 2. Therefore, the gateway node 1 can recognize the topology of the wireless communication system 100.

FIG. 2 shows an example of flooding. In the example shown in FIG. 2, the gateway node 1 distributes information to all the nodes 2a to 2e and 2p to 2v. That is, the gateway node 1 transmits a flooding packet. However, the flooding packet transmitted from the gateway node 1 reaches the nodes 2a to 2e, but does not reach the nodes 2p to 2v. A broadcast address is set as the destination address in the flooding packet, for example.

Each node 2a to 2e broadcasts the flooding packet received from the gateway node 1. At this time, the flooding packet transmitted from the node 2a reaches the nodes 2p to 2r. Similarly, the flooding packet transmitted from the node 2b reaches the nodes 2q to 2s, the flooding packet transmitted from the node 2c reaches the nodes 2r to 2t, and the flooding packet transmitted from the node 2d reaches the nodes 2s to 2u. The flooding packet transmitted from the node 2e reaches the nodes 2t to 2v. As a result, the information transmitted from the gateway node 1 is received by all the nodes 2a to 2e and 2p to 2v.

The flooding packet transmitted from the node 2a can reach a node other than the nodes 2p to 2r. For example, the flooding packet transmitted from the node 2a reaches the gateway node 1. However, the information included in this flooding packet is the same as the information transmitted by the gateway node 1. Therefore, in this case, the gateway node 1 does not transfer the flooding packet received from the node 2a. Further, it is assumed that the flooding packet transmitted from the node 2a reaches the node 2b. However, the information included in this flooding packet is the same as the information previously received by the node 2b. Therefore, in this case, the node 2b does not retransfer the flooding packet received from the node 2a.

As described above, in the example shown in FIG. 2, each node 2 that has received the flooding packet broadcast-transfers the flooding packet (excluding re-transfer). Specifically, the nodes 2a to 2e perform broadcast transfer, respectively. Therefore, packet collision is likely to occur, and communication efficiency may decrease.

These problems are alleviated, for example, by selecting the MPR node. The MPR node is selected from the nodes 2a to 2e and 2p to 2v and executes broadcast transfer. That is, the MPR node is an example of a relay node in flooding. Note that the node 2 not selected as the MPR node does not execute the broadcast transfer even if it receives the flooding packet.

FIG. 3 shows an example of flooding using the MPR node. In the example shown in FIG. 3, nodes 2a, 2c, and 2e are selected as MPR nodes.

The gateway node 1 transmits a flooding packet as in the case shown in FIG. Then, the flooding packet transmitted from the gateway node 1 reaches the nodes 2a to 2e.

The nodes 2a, 2c, and 2e each transfer the flooding packet received from the gateway node 1. At this time, the flooding packet transmitted from the node 2a reaches the nodes 2p to 2r, the flooding packet transmitted from the node 2c reaches the nodes 2r to 2t, and the flooding packet transmitted from the node 2e reaches the nodes 2t to 2v. To reach. Therefore, the information transmitted from the gateway node 1 is received by all the nodes 2a to 2e and 2p to 2v.

The method of selecting the MPR node is not particularly limited. For example, when a Willingness value is set in advance for each node 2, the MPR node is selected based on the topology of the wireless communication system 100 and the Willingness value of each node 2. Here, the Willingness value represents the degree of aggressiveness regarding packet transfer. In this case, the gateway node 1 selects the MPR nodes in order from the node 2 having the largest Willingness value. Alternatively, the gateway node 1 may select MPR nodes in order from the node 2 having the largest number of adjacent nodes. In any case, the required number of MPR nodes are selected so that the flooding packets reach all the nodes 2.

On the other hand, in the flooding procedure described above, the nodes 2b and 2d do not perform broadcast transfer. Therefore, as compared with the case shown in FIG. 2, the probability of occurrence of packet collision is reduced, and the communication efficiency can be improved.

However, even when flooding is performed using the MPR node, it is difficult to eliminate packet collision. For example, in order to ensure that flooding packets reach all nodes 2, it is necessary to select MPR nodes so that each node 2 receives packets from at least one MPR node. Then, when the MPR node is selected by such a policy, there is a high possibility that some nodes receive packets from a plurality of MPR nodes. In the case shown in FIG. 3, in the node 2r, interference between the radio wave transmitted from the node 2a and the radio wave transmitted from the node 2c may occur. Further, at the node 2t, interference between the radio wave transmitted from the node 2c and the radio wave transmitted from the node 2e may occur. Then, when such interference occurs, the wireless terminal device mounted at the interference point cannot acquire the flooded information.

The communication method according to the embodiment of the present invention provides a function of solving or alleviating the above-mentioned problems. As an example, when there is a node where interference can occur in flooding (hereinafter, interference point node), the transmission timing is adjusted among a plurality of relay nodes that transmit packets to the interference point node.

FIG. 4 shows an example of a wireless communication device according to an embodiment of the present invention. The wireless communication device 10 is mounted on the gateway node 1 in the wireless communication system 100 shown in FIG. The wireless communication device 10 is connected to, for example, a server computer (not shown). Further, the wireless communication system 100 may include a plurality of wireless communication devices 10.

As shown in FIG. 4, the wireless communication device 10 includes a wireless transmission / reception unit 11, a reception processing unit 12, a communication control unit 13, a transmission processing unit 19, and a storage unit 20. However, the wireless communication device 10 may include other circuits or functions not shown in FIG.

The radio transmission / reception unit 11 receives a radio signal transmitted from an adjacent node. In addition, the wireless transmission / reception unit 11 transmits a wireless signal. The reception processing unit 12 decodes the received signal and reproduces the packet. Then, the packet reproduced from the received signal (that is, the received packet) is passed to the communication control unit 13. The transmission processing unit 19 generates a transmission signal from the transmission packet and passes it to the wireless transmission / reception unit 11.

The communication control unit 13 controls the operation of the wireless communication device 10. Further, the communication control unit 13 includes an interference point node identification unit 14, a relay node identification unit 15, a grouping unit 16, a setting unit 17, and a notification unit 18 in order to control the flooding procedure in the wireless communication system 100. The communication control unit 13 is realized by the processor in this embodiment. In this case, the functions of the interference point node identification unit 14, the relay node identification unit 15, the grouping unit 16, the setting unit 17, and the notification unit 18 are provided by the processor executing the communication control program.

The storage unit 20 stores information used by the communication control unit 13. In this embodiment, the storage unit 20 stores the adjacent node information 21, the flooding route table 22, the mutual interference table 23, and the flooding order table 24. Further, the storage unit 20 stores a communication control program executed by the processor (that is, the communication control unit 13).

As shown in FIG. 5A, the adjacent node information 21 represents an adjacent node for each node in the wireless communication system 100. For example, the first record of the adjacency node information 21 indicates that the adjacency nodes of the gateway node 1 are nodes 2a, 2b, 2c, 2d, and 2e. Further, the second record of the adjacent node information 21 indicates that the adjacent nodes of the node 2a are the gateway node 1 and the nodes 2p, 2q, and 2r. The adjacent node information 21 is created based on the adjacent node information created in each node 2a to 2e and 2p to 2v. As described above, each of the nodes 2a to 2e and 2p to 2v can recognize the node adjacent to the own node by detecting the Hello packet transmitted from the adjacent node.

The flooding route table 22 represents a flooding packet receiving node for each MPR node, as shown in FIG. 5 (b). In this embodiment, nodes 2a, 2c, and 2e are selected as MPR nodes by the wireless communication device 10. The flooding route table 22 represents the nodes to which the packets to be broadcast-transferred at the time of flooding arrive for each of the nodes 2a, 2c, and 2e. Specifically, the flooding route table 22 shows that the packet transmitted from the node 2a reaches the nodes 2p to 2r, the packet transmitted from the node 2c reaches the nodes 2r to 2t, and the node It indicates that the packet transmitted from 2e reaches the nodes 2t to 2v.

The flooding route table 22 is created, for example, in the process of selecting an MPR node. Here, an example of selecting an MPR node and creating a flooding route table 22 is shown. Here, it is assumed that each node 2 has the above-mentioned Willingness value.

(1) The wireless communication device 10 selects the node having the largest Willingness value from the nodes (that is, 2a to 2e) adjacent to the wireless communication device 10. Here, it is assumed that the node 2a is selected. In this case, the node 2a is registered as an MPR node in the first record of the flooding route table 22. Further, the wireless communication device 10 identifies the adjacent node of the node 2a with reference to the adjacent node information 21. In this case, nodes 2p to 2r are specified. Then, the specified adjacent nodes (that is, nodes 2p to 2r) are registered as receiving nodes in association with the nodes 2a in the flooding route table 22.

(2) The wireless communication device 10 determines whether or not there are any nodes other than the nodes adjacent to the wireless communication device 10 that are not registered in the flooding route table 22. In this example, nodes 2s to 2v remain. Therefore, the wireless communication device 10 executes a process of selecting the next MPR node.

(3) It is assumed that node 2c is selected as the next MPR node. In this case, the node 2c is registered as an MPR node in the second record of the flooding route table 22. Further, the wireless communication device 10 identifies the adjacent node of the node 2c with reference to the adjacent node information 21. In this case, nodes 2r to 2t are specified. Then, the specified adjacent nodes (that is, nodes 2r to 2t) are associated with the nodes 2c in the flooding route table 22 and registered as receiving nodes.

(4) The wireless communication device 10 determines whether or not there are any nodes other than the nodes adjacent to the wireless communication device 10 that are not registered in the flooding route table 22. In this example, nodes 2u-2v remain. Therefore, the wireless communication device 10 executes a process of selecting the next MPR node.

(5) It is assumed that node 2e is selected as the next MPR node. In this case, the node 2e is registered as an MPR node in the third record of the flooding route table 22. Further, the wireless communication device 10 identifies the adjacent node of the node 2e with reference to the adjacent node information 21. In this case, nodes 2t to 2v are specified. Then, the specified adjacent nodes (that is, nodes 2t to 2v) are associated with the nodes 2e in the flooding route table 22 and registered as receiving nodes.

(6) The wireless communication device 10 determines whether or not there are any nodes other than the nodes adjacent to the wireless communication device 10 that are not registered in the flooding route table 22. In this example, no such node remains. Therefore, the wireless communication device 10 finishes selecting the MPR node and creating the flooding route table 22.

In this way, the wireless communication device 10 selects the MPR node and creates the flooding route table 22. Flooding Route Table 22 represents, for each MPR node, the nodes that receive the flooding packets transmitted by broadcast transfer.

The interference point node identification unit 14 identifies an interference point node to which flooding packets arrive from a plurality of relay nodes based on the flooding route table 22. In the example shown in FIG. 5B, the node 2r is registered in both the first record and the second record. This state indicates that the radio wave transmitted from the node 2a registered in the first record and the radio wave transmitted from the node 2c registered in the second record reach the node 2r. That is, the flooding route table 22 shown in FIG. 5B shows that the radio waves transmitted from the node 2a and the radio waves transmitted from the node 2c can interfere with each other at the node 2r. Therefore, the node 2r is specified as an interference point node.

Similarly, the node 2t is registered in both the second record and the third record. This state indicates that the radio wave transmitted from the node 2c registered in the second record and the radio wave transmitted from the node 2e registered in the third record reach the node 2t. That is, the flooding route table 22 shown in FIG. 5B shows that the radio waves transmitted from the node 2c and the radio waves transmitted from the node 2e can interfere with each other at the node 2t. Therefore, the node 2t is also specified as an interference point node.

The relay node specifying unit 15 specifies a relay node (hereinafter, a source relay node) that transmits a flooding packet that reaches the interference point node for each interference point node specified by the interference point node specifying unit 14. For example, as described above, the radio wave transmitted from the node 2a and the radio wave transmitted from the node 2c reach the node 2r. That is, the node 2r receives flooding packets from both the nodes 2a and 2c in the flooding procedure. Therefore, the nodes 2a and 2c are specified as the source relay node of the flooding packet with respect to the node 2r.

Similarly, the radio wave transmitted from the node 2c and the radio wave transmitted from the node 2e reach the node 2t. That is, the node 2t receives flooding packets from both the nodes 2c and 2e in the flooding procedure. Therefore, for the node 2t, the nodes 2c and 2e are specified as the source relay node of the flooding packet.

In the mutual interference table 23, the nodes specified by the interference point node identification unit 14 and the relay node identification unit 15 are registered. That is, the mutual interference table 23 represents the source relay node of the flooding packet for each interference point node. In this example, as shown in FIG. 6A, nodes 2a and 2c are registered as relay nodes for transmitting flooding packets to node 2r, and nodes 2c and 2e are relay nodes for transmitting flooding packets to node 2t. Is registered.

FIG. 7 is a flowchart showing an example of the process of creating the mutual interference table 23. The processing of this flowchart is executed, for example, when the flooding route table 22 is created or updated. The flooding route table 22 is created or updated, for example, when the adjacent node information 21 is updated.

In S1, the communication control unit 13 selects the first record from the flooding route table 22. In S2, the interference point node identification unit 14 selects the receiving node registered in the record selected in S1 or S9. In the following description, the receiving node selected in S2 may be referred to as "node i".

In S3, the interference point node identification unit 14 determines whether or not the node i is registered in another record of the flooding route table 22. If the node i is registered in another record of the flooding route table 22, the interference point node specifying unit 14 identifies the node i as the interference point node in S4. In S5, the relay node specifying unit 15 identifies the MPR node registered in each record in which the node i is registered as the source relay node. In S6, the communication control unit 13 registers the interference point node specified by the interference point node identification unit 14 and the source relay node specified by the relay node identification unit 15 in the mutual interference table 23 in association with each other. If the node i is not registered in the other records of the flooding route table 22, the processes of S4 to S6 are skipped.

In S7, the communication control unit 13 determines whether or not a receiving node that has not been selected remains in the record selected in S1 or S9. Then, if the unselected receiving node remains, the processing of the communication control unit 13 returns to S2. That is, the processes S3 to S6 are executed for all the receiving nodes registered in the record selected in S1 or S9.

In S8, the communication control unit 13 determines whether or not a record not selected in the flooding route table 22 remains. If a record that has not been selected remains, the communication control unit 13 selects the next record from the flooding route table 22 in S9. After that, the processing of the communication control unit 13 returns to S2. Therefore, the processes S3 to S6 are executed for each receiving node registered in each record of the flooding route table 22. As a result, the mutual interference table 23 is created.

A procedure for creating the mutual interference table 23 from the flooding route table 22 shown in FIG. 5B will be described according to the flowchart shown in FIG.

(1) In S1, the first record of the flooding route table 22 is selected. In S2, node 2p is selected from this record. In S3, it is determined that the node 2p is not registered in another record. Therefore, S4 to S6 are skipped, and the processing of the communication control unit 13 returns to S2.

(2) In S2, node 2q is selected. In S3, it is determined that the node 2q is not registered in another record. Therefore, S4 to S6 are skipped, and the processing of the communication control unit 13 returns to S2.

(3) In S2, node 2r is selected. In S3, it is determined that the node 2r is registered in the second record. Therefore, S4 to S6 are executed. In S4, node 2r is identified as an interference point node. Here, the node 2r is registered in the first record and the second record. In this case, in S5, the MPR node (that is, node 2a) registered in the first record and the MPR node (that is, node 2c) registered in the second record are the source relay nodes corresponding to the node 2r. Specified as. Then, in S6, the interference point node (that is, the node 2r) and the source relay node (that is, the nodes 2a and 2c) are registered in the first record of the mutual interference table 23.

After that, the same processing is executed for the second record and the third record of the flooding route table 22. As a result, the mutual interference table 23 shown in FIG. 6A is completed.

The grouping unit 16 groups the source relay nodes specified by the relay node specifying unit 15 so as to satisfy the following two conditions.
(1) Source relay nodes that transmit flooding packets to the same interference point node belong to different groups.
(2) Source relay nodes that do not send flooding packets to the same interference point node belong to the same group.

In the example shown in FIG. 6A, the source relay nodes that transmit the flooding packet to the node 2r are the nodes 2a and 2c. Therefore, the nodes 2a and 2c are registered in different groups. The source relay node that transmits the flooding packet to the node 2t is the node 2c and 2e. Therefore, the nodes 2c and 2e are registered in different groups. However, the nodes 2a and 2e do not transmit the flooding packet to the same interference point node. Therefore, the nodes 2a and 2e are registered in the same group.

As a result, the nodes 2a and 2e are registered in the same group as each other, and the node 2c is registered in a group different from the nodes 2a and 2e. In the example shown in FIG. 6B, the nodes 2a and 2e are registered in the group 1, and the nodes 2c are registered in the group 2.

FIG. 8 is a flowchart showing an example of grouping of source relay nodes. The processing of this flowchart is executed, for example, when the mutual interference table 23 is created or updated.

In S11, the grouping unit 16 registers each source relay node registered in the first record of the mutual interference table 23 in a different group from each other. In S12, the grouping unit 16 selects the next record from the mutual interference table 23. In S13, the grouping unit 16 selects the source relay node from the records selected in S12. In the following description, the source relay node selected in S13 may be referred to as "node j".

In S14, the grouping unit 16 determines whether or not the node j is already registered in any of the groups. When the node j is not registered in any of the groups, the grouping unit 16 has a group (hereinafter, group X) in S15 that does not include the source relay node whose transmission destination is the same interference point node. Judge whether or not. That is, the grouping unit 16 determines in S15 whether or not there is a group that does not include the source relay node that transmits the packet to the interference point node included in the destination node of the node j.

When the group X exists, the grouping unit 16 registers the node j in the group X in S16. When a plurality of groups X exist for the node j, the grouping unit 16 registers the node j in any one group X. On the other hand, when the group X does not exist, the grouping unit 16 creates a new group in S17. Then, the grouping unit 16 registers the node j in the new group. When the node j is already registered in any of the groups, the processes of S15 to S17 are skipped.

In S18, the grouping unit 16 determines whether or not an unprocessed source relay node remains in the record selected in S12. Then, when the unprocessed source relay node remains, the processing of the grouping unit 16 returns to S13. Further, in S19, the grouping unit 16 determines whether or not unprocessed records remain. Then, when an unprocessed record remains, the processing of the grouping unit 16 returns to S12. That is, the processes S15 to S17 are executed for each source relay node registered in each record of the mutual interference table 23. As a result, the source relay nodes are grouped.

A procedure for grouping the source relay nodes registered in the mutual interference table 23 shown in FIG. 6A will be described according to the flowchart shown in FIG.

(1) Nodes 2a and 2c are registered as source relay nodes in the first record of the mutual interference table 23. Therefore, the nodes 2a and 2c are registered in different groups in S11. In this example, node 2a is registered in group # 1 and node 2c is registered in group # 2.

(2) In S12, the second record of the mutual interference table 23 is selected, and in S13, the node 2c is selected from the second record. However, the node 2c is already registered in the group # 2 (S14: Yes). Therefore, the processes S15 to S17 are not executed.

(3) In S13, the node 2e is selected from the second record. Here, the destination node of the node 2e includes the interference point node 2t. On the other hand, the destination node of the node 2a registered in the group # 1 at this point does not include the node 2t. That is, in S15, there is a group (group # 1) that does not include the source relay node whose destination node is the same interference point node. Therefore, in S16, the node 2e is registered in the group # 1. The destination of the node 2c registered in the group # 1 includes the node 2t. Therefore, the node 2e is not registered in the group # 2.

The setting unit 17 sets different transmission timings for each group. The transmission timing is represented, for example, in the order in which flooding packets are transmitted. In this embodiment, group # 1 is given a "transmission order: first" and group # 2 is given a "transmission order: second". Then, the determined transmission order is recorded in the flooding order table 24 as shown in FIG. 6 (b). However, the transmission timing of each group may be represented by other parameters. For example, the transmission timing of each group may be the waiting time from the time when the relay node receives the flooding packet to the time when the flooding packet is transferred.

The notification unit 18 notifies each transmission source relay node of the transmission timing (transmission order in this example) set by the setting unit 17. That is, the notification unit 18 notifies the nodes 2a, 2c, and 2e of the transmission order of the flooding packets. Specifically, the "transmission order: 1st" is notified to the nodes 2a and 2e belonging to the group # 1, and the "transmission order: 2nd" is notified to the nodes 2c belonging to the group # 2. Note that this notification may be realized by flooding or by unicast communication.

FIG. 9 shows an example of a wireless terminal device according to an embodiment of the present invention. The wireless terminal device 30 is mounted on each node 2 in the wireless communication system 100 shown in FIG.

As shown in FIG. 9, the wireless terminal device 30 includes a wireless transmission / reception unit 31, a reception processing unit 32, a communication control unit 33, a transmission processing unit 34, and a storage unit 40. However, the wireless terminal device 30 may include other circuits or functions not shown in FIG.

The radio transmission / reception unit 31 receives a radio signal transmitted from an adjacent node. In addition, the wireless transmission / reception unit 31 transmits a wireless signal. The reception processing unit 32 decodes the received signal and reproduces the packet. Then, the packet reproduced from the received signal (that is, the received packet) is passed to the communication control unit 33. The transmission control unit 34 generates a transmission signal from the transmission packet and passes it to the wireless transmission / reception unit 31.

The communication control unit 33 controls the operation of the wireless terminal device 30. The communication control unit 33 is realized by the processor in this embodiment. The storage unit 40 stores information used by the communication control unit 33. In this embodiment, the storage unit 40 stores the adjacent node information 41, the MPR information 42, and the flooding order information 43. Further, the storage unit 40 stores a program executed by the communication control unit 33.

The adjacent node information 41 represents a node adjacent to the own node. Further, the adjacent node information 41 may include information representing the node of the second hop from the own node. The MPR information 42 indicates whether or not the own node operates as an MPR node. The node that operates as the MPR node is designated by, for example, the gateway node 1. The flooding order information 43 represents the transmission order of flooding packets. The flooding order information is generated by the setting unit 18 at the gateway node 1 as described above.

FIG. 10 is a flowchart showing an example of the operation of the wireless terminal device 30. Note that this flowchart shows the operation when the wireless terminal device 30 receives the flooding packet.

In S21, the communication control unit 33 determines whether or not the newly received packet is the same as the previously received packet. When the newly received packet is the same as the previously received packet, the communication control unit 33 discards the packet without forwarding it in order to avoid duplicate transmission.

When the newly received packet is not the same as the previously received packet, the communication control unit 33 determines in S22 whether or not the own node is an MPR node. Whether or not the own node is an MPR node is described in the MPR information 42. Then, when the local node is not an MPR node, the communication control unit 33 discards the packet without forwarding it.

When the own node is an MPR node, the communication control unit 33 determines the transmission timing in S23 based on the flooding order information 43. Then, in S24, the wireless terminal device 30 broadcasts the received packet at the determined transmission timing. For example, when the transmission order of the own node is "kth", the wireless terminal device 30 broadcasts the packet when "k × ΔT" has elapsed from the reception time of the packet.

In this case, ΔT is determined so that interference does not occur between the radio wave transmitted from the node having the kth transmission order and the radio wave transmitted from the node having the kth transmission order. .. Therefore, ΔT is required to be a value larger than a predetermined threshold value. However, if ΔT is too large, the time required to complete flooding will be long. Therefore, ΔT is preferably a value as small as possible within a range in which interference is avoided.

FIG. 11 shows an example of a communication method according to the embodiment of the present invention. In this example, flooding from the gateway node 1 to the nodes 2a to 2e and 2p to 2v is performed as in the case shown in FIGS. 2 to 3. Further, as in the case shown in FIG. 3, nodes 2a, 2c, and 2e are designated as MPR nodes. Further, in the gateway node 1, the mutual interference table 23 shown in FIG. 6A and the flooding sequence table shown in FIG. 6B are created. That is, the "transmission order: 1st" is given to the nodes 2a and 2e, and the "transmission order: 2nd" is given to the nodes 2c.

The gateway node 1 broadcasts a flooding packet. Then, the nodes 2a to 2e receive this flooding packet. Then, each of the nodes 2a to 2e executes the processing of the flowchart shown in FIG.

Nodes 2a and 2e are selected as MPR nodes and are given a "transmission order: 1st". Therefore, the nodes 2a and 2e obtain "transmission waiting time: ΔT". Node 2c is selected as the MPR node and is given a "transmission order: second". Therefore, the node 2c obtains "transmission waiting time: 2ΔT". Since the nodes 2b and 2d are not selected as MPR nodes, the transfer process is not performed.

When ΔT elapses from the time when the nodes 2a to 2e receive the flooding packet, the nodes 2a and 2e broadcast the received packet as shown in FIG. 11A. As a result, the nodes 2p to 2r and 2t to 2v receive the flooding packet. Further, when ΔT elapses from the time when the nodes 2a and 2e perform the broadcast transfer, the node 2c broadcasts the received packet as shown in FIG. 11B. As a result, the nodes 2r to 2t receive the flooding packet.

As described above, according to the communication method according to the embodiment of the present invention, when the interference point node exists in the wireless network, the relay node transfers the packet at different timings. Therefore, when flooding is performed in the wireless multi-hop network, the occurrence of interference is avoided or suppressed, and the communication efficiency is improved. For example, node 2r receives packets from nodes 2a and 2c. However, as shown in FIG. 11, the nodes 2a and 2c transfer packets at different timings from each other. Therefore, no interference occurs at the node 2r.

In the case shown in FIG. 3, if the MPR nodes (2a, 2c, 2e) transfer packets at different timings, interference does not occur at the nodes 2r and 2t. For example, if the nodes 2a, 2c, and 2e perform packet transfer while shifting the transmission timing by ΔT in order, no interference occurs at the nodes 2r and 2t. However, in this procedure, the time required for flooding to be completed becomes longer than that in the communication method according to the embodiment of the present invention shown in FIG. In other words, according to the communication method according to the embodiment of the present invention, the occurrence of interference is avoided or suppressed while shortening the time required for the flooding to be completed.

Further, in the above-described embodiment, the transmission order is determined at the gateway node 1 and the transmission timing is calculated at each relay node, but the embodiment of the present invention is not limited to this method. For example, the gateway node 1 may calculate the transmission timing of each relay node, and the calculation result may be notified to each relay node.

1 Gateway node 2 (2a to 2e, 2p to 2v) Node 10 Wireless communication device 11 Wireless transmission / reception unit 12 Reception processing unit 13 Communication control unit 14 Interference point node identification unit 15 Relay node identification unit 16 Grouping unit 17 Setting unit 18 Notification Unit 19 Transmission processing unit 20 Storage unit 30 Wireless terminal device 100 Wireless communication system

Claims (4)

A wireless communication device used in a wireless network containing multiple nodes.
For each relay node that executes broadcast transfer among the plurality of nodes, a storage unit that stores route information representing a node that receives a packet transmitted by the broadcast transfer, and a storage unit.
An interference point node identification unit that identifies an interference point node to which a packet arrives from a plurality of relay nodes based on the route information,
For each interference point node, a relay node identification unit that specifies a relay node that transmits a packet that reaches the interference point node, and
A grouping unit that groups the relay nodes specified by the relay node identification unit so that two or more relay nodes that send packets to the same interference point node belong to different groups.
A setting unit that sets different transmission timings for each group,
A notification unit that notifies each relay node specified by the relay node identification unit of the transmission timing set by the setting unit, and a notification unit.
A wireless communication device equipped with. In the grouping unit, two or more relay nodes that send packets to the same interference point node belong to different groups, and two or more relay nodes that do not send packets to the same interference point node belong to the same group. The wireless communication device according to claim 1, wherein the relay nodes specified by the relay node identification unit are grouped. In a wireless communication device used in a wireless network containing multiple nodes
For each relay node that executes broadcast transfer among the plurality of nodes, an interference point node in which packets arrive from the plurality of relay nodes based on route information representing a node that receives a packet transmitted by the broadcast transfer. Identify and
For each interference point node, identify the relay node that sends the packet that reaches the interference point node.
The relay nodes are grouped so that two or more relay nodes that send packets to the same interference point node belong to different groups.
Set different transmission timing for each group,
A communication control program that causes a processor to execute a process of notifying each relay node of the transmission timing. A wireless communication system that includes a gateway node and multiple nodes.
The gateway node
For each relay node that executes broadcast transfer among the plurality of nodes, a storage unit that stores route information representing a node that receives a packet transmitted by the broadcast transfer, and a storage unit.
An interference point node identification unit that identifies an interference point node to which a packet arrives from a plurality of relay nodes based on the route information,
For each interference point node, a relay node identification unit that specifies a relay node that transmits a packet that reaches the interference point node, and
A grouping unit that groups the relay nodes specified by the relay node identification unit so that two or more relay nodes that send packets to the same interference point node belong to different groups.
A setting unit that sets different transmission timings for each group,
A notification unit for notifying each relay node specified by the relay node identification unit of the transmission timing set by the setting unit is provided.
A wireless communication system in which each node specified as a relay node broadcasts a received packet based on a transmission timing notified by the notification unit.

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