JP2021125857A - Wireless communication device and wireless communication method - Google Patents

Abstract

To prevent collision of broadcast packets in a wireless multi-hop network.SOLUTION: A wireless communication device used in a wireless multi-hop network includes a wireless reception unit, a wireless transmission unit, a storage unit, and a timing determination unit. The wireless reception unit receives a packet. The wireless transmission unit transmits a packet. The storage unit stores number-of-hops information indicating the number of hops from a parent node to an own node. The timing determination unit determines, when the wireless reception unit receives a broadcast packet in which the number of hops from the parent node is set, a timing for transmitting the broadcast packet, based on a difference between the number of hops which is set in the broadcast packet and the number of hops which is indicated by the number-of-hops information. The wireless transmission unit transmits the broadcast packet at the timing which is determined by the timing determination unit.SELECTED DRAWING: Figure 12

Description

The present invention relates to wireless communication devices and wireless communication methods used in wireless multi-hop networks.

In a wireless network including a plurality of nodes, when distributing information to all the nodes by the multi-hop method, for example, a packet is 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).

According to the above procedure, information can be efficiently distributed to all the nodes in the wireless network. 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.

Therefore, a method of avoiding a collision of broadcast communication in a wireless multi-hop network has been proposed. For example, the wireless communication device has route information in which the destination of the node that is the relay destination of the received packet is registered. Then, this wireless communication device relays the received packet only when the destination of the received packet is registered in the route information. (For example, Patent Document 1)

Japanese Unexamined Patent Publication No. 2016-096450

In the conventional technique, when a broadcast packet directly reaches a node two or more hops ahead, relay processing may be performed simultaneously on a plurality of nodes. In this case, packet collision occurs and the communication efficiency is lowered. Alternatively, the information may not reach all the nodes.

An object according to one aspect of the present invention is to suppress the collision of broadcast packets in a wireless multi-hop network.

The communication control device of one aspect of the present invention is used in a wireless multi-hop network. The wireless communication device includes a wireless receiving unit that receives a packet, a wireless transmitting unit that transmits a packet, a storage unit that stores hop number information indicating the number of hops from a parent node to its own node, and the wireless receiving unit. When a broadcast packet with a set number of hops is received from the parent node, the broadcast packet is sent based on the difference between the number of hops set in the broadcast packet and the number of hops represented by the hop number information. It includes a timing determination unit that determines the transmission timing. The wireless transmission unit transmits the broadcast packet at a timing determined by the timing determination unit.

According to the above aspect, the collision of broadcast packets is suppressed in the 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 a broadcast. It is a figure which shows an example of the broadcast using the MPR node. It is a figure which shows the configuration example of a wireless communication system, and an example of a multi-hop route. It is a figure which shows an example of broadcasting by multi-hop communication. It is a figure which shows an example of a packet collision. It is a timing chart of the case where a packet collision occurs. It is a figure which shows an example of the wireless communication apparatus mounted on each node. It is a figure which shows an example of own node information and adjacent node information. It is a figure which shows an example of the wireless communication device mounted on a parent node. It is a figure which shows an example of the broadcasting by embodiment of this invention. It is a timing chart which shows an example of the broadcast which concerns on embodiment of this invention. It is a flowchart which shows an example of the processing of the wireless communication apparatus implemented in each node. It is a figure which shows an example of the operation when a packet transmitted from a relay node reaches a node 2 hops or more ahead.

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 transmits packets according to, for example, the OLSR protocol.

The wireless communication system 100 includes a parent node 1 and a plurality of nodes 2 (2a to 2e, 2p to 2v). Here, the wireless communication system 100 is not particularly limited, but is, for example, a sensor network. In this case, a sensor is provided at each node. Then, the sensor data detected in each node is transmitted to the parent node 1. At this time, the sensor data detected in the node not adjacent to the parent node 1 is transferred to the parent node 1 via one or a plurality of nodes. That is, multi-hop transfer is performed.

The host device 50 is connected to the parent node 1. That is, the parent node 1 operates as a gateway. The host device 50 is, for example, a server computer that analyzes data collected from each node 2. Further, the host device 50 can give a necessary communication control instruction to the wireless communication system 100.

A wireless communication device is mounted on the parent node 1 and each node 2. 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.

The parent node 1 may distribute data to all the nodes 2a to 2e and 2p to 2v. In this case, the data is stored in a broadcast packet and transmitted. For example, when a program to be executed by a wireless communication device is distributed to each node 2, the program is stored in a broadcast packet and transmitted. In this case, the parent node 1 is the source of the data broadcast in the wireless communication system 100. Therefore, in the following description, the parent node 1 may be referred to as a "source node".

Node 2 can forward packets received from neighboring nodes to other nodes. That is, the node 2 may operate as a relay node. For example, when a broadcast packet is transmitted from the parent node 1, the node 2 transfers the broadcast packet received from the parent node 1 or an adjacent node as needed.

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.

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

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

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

The packet transmitted from the node 2a can reach a node other than the nodes 2p to 2r. For example, the packet transmitted from the node 2a reaches the parent node 1. However, the data included in this packet is the same as the data transmitted by the parent node 1. Therefore, in this case, the parent node 1 does not forward the packet received from the node 2a. Further, it is assumed that the packet transmitted from the node 2a also reaches the node 2b. However, the data included in this packet is the same as the data that the node 2b has previously received from the parent node 1. Therefore, in this case, the node 2b does not re-forward the packet received from the node 2a.

As described above, in the example shown in FIG. 2, each node 2 that has received the broadcast packet broadcasts the packet (excluding reforwarding). 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 an MPR (multipoint relay) 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 operates as a relay node in broadcast communication. On the other hand, the node 2 not selected as the MPR node does not execute the broadcast transfer even if it receives the broadcast packet. As a result, excessive packet transfer is suppressed, so packet collision is suppressed and communication efficiency is improved.

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

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

Since the nodes 2a, 2c, and 2e are selected as MPR nodes, they each transfer the broadcast packet received from the parent node 1. At this time, 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 packet transmitted from the node 2e reaches the nodes 2t to 2v. .. Therefore, the data transmitted from the parent node 1 is received by all the nodes 2a to 2e and 2p to 2v.

On the other hand, the nodes not selected as MPR nodes (nodes 2b and 2d in the example shown in FIG. 3) do not perform broadcast transfer. Therefore, as compared with the case shown in FIG. 2, the probability of packet collision is reduced, and the communication efficiency can be improved.

FIG. 4 shows a configuration example of a wireless communication system and an example of a multi-hop route. In this embodiment, the wireless communication system includes a parent node P and a plurality of nodes A to H, as shown in FIG. 4 (a). A wireless communication device is mounted on the parent node P and the plurality of nodes A to H, respectively.

As described above, each node A to H detects an adjacent node by using the Hello packet. For example, each node A to H detects an adjacent node based on the reception level of a radio signal transmitted from another node. In this case, when the reception level of the radio signal transmitted from a certain node is higher than a predetermined threshold value, that node is determined to be an adjacent node. Alternatively, the adjacent node may be detected based on other parameters. For example, the adjacent node may be detected based on the communication success rate or the signal-to-noise ratio of the received signal.

Each of the nodes A to H stores the adjacent node information representing the detected adjacent node in the memory in the own node, and transmits the adjacent node information to the parent node P. That is, the parent node P receives the adjacent node information of each node A to H. Therefore, the parent node P can recognize the network topology of the wireless communication system. In this embodiment, it is assumed that the network topology shown in FIG. 4 (b) is obtained. In FIG. 4B, the solid line connecting the nodes represents a link. Further, a set of nodes connected by one link are adjacent nodes to each other.

The parent node P determines a multi-hop route for broadcasting based on the network topology. The determination of the multi-hop route is realized by designating a relay node (MPR node in the example shown in FIG. 3). In this embodiment, as shown in FIG. 4C, nodes A, B, and C are selected as relay nodes.

Broadcasting from the parent node P to each of the nodes A to H is performed as follows. First, as shown in FIG. 5A, the parent node P transmits a broadcast packet. This packet reaches an adjacent node (that is, nodes A and E) of the parent node P. Then, the node A selected as the relay node broadcasts the received packet as shown in FIG. 5 (b). This packet reaches the adjacent nodes of node A (ie, nodes B, F, E, and parent node P). However, since the node E has previously received the same packet from the parent node P, the node E discards the packet. Also, since the parent node is the source of the packet, the packet is discarded.

Node B, which is selected as the relay node, broadcasts the received packet as shown in FIG. 5 (c). This packet arrives at a node adjacent to node B (ie, nodes C, G, F, E, A). However, since the nodes F, E, and A have received the same packet first, the packet is discarded. Further, the node C selected as the relay node broadcasts the received packet as shown in FIG. 5 (d). This packet arrives at a node adjacent to node C (ie, nodes D, H, G, F, B). However, since the nodes G, F, and B have received the same packet first, the packet is discarded.

In this way, the broadcast packet transmitted from the parent node P is broadcast to all the nodes A to H by multi-hop communication. The values (1 to 4) given to each node in FIG. 4 (c) are from the parent node P to each node when broadcasting is performed from the parent node P to each node A to H by multi-hop communication. Represents the number of hops.

However, in wireless communication, a packet transmitted from a certain node may reach not only an adjacent node but also a node two or more hops ahead. For example, in the example shown in FIG. 6A, the broadcast packet transmitted from the parent node P directly reaches not only the nodes A and E but also the nodes B and C.

In this case, the nodes A, B, and C selected as the relay nodes each broadcast the received packet. For example, in the example shown in FIG. 7, the node A broadcasts the packet at the timing when the time T1a elapses from the time when the packet is received from the parent node P. Similarly, the node B broadcasts the packet at the timing when the time T1b elapses from the time when the packet is received from the parent node P, and the node C elapses the time T1c from the time when the packet is received from the parent node P. Broadcast the packet at the timing. Here, for the sake of simplicity, it is assumed that T1a, T1b, and T1c are the same as each other. Then, the nodes A to C broadcast the received packet almost at the same time.

In this case, as shown in FIG. 6B, packet collision may occur. For example, packets forwarded by nodes A, B, and C arrive at node F at almost the same time. Therefore, the node F may not be able to receive the packet correctly.

The wireless communication method according to the embodiment of the present invention has a function of solving or alleviating this problem. That is, the wireless communication method according to the embodiment of the present invention has a function of avoiding or suppressing packet collision in the case where the broadcast packet directly reaches the node two or more hops ahead.

FIG. 8 shows an example of a wireless communication device mounted on each node. As shown in FIG. 8, the wireless communication device 10 mounted on each node includes a wireless transmission unit 11, a wireless reception unit 12, a communication IF 13, a memory 14, and a control unit 15. The wireless communication device 10 may include other circuits or functions not shown in FIG.

The radio transmission unit 11 transmits a radio signal according to an instruction given from the control unit 15. Therefore, when the control unit 15 outputs a transmission packet or a transfer packet, the radio transmission unit 11 transmits the packet. The radio receiving unit 12 receives a radio signal transmitted from another node. Therefore, when a packet is transmitted from another node, the radio receiving unit 12 receives the packet. The communication IF 13 provides an interface with a device implemented in the own node. In this example, sensors are mounted on each node. Therefore, the communication IF 13 can receive the sensor data output from the sensor.

The local node information and the adjacent node information are stored in the memory 14. Further, the memory 14 includes a packet buffer for temporarily storing the packet received by the wireless receiving unit 12. Although not particularly shown, the memory 14 stores a program that describes the operation of the wireless communication device 10.

As shown in FIG. 9A, the local node information includes the local node address, the upstream node address, the number of hops, and the relay node flag. The local node address identifies the node on which the wireless communication device 10 is mounted. The upstream node address identifies an adjacent node on the parent node side in the multi-hop route for broadcasting from the parent node P to each node A to H. For example, in the example shown in FIG. 4C, the upstream node for node G is node B, and the upstream node for node B is node A.

The number of hops represents the number of hops from the parent node P to the node in the multi-hop route for broadcasting from the parent node P to each node A to H. The values (1 to 4) given to each node in FIG. 4C represent the number of hops from the parent node P to each node. The relay node flag indicates whether or not to relay the broadcast packet. In the example shown in FIG. 4C, nodes A to C are selected as relay nodes, respectively.

The own node address is assigned to each node in advance. Further, the upstream node address, the number of hops, and the relay node flag are notified to each node from, for example, the parent node P.

Adjacent node information includes information representing the address and reception quality of one or more nodes detected in the reception monitoring procedure, as shown in FIG. 9B. The reception monitoring procedure monitors, for example, Hello packets. As the reception quality, for example, the reception level, the communication success rate, or the signal-to-noise ratio of the received signal is detected. Then, as the adjacent node information, for example, a node that provides reception quality better than a predetermined threshold value is registered. Alternatively, as the adjacent node information, a predetermined number of nodes are registered in order from the one with the best reception quality.

The control unit 15 controls packet communication of the wireless communication device 10. For example, when the communication IF 13 acquires the sensor data, the control unit 15 creates a packet including the sensor data and transmits the packet using the wireless transmission unit 11. When the wireless communication unit 12 receives a packet from another node, the control unit 15 analyzes and processes the packet. Further, the control unit 15 includes a timing determination unit 16. The timing determination unit 16 determines the transmission timing when the wireless communication device 10 transfers the received packet to another node. In this embodiment, the control unit 15 is realized by a processor.

FIG. 10 shows an example of a wireless communication device mounted on the parent node P. As shown in FIG. 10, the wireless communication device 20 mounted on the parent node P includes a wireless transmission unit 21, a wireless reception unit 22, a communication IF 23, a memory 24, and a control unit 25. The wireless communication device 20 may include other circuits or functions not shown in FIG.

The radio transmission unit 21 transmits a radio signal according to an instruction given from the control unit 25. Therefore, when the control unit 25 outputs a transmission packet, the wireless transmission unit 21 transmits the packet. The radio receiving unit 22 receives a radio signal transmitted from another node. Therefore, when a packet is transmitted from another node, the radio receiving unit 22 receives the packet. The communication IF 23 provides an interface with the host device 50.

The local node information, topology information, and route information are stored in the memory 24. The local node information includes the address information that identifies the parent node P. The topology information is created based on the adjacent node information transmitted from each node and represents the network topology of the wireless communication system. In this embodiment, the topology information represents the configuration shown in FIG. 4 (b). The route information represents a multi-hop route for broadcasting from the parent node P to each node A to H. In this embodiment, the route information represents the multi-hop route shown in FIG. 4 (c). In this case, the route information includes information that specifies one or more relay nodes.

The memory 24 includes a packet buffer that temporarily stores the packet received by the wireless receiving unit 22. Further, although not particularly shown, the memory 24 stores a program that describes the operation of the wireless communication device 20.

The control unit 25 creates topology information based on the adjacent node information collected from each node. Further, the control unit 25 includes a route information creation unit 26, and creates a multi-hop route by using the topology information. Creating a multi-hop route involves selecting a relay node. That is, for each node, a relay node flag indicating whether or not to operate as a relay node is set. Further, the control unit 25 specifies the number of hops from the parent node P to each node on the multi-hop route. The relay node flags and the number of hops for each node A to H are as follows.
Node A: Number of hops = 1, Relay node flag = ON
Node B: Number of hops = 2, Relay node flag = ON
Node C: Number of hops = 3, relay node flag = ON
Node D: Number of hops = 4, Relay node flag = OFF
Node E: Number of hops = 1, Relay node flag = OFF
Node F: Number of hops = 2, Relay node flag = OFF
Node G: Number of hops = 3, Relay node flag = OFF
Node H: Number of hops = 4, Relay node flag = OFF
Then, the relay node flag and the number of hops are notified to the corresponding nodes. Then, the wireless communication device 10 mounted on each node stores the notified relay node flag and the number of hops in the memory 14 as own node information. The control unit 25 is realized by the processor in this embodiment.

FIG. 11 shows an example of a broadcast according to an embodiment of the present invention. In this example, as shown in FIG. 11A, the broadcast packet transmitted from the parent node P is not only the adjacent nodes (that is, nodes A and E) of the parent node P but also two or more hops from the parent node P. The previous nodes (here, nodes B and C) are also reached directly. Here, the nodes A, B, and C are each selected as relay nodes by the parent node P. Therefore, the nodes A, B, and C each broadcast the received packet. However, in the wireless communication method according to the embodiment of the present invention, the timing at which each relay node transfers a received packet depends on the number of hops between the parent node P and each relay node.

FIG. 12 is a timing chart showing an example of a broadcast according to the embodiment of the present invention. This timing chart represents the broadcast shown in FIG. That is, the broadcast packet transmitted from the parent node P reaches not only the nodes A and E but also the nodes B and C directly. Note that in FIG. 12, node E is omitted because it is not a relay node.

Here, in the multi-hop route for broadcasting, the number of hops from the parent node P to each node is predetermined. In this example, the number of hops from the parent node P to the node A is "1", the number of hops from the parent node P to the node B is "2", and the number of hops from the parent node P to the node C is "1". 3 ". Then, each node recognizes its own number of hops as its own node information.

On the other hand, when the parent node P transmits a broadcast packet, the parent node P sets the number of hops in the header of the packet. In this embodiment, the initial value of the number of hops set in the header of the broadcast packet is "1". The value of the number of hops set in the header of the broadcast packet is incremented by 1 when transferred by the relay node.

When each relay node (that is, nodes A to C) receives a broadcast packet, the number of hops set in the header of the packet and the number of hops stored in the memory 14 of the own node as own node information are calculated. compare. In the following description, the number of hops set in the header of the broadcast packet may be referred to as "packet hop number". Further, the number of hops stored in the memory 14 of the own node as the own node information may be referred to as "the number of own hops".

Each relay node calculates the waiting time based on the difference between the number of own hops and the number of packet hops. The waiting time is calculated by, for example, the following formula.
Standby time = Own node standby time + Transfer standby time Transfer standby time = (Number of own hops-Number of packet hops) x 1 hop communication time Note that "1 hop communication time" transfers packets by 1 hop in a wireless multi-hop network. It represents the time required for this purpose, and is determined in advance based on, for example, the retry time related to carrier detection at the time of packet transmission, the packet transmission time, the own node standby time, and the like.

In the example shown in FIGS. 11 to 12, the waiting time of each node A to C is calculated as follows. It is assumed that the number of packet hops set for the packets arriving from the parent node P to each of the nodes A to C is "1". In FIG. 12, “h = 1” represents a state in which the number of hops set in the packet is “1”.

In this case, the number of own hops of node A is "1", and the difference between the number of own hops and the number of packet hops is zero. That is, the transfer waiting time is zero. Therefore, the waiting time Ta of the node A is the "own node waiting time". The number of own hops of node B is "2", and the difference between the number of own hops and the number of packet hops is "1". Therefore, the standby time Tb of the node B is "1 hop communication time + own node standby time". The number of own hops of node C is "3", and the difference between the number of own hops and the number of packet hops is "2". Therefore, the standby time Tc of the node C is "2 × 1 hop communication time + own node standby time".

Nodes A to C each broadcast the received packet at the timing when the waiting time has elapsed. That is, as shown in FIG. 12, the node A transmits the packet at the timing when the waiting time Ta has elapsed from the reception time of the packet transmitted from the parent node P. Further, the node B transmits the packet at the timing when the waiting time Tb has elapsed from the reception time of the packet transmitted from the parent node P. Further, the node C transmits the packet at the timing when the waiting time Tc has elapsed from the reception time of the packet transmitted from the parent node P. Here, the standby time Tb is longer than the standby time Ta by one hop communication time, and the standby time Tc is longer than the standby time Tb by one hop communication time. Therefore, the nodes A to C transmit packets at different timings from each other.

Specifically, as shown in FIG. 11A, when the broadcast packet transmitted from the parent node P reaches the nodes A to C (and the node E), the following packet transfer is performed. That is, when the time Ta elapses from the time when the broadcast packet reaches the nodes A to C, the node A broadcasts the packet as shown in FIG. 11 (b). As a result, the packet arrives at the node F. Further, when the time Tb elapses from the time when the broadcast packet arrives at the nodes A to C, the node B broadcasts the packet as shown in FIG. 11 (c). As a result, the packet arrives at the node G. Further, when the time Tc elapses from the time when the broadcast packet arrives at the nodes A to C, the node C broadcasts the packet as shown in FIG. 11 (d). As a result, the packet arrives at the node H. As a result, the packet reaches all the nodes.

In this way, the nodes A to C transfer packets at different timings from each other. Specifically, when the node B directly receives the packet transmitted from the parent node P, the node B receives the packet transmitted from the parent node P via the node A at substantially the same timing. Forward the packet. Further, when the node C directly receives the packet transmitted from the parent node P, the node C has substantially the same timing as when the packet transmitted from the parent node P is received via the node A and the node B. Forward the packet. Therefore, even when the broadcast packet transmitted from the parent node P directly reaches the node two or more hops ahead, the packet collision is avoided or suppressed.

FIG. 13 is a flowchart showing an example of processing of the wireless communication device mounted on each node. Before the processing of this flowchart is executed, it is assumed that the own node information and the adjacent node information described with reference to FIGS. 8 to 9 are stored in the memory 14. Further, it is assumed that the own node standby time and the one-hop communication time described with reference to FIG. 12 are predetermined.

In S1, the control unit 15 determines whether or not the received packet is a broadcast packet by checking the destination address set in the header of the received packet. When the received packet is a broadcast packet, the process of the control unit 15 proceeds to S2. On the other hand, when the received packet is not a broadcast packet, the control unit 15 determines in S12 whether or not the destination of the received packet is its own node. Then, when the destination of the received packet is its own node, the control unit 15 processes the packet.

In S2, the control unit 15 checks the sequence number set in the header of the received packet to determine whether or not the same packet has been received in the past. If the same packet has not been received in the past, the process of the control unit 15 proceeds to S3. On the other hand, if the same packet has been received in the past, the control unit 15 discards the received packet.

In S3, the control unit 15 determines whether or not the received packet is valid. For example, it is determined whether the received packet is valid or not based on the error check or the packet configuration check. Then, if the received packet is valid, the control unit 15 stores the received packet in the memory 14 in S4. On the other hand, when the received packet is not valid, the control unit 15 discards the received packet.

In S5, the control unit 15 determines whether or not the own node is selected as the relay note by referring to the relay node flag in the own node information stored in the memory 14. Then, when the own node is selected as the relay note, the control unit 15 sets the own node standby time in S6. The standby time of the own node shall be determined in advance.

In S7, the control unit 15 compares the number of packet hops set in the header of the received packet with the number of hops in the own node information stored in the memory 14 (that is, the number of own hops). Then, when the number of packet hops and the number of own hops match each other, the control unit 15 activates the timer in S9. In this case, the timer expires when the standby time of its own node elapses from the time it is started.

On the other hand, when the number of packet hops and the number of own hops do not match each other, the control unit 15 adds the transfer waiting time to the own node waiting time in S8. In this embodiment, the transfer standby time is obtained by multiplying the difference between the number of packet hops and the number of own hops by one hop communication time, as described above. Then, the control unit 15 activates the timer in S9. In this case, the timer expires when the time obtained by adding the transfer standby time to the own node standby time elapses from the time when it is started.

In S10, the control unit 15 monitors the expiration of the timer. Then, when the timer expires, the control unit 15 gives a transmission instruction to the wireless transmission unit 11 in S11. Then, the wireless transmission unit 11 transmits the received packet stored in the memory 14. At this time, the number of hops set in the header of this packet (that is, the number of packet hops) is incremented.

Next, the processing of the flowchart shown in FIG. 13 will be described based on the embodiment shown in FIG. For example, it is assumed that the broadcast packet transmitted from the parent node P reaches the node A as shown in FIG. 11 (a). Here, since the node A is selected as the relay node, the "own node standby time" is set as the standby time in S6. However, since the number of packet hops at the node A matches the number of own hops, the wireless communication device does not execute S8. Therefore, the wireless communication device clocks the "own node standby time" in S9 to S10. That is, the wireless communication device transfers the packet at the timing when the "own node standby time" has elapsed from the time when the broadcast packet is received.

The broadcast packet transmitted from the parent node P also reaches the node B as shown in FIG. 11 (a). Here, since the node B is selected as the relay node, the "own node standby time" is set as the standby time in S6. Further, in the node B, since the number of packet hops does not match the number of own hops, the wireless communication device executes S8. That is, the "transfer standby time" is added to the "own node standby time". At this time, since the difference between the number of packet hops and the number of own hops is "1", the transfer standby time is "1 hop communication time". Therefore, the wireless communication device clocks "own node standby time + 1 hop communication time" in S9 to S10. That is, the wireless communication device transfers the packet at the timing when "own node standby time + 1 hop communication time" has elapsed from the time when the broadcast packet is received.

The broadcast packet transmitted from the parent node P also reaches the node C as shown in FIG. 11 (a). Here, since the node C is selected as the relay node, the "own node standby time" is set as the standby time in S6. Further, at the node C, since the number of packet hops does not match the number of own hops, the wireless communication device executes S8. That is, the "transfer standby time" is added to the "own node standby time". At this time, since the difference between the number of packet hops and the number of own hops is "2", the transfer standby time is "2 x 1 hop communication time". Therefore, the wireless communication device clocks "own node standby time + 2 × 1 hop communication time" in S9 to S10. That is, the wireless communication device transfers the packet at the timing when "own node standby time + 2 × 1 hop communication time" has elapsed from the time when the broadcast packet is received.

Nodes D to H are not selected as relay nodes, respectively. Therefore, since the determination result of S5 is "No", the wireless communication device does not execute the transfer process. Further, in the example shown in FIG. 11, the same packet may arrive at each node twice or more. However, when the same packet arrives first, the determination result of S2 is "Yes", so that the wireless communication device does not execute the transfer process also in this case as well.

As described above, when the wireless communication device 10 receives the broadcast packet, the wireless communication device 10 determines the timing of transmitting the packet based on the difference between the number of packet hops and the number of own hops. Therefore, even when the broadcast packet transmitted from the parent node P directly reaches the node two or more hops ahead, the packet collision is avoided or suppressed.

In the above embodiment, it is assumed that the broadcast packet transmitted from the parent node P directly reaches the node two or more hops ahead, but the present invention is not limited to such a case. .. That is, the present invention is applied to the case where a broadcast packet transmitted from an arbitrary node directly reaches a node two or more hops ahead in a broadcast by multi-hop communication.

For example, in the case shown in FIG. 14, the broadcast packet transmitted from the parent node P reaches the nodes A and E as shown in FIG. 14 (a). Then, the node A selected as the relay node broadcasts the received packet. Here, it is assumed that this packet reaches not only nodes B, F, E, and P but also node C, which is two hops away from node A, as shown in FIG. 14 (b). The number of hops set in the packet transmitted from the node A is incremented from "1" to "2" in the node A.

In this case, since the number of packet hops and the number of own hops match in node B, node B shows that the own node waiting time elapses from the time when the packet is received from node A, as shown in FIG. 14 (c). To broadcast the received packet. On the other hand, in node C, the difference between the number of packet hops and the number of own hops is "1". Then, as shown in FIG. 14D, the received packet is broadcast. Therefore, packet collisions are avoided.

In addition, the standby time of the own node of each node may be different for each node. For example, when there are a plurality of relay nodes having the same number of hops from the parent node, different local node standby times may be set for the plurality of relay nodes.

Further, in the above embodiment, the initial value of the number of hops (that is, the number of packet hops) set in the packet transmitted from the parent node P is 1, but the initial value of the number of packet hops is zero. May be good. However, in this case, each node sets the waiting time based on the difference between the value obtained by adding 1 to the number of packet hops of the received packet and the number of own hops.

Further, in a wireless multi-hop network, the number of packet hops set for a packet is usually incremented by 1 each time the packet passes through a node. However, in a certain relay node, when the number of packet hops and the number of own hops do not match, the number of packet hops may be corrected according to the difference between the number of packet hops and the number of own hops. For example, in FIG. 11A, it is assumed that the number of hops set in the packet transmitted from the parent node P is “1”. In this case, since the number of packet hops and the number of own hops match at node A, node A increments the number of packet hops as usual. On the other hand, in the node B, the difference between the number of packet hops and the number of own hops is "1". In this case, the node B adds the difference (that is, 1) between the number of packet hops and the number of own hops to the number of packet hops, and performs a normal increment. By performing this correction, even in the case where the broadcast packet directly reaches the node two or more hops ahead is repeated, the number of packet hops represents the original number of hops, so that packet collision can be suppressed.

10, 20 Wireless communication device 11, 21 Wireless transmitter 12, 22 Wireless receiver 13, 23 Communication IF
14, 24 Memory 15, 25 Control unit 16 Timing determination unit 26 Route information creation unit 100 Wireless communication system

Claims (4)

A wireless communication device used in a wireless multi-hop network.
A wireless receiver that receives packets and
A wireless transmitter that sends packets and
A storage unit that stores hop count information that represents the number of hops from the parent node to the local node,
When the radio receiver receives a broadcast packet in which the number of hops is set from the parent node, it is based on the difference between the number of hops set in the broadcast packet and the number of hops represented by the hop number information. A timing determination unit for determining the timing of transmitting the broadcast packet is provided.
The wireless transmission unit is a wireless communication device that transmits the broadcast packet at a timing determined by the timing determination unit. The wireless communication device according to claim 1, wherein the timing determination unit determines a later timing as the difference becomes larger. The timing determination unit is obtained by adding the multiplication result of the predetermined one-hop communication time and the difference to the predetermined own node standby time from the time when the wireless reception unit receives the broadcast packet. The wireless communication device according to claim 1, wherein the timing at which the waiting time has elapsed is determined. A wireless communication method used in a wireless multi-hop network having a parent node and multiple nodes.
Determine a multi-hop route for broadcasting packets from the parent node to the plurality of nodes.
For each of the plurality of nodes, the number of hops when a packet is transferred from the parent node to each node via the multi-hop route is set.
The wireless communication device implemented in the parent node transmits a broadcast packet in which the number of hops is set from the parent node.
When the wireless communication device mounted on each node receives the broadcast packet, the timing is determined based on the difference between the number of hops set in the broadcast packet and the number of hops set in the own node. A wireless communication method comprising transmitting the broadcast packet.

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