DESCRIPTION Title of Invention:
WIRELESS COMMUNICATION APPARATUS AND WIRELESS COMMUNICATION METHOD Technical Field
[0001 ] The present invention relates to a technology of transmitting route information to a wireless communication apparatus which constitutes a multihop network and performs intermittent control. Background Art
[0002] Along with the trend for a low-cost wireless module and, accompanying frequency reallocation, expansion of a band that does not require a license, the application of a wireless M2M (Machine-to-Machine) system is spreading. The wireless M2M system is a system that transmits and receives monitor information and control data between devices by wireless communication. In the wireless M2M system, since communication is performed with devices arranged in a wide area, elongation of the communication distance is one problem. Since installation of a wireless node in an environment where power supply cannot be secured is also anticipated, another problem is to achieve low power consumption which allows the wireless node to operate for a long time with a battery.
[0003] As a technology of elongating the communication distance, a multihop communication technology is available with which a relay node is arranged between a transmission source node and a destination node, data transmitted from the transmission source node is received by the relay node, and the data is transmitted from the relay node to the destination node. By applying the multihop communication technology, it becomes nossible to elongate the communication distance between the transmission

source node and the destination node without extending the communication distance of a wireless link. An example of the multihop communication technology is IPv6 Routing Protocol for Low Power and Lossy Networks (RPL) standardized by IETF (see Non-Patent Literature 1 below).
[0004] RPL updates communication routes by periodically exchanging control messages. In wireless communication, the situation of radio waves changes every moment, so periodical route update is indispensable. Nodes constitute a tree-structure multihop network with a gateway as a root. A route toward the gateway (to be referred to as an upward route hereinafter) extends from each node and a route toward each node (to be referred to as a downstream route hereinafter) extends from the gateway. These routes are updated by the following means. [0005] First, update of the upward route will be described.
The gateway sets upstream-route information in an upstream-route control message and periodically transmits the upstream-route control message by broadcast. A node that has received the upstream-route control message updates the upstream-route information it holds, sets the updated upstream-route information in the upstream-route control message, and transmits the upstream-route control message by broadcast.
Fig. 19 is a diagram illustrating a sequence for updating the upstream route. In Fig. 19, nodes A to C exist. The node A is a node adjacent to the node B and of a lower order than the node B and node C. The node B is a low-order node adjacent to the node C.
The node C, having received the upstream-route control message, updates the upstream-route information it holds, sets the updated upstream-route information in the upstream-route control message, and transmits the upstream-route control message by

broadcast (SI901). The node B receives the upstream-route control message from the node C and updates the upstream-route information (S1902). The node B sets the updated upstream-route information of its own in the upstream-route control message and transmits the upstream-route control message by broadcast (S1903). The node A receives the upstream-route control message from the node B and updates the upstream-route information (SI904). [0006] Update of the downstream route will now be described.
Fig. 20 is a diagram illustrating a sequence for updating the downstream route. In Fig. 20, the nodes A to C exist. The nodes A to C periodically transmit a downstream-route control message to an adjacent upper-order node by unicast.
The node A transmits the downstream-route control message to the node B by unicast (S2001). The node B, having received the downstream-route control message, updates downstream-route information (S2002). The node B also transmits the downstream-route control message having the updated contents to the node C (S2003). The node C, having received the downstream-route control message, updates the downstream-route information (S2004).
[0007] As a technology of realizing low power consumption, intermittent control is available with which a node repeats startup and sleep. For example, IEEE 802.15.4e standardizes Receiver Initiated Transmission (RIP) as a method of intermittent control (see Non-Patent Literature 2 below).
[0008] Fig. 21 is a diagram illustrating a sequence of intermittent control by RIP. In Fig. 21, nodes A and B exist. The nodes A and B are nodes adjacent to each other and constituting a multihop network. The nodes A and B repeat startup and sleep. The node B grasps in advance that the node A is a node that performs intermittent control.
When the node B receives data addressed to the node A from another node, the

node B does not transfer the data immediately (S2101). Upon startup, the node A transmits a data request to the adjacent node B to request data transmission (S2102). The node B, having received the data request from the node A, transmits the data addressed to the node A (S2103). The node A receives the data. At the timing of sleep of the intermittent cycle, the node A sleeps.
The data addressed to the node A is application data; not control information such as a routing control message. Citation List Patent Literature
[0009] Non-Patent Literature 1: IETF RFC 6550, "IPv6 Routing Protocol for Low-Power and Lossy Networks"
Non-Patent Literature 2: IEEE Std 802.15.5e-2012 Summary of Invention Technical Problem
[0010] However, the update method of the communication route by RPL of Non-Patent Literature 1, when combined with the intermittent control by RIP of Non-Patent Literature 2, poses a problem that a route control message transmitted while the node is sleeping cannot be received, and route information cannot be updated. [0011] The present invention has been made to solve the above problem and has as its object to obtain a wireless communication apparatus capable of updating a communication route even when a node constituting a multihop network performs intermittent control. Solution to Problem
[0012] A wireless communication apparatus which constitutes a multihop network having a tree structure and repeats startup and sleep, includes: a network control unit to

hold downstream-route information being information of a route toward a wireless
communication apparatus of a lower order than the own apparatus in the tree structure,
and upstream-route information being information of a route toward a wireless
communication apparatus of an upper order than the own apparatus in the tree structure,
and to generate a downstream-route control message notifying the downstream-route
information; and a wireless transmission/reception unit to transmit the
downstream-route control message to an adjacent wireless communication apparatus of
the upper order than the own apparatus in the tree structure, and thereafter, if having
received a transmission acknowledgment for the downstream-route control message
from the upper-order adjacent wireless apparatus, to instruct the network control unit to
update the upstream-route information.
Advantageous Effects of Invention
[0013] According to the present invention, it is possible to update a communication
route even when a node constituting a multihop network is performing intermittent
control.
Brief Description of Drawings
[0014] Fig. 1 is a block diagram illustrating a configuration of a network according to
Embodiment 1.
Fig. 2 is a block diagram illustrating a configuration of a node according to Embodiment 1.
Fig. 3 is a flowchart illustrating a flow of reception processing of the node according to the Embodiment 1.
Fig. 4 is a flowchart illustrating a flow of route information update processing of the node according to Embodiment 1.
Fig. 5 is a flowchart illustrating a flow of transmission processing of the node

according to Embodiment 1.
Fig. 6 is a flowchart illustrating a flow of downstream-route control message transmission processing of the node according to Embodiment 1.
Fig. 7 is a diagram illustrating a sequence for updating an upstream route of a node and a downstream route of a node according to Embodiment 1.
Fig. 8 is a block diagram illustrating an example of a hardware configuration of the node according to Embodiment 1.
Fig. 9 is a flowchart illustrating a flow of downstream-route control message reception processing and upstream-route control message transmission processing of a node according to Embodiment 2.
Fig. 10 is a flowchart illustrating a flow of upstream-route control message reception processing of the node according to Embodiment 2.
Fig. 11 is a diagram illustrating a sequence for updating an upstream route of a node and a downstream route of a node according to Embodiment 2.
Fig. 12 is a flowchart illustrating a flow of downstream-route control message reception processing and upstream-route control message transmission processing of a node according to Embodiment 3.
Fig. 13 is a flowchart illustrating a flow of upstream-route control message transmission processing and downstream-route control message reception processing of a node according to Embodiment 4.
Fig. 14 is a flowchart illustrating a flow of upstream-route control message reception processing and downstream-route control message transmission processing of the node according to Embodiment 4.
Fig. 15 is a diagram illustrating a sequence for updating an upstream route of a node and a downstream route of a node according to Embodiment 4.

Fig. 16 is a flowchart illustrating a flow of downstream-route control message transmission processing of a node according to Embodiment 5.
Fig. 17 is a flowchart illustrating a flow of downstream-route control message reception processing of the node according to Embodiment 5.
Fig. 18 is a diagram illustrating a sequence for updating an upstream route of a node and a downstream route of a node according to Embodiment 5.
Fig. 19 is a diagram illustrating a sequence for updating an upstream route.
Fig. 20 is a diagram illustrating a sequence for updating a downstream route.
Fig. 21 is a diagram illustrating a sequence of intermittent control by RIP. Description of Embodiments [0015] Embodiment 1.
First, a network configuration of the present invention will be described.
Fig. 1 is a diagram illustrating a configuration of a network according to Embodiment 1. The network is a multihop network constituted of nodes 10a to 10c as wireless communication devices, and a gateway 11. The network of Fig. 1 is a tree-structure network having the gateway 11 as a root. The gateway 11 builds the network and manages it. The gateway 11 transmits/receives data to/from the node directly or via another node. Also, the gateway 11 transmits/receives data to/from a device connected to a higher order of the gateway 11, or to/from another network. [0016] The direction from the node toward the gateway 11 is upstream. The direction from the gateway 11 toward the node is downstream. In Fig. 1, routes from the node 10a, 10b, and 10c to the gateway 11 via other nodes are built. The node 10a is a lower-order node of the node 10b and node 10c. The node 10b is a lower-order node of the node 10c and at the same time an upper-order node of the node 10c. The node c is an upper-order node of the node a and the node b. The nodes 10a to 10c

perform intermittent control. The nodes 10a to 10c repeat startup and sleep cyclically. The nodes 10a to 10c may start up when the period of validity or the like of route information approaches to an end.
[0017] A configuration of a node 10 will now be described. Each of the nodes 10a to 10c has the same configuration as that of the node 10.
Fig. 2 is a block diagram illustrating the configuration of the node 10 according to Embodiment 1.
The node 10 is constituted of an antenna 21, a wireless transmission/reception unit 22, an application data transmission/reception unit 23, a network control unit 24, and an intermittent control unit 25. The network control unit 24 is constituted of an upstream-route management unit 26 and a downstream-route management unit 27. The intermittent control unit 25 is constituted of a node management unit 28 and a startup management unit 29. The node 10 is sometimes connected to a sensor. In this case, the application data transmission/reception unit 23 transmits/receives data to/from the sensor. [0018] A case where the node 10 receives data will be described.
The antenna 21, having received a wireless signal from another node, outputs the wireless signal to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transforms the wireless signal into a frame and checks the destination of the frame. Two types of address, or a network address and a MAC address, are set in the frame. The network address designates the destination of data transmitted by the frame. The MAC address designates the destination indicating the next node on the multihop route. The network address and the MAC address may be of any values that can uniquely identify a node. Regarding the transmission source, a transmission source network address and a transmission source MAC address are set in

the frame, as with the destination.
[0019] The wireless transmission/reception unit 22 outputs data transmitted by the frame to either the application data transmission/reception unit 23 or the network control unit 24 depending on the contents of the data. The application data transmission/reception unit 23 processes application data inputted from the wireless transmission/reception unit 22. When a route control message is inputted to the network control unit 24 from the wireless transmission/reception unit 22, the network control unit 24 updates route information.
[0020] The upstream-route management unit 26 holds the MAC address of an upper-order node, the rank information, the MAC address of the next node, and the period of validity of the route information in relation to each other. The rank information is a value indicating the distance from the gateway 11 to the node. The distance is expressed by, for example, the number of hops. The number of hops is the number of nodes to pass through until a destination node. The MAC address of the next node designates the node located next on the route of when transmitting data addressed to the upper-order node, or the node adjacent to the node 10. The upstream-route management unit 26 saves the transmission source MAC address of an upstream-route control message, as the MAC address of the next node. The MAC address of the upper-order node, the rank information, and the period of validity of the route information have values notified by the upstream-route control message. [0021 ] The downstream-route management unit 27 holds the MAC address of a lower-order node, the rank information, the MAC address of the next node, and the period of validity of the route information, in relation to each other. The next node is the node located next on the route of when transmitting data addressed to the lower-order node, or the node adjacent to the node 10. The downstream-route

management unit 27 saves the transmission source MAC address of a downstream-route control message, as the MAC address of the next node. The MAC address of the lower-order node, the rank information, and the period of validity of the route information have values notified by the downstream-route control message.
The upstream-route management unit 26 and the downstream-route management unit 27 sometimes hold route information of a plurality of nodes. [0022] The node management unit 28 holds the MAC address of the adjacent node and information of whether the nodes perform intermittent control, in relation to each other. When entering a network, each node notifies its own MAC address and whether it will perform intermittent control, to the surrounding nodes. Based on the information of this transmission, the node management unit 28 can grasp whether or not an adjacent node is performing intermittent control.
The startup management unit 29 holds the intermittent cycle of its own node. [0023] A case where the node 10 transmits data will now be described.
The application data transmission/reception unit 23 outputs the application data generated by the sensor connected to the node 10 or by an application, to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 inquires of the node management unit 28 whether or not the next node is performing intermittent control. If the next node is performing intermittent control, the wireless transmission/reception unit 22, upon reception of a data request from the next node, transmits the application data to the next node via the antenna 21. If the next node is not performing intermittent control, the wireless transmission/reception unit 22 transmits the data to the next node without waiting for reception of the data request. [0024] A case where the node 10 transmits a route control message will now be described.

The network control unit 24 generates the route control message with referring to the upstream-route management unit 26 or downstream-route management unit 27 and by adding information of its own node. The upstream-route control message is constituted of the MAC address of the upper-order node, the rank information, and the period of validity of the route. The network control unit 24 sets the MAC address of its own node in the MAC address of the upper-order node, as the route information of its own node. The network control unit 24 holds the rank information of its own node and the period of validity of the route, and sets the values it holds, in the upstream-route control message. The network control unit 24 outputs the generated upstream-route control message and the MAC address of the next node to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transmits the upstream-route control message toward the lower-order node via the antenna 21 by broadcast.
[0025] The downstream-route control message is constituted of the MAC address of the lower-order node, the rank information, and the period of validity of the route. The network control unit 24 sets the MAC address of its own node in the MAC address of the lower-order node, as the route information of its own node. The network control unit 24 holds the rank information of its own node and the period of validity of the route, and sets the values it holds, in the downstream-route control message. The network control unit 24 outputs the generated downstream-route control message and the MAC address of the next node, to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transmits the downstream-route control message toward the upper-order node via the antenna 21 by unicast. [0026] When transmitting the route control message, the wireless transmission/reception unit 22 transmits the route control message without inquiring of

the node management unit 28 whether or not the next node is performing intermittent
control.
[0027] How the node 10 receives data from another node will now be described in
detail.
Fig. 3 is a flowchart illustrating a flow of reception processing of the node 10 according to the Embodiment 1.
When a wireless signal is received from the antenna 21, the wireless transmission/reception unit 22 starts processing with step S301.
[0028] In step S301, the wireless transmission/reception unit 22 checks whether or not the data transmitted by the frame is addressed to its own node. If the destination network address of the frame designates its own node, processing proceeds to step S302.
In step S302, the wireless transmission/reception unit 22 checks whether or not the data transmitted by the frame is application data. If the data transmitted by the frame is application data, the wireless transmission/reception unit 22 outputs the application data to the application data transmission/reception unit 23.
In step S303, the application data transmission/reception unit 23 processes the inputted application data. Sometimes the application data transmission/reception unit 23 may further output the data to the sensor connected to its own node. Processing ends.
[0029] In step S302, if the data transmitted by the frame is not application data, processing proceeds to step S304.
In step S304, if the data transmitted by the frame is a route control message, the wireless transmission/reception unit 22 outputs the route control message to the network control unit 24.

In step S305, the network control unit 24 updates the route information. The process of step S305 will be described later in detail. Processing ends.
In step S304, if the data transmitted by the frame is not a route control message, the wireless transmission/reception unit 22 performs a process according to the contents of the message. Processing ends.
[0030] In step S301, if the destination network address of the frame does not designate its own node, processing proceeds to step S306. This is a case of transferring the frame to another node.
In step S306, if the destination MAC address of the frame designates its own node, processing proceeds to step S307.
In step S307, the wireless transmission/reception unit 22 transfers data received from another node to the next node. This process will be described later in detail.
In step S306, if the destination MAC address of the frame does not designate its own node, processing proceeds to step S308.
In step S308, the wireless transmission/reception unit 22 discards the fame. Processing ends.
[0031] The process of step S305 of Fig. 3 will now be described in detail. In step S305, the network control unit 24 updates the route information.
Fig. 4 is a flowchart illustrating a flow of route information update processing of the node 10 according to Embodiment 1.
Upon reception of the route control message, the wireless transmission/reception unit 22 starts processing.
[0032] In step S401, the wireless transmission/reception unit 22 transmits, via the antenna 21, a transmission acknowledgment to the node that has transmitted the route

control message. The wireless transmission/reception unit 22 also outputs the route control message to the network control unit 24.
In step S402, the network control unit 24 checks whether or not an upstream-route control message is inputted. If an upstream-route control message is inputted, processing proceeds to step S403.
In step S403, the network control unit 24 saves the route information to the upstream-route management unit 26.
In step S402, if an upstream-route control message is not inputted, this is a case where a downstream control message is inputted. Processing proceeds to step S404.
In step S404, the network control unit 24 saves the route information to the downstream-route management unit 27.
[0033] How the node 10 transmits the application data to another node will now be described in detail.
Fig. 5 is a flowchart illustrating a flow of transmission processing of the node 10 according to Embodiment 1. Explanation will be made on a case where the node 10 transmits the generated data. This processing is also performed when transferring data received from another node. The case of transferring data received from another data corresponds to step S307 of Fig. 3.
The application data transmission/reception unit 23 transmits the application data to another node by a process according to an input from the sensor or the received application data. The application data transmission/reception unit 23 outputs the application data and the destination network address to the wireless transmission/reception unit 22. [0034] Upon input of data transmitted from the application data

transmission/reception unit 23, the wireless transmission/reception unit 22 starts processing with step S501.
In step S501, the wireless transmission/reception unit 22 outputs the destination network address to the network control unit 24 and inquires about the next node. The network control unit 24 outputs to the wireless transmission/reception unit 22 the MAC address of the next node which corresponds to the destination network address. The wireless transmission/reception unit 22 sets the destination network address inputted from the application data transmission/reception unit 23 in the destination network address of the frame. The wireless transmission/reception unit 22 also sets the MAC address of the next node which is inputted from the network control unit 24, in the destination MAC address of the frame.
[0035] In step S502, the wireless transmission/reception unit 22 outputs the MAC address of the next node to the intermittent control unit 25 and inquires whether the next node is performing intermittent control. The intermittent control unit 25 refers to the node management unit 28 and outputs a response to whether the next node is performing intermittent control, to the wireless transmission/reception unit 22. If the next node is performing intermittent control, processing proceeds to step S503. If the next node is not performing intermittent control, processing proceeds to step S504.
In step S503, the wireless transmission/reception unit 22 waits until it receives a data request from the next node. When the wireless transmission/reception unit 22 receives a data request from the next node, processing proceeds to step S504. [0036] In step S504, the wireless transmission/reception unit 22 sets the MAC address of the next node in the destination MAC address of the frame and sets the application data in the data portion of the frame. The wireless transmission/reception unit 22 also transforms the frame into a wireless signal and outputs the wireless signal to the antenna

21. The antenna 21 transmits the wireless signal to the next node. Processing ends. [0037] How the node 10 transmits the downstream-route control message will now be described in detail.
Fig. 6 is a flowchart illustrating a flow of downstream-route control message transmission processing of the node 10 according to Embodiment 1.
When the timing to transmit the downstream-route control message is reached, the network control unit 24 starts processing with step S601. The network control unit 24 may transmit the downstream-route control message cyclically. The network control unit 24 may transmit the downstream-route control message when the period of validity of the downstream-route control message approaches to an end, or when the node 10 has started up.
[0038] In step S601, the network control unit 24 generates the downstream-route control message by referring to the downstream-route management unit 27 and outputs the downstream-route control message as well as the MAC address of the transmission destination node to the wireless transmission/reception unit 22. The transmission destination node is an adjacent upper-order node. The wireless transmission/reception unit 22 sets the downstream-route control message in the data portion of the frame and converts the frame into a wireless signal. The wireless transmission/reception unit 22 transmits the wireless signal to the transmission destination node via the antenna 21.
In step S602, the wireless transmission/reception unit 22 checks whether or not a transmission acknowledgment is received from the node that has transmitted the route control message. If a transmission acknowledge is received, the wireless transmission/reception unit 22 notifies the network control unit 24 that a transmission acknowledge is received and proceeds to step S603. [0039] In step S603, the network control unit 24 starts up the timer. The duration of

the timer time is the time obtained by subtracting the time required for updating the route information from the time that takes until the node 10 sleeps next.
In step S604, the network control unit 24 checks whether or not the timer time expires. If the timer time expires, processing proceeds to step S605. If the timer time does not expire, processing returns to step S604.
In step S605, the network control unit 24 updates the period of validity of the route information held by the upstream-route management unit 26. If the upstream-route management unit 26 holds a plurality of pieces of route information, the network control unit 24 updates the period of validity of the upstream-route information whose next node is designated as the transmission destination of the downstream-route control message. This is because the validity of the upstream route for which the transmission destination node of the downstream-route control message is the next node is confirmed as the transmission acknowledge is received from the transmission destination node of the downstream-route control message. Processing ends. [0040] In step S602, if a transmission acknowledgment is not received, processing proceeds to step S606. In step S606, if it is determined that the wireless transmission/reception unit 22 failed in transmission of the downstream-route control message, processing ends. If it is determined that the wireless transmission/reception unit 22 did not fail in transmission of the downstream-route control message, processing returns to step S602. Transmission of the downstream-route control message that has failed corresponds to a case where the reception waiting time for a transmission acknowledgment expires or a case where a transmission acknowledgment has not been received when the downstream-route control message is re-sent a prescribed number of times. [0041] A sequence for updating the route will now be described. For the sake of

descriptive simplicity, the operation will be described mainly with referring to the unit names.
Fig. 7 is a diagram illustrating a sequence for updating the upstream route of the node 10 and the downstream route of the node 10b according to Embodiment 1. [0042] The node 10a transmits the downstream-route control message to the node 10b by unicast (S701). The node 10b transmits a transmission acknowledgment to the node 10a (S702) and updates the downstream-route information (S703). When the node 10a receives a transmission acknowledgement for transmission of the downstream-route control message from the node 10b, the node 10a starts up the timer (S704). If no upstream-route control information has been received until the timer time expires, the node 10a updates the period of validity of the upstream-route information for which the node 10b is the next node (S705). The duration of the timer time is the time obtained by subtracting the time required for updating the route information from the time that takes until the node 10 sleeps next. If an upstream-route control message is received from the node 10b before the timer time expires, the node 10a saves the contents of the message to the upstream-route information, thereby updating the upstream-route information.
[0043] In this embodiment, the network control unit 24 holds the period of validity of the upstream route by the upstream-route management unit 26. However, it does not matter if the period of validity of the upstream route is not saved. When a transmission acknowledgment is received, it may be determined that the route information for which the transmission source node of the transmission acknowledgment is the next node is valid, and the route information may be held. When a transmission acknowledgment cannot be received, this route information may be determined as invalid. When the route information is determined as invalid, it may

be deleted.
[0044] The hardware configuration of the node 10 will now be described.
Fig. 8 is a block diagram illustrating an example of a hardware configuration of the node 10 according to Embodiment 1.
The node 10 is constituted of a memory 81, a processor 82, and a wireless communicator 83. The wireless communicator 83 is connected to an antenna 21. [0045] The memory 81 stores programs and data to implement the functions of the wireless transmission/reception unit 22, application data transmission/reception unit 23, network control unit 24, and intermittent control unit 25. The memory 81 also stores data to implement the functions of the upstream-route management unit 26, downstream-route management unit 27, node management unit 28, and startup management unit 29. The memory is formed of, for example, a Read Only Memory (ROM), a Hard Disk Drive (HDD), and a Solid State Drive (SSD). [0046] The processor 82 reads the programs and data stored in the memory 81 and implements the functions of the wireless transmission/reception unit 22, application data transmission/reception unit 23, network control unit 24, and intermittent control unit 25. The processor 82 is implemented by processing circuits such as a CPU which executes the programs stored in the memory, a system LSI (Large Scale Integration), and so on.
A plurality of processing circuits may cooperate to execute the functions of the wireless transmission/reception unit 22, application data transmission/reception unit 23, network control unit 24, and intermittent control unit 25.
[0047] The wireless communicator 83, in cooperation with the memory 81 and the processor 82, implements the function of the wireless transmission/reception unit 22. The wireless communicator 83 is formed of a wireless transmitter and a wireless receiver, and transmits/receives a wireless signal to/from another apparatus via a

wireless circuit.
[0048] It is described above that when entering a network, a node transmits a notification of whether it will perform intermittent control to the surrounding nodes. The node may transmit this notification by adding it to an upstream-route control message, a downstream-route control message, application data, a transmission acknowledgment, or the like.
[0049] In the network of Fig. 1, a node that performs intermittent control and a node that does not perform intermittent control may mix. For example, in a factory having a Factory Automation (FA) system, if the system collects data of heat generated by a plurality of manufacturing apparatuses, a node that performs intermittent control and a node that does not perform intermittent control may mix. Whether or not a node can obtain power supply depends on the location where the node is installed. A node that cannot obtain power supply performs intermittent control to reduce power consumption. [0050] Therefore, in this embodiment, a wireless communication apparatus which constitutes a multihop network having a tree structure and repeats startup and sleep comprises a network control unit to hold downstream-route information being information of a route toward a wireless communication apparatus of a lower order than the own apparatus in the tree structure, and upstream-route information being information of a route toward a wireless communication apparatus of an upper order than the own apparatus in the tree structure, and to generate a downstream-route control message notifying the downstream-route information, and a wireless transmission/reception unit to transmit the downstream-route control message to an adjacent wireless communication apparatus of the upper order than the own apparatus in the tree structure, and thereafter, if having received a transmission acknowledgment for the downstream-route control message from the upper-order adjacent wireless apparatus,

to instruct the network control unit to update the upstream-route information. Therefore, even when the wireless communication apparatus constituting the multihop network is performing intermittent control, the communication route can be updated. When the transmission acknowledgment for the downstream-route control message is received, the upstream-route information is updated. Hence, even if no upstream-route control message has been received until the wireless communication apparatus starts sleeping in an intermittent cycle, the upstream-route information can be updated. [0051] Embodiment 2.
In Embodiment 1 described above, an upstream-route information is updated by receiving a transmission acknowledgment for a downstream-route control message. In Embodiment 2, an upstream-route control message is transmitted when a downstream-route control message is received.
In this embodiment, portions that are different from Embodiment 1 will be described.
[0052] How a network control unit 24, having received a downstream-route control message, transmits an upstream-route control message will now be described in detail.
Fig. 9 is a flowchart illustrating a flow of downstream-route control message reception processing and upstream-route control message transmission processing of a node 10 according to Embodiment 2.
Upon reception of a downstream-stream control message, a wireless transmission/reception unit 22 starts processing with step S901. [0053] In step S901, the wireless transmission/reception unit 22 transmits a transmission acknowledgment to the transmission source node of the downstream-route control message and outputs downstream-route information to a network control unit

In step S902, the network control unit 24 saves the inputted downstream-route information to a downstream-route management unit 27 and updates route information.
In step S903, the network control unit 24 refers to an upstream-route management unit 26 to check whether upstream-route information is held. If upstream-route information is held, processing proceeds to step S904.
In step S904, the network control unit 24 generates an upstream-route control message and outputs it to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transmits the inputted upstream-route control message by broadcast. Processing ends.
[0054] In step S903, if upstream-route information is not held, processing proceeds to step S905. The network control unit 24 generates an upstream-route control message added with a notification that upstream-route information is not held, and outputs the upstream-route control message to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transmits the inputted upstream-route control message by broadcast. Processing ends.
A notification that upstream-route information is not held is added to the upstream-route control message. Alternatively, this notification may be added to another message such as an upstream-route search message which searches an upstream route, and this another message may be transmitted.
[0055] How the network control unit 24 receives the upstream-route control message will now be described in detail.
Fig. 10 is a flowchart illustrating a flow of upstream-route control message reception processing of the node 10 according to Embodiment 2.
Upon reception of an upstream-route control message, the wireless transmission/reception unit 22 starts processing with step SI001.

[0056] In step S1001, the wireless transmission/reception unit 22 outputs the up stream-route information to the network control unit 24.
In step SI 002, if the upstream-route information contains information, processing proceeds to step SI003.
In step SI003, the network control unit 24 saves the inputted upstream-route information to the upstream-route management unit 26 and updates route information.
In step SI 002, if the upstream-route information does not contain information, the network control unit 24 updates the upstream-route information of the upstream-route management unit 26 and searches another upstream route. Processing ends.
[0057] A sequence of updating the route will now be described. For the sake of descriptive simplicity, the operation will be described mainly with referring to the unit names.
Fig. 11 is a diagram illustrating a sequence for updating an upstream route of the node 10a and a downstream route of the node 10b according to Embodiment 2.
The node 10a transmits the downstream-route control message to the node 10b by unicast (S1101). The node 10b transmits a transmission acknowledgment to the node 10a (SI 102) and updates downstream-route information (SI 103). The node 10b transmits the upstream-route control message by broadcast (S1104). Meanwhile, when the transmission acknowledgment for transmission of the downstream-stream control message is received from the node 10b, the node 10a starts up the timer (SI 105). The upstream-route control information is received until the timer time expires. The node 10a updates the upstream-route information (SI 106).
[0058] In this embodiment, a network control unit generates an upstream-route control message that notifies upstream-route information. A wireless transmission/reception

unit, upon reception of a downstream-route control message from an adjacent wireless communication apparatus of a lower order than the own apparatus in the tree structure, instructs the network control unit to update downstream-route information, and transmits the upstream-route control message to the lower-order adjacent wireless communication apparatus. Therefore, upstream-route information can be updated while a node that has transmitted the downstream-route control message is ON. Also, a node to transmit the upstream-route control message can update the upstream-route information without grasping the timing at which the node having transmitted the downstream-route control message starts up.
The network control unit, if not holding information of the upstream route, generates an upstream-route control message indicating not holding of the upstream-route information. The wireless transmission/reception unit, upon reception of a downstream-route control message from the adjacent wireless communication apparatus of the lower order than the own apparatus in the tree structure, transmits the upstream-route control message to the lower-order adjacent wireless communication apparatus. Therefore, if no upstream-route information is held, the lower-order adjacent wireless communication apparatus can search a new upstream route. [0059] Embodiments.
In Embodiment 2 described above, an upstream-route control message is transmitted when a downstream-route control message is received. In Embodiment 3, whether to transmit an upstream-route control message is determined in accordance with whether or not a transmission source node of a downstream-route control message is performing intermittent control.
In this embodiment, portions that are different from Embodiment 2 will be described.

How a network control unit 24, having received a downstream-route control message, transmits an up stream-route control message will be described in detail.
Fig. 12 is a flowchart illustrating a flow of downstream-route control message reception processing and upstream-route control message transmission processing of a node 10 according to Embodiment 3. The processes of steps SI201 to SI203 and S1206 are the same as the processes of steps S901 to S903 and S905 of Fig. 9, and their description will accordingly be omitted.
[0060] In step S1203, if the network control unit 24 holds upstream-route information, processing proceeds to step SI204.
In step S1204, the network control unit 24 inquires of a node management unit 28 of an intermittent control unit 25 whether or not a node 10a performs intermittent control. If the node 10a is performing intermittent control, the network control unit 24 generates an upstream-route control message and outputs it to a wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transmits the inputted upstream-route control message by broadcast. If the node 10a is not performing intermittent control, processing ends.
[0061] In this embodiment, an intermittent control unit is provided which holds information of whether or not an adjacent wireless communication apparatus performs intermittent control. If a lower-order adjacent wireless communication apparatus performs intermittent control, a wireless transmission/reception unit, upon reception of a downstream-route control message from the lower-order adjacent wireless communication apparatus, transmits an upstream-route control message to the lower-order adjacent wireless transmission/reception unit. Therefore, if a node that has transmitted a downstream-route control message is performing intermittent control, the upstream-route information can be updated while the node is ON.

[0062] Embodiment 4.
In Embodiment 3 described above, whether to transmit an up stream-route control message is determined in accordance with whether or not a transmission source node of a downstream-route control message is performing intermittent control. In Embodiment 4, a downstream-route control message is transmitted when an upstream-route control message is received.
In this embodiment, portions that are different from Embodiments 1 to 3 will be described.
[0063] How a network control unit 24 transmits an upstream-route control message will be described in detail.
Fig. 13 is a flowchart illustrating a flow of upstream-route control message transmission processing and downstream-route control message reception processing of a node 10 according to Embodiment 4.
When the timing to transmit the downstream-route control message is reached, a wireless transmission/reception unit 22 starts processing with step S1301. The network control unit 24 may transmit the upstream-route control message cyclically. The network control unit 24 may transmit the upstream-route control message when the period of validity of the upstream-route control message approaches to an end, or when the node 10 has started up.
[0064] In step S1301, the network control unit 24 generates the upstream-route control message by referring to an upstream-route management unit 26 and outputs the upstream-route control message as well as the MAC address of the transmission destination node to the wireless transmission/reception unit 22. The transmission destination node is an adjacent lower-order node. The wireless transmission/reception unit 22 sets the upstream-route control message in the data portion of the frame and

converts the frame into a wireless signal. The wireless transmission/reception unit 22 transmits the wireless signal to the transmission destination node via an antenna 21.
In step SI302, the wireless transmission/reception unit 22 receives a transmission acknowledgment from the node that has transmitted the upstream-route control message. The wireless transmission/reception unit 22 notifies the network control unit 24 that a transmission acknowledges is received.
[0065] In step S1303, the network control unit 24 starts up the timer. The duration of the timer time is the time obtained by subtracting the time required for updating the route information from the time that takes until the node 10 sleeps next.
In step S1304, if the wireless transmission/reception unit 22 checks whether or not a downstream-route control message is received. If a downstream-route control message is received, processing proceeds to step SI304.
In step S1305, the wireless transmission/reception unit 22 outputs the downstream-route control message to the network control unit 24. The network control unit 24 updates the downstream route. Processing ends. [0066] In step S1304, if a downstream-route control message is not received, processing proceeds to step S1306.
In step SI306, the network control unit 24 checks whether or not the timer time has expired. If the timer time has expired, processing ends. If the timer time has not expired, processing returns to step SI304.
[0067] How the network control unit 24 transmits the downstream-route control message upon reception of the upstream-route control message will now be described.
Fig. 14 is a flowchart illustrating a flow of upstream-route control message reception processing and downstream-route control message transmission processing of the node 10 according to Embodiment 4.

Upon reception of the up stream-route control message, the wireless transmission/reception unit 22 starts processing with step SI401. [0068] In step S1401, the wireless transmission/reception unit 22 transmits a transmission acknowledgment to the transmission source node of the upstream-route control message and outputs the upstream-route information to the network control unit 24.
In step SI402, the network control unit 24 saves the inputted upstream-route information to the upstream-route management unit 26 and updates the upstream-route information.
In step S1403, the network control unit 24 generates a downstream-route control message by referring to the downstream-route management unit 27 and outputs the generated downstream-route control message to the wireless transmission/reception unit 22. The wireless transmission/reception unit 22 transmits the inputted downstream-route control message by unicast. Processing ends. [0069] A sequence for updating the route will now be described. For the sake of descriptive simplicity, the operation will now be described mainly with referring to the unit names.
Fig. 15 is a diagram illustrating a sequence for updating an upstream route of a node 10a and a downstream route of a node 10b according to Embodiment 4.
The node 10b transmits the upstream-route control message by broadcast (S1501). The node 10b starts up the timer (S1502). The node 10a receives the upstream-route control message and updates the upstream-route information (SI503). The node 10a transmits the downstream-route control message to the node 10b by unicast (SI504). The node 10b transmits a transmission acknowledgment to the node 10a (S1505) and updates the downstream-route information (S1506). In this case, the

node 10b has successfully updated the downstream-route information before the timer time expired.
[0070] The node 10b may transmit to the node 10a an up stream-route control message added with information requesting the downstream-route information. The node 10 may transmit the downstream-route control message to the node 10b if information requesting the downstream-route information has been added to the upstream-route control message.
[0071] Hence, in this embodiment, a wireless transmission/reception unit, upon reception of an upstream-route control message from an upper-order adjacent wireless communication apparatus, instructs a network control unit to update upstream-route information, and transmits a downstream-route control message to the upper-order adjacent wireless communication apparatus. Therefore, a downstream route can be updated while the node is ON. Also, a node to transmit the downstream-route control message can update the downstream-route information without grasping the timing at which the node having transmitted the upstream-route control message starts up.
The network control unit generates an upstream-route control message which notifies the upstream-route information. The wireless transmission/reception unit includes, in the upstream-route control message, a request requesting a downstream-route information held by an adjacent wireless communication apparatus of a lower order than the own apparatus in the tree structure, and transmits the upstream-route control message to a lower-order adjacent wireless communication apparatus. Therefore, a downstream route can be updated reliably while a node that has transmitted the upstream-route control message is ON. [0072] Embodiment 5.
In Embodiment 4, an upstream route control message is transmitted when an

upstream-route control message is received. In Embodiment 5, upstream route information is included in a transmission acknowledgment for reception of a downstream-route control message.
In this embodiment, portions that are different from Embodiments 1 to 4 will be described.
[0073] How a network control unit 24 transmits a downstream-route control message will be described in detail.
Fig. 16 is a flowchart illustrating a flow of downstream-route control message transmission processing of a node 10 according to Embodiment 5. The processes of steps SI 601 to SI 602 and SI 604 to SI 607 are the same as the processes of steps S601 to 606 of Fig. 6, and their description will accordingly be omitted.
In step SI602, when a wireless transmission/reception unit 22 receives a transmission acknowledgment from a node that has transmitted a route control message, processing proceeds to step SI603.
[0074] In step SI603, the wireless transmission/reception unit 22 checks whether or not upstream-route information is added to the transmission acknowledgment. If upstream-route information is added to the transmission acknowledgment, the wireless transmission/reception unit 22 notifies the network control unit 24 of reception of the transmission acknowledgment and the upstream-route information. Processing proceeds to step SI 606. If upstream-route information is not added to the transmission acknowledgment, the wireless transmission/reception unit 22 notifies the network control unit 24 of reception of the transmission acknowledgment. Processing proceeds to step SI604.
The processes of step SI604 and beyond are the same as steps S603 to S605 of Fig. 6. Processing ends.

[0075] How the network control unit 24 receives the downstream-route control message will now be described in detail.
Fig. 17 is a flowchart illustrating a flow of downstream-route control message reception processing of the node 10 according to Embodiment 5. [0076] Upon reception of the downstream-route control message, the wireless transmission/reception unit 22 starts processing with step SI701.
In step SI701, the wireless transmission/reception unit 22 acquires upstream-route information from an upstream-route management unit 26 of the network control unit 24. The wireless transmission/reception unit 22 adds the upstream-route information to a transmission acknowledgment and transmits the transmission acknowledgment to the transmission source node of the downstream-route control message. The upstream-route information added to the transmission acknowledgment is, for example, information of the period of validity.
In step SI702, the wireless transmission/reception unit 22 outputs the downstream-route information to the network control unit 24. The network control unit 24 saves the inputted downstream-route information to a downstream-route management unit 27 and updates the route information. Processing ends. [0077] A sequence for updating the route will now be described. For the sake of descriptive simplicity, the operation will now be described mainly with referring to the unit names.
Fig. 18 is a diagram illustrating a sequence for updating an upstream route of a node 10a and a downstream route of a node 10b according to Embodiment 5.
The node 10a transmits a downstream-route control message to the node 10b by unicast (S1801). The node 10b transmits a transmission acknowledgment and upstream-route information to the node 10a (SI802) and updates downstream-route

information (S1803). The node 10a updates the upstream-route information (S1804). [0078] In this embodiment, a wireless transmission/reception unit, upon reception of a downstream-route control message from an adjacent wireless communication apparatus of a lower order than the own apparatus in a tree structure, acquires upstream-route information from the network control unit. The wireless transmission/reception unit includes the upstream-route information in the transmission acknowledgment, and transmits the transmission acknowledgment to the lower-order adjacent wireless communication apparatus. Therefore, the communication route can be updated even when the wireless communication apparatus constituting the multihop network is performing intermittent control. Also, the ON time duration of the node that has transmitted the downstream-route control message can be reduced. Reference Signs List [0079] 10, 10a to 10c: node
11: gateway
21: antenna
22: wireless transmission/reception unit
23: application data transmission/reception unit
24: network control unit
25: intermittent control unit
26: upstream-route management unit
27: downstream-route management unit
28: node management unit
29: startup management unit
81: memory
82: processor

83: wireless communicator

CLAIMS
[Claim 1] A wireless communication apparatus which constitutes a multihop
network having a tree structure and repeats startup and sleep, comprising:
a network control unit to hold downstream-route information being information of a route toward the wireless communication apparatus of a lower order than the own apparatus in the tree structure, and upstream-route information being information of a route toward the wireless communication apparatus of an upper order than the own apparatus in the tree structure, and to generate a downstream-route control message notifying the downstream-route information; and
a wireless transmission/reception unit to transmit the downstream-route control
message to the upper-order adjacent wireless communication apparatus being the
adjacent wireless communication apparatus of the upper order than the own apparatus in
the tree structure, and thereafter, if having received a transmission acknowledgment for
the downstream-route control message from the upper-order adjacent wireless apparatus,
to instruct the network control unit to update the upstream-route information.
[Claim 2] The wireless communication apparatus according to claim 1,
wherein the network control unit generates an upstream-route control message that notifies the upstream-route information, and
wherein the wireless transmission/reception unit, upon reception of a
downstream-route control message from a lower-order adjacent wireless communication
apparatus being the adjacent wireless communication apparatus of the lower order than
the own apparatus in the tree structure, instructs the network control unit to update the
downstream-route information and transmits the upstream-route control message to the
lower-order adjacent wireless communication apparatus.
[Claim 3] The wireless communication apparatus according to claim 1,

wherein the network control unit, if not holding the upstream-route information, generates an upstream-route control message indicating not holding of the upstream-route information, and
the wireless transmission/reception unit, upon reception of a downstream-route control message from a lower-order wireless communication apparatus being the adjacent wireless communication apparatus of the lower order than the own apparatus in the tree structure, transmits the upstream-route control message to the lower-order adjacent wireless communication apparatus.
[Claim 4] The wireless communication apparatus according to claim 2,
comprising an intermittent control unit to hold information of whether or not the adjacent wireless communication apparatus performs intermittent control,
wherein if the lower-order adjacent wireless communication apparatus performs intermittent control, the wireless transmission/reception unit, upon reception of a downstream-route control message from the lower-order adjacent wireless communication apparatus, transmits the upstream-route control message to the lower-order adjacent wireless communication apparatus.
[Claim 5] The wireless communication apparatus according to any one of
claims 1 to 4, wherein the wireless transmission/reception unit, upon reception of an upstream-route control message from the upper-order adjacent wireless communication apparatus, instructs the network control unit to update the upstream-route information, and transmits the downstream-route control message to the upper-order adjacent wireless communication apparatus.
[Claim 6] The wireless communication apparatus according to any one of
claims 1 to 5,
wherein the network control unit generates an upstream-route control message

which notifies the upstream-route information, and
wherein the wireless transmission/reception unit includes, in the upstream-route control message, a request requesting downstream-route information held by a lower-order adjacent wireless communication apparatus being the adjacent wireless communication apparatus of a lower order than the own apparatus in the tree structure, and transmits the upstream-route control message to the lower-order adjacent wireless communication apparatus.
[Claim 7] The wireless communication apparatus according to any one of
claims 1 to 6, wherein the wireless transmission/reception unit, upon reception of a downstream-route control message from a lower-order adjacent wireless communication apparatus being the adjacent wireless communication apparatus of the lower order than the own apparatus in the tree structure, acquires the upstream-route information from the network control unit, includes the upstream-route information in the transmission acknowledgment, and transmits the transmission acknowledgment to the lower-order adjacent wireless communication apparatus.
[Claim 8] A wireless communication method which constitutes a multihop
network having a tree structure and repeats startup and sleep, the wireless communication apparatus comprising:
a network control step of holding downstream-route information being information of a route toward the wireless communication apparatus of a lower order than the own apparatus in the tree structure, and upstream-route information being information of a route toward the wireless communication apparatus of an upper order than the own apparatus in the tree structure, and generating a downstream-route control message notifying the downstream-route information; and
a wireless transmission/reception step of transmitting the downstream-route

control message to the upper-order adjacent wireless communication apparatus being the adjacent wireless communication apparatus of the upper order than the own apparatus in the tree structure, and thereafter, if having received a transmission acknowledgment for the downstream-route control message from the upper-order adjacent wireless apparatus, instructing the network control unit to update the upstream-route information.