JP5455820B2 - Route selection method, communication apparatus, and communication system - Google Patents

Description

  The present invention relates to a topology discovery method, a route selection method, a communication device, and a communication system.

  In industrial wireless communication used for FA (Factory Automation) and the like, it is necessary to control a device in real time, and short latency (low latency) is often required. For this reason, in the conventional topology discovery method for industrial wireless communication, a study is performed on the premise of a star topology in which a gateway device communicates directly with a wireless node device. In the star topology, since the gateway device communicates directly with the wireless node device, there is no alternative route when a failure occurs in a certain link.

  On the other hand, multi-hop communication that adaptively selects a route has recently been used. In multi-hop communication, a route is adaptively selected by flexibly responding to the addition of a wireless node or a location change. For example, Patent Document 1 below proposes a method of selecting a route while avoiding a link with degraded quality by exchanging and managing communication quality evaluation values using a HELLO message.

JP 2008-301444 A

  However, according to the above-mentioned conventional industrial wireless communication technology, since it is premised on star-type topology, there is no alternative route when a failure occurs in the direct communication route as described above, failure notification, setting change instruction, etc. There was a problem that the message of could not be sent. Further, the gateway device cannot find the presence of the wireless node when the wireless node device exists in a place where direct communication is not possible. For this reason, there has been a problem that it is not possible to start processing for prompting a change in the setting of the installation location or the like.

  On the other hand, in multi-hop communication, since a route can be selected adaptively, each wireless node device can communicate with a wireless node device that cannot communicate directly. However, in multi-hop communication, the number of wireless node devices to be relayed is larger than that in direct communication, and the number of wireless node devices to be relayed is indeterminate, so there is a high possibility that latency will increase. Therefore, there is a problem that there is a possibility that the request is not satisfied for the communication requiring a short latency.

  The present invention has been made in view of the above, and has a topology discovery method, a route selection method, a communication device, and a communication system that can suppress latency and discover a communication route between wireless node devices that cannot perform direct wireless communication. The purpose is to obtain.

In order to solve the above-described problems and achieve the object, the present invention provides a topology discovery method in a communication system including a plurality of communication devices that perform wireless communication, and includes a communication path in the communication system among the communication devices. A link information acquisition step of acquiring link information indicating the quality of each link that constitutes the communication path, for each communication path within a predetermined number of hops with the other communication apparatus. An ordering step in which the transmission source device determines a priority order of the communication path for each communication device of a communication partner based on the link information; and the transmission source device defines the communication path for each communication path. between the table holding step for holding the priority as the topology table, the transmission source device, and the communication device of the communication partner based on said priority A route selection step for selecting a communication route to be used, and the transmission source device, for each communication device, among the communication routes selected by the route selection step and the transmission source device via the communication device and the other A relay device number calculating step for determining the number of communication paths with the communication device as the number of relay devices, and in the route selection step, based on the number of relay devices, between the communication devices of communication partners The communication path to be used in is selected .

  According to the present invention, it is possible to suppress latency and to discover a communication path between wireless node devices that cannot perform direct wireless communication.

FIG. 1 is a diagram illustrating a configuration example of a communication system according to an embodiment. FIG. 2 is a diagram illustrating a functional configuration example of a node. FIG. 3 is a diagram illustrating a functional configuration example of the gateway. FIG. 4 is a diagram illustrating a format example of the HELLO message. FIG. 5 is a flowchart illustrating an example of the topology discovery processing procedure. FIG. 6 is a diagram illustrating an example of a topology table. FIG. 7 is a flowchart illustrating an example of a route selection procedure. FIG. 8 is a diagram illustrating an example of a topology table in the case where three types of information are used as the local station link information. FIG. 9 is a chart showing an example of an RTT measurement method.

  Embodiments of a topology discovery method, a route selection method, a communication device, and a communication system according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a diagram showing a configuration example of an embodiment of a communication system according to the present invention. As shown in FIG. 1, the communication system according to the present embodiment includes a gateway 1 having a wireless communication function and nodes 2-1 to 2-4 that are wireless communication devices. In the configuration example of FIG. 1, the number of nodes is four, but the number of nodes is not limited to this and may be any number. In FIG. 1, links that can be directly connected by radio are indicated by dotted arrows.

  FIG. 2 is a diagram illustrating a functional configuration example of the node 2-1 according to the present embodiment. The configuration of the nodes 2-2 to 2-4 is the same as the configuration of the node 2-1. As illustrated in FIG. 2, the node 2-1 performs a predetermined reception process on the received radio signal, performs a predetermined transmission process on data to be transmitted, and transmits the data as a radio signal; A control unit (link information acquisition unit) 22 that generates each message to be transmitted as a signal, processes each received message, and manages link information (information indicating link quality, etc.) for each link in the communication system; And a table holding unit 23 that holds a HELLO message information management table that is information transmitted and received by the HELLO message.

  FIG. 3 is a diagram illustrating a functional configuration example of the gateway 1 according to the present embodiment. The gateway 1 includes a wireless transmission / reception unit 21 and a control unit 22 similar to those of the node 2-1, and further includes a route selection unit 24 that selects a communication route and a table holding unit 25. Further, the table holding unit 25 of the gateway 1 holds a HELLO message management table as well as the table holding unit 23 of the node 2-1, and further holds a topology table used for route selection.

  The communication system of the present embodiment is a communication system that performs, for example, industrial wireless communication. For example, an industrial controller is connected to the gateway 1, industrial sensors and actuators are connected to the nodes 2-1 to 2-4, and the gateway 1 and the nodes 2-1 to 2-4 perform wireless communication. Thus, communication between the controller and the sensor or actuator can be realized.

  In the conventional industrial wireless communication technology, in order to shorten the latency, a star-type topology in which the gateway and each node directly perform wireless communication is assumed. For example, the IEEE 802.15.4g working group has an operating state of discovery mode, configuration mode, and operation mode in a star topology, and topology discovery processing such as network setup and addition of a new device to an existing network in the discovery mode. Has been proposed to do. In this topology discovery process, the wireless node device receives the beacon signal transmitted by the gateway, and the wireless node device returns a response signal to the topology discovery.

  On the other hand, the topology discovery processing as discussed in the above IEEE 802.15.4g working group assumes a star-type topology, so there is no alternative route when a failure occurs in the direct communication route, and the failure notification And messages such as setting change instructions cannot be sent.

  On the other hand, in the present embodiment, as a communication path between the gateway 1 and the nodes 2-1 to 2-4, not only a direct wireless communication path but also a path that is equal to or less than a predetermined number of hops (the number of relay nodes) And the route used for communication is selected from the grasped routes. Therefore, even when a failure occurs in the direct communication path, it is possible to secure a communication path that uses the other nodes 2-1 to 2-4 as relay nodes.

  The predetermined number of hops is determined based on, for example, a request value for latency. Although the required value for latency differs depending on the communication system, in the ISA (International Society of Automation) 100 WG (Working Group) 16 that is studying technical standards for FA, the latency reference value is 10 ms. Although the time required for one hop (one transmission or transfer) depends on the apparatus, it is considered to be several ms. Assuming that the required time for one hop is 5 ms, the ISA100 WG16 may have a latency reference value of 10 ms or less, and may be 2 hops or less. Therefore, in this case, 2 is set as the predetermined number of hops. In the following description, a case where the predetermined number of hops is 2 will be described as an example. Note that the predetermined number of hops is not limited to two, and may be appropriately set according to a request for the communication system, a processing time in the communication system, and the like.

  For example, in the configuration example of FIG. 1, when the gateway 1 and the node 2-1 are wirelessly connected, several communication paths can be considered. First, there is a communication path 10 for directly connecting the gateway 1 and the node 2-1 wirelessly. Next, the communication path 11 via the node 2-2 is used as a communication path (two-hop path) for connecting the gateway 1 and the node 2-1 in two hops via another node that is directly wirelessly connected to the gateway 1. There are three communication paths: a communication path 12 via the node 2-3 and a communication path 13 via the node 2-4. Such a topology is called a 2-hop mesh network type topology.

  As the mesh network type topology, for example, a three-hop route that wirelessly connects the gateway 1 and the node 2-1 via the node 2-3 and the node 2-4, or the node 2-3, the node 2-4, and the node 2-2. In this embodiment, as described above, since the predetermined number of hops is set to 2, a star topology (direct radio between the gateway 1 and the nodes 2-1 to 2-4 is used. Communication) and 2-hop mesh network topology.

  Further, in the present embodiment, the gateway 1 and the nodes 2-1 to 2-4 periodically exchange notification messages in order to grasp the route to a predetermined number of hops (2 hops). Based on the above, topology discovery processing is performed. In the present embodiment, an OLSR (Optimized Link State Routing) protocol (RFC (Request For Comments)) 3626 studied by the MANET (Mobile Ad-hoc Networks) working group of the Internet Engineering Task Force (IETF) is used as the notification message. ) Based on the extended HELLO message. In FIG. 1, the HELLO message transmission direction 14 indicated by the block arrow indicates the direction in which the HELLO message of this embodiment is transmitted. In FIG. 1, for simplicity, the reference numeral is attached to only one HELLO message transmission direction 14, but the other block arrows similarly indicate the HELLO message transmission direction.

  In the OLSR protocol, each node periodically transmits a HELLO message carrying its own node information and adjacent link information by broadcasting. Each node acquires an address of an adjacent node based on the received HELLO message. Based on the acquired information, management of adjacent link information, adjacent node information, 2-hop adjacent link information, and the like is performed. Specifically, in the OLSR protocol, first, a HELLO message containing its own address is transmitted to the adjacent node. When all the nodes do this, each node can know adjacent node information (adjacent node address). Each node stores the adjacent node information grasped by itself in a HELLO message and transmits it. Thereby, each node can know information of a node (two hops) ahead of its own adjacent node.

  FIG. 4 is a diagram illustrating a format example of the HELLO message according to the present embodiment. Of the HELLO message format of the present embodiment, Reserved (reserved) indicating a reserved field, Htime indicating a transmission interval of the HELLO message, Willingness indicating aggressiveness to retransmission, and the link between adjacent nodes The Link Code indicating the link information such as the status, the Link Message Size indicating the size of the link message, and the Neighbor Interface Address #N (N = 1, 2,...) Indicating the interface address of the adjacent node are the normal OSLR. This is the same as the HELLO message.

  FIG. 4 shows the message portion of the packet to which the HELLO message is transmitted. In addition, a predetermined header is added to the packet storing the HELLO message, and this header contains the destination address. Assume that the address and the source address are stored. For example, in the OSLR packet, the source address is stored in the Originator Address field.

  The HELLO message of this embodiment includes, in addition to each field of a normal OSLR HELLO message, for each adjacent node (for each interface address of the adjacent node), own station link information (LI: Link Information) and adjacent station link information. (NLI: Neighbor Link Information) field. The local station link information is composed of two types of information, LI0 and LI1, and the adjacent station link information is composed of two types of information, NLI0 and NLI1.

  LI0 and LI1 are information indicating the quality of a link with an adjacent node, respectively, packet transmission quality (such as a HELLO message reception rate (loss rate), PER (Packet Error Rate)), and radio quality (RSSI (Received)). One or more of Signal Strength Indicator, SINR (Signal to Interference and Noise Power Ratio), traffic amount, communication (modulation) rate, and the like can be used. For example, RSSI (Received Signal Strength Indicator) can be used as LI0, and PER (Packet Error Rate) can be used as LI1.

  Further, the gateway 1 and each of the nodes 2-1 to 2-4 receive the LI0 and LI1 of the reverse link with the adjacent node based on the radio signal transmitted from the own device in the adjacent node by the received HELLO message. The calculated LI0, LI1) can be acquired. The gateway 1 and each of the nodes 2-1 to 2-4 determine NLI0 and NLI1 as NLI0 and NLI1 based on the LI0 and LI1 stored in the received HELLO message. For example, the gateway 1 stores LI0 and LI1 corresponding to the gateway 1 stored in the HELLO message received from the node 2-1, in the NLI0 and NLI1 fields corresponding to the node 2-1 of the HELLO message to be transmitted. .

  Note that the number of bits of LI0, LI1, NLI0, and NLI1 may be any number, but FIG. 4 shows the case of 8 bits as an example. Further, FIG. 4 shows an example in which the local station link information and the adjacent station link information are each two types, but the local station link information and the adjacent station link information may be one type each, or three or more types. It is good. The storage order of the local station link information and the adjacent station link information is not limited to the example of FIG. 4 and may be any order.

  In this embodiment, an example of using a HELLO message that is an extension of the OSLR HELLO message has been described. However, any other type of notification message may be used as long as it is a broadcast message storing the local station link information and the adjacent station link information for each adjacent node. An information message may be used.

  Next, the operation of the present embodiment will be described. FIG. 5 is a flowchart illustrating an example of a topology discovery processing procedure performed by the gateway 1 and the nodes 2-1 to 2-4. In the gateway 1 and the nodes 2-1 to 2-4, the control unit 22 generates a HELLO message and transmits the HELLO message via the wireless transmission / reception unit 21 at regular intervals (a period to store the HELLO message as Htime). And In the initial stage (in a state where HELLO messages from other gateway 1 and nodes 2-1 to 2-4 have not been received), the interface address of the adjacent node, the local station link information, the adjacent station link information, etc. are grasped. Since it is not completed, these items do not need to be stored, and the address of the own node only needs to be stored. Here, although the operation of the gateway 1 will be described as an example, the nodes 2-1 to 2-4 also perform the same operation.

  The control unit 22 of the gateway 1 initializes the time t of the timer for measuring the elapsed time within the update period of the local station link information to 0 (step S11). And the control part 22 of the gateway 1 waits for reception of a HELLO message (step S12).

  When the control unit 22 of the gateway 1 receives the HELLO message via the wireless transmission / reception unit 21, the control unit 22 holds the information stored in the HELLO message and, based on the received HELLO message, the gateway 1 that is the transmission source of the HELLO message. Or the information for calculating the local link information about the link between the nodes 2-2 to 2-4 is held as temporary information (step S13).

  As described above, the local station link information is one or more of packet transmission quality, wireless quality, traffic volume, communication (modulation) rate, and the like. Here, for example, assuming that RSSI is used as LI0 and PER is used as LI1, in step S13, the RSSI at the time of receiving one HELLO message is obtained and held as temporary information, and at the time of receiving one HELLO message. It is assumed that the presence / absence of an error for each packet is held as temporary information. When HELLO messages are received from a plurality of nodes 2-1 to 2-4, temporary information is held for each source (for each link) of these HELLO messages.

  Next, the control unit 22 of the gateway 1 determines whether or not t is equal to or less than a predetermined threshold T (whether or not the time T has elapsed since t = 0) (step S14). If t is smaller than T (step S14 Yes), the process returns to step S12 and waits for the reception of the HELLO message.

  If t is equal to or greater than T (No in step S14), the process returns to step S11 to perform the processing from step S11, and calculates the local station link information based on the stored temporary information (step S15). For example, when LI0 is RSSI, assuming that the number of temporary RSSI information held is N, these N pieces of average values, moving average values, maximum values, and the like are obtained, and this calculation is performed. The value is LI0. When LI1 is PER, PER is calculated based on the stored temporary information of PER (presence / absence of packet error). In this way, LI0 and LI1 can be updated every period T.

  Then, the control unit 22 of the gateway 1 stores, for each adjacent node, a HELLO message storing the address of the adjacent node notified by the received HELLO message and the calculated local station link information corresponding to the adjacent node. Generate (step S16). At this time, when LI0 and LI1 corresponding to the gateway 1 are stored in the HELLO message received in step S13, the stored LI0 and LI1 are stored in the NLI0 and LILO corresponding to the transmission source node of the HELLO message. Stored in the generated HELLO message as NLI1.

  Specifically, for example, the address of the gateway 1 is stored in the Neighbor Interface Address # 1 of the HELLO message received by the gateway 1 from the node 2-1, and LI0 and LI1 (reception LI0 and reception LI1) corresponding to the address are stored. ) Is stored. Assume that the address of the node 2-1 is stored as Neighbor Interface Address # 1 of the HELLO message transmitted from the gateway 1. In this case, the gateway 1 stores the reception LI0 and the reception LI1, respectively, as NLI0 and NLI1 corresponding to the Neighbor Interface Address # 1 of the generated HELLO message.

  Next, the control unit 22 of the gateway 1 creates a table based on the calculated local station link information and information obtained based on the received HELLO message (interface addresses of adjacent nodes, LI0, NLI0, etc. for each adjacent node). The HELLO message information management table stored in the holding unit 25 is updated (step S17). The HELLO message information management table stores information stored in the HELLO message transmitted by the own station and information extracted from the received HELLO message.

  When the gateway 1 and the nodes 2-1 to 2-4 perform the topology discovery process as described above, the gateway 1 and the nodes 2-1 to 2-4 are linked in the communication system by the HELLO message information management table. Each link information (including link quality information) can be managed.

  In the above description, the local station link information is obtained based on the temporary information every period T. However, without managing by the period, for example, when the number of received HELLO messages is N, The local station link information may be obtained based on N pieces of temporary information. In addition, when the time when the gateway 1 starts to receive the HELLO message differs depending on the transmission source nodes 2-1 to 2-4, the elapsed time is managed for each transmission source of the HELLO message, and predetermined for each transmission source. The local station link information may be obtained in a cycle of

  In the above description, the local station link information is calculated based on the HELLO message. However, the local station link information is the link quality with the adjacent node (in the direction in which the local station receives from the adjacent node). For example, it may be a wireless quality calculated based on a received signal other than the HELLO message.

  FIG. 6 is a diagram illustrating an example of a topology table according to the present embodiment. FIG. 6 shows an example in which one piece of information (LI0) is used as the local station link information. The control unit 22 of the gateway 1 determines the local station link information obtained based on the HELLO message received from each of the nodes 2-1 to 2-4 and the other nodes 2-1 to 2-stored in the received HELLO message. 4 generates and updates the topology table based on the local station link information and the adjacent station link information in 4 and stores the topology table in the table holding unit 25.

  As shown in FIG. 6, the topology table first has information for each 1-hop node (nodes 2-1 to 2-4) in which the device itself can directly perform wireless communication. Then, for each hop node, route information (corresponding to information for one line of the table in FIG. 6) to a node (two-hop node) through which the own device can perform wireless communication with two hops is obtained. Have.

  For example, the information that the 1-hop node is the node 2-1 is the route information of the 2-hop node being none (that is, direct wireless communication with the node 2-1), and the node 2-2 via the node 2-1. Information on the route, information on the route to the node 2-3 via the node 2-1, and information on the route to the node 2-4 via the node 2-1. Composed.

  The information of each path in the topology table is composed of own station link information, adjacent station link information, round trip link information, link information metric, path candidate priority, first relay number, and second relay number.

  As the local station link information, the local link information calculated in step S16 described above is stored for a route with a two-hop node of none, and the local link information calculated by the 1-hop node for a route other than the two-hop node is none. Stores station link information (ie, LI0 corresponding to the interface address of the 2-hop node stored in the HELLO message received from the 1-hop node).

  As the neighboring station link information, for a route with a two-hop node of none, the local station link information of the route to the gateway 1 calculated by the one-hop node (corresponding to the interface address of the gateway 1 received from the one-hop node) LI0) is stored. For a route other than the one where the 2-hop node is none, the neighbor link information includes the neighbor link information at the one-hop node (that is, the interface address of the two-hop node stored in the HELLO message received from the one-hop node). The corresponding NLI0) is stored.

  In FIG. 6, the local station link information and the adjacent station link information are represented by normalizing good radio quality as a numerical value between 0 (poor quality) and 1 (good quality). For example, when RSSI is used as the local station link information and the neighbor station link information, the larger the value, the higher the power intensity and the better the radio quality. Therefore, for example, by multiplying (or dividing by a predetermined value) the local station link information and the adjacent station link information expressed in RSSI, 0 (poor quality) to 1 (quality is low). To good) value. Further, in the case of PER, the smaller the numerical value, the better the quality. Therefore, calculation such as normalization is performed by subtracting the values of the local station link information and the adjacent station link information expressed by PER from 1.

  FIG. 6 shows an example in which a communication route is selected from communication routes up to a 2-hop route. When a communication route is selected from among communication routes up to three or more M-hop routes, a column from 3 hop nodes to M hop nodes is added to FIG. What is necessary is just to obtain | require a link information metric etc. for every.

  Round-trip link information (RTLI: Round Trip-Link Information) stores a calculated value obtained based on the local station link information (LI) and the adjacent station link information (NLI) of the route. As this calculation value, for example, the local station link information (LI), the adjacent station link information (NLI), and the product (RTLI = LI * NLI) can be used. It should be noted that any calculation method may be used as long as each of NLI and LI increases such that RTLI becomes larger, such as using sum instead of product or adding a predetermined weighting coefficient. . The local station link information and the adjacent station link information indicate link information regarding links in the reverse direction of the same route. Therefore, the round-trip link information is link information reflecting bidirectional link information.

  As the link information metric (LIM), when the two-hop node is none, the reciprocal number of the round-trip link information (LIM = 1 / (LI * NLI)) is stored. When the 2-hop node is other than none, the sum of the reciprocal of the round-trip link information and the link information metric when the 2-hop node in the same 1-hop node information is none is stored as the link information metric. . The link information metric indicates a metric for each route. In general, when a route is selected, a route with a small metric is preferentially selected. On the other hand, the link information of the local station (same for the link information of the neighboring station) is normalized so that the higher the value, the better the quality. Therefore, by taking the reciprocal of the round-trip link information as the link information metric, By selecting a route with a small information metric, a route with good quality is selected.

  For example, in a route in which the 1-hop node is the node 2-1 and the 2-hop node is none (the route in the uppermost row in FIG. 6), the local link information column is based on the HELLO message received from the node 2-1. A value obtained by normalizing the calculated local station link information is stored, and a value obtained by normalizing LI0 corresponding to the gateway node 1 stored in the HELLO message received from the node 2-1 is stored in the adjacent station link information column. Is stored. The round trip link information stores the product (0.50 × 0.60 = 0.30) of the local station link information (0.60) and the adjacent station link information (0.50), and the link information metric. Stores the reciprocal of the round trip link information (1 / 0.30 = 3.33).

  In the route where the 1-hop node is the node 2-1 and the 2-hop node is the node 2-2 (route in the second row from the top in FIG. 6), the HELLO message received from the node 2-1 is displayed in the local link information column. The value obtained by normalizing LI0 corresponding to the node 2-2 stored in the node 2-2 is stored, and the adjacent link information column corresponds to the node 2-2 stored in the HELLO message received from the node 2-1. A value obtained by normalizing NLI0 to be stored is stored. The round trip link information stores the product (0.90 × 0.90 = 0.81) of the local station link information (0.90) and the adjacent station link information (0.90), and the link information metric is The sum (1 / 0.81 + 3.33 = 4.57) of the reciprocal of the round-trip link information and the link information metric when the two-hop node is none is stored.

  Here, the reciprocal number of the round trip link information is taken as the link information metric, but other computations can be used as long as the link information metric is determined based on the round trip link information so that the value of the route having a better quality becomes smaller. A method may be used. Further, the information link information metric may be obtained directly so that the value becomes smaller as the quality is higher, without using the round trip link, using the local station link information and the adjacent station link information.

  In the route candidate priority, the priority of the communication route for each communication destination is stored. The route candidate priority order is obtained as follows. First, a route with the same communication destination is extracted from the topology table illustrated in FIG. Then, the link information metrics of the extracted routes are ranked so as to have a high rank (low rank value) in ascending order, and this rank is stored as a route candidate priority for each communication destination. In the example of FIG. 6, the communication destination node is described in parentheses in the path candidate priority column. These processes are performed for each communication destination.

  For example, as a route (communication route between the gateway 1 and the node 2-1) having the node 2-1 as a communication destination, "gateway 1-node 2-1", "gateway 1-node 2-2 node" 2-1 ”,“ Gateway 1-Node 2-3-Node 2-1, ”“ Gateway 1-Node 2-4-Node 2-1, ”(the top row, the 6th row, the 10th row, Four routes (route 14) are extracted. Since the link information metrics of these routes are 3.33, 2.35, 2.95, and 5.37, respectively, the route having the smallest value 2.35, that is, “gateway 1-node 2-2 node The route “2-1” has the priority 1.

  Further, the number of relays in the first place is the number of routes whose route candidate priority is 1 among routes (routes including relay nodes) other than the directly wirelessly connected route among a set of routes having the same 1-hop node. The number of relays in the second place indicates the number of routes having a route candidate priority of 2 among routes other than those directly connected by radio among the set of routes having the same 1-hop node. . In FIG. 6, a circle other than the direct wireless connection route having a route candidate priority of 1 is indicated with a circle in the first relay number column. Similarly, a circle other than the direct wireless connection route with a route candidate priority of 2 is marked with a circle in the second relay number column.

  Further, in FIG. 6, for each 1-hop node, in the column of 1st relay number and 2nd relay number in the row where 2 hop node is none, among the set of routes having the 1 hop node as 1 hop node The number of routes that have a route candidate priority of 1 in routes other than those directly connected by wireless connection is described.

  The columns for the number of first relays and the number of second relays are provided for reference when performing processing (relay load reduction processing) for preventing relay processing from concentrating on a specific node. When the reduction process is not performed, the first relay number and second relay number columns need not be provided in the topology table. The two-hop communication path performs communication via another node (relay node). Even when the communication destination nodes are different, the same relay node may be used. In such a case, since the processing load at the relay node is concentrated, it is possible to avoid the concentration of the processing load by obtaining a limit on the number of communication paths relayed by one relay node (hereinafter referred to as the number of relay devices). it can.

  Therefore, in the present embodiment, as the relay load reduction process, a process is performed in consideration of not only the priority for each communication path but also the number of relay nodes of each relay path when selecting a path. For example, in the example of FIG. 6, the number of relays of the first place and the number of relays of the second place are large in the node 2-2 and the node 2-3, and the number of relays of the first place in the nodes 2-1 and 2-4. There are few routes of the second number of relays. Therefore, the node 2-2 and the node 2-3 are more likely to concentrate relay loads than the nodes 2-1 and 2-4.

  For example, the upper limit of the number of relay devices between the gateway 1 and the node 2-3 is 1. For example, as a communication path between the gateway 1 and the node 2-1, a communication path via the node 2-2 is selected, and a communication path for direct wireless connection between the gateway 1 and the node 2-3 is selected. Suppose that In this case, when a link failure occurs between the gateway 1 and the node 2-3, the second priority communication path between the gateway 1 and the node 2-3 is the gateway 1-node 2-2 node. If the number of relay devices is already 1 and the upper limit of the number of relay devices is 1, the route for gateway 1-node 2-2 and node 2-3 is selected. Can not. Therefore, in this case, the gateway 1-node 2-4-node 2-3 having the third priority is selected.

  Thus, for example, an upper limit is set for the number of relay devices, and a communication path with the highest priority is selected within a range where the relay node performs relaying within the upper limit of the number of relay devices. The gateway 1 manages the number of relay apparatuses for each of the nodes 2-1 to 2-4. A column of the number of relay devices may be provided in the topology table, and the number of relay devices may be stored for each of the nodes 2-1 to 2-4. Alternatively, a column indicating the currently selected route may be provided in the topology table, and the number of relay devices for each of the nodes 2-1 to 2-4 may be obtained by referring to the column when the route is selected.

  In this embodiment, the gateway 1 uses the HELLO message to generate and update the topology table shown in FIG. 6. However, the gateway 1 acquires the quality of each link constituting the communication path up to 2 hops. In this case, any method may be used without being limited to the method using the HELLO message.

  FIG. 7 is a flowchart illustrating an example of a route selection procedure according to the present embodiment. The route selection procedure shown in FIG. 7 is performed after the topology discovery process described in FIG. 5 is performed. The route selection unit 24 of the gateway 1 extracts link information (local link information and adjacent link information) of the communication route up to 2 hops from the HELLO message information management table updated in step S17, and stores it in the topology table. Round-trip link information and link information metrics are calculated for each communication path, and the calculation results are further stored in the topology table (step S21).

  Next, the route selection unit 24 of the gateway 1 ranks communication routes for each communication destination node based on the link information metric, and stores the ranking as route candidate priority in the topology table (step S22). Then, the route selection unit 24 of the gateway 1 selects a route for each communication destination based on the route candidate priority (step S23). Normally, a route with higher priority is selected with priority. Although the route selection unit 24 performs the above route selection procedure here, the control unit 22 may also perform this process.

  The gateway 1 can select a high-quality route within 2 hops as a communication route between the nodes 2-1 to 2-4 by the procedure as described above.

  Information stored in the HELLO message and information extracted from the HELLO message (corresponding to own station link information and adjacent station link information in FIG. 6) are held in the HELLO message information management table. Here, for the sake of explanation, information overlapping with the HELLO message information management table may not be included in the topology table. When information overlapping with the HELLO message information management table is not included in the topology table, the local station link information and the neighboring station link information are read from the HELLO message information management table and based on the read values, the above-described round-trip link information, A link information metric or the like may be calculated, and the calculated value may be held as a topology table for each route. That is, the topology table only needs to store round-trip link information, link information metrics, and route candidate presence ranks. In this case, normalization of the local station link information and the adjacent station link information described above may be performed when the round-trip link information is obtained.

  In the present embodiment, it is assumed that the gateway 1 selects a communication path and each of the nodes 2-1 to 2-4 conforms to a master-slave configuration in which path selection is not performed. When all nodes select communication paths, the nodes constituting the communication system have the same configuration as that of the gateway 1 shown in FIG. The selection procedure may be performed. That is, a source node (including gateway 1) that selects a data communication path in the communication system performs a route selection procedure using the topology table in the same manner as the gateway 1 described above, thereby Route selection can be performed with a route of up to two hops.

  In the present embodiment, the same communication path is used for round-trip communication, and the gateway 1 calculates the link information metric based on the round-trip link information and selects the communication path. When it is not necessary to use the same communication path (for example, when a transmission path is selected by each transmission source node), a link information metric may be calculated based on link information in the transmission direction.

In the topology table of FIG. 6, the local station link information is shown as one piece of information. However, the local station link information may be a value calculated based on a plurality of types of information. Specifically, the calculated value for N times of packet transmission quality evaluation values (such as PER) is V1, the calculated value for N times of wireless quality evaluation values (such as RSSI) (for HELLO messages N times) is V2, and the traffic volume The calculated value of the value for evaluating the wireless usage status, such as V3, is set to Vi (i is an integer equal to or greater than 1) as the calculated value for the i-th type N times. In that case, the gateway 1 and the nodes 2-1 to 2-4 calculate the local station link information (LI) based on the following formula (1), for example. Note that a1, a2, a3,... Are weighting coefficients.
LI = a1 * V1 + a2 * V2 + a3 * V3 + (1)

  a1, a2, a3,... are set in advance based on the importance of each information. Note that a means for updating a1, a2, a3,... May be provided so that a1, a2, a3,.

  Also, a plurality of types of information are managed as a plurality of link information (stored in a HELLO message and transmitted) without being integrated as a single local station link information as described above, and a plurality of types of information are selected at the time of route selection. May be integrated.

  FIG. 8 is a diagram showing an example of a topology table held by the gateway 1 when three types of information are used as the local station link information. In this example, three of LI0, LI1, and LI2 are used as own station link information, and three of NLI0, NLI1, and NLI2 are used as adjacent station link information. For example, RSSI can be used as LI0 and NLI0, PER can be used as LI1 and NLI1, and round trip time (RTT (Round Trip Time)) can be used as LI2 and NLI2.

  In FIG. 8, the local station link information (LI0, LI1, LI2) and the adjacent station link information (NLI0, NLI1, NLI1) exchanged and managed by the HELLO message are not described. The local station link information (LI) and the adjacent station link information (NLI) are stored in the HELLO message information management table, and the example of FIG. 8 shows an example that does not include information overlapping with the HELLO message information management table. .

  In the topology table of FIG. 8, for each link information, round-trip link information is calculated based on the local station link information and neighboring station link information for the same link, and the link information metric for each link information is calculated based on the calculated round-trip link information. Ask for. That is, round trip link information # 0 is calculated based on LI0 and NLI0, round trip link information # 1 is calculated based on LI1 and NLI1, and round trip link information # 2 is calculated based on LI2 and NLI2. . Then, based on the round trip link information # 0, the link information metric # 0 is calculated as in the example of FIG. 6, the link information metric # 1 is calculated based on the reverse link information # 1, and the round trip link information # 2 is obtained. Based on this, link information metric # 2 is calculated.

  Then, the sum of link information metric # 0 to link information metric # 2 is stored as the link information metric (total). The route candidate priorities are ranked based on link information metrics (overall). The first relay number and the second relay number are the same as in the example of FIG.

  For example, for the route in which the 1-hop node is the node 2-1 and the 2-hop node is none (the top row in FIG. 8), the column of link information metrics # 0, # 1, and # 2 includes round-trip link information # 0. , # 1 and # 2 are stored. In the link information metric (sum) column, the sum of the link information metrics # 0, # 1, and # 2 is stored.

  Further, for example, in the route (the second line in FIG. 8) where the 1-hop node is the node 2-1 and the 2-hop node is the node 2-2, the link information metric # 0 column includes the second line in FIG. The sum of the reciprocal of the value of the round-trip link information # 0 and the value of the link information metric # 0 when the two-hop node is none (the top row in FIG. 8) is stored. Similarly, in the column of link information metric # 1, the reciprocal of the value of round-trip link information # 1 in the second row in FIG. 8 and the link information metric # in the case where the two-hop node is none (the top row in FIG. 8). 1 and the sum of the values are respectively stored, and in the column of link information metric # 2, the reciprocal of the value of round-trip link information # 2 in the second row of FIG. 8 and the case where the two-hop node is none (FIG. 8). And the sum of the link information metric # 2 in the top row). Then, the link information metric (sum) in the second row in FIG. 8 stores the sum of the link information metrics # 0, # 1, and # 2 in the second row in FIG.

  Then, the gateway 1 selects a communication path to be used for each communication destination based on the topology table illustrated in FIG. 8 as in the above-described route selection procedure. In the example of FIG. 8, for example, as a communication path between the gateway 1 and the node 2-1, “Gateway 1 -Node 2-1”, “Gateway 1 -Node 2 -2 2-1”, “Gateway” 1-node 2-3-node 2-1 "," gateway 1-node 2-4-node 2-1 "(the top line, the 6th line, the 10th line, the 14th line in FIG. 8) There are four paths. The values of link information metrics (total) of these routes are 9.37, 7.47, 10.31, and 17.71, respectively. Therefore, the route of “gateway 1-node 2-2 node 2-1” having the smallest value of the link information metric (total) is selected.

  Next, the RTT measurement method used as the local station link information # 2 (LI2) in the example of FIG. 8 will be described. Any measurement method may be used as the RTT measurement method. For example, it can be measured by the following method. Since the RTT itself is a value representing the reciprocal link state, a numerical value obtained by normalizing the measured value of the RTT may be used as the local station link information # 2 corresponding to the RTT. Since it is not necessary to exchange information about the RTT by the HELLO message, it is assumed here that the gateway 1 measures the RTT. When only RTT is used as the link information, the local station link information and the adjacent station link information may not be included in the HELLO message.

  FIG. 9 is a chart showing an example of an RTT measurement method. First, the above-described topology discovery process is performed between the gateway 1 and the nodes 2-1 to 2-4 (step S31). The gateway 1 can acquire the interface addresses of the 1-hop node and the 2-hop node by the topology discovery process. After acquiring the interface addresses of the 1-hop node and 2-hop node, the gateway 1 transmits a probe packet (Probe) requesting a response by unicast to one of the 1-hop nodes (step S32). When receiving the probe packet, the 1-hop node returns the probe packet to the gateway 1 as a response to the probe packet received in the shortest time (step S33).

  The gateway 1 holds the transmission time when the probe packet is transmitted in step S3, holds the reception time when the returned probe packet is received, and calculates the RTT based on the transmission time and the reception time (step) S34).

  Then, the gateway 1 unicasts the probe packet (Probe) to one of the two hop nodes that pass through the one hop node when the probe packet is transmitted in step S32. ) Is transmitted (steps S35 and S36). When the 2-hop node receives the probe packet, it returns the probe packet to the gateway 1 via the 1-hop node in the shortest time (steps S37 and S38).

  The gateway 1 holds the transmission time when the probe packet is transmitted in step S35, holds the reception time when the returned probe packet is received, and calculates the RTT based on the transmission time and the reception time. (Step S39). Then, Steps S35 to S39 are performed for each two-hop node passing through the same one-hop node, and the RTT is obtained for each two-hop node. Further, when these processes are completed for each one-hop node, the processes after step S32 are similarly performed for the other one-hop nodes.

  Note that the procedure of FIG. 9 is an example, and the order of probe packet transmission may be any order as long as the RTT can be calculated for each route up to two hops. Here, the RTT is calculated for each one-hop node as described above. However, these processes may be simultaneously performed for a plurality of one-hop nodes to obtain each RTT.

  As described above, in the present embodiment, the gateway 1 and the nodes 2-1 to 2-4 transmit the HELLO message, and based on the received HELLO message, link information indicating the quality of the link with the adjacent node is transmitted. It is calculated as link information, and the local station link information for each adjacent node is stored in a HELLO message and transmitted. Then, the gateway 1 and the nodes 2-1 to 2-4 extract the local station link information indicating the quality of the link with the local station calculated by the adjacent node as the adjacent station link information based on the received HELLO message. To do. For each communication path, the gateway 1 obtains a link information metric indicating the quality of the communication path based on the local station link information and the neighboring station link information, and selects the communication path based on the link information metric. Therefore, it is possible to suppress latency and set a communication path between wireless node devices that cannot perform direct wireless communication.

  As described above, the topology discovery method, route selection method, communication apparatus, and communication system according to the present invention are useful for industrial wireless communication systems, and in particular, industrial wireless communication systems that are required to reduce latency. Suitable for

1 Gateway
2-1 to 2-4 Node (Node)
10, 11, 12, 13 Communication path 14 HELLO message transmission direction 21 Wireless transmission / reception unit 22 Control unit 23, 25 Table holding unit 24 Route selection unit

Claims (16)

A route selection method in a communication system including a plurality of communication devices that perform wireless communication,
The quality of each link that constitutes the communication path for each communication path within a predetermined number of hops between the source apparatus that selects a communication path in the communication system among the communication apparatuses. A link information acquisition step for acquiring link information indicating
A ranking step in which the transmission source device determines a priority of the communication path for each communication device of a communication partner based on the link information;
A table holding step in which the transmission source device holds the priority of the communication path for each communication path as a topology table;
A route selection step in which the transmission source device selects a communication route to be used with the communication device of a communication partner based on the priority order;
The transmission source device determines, for each communication device, the number of communication paths between the transmission source device and other communication devices that pass through the communication device among the communication routes selected in the route selection step. A step of calculating the number of relay devices to be obtained as the number of relay devices;
Including
In the route selection step, a route selection method further comprising: selecting a communication route to be used with the communication device as a communication partner based on the number of relay devices. The communication device calculates the local station link information that is the link information with the adjacent communication device based on the received signal received from the adjacent communication device, and stores the local station link information for each adjacent communication device. A local station link information transmission step for transmitting a notification message;
When the communication device that has received the notification message uses the local station link information in which the local station included in the notification message is the adjacent communication device, and the communication device that is the transmission source of the notification message is the adjacent communication device Neighboring station link information, the neighboring station link information transmission step of further storing and transmitting the neighboring station link information for each neighboring communication device in the notification message transmitted by the own station,
Further including
In the link information acquisition step, the link information is acquired based on the notification message received by the transmission source device.
The route selection method according to claim 1, wherein: In the local station link information transmission step, the notification message is used as the received signal.
The route selection method according to claim 2, wherein: The local station link information is information indicating one or more of packet transmission quality, radio quality, traffic volume, and communication rate.
The route selection method according to claim 2 or 3, wherein The communication device periodically transmits the notification message,
In the local station link information transmission step, the local station link information is calculated by performing a predetermined calculation for the predetermined number of received notification messages.
The route selection method according to claim 2, 3, or 4. The predetermined calculation is one of an average value calculation calculation and a maximum value calculation calculation,
The route selection method according to claim 5, wherein: For the communication path in which the transmission source device directly wirelessly connects to the own station for each communication device, the own station link information calculated by the own station for each communication partner device that is the communication device of the communication partner, A round-trip link information indicating a round-trip quality of a link with the communication counterpart device based on the neighbor link information corresponding to the communication counterpart device stored in the notification message transmitted by a station, for the communication path via the relay device is a pre-Symbol communications device for relaying, and the own station link information local station is calculated for each communication partner device is the communication device of the communication partner, the mobile station transmits The neighboring station link information corresponding to the communication partner apparatus stored in the notification message, the own station link information stored in the notification message received from the relay apparatus, and the neighboring station link Information, and round trip link information indicating the round trip quality of the link with the communication partner device is calculated, a link information metric is obtained based on the calculated round trip link information, and the link information metric is further calculated Metric calculation step for storing each communication path in the topology table,
Further including
In the ranking step, the priority of the communication path for each communication path is determined based on the link information metric.
The route selection method according to any one of claims 2 to 6. For communication paths of two or more hops, the local station link information calculated by the local station for each communication partner apparatus that is the communication apparatus of the communication partner and the communication partner apparatus stored in the notification message transmitted by the local station Direct round-trip link information which is round-trip link information obtained based on the corresponding neighboring station link information, the local station link information and the neighboring station link information stored in the notification message received from the relay device, The round-trip link information is calculated by summing or weighted addition of the relay link information obtained based on
The route selection method according to claim 7. Calculating the round-trip link information as a product or sum of the local station link information and the neighboring station link information;
9. The route selection method according to claim 7 or 8, wherein: The local station link information and the neighbor station link information are composed of one or more types of link information,
In the metric calculation step, the link information metric for each communication path is calculated for each type, the total link information metric for each communication path is calculated based on the link information metric for each type, and the total link information metric Further, a total metric calculation step for storing each communication path in the topology table,
Further including
In the ranking step, the priority of the communication path for each communication path is determined based on the total link information metric.
The route selection method according to claim 7, 8 or 9. A packet transmission step in which the transmission source device transmits a probe packet for requesting a response packet to a communication partner device of the communication path using the communication path for each of the communication paths;
The communication partner device that has received the probe packet transmits a response packet to the probe packet to the transmission source device; and
A response time calculating step for obtaining a round-trip response time for each of the communication paths based on the time when the transmission source device transmits the probe packet and the time when the response packet is received;
Further including
In the total metric calculation step, a link information metric is further calculated based on the round-trip response time, and the total link information metric is further calculated based on the link information metric.
The route selection method according to claim 10. A route selection method in a communication system including a plurality of communication devices that perform wireless communication,
A transmission source device that selects a communication route in the communication system among the communication devices uses the communication route for each communication route within a predetermined number of hops with the other communication device. A packet transmission step of transmitting a probe packet for requesting a response packet to the communication partner device;
The communication partner device that has received the probe packet transmits a response packet to the probe packet to the transmission source device; and
A response time calculating step for obtaining a round-trip response time for each of the communication paths based on the time when the transmission source device transmits the probe packet and the time when the response packet is received;
A ranking step in which the transmission source device determines the priority of the communication path for each communication partner device based on the response time;
A table holding step in which the transmission source device holds the priority of the communication path for each communication path as a topology table;
A route selection step in which the transmission source device selects a communication route to be used with the communication device of a communication partner based on the priority order;
The transmission source device determines, for each communication device, the number of communication paths between the transmission source device and other communication devices that pass through the communication device among the communication routes selected in the route selection step. A step of calculating the number of relay devices to be obtained as the number of relay devices;
Including
In the route selection step, further, based on the number of relay devices, select a communication route to be used with the communication device of the communication partner,
A route selection method characterized by that. The transmission source device is a gateway device that is one of the communication devices,
The route selection method according to any one of claims 1 to 12. In the route selection step, as a communication route to be used with the communication device of the communication partner, a communication route having the highest priority is selected in a range where the number of relay devices is within a predetermined upper limit value.
The route selection method according to any one of claims 1 to 13, wherein the method is selected. The communication device in a communication system including a plurality of communication devices that perform wireless communication,
A topology holding unit for storing a topology table storing priorities for each communication path;
Link information indicating the quality of each link constituting the communication path is acquired for each communication path within a predetermined number of hops with another communication apparatus, and the communication apparatus of the communication partner is acquired based on the link information A link information acquisition unit that determines the priority of the communication path for each and stores the priority as the topology table;
A route selection unit that selects a communication route to be used with the communication device of the communication partner based on the priority order stored in the topology table;
With
The path selection unit determines, for each communication device, the number of communication paths between the transmission source device and the other communication devices that pass through the communication device among the communication routes selected by the route selection unit. determined as a relay device number, further on the basis of the relay device number, a communication device according to claim you to select the communication channel to be used with the communication device of the communication partner. A communication system including a plurality of communication devices that perform wireless communication, wherein a transmission source device that selects a communication path in the communication system among the communication devices is
A topology holding unit for storing a topology table storing priorities for each communication path;
Link information indicating the quality of each link constituting the communication path is acquired for each communication path within a predetermined number of hops with another communication apparatus, and the communication apparatus of the communication partner is acquired based on the link information A link information acquisition unit that determines the priority of the communication path for each and stores the priority as the topology table;
A route selection unit that selects a communication route to be used with the communication device of the communication partner based on the priority order stored in the topology table;
With
The path selection unit determines, for each communication device, the number of communication paths between the transmission source device and the other communication devices that pass through the communication device among the communication routes selected by the route selection unit. communication system determined as a relay device number, further based on the relay device number, features that you select a communication channel to be used with the communication device of the communication partner.

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