Communication systems, aggregation devices, centralized devices, terminals, and communication methods.

Abstract

Invention details;

Description

Communication system, aggregation device, central device, terminal, communication method, and communication program

[0001] The present disclosure relates to a communication system that performs multi-hop communication, an aggregation device, a central device, a terminal, a communication method, and a communication program.

[0002] In recent years, interest in an energy-saving society has grown, and the introduction of automatic meter-reading devices called smart meters, which enable visualization of power consumption through automatic meter reading and control of power supply and demand, is being promoted. Smart meters are installed in all households and are constructed and operated as a wide-area large-scale network within the jurisdiction of each electric power company.

[0003] A large number of smart meters form a multi-hop network, and each smart meter transmits metering data to a concentrator that serves as the root of the multi-hop network. Generally, a smart meter network, which is a multi-hop network including a large number of smart meters, includes multiple concentrators, and the metering data aggregated by each concentrator is collected by a central device called a head end system (HES).

[0004] Conventional smart meter networks use the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) as their routing protocol. In RPL, source routing is performed for the downlink communication path from the aggregation device to the smart meter, where the aggregation device, which is the parent station, specifies the path.

[0005] Patent document 1 describes a technology in which a gateway, which is an aggregation device, performs source routing by determining a downstream route using information indicating the upstream route contained in an upstream message from a smart meter to the aggregation device.

[0006] Patent No. 6016646

[0007] In the technology described in Patent Document 1, a single downstream path is set, and if a failure occurs in this downstream path, the smart meter cannot receive downstream data. Therefore, in the technology described in Patent Document 1, when a failure occurs in the downstream path, a downstream path search message is sent to search for a new downstream path, and a new downstream path is set using response messages from each smart meter. This results in delays in the downstream data. Automatic energy meter reading mainly involves collection of measurement data from each smart meter, i.e., upstream communication, and downstream communication is infrequent and a certain degree of delay is tolerable. Therefore, there is no problem with using the method described in Patent Document 1. However, in recent years, there has been consideration of utilizing smart meter networks built for automatic energy meter reading as infrastructure. For example, it is desirable to use them for controlling and collecting sensor information for monitoring switches in a power distribution system. Such applications require downstream communication with higher reliability and lower latency than ever before.

[0008] The present disclosure has been made in view of the above, and aims to provide a communication system that can achieve highly reliable, low-latency downstream communication.

[0009] In order to solve the above-mentioned problems and achieve the objectives, the communication system disclosed herein is a communication system that includes one or more aggregation devices and a plurality of terminals that transmit upstream data to the aggregation devices, and is capable of configuring a wireless multi-hop network, and determines a plurality of downlink routes to the source terminal using identification information of the terminal through which the upstream signal has passed, which is stored in the upstream signal transmitted from a source terminal that is one of the plurality of terminals to the aggregation device, and transmits the same downstream data addressed to the source terminal using each of the determined downlink routes.

[0010] The communication system according to the present disclosure has an effect of realizing highly reliable and low-latency downstream communication.

[0011] FIG. 1 is a diagram showing an example of the configuration of a communication system according to a first embodiment. FIG. 1 is a diagram showing an example of the configuration of a central device according to the first embodiment. FIG. 1 is a diagram showing an example of the configuration of an aggregation device according to the first embodiment. FIG. 1 is a diagram showing an example of the configuration of a terminal according to the first embodiment. FIG. 2 is a diagram showing an example of a control circuit according to the first embodiment. FIG. 2 is a diagram showing an example of an upstream path according to the first embodiment.

[0012] A communication system, an aggregation device, a central device, a terminal, a communication method, and a communication program according to an embodiment will be described in detail below with reference to the accompanying drawings.

[0013] First Embodiment. FIG. 1 is a diagram illustrating an example of the configuration of a communication system according to a first embodiment. The communication system of this embodiment is used for automatic meter reading of electric energy, but may also be used for other purposes in addition to automatic meter reading of electric energy. As shown in FIG. 1, the communication system of this embodiment includes a central device 1, which is a communication management device, aggregation devices 2-1 and 2-2, and terminals 3-1 to 3-12. The communication system of this embodiment includes aggregation devices 2-1 and 2-2, which are examples of one or more aggregation devices, and terminals 3-1 to 3-12, which are examples of multiple terminals, and is capable of configuring a wireless multi-hop network. Note that, although FIG. 1 illustrates two aggregation devices and 12 terminals, the number of aggregation devices and terminals is not limited to the example illustrated in FIG. 1. The number of aggregation devices may be one.

[0014] Terminals 3-1 to 3-12 are communication devices connected to metering devices (not shown) that measure the amount of electricity, and each of terminals 3-1 to 3-12 and the corresponding metering device constitutes a smart meter. In other words, terminals 3-1 to 3-12 are part of the smart meter and transmit metered data on the amount of electricity to the corresponding aggregation devices 2-1 and 2-2. The metered data is an example of upstream data. Terminals 3-1 to 3-12 are installed, for example, at electricity consumers. Furthermore, when the communication system of this embodiment is used for purposes other than automatic meter reading of electricity, terminals 3-1 to 3-12 communicate with devices other than metering devices depending on the purpose and transmit data acquired from the other devices to the corresponding aggregation devices 2-1 and 2-2. Hereinafter, when terminals 3-1 to 3-12 are referred to without being individually distinguished, they will be referred to as terminal 3.

[0015] The aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 form a wireless multi-hop network with the aggregation devices 2-1 and 2-2 as roots. The aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 that form the wireless multi-hop network are also referred to as nodes hereinafter. Note that the lines connecting the aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 in FIG. 1 indicate wireless links. Note that, although an example in which the communication system of this embodiment is a wireless multi-hop network will be described below, a multi-hop network using power line communication or the like may also be used.

[0016] The aggregation devices 2-1 and 2-2 collect measurement data from the terminals 3-1 to 3-12 and transmit the collected measurement data to the central device 1 via a network. The network between the aggregation devices 2-1 and 2-2 and the central device 1 is an IP (Internet Protocol) network, such as, but not limited to, an optical fiber network or a mobile phone network. The aggregation devices 2-1 and 2-2 are installed, for example, on utility poles, but their installation locations are not limited to utility poles. When the communication system of this embodiment is used for purposes other than automatic meter reading of electric energy, the aggregation devices 2-1 and 2-2 transmit data for other purposes received from the terminals 3-1 to 3-12 to the central device 1 via the network. Hereinafter, when the aggregation devices 2-1 and 2-2 are referred to without being individually distinguished, they will be referred to as aggregation device 2.

[0017] The central device 1 collects measurement data from the aggregation devices 2-1 and 2-2 and transmits the collected measurement data to a meter data management system (MDMS) (not shown). The MDMS is a device that manages measurement data. Furthermore, when the communication system of this embodiment is used for purposes other than automatic meter reading of electric energy, the central device 1 transmits data collected from the terminals 3-1 to 3-12 for other purposes to a management device for the other purposes. Furthermore, the central device 1 transmits control signals for controlling the terminals 3-1 to 3-12 to the terminals 3-1 to 3-12 via the aggregation devices 2-1 and 2-2. For example, when the communication system of this embodiment is used to control switches in a power distribution system, the central device 1 receives control signals for controlling the switches from a power distribution system management device that manages the power distribution system and transmits the control signals to the terminals 3-1 to 3-12 corresponding to the switches.

[0018] Next, an example of the configuration of each device constituting the communication system of this embodiment will be described. Fig. 2 is a diagram showing an example of the configuration of the central device 1 of this embodiment. The central device 1 includes a transmitting / receiving unit 11, a communication control unit 12, a control processing unit 14, and a route information storage unit 13. The route information storage unit 13 stores the correspondence between the aggregation device 2 and the terminal 3 subordinate to the aggregation device 2 as aggregation device information. Details of the aggregation device information will be described later.

[0019] The transmitter / receiver 11 performs IP communication with the aggregation device 2. The communication control unit 12 controls communication between the aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 using the aggregation device information stored in the route information storage unit 13. For example, when the communication control unit 12 receives a control signal from the control processing unit 14, if the received control signal is addressed to the aggregation device 2, the communication control unit 12 causes the transmitter / receiver 11 to transmit the control signal to the corresponding aggregation device 2. Furthermore, if the received control signal is addressed to terminal 3, the communication control unit 12 uses the aggregation device information to find the aggregation device 2 corresponding to terminal 3, and transmits the control signal to the found aggregation device 2 via the transmitter / receiver 11. Furthermore, when the communication control unit 12 receives signals transmitted from the aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 via the transmitter / receiver 11, it outputs the signals to the control processing unit 14.

[0020] The control processing unit 14 generates control signals for controlling the aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 and outputs them to the communication control unit 12. Furthermore, when the control processing unit 14 receives signals transmitted from the aggregation devices 2-1 and 2-2 and the terminals 3-1 to 3-12 via the communication control unit 12, it uses the signals to perform predetermined processing. For example, if the received signal contains measurement data on the amount of power, the data is temporarily stored in a storage unit (not shown) and transmitted to the MDMS via the communication control unit 12 and the transceiver unit 11 at a predetermined timing.

[0021] 3 is a diagram showing an example of the configuration of the aggregation device 2 of this embodiment. The aggregation device 2 includes a first transceiver 21, a second transceiver 22, a communication control unit 23, a route information storage unit 24, and a control processing unit 25. The route information storage unit 24 stores downlink route information. The downlink route information stores information indicating a downlink route corresponding to an uplink route of a terminal obtained based on a signal received from the terminal 3. In this embodiment, the downlink route information stores multiple downlink routes for one terminal 3. Details of the downlink route information will be described later.

[0022] The first transmitter / receiver 21 performs wireless communication with the terminal 3. When the first transmitter / receiver 21 receives a signal from the terminal 3, it outputs the signal to the communication control unit 23. The first transmitter / receiver 21 also transmits various signals to the terminal 3 based on instructions from the communication control unit 23. The second transmitter / receiver 22 performs IP communication with the central device 1. When the second transmitter / receiver 22 receives a signal from the central device 1, it outputs the signal to the communication control unit 23. The second transmitter / receiver 22 also transmits various signals to the central device 1 based on instructions from the communication control unit 23.

[0023] When the communication control unit 23 receives a signal transmitted from the terminal 3 from the first transceiver unit 21, if the data is an upstream communication control signal used for route construction, it stores a downstream route corresponding to the upstream route stored in the data, i.e., a downstream route opposite to the upstream route, as downstream route information in the route information storage unit 24. The communication control unit 23 also determines multiple downstream routes using the downstream route information and transmits the same downstream data using the multiple downstream routes. When the communication control unit 23 receives a signal transmitted from the terminal 3 from the first transceiver unit 21, if the signal contains data to be transmitted to the central device 1, such as measurement data, it outputs the data to the control processing unit 25. When the communication control unit 23 receives a signal from the second transceiver unit 22, if the signal is addressed to the terminal 3, it outputs the data contained in the signal to the control processing unit 25. If the signal is not addressed to the terminal 3, it transmits the signal to the terminal 3 via the first transceiver unit 21.

[0024] When the control processing unit 25 receives data such as measurement data transmitted from the terminal 3 via the communication control unit 23, it temporarily stores the data and passes it to the communication control unit 23 at a predetermined timing, and transmits the data from the communication control unit 23 to the central device 1 via the second transceiver unit 22.

[0025] 4 is a diagram showing an example of the configuration of the terminal 3 according to this embodiment. The terminal 3 includes a transmitter / receiver 31, a communication controller 32, a route information storage unit 33, and a control processor 34. The route information storage unit 33 stores a terminal table in which upstream route information indicating upstream routes is stored. The terminal table will be described in detail later.

[0026] The transmitter / receiver 31 performs wireless communication with another node in the wireless multi-hop network, which is an aggregation device 2 or a terminal 3. When the transmitter / receiver 31 receives a signal from another node, the transmitter / receiver 31 outputs the signal to the communication control unit 32. Furthermore, the transmitter / receiver 31 transmits the signal to the other node based on an instruction from the communication control unit 32.

[0027] When the communication control unit 32 receives a signal from the transmitting / receiving unit 31, if the destination of the signal is its own terminal, it outputs the data contained in the signal to the control processing unit 34, and if the signal is addressed to another node, it forwards the signal to the destination node by having the transmitting / receiving unit 31 transmit the signal toward the destination node. Furthermore, when the communication control unit 32 receives data such as metric data from the control processing unit 34, it transmits the data to an adjacent node in the upstream direction via the transmitting / receiving unit 31 using the terminal table stored in the route information storage unit 33. The upstream data arrives at the destination node as each node forwards it.

[0028] When the control processing unit 34 receives data from the communication control unit 32, it performs a predetermined process based on the received data. The control processing unit 34 also acquires data such as measurement data transmitted from other devices such as a weighing device (not shown) to the aggregation device 2, and outputs the acquired data to the communication control unit 32.

[0029] Next, the hardware configuration of each device in this embodiment will be described. The transmitting / receiving unit 11 of the central device 1 in this embodiment is realized by a transmitter and a receiver, and the communication control unit 12 and the control processing unit 14 are realized by a control circuit. The route information storage unit 13 is realized by a memory.

[0030] FIG. 5 is a diagram illustrating an example of a control circuit according to the present embodiment. The control circuit 100 illustrated in FIG. 5 includes a processor 101, such as a central processing unit (CPU) or a microprocessor unit (MPU), and a memory 102. The memory 102 includes semiconductor memory, such as a random access memory (RAM) or a read-only memory (ROM), and a magnetic disk. The communication control unit 12 and the control processing unit 14 of the central device 1 are realized by the processor 101 executing a communication program stored in the memory 102 for implementing the operation of the central device 1. The communication program may be provided by a recording medium or a communication medium. The memory for implementing the route information storage unit 13 may be part of the memory 102 or may be a memory separate from the control circuit.

[0031] Furthermore, the central device 1 is generally realized by a computer system, and in addition to the control circuit 100, may also include a display unit such as a monitor or display, and an input unit such as a keyboard or mouse, although not shown.

[0032] In this embodiment, the first transceiver 21 and the second transceiver 22 of the aggregation device 2 are realized by a transmitter and a receiver. The communication control unit 23 and the control processing unit 25 are realized by a processing circuit, and the route information storage unit 24 is realized by a memory. The processing circuit may be a control circuit 100 as shown in FIG. 5 or a dedicated circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). When the communication control unit 23 and the control processing unit 25 are realized by the control circuit 100, the communication control unit 23 and the control processing unit 25 are realized by the processor 101 executing a communication program stored in the memory 102 to realize the operation of the aggregation device 2. The communication program may be provided by a recording medium or a communication medium. Furthermore, the memory that realizes the route information storage unit 24 may be part of the memory 102 or may be a memory separate from the control circuit.

[0033] In this embodiment, the transceiver 31 of the terminal 3 is realized by a transmitter and a receiver. The communication control unit 32 and the control processing unit 34 are realized by a processing circuit, and the route information storage unit 33 is realized by a memory. The processing circuit may be the control circuit 100 shown in FIG. 5 or a dedicated circuit such as an FPGA or an ASIC. When the communication control unit 32 and the control processing unit 34 are realized by the control circuit 100, the communication control unit 32 and the control processing unit 34 are realized by the processor 101 executing a communication program for realizing the operation of the terminal 3 stored in the memory 102. The communication program may be provided by a recording medium or a communication medium. Furthermore, the memory for realizing the route information storage unit 33 may be part of the memory 102 or may be a memory separate from the control circuit.

[0034] The communication program of this embodiment causes the communication system of this embodiment to execute, for example, the steps of determining multiple downlink routes to the source terminal using identification information of the terminal 3 through which the upstream signal passed, stored in the upstream signal transmitted from the source terminal, which is one of the multiple terminals 3, to the aggregation device 2, and transmitting the same downstream data addressed to the source terminal using each of the determined multiple downlink routes.

[0035] Next, the operation of this embodiment will be described. FIG. 6 is a diagram showing an example of an upstream path in this embodiment. FIG. 6 illustrates three upstream paths 4-1 to 4-3 as upstream paths from terminal 3-9 to the central device 1. Each terminal 3 stores upstream path information in a terminal table using signals received from other terminals 3. The aggregation device 2 determines the downstream path using the upstream path stored in the signal received from each terminal 3. The aggregation device 2 performs downstream communication by source routing using the determined downstream path. In a conventional smart meter network using RPL, the terminal 3 stores information on multiple upstream paths, but for the downstream path, the aggregation device 2 selects and stores one downstream path for each terminal 3. Therefore, if a communication failure or error occurs on this downstream path, the terminal 3 cannot correctly receive the downstream signal transmitted from the aggregation device 2. In a smart meter network using conventional RPL, when the aggregation device 2 detects that a failure has occurred in the downstream path because there is no response signal from the terminal 3 for a certain period of time, it reconstructs the downstream path and transmits the downstream signal again, but the process of reconstructing the path causes a large delay in the reception of the downstream signal by the terminal 3.

[0036] In this embodiment, in order to improve the reliability of downstream communication and reduce delay, the aggregation device 2 holds multiple downstream routes as downstream route information for each terminal 3 and transmits the same data continuously over the multiple downstream routes, thereby achieving highly reliable, low-delay downstream communication.

[0037] 7 is a chart showing an example of a path construction procedure in the communication system of this embodiment. Fig. 7 shows an example of a path construction procedure when aggregation device 2-1 is newly connected to the communication system. First, aggregation device 2-1 performs a connection establishment process with central device 1 (step S1). In detail, second transceiver 22 of aggregation device 2-1 establishes a connection in accordance with TCP (Transmission Control Protocol) / IP, and notifies communication control unit 23 of the connection establishment completion.

[0038] Next, the aggregation device 2-1 transmits a wireless multi-hop establishment signal for establishing a route in the wireless multi-hop network between the aggregation device 2-1 and the terminal 3 (step S2). Specifically, when the communication control unit 23 of the aggregation device 2-1 is notified by the second transceiver unit 22 that the connection establishment has been completed, the communication control unit 23 generates a communication wireless multi-hop establishment signal and broadcasts the communication wireless multi-hop establishment signal via the first transceiver unit 21. The communication wireless multi-hop establishment signal stores the aggregation device ID (identifier) ​​of the aggregation device 2-1, which is the root of the upstream communication, as well as identification information of the node that transmitted the communication wireless multi-hop establishment signal and the number of hops to the aggregation device 2-1. In the aggregation device 2-1, the identification information of the node that transmitted the communication wireless multi-hop establishment signal is the aggregation device ID of the aggregation device 2-1, and the number of hops is 0. The aggregation device ID is identification information for identifying each aggregation device 2. In Figure 7, terminal 3-1 receives a wireless multi-hop establishment signal directly from aggregation device 2-1, but although not shown, terminal 3-2 also receives a wireless multi-hop establishment signal directly from aggregation device 2-1 and performs the same operation as terminal 3-1 described below.

[0039] Upon receiving the wireless multi-hop establishment signal, terminal 3-1 updates the number of hops to aggregation device 2-1 and the identification information of the node that transmitted the wireless multi-hop establishment signal, and broadcasts the multi-hop route establishment signal (step S3). The terminal ID is identification information for identifying each terminal 3. Specifically, upon receiving the wireless multi-hop establishment signal, the transceiver 31 passes the signal to the communication control unit 32, and the communication control unit 32 extracts the identification information of the node that transmitted the wireless multi-hop establishment signal and the number of hops from the signal received from the transceiver 31. The communication control unit 32 updates the identification information of the node that transmitted the wireless multi-hop establishment signal from the transceiver 31 to the terminal ID of terminal 3-1, and updates the number of hops in the signal to a value obtained by adding 1 to the extracted number of hops. In this example, the communication control unit 32 of terminal 3-1 updates the number of hops to 1 because the number of hops extracted from the data received from the transceiver 31 is 0. The communication control unit 32 outputs the signal after the above-described update to the transmission / reception unit 31, and the transmission / reception unit 31 broadcasts the signal received from the communication control unit 32 as a multi-hop route construction signal.

[0040] Furthermore, upon receiving the wireless multihop establishment signal, the terminal 3-1 transmits an upstream communication control signal (step S4). Specifically, the communication control unit 32 identifies the aggregation device 2-1, which is the root node in the wireless multihop establishment signal received from the transmission / reception unit 31, generates an upstream communication control signal addressed to the aggregation device 2-1, stores the terminal ID of the terminal 3-1 in the upstream communication control signal as identification information of the node from which the signal was sent, and transmits the upstream communication control signal via the transmission / reception unit 31. Each terminal 3 may wait for a certain period of time after receiving the wireless multihop establishment signal without transmitting an upstream control signal, and if it receives wireless multihop establishment signals from multiple other terminals 3 within the certain period of time, it may select a terminal 3 with good communication quality based on the signal strength of the received wireless multihop establishment signal and transmit an upstream communication control signal to the selected terminal 3. Alternatively, instead of transmitting an upstream control signal after receiving the wireless multihop establishment signal, it may transmit a periodically transmitted upstream communication signal, i.e., a signal including metric data.

[0041] Furthermore, upon receiving the wireless multi-hop establishment signal, the terminal 3-1 stores the upstream route in the terminal table (step S5). Specifically, the communication control unit 32 stores, in the terminal table of the route information storage unit 33, the identification information of the node that transmitted the wireless multi-hop establishment signal received from the transceiver 31 and the hop count obtained by adding 1 to the hop count included in the signal, as upstream route information related to the upstream route. FIG. 8 is a diagram showing an example of the terminal table of this embodiment. The terminal table stores information about n routes from upstream route #1 to upstream route #n. n is the number of upstream routes held by each terminal 3 and is an integer equal to or greater than 2. n is determined in advance, but may be changeable by an instruction from the central device 1 or the aggregation device 2, for example. The information about each route includes the identification information of the next node on the route and the number of hops to the aggregation device 2. Each terminal 3 stores the identification information of the node that transmitted the wireless multi-hop establishment signal as the identification information of the next node on the upstream route.

[0042] In the example shown in Fig. 7, terminal 3-1 receives a wireless multi-hop establishment signal directly from aggregation device 2-1, and the identification information of the node that is the sender of the wireless multi-hop establishment signal is the aggregation device ID of aggregation device 2-1. Therefore, in step S3, for example, the aggregation device ID of aggregation device 2-1 is stored as the identification information of the next node in the information of uplink route #1, and 1 is stored as the number of hops. Note that the processing order of steps S3 to S5 is not limited to this example, and these may be performed simultaneously or in an order different from that shown in Fig. 7. As described above, steps S1 to S3 are also performed in terminal 3-2 in the same way as in terminal 3-1.

[0043] 7, when terminal 3-4 receives the wireless multi-hop establishment signal transmitted from terminal 3-1 in step S3, it updates the number of hops to aggregation device 2-1 in the wireless multi-hop establishment signal and the identification information of the source node, and broadcasts the multi-hop route establishment signal (step 6). Similar to terminal 3-1 described above, terminal 3-4 updates the identification information of the source node in the received wireless multi-hop establishment signal to the terminal ID of terminal 3-4, and updates the number of hops in the data to a value obtained by adding 1 to the extracted number of hops. In this example, terminal 3-4 updates the number of hops to 2.

[0044] Similarly to terminal 3-1, terminal 3-4 transmits an upstream communication control signal addressed to aggregation device 2-1 (step S7). Note that, since terminal 3-4 has received the wireless multi-hop establishment signal from terminal 3-1, terminal 3-4 transmits an upstream communication control signal addressed to aggregation device 2-1 to terminal 3-1.

[0045] Similarly to terminal 3-1, terminal 3-4 stores the upstream route in the terminal table (step S8). Since terminal 3-4 has received the wireless multi-hop establishment signal from terminal 3-1, for example, the terminal ID of terminal 3-1 is stored as the identification information of the next node in the information on upstream route #1, and 2 is stored as the number of hops. Note that, like the processing order of steps S3 to S5, the processing order of steps S6 to S8 is not limited to this example, and these steps may be performed simultaneously or in an order different from that shown in FIG. 7 . Also, although not shown, terminal 3-5, like terminal 3-4, receives the wireless multi-hop establishment signal transmitted from terminal 3-1 in step S2 and performs steps S6 to S8. Furthermore, terminals 3-5 and 3-6, which have received the wireless multi-hop establishment signal from terminal 3-2, also receive the wireless multi-hop establishment signal transmitted from terminal 3-1 in step S3 and perform steps S6 to S8, like terminal 3-4.

[0046] Although not shown in the figure, terminals 3-8 and 3-9 that receive the wireless multi-hop establishment signal transmitted from terminal 3-4 also perform steps S6 to S8 in the same manner as terminal 3-4. Similarly, not limited to these terminals, terminals 3 that receive the wireless multi-hop establishment signal from other terminals 3 also perform steps S6 to S8 in the same manner as terminal 3-4. Therefore, in the configuration example shown in FIG. 6, terminal 3-9 receives the wireless multi-hop establishment signal transmitted from aggregation device 2-1 from terminals 3-4 and 3-5. For this reason, in the terminal table of terminal 3-9, for example, the terminal ID of terminal 3-4 is stored as the identification information of the next node in the information of uplink route #2, and 3 is stored as the number of hops, and the terminal ID of terminal 3-5 is stored as the identification information of the next node in the information of uplink route #2, and 3 is stored as the number of hops. In this way, information on multiple uplink routes is stored in the terminal table. An upper limit may be set for the number of hops, and the terminal 3 may not perform steps S6 to S8 if the number of hops extracted from the received wireless multi-hop establishment signal has reached the upper limit.

[0047] Returning to the description of FIG. 7 , upon receiving the upstream communication control signal transmitted in step S7, terminal 3-1 adds the identification information of terminal 3-1 to the upstream communication control signal (step S9) and transmits the upstream communication control signal with the identification information of terminal 3-1 added to it to aggregation device 2-1 (step S10). Specifically, upon receiving the upstream communication control signal, transceiver 31 passes the signal to communication control unit 32, which then adds the terminal ID of terminal 3-1 to the upstream communication control signal received from transceiver 31. Then, communication control unit 23 transmits the upstream communication control signal with the terminal ID of terminal 3-1 added to it via transceiver 31 to the next node on the upstream route in the terminal table stored in route information storage unit 33. At this point, only the upstream route whose next node is aggregation device 2-1 is stored in the terminal table of terminal 3-1, and communication control unit 32 transmits the upstream communication control signal to aggregation device 2-1 based on the information on this upstream route. Furthermore, if information about a plurality of upstream routes is stored in the terminal table of the terminal 3-1, the communication control unit 32 transmits an upstream communication control signal to an upstream route selected based on the number of hops, communication quality, and the like.

[0048] When the aggregation device 2-1 receives the upstream communication control signal transmitted in step S4, it records the downstream route of terminal 3-1 (step S11), and when the aggregation device 2-1 receives the upstream communication control signal transmitted in step S10, it records the downstream route of terminal 3-4 (step S12). Specifically, when the first transceiver 21 receives the upstream communication control signal, it passes the signal to the communication control unit 23. The communication control unit 23 extracts, from the upstream communication control signal received from the first transceiver 21, the terminal identification information of the terminal 3 on the route through which the upstream communication control signal passed, thereby determining the upstream route, and records the downstream route corresponding to the determined upstream route in the downstream route information of the route information storage unit 24. Since the upstream communication control signal transmitted in step S4 was transmitted directly from terminal 3-1 to the aggregation device 2-1 without passing through any other terminal 3, the communication control unit 23 stores the terminal ID of terminal 3-1 as downstream route information indicating the downstream route corresponding to the upstream route of the upstream communication control signal transmitted in step S4. Furthermore, the upstream communication control signal transmitted in step S10 is added with the terminal ID of terminal 3-1 because it was transmitted from terminal 3-4 and passed through terminal 3-1. Therefore, the communication control unit 23 records the terminal ID of terminal 3-4 and the terminal ID of terminal 3-1 as downstream route information for terminal 3-4 based on the upstream communication control signal transmitted in step S10. Note that here, the downstream route information also includes the terminal ID of the sender of the upstream communication control signal, but because downstream route information is managed for each sender terminal, the information indicating each downstream route may also store the terminal ID of the terminal 3 that was passed through.

[0049] Similarly, the aggregation device 2-1 sequentially receives upstream communication control signals transmitted from other terminals 3, and each time a downstream route is received, it adds a downstream route to the downstream route information in the route information storage unit 24. When a certain time has elapsed since transmitting the wireless multi-hop establishment signal in step S2 and the aggregation device 2-1 has received upstream communication control signals from all terminals 3, the aggregation device 2-1 stores multiple downstream routes in the downstream route information for each terminal 3 using the upstream route (step S13). In detail, for each terminal 3 that is the destination of the downstream route, the communication control unit 23 obtains multiple downstream routes recorded based on the upstream communication control signals transmitted from the terminal 3 from the downstream route information in the route information storage unit 24, and stores the obtained multiple downstream routes in the route information storage unit 24 as downstream route information.

[0050] FIG. 9 is a diagram illustrating an example of downlink route information according to this embodiment. As shown in FIG. 9, the downlink route information stores information indicating p downlink routes, from downlink route #1 to downlink route #p, for each terminal 3. p is an integer greater than or equal to 2 and is predetermined. p may be changeable, for example, by an instruction from the central device 1. Here, step S13 is performed when a certain time has elapsed since the wireless multi-hop establishment signal was transmitted. However, if the terminals 3 subordinate to the aggregation device 2-1 are predetermined and set to the aggregation device 2-1, the communication control unit 23 may perform step S13 when it receives upstream communication control signals from all terminals 3 predetermined as terminals 3 subordinate to the aggregation device 2-1. The terminals 3 subordinate to the aggregation device 2-1 are terminals 3 that perform wireless multi-hop communication with the aggregation device 2-1 as the root, i.e., terminals 3 for which the aggregation device 2-1 relays communication between the central device 1 and terminals 3.

[0051] Next, the aggregation device 2-1 transmits a terminal notification signal to the central device 1 (step S14). In detail, the communication control unit 23 uses the downstream route information stored in the route information storage unit 24 to obtain the terminal ID of the terminal 3 under the aggregation device 2-1, generates a terminal notification signal including the terminal ID of the terminal 3 under the aggregation device 2-1, and transmits it to the central device 1 via the second transceiver unit 22. This allows the central device 1 to know which terminals 3 are under the aggregation device 2-1. When the transceiver unit 11 of the central device 1 receives the terminal notification signal, it outputs it to the communication control unit 12, and the communication control unit 12 uses the terminal notification signal to update the aggregation device information in the route information storage unit 13. The aggregation device information is information indicating the correspondence between the terminal 3 and the aggregation device 2.

[0052] 10 is a diagram showing an example of aggregation device information according to this embodiment. Fig. 10 shows information relating to terminal 3-9 from the aggregation device information, and in this example, indicates that terminal 3-9 is under the control of aggregation device 2-1. The central device 1 holds, for each terminal 3, information indicating which aggregation device 2 the terminal 3 is under as aggregation device information.

[0053] FIG. 7 illustrates the path construction operation when aggregation device 2 is connected to central device 1, but similar operations are performed when aggregation device 2-2 is connected. As a result, aggregation device 2-2 maintains p downstream paths to each subordinate terminal 3. In this embodiment, central device 1 predetermines one aggregation device 2 corresponding to each terminal 3. For example, as shown in FIG. 6, the upstream path from terminal 3-9 to central device 1 can be either a path via aggregation device 2-1 or a path via aggregation device 2-2. However, central device 1 determines either aggregation device 2-1 or aggregation device 2-2 as the aggregation device 2 corresponding to terminal 3-9. Regarding the upstream path, each terminal 3 may maintain two aggregation devices, a primary and a secondary, as destinations, and may transmit upstream data to the secondary aggregation device 2 if it determines that a failure has occurred in communication with the primary aggregation device 2.

[0054] Fig. 11 is a diagram showing an example of a downlink route in this embodiment. Fig. 11 shows an example of a downlink route for terminal 3-9 determined based on the uplink route for terminal 3-9 shown in Fig. 6. In this way, in this embodiment, multiple downlink routes are set for each terminal 3.

[0055] As described above, in this embodiment, the aggregation device 2 holds p downlink routes, but if more than p uplink communication control signals are received from one terminal 3, i.e., if there are more than p uplink routes from one terminal 3 to the aggregation device 2, the aggregation device 2 selects p uplink routes based on the number of hops, communication quality, etc., and holds the downlink routes corresponding to the selected uplink routes as downlink route information.

[0056] Furthermore, if a terminal 3 newly joins the communication system after a route has been established between the aggregation device 2 and the terminal 3, the terminal 3 broadcasts an entry message. Upon receiving the entry message, each terminal 3 transmits a response message to the terminal 3 that sent the entry message, the response message including the aggregation device ID of the aggregation device 2 corresponding to the terminal 3 and the minimum number of hops among the downstream routes stored in the terminal table. The terminal 3 also adds its own terminal ID to the entry message and forwards it to the upstream route, similar to the upstream communication control signal described above. The terminal that sent the entry message stores the terminal ID of the terminal 3 that sent each response message in the terminal table as the terminal ID of the next hop node in one of the upstream routes, and stores the value obtained by adding 1 to the number of hops included in the response message as the number of hops for the upstream route. This allows the newly joined terminal 3 to store information about the upstream route in the terminal table. Furthermore, by receiving the entry message, the aggregation device 2 can store multiple downstream routes to the newly joined terminal 3 in the downstream route information, similar to the case of receiving the downstream communication control signal described above. Alternatively, when a terminal 3 newly joins a communication system, the newly joining terminal 3 may wait for a multi-hop construction signal sent by a surrounding terminal 3, and upon receiving the multi-hop construction signal, may transmit an uplink control signal or an uplink communication signal.

[0057] Next, a description will be given of downstream communication in the aggregation device 2 of this embodiment. When the central device 1 transmits a signal including data addressed to the terminal 3, the central device 1 uses the aggregation device information stored in the route information storage unit 13 to find the corresponding aggregation device 2, and transmits the signal addressed to the terminal 3 to the found aggregation device 2.

[0058] When the aggregation device 2 receives a signal addressed to the terminal 3 from the central device 1, it uses the downstream route information to copy the data contained in the signal and generate multiple signals each containing the multiple copies of data. The aggregation device 2 transmits multiple signals containing the same data via multiple downstream routes. For example, the aggregation device 2 transmits multiple signals consecutively via different downstream routes. Note that, although an example of consecutively transmitting multiple signals containing the same data via different downstream routes will be described here, multiple signals containing the same data may also be transmitted simultaneously if they can be transmitted simultaneously via different downstream routes.

[0059] 12 is a flowchart showing an example of a procedure for transmitting a downstream signal in the aggregation device 2 according to the present embodiment. As shown in FIG. 12, the communication control unit 23 of the aggregation device 2 copies data addressed to the terminal 3 and initializes ns, a variable indicating the number of times the same data is transmitted, to 0 (step S21). The communication control unit 23 selects a downstream route from multiple downstream routes (step S22). In detail, the communication control unit 23 reads multiple downstream routes corresponding to the destination terminal 3 from the downstream route information stored in the route information storage unit 24, and selects one of the read downstream routes.

[0060] The communication control unit 23 transmits the data to the selected downlink path (step S23). Specifically, the communication control unit 23 adds information indicating the selected downlink path as a header to one of the multiple copies of data, stores the terminal ID of the destination terminal 3 in the destination field of the header, and transmits the data to the terminal 3 at the next hop on the selected downlink path via the first transceiver 21. In this manner, each piece of data addressed to the terminal 3 is transmitted by unicast. At this time, the communication control unit 23 assigns the same sequence number to data copied from the same data. FIG. 13 is a diagram showing an example of the format of a downlink packet, which is a downlink signal in this embodiment. As shown in FIG. 13, the downlink signal is composed of a header section and a data section, and the above-mentioned duplicated data is stored in the data section. The header section includes destination information, message information, and a sequence number. The message information indicates the type of signal to be transmitted, i.e., the type of message corresponding to the signal. The destination information in the header section stores identification information of the next node of the destination. Although not shown, the header section also stores information indicating the downlink path.

[0061] Returning to the description of FIG. 12, the communication control unit 23 increments the value of ns by 1 (step S24) and determines whether ns is smaller than the number of downstream routes, i.e., p (step S25). If ns is smaller than the number of downstream routes (step S25: Yes), the process from step S22 is repeated. In step S22 from the second time onwards, a downstream route for transmitting a downstream signal is selected from among the downstream routes for which no downstream signal is being transmitted. If ns is equal to or greater than the number of downstream routes (step S25: No), the communication control unit 23 terminates the process of transmitting the downstream signal.

[0062] Through the above processing, multiple downlink signals containing the same data are transmitted via multiple downlink paths. In this manner, the communication control unit 23 of the aggregation device 2 of this embodiment determines multiple downlink paths to the source terminal using identification information of the terminal 3 via an uplink control signal, which is an example of an uplink signal, stored in an uplink signal transmitted from a source terminal (one of the multiple terminals 3) to the aggregation device 2, and transmits the same downlink data addressed to the source terminal via each of the determined multiple downlink paths. As a result, even if a communication failure or error occurs on a downlink path, the downlink signal will reach the destination terminal 3 via another downlink path, thereby improving reliability compared to transmission via a single downlink path. Furthermore, even if a communication failure occurs on a downlink path, if the downlink signal reaches the terminal 3 via another downlink path, retransmission is not required, thereby achieving low-latency downlink communication.

[0063] Next, the process of receiving a downstream signal in the terminal 3 will be described. Fig. 14 is a flowchart showing an example of the process of receiving a downstream signal in the terminal 3 of this embodiment. In the terminal 3, when the transmitter / receiver 31 receives a signal, it passes the signal to the communication control unit 32. If the destination of the signal received from the transmitter / receiver 31 is not the aggregation device 2, the communication control unit 32 determines that the signal received from the transmitter / receiver 31 is a downstream signal and performs the process shown in Fig. 14. Note that if the destination of the signal received from the transmitter / receiver 31 is the aggregation device 2, the communication control unit 32 transfers the signal to the upstream route using the terminal table stored in the route information storage unit 33.

[0064] 14, upon receiving a downstream signal, the communication control unit 32 determines whether the destination is the terminal itself (step S31). If the destination is the terminal itself (step S31: Yes), the communication control unit 32 determines whether the same data has already been received (step S32). As described above, the same sequence number is assigned to the same data. Therefore, if the communication control unit 32 of the terminal 3 has already received data with the same sequence number as the sequence number assigned to the data currently received, the communication control unit 32 can determine that the same data has already been received. Note that the method for determining whether the received data is the same as the previously received data is not limited to this, and may be, for example, a method in which the terminal 3 stores previously received data for a certain period of time and compares the data with the stored data.

[0065] If the same data has not been received (step S32: No), the communication control unit 32 passes the data to the control processing unit 34, which processes the data (step S33), and ends the reception process. If the same data has been received (step S32: Yes), the communication control unit 32 discards the data received this time (step S34), and ends the reception process. In this way, when the terminal 3 receives new downlink data that has the same sequence number as previously received downlink data, it discards the newly received downlink data.

[0066] If the destination is not the terminal itself (step S31 No), the communication control unit 32 transfers the data to the lower terminal 3, which is the next node on the downstream route, via the transmission / reception unit 31 based on the downstream route information attached to the received data (step S35), and ends the receiving process.

[0067] As described above, the aggregation device 2 transmits the same data to the terminal 3 using multiple downstream paths. However, if a communication error occurs after transmitting the same data using multiple downstream paths because there is no response from the terminal 3 for a certain period of time, the aggregation device 2 may retransmit the data by performing the transmission shown in FIG. 12 again. That is, if a communication error occurs in all of the downstream data transmitted using multiple downstream paths, the downstream data may be retransmitted using multiple downstream paths. Furthermore, if a communication error occurs in all of the downstream data even during retransmission, the downstream data addressed to the terminal 3 may be transmitted by broadcast. In this case, the terminals 3 other than the destination terminal 3 forward the data received by broadcast.

[0068] In general, signals transmitted and received between nodes are provided with check bits for CRC (Cyclic Redundancy Code) checks to enable error detection using CRC. Data that results in an error during the CRC check is generally discarded. However, in this embodiment, the same data is transmitted over multiple downstream paths as described above, and therefore terminal 3 receives the same data multiple times. Therefore, terminal 3 may temporarily store data that results in an error during the CRC check rather than discarding it, and then perform statistical processing or error correction processing on the data together with later received data to restore the correct data. That is, detection bits for error detection are added to the downstream data, and terminal 3 uses the detection bits to perform error detection on the downstream signal containing the downstream data. If an error is detected in the downstream data addressed to terminal 3 through error detection, terminal 3 may retain the downstream data and restore the downstream data using the multiple retained downstream data corresponding to the same sequence number.

[0069] 15 is a flowchart showing an example of a procedure for receiving a downstream signal including a restoration process using a CRC according to the present embodiment. As shown in FIG. 15, upon receiving a downstream signal, the communication control unit 32 performs error detection using a CRC (step 41). If the error detection does not find any error in the header portion of the downstream signal (step S42: No), the communication control unit 32 performs step S31 described above.

[0070] If step S31 returns Yes, it is determined whether or not there is an error in the data section (step S43). If there is an error in the data section (step S43: Yes), the data is temporarily stored (step S44). The communication control unit 32 then determines whether or not there is a certain number of temporarily stored identical data pieces with the same sequence number (step S45). If there is a certain number of temporarily stored identical data pieces (step S45: Yes), the communication control unit 32 restores the correct data using the temporarily stored data (step S46). For example, if, for a bit value at the same position, only one of the temporarily stored data pieces has a different first value and the others have the same second value, the bit value is determined to be the second value. After step S46, the same processing as in step S33 of FIG. 14 is performed.

[0071] If the number of temporarily stored identical data items is less than a certain number (No in step S45), the communication control unit 32 ends the reception process. If the answer is No in step S43, the process of step S33 is performed. If the answer is No in step S31, the process of step S35 is performed as in FIG. 14. If the answer is Yes in step S42, the communication control unit 32 discards the data (step S47) and ends the reception process.

[0072] By the above processing, even if a communication error occurs in multiple downlink signals among multiple downlink signals containing the same data received by terminal 3, the data can be temporarily stored and the correct data can be restored using the multiple pieces of data.

[0073] As described above, in this embodiment, the aggregation device 2 holds downlink route information that stores information indicating multiple downlink routes, and transmits multiple downlink signals that store the same data via each of the multiple downlink routes. As a result, even if a communication failure or error occurs on a downlink route, the downlink signal will reach the destination terminal 3 via another downlink route, thereby improving reliability compared to transmission via a single downlink route. Furthermore, even if a communication failure occurs on a downlink route, if the downlink signal reaches the terminal 3 via another downlink route, retransmission is not necessary, thereby achieving low-latency downlink communication.

[0074] Second Embodiment. FIG. 16 is a diagram illustrating a configuration example of a central device according to a second embodiment. FIG. 17 is a diagram illustrating a configuration example of an aggregation device according to a second embodiment. The communication system of this embodiment is similar to the communication system of the first embodiment, except that it includes a central device 1a shown in FIG. 16 instead of the central device 1 shown in FIG. 1, and aggregation devices 2a-1 and 2a-2, each of which is the aggregation device 2a shown in FIG. 17 instead of the aggregation devices 2-1 and 2-2. As with the first embodiment, the number of aggregation devices 2a and the number of terminals 3 of this embodiment are not limited to the example shown in FIG. 1. Components having the same functions as those of the first embodiment are assigned the same reference numerals, and redundant explanations will be omitted. Below, differences from the first embodiment will be mainly explained.

[0075] In the second embodiment, the aggregation device 2a determines a downlink route corresponding to the uplink route of each terminal using an uplink communication control signal transmitted from the terminal 3, as in the first embodiment, and transmits downlink route information indicating the downlink route of each terminal to the central device 1a. The central device 1a then holds multiple downlink routes to each terminal 3, including the aggregation device 2a, and when transmitting downlink data addressed to the terminal 3, the central device 1a copies the data and transmits it via each of the multiple downlink routes.

[0076] As shown in Figure 16, the central device 1a has a communication control unit 12a instead of the communication control unit 12, and a route information storage unit 13a instead of the route information storage unit 13, but other than this it is the same as the central device 1 of embodiment 1.

[0077] As shown in Figure 17, the aggregation device 2a has a communication control unit 23a instead of the communication control unit 23, and a route information storage unit 24a instead of the route information storage unit 24, but other than this it is the same as the aggregation device 2 of embodiment 1.

[0078] Next, the route construction operation of this embodiment will be described. Steps S1 to S12 shown in Fig. 7 are performed as in the first embodiment. When a certain time has elapsed since the wireless multi-hop construction signal was transmitted in step S2 and upstream communication control signals have been received from all terminals 3, the communication control unit 23a of the aggregation device 2a includes downstream route information, which is information recording the downstream routes determined from the upstream communication control signals transmitted from each terminal 3, in a terminal notification signal, and transmits the terminal notification signal to the central device 1a via the second transceiver unit 22.

[0079] When the communication control unit 12a of the central device 1a receives a terminal notification signal via the transceiver unit 11, the communication control unit 12a determines a downlink route for each terminal as a route opposite to the uplink route using the uplink route for each terminal 3 included in the terminal notification signal, and stores the determined downlink route as downlink route information in the route information storage unit 13a. FIG. 18 is a diagram showing an example of downlink route information according to this embodiment. The downlink route information stores information indicating m downlink routes, from downlink route #1 to downlink route #m, for each terminal 3. m is an integer equal to or greater than 2 and is determined in advance. m may be changeable by input from an operator or an instruction from another device (not shown). In this embodiment, the downlink route stored as the downlink route information also includes the aggregation device ID of the aggregation device 2a that relays communication from the central device 1a to the terminal 3. For example, in the configuration example shown in Figure 6 of the first embodiment, if the central device 1 is replaced with the central device 1a and the aggregation devices 2-1 and 2-2 are replaced with the aggregation devices 2a-1 and 2a-2, the downstream route of the terminal 3-9 can be the reverse route of each of the upstream routes 4-1 to 4-3. Therefore, the multiple downstream routes of the terminal 3-9 will include a route that passes through the aggregation device 2a-1 and a route that passes through the aggregation device 2a-2.

[0080] Next, a transmission procedure for a downlink signal including downlink data addressed to terminal 3 will be described. In this embodiment, the central device 1a performs the process shown in FIG. 12. That is, the communication control unit 12a of the central device 1a duplicates the data addressed to the terminal and performs the process shown in FIG. 12 using the downlink route information. At this time, the same sequence number is assigned to the same data, as in the first embodiment. Furthermore, information indicating the downlink route is assigned to each piece of data. However, the aggregation device ID of the aggregation device 2a on the downlink route does not need to be included in the information indicating the downlink route assigned to each piece of data, since the communication control unit 12a of the central device 1a simply transmits the downlink signal to the corresponding aggregation device 2a for each downlink route. When the communication control unit 23a of the aggregation device 2a receives a downlink signal via the second transceiver 22, it transmits the downlink signal to the next node in accordance with the information indicating the downlink route stored in the downlink signal. The operation of each terminal 3 is the same as in the first embodiment. Note that in this embodiment, since multiple aggregation devices correspond to one terminal 3, multiple aggregation device IDs per terminal 3 are stored in the aggregation device information.

[0081] As described above, in this embodiment, the aggregation device 2a transmits identification information of the terminal through which the upstream communication control signal has passed to the central device 1a as downstream route information, and the central device 1a determines multiple downstream routes to the source terminal using the downstream route information, and transmits the same downstream data destined for the source terminal using each of the determined multiple downstream routes. In this embodiment, multiple downstream routes, including the aggregation device 2a, can be distributed, and the same data is transmitted using the distributed multiple downstream routes, thereby increasing the independence of the multiple downstream routes compared to embodiment 1. As a result, even if a communication failure occurs near a certain aggregation device 2a, downstream data destined for terminal 3 can reach terminal 3 via another aggregation device 2a, thereby achieving highly reliable and low-latency downstream communication.

[0082] In this embodiment, the central device 1a manages multiple downlink routes for each terminal 3. However, the central device 1a may retain multiple aggregation devices per terminal 3 as aggregation device information, and the aggregation device may manage downlink route information for the terminals lower than the aggregation device 2a. In this case, the same aggregation device 2 as in embodiment 1 is used as the aggregation device, and the central device 1a stores the aggregation device IDs of the multiple aggregation devices 2 corresponding to each terminal 3 in the aggregation device information instead of the multiple downlink routes for each terminal 3. The communication control unit 12a of the central device 1a then duplicates the downlink data addressed to the terminal 3 and transmits it to each of the multiple aggregation devices 2 based on the aggregation device information. That is, the aggregation device 2 transmits information indicating the terminal 3 communicating with the central device 1a via the aggregation device 2 to the central device 1a, and the central device 1a uses the information received from the aggregation device 2 to transmit the same downlink data addressed to the source terminal to two or more aggregation devices 2 corresponding to the source terminal. In this case, the same data is transmitted to the terminal 3 via the multiple aggregation devices 2.

[0083] The communication system of this embodiment may also have the functions of the communication system of the first embodiment, so that both operations can be realized.

[0084] The hardware configurations of the central device 1a and the aggregation device 2a of this embodiment are similar to those of the central device 1 and the aggregation device 2 of the first embodiment, respectively.

[0085] As described above, in this embodiment, the same data is transmitted to terminal 3 via multiple downlink routes, including downlink routes that pass through different aggregation devices. Therefore, the same effects as in embodiment 1 are achieved, and the aggregation devices included in each downlink route can also be distributed, thereby increasing the probability that the downlink data will reach terminal 3.

[0086] Third embodiment. Next, the operation according to the third embodiment will be described. The configuration of the communication system of this embodiment and the configurations of the central device 1, aggregation device 2, and terminal 3 are the same as those of the first embodiment. The operation of each device of this embodiment is the same as that of the first embodiment, except for a partial difference in the method of transmitting downstream signals, which will be described below. Components having the same functions as those of the first embodiment are given the same reference numerals, and duplicated explanations will be omitted. Below, the differences from the first embodiment will be mainly described.

[0087] 19 is a flowchart showing an example of a transmission procedure for a downlink signal including downlink data in aggregation device 2 of this embodiment. Steps S21 and S22 are the same as in embodiment 1. After step S22, communication control unit 23 transmits the same data multiple times to the selected route (step S26). That is, communication control unit 23 transmits the same downlink data multiple times to one downlink route. Steps S24 and S25 are the same as in embodiment 1.

[0088] In addition, in the above example, the same data is transmitted multiple times to each downlink path regardless of the number of downlink paths, but the operation shown in Figure 19 may be performed for terminal 3 whose number of downlink paths is less than a threshold, and the operation of embodiment 1 may be performed for terminals whose number of downlink paths is equal to or greater than the threshold.

[0089] In the above example, the aggregation device 2 transmits the same data multiple times to the downlink path, but the central device 1a that manages multiple downlink paths in embodiment 2 may similarly transmit the same data multiple times to the downlink path. Also, in the case where the central device 1a described in embodiment 2 manages information on multiple aggregation devices 2a per terminal 3 and the aggregation device 2 manages multiple downlink paths, the aggregation device 2a may similarly transmit the same data multiple times to the downlink path.

[0090] As described above, in this embodiment, the same data is transmitted to multiple downlink paths, and the same data is transmitted multiple times in succession to one downlink path. Therefore, the same effect as in the first embodiment is achieved, and in the event that a temporary failure occurs on the downlink path, the downlink data will arrive at terminal 3 once the communication failure is resolved, thereby further improving reliability and reducing delays.

[0091] Fourth Embodiment Next, a method for transmitting an upstream communication control signal according to a fourth embodiment will be described. The configuration of the communication system according to this embodiment and the configurations of the central device 1, aggregation device 2, and terminal 3 are the same as those of the first embodiment. The operation of each device according to this embodiment is the same as that of the first embodiment, except for the operations described below. Components having the same functions as those of the first embodiment are given the same reference numerals, and duplicated explanations will be omitted. Below, differences from the first embodiment will be mainly described.

[0092] In the first embodiment, the terminal 3 transmits an upstream communication control signal every time it receives a wireless multihop establishment signal. In the present embodiment, each terminal 3 does not transmit an upstream communication control signal immediately upon receiving a wireless multihop establishment signal, but selects multiple upstream routes using wireless multihop establishment signals received within a certain period of time, and transmits an upstream communication control signal to the next node on the upstream route corresponding to the selected upstream route.

[0093] For example, the communication control unit 32 of terminal 3 selects k upstream routes using the signal strength of a wireless multi-hop establishment signal received from another terminal 3 or a signal other than the wireless multi-hop establishment signal from another terminal 3. Specifically, the communication control unit 32 calculates average values, such as a moving average or a section average, of the signal strength of the signal received for each terminal 3 with respect to the signals received from the other terminals 3, and stores the calculated average values ​​as a signal strength table for each terminal 3. FIG. 20 is a diagram showing an example of a signal strength table stored by terminal 3-9 of this embodiment. As shown in FIG. 20 , the signal strength is stored as a signal strength table for each terminal 3 that is the source of the signal, i.e., for each next node on the upstream route. The communication control unit 32 of terminal 3-9 uses the signal strength table to select k upstream routes in descending order of signal strength, stores information indicating the selected k upstream routes as a terminal table, and transmits upstream communication control signals via the selected k upstream routes. Furthermore, the signal for communicating on the upstream route is not limited to the upstream communication control signal, and may be another upstream signal. That is, the terminal 3 selects k upstream routes, which are the first number of upstream routes, using the signal strength of the signal received from the other terminal 3, and transmits the upstream signal using the k upstream routes.

[0094] The communication control unit 32 of the terminal 3 may transmit an upstream communication control signal or other upstream signals using a round robin method for the selected k upstream routes. Alternatively, the communication control unit 32 may transmit an upstream communication control signal or other upstream signals using a weighted round robin method for the selected k upstream routes, in which routes with higher signal strength are selected with higher priority. In other words, the communication control unit 32 may select an upstream route using a weighted round robin method based on signal strength and transmit an upstream signal using the selected upstream route.

[0095] The k upstream communication control signals are each assigned the terminal ID of a terminal 3 passed through on each upstream route, as in embodiment 1. This allows the aggregation device 2 to determine k upstream routes for each terminal 3, select p upstream routes, which are the second number of upstream routes, from among the k upstream routes, and store the reverse routes of the selected p upstream routes as downstream routes in the downstream route information. Note that the aggregation device 2 may also store downstream routes corresponding to all of the identified upstream routes as downstream routes in the downstream route information. In other words, p and k may be equal.

[0096] The communication control unit 23 of the aggregation device 2 selects p upstream routes, which are a second number of upstream routes, from among the k upstream routes based on the route cost value of each upstream route. The route cost value is calculated, for example, using the signal strength of each terminal 3 and the number of hops of each route. For example, it is calculated by a weighted sum of the inverse of the signal strength and the number of hops. The signal strength is, for example, a moving average or section average of the signal strength of the signal received by the aggregation device 2. Alternatively, each terminal 3 may add the signal strength corresponding to each upstream route from the signal strengths in the signal strength table described above, so that the aggregation device 2 can grasp the signal strength of each link of the upstream route and calculate the route cost value based on the signal strength and hops of each link. The communication control unit 23 selects n upstream routes from the k upstream routes in order of lowest route cost value, and determines n downstream routes using the n upstream routes. In this way, the aggregation device 2 calculates a route cost value for each upstream route of the terminal 3 based on the signal strength of the upstream signal and the corresponding number of hops, and determines a second number of downstream routes based on the route cost value.

[0097] Since communication conditions may change, the downlink route may be updated periodically. Note that the term "update" as used herein includes cases where the downlink route does not change as a result of the update process. The aggregation device 2 updates the downlink route based on past signal strength, for example, as follows. For example, the aggregation device 2 collects information about the uplink route by periodically transmitting a wireless multi-hop establishment signal. When the period for collecting data about the uplink route is defined as a first period, the communication control unit 23 stores the number of hops and signal strength of the uplink route received during the first period, calculates a weighted average of the route cost values ​​calculated from the stored number of hops and signal strength, and determines p downlink routes using the average value obtained by the weighted average. The first period may be 24 hours, 30 days, one month, or any other period. Alternatively, the collected information for the first period may be divided into data for each second period shorter than the first period, calculates an average value of the route cost values ​​using the number of hops and signal strength for each second period, weights the average values ​​for each second period, and determines n downlink routes using the weighted average. For example, a weighted average may be calculated every t hours for data collected over 24 hours, a weighted average may be calculated every d days for data collected over 30 days, or a weighted average may be calculated every month for data collected over several months. In this case, when calculating the weighted average, the weight value is set smaller for the most recent information so that the most recent information is reflected more frequently across multiple second time periods. In other words, the weights in the weighted average are determined so that the route cost value calculated based on the most recent uplink signal is smaller.

[0098] Furthermore, when the aggregation device 2 acquires information on p+1 or more upstream routes from the terminal 3, it extracts routes that pass through the same terminal 3 from among these upstream routes, and excludes from the selection candidates those upstream routes with high route cost values ​​among the extracted routes. In other words, when the aggregation device 2 receives upstream signals corresponding to more than the second number of upstream routes, it determines the second number of downstream routes by prioritizing downstream routes that do not pass through overlapping terminals 3. This makes it possible to distribute the multiple downstream routes so that they do not pass through overlapping terminals 3 as much as possible, thereby improving reliability. Note that each operation of this embodiment may be applied to embodiment 2.

[0099] This embodiment may be combined with either embodiment 2 or embodiment 3. Furthermore, this embodiment may be combined with either embodiment 2 or embodiment 3.

[0100] As described above, in this embodiment, the terminal 3 selects multiple upstream routes based on route cost values ​​and transmits an upstream communication control signal via the selected upstream route. This achieves the same effects as in the first embodiment, and also reduces communication bandwidth consumption by not notifying upstream routes with high route cost values. Furthermore, the aggregation device 2 selects a downstream route based on the average route cost, making it possible to select a route with stable, good communication conditions without being affected by temporary route conditions. Furthermore, by selecting multiple downstream routes in a distributed manner, reliability can be improved.

[0101] Fifth embodiment. Next, the operation according to the fifth embodiment will be described. The configuration of the communication system of this embodiment and the configurations of the central device 1, aggregation device 2, and terminal 3 are the same as those of the first embodiment. The operation of each device of this embodiment is the same as that of the first embodiment, except for a partial difference in the method of transmitting downstream signals, which will be described below. Components having the same functions as those of the first embodiment are given the same reference numerals, and duplicated explanations will be omitted. Below, the differences from the first embodiment will be mainly described.

[0102] In this embodiment, when transmitting downstream data that requires reliability, broadcast transfer is utilized as follows to improve the rate of arrival at the destination terminal 3.

[0103] The communication control unit 23 of the aggregation device 2 transmits downstream data by unicast for a route with one hop to the destination terminal 3, as in embodiment 1. If the number of hops to the destination terminal 3 is two or more, the communication control unit 23 of the aggregation device transmits the downstream data by broadcast on at least a portion of the downstream route when transmitting the downstream data.

[0104] In detail, for example, the communication control unit 23 of the aggregation device 2 adds to the downstream data information indicating the corresponding downstream route, information indicating whether the terminal 3 will forward the data by broadcast or unicast for each terminal 3 on the downstream route, and the forwarding limit number for broadcast forwarding. The forwarding limit number is one less than the number of hops from the corresponding terminal 3 to the destination of the downstream data. When a terminal 3 receives downstream data with a forwarding limit number set to one via broadcast, it forwards the downstream data by unicast. The communication control unit 32 of each terminal 3 uses the information indicating the downstream route added to the downstream data and the information indicating whether the forwarding will be by broadcast or unicast, and when instructed to forward the data by broadcast, sets the instructed forwarding limit number and forwards the data by broadcast. The same sequence number is assigned to all of this downstream data. For example, the communication control unit 23 of the aggregation device 2 sets the above information so that terminals 3 with a hop count to the destination terminal 3 greater than a threshold j will forward the data by unicast, and terminals 3 with a hop count to the destination terminal 3 less than the threshold will forward the data by broadcast.

[0105] FIG. 21 is a diagram illustrating an example of a method for transmitting a downlink signal according to this embodiment. In the example shown in FIG. 21, the value of j, which is the threshold, is 3, and the destination of the downlink signal containing downlink data is terminal 3-9. In FIG. 21, broadcast transmission is performed at the locations marked "B," and unicast transmission is performed at the locations marked "U." In the example shown in FIG. 21, the nodes with a hop count of 3 to terminal 3-9 are aggregation devices 2-1 and 2-2, so aggregation devices 2-1 and 2-2 set the forwarding limit to 2 and transmit a downlink signal containing downlink data addressed to terminal 3 by broadcast. Terminals 3-1 and 3-2, which receive the downlink signal transmitted by broadcast from aggregation devices 2-1 and 2-2, have a hop count of 2 to terminal 3-9, which is less than j, and the forwarding limit for the downlink signal received from aggregation devices 2-1 and 2-2 is 2, so they change the forwarding limit to a value obtained by subtracting 1 and transmit the downlink signal by broadcast. When the terminals 3-4 and 3-5 receive the downstream signals transmitted by broadcast from the terminals 3-1 and 3-2, the transfer limit number of the received downstream signals is 1, so they transmit the downstream signals to the terminal 3-9 by unicast.

[0106] This embodiment may be combined with one or more of Embodiments 2, 3, and 4. When the central device 1a determines the downstream route as in Embodiment 2, the setting of the information on whether or not to use broadcast using the above-mentioned number of hops is performed by the communication control unit 12a of the central device 1a.

[0107] In this way, in this embodiment, by performing broadcast forwarding on at least a portion of the downstream path, it is possible to improve the rate at which downstream data reaches terminal 3. Furthermore, rather than all terminals 3 performing broadcast forwarding, the number of terminals 3 that perform broadcast forwarding is limited in accordance with the number of hops to the destination, the limited number of broadcast forwardings, etc., thereby making it possible to suppress the communication bandwidth used.

[0108] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0109] 1, 1a central device, 2, 2a, 2-1, 2-2 aggregation device, 3, 3-1 to 3-12 terminal, 11, 31 transmission / reception unit, 12, 12a, 23, 23a, 32 communication control unit, 13, 13a, 24, 24a, 33 route information storage unit, 14, 25, 34 control processing unit, 21 first transmission / reception unit, 22 second transmission / reception unit.

Claims

DEPCT661. A communication system composed of: one or more aggregate devices and more than one terminal that transmits uplink data to the aggregate devices. The communication system is capable of forming a multi-range wireless network where more than one downlink path to a single source terminal is determined using terminal identification information through which the uplink signal transmitted from the source terminal to the aggregate device travels. The identification information contained in the uplink signal and the identical downlink data, which are assigned addresses to the source terminal, are transmitted using more than one defined downlink path.2.A communication system under claim 1 in which aggregation devices establish more than one down link path to the originating end using the end identification information contained in the up link signal and transmit identical down link information, addressed to the originating end, using more than one defined down link path.

3. A communication system under claim 2 consisting of more than one aggregation device and additionally consisting of a central device to communicate with more than one aggregation device, in which aggregation devices transmit end identification information communicating with the central device through the aggregation device to the central device, and the central device transmits identical down link information, addressed to the originating end, to two or more aggregation devices corresponding to the originating end using the information. 4.A communication system under claim 1 consisting of more than one aggregate device and additionally consisting of a central device to communicate with more than one aggregate device, where the aggregate device transmits terminal identification information present in the uplink signal as uplink path information to the central device, and the central device determines more than one downlink path to the originating terminal using the uplink path information and transmits identical and addressed downlink information to the originating terminal using more than one designated downlink path.

5. Any one of the communication systems under claims 1 through 4 in which identical and addressed downlink information to the originating terminal is transmitted multiple times over one downlink path.

6. Any one of the communication systems under claims 1 through 5 in which identical and addressed downlink information to the originating terminal is assigned an identical sequence. 7.

8. A communication system under any of the claims 1 through 6 where, upon receiving a new down link with the same sequence number as a received down link, the receiving end discards the new down link.

9. A communication system under claim 1 where the down link is assigned a check bit for error detection, and the receiving end performs error detection on the down link signal, including the down link data, using the check bit to store the down link data in response to an error detection in the down link data addressed to the receiving end, and returns the down link data using multiple stored down link pieces corresponding to the same sequence number.

10. A communication system under any of the claims 1 through 8 where the source end selects a first number of up link paths using the signal strength of the signal received from another receiving end and transmits the up link signal using a first number of up link paths.A communication system under claim 9 where the terminal selects the uplink path using a weighted loop method based on signal strength and transmits the uplink signal using the selected uplink path.

11. A communication system under claim 9 or 10 where, using the first number of uplink signals transmitted from the source terminal, a second number of downlink paths is designated as the downlink path for transmitting downlink data to the source terminal.

12. A communication system under claim 11 where the path cost is calculated individually for one uplink path, identified by the terminal identifier through which the uplink signal travels, based on the uplink signal signal strength and the number of corresponding connection points, and the second number of downlink paths is determined based on the path cost. 13.A communication system under claim 12 in which the weighted average calculation is performed on the path cost calculated based on the uplink signal received during the first time period, and the second number of downlink paths is determined based on the weighted average calculation.

14. A communication system under claim 13 in which the weights in the weighted average calculation are determined in such a way that the path cost calculated based on the subsequent uplink signal is less.

15. Any communication system under claim 12 through 14 in which, when an uplink signal corresponding to a number greater than the second uplink path is received relative to the originating end, the second number of downlink paths is arbitrarily determined from the non-overlapping downlink paths at the end for passage.

16. Any communication system under claim 1 through 15 in which, in the transmission of downlink data, the downlink data is transmitted by broadcasting in at least part of the downlink path. 17.The communication system under claim16, where downlink information is defined, contains information specifying one corresponding path of downlink information, specifying that each terminal in the downlink path transfers by broadcasting or by one-to-one data transmission, and a transfer limit specifying the limit of the number of transfers by broadcasting. The transfer limit is the value obtained by subtracting one from the count of connection segments from one corresponding terminal to the downlink destination. The information is specified in such a way that terminals whose count of connection segments to the destination is greater than the threshold transfer by one-to-one data transmission, and terminals whose count of connection segments to the destination is equal to or less than the threshold transfer by broadcasting, and when receiving by broadcasting, the downlink information with the specified transfer limit is one terminal that transmits the downlink information by one-to-one data transmission.18.Any communication system under claims 1 through 17 where, when the entire transmission of downlink data over more than one downlink path results in a communication error, the downlink data is retransmitted using more than one downlink path, and when the entire retransmission of the downlink data also results in a communication error, the downlink data is transmitted by broadcast.

19. Any communication system under claims 1 through 18 where the uplink data is meter data. 20.A group of devices in a communication system includes one or more aggregation devices and more than one terminal that transmits uplink data to the aggregation device, forming a multi-range wireless network. The aggregation device consists of: a transmitting / receiving unit to receive the uplink signal transmitted to the aggregation device from one or more source terminals; and a communication control unit to: determine more than one downlink path to the source terminal using the terminal identification information through which the uplink signal travels (the identification information contained in the uplink signal) and transmit the same downlink data, which is addressed to the source terminal, using more than one defined downlink path.21.A central device integrated into a communication system, including a multi-range wireless network, is configured by more than one aggregation device and more than one terminal that transmits uplink information to the aggregation device. The central device, configured to communicate with more than one aggregation device, consists of: a transmitting / receiving unit to receive terminal identification information through which the uplink signal travels from the aggregation device as downlink path information; an uplink signal transmitted to the aggregation device from one of more than one source terminals; identification information incorporated into the uplink signal; and a communication control unit to determine more than one downlink path to the source terminal using the downlink path information and transmit the same downlink information, which is addressed to the source terminal using more than one defined downlink path.22.A terminal in a communication system, including one or more aggregate devices and more than one terminal, transmits uplink data to an aggregate device, forming a multi-range wireless network that is configured to: route more than one downlink to a single source terminal using the terminal identification information through which the uplink signal transmitted from the source terminal to the aggregate device passes; transmit the same downlink data addressed to the source terminal using more than one designated downlink path, where the terminal receives the same downlink data via more than one downlink path, and upon receiving a new downlink data identical to the previously received downlink data, discards the newly received downlink data.23.The communication method for a communication system that includes one or more aggregate devices and more than one terminal device that transmits uplink data to the aggregate devices, forming a multi-range wireless network, involves the following steps: routing more than one downlink path to one of the more than one source terminal using terminal identification information—the uplink signal transmitted from the source terminal to the aggregate device travels through that terminal (the identification information contained in the uplink signal)—and the transmission of the same downlink data, which is addressed to the source terminal using more than one defined downlink path.24.A communication program for a communication system that includes one or more aggregate devices and more than one terminal device that transmits uplink data to the aggregate devices. This communication system, capable of forming a multi-range wireless network, enables the communication system to perform the following actions: routing more than one downlink path to a single source terminal (of more than one terminal) using terminal identification information; the uplink signal transmitted from the source terminal to the aggregate device travels through that terminal; the identification information contained in the uplink signal and the downlink data transmission steps are identical and assigned addresses to the source terminals using more than one defined downlink path.

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