JP2015216581A - Transfer node, sensor node, and sensor network system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption in a battery-driven node.SOLUTION: A transfer node includes: a wireless communication device for performing wireless communication with a sensor node including a sensor for observing an observation target; a calculation unit including a processor and a memory; and a battery for supplying power to the wireless communication device and the calculation unit. The processor executes: setting processing that sets reception timing for observation data to be received using a slot by which the observation data is received from the sensor node on the basis of the slot and a reception interval until the observation data is received from the sensor node, and transmits a transmission interval which is the same time interval as the reception interval to the sensor node; stop processing of stopping supplying power from the battery to the wireless communication device and the calculation unit, in the case that the setting is completed; and reception awaiting processing of supplying power from the battery to the wireless communication device and the calculation unit every time the reception timing comes after the setting, and awaiting, by slot time, reception of observation data from the sensor node.

Description

  The present invention relates to a sensor node that transmits observation data via wireless communication, a transfer node that transfers observation data collected via wireless communication, and a sensor network system having the sensor node and the transfer node.

  As an example of a wireless sensor network, an asynchronous wireless network using IEEE802.15.4 or ZigBee (registered trademark, hereinafter the same) communication standard is widely adopted. ZigBee classifies the nodes constituting the sensor network into FFD (Full-Function Device) and RFD (Reduced-Function Device).

  The router node and the gateway node are FFDs. The router node and the gateway node have a function of constructing a mesh-structured communication network and transferring observation data in multiple stages. Since the FFD needs to constantly monitor communication from other nodes, it is always activated by AC (Alternating Current) driving. On the other hand, the sensor node is an RFD, and after observing by the sensor and wirelessly transmitting the observation data, the power consumption is reduced by sleeping, and as a result, battery driving is realized.

  On the other hand, since it is difficult to secure the power supply of the router node in a wide field, for example, the battery-driven router node shown in Patent Document 1 and Patent Document 2 is disclosed.

  Patent Document 1 discloses a method in which a router node performs time synchronization with a plurality of sensor nodes managed as its children, and performs communication using a TDMA (Time Division Multiple Access) method between the sensor node and the router node. . That is, the router node assigns a time slot to each sensor node, and it is guaranteed that the sensor node that communicates with the router node in each time slot is independent. This ensures that no communication collision (congestion) occurs due to simultaneous communication from a plurality of sensor nodes. The router node saves power by sleeping at times other than the time slots, and as a result, the router node is driven by a battery.

  In Patent Document 2, the TDMA method is adopted, information indicating that communication from a sensor node is necessary is transmitted to a router node by a preamble, the router node transmits a communication start time to the sensor node, and the communication start time A method for saving power by putting a router node to sleep is disclosed.

JP 2008-244756 A JP 2012-170068 A

  In the field where a plurality of sensor nodes and router nodes are used, the work cost of battery replacement of the sensor nodes and router nodes becomes an issue. For this reason, it is necessary to suppress the power consumption of the router node to at least the same level as the power consumption of the sensor node.

  On the other hand, in the methods disclosed in Patent Document 1 and Patent Document 2, there is a problem in the constant reception standby of the router node. The router node must always wait for reception at the transmission interval of the sensor node. Many observation data waveforms are sufficiently gentle with respect to the observation interval of the sensor nodes. When sensor nodes are observed at regular intervals, the number of sensor node transmissions can be reduced by thinning out observation data that takes the same value within a certain allowable error range. Can be reduced.

  On the other hand, the router node has no means for detecting that observation data has been thinned out at the sensor node. Therefore, the router node needs to wait for reception in all time slots in which the sensor node may transmit.

  As described above, the conventional battery-powered router node requires power consumption equivalent to a value obtained by multiplying the power consumption of the sensor node by the number of sensor nodes connected. Therefore, it is necessary to make the battery of the router node have a larger capacity than the battery of the sensor node, or it is necessary to perform the battery replacement frequency of the router node more frequently than the battery replacement frequency of the sensor node.

  Further, since the sensor node does not perform observation data transmission processing during the observation processing by the sensor, the power consumption increases when the wireless communication device is activated. Similarly, during the observation data transmission process, since the observation process by the sensor is not performed, the power consumption increases when the sensor is activated.

  An object of the present invention is to reduce power consumption in a battery-driven node.

  A sensor network system according to an aspect of the invention disclosed in the present application includes a sensor node having a sensor that observes an observation target, and a transfer node that receives observation data observed by the sensor from the sensor node. The transfer node includes a first wireless communication device that wirelessly communicates with the sensor node, a first arithmetic unit having a first processor and a first memory, the first wireless communication device, and the first wireless communication device. A first battery that supplies power to the computing unit, and the sensor node includes a second wireless communication device that wirelessly communicates the observation data to the transfer node, a second processor, and a second memory. And a second battery that supplies power to the sensor, the second wireless communication device, and the second computing unit. Hereinafter, the forwarding node is referred to as a router node.

  In the router node, the first processor receives a measurement interval observed by the sensor from the sensor node, and a reception time slot for receiving the observation data from the sensor node, A first setting process for setting a reception timing of the observation data received in the slot and transmitting a transmission interval that is the same time interval as the reception interval to the sensor node; When the setting by the setting process is completed, the first stop process for stopping the power supply from the first battery to the first wireless communication device and the first arithmetic unit, and the first setting process. Power is supplied from the first battery to the first wireless communication device and the first arithmetic unit every time the reception timing comes from the setting. It executes a reception standby process for waiting time of the reception of the slots of the observation data from the sensor nodes.

  In the sensor node, the second processor sets an observation timing with an observation interval shorter than the transmission interval until the observation target is observed by the sensor, and a reception interval at which the router node receives the observation data; A transmission interval for receiving the transmission interval from the router node until the sensor node transmits the observation data to the router node, and setting a transmission timing for transmitting the observation data to the router node. And a second stop process for stopping power supply from the second battery to the second wireless communication device and the second arithmetic unit when the setting by the second setting process is completed. And one of the observation timing and the transmission timing is reached from the setting by the second setting process. Each time, the power supply process for supplying power from the second battery to the second arithmetic unit, and whenever the observation timing arrives, the sensor is supplied with power, and the sensor is allowed to observe the observation target. Observation processing for acquiring observation data and holding it in the memory, and stopping the power supply from the second battery to the sensor after a predetermined observation time, and the second memory each time the transmission timing arrives Reading the observation data held in the transmission node, transmitting the observation data to the router node, and stopping the power supply from the second battery to the second wireless communication device after a lapse of time in the slot, and the observation When the process or the transmission process ends, a third stop process for stopping power supply from the second battery to the second arithmetic unit is executed.

  According to the exemplary embodiment of the present invention, it is possible to reduce power consumption in a battery-driven node. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments.

1 is an explanatory diagram illustrating a configuration example of a sensor network system according to Embodiment 1. FIG. It is explanatory drawing which shows the communication sequence example 1 of the sensor network system in Example 1. FIG. It is a block diagram which shows the hardware structural example of the sensor node concerning FIG. 1 is a block diagram illustrating a hardware configuration example of a router node according to Embodiment 1. FIG. FIG. 3 is a block diagram illustrating a hardware configuration example of the gateway node according to the first embodiment. FIG. 1 is a block diagram illustrating a hardware configuration example of a server according to the first embodiment. FIG. 3 is a block diagram illustrating a functional configuration example of a sensor node according to the first embodiment. FIG. 3 is a block diagram illustrating a functional configuration example of a router node according to the first embodiment; It is a block diagram which shows the functional structural example of the gateway node concerning Example 1. FIG. It is a block diagram which shows the functional structural example of the server concerning Example 1. FIG. It is explanatory drawing which shows the example of a data structure of the communication message in a sensor network system. It is a flowchart which shows an example of the operation process of a router node. It is a flowchart which shows an example of the operation process of a sensor node. It is a state transition diagram of the sensor node 104 regarding the communication trial process (step S1312) shown in FIG. It is a flowchart which shows an example of the communication trial process (step S1312) shown in FIG. 16 is a flowchart illustrating an example of an event transmission trial process (step S1503) illustrated in FIG. 16 is a flowchart illustrating an example of command reception trial processing (step S1505) illustrated in FIG. 15. It is explanatory drawing which shows the communication sequence example 2 of the sensor network system in Example 1. FIG. It is a conceptual diagram of linear approximation compression. It is a conceptual diagram for performing linear approximation compression sequentially. It is a flowchart which shows an example of the linear approximation compression process by the compression part of a sensor node. FIG. 10 is a state transition diagram of a sensor node related to a communication trial process according to the third embodiment. 12 is a flowchart of communication trial processing (step S2204) according to the third embodiment. FIG. 10 is an explanatory diagram illustrating a communication sequence example of a sensor network system according to a third embodiment. FIG. 10 is a state transition diagram of a sensor node related to a communication trial process according to the fourth embodiment. 10 is a flowchart illustrating an example of a communication trial process according to the fourth embodiment. FIG. 10 is an explanatory diagram illustrating a communication sequence example of a sensor network system according to a fourth embodiment. It is explanatory drawing which shows the structural example of the sensor network system of a multistage structure. FIG. 10 is an explanatory diagram illustrating a communication sequence example of a sensor network system according to a fifth embodiment. It is explanatory drawing which shows the concept of the space compression in the event coupling | bonding (step S1209) shown in FIG. 10 is a flowchart illustrating an example of a spatial compression process according to a fifth embodiment. 14 is a flowchart illustrating an example of operation processing of a control unit of a router node according to the sixth embodiment.

Example 1
<System configuration example>
FIG. 1 is an explanatory diagram of a configuration example of the sensor network system according to the first embodiment. A sensor network system is a system that acquires observation data that changes over time, such as temperature for maintenance of railway, road, and bridge facilities, temperature monitoring for farmland growth, power consumption, and apparatus vibration stress, using sensor nodes. It is.

  The sensor network system 100 includes a server 101, a gateway node 102 connected via a wired communication means 107, a router node 103 connected in a tree shape via the gateway node 102 and a wireless communication means 108, and wireless communication with the router node 103. And a sensor node 104 connected via the means 108. The router node 103 and the sensor node 104 are battery driven.

  The wired communication means 107 is, for example, a LAN (Local Area Network), and uses existing TCP / IP (Transmission Control Protocol / Internet Protocol) or UDP / IP (User Datagram Protocol / Internet Protocol) to communicate with each other. Communication channel. The wireless communication means 108 is a wireless communication path to which, for example, the IEEE 802.15.4 protocol or the ZigBee protocol is applied.

  The server 101 controls the gateway node 102, the router node 103, and the sensor node 104, and acquires observation data observed by the sensor node 104 via the router node 103 and the gateway node 102. The gateway node 102 is arranged at the boundary between the wired communication unit 107 and the wireless communication unit 108 and relays data between the server 101 and the router node 103.

  The router node 103 receives the observation data from the sensor node 104 directly or indirectly from the subordinate router node 103 and transmits it to the gateway node 102. Further, the router node 103 transmits the data from the gateway node 102 to the sensor node 104 or the subordinate router node 103. One or a plurality of router nodes 103 are arranged according to the distance between the gateway node 102 and the sensor node 104 arranged at the observation point. The sensor node 104 is arranged at an observation point, acquires observation data that changes with the passage of time, and transmits it to the router node 103.

<Communication Sequence Example 1 of Sensor Network System 100>
FIG. 2 is an explanatory diagram illustrating a communication sequence example 1 of the sensor network system 100 according to the first embodiment. In FIG. 2, the router node 103 and the sensor node 104 are assumed to be one in order to simplify the description. In FIG. 2, the vertical lines of the server 101, the gateway node 102, the router node 103, and the sensor node 104 are time axes. The arrows between the time axes indicate the data flow.

  Further, the rectangles on the time axis in the router node 103 and the sensor node 104 schematically indicate the time at which the router node 103 and the sensor node 104 are activated and the processing at the time. For example, a rectangular symbol “b” in the router node 103 indicates a command transmission process to the sensor node 104. A rectangular symbol “r” indicates command reception processing for receiving a communication message from the sensor node 104. When the command transmission process b and the command reception process r are completed, the router node 103 sleeps in order to reduce power consumption. For these processes, the interval from the start of the previous process (which may be based on the end) to the start of the next process is the reception interval of the router node 103.

  A rectangular symbol “i” in the sensor node 104 indicates a command reception process from the router node 103. A rectangular symbol “o” indicates an observation process by the sensor. A rectangular symbol “s” indicates a communication trial process for transmitting the observation data observed by the observation process to the router node 103. When these processes are completed, the sensor node 104 sleeps in order to reduce power consumption. The interval from the start of the command reception process i (which may be based on the end) to the start of the communication trial process s is the transmission interval of the sensor node 104. The interval from the start of the previous communication trial process s (which may be based on the end) to the next communication trial process s is also the transmission interval of the sensor node 104.

  As an initial process, the server 101 issues a setting command c201 for changing the reception interval of the router node 103 to Δ seconds. The gateway node 102 receives the setting command c201 from the server 101 and transfers it to the router node 103. The gateway node 102 may issue the setting command c201. The router node 103 receives the setting command c201, issues a setting command c202 for setting the transmission interval to Δ seconds to all the subordinate sensor nodes 104 managed by itself, and sets the reception interval of the router node 103 itself. Set to Δ seconds interval and start sleeping. The sensor node 104 receives the setting command c202, sets the transmission interval to Δ seconds, and starts sleeping. Thereby, the reception interval of the router node 103 and the transmission interval of the sensor node 104 are synchronized.

  The sensor node 104 performs an observation process o at a given observation interval, and acquires observation data. All of the observation data may be transmitted, and it may be determined whether or not it is a transmission target in the sensor node 104. In the case 205, the observation process o is performed three times at the time of executing the communication trial process s, and in the two observation processes o, the sensor node 104 accumulates the observation data as events in the transmission queue. To do.

  In the case 205, the sensor node 104 issues an event e203 in the communication trial process s because an event exists in the transmission queue. In addition, the sensor node 104 can store and transmit two observation data that are the event e203 in a single communication message.

  The router node 103 receives the event e203 and transmits the event e204 to the gateway node 102. Then, the gateway node 102 transmits the received event e204 to the server 101 through the wired communication unit 107.

  In the case 206, the observation process o is performed three times when the communication trial process s is executed, and no event is accumulated in the transmission queue in all the observation processes o. In the case 206, the sensor node 104 does not issue an event because there is no event in the transmission queue in the communication trial process s.

  On the other hand, the router node 103 starts from a sleep state and returns to the command reception process r when Δ seconds have elapsed from the previous command reception process r (case 205), but no event is transmitted from the sensor node 104 in the case 206. Therefore, the sleep state is again entered after a predetermined time has elapsed.

  The effects of the first embodiment shown in FIG. 2 are the following three points. First, since the sensor node 104 does not transmit every time at the observation timing but transmits only at the reception timing of the router node 103, it is not necessary to start the wireless communication device at the observation timing of the sensor node 104, and at the observation timing Since the communication time with the router node 103 can be reduced, the power consumption of the sensor node 104 can be reduced.

  Second, even at the transmission attempt timing of the sensor node 104, when there is no data to be transmitted in the sensor node 104, the activation time of the wireless communication device and the communication time with the router node 103 can be reduced. The amount can be reduced.

  Thirdly, in the router node 103, communication from the sensor node 104 is limited only to the reception timing of the router node 103. Therefore, the router can sleep at other times. Therefore, the power consumption of the router node 103 can be reduced.

  In general, the change in observation data observed by the sensor node 104 is often sufficiently gradual with respect to the observation interval, which is the interval between successive observation processes o. Therefore, when the sensor node 104 transmits the observation data change, it is not always necessary to transmit the observation data in all the observation processes o.

<Hardware configuration example>
Next, a hardware configuration example of the server 101, the gateway node 102, the router node 103, and the sensor node 104 will be described.

  FIG. 3 is a block diagram of a hardware configuration example of the sensor node 104 according to the first embodiment. The sensor node 104 includes a battery 301, an RTC (Real time Clock) 302 that is an integrated circuit having a function of keeping the current time, a sensor 303 having a function of observing a real world environment, a processor 306, The configuration includes a memory 307, a nonvolatile memory 308, and a wireless communication device 309. The sensor 303, the processor 306, the volatile memory 307, and the nonvolatile memory 308 constitute an arithmetic unit 304. The battery 301 has a function of supplying power to each of the RTC 302, the calculation unit 304, and the wireless communication device 309.

  FIG. 4 is a block diagram of a hardware configuration example of the router node 103 according to the first embodiment. The router node 103 includes a battery 401, an RTC 402, a processor 506, a volatile memory 407, a nonvolatile memory 408, and a wireless communication device 409. The processor 406, the volatile memory 407, and the nonvolatile memory 408 constitute an arithmetic unit 404. The battery 401 supplies power to each of the RTC 402 and the calculation unit 404.

  FIG. 5 is a block diagram of a hardware configuration example of the gateway node 102 according to the first embodiment. The gateway node 102 includes a processor 506, a volatile memory 507, a nonvolatile memory 508, a wireless communication device 509, and a wired communication device 510.

  FIG. 6 is a block diagram of a hardware configuration example of the server 101 according to the first embodiment. The server 101 includes an input / output interface 602 such as a keyboard, a mouse, and a display, a processor 606, a volatile memory 607, a non-volatile memory 608 such as a hard disk, a wired communication device 610, and a DB (which stores observation data). Database) 603.

<Functional configuration example>
Next, functional configuration examples of the server 101, the gateway node 102, the router node 103, and the sensor node 104 will be described.

  FIG. 7 is a block diagram of a functional configuration example of the sensor node 104 according to the first embodiment. The sensor node 104 includes a sleep management unit 701, a command processing unit 703, a command reception unit 706, a power supply unit 704, a state management unit 705, an observation unit 707, an event generation unit 708, and an event transmission unit 710. And a compression unit 711 and an event combination unit 712. The sensor node 104 manages a state 713, an observation interval 714, a transmission interval 715, a parameter 702 including a slot number, and a transmission queue 709 that accumulates events to be transmitted. The parameter 702 and the transmission queue 709 are realized by the nonvolatile memory 408, for example.

  The state 713 includes a transmission standby state and a transmission non-standby state. The observation interval 714 is a time interval of continuous observation processing o as described in FIG. As described in FIG. 2, the transmission interval 715 is a time interval from the start of the previous processes i and s (which may be based on the end) to the start of the next process s.

  The slot information 716 is information regarding the slot, and includes a slot number and a slot. The slot number is a number that uniquely identifies the slot. The slot is a predetermined reception time in the event reception process r executed by the router node 103. A slot number (hereinafter, a slot having a certain slot number is referred to as “slot #”) is assigned to each sensor node 104, and an event from the sensor node 104 to which the slot number is assigned is received in the corresponding slot #. The

  Specifically, the time at which the time interval obtained by adding the delay time due to the transmission interval 715 and slot # has elapsed from the command reception process i of the sensor node 104 is the first transmission timing, and the second and subsequent transmission timings Is the time obtained by adding the transmission interval 715 to the previous transmission timing.

  The delay time due to slot # is a delay time for the router node 103 to receive an event in a time division manner for each slot # so that a plurality of slots # do not overlap. For example, if n slots # are prepared and the time interval of each slot # is 10 seconds, the delay time by slot 1 is 0 seconds, slot 2 is 10 seconds, slot 3 is 20 seconds,. (N-1) × 10 seconds.

  The hibernation management unit 701 instructs the sensor node 104 to turn off power and the RTC 302 to turn on power according to the parameter 702. For example, with reference to the observation interval 714 and transmission interval 715 and the current time of the RTC 302, the sleep management unit 701 turns on the power supply unit 704 when the observation process o and the communication trial process s are started. Give instructions. When the end time of the command reception process i, the observation process o, and the communication trial process s is reached, the sensor node 104 is powered off.

  The state management unit 705 controls the power supply unit 704, the observation unit 707, the compression unit 711, the event generation unit 708, the event combination unit 712, the event transmission unit 710, the command reception unit 706, and the command processing unit 703.

  Specifically, for example, the state management unit 705 turns off or on the power of the sensor 303 or the wireless communication device 309 by the power supply unit 704 according to the state 713. When the state 713 transitions to the transmission standby state, the power supply unit 704 receives a power-on instruction from the sleep management unit 701 and powers on the wireless communication device 309. Then, when the state transits to the non-transmission state after communication, the power supply unit 704 receives the power cutoff instruction from the sleep management unit 701 and performs the power cutoff of the wireless communication device 309. When the state 713 is a transmission non-standby state, the power supply unit 704 receives a power-on instruction from the sleep management unit 701, turns on the sensor 303 at the observation timing, and shuts off the power from the sleep management unit 701. In response to the instruction, the power of the sensor 303 is shut off.

  In addition, the state management unit 705 acquires observation data from the sensor 303 by the observation unit 707 according to the observation interval 714, compresses the time series data of the observation data by the compression unit 711, and selects an event to be transmitted by the event generation unit 708. It is generated and stored in the transmission queue 709.

  Further, the state management unit 705 encapsulates a plurality of events accumulated in the transmission queue 709 into one event by the event combination unit 712, and wirelessly transmits the event by the event transmission unit 710 and the wireless communication device 309 according to the transmission interval 715. .

  Further, the state management unit 705 acquires commands received from the wireless communication device 309 and the command reception unit 706, performs processing by the command processing unit 703, and sets parameters 702.

  The sleep management unit 701, the command processing unit 703, the command reception unit 706, the power supply unit 704, the state management unit 705, the observation unit 707, the event generation unit 708, the event transmission unit 710, the compression unit 711, and the event combination unit 712 include: Specifically, for example, the function is realized by causing the processor 306 to execute the program stored in the nonvolatile memory 308 of FIG. 3 or by the wireless communication device 309.

  FIG. 8 is a block diagram of a functional configuration example of the router node 103 according to the first embodiment. The router node 103 includes a sleep management unit 801, a command processing unit 812, a command reception unit 811, a power supply unit 803, a state management unit 804, an event reception unit 805, an event transmission unit 807, and an event combination unit. 810, a command transmission unit 808, and a control unit 814.

  The router node 103 also manages a parameter 802 including a reception interval 815 and slot information 813, an event queue 806 that stores events received from the sensor node 104, and a command queue 809 that stores commands to be transmitted to the sensor node 104. To do. The parameter 802, the event queue 806, and the command queue 809 are realized by, for example, the nonvolatile memory 508.

  As described with reference to FIG. 2, the reception interval 815 is a time interval from the start of the previous processes b and r (which may be based on the end) to the start of the next process r. The slot information 813 includes a slot number, a slot, and the number of slots. The number of slots is the number of slots. As shown in FIG. 2, when the number of subordinate sensor nodes 104 is one, the number of slots is one. When the number of subordinate sensor nodes 104 is two or more, the number of sensor nodes 104 is as follows. Less than. That is, a plurality of sensor nodes 104 share the same slot #.

  When the number of slots is smaller than the number of sensor nodes 104, congestion may occur. In this case, retransmission may be performed at the next transmission timing. That is, the state management unit 804 performs transmission / reception control of the event reception unit 905 and the event transmission unit 907 in a time-sharing manner using slots. The number of slots may be a preset value or may be changed dynamically. An example of dynamically changing will be described later in a sixth embodiment.

  The hibernation management unit 801 issues a power-off instruction by the RTC 402 and power-off of the router node 103 according to the reception interval 815. For example, with reference to the reception interval 815 and the current time of the RTC 402, the sleep management unit 701 turns on the sensor node 104 when the command reception processing r starts. When the command transmission process b and the command reception process r are finished, the power of the router node 103 is shut off.

  The state management unit 804 controls the power supply unit 803, the event reception unit 805, the event combination unit 810, the event transmission unit 807, the command processing unit 812, and the command transmission unit 808.

  Specifically, for example, the state management unit 804 receives a power-on instruction from the sleep management unit 701 and powers on the wireless communication device 409 by the power supply unit 803. In response to the power-off instruction from the sleep management unit 701, the state management unit 804 uses the power supply unit 803 to turn off the wireless communication device 409.

  Further, according to the number of slots, the state management unit 804 receives events from the sensor node 104 by the event reception unit 805, accumulates them in the event queue 806, encapsulates a plurality of events by the event combination unit 810, and sends an event transmission unit In step S807, the data is wirelessly transmitted to the upper router node 103 or the gateway node 102.

  In addition, the state management unit 804 acquires commands received from the wireless communication device 409 and the command reception unit 811, performs processing by the command processing unit 812, sets parameters 802 such as a reception interval 815 and the number of slots, Further, the command transmission unit 808 transfers the command to the sensor node 104.

  The control unit 814 executes processing for dynamically changing the number of slots and the reception interval 815. Details of the control unit 814 will be described later in a sixth embodiment.

  The sleep management unit 801, command processing unit 812, command reception unit 811, power supply unit 803, state management unit 804, event reception unit 805, event transmission unit 807, event combination unit 810, command transmission unit 808, and control unit 814 Specifically, for example, the function is realized by causing the processor 406 to execute the program stored in the nonvolatile memory 408 of FIG. 4 or by the wireless communication device 409.

  FIG. 9 is a block diagram of a functional configuration example of the gateway node 102 according to the first embodiment. The gateway node 102 is almost in common with the functional blocks of the router node 103. The gateway node 102 is always activated, so that the RTC 402 and the sleep management unit 801 do not exist, the event transmission unit 807 to the server 101, and the command reception unit 811. Is different from the wired communication device 510 only.

  FIG. 10 is a block diagram of a functional configuration example of the server 101 according to the first embodiment. The server 101 includes an event reception unit 1002, a command transmission unit 1003, an alarm unit 1004, a search unit 1006, and a control unit 1010.

  The server 101 also includes observation data 1007, a DB 603 that stores configuration information 1009 that manages the tree structure of the router node 103 and the sensor node 104, and an interface 602 that performs input / output with the user terminal 1001.

  The event reception unit 1002 receives an event that has arrived from the wired communication device 610 from the sensor node 104 via the router node 103 and the gateway node 102. For example, as illustrated in FIG. 2, the event receiving unit 1002 receives an event e204. The event receiving unit 1002 stores observation data 1007 included in the received event in the DB 603.

  The command transmission unit 1003 transmits a command to the router node 103 and the sensor node 104 via the gateway node 102. For example, as illustrated in FIG. 2, the command transmission unit 1003 transmits a command c201.

  The alarm unit 1004 notifies the user terminal 1001 of an alarm. For example, when the observation data included in the event received by the event receiving unit 1002 is a value outside the allowable range, the alarm unit 1004 notifies the user terminal 1001 of an alarm.

  The search unit 1006 searches the DB 603 in response to the observation data search request from the user terminal 1001 and returns the search result to the user terminal 1001.

  The control unit 1010 issues a command to the sensor node 104 and the router node 103 and sets a reception interval of the router node 103 and a transmission interval of the sensor node 104. The issued command is transmitted by the command transmission unit 1003 as described above.

  Specifically, the event reception unit 1002, the command transmission unit 1003, the alarm unit 1004, the search unit 1006, and the control unit 1010, for example, cause the processor 606 to execute a program stored in the nonvolatile memory 608 of FIG. Or by the wired communication device 610.

<Example of Data Structure of Communication Message in Sensor Network System 100>
FIG. 11 is an explanatory diagram illustrating an example of a data structure of a communication message in the sensor network system 100. The communication message 1100 includes a header (Header) 1101 including various information such as a transmission destination node and a transmission source node, command, command response, message type information (Type) 1102 indicating the type of event, a continuation flag (Cont) 1103, and a payload. (Payload) 1104 and a footer 1105 including error correction information such as a checksum.

  The size of the communication message 1100 is, for example, 256 [Bytes], and the size of the payload 1104 is about half that of 100 [Bytes]. The node that has received the communication message 1100 for which the continuation flag 1103 is true enables the communication message 1100 whose payload 1104 size exceeds the above limit to be received by waiting for the subsequent communication message 1100 to connect. .

  The message type information 1102 includes three types: a command that requests some processing such as setting reference or setting change, a command response that is a response to the command, and an event that represents a change in observation data or state.

  When the message type information 1102 is a command, the structure of the payload 1104 is “Payload1”, CommandID indicating the type of command, SeqID that is the command issue number, ParamNum indicating the number of arguments, and zero or more argument Parameters. Is stored. In FIG. 11, a structure surrounded by angle brackets [] indicates that the structure is repeated zero or more times.

  When the message type information 1102 is a command response, the structure of the payload 1104 is “Payload2”, CommandID indicating the command type, SeqID that is the issue number of the command corresponding to the command response, ParamNum indicating the number of arguments, and 0 More than one argument Parameter is stored.

  The structure of the payload 1104 when the message type information 1102 is an event is one of Payload3 to Payload8. For example, when only a single sensor 303 is mounted on the sensor node 104, the structure of Payload3 is used, and the observation time TimeStamp and the observation value Value are stored as DataNum. Further, when the number of observation data is large, the structure of Payload4 is taken, the observation time TimeStamp and the observation value Value of the oldest observation data are stored, and the subsequent observation data is the observation time difference dT from the observation time TimeStamp and the observation The observation value difference dV from the value Value may be stored. Further, the Payload 5 structure may be used, and only the time difference dT and the observation value difference dV for the event sent last time may be sent.

  When the sensor node 104 is equipped with a plurality of sensors 303, the number of sensors 303 to be transmitted in the payload 1104 for Payload3, Payload4, and Payload5, SensorNum, and Payload6, Payload7, and Payload8 to which a SensorID for identifying the sensor 303 is assigned. The structure may be stored.

<Operation procedure of router node 103>
FIG. 12 is a flowchart illustrating an example of operation processing of the router node 103. The RTC 402 of the router node 103 detects the power-on timing (step S1201). When the power-on timing is detected, in response to a power-on instruction from the RTC 402, the sleep management unit 801 supplies power to the calculation unit 404 by the power supply unit 803 and activates the calculation unit 404 (step S1202). Next, the power supply unit 803 supplies power to the wireless communication device 409 and activates the wireless communication device 409 (step S1203). Thereafter, the router node 103 waits for reception of an event from the sensor node 104 (step S1204).

  The router node 103 determines whether or not an event has been received (step S1205). If the event has been received (step S1205: reception), the event including the observation data is stored in the event queue 806, and an ACK is returned to the sensor node 104 ( Step S1206), the process proceeds to Step S1207. On the other hand, if a timeout has occurred (step S1205: timeout), the process proceeds to step S1207.

  The router node 103 determines whether or not the event reception processing from steps S1204 to S1206 has been executed the number of times specified by the number of slots (step S1207). If it has not been executed up to the number of times designated by the number of slots (step S1207: No), the process returns to step S1204. On the other hand, after being executed for the number of times designated by the number of slots (step S1207: Yes), the router node 103 transmits a command to the sensor node 104 when there is a command for the sensor node 104 in the command queue 809 (step S1207). S1208). For example, the command is transmitted to the sensor node 104 within a predetermined time (for example, 20 milliseconds) from the reception of step S1205 in which the sensor node 104 is activated. An example of the command is a command for performing time synchronization.

  Next, the router node 103 performs operations such as event combination on the observation data stored in the event queue 806 (step S1209). Further, the router node 103 performs a decoding process when the observation data is encoded. The details of these calculations will be described later.

  Thereafter, the router node 103 determines whether there is an event to be transmitted to the gateway node 102 (or the upper router node 103) (step S1210). When there is an event to be transmitted (step S1210: T), the router node 103 transmits the event to the gateway node 102 (or the upper router node 103) (step S1211), and proceeds to step S1212.

  On the other hand, if there is no event to be transmitted (step S1210: F), the process proceeds to step S1212. Thereafter, the router node 103 stops supplying power to the calculation unit 404 and the wireless communication device 409 by the power supply unit 803, and enters a sleep state until the RTC 402 detects the power-on timing (step S1201).

<Operation processing procedure of sensor node 104>
FIG. 13 is a flowchart illustrating an example of operation processing of the sensor node 104. The RTC 302 of the sensor node 104 detects the power-on timing (step S1301). When the power-on timing is detected, in response to a power-on instruction from the RTC 302, the sleep management unit 701 supplies power to the calculation unit 304 by the power supply unit 704 and activates the calculation unit 304 (step S1302). Here, the power-on timing is, for example, either an observation timing when the observation interval 714 has elapsed or a transmission timing when the transmission interval 715 has elapsed.

  Next, the sensor node 104 makes a timer determination (step S1303). For example, when the state management unit 705 refers to the observation interval 714 of the parameter 702 and the observation timing comes (step S1303: observation), the process proceeds to step S1304. Steps S1304 to S1310 are processes corresponding to the observation process o shown in FIG. 2, for example. On the other hand, when the state management unit 705 refers to the transmission interval 715 of the parameter 702 and the transmission timing is reached (step S1303: communication), the process proceeds to step S1312.

  When the observation timing comes (step S1303: observation), the sensor node 104 supplies power to the sensor 303 and activates the sensor 303 (step S1304). As described above, since power is not supplied to the sensor 303 except for the observation timing, power consumption can be reduced. The sensor node 104 acquires observation data from the sensor 303 (step S1305). Thereafter, the sensor node 104 performs an operation on the acquired observation data (step S1306). For example, the sensor node 104 performs an operation for obtaining an average of observation data including past observation data stored in the nonvolatile memory 308.

  As a result of the calculation, the sensor node 104 determines whether the observation data is a transmission target (step S1307). For example, the sensor node 104 determines that the observation data is a transmission target when the observation data has an abnormal value or a singular value (step S1307: T), and stores the observation data in the transmission queue 709 (step S1308).

  In addition, when the lower limit value and the upper limit value of the normal range are given to the observation data, the sensor node 104 determines that an abnormality has occurred at the timing when the observation data falls below the lower limit value or exceeds the upper limit value, It is determined that it is a transmission target (step S1307: T). Then, the sensor node 104 stores the observation data in the transmission queue 709 (step S1308). Further, after the occurrence of an abnormality, the sensor node 104 determines that the abnormality has been canceled at a timing at which it again falls below the upper limit value or again exceeds the lower limit value, and determines that it is a transmission target (step S1307: T). Then, the sensor node 104 stores the observation data in the transmission queue 709 (step S1308).

  After step S1308, the sensor node 104 changes the state 713 to the transmission standby state (step S1309), and proceeds to step S1310. On the other hand, if it is determined that it is not a transmission target (step S1307: F), the process proceeds to step S1310. Thereafter, the sensor node 104 stops the power supply to the sensor 303 (step S1310), and stops the power supply to the calculation unit 304 (step S1311).

  In step S1303, when the transmission timing comes (step S1303: communication), the sensor node 104 executes a communication trial process (step S1312). The communication trial process (step S1312) is, for example, a process corresponding to the command reception process i and the communication trial process s shown in FIG. Details of the communication trial (step S1312) will be described later. Then, the sensor node 104 stops supplying power to the calculation unit 304 (step S1311). Thereafter, the sensor node 104 enters a sleep state until the RTC 302 detects the power-on timing (step S1301).

<State transition of sensor node 104>
FIG. 14 is a state transition diagram of the sensor node 104 related to the communication trial process (step S1312) illustrated in FIG. The communication trial process (step S1312) is executed when the transmission timing is reached in the transmission standby state 1400 (step S1303: transmission), and the state 713 transitions to the transmission non-standby state 1401. When the observation timing comes (step S1303: observation) and the observation data is to be transmitted (step S1307: T), the state 713 transitions from the transmission non-standby state 1401 to the transmission standby state 1400 (step S1309). .

<Communication trial process (step S1312)>
FIG. 15 is a flowchart illustrating an example of the communication trial process (step S1312) illustrated in FIG. First, the sensor node 104 refers to the state 713 in the parameter 702 (step S1501). When the state 713 is the transmission non-standby state 1401 (step S1501: non-standby), the sensor node 104 ends the communication trial process (step S1312).

  On the other hand, when the state 713 is the transmission standby state 1400 (step S1501: standby), the sensor node 104 supplies power to the wireless communication device 309 and activates the wireless communication device 309 (step S1502). Then, the sensor node 104 executes event transmission trial processing (step S1503). The event transmission trial process (step S1503) is a process of trying to transmit an event including observation data to the router node 103, and corresponds to, for example, the communication trial process s shown in FIG. Details of the event transmission trial process (step S1503) will be described with reference to FIG.

  Then, the sensor node 104 determines whether or not the wireless communication by the event transmission trial process (step S1503) is successful (step S1504). If unsuccessful (step S1504: F), the process proceeds to step S1506. On the other hand, in the case of success (step S1504: T), the sensor node 104 executes a command reception trial process (step S1505). The command reception trial process (step S1505) is a process of trying to receive a command from the router node 103, and corresponds to, for example, the command reception process i shown in FIG. Details of the command reception trial process (step S1505) will be described with reference to FIG.

  Thereafter, the sensor node 104 changes the state 713 to the transmission non-standby state 1401 (step S1506), and stops the power supply of the wireless communication device 310 (step S1507). As a result, the sensor node 104 ends the communication trial process (step S1312).

<Event transmission trial process (step S1503)>
FIG. 16 is a flowchart showing an example of the event transmission trial process (step S1503) shown in FIG. The sensor node 104 encapsulates a plurality of events accumulated in the transmission queue 709 by the event combining unit 712, and creates the payload 1104 of the communication message 1100 as shown in FIG. 11 (step S1601). The creation result has, for example, the structure of Payload 3, Payload 4, or Payload 5 in FIG. Furthermore, it is possible to compress the structure of the payload 1104 by performing Golomb coding on part or all of the structure of the payload 1104 in FIG.

  In Golomb coding, numerical value 0 is 1 [bit], 1-2 is 3 [bit], 3-6 is 5 [bit], 7-14 is 7 [bit], 15-30 is 9 [bit], 31 ˜62 are encoded into a value of 11 [bits]. Therefore, when the observation time difference dT and the observation value difference dV of Payload4, Payload5, Payload7, and Payload8 are sufficiently small, efficient compression of the payload 1104 can be realized, and thus many observations are made in one communication message 1100. Since data can be stored, the number of communication messages 1100 can be reduced.

  Next, the sensor node 104 generates a communication message 1100 including the payload 1104, and wirelessly transmits an event to the router node 103 (step S1602). The event transmitted by event transmission (step S1602) is received in the reception standby (step S1204) of the router node 103 shown in FIG. Here, when the number of slots of the router node 103 is 1, the sensor node 104 may transmit as it is at the transmission trial timing. However, when the number of slots is larger than 1, the sensor node 104 uses the slot number to correspond. A slot is selected and transmitted at the timing of the selected slot.

  As a slot selection method, for example, the slot number of the router node 103 may be used, and the slot number may be selected at random. The router node 103 may designate a slot number for the sensor node 104 in advance. For example, the router node 103 designates the slot of the sensor node 104 by assigning a slot number to the sensor node 104 connected to the router node 103 and designating a remainder obtained by dividing the slot number by the number of slots. Good. In addition, sensor nodes 104 located spatially nearby tend to detect and transmit environmental changes at the same timing. For this reason, different slot numbers may be assigned to the sensor nodes 104 located spatially in the vicinity.

  Thereafter, the sensor node 104 waits for an ACK response from the router node 103 (step S1603). When the ACK response is returned (step S1604: T), the transmission queue 709 is updated by removing the event for which transmission has been completed from the transmission queue 709 (step S1604), and the sensor node 104 performs event transmission trial processing (step S1604). S1503) is terminated. Even when the ACK response is not returned (step S1604: F), the sensor node 104 ends the event transmission trial process (step S1503).

<Command reception trial process (step S1505)>
FIG. 17 is a flowchart showing an example of the command reception trial process (step S1505) shown in FIG. The sensor node 104 waits for command reception from the router node 103 (step S1701). Next, the sensor node 104 uses the command processing unit 703 to process the received command (step S1702). For example, when the received command is a time adjustment command, the command processing unit 703 corrects the current time of the RTC 302. When the received command is a setting change command, the command processing unit 703 sets parameters 702 such as an observation interval 714 and a transmission interval 715.

  Thereafter, the sensor node 104 transmits the command processing result to the router node 103 (step S1703). Then, the sensor node 104 waits for ACK reception for the transmitted command processing result (step S1704). If ACK reception is not obtained for the specified time (step S1704: F), the sensor node 104 ends the command reception trial process (step S1505).

  On the other hand, when ACK is received (step S1704: T), the process proceeds to step S1705. The sensor node 104 determines whether or not there is an untransmitted command in the command queue 809 of the router node 103 (step S1705). Here, as to whether or not there is an unsent command in the command queue 809 of the router node 103, the router node 103 writes it in the ACK that arrives from the router node 103 in step 1704, and the sensor node 104 writes the written content. This can be realized by referring to. If there is an unsent command (step S1705: T), the process returns to step S1701. If there is no unsent command (step S1705: F), the sensor node 104 ends the command reception trial process (step S1505).

<Communication Sequence Example 2 of Sensor Network System 100>
FIG. 18 is an explanatory diagram illustrating a communication sequence example 2 of the sensor network system 100 according to the first embodiment. In FIG. 18, it is assumed that there are a plurality (for example, two) of sensor nodes 104 (SN # 1, SN # 2) under one router node 103. The symbols used in FIG. 18 are the same as those used in FIG.

  As an initial process, the server 101 issues a setting command c1801 for changing the reception interval 815 of the router node 103 to Δ seconds.

  The gateway node 102 receives the setting command c1801 from the server 101 and transfers it to the router node 103.

  The router node 103 receives the setting command c1801 and issues a setting command c1802 for setting the transmission interval 715 to Δ seconds to all the sensor nodes 104 (SN # 1, SN # 2) managed by itself. The reception interval 815 of the node 103 itself is set to an interval of Δ seconds, and sleep is started.

  Each of the plurality of sensor nodes 104 receives the setting command c1802, sets the transmission interval 715 to Δ seconds, and starts sleeping. The sensor node 104 performs the observation process o shown in steps S1304 to S1310 at a predetermined observation interval 714 according to the flowchart of FIG. 13, and determines whether the observation data obtained in the observation process o is a transmission target in step S1307. To do.

  In the case of Case 1811, since the event accumulated in the transmission queue 709 does not exist at the time of executing the communication trial process (step S1312) of the sensor node 104 of SN # 1, SN # 1 does not transmit. On the other hand, since there is an event accumulated in the transmission queue 709 at the time of executing the communication trial process (step S1312) of the sensor node 104 of SN # 2, SN # 2 performs transmission.

  Similarly, in the case of Case 1812, since there is an event accumulated in the transmission queue 709 when the communication trial process (step S1312) of the sensor node 104 of SN # 1 is executed, SN # 1 performs transmission. Since there is no event accumulated in the transmission queue 709 at the time of executing the communication trial process (step S1312) of the sensor node 104 of SN # 2, SN # 2 does not transmit. The router node 103 receives the event in step S1205 in FIG. 12, and transmits an event e1804 to the gateway node 102 in accordance with a transmission determination process (step S1210).

  In the case of Case 1813, since events accumulated in the transmission queues 709 of both SN # 1 and SN # 2 exist, SN # 1 and SN # 2 transmit to the router node 103 at the same time, resulting in congestion. Occur. As a result, the router node 103 receives an event of either SN # 1 or SN # 2 (SN # 1 in this example), returns an ACK to the sensor node 104 that has been successfully received, and then determines transmission. Event e1804 is transmitted to gateway node 102 in accordance with the processing (step S1210).

  When the router node 103 fails to receive any event of SN # 1 and SN # 2, ACK return and event transmission to the gateway node 102 are not performed. Case 1813 shows an example in which event reception from SN # 2 has failed.

  An example of Case 1814 shows a retransmission process of the sensor node 104 that failed to transmit an event due to congestion. Since the sensor node 104 of SN # 2 that does not receive ACK in Case 1813 does not execute Step S1604 by the ACK reception determination process (Step S1603) in FIG. 16, the event is not deleted from the transmission queue 709. Regardless of communication success or failure, the state 713 transits to the transmission non-standby state 1401 by step S1506 in FIG.

  The state 713 transits to the transmission standby state 1400 only when it is determined as a transmission target in the transmission target determination process (step S1307) in FIG. 13 at the next observation timing of SN # 2 (step S1307: T). (Step S1309), the event is transmitted at the reception timing of the next router node 103. The communication message 1100 transmitted here has an event encapsulation process (step S1601) in FIG. 16 in which the event that has been congested and failed to transmit and the newly observed event have a structure of any one of Payload 3 to Payload 8 in FIG. One message.

  The effects when there are a plurality of sensor nodes 104 are the following three points. First, the router node 103 prepares only a predetermined number of slots regardless of the number of sensor nodes 104 connected to the router node 103. For example, when the number of slots is one, reception standby time from a plurality of sensor nodes 104 is prepared only once. Thereby, the power consumption of the router node 103 does not increase in proportion to the number of sensor nodes 104 to be connected.

  Secondly, the observation data that failed to be transmitted due to congestion is routed to the next reception timing when the next observation data is generated. Therefore, for the router node 103, transmission from the sensor node 104 is limited only to the reception timing of the router node 103, and can sleep at other times, thereby reducing the power consumption of the router node 103. be able to.

  Third, the observation data that has failed to be transmitted due to congestion is transmitted together with the next observation data in the structure of Payload 3 to Payload 8 in FIG. Therefore, it is possible to suppress a situation in which the number of transmissions increases due to congestion and further congestion is caused.

  On the other hand, as a side effect of this method, the time at which the congested observation data is retransmitted is delayed to the transmission timing of the next observation data, so that the data arrival time is delayed. However, when the transmission interval of the observation data from the sensor node group is sufficiently small with respect to the reception interval of the router node 103, the probability of occurrence of this side effect is sufficiently small, and there is no practical problem.

(Example 2)
A sensor network system according to a second embodiment will be described. The second embodiment is an example in which linear approximate compression, which is an algorithm for irreversibly compressing time series data of observation data, is applied to the event generation unit 708 and the compression unit 711 of the sensor node 104 in the first embodiment. Since the number of events to be transmitted can be reduced by linear approximation compression, the power consumption required for communication of the sensor node 104 can be reduced in proportion to the compression rate of linear approximation compression. In addition, since the number of events to be transmitted is reduced, the probability of occurrence of congestion with other sensor nodes 104 can be reduced. In the second embodiment, only the difference from the first embodiment will be described, and the rest is the same as the first embodiment, and the description thereof will be omitted.

  FIG. 19 is a conceptual diagram of linear approximate compression. (A) shows time-series data 1901 of observation data measured at fixed observation intervals, and (B) shows time-series data 1902 of observation data subjected to linear approximation compression. The linear approximate compression is a time series data having a structure in which the observation data 1903 and 1904 that are not thinned out are connected by thinning the observation data from the time series data 1901 so that each observation data is within a given allowable miscalculation range. 1901 is approximated by time series data 1902. The observation data marked with a circle in the time series data 1902 are control points that were not thinned out by linear approximation compression.

FIG. 20 is a conceptual diagram for performing linear approximation compression sequentially. In FIG. 20, the horizontal direction is time, and the vertical direction is an observed value (similar to FIG. 19). Linear approximate compression, which is one implementation example of the compression unit 711, manages past observation points S and C having time and observation values as internal information. When the observation point A newly generated by the observation process o is input, the compression unit 711 determines whether the observation point C can be approximated by a straight line SA connecting the observation points S and A. The error between the straight line SC and the straight line SA at the observation point C is expressed by the following equation (1). However, V _S , V _C and V _A are observation values at observation points S, C and A, and T _S , T _C and T _A are observation times at observation points S, C and A. Here, when the error of the expression (1) is less than a given allowable error which is a threshold value, the compression unit 711 deletes the observation point C.

Error = (V _A −V _S ) × (T _C −T _S ) / (T _A −T _S ) − (V _C −V _S ) (1)

  FIG. 21 is a flowchart illustrating an example of linear approximate compression processing by the compression unit 711 of the sensor node 104. First, the compression unit 711 determines the number of times of the observation process o (step S2101). In the case of the first observation process o (step S2101: first time), the compression unit 711 substitutes the observation time and the observation value in the observation process o into the observation point S (step S2102). Then, the compression unit 711 stores the observation point S in the transmission queue 709 and ends the process.

  In the case of the second observation process o (step S2101: second time), the compression unit 711 substitutes the observation time and the observation value in the observation process o into the observation point C (step S2104), and enters the transmission queue 709. The process ends without storing.

  In the case of the third or subsequent observation process o (step S2101: after the third time), the compression unit 711 substitutes the observation time and the observed value in the observation process o into the observation point A (step S2105). Then, the compression unit 711 calculates the error of the observation value at the observation point C according to the above (1) (step S2106), and determines whether or not the error is greater than a given allowable error (step S2107). .

  If the error is less than the given allowable error (step S2107: F), the process ends. Since the observation point C is not stored in the transmission queue 709, the observation time and the observation value assigned to the observation point C are deleted and are not transmitted to the router node 103. On the other hand, when the error is equal to or larger than the given allowable error (step S2107: Yes), the compression unit 711 stores the observation point C in the transmission queue 709 (step S2108). That is, the observation time and the observation value assigned to the observation point C are held. Then, the compression unit 711 assigns the observation time and observation value assigned to the observation point C to the observation point S, substitutes the observation time and observation value assigned to the observation point A to the observation point C, and In preparation for the observation process o, the process ends.

  The effects of Example 2 are the following two points. First, the sensor node 104 performs observation at each time of the time-series data 1901 shown in FIG. 19, but the data to be transmitted is only the control points (◯ marks) constituting the time-series data 1902. Therefore, the power consumption required for the communication of the sensor node 104 can be reduced in proportion to the compression rate of the linear approximate compression.

For example, when the observation data can be compressed to 5%, the average number of events accumulated in the transmission queue is 100 for 100 observation processes o. When the observation interval is 1 minute and the transmission interval is 10 minutes, the probability of transmission in the communication trial process s of the sensor node 104 is 1− (0.95) ¹⁰ = 0.40, which is about 40%. Become. Therefore, the ratio of performing communication with respect to the observation interval is 1/10 × 40% = 4%. Therefore, compared with the method of transmitting each observation, this method can reduce the power consumption related to the communication of the sensor node 104 to 4%. Similarly, when the transmission interval is 20 minutes, the ratio of communication with respect to the observation interval is 1/20 × (1− (0.95) ²⁰ ) = 3.2%.

  Secondly, the probability of occurrence of congestion shown in Case 1813 in FIG. 18 is equal to the probability of simultaneous occurrence of control points at a certain interval in the plurality of sensor nodes 104. Therefore, if the observation data is sufficiently gentle with respect to the transmission interval 715 of the sensor node 104 and the shape of the time series data of the plurality of sensor nodes 104 is different, the probability of occurrence of congestion can be reduced.

  On the other hand, as a feature of linear approximation compression, when the observation data takes a constant value within a given allowable error range, that is, when the observation data keeps a constant value or keeps a constant slope, in FIG. Does not send observation data. Therefore, the observation data stored in the server 101 is not transmitted because the observation data of the sensor node keeps a constant value within the allowable error range, or the observation data is not transmitted due to a failure of the sensor node 104 or a communication failure. I cannot tell if it has not arrived.

  In order to avoid this problem, in the second embodiment, step S2107 may be changed to the following step S2107-2.

[Step S2107-2] Even if the error is less than a given allowable error, if the difference between the observation time at observation point A and the observation time at observation point C is equal to or greater than the threshold time interval, the process proceeds to step S2108.

  By step S2107-2, it is ensured that communication comes from the sensor node 104 at regular intervals, so that it is possible to distinguish a failure or communication failure of the sensor node 104. For example, when the observation interval is a one minute cycle, consider setting the threshold time interval as a one hour cycle. Assuming that the probability that observation data is not generated for one hour by linear approximation compression is 5%, the number of transmission data increases by 5% in step S2107-2, but a failure or communication failure of the sensor node 104 has a delay of at least one hour. It can be detected.

  Further, as a feature of linear approximation compression, time series data after the control point cannot be estimated at the timing when the observation data as the control point is sent. That is, in FIG. 19, the slope of the straight line connecting the observation data 1903 and the observation data 1904 can be obtained only when the control point 1904 arrives at the server 101. In order to obtain the slope of the straight line on the server 101 side before the time when the control point 1904 arrives, the threshold time interval in step S2107-2 may be set to a shorter time. For example, when the observation interval is a 1-minute cycle, the threshold time interval is set to a 5-minute cycle. By making the threshold time interval shorter, the number of transmission data almost doubles. However, since the slope of the time series after the control point is obtained, it is possible to estimate the transition of the time series data after that control point. it can.

  A method for transmitting multivariate observation data in the sensor node 104 will be described. There are cases where a plurality of sensors 303 are connected to the sensor node 104. In other cases, RSSI (Received Signal Strength Indication) indicating the remaining voltage of the sensor node 104 and the communication quality between the sensor node 104 and the router node 103 may be transmitted as supplementary information for operation monitoring. Exists. The amount of data can be reduced by separately performing linear approximation compression on each of the plurality of time series data.

  In particular, since the remaining voltage takes a substantially constant value until immediately before the battery capacity is exhausted, the compression effect is high. On the other hand, since the control points are generated at different timings by linearly approximating a plurality of time series data, the number of transmissions increases. In order to prevent this, in step S1308 in FIG. 13, the control points are generated with specific single time-series data instead of being stored in the transmission queue 709 at the timing when the control points are generated with a plurality of time-series data. At this time, it is preferable to store the time series data of the other observation data in the transmission queue 709 in the form of sharing them together. The format for storing a plurality of types of observation data in the payload 1104 is Payload 6, Payload 7, and Payload 8 shown in FIG.

(Example 3)
Example 3 will be described. The third embodiment is an example of reducing the delay of the data arrival time in the first and second embodiments. Specifically, in the third embodiment, even when an event cannot be transmitted due to the occurrence of congestion with another sensor node 104, the sensor node 104 is not updated at the observation timing after the congestion occurrence time. Even when an event does not occur, the event is retransmitted after a certain time has elapsed. That is, retransmission when communication fails is determined randomly from the next transmission timing. Thereby, it is possible to suppress the congestion again. In the third embodiment, only the differences from the first and second embodiments will be described, and the other portions are the same as those in the first embodiment, and thus the description thereof is omitted. In the third embodiment, the state transition of the sensor node 104 is different from the state transition (FIG. 14) shown in the first and second embodiments in the communication trial process (step S1303).

  FIG. 22 is a state transition diagram of the sensor node 104 regarding communication trial processing according to the third embodiment. The sensor node 104 takes one of the three states of the transmission standby state 2202, the transmission non-standby state 2203, and the delay standby state 2201 as the state 713. The delay standby state 2201 is a state in which transmission of an event can be made to wait after the next time due to transmission failure. When the sensor node 104 is in the transmission standby state 2202, when the transmission timing comes in step S1303, the sensor node 104 performs a communication trial process (step S2204) instead of the communication trial process (step S1303) shown in FIG. Do. Details of the communication trial process (step S2204) will be described later.

  Further, in the transmission non-standby state 2203 or the delay standby state 2201, the sensor node 104 does not perform the communication trial process (step S2204) even when the transmission timing comes in step S1303.

  As a result of the communication trial process (step S2204), the state 713 transitions to the transmission non-standby state 2203 when transmission is successful, and transitions to the delay standby state 2201 when transmission fails. In the delay standby state 2201, the state 713 transitions to the transmission standby state 2202 at a delay timing described later. Further, as described in the transmission queue addition (step S1308) of FIG. 13, when it is determined that the observation data is a transmission target, the state 713 transitions to the transmission standby state 2202 (step S1309).

  FIG. 23 is a flowchart of the communication trial process (step S2204) according to the third embodiment. The communication trial process (step S2204) is a process that replaces the communication trial process (step S1303) shown in FIG. First, when the state 713 is the transmission non-standby state 2203 (step S2301: non-standby), the communication trial process (step S2204) is terminated. When the state 713 is the transmission standby state 2202 (step S2301: standby), the process proceeds to step S2302, and when the state 713 is the delay standby state 2201 (step S2301: delay standby), the process proceeds to step S2310.

  When the state 713 is the transmission standby state 2202 (step S2301: standby), the sensor node 104 supplies power to the wireless communication device 309 by the power supply unit 704 and activates the wireless communication device 309 (step S2302).

  Next, the sensor node 104 executes the event transmission trial process shown in FIG. 16 (step S2303). If the wireless communication is successful (step S2304: T) by the event transmission trial process (step S2303), the process proceeds to step S2305. If the wireless communication fails (step S2304: F), the process proceeds to step S2308.

  The sensor node 104 calculates the delay standby time (step S2308). The delay waiting time is generated by a random number with a given period as a threshold value at the next and subsequent transmission timings. Thereafter, the sensor node 104 changes the state 713 to the delay standby state 2201 (step S2309), and stops the power supply of the wireless communication device 310 (step S2307). Thereby, the sensor node 104 ends the communication trial process (step S2204).

  If wireless communication is successful (step S2304: T), the sensor node 104 changes the state 713 of the sensor node 104 to a transmission non-standby state (step S2305), and executes the command reception trial process shown in FIG. (Step S2306), the power supply of the wireless communication device 310 is stopped (Step S2307). Thereby, the sensor node 104 ends the communication trial process (step S2204).

  In step S2301, if the state 713 is the delay standby state 2201 (step S2301: delay standby), the sensor node 104 compares the current time with the delay standby time calculated in step S2308 (step S2310), If the time does not exceed the delay waiting time (step S2310: F), the communication trial process (step S2204) is terminated. On the other hand, when the current time becomes the delay standby time (step S2310: T), the sensor node 104 changes the state 713 of the sensor node 104 to the transmission standby state 2202 (step S2311), and a communication trial process (step S2204). Exit.

  FIG. 24 is an explanatory diagram illustrating a communication sequence example of the sensor network system 100 according to the third embodiment. In the case of Case 2400 in FIG. 24, since events accumulated in both the transmission queues 709 of SN # 1 and SN # 2 exist as in Case 1813 of FIG. 18, SN # 1 and SN # 2 are simultaneously connected to router nodes. As a result, congestion occurs. As a result, the router node 103 receives an event (SN # 1 in this example) from either SN # 1 or SN # 2.

  The router node 103 returns an ACK to the sensor node 104 (SN # 1 in this example) that has been successfully received, and then sends an event e104 to the gateway node 102 in accordance with the transmission determination process (step S1210) in FIG. Send. If the router node 103 fails to receive any event of SN # 1 and SN # 2, ACK return and event transmission to the gateway node 102 are not performed.

  An example of Case 2407 indicates a retransmission process of a sensor node that failed to transmit an event due to congestion. Since the sensor node 104 of SN # 2 that does not receive ACK in Case 2400 does not execute step S1604 by the ACK reception determination process (step S1603) illustrated in FIG. 16, the event is not deleted from the transmission queue 709.

  Since the communication has failed, as shown in FIG. 23, the state 713 transitions to the delay standby state 2201 (step S2309). SN # 2 transitions the state 713 to the transmission standby state at the next transmission timing and the next time in the time confirmation process (step S2310) shown in FIG. 23 with the current time exceeding the delay standby time. The event is transmitted at the transmission timing.

  SN # 2 is also determined when the transmission target is determined in the transmission target determination process (step S1307) shown in FIG. 13 at the next and subsequent observation timings even when the delay waiting time has not arrived (step S1307). : T), the state 713 transits to the transmission standby state 1400, and the event is transmitted at the next transmission timing.

  In addition, an example of the delay standby time (step S2308) calculated by the sensor node 104 will be described with reference to FIG. For example, it is assumed that the transmission timing for three times is included within a given threshold value of the delay waiting time. When congestion occurs in Case 2400, the sensor node 104 transmits at any timing among the transmission timings for three times after the next time. In this example, as shown in Case 2407, the sensor node 104 of SN # 2 calculates the second transmission timing as the delay waiting time, and transmits the event e2405 to the router node 103.

  The effect of Example 3 is as follows. As shown in FIG. 14, in the first embodiment, at the observation timing after the time when congestion occurs, the event is retransmitted for the first time after the time when the event occurs. On the other hand, in the third embodiment, even when an event does not occur at the observation timing after the time when congestion occurs, the event is retransmitted after a certain time has elapsed. Further, by setting the retransmission timing after a random time, it is possible to suppress congestion again between the congested sensor nodes 104.

Example 4
Example 4 will be described. The fourth embodiment is an example in which the maximum delay time of the data arrival time in the first embodiment is guaranteed. Specifically, in the fourth embodiment, the sensor node 104 includes, in the parameter 702, a second transmission interval having a time interval longer than the transmission interval 715 in addition to the transmission interval 715. Similarly, the router node 103 includes a second reception interval in addition to the reception interval 815 in the parameter 802. The second transmission interval and the second reception interval are the same time length. The second reception interval is set by the router node 103 receiving from the server 101 via the gateway node 102 in the same communication sequence as the reception interval 815. Similarly, the second transmission interval is set by receiving a command from the sensor node 104 in the same communication sequence as the transmission interval 715.

  The router node 103 prepares a slot for receiving events from all the subordinate sensor nodes 104 at the second reception interval. As a result, even when congestion occurs between the sensor nodes 104 at the transmission timing according to the transmission interval 715, the event is transmitted from each sensor node 104 at the transmission timing according to the second transmission interval (hereinafter referred to as the second transmission timing). Even in this case, the router node 103 can receive each event without causing congestion, and the maximum delay time of data arrival from the sensor node 104 is guaranteed.

  Note that the time at which the sensor node 104 receives an event to the router node 103 at the second transmission timing is referred to as a second transmission time. That is, the first transmission time of the sensor node 104 or a time obtained by adding the second transmission interval from the previous second transmission time becomes the second transmission time. Similarly, the time at which the router node 103 receives an event from each sensor node 104 at the second transmission timing is referred to as a second reception time. The first activation of the router node 103 or the time obtained by adding the second reception interval from the previous second reception time becomes the second reception time.

  In addition, in the fourth embodiment, only the difference from the first and second embodiments will be described, and the rest is the same as the first and second embodiments, and the description thereof will be omitted. In the fourth embodiment, the state transition of the sensor node 104 is different from the state transition (FIG. 14) shown in the first and second embodiments and the communication trial process (step S1303).

  FIG. 25 is a state transition diagram of the sensor node 104 regarding communication trial processing according to the fourth embodiment. The sensor node 104 takes either the transmission standby state 2501 or the transmission non-standby state 2502 as the state 713. When the sensor node 104 is in the transmission standby state 2501, when the communication timing comes in step S1303, the sensor node 104 performs a communication trial process (step S2503) instead of the communication trial process (steps S1303 and 2204). Details of the communication trial process (step S2503) will be described later.

  In the non-transmission state 2502, when the communication timing comes in step S1303, the sensor node 104 determines the second communication timing and performs the second communication trial process (step S2504). As a result of the communication trial process (step S2503), the state 713 transitions to a transmission non-standby state (step S2504). Further, as described in step S1308, when it is determined that the observation data is a transmission target (step S1308: T), the state 713 transitions to the transmission standby state 2501 (step S1309).

  FIG. 26 is a flowchart illustrating an example of a communication trial process according to the fourth embodiment. First, the sensor node 104 determines which state is the current state 713 (step S2601). When the state 713 is the transmission non-standby state 2502 (step S2601: non-standby), the process proceeds to the second communication trial process (step S2608). On the other hand, when the state 713 is the transmission standby state 2501 (step S2601: standby), the process proceeds to a communication trial process (step S2503).

  In the communication trial process (step S2503), the sensor node 104 first supplies power to the wireless communication device 309 by the power supply unit 704 and activates the wireless communication device 309 (step S2602). Next, the sensor node 104 executes the event transmission trial process shown in FIG. 16 (step S2603). In the event transmission trial process (step S2603), when the wireless communication is successful (step S2604: T), the process proceeds to the command reception trial process (step S2605) shown in FIG. (Step S2604: F), the process proceeds to step S2606.

  After executing the command reception trial process (step S2605) or when the wireless communication fails (step S2604: F), the sensor node 104 changes the state 713 to the transmission non-standby state 2502 (step S2606) and supplies power. The power supply to the wireless communication device 310 by the unit 704 is stopped (step S2607), and the communication trial process (step S2503) is ended.

  On the other hand, in step S2601, if the state 713 is the transmission non-standby state 2502 (step S2601: non-standby), the second communication trial process (step S2504) is executed. Specifically, for example, the sensor node 104 compares the current time with the second transmission time (step S2608), and if the current time does not exceed the second transmission time (step S2608: F), the second The communication trial process (step S2504) ends.

  On the other hand, when the current time is the second transmission time (step S2608: T), the sensor node 104 first supplies power to the wireless communication device 309 by the power supply unit 704 and starts the wireless communication device 309. (Step S2609). Then, the sensor node 104 executes a second event communication trial process (step S2504). Similar to the event transmission trial process (step S2603), the second event communication trial process (step S2504) is the event transmission trial process shown in FIG. After the second event communication trial process (step S2504), the process proceeds to step S2604. The processing after step S2604 is the same as the communication trial processing (step S2503).

  FIG. 27 is an explanatory diagram illustrating a communication sequence example of the sensor network system 100 according to the fourth embodiment. As an initial process, the server 101 changes the reception interval 815 of the router node 103 to Δ seconds, changes the reception interval 815 of the router node 103 to Δ seconds, and sets the second reception interval of the router node 103 to Δ2 A setting command c2701 to be changed to is issued. The gateway node 102 receives the setting command c 2701 from the server 101 and transfers it to the router node 103.

  The router node 103 receives the setting command c2701, and changes the transmission interval 715 to Δ seconds and changes the second transmission interval to Δ2 seconds for all sensor nodes 104 managed by itself. Issued, sets the reception interval 815 of the router node 103 itself to Δ seconds, sets the second reception interval to Δ2 seconds, and starts sleeping. Each of the plurality of sensor nodes 104 receives the setting command c 2702, sets the transmission interval 715 to Δ seconds, sets the second transmission interval to Δ 2 seconds, and starts sleeping.

  Case 2703 indicates the operation of the reception timing at the reception interval 815 (Δ seconds) of the router node 103. Like Case 1813 in FIG. 18, congestion may occur depending on the transmission timing of the sensor node 104.

  Case 2706 shows the operation of the reception timing in the second reception interval (Δ2 seconds) of the router node 103. In the second reception interval, the router node 103 executes the flow shown in FIG. 12 with the number of slots as the number of sensor nodes 104 connected to the router node 103. In the event transmission trial process (step S2603) of FIG. 26, the sensor node 104 waits for a predetermined interval TW seconds, and then performs transmission at the time of the slot allocated to itself.

  In the event transmission trial process (step S2603), since the slot is opened for all the sensor nodes 104 to which the router node 103 is connected, communication in the event transmission trial process (step S2603) is successful except for a communication failure. As a means for the sensor node 104 to acquire the predetermined interval TW, for example, when the sensor node 104 issues an initial connection request command to the router node 103, the serial number of the sensor node 104 registered in the router node 103 by the router node 103 The predetermined interval TW is calculated by multiplying and the slot interval, and this is returned to the sensor node 104 by command response communication. As a result, even if the sensor node 104 has a common slot at the reception interval 815 (Δ second), it becomes an independent slot for each sensor node 104 at the second reception interval (Δ 2 seconds), thereby preventing the occurrence of congestion. be able to.

  As an effect of the fourth embodiment, since the router node 103 prepares a slot for receiving an event for each subordinate sensor node 104 independently in the second reception interval, communication with all of the subordinate sensor nodes 104 is possible. success. Since the event is transmitted at this transmission timing, the maximum delay time for data arrival from the sensor node 104 is guaranteed.

  On the other hand, as a side effect of the fourth embodiment, power supply and activation are performed at the second reception interval, so that the power consumption of the router node 103 increases. However, this side effect is in an allowable range by adjusting the transmission interval 715 (Δ seconds) and the second transmission interval (Δ2 seconds). For example, if the transmission interval 715 is Δ = T1 seconds, the second transmission interval is Δ2 = T2 seconds, and the number of sensor nodes 104 connected to the router node 103 is N, the reception waiting time of the router node 103 is 1 It is proportional to / T1 + N / T2. For example, if T1 = 1 minute, T2 = 1 hour, and N is ten, the reception standby time of the router node 103 is 1/1 + 10/60, and the power consumption of the router node 103 is 1.17 times that of the first embodiment. 1 hour delay guarantee can be realized at the power consumption cost.

(Example 5)
Next, Example 5 will be described. The fifth embodiment is a processing example of the event combining unit 810 of the router node 103 when the router node 103 has a multi-stage configuration in the first to fourth embodiments. As shown in FIG. 1, the sensor network system 100 forms a tree-structured network in which a plurality of router nodes 103 are connected in series and in parallel. The sensor network system 100 includes, for example, a configuration in which a plurality of router nodes 103 are connected in series in a long section such as a track or a road, and a plurality of sensor nodes 104 are connected to each router node 103, or a vast area such as a farm field. A plurality of router nodes 103 may be connected in series and in parallel, and a plurality of sensor nodes 104 may be connected to each router node 103.

  In the fifth embodiment, only the differences from the first to fourth embodiments will be described, and the other portions are the same as those of the first to fourth embodiments, and the description thereof will be omitted.

  FIG. 28 is an explanatory diagram illustrating a configuration example of the sensor network system 100 having a plurality of stages. In the example of FIG. 28, RN # 1 that is the router node 103 is connected to the gateway node 102, RN # 2 and RN # 3 that are the plurality of router nodes 103 are connected to RN # 1, and the sensor node is connected to RN # 2. SN # 1, which is 104, is connected. Also, the reception interval 815 of RN # 1 to RN # 3 is the same, and the number of slots of RN # 2 is K1, and the number of slots of RN # 1 is K2 (≠ K1). Here, other sensor nodes 104 are connected to RN # 1, RN # 2, and RN # 3, respectively, but are omitted from FIG.

  FIG. 29 is an explanatory diagram illustrating a communication sequence example of the sensor network system 100 according to the fifth embodiment. As an initial process, the server 101 issues a setting command c2901 for changing the reception interval 815 of the router node 103 to Δ seconds. The gateway node 102 receives the setting command c 2901 from the server 101 and transfers it to the router node 103.

  The router node 103 that has received the setting command c2901 issues a setting command c2903 that sets the transmission interval 715 to Δ seconds to all of the subordinate sensor nodes 104 that it manages, and all of the subordinates that it manages. The setting command c2903 is transferred to the router node 103, the reception interval 815 of the router node 103 is set to the Δ second interval, and sleep is started.

  Each of the plurality of sensor nodes 104 receives the setting command c2903, sets the transmission interval 715 to Δ seconds, and starts sleeping. The sensor node 104 performs the observation processing shown in steps S1304 to S1310 at a predetermined observation interval 714 according to the flowchart of FIG. 13, and determines whether the observation data is a transmission target (step S1307).

  In the Case 2807 example, an event e2904 is issued when the communication trial process of the sensor node 104 of SN # 1 is executed. The router node 103 of RN # 2 that has received the event e2904 receives a plurality of events in step S1205 of FIG. 12, stores them in the event queue 806, and combines the plurality of events in step S1209. Then, the router node 103 of RN # 2 transmits the event combined with RN # 1, which is the upper router node 103, in step S1211.

  The RN # 1 receives the event from the RN # 2 and the event from the RN # 3, stores each received event in the event queue 806, and the event combination unit 810 receives the plurality of events received in step S1209. In step S1211, the combined event is transmitted to the gateway node 102, which is a higher level.

  The event combination (step S1209) may be, for example, a method similar to the encapsulation of multiple events accumulated in the transmission queue 709 of the sensor node 104 described in step S1601 of FIG. As a result, for example, in FIG. 28, RN # 1 combines observation data A and B from event e2904 including observation data A coming from SN # 1 and event e2905 including observation data B coming from RN # 3. Then, an event e2906 including the observation data A and B is created and transmitted to the gateway node 102.

  The payload 1104 generated by the router node 103 has, for example, the structure of Payload 9, Payload 10, or Payload 11 in FIG. 11, and further includes an event issuing node number NodeNum and each node in the payload 1104 issued by the sensor node 104. NodeID, which is the identifier of. Thus, as described above with reference to FIG. 11 and step S1601 of FIG. 16, the router node 103 can store a plurality of observation data in the payload 1104 of the communication message 1100.

  Next, another example of event combination (step S1209) shown in FIG. 12 will be described.

  FIG. 30 is an explanatory diagram showing the concept of spatial compression in the event combination (step S1209) shown in FIG. A graph 3001 shows a temporal and spatial arrangement example of observation data groups accumulated in the event queue 806 in the router node 103 during a certain period. A graph 2901 represents a three-dimensional space composed of a position X, a time T, and an observation value V. The horizontal axis is the position X of the sensor node 104 in the space, the vertical axis is the observation time T of the observation value V in time, and The observed value V is in the vertical direction. Here, it is assumed that the observation data of the five sensor nodes 104 from SN # 1 to SN # 5 are accumulated in the event queue 806 at 16 points including the point p (circle figure in the graph 3001). Here, if the distance between the observation data of the point p and the plane abc formed by the points a, b, and c that are nearest to the point p is equal to or smaller than the threshold value, the point p can be deleted. A graph 3002 is a graph after the point p is deleted from the graph 3001.

  FIG. 31 is a flowchart illustrating an example of the spatial compression processing according to the fifth embodiment. The router node 103 selects an unselected event from the event sequence stored in the event queue 806 (step S3101). Since the event in the event sequence includes observation data, it corresponds to a point (circle) in the graph 3001. Here, it is assumed that the point p is selected as an example. The selected point is called a candidate point.

  Next, the router node 103 selects the nearest point of the candidate point p by the number of dimensions (step S3102). In the example of FIG. 30, since the position X, the time T, and the observed value V, the number of dimensions is 3, and points a to c are selected. In the case of position (X, Y), time T, and observed value V, the number of dimensions is 4.

  Then, the router node 103 determines the distance between the plane (the hyperplane in the case of four or more dimensions) constituted by the selected nearest point and the candidate point p (the point q where the perpendicular of the hyperplane passing through the candidate point p intersects the hyperplane) And the Euclidean distance from the candidate point p) are calculated and set as errors (step S3103).

  The router node 103 applies steps S3101 to S3103 to all events in the event queue 806 (step S3104: F). When applied to all events (step S3104: T), the router node 103 selects and deletes the candidate point p that minimizes the error (step S3105). Thereafter, the router node 103 makes an end determination (step S3106), and in the case of non-end (step S3106: F), repeats steps S3001 to S3105. In the case of termination (step S3106: T), the router node 103 ends the spatial compression processing.

  In the end determination (step S3106), for example, the router node 103 determines that there is no candidate point p that can be deleted with a given threshold value or less, or when the candidate points p accumulated in the event queue 806 are a certain number or less. , It is determined to end.

  The event encapsulation (step S1601) shown in FIG. 16 or the spatial compression described in FIG. 30 is performed, and each router node 103 reduces the number of events, so that each router node 103 communicates with a given number of slots. The power consumption required for communication can be reduced.

(Example 6)
Next, Example 6 will be described. In the initial processing of the first to fifth embodiments, the server 101 issues a setting command including the contents for changing the reception interval 815 of the router node 103 via the gateway node 102. By monitoring an event from the node 104, a setting command including contents for periodically changing the reception interval 815 of the router node 103 is issued. That is, the fourth embodiment is an example in which the reception interval 815 is autonomously changed.

  FIG. 32 is a flowchart of an example of operation processing of the control unit 814 of the router node 103 according to the sixth embodiment. The router node 103 monitors the operation of the event receiving unit 805 and calculates statistical information (step S3201). The statistical information is the maximum value of the received flow rate, the number of congestions, and the difference between the event observation time at the sensor node 104 and the current time at the router node 103. The maximum value of the reception flow rate is a value obtained by dividing the number of slots by the reception interval 815.

  Next, the router node 103 detects the event reception frequency (step S3202). Based on the reception interval 815 and the number of slots, the router node 103 waits for reception from the sensor node 104 during the slot specified by the number of slots at the reception interval 815 (step S1204 in FIG. 12). That is, the router node 103 waits for reception in a time division manner for each slot corresponding to the number of slots.

  The number of events received by the event receiving unit 805 per unit time and stored in the event queue 806 is the reception flow rate. If the value obtained by dividing the received flow rate by the maximum received flow rate is equal to or less than a certain value (step S3102: T), the router node 103 is receiving wastefully. In this case, the router node 103 reduces the number of slots as parameter setting (step S3206). Note that when the number of slots is 1, no further reduction is possible, so the router node 103 sets the reception interval 815 for a longer period as a parameter setting (step S3206). If the value obtained by dividing the received flow rate by the maximum received flow rate is not equal to or less than the predetermined value (step S3102: F), the router node 103 proceeds to step S3203.

  Next, the router node 103 detects event congestion (step S3203). In step S1603 of FIG. 16 in the sensor node 104, the congestion count is counted when the congestion occurs, and the congestion count is detected at the router node 103 by transmitting the congestion count at the next transmission to the router node 103. be able to. That is, when the router node 103 receives the number of times of congestion from the sensor node 104, the router node 103 has detected event congestion (step S3203: T).

  Also, when an event from a specific sensor node 104 does not arrive for a certain period, it may be determined that the congestion is from the sensor node 104 (step S3203: T). If event congestion is detected (step S3203: YES), the router node 103 sets the reception interval 815 in a shorter time or increases the number of slots as a parameter setting (step S3206). However, the upper limit of the number of slots is one less than the number of sensor nodes 104. If event congestion is not detected (step S3203: F), the process proceeds to step S3204.

  Next, the router node 103 performs event delay detection (step S3204). In the delay detection, the difference between the observation time of the event received by the event receiving unit 805 and the current time in the router node 103 is used as a delay value. The difference is calculated as statistical information (step S3201).

  When the delay value is larger than the certain value (step S3204: T), the router node 103 sets the reception interval 815 in a shorter time or increases the number of slots as a parameter setting (step S3206). However, the upper limit of the number of slots is one less than the number of sensor nodes 104. Further, as a parameter setting, the router node 103 may switch to the communication method shown in the third or fourth embodiment. When the delay value is equal to or smaller than the predetermined value (step S3204: F), the process proceeds to step S3205.

  Next, the router node 103 detects the remaining battery level of the router node 103 (step S3205). If the remaining battery level of the router node 103 is equal to or less than the predetermined amount (step S3205: T), the number of slots is reduced as a parameter setting (step S3206). The node 103 sets the reception interval 815 for a longer period as the parameter setting (step S3206). When the remaining battery level of the router node 103 is not less than or equal to the predetermined amount (step S3205: F), the router node 103 ends a series of processes.

  After step S3206, the router node 103 issues a command for changing to the parameter set in step S3206 to the sensor node 104 (step S3207), and the series of processing ends.

  As described above, in the sixth embodiment, the router node 103 can autonomously change the reception interval 815 and the number of slots to the contents according to the state of the router node 103 or the sensor node 104, thereby reducing power consumption. be able to.

  As described above, according to this embodiment, the sensor node 104 does not transmit an event every time at the observation timing, but transmits an event only at the reception timing of the router node 103. There is no need to start the communication device. Further, since the communication time with the router node 103 can be reduced at the observation timing, the power consumption of the sensor node 104 can be reduced.

  Also, at the transmission attempt timing of the sensor node 104, when there is no data to be transmitted in the sensor node 104, the wireless communication device activation and the communication time with the router node 103 can be reduced. The amount can be reduced.

  Further, in the router node 103, communication from the sensor node 104 is limited only to the reception timing of the router node 103, so that it can sleep at other times. Therefore, the power consumption of the router node 103 can be reduced.

  The present invention is not limited to the above-described embodiments, and includes various modifications and equivalent configurations within the scope of the appended claims. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the configurations described. A part of the configuration of one embodiment may be replaced with the configuration of another embodiment. Moreover, you may add the structure of another Example to the structure of a certain Example. In addition, for a part of the configuration of each embodiment, another configuration may be added, deleted, or replaced.

  In addition, each of the above-described configurations, functions, processing units, processing means, etc. may be realized in hardware by designing a part or all of them, for example, with an integrated circuit, etc. It may be realized by software by interpreting and executing the program to be realized.

  Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  Further, the control lines and the information lines are those that are considered necessary for the explanation, and not all the control lines and the information lines that are necessary for the mounting are shown. In practice, it can be considered that almost all the components are connected to each other.

DESCRIPTION OF SYMBOLS 100 Sensor network system 101 Server 102 Gateway node 103 Router node 104 Sensor node 303 Sensor 701 Dormancy management part 702 Parameter 703 Command processing part 704 Power supply part 705 State management part 706 Command reception part 707 Observation part 708 Event generation part 709 Transmission queue 710 Event transmission unit 711 Compression unit 712 Event combination unit 801 Dormancy management unit 803 Power supply unit 804 State management unit 805 Event reception unit 807 Event transmission unit 808 Command transmission unit 810 Event combination unit 811 Command reception unit 812 Command processing unit 814 Control unit

Claims (15)

A transfer node comprising: a wireless communication device that wirelessly communicates with a sensor node having a sensor for observing an observation target; an arithmetic unit having a processor and a memory; and a battery that supplies power to the wireless communication device and the arithmetic unit. ,
The processor is
The observation data received in the slot based on a reception interval until the observation data observed by the sensor is received from the sensor node and a slot which is a reception time for receiving the observation data from the sensor node. And setting processing for transmitting a transmission interval that is the same time interval as the reception interval to the sensor node,
When the setting by the setting process is completed, a stop process for stopping power supply from the battery to the wireless communication device and the arithmetic unit,
Each time the reception timing comes from the setting by the setting process, power is supplied from the battery to the wireless communication device and the arithmetic unit, and reception of the observation data from the sensor node is waited for the time of the slot. Standby processing,
A forwarding node characterized by executing   In the setting process, when there are a plurality of sensor nodes capable of wireless communication, the reception timing is set for each of a plurality of slots smaller than the number of sensor nodes, and a slot corresponding to each sensor node is assigned. The forwarding node according to claim 1. In the setting process, based on a specific reception interval longer than the reception interval and the number of sensor nodes, a specific reception timing assigned the slot for each sensor node is set,
In the reception standby process, each time the specific reception timing arrives, power is supplied from the battery to the wireless communication device and the calculation unit, and reception of the observation data from each sensor node is performed for the time of the slot. The forwarding node according to claim 2, wherein the forwarding node waits. The wireless communication device is further capable of wireless communication with an upper node,
The processor is
A selection process for selecting first observation data from the four or more observation data when receiving four or more observation data from the plurality of sensor nodes within the time of the slot;
In the n-dimensional space defined by n types of feature quantities, which are three or more integers, included in each of the four or more observation data, the selection process selected from the four or more observation data An acquisition process for acquiring n second observation data close to the first observation data;
A calculation process for calculating a distance between the position of the first observation data in the n-dimensional space and a plane formed by the n second observation data acquired by the acquisition process;
A deletion process for deleting the first observation data from the four or more observation data based on the distance calculated by the calculation process;
A combining process for generating a communication message that combines observation data groups after the deletion process;
A transmission process for wirelessly transmitting the communication message obtained by the combining process to the upper node;
The forwarding node according to claim 2, wherein the forwarding node is executed. The wireless communication device is further capable of wireless communication with an upper node,
The processor is
2. The transmission processing for wirelessly transmitting the observation data to the upper node is performed by the wireless communication device when the observation data is received from the sensor node within the time of the slot. The forwarding node described. The processor is
When receiving a plurality of observation data within the time of the slot, execute a combining process to generate a communication message that combines the plurality of observation data,
6. The forwarding node according to claim 5, wherein, in the transmission process, a communication message obtained by the combining process is wirelessly transmitted to the higher order node. The processor is
Based on the number of observation data in one reception standby in the reception standby processing and the maximum reception flow rate defined by the number of slots and the reception interval, redundancy of the time of one reception standby is detected. Execute detection process to
In the setting process, when it is detected that the detection process is redundant, the setting process is executed by reducing the number of the slots or extending the reception interval.
The transfer node according to claim 1, wherein in the transmission process, a change result by the setting change is transmitted to the sensor node. A sensor for observing an observation target, a wireless communication device that wirelessly communicates with a transfer node that transfers observation data observed by the sensor, a calculation unit having a processor and a memory, the sensor, the wireless communication device, and the calculation unit A battery node for supplying power to the sensor node,
The processor is
The sensor node sets the observation timing by an observation interval shorter than the transmission interval until the observation target is observed by the sensor, and the sensor node has the same time interval as the reception interval at which the transfer node receives the observation data. A setting process for receiving a transmission interval until data is transmitted to the forwarding node from the forwarding node and setting a transmission timing for transmitting the observation data to the forwarding node;
When the setting by the setting process is completed, a first stop process for stopping power supply from the battery to the wireless communication device and the calculation unit;
Whenever one of the observation timing or the transmission timing arrives from the setting by the setting process, a power supply process for supplying power from the battery to the arithmetic unit;
Each time the observation timing arrives, power is supplied from the battery to the sensor, the sensor observes the observation target, the observation data is acquired and stored in the memory, and the battery is stored after a predetermined observation time has elapsed. An observation process for stopping power supply to the sensor from
Each time the transmission timing arrives, the observation data stored in the memory is read out and transmitted to the transfer node, and the power supply from the battery to the wireless communication device is stopped after the time of the slot has elapsed. When,
When the observation process or the transmission process ends, a second stop process for stopping power supply from the battery to the arithmetic unit;
A sensor node characterized by executing   In the setting process, when a slot, which is a reception time for the transfer node to receive the observation data from the sensor node, is allocated to the sensor node, the transmission timing is determined based on information specifying the slot and the reception interval. The sensor node according to claim 8, wherein: is set.   The said transmission process WHEREIN: When the confirmation message which shows having received the said observation data from the said forwarding node is received by the said wireless communication device, the said observation data are erase | eliminated from the said memory. Sensor node. The sensor node can be set to either a transmission standby state for waiting for transmission of the observation data and a transmission non-waiting state for not waiting for transmission of the observation data,
In the observation process, it is determined whether or not the observation data should be a transmission target. If it is determined that the observation data should be a transmission target, the observation data is held in the memory and the state of the sensor node is changed. Transition to the transmission standby state, stop the power supply from the battery to the sensor after the lapse of the predetermined observation time, and if it is determined that it should not be a transmission target, after the lapse of the predetermined observation time Stop power supply from the battery to the sensor,
In the transmission process, when the state when the transmission timing arrives is the transmission standby state, the observation data held in the memory is read and transmitted to the forwarding node, and the state is transmitted to the transmission node. Transition from the standby state to the non-transmission state for transmission, the power supply from the battery to the wireless communication device is stopped after the elapse of time for the slot, and the state when the transmission timing arrives is the non-transmission state for transmission The sensor node according to claim 8, wherein in the state, power is not supplied from the battery to the wireless communication device. In the setting process, a specific reception interval longer than the reception interval and information specifying the slot assigned to the sensor node are received from the forwarding node, and a specific time interval that is the same time interval as the specific reception interval is received. Based on the transmission interval and the information specifying the slot, set a specific transmission timing,
In the transmission process, if the state when the transmission timing has arrived is the non-transmission state, it is determined whether or not the specific transmission timing has arrived, and the specific transmission timing has arrived In this case, power is supplied from the battery to the wireless communication device, the observation data stored in the memory is read and transmitted to the transfer node, and after the time of the slot has elapsed, the battery is transferred to the wireless communication device. The sensor node according to claim 8, wherein the power supply is stopped.   In the observation processing, when a plurality of the observation data is acquired, the intermediate observation data between the oldest observation data and the latest observation data is deleted by linear approximation compression among the three time-series observation data. The sensor node according to claim 8, wherein it is determined whether or not it is possible to delete the intermediate observation data in the memory if it can be deleted. The sensor node waits to retransmit the observation data in a transmission standby state in which the observation data is waited to be transmitted, a transmission non-waiting state in which the observation data is not waited to be transmitted, and transmission of the observation data fails. It can be set to one of the delay wait states,
In the transmission process, when the state when the transmission timing has arrived is the transmission standby state, the observation data held in the memory is read and transmitted to the forwarding node, and the transmission is successful. When the state is changed from the transmission standby state to the non-transmission state, the power supply from the battery to the wireless communication device is stopped after the predetermined transmission time has elapsed, and when the transmission fails Determining a transmission timing from among a plurality of transmission timings, transitioning the state to the delay standby state, and stopping power supply from the battery to the wireless communication device after the predetermined transmission time has elapsed If the state when the transmission timing arrives is the non-transmission state, power supply from the battery to the wireless communication device is performed. Without, if the one of transmission timing in said delay standby state is reached, the sensor node according to claim 8, characterized in that shifts the state to the transmission standby state. A sensor network system comprising: a sensor node having a sensor for observing an observation target; and a transfer node for receiving observation data observed by the sensor from the sensor node,
The transfer node includes a first wireless communication device that wirelessly communicates with the sensor node, a first arithmetic unit having a first processor and a first memory, the first wireless communication device, and the first wireless communication device. A first battery for supplying power to the arithmetic unit,
The sensor node includes a second wireless communication device that wirelessly communicates the observation data to the transfer node, a second arithmetic unit having a second processor and a second memory, the sensor, and the second wireless A second battery for supplying power to the communication device and the second arithmetic unit;
In the forwarding node:
The first processor comprises:
The observation data received in the slot based on a reception interval until the observation data observed by the sensor is received from the sensor node and a slot which is a reception time for receiving the observation data from the sensor node. And a first setting process for transmitting a transmission interval that is the same time interval as the reception interval to the sensor node;
A first stop process for stopping power supply from the first battery to the first wireless communication device and the first arithmetic unit when the setting by the first setting process is completed;
Each time the reception timing arrives from the setting by the first setting process, power is supplied from the first battery to the first wireless communication device and the first arithmetic unit, and the observation from the sensor node is performed. A reception standby process for waiting for reception of data for the time of the slot, and
In the sensor node,
The second processor comprises:
The sensor node sets the observation timing by an observation interval shorter than the transmission interval until the observation target is observed by the sensor, and the sensor node has the same time interval as the reception interval at which the transfer node receives the observation data. Receiving a transmission interval until data is transmitted to the forwarding node from the forwarding node, and setting a transmission timing for transmitting the observation data to the forwarding node;
A second stop process for stopping power supply from the second battery to the second wireless communication device and the second arithmetic unit when the setting by the second setting process is completed;
A power supply process for supplying power from the second battery to the second arithmetic unit each time one of the observation timing or the transmission timing arrives from the setting by the second setting process;
Whenever the observation timing arrives, power is supplied from the second battery to the sensor, the observation object is observed by the sensor, the observation data is acquired and stored in the memory, and a predetermined observation time has elapsed. An observation process to stop power supply from the second battery to the sensor later;
Each time the transmission timing arrives, the observation data held in the second memory is read out and transmitted to the transfer node, and the second wireless communication device from the second battery after the lapse of the time of the slot Transmission processing to stop power supply to
And a third stop process for stopping power supply from the second battery to the second arithmetic unit when the observation process or the transmission process ends.

Images