JP2017228962A - Radio sensor terminal, radio data aggregation device, and radio sensor network system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mechanism that can reduce delay time and power consumption even when a radio sensor network system is constructed by arranging radio sensor terminals at sufficiently shorter intervals compared with their communication maximum distance.SOLUTION: A radio sensor terminal includes a sensor, a radio communication unit, and a processor. The processor selects, as a connection destination of the terminal, another terminal smaller in reception radio wave strength of a radio notification packet than other terminals when the terminal connects to a radio sensor network system, and makes the radio communication unit periodically transmit a radio notification packet after completion of connection to the radio sensor network system.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a wireless sensor network system, and a wireless sensor terminal and a wireless data aggregation device that construct the system.

  Responding to increasing natural resource demand has become an international issue, and in the field of resource exploration, it is important to find natural resources (oil, gas, etc.) accurately in a short time. On the other hand, resource exploration has been deepening due to a decrease in production in major oil fields and a decrease in oil fields that are easy to explore and develop. In addition, competition for exploration and development is intensifying. Along with this, there is an increasing need to provide high-sensitivity exploration sensor technology at low cost.

  Recently, instead of a resource exploration system using a geophone, an accelerometer using a MEMS (Micro Electro Mechanical Systems) sensor has attracted attention and is used for various developments. Resource exploration systems are accelerating the flow toward larger systems, and the importance of high-resolution measurement of underground structures is increasing by densely arranging sensors. However, in the wired connection type resource exploration system, there is a limit to the system scale that can be constructed.

  There are various methods for resource exploration depending on the survey phase. For example, one of the main methods used to finally identify resource reserves is a method called reflection seismic survey. In this method, artificial vibrations generated from an artificial seismic source placed on the ground surface are reflected back from each layer in the ground (soil layer, water layer, oil and gas storage layer, bedrock layer, etc.). This is a technique for grasping the geological structure and the crustal structure by receiving the incoming wave with a vibration sensor (acceleration sensor) arranged on the ground surface and analyzing the signal waveform.

  As the artificial seismic source, dynamite is used, and a special vehicle (called a seismic vehicle) that can artificially generate vibration may be used. In the case of reflection seismic exploration, the seismic vehicle as an artificial seismic source, a sensor network system (hereinafter referred to as “sensor network”) that transfers the acquired vibration data, and the acquired vibration data are stored in the survey target field. A data center (data collection vehicle) is required.

  As described above, in the conventional system, the vibration sensors are connected by the signal line. However, in the wired connection type configuration, there is a limit to the number of sensors that can be measured simultaneously. In addition, the design of this configuration is limited by the obstacles (trees, rocks, rivers, etc.) present in the surveyed fields (forests, dense forests, etc.). Furthermore, this configuration requires field facilities such as a large-capacity power supply facility and a large data center (data collection vehicle) for supplying power to each vibration sensor. Both of these are factors that increase the cost of the sensor network.

TSMP: TIME SYNCHRONIZED MESH PROTOCOL, Proceedings of the IASTED International Symposium of Distributed Sensor Networks (DSN 2008), November 16-18, 2008, Orland, Florida, USA

  Increasing the scale of sensor networks is effective for improving the efficiency of resource exploration. However, as described above, the wired connection type sensor network has a limit to the number of sensors that can be used for measurement. Specifically, in a sensor network that collects and supplies data via cables, the installation cost of a storage vehicle or power supply facility that accumulates an enormous amount of data is a factor, and the number of sensors constituting the system is several thousand. ~ 10,000 is the limit. Also, the installation conditions are limited by obstacles on the surveyed field.

  However, as described above, in recent years, there is an increasing need to install a large-scale sensor network composed of tens of thousands to 100,000 or more sensors in a field to be investigated to make resource exploration more efficient. However, as described above, it is difficult to further increase the efficiency of the wired connection type sensor network.

  Therefore, the construction of a resource exploration system using a cableless system is examined. By adopting a cableless system, sensors can be installed in places that could not be installed in a wired connection type sensor network. Furthermore, field facilities and cables themselves are not required, and installation costs can be greatly reduced. On the other hand, in order to realize a cableless system, it is necessary to transfer data (sensor data, information necessary for operation and management) by battery driving of a sensor and a wireless multi-hop method.

  However, depending on the field to be surveyed (for example, a field in which resource exploration is performed), a flow of a large number of sensors arranged densely and used for exploration is accelerating, and the distance between sensors is several meters to several tens of meters. It is assumed that However, the communication distance by generally used sub-GHz or several-GHz band wireless communication is sufficiently longer than the above-described installation interval. For this reason, in a densely arranged large-scale sensor network, a large number of sensors are arranged within the communicable range of each sensor.

  However, in a general wireless sensor network construction method, a sensor with good communication quality (that is, a high received radio wave intensity) is selected as a connection destination. Therefore, a connection is established between the nearest sensors. However, such a connection form increases the number of wireless multihops in the entire network, and causes an increase in delay time and power consumption. This technical problem is a problem common to wireless sensor networks having the same arrangement configuration.

  Therefore, the present invention provides a mechanism capable of reducing delay time and power consumption even when a wireless sensor network system is constructed by arranging wireless sensor terminals at intervals sufficiently shorter than the communicable distance.

  In order to solve the above problems, the present invention employs, for example, the configurations described in the claims. The present specification includes a plurality of means for solving the above-mentioned problems. For example, “When the sensor, the wireless communication unit, and the wireless sensor network system are connected, the received radio wave intensity of the wireless notification packet is Select the other terminal whose received radio wave intensity of the wireless notification packet is smaller than that of the other large terminal as the connection destination of the own terminal, and after completing the connection to the wireless sensor network system, periodically wirelessly communicate with the wireless communication unit A wireless sensor terminal having a processor for sending a notification packet.

  According to the present invention, each wireless sensor terminal constructing a wireless sensor network system is not a wireless sensor terminal with good communication quality (high received radio wave intensity) but a wireless sensor terminal with low received radio wave intensity is selected as the connection destination. To do. As a result, even when wireless sensor terminals are densely arranged, for example, the distance between wireless sensor terminals connected to each other can be increased, the number of multihops can be reduced, and the delay time and power consumption can be reduced. Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

The figure which shows the whole structure of the wireless sensor network system which concerns on an Example. The figure explaining the difference of the radio | wireless multihop connection (multihop 2) by the Example, and a general radio | wireless multihop connection (multihop 1). The figure which shows the internal structure of the wireless sensor terminal which concerns on an Example. The figure which shows the internal structure of the aggregator which concerns on an Example. The figure explaining the communication timing chart performed at the time of participation to a wireless sensor network system. The figure explaining the positional relationship of the communicable range of a wireless sensor network system and the wireless sensor terminal 1s. The figure which shows the zone | band of the received radio wave intensity | strength requested | required of the wireless sensor terminal used as the selection object of a connection destination. The flowchart which shows the process operation example performed with the wireless sensor terminal which concerns on an Example. The figure which shows the format of the radio | wireless notification packet used in an Example. The figure which shows the data structure of the neighborhood wireless sensor terminal list used in an Example. The figure explaining the adjustment procedure of a network configuration after building a wireless sensor network system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment of the present invention is not limited to the examples described later, and various modifications are possible within the scope of the technical idea.

  As will be described later, the state transition flow in each embodiment is assumed to be implemented through execution of software on a general-purpose computer including a microcomputer (hereinafter referred to as “microcomputer” or “processor”). Hardware or a combination of software and hardware. In addition, specific numerical values such as the number of sensor terminals to be installed, an installation interval, a communication speed, and an operation period are numerical values for explaining the embodiments, and are not limited to numerical values used in the following description.

(1) Example 1
(1-1) Wireless Sensor Network System FIG. 1 shows an overall configuration of a wireless sensor network system 1 (hereinafter referred to as “system 1”) according to an embodiment. The system 1 is arranged in a wireless sensor terminal 1s to 10000s arranged in the measurement target field F, an aggregator 1a to ia (i represents an arbitrary numerical value) that aggregates these data, and a data center D. It is constituted by a data server sv. The narrowly-defined system 1 includes wireless sensor terminals 1s to 10000s and aggregators 1a to ia arranged in the measurement target field F.

  The system 1 in this embodiment has a large system scale, and the wireless sensor terminals 1s to 10000s are densely arranged. In this embodiment, 10,000 wireless sensor terminals are used, but the number is arbitrary. Accordingly, the number of wireless sensor terminals may be larger or smaller. As will be described later, the wireless sensor terminal is equipped with various sensors and a wireless communication function. In the case of the present embodiment, the wireless sensor terminal and the aggregator are arranged at intervals of 5 to 10 m.

  The aggregator (that is, the wireless data aggregating apparatus) is configured by one or a plurality of wirelessly connected data (hereinafter also referred to as “sensor data”) sensed by various sensors mounted on individual wireless sensor terminals. Aggregate through wireless sensor terminals. Each aggregator is arranged in the measurement target field F at regular intervals, and each aggregates data from approximately 100 to 1000 wireless sensor terminals. Of course, this numerical value is an example. The measurement target field F is not limited to the outdoors, and may be indoors, or may be a field in which indoors and outdoors are mixed. The aggregator transmits the aggregated data to the data server sv in the data center D via the communication cable L. In this specification, data includes not only physical quantity data acquired by various sensors but also information necessary for one or both of system operation and management.

(1-2) Wireless Multi-hop Connection The difference between the wireless multi-hop connection according to the embodiment (multi-hop 2) and the wireless multi-hop connection according to the comparative example (multi-hop 1) will be described with reference to FIG. 2 shows in detail the portion of the measurement target field F in FIG. In FIG. 2, the installation interval of the wireless sensor terminals is set to about 10 m, and the wireless communicable distance is about 50 m.

  In the case of a general wireless multi-hop connection, each wireless sensor terminal establishes a link with a wireless sensor terminal located in the nearest neighborhood as shown in “multi-hop 1”. That is, the communication distance of each wireless sensor terminal has a sufficient margin with respect to the communicable distance. In this case, the wireless sensor terminal ls to the wireless sensor terminal ks transfer data one hop at a time. That is, data is transferred with 5 hops. As a result, in “multihop 1”, the number of multihops increases, and the data transmission delay and power consumption increase.

  On the other hand, in the case of the wireless multi-hop connection according to the embodiment, the wireless sensor terminal ls communicates with a wireless sensor terminal located in the vicinity of 50 m that is the communicable distance. In the case of FIG. 2, the communicable distance of the wireless sensor terminal ls and the distance to the wireless sensor terminal ks are substantially the same. For this reason, the wireless sensor terminal ls connects to the wireless sensor terminal ks with one hop as shown in “multihop 2”. The wireless sensor terminal ls selects the wireless sensor terminal ks as a connection destination of the wireless link when the wireless network is constructed. The connection method according to this embodiment makes it possible to minimize the number of multi-hops required for data transfer, and to reduce data transmission delay time and power consumption.

(1-3) Configuration of Wireless Sensor Terminal and Aggregator FIG. 3 shows an internal configuration example of the wireless sensor terminals 1s to 10000s. Note that it is not necessary that all the components shown in FIG. 3 are mounted on the wireless sensor terminal, and only a part of the components may be mounted, or a configuration in which a component (not shown) is mounted may be used.

  The wireless sensor terminal shown in FIG. 3 includes a microcomputer 301, a wireless communication unit 302, a timer 303, a sensor 304, a memory 305, a battery control unit 306, a battery 307, a GPS (Global Positioning System) signal reception unit 308, and an antenna 309. . The microcomputer 301 controls the operations of the wireless communication unit 302, the timer 303, the sensor 304, the memory 305, the battery control unit 306, and the GPS signal reception unit 308 according to the control program recorded in the internal memory, and through this control, Control the state.

  The sensor 304 returns a sensor value to the microcomputer 301 in response to the sensor acquisition request received from the microcomputer 301. The sensor 304 is, for example, a vibrometer. The microcomputer 301 stores the acquired sensor value in the memory 305. The GPS signal receiving unit 308 is used for identifying the installation location of the wireless sensor terminal (own terminal) and for synchronizing the acquisition time of the sensor data acquired by each sensor terminal existing in large quantities in the measurement target field F.

  The wireless communication unit 302 receives (or demodulates) the wireless notification packet or the wireless communication packet received from another terminal (wireless sensor terminal), and transfers it to the microcomputer 301. In this specification, a wireless communication packet periodically broadcast by invalid sensor terminals that have participated in the system 1 is referred to as a “wireless notification packet” and is distinguished from a wireless communication packet during normal communication. In addition, the wireless communication unit 302 converts (modulates) a response from the microcomputer 301 into a wireless communication packet, and transmits it to the external space via the antenna 309. In addition, the microcomputer 301 respond | corresponds also to the state transition for the time management of backup and microcomputer control when radio | wireless control cannot be implement | achieved by the radio | wireless packet error etc. by using the timer 303. FIG. Here, the microcomputer 301 calculates the received radio wave intensity of the radio notification packet received from other radio sensor terminals located in the vicinity, and selects a radio sensor terminal having a relatively low received radio wave intensity as a connection destination of the own terminal. To do.

  Here, “can receive a wireless notification packet” means that a wireless sensor terminal as a transmission source is located within a range in which a wireless notification packet can be transmitted to and received from the terminal itself. In addition, when there are a plurality of wireless sensor terminals that can communicate, the wireless sensor terminal having the smallest received radio wave intensity means a wireless sensor terminal that is farthest from the terminal itself. Here, the closer to the minimum reception sensitivity of the radio communication unit 302 and the antenna 309, the closer to the communicable distance. Multi-hop 2 in FIG. 2 is a result of selecting a wireless sensor terminal with the lowest received radio wave intensity.

  However, the wireless sensor terminal to be selected as the connection destination is not limited to other terminals (wireless sensor terminals) having the minimum received radio wave intensity, and the received radio wave intensity is within a range in which the wireless notification packet can be received. A relatively low one is sufficient. As the received radio wave intensity is lower, the distance between the own terminal and other terminals is generally increased, which contributes to the reduction of the number of mappings. Further, as will be described in an embodiment described later, the wireless sensor terminal to be selected as a connection destination is determined in consideration of various selection conditions.

  FIG. 4 shows an internal configuration example of the aggregators 1a to ia. Note that it is not necessary that all the constituent elements shown in FIG. 4 are mounted on the aggregator, and only a part of the constituent elements may be mounted, or a constituent element (not shown) may be mounted.

  The basic configuration of the aggregator is the same as that of the wireless sensor terminal. The difference is that a power supply interface (IF) 406 and a wired communication unit 410 are added to the aggregator. That is, the aggregator is equipped with a sensor 404, and the sensor 404 also functions as a wireless sensor terminal.

  Unlike the wireless sensor terminal, the aggregator operates by receiving power supply through a power interface (IF) 406. A CPU having a higher processing capability than the microcomputer 301 on the wireless sensor terminal 1s to 10000s side can be used as the microcomputer 401 for the amount of power supplied through the power interface (IF) 406.

  When the microcomputer 401 converts the sensor data (wireless packet) collected through the antenna 409 and the wireless communication unit 402 into a wired packet, the microcomputer 401 outputs it to the wired communication unit 410. A wired communication unit 410 serving as an interface with an external device transmits a wired packet to the data server sv via the communication cable L.

(1-4) Timing Chart FIG. 5 shows a processing procedure executed when the wireless sensor terminal ls participates in an existing wireless sensor network system. First, the wireless sensor terminal 1s receives wireless notification packets 501 and 502 periodically broadcast from wireless sensor terminals that have already participated in the system 1. The wireless notification packets 501 and 502 correspond to the wireless sensor terminals js and ks, respectively.

  As described above, the wireless sensor terminal 1s calculates the received radio wave strengths of the wireless notification packets 501 and 502, and selects the wireless sensor terminal ks having a relatively low strength as a connection destination (parent terminal). Thereafter, the wireless sensor terminal 1s transmits a network participation request packet 503 to the selected wireless sensor terminal ks. Since the wireless sensor terminal ks has already participated in the system 1, it holds the route information to the aggregator 1a. Therefore, the wireless sensor terminal ks transfers the received network participation request packet 503 to the aggregator 1a as the network participation request packet 504 based on the route information. In the case of FIG. 5, the wireless sensor terminal ks can directly transfer the network participation request packet 504 to the aggregator 1a, but is actually transferred through a plurality of hops.

  The aggregator 1a that has received the network participation request packet 504 calculates communication band allocation for the wireless sensor terminal ls, and returns a network participation response packet 505 including network participation permission information and the calculation result to the wireless sensor terminal ls. The wireless sensor terminal ks that has received the network participation response packet 505 returns the network participation response packet 506 to the wireless sensor terminal ls. The calculation result here includes communication frequency channel information, information about timing at which the wireless sensor terminal ls can communicate, and the like.

  The wireless sensor terminal ls that has received the network participation response packet 506 secures the communication band assigned to the terminal based on the band information included in the packet, and shifts to the normal packet transmission mode. That is, when a communication request is generated by an application executed on the wireless sensor terminal 1s, the information (sensor data) is transmitted as wireless communication packets 507 and 508 to the wireless sensor terminal ks that is a relay station.

  In the above description, it is assumed that the aggregator 1a and the wireless sensor terminals ks and js are participating in the existing system 1, but even when only the aggregator 1a exists in the system 1, Can participate in system 1. In that case, a series of operations is started when the wireless notification terminal 1s newly participating receives the wireless notification packet broadcast by the aggregator 1a.

  When transmitting and transferring the network participation request packets 503 and 504, the wireless sensor terminals 1s and js that are the transmission sources add an identifier (ID) that identifies the transmission source in the packet as tracking information of the communication path. Also good. When the identifier is added, the aggregator 1a can obtain the network topology information of the wireless sensor terminal 1s that is the participation request source.

(1-5) Effect As described above, in the case of the present embodiment, the wireless sensor terminals 1 s to 10000 s constructing the system 1 are not wireless sensor terminals with good communication quality (high received radio wave intensity) and can communicate with each other. A wireless sensor terminal (low received radio wave intensity) located near the distance is selected as the connection destination. As a result, even when the wireless sensor terminals are densely arranged, for example, the distance between the wireless sensor terminals connected to each other can be increased, and the number of multihops can be greatly reduced and the delay time can be shortened. For this reason, the communication delay time of data collection and the amount of power consumed by the wireless sensor terminal can be reduced. This is advantageous for extending the operating time of the battery-powered wireless sensor terminal.

(2) Example 2
In this embodiment, a specific method for selecting a wireless sensor terminal as a connection destination will be described. FIG. 6 shows the positional relationship between the system 1 in which a large number of wireless sensor terminals are densely arranged and the communicable range 601 of the wireless sensor terminal 1s. In the case of FIG. 6, there is one aggregator in the measurement target field F. Therefore, the sensor data of all the wireless sensor terminals located in the measurement target field F are collected in the aggregator 1a.

  When participating in the system 1, the wireless sensor terminal ls is transmitted from wireless sensor terminals that are already participating in the system 1 and are located around the terminal for a certain time counted by the microcomputer 301 and the timer 303. Waiting for reception of wireless notification packets 501 and 502.

In FIG. 6, there are eight wireless sensor terminals 9 s, 10 s, 18 s, 19 s, 20 s, 29 s, 30 s, and 31 s within the communicable range 601 of the wireless sensor terminal ls. Therefore, the wireless sensor terminal 1s receives wireless notification packets from eight wireless sensor terminals at the maximum. Here, the wireless sensor terminal ls lists information of all received wireless notification packets, and determines whether or not the received radio wave intensity when receiving each wireless notification packet satisfies the following conditional expression.
Minimum reception sensitivity + α + β ≧ Receiving radio wave strength ≧ Minimum reception sensitivity + α ... Formula 1
The received radio wave intensity satisfying the conditional expression corresponds to a band indicated by hatching in FIG.

  If there is a received radio wave intensity satisfying the condition, the wireless sensor terminal ls selects the wireless sensor terminal having the lowest received radio wave intensity satisfying the condition as a connection destination (parent terminal), and participates in the network. A request packet 503 is transmitted. Here, the minimum reception sensitivity is a parameter unique to the receiver, and can be acquired by examining a data sheet or the like if it is a normal wireless IC. α is a constant margin and is a parameter that takes into account variations in received radio wave intensity due to the influence of fading or the like according to the radio wave propagation environment. Generally, the value is about 20 dB. β is a parameter representing the selection range of received radio wave intensity, and is a parameter of the wireless sensor terminal.

  As described above, in this example, a predetermined connection condition (the best received radio wave intensity is obtained by deliberately selecting a wireless sensor terminal having the weakest received radio wave intensity as a connection destination while satisfying predetermined communication conditions. The increase in the number of multi-hops is reduced as compared with a method of establishing a wireless link with the nearest wireless sensor terminal having the best communication quality.

  In the case of FIG. 6, it is assumed that the radio propagation is proportional to the distance and there is no variation in the received radio wave intensity due to fading or the like depending on the radio wave propagation environment, and when α is set to 0 dB, the communication of the radio sensor terminal ls The wireless sensor terminal 18s having the longest distance from the possible range 601 is selected as the connection destination.

  In the following, specific examples of (α, β) are listed. The following (α, β) examples show specific parameter setting method examples in each installation condition, and should be set based on the radio wave design for each condition.

α is a safety margin value for ensuring communication quality, taking into account the dispersion range of the received radio wave intensity due to the fading phenomenon peculiar to the installation environment. In general, the following values are often adopted.
・ Outdoor viewing environment: about 10 dB ・ Outdoor non-viewing environment: about 20 dB ・ Indoor viewing environment: about 20 dB ・ Indoor non-viewing environment: about 30 dB

β is a value that should be determined from the installation environment conditions and the installation interval of the wireless sensor terminals. For example, it is assumed that the installation environment is an environment described by the radio wave propagation formula shown in Formula 2.
PL = 30 * log (d)… Formula 2
Here, PL is a path loss (radio wave attenuation [dB]), and d is a distance [m]. The transmission power of the wireless sensor terminal is 0 dBm, and the reception sensitivity is -90 dBm. Furthermore, assuming an outdoor non-line-of-sight environment, α = 20 dB. In the following description, the case where the installation interval of the wireless sensor terminals is 10 m and the case where the installation interval is 50 m will be described.

When the installation interval is 10 m From the radio wave propagation equation shown in Equation 2, when viewed from a certain wireless sensor terminal, the distance corresponding to the attenuation of 70 dB (= | α + (− 90 dBm) |) is 210 m. In this case, since the installation interval of the wireless sensor terminals is 10 m (about 8 wireless sensor terminals in the case of a grid pattern), the connection destination candidates are considered in consideration of securing the number of wireless sensor terminals that are connection destination candidates. The range is 20 m, which is twice the installation interval, and a wireless sensor terminal located between 210 m and 190 m is considered as a target. In this case, from the radio wave propagation equation shown in Equation 2, the set value of β can be set to 1 to 2 dB (about 5 dB in view of safety).

When the installation interval is 50 m From the radio wave propagation equation shown in Equation 2, when viewed from a certain wireless sensor terminal, the distance corresponding to the attenuation of 70 dB (= | α + (− 90 dBm) |) is 210 m. In this case, since the installation interval of the wireless sensor terminals is 50 m (about 8 wireless sensor terminals in the case of a grid pattern), the connection destination candidate range is set in consideration of securing the number of wireless sensor terminals as connection destination candidates. A wireless sensor terminal located between 210 m and 110 m is considered as a target, with 100 m being twice the installation interval. In this case, from the radio wave propagation equation shown in Equation 2, the set value of β can be set to 8 to 9 dB (about 12 dB in view of safety).

  FIG. 8 shows a processing operation example executed in each of the wireless sensor terminals 1s to 10000s. The processing is executed by the microcomputer 301 in cooperation with the wireless communication unit 302, the timer 303, the sensor 304, the memory 305, the battery control unit 306, and the GPS signal receiver 308.

  The process is started when the wireless sensor terminal is turned on (S801). After the power is turned on, the wireless sensor terminal shifts to a reception standby state for receiving a wireless notification packet (S802). FIG. 9 shows a format example of the radio notification packet. The radio notification packet includes a header part and a data part. The header part is composed of a notification packet header 901. The data part includes a multi-hop number 902 from the aggregator, a remaining battery level 903, a child terminal number 904, GPS position information 905, a sequence number 906, and the like.

  Returning to the description of FIG. The microcomputer 301 in the reception standby state performs countdown processing of the timer 303 until the time timeout time set in advance in cooperation with the timer 303 (S803). If a wireless notification packet is received within this period (Yes in S804), the microcomputer 301 stores or updates the information related to the received wireless notification packet in the memory 305 as a neighboring wireless sensor terminal list (S805). Note that after the processing, the microcomputer 301 returns to S802.

  Although details will be described later, the neighboring wireless sensor terminal list 1000 (FIG. 10) includes a received radio wave intensity 1001, a multihop number 1002, a remaining battery capacity 1003, a child terminal number 1004, GPS position information 1005, a wireless notification packet reception rate. 1006, the number of received radio notification packets 1007, the sequence number 1008 of the initial radio notification packet, and their priority 1010 are stored.

  Returning to the description of FIG. The microcomputer 301 proceeds to the next step when update information is stored in the neighboring wireless sensor terminal list 1000 at the time when the timeout time elapses (Yes in S806). If update information is not stored in the neighboring wireless sensor terminal list 1000 (No in S806), this means that a wireless notification packet has not been received. Accordingly, in the case of a negative result in S806, the microcomputer 301 shifts again to the reception standby state and resets the timer 303.

  When update information is stored in the neighboring wireless sensor terminal list 1000, the microcomputer 301 selects a connection destination from the list (S807). At this time, the microcomputer 301 selects a wireless center terminal whose received radio wave intensity satisfies Equation 1 above. Thereby, the microcomputer 301 can connect its own terminal to a connection destination (another terminal) that can minimize the number of multihops within a communicable range.

  After selecting the connection destination, the microcomputer 301 transmits a participation request packet to the aggregator 1a via the connection destination (S808), and transitions to a reception standby state for receiving a participation response packet from the aggregator (S809). If a participation response packet is received during reception standby and network participation is permitted (positive result in S810), the microcomputer 301 updates the network information of its own terminal (S812), and joins the network after setting the bandwidth. Is completed (S813).

  Thereafter, the microcomputer 301 periodically transmits a wireless notification packet in the same manner as other wireless sensor terminals that have already participated in the system 1, and waits for a new participation request from another wireless sensor terminal. On the other hand, if the participation response packet has not been received (negative result in S810), the microcomputer 301 further determines whether or not it is within the timeout period (S811), and if it is within the timeout period (negative result in S811), the microcomputer 301 receives it. The standby state is continued (S809). On the other hand, if the timeout time has already elapsed (Yes in S811), the microcomputer 301 transmits the participation request packet again (S808).

  As described above, each of the wireless sensor terminals 1 s to 10000 s is positioned between the wireless sensor terminal farthest from the terminal itself by selecting the wireless sensor terminal having the lowest received radio wave intensity as the connection destination. Hops with the wireless sensor terminal can be reduced. For this reason, the communication delay time of data collection and the reduction effect of the electric energy consumed by the wireless sensor terminal can be maximized. Of course, it is advantageous for extending the operating time of the battery-powered wireless sensor terminal.

(3) Example 3
In the second embodiment, in the connection destination selection process (S807), by selecting a wireless sensor terminal corresponding to the received radio wave intensity satisfying Equation 1, it contributes to minimizing the number of multihops within a communicable range. Although connected to the connection destination, depending on the number of wireless sensor terminals constituting the system 1 and the situation of the arrangement, there is a possibility that a path through which data does not go to the aggregator 1a that is the data aggregation destination may be formed. Moreover, there is a possibility that the communication load is biased on a specific wireless sensor terminal and the remaining battery level is biased. In addition, even though the physical distance between the wireless sensor terminals is short, there is a possibility of connecting to a wireless sensor terminal where the apparent distance on the received radio wave intensity appears to be long due to the influence of an obstacle. . There may be other problems.

  Therefore, in this embodiment, connection is made including information such as information (multi-hop number 902, remaining battery level 903, child terminal number 904, GPS position information 905, sequence number 906) included in the wireless notification packet (FIG. 9). A destination is selected (S807) to avoid the above problem. Hereinafter, each piece of information in the neighboring wireless sensor terminal list 1000 that the microcomputer 301 of each wireless sensor terminal refers to when selecting a connection destination will be described.

・ Received signal strength 1001
The information is information acquired by the wireless communication unit 302 when receiving wireless notification packets from other wireless sensor terminals existing in the vicinity, and is the most basic information used for selecting a connection destination. Using the information, the microcomputer 301 deliberately selects a wireless sensor terminal with weak received radio wave intensity as a connection destination, thereby minimizing the number of multihops within a communicable range.

  However, there may be no wireless sensor terminal that satisfies Equation 1. In such a case, it is desirable that the microcomputer 301 increase the number of wireless sensor terminal candidates that may satisfy Equation 1 by reducing the value of α. In order to reduce the number of multi-hops, priority is given to reducing the value of α, but if no candidate is still found, the value of β is increased to give priority to participation in the wireless sensor network system.

・ 1002 multi-hops
This information is information that each wireless sensor terminal holds internally as information regarding the communication state of the terminal itself. Specifically, when the connection destination is determined and the network connection permission is obtained from the aggregator 1a, the microcomputer 301 holds in the internal memory a value obtained by adding 1 to the multihop number received from the determined connection destination. Information. The microcomputer 301 can accurately count and grasp the number of multihops from the aggregator 1a by using the information.

  Added a function to select a wireless sensor terminal with the smallest number of multi-hops included in a wireless notification packet as a connection destination among a plurality of wireless sensor terminals satisfying Equation 1 to wireless sensor terminals newly participating in the system 1 Then, the data transmission path in the direction approaching the aggregator 1a can be selected.

-Battery level 1003
This information is information that is included in the data portion of the wireless notification packet by accessing the battery control unit 306 to acquire the remaining amount of the battery 307 when the wireless sensor terminal transmits the wireless notification packet. If a function of selecting a wireless sensor terminal with the maximum remaining battery power as a connection destination among a plurality of wireless sensor terminals satisfying Expression 1 is added to a wireless sensor terminal newly participating in the system 1, a specific wireless sensor terminal The communication load on can be reduced. Thereby, the load on the battery 307 can be smoothed over the entire network.

・ Number of child terminals: 1004
The wireless sensor terminal that relays data from another terminal receives the network participation response packet for the wireless sensor terminal requesting new participation in the system 1 from the aggregator 1a and transfers the information, and the corresponding wireless sensor terminal The information is counted up when Ack is received from. That is, the information represents the number of child terminals connected to each wireless sensor terminal that relays data from other terminals.

  As a wireless sensor terminal newly participating in the system 1, a wireless sensor terminal having the smallest number of child terminals described in the neighboring wireless sensor terminal list 1000 among a plurality of wireless sensor terminals satisfying Expression 1 is selected as a connection destination. By adding this function, the concentration of communication load on a specific wireless sensor terminal can be reduced, and load distribution can be realized over the entire network.

・ GPS location information 1005
The information is installation position information acquired from the GPS signal receiver 308 as a response to the acquisition request issued by the microcomputer 301. Generally, the installation position can be grasped with an accuracy of about 1 m or more. The wireless sensor terminal already connected to the system 1 includes the GPS position information 905 in the wireless notification packet. For this reason, the wireless sensor terminal newly participating in the system 1 is provided with a function of monitoring the information included in the wireless notification packet and grasping the installation environment of the wireless sensor terminal located in the vicinity of the own terminal. Wireless sensor terminals that are not suitable for the connection can be excluded from connection destination candidates.

  Specifically, the following functions are added to the microcomputer 301. First, the microcomputer 301 calculates the difference between the GPS position information included in the received wireless notification packet and the GPS position information held in the own terminal, and each wireless sensor terminal and the own terminal that transmitted the wireless notification packet The distance information is calculated.

  Next, the microcomputer 301 substitutes the received radio wave intensity calculated by substituting the calculated distance information into the radio wave propagation equation representing the installation environment condition (that is, the equation 2) and the received radio wave intensity actually measured by the terminal itself. Calculate the difference. Furthermore, the microcomputer 301 determines whether or not the calculated difference value is larger than a preset determination threshold value. If the difference value is larger, the microcomputer 301 excludes the corresponding other terminal from the connection destination candidates. The state in which the difference value is larger than the determination threshold occurs when the actual received radio wave intensity is too low with respect to the distance to the terminal itself. Such a state means a case where the apparent distance on the received radio wave intensity appears to be long due to the influence of obstacles and the like present in the vicinity even though the physical distance is short. In such a case, even if Expression 1 is satisfied, it is not suitable for connection, and is excluded from candidates for connection.

-Radio notification packet reception rate 1006
The information is information calculated based on the sequence number 906 included in the wireless notification packet and the number of actually received wireless notification packets. The information can be obtained by the following procedure. In the wireless sensor terminal newly participating in the system 1, the sequence number 906 included in the wireless notification packet (initial wireless notification packet) received for the first time from each of the other terminals (wireless sensor terminals) located in the vicinity of the own terminal is The data is stored in the wireless sensor terminal list 1000 for each terminal.

  Even after joining the system 1, each wireless sensor terminal continues to receive wireless notification packets from other terminals (wireless sensor terminals) located in the vicinity of its own terminal, and the sequence number 906 and the sequence number of the initial wireless notification packet are received. From the difference from 1008, the number (difference value) of radio notification packets transmitted from other terminals from the time of initial reception to the current time is calculated.

  At the same time, each wireless sensor terminal counts up the number (number of receptions) of wireless notification packets received by the terminal for each transmission source (for each terminal), and sets the count value as the number of received wireless notification packets 1007. Store in the list 1000 for each terminal. Thereafter, the microcomputer 301 divides the calculated count value by the difference value described above to calculate the wireless notification packet reception rate 1006. Here, a high wireless notification packet reception rate 1006 means a high reception success rate.

  Therefore, by adding a function to select a wireless sensor terminal having the highest reception success rate among a plurality of wireless sensor terminals satisfying Equation 1 to a wireless sensor terminal newly participating in the system 1, among the connection destination candidates. A wireless sensor terminal having a high communication state can be selected as a connection destination.

・ Priority 1010
This information is information that prescribes which information is preferentially applied when the connection destination is narrowed down using any of the above-described information. In the case of the present embodiment, the priority 1010 has a higher priority as the numerical value is smaller. For example, “1” has a higher priority than “2”. In the case of the neighboring wireless sensor terminal list 1000 shown in FIG. 10, the reception radio wave intensity 1001, the number of multihops 1002, the remaining battery capacity 1003, the number of child terminals 1004, the GPS position information 1005, and the wireless notification packet reception rate 1006 are applied in this order. One connection destination is selected. If the connection destination cannot still be narrowed down to one, the microcomputer 301 selects at random.

  The priority 1010 assigned to each information may be a specification that can be changed by a user, a maintenance manager, or the like. If a user, a maintenance manager, or the like can change the priority 1010 according to the required specifications required for the system 1, it can be applied to a wide range of uses.

(4) Example 4
In the present embodiment, a function for the aggregator 1a to correct the network configuration after the construction of an autonomous network by a plurality of wireless sensor terminals constituting the system 1 will be described. Note that “after construction” in the present embodiment means not only the point in time when the installation of all wireless sensor terminals is completed, but also includes the middle stage of grounding.

  In the system 1 in which the network is autonomously constructed in parallel with the arrangement of the new wireless sensor terminals, the network having the connection form shown in FIG. 11 is constructed depending on the arrangement of the wireless sensor terminals and the turn-on order. For example, the wireless sensor terminal 20s is connected to the aggregator 1a via three wireless sensor terminals. However, as can be seen from FIG. 11, there is a path passing through the wireless sensor terminal 19s in the vicinity of the wireless sensor terminal 20s, and the number of hops is smaller than the current connection route. That is, the network shown in FIG. 11 has not been able to construct an optimal wireless multi-hop at least from the viewpoint of the arrangement of wireless sensor terminals.

  Therefore, in this embodiment, the aggregator 1a is equipped with a function of transmitting a wireless communication packet for requesting GPS position information to each wireless sensor terminal during or after the construction of the network. Each wireless sensor terminal that has received the wireless communication packet transmits GPS position information to the aggregator 1a as a response thereto. Thereby, the aggregator 1a grasps the logical configuration and physical configuration of the network topology.

  Here, the logical configuration of the network topology is a configuration in which individual wireless sensor terminals are connected. For example, in FIG. 11, it is given by a plurality of wireless sensor terminals connected by line segments. On the other hand, the physical configuration of the network topology is a physical arrangement relationship of the wireless sensor terminals. For example, in FIG. 11, the physical positional relationship (the positional relationship specified by the GPS positional information) in the field of the wireless sensor terminal corresponds.

  First, the aggregator 1a detects a radio link in which the number of multihops is not minimized based on information on the logical network topology. Next, the aggregator 1a extracts a connection destination that can improve the number of multihops using the physical network topology information and the radio wave propagation model for the detected wireless sensor terminal (for example, 20s in FIG. 11). Furthermore, the aggregator 1a issues a wireless communication packet requesting a disconnection (detachment) or a restart request (reconnection) to the extracted wireless sensor terminal (for example, 20s in FIG. 11).

  Since the aggregator 1a has this function, the network can be optimized later. In the above description, when the network construction is completed (including during construction), the aggregator 1a transmits a wireless communication packet requesting GPS position information to each wireless sensor terminal, and each wireless sensor terminal The GPS position information is returned to the aggregator 1a as a response thereto, but the GPS position information may be included in the network participation request packets 503 and 504.

(5) Other Embodiments The functions of the above-described embodiments can be realized by software program codes. In this case, a storage medium in which the program code is recorded is provided to the system or apparatus, and the computer (or CPU or MPU) of the system or apparatus reads the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing it constitute the present invention. Examples of storage media for supplying such program codes include flexible disks, CD-ROMs, DVD-ROMs, hard disks, optical disks, magneto-optical disks, CD-Rs, magnetic tapes, nonvolatile memory cards, ROMs, etc. Is used.

  Also, based on the instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. May be. Furthermore, after the program code read from the storage medium is written in the memory on the computer, the CPU of the computer or the like performs part or all of the actual processing based on the instruction of the program code. You may make it implement | achieve the function of the above-mentioned Example.

  Further, by distributing the program code of the software that realizes the functions of the above-described embodiments via a network, the program code is stored in a storage unit such as a hard disk or a memory of a system or apparatus or a storage such as a CD-RW or CD-R. The program may be stored in a medium, and a computer (or CPU or MPU) of the system or apparatus may read and execute the program code stored in the storage unit or the storage medium when used.

  Finally, it should be understood that the processes and techniques described herein are not inherently related to any particular apparatus and can be implemented by any suitable combination of components. In addition, various types of devices for general purpose can be used in accordance with the teachings described herein. It may prove useful to build a dedicated device to perform the method steps described herein. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments.

  For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined. Although the present invention has been described with reference to specific examples, they are in all respects illustrative and not restrictive. Those skilled in the art will appreciate that there are numerous combinations of hardware, software, and firmware that are suitable for implementing the present invention. For example, the described software can be implemented in a wide range of programs or script languages such as assembler, C / C ++, perl, Shell, PHP, Java (registered trademark).

  Furthermore, in the above-described embodiment, control lines and information lines are those that are considered necessary for explanation, and not all control lines and information lines on the product are necessarily shown. All the components may be connected to each other.

  In addition, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and embodiments of the invention disclosed herein. Various aspects and / or components of the described embodiments can be used singly or in any combination in a computerized storage system capable of managing data.

F: Measurement target field
D ... data center 1s, 2s, ..., is, (i + 1) s, ... js, ... 10000s ... wireless sensor terminal 1a, ia ... aggregator (wireless data aggregation device)
sv ... data server L ... communication cable 301, 401 ... microcomputer 302, 402 ... wireless communication unit 303, 403 ... timer 304, 404 ... sensor 305, 405 ... memory 306 ... battery control unit 307 ... battery 308, 408 ... GPS signal reception 309, 409 ... Antenna 406 ... Interface for power supply (IF)
410: Wired communication unit

Claims (14)

A sensor,
A wireless communication unit;
When connecting to the wireless sensor network system, the wireless sensor network system selects another terminal having a lower reception radio wave strength of the wireless notification packet than the other terminal having a higher reception radio wave strength of the wireless notification packet as a connection destination of the own terminal. A wireless sensor terminal comprising: a processor that periodically transmits a wireless notification packet to the wireless communication unit after connection to the wireless communication unit is completed. The wireless sensor terminal according to claim 1,
The wireless sensor terminal, wherein the processor selects, as a connection destination of the self terminal, another terminal that can obtain a received radio wave intensity exceeding a first threshold value obtained by adding a margin value to the minimum reception sensitivity of the self terminal. The wireless sensor terminal according to claim 2,
The said processor selects the other terminal from which the received radio wave intensity smaller than a 2nd threshold value (> 1st threshold value) is obtained as a connecting point of a self-terminal. The wireless sensor terminal characterized by the above-mentioned. In the wireless sensor terminal according to claim 3,
In a case where there are a plurality of other terminals that have a received radio wave intensity that exceeds the first threshold and is smaller than the second threshold, the processor selects the other terminal with the lowest received radio wave intensity as a connection destination of the own terminal. The wireless sensor terminal characterized by selecting. In the wireless sensor terminal according to claim 3,
The wireless sensor terminal, wherein the processor changes the first threshold value to a smaller value when there is no other terminal capable of obtaining a received radio wave intensity exceeding the first threshold value. In the wireless sensor terminal according to claim 3,
The processor, when there are a plurality of other terminals that have a received radio wave intensity that exceeds the first threshold and is smaller than the second threshold, obtains multihop number information from a radio notification packet received from the other terminal. A wireless sensor terminal characterized by taking out and selecting another terminal corresponding to the smallest multi-hop number information as a connection destination. In the wireless sensor terminal according to claim 3,
The processor, when there are a plurality of other terminals that have a received radio wave intensity that exceeds the first threshold and is smaller than the second threshold, obtains remaining battery information from the wireless notification packet received from the other terminal. A wireless sensor terminal that is picked up and selects another terminal corresponding to the most battery remaining amount information as a connection destination. In the wireless sensor terminal according to claim 3,
The processor, when there are a plurality of other terminals that can obtain a received radio wave intensity that exceeds the first threshold and is smaller than the second threshold, obtains the number of connected terminals from a radio notification packet received from the other terminal. A wireless sensor terminal characterized by taking out and selecting another terminal corresponding to the smallest number of connected terminals as a connection destination. In the wireless sensor terminal according to claim 3,
The processor is
GPS location information of the other terminal included in the wireless notification packet received from the other terminal when there are a plurality of other terminals that exceed the first threshold and have a received radio wave intensity smaller than the second threshold And calculating the distance information between the other terminal and the own terminal based on the GPS position information held by the own terminal,
A process of calculating a difference between a received radio wave intensity calculated from a radio wave propagation formula determined according to the distance information and an installation environment and a received radio wave intensity of a radio notification packet actually received from the other terminal;
When the calculated difference is larger than a preset determination threshold, a process of excluding the corresponding other terminal from the connection destination candidates is executed. In the wireless sensor terminal according to claim 3,
The processor is
When there are a plurality of other terminals that exceed the first threshold and have a received radio wave intensity smaller than the second threshold, the sequence number extracted from the wireless notification packet received from the other terminal, A process of calculating a reception success rate of the wireless notification packet based on a count value of the number of reception times of the received wireless notification packet;
A wireless sensor terminal, wherein another terminal corresponding to the largest reception success rate is selected as a connection destination. In the wireless sensor terminal according to claim 3,
The processor, when there are a plurality of other terminals that exceed the first threshold and can obtain a received radio wave intensity smaller than the second threshold,
Processing for extracting multihop number information from the radio notification packet received from the other terminal and selecting the other terminal corresponding to the smallest multihop number information as a connection destination;
A process of extracting battery remaining amount information from the wireless notification packet received from the other terminal and selecting the other terminal corresponding to the most battery remaining amount information as a connection destination;
A process of extracting the connected terminal number information from the wireless notification packet received from the other terminal and selecting the other terminal corresponding to the smallest connected terminal number information as a connection destination,
Calculate distance information between the other terminal and the own terminal based on the GPS position information of the other terminal included in the wireless notification packet received from the other terminal and the GPS position information held by the own terminal, and further, the distance information The difference between the received radio wave intensity calculated from the radio wave propagation formula determined according to the installation environment and the received radio wave intensity of the radio notification packet actually received from the other terminal is calculated, and then the calculated difference is calculated in advance. When the threshold value is larger than the determination threshold set in the above, the process of excluding the corresponding other terminal from the connection destination candidates,
Calculate the reception success rate of the wireless notification packet based on the sequence number information extracted from the wireless notification packet received from the other terminal and the count value of the reception frequency of the wireless notification packet, and correspond to the largest reception success rate A wireless sensor terminal characterized in that part or all of the process of selecting other terminals as connection destinations is executed in a predetermined priority order to narrow down other terminals to be selected as connection destinations. A plurality of wireless sensors having a function of selecting, as a connection destination of its own terminal, another terminal having a smaller reception radio wave strength of the radio notification packet than another terminal having a higher radio wave reception strength of the radio notification packet when connected to the wireless sensor network system A wireless communication unit that communicates with the terminal;
During or after the construction of the wireless sensor network system, a process of collecting each GPS position information of the plurality of wireless sensor terminals and connection information between the wireless sensor terminals, and the collected GPS position information and the connection information A process for grasping the network topology based on the above, a process for detecting a wireless link whose multi-hop number is not minimized, and a radio wave propagation formula determined according to the distance information calculated by the GPS position information and the installation environment. A processor that executes a process of selecting a connection destination that can be used to improve the number of multi-hops, and a process of requesting the selected wireless sensor terminal to leave or reconnect to the wireless sensor network system. Wireless data aggregation device. When connecting to the wireless sensor network system, select another terminal having a lower reception radio wave intensity of the radio notification packet than the other terminal having a higher radio wave reception intensity of the radio notification packet as a connection destination of the own terminal, and go to the wireless sensor network system After completing the connection, a plurality of wireless sensor terminals that periodically send out wireless notification packets to the wireless communication unit,
A wireless sensor network system comprising: one or a plurality of wireless data aggregation devices that communicate with a plurality of the wireless sensor terminals. The wireless sensor network system according to claim 13.
The wireless data aggregation device includes:
A process of collecting each GPS position information of a plurality of the wireless sensor terminals and connection information between the wireless sensor terminals during or after construction of the wireless sensor network system;
Processing to grasp the network topology based on the collected GPS location information and the connection information;
A process for detecting a radio link whose multihop count is not minimized;
A process of selecting a connection destination that can improve the number of multihops using a radio wave propagation formula determined according to the distance information calculated by the GPS position information and the installation environment;
A process for requesting the selected wireless sensor terminal to leave or reconnect to the wireless sensor network system.

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