JP6469475B2 - Wireless sensor network system and information collection method - Google Patents

Description

  The present invention relates to a wireless sensor network system and an information collecting method used therefor, for example, a wireless sensor network system including a plurality of sensor nodes and a fusion center which is a base station collecting observation data, and an information collecting method used therefor It can be used suitably.

In recent years, research and development of technologies related to wireless sensor networks have been actively conducted. A wireless sensor network is a wireless network that controls a sensor node including a sensor for observation or the like via a network configured by wireless communication, and uses the information for collecting information related to a location and an environment.
Wireless sensor networks are expected to be used in various fields such as monitoring systems and home automation. By constructing the sensor network with wireless communication, benefits such as cost reduction, expansion of the sensing range, and flexibility in changing the network can be expected.

In such a wireless sensor network, as a technique for sharing a plurality of pieces of sensor information at the same frequency, carrier sense that transmits data at each timing when each sensor node detects an empty channel has been used.
At this time, in order to effectively use a short idle channel, a packet containing data to be transmitted is generated and transmitted to each sensor node. Packets are usually sent with header information such as the source and destination, but it is necessary to put header information in all data according to a determined format. Information is given even when information is unnecessary, and in this case, power consumption in each node is wasted.
In order to solve the above problems, Patent Document 1 (Japanese Patent No. 5182713) and Patent Document 2 (Japanese Patent Laid-Open No. 2013-187552) disclose inventions related to a novel wireless communication method.

Japanese Patent No. 5182713 JP 2013-187552 A

In embodying the above inventions, there is a need for a communication protocol for efficient communication between a plurality of sensor nodes and a fusion center included in a wireless sensor network system.
The invention according to the present application provides a network system and an information collection method that allow a plurality of sensor nodes and a fusion center included in a wireless sensor network system to communicate efficiently.

Further, when a plurality of sensor nodes and a fusion center included in the wireless sensor network system communicate with each other, there is a possibility that interference occurs with another communication system that uses the same frequency band. Therefore, a communication protocol that can avoid such interference is required.
The invention according to the present application provides a wireless sensor network system capable of avoiding mutual interference with other communication systems using the same frequency band, and an information collecting method used therefor.

Hereinafter, means for solving the problem will be described using the numbers used in [DETAILED DESCRIPTION]. These numbers are added to clarify the correspondence between the description of [Claims] and [Mode for Carrying Out the Invention].
A wireless sensor network system according to an embodiment of the present invention includes a plurality of sensor nodes (2) and a fusion center (1).
The fusion center (1) includes a carrier sense unit (111), a request signal generation unit (113), and a transmission / reception unit (114). Here, the carrier sense unit (111) communicates in a predetermined frequency band used by the fusion center (1) and the sensor node (2), and is a peripheral communication device (4) other than the plurality of sensor nodes (2). The presence or absence of communication by is detected. The request signal generator (113) generates a request signal directed to the sensor node (2). The transmission / reception unit (114) of the fusion center transmits the generated request signal.
Each of the plurality of sensor nodes (2) includes a sensor node transmission / reception unit (214) and a response signal generation unit (213). Here, the transmission / reception unit (214) of the sensor node receives the request signal.
The plurality of sensor nodes (2) each independently measure an observation target, and the response signal generation unit (213) generates a response signal (3) having a frequency corresponding to the measurement result. The sensor node (2) requested to respond transmits the response signal (3) to the fusion center (1) in accordance with the received request signal regardless of the presence / absence of communication by the sensor node (2) other than itself. To do.
The fusion center (1) receives the response signal (3) transmitted from the sensor node (2).

A wireless sensor network system according to an embodiment of the present invention includes a plurality of sensor nodes (2) and a fusion center (1).
The fusion center (1) includes a carrier sense unit (111), a communication condition calculation unit (112), a request signal generation unit (113), and a transmission / reception unit (114). Here, the carrier sense unit (111) communicates in a predetermined frequency band used by the fusion center (1) and the plurality of sensor nodes (2), and is a peripheral communication device other than the plurality of sensor nodes (2) ( 4) Detect (5). The communication condition calculation unit (112) calculates a communication condition for avoiding interference or interference in the frequency band with the peripheral communication devices (4) and (5) based on the detection result of the carrier sense unit (111). The request signal generation unit (113) generates request signals directed to the plurality of sensor nodes (2) based on the calculated communication conditions. The transmission / reception unit (114) of the fusion center transmits the generated request signal.
Each of the plurality of sensor nodes (2) includes a sensor node transmission / reception unit (214), a communication condition detection unit (212), and a response signal generation unit (213). Here, the transmission / reception unit (214) of the sensor node receives the request signal. A communication condition detection unit (212) detects a communication condition from the received request signal. The plurality of sensor nodes (2) each independently measure an observation target, and the response signal generation unit (213) has a response signal (frequency) corresponding to the measurement result based on the detected communication condition ( 3) is generated. The sensor node (2) requested to respond transmits the response signal (3) to the fusion center (1) in accordance with the received request signal regardless of the presence / absence of communication by the sensor node (2) other than itself. To do.
The fusion center (1) receives the response signal (3) transmitted from the sensor node (2).

  In the information collecting method according to an embodiment of the present invention, a plurality of sensor nodes (2) measure an observation target independently of each other, and a fusion center (1) is connected to a plurality of sensor nodes (2). The request signal is transmitted, the plurality of sensor nodes (2) receive the request signal, and each of the plurality of sensor nodes (2) performs measurement at a timing according to the received request signal. A response signal (3) having a frequency corresponding to the result is transmitted to the fusion center (1), and the fusion center (1) transmits a plurality of response signals (from the plurality of sensor nodes (2)). 3). Here, the transmission of the request signal means that peripheral communication devices other than the plurality of sensor nodes (2) that are communicating in the predetermined frequency band used by the fusion center (1) and the plurality of sensor nodes (2) ( 4) detecting (5), and calculating communication conditions for avoiding interference or interference in the frequency band with the peripheral communication device (4) (5) based on the detection result of the peripheral radio transmitter; Generating request signals for the plurality of sensor nodes (2) based on the calculated communication conditions. Transmitting the response signal includes detecting a communication condition from the received request signal and generating a response signal (3) based on the detected communication condition.

  According to the present invention, when a plurality of sensor nodes and a fusion center included in a wireless sensor network system communicate with each other, it is possible to avoid mutual interference with another communication system that uses the same frequency band.

FIG. 1 is a diagram illustrating a configuration of a wireless sensor network system according to a first embodiment of the present invention. FIG. 2A is a diagram showing the configuration of the fusion center according to the first embodiment of the present invention from a physical viewpoint. FIG. 2B is a diagram showing the configuration of the fusion center according to the first embodiment of the present invention from a functional viewpoint. FIG. 3A is a diagram illustrating the configuration of the sensor node according to the first embodiment of the present invention from a physical viewpoint. FIG. 3B is a diagram illustrating the configuration of the sensor node according to the first embodiment of the present invention from a functional viewpoint. FIG. 4A is a diagram for explaining the correspondence between the frequency of the tone signal transmitted and received by the wireless sensor network system according to the first embodiment of the present invention and the observed value. FIG. 4B is a diagram illustrating a specific example explaining the correspondence between the frequency of the tone signal transmitted and received in the wireless sensor network system according to the first embodiment of the present invention and the observed value. FIG. 5A is a diagram illustrating an example of a tone signal transmitted by the sensor node according to the first embodiment of the present invention. FIG. 5B is a diagram illustrating an example of a tone signal transmitted by another sensor node according to the first embodiment of the present invention. FIG. 5C is a diagram illustrating an example of a tone signal transmitted by still another sensor node according to the first embodiment of the present invention. FIG. 5D is a diagram illustrating an example of an aggregate of a plurality of tone signals that are collectively received as one received signal by the fusion center according to the first embodiment of the present invention. FIG. 6A is a diagram for explaining a mutual interference problem between the wireless sensor network system according to the first embodiment of the present invention and other radios communicating in the vicinity thereof from the viewpoint of distance. FIG. 6B is a diagram for explaining a problem of mutual interference between the wireless sensor network system illustrated in FIG. 6A and other wireless devices communicating in the vicinity thereof from the viewpoint of frequency and signal strength. FIG. 6C is a diagram illustrating an assumed interference range calculated by the fusion center according to the first embodiment of the present invention. FIG. 6D is a diagram illustrating an information collection range calculated by the fusion center 1 illustrated in FIG. 6C. FIG. 7A is a sequence diagram showing an example of the operation of the wireless sensor network system according to the first embodiment of the present invention. FIG. 7B is a flowchart showing an example of the operation of the fusion center according to the first embodiment of the present invention. FIG. 7C is a flowchart illustrating an example of the operation of the sensor node according to the first embodiment of the present invention. FIG. 8 is a graph illustrating an example of a result of comparing the wireless sensor network system and the information collection method according to the first embodiment of the present invention with the related art in terms of the number of times of information collection. FIG. 9 is a diagram illustrating an information collection method according to the second embodiment of the present invention. FIG. 10 is a diagram for explaining an information collecting method according to the third embodiment of the present invention. FIG. 11 is a diagram illustrating an information collection method according to the fourth embodiment of the present invention.

  With reference to the attached drawings, a wireless sensor network system according to the present invention and an information collecting method used therefor will be described below. Each figure in the present application is a conceptual diagram for explaining the present invention, and each physical configuration and functional configuration illustrated can be configured by hardware or software and a combination thereof.

[First Embodiment]
FIG. 1 is a diagram illustrating a configuration of a wireless sensor network system according to a first embodiment of the present invention.
The wireless sensor network system shown in FIG. 1 includes a fusion center 1 and a plurality of sensor nodes 2-A to 2-F. The sensor node 2 is a sensor that observes information related to the position and the environment. The fusion center 1 is a base station that collects observation data observed at each of the sensor nodes 2-A to 2-F. In FIG. 1, six sensor nodes 2-A to 2-F are illustrated as an example, but the number of sensor nodes is not particularly limited. Henceforth, when not distinguishing each of a some sensor node, it describes with the sensor node 2 grade | etc.,.

There may be a peripheral wireless transmitter 4 and a peripheral wireless receiver 5 around the wireless sensor network system shown in FIG. Here, the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 are not included in the wireless sensor network system including the fusion center 1 and the plurality of sensor nodes 2. That is, it is a component of another network system.
In FIG. 1, one peripheral wireless transmitter 4 and one peripheral wireless receiver 5 are illustrated as an example, but the number of the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 is limited. There is no particular. In addition, the same peripheral wireless device may operate as the peripheral wireless transmitter 4 in some cases, and may operate as the peripheral wireless receiver 5 in other cases. Hereinafter, a set of the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 is referred to as a peripheral wireless system.

In FIG. 1, the sensor nodes 2-A to 2-F transmit tone signals 3-A to 3-F, respectively. The fusion center 1 receives tone signals 3-A to 3-F. Hereinafter, when each tone signal is not distinguished, it is referred to as tone signal 3 or the like.
As will be described later, the fusion center 1 also transmits a signal, and the sensor node 2 receives this signal. Thus, in the wireless sensor network system according to the present embodiment, the fusion center 1 and the sensor node 2 communicate wirelessly.
The tone signal 3 is a sine wave signal having a single frequency. Therefore, the tone signal 3 normally does not include information such as various data included in a general packet signal. The tone signal 3 can be defined by the frequency, signal strength, and transmission / reception time. However, in the present invention, not only the normal tone signal 3 but also each sensor node 2 is identified, so that a response including very small information such as an ID such as changing the frequency of the tone signal with time or performing low-speed modulation. It is also applicable to signals. In the present application, the response signal is a signal transmitted from the sensor node 2 to the fusion center 1 in response to a transmission request signal transmitted from the fusion center 1 and includes a tone signal 3. In the embodiment, as an example of the response signal, a tone signal 3 that can exhibit the most effects of the present invention will be described as an example.

  Similarly, the peripheral wireless transmitter 4 transmits a peripheral wireless signal 6 and the peripheral wireless receiver 5 receives the peripheral wireless signal 6. If the peripheral radio signal 6 is included in the same frequency band as the tone signal 3, interference may occur between the wireless sensor network system and the peripheral radio system. It is one of the objects of the present invention to avoid such interference.

  The plurality of sensor nodes 2 measure the observation object independently of each other, and transmit the tone signal 3 representing the measurement result toward the fusion center 1 all at once. The fusion center 1 collects and collects the tone signals 3 as the measurement results transmitted from the plurality of sensor nodes 2 collectively by wireless communication, and analyzes the collected tone signals. Details of these operations will be described later.

FIG. 2A is a diagram showing the configuration of the fusion center 1 according to the first embodiment of the present invention from a physical viewpoint. The fusion center 1 shown in FIG. 2A includes a bus 10, a processor 11 that is a calculation unit, a memory 12 that is a storage unit, a transmission / reception device 13, a transmission / reception antenna 131, and an input / output device 14. ing.
The memory 12 includes a data area 121 for storing data and a program area 122 for storing a control program. The memory 12 may be a temporary storage type memory, a long-term storage type hard disk, or a combination thereof.
The fusion center 1 may further include a storage medium 141 that stores programs and data. The storage medium 141 may be removed from the fusion center 1 after moving or copying the program or data to the memory 12.

The fusion center 1 further includes a power source (not shown). The fusion center 1 consumes a large amount of power because it controls each sensor node 2 and processes the received information. Therefore, it is desirable that the fusion center 1 supply power from a power outlet or the like so that power can be constantly supplied.
As the bus 10, the processor 11, the memory 12, and the input / output device 14, a general-purpose computer can be used. By connecting the transmission / reception device 13 including the transmission / reception antenna 131 to the computer by wire or wirelessly, the fusion center 1. It can be. Further, the fusion center 1 may be a computer itself provided with the transmission / reception device 13.

The connection relationship of each component of the fusion center 1 shown in FIG. 2A will be described. The processor 11, the memory 12, the transmission / reception device 13, the antenna 131, and the input / output device 14 are connected to each other via the bus 10. Here, the bus 10 represents, as an example, a connection relationship in which signals are transmitted and received between the components, and the components do not necessarily have to be connected as illustrated.
The antenna 131 is connected to the transmission / reception device 13.
The storage medium 141 is detachably connected to the input / output device 14.

The operation of the components of the fusion center 1 shown in FIG. 2A will be described. The processor 11 executes a program stored in the program area 122. At this time, the processor 11 may access the data area 121 to read / write data, or may control the transmission / reception device 13 and the input / output device 14.
The data area 121 stores data in a readable / writable manner. The program area 122 stores the program in a readable / writable manner.
The transmission / reception device 13 transmits and receives a radio signal via the antenna 131.

  The input / output device 14 inputs and outputs data, programs, control signals, and the like. As an example, the input / output device 14 may be a drive for reading and writing the storage medium 141, a user interface such as a button, mouse, or keyboard for controlling the operation of the fusion center 1, or a processor. 11 may be a display for displaying a result of executing the program, or a set of these.

FIG. 2B is a diagram showing the configuration of the fusion center 1 according to the first embodiment of the present invention from a functional viewpoint. 2B includes a virtual bus 110, a carrier sense unit 111, a communication condition calculation unit 112, a transmission request signal generation unit 113, a transmission / reception unit 114, and an analysis unit 115. .
The carrier sense unit 111, the communication condition calculation unit 112, the transmission request signal generation unit 113, the transmission / reception unit 114, and the analysis unit 115 are connected via the virtual bus 110, respectively. Here, the virtual bus 110 represents, as an example, a connection relationship in which signals are transmitted and received between the components, and the components may not necessarily be connected as illustrated.

Next, the operation of the components of the fusion center 1 shown in FIG. 2B will be described. The carrier sense unit 111 detects peripheral wireless transmitters 4 other than the sensor node 2 that are communicating in a predetermined frequency band used by the fusion center 1 and the sensor node 2 around the fusion center 1.
The communication condition calculation unit 112 determines communication conditions that can avoid interference in the frequency band between the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 that communicates with the peripheral wireless transmitter 4. Calculation is performed based on the detection result.
The transmission request signal generation unit 113 generates a transmission request signal for all of the plurality of sensor nodes 2 based on the communication condition calculated by the communication condition calculation unit 112.
The operations of the carrier sense unit 111, the communication condition calculation unit 112, and the transmission request signal generation unit 113 are executed by the processor 11 executing the carrier sense program, the communication condition calculation program, and the transmission request signal generation program stored in the program area 122, respectively. This is realized by accessing the data area 121 and reading / writing data.

  The transmission / reception unit 114 transmits the transmission request signal generated by the transmission request signal generation unit 113 to the sensor node 2. Further, the transmission / reception unit 114 collectively receives an aggregate of a plurality of tone signals 3 transmitted simultaneously from the plurality of sensor nodes 2 as a reception signal. In the operation of the transmission / reception unit 114, the processor 11 executes the transmission request signal transmission program or the reception signal reception program stored in the program area 122, controls the transmission / reception apparatus 13, and accesses the data area 121 to read / write data. Realize by doing things.

  The analysis unit 115 analyzes the reception signal received by the transmission / reception unit 114. The operation of the analysis unit 115 is realized by the processor 11 executing the analysis program stored in the program area 122 and accessing the data area 121 to read / write data.

FIG. 3A is a diagram showing the configuration of the sensor node 2 according to the first embodiment of the present invention from a physical viewpoint. The sensor node 2 illustrated in FIG. 3A includes a bus 20, a processor 21, a memory 22, a transmission / reception device 23, an antenna 231, an input / output device 24, and a sensor 25. The memory 22 includes a data area 221 and a program area 222. The sensor node 2 may further include a storage medium 241 that stores programs and data. The storage medium 241 may be removed from the sensor node 2 after moving or copying the program or data to the memory 22.
Further, it is desirable that the sensor node 2 further has a power source (not shown). Since the sensor node 2 in the present invention has low power consumption, a dry battery or the like can be used as a power source, and the size can be reduced.

The connection relationship of the components of the sensor node 2 shown in FIG. 3A will be described. The processor 21, the memory 22, the transmission / reception device 23, the antenna 231, the input / output device 24, and the sensor 25 are connected via the bus 20. Here, the bus 20 represents, as an example, a connection relationship in which signals are transmitted and received between the components, and the components may not necessarily be connected as illustrated.
The antenna 231 is connected to the transmission / reception device 23.
The storage medium 241 is detachably connected to the input / output device 24.

The operation of the components of the sensor node 2 shown in FIG. 3A will be described. The processor 21 executes a program stored in the program area 222. At this time, the processor 21 may access the data area 221 to read / write data, or may control the transmission / reception device 23, the input / output device 24, and the sensor 25.
The data area 221 stores data in a readable / writable manner. The program area 222 stores the program in a readable / writable manner.
The transmission / reception device 23 transmits and receives wireless signals via the antenna 231.

The input / output device 24 inputs and outputs data, programs, control signals, and the like. As an example, the input / output device 24 may be a drive for reading and writing the storage medium 241, a user interface such as a button, mouse, or keyboard for controlling the operation of the sensor node 2, or a processor. 21 may be a display for displaying the result of executing the program, or a set of these.
The sensor 25 measures the observation target, for example, controlled by the processor 21. The measurement result is preferably stored in the data area 221 via the bus 20 or the processor 21.

FIG. 3B is a diagram showing the configuration of the sensor node 2 according to the first embodiment of the present invention from a functional viewpoint. The sensor node 2 illustrated in FIG. 3B includes a virtual bus 210, a measurement unit 211, a communication condition detection unit 212, a tone signal generation unit 213, and a transmission / reception unit 214.
The measurement unit 211, the communication condition detection unit 212, the tone signal generation unit 213, and the transmission / reception unit 214 are connected via a virtual bus 210. Here, the virtual bus 210 represents, as an example, a connection relationship in which signals are transmitted and received between the components, and the components may not necessarily be connected as illustrated.

  Next, the operation of the components of the sensor node 2 shown in FIG. 3B will be described. The measuring unit 211 measures the observation target at the place where the sensor node 2 is installed. 3A, the processor 21 executes the measurement program stored in the program area 222, controls the sensor 25, accesses the data area 221 to read / write data, etc. Realize.

The communication condition detection unit 212 detects a communication condition from the received transmission request signal. The detected communication condition is preferably stored in the data area 221.
The tone signal generation unit 213 generates the tone signal 3 representing the measurement result based on the detected communication condition.
In the operations of the communication condition detection unit 212 and the tone signal generation unit 213, the processor 21 executes the communication condition detection program / tone signal generation program stored in the program area 222, and accesses the data area 221 to read / write data. It is realized by doing.

The transmission / reception unit 214 receives the transmission request signal transmitted from the fusion center 1. The received transmission request signal is preferably stored in the data area 221. Further, the transmission / reception unit 214 transmits the tone signal 3 generated by the tone signal generation unit 213 toward the fusion center 1 at a timing corresponding to the transmission request signal.
In the operation of the transmission / reception unit 214, the processor 21 executes the transmission request signal reception program or tone signal transmission program stored in the program area 222, controls the transmission / reception apparatus 23, accesses the data area 221, and reads / writes data. Realize by doing things.
Up to this point, the configuration of the wireless sensor network system according to the present embodiment has been mainly described. From here, the operation of the wireless sensor network according to the present embodiment, that is, the information collecting method according to the present embodiment will be mainly described.

First, details of the operation of the measurement unit 211 will be described. The observation target measured by the measurement unit 211 may be, for example, temperature, humidity, atmospheric pressure, brightness, concentration, dose, latitude, longitude, and the like. In any case, suitable measuring means such as a thermometer, hygrometer, barometer, illuminometer, densitometer, Geiger counter, GPS (Global Positioning System) receiver is prepared as the sensor 25. It is desirable. The observation object is not limited to the above, and various objects can be considered.
Here, as an example, a case where the observation target is the temperature around the sensor node 2 and the sensor 25 is a thermometer will be described.

  In order for the measurement unit 211 to measure the observation target, for example, the sensor 25 measures the temperature under the control of the processor 21. The measurement result is preferably stored in the data area 221. This measurement operation is desirably performed only when a transmission request signal is received from the viewpoint of saving power consumption of the sensor node 2. However, for example, since a relatively long time is required for measuring a dose with a Geiger counter, a series of measurement operations are performed from the viewpoint of minimizing a time lag from receiving a transmission request signal to transmitting a tone signal 3. May be executed repeatedly at all times.

Next, details of the operation of the tone signal generation unit 213 will be described. The tone signal generation unit 213 generates the tone signal 3 using an OFDM (Orthogonal Frequency-Division Multiplexing) scheme. That is, the frequency of tone signal 3 is selected and set from a set of OFDM subcarrier frequencies. This method of converting the observed value into the frequency of the tone signal 3 is hereinafter referred to as frequency axis mapping.
FIG. 4A is a diagram schematically illustrating the principle of frequency axis mapping according to the present invention. FIG. 4A shows a first axis indicating the observed value and a second axis indicating the subcarrier frequency number.

First, the observation value is set as k, the minimum value of the observation range is set as K _min , the maximum value is set as K _max , and the center value is set as K _C. Herein, the observation area center value K _C is the center value of the maximum and minimum values of the observation range to be defined by the following equation.
K _C = (K _max + K _min ) / 2
The value W that is half the width of the observation range is defined as follows.
W = (K _max −K _min ) / 2

Next, the subcarrier frequency number is set to n _C , the minimum value of the subcarrier frequency number is set to N _min , the maximum value is set to N _max , and the center value is set to N _C. Here, the subcarrier frequency center number N _C is the center value of the maximum value and the minimum value of the subcarrier frequency number, and is defined by the following equation.
N _C = (N _max + N _min ) / 2
In order to such a sub-carrier frequency center number N _C is present, the total number of sub-carriers must be odd, it is assumed that there are an integer A which is defined as follows.
N _max −N _min = 2A

すなわち、観測値ｋと、観測範囲中心値Ｋ_Ｃとの差を、整数２Ａの逆数で離散化し、小数点以下を切り捨てた上で、対応するサブキャリア周波数番号ｎ_Ｃと、サブキャリア周波数中心番号Ｎ_Ｃとの差に置き換えることが出来る。 A specific calculation method of frequency axis mapping will be described. If the observation value k is less than or equal to the observation range minimum value _Kmin , a subcarrier frequency minimum number _Nmin is assigned. Similarly, if the observed value k is greater than or equal to the observed range maximum value _Kmax , a subcarrier frequency maximum number _Nmax is assigned.
The observed value k is other than the above, that is, K _min <k <K _max
Is satisfied relationships allocated to sub-carrier frequency number n _C carved observations k an integer 2A. At this time, the assigned subcarrier frequency number n _C is calculated by the following equation.

That is, the difference between the observed value k and the observed range center value K _C is discretized by the reciprocal of the integer 2A, and after the decimal point is rounded down, the corresponding subcarrier frequency number n _C and subcarrier frequency center number N It can be replaced with the difference from _C.

FIG. 4B is a diagram illustrating a specific example of frequency axis mapping according to the present invention. In this example, the temperature is measured in a range of 20 to 30 ° C., and mapping is performed in a range of subcarrier frequency numbers 0 to 100. Considering FIG. 4A,
K _min = 20
K _max = 30
K _C = 25
W = 5
N _min = 0
N _max = 100
N _C = 50
A = 50
More specifically, the frequency axis mapping is equivalent to calculating the following expression.

The frequency of the tone signal 3 is determined by the frequency axis mapping as described above, that is, according to the measurement result of the observation target.
The determined tone signal frequency is preferably stored in the data area 221 as tone signal frequency data at least until the tone signal transmission time. Note that the tone signal frequency data stored in the data area 221 may be deleted in exchange for the frequency determined next time, or may be accumulated as long as an empty area remains in the data area 221. Alternatively, if there is not enough space for storing the latest tone signal frequency data in the data area 221, the old tone signal frequency data may be replaced in order and deleted.

Here, the details of the operation of transmitting the tone signal 3 among the operations of the transmission / reception unit 214 of the sensor node 2 will be described.
The transmission / reception unit 214 reads tone signal frequency data, tone signal strength data representing the signal strength of the tone signal 3, and tone signal transmission time data representing the time at which the tone signal 3 is transmitted from the data area 221. Although details will be described later, the tone signal strength data and the tone signal transmission time data are both stored in the data area 221 by the operation of the communication condition detection unit 212 described later.

The transmission / reception unit 214 transmits the tone signal 3 having the tone signal frequency corresponding to the observation result toward the fusion center 1 at the tone signal transmission time. Transmission of the tone signal 3 is performed simultaneously in all the sensor nodes 2 or a part thereof.
As described above, the transmission of the tone signal 3 from the sensor node 2 to the fusion center 1 is executed simultaneously in addition to each of the tone signals 3 being very short, so that one transmission is completed in a very short time. .

Here, among the operations of the transmission / reception unit 114 of the fusion center 1, details of the operation of collectively receiving the tone signal 3 will be described.
The plurality of tone signals 3 transmitted simultaneously from the transmission / reception units 214 of the plurality of sensor nodes 2 reach the fusion center 1 almost simultaneously. Strictly speaking, since the distance from each sensor node 2 to the fusion center 1 is different, there may be some deviation in the arrival time of each tone signal 3, but this deviation is ignored here.
The transmission / reception unit 114 of the fusion center 1 only needs to collectively receive an aggregate of a plurality of tone signals 3 transmitted simultaneously from the plurality of sensor nodes 2 as one reception signal. An example of this operation will be described with reference to FIGS. 5A to 5D.

  FIG. 5A is a diagram illustrating an example of a tone signal 3-A transmitted by the sensor node 2-A according to the first embodiment of the present invention. FIG. 5B is a diagram illustrating an example of a tone signal 3-B transmitted by another sensor node 2-B according to the first embodiment of the present invention. FIG. 5C is a diagram illustrating an example of a tone signal 3-C transmitted by still another sensor node 2-C according to the first embodiment of the present invention. In the example shown in FIGS. 5A to 5C, the three tone signals 3-A to 3-C transmitted by the three sensor nodes 2-A to 2-C have different frequencies, but a part of them. Alternatively, all tone signals 3 may have the same frequency. Note that the signal strengths of the three tone signals 3-A to 3-C transmitted by the three sensor nodes 2-A to 2-C are preferably the same.

FIG. 5D is a diagram illustrating an example of an aggregate of a plurality of tone signals 3-A to 3-C that the fusion center 1 according to the first embodiment of the present invention collectively receives as one reception signal.
In the example shown in FIG. 5D, the signal received by the fusion center 1 has three frequency components. These three frequency components respectively correspond to the frequencies of the three tone signals 3-A to 3-C. Note that the plurality of tone signals 3 having the same frequency are naturally received as one frequency component having a high signal strength.

The signal strengths of these three frequency components are not necessarily the same. The difference in signal strength at the time of reception originates from the fact that the signal strength attenuates in inverse proportion to the distance from the transmission source to the transmission destination. In any case, the signal strength of each frequency component must be larger than the desired received power _PrFC which is a threshold value. Therefore, it is desirable that the signal strength at the time of transmission of the tone signal 3 is set by calculating backward from the value of the desired received power _PrFC , the maximum distance from each sensor node 2 to the fusion center 1, and the like.
_Desirably , the desired reception power _PrFC and the signal strength at the time of transmission of the tone signal 3 are sufficiently larger than the noise power in the frequency band to be used.
Note that the signal intensity of the tone signal 3 does not have to be set to a predetermined value in advance. By including tone signal strength information specifying the signal strength of the tone signal 3 in the transmission request signal transmitted from the fusion center 1, the signal strength of the tone signal 3 is specified by the transmission request signal transmitted from the fusion center 1. It is also possible to use a configuration.

Here, details of the operation of the analysis unit 115 will be described.
Of the information contained in the aggregate of tone signals 3 received by the fusion center 1, the frequency component is mainly used by the analysis unit 115. That is, the analysis unit 115 detects which of the OFDM subcarrier frequencies is used and which is not used.

As an example, among the prepared subcarrier frequencies from No. 0 to No. 100, 11 types of No. 20 through No. 30 and No. 80, frequency components corresponding to a total of 12 types of subcarrier frequencies are tone signals. Consider the case of detection from a set of three. In such a case, it can be estimated that the frequency component corresponding to the 80th subcarrier frequency is exceptional. This is because, for example, when 30 sensor nodes 2 for temperature measurement are scattered in one room, the sensor nodes indicating normal responses output tone signals 3 at subcarrier frequencies of 20th to 30th, respectively. This means that one or several sensor nodes exceptionally transmit tone signal 3 at the 80th subcarrier frequency.
Here, No.20, No.21, No.22 ... No.30 is sent by the sensor node when 22.0 ° C, 22.1 ° C, 22.2 ° C ... 23.0 ° C are observed. This is the subcarrier frequency of the tone signal to be played. In addition, No. 80 is a subcarrier frequency of the tone signal transmitted from the sensor node when 28.0 ° C. is observed. The fact that only one or several sensor nodes transmit tone signal 3 at the 80th subcarrier frequency indicates that there is a location of 28 ° C. in a part of the 22-23 ° C. room. By detecting such exceptional abnormal values in the aggregate of tone signals 3 received by the fusion center 1, it is possible to find out, for example, that a fire has occurred in a part of the room.

Note that the received power of each frequency component depends on the total number of sensor nodes 2 that have transmitted tone signals 3 of the same frequency, the distance to the fusion center 1 for each sensor node 2, and so on. It is not used for analysis other than the threshold judgment.
The analysis unit 115 may store the result of the above analysis in the data area 121 or may output it from the input / output device 14.

Next, carrier sense performed to realize interference avoidance with a peripheral wireless system, which is one of the problems of the present invention, will be described.
First, details of the operation of the carrier sense unit 111 will be described. FIG. 6A is a diagram for explaining a mutual interference problem between the wireless sensor network system according to the first embodiment of the present invention and a radio of a peripheral wireless system that communicates in the vicinity from the viewpoint of distance.

6A shows a positional relationship in which the fusion center 1, the two sensor nodes 2-A and 2-B, the two peripheral wireless transmitters 4-A and 4-B, and the peripheral wireless receiver 5 are arranged. An example is shown. Here, the peripheral wireless transmitters 4-A and 4-B and the peripheral wireless receiver 5 are not included in the wireless sensor network system including the fusion center 1 and the sensor nodes 2-A and 2-B. That is, it is a component of another network system.
The communication range 200-A indicates a range where the tone signal 3-A transmitted from the sensor node 2-A reaches, and the shape thereof is, for example, a circle centered on the sensor node 2-A. Similarly, the communication range 200-B indicates a range where the tone signal 3-B transmitted from the sensor node 2-B reaches, and the shape thereof is, for example, a circle centered on the sensor node 2-B. .
The communication range 400-A indicates a range where the peripheral wireless signal 6-A transmitted by the peripheral wireless transmitter 4-A reaches, and the shape thereof is centered on the peripheral wireless transmitter 4-A, for example. It is a circle. In addition, a peripheral wireless signal 6-B is transmitted from the peripheral wireless transmitter 4-B. In the present embodiment, since the plane distance is particularly a problem, the circle centered on the transmitter is used as a reference, but the present invention can be applied to a case where a spherical surface centered on the transmitter is used as a reference. The same applies.

  The position of the fusion center 1 is inside the communication range 200-A and inside the communication range 200-B, but outside the communication range 400-A. Further, the distance from the fusion center 1 to the peripheral wireless transmitter 4-B is longer than the distance from the fusion center 1 to the peripheral wireless transmitter 4-A.

FIG. 6B is a diagram for explaining a problem of mutual interference between the wireless sensor network system illustrated in FIG. 6A and other wireless devices communicating in the vicinity thereof from the viewpoint of frequency and signal strength.
FIG. 6B is a graph in which the horizontal axis represents frequency and the vertical axis represents received power. The graph of FIG. 6B includes the four signals illustrated in FIG. 6A, that is, the tone signals 3-A and 3-B and the surrounding radio signals 6-A and 6-B, and other noise N. . Here, the noise refers to an irregular signal mainly generated in the circuit of the fusion center 1 and is detected even though the peripheral wireless system does not transmit an information signal using a carrier sense target channel. Means the signal to be played. Therefore, the noise includes a case where it is negligibly small compared to the information signal.
In the example shown in FIG. 6B, the four signals have different frequencies, but in reality, some of the signals may have the same frequency. On the other hand, the noise N is spread over a wide frequency band.

In the vertical axis of FIG. 6B, the carrier sense level _PCS is the minimum received power that can be detected by the carrier sense unit 111 for each frequency component of the received signal. In other words, as near radio signals 6-B, the received power is a signal below the carrier sense level P _CS, the carrier sense unit 111 to ignore. Thus, the carrier sense level P _CS, sets the value of the received power to the extent that the carrier sense negligible as free channels. The carrier sense level _PCS is desirably set sufficiently higher than the power of the noise N.

In the vertical axis of FIG. 6B, the information determination threshold _PTH is the minimum received power that the carrier sense unit 111 determines to be valid for each frequency component of the received signal. In other words, among the received signals, a desired tone signal 3-A, 3-B is a component, as illustrated in Figure 6B, it is necessary that the above information determination threshold P _TH. On the other hand, in the example shown in FIG. 6B, the undesired peripheral radio signal 6-A also exceeds the information determination threshold value _PTH .
Such a peripheral wireless signal 6-A may be indistinguishable from the tone signal 3 transmitted from the sensor node 2 in the analysis unit 115. In other words, the fusion center 1 and the sensor node 2 may be adversely affected by the peripheral wireless transmitter 4 and the peripheral wireless receiver 5. Such an adverse effect is hereinafter referred to as interference. In the present application, avoiding interference with the surrounding wireless system does not only mean a state in which no interference occurs, but the adverse effect of the surrounding wireless system when the wireless sensor network system transmits and receives information is a problem. The state suppressed to such an extent that it does not become is included.
In addition, the presence of the peripheral wireless signal 6 on the contrary may cause the fusion center 1 and the sensor node 2 to adversely affect the peripheral wireless system including the peripheral wireless transmitter 4 and the peripheral wireless receiver 5. Suggests. Such an adverse effect is hereinafter referred to as interference. In the present application, avoiding interference does not only mean a state in which interference does not occur at all. To the extent that the adverse effect received from the wireless sensor network system does not become a problem when the peripheral wireless system transmits and receives information. Suppressed states are also included.

  In order to avoid the interference or the interference described above, in the wireless sensor network system according to the present embodiment, before communication is performed between the fusion center 1 and the sensor node 2, the peripheral radio is used in the frequency band used for this communication. It is detected whether the transmitter 4 and the peripheral wireless receiver 5 are communicating. Such detection is referred to as carrier sense. If carrier sense is performed, communication can be performed at the timing when the channel is free. As a result, since the wireless sensor network system can transmit and receive information when the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 are not communicating, interference from the peripheral wireless system can be avoided. .

As a prior art, a wireless communication system includes a method in which a plurality of wireless transceivers included therein perform carrier sensing. In such a method, the time required for carrier sense increases as the total number of radio transceivers increases. In addition, since each radio transceiver has a structure necessary for carrier sense, the size of the radio transceiver increases and the power consumption also increases.
On the other hand, in the wireless sensor network system according to the present embodiment, the fusion center 1 performs carrier sense, and the sensor node 2 does not perform carrier sense. In this method, in the wireless sensor network system according to the present embodiment, all or some of the plurality of sensor nodes 2 perform communication with the fusion center 1 at the same time, and one communication is completed in a very short time. Only possible.

FIG. 6C is a diagram illustrating an assumed interference range calculated by the fusion center 1 according to the first embodiment of the present invention. Here, the assumed interference range is a range in which interference to the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 communicating in the same frequency band can occur when the fusion center 1 and the plurality of sensor nodes 2 communicate. It is.
By performing carrier sense, it is possible to detect the presence / absence of communication by the peripheral wireless system, and the presence of the peripheral wireless transmitter 4 that transmits the peripheral wireless signal 6. Further, the distance from the fusion center 1 to the peripheral wireless transmitter 4 can be estimated based on the reception power of the peripheral wireless signal 6 viewed from the fusion center 1.

Also, the fusion center 1 receives the peripheral wireless signal from the peripheral wireless transmitter 4 based on the information related to the type of packet data included in the peripheral wireless signal 6 and the density at which the plurality of peripheral wireless transmitters 4 are arranged. The distance to the machine 5 can be estimated. In FIG. 6C, the distance from the peripheral wireless transmitter 4 to the peripheral wireless receiver 5 is denoted as d1.
However, in order to calculate the assumed interference range, it is necessary to estimate not only the distance to the surrounding radio transmitter 4 but also the distance to the surrounding radio receiver 5. In FIG. 6C, the distance from the fusion center 1 to the peripheral wireless receiver 5 is denoted as d2.
The fusion center 1 not only detects the presence of the peripheral wireless transmitter 4 that performs communication in a predetermined frequency band by performing carrier sense, but also receives the peripheral wireless signal 6 transmitted by the peripheral wireless transmitter 4. A place where the peripheral wireless receiver 5 may exist is also estimated. This operation will be described.

First, the carrier sense unit 111 of the fusion center 1 determines the carrier sense level. The carrier sense level is a reception power threshold value that serves as a reference for determining whether or not to consider a signal received in a frequency band that is a target of carrier sense. Therefore, determining the carrier sense level is equivalent to determining the carrier sense range 401 shown in FIG. 6C.
Setting the carrier sense level low means that even a small reception power is targeted for carrier sense. That is, the carrier sense range 401 is widened from the fusion center 1 to the peripheral wireless transmitter 4 far from the fusion center 1.
On the contrary, setting the carrier sense level high means that the carrier sense level is not set when the received power is small. That is, only the peripheral wireless transmitter 4 near the fusion center 1 is targeted for carrier sense, and the carrier sense range 401 becomes narrow.
The shape of the carrier sense range 401 is, for example, a circle centered on the fusion center 1.
Here, the carrier sense level may be arbitrarily determined. For example, a table in which pairs of carrier sense level candidate values and corresponding carrier sense range radii are listed in advance in the data area 121 is prepared in advance, and the carrier sense level is selected by selecting from this table. Just decide. In this case, a plurality of carrier senses may be executed at different carrier sense levels. Also, the carrier sense level may be artificially determined and input from the input / output device 14 to be a determined value in the carrier sense unit 111.

Next, it is assumed that the peripheral wireless transmitter 4 is located outside the carrier sense range 401. Here, it is assumed that it is located on the boundary line of the carrier sense range 401.
As described above, assuming the distance d1 from the peripheral wireless transmitter 4 to the peripheral wireless receiver 5, the communication range 400 of the peripheral wireless transmitter 4 shown in FIG. 6C is estimated. In the example shown in FIG. 6C, the shape of the communication range 400 is a circle with the peripheral wireless transmitter 4 as the center and the distance d1 as the radius.

  Then, it is estimated that the peripheral wireless receiver 5 is located at a point where the distance from the fusion center 1 is minimum in the communication range 400. At this time, the distance d2 shown in FIG. 6C is the distance from the fusion center 1 to the peripheral wireless receiver 5.

Next, an assumed interference range 402 is calculated. In the example shown in FIG. 6C, the shape of the assumed interference range 402 is a circle having the fusion center 1 as the center and the distance d2 as the radius.
After calculating the assumed interference range 402, a range in which communication can be performed between the fusion center 1 and the sensor node 2 is calculated while avoiding interference and interference with the peripheral wireless transmitter 4 and the peripheral wireless receiver 5. Such a range is hereinafter referred to as an information collection range.

FIG. 6D is a conceptual diagram illustrating the information collection range 403 calculated by the fusion center 1 illustrated in FIG. 6C.
6D shows the fusion center 1, sensor nodes 2 -A to 2 -C illustrated in FIG. 6C, the peripheral wireless transmitter 4, the peripheral wireless receiver 5, the communication range 400, the carrier sense range 401, and the assumed interference range 402. In addition, the information collection range 403 is further illustrated.
The information collection range 403 is basically narrower than the assumed interference range 402.

Details of the operation of the communication condition calculation unit 112 will be described here. The communication condition calculation unit 112 calculates the following communication conditions.
The fusion center 1 recognizes the tone signal 3 from the sensor node 2 when the received power received by the transmission / reception device 13 of the fusion center 1 exceeds the received power _PrFC that is a desired threshold.
Therefore, it is necessary to design the transmission power P _tSN when the sensor node 2 transmits the tone signal 3 to exceed the desired reception power P _rFC when the tone signal 3 is received by the fusion center 1.
A method for designing the transmission power P _tSN of the sensor node 2 will be described below.

ここで、ＳＮＲ_ＦＣはフュージョンセンタ１における所望ＳＮＲを示し、Ｐ_ｒＦＣはフュージョンセンタ１における所望受信電力を示す。Ｎはトーン信号３の帯域幅における雑音電力を示し、Ｗ_ＳＴはトーン信号３の使用帯域幅を示す。Ｗ_ＳＮはＯＦＤＭサブキャリアの総帯域幅を示し、ＳＣはサブキャリアの総数を示す。数３の分母は１サブキャリアあたりの雑音電力を表している。 The relationship between the desired received power _PrFC of the fusion center 1 per OFDM subcarrier and the SNR (Signal to Noise ratio) is given by the following calculation formula.

Here, SNR _FC indicates the desired SNR at the fusion center 1, and _PrFC indicates the desired received power at the fusion center 1. N indicates the noise power in the bandwidth of the tone signal 3, and W _ST indicates the used bandwidth of the tone signal 3. W _SN indicates the total bandwidth of the OFDM subcarrier, and SC indicates the total number of subcarriers. The denominator of Equation 3 represents the noise power per subcarrier.

ここで、Ｐ_ｔＳＮは１つのセンサノード２あたりの送信電力を示し、Ｐ_ｒＦＣはフュージョンセンタ１の所望受信電力を示す。λはトーン信号３の波長を示し、ｄ_ｃは情報収集範囲４０３の半径を示す。ｄ_０は所定の参照距離を示し、ｎは伝搬減衰係数を示している。 The transmission power P _tSN per sensor node 2 is calculated from the relationship between the reception power and attenuation due to distance. Here, a case where the transmission power of the tone signal 3 transmitted by each sensor node 2 is uniform will be described. Even if the farthest sensor node from the fusion center 1, it is desirable to transmit power P _TSN is not less than the desired received power P _rFC by by attenuation distance. Such a condition is expressed by the following equation.

Here, P _tSN indicates transmission power per one sensor node 2, and _PrFC indicates desired reception power of the fusion center 1. λ represents the wavelength of the tone signal 3, d _c denotes the radius of the information acquisition range 403. d ₀ represents a predetermined reference distance, and n represents a propagation attenuation coefficient.

ここで、Ｉ_ａｇｇは周辺無線システムへ与える合成干渉電力を示し、ｒはフュージョンセンタ１からの距離を示す。また、θはフュージョンセンタ１を中心とした所定方向との角度を示し、ｄ_ｃは情報収集範囲４０３の半径を示す。Ｐ_ｔＳＮ（ｄ_ｃ）はフュージョンセンタ１からの距離ｄ_ｃに位置するセンサノード２の送信電力を示し、ρ_ＳＮ（ｒ，θ）はフュージョンセンタ１を中心として距離ｒ、角度θの範囲におけるセンサノード２の密度を示す。ｄ_０は所定の参照距離を示し、ｚはセンサノード２から周辺無線受信機５までの距離を示す。 Gradually set larger radius at which the distance d _c information acquisition range 403 centered on the fusion center 1, is calculated from the number 4 the desired transmission power P _TSN at that time.
Then, the combined interference power I _agg given to the peripheral wireless transmitter 4 and the peripheral wireless receiver 5 by the fusion center 1 and each sensor node 2 is calculated from the following equation (5) using the following equation.

Here, I _agg represents the combined interference power applied to the peripheral wireless system, and r represents the distance from the fusion center 1. Further, theta represents the angle between a predetermined direction around the fusion center 1, d _c denotes the radius of the information acquisition range 403. Sensor in range of the distance _{d c} shows the transmission power of the sensor node 2 located, ρ _SN (r, θ) is the distance r, the angle theta about the fusion center 1 from P tSN _{(d c)} Fusion center 1 The density of node 2 is shown. d ₀ indicates a predetermined reference distance, and z indicates a distance from the sensor node 2 to the peripheral wireless receiver 5.

If the calculated synthesized interference power I _agg is smaller than the allowable value, gradually increasing the distance d _c is the radius of the information acquisition range 403, the calculation of the desired transmission power P _TSN and synthetic interference power I _agg repeat.
If the calculated synthesized interference power I _agg exceeds the allowable value ends the repetition of the calculation therein, it adopts the distance d _c is the previous radius of d _c when exceeded, information acquisition range 403 To decide.
The transmission power P _tSN of the tone signal 3 calculated under the conditions of the adopted information collection range 403 is adopted as the transmission power satisfying the allowable interference value and designed in advance for the sensor node 2 within the collection range. be able to. In that case, this transmission power is preferably stored in the data area 221 of the sensor node 2.

Alternatively, the transmission power of the adopted tone signal 3 can be set for each sensor node 2 in the information collection range 403 each time. In that case, the value of the adopted transmission power _PtSN is included in the communication condition as tone signal strength information, and is transmitted from the fusion center 1 to each sensor node 2 as one of the communication conditions included in the transmission request signal. The sensor node 2 that has received the transmission request signal detects the tone signal strength information included in the transmission request signal received by the transmission / reception device 23 with the communication condition detection unit 212, and outputs the tone signal 3 with the transmission power _PtSN as the fusion center. 1 to send. As a result, the fusion center 1 can receive the tone signal 3 exceeding the received power _PrFC from the sensor node 2 within the information collection range 403.
Note that the communication conditions may further include a classification condition in which some sensor nodes 2 are requested to transmit tone signals and other sensor nodes 2 are excluded from the request. This sorting condition will be described later as another embodiment of the present invention.

Further, as transmission request signal to the sensor node 2 within the information acquisition range 403 is determined by adopting the distance d _c obtained above to arrive, may determine the transmission power of the transmission request signal. In this case, the transmission request signal may not include communication conditions.
The plurality of sensor nodes 2 that have received the transmission request signal send the tone signal 3 to the fusion center 1 only when the signal power of the transmission request signal received by the transmission / reception device 23 exceeds the threshold set in the sensor node. Send. Thus, fusion center 1 can receive the transmission of the viewing tone signal 3 from the sensor node 2 with a distance d _c adoption researched range 403 is determined.
The transmission power of the transmission request signal is preferably stored in the data area 121 of the fusion center 1 as a communication condition.

Alternatively, the ID information that specifies only the sensor node 2 in the information acquisition range 403 is determined by adopting the distance d _c obtained above, it may be included in the transmission request signal as the communication condition. In this case, when the plurality of sensor nodes 2 that have received the transmission request signal detect the ID information included in the transmission request signal received by the transmission / reception device 23 by the communication condition detection unit 212 and determine that they are specified. Only the tone signal 3 is transmitted to the fusion center 1. Thus, fusion center 1 can receive the transmission of the viewing tone signal 3 from the sensor node 2 with a distance d _c adoption researched range 403 is determined.
The ID information as the sensor node classification information is preferably stored in the data area 121 of the fusion center 1 as a communication condition.
The communication condition calculation unit 112 calculates the communication conditions described above.

Here, details of the operation of the transmission request signal generator 113 will be described.
The transmission request signal generation unit 113 generates a transmission request signal for requesting transmission of the tone signal 3 as an observation result from the sensor node 2. Each sensor node 2 is configured to transmit a tone signal 3 having a frequency corresponding to the observation result to the fusion center 1 when a transmission request signal is received. Therefore, this transmission request signal may consist of only a signal requesting a response from the sensor node 2 or may include various communication conditions. Here, the communication condition may _include the value of the transmission power _PtSN described above as tone signal strength information.
The communication condition included in the transmission request signal may further include information specifying the timing at which each sensor node 2 transmits the tone signal 3 toward the fusion center 1. However, in actuality, there is always a possibility that transmission of the peripheral wireless signal 6 by the peripheral wireless transmitter 4 is started, so it is desirable that each sensor node 2 transmits the tone signal 3 immediately after receiving the transmission request signal. In this case, there is no need to specify the timing.

Here, among the operations of the transmission / reception unit 114, details of an operation of transmitting a transmission request signal will be described.
First, the carrier sense in the carrier sense unit 111 of the fusion center 1 confirms that the received power exceeding the carrier sense level P _CS no. The fact that the received power exceeding the carrier sense level is not detected means that the peripheral wireless system is not communicating or is at a level that can be ignored even if communicating. That is, the frequency band used by the fusion center 1 and the sensor node 2 is free.
When detecting that the frequency band is free, the transmission / reception unit 114 transmits the generated transmission request signal to all the sensor nodes 2 at a predetermined timing. However, as described above, since there is always a possibility that the transmission of the peripheral wireless signal 6 by the peripheral wireless transmitter 4 is started, the transmission request signal generation unit 113 may transmit the transmission request signal immediately after the transmission request signal is generated. desirable. However, data representing various conditions defining the transmission request signal may be stored in the data area 121 during that time.

Here, the operation of the wireless sensor network system according to the present embodiment, that is, the information collecting method according to the present embodiment will be summarized. FIG. 7A is a sequence diagram showing an example of the operation of the wireless sensor network system according to the first embodiment of the present invention.
FIG. 7A shows an example of the operation of the fusion center 1 and the sensor nodes 2-A to 2-F. However, illustration of the operation of the sensor nodes 2-C to 2-E is omitted. As described above, the total number of sensor nodes 2 is not particularly limited.

  In the example shown in FIG. 7A, first, the fusion center 1 performs carrier sense as the first step S11. Next, the fusion center 1 calculates communication conditions as a second step S12. Then, the fusion center 1 generates a transmission request signal as the third step S13. Next, the fusion center 1 transmits a transmission request signal toward the sensor nodes 2-A to 2-F as the fourth step S14.

Subsequently, each of the sensor nodes 2-A to 2-F receives the transmission request signal as the fifth steps S21A to S21F. Next, each of the sensor nodes 2-A to 2-F confirms the communication conditions as the sixth steps S22A to S22F. And each of sensor node 2-A-2F measures an observation object as 7th step S23A-S23F.
Each of the sensor nodes 2-A to 2-F generates a tone signal as the eighth steps S24A to S24F. Next, each of the sensor nodes 2-A to 2-F transmits the tone signal 3 toward the fusion center 1 as ninth steps S25A to S25F.

  The fusion center 1 collectively receives the aggregate of tone signals 3 as the tenth step S15. Then, the fusion center 1 analyzes the aggregate of the tone signals 3 as an eleventh step S16.

Here, the operation of the fusion center 1 according to the present embodiment, that is, the information collecting method by the fusion center 1 according to the present embodiment will be summarized. FIG. 7B is a flowchart showing an example of the operation of the fusion center 1 according to the first embodiment of the present invention.
First, the fusion center 1 detects whether or not the peripheral wireless system is communicating as step S111 included in the first step S11.
When the surrounding wireless system in communication is detected (YES), the process waits until the communication of the surrounding wireless system is ended as step S112 included in the first step S11. After that, as step S113 included in the first step S11, waiting for NAV (Network Allocation Vector) time and waiting for DIFS (Distributed coordination function Frame Space) time is performed. Thereafter, standby for a random back-off time is performed as step S114 included in the first step S11. Then, the process returns to step S111.

When the peripheral wireless system in communication is not detected (NO), the communication condition is calculated as the second step S12. Subsequently, a transmission request signal is generated as a third step S13. And a transmission request signal is transmitted as 4th step S14.
The tone signal reception mode is started as step S151 included in the tenth step S15. As shown in FIG. 7A, tone signal 3 is received in the tenth step S15. And tone signal reception mode is complete | finished as step S152 contained in 10th step S15.

  Next, while analyzing as 11th step S16, it waits for DIFS (Distributed coordination function InterFrame Space) time as 12th step S17. Thereafter, in a thirteenth step S18, a random back-off time is waited. Next, the process returns to step S111.

  The operation of the fusion center 1 described above is preferably stored in the program area 122 as a program. Note that this program may be supplied from the storage medium 141 to the program area 122.

Here, the operation of the sensor node 2 according to the present embodiment, that is, the information measurement method by the sensor node 2 according to the present embodiment will be summarized. FIG. 7C is a flowchart showing an example of the operation of the sensor node 2 according to the first embodiment of the present invention.
Each sensor node 2 first waits for receiving a transmission request signal as step S211 included in the fifth step S21. Next, a transmission request signal is received as step S212 included in the fifth step S21.
Subsequently, each sensor node 2 detects a communication condition as step S221 included in the sixth step S22. Then, in step S222 included in the sixth step S22, each sensor node 2 confirms whether or not it is a target for which transmission of the tone signal 3 is requested.

When the sensor node 2 itself is not the target for which the transmission of the tone signal 3 is requested (NO), each sensor node 2 returns to Step S211.
On the other hand, when the subject itself is an object for which transmission of the tone signal 3 is requested (YES), each sensor node 2 measures the observation object as the seventh step S23.

Thereafter, each sensor node 2 generates a tone signal 3 as an eighth step S24. Next, each sensor node 2 transmits the tone signal 3 toward the fusion center 1 as a ninth step S25. Then, each sensor node 2 returns to step S211.
The operation of the sensor node 2 described above is preferably stored in the program area 222 as a program. Note that this program may be supplied from the storage medium 241 to the program area 222.

Here, the effects obtained by the wireless sensor network system according to the present embodiment and the information collection method using the wireless sensor network system will be described.
FIG. 8 shows an example of a simulation result in which the wireless sensor network system and information collection method according to the first embodiment of the present invention are compared with the prior art in which a plurality of wireless transceivers perform carrier sense on the basis of the number of times of information collection. It is a graph to show.
FIG. 8 shows a graph in which the horizontal axis indicates the number of peripheral wireless systems in the carrier sense area and the vertical axis indicates the number of collections. This graph includes a total of six graphs a to f. Here, the number of peripheral wireless systems in the carrier sense area means the total number of pairs of peripheral wireless transmitters and peripheral wireless receivers.

  The first graph a shows the total number of tone signals 3 that the fusion center 1 has been able to receive at a time out of the tone signals 3 transmitted from a number of sensor nodes 2 using the wireless sensor network system and information collection method according to the present embodiment. Show. The second graph b to the sixth graph f show the number of times signals can be transmitted / received between the transceivers using CSMA / CA (Carrier Sense Multiple Access with Interaction Avidity) according to the prior art as a comparison object with the present embodiment. Show. CSMA / CA is a communication protocol employed in communication means such as a wireless LAN (Local Area Network).

  Here, the example shown in the 2nd graph b-the 6th graph f differs in the total number of sensor nodes. That is, the second graph b shows a case where the total number of sensor nodes is 1, the third graph c shows a case where the total number of sensor nodes is 3, and the fourth graph d shows a total number of 5 sensor nodes. The fifth graph e shows the case where the total number of sensor nodes is 10, and the sixth graph f shows the case where the total number of sensor nodes is 25.

As can be seen from FIG. 8, in any case, if the number of peripheral wireless systems in the carrier sense area increases, the number of collections tends to decrease exponentially. This is considered to be because if the number of peripheral wireless systems in the carrier sense area increases, the time during which communication cannot be performed increases.
Further, as can be read from the second graph b to the sixth graph f, if the total number of sensor nodes increases, the number of collections tends to decrease in inverse proportion. This is considered because one sensor node can communicate with the same fusion center at a time.

On the other hand, the first graph a is a graph when information is collected using about 500 subcarrier frequencies. According to the present invention, information can be collectively received from a plurality of sensor nodes. Therefore, the number of collections is theoretically the same regardless of the number of sensor nodes. Therefore, in the first graph a of FIG. 8, the number of sensor nodes as in the second graph b to the sixth graph f, which is the conventional technology, is not conceived.
As can be read from the first graph a, according to the present embodiment, the number of sensor nodes is not limited, so even when the number of sensor nodes is as large as 100 or more, in the CSMA / CA shown in the second graph b, It can be seen that when the total number of sensor nodes is one, it is possible to obtain an excellent effect that information can be collected with substantially the same performance. One of the reasons is the feature of the present invention that a plurality of sensor nodes 2 can communicate simultaneously with the same fusion center 1.

As the simplest configuration of the present invention, the fusion center 1 may not have the communication condition calculation unit 112. The sensor node 2 may not have the communication condition detection unit 212.
In this case, the fusion center 1 transmits a transmission request signal that does not include a communication condition to all the sensor nodes 2 using an empty channel according to the result of carrier sense. As soon as the sensor node 2 receives the transmission request signal, the sensor node 2 transmits the tone signal 3 to the fusion center 1 at a frequency corresponding to the observation result. As a result, a large amount of information can be collected in a lump using an empty channel for an extremely short time. Since the sensor node 2 does not have a communication condition detection unit, the configuration is simplified, and downsizing and low power consumption can be realized.

[Second Embodiment]
In 1st Embodiment of this invention, the transmission request signal was transmitted toward all the some sensor nodes 2, and the form which collects information from all the sensor nodes 2 was demonstrated. In the second embodiment of the present invention, a mode will be described in which information is collected from only a part of sensor nodes by being classified into a target requesting transmission of the tone signal 3 and a non-target.
According to the present embodiment, by limiting the information collection target to a part of the sensor nodes 2, the density of the sensor nodes 2 can be virtually reduced, leading to an expansion of the information collection range.

FIG. 9 is a diagram illustrating an information collection method according to the second embodiment of the present invention. FIG. 9 shows a table in which each sensor node 2 is associated with a unique ID number. Such a table is stored in the data area 121 of the fusion center 1, for example.
Each sensor node 2 stores its ID number in the data area 221.
In the table of FIG. 9, each sensor node 2 is further assigned to group 1 or group 2. In the example shown in FIG. 9, the sensor node 2 with an odd ID number belongs to the group 1, and the sensor node 2 with an even ID number belongs to the group 2.

  When the fusion center 1 transmits a transmission request signal, a communication condition including 1-bit information indicating “ID number is odd” or “ID number is even” is included. Each sensor node 2 that has received the transmission request signal reads its own ID number from the data area 221 and compares it with the communication conditions to determine whether or not it is a target for which a tone signal response is requested. According to the determination result, each sensor node 2 transmits the tone signal 3 when it is requested to respond, and does not transmit the tone signal 3 when it is not requested. When the tone signal 3 is not transmitted, the measurement operation in the sensor 25 may be omitted in order to save power consumption.

  By reducing the number of sensor nodes 2 to be responded to half, the total number of sensor nodes 2 transmitting the tone signal 3 is also halved, and the transmission power of the entire tone signal is also halved. As a result, the interference power is reduced, and the information collection range 403 can be expanded accordingly.

In addition, the next transmission request signal sets the target and non-target separation conditions in reverse, so that only the sensor node 2 that did not transmit the tone signal 3 in the previous transmission request signal requests transmission of the tone signal 3. I can do it. By repeating this operation, the information collection range 403 can be expanded although the time required for information collection is doubled.
As an example of the target sensor node 2, an example is shown in which the odd ID and the even ID are sorted. However, the target sensor node 2 can be selected by limiting the ID to a multiple of 3 or by selecting at random. It is also possible to change the ratio. In addition, it is desirable that the number of sensor nodes for which information is collected at a time is two or more.
9 shows a table in which each sensor node 2 is associated with a unique ID number. However, the table may further include arrangement information of each sensor node 2 in association with the ID number.

[Third Embodiment]
As a different classification condition from the second embodiment of the present invention, a method for changing the transmission power of the transmission request signal will be described as a third embodiment of the present invention.
FIG. 10 is a diagram for explaining an information collecting method according to the third embodiment of the present invention. In the example illustrated in FIG. 10, the information collection range is divided into three concentric communication ranges 201, 202, and 203. The fusion center 1 is located at the center of the communication ranges 201, 202, and 203. The sensor nodes 2-A and 2-B are located inside the communication range 201. The sensor nodes 2-C and 2-D are located inside the communication range 202 and outside the communication range 201. The sensor nodes 2-E and 2-F are located inside the communication range 203 and outside the communication range 202.

  In the present embodiment, information collection is performed in three steps. At the first time, the fusion center 1 transmits a transmission request signal with transmission power reaching only inside the communication range 201. Furthermore, a designation for ignoring the transmission request signal received thereafter only twice is added as a communication condition included in the transmission request signal. As a result, only the sensor nodes 2-A and 2-B receive the transmission request signal and transmit the tone signal 3.

  At the second time, the fusion center 1 transmits a transmission request signal with transmission power reaching only inside the communication range 202. Further, a designation for ignoring a transmission request signal received thereafter only once is added as a communication condition included in the transmission request signal. As a result, only the sensor nodes 2-A to 2-D receive the transmission request signal, and only the sensor nodes 2-C and 2-D transmit the tone signal 3.

  At the third time, the fusion center 1 transmits a transmission request signal with transmission power reaching the entire communication range 203. As a result, all of the sensor nodes 2-A to 2-F receive the transmission request signal, and only the sensor nodes 2-E and 2-F transmit the tone signal 3.

By doing so, it is possible to obtain an excellent operational effect that measurement information can be collected individually for each concentric range centering on the fusion center 1. As in the second embodiment, the total number of sensor nodes 2 that transmit the tone signal 3 at one time is reduced to one third, so the transmission power of the entire tone signal is also reduced to one third, and only that much. The effect of expanding the information collection range can be obtained at the same time.
In the above example, information is collected in three stages, but the number of stages can be freely changed. Also in the present embodiment, it is desirable that the number of sensor nodes to be collected at a time is two or more.

[Fourth Embodiment]
Combining the ID number unique to each sensor node 2 used in the second embodiment of the present invention with the frequency axis mapping described in the first embodiment of the present invention will be described as a fourth embodiment of the present invention.
FIG. 11 is a diagram illustrating an information collection method according to the fourth embodiment of the present invention. FIG. 11 shows an example of a table that defines the correspondence relationship between the ID number of the sensor node 2, the observed value used in the frequency axis mapping, and the OFDM subcarrier number used in the frequency axis mapping. This table is preferably stored in the data area 121 of the fusion center 1. Each sensor node 2 preferably stores at least a portion related to itself in this table in the data area 221.

  In the present embodiment, the total number of OFDM subcarriers is multiplied by the number of sensor nodes 2 to be used. That is, the total number of OFDM subcarriers that is 101 in the first embodiment of the present invention is increased to 606 or more if the total number of sensor nodes 2 is 6, for example. At this time, the frequency band to be used may be widened, or the frequency band assigned to each subcarrier may be narrowed.

  Each sensor node 2 refers to a table stored in its own data area 221 or a part thereof, generates a tone signal 3 having a frequency corresponding to the correspondence defined in this table, and sends it to the fusion center 1. Send to. Even if the fusion center 1 receives the aggregate of the tone signals 3 at the same time as in the first embodiment, the analysis unit 115 refers to the table stored in the data area 121 so that which frequency component has which ID. It can be read from the sensor node 2 having the number and which observation value is meant. As a result, the wireless sensor network system and the information collection method according to the present embodiment can collect more detailed information. Also in the present embodiment, it is desirable that the number of sensor nodes to be collected information at a time is two or more.

In the second to fourth embodiments, various variations for narrowing down the sensor node 2 as a response target have been described. However, this is an example suggesting that various methods for narrowing down the sensor node 2 exist.
Further, although the tone signal 3 has been described as an example of the response signal of each sensor node 2, the response signal does not need to be a tone signal, and may be another signal having a predetermined frequency corresponding to the measurement result.
The invention made by the inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  In addition, the features described in the embodiments can be freely combined within a technically consistent range. Specifically, by combining the fourth embodiment with the second embodiment or the third embodiment, it is possible to reduce the coefficient by which the total number of OFDM subcarriers is multiplied and to execute the fourth embodiment more stably. It becomes.

DESCRIPTION OF SYMBOLS 1 Fusion center 10 Bus 11 Processor 110 Virtual bus 111 Carrier sense part 112 Communication condition calculation part 113 Transmission request signal generation part 114 Transmission / reception part 115 Analysis part 12 Memory 121 Data area 122 Program area 13 Transmission / reception apparatus 131 Antenna 14 Input / output apparatus 141 Storage Medium 2, 2-A to 2-F Sensor node 20 Bus 200-A, 200-B Communication range 201 to 203 Communication range 21 Processor 210 Virtual bus 211 Measurement unit 212 Communication condition detection unit 213 Tone signal generation unit 214 Transmission / reception unit 22 Memory 221 Data area 222 Program area 23 Transmission / reception device 231 Antenna 24 Input / output device 241 Storage medium 25 Sensor 3, 3-A to 3-F, 3-0 to 3-100 Tone signal 4, 4-A, 4-B Peripheral radio transmitter 400, 400-A, 400-B Communication range 401 Carrier sense range 402 Assumed interference range 403 Information collection range 5 Peripheral radio receiver 6, 6-A, 6-B Peripheral radio signal N Noise P _CS carrier Sense level P _N noise power P _TH information determination threshold P _rFC desired received power

Claims (8)

A plurality of sensor nodes capable of measuring an observation object independently of each other and transmitting a response signal having a frequency corresponding to a result of the measurement;
A wireless sensor network system comprising a fusion center that receives the response signal transmitted from the sensor node,
The fusion center is
A carrier sense unit for detecting peripheral communication devices other than the plurality of sensor nodes, communicating in a predetermined frequency band used by the fusion center and the sensor node;
A communication condition to avoid interference or causing interference in the frequency band between the peripheral communication devices, is calculated on the basis of the detection result, based on the calculated communication conditions, each of the plurality of sensor nodes, A communication condition calculation unit that separates target sensor nodes that request transmission of the response signal or non-target sensor nodes that do not request transmission of the response signal ;
A request signal generation unit that generates a request signal directed to the target sensor node other than the non-target sensor node among the plurality of sensor nodes ;
A transmission / reception unit for transmitting the generated request signal;
Each of the plurality of sensor nodes is
A transceiver for receiving the request signal;
A response signal generation unit for generating the response signal;
The target sensor node requested to respond transmits the response signal to the fusion center according to the received request signal regardless of the presence / absence of communication by a sensor node other than the wireless sensor network system. The wireless sensor network system according to claim 1 ,
Each sensor node is
A memory for storing a unique number set for itself;
A communication condition detection unit for detecting the communication condition from the received request signal;
The fusion center is
A memory for storing a table in which the unique numbers are associated with the plurality of sensor nodes;
The communication condition calculation unit
As the communication condition, calculate an information collection range in which communication in the frequency band with the peripheral communication device can be performed while avoiding interference or interference,
Based on the information acquisition range, each of the plurality of sensor nodes, further calculates a sensor node separation information for separating said target sensor node or the non-target sensor nodes,
The request signal further includes the sensor node classification information,
The communication condition detection unit detects the sensor node classification information from the request signal,
Each sensor node transmits the response signal only when it is classified as the target sensor node. Wireless sensor network system. The wireless sensor network system according to claim 2 ,
The information collection range includes a first area;
The first region includes a second region;
The plurality of sensor nodes are:
A first sensor node group disposed inside the first region and outside the second region;
A second sensor node group disposed inside the second region,
The transmission power of the request signal that the request signal selectively reaches from the fusion center to both the first sensor node group and the second sensor node group is a first transmission power,
The transmission power of the request signal that the request signal selectively reaches from the fusion center to the second sensor node group is a second transmission power,
The fusion center is
After transmitting the second request signal having the second transmission power toward the second sensor node group, the first having the first transmission power toward the first sensor node group and the second sensor node group. Send a request signal,
The second request signal includes a communication condition in which the second sensor node group ignores the first request signal. Wireless sensor network system. In the wireless sensor network system according to any one of claims 1 to 3 ,
The transmission / reception unit of the sensor node generates and transmits the response signal by an OFDM (Orthogonal Frequency-Division Multiplexing) scheme,
The transmission / reception unit of the fusion center receives the response signal by the OFDM method. Wireless sensor network system. In the wireless sensor network system according to any one of claims 1 to 3,
The wireless sensor network system, wherein the response signal is a tone signal. The fusion center transmitting a request signal to a target sensor node other than the non-target sensor node among the plurality of sensor nodes;
A plurality of sensor nodes receiving the request signal;
Each of the target sensor nodes directs a response signal having a frequency corresponding to the measurement result of the observation target to the fusion center in accordance with the received request signal regardless of presence / absence of communication by a sensor node other than itself. Sending and
The fusion center receiving a plurality of the response signals transmitted from the target sensor node,
Sending the request signal comprises:
Detecting presence / absence of communication by peripheral communication devices other than the plurality of sensor nodes, which are communicating in a predetermined frequency band used by the fusion center and the sensor node;
Calculating, based on the communication conditions to avoid interference or causing interference in the frequency band between the peripheral communication devices, wherein the detection result,
Separating each of the plurality of sensor nodes into the target sensor node that requests transmission of the response signal or the non-target sensor node that does not request transmission of the response signal based on the calculated communication condition ; ,
Generating a request signal directed to the target sensor node other than the non-target sensor node among the plurality of sensor nodes . The information collection method according to claim 6,
The step of calculating the communication condition includes:
Calculating an information collection range capable of communicating while avoiding interference or interference in the frequency band with the peripheral communication device as the communication condition;
Calculating sensor node classification information for classifying each of the plurality of sensor nodes into the target sensor node or the non-target sensor node based on the information collection range;
Including
The request signal further includes the sensor node classification information,
Transmitting the response signal comprises:
Detecting the communication condition from the request signal;
Detecting the sensor node classification information from the request signal;
Transmitting the response signal only when each of the sensor nodes is classified as the target sensor node;
including
Information collection method. The program which implement | achieves the step which the said fusion center performs among the steps contained in the information collection method of Claim 6 or 7 by the processor of the said fusion center.

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