JP7609399B2 - Sensor network system, sink, node, data communication processing method and program - Google Patents

Description

The present invention relates to a sensor network system, a sink and a node used in the sensor network system, a data communication processing method using the sensor network system, and a program used in the sink and the node.

A sensor network system is known that collects and processes data acquired at multiple locations scattered across a given area. The sensor network system comprises multiple sensor node devices (hereinafter abbreviated as "nodes") and a single sink server device (hereinafter abbreviated as "sink"). The multiple nodes are arranged at multiple locations, and each node acquires data at its location and transmits it to the sink. The sink processes the multiple data collected from the multiple nodes to obtain overall data about the given area.

Normally, to prevent interference, the sink communicates wirelessly with one node at a time. In this case, data collection can be done digitally, but in order for the sink to collect data from all nodes, it needs the same number of time slots as the total number of nodes. In other words, as the total number of nodes increases, the time it takes to collect data at one time also increases.

In a system like LoRa (Long Range), which is a type of LPWA (Low Power, Wide Area), multiple nodes share the same competing communication channel to transmit to a sink, so as the number of nodes increases, not only does it take longer to collect data, but the frequency of data collisions also increases.

In some cases, the sink does not need the individual data acquired by each node to obtain overall data for a given area. For example, to find out the temperature in a certain area, it is sufficient to know the average temperature acquired at multiple points. This average can be calculated by knowing the total number of nodes that successfully communicated with the sink and the sum of the data collected from these nodes.

In relation to the above, Non-Patent Document 1 (Wanchun Liu et al., "Over-the-Air Computation Systems: Optimization, Analysis and Scaling Laws," IEEE Transaction on Wireless Communications, 2020, pp. 1536-1276) discloses Over-the-Air Computation Systems (hereinafter abbreviated as "AirComp").

In AirComp, when multiple nodes send data to a single sink, they communicate using analog signals. All nodes send data at the same time, and the sink receives this data all at once, allowing one data collection to be performed in a single time slot. Also, by receiving multiple analog signals simultaneously, the sink can obtain the sum of these data values without performing any calculations.

In this case, it is preferable that the power or field strength of the analog signal representing the data arriving from each node to the sink is proportional to the analog value of the data. However, the channel coefficient and channel gain between the node and each node differ depending on the distance between them and the communication environment. Therefore, each node adjusts the transmission power appropriately depending on the channel gain between the node and the sink. In this way, the power or field strength of the analog signal arriving at the sink is proportional to the analog value of the data.

However, in practice, there is an upper limit to the transmission power of a node operating with limited power. When the channel gain is below a certain threshold, even if a node transmits an analog signal using its maximum transmission power, the power is not proportional to the analog value of the data. As a result, distortion occurs in the analog data received on the multi-access channel, and the accuracy of the sum of the analog values obtained by the sink may decrease.

Wanchun Liu et al., “Over-the-Air Computation Systems: Optimization, Analysis and Scaling Laws”, IEEE Transaction on Wireless Communications, 2020, pp. 1536-1276

A sensor network system, sink, node, data communication processing method and program are provided that improve the efficiency and accuracy of data collection. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

Below, the means for solving the problem are explained using the numbers used in (Mode for carrying out the invention). These numbers are added to clarify the correspondence between the description in (Claims) and (Mode for carrying out the invention). However, these numbers should not be used to interpret the technical scope of the invention described in (Claims).

According to one embodiment, the sensor network system (100) includes a plurality of nodes (1) and a sink (2). Each of the plurality of nodes (1) acquires data (x). The sink (2) collects the data (x) from the plurality of nodes (1) for each data collection period including a plurality of time slots. The sink (2) includes a first transmission control device (223). The first transmission control device (223) transmits a beacon including information representing a channel gain threshold (g _th ) to the plurality of nodes (1) in each of the plurality of time slots. Each of the plurality of nodes (1) includes a channel gain detection device (122) and a second transmission control device (123). The channel gain detection device (122) detects a channel gain (g _h ) between the node (1) and the sink (2) based on the beacon. The second transmission control device (123) transmits the data (x) to the sink (2) in a time slot that satisfies a predetermined communication condition only once during the data collection period. The communication condition is met if the channel gain (g _h ) is greater than or equal to the channel gain threshold (g _th ) and the time slot is the last time slot of the data collection period.

According to one embodiment, the sink (2) includes a parameter calculation device (221), a transmission control device (223), a reception control device (224), and a post-processing device (225). The parameter calculation device (221) calculates the total number (N) of a plurality of time slots included in a data collection period based on the total number (K) of a plurality of external nodes (1), and calculates a channel gain threshold (g _th ) and a target value (α) of a signal amplitude based on the total number (N) of a plurality of time slots. The transmission control device (223) transmits a beacon including information representing the total number (N) of a plurality of time slots, a channel gain threshold (g _th ), and a target value (α) of a signal amplitude to the plurality of nodes (1) in each of the plurality of time slots. The reception control device (224) receives a plurality of data (x) transmitted from the plurality of nodes (1) in response to the beacon. The post-processing device (225) obtains the sum of the plurality of data (x) received during the data collection period.

According to one embodiment, the node (1) includes a sensing device (15), a beacon receiving device (121), a channel gain detection device (122), and a transmission control device (123). The beacon receiving device (121) receives a beacon including information representing a channel gain threshold (g _th ) transmitted from an external sink (2) in each of a plurality of time slots included in a data collection period. The channel gain detection device (122) detects a channel gain (g _h ) between the node (1) and the sink (2) based on the beacon. The transmission control device (123) transmits data (x) to the sink (2) in a time slot that satisfies a predetermined communication condition only once during the data collection period. The communication condition is satisfied if the channel gain (g _h ) is equal to or greater than the channel gain threshold (g _th ), and is satisfied if the time slot is the last time slot of the data collection period.

According to one embodiment, the data communication processing method includes each of the plurality of nodes (1) acquiring data (x) (S202), and transmitting a beacon including information representing a channel gain threshold (g _th ) from the sink (2) to the plurality of nodes (1) in each of a plurality of time slots included in a data collection period (S106). The data communication processing method further includes each node (1) detecting a channel gain (g _h ) between the node (1) and the sink (2) based on the beacon (S208). The data communication processing method further includes each node (1) transmitting the data (x) to the sink (2) in a time slot that satisfies a predetermined communication condition only once during the data collection period (S211). The data communication processing method further includes the sink (2) collecting the data (x) from the plurality of nodes (1) for each data collection period (S107). The communication condition is satisfied if the channel gain (g _h ) is equal to or greater than the channel gain threshold (g _th ), and is satisfied if the time slot is the last time slot of the data collection period.

According to one embodiment, in a program for implementing processing by being executed by a calculation device (22) of a sink (2), the processing includes calculating (S102) a total number (N) of a plurality of time slots included in a data collection period based on a total number (K) of a plurality of external nodes (1), and calculating (S102) a channel gain threshold (g _th ) and a target value (α) of a signal amplitude based on the total number (N) of a plurality of time slots. The processing further includes transmitting (S106) a beacon including information representing the total number (N) of a plurality of time slots, a channel gain threshold (g _th ), and a target value (α) of a signal amplitude, for each of the plurality of time slots, to the plurality of nodes (1). The processing further includes receiving (S107) a plurality of data (x) transmitted from the plurality of nodes (1) in response to the beacon. The processing further includes obtaining (S109) a sum of the plurality of data (x) received during the data collection period.

According to one embodiment, in a program for implementing processing by being executed by a computing device (12) of a node (1), the processing includes acquiring data (x) (S202) and receiving a beacon including information representing a channel gain threshold (g _th ) transmitted from an external sink (2) in each of a plurality of time slots included in a data collection period (S203). The processing further includes detecting a channel gain (g _h ) between the sink (2) based on the beacon (S208). The processing further includes transmitting the data (x) to the sink (2) in a time slot that satisfies a predetermined communication condition only once during the data collection period (S211). The communication condition is satisfied if the channel gain (g _h ) is equal to or greater than the channel gain threshold (g _th ), and is satisfied if the time slot is the last time slot of the data collection period.

According to one embodiment, the efficiency and accuracy of data collection can be improved.

FIG. 1 is a diagram showing an example of the configuration of a sensor network system according to a first related technique. FIG. 2 is a diagram showing an example of an operation of the sensor network system according to the first related art. FIG. 3 is a diagram showing an example of an operation of a sensor network system according to the second related art. FIG. 4 is a diagram showing an example of an operation of the sensor network system according to the second related technique. FIG. 5 is a diagram showing an example of the channel gain, the transmission power, and the reception power coefficient in the sensor network system according to the second related art. FIG. 6 is a diagram showing another example of the channel gain, the transmission power, and the reception power coefficient in the sensor network system according to the second related art. FIG. 7 is a diagram showing an example of an operation of a sensor network system according to the fourth related technique. FIG. 8 is a diagram illustrating an example of a configuration of a sensor network system according to an embodiment. FIG. 9 is a diagram illustrating an example of a configuration of a node according to an embodiment. FIG. 10 is a diagram illustrating an example of a configuration of a sink according to an embodiment. FIG. 11 is a flowchart illustrating an example of an operation of the sink according to an embodiment. FIG. 12A is a portion of a flowchart illustrating an example of an operation of a node according to an embodiment. FIG. 12B is a part of a flowchart illustrating an example of an operation of a node according to one embodiment. FIG. 13 is a diagram illustrating an example of an operation of the sensor network system according to an embodiment. FIG. 14 is a diagram illustrating an example of an operation of the sensor network system according to an embodiment. FIG. 15 is a diagram illustrating an example of channel gain, transmission power, and reception power coefficient in a sensor network system according to an embodiment. FIG. 16 is a graph comparing cumulative distribution functions of transmission power between a sensor network system according to an embodiment and a sensor network system according to a related technique. FIG. 17 is a graph comparing the cumulative distribution function of the mean square error between the received power and the target power between a sensor network system according to an embodiment and a sensor network system according to a related technique.

The following describes embodiments for implementing the sensor network system, sink, node, data communication processing method, and program according to the present invention with reference to the accompanying drawings.

To better understand the embodiment, a sensor network system according to the related art will be described first.

Figure 1 is a diagram showing an example of the configuration of a sensor network system 1000 according to the first related technology. The sensor network system 1000 comprises multiple nodes 101-1 to 101-K and a sink 102. Here, the total number of nodes 101-1 to 101-K is K. When the multiple nodes 101-1 to 101-K are not differentiated from one another, they are collectively referred to as node 101-k or node 101. Here, the branch number k is any integer in the range from 1 to K.

The multiple nodes 101 are arranged at multiple positions in a predetermined area. Each node 101 acquires desired data using a sensor at the position where it is arranged. Each node 101 transmits the acquired data to the sink 102. The timing at which the multiple nodes 101 acquire data and the timing at which they transmit data to the sink 102 may be controlled, for example, based on a clock built into each node 101, or may be controlled based on a wireless signal transmitted to the node 101 from an external sink 102 or the like.

FIG. 2 is a diagram showing an example of an operation of the sensor network system 1000 according to the first related art. The horizontal axis in FIG. 2 indicates time. From time t ₁₀₁ to time t ₁₀₂ , a process P101 is executed in which the first node 101-1 transmits the first data x ₁ to the sink 102. Here, the period from time t ₁₀₁ to time t ₁₀₂ is called the first time slot. Thereafter, in the second time slot from time t ₁₀₃ to time t ₁₀₄ , a process P102 is executed in which the second node 101-2 transmits the second data x ₂ to the sink 102. Similarly, all the nodes 101-k transmit data x _k to the sink 102 one by one in order. In the Kth time slot from time t ₁₀₅ to time t ₁₀₆ , a process P10K is executed in which the Kth node 101-K transmits the Kth data x _K to the sink 102. Thereafter, from time _t107 to time _t108 , a process P100 is executed in which the sink 102 processes data. When the multiple data x ₁ to x _K are not differentiated from one another, they are collectively referred to as data _xk or data x.

As shown in FIG. 2, in the sensor network system 1000 of FIG. 1, the sink 102 collects data x acquired by multiple nodes 101 by wirelessly communicating with one node 101 at a time. In this case, interference between the multiple nodes 101 can be suppressed, and the data x can be collected as a digital signal. On the other hand, in order for the sink 102 to collect data x from all nodes 101, the same number of time slots as the total number K of nodes 101 are required. In other words, as the total number K of nodes 101 increases, the time required to collect data at one time also increases. Depending on the total number K of nodes 101, the time required to collect data at one time may become too long, making it difficult to operate the sensor network system 1000 in a practical manner.

In order for the sink 102 to obtain overall data x for a given area, the individual data x acquired by each node 101 may not be necessary. For example, to check the temperature in a certain area, it is sufficient to know the average temperature value acquired at multiple points. This average value can be calculated by knowing the total number K of nodes 101 and the sum of the data x collected from these nodes 101.

A sensor network system 1000 based on a second related technology that has been improved from this perspective is known. This second related technology is called Over-the-Air Computation Systems (hereinafter abbreviated as "AirComp").

The sensor network system 1000 according to the second related technology by AirComp has multiple nodes 101 and a single sink 102, similar to the configuration example of the sensor network system 1000 according to the first related technology shown in Figure 1.

3 is a diagram showing an example of an operation of the sensor network system 1000 according to the second related art. The first data _x1 is transmitted to the sink 102 as a first analog signal generated by the first node 101-1 with a first transmission power _b1 . At this time, the power of the first analog signal representing the first data _x1 can be expressed as _b1x1 . The operation of the first node _101-1 outputting the first analog signal having power _b1x1 is shown in FIG. ₃ as the operation of a virtual integrator M101.

The amplitude of the first analog signal having power b ₁ x ₁ is attenuated by the amplitude component of the first channel coefficient h ₁ while propagating through free space and being received by the sink 102. The power of the first analog signal received by the sink 102 can be expressed as h ₁ b ₁ x _1. The operation of the free space propagating the first analog signal from the first node 101-1 to the sink 102 is shown as the operation of a virtual integrator M102 in FIG. 3. The channel coefficient h ₁ is expressed as a complex number including a component related to the amplitude and a component related to the phase. Of these, the component related to the amplitude can be calculated by squaring the absolute value of the channel coefficient h 1, and is called the channel gain g _1. The channel gain g ₁ is expressed as a positive real number.

Similarly, the second data x ₂ is transmitted to the sink 102 as a second analog signal having power b ₂ x ₂ generated by the second node 101-2 at the second transmission power b ₂ as shown by the operation of the virtual integrator M201. As shown by the operation of the virtual integrator M202, the amplitude of the second analog signal is attenuated by the amplitude component of the second channel coefficient h ₂ and is received by the sink 102 as a second analog signal having power h ₂ b ₂ x _2. Similarly, the Kth data x _K is transmitted as a Kth analog signal having power b _K x _K generated by the Kth node 101-K at the Kth transmission power b _K as shown by the operation of the virtual integrator M301. As shown by the operation of the virtual integrator M302, the amplitude of the Kth analog signal is attenuated by the amplitude component of the Kth channel coefficient _hK , and is received by the sink _{102 as a Kth analog signal having power hKbKxK . In} this manner, all data x are transmitted as analog signals by all nodes 101, respectively, to the sink 102, propagate through free space, and are received by the sink 102.

Fig. 4 is a diagram showing an example of an operation of the sensor network system 1000 according to the second related art. The horizontal axis in Fig. 4 represents time. First, in a period from time t ₂₀₁ to time t ₂₀₂ , the sink 102 transmits a beacon to all the nodes 101 as process P201. Next, in a period from time t ₂₀₃ to time t ₂₀₄ , in response to the beacon, the node 101 transmits data x to the sink 102 as process P202, and the sink 102 receives the data x and processes the received data x.

In process P202, all analog signals having powers _b1x1 , _b2x2 , ... _{, bKxK} are simultaneously transmitted from all nodes 101 and simultaneously received by sink ₁₀₂ as all analog signals having powers _{h1b1x1 , h2b2x2} , _... , _{hKbKxK .} At this time _, sink 102 obtains the sum of powers _h1b1x1 , _{h2b2x2 ,} ... _{, hKbKxK} possessed by all analog _signals . In Fig _. 3 _{, the} operation of obtaining _this sum is shown as _the operation of a virtual adder _A100 .

In FIG. 3, noise generated in wireless communication from node 101 to sink 102 is shown as noise n that is added to the total power of the analog signal by adder A100.

In addition, in process P202 of FIG. 4, the sink 102 performs a predetermined post-processing on the sum of the power of the received analog signals. As an example of the post-processing, the sink 102 may obtain an average value of the power of the received analog signals by dividing the sum of the power of the received analog signals by the total number of received analog signals. In FIG. 3, the post-processing by the sink 102 is shown as an operation of a virtual integrator M100 multiplying the sum of the power of the received analog signals by a coefficient a.

Here, if the coefficient a is the reciprocal of the total number _K of nodes 101, the integrator M100 can calculate _the average value of _{power h1b1x1} , _{h2b2x2 ,} . . . _{, hKbKxK .}

Furthermore, for any integer k between 1 and K, if all of the amplitude components of the reception power _{coefficient hkbk obtained} by multiplying the transmission power _bk and the channel coefficient _hk are the same constant α, and the coefficient a is the inverse (1/Kα) of the product Kα obtained by multiplying the total number K of nodes 101 by the constant α, then the integrator M100 can calculate the average value of the data _x1 to _xK acquired by all of the nodes 101.

Fig. 5 is a diagram showing an example of the channel coefficient _hk , transmission power _bk, and reception power _{coefficient hkbk} in the sensor network system 1000 according to the second related technique. In Fig. 5, the horizontal axis shows the node 101 number corresponding to the data _xk transmitted by each node 101, and the vertical axis shows the reception power coefficient _hkbk in logarithm. However, strictly speaking, Fig. 5 shows the amplitude component as the reception power coefficient _hkbk . The reception power coefficient _hkbk in each node 101- _k is the _quotient obtained by _dividing the _{power hkbkxk} of the analog signal received by the sink ₁₀₂ by the analog _{value representing the data xk ,} and is equal to the product _hkbk obtained by multiplying the transmission power _bk and the channel coefficient _hk . In each of the bar graphs in Fig. 5, the length of the black portion on the lower side indicates the value of the amplitude component of the channel coefficient _hk , i.e., the value of the channel gain _gk , and the length of the white portion on the upper side indicates the value of the transmission power _bk . For ease of understanding, the numbers of the nodes 101 on the horizontal axis of Fig. 5 are arranged from left to right in ascending order of the channel coefficient _hk .

Each node 101-k appropriately adjusts the transmission power b _k based on the channel coefficient h _k and the constant α between the sink 102. In this way, in each node 101-k, the amplitude component of the product h _k b _k obtained by multiplying the transmission power b _k and the channel coefficient h _k can be made equal to the constant α.

However, the transmission power b _k of the node 101 has an upper limit due to the physical performance of the node 101. Therefore, when the amplitude component of the channel coefficient h _k falls below a predetermined threshold, even if the node 101-k sets the transmission power b _k to the maximum transmission power, the amplitude component of the product h _k b _k obtained by multiplying the transmission power b _k and the channel coefficient h _k may be smaller than the constant α.

FIG. 6 is a diagram showing another example of the channel coefficient h _k , the transmission power b _k and the reception power coefficient h _k b _k in the sensor network system 1000 according to the second related technique. In the example of FIG. 6, in the five nodes 101 from the first node 101-1 that acquired the first data x ₁ to the fifth node 101-5 that acquired the fifth data x ₅ , the amplitude component of the channel coefficient h _k is too low, so even if the transmission power b _k is set to the maximum transmission power, the amplitude component of the reception power coefficient h _k b _k obtained by multiplying the transmission power b _k and the channel coefficient h k is smaller than the constant α. Therefore, the insufficient portion from the amplitude component of the reception power coefficient h _k b _k to the constant _α occurs as distortion in the calculation result of the adder A100 in FIG. 3. In other words, the greater the distortion shown in FIG. 6, the lower the accuracy of the result of the process P202 by the sink 102.

The sensor network system 1000 according to the third related technology, which is an improvement of the second related technology from the viewpoint of suppressing the occurrence of distortion, will be described. The sensor network system 1000 according to the third related technology is also configured in the same manner as in FIG. 1. However, unlike the second related technology, its application is limited to federated learning. In other words, the information transmitted from the node 101 to the sink 102 is not the data x itself acquired by each node 101, but a model obtained by machine learning for predicting data x to be acquired in the future based on multiple data x acquired by each node 101 in the past. Each node 101 updates its own model every time it acquires data x, and transmits the latest model to the sink 102 in response to a request from the sink 102. The sink 102 transmits a model obtained by averaging the models received from multiple nodes 101 to each node 101.

Here, the sink 102 does not necessarily receive models from all the nodes 101 every time. That is, among all the nodes 101, only some of the nodes 101 whose channel gain g _k at a certain time is equal to or greater than a desired threshold may transmit models to the sink 102. That is, even if the positions of the node 101 and the sink 102 are fixed, the communication environment therebetween changes dynamically with time. This change includes, for example, dynamic changes in channel coefficients due to the influence of channel fading. Therefore, in the sensor network system 1000 according to the third related technology, only the node 101 whose channel gain g _k between the node 101 and the sink 102 at a certain time is greater than a predetermined threshold transmits a model to the sink 102 at that time. In this way, the occurrence of the distortion shown in FIG. 6 can be suppressed.

However, since not all nodes 101 will necessarily transmit data x to the sink 102 at the same time, this cannot be directly applied to the second related technology.

A sensor network system 1000 according to a fourth related technique, which is an improvement of the first related technique from the viewpoint of suppressing the influence of channel fading, will be described with reference to FIG. 7. FIG. 7 is a diagram showing an example of an operation of the sensor network system 1000 according to the fourth related technique. FIG. 7 includes a first graph G101, a second graph G102, and a third graph G103. The first graph G101, the second graph G102, and the third graph G103 correspond to the first node 101-1, the second node 101-2, and the third node 101-3, respectively. In each graph in FIG. 7, the horizontal axis represents time, and the vertical axis represents the channel gain g _k . In each graph, a black bar graph represents a value of the channel gain g _k that is less than a predetermined threshold. Also, a white bar graph represents a value of the channel gain g _{k that} is equal to or greater than a predetermined threshold.

As shown in FIG. 7, in the fourth related technology, in order to suppress the effects of channel fading, the timing at which each node 101 transmits data x to the sink 102 is controlled. Basically, it is preferable to centrally control all nodes 101 so that only one node 101 transmits at a time. However, it is difficult to completely control a large number of nodes 101, and as shown in the example of FIG. 7, a time t307 may occur at which none of the nodes 101 transmits data x. Conversely, a time t308 may occur at which multiple nodes 101 transmit data x simultaneously.

(Embodiment)
In the sensor network system 100 according to an embodiment, the efficiency and accuracy of data collection are improved in consideration of the above-mentioned first related technique, second related technique, third related technique, and fourth related technique.

In terms of efficiency, the first related technology required the same number of time slots as the total number K of nodes 101 in one data collection period. On the other hand, in one embodiment, all nodes transmit to the sink in a number of time slots that is much smaller than the total number K of nodes 1 in one data collection period.

Also, in terms of accuracy, in the second related technology, each node 101 is provided with only one opportunity to transmit data x to the sink 102, so if the desired communication conditions are not met at the moment the data x is transmitted because the channel gain g _k is too low, for example, distortion may occur in part of the data x received by the sink 102. On the other hand, in one embodiment, each node is provided with multiple opportunities to transmit data x to the sink, so that if the desired communication conditions are not met in a certain time slot, there is a possibility that data transmission to the sink can be performed when the desired communication conditions are met in a subsequent time slot. As a result, the probability that distortion occurs in part of the data x received by the sink is suppressed, and the accuracy of data collection is improved.

Figure 8 is a diagram showing an example of a configuration of a sensor network system 100 according to an embodiment. The sensor network system 100, like the sensor network system 1000 in Figure 1, comprises multiple nodes 1-1 to 1-K and a sink 2. Here, the total number of nodes 1-1 to 1-K is K. When the multiple nodes 1-1 to 1-K are not differentiated from one another, they are collectively referred to as node 1-k or node 1. Here, the number k is any integer in the range from 1 to K.

The multiple nodes 1 are arranged at multiple positions in a predetermined area. Each node 1 acquires predetermined data x by a sensor at the position where it is arranged. Each node 1 transmits the acquired data x to the sink 2. The timing at which the multiple nodes 1 acquire the data x may be controlled, for example, based on a clock built into each node 1, or may be controlled based on a wireless signal transmitted to the node 1 from an external sink 2 or the like. The timing at which the multiple nodes 1 transmit the data x to the sink 2 is controlled based on a beacon transmitted from the sink 2, as described below.

Figure 9 is a diagram showing an example of a configuration of a node 1 according to an embodiment. The node 1 includes a bus 10, a computing device 12, a memory device 13, an external storage device 14, and a sensing device 15. The node 1 further includes an antenna 112 and a power supply device (not shown). The computing device 12, the memory device 13, the external storage device 14, and the sensing device 15 are connected to each other via the bus 10.

The input/output device 11 transmits and receives data x to and from an external device such as the sink 2. The calculation device 12 executes a program stored in the memory device 13 to perform a predetermined process. The memory device 13 stores the program and data and provides them to the calculation device 12. The external storage device 14 reads out the program and data stored in a non-transitory recording medium 141 and stores them in the memory device 13. The sensing device 15 acquires predetermined data x at the position where the node 1 is located under the control of the calculation device 12.

The input/output device 11 includes a communication device 111. The communication device 111 is connected to an antenna 112. The calculation device 12 includes a beacon receiving device 121, a channel gain detection device 122, and a transmission control device 123.

The communication device 111 performs wireless communication with an external device such as the sink 2 via the antenna 112. The beacon receiving device 121 is a virtual device that receives a beacon transmitted from the sink 2 by the calculation device 12 executing a predetermined program. The channel gain detection device 122 is a virtual device that detects a channel coefficient _hk in wireless communication between the node 1 and the sink 2 and calculates a channel gain gk that is an amplitude component of the channel coefficient _hk by the calculation device 12 executing a predetermined program. The transmission control device 123 is a virtual device that controls the communication device 111 to transmit a signal indicating data x to the sink 2 by the calculation device 12 executing a predetermined program.

Figure 10 is a diagram showing an example of the configuration of the sink 2 according to one embodiment. The sink 2 includes a bus 20, a computing device 22, a memory device 23, and an external storage device 24. The sink 2 further includes an antenna 212 and a power supply device (not shown). The computing device 22, the memory device 23, and the external storage device 24 are connected to each other via the bus 20.

The input/output device 21 transmits and receives data x to and from an external device such as node 1. The calculation device 22 executes a program stored in the memory device 23 to perform a predetermined process. The memory device 23 stores the program and data and provides them to the calculation device 22. The external storage device 24 reads out the program and data stored in a non-transitory and tangible recording medium 241 and stores them in the memory device 23.

The input/output device 21 includes a communication device 211. The communication device 211 is connected to an antenna 212. The calculation device 22 includes a parameter calculation device 221, a beacon generation device 222, a transmission control device 223, a reception control device 224, and a post-processing device 225.

The communication device 211 performs wireless communication with an external device such as node 1 via the antenna 212. The parameter calculation device 221 is a virtual device that performs an operation of calculating a predetermined parameter by the calculation device 22 executing a predetermined program. The beacon generation device 222 is a virtual device that performs an operation of generating a beacon by the calculation device 22 executing a predetermined program. The transmission control device 223 is a virtual device that performs an operation of controlling the communication device 211 to transmit a beacon to node 1 by the calculation device 22 executing a predetermined program. The reception control device 224 is a virtual device that performs an operation of controlling the communication device 211 to receive a signal transmitted from node 1 by the calculation device 22 executing a predetermined program. The post-processing device 225 is a virtual device that performs an operation of processing to consolidate signals received from node 1 by the calculation device 22 executing a predetermined program.

Figure 11 is a flowchart showing an example of an operation of sink 2 according to one embodiment. Figures 12A and 12B are each a part of a flowchart showing an example of an operation of node 1 according to one embodiment. An example of the operation of sensor network system 100 according to one embodiment will be described with reference to Figures 11, 12A, and 12B.

In step S101 of Fig. 11, the sink 2 starts its operation. In step S102, the parameter calculation device 221 of the sink 2 calculates parameters. The calculated parameters include the total number N of time slots included in one data collection period, a channel gain threshold g _th , and a target value α of the signal amplitude. Here, the total number N is also the maximum value N of the number assigned to the time slots included in one data collection period.

As an example, the parameter calculation device 221 first determines the total number N of time slots. The total number N of time slots may be selected, for example, from among integers that are sufficiently smaller than the total number K of nodes 1. The parameter calculation device 221 then calculates a channel gain threshold g _th based on the total number N of time slots. The parameter calculation device 221 then calculates a target value α of the signal amplitude based on the total number N of time slots and the channel gain threshold g _th .

In step S103, the sink 2 initializes the slot number of the time slot. As an example, the slot number is set to zero. In step S104, the calculation device 22 of the sink 2 increments the slot number. In step S105, the beacon generation device 222 of the sink 2 generates a beacon based on the total number N of time slots, the channel gain threshold g _th , and the target value α of the signal amplitude. The beacon is generated to include information representing the total number N of time slots, the channel gain threshold g _th , and the target value α of the signal amplitude. The beacon may be generated to further include information representing the current slot number. In step S106, the transmission control device 223 of the sink 2 controls the communication device 211 to transmit a beacon toward the node 1.

Meanwhile, in step S201 of FIG. 12A, each node 1 starts operating. Then, in step S202, the sensing device 15 of each node 1 acquires data x _k under the control of the calculation device 12. The acquired data x _k is stored in the memory device 13 of the node 1. In step S203, the calculation device 12 determines whether the beacon receiving device 121 has received a beacon from the sink 2. Here, if the beacon has not been received (No), step S203 is executed again. In other words, step S203 is repeated until the beacon is received. On the other hand, if the beacon has been received (Yes), step S204 is executed.

In step S204, the beacon receiving device 121 acquires parameters from the received beacon. The acquired parameters include the total number N of time slots included in one data collection period, the channel gain threshold g _th , and the target value α of the signal amplitude. In step S205, the beacon receiving device 121 judges whether the currently received beacon is the first beacon received in the currently received data collection period. This judgment may be made, for example, based on information included in the beacon. In this case, the beacon generating device 222 of the sink 2 generates a beacon so as to include information indicating whether the currently received beacon is the first beacon. If the currently received beacon is the first beacon (Yes), the slot number and the transmitted flag are initialized in step S206, and then step S207 in FIG. 12B is executed. Here, the initialized slot number is set to, for example, zero. Also, the initialized transmitted flag is set to "not transmitted". On the other hand, if it is not the first beacon (No), step S207 is executed without executing step S206.

In step S207 of Fig. 12B, the calculation device 12 of the node 1 increments the slot number. In step S208, the channel gain detection device 122 detects the channel coefficient _hk in the wireless communication between the sink 2 and the node 1 based on the power of the received beacon, and calculates the channel gain _gk . For example, information indicating the transmission power of the beacon transmitted by the sink 2 is stored in advance in the memory device 13 of the node 1, and the channel coefficient _hk in the wireless communication between the sink 2 and the node 1 is calculated based on this transmission power and the power of the beacon actually received, and the channel gain _gk, which is an amplitude component related to attenuation, is calculated from this channel coefficient _hk , thereby detecting the channel gain _gk .

In step S209, the transmission control device 123 of the node 1 determines whether or not the communication conditions for transmitting the data x to the sink 2 are satisfied. Specifically, if a first condition is satisfied that the current transmission flag is “not transmitted” and a second condition is satisfied that the detected channel gain g _k is equal to or greater than a threshold value g _th or the slot number is the maximum value N, the communication conditions are determined to be satisfied.

In other words, if the current transmission flag is "transmitted", it is determined that the communication conditions are not met. This determination makes it possible to realize control so that one node 1 transmits data x to the sink 2 only once during one data collection period.

Even if the current transmission flag is "not transmitted", it is determined that the communication conditions are not satisfied if the detected channel gain g _k is less than the threshold value g _th and the slot number is less than the maximum value N. This determination makes it possible to realize control to postpone the transmission of data x to the sink 2 to the next or subsequent timeslot if the channel gain g _k has not reached the threshold value g _th in the current timeslot, and control to forcibly transmit data x to the sink 2 in the current timeslot even if the channel gain g _k has not reached the threshold value g _th if the current timeslot is the last timeslot of the current data collection period.

In other words, under the precondition that node 1 transmits data x to sink 2 only once during a data collection period in a time slot that satisfies a predetermined communication condition, this predetermined communication condition is satisfied if the channel gain g _k is equal to or greater than a channel gain threshold g _th and if the time slot is the last time slot of the data collection period.

If it is determined that the communication conditions are met (Yes), steps S210 and S211 are executed, and then step S212 is executed. Conversely, if it is determined that the communication conditions are not met (No), steps S210 and S211 are not executed, and step S212 is executed.

In step S210, the calculation device 12 of the node 1 calculates the transmission power b _k based on the target value α of the signal amplitude and the channel coefficient h _k . Specifically, the quotient obtained by dividing the target value α of the signal amplitude by the channel coefficient h _k is calculated as the transmission power b _k . In step S211, the transmission control device 123 transmits the data x to the sink 2 and sets the transmission completion flag to "transmitted". Here, the data x _k to be transmitted is transmitted to the sink 2 as an analog signal having power b _k x _k .

In step S212, the computing device 12 of node 1 determines whether the current slot number is the maximum value N. If the current slot number is the maximum value N (Yes), step S213 is executed and then step S202 is executed again. If the current slot number is not the maximum value N (No), step S203 is executed again without executing step S213.

In this way, the node 1 generates an analog signal representing the data _xk in response to the beacon transmitted by the sink 2 and transmits it to the sink 2. The reception control device 224 of the sink 2 receives the data _xk as this analog signal by controlling the communication device 211 in step S107 of FIG.

Here, there may be a plurality of nodes 1 that transmit analog signals to the sink 2 in response to a beacon in the same time slot. In this case, the reception control device 224 of the sink 2 receives a plurality of data _xk as a plurality of analog signals. This operation will be described with reference to FIG.

13 is a diagram showing an example of an operation of the sensor network system 100 according to an embodiment. In step S211, the first data x ₁ is transmitted to the sink 2 as a first analog signal generated by the transmission control device 123 of the first node 1-1 with a first transmission power b _1. At this time, the power of the first analog signal representing the first data x ₁ can be expressed as b ₁ x _1. In FIG. 13, the operation of the first node 1-1 outputting the first analog signal having power b ₁ x ₁ is shown as the operation of a virtual integrator M11.

The power of the first analog signal having power b ₁ x ₁ attenuates by a first channel coefficient h ₁ before it reaches and is received by the sink 2. The power of the first analog signal received by the sink 2 can be represented as h ₁ b ₁ x _1. The operation of free space propagating the first analog signal from the first node 1-1 to the sink 2 is shown in FIG. 13 as the operation of a virtual integrator M12.

There is a case where another node 1 operates in the same time slot as the time slot in which the first node 1-1 operates as described above as the operation of the integrator M11 and the integrator M12. In this case, for example, the i-th data x _i is generated by the transmission control device 123 of the i-th node 1-i with the i-th transmission power _bi and transmitted to the sink 2 as the i-th analog signal having power _bi x _i . Also, the i-th analog signal is attenuated by the i-th channel coefficient h _i , and arrives at the sink 2 as the i-th analog signal having power h _i bi _{x i and} is received.

At this time, the sink 2 simultaneously receives two analog signals transmitted by the first node 1-1 and the i-th node 1-i through the multi-access channel. Here, the sink 2 may receive these two analog signals as one analog signal having a power that is the sum of the power h ₁ b ₁ x ₁ and the power h _i b _i x _i of these two analog signals. The operation of obtaining this sum is shown in FIG. 13 as the operation of a virtual adder A1. In FIG. 13, noise generated in the wireless communication from the first node 1-1 and the i-th node 1-i to the sink 2 is shown as noise n ₁ that is added to the sum of the power of the analog signals by the adder A1.

Note that, although the case where two nodes 1 transmit analog signals to the sink 2 in one time slot has been described here, this is merely an example, and the number of nodes 1 may be less than two or more than two. The operation of another node 1 transmitting an analog signal to the sink 2 in another time slot will be described later.

After the reception control device 224 of sink 2 receives data x from node 1, in step S108 of FIG. 11, the calculation device 22 of sink 2 determines whether the current slot number is less than the maximum value N.

If the current slot number is less than the maximum value N in step S108 (Yes), sink 2 executes steps S104 to S107 again. At this time, node 1 executes steps S203 in FIG. 12A to step S211 in FIG. 12B again. As a result, among nodes 1 that did not transmit data x to sink 2 in the same time slot as the previous time because the communication conditions were not met, nodes 1 that satisfy the communication conditions in the current time slot transmit data x to sink 2.

Here, referring again to FIG. 13, the transmission process by the virtual integrator M31 in another time slot and the reception process by the virtual integrator M32 and the virtual adder A2 will be described. That is, in the example of FIG. 13, similar to the case of the first node 1-1 and the i-th node 1-i in the past time slot, in the current time slot, the j-th node 1-j and the K-th node 1-K have satisfied the communication conditions and are transmitting data x to the sink 2, and the sink 2 is receiving these data x simultaneously. In the current time slot, the case where two nodes 1 transmit analog signals to the sink 2 has been described, but this is merely an example, and the number of nodes 1 may be less than two or more than two.

Furthermore, referring again to FIG. 13, the transmission process by the virtual integrator M21 in yet another time slot and the reception process by the virtual integrator M22 and the virtual adder A3 will also be described. That is, in the example of FIG. 13, similar to the case of the first node 1-1 and the i-th node 1-i in the past time slot, and similar to the case of the j-th node 1-j and the K-th node 1-K in the other time slot described above, in the current time slot, the k-th node 1-k and the K-1-th node 1-(K-1) have satisfied the communication conditions and are transmitting data x to the sink 2, and the sink 2 is receiving these data x simultaneously. In the current time slot, the case where two nodes 1 transmit analog signals to the sink 2 has been described, but this is merely an example, and the number of nodes 1 may be less than two or more than two.

If the current slot number is not less than the maximum value N in step S108 of FIG. 11 (No), execute steps S109 and S110, execute steps S102 and S103 again, and then execute step S104 again.

In step S109, since all time slots included in the current data collection period have ended, the post-processing device 225 of sink 2 performs post-processing to consolidate the collected data x. Here, as an example, a case where the average value of the data x collected from node 1 is calculated by this post-processing will be described with reference to FIG. 13.

The data x received for each time slot is stored in the memory device 23 as the sum of the data x received in each time slot. In the example of Fig. 13, the output value of the virtual adder A1 is _h1b1x1 + _hbixi . Here, as described above, _the transmission powers _b1 , _bi and _the channel _{coefficients h1 , h1 satisfy} the relationship that the amplitude component of _h1b1 = the amplitude component of _hbi = the target value _α of the signal amplitude. Therefore, the output value of the virtual adder _A1 is equal to α( _x1 + _xi ).

The post-processing unit 225 multiplies this output value by a coefficient a, which is set equal to 1/(Kα). In Fig. 13, this multiplication by the post-processing unit 225 is shown as post-processing by a virtual integrator M13. The output value _r1 of the virtual integrator M13 is equal to ( _x1 + _xi )/K.

The post-processing device 225 performs similar post-processing on the sum of the data x received in all time slots. As a result, in the example of Fig. 13, ( _xj + _xK )/K is obtained as the output value _r2 of the virtual integrator M23, and ( _xk + _xK-1 )/K is obtained as the output value _rN of the virtual integrator M33.

Furthermore, the post-processing device 225 calculates the sum r of these output values r ₁ , r ₂ , ..., r _N. As a result, (1/K)Σx is obtained as the sum r. This value is the average value of the data x collected from K nodes 1. In the example of Fig. 13, the process of calculating this sum is shown as post-processing by a virtual adder A0.

As a modification of the configuration shown in FIG. 13, instead of the three virtual integrators M13, M23, and M33 connected in front of the virtual adder A0 in post-processing, another virtual integrator may be placed in the rear stage of the virtual adder A0. In other words, the average value of data x can be obtained by first obtaining the sum of the outputs of the three virtual adders A1, A2, and A3, and then multiplying this sum by the coefficient a. As yet another modification, the other virtual integrator may be removed from the configuration of the above modification. In this case, the sum of data x is obtained instead of the average value of data x.

In step S110, all processing performed during the current data collection period has been completed, so sink 2 moves on to the next data collection period and executes step S102 again.

The overall operation of the sensor network system 100 according to the embodiment described above will be explained with reference to FIG. 14.

FIG. 14 is a diagram showing an example of an operation of the sensor network system 100 according to an embodiment. The horizontal axis of FIG. 14 indicates time, and the period from time t ₀₁ to time t ₀₄ corresponds to one data collection period. The period from time t ₀₁ to time t ₀₄ is a first time slot. In the first time slot, a process P1 is executed in which the sink 2 transmits a beacon to the node ₁ during the period from time t ₀₁ to time t _02. Next, in the first time slot, a process P2 is executed in which the node 1, whose communication condition is satisfied, transmits data x to the sink 2 to obtain the output value r ₁ of FIG. 13 in response to the beacon of the process P1 during the period from time t 03 to time t ₀₄ .

Similarly, the period from time _t05 to time _t08 is the second time slot. In the period from time _t05 to time _t06 , a process P3 is executed in which the sink 2 transmits a beacon to the node 1. In the period from time _t07 to time _t08 , the node 1, which has not transmitted data x to the sink 2 in the first time slot and for which the communication condition is satisfied, transmits data x to the sink 2 in response to the beacon of the process P3 to obtain the output value _r2 in FIG. 13 .

Similarly, the period from time _t09 to time _t12 is the Nth time slot. In the period from time _t09 to time _t10 , a process P5 is executed in which the sink 2 transmits a beacon to the node 1. In the period from time _t11 to time _t12 , a process P6 is executed in which all nodes 1 that have not transmitted data x to the sink 2 in the previous time slots transmit data x to the sink 2 to obtain the output value _rN in Fig. 13 in response to the beacon in the process P5. In the process P6, the post-processing performed in step S109 in Fig. 11 may be further executed.

In this way, in the sensor network system 100 according to one embodiment, one data collection period is divided into multiple time slots, and in each time slot, multiple nodes 1 simultaneously transmit data x to the sink 2 in response to the same beacon transmitted from the sink 2. Therefore, unlike the first related technology, it is possible to set the total number of multiple time slots included in one data collection period to be much less than the total number K of nodes 1.

With reference to Fig. 15, it will be described how the accuracy of data x collected by the sink 2 from the node 1 is improved in the sensor network system 100 according to an embodiment. Fig. 15 is a diagram showing an example of the channel coefficient _hk , transmission power _bk, and reception power coefficient _hkbk in the sensor network system ₁₀₀ according to an embodiment. As in Figs. 5 and 6, in Fig. 15, the horizontal axis indicates the number of the node 1 corresponding to the data _xk transmitted by each node 1, and the vertical axis indicates the amplitude component of the reception power _{coefficient hkbk} in logarithm.

However, the numbers of the nodes 1 in Fig. 15 are arranged from left to right in ascending order of the amplitude component of the channel coefficient _hk in the first time slot, regardless of the numbers of the nodes 1 in Fig. 13. Here, the length of the dashed bar graphs from the first node 1-1 to the k-th node 1-k represents the amplitude component of the channel coefficient _{hk in the first time slot. Furthermore, in all the nodes 1, the length of the black bar graph represents the value of the amplitude component of the channel coefficient hk in} the time slot in which each node 1 transmits data x to the sink 2. Furthermore, in all the nodes 1, the length of the white bar graph represents the value of the transmission power _bk in the time slot in which each node 1 transmits data x to the sink 2.

In the sensor network system 100 according to one embodiment, each node 1 is provided with multiple opportunities to transmit data x to the sink 2 in one data collection period, the number of which is equal to the total number N of time slots. Therefore, the possibility that the communication condition of one node 1 is satisfied in any of the time slots is higher than in the case of the second related technique. This is shown in FIG. 15 by showing that only the fourth node 1-4 among all the nodes 1 transmits data x to the sink 2 using the maximum transmission power in the last N-th time slot without the channel gain g ₄ corresponding to the channel coefficient h ₄ reaching the threshold g _th in all the time slots. As a result, in the sensor network system 100 according to one embodiment, the sink 2 is more likely to have less distortion of the data x collected from the node 1 than in the case of the second related technique, and therefore the accuracy of the data x is improved.

With reference to FIG. 16, a comparison of the cumulative distribution functions of the transmission power of nodes 1 and 101 between a sensor network system 100 according to one embodiment, a modified example of the sensor network system 100 according to one embodiment, and a sensor network system 1000 according to the second related technology will be described.

Figure 16 is a graph comparing the cumulative distribution function of transmission power between a sensor network system 100 according to one embodiment and a sensor network system 1000 according to a related technology. Figure 16 includes a first graph G11 corresponding to the sensor network system 1000 according to a second related technology, a second graph G12 corresponding to the sensor network system 100 according to one embodiment, and a third graph G13 corresponding to a modified example of the sensor network system 100 according to one embodiment. In Figure 16, the horizontal axis represents transmission power, and the vertical axis represents the cumulative distribution function.

The first graph G11, the second graph G12, and the third graph G13 show the results of a computer simulation. Comparing the first graph G11, the second graph G12, and the third graph G13, the transmission power is almost the same.

With reference to FIG. 17, a comparison of the cumulative distribution function of the mean square error between the received power and the target power between the sensor network system 100 according to one embodiment and the sensor network system 1000 according to the second related technology will be described.

FIG. 17 is a graph comparing the cumulative distribution function of the mean square error between the received power and the target power between the sensor network system 100 according to an embodiment and the sensor network system 1000 according to a related technique. FIG. 17 includes a first graph G21 corresponding to the sensor network system 1000 according to the related technique and a second graph G22 corresponding to the sensor network system 100 according to an embodiment. In FIG. 17, the horizontal axis represents the mean square error between the received power and the target power, and the vertical axis represents the cumulative distribution function. Here, the received power represents the power of the analog signal received by the sink 2, 102, and may include distortion that occurs when the channel gain g _k falls below the threshold g _th . On the other hand, the target power represents the power of the analog signal received by the sink 2, 102 when the channel gain g _k exceeds the threshold g _th , and does not include distortion.

The first graph G21 and the second graph G22 show the results of a computer simulation. Comparing the first graph G21 and the second graph G22, the sensor network system 100 according to one embodiment has a smaller mean square error between the received power and the target power than the sensor network system 1000 according to the second related technology, meaning that the distortion of the analog signal received by the sink 2 is effectively reduced.

In this way, in one embodiment of the sensor network system 100, even if the accuracy of the data x received by the sink 2 is improved, the power consumed by the node 1 remains almost unchanged.

The invention made by the inventor has been specifically described above based on the embodiment, but it goes without saying that the present invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention. Furthermore, the features described in the above embodiment can be freely combined as long as they are not technically inconsistent.

100, 1000 Sensor network system 1, 1-k, 1-1 to 1-K, 101, 101-k, 101-1 to 101-K Node 10 Bus 11 Input/output device 111 Communication device 112 Antenna 12 Arithmetic device 121 Beacon receiving device 122 Channel gain detection device 123 Transmission control device 13 Memory device 14 External storage device 141 Recording medium 15 Sensing device 2, 102 Sink 20 Bus 21 Input/output device 211 Communication device 212 Antenna 22 Arithmetic device 221 Parameter calculation device 222 Beacon generation device 223 Transmission control device 224 Reception control device 225 Post-processing device 23 Memory device 24 External storage device 241 Recording medium A0, A1, A2, A3, A100 Adder P1 to P6, P100, P101, P102, P10K, P201, P202 Processing M100, M101, M102, M201, M202, M301, M302 Accumulator M11, M12, M13, M21, M22, M23, M31, M32, M33 Accumulator

Claims (9)

Multiple nodes each of which retrieves data;
a sink that collects the data from the plurality of nodes for each data collection period that includes a plurality of time slots;
The sink is
a first transmission control device that transmits a beacon including information representing a channel gain threshold to the plurality of nodes in each of the plurality of time slots;
Each of the plurality of nodes
a channel gain detection device for detecting a channel gain between the sink and the beacon based on the beacon;
a second transmission control device that transmits the data to the sink only once during the data collection period when a predetermined communication condition is satisfied in any one of the plurality of time slots ;
The communication conditions are:
is satisfied if the channel gain is greater than or equal to the channel gain threshold;
The time slot is satisfied if the time slot is the last time slot of the data collection period. 2. The sensor network system according to claim 1,
The sink is
a parameter calculation device that calculates a total number of a plurality of time slots included in a data collection period based on a total number of a plurality of external nodes, and calculates the channel gain threshold and a target value of a signal amplitude based on the total number of the plurality of time slots;
a beacon generating device for generating the beacon including information representing the total number of the plurality of time slots, the channel gain threshold, and the target value of the signal amplitude in each of the plurality of time slots;
a reception control device for receiving a plurality of data transmitted from the plurality of nodes in response to the beacon;
a post-processing device for obtaining a sum of the plurality of pieces of data received during the data collection period. 3. The sensor network system according to claim 2,
The second transmission control device includes:
When the channel gain is equal to or greater than the channel gain threshold, the target value of the signal amplitude is set to a transmission power based on the channel gain;
when the channel gain is less than the channel gain threshold, setting the transmit power based on a maximum transmit power of the node;
generating an analog signal representing the data in terms of power based on the analog value representing the data and the transmission power;
The sensor network system transmits the analog signal as the data to the sink. 4. The sensor network system according to claim 3,
The reception control device includes:
an adder that simultaneously receives a plurality of the analog signals representing the plurality of data transmitted simultaneously from the plurality of nodes in each of the time slots and obtains a sum of powers of the plurality of analog signals. a parameter calculation device that calculates a total number of a plurality of time slots included in a data collection period based on a total number of a plurality of external nodes, and calculates a channel gain threshold and a target value of a signal amplitude based on the total number of the plurality of time slots;
a transmission control device that transmits a beacon to the plurality of nodes in each of the plurality of time slots, the beacon including information representing the total number of the plurality of time slots, the channel gain threshold, and the target value of the signal amplitude;
a reception control device for receiving a plurality of data transmitted from the plurality of nodes in response to the beacon;
a post-processing device that obtains a sum of the plurality of data received during the data collection period. A sensing device for acquiring data;
a beacon receiving device that receives a beacon including information indicating a channel gain threshold, the beacon being transmitted from an external sink in each of a plurality of time slots included in a data collection period;
a channel gain detection device for detecting a channel gain between the sink and the beacon based on the beacon;
a transmission control device that transmits the data to the sink only once during the data collection period when a predetermined communication condition is satisfied in any one of the plurality of time slots ;
The communication conditions are:
is satisfied if the channel gain is greater than or equal to the channel gain threshold;
The node is satisfied if the time slot is the last time slot of the data collection period. Each of the plurality of nodes acquires data;
transmitting a beacon including information representing a channel gain threshold from a sink to the plurality of nodes in each of a plurality of time slots included in a data collection period;
each of the nodes detecting a channel gain between the node and the sink based on the beacon;
each of the nodes transmitting the data to the sink only once during the data collection period when a predetermined communication condition is satisfied in any one of the plurality of time slots ;
The sink collects the data from the plurality of nodes for each data collection period;
The communication conditions are:
is satisfied if the channel gain is greater than or equal to the channel gain threshold;
The method is satisfied if the time slot is the last time slot of the data collection period. A program for implementing processing by causing a sink computing device to execute the program,
The process comprises:
Calculating a total number of a plurality of time slots included in a data collection period based on a total number of a plurality of external nodes;
calculating a channel gain threshold and a signal amplitude target value based on the total number of the plurality of time slots;
transmitting a beacon to the plurality of nodes in each of the plurality of time slots, the beacon including information representative of the total number of the plurality of time slots, the channel gain threshold, and the target value of the signal amplitude;
receiving a plurality of data transmitted from the plurality of nodes in response to the beacon;
obtaining a sum of the plurality of pieces of data received during the data collection period. A program that realizes processing by being executed by a computing device of a node,
The process comprises:
Obtaining data and
receiving a beacon transmitted from an external sink in each of a plurality of time slots included in a data collection period, the beacon including information representing a channel gain threshold;
Detecting a channel gain between the sink and the beacon based on the beacon;
transmitting the data to the sink only once during the data collection period when a predetermined communication condition is satisfied in any one of the plurality of time slots ;
The communication conditions are:
is satisfied if the channel gain is greater than or equal to the channel gain threshold;
The program is satisfied if the time slot is the last time slot of the data collection period.

Images