WO2015087751A1

WO2015087751A1 - Time correction device, measurement device, and time correction method

Info

Publication number: WO2015087751A1
Application number: PCT/JP2014/081952
Authority: WO
Inventors: 亮太赤井; 鮫島　裕; 智博尾崎; 優樹井上
Original assignee: オムロン株式会社
Priority date: 2013-12-13
Filing date: 2014-12-03
Publication date: 2015-06-18
Also published as: JP2015114290A

Abstract

Disclosed is a time correction device that corrects the time of an internal clock of a wireless terminal in a wireless network, the time correction device comprising: a synchronous time information acquisition means that acquires a reference time corresponding to the internal clock time; and a time correction means that finds a relational expression between the internal clock time and the reference time on the basis of correspondences between the internal clock time and the reference time at a plurality of points in time, and that calculates the reference time corresponding to the internal clock time on the basis of the relational expression.

Description

Time correction device, measurement device, and time correction method

The present invention relates to a time correction technique for correcting an internal clock of a wireless terminal in a wireless network.

In recent years, it has been assumed that wireless sensor networks are used in health monitoring for diagnosing and grasping the health status of structures such as bridges and tunnels. The wireless sensor network is composed of a plurality of wireless sensor nodes. By collecting and analyzing sensor information measured by the plurality of sensor nodes, early detection of abnormality is expected.

For health condition diagnosis, it is preferable to synchronize the time of each sensor node accurately and align the time axis. There exists a thing of patent document 1 as an existing time synchronization method. This technique eliminates the influence of communication delay between the master device and the slave device, and enables highly accurate time synchronization.

JP 2009-111654 A

Although the time synchronization becomes possible by using the technology of Patent Document 1, there may be a shift in the internal clock of the sensor node after the time synchronization. In particular, when the sensor node is installed outdoors or in a factory, the internal clock may shift due to environmental changes such as temperature changes. Therefore, when the technique of Patent Document 1 is adopted, it is necessary to perform time synchronization for each timing to be synchronized such as measurement timing.

By the way, a sensor node generally used for a wireless sensor network is required to have low power consumption because it is premised on battery driving. In order to perform time synchronization, it is necessary to perform wireless communication, and the power consumption of the wireless communication is generally much larger than the power consumption of other operations during measurement. Therefore, if continuous data is measured at the sensor node and wireless communication is performed for time synchronization at each measurement, there is a problem that power consumption increases.

Also, the technique of Patent Document 1 has a problem that time synchronization cannot be performed under a situation where wireless communication cannot be performed.

The present invention has been made in consideration of the above problems, and can suppress the time of the internal clock of the wireless terminal in the wireless network even in a situation where wireless communication cannot be performed while suppressing power consumption by wireless communication. The purpose is to provide technology.

The time correction apparatus according to claim 1 is a time correction apparatus that corrects the time of an internal clock of a wireless terminal in a wireless network, and includes a synchronization time information acquisition unit that acquires a correspondence between an internal clock time and a reference time, Time correction means for obtaining a relational expression between the internal clock time and the reference time based on the correspondence between the internal clock time and the reference time at the time, and calculating a reference time corresponding to the internal clock time based on the relational expression. It is characterized by that.

According to the time correction apparatus of the first aspect, the reference time corresponding to the internal clock time at an arbitrary time can be obtained by using the above relational expression. This relational expression can be obtained by only obtaining the correspondence between the internal clock time and the reference time several times. That is, it is not necessary to acquire the reference time by wireless communication at all points where the reference time is required, and the power consumption can be suppressed.

The above relational expression includes a relational expression (function) in an arbitrary format as long as it is a relational expression that approximates the internal clock time and the reference time at a plurality of time points acquired by the synchronization time information acquisition means. For example, if the correspondence between the internal clock time and the reference time is two points, a linear expression (straight line) can be adopted as the relational expression. When there are three or more corresponding points, a polynomial obtained by regression analysis such as a least square method or a polynomial obtained by interpolation such as spline interpolation can be employed. Alternatively, a correspondence (second correspondence) between the internal clock time and the reference time is obtained for each of a plurality of correspondence groups each consisting of a correspondence between a plurality of internal clock times and a reference time, and regression analysis is performed using the plurality of second correspondences. The above relational expression may be calculated by interpolation or interpolation.

The wireless network in claim 1 is an arbitrary system composed of wireless terminals capable of wireless communication, and although not limited, a wireless sensor network including sensor nodes as wireless terminals can be given as an example.

The time correction apparatus according to claim 1 may be provided in a wireless terminal having an internal clock for calculating a corresponding reference time, or may be provided in a node different from the wireless terminal.

The reference time is a time based on an arbitrary time information source. As the reference time, for example, accurate time information such as Coordinated Universal Time (UTC) or GPS time can be adopted. By adopting these times as the reference time, each wireless terminal in the wireless network can be made to coincide with an accurate time. On the other hand, if the purpose is to match the time of each node in the system, the reference time may be time information deviated from Coordinated Universal Time or GPS time.

The same time information acquisition means in claim 1 may be configured to acquire the reference time from a GPS satellite signal or a reference radio wave and acquire the internal clock time at that time, for example. Note that the synchronization time information acquisition unit may acquire the reference time indirectly instead of directly acquiring the reference time. That is, when the time correction device is mounted on a wireless terminal other than the wireless terminal having the internal clock, the wireless terminal acquires the reference time and the internal clock time at that time, and the synchronization time information acquisition means receives the reference time from the wireless terminal. And the correspondence between the internal clock time and the internal clock time.

The time correction apparatus according to claim 2 is characterized in that the relational expression is a linear expression based on the correspondence between the internal clock time and the reference time at two time points.

With the configuration according to claim 2, it is possible to calculate the reference time for an arbitrary time point simply by acquiring the correspondence between the internal clock time and the reference time at the two time points. Further, since the linear expression is used, the calculation processing load is reduced.

The time correction apparatus according to claim 3 is a polynomial that approximates the correspondence between the internal clock time and the reference time at three or more time points.

According to the configuration of the third aspect, since a polynomial approximated from the correspondence between the internal clock time and the reference time at three or more time points is employed, the reference time at any time point can be calculated more accurately. it can.

In the time correction device according to claim 4, the time correction unit calculates a reference time corresponding to the internal clock time by using the relational expression obtained at the time correction at a certain time for time correction at another time. It is characterized by that.

According to the configuration of the fourth aspect, the internal clock can be corrected with high accuracy using a relational expression based on the correspondence between the internal clock time acquired at a time different from the time when the time correction is performed and the reference time. That is, since the correspondence between the internal clock time and the reference time at the time correction target time is not required, the time can be corrected even if the reference time at the time correction target time cannot be acquired (or is not acquired).

The time correction apparatus according to claim 5 is characterized in that the time correction means updates the relational expression each time the synchronization time information acquisition means acquires a reference time corresponding to an internal clock time. According to this configuration, the reference time can be calculated based on the latest information.

6. The time correction device according to claim 6, wherein the time correction unit is configured to use the relational expression based on the most recent predetermined number of correspondences each time the synchronization time information acquisition unit acquires a reference time corresponding to an internal clock time. Is calculated. The most recent predetermined number may be a predetermined number or a number determined (changed) based on other information. According to the configuration of the sixth aspect, since the relational expression is calculated based on the most recent predetermined number of correspondences, the relational expression can be obtained based on the correspondence relation close to the current time, and the reference time can be obtained more accurately. Can do.

The time correction device according to claim 7 is characterized in that the synchronization time information acquisition means acquires the reference time from a synchronization time information sender node. According to this configuration, the time correction apparatus can acquire the reference time by wireless communication, and can acquire the reference time with relatively low cost and low power consumption. In addition, since the time correction device can acquire the reference time information if it can wirelessly communicate with the synchronous time information sender node, restrictions on the installation of the time correction device are reduced.

The time correction device according to claim 8 is characterized in that the synchronization time information acquisition means acquires the reference time information from a GPS device. Even with this configuration, the time correction apparatus can acquire the reference time information.

The measurement device according to claim 9 is a measurement device in a wireless network, and includes a measurement unit, an internal clock that provides an internal clock time in its own node, measurement data measured by the measurement unit, and the measurement A measurement data storage means for storing the internal clock time at the time in association with the time correction device according to any one of claims 1 to 8, wherein the time correction device performs the measurement. A reference time corresponding to the internal clock time is calculated.

According to the configuration of the ninth aspect, it is possible to acquire the reference time when the measurement is performed by the measurement unit. Since the exact time of measurement can be known, for example, measurement data obtained from a plurality of measurement devices can be aggregated, and analysis based on the measurement data measured at the same time can be performed.

The physical quantity measured by the measuring means in claim 9 may be any physical quantity. Examples of the measuring means include an acceleration sensor, a speed sensor, a distance measuring sensor, a stress sensor, an optical sensor, and a temperature sensor.

The measurement apparatus according to claim 10 further includes measurement data storage means for storing the measurement data measured by the measurement means and the internal clock time when the measurement is performed, and the time correction means includes: A reference time corresponding to an internal clock time at the time of the measurement stored in the measurement data storage means is calculated.

According to the configuration of the tenth aspect, at the time of measurement by the measuring means, the measurement data and the internal clock time are stored in association with each other, and the reference time at the time of measurement can be calculated later. Further, according to this configuration, the reference time at the time of measurement can be calculated using the correspondence between the internal clock time after the time of measurement and the reference time.

The measuring device according to claim 9 may calculate the reference time based on the above relational expression at the time of measurement.

In the wireless terminal according to claim 11, the measurement unit repeatedly performs measurement within a predetermined measurement period, and the time correction unit performs at least the measurement period before, after the measurement period, and during the measurement period. The relational expression is obtained based on the correspondence between the internal clock time and the reference time at a plurality of time points including any one of them. According to this configuration, the reference time during the measurement period can be accurately calculated using the above relational expression.

The measurement device according to claim 12 is one in which the measurement unit repeatedly performs measurement within a predetermined measurement period, and the time correction unit includes internal components at a plurality of time points including before the measurement period and after the measurement period. The relational expression is obtained based on the correspondence between the clock time and the reference time. According to this configuration, even when the measurement period is long, the reference time at least at the start of measurement and at the end of measurement can be obtained. Therefore, the reference time can be accurately obtained over the entire measurement period.

The radio terminal according to claim 12 may further obtain the relational expression based on the correspondence between the internal clock time and the reference time during the measurement period. As the number of corresponding points for obtaining the relational expression increases and the time interval increases, the reference time can be obtained with higher accuracy over a longer period. In the configuration that does not use the correspondence during the measurement period, there is an advantage that it is possible to avoid adversely affecting the measurement by the measurement means by acquiring the reference time.

Note that the present invention can be understood as a time correction device or a wireless terminal having at least a part of the above means. Further, the present invention can be understood as a wireless network system having the above wireless terminal. The present invention can also be understood as a time correction method having at least a part of the above processing, a computer program for causing a computer to execute the method, or a computer-readable recording medium storing the computer program. Each of the above configurations and processes can be combined with each other as long as no technical contradiction occurs.

According to the present invention, it is possible to correct the time of the internal clock of the wireless terminal in the wireless network even in a situation where wireless communication cannot be performed while suppressing power consumption by wireless communication.

The figure which shows the outline | summary of the structure health monitoring system concerning embodiment. The functional block diagram of each node which comprises the radio | wireless sensor network system concerning 1st and 2nd embodiment. The flowchart which shows the process in the sensor node of 1st Embodiment. The figure explaining the relational expression in the time correction of 1st Embodiment. The figure explaining another example of the relational expression in the time correction of 1st Embodiment. The figure explaining another example of the relational expression in the time correction of 1st Embodiment. The flowchart which shows the process in the sensor node of 2nd Embodiment. The figure explaining the relational expression in the time correction of 2nd Embodiment. The functional block diagram of each node which comprises the radio | wireless sensor network system concerning 3rd Embodiment. The functional block diagram of each node which comprises the wireless sensor network system concerning 4th Embodiment.

DETAILED DESCRIPTION Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

<Embodiment 1>
(Overview)
This embodiment is a structure health monitoring system using a sensor network. In FIG. 1, the outline | summary of the structure health monitoring system of this embodiment is shown. The structure health monitoring system has a tree structure as shown in FIG. 1 and is configured to aggregate measurement data acquired by sensor nodes. Examples of structures to be diagnosed by the structure health monitoring system of the present embodiment include outdoor structures such as bridges, tunnels, and railways. In addition to outdoor buildings, machines such as motors and semiconductor equipment may be targeted.

The sensor node 10 is a node that measures various physical quantities, and is installed in various places such as a bridge. The measurement data acquired by the sensor node 10 is transmitted to the sink node 30 by wireless communication. The sensor node 10 is low-cost and low-power, whereas the sink node 30 is a node rich in power capacity and computing resources. The time synchronization sender node 20 is a node that acquires a reference time and transmits it to the sensor node 10 as synchronization time information. The time synchronization sender node 20 can accurately synchronize the time of each sensor node 10, and therefore measurement data at the same time can be acquired from each sensor node 10.

The overall system configuration is not limited to the above configuration. A plurality of systems shown in FIG. 1 may be prepared, and a server node that acquires sensor data from each sink node may be provided, so that a tree structure with a plurality of layers may be used. In addition, measurement data can be analyzed by a sink node or a higher-level server.

(Constitution)
FIG. 2 is a diagram illustrating functional blocks of the sensor node 10, the time synchronization sender node 20, and the sink node 30 that constitute the wireless sensor network.

[Time synchronization sender node]
The time synchronization sender node 20 includes a reference time information acquisition unit 201 and a synchronization time information distribution unit 202. The reference time information acquisition unit 201 acquires time information from, for example, a GPS satellite signal or a standard radio wave. Each node in the wireless sensor network is synchronized at this time. Therefore, the time information acquired by the reference time information acquisition unit 201 is referred to as reference time information or simply as reference time. When only time synchronization between sensor nodes in the wireless sensor network system is required, it is not always necessary to use an accurate time as a reference time, and any master clock in the system may be used as a reference time. .

The synchronization time information distribution unit 202 is a functional unit that distributes the reference time information to the sensor node 10 by wireless communication. The synchronization time information distribution unit 202 may transmit the synchronization time information using an existing well-known protocol (FTSP, SNTP, etc.).

[Sensor node]
The sensor node 10 includes a power supply unit 100, an internal clock 102 as a load unit 101, a measurement unit 103, a measurement data storage unit 104, a synchronization time information acquisition unit 105, a synchronization time information storage unit 106, a time correction processing unit 107, a measurement A data communication unit 108 and a control unit 109 are provided. Each function of the load unit 101 may be realized by an integrated circuit such as an ASIC, may be realized by a processor executing a program stored in a memory, or may be realized by a combination thereof. .

The internal clock 102 is a circuit having a clock function, holds and updates internal clock information, and outputs it as a clock signal to each function unit in the apparatus. Hereinafter, in order to distinguish the time indicated by the internal clock 102 from the reference time, it is referred to as an internal clock time or a sensor node time.

The measuring unit 103 includes a plurality of sensors 103a. The physical quantity measured by the sensor 103a may be arbitrary, and the sensor 103a is one or more of an acceleration sensor, a speed sensor, a distance measurement sensor, a stress sensor, an optical sensor, a temperature sensor, and the like. The measurement unit 103 stores the data measured by the sensor 103a in the measurement data storage unit 104. At this time, the measurement time is acquired from the internal clock 102, and the measurement data and the internal clock time are stored in association with each other.

The synchronization time information acquisition unit 105 acquires the synchronization time information from the time synchronization sender node 20 by wireless communication. The synchronization time information acquisition unit 105 obtains a correspondence relationship between the internal clock time and the reference time from the internal clock time from which the synchronization time information is acquired and the reference time and distribution error obtained from the synchronization time information. The synchronization time information acquired by the synchronization time information acquisition unit 105 and the correspondence between the internal clock time and the reference time are stored in the synchronization time information storage unit 106. A pair of the internal clock time and the reference time indicating the same time is hereinafter referred to as a reference point.

The time correction processing unit 107 corrects the internal clock time based on the synchronization time information stored in the synchronization time information storage unit 106. The time correction processing unit 107 calculates a reference time corresponding to the internal clock time (including the current time and the time before and after the current time) at an arbitrary time. In the present embodiment, the time correction processing unit 107 calculates a reference time corresponding to the internal clock time stored in the measurement data storage unit 104 in association with the measurement data, based on the synchronization time information. Thereby, the exact time (reference time) when measurement is performed by the measurement unit 103 can be obtained. At this time, the internal clock 102 may be adjusted. Details of the time correction processing by the time correction processing unit 107 will be described in detail later.

The measurement data communication unit 108 transmits the measurement data subjected to the time correction process to the sink node 30 by wireless communication. The wireless communication system is not particularly limited.

The control unit 109 controls the entire process in the sensor node 10. In particular, based on the internal clock, measurement processing by the measurement unit 103, acquisition processing of synchronization time information by the synchronization time information acquisition unit 105, time correction processing by the time correction processing unit 107, and measurement data transmission processing by the measurement data communication unit 108 are performed. Control. The measurement process by the measurement unit 103 is periodically performed. For example, a measurement period of 1 minute can be taken once every 10 minutes. Within each measurement period, measurement is repeatedly performed by the sensor 103a. For example, sensor information is acquired every 50 milliseconds. The specific time intervals shown here are merely examples, and the values may be arbitrary. The acquisition timing of synchronization time information and the timing of time correction processing will be described in detail later. The transmission process of the measurement data may be arbitrary as long as the timing is after the time correction process is performed.

[Sink node]
The sink node 30 is a node (measurement data receiving node) that receives and aggregates measurement data from the plurality of sensor nodes 10. The sink node 30 is a node that is relatively excellent in power supply capacity and computing resources. The sink node 30 includes a measurement data acquisition unit 301 and a measurement data storage unit 302. The measurement data acquisition unit 301 is a functional unit that receives measurement data transmitted from the sensor node 10. The measurement data acquired by the measurement data acquisition unit 301 is stored in the measurement data storage unit 302. Although not shown in FIG. 2, the sink node 30 also has a function unit that transmits measurement data stored in the measurement data storage unit 302 to an external data server.

(Whole process of sensor node)
FIG. 3 is a flowchart showing a flow of measurement processing and measurement data transmission processing performed by the sensor node 10. Processing performed by the sensor node 10 will be described with reference to FIG.

Sensor node 10 performs continuous measurement periodically. For example, measurement is performed once every 10 minutes for 1 minute. Therefore, the control unit 109 of the sensor node 10 waits for the measurement period to start based on the time information from the internal clock 102 (S1). When the measurement period starts (S2), the synchronization time information acquisition unit 105 acquires the synchronization time information from the time synchronization sender node 20 and stores it in the synchronization time information storage unit 106 (S3). Note that the start of measurement and acquisition of synchronization time information may be performed simultaneously (in parallel), or measurement may be started after acquisition of synchronization time information first. When the synchronization time information is performed first, it is preferable to acquire the synchronization time information before the measurement start time so that the measurement can be started at the designated time.

During the measurement period, the measurement unit 103 (sensor 103a) periodically acquires measurement data and stores it in the measurement data storage unit 104 (S4). The measurement interval is, for example, 50 milliseconds. When the measurement data is stored in the measurement data storage unit 104, the sensor data is stored in association with the internal clock time obtained from the internal clock 102.

The control unit 109 determines whether or not a predetermined synchronization time information acquisition timing has arrived during the measurement period (S5). When the synchronization time information acquisition timing has arrived, the synchronization time information acquisition unit 105 acquires the synchronization time information from the time synchronization sender node 20 and stores it in the synchronization time information storage unit 106. Note that it is preferable to set the acquisition timing of the synchronization time information and the measurement timing by the measurement unit so that they do not overlap in consideration of the software load.

When the measurement period ends, the synchronization time information acquisition unit 105 acquires the synchronization time information from the time synchronization sender node 20 and stores it in the synchronization time information storage unit 106 (S7). The acquisition of the synchronization time information after this measurement period may be performed immediately after the last measurement data acquisition, or may be performed after a certain interval.

Thereafter, the time correction processing unit 107 performs time correction processing (S8 to S9). Specifically, a relational expression between the sensor node time and the reference time is derived based on the synchronization time information (a plurality of reference points) stored in the synchronization time information storage unit 106 (S8), and based on this relational expression. Then, a reference time corresponding to the sensor node time stored in the measurement data storage unit 104 in association with the measurement data is calculated (S9). At this time, setting adjustment such as sensitivity correction of the internal clock 102 may be performed. The sensitivity correction is a clock frequency sensitivity correction, and is a process of correcting the time required to advance one clock.

When the time correction is completed, measurement data obtained by correcting the sensor node time with the reference time is transmitted from the measurement data communication unit 108 to the sink node (S10).

A series of measurement processes in one measurement period is completed by the above process. The sensor node waits until the next measurement period starts.

In the flowchart of FIG. 3, the time correction process and the measurement data transmission process are performed every time one measurement period ends. However, the time correction process is performed after a plurality of measurement periods are completed. Also good. The measurement data transmission process may also be performed after a plurality of time correction processes are completed.

(Time correction processing)
Next, the time correction processing (steps S8 and S9) performed by the time correction processing unit 107 will be described in detail.

As described above, the synchronization time information is acquired before the measurement period, during the measurement period, and after the measurement period. Therefore, a plurality of reference points as shown in FIG. 4A are stored in the synchronization time information storage unit 106. In FIG. 4A, one reference point is acquired before and after the measurement period, and two reference points are acquired during the measurement period. The time correction processing unit 107 calculates a relational expression representing the relationship between the sensor node time and the reference time based on these reference points (that is, the correspondence between the sensor node time and the reference time). The relational expression can be expressed in the form of a function T (L) that gives a reference time T corresponding to an arbitrary internal clock time L.

FIG. 4A shows an example in which a straight line (primary expression) representing the relationship between the sensor node time and the reference time is obtained by linear approximation using least square approximation.

In this case, the relational expression T (L) representing the reference time T corresponding to an arbitrary internal clock time L can be obtained as follows.

Note that n is the number of reference points, and Ti and Li represent the reference time and internal clock time for the i-th reference point.

It should be noted that the relational expression is not limited to a linear expression, and may be approximated by a second or higher order polynomial as shown in FIG. Even in the case of approximation by a second-order or higher-order polynomial, although specific mathematical expressions are omitted, each coefficient can be calculated using the least square method in the same manner as described above. Note that the approximation is not limited to polynomial approximation and may be approximated by a function other than polynomial.

Further, as shown in FIG. 4C, a straight line passing through adjacent reference points may be used as a relational expression. In this case, the relational expression T (L) representing the reference time T corresponding to an arbitrary internal clock time L can be obtained as follows.

Although not shown, a polynomial that passes through all reference points using interpolation such as spline interpolation may be used as a relational expression.

Regardless of which relational expression is employed, it is possible to calculate a reference time corresponding to the sensor node time other than the reference point using the relational expression. Therefore, the time correction processing unit 107 calculates a reference time corresponding to the sensor node time stored in the measurement data storage unit 104 based on the relational expression, and the reference time when the measurement unit 103 performs the measurement. Can be requested.

(Preferable effects of this embodiment)
With the time correction processing according to the present embodiment, the reference time corresponding to the sensor node time at an arbitrary time can be accurately obtained by only acquiring the synchronization time information from the time synchronization sender node 20 several times. That is, in order to improve the accuracy of time synchronization, it is not necessary to increase the number of times of wireless communication for acquiring synchronization time information. Therefore, accurate time synchronization is possible without increasing the power consumption.

In addition, since the time correction is performed at a different time using the relational expression obtained at a certain time, communication with the time synchronization sender node 20 is not possible (no communication is performed), and the correspondence between the internal clock time and the reference time is It is possible to accurately correct the internal clock time when it was not obtained.

In addition, since accurate time synchronization can be performed, sensor information can be measured simultaneously at a plurality of sensor nodes, and the accuracy of the diagnosis result is improved.

(Modification of time correction)
In the above description, the synchronization time information is acquired before and after the measurement period and during the measurement period. However, as long as a plurality of reference points can be acquired, the acquisition timing may be arbitrary.

For example, as shown in FIG. 5A, a relational expression between the sensor node time and the reference time may be obtained based on a plurality of reference points before the start of the measurement period. In the flowchart of FIG. 3, the synchronization time information is acquired only in step S3, and steps S5 to S6 and S7 are omitted. In this method, the time after the acquisition time of the synchronization time information is corrected. Since the relational expression is obtained before the measurement period, time correction can be performed immediately during the measurement period. The synchronization time information acquisition unit 105 can acquire a plurality of synchronization time information from the time synchronization sender node 20 in a relatively short period of time.

Further, as shown in FIG. 5B, a relational expression between the sensor node time and the reference time may be obtained based on a plurality of reference points after the end of the measurement period. In this case, the time before the acquisition time of the synchronization time information is corrected. In the flowchart of FIG. 3, the synchronization time information is acquired only in step S7, and steps S3 and S5 to S6 are omitted. Since the time correction process is performed after the measurement period, the processing load during measurement is reduced. Therefore, it is effective when the processing load during measurement is large, such as when performing high-frequency sampling, and time synchronization processing cannot be performed during measurement (not appropriate).

Also, as shown in FIG. 5C, a relational expression between the sensor node time and the reference time may be obtained based on a plurality of reference points during the measurement period. In this case, the time before and after the acquisition time of the synchronization time information is corrected. In the flowchart of FIG. 3, the synchronization time information is acquired only in step S6, and steps S3 and S7 are omitted. By performing time synchronization during the measurement period, the overall processing time is shortened, and the next measurement waiting time is shortened. In addition, it is possible to perform time synchronization with higher accuracy than in the case where time synchronization processing is performed before and after the measurement period.

Note that multiple pieces of synchronization time information can be acquired in a relatively short period of time. If the synchronization time information in a short period is regarded as one synchronization time information group (or one reference point group), the time correction according to the present embodiment is one synchronization time before the measurement period, after the measurement period, or during the measurement period. A relational expression between the sensor node time and the reference time is obtained based on the information group, and can be regarded as a process of correcting the time using this relational expression.

Further, as shown in FIG. 6, reference point groups may be acquired in each of the measurement period, after the measurement period, and during the measurement period, and time correction may be performed using a relational expression obtained therefrom. In FIG. 6,

reference point groups

61, 2, and 63 before, during, and after the measurement period are shown. In this case, for example, a correspondence 61a between the internal clock time and the reference time is obtained from a plurality of reference points (black circles in the enlarged view) included in the reference point group 61. Similarly,

correspondences

62a and 63a between the internal clock time and the reference time are obtained from the

reference point groups

62 and 63, respectively. Then, a relational expression may be obtained by regression analysis or interpolation using the

correspondences

61a, 62a, 63a. The

correspondence

61a, 62a, 63a may be determined arbitrarily. For example, a relational expression is calculated from the reference points in each of the

reference point groups

61, 62, 63, and an arbitrary point on the relational expression is calculated. The

correspondence

61a, 62a, and 63a can be used.

In addition to the example shown in FIG. 6, reference point groups at a plurality of arbitrary time points such as a combination before and after the measurement period, a combination before and during the measurement period, and a combination during and after the measurement period. To obtain the relational expression.

<Embodiment 2>
In the first embodiment, the reference time corresponding to the sensor node time at the time of measurement is obtained after the end of the measurement period. However, in this embodiment, the reference time at that time is obtained for each measurement. Since the functional configuration of this embodiment is the same as that of the first embodiment, description thereof is omitted. In the following description, differences from the first embodiment will be mainly described regarding the measurement process and the time correction process.

FIG. 7 is a flowchart showing a flow of measurement processing and measurement data transmission processing of the sensor node 10 in the present embodiment. The same number is attached | subjected about the process similar to 1st Embodiment (FIG. 3).

Steps S1 to S3 are the same as in the first embodiment. However, a difference is that a plurality of reference points are acquired in step S3, and a relational expression between the sensor node time and the reference time is obtained based on the plurality of reference points in the next step S11. Thus, since the relational expression is determined prior to the measurement period, the reference time at the measurement time can be calculated during the measurement period (S12). If it demonstrates with reference to Fig.8 (a), the two

reference points

81 and 82 will be acquired before the measurement period start, and the relational expression 83 will be calculated from these reference points. Therefore, the reference time corresponding to the sensor node time can be calculated using this relational expression 83 immediately after the start of measurement.

The point that the synchronization time information is acquired when the acquisition timing of the synchronization time information arrives during the measurement period (steps S5 to S6) is the same as in the first embodiment. In the present embodiment, when the synchronization time information is acquired during the measurement period, the relational expression between the sensor node time and the reference time is recalculated (updated) (S12). This will be described with reference to FIG. In FIG. 8B, the timing for acquiring new synchronization time information has arrived, and a new reference point 84 has been acquired. At this time, the relational expression 85 is calculated from the two

latest reference points

82 and 84, and thereafter, the reference time corresponding to the sensor node time is calculated using the relational expression 85.

When the measurement period ends, the correction of the sensor node time for all measurement data has been completed, so that the measurement data can be immediately transmitted to the sink node (S10).

According to the method of the present embodiment, since the relational expression is calculated using only the information of the already acquired reference point and the time is corrected, the reference time corresponding to the current time can be obtained immediately at any time. There are advantages.

In the above description, the relational expression is calculated from the two most recent reference points. However, the number of the nearest reference points to calculate the relational expression may be arbitrary. In the above description, a straight line (primary expression) is used as the relational expression. However, a relational expression using an arbitrary function as described in the first embodiment can be used. Further, as described with reference to FIG. 6, a relational expression may be calculated from corresponding points obtained from two or more reference point groups.

In the above description, measurement data acquisition (S4), synchronization time information acquisition and relational expression calculation (S5 to S6), and reference time corresponding to the internal clock time (S13) are performed in this order. However, these processes may be performed in parallel. Alternatively, the relational expression in steps S5 to S6 may be calculated first to calculate the reference clock at that time simultaneously with the acquisition of the measurement data.

<Embodiment 3>
In the present embodiment, the time synchronization sender node is omitted from the sensor network. FIG. 9 shows functional blocks of the sensor node 10 and the sink node 30 according to the present embodiment. The sensor node 10 according to the present embodiment includes a reference time information acquisition unit 110 instead of the synchronization time information acquisition unit 105. The reference time information acquisition unit 110 is a GPS receiver that acquires GPS time from, for example, a GPS satellite signal.

The difference from the first and second embodiments is that the sensor node 10 acquires the reference time directly from a GPS satellite radio wave or the like instead of acquiring the reference time from the time synchronization sender node. However, when only time synchronization between the sensor nodes in the wireless sensor network system is required, it is not always necessary to use an accurate time as the reference time, and any master clock in the system may be used as the reference time. . Except for the difference in the method for obtaining the reference time, the contents of the process are the same as those in the first and second embodiments.

In this embodiment, since the sensor node 10 can acquire GPS time, it can be said that accurate time can always be acquired. However, for this purpose, the GPS receiver (reference time information acquisition unit) must always be operated, which increases power consumption. Therefore, in this embodiment, the reference time at an arbitrary time is estimated based on the reference time acquired from the GPS receiver at several points. By doing in this way, the frequency | count of operation of a GPS receiver can be reduced and power consumption can be suppressed.

The sensor node 10 may include a synchronization time information acquisition unit that acquires synchronization time information from the time synchronization sender node in addition to the configuration of the present embodiment. In this way, basically, the synchronization time information is received from the time synchronization sender node via the synchronization time information acquisition unit, and if it cannot be received, the reference time is obtained from the GPS receiver (reference time information acquisition unit). To get. Thereby, time synchronization can be performed more reliably while suppressing an increase in power consumption in the sensor node.

<Embodiment 4>
In the present embodiment, a time correction processing unit is provided in the sink node 30. FIG. 10 shows functional blocks of each node in the present embodiment. In addition, although the structure demonstrated here is a structure based on 1st Embodiment, the same deformation | transformation is added also to 2nd and 3rd embodiment.

The time correction processing unit 107 is omitted from the sensor node 10 in this embodiment, and the measurement data / synchronized time information communication unit 111 is provided instead of the measurement data communication unit 108. The measurement data / synchronization time information communication unit 111 corresponds to the measurement data stored in the measurement data storage unit 104 and the internal clock time at the time of measurement, and the correspondence between the internal clock time stored in the synchronization time information storage unit 106 and the reference time. (Reference point) is transmitted to the sink node 30.

The sync node 30 is different from the first embodiment in that it includes a measurement data / synchronization time information acquisition unit 303 and a time correction processing unit 304. The measurement data / synchronization time information acquisition unit 303 acquires the measurement data and the internal clock time at the time of measurement and the correspondence (reference point) between the internal clock time and the reference time transmitted from the sensor node 10. In addition, the time correction processing unit 304 calculates a reference time corresponding to the internal clock time at the measurement data acquisition time of the sensor node 10 using the acquired reference point, and associates the reference time with the measurement data to measure the measurement data. Store in the storage unit 302. Note that the content of the time correction processing in the time correction processing unit 304 can be performed by the processing described in the first and second embodiments, and thus description thereof is omitted here.

In the present embodiment, the function of acquiring a reference point from the sensor node 10 (a part of the measurement data / synchronization time information acquisition unit 303 of the sink node 30) corresponds to the synchronization time information acquisition means in the present invention.

According to the present embodiment, since the time correction process at the sensor node 10 can be omitted, advantageous effects such as a reduction in processing load on the sensor node 10 and a reduction in power consumption can be obtained.

<Others>
The description of the above embodiment is merely illustrative of the present invention, and the present invention is not limited to the above specific form. The present invention can be variously modified within the scope of its technical idea.

For example, in the description of the above embodiment, an example in which a wireless sensor network system is used for a health monitoring system of an outdoor structure such as a bridge or a tunnel has been described, but the application destination of the wireless sensor network system is not limited to the above. For example, the above wireless sensor network system can be applied to a health monitoring system other than outdoor structures such as semiconductor equipment and motors, and any other measurement system.

In the above description of the embodiment, a wireless sensor network system including a sensor node is described as an example. However, the present invention is applicable to a wireless sensor network system including an arbitrary wireless terminal. That is, a wireless terminal having an internal clock to be corrected does not necessarily have a sensor (measuring unit).

10: Sensor node 20: Time synchronization sender node 30: Sink node 102: Internal clock 103: Measurement unit 104: Measurement data storage unit 105: Synchronization time information acquisition unit 106: Synchronization time information storage unit 107: Time correction processing unit 108: Measurement Data communication unit 109: Control unit

Claims

A time correction device for correcting the time of an internal clock of a wireless terminal in a wireless network,
Synchronization time information acquisition means for acquiring the correspondence between the internal clock time and the reference time;
Time correction means for obtaining a relational expression between the internal clock time and the reference time based on the correspondence between the internal clock time and the reference time at a plurality of time points, and calculating a reference time corresponding to the internal clock time based on the relational expression;
A time correction apparatus comprising:
The relational expression is a linear expression based on the correspondence between the internal clock time and the reference time at two time points.
The time correction apparatus according to claim 1.
The relational expression is a polynomial that approximates the correspondence between the internal clock time and the reference time at three or more time points.
The time correction apparatus according to claim 1.
The time correction means calculates the reference time corresponding to the internal clock time by using the relational expression obtained at the time correction at a certain time for time correction at another time.
The time correction apparatus of any one of Claim 1 to 3.
The time correction unit updates the relational expression each time the synchronization time information acquisition unit acquires a reference time corresponding to an internal clock time.
The time correction apparatus of any one of Claim 1 to 4.
The time correction means calculates the relational expression based on the most recent predetermined number of correspondences each time the synchronous time information acquisition means acquires a reference time corresponding to an internal clock time.
The time correction apparatus according to claim 5.
The synchronization time information acquisition means acquires the reference time from a synchronization time information sender node.
The time correction apparatus of any one of Claim 1 to 6.
The synchronization time information acquisition means acquires the reference time information from a GPS device;
The time correction apparatus of any one of Claim 1 to 7.
A measuring device in a wireless sensor network,
Measuring means;
An internal clock that provides the internal clock time within its own node;
Measurement data storage means for storing the measurement data measured by the measurement means in association with the internal clock time at the time of the measurement,
The time correction apparatus according to any one of claims 1 to 8,
With
The time correction device calculates a reference time corresponding to an internal clock time when the measurement is performed;
Measuring device.
Measurement data storage means for storing the measurement data measured by the measurement means and the internal clock time when the measurement is performed in association with each other;
The time correction means calculates a reference time corresponding to an internal clock time at the time of measurement stored in the measurement data storage means;
The measuring device according to claim 9.
The measurement means repeatedly measures within a predetermined measurement period,
The time correction means obtains the relational expression based on correspondence between internal clock time and reference time at a plurality of time points including at least one of the measurement period, before the measurement period, after the measurement period,
The measuring device according to claim 9 or 10.
The measurement means repeatedly measures within a predetermined measurement period,
The time correction means obtains the relational expression based on the correspondence between the internal clock time and the reference time at a plurality of time points including before the measurement period and after the measurement period.
The measuring device according to claim 9 or 10.
A wireless sensor network system comprising the measurement device according to any one of claims 9 to 12 and a measurement data receiving node,
The measurement device includes measurement data transmission means for transmitting measurement data stored in the measurement data storage means and a reference time for the measurement to the measurement data receiving node.
Wireless sensor network system.
A time correction method for correcting the time of an internal clock of a wireless terminal in a wireless network,
The wireless terminal is
A synchronization time information acquisition step for acquiring the correspondence between the internal clock time and the reference time;
A relational expression calculating step for obtaining a relational expression between the internal clock time and the quasi-time based on the correspondence between the internal clock time and the reference time at a plurality of time points;
A time correction step of calculating a reference time corresponding to the internal clock time based on the relational expression;
Including a time correction method.
The computer program for making a computer perform each step of the method of Claim 14.