JP2011091624A - Mesh network system and time synchronizing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the efficiency of a data collection processing using a data collector by reducing an overhead required for a time synchronization processing. <P>SOLUTION: A data collector 2 stores time information of a timer, which the data collector itself uses, in a data collection request message and transmits the data collection request message to a relay terminal 3a. In the relay terminal 3a, a transfer processing delay time is measured, the time information stored in the data collection request message is corrected and then, the data collection request message is transmitted to a relay terminal 3b as a transfer message. A destination terminal 4 receives the transfer message from the relay terminal 3b and performs time synchronization processing, together with data collection that the data collector 2 requests, using the time information stored in the transfer message. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a mesh network system including a data collection device and a plurality of terminals, and a time synchronization method thereof.

In a mesh network system composed of a data collection device and a plurality of sensor nodes, FTSP (the flooding time synchronization protocol) has been proposed as a conventional technique for synchronizing the times of the collection device and the sensor nodes.
In this prior art, time synchronization is performed according to the procedure shown in FIG. First, the collection device connected to the external network becomes the first time master, broadcasts a time synchronization message to the nodes existing in the communication range (S51), and the node #A as the receiving terminal performs time synchronization ( S52). Next, node #A, which has completed synchronization, becomes a time master, and transmits a time synchronization message to terminals within its communication range by broadcasting (S53). The node #B that has received the time synchronization message from the node #A performs time synchronization (S54), and transmits the time synchronization message by broadcast to terminals within its communication range (S55). This process is repeated until it is transmitted to all terminals (S56 to S57).

Such processing for time synchronization is performed separately from processing (S58 to S513) in which the data collection device collects data from the receiving terminal. For example, when the data collection device collects data from the node #C, a data collection request message addressed to the node #C is transmitted to the node #A (S58). Node #A and node #B forward the data collection request message to node #C (S59, S510), and node #C receives the data collection request message. The node #C inserts the data requested by the data collection device into the data collection response message and transmits it to the node #B (S511). Node #B and node #A transfer the data collection response message to the data collection device.

M. Maroti, B. Kusy, G. Simon and A. Ledeczi, "The Flooding Time Synchronization Protocol", Proc. Of the 2nd International Conference on Embedded Network Sensor Systems (SenSys '04), pp.39--49, 2004

In a conventional mesh network system, a series of time synchronization processing (S51 to S57) and data collection processing (S58 to S513) cannot be performed at the same timing. For example, when data collection is performed during the time synchronization process, a message collision may occur, which may cause a data collection error or a time synchronization message reception failure. For this reason, as shown in FIG. 14, the transmission and transfer of the data collection request message and the data collection response message need to be performed at a timing different from the transmission and transfer processing of the time synchronization message.

  In addition, when an application that collects data from a large number of sensor nodes at a fixed time is executed by polling from the collection device, the data collection application occupies the bandwidth. Broadcasting causes the data collection rate to deteriorate.

Furthermore, since the FTSP does not confirm whether the sensor node is time-synchronized, it is required to transmit a time-synchronization message in a short cycle, which also causes the collection rate to deteriorate. In addition, when a terminal whose time information is initialized due to a power failure or the like occurs, even in order to synchronize the time of the corresponding terminal with this method, a message is transmitted by broadcast to the whole, so the band is compressed.
It is necessary to realize time synchronization that does not degrade the performance of application services such as data collection.

The present invention has been made to solve the above-described problems, and has as its object to reduce the overhead required for time synchronization processing and to improve the efficiency of data collection processing by a data collection device.

The mesh network system according to the present invention is:
Wireless communication is performed between the first wireless terminal, the second wireless terminal that performs wireless communication with the first wireless terminal, and the second wireless terminal, and the first wireless terminal A mesh network system having a data collection device for collecting data,
The data collection device includes:
First time information storage means for storing time information of a timer of the data collection device in a data collection request message for requesting data from the first wireless terminal;
First transmission means for transmitting the data collection request message,
The second wireless terminal is
First measuring means for measuring a transfer delay time required for the transfer process of the data collection request message;
First correction means for correcting time information stored in the data collection request message based on the transfer delay time measured by the first measurement means;
Second time information storage means for storing time information corrected by the first correction means in a transfer message generated by performing the transfer processing on the data collection request message;
Second transmitting means for transmitting the transfer message;
The first wireless terminal is
Data collection means for collecting data requested by the data collection device based on the transfer message;
First time synchronization means for adjusting the time of a timer used by the first wireless terminal based on time information in the transfer message.

Also,
The first wireless terminal is
Second measuring means for measuring a reception delay time required for the reception process of the transfer message;
Second correction means for correcting time information in the transfer message based on the reception delay time measured by the second measurement means;
The first time synchronization means adjusts the time of a timer used by the first wireless terminal based on the time information corrected by the second correction means.

Furthermore, the first wireless terminal is
Request data storage means for storing data collected by the data collection means in a data collection response message;
And a third transmission means for transmitting the data collection response message.

Further, the data collection device has transmission source information storage means for storing information indicating the transmission source of the message in the data collection request message,
The second wireless terminal is
Determining means for determining whether or not the transmission source of the data collection request message is the data collection device based on the information indicating the transmission source;
Third measuring means for measuring a reception delay time required for the reception process of the data collection request message;
Third correction means for correcting time information in the data collection request message based on the reception delay time measured by the third measurement means;
A timer used by the second wireless terminal based on the time information corrected by the third correction unit when the determination unit determines that the transmission source of the data collection request message is the data collection device; And second time synchronization means for adjusting the time.

  Further, the first wireless terminal has a communication timer that is time-synchronized in the first time synchronization means, and an application timer that is used for an application that is activated in the first wireless terminal, The time of the application timer is adjusted based on the time of the communication timer.

The time synchronization method in this invention is:
Wireless communication is performed between the first wireless terminal, the second wireless terminal that performs wireless communication with the first wireless terminal, and the second wireless terminal, and the first wireless terminal A mesh network system time synchronization method having a data collection device for collecting data,
A first time information storage step in which the data collection device stores time information of a timer of the data collection device in a data collection request message for requesting data from the first wireless terminal;
A first transmission step in which the data collection device transmits the data collection request message;
A first measurement step in which the second wireless terminal measures a transfer delay time required for the transfer process of the data collection request message;
A first correction step in which the second wireless terminal corrects the time information stored in the data collection request message based on the transfer delay time measured in the first measurement step;
A second time information storage step in which the second wireless terminal stores the time information corrected in the first correction step in a transfer message generated by performing the transfer process on the data collection request message. When,
A second transmission step in which the second wireless terminal transmits the transfer message;
A data collection step in which the first wireless terminal performs data collection requested by the data collection device based on the transfer message;
A first time synchronization step in which the first wireless terminal adjusts the time of a timer used by the first wireless terminal based on time information in the transfer message;
It is what has.

According to the present invention, it is possible to reduce the overhead required for time synchronization processing and to improve the efficiency of data collection processing by the data collection device.

1 is a configuration diagram of a mesh network system in Embodiment 1. FIG. 3 is an internal configuration diagram of the data collection device 2. FIG. It is an internal block diagram of relay terminal 3a, 3b. 3 is an internal configuration diagram of a destination terminal 4. FIG. FIG. 3 is a sequence diagram showing a procedure of time synchronization processing in the first embodiment. 4 is a data format diagram of a message used in the first embodiment. FIG. 5 is a diagram showing details of each field of application data 600. FIG. It is a figure which shows the detail of each field of a data format FIG. 10 is a data format diagram of a message used in the second embodiment. 5 is a diagram illustrating details of each field of a MAC header 620. FIG. 5 is a diagram showing details of each field of application data 600. FIG. It is a sequence diagram which shows the procedure of the time synchronous process in relay terminal 3a, 3b. It is a sequence diagram which shows the procedure of the time synchronous process in a terminal. It is a sequence diagram which shows the procedure of the time synchronous process in the conventional mesh network system.

An embodiment of a mesh network system according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is an overall configuration diagram of a mesh network system according to the present embodiment. Reference numeral 1 denotes an operation center that supervises a data collection device described later, and 2 denotes a data collection device connected to the operation center 1. The operation center 1 has a function of controlling the entire network including the data collection device 2.

  Reference numerals 3a, 3b, and 4 denote wireless terminals, and the data collection device 2 and the wireless terminals 3a, 3b, and 4 have a function of building a mesh network system with a wireless function. FIG. 2 shows an example in which a mesh network system starting from 2 is constructed. Each of the wireless terminals 3a, 3b, and 4 is a sensor node that mounts a sensor (not shown), for example, and acquires information such as temperature measured by the sensor. As another example, the wireless terminals 3a, 3b, and 4 may be nodes that acquire data from other devices using serial communication, infrared communication, or the like. Each of the wireless terminals 3 a, 3 b, 4 transmits the acquired data to the data collection device 2 in response to a request from the data collection device 2.

  The data collection device 2 executes an application that collects data from all wireless terminals at regular intervals. Data collection is performed by transmitting a data collection request message from the data collection device 2 to each wireless terminal, generating a data collection response message in which each wireless terminal stores the data, and transmitting the data collection response message to the data collection device 2. Realize.

The connection between the operation center 1 and the data collection device 2 is wired or wirelessly communicated. When the operation center 1 and the data collection device 2 are wirelessly connected, this wireless communication band uses a band that is significantly different from the wireless communication band used between the data collection device 2 and the wireless terminals 3a, 3b, and 4.

Various route construction methods in the mesh network system have been proposed, but any routing protocol may be used in the present embodiment. Also, any method and hardware may be used for the wireless protocol and the wireless chip. The data collection device 2 performs time synchronization with the operation center 1 at regular intervals using a time synchronization protocol such as NTP (Network Time Protocol).

The wireless terminals 3a, 3b, and 4 include a wireless driver that processes wireless chip control and a MAC layer, a middle task that processes a network layer, a time task that manages time, and an application task that processes an application.

  In the following description, a case where the data collection device 2 transmits a data collection request message to the wireless terminal 4 will be described as an example. In this example, since the wireless terminals 3a and 3b function as relay terminals that perform transfer processing of messages exchanged between the data collection device 2 and the wireless terminal 4, they are called relay terminals 3a and 3b. The wireless terminal 4 is designated as the destination terminal 4 because it is designated as the destination of the message from the data collection device 2.

  The procedure of the time synchronization process of this embodiment will be described with reference to FIGS. 2 to 4 are internal configuration diagrams of the data collection device 2, the relay terminals 3a and 3b, and the destination terminal 4, and FIG. 5 is a sequence diagram illustrating a time synchronization procedure according to this embodiment. In this embodiment, time information necessary for time synchronization is stored in the data collection request message.

First, the data collection control unit 22 in the data collection device 2 determines whether or not data collection from the destination terminal 4 is necessary. If it is determined that data collection is necessary, a message generation instruction for transmitting a data collection request message is generated. To the unit 23. The time synchronization control unit 20 of the data collection device 2 measures the time elapsed since the previous time synchronization was performed using the timer 21, and determines whether or not the time synchronization is necessary based on whether or not a predetermined time has elapsed. To do. When it is determined that time synchronization is necessary, the time synchronization control unit 20 sends the current time information of the timer 21 to the message generation unit 23, and the message generation unit 23 stores the current time information in the data collection request message. (S1). The timing for storing the time information in the data collection request message may be after carrier sense detection or before detection.
Then, the transmission unit 24 in the data collection device 2 transmits a data collection request message (S2).

When receiving the data collection request message from the data collection device 2, the reception unit 30 of the relay terminal 3 a outputs a measurement start notification to the delay measurement unit 31. The reception processing unit 33 performs reception processing of the data collection request message and instructs the message generation unit 34 to generate a transfer message for transferring the data collection request message to the relay terminal 3b. The message generation unit 34 outputs a measurement end notification to the delay measurement unit 31, and obtains measurement delay time information obtained by the measurement from the delay measurement unit 31 (S3).

The measured delay time information is information indicating the measured delay time measured by the delay measuring unit 31, and this measured delay time is the time required for the transfer process (transfer delay time). The message generator 34 adds the transfer delay time to the time indicated by the time information stored in the data collection request message, and stores the time information indicating the time after the addition in the transfer message.
After the completion of the transfer process (S4), the transmission unit 35 transmits a transfer message to the relay terminal 3b (S5).

The relay terminal 3b performs the same processing as that of the relay terminal 3a, and transmits the obtained transfer message to the destination terminal 4 (S6, S7, S8). The time information stored in the transfer message at the relay terminal 3b is time information obtained by adding the transfer delay time at the relay terminal 3b to the time indicated by the time information stored in the transfer message from the relay terminal 3a. The time after the addition is equal to the time obtained by adding the transfer delay time at the relay terminals 3a and 3b to the time of the data collection device 2.

When receiving the transfer message from the relay terminal 3b, the receiving unit 40 of the destination terminal 4 outputs a measurement start notification to the delay measuring unit 41. The reception processing unit 43 performs a transfer message reception process, and notifies the delay measurement unit 41 of a measurement end notification when the reception process is completed. In addition, the reception processing unit 43 outputs the time information (time information obtained by adding the transfer delay time at the relay terminals 3a and 3b to the time of the data collection device 2) stored in the transfer message to the time correction unit 44. .

The delay measurement unit 41 measures the time from receiving the measurement start notification to receiving the measurement end notification using the delay measurement timer 42 (S9), and outputs the measured delay time information to the time correction unit 44. This measurement delay time indicates the time (reception delay time) required for the reception process in the destination terminal 4.
The time correction unit 44 adds the reception delay time in the destination terminal 4 to the time indicated by the time information stored in the transfer message, and the time synchronization processing unit 45 uses the time information indicating the added time as the correction time information. Notify The time synchronization processing unit 45 performs time synchronization based on the corrected time information (S10). That is, the timer time of the destination terminal 4 is adjusted to the time obtained by adding the transfer delay time at the relay terminals 3 a and 3 b and the reception delay time at the destination terminal 4 to the time of the data collection device 2.

Time synchronization in the destination terminal 4 is executed when it is determined whether the middle task can synchronize time, and when it is determined that time synchronization is possible. For example, (1) when a predetermined time has elapsed since the previous time synchronization processing was performed, (2) when time information in the destination terminal has disappeared, or (3) inside the destination terminal by time synchronization If the processing is not affected, it is determined that time synchronization is possible. As another example, it may be determined that time synchronization is possible by a combination of the above conditions (1) to (3).

On the other hand, when receiving the transfer message, the reception processing unit 43 instructs the data collection unit 47 to collect the data requested by the data collection device 2 based on the information of the transfer message.
The data collection unit 47 obtains data measured by a sensor mounted on the destination terminal 4 and data obtained from other devices connected to the destination terminal 4.
The message generation unit 48 stores the collected data output from the data collection unit 47 in a data collection response message, and generates a data collection response message. The transmission unit 49 transmits a data collection response message (S11).

The data collection response message is transferred by the relay terminals 3b and 3a (S12 and S13), and finally received by the receiving unit 25 of the data collection device 2. The reception processing unit 26 extracts the collected data stored in the data collection response message.
Through the series of processes described above, the data collection device 2 receives the requested data from the destination terminal 4 and completes time synchronization with the destination terminal 4.

  The common data format shown in FIGS. 6 to 8 is used for the above-described data collection request message, transfer message, and data collection response message.

Data collection request message When the data format of FIG. 6 is used as a data request message, a flag indicating a data collection request is set in the field of the command type 601 in the application data 600, and an application is displayed in the field of the data length 602. Data indicating the data length is set. In the field of user data 603, time information of the timer 21 of the data collection device 2 is stored (FIG. 7).
In the transmission destination node ID 612 of FIG. 6, the node ID of the destination terminal 4 that is the destination of the data request is set, and in the transmission source node ID 613, the node ID of the data collection device 2 is set.
The MAC ID of the relay terminal 3a is set in the transmission destination MAC ID 623, and the MAC ID of the data collection terminal 2 is set in the transmission source MAC ID 624.
The fields other than these are determined according to the network communication protocol.

Transfer message from relay terminal 3a to relay terminal 3b The transfer message is generated by changing information of some fields in the data collection request message.
Specifically, the relay terminal 3a rewrites the time information stored in the user data 603 in the data collection request message. The time information after rewriting indicates the time obtained by adding the transfer delay time at the relay terminal 3a to the time indicated by the time information stored in the data collection request message (the transfer delay at the relay terminal 3a at the time of the data collection device 2). Time plus hours).

The transmission destination MAC ID 623 is rewritten to the MAC ID of the relay terminal 3b, and the transmission source MAC ID 624 is rewritten to the MAC ID of the relay terminal 3a.
Although the life expectancy time is set in TTL 614, it is rewritten to a value obtained by subtracting a predetermined number from the value set in the data collection request message.
The fields other than these are not changed in the relay terminal 3a.

Transfer message from relay terminal 3b to destination terminal 4 The relay terminal 3b rewrites the time information stored in the user data 603 in the transfer message received from the relay terminal 3a. The time information after rewriting indicates the time obtained by adding the transfer delay time at the relay terminal 3a to the time indicated by the time information stored in the transfer message from the relay terminal 3a (the relay terminal 3a and the time at the time of the data collection device 2). The time obtained by adding the transfer delay time in 3b).
The transmission destination MAC ID 623 is rewritten with the MAC ID of the destination terminal 4, and the transmission source MAC ID 624 is rewritten with the MAC ID of the relay terminal 3b.
Although the life expectancy time is set in the TTL 614, it is rewritten to a value obtained by subtracting a predetermined number from the value set in the transfer message from the relay terminal 3a.
The fields other than these are not changed in the relay terminal 3b.

Data collection response message In the data collection response message transmitted from the destination terminal 4, a flag indicating a data collection response is set in the command type 601 field in the application header 600, and data collection is performed in the user data 603 field. Data (request data) collected by the destination terminal 4 in response to a request from the device 2 is stored (FIG. 7). Therefore, the time information corrected by the destination terminal 4 is not stored in the data collection response message.
The node ID of the data collection device 2 is set in the transmission destination node ID 612, and the node ID of the destination terminal 4 is set in the transmission source node ID 613.
The MAC ID of the relay terminal 3b is set in the transmission destination MAC ID 623, and the MAC ID of the destination terminal 4 is set in the transmission source MAC ID 624.
The fields other than these are determined according to the network communication protocol.

  As described above, using a common data format as the data collection request message, the transfer message, and the data collection response message makes the message generation program of the data collection device 2, the relay terminals 3a and 3b, and the destination terminal 4 common. This is advantageous in that

As described above, the relay terminals 3a and 3b measure the transfer delay time by the delay measuring unit 31, and this transfer delay time is used to transmit a message to the next terminal after the relay terminal receives the message. Shows the time until the message is generated. For example, measurement is started when a start frame delimiter (SFD) 632 in a message is received, and time information is stored in a field of user data 603 after completion of carrier sense for transmitting a message to the next terminal. The transfer delay time may be measured by terminating the measurement at the stage of performing. Alternatively, measurement may be started when a reception notification is obtained from the wireless driver, and measurement may be terminated when a message is passed to the wireless driver.
Carrier sense refers to processing for confirming whether another device is using a channel before sending a signal over the network.

  The destination terminal 4 measures the reception delay time by the delay measuring unit 41. The reception delay time indicates the time from when the destination terminal 4 receives the message until the destination terminal completes the reception process. ing. For example, the reception delay time may be measured by starting measurement when the start frame delimiter 632 in the message is received and ending the measurement when the time task of the destination terminal 4 performs time synchronization processing. Alternatively, measurement may be started when a reception notification is obtained from the wireless driver.

In the mesh network system of this embodiment, the time information necessary for time synchronization is stored in the data collection request message, so that the overhead required for the time synchronization processing can be reduced as compared with the prior art.
Further, since the relay terminals 3a and 3b correct the time required for the transfer process, and store the corrected time information in the message and transmit it to the next terminal, the time error between the destination terminal 4 and the data collection device 2 is reduced. Can be reduced. Further, since the destination terminal 4 performs time synchronization after correcting the time required for the reception process, the time error between the destination terminal 4 and the data collection device 2 can be reduced.

  Since the data collection response message is sent from the destination terminal 4 to the data collection device 2, the reception of this message enables the data collection device 2 to confirm that the time synchronization has been completed at the destination terminal 4.

Embodiment 2. FIG.
In the present embodiment, a data collection request message, a transfer message, and a data collection response message are transmitted using a data format different from that in the first embodiment.
Data formats used in the mesh network system of this embodiment are shown in FIGS. FIG. 9 shows the structure of the message format, and FIGS. 10 and 11 show the contents of each field.

The difference from the message format described in the first embodiment is that a time information 626 field is added in the MAC header 620. This time information 626 stores time information used for time synchronization (FIGS. 9 and 10).
When the message format of FIG. 9 is used as the data collection request message, the time information of the timer of the data collection device 2 is stored in the time information 626 field.

When the relay terminal 3a generates a transfer message, time information obtained by adding the transfer delay time at the relay terminal 3a to the time indicated by the time information stored in the data collection request message is stored in the time information 626 field. Is done.
When the relay terminal 3b generates the transfer message, the time information 626 is a time obtained by adding the transfer delay time at the relay terminal 3b to the time indicated by the time information stored in the transfer message from the relay terminal 3a. Information is stored.

  When the destination terminal 4 generates the data collection response message, the reception delay time at the destination terminal 4 is added to the time indicated by the time information stored in the transfer message from the relay terminal 3b in the time information 626 field. Stored time information is stored.

Since the time information field 626 is provided in the MAC header 620, in this embodiment, time information is not stored in the field of the user data 603 (FIG. 11).
The other points are the same as the format of the first embodiment.

In this embodiment, it is assumed that time synchronization is also performed in the relay terminals 3a and 3b unlike the first embodiment, and a method for determining whether or not to perform time synchronization will be described with reference to FIG.
When the relay terminals 3a and 3b receive a message such as a data collection request message and a transfer message, measurement of the reception delay time is started (S22). For example, the delay time measurement is started when the start frame delimiter (SFD) 632 in the message is detected (S21) (S22), and the time until the relay terminal completes the reception process (S24) is measured as the delay time. (S25).

  Thereafter, it is determined whether or not a predetermined time has elapsed since the previous time synchronization was performed (S26), and if it has elapsed, the process proceeds to the next determination (S27). In step S27, it is confirmed whether or not the transmission source node ID 613 of the received message indicates the data collection device 2. When the transmission source node ID 613 indicates the data collection device 2, time synchronization processing is performed (S28). Specifically, the reception delay time measured in S25 is added to the time information stored in the time information 626 in the message, and the timers of the relay terminals 3a and 3b are set at the time obtained by the addition. The time synchronization process is performed in the relay terminals 3a and 3b in such a procedure.

  If the source node ID 613 does not indicate the data collection device 2 in S27, the process is terminated without performing the time synchronization process. For example, when the relay terminals 3a and 3b receive the data collection response message transmitted from the destination terminal 4 in the sequence of FIG. 5, the transmission source node ID 613 of the received message indicates the data collection device 2 in S27. Therefore, the time synchronization process is not performed. On the other hand, when the relay terminal 3b receives the transfer message from the relay terminal 3a, since the transmission source node ID 613 indicates the data collection device 2, time synchronization processing is performed.

  Usually, the larger the number of pops from the data collection device 2, the more likely it is that the synchronization time error will occur. Therefore, the time error can be reduced by making the determination in S27.

As another example, the determination in S27 may be determined based on the message transmission source MAC ID 624. That is, the terminal of the transmission source is discriminated from the information of the transmission source MAC ID 624, and when the number of pops from the data collection device 2 of this terminal is smaller than the number of pops of the own station, the time synchronization processing is performed based on the received message. You may decide to do.

  The relay terminals 3a and 3b in this embodiment have the same configuration as the delay measurement unit 41, the time correction unit 44, and the time synchronization processing unit 45 of the destination terminal 4 in addition to the configuration shown in FIG. In addition, it also includes a determination unit that performs the process of S27 described above.

Embodiment 3 FIG.
This embodiment shows the procedure of time synchronization processing when two timers are provided in the destination terminal 4 and the relay terminals 3a and 3b.
When the time synchronization processing is performed at the destination terminal 4 and the relay terminals 3a and 3b, the operation of the application activated on the terminal may be unstable depending on the timing of time synchronization. For this reason, in this embodiment, the destination terminal 4 and the relay terminals 3a and 3b are provided with a timer (application timer) used in the application and a timer (communication timer) used for communication in the network. These timers may be realized by either software or hardware.

  The time synchronization of the communication timer is realized via the network according to the procedure described in the first or second embodiment. On the other hand, the time synchronization of the application timer is realized by synchronizing with the communication timer. This procedure is shown in FIG.

  FIG. 13a shows a procedure in which the application timer acquires time from the communication timer. When the time information is transmitted via the network (S31, 33), the task for managing the communication timer performs time synchronization processing of the communication timer (S32, 34). On the other hand, the task that manages the application timer makes a time information acquisition request to the task that manages the communication timer at a cycle determined according to the time accuracy of the timer or at an arbitrary timing (S35). The task for managing the communication timer makes a time information acquisition response to the task for managing the application timer, and the time of the application timer is adjusted to the time of the communication timer.

As another procedure, a procedure for notifying the time from the communication timer to the application timer is shown in FIG. 13b. The task for managing the communication timer is to synchronize the time of the communication timer (S42, S45) whenever the time synchronization is performed via the network (S42, S45), and to the task for managing the application timer. Time information is notified (S43, S46). The task for managing the application timer performs time synchronization at a timing determined not to affect the operation of the application (S47).

It will be understood by those skilled in the art that the above embodiments are exemplifications, and various modifications can be made to the combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. It is a place.

As described above, the time synchronization method according to the present invention is useful in a mesh network system including a data collection device and a plurality of terminals. For example, the present invention can be applied to a sensor network configured by a data collection device and a sensor node.

DESCRIPTION OF SYMBOLS 1 Operation center 2 Data collection device 3a, 3b Relay terminal 4 Destination terminal 20 Time synchronization control part 21 Timer 22 Data collection control part 23 Message generation part 24 Transmission part 30 Reception part 31 Delay measurement part 32 Delay measurement timer 33 Reception processing part 34 Message generation unit 35 Transmission unit 40 Reception unit 41 Delay measurement unit 42 Delay measurement timer 43 Reception processing unit 44 Time correction unit 45 Time synchronization processing unit 46 Timer 47 Data collection unit 48 Message generation unit 49 Transmission unit

Claims (6)

Wireless communication is performed between the first wireless terminal, the second wireless terminal that performs wireless communication with the first wireless terminal, and the second wireless terminal, and the first wireless terminal A mesh network system having a data collection device for collecting data,
The data collection device includes:
First time information storage means for storing time information of a timer of the data collection device in a data collection request message for requesting data from the first wireless terminal;
First transmission means for transmitting the data collection request message,
The second wireless terminal is
First measuring means for measuring a transfer delay time required for the transfer process of the data collection request message;
First correction means for correcting time information stored in the data collection request message based on the transfer delay time measured by the first measurement means;
Second time information storage means for storing time information corrected by the first correction means in a transfer message generated by performing the transfer processing on the data collection request message;
Second transmitting means for transmitting the transfer message;
The first wireless terminal is
Data collection means for collecting data requested by the data collection device based on the transfer message;
1. A mesh network system comprising: first time synchronization means for adjusting a time of a timer used by the first wireless terminal based on time information in the transfer message. The first wireless terminal is
Second measuring means for measuring a reception delay time required for the reception process of the transfer message;
Second correction means for correcting time information in the transfer message based on the reception delay time measured by the second measurement means;
The mesh network according to claim 1, wherein the first time synchronization means adjusts the time of a timer used by the first wireless terminal based on the time information corrected by the second correction means. system. The first wireless terminal is
Request data storage means for storing data collected by the data collection means in a data collection response message;
The mesh network system according to claim 1, further comprising third transmission means for transmitting the data collection response message. The data collection device has transmission source information storage means for storing information indicating the transmission source of the message in the data collection request message;
The second wireless terminal is
Determining means for determining whether or not the transmission source of the data collection request message is the data collection device based on the information indicating the transmission source;
Third measuring means for measuring a reception delay time required for the reception process of the data collection request message;
Third correction means for correcting time information in the data collection request message based on the reception delay time measured by the third measurement means;
A timer used by the second wireless terminal based on the time information corrected by the third correction unit when the determination unit determines that the transmission source of the data collection request message is the data collection device; The mesh network system according to claim 1, further comprising second time synchronization means for adjusting time.   The first wireless terminal includes a communication timer for which time synchronization processing is performed in the first time synchronization means, and an application timer used for an application activated in the first wireless terminal. The mesh network system according to claim 1, wherein the time of the application timer is adjusted based on the time of the timer. Wireless communication is performed between the first wireless terminal, the second wireless terminal that performs wireless communication with the first wireless terminal, and the second wireless terminal, and the first wireless terminal A mesh network system time synchronization method having a data collection device for collecting data,
A first time information storage step in which the data collection device stores time information of a timer of the data collection device in a data collection request message for requesting data from the first wireless terminal;
A first transmission step in which the data collection device transmits the data collection request message;
A first measurement step in which the second wireless terminal measures a transfer delay time required for the transfer process of the data collection request message;
A first correction step in which the second wireless terminal corrects the time information stored in the data collection request message based on the transfer delay time measured in the first measurement step;
A second time information storage step in which the second wireless terminal stores the time information corrected in the first correction step in a transfer message generated by performing the transfer process on the data collection request message. When,
A second transmission step in which the second wireless terminal transmits the transfer message;
A data collection step in which the first wireless terminal performs data collection requested by the data collection device based on the transfer message;
A first time synchronization step in which the first wireless terminal adjusts the time of a timer used by the first wireless terminal based on time information in the transfer message;
A time synchronization method characterized by comprising:

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