Synchronization system and synchronization method of clock

It is provided a synchronization system capable of managing execution of synchronization for clocks to be mounted on various devices.A synchronization system of clocks comprising: a leader device; a follower device capable of establishing communication connection with the leader device; and a server apparatus capable of establishing communication connection with the leader device and/or the follower device, the system further comprising: a time deviation calculator configured to calculate a time deviation between the leader device and the follower device; and a time corrector configured to correct a time in the follower device based on the calculated time deviation, wherein the synchronization system executes the time deviation calculator and/or the time corrector when the server apparatus generates, transmits, and/or receives predetermined information.

TECHNICAL FIELD

The embodiment of the present invention relates to synchronization system and synchronization method of clock.

BACKGROUND ART

As a synchronization method of clocks, it has been proposed to perform wireless communication in both directions between a leader node and a follower node, which are two stations on the ground, obtain a time difference between a clock of the leader node and a clock of the follower node from a propagation delay time corresponding to a round trip by data communication between the leader node and the follower node, and perform time correction of the follower node based on the time difference (e.g., refer to Patent Literature 1).

Meanwhile, in recent years, the number of sensors being shipped is increasing year by year due to the spread of IoT devices, and the number of sensors to be used in Japan and abroad is expected to increase further with the introduction of self-driving vehicles in the future. In a sensor or the like used in a self-driving vehicle, it is necessary to sense necessary information at an accurate timing, and thus, it is required to have a more precise clocking function. Therefore, a clock mounted on a sensor is required to be synchronized with a highly accurate leader clock and to maintain a precise clocking function, and furthermore, execution management of synchronization is required.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2014-115794 A

SUMMARY OF INVENTION

Technical Problem

An object of the present invention is to provide a synchronization system and a synchronization method capable of managing execution of synchronization in a synchronization system of clocks to be mounted on various devices.

Solution to Problem

The present invention solves the above problem by any of the following [1] to [16].[1] A synchronization system of clocks comprising: a leader device; a follower device capable of establishing communication connection with the leader device; and a server apparatus capable of establishing communication connection with the leader device and/or the follower device, the system further comprising: a time deviation calculator configured to calculate a time deviation between the leader device and the follower device; and a time corrector configured to correct a time in the follower device based on the calculated time deviation, wherein the synchronization system executes the time deviation calculator and/or the time corrector when the server apparatus generates, transmits, and/or receives predetermined information;[2] The synchronization system according to [1], wherein the follower device includes: a transmission requestor configured to transmit a transmission request of predetermined information to the server apparatus; and a second predetermined information transmitter configured to transmit, upon receiving predetermined information from the server apparatus, the received predetermined information to the leader device, the server apparatus includes: a first predetermined information transmitter configured to transmit, upon receiving a transmission request for predetermined information from the follower device, the predetermined information to the follower device; and a predetermined information determinator configured to determine, upon receiving predetermined information from the leader device, whether the predetermined information received from the leader device corresponds to the predetermined information transmitted to the follower device, the leader device includes a third predetermined information transmitter configured to transmit, upon receiving predetermined information from the follower device, the predetermined information to the server apparatus, and the synchronization system executes the time deviation calculator and/or the time corrector when it is determined that the predetermined information received from the leader device corresponds to the predetermined information transmitted to the follower device;[3] The synchronization system according to [1] or [2], wherein the follower device includes a first information transmitter configured to transmit information or a signal to the leader device, the leader device includes a second information transmitter configured to transmit information or a signal to the follower device, and the time deviation calculator calculates a time deviation between the leader device and the follower device based on a time at which information or a signal is transmitted from the leader device to the follower device, a time at which information or a signal is transmitted from the follower device to the leader device, a time at which the leader device transmits and the follower device receives and clocks the time, and a time at which the follower device transmits and the leader device receives and clocks the time;[4] The synchronization system according to [3], wherein the time deviation calculator calculates a time deviation between the time of the leader device and the time of the follower device by calculating ½×((TSM−TS)−(TMS−TM)), by defining: as TM, a time at which information or a signal is transmitted from the leader device to the follower device; as TS, a time at which information or a signal is transmitted from the follower device to the leader device; as TMS, a time clocked by the follower device3at which the follower device3received information or a signal transmitted from the leader device1; and further as TSM, a time clocked by the leader device1at which the leader device1received information or a signal transmitted from the follower device3;[5] A synchronization system of clocks comprising: a leader device; a follower device capable of establishing communication connection with the leader device; and a server apparatus capable of establishing communication connection with the leader device and/or the follower device, the system further comprising: a phase deviation calculator configured to calculate clocks phase deviation between the leader device and the follower device; and a phase corrector configured to correct a phase in the follower device based on the calculated phase deviation, wherein the synchronization system executes the phase deviation calculator and/or the phase corrector when the server apparatus generates, transmits, and/or receives predetermined information;[6] The synchronization system according to [5], wherein the follower device includes: a transmission requestor configured to transmit a transmission request of predetermined information to a server apparatus; and a second predetermined information transmitter configured to transmit, upon receiving predetermined information from the server apparatus, the received predetermined information to the leader device, the server apparatus includes: a first predetermined information transmitter configured to transmit, upon receiving a transmission request for predetermined information from the follower device, the predetermined information to the follower device; and a predetermined information determinator configured to determine, upon receiving predetermined information from the leader device, whether the predetermined information received from the leader device corresponds to the predetermined information transmitted to the follower device, the leader device includes a third predetermined information transmitter configured to transmit, upon receiving predetermined information from the follower device, the predetermined information to the server apparatus, and the synchronization system executes the phase deviation calculator and/or the phase corrector when it is determined that the predetermined information received from the leader device corresponds to the predetermined information transmitted to the follower device;[7] The synchronization system according to [5] or [6], wherein the follower device includes a first information transmitter configured to transmit information or a signal to the leader device, the leader device includes a second information transmitter configured to transmit information or a signal to the follower device, and the phase deviation calculator calculates a phase deviation based on a phase difference between a phase of a carrier wave constituting information or a signal transmitted from the leader device to the follower device and a phase of a signal oscillated by an oscillator of a clock of the follower device when the information or the signal is received by the follower device, and a phase difference between a phase of a carrier wave constituting information or a signal transmitted from the follower device to the leader device and a phase of a signal oscillated by an oscillator of a clock of the leader device when the information or the signal is received by the leader device;[8] The synchronization system according to [7], wherein the phase deviation calculator calculates a phase deviation between the leader device and the follower device by calculating ΔΦP=½×(ΔΦS−ΔΦM), by defining: as ΔΦS, a phase difference between a phase of a carrier wave constituting information or a signal transmitted from the leader device to the follower device and a phase of a signal oscillated by an oscillator of a clock when the information or the signal is received by the follower device; and as ΔΦM, a phase difference between a phase of a carrier wave constituting information or a signal transmitted from the follower device to the leader device and a phase of a signal oscillated by an oscillator of a clock when the information or the signal is received by the leader device;[9] The synchronization system according to any one of [1] to [8], comprising a charger configured to charge an owner or a user of the follower device in accordance with generation, transmission, and/or reception of the predetermined information, calculation of a time deviation, correction of a time, calculation of a phase deviation, or correction of a phase;[10] The synchronization system according to any one of [1] to [9], comprising a controller configured to control according to a charging amount by the charger: a frequency of executing the time corrector or the phase corrector; accuracy of a clock of the leader device that serves as a basis of calculation of the time deviation calculator or the phase deviation calculator; a distance between the leader device and the follower device; or a response speed of the leader device, the follower device, and/or the server apparatus;[11] A synchronization method of clocks to be executed in a synchronization system of clocks, the system including a leader device, a follower device capable of establishing communication connection with the leader device, and a server apparatus capable of establishing communication connection with the leader device and/or the follower device, the method comprising: a time deviation calculating step of calculating a time deviation between the leader device and the follower device; and a time correcting step of correcting the time in the follower device based on the calculated time deviation, wherein the synchronization method executes the time deviation calculating step and/or the time correcting step when the server apparatus generates, transmits, and/or receives predetermined information;[12] A synchronization method of clocks to be executed in a synchronization system of clocks, the system including a leader device, a follower device capable of establishing communication connection with the leader device, and a server apparatus capable of establishing communication connection with the leader device and/or the follower device, the method comprising: a phase deviation calculating step of calculating a phase deviation of clocks between the leader device and the follower device; and a phase correcting step of correcting a phase in the follower device based on the calculated phase deviation, wherein the synchronization method executes the phase deviation calculating step and/or the phase correcting step when the server apparatus generates, transmits, and/or receives predetermined information;[13] A synchronization system of clocks comprising a leader device and a follower device capable of communicating with the leader device, the system further comprising: a time deviation calculator configured to calculate a time deviation between the leader device and the follower device; and a time corrector configured to correct a time in the follower device based on the calculated time deviation, wherein the synchronization system executes a time deviation calculator and/or a time corrector when the leader device generates, transmits, and/or receives predetermined information;[14] A synchronization system of clocks comprising a leader device and a follower device capable of communicating with the leader device, the system further comprising: a phase deviation calculator configured to calculate a phase deviation of clocks between the leader device and the follower device; and a phase corrector configured to correct a phase in the follower device based on the calculated phase deviation, wherein the synchronization system executes the phase deviation calculator and/or the phase corrector when the leader device generates, transmits, and/or receives predetermined information;[15] A synchronization method of clocks to be executed in a synchronization system of clocks, the system including a leader device and a follower device capable of communicating with the leader device, the method comprising: a time deviation calculating step of calculating a time deviation between the leader device and the follower device; and a time correcting step of correcting the time in the follower device based on the calculated time deviation, wherein the synchronization method executes the time deviation calculating step and/or a time correcting step when the leader device generates, transmits, and/or receives predetermined information;[16] A synchronization method of clocks to be executed in a synchronization system of clocks, the system including a leader device and a follower device capable of communicating with the leader device, the method comprising: a phase deviation calculating step of calculating a phase deviation of clocks between the leader device and the follower device; and a phase correcting step of correcting a phase in the follower device based on the calculated phase deviation, wherein the synchronization method executes the phase deviation calculating step and/or the phase correcting step when the leader device generates, transmits, and/or receives predetermined information.

Advantageous Effects of Invention

The present invention can provide a synchronization system and a synchronization method capable of managing execution of synchronization in a synchronization system of clocks to be mounted on various devices.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. Hereinafter, description relating to effects shows an aspect of the effects of the embodiments of the invention and does not limit the effects.

FIG.1is a block diagram illustrating a configuration of a synchronization system corresponding to at least one of the embodiments of the present invention. As illustrated, the synchronization system includes a leader device1, a server apparatus2, and a follower device3. The leader device1can establish communication connection with each of the server apparatus2and the follower device3via a communication network. The leader device1is a reference device for synchronizing a clock of the follower device3, and one leader device1can also function as a leader device for a plurality of follower devices3. The synchronization system of the present invention may also include a plurality of leader devices1.

Furthermore, what functions as the follower device3for one leader device1can also function as the leader device for another follower device. The plurality of follower devices3exist for one leader device1, and each of the plurality of follower devices3functions as the leader device for a plurality of other follower devices, thereby forming a pyramidal relationship.

The follower devices3can establish communication connection with each of the leader device1and the server apparatus2via a communication network. In this synchronization system, the time of each follower device3is synchronized with reference to the time clocked by the leader device1, and the phase of the signal generated by an oscillator in the follower device3is synchronized with reference to the phase of the signal generated by the oscillator in the leader device1.

Furthermore, the follower device3can function as a leader with respect to the other follower devices, each time of the other follower devices is synchronized with reference to the time clocked by the follower device3, and each phase of the signal generated by the oscillator in the other follower devices is synchronized with reference to the phase of the signal generated by the oscillator in the follower device3. The present synchronization system can also be applied when the follower device3is caused to function as a leader.

The leader device1of the present invention will be described.FIG.2is a block diagram illustrating a configuration of a leader device corresponding to at least one of the embodiments of the present invention. The leader device1includes a control unit11, an RF chip12, an oscillator13, a clock14, and a phase detector15. The RF chip12includes the clock14and the phase detector15. In a case where the leader device1functions as, for example, a sensor device, other elements such as a sensor may be provided as necessary in addition to the control unit11, the RF chip12, the oscillator13, the clock14, and the phase detector15.

The control unit11is not particularly limited, but for example, a microcomputer (microcontroller) can be used. The control unit11performs a program execution process based on a program and data. The RF chip12performs processes of receiving and transmitting a radio signal via a communication network2. Data received by the RF chip12is subjected to an arithmetic process by the control unit11.

The oscillator13oscillates at a predetermined frequency and outputs a signal for giving an operation timing of each unit of the apparatus. As the oscillator13, an atomic oscillator or a crystal oscillator can be used. The clock14clocks the output signal of the oscillator13as a source vibration and outputs time. The time clocked by the clock14is controlled by the control unit11so as to be transmitted to the follower device3via the RF chip12. The phase detector15detects the phase of a carrier wave constituting information received from the follower device3, and detects the phase of the signal oscillated by the oscillator13in the leader device1.

The follower device3of the present invention will be described.FIG.3is a diagram illustrating a configuration of a follower device corresponding to at least one of the embodiments of the present invention. The follower device3includes a control unit31, an RF chip32, an oscillator33, a clock34, and a phase detector35. The RF chip32includes the clock34and the phase detector35. In a case where the follower device3functions as, for example, a sensor device, other elements such as a sensor may be provided as necessary in addition to the control unit31, the RF chip32, the oscillator33, the clock34, and the phase detector35.

The control unit31is not particularly limited, but for example, the microcomputer can be used. The control unit31performs a program execution process based on a program and data. The RF chip32performs processes of receiving and transmitting the radio signal via the communication network2. Data received by the RF chip32is subjected to the arithmetic process by the control unit11.

The oscillator33oscillates at the predetermined frequency and outputs a signal for giving an operation timing of each unit of the apparatus. As the oscillator33, for example, the crystal oscillator can be used. The clock34clocks the output signal of the oscillator33as the source vibration and outputs time. The time clocked by the clock34is controlled by the control unit31so as to be transmitted to the leader device1via the RF chip32. The phase detector35detects the phase of the carrier wave constituting information received from the leader device1and detects the phase of the signal oscillated by the oscillator33of the follower device3.

Next, a server apparatus of the present invention will be described.FIG.4is a block diagram illustrating a configuration of the server apparatus corresponding to at least one of the embodiments of the present invention. The server apparatus2includes at least a control unit21, a RAM22, a storage unit23, and a communication interface24, which are connected by an internal bus.

The control unit21includes a CPU and a ROM, executes a program stored in the storage unit23, and controls the server apparatus2. In addition, the control unit21includes an internal timer that clocks time. The RAM22is a work area of the control unit21. The storage unit23is a storage area for storing programs and data. The control unit21reads the program and the data from the RAM22, and performs a program execution process based on information or the like received from the leader device1or the follower device3.

Next, a synchronization process of clocks according to one embodiment of the present invention will be described.FIGS.5and6are flowcharts illustrating the synchronization process of clocks corresponding to at least one of the embodiments of the present invention. A flowchart of one synchronization process is illustrated separately inFIGS.5and6. The order of each process constituting the flowchart may be a random order as long as there is no occurrence of contradiction or inconsistency in the processing content.

The synchronization process of the follower device3can be executed periodically. For example, it is possible to set such that the synchronization processes of steps S1to S38is started once a day at a predetermined time set in advance.

First, the leader device1transmits identification information for identifying the leader device1to the follower device3(step S1). In each of the leader devices1, the identification information such as an identification number that enables to uniquely identify the leader device1is registered in advance. The leader device1clocks the time at which the information was transmitted in step S1, and measures the phase at the time of transmission (step S2). Then, the clocked time and the measured phase are stored in the memory in the control unit11(step S3).

Next, the follower device3receives the identification information of the leader device1(step S4). The leader device1clocks the time at which the identification information was received in step S4and measures the phase at the time of transmission (step S5). Then, the clocked time and the measured phase are stored in the memory in the control unit31(step S6).

The follower device3determines whether the leader device1is a synchronization target of the follower device3based on the identification information of the leader device1received in step S4(step S7). When it is determined that the leader device1is not the synchronization target of the follower device3(No in step S7), the process ends.

When it is determined that the leader device1is the synchronization target of the follower device3(Yes in step S7), the follower device3transmits a transmission request for predetermined information to the server apparatus2(step S8). Here, the predetermined information is, for example, information for proving that the clock of the follower device3is synchronized using the synchronization system of the present invention. Hereinafter, the predetermined information is referred to as proof information.

Next, when the server apparatus2receives the transmission request for the proof information from the follower device3(step S9), the control unit21of the server apparatus2generates the proof information (step S10). The generated proof information may be non-falsifiable.

The generated proof information is transmitted from the server apparatus2to the follower device3(step S11). As the proof information, for example, a randomly generated character string can be used. In addition to the proof information, the information to be transmitted in step S1lcan include other information such as identification information that can identify the follower device3or identification information that can identify the leader device1serving as a synchronization reference of the follower device3. Furthermore, in step S11, information obtained by encrypting the proof information and other information may be transmitted. The encrypted information including the proof information is decrypted by the leader device1or the server apparatus2and used.

An operator of the synchronization system of the present invention can charge an owner or a user of the follower device3as a reward for executing the synchronization process of the follower device3. When the proof information is transmitted from the server apparatus2to the follower device3in step S11, the server apparatus2performs a process of executing the charging (step S12). For example, when calculating the charging amount according to the number of times the synchronization process has been executed by the follower device3, the number of times the proof information has been transmitted from the server apparatus2to the follower device3is counted in step S12, and the counted number of times is stored in the storage unit23to possible to execute the charging. It is also possible to charge the owner or the user of the follower device3collectively for each predetermined period such as once a month, or charge the owner or the user for each synchronization.

In the present embodiment, the charging is executed according to the number of times the proof information has been transmitted from the server apparatus2to the follower device3, but the charging may be executed according to generation of the proof information in the server apparatus2, reception of the proof information by the leader device1and/or the follower device3, calculation of a time deviation or calculation of a phase deviation between the leader device1and the follower device3, or correction of a time or correction of a phase of the follower device3.

Upon receiving the proof information from the server apparatus2(step S13), the follower device3transmits the received proof information to the leader device1(step S14). The proof information to be transmitted in step S14may be newly generated by the follower device3based on the proof information that has been received in step S11.

Furthermore, the follower device3transmits a synchronization request to the leader device1(step S15). The follower device3clocks the time at which the synchronization request was transmitted and measures the phase at the time of transmission (step S16). Then, the clocked time and the measured phase are stored in the memory in the control unit31(step S17).

The leader device1receives the proof information transmitted from the follower device3in step S14(step S18), and further receives the synchronization request transmitted in step S15(step S19). When the pieces of information in steps S14and S15are transmitted at the same time, the pieces of information in steps S18and S19are received at the same time in the leader device1.

When the synchronization request is received in the leader device1in step S19, the time at which the synchronization request was received in step S19is clocked, and the phase at the time of reception is measured (step S20). Then, the clocked time and the measured phase are stored in the memory in the control unit11(step S21). When step S21ends, the process proceeds to step S22.

The leader device1transmits the proof information and a confirmation request for the proof information to the server apparatus2(step S22). As the proof information to be transmitted in step S22, the one newly generated by the leader device1based on the proof information that has been received in step S18may be used.

Similarly to step S11, the information to be transmitted in step S14or step S22can include not only the proof information but also other information such as the identification information of the follower device3or the leader device1. Similarly, in step S14or step S22, information obtained by encrypting the proof information and other information may be transmitted.

When the server apparatus2receives the proof information and the confirmation request for the proof information from the leader device1(step S23), it is determined whether the proof information received from the leader device1corresponds to the proof information transmitted from the server apparatus2to the follower device3(step S22). Then, the information on the determination result of step S24is transmitted from the server apparatus2to the leader device1(step S25).

Next, the leader device1receives the information on the determination result of step S24(step S26). When it is determined that the proof information received from the leader device1does not correspond to the proof information transmitted from the server apparatus2to the follower device3(No in step S27), time synchronization of the follower device3is not performed, and the process ends.

On the other hand, when it is determined that the proof information received from the leader device1corresponds to the proof information transmitted from the server apparatus2to the follower device3(Yes in step S27), the leader device1transmits, to the follower device3by the RF chip12, the information related to the time and phase when the identification information was transmitted in step S1, which has been stored in step S3, and the information related to the time and phase when the synchronization request was received in step S19, which has been stored in step S21(step S28).

Then, the follower device3receives the information related to the time and phase when the identification information was transmitted in step S1, and the information related to the time and phase when the leader device1received the synchronization request in step S19(step S29).

Next, the control unit31of the follower device3calculates a phase deviation between the phase of a signal generated by the oscillator of the leader device1and the phase of a signal generated by the oscillator of the follower device3(step S30). The phase deviation can be calculated based on a phase difference between the phase of the carrier wave constituting information or a signal transmitted from the leader device1to the follower device3and the phase of a signal oscillated by an oscillator of the follower device3when the information or the signal was received by the follower device3, and a phase difference between the phase of the carrier wave constituting information or a signal transmitted from the follower device3to the leader device1and the phase of a signal oscillated by an oscillator of a clock of the leader device1when the information or the signal was received by the leader device1.

The phase of the carrier wave constituting the information or the signal transmitted from the leader device1to the follower device3is the phase of the information transmitted in step S1. The information related to the phase is transmitted from the leader device1to the follower device3in step S28. The phase of a signal oscillated by the oscillator of the follower device3when the information or the signal was received by the follower device3is the phase of the information received in step S4. The information related to the phase is measured by the follower device3in step S5and stored in step S6. The phase of the carrier wave constituting information or a signal transmitted from the follower device3to the leader device1is, for example, the phase of the synchronization request transmitted in step S15. The information related to the phase is stored by the follower device3in step S17. The phase of the signal oscillated by the oscillator of the clock of the leader device1when the information or the signal was received by the leader device1is, for example, the phase of the synchronization request received in step S19. The information related to the phase is measured in step S20and transmitted from the leader device1to the follower device3in step S28.

Here, the phase of the carrier wave constituting the information or the signal transmitted from the leader device1to the follower device3is a concept including not only the phase of the carrier wave constituting the information or the signal transmitted from the leader device1to the follower device3but also the phase of the carrier wave constituting the signal obtained by mixing down the information or the signal. Similarly, the phase of the carrier wave constituting the information or the signal transmitted from the follower device3to the leader device1is a concept including not only the phase of the carrier wave constituting the information or the signal transmitted from the follower device3to the leader device1but also the phase of the carrier wave constituting the signal obtained by mixing down the information or the signal.

A phase difference ΔΦPgenerated by the signal propagation between the leader device1and the follower device3can be calculated from the arithmetic mean of a phase difference ΔΦSand a phase difference ΔΦM, by defining: as ΔΦS, the phase difference between the phase of the carrier wave constituting information or a signal transmitted from the leader device1to the follower device3and the phase of the signal oscillated by the oscillator of the follower device3when the information or the signal was received by the follower device3; and as ΔΦM, the phase difference between the phase of the carrier wave constituting information or a signal transmitted from the follower device3to the leader device1and the phase of the signal oscillated by the oscillator of the leader device1when the information or the signal was received by the leader device1. That is, the phase difference ΔΦPcan be calculated by Equation (1): ΔΦP=½×(ΔΦS+ΔΦM).

When the phase deviation between the leader device1and the follower device3is defined as ΔΦC, the relationship expressed by Equation (2): ΔΦM=ΔΦP+(−ΔΦC) is established, so that the phase deviation ΔΦCcan be calculated by subtracting the phase difference ΔΦMfrom the phase difference ΔΦP. That is, the phase difference ΔΦCcan be calculated by Equation (2): ΔΦC=½×(ΔΦS−ΔΦM). In step S30, the phase deviation between the leader device1and the follower device3is calculated using Equation (2).

Here, the phase deviation ΔΦCis calculated by Equation (2), but in some cases, the phase deviation ΔΦCto be calculated may be obtained by further subtracting 2Π or 4Π, that is, 2nΠ. n may take zero or a positive integer. Therefore, it is also possible to specify whether n is zero, or an integer such as 1 or 2 (that is, whether the value obtained by further subtracting 2nΠ from the phase difference ΔΦCobtained by Equation (2) is the original phase deviation or whether the value not subtracted is the original phase deviation) based on a propagation time TPto be described later or a time deviation between the leader device1and the follower device3.

There may be a case such that the signal transmitted from the leader device1to the follower device3and the signal transmitted from the follower device3to the leader device1start with an output that is not zero but is an arbitrary value at the start of transmission. In such a case, it is necessary to correct the phase deviation ΔΦCby measuring the phase at the start of transmission and the transmission time. Meanwhile, by configuring such that the phase at the start of transmission is always constant and transmission is performed at a predetermined time, it is possible to omit such a process of correcting ΔΦCafter measuring the phase at the start of transmission and the transmission time.

The follower device3corrects the phase of the signal generated by the oscillator of the follower device3so as to be synchronized with the signal generated by the oscillator of the leader device1based on the calculated phase deviation ΔΦC(step S31). The correction of the phase in step S31is controlled and executed by the control unit11. The phase deviation of the oscillator of the follower device3occurs due to the surrounding environment of the follower device3. By periodically performing the synchronization process in this manner, the clock34of the follower device3can be continuously clocked with high accuracy.

Next, the leader device1calculates a time deviation between the leader device1and the follower device3based on the time at which information or a signal was transmitted from the leader device1to the follower device3, the time at which information or a signal was transmitted from the follower device3to the leader device1, the time clocked by the follower device3at which the follower device3received information or a signal transmitted from the leader device1, the time clocked by the leader device1at which the leader device1received information or a signal transmitted from the follower device3(step S32).

The time at which information or a signal was transmitted from the leader device1to the follower device3is the time at which the information was transmitted in step S1. The information related to the time is transmitted from the leader device1to the follower device3in step S28. The time at which information or a signal was transmitted from the follower device3to the leader device1is the time at which the synchronization request was transmitted in step S15. The information related to the time is stored by the follower device3in step S17. Next, the time clocked by the follower device3at which the follower device3received information or a signal transmitted from the leader device1is the time at which the information was received in step S4. The information related to the time is clocked by the follower device3in step S5and stored in step S6. The time clocked by the leader device1at which the leader device1received information or a signal transmitted from the follower device3is the time at which the synchronization request was received in step S19. The information related to the time is clocked in step S20and transmitted from the leader device1to the follower device3in step S28.

The time deviation between the leader device1and the follower device3can be calculated by Equation (3): TL=½×((TSM−TS)−(TMS−TM)) by defining: as TM, a time at which information or a signal was transmitted from the leader device1to the follower device3; as TS, a time at which information or a signal was transmitted from the follower device3to the leader device1; as TMS, a time clocked by the follower device3at which the follower device3received information or a signal transmitted from the leader device1; and further as TSM, a time clocked by the leader device1at which the leader device1received information or a signal transmitted from the follower device3. In step S32, the time deviation between the leader device1and the follower device3is calculated by Equation (3).

The follower device3corrects the time in the follower device3so as to be synchronized with the time in the leader device1based on the calculated time deviation (step S33).

Next, the follower device3transmits, to the leader device1together with a time evaluation request, information related to the time at which the identification information was received in step4and the phase of the received identification information, and, the time at which the synchronization request was transmitted in step S15and the phase of the transmitted synchronization request (step S34). The time at which the identification information was received and the phase of the identification information are the ones that have been measured in step S5and stored in the follower device3in step S6. The time at which the synchronization request was transmitted and the phase of the synchronization request are the ones that have been measured in step S16and stored in the follower device3in step S17. The leader device1receives the time at which the identification information was received in step4and the phase of the received identification information together with the time evaluation request (step S35).

The leader device1evaluates a time accuracy of the follower device3based on the information received in step S35(step S36). In step S36, the time accuracy of the follower device3is evaluated by calculating the phase deviation in the follower device3by the method similar to step S30and calculating the time deviation in the follower device3by the method similar to step S32. It is possible to assign a time accuracy grade to the calculated time deviation and phase deviation based on a predetermined reference. The time accuracy grade assigned to the follower device3is transmitted as qualification information from the leader device1to the follower device3(step S37). When the follower device3receives the qualification information (step S38), a series of processes ends.

In the above embodiment, the description has been made on the assumption that the leader device1and the server apparatus2are separate devices, but the leader device1and the server apparatus2may be configured as an integrated device. In this case, the processes executed by the server apparatus2in the above embodiment are executed by the leader device1. For example, the processes of steps S9to S12and S23to S25are executed by the leader device1.

In the above embodiment, the server apparatus2generates the proof information every time the synchronization process is executed. It also can be configured such that when executing the synchronization of the follower device3, the time deviation and the phase deviation of the follower device3are corrected without: generating the proof information in the server apparatus2; transmitting the proof information from the server apparatus2to the follower device3; and transmitting the proof information from the follower device3to the leader device. For example, the proof information may include information related to a period or a condition in which the synchronization process of the follower device3can be executed. Once the follower device3receives the proof information from the server apparatus2, the follower device3can execute the synchronization process a plurality of times without receiving the proof information from the server apparatus2as long as the period and the condition are satisfied.

Furthermore, in a case where the plurality of follower devices3exist, one of the follower devices3receives the proof information from the server apparatus2, so that not only the follower device3that has received the proof information but also the other follower devices3can be configured to execute the synchronization process. In this case, the proof information includes information that can identify the follower device3that can be a target of the synchronization process, and the synchronization process can be executed on the identified follower device3without receiving the proof information from the server apparatus2.

In the above embodiment, the matter of executing the process of charging has been described. It can be configured in such a way that the frequency of executing the time correction or the phase correction, the accuracy of the clock of the leader device1to be a basis for the calculation of time deviation or phase deviation, a distance between the leader device1and the follower device3, or response speed of the leader device1, the follower device3, and/or the server apparatus2, are controlled to be different according to the charging amount. For example, as the charging amount per predetermined number of times or the charging amount per predetermined period becomes higher, the frequency of the time correction or the phase correction can be increased, or the time deviation or the phase deviation can be calculated based on a clock with higher accuracy. In addition, as the charging amount per predetermined number of times or the charging amount per predetermined period becomes higher, it is possible to perform control such that after information has been transmitted from any one of the leader device1, the follower device3, and the server apparatus2, the response speed (for example, the speed until the next process is executed in the device that has received the information, or the speed until the information is transmitted from the device that has received the information to the next device) in the device that has received the information becomes faster.

REFERENCE SIGNS LIST