Information communication system and information communication device

Abstract

To provide an information communication system and an information communication device, capable of performing synchronous control with a reduced error by absorbing variation in a propagation time of information communication without using a reference clock such as a GMC or a relay device such as a BC or TC.SOLUTION: An information communication system 100 includes: a communication control unit 73 for making a communication unit 10 perform transmission / reception of synchronization information within a predetermined time in which a time difference can be regarded as constant between information communication devices 1; a time acquisition unit 76 for acquiring transmission / reception time of synchronization information of an own device CLa (1) and transmission / reception time of the synchronization information of an other device CLb (1); a time difference calculation unit 77 for calculating time differences between a clock 20 of the own device CLa and clocks 20 of all other devices CLb, on the basis of the time acquired by the time acquisition unit 76; a virtual time difference calculation unit 78 for calculating a virtual time difference, which is a time difference between the clock 20 of the own device CLa and a virtual clock; and a synchronization control unit 79 for performing time synchronization of the clock 20 of the own device CLa with the virtual clock on the basis of the virtual time difference.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an information and communication system and an information and communication device that synchronizes a plurality of information and communication devices through communication. [Background technology]

[0002] A common time synchronization method between multiple information communication devices is, for example, the IEEE1588 Precision Time Protocol (PTP) described in Non-Patent Document 1. Non-Patent Document 1 defines a master device having a reference time and a slave device that synchronizes with the time of the master device, and corrects the time of the slave device by periodically exchanging time synchronization packets between the master device and the slave device.

[0003] Specifically, the slave device estimates and corrects the time offset, which is the time difference between the master device and the slave device, using the master device's transmission time and the slave device's reception time of a packet transmitted from the master device to the slave device, and the slave device's transmission time and the master device's reception time of a packet transmitted from the slave device to the master device. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] “IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems.”IEEE Standard 1588-2008. [Patent Document 1] JP 2016-225880 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the PTP system, the Grandmaster Clock (GMC) is used as the reference clock supplied to the master device. The GMC is a reference clock for synchronizing the clocks of all devices in the network.

[0006] In addition, the PTP system uses network relay devices such as BC and TC to cancel out fluctuating propagation times and reduce the problem of reduced time synchronization accuracy caused by fluctuations in propagation times. The Boundary Clock (BC) corrects delays and fluctuations based on the time received from the higher-level master device and generates the time as a master for lower-level slaves. The Transparent Clock (TC) adds the residence time in the relay device when relaying packets and sends it to the lower-level slaves.

[0007] However, GMC, BC, and TC are generally expensive, which increases the cost of building a time synchronization system. For this reason, there is a need for alternatives that can satisfy the system requirements for time synchronization accuracy without introducing GMC, BC, or TC.

[0008] For example, Patent Document 1 proposes a method of absorbing fluctuations in propagation time by using the minimum packet time. However, since the minimum packet time in each direction of information communication is calculated independently from moment to moment, the symmetry of the propagation time is not evaluated, which leads to a decrease in the accuracy of time synchronization.

[0009] In addition, because the main cause of time difference fluctuations is the frequency deviation of the clocks between devices, some implementations of PTP provide an option to determine and cancel this frequency deviation. However, this does not remove the error factor caused by fluctuations in propagation time, resulting in a decrease in the accuracy of time synchronization.

[0010] The present invention has been made to solve the above-mentioned problems, and aims to provide an information and communications system and an information and communications device that are capable of synchronous control with reduced error by absorbing fluctuations in the propagation time of information and communications without using a reference clock such as GMC or a relay device such as BC or TC. [Means for solving the problem]

[0011] The present invention is an information and communication system in which a communication unit of a plurality of information and communication devices communicates information according to the time of their own clocks without using a reference clock, the system including a communication control unit that causes the communication unit to transmit and receive synchronization information within a predetermined time period that can be considered as a constant time difference between the information and communication devices, and a time acquisition unit that acquires a transmission time of the synchronization information from one of the information and communication devices, a reception time of the synchronization information transmitted from the own device by another device that is an information and communication device other than the own device, a transmission time of the synchronization information from all of the other devices, and a reception time of the synchronization information transmitted from all of the other devices by the own device. The information communication device has a time acquisition unit, a time difference calculation unit that calculates the time difference between the clock of the own device and the clocks of all of the other devices based on the transmission time of the own device, the reception time of the own device, the transmission times of all of the other devices, and the reception times of all of the other devices acquired by the time acquisition unit, a virtual time difference calculation unit that calculates a virtual time difference, which is the time difference between the clock of the own device and a virtual clock that is a virtual clock that can be regarded as a common time source for all of the information communication devices, based on the time difference between the clock of the own device and all of the clocks, and a synchronization control unit that time-synchronizes the clock of the own device with the virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit.

[0012] The present invention relates to a communication control unit that causes the communication unit to transmit and receive synchronization information within a predetermined time period that can be considered as a constant time difference between the communication unit, which is a local device that communicates information with other devices that are multiple other information communication devices, without using a reference clock and in accordance with a clock that the local device has; a time acquisition unit that acquires a transmission time of the synchronization information from the local device, a reception time of the synchronization information transmitted from the local device by the other device, a transmission time of the synchronization information from all of the other devices, and a reception time of the synchronization information transmitted from all of the other devices by the local device; The information communication device has a time difference calculation unit that calculates the time difference between the clock of the own device and all clocks based on the transmission time of the own device, the reception time of the own device, the transmission times of all the other devices, and the reception times of all the other devices acquired by the acquisition unit; a virtual time difference calculation unit that calculates a virtual time difference, which is the time difference between the clock of the own device and a virtual clock, which is a virtual clock that can be regarded as a common time source for all the information communication devices, based on the time difference between the clock of the own device and all clocks; and a synchronization control unit that time-synchronizes the clock of the own device with the virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit. Effect of the Invention

[0013] According to the present invention, it is possible to provide an information and communication system and an information and communication device that are capable of synchronous control with reduced error by absorbing fluctuations in the propagation time of information and communication without using a reference clock such as GMC or a relay device such as BC or TC. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an information communication system according to an embodiment. [Diagram 2] 1 is a functional block diagram of an information communication device constituting an information communication system according to an embodiment. [Diagram 3] FIG. 2 is a diagram showing a mode of communication between information communication devices. [Figure 4] FIG. 2 is a functional block diagram of a control unit according to the embodiment. [Diagram 5]FIG. 1 is a diagram showing an aspect of communication having symmetry in propagation time. [Figure 6] FIG. 1 is a diagram showing a mode of communication that does not have propagation time symmetry. [Figure 7] FIG. 13 is a diagram showing a synchronization state vector without errors due to variations in propagation time and time difference. [Figure 8] FIG. 13 is a diagram showing a synchronization state vector including errors due to fluctuations in propagation time and time difference. [Figure 9] FIG. 2 is a diagram showing a set of information communications in the information communication system according to the embodiment. [Figure 10] 1 is a graph showing a schematic relationship between a clock of an error-free information communication device and a virtual clock. [Figure 11] 1 is a graph showing a schematic relationship between a clock of an information communication device including an error and a virtual clock. [Figure 12] 1 is a graph showing a probability distribution of time fluctuations that an information communication device can exhibit within a predetermined interval. [Figure 13] 1 is a flowchart illustrating a procedure for a synchronization control process according to an embodiment. [Figure 14] FIG. 4 is an explanatory diagram showing communication for acquiring transmission and reception times in the synchronous control of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an information communication system and an information communication device according to an embodiment will be described with reference to the drawings.

[0016] [composition] Fig. 1 is a schematic diagram of an information communication system 100 according to an embodiment. Fig. 2 is a functional block diagram of an information communication device 1 constituting the information communication system 100 according to the embodiment. Fig. 3 is a diagram showing a mode of communication between the information communication devices 1, and Fig. 4 is a functional block diagram of a control unit 70 in Fig. 2.

[0017] The information communication system 100 according to the present embodiment is a system in which information is communicated between information communication devices 1 (devices A to D) via a synchronous network. In the information communication system 100, each information communication device 1 communicates information according to its own clock without using a reference clock. The reference clock is a clock that actually exists on the synchronous network, such as GMC, and serves as a reference for all information communication devices 1 in the synchronous network to synchronize their respective clocks. Each information communication device 1 attempts synchronization by transmitting and receiving synchronization information. The synchronous network is preferably a complete network. A complete network is a network in which each node can directly communicate with all other nodes. For example, the synchronous network NE shown in FIG. 1 is a complete network with the number of nodes N=5. That is, N is the number of information communication devices 1 connected to the synchronous network NE, and five information communication devices 1 are connected in FIG. 1.

[0018] In this embodiment, there is no distinction between the role of the master device and the role of the slave device in each information communication device 1. In the following description, any one of the information communication devices 1 may be referred to as the local device (CLa, i, etc.), and the information communication devices 1 other than the local device may be referred to as other devices (CLb, j, etc.). There are N-1 other devices, but they may be denoted by a common reference symbol for convenience. In this embodiment, an example will be described in which the information communication device 1 transmits and receives information via a wire to achieve synchronization, but wireless communication may also be used.

[0019] (Information and communication devices) The information communication device 1 includes a computer, and a processor including a CPU or the like executes a program stored in advance in a storage unit such as an HDD or SSD to perform necessary calculations.

[0020] 2, the information communication device 1 has a communication unit 10, a clock 20, a timepiece 30, a storage unit 50, an external interface 60, and a control unit 70. For example, each of the units 10 to 70 is configured as hardware, but all or part of each of the units 10 to 70 may be configured as software including programs and data. Which part of the control unit 70 is configured as software can be appropriately changed in design.

[0021] The communication unit 10 transmits and receives information to and from another information communication device 1. That is, the communication unit 10 transmits information to the outside of the information communication device 1, receives information from the outside of the information communication device 1, or performs both. The communication unit 10 has a transmitter 11, a receiver 12, a transmission timing detection unit 13, and a reception timing detection unit 14.

[0022] The transmitter 11 is a device that transmits input information. Specifically, the transmitter 11 breaks down the information into its smallest components in time series and transmits the information to the outside. The packet length of the information (amount of communication information) is arbitrary and may be different for each communication. For example, an input unit that converts a voice signal input from a microphone into voice data is connected to the information communication device 1, and the voice data as information is input from the input unit to the information communication device 1.

[0023] The receiver 12 is a device that receives information from outside. Specifically, the receiver 12 reconstructs information that has been decomposed into minimum components in time series and received from outside the information communication device 1, and outputs the reconstructed information to other components in the information communication device 1. For example, a playback unit such as an ear receiver or speaker that outputs audio is connected to the information communication device 1, and the receiver 12 converts audio data into an audio signal and outputs the audio signal to the playback unit. In this way, the information that has been decomposed into minimum components in time series and transmitted / received can identify the position of each element in time series, i.e., the information element position.

[0024] Here, the information communicated by the information communication device 1, that is, the information transmitted by the transmitter 11 and the information received by the receiver 12, includes synchronization information for synchronizing time. The synchronization information is composed of synchronization timing or time information corresponding to the synchronization timing.

[0025] The transmission timing detection unit 13 detects the transmission timing. The transmission timing is the timing at which a predetermined information element position of the information transmitted by the transmitter 11 is transmitted to the outside of the information communication device 1. This transmission timing is detected based on the clock period of a clock 20 (in other words, the period of a pulse oscillated by the clock 20), which will be described later. In other words, the transmission timing is expressed based on an integer multiple of the clock period.

[0026] Moreover, the transmission timing detection unit 13 can also output the detection result to other components in the information communication device 1. The information here is, for example, a packet, and in this case, the predetermined information element position (hereinafter, referred to as the predetermined information element position) is a bit position.

[0027] The reception timing detection unit 14 detects the reception timing. The reception timing is the timing at which information received by the receiver 12 is received from outside the information communication device 1. This reception timing is detected based on the clock period of a clock 20, which will be described later. In other words, the reception timing is expressed as an integer multiple of the clock period. Furthermore, the reception timing detection unit 14 outputs the detection result to other components within the information communication device 1.

[0028] FIG. 3 shows an example of wired communication, in which in packet transmission between information communication devices 1, a specific bit position in a packet is detected as a transmission / reception timing, and a transmission interval and a reception interval are calculated from adjacent transmission timings and reception timings, respectively.

[0029] Note that the transmission timing and reception timing may both detect the position of the same smallest component, but as long as a predetermined relationship is maintained between the transmitting and receiving information communication devices 1 at each timing detection, it is not necessary to detect the same position, and any deviation in the detected element position can be ignored or corrected.

[0030] Furthermore, the transmission timing may be detected a predetermined time before or after the actual transmission timing, and the reception timing may be detected a predetermined time before or after the actual reception timing. These predetermined values ​​may be fixed within the communication unit 10, or may be set statically or dynamically from the outside.

[0031] The clock 20 oscillates at a predetermined frequency and outputs a signal that provides operation timing to each unit of the information communication device 1. As a result, each unit in the information communication device 1 operates in synchronization with the clock 20. The entire information communication device 1 may be synchronized simultaneously with a single clock 20, or multiple clocks 20 may be used to independently synchronize multiple functional units. This clock 20 has an inherent finite oscillation frequency tolerance. In other words, the clock 20 has an error (e.g., 20 ppm) relative to a predetermined oscillation frequency (e.g., 10 MHz). For example, a fixed frequency oscillator such as a quartz crystal resonator can be used as the clock 20.

[0032] Even if the nominal frequency of the clock 20 of the information communication devices 1 is the same, there are actually individual differences. That is, there is a frequency deviation between the frequencies of the clocks 20 of a plurality of information communication devices 1. The clock 20 may receive a frequency control signal from the outside and variably control the oscillation frequency in response to the signal.

[0033] The clock 30 keeps time using the output signal of the clock 20 as the oscillation source, and outputs the relative time from the start of the information communication device 1. The clocking may be synchronized with a divided frequency of the input clock signal. The advance amount per clock may be variable, and even if the clock frequency is fixed, the drive frequency of the clock 30 may be intermittently controllable. The time is referenced in a specified unit, and this specified value may be fixed within the clock 30, or may be set statically or dynamically from outside. The clock 30 outputs the relative time in response to a reference request from outside, for example.

[0034] The storage unit 50 is a recording medium such as an HDD, SSD, memory, or register. The storage unit 50 stores information necessary for the control unit 70 to perform calculations. The time of the clock 30 corresponding to the transmission timing or reception timing described below is preferably stored in a recording medium that can be accessed only by hardware, without the intervention of a CPU or software. This is because jitter caused by software can be eliminated. It is important that the correspondence between the transmission / reception timing and the time is not affected by software jitter, and after the transmission / reception timing and the time are associated, the time may be stored in a slow access area.

[0035] The memory as the storage unit 50 inputs and outputs any information, and stores the information in a specified storage area. Information is stored in response to an external storage request, at which time the information to be stored and the storage area are input. Information is referenced in response to an external reference request, at which time the storage area for the reference information is input, and the information in the storage area specified by the input is output. Information may be stored only while the device is in operation, or may be retained permanently, including when the device is stopped.

[0036] The external interface 60 (hereinafter also referred to as external I / F 60) connects the inside of the information communication device 1 with the outside, and inputs and outputs any information. The information includes transmission and reception data such as synchronization information, the time of the clock 30, and other information to be stored in the storage unit 50. Furthermore, the information communication device 1 may have a user interface such as a display device capable of controlling and displaying the internal state.

[0037] The control unit 70 controls the overall operation of each unit of the information communication device 1. Fig. 4 is a functional block diagram of the control unit 70. As shown in Fig. 4, the control unit 70 has a main control unit 71, a transmission / reception data I / F 72, a communication control unit 73, a scheduler 74, a time recording unit 75, a time acquisition unit 76, a time difference calculation unit 77, a virtual time difference calculation unit 78, and a synchronization control unit 79.

[0038] The main control unit 71 is linked to each unit in the control unit 70 and controls the operation of each unit in the control unit 70. The transmission / reception data I / F 72 converts information in the storage unit 50 and the external I / F 60 into a format that can be transmitted outside the device. In addition, the transmission / reception data I / F 72 converts information received from outside the device into a format suitable for the control unit 70 and the storage unit 50.

[0039] The communication control unit 73 controls the operation of the communication unit 10. The communication control unit 73 inputs and outputs transmission and reception information between the communication unit 10 and the control unit 70.

[0040] The scheduler 74 sets a schedule (time) for the communication control unit 73 to transmit or receive information. For example, the scheduler 74 on the transmitting side sets an interval for transmitting information, or sets a schedule for detecting the timing for transmitting information at a predetermined time.

[0041] The scheduler 74 of this embodiment sets the transmission time of the synchronization information and the transmission of the synchronization information for the information communication devices 1 to acquire the reception time of the synchronization information to be performed within a predetermined time that can be considered as a constant time difference. As described later, this predetermined time is the minimum interval time at which the influence of the frequency deviation in the own device CLa and the other device CLb appears in the information propagation time between the own device CLa and the other device CLb. The frequency deviation is the difference between the clock frequencies of the devices. For example, the transmission timing of the synchronization information including the transmission time from the own device CLa to the other device CLb and the transmission timing of the synchronization information including the transmission time from the other device CLb to the own device CLa are set to be within the predetermined time.

[0042] The time recording unit 75 records the time when information is transmitted or received. That is, the time recording unit 75 associates the transmission timing of the information detected by the transmission timing detection unit 13 with the time of the clock 30 at the transmission timing, and stores them in the memory. The time recording unit 75 also associates the reception timing of the information detected by the reception timing detection unit 14 with the time of the clock 30 at the reception timing, and stores them in the memory. For example, the time recording unit 75 receives a signal from the transmission timing detection unit 13 and the reception timing detection unit 14 indicating that the transmission and reception timing of the transmitted and received information has been detected, refers to the time of the clock 30, and associates the time with the transmission and reception timing.

[0043] Thus, in this embodiment, "time" refers to the time of the clock 30 corresponding to the detected reception timing or transmission timing of a specific information element position of information, and "hours" refers to the difference between the times.

[0044] The time acquisition unit 76 acquires the transmission time of the synchronization information from the own device CLa, the reception time of the synchronization information transmitted from the own device CLa by the other device CLb, the transmission time of the synchronization information from all the other devices CLb, and the reception time of the synchronization information transmitted from all the other devices CLb by the own device CLa. The transmission time and reception time of the own device CLa are acquired from the memory of the own device CLa. The reception time and transmission time of the other device CLb are acquired from the synchronization information received by the own device CLa from the other device CLb and stored in the memory.

[0045] The time difference calculation unit 77 calculates the time difference between the clock 20 of the own device CLa and the clock 20 of all other devices CLb based on the transmission time of the own device CLa, the reception time of the own device CLa, the transmission times of all other devices CLb, and the reception times of all other devices CLb acquired by the time acquisition unit 76.

[0046] The virtual time difference calculation unit 78 calculates a virtual time difference between the clock 20 of the own device CLa and the virtual clock based on the time difference between the clock 20 of the own device CLa and the clock 20 of all other devices CLb. The virtual time difference in this embodiment is the average value of the time differences between the clock 20 of the own device CLa and all the clocks 20. The virtual clock is not a clock that is actually operating, but a virtual clock that all information communication devices 1 can regard as a common time source.

[0047] The synchronization control unit 79 synchronizes the clock 20 of the own device CLa with the virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit 78. That is, the synchronization control unit 79 performs time synchronization using the virtual time difference as a correction value. The synchronization control unit 79 performs synchronization control assuming that the propagation time between the clock 20 of the own device CLa and the virtual clock is symmetrical. For example, as described later, the time difference with the virtual clock, that is, the time difference is calculated, and the value clocked by the clock 30 is corrected based on that time difference. For example, the correction may be performed by controlling the clock 30 itself to correct the time. Alternatively, the correction may be performed based on the time difference when the clock 30 outputs the time. That is, the time of the clock 30 itself may not be corrected, and the clock 30 may be controlled so that the clock 30 outputs a time corrected for the amount of deviation when the clock 30 outputs the time.

[0048] [Measurement of time difference when propagation times are symmetric] Next, the measurement of the propagation time and the time difference when the propagation time is symmetrical will be described with reference to Fig. 5. Fig. 5 shows the relationship between the time difference between the clocks and the propagation time of information between a pair of a local device CLa and another device CLb, and the transmission and reception timing observed by the information communication, using wired communication as an example.

[0049] Note that the synchronization information transmitted by the own device CLa and the other synchronization information transmitted by the other device CLb are intended to measure the timing for synchronization, and the synchronization information includes the transmission time of the own device CLa, etc., but the contents of the synchronization information and the other synchronization information are arbitrary.

[0050] As shown in FIG. 5, the device CLa transmits information at time t a,T and after a propagation time of d, the signal is transmitted to b,R The other device CLb receives it at Δt b Later, another device CLb sends another piece of information at time t b,T After the same propagation time d, the own device CLa transmits the a,R Receive at.

[0051] Here, the interval from transmission to reception in the own device CLa is Δt a Let the interval from reception to transmission in the other device CLb be Δt b The transmission timing t a,T The same timing is t´ in other device CLb. a,T The time difference g between the clock 20 of the other device CLb and the own device CLa at a certain moment can be calculated by the formula (1). Furthermore, the time difference between the clock of the own device CLa and the clock of the other device CLb at the same moment can be expressed as -g.

[0052] TIFF2025040875000002.tif11161 Note that, as described above, it is assumed that the propagation time d from device CLa to other device CLb and the propagation time d from other device CLb to device CLa are the same, that is, symmetrical in the direction of information communication.

[0053] From these conditions, the propagation time d can be calculated as shown in equation (2). TIFF2025040875000003.tif15159

[0054] Therefore, the time difference g between the clocks 20 can be calculated using equation (2) as shown in equation (3). TIFF2025040875000004.tif14158

[0055] The synchronization control unit 79 of the other device CLb can be time-synchronized with the own device CLa by repeatedly adjusting the clock frequency and time so that the time difference g between the clocks 20 becomes 0. Similarly, the synchronization control unit 79 of the own device CLa can be time-synchronized with the other device CLb by repeatedly adjusting the clock frequency and time so that the time difference -g between the clocks 20 becomes minimum.

[0056] If the clock frequencies of the own device CLa and the other device CLb are the same, that is, if the clock domain is single, time synchronization can be achieved by simply adjusting the time once, but since there is generally a frequency deviation between the two clocks, adjustment of the clock frequency is essential for time synchronization. Even in a system in which the clock frequency cannot be directly adjusted, the driving frequency of the clock 30 can be controlled and time synchronization can be achieved by repeatedly adjusting the advance of the time per clock. In these frequency adjustments, closed loop control is periodically performed with the synchronization phase as input and the frequency adjustment value as output, and the output value is controlled so that the input synchronization phase becomes 0.

[0057] In addition, the propagation time and internal delay between the transmission and reception timings can be ignored or corrected depending on the system requirements. Also, instead of starting the transmission of synchronization information from the own device CLa, the other device CLb may transmit the synchronization information. Furthermore, although one interface is necessary and sufficient for information communication, a configuration in which multiple interfaces are used simultaneously, for example, by implementing a transmission interface and a reception interface independently, may also be used.

[0058] [Effects of time difference and propagation time variations] The above explanation is based on the premise that the time difference is constant and the propagation time is symmetrical in the direction of information communication. However, the frequency deviation from the nominal frequency of the clock 20 between the actual information communication devices 1 is different and varies from moment to moment. For this reason, the time difference between the information communication devices 1 also varies, and depending on the network system to which the local device CLa and the other device CLb are connected, the propagation time is generally asymmetrical as shown in FIG. 6 due to the influence of the information propagation path and communication arbitration.

[0059] That is, the time difference g between the own device CLa and the other device CLb at a certain moment b / a Then, after a certain period of time has elapsed, the time difference g between the same device CLa and another device CLb a / b In addition, the propagation time d of information from the own device CLa to the other device CLb is not the same. b / a is the information propagation time d from another device CLb to its own device CLa a / b In general, the time difference in Figure 6 is expressed as g b / a and g a / b have the same sign, and g b / a ·g a / b ≧0. Furthermore, as mentioned above, the time difference and propagation time fluctuate from moment to moment, and the time difference g b / a [m] and propagation time d b / a [m] is the time difference g observed at different moments b / a [n] and propagation time d b / a It is common for these to be different from [n].

[0060] Here, from the relationship between the times in Figure 6, the propagation time d b / a ,d a / b and time difference g b / a ,g a / b Using this, equations (2) and (3) are rearranged into equations (4) and (5), respectively. TIFF2025040875000005.tif15162TIFF2025040875000006.tif13162

[0061] With equation (2), it is possible to calculate the propagation time under the assumption of symmetry, but with equation (4), it is clear that the average propagation time includes the fluctuating component of the time difference. Similarly, with equation (3), it is possible to calculate the time difference under the assumption that the time difference is constant, but with equation (5), it is clear that the average time difference includes the fluctuating component of the propagation time. In this way, the inclusion of fluctuating components of the time difference and propagation time leads to a decrease in the accuracy of time synchronization.

[0062] [Errors due to time difference and fluctuations in propagation time] We will explain the time synchronization error caused by the time difference and the fluctuation of the propagation time in a time synchronization system. First, we combine the formulas (4) and (5) and transform them into a matrix form as shown in formula (6). TIFF2025040875000007.tif13156

[0063] Here, the two-dimensional rotation matrix R θ is expressed as equation (7). TIFF2025040875000008.tif11161

[0064] Then, by focusing on the common factor in equation (6), R in equation (7) θ By using this, equation (6) can be transformed into equation (8). TIFF2025040875000009.tif14162

[0065] As shown in FIG. 7, the horizontal axis represents the time difference g when communication is performed from the own device CLa to another device CLb. b / a and propagation time d b / a The vertical axis represents the time difference g when communication is performed from another device CLb to its own device CLa. a / b and propagation time d a / b Consider a two-dimensional space with components of (g b / a - g a / b ) T The time difference vector g, (d b / a d a / b ) T If the propagation time vector d is taken as the propagation time vector, the synchronization state vector s = (gd d g ) T can be interpreted as the sum of the time difference vector g and the propagation time vector d rotated by +π / 4 on the same space and scaled in each dimension.

[0066] In the operation of equation (8), element g of the time difference vector g b / a , g a / b There is no change in, and the element d of the propagation time vector d b / a , d a / b There is no change in g b / a =g a / b And d b / a =d a / b Then, as shown in FIG. 7, the synchronization state vector s is d g Ingredients and g d It can be seen that by orthogonally decomposing the components, it is possible to obtain the time difference and delay time without including any error.

[0067] However, in general, the time difference vector g and the propagation time vector d each contain a fluctuation error in their respective elements, as shown in Figure 8. For this reason, because the orthogonal components each contain their own error, it is not possible to remove the errors from the time difference and propagation time by simply manipulating equation (8), which leads to a decrease in the accuracy of time synchronization.

[0068] Since equations (4) and (5) are linearly dependent, an analytical solution cannot be found unless other independent operations are introduced, but by measuring only the transmission and reception timing of synchronization information, it is not possible to find new independent operations that result in the vectors shown in Figure 7. Therefore, a different approach must be introduced to eliminate the fluctuation error.

[0069] [Relationship between time difference fluctuation and frequency deviation] The oscillation frequency f of the clock 20 of each information communication device 1 used for time synchronization is a nominal frequency f NThe frequency deviation e with respect to the oscillation frequency f[n] is also fluctuating from moment to moment depending on the mechanical and electromagnetic operating environment of the clock 20. Therefore, the relationship between the oscillation frequency f[n] and the frequency deviation e[n] at the observation timing n can be expressed as shown in equation (9). Note that the frequency deviation e[n] is sufficiently smaller than 1, and r[n] represents the frequency ratio. TIFF2025040875000010.tif10157

[0070] FIG. 9 shows the relationship between the transmission / reception timing, the time difference, and the propagation time when communicating information from a local device CLa to another device CLb.

[0071] The nominal frequency of the clock 20 used for time synchronization in both the own device CLa and the other device CLb is the same. However, the frequency deviation of the own device CLa is e a [n], other device CLb is e b At this time, the frequency deviation of the other device CLb seen from the own device CLa is (e b [n]-e a The frequency ratio r b / a [n] is r b / a [n]=1+(e b [n]-e a Similarly, the frequency deviation of the own device CLa as seen from the other device CLb can be expressed as (e a [n]-e b The frequency ratio r a / b [n] is r a / b [n]=1+(e a [n]-e b [n]).

[0072] If the clock frequencies of the own device CLa and other device CLb are different, the advance of the clocks will also differ, resulting in a time difference from moment to moment. b / a [m] ≠ g b / a There are also observation timings where the frequency deviation is [n], and so corrections that take frequency deviation into account are required when calculating time between devices. If corrections are not performed, errors will occur in the time calculations, leading to a decrease in the accuracy of time synchronization.

[0073] In FIG. 9, the average frequency ratio of another device CLb seen from the own device CLa from timing m to timing n is expressed as r b / a If we set it to [n,m], the relationship in equation (10) can be stated. TIFF2025040875000011.tif20158

[0074] From this equation (10), g b / a [n]=g b / a [m]+(r b / a [n,m]-1)(t a,T [n]-t a,T It can be seen that the time difference changes due to the effect of frequency deviation.

[0075] In equation (10), the frequency deviation does not affect the propagation time, and no correction is required. This is because the nominal frequency f N The minimum time L that a time difference occurs between the observation times of two devices with an apparent frequency deviation e[n] g [n] can be expressed as in equation (11), but the propagation time is generally the minimum time L g This is because the period T N =1 / f N It states that: TIFF2025040875000012.tif13158

[0076] That is, L g [n] is the time T for one period corresponding to the nominal frequency plus the observed time difference between the instruments N is the interval time to be added or subtracted. Therefore, within this interval time, the time difference is at most ±T N Only nothing changes.

[0077] Also, L g [n] changes from moment to moment and cannot be calculated directly. However, if the allowable frequency deviation of the clock 20 is e, the absolute value of the apparent frequency deviation between devices using the same type of clock 20 will not exceed |2e|. Therefore, L g =T NLet / |2e| be the minimum time for which these clocks 20 have a constant time difference.

[0078] [Formation of virtual clock] Next, a description will be given of the formation of a virtual clock v for synchronizing the clocks 20 of all the information communication devices 1. In the following description, the symbols of the "device" which is the information communication device 1 and the "clock" contained therein will be the same.

[0079] The transmission time of the synchronization information of the device i including the clock i is t i,T Then, {t i,T} j A i,T The same timing is the time of another device j including a clock j with the same timing as t. The same timing is an ideal single timing in which the times of clocks i and j are observed with a propagation time of 0 in an observation system that includes clocks i and j. By definition, t i,T is {t i,T} i It can also be written as:

[0080] Synchronization information at time t i,T The time difference between clock i and clock j at the time of transmission is g j / i is newly defined as equation (12). TIFF2025040875000013.tif14158

[0081] N pieces of information communication devices 1 are connected to a synchronization network NE, and one of the information communication devices 1, i, is assumed to implement a clock i. i,T and the sum of the transmission times of the synchronization information of all devices k at the same timing, that is, the sum of the transmission times of all information communication devices 1, can be expressed as equation (13). TIFF2025040875000014.tif15159

[0082] Equation (13) is transformed into an equation to obtain equation (14). In equation (14), the first term on the rightmost side corresponds to the sum of the time differences between all N information communication devices 1 as seen from device i. Although device i is included in all information communication devices 1, the time difference between device i and other devices is 0. The second term on the rightmost side is the transmission time of the synchronization information of device i multiplied by N. TIFF2025040875000015.tif16156

[0083] From equation (12), equation (14) can be expressed as equation (15). TIFF2025040875000016.tif16156

[0084] Multiplying both sides of equation (15) by 1 / N gives equation (16). The left side of equation (15) is the average value of the transmission times of all information communication devices 1, and the first term on the right side is the average value of the time differences between device i and all information communication devices 1 as seen from device i. TIFF2025040875000017.tif15156

[0085] In this case, the left side of equation (16) is i,T Assume the existence of a device v that includes a clock v that has the same time as i. This clock v is called a virtual clock v. If the first term on the right-hand side of equation (16) is the time difference between virtual clock v observed from clock i, equation (16) can be rewritten as equation (17) assuming device v, which becomes a modified version of equation (12). In other words, the virtual clock v can be formed by looking at the time differences between clock i and all other clocks and taking the average. TIFF2025040875000018.tif11156

[0086] This t i,T At the same time, device j transmits synchronization information at time t j,T If you send to t j,T ={t i,T} j And i,T ={t j,T} i Since {t i,T} v={t j,T} v Thus, both device i and device j can assert that the same device v exists.

[0087] In equation (17), t i,T At a different timing, device j transmits synchronization information at time t j,T If equation (17) holds for other device j when transmitting to the virtual clock v, each device connected to this synchronous network NE can transmit the virtual clock v with a time difference g v / k By performing time synchronization control to cancel the time synchronization, it is possible to synchronize with the device v whose existence is assumed.

[0088] The relationship between such a virtual clock and the clock of the information communication device 1 is shown diagrammatically in Fig. 10. The horizontal axis in Fig. 10 indicates the passage of absolute time, and the vertical axis indicates the time difference between each clock. The virtual clock is Cv, and the clocks of the information communication device 1 are indicated by C1 to C3. Of the four points enclosed by each of the three dotted ellipses in Fig. 10, the line connecting the points that take the average of the time differences of C1 to C3 represents the virtual clock Cv.

[0089] t of clock C1 1,T and {t 1,T} v The time difference between v / 1 , t of clock C2 2,T and {t 2,T} v The time difference between v / 2 , t of clock C3 3,T and {t 3,T} v The time difference between v / 3 The clocks C1, C2, and C3 have the time difference g v / 1 , g v / 2 , g v / 3 If you cancel this, you will be able to synchronize.

[0090] However, FIG. 10 shows only the time difference without errors including deviation in propagation time and frequency deviation. In reality, the time difference includes an error. This error is shown diagrammatically in FIG. 11. FIG. 11 shows the time difference between clocks C1 and C2, which is the minimum unit of ±1 / f. N This shows the deviation from the normal. We will discuss this type of error later.

[0091] [Effect of time zone variations on virtual clocks] It is common for different devices i and j to transmit synchronization information at different times. In addition, the propagation time of the synchronization information is longer than 0, and the reception timing is different from the transmission timing. The interval between these timings is the time L during which the time difference fluctuation due to the clock frequency deviation is observed. g Consider the case where the above condition is met.

[0092] Without loss of generality, let the nominal frequency of the clock implemented by each device be f N Then, each clock operates independently, so device k will operate at time L g The time variation that can be taken within (time difference variation from an ideal clock with a permissible frequency deviation of 0) Δk is expressed as {-1 / f N ,0,1 / f N}. That is, even if L g Even if the time difference is repeatedly observed at intervals shorter than ±2 / f, the smallest unit at which the time difference fluctuation can be observed N It is possible to observe changes in

[0093] Similarly, the time variation Δv that the virtual clock v formed in the synchronization network NE to which N devices are connected can have during this interval can be calculated using equation (18). TIFF2025040875000019.tif15152

[0094] However, the sum of Δk forms a trinomial distribution, and its probability distribution is shown in Figure 12. Therefore, the probability that the equality on both sides of equation (18) holds is at most 1 / 3. N That is, Δk is always -1 / f N or 1 / fN That is, at most 2 / 3 N The probability of Δk being {-1 / f N ,0,1 / f N} appears with equal probability, and is normalized to the range of ±1 in Figure 12. The probability of being less than -0.5 or more than 0.5 is 8 × 10 when N = 10. -2 , 8×10 for N=20 units -3 , 1×10 for N=50 units -5 , 5×10 for N=100 units -10 It is.

[0095] Therefore, the time difference between the virtual clock v observed from device k and the virtual clock v is Δg v / k = Δv-Δk is -2 / f N <Δg v / k <2 / f N The range of Δg v / k =±2 / f N This is because the condition for the equality of equation (18) to hold is met. In other words, Δ i =-1 / f N , Δ k≠i =1 / f N When Δ v =(N-2) / Nf N and Δg v / k is the maximum value (2N-2) / Nf N <2 / f N Take Δ i =1 / f N As in Δ k Similarly, when the sign of is inverted, Δg v / k is the minimum value - (2N-2) / Nf N >-2 / f N Take.

[0096] Using this time lag variation, i / j =-(g j / i +Δg j / i ), the expected value of the first term on the right-hand side of equation (5) when device i observes device j can be expressed as equation (19), taking into consideration the change in the definition of the time difference in equation (12). This is because Δ v From the probability distribution (Figure 12), the second term on the second side of the right side, Δg v / i / 2 is -1 / 2f N Beyond 1 / 2f N Since the range is considered to be less than 1 / f N can be rounded to 0 in increments. TIFF2025040875000020.tif16154

[0097] Therefore, the time fluctuation of each device is at most ±1 / f N If the observation of equation (19) is completed within the period during which only the virtual clock occurs, the time difference with the virtual clock can be obtained without causing a time difference error due to fluctuations in the clock frequency deviation.

[0098] Under these conditions, the time difference g calculated by equation (17) for each device k at different times is v / k is the time difference relative to the same virtual clock.

[0099] [Effect of propagation time variations on virtual clocks] Until now, the ideal time difference g j / i However, in reality, the propagation time d is longer than 0 and is different as shown in equation (5). j / i ,d i / j The time difference can be observed via

[0100] g a / b =g b / a +Δg b / a , Δd b / a =d b / a -d a / b Then, equation (5) is rewritten as equation (20). TIFF2025040875000021.tif12152

[0101] For device i and other devices k connected to the synchronization network NE, time L g By completing the transmission and reception of synchronization information within the time limit, and calculating equation (20) while paying attention to the change in the definition of the time difference in equation (12), and taking their expected values, we can obtain equation (21). TIFF2025040875000022.tif15157

[0102] In other words, the error due to the propagation time deviation included in the time difference between device i and the virtual clock is the expected value (average value) of the error due to the propagation time deviation between device i and each of other devices k. Therefore, time synchronization with the virtual clock can reduce errors due to the propagation time deviation of synchronization information.

[0103] Furthermore, the propagation time deviation Δd j / i [i] and the propagation time deviation Δd between the timing of device j i / j [j] is Δd j / i [i]=-Δd i / j If the synchronization information is transmitted and received while maintaining the relationship [j], the expected value of the time difference error due to the propagation time deviation can be calculated as follows: Δd i / j [j] is Δd j / i Since it has the opposite sign to [i] but the same absolute value, the result is 0. The leftmost side of equation (22) is the expected value of the second term on the rightmost side of equation (21), which is the expected value of the error due to the propagation time deviation from the virtual clock, and this is 0. In other words, each information communication device 1 is premised on the fact that the communication unit 10 transmits and receives synchronization information while maintaining an equal relationship between the absolute value of the propagation time deviation at the timing of device i and the absolute value of the propagation time deviation at the timing of other device j. TIFF2025040875000023.tif16158

[0104] In other words, the expected value of the synchronization phase difference due to time synchronization to the virtual clock in the entire synchronization network NE is 0, achieving balanced and accurate time synchronization.

[0105] [Operation] According to the present embodiment as described above, a procedure for a plurality of devices connected to a synchronous network NE to time synchronize with a virtual clock formed in the synchronous network NE will be described with reference to the flowchart in Fig. 13 and the explanatory diagram in Fig. 14. In the following description, any one of the information communication devices 1 will be referred to as the local device i, and an information communication device 1 other than the local device i will be referred to as another device j. The flowchart in Fig. 13 shows the flow of processing in the local device i.

[0106] First, as shown in FIG. 14, the communication control unit 73 of the own device i and the other device j sends a time L that can be regarded as a constant time difference to the communication unit 10 according to the scheduler 74. g The synchronization information is then multicast within t i,T , and the time when the other device j receives it is t j / i,R , the transmission time t of the synchronization information from all other devices j j,T , the reception time t i / j,R It is.

[0107] More specifically, the own device i transmits synchronization information simultaneously (multicast), and other devices j≠i receive this synchronization information. At this time, the own device i i,T The other device j is t j / i,R Similarly, other devices j≠i broadcast synchronization information, and device i receives the synchronization information. At this time, other devices j obtain t j,T The own device i is t i / j,R (Process 2). The time L that all the own device i and other devices j can consider processes 1 and 2 to have a constant time difference is obtained. g Execute within.

[0108] Then, the own device i sends the t i,T and t of process 2 i / j,R The synchronization information including t is transmitted by unicast, and other device j receives this synchronization information (process 3). j,T ,t j / i,R ,t i,T ,t i / j,R Furthermore, other device j≠i can send the t j,T and t for process 1 j / i,R The synchronization information including t is transmitted to the device i, and the device i receives the synchronization information. i,T ,t i / j,R ,t j,T ,t j / i,R(Process 4). All the information communication devices 1 execute Processes 3 and 4.

[0109] Next, the time difference calculation unit 77 of the device i calculates the time difference g d,j / i is calculated (step S102). TIFF2025040875000024.tif14158

[0110] Then, the virtual time difference calculation unit 78 of the device i calculates the time difference g with the virtual clock v by using the formula (24). d,v / i A (virtual time difference) is calculated (step S103). TIFF2025040875000025.tif17157

[0111] Device i is now at a time difference of g d,v / i The time or clock frequency is adjusted so as to add, and time is synchronized with the virtual clock v (step S104).

[0112] All the information communication devices 1 execute steps S102, S103, and S104, and if the time synchronization is to be continued, the process waits for a specified period and returns to step S101. j / i [i]=-Δd i / j The transmission and reception of synchronization information is realized by maintaining the relationship [j].

[0113] [effect] (1) In this embodiment, an information communication system 100 in which a communication unit 10 of a plurality of information communication devices 1 communicates information according to the time of a clock 20 that each of the information communication devices 1 has includes a communication control unit 73 that causes the communication unit 10 to transmit and receive synchronization information within a predetermined time period that can be considered to be a constant time difference between the information communication devices 1, a time acquisition unit 76 that acquires a transmission time of the synchronization information from a local device CLa that is any one of the information communication devices 1, a reception time of the synchronization information transmitted from the local device CLa by another device CLb that is an information communication device 1 other than the local device CLa, a transmission time of the synchronization information from all the other devices CLb, and a reception time of the synchronization information transmitted from all the other devices CLb by the local device CLa, and The information communication device 1 includes a time difference calculation unit 77 that calculates the time difference between the clock 20 of the device itself CLa and the clock 20 of all other devices CLb based on the transmission time of the device itself CLa, the reception time of the device itself CLa, the transmission times of all other devices CLb, and the reception times of all other devices CLb acquired by the acquisition unit 76, a virtual time difference calculation unit 78 that calculates a virtual time difference between the clock 20 of the device itself CLa and a virtual clock that is a virtual clock that can be regarded as a common time source for all information communication devices 1, based on the time difference between the clock 20 of the device itself CLa and all clocks 20, and a synchronization control unit 79 that time-synchronizes the clock 20 of the device itself CLa with the virtual clock based on the virtual time difference calculated by the time difference calculation unit 77.

[0114] In addition, the present embodiment relates to an information communication device 1 that is a local device CLa, whose communication unit 10 communicates information with other devices CLb that are multiple other information communication devices 1, according to the time of a clock 20, and includes a communication control unit 73 that causes the communication unit 10 to transmit and receive synchronization information within a predetermined time period that can be considered to have a constant time difference with the other devices CLb, a time acquisition unit 76 that acquires a transmission time of the synchronization information from the local device CLa, a reception time of the synchronization information transmitted from the local device CLa by the other devices CLb, a transmission time of the synchronization information from all the other devices CLb, and a reception time of the synchronization information transmitted from all the other devices CLb by the local device CLa, and The information communication device 1 has a time difference calculation unit 77 that calculates the time difference between the clock 20 of its own device CLa and the clock 20 of all other devices CLb based on the transmission time of the clock 20, the reception time of its own device CLa, the transmission times of all other devices CLb, and the reception times of all other devices CLb; a virtual time difference calculation unit 78 that calculates a virtual time difference between the clock 20 of its own device CLa and a virtual clock that is a virtual clock that can be regarded as a common time source for all information communication devices 1 based on the time difference between the clock 20 of its own device CLa and all clocks 20; and a synchronization control unit 79 that time-synchronizes the clock 20 of its own device CLa with the virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit 78.

[0115] In this way, by assuming a virtual clock based on the time difference between the clock 20 of the own device CLa and the other device CLb, it is possible to absorb fluctuations in the propagation time of information communication and perform synchronization control with reduced errors only by information communication between the information communication devices 1 without using a reference clock such as GMC or a relay device such as BC or TC. By having the communication unit 10 transmit and receive synchronization information within a predetermined time period in which the time difference between the information communication devices 1 can be considered constant, synchronization control can be performed without causing time difference errors due to frequency deviation fluctuations and propagation time fluctuations of each clock 20. As described above, in this embodiment, the average value of the time difference with the clock 20 of the other device CLb is set as the time difference between the clock 20 of the own device CLa and the virtual clock.

[0116] (2) Communication units 10 of device CLa and other device CLb are connected via a complete network, so that it is possible to obtain the time difference with all other devices CLb other than device CLa.

[0117] (3) The communication control units 73 of the own device CLa and the other device CLb cause the communication units 10 to simultaneously transmit the synchronization information within a predetermined time period, so that the time acquisition unit 76 can efficiently acquire the four transmission and reception times.

[0118] (4) The communication unit 10 transmits and receives synchronization information while maintaining an equal relationship between the absolute value of the propagation time deviation at the timing of the own device CLa and the absolute value of the propagation time deviation at the timing of the other device CLb. Therefore, the expected value of the synchronization phase difference with the virtual clock is 0, that is, time synchronization centered on the virtual clock can be realized.

[0119] [Variations] As described above, it is preferable that the form of the synchronization network NE is a complete network. However, the physical form does not need to be a complete network, and even a star-shaped synchronization network NE with one hub at the center can be used as long as it can realize a complete network in the communication mode of synchronization information. Even if the synchronization network NE does not form a complete network, it is possible to synchronize with the virtual clock v using this principle. However, a synchronization error occurs because the equation (16) obtained for each information communication device 1 is not the same. Even if any one of the information communication devices 1 fails, the current time synchronization can be maintained by degenerating the synchronization network NE and configuring a complete network.

[0120] [Other embodiments] The present invention is not limited to the above-described embodiment, and the components can be modified without departing from the spirit of the invention. In addition, various inventions can be formed by appropriately combining the components disclosed in the above-described embodiment. [Explanation of symbols]

[0121] 1 Information and communication devices 10. Communications Department 11 Transmitter 12 Receiver 13 Transmission timing detector 14 Reception timing detection section 20 Clock 30 Clock 50 Storage section 60 External Interfaces 70 Control section 71 Main control unit 72 Transmission and reception data interface 73 Communication Control Unit 74 Scheduler 75 Time Recording Section 76 Time acquisition part 77 Time Difference Calculator 78 Virtual time difference calculation unit 79 Synchronization control section 100 Information and Communication Systems

Claims

1. An information and communication system in which a communication unit of a plurality of information and communication devices communicates information according to the time of a clock that each device has, without using a reference clock, a communication control unit that causes the communication unit to transmit and receive synchronization information within a predetermined time period that can be considered as a constant time difference between the information communication devices; a time acquisition unit that acquires a transmission time of the synchronization information from a local device that is any one of the information communication devices, a reception time of the synchronization information transmitted from the local device by another device that is an information communication device other than the local device, a transmission time of the synchronization information from all of the other devices, and a reception time of the synchronization information transmitted from all of the other devices by the local device; a time difference calculation unit that calculates a time difference between a clock of the own device and a clock of all of the other devices based on the transmission time of the own device, the reception time of the own device, the transmission times of all of the other devices, and the reception times of all of the other devices acquired by the time acquisition unit; a virtual time difference calculation unit that calculates a virtual time difference between the clock of the local device and a virtual clock that is a virtual clock that can be regarded as a common time source for all of the information communication devices, based on a time difference between the clock of the local device and all of the clocks; a synchronization control unit that time-synchronizes a clock of the device with a virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit; An information and communication system having the above configuration.

2. 2. The information communication system according to claim 1, wherein the communication units of the local device and the other devices are connected via a complete network.

3. 3. The information communication system according to claim 1, wherein the communication control units of the local device and the other devices cause the communication units to simultaneously transmit the synchronization information within the predetermined time period.

4. 3. The information and communication system according to claim 1, wherein the communication unit transmits and receives the synchronization information while maintaining an equal relationship between an absolute value of a propagation time deviation at the timing of the own device and an absolute value of a propagation time deviation at the timing of the other device.

5. The communication unit is a device that communicates information with other devices that are multiple other information communication devices, and the information communication device communicates information according to a clock that the device has without using a reference clock, a communication control unit that causes the communication unit to transmit and receive synchronization information within a predetermined time period that can be considered to have a constant time difference with the other device; a time acquisition unit that acquires a transmission time of the synchronization information from the own device, a reception time of the synchronization information transmitted from the own device by the other device, a transmission time of the synchronization information from all of the other devices, and a reception time of the synchronization information transmitted from all of the other devices by the own device; a time difference calculation unit that calculates a time difference between a clock of the own device and all clocks based on the transmission time of the own device, the reception time of the own device, the transmission times of all the other devices, and the reception times of all the other devices acquired by the time acquisition unit; a virtual time difference calculation unit that calculates a virtual time difference between the clock of the local device and a virtual clock that is a virtual clock that can be regarded as a common time source for all of the information communication devices, based on a time difference between the clock of the local device and all of the clocks; a synchronization control unit that time-synchronizes a clock of the device with a virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit; An information communication device comprising:

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