Information synchronization system and information synchronization device

Abstract

The present invention provides an information synchronization system and information synchronization device that can record multiple pieces of external information in a synchronized and replayable format. [Solution] The information synchronization system 100 of the embodiment is an information synchronization system 100 in which a time synchronization unit 3 of a plurality of information synchronization devices 1 performs time synchronization based on time information, and the information synchronization device 1 has an external information input unit 4 that inputs external information, an information embedding unit 6 that embeds time information synchronized by the time synchronization unit 3 into the external information, and an external information recording unit 7 that records the external information in which the time information has been embedded.

Description

[Technical Field]

[0001] This invention relates to an information synchronization system and an information synchronization device. [Background technology]

[0002] It is common practice to record external information such as audio and video onto the recording medium of a recording device, and then to play back the recorded external information using a playback device. For example, for specific research or investigation purposes, audio and video of the subject of observation or surveillance are recorded using microphones or video cameras installed at specific locations. The collected audio and video can be played back by outputting them through speakers or displaying them on a screen, respectively, and can be used for research and investigation. [Prior art documents] [Non-patent literature]

[0003] [Patent Document 1] Patent No. 6163680 [Overview of the project] [Problems that the invention aims to solve]

[0004] In research and investigations, it is sometimes necessary to accurately recreate a location by aggregating and replaying multiple pieces of external information, recorded separately by recording devices such as recorders installed in multiple locations, using a playback device.

[0005] However, since multiple recording devices operate according to independent clocks, there is a time difference between them. In other words, multiple audio recordings made on different recorders will have different timestamps. Therefore, in order to play back multiple audio recordings with synchronized timestamps, an operator needs to identify the point in time that should be the same for each audio recording and adjust the playback timing based on that point—a process known as cueing.

[0006] Furthermore, there are cases where we want to aggregate multiple pieces of information, such as audio, video, and vibration, and play them back on a single timeline for analysis. However, even in such cases, the process of extracting each piece of information and applying an offset to account for the time differences between them must be done manually.

[0007] This invention was made to solve the above-mentioned problems, and aims to provide an information synchronization system and information synchronization device that can record multiple pieces of external information in a synchronized and reproducible state. [Means for solving the problem]

[0008] The information synchronization system of the present invention is an information synchronization system in which the time synchronization units of a plurality of information synchronization devices perform time synchronization based on time information, wherein the information synchronization device includes an external information input unit that inputs external information, an information embedding unit that embeds the time information synchronized by the time synchronization unit into the external information, and an external information recording unit that records the external information into which the time information has been embedded.

[0009] The information synchronization device of the present invention comprises: a time synchronization unit that performs time synchronization with other information synchronization devices based on time information; an external information input unit that inputs external information; an information embedding unit that embeds the time information synchronized by the time synchronization unit into the external information; and an external information recording unit that records the external information into which the time information has been embedded. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an information synchronization system and information synchronization device that can record multiple pieces of external information in a synchronized and reproducible state. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the information synchronization system according to the embodiment. [Figure 2]This is a block diagram of an information synchronization device that constitutes an information synchronization system according to an embodiment. [Figure 3] This flowchart shows the flow of the information synchronization process of the information synchronization device according to the embodiment. [Figure 4] This is a block diagram showing a communication unit in which the time synchronization unit synchronizes with a virtual clock. [Figure 5] This is a block diagram showing a time synchronization unit in an embodiment where the time synchronization unit synchronizes with a virtual clock. [Figure 6] This diagram shows the communication patterns between information synchronization devices. [Figure 7] This figure shows a communication mode that exhibits symmetry in propagation time. [Figure 8] This figure shows a mode of communication that does not have symmetry in propagation time. [Figure 9] This figure shows a synchronization state vector free from errors due to variations in propagation time and time difference. [Figure 10] This figure shows the synchronization state vector, which includes errors due to variations in propagation time and time difference. [Figure 11] This diagram shows the set of information communications in an information synchronization system. [Figure 12] This graph schematically illustrates the relationship between the clock and virtual clock of an error-free information synchronization device. [Figure 13] This graph schematically illustrates the relationship between the clock and virtual clock of an information synchronization device, including errors. [Figure 14] This graph shows the probability distribution of time variations that an information synchronization device can exhibit within a predetermined interval. [Figure 15] This flowchart shows the procedure for synchronous control processing. [Figure 16] This is an explanatory diagram showing the communication used to obtain the transmission and reception times for synchronous control. [Modes for carrying out the invention]

[0012] The information synchronization system and information synchronization device according to the embodiment will be described below with reference to the drawings.

[0013] [composition] Figure 1 is a schematic diagram of the information synchronization system 100 according to the embodiment. Figure 2 is a functional block diagram of the information synchronization device 1 that constitutes the information synchronization system 100 according to the embodiment.

[0014] As shown in Figure 1, the information synchronization system 100 according to this embodiment is a system that synchronizes information between information synchronization devices 1 (devices A to E) via a synchronization network. Each information synchronization device 1 only needs to be connected by a medium capable of sending and receiving information, and it does not matter whether the medium is wired or wireless.

[0015] The information synchronization system 100 consists of information synchronization devices 1 that communicate information according to a reference time. Each information synchronization device 1 synchronizes by sending and receiving synchronization information.

[0016] For example, the synchronous network NE shown in Figure 1 is a network with N=5 nodes. In other words, N is the number of information synchronization devices 1 connected to the synchronous network NE, and in Figure 1, 5 information synchronization devices 1 are connected.

[0017] In the following explanation, one of the information synchronization devices 1 may be referred to as "the local device," and other information synchronization devices 1 may be referred to as "other devices." There are N-1 other devices, but for convenience, they may be represented by a common code. Each information synchronization device 1 has the same configuration and can function as either the local device or another device.

[0018] [Information synchronization device] The information synchronization device 1 includes a computer and performs necessary calculations by executing programs pre-stored in a storage unit such as an HDD or SSD using a processor including a CPU.

[0019] Specifically, as shown in Figure 2, the information synchronization device 1 includes a control unit 2, a time synchronization unit 3, an external information input unit 4, a position detection unit 5, an information embedding unit 6, an external information recording unit 7, an external information playback unit 8, an external interface 9, a communication unit 10, a clock 20, a timestamp 30, and a storage unit 40. All or part of each unit 2 to 40 may be configured as hardware or as software including programs and data. The configuration of which parts of the control unit 2 are configured as hardware and which as software can be changed as appropriate in the design.

[0020] (Control Unit) The control unit 2 controls the overall operation of each part of the information synchronization device 1. The control unit 2 has the function of controlling or referencing the setting state and operating state of each part within the device according to control information input from the outside or stored inside the information synchronization device 1. In addition, the control unit 2 communicates information input from the outside and various types of information stored inside the device according to the control information. Such information includes external information, reproducible information, embedded spatiotemporal information, etc.

[0021] (Time synchronization section) The time synchronization unit 3 performs time synchronization based on time information. In this embodiment, the time synchronization unit 3 performs time synchronization based on an external reference time. For example, the time synchronization unit 3 controls the clock 20 (system clock or clock oscillator), which will be described later, provided by the information synchronization device 1, in response to time information, which is the standard time and its corresponding timing, input from the control unit 2, and performs time synchronization. The standard time is, for example, Coordinated Universal Time (UTC) or Japan Standard Time (JST).

[0022] Furthermore, for example, the time synchronization unit 3 may synchronize its time using a reference clock as time information. The reference clock is a clock that actually exists on the synchronization network, which serves as a reference for all information synchronization devices 1 in the synchronization network to synchronize their respective clocks, such as a GMC. Note that the time information used as the reference for time synchronization is not limited to standard time or a reference clock. The time synchronization unit 3 may synchronize its time using any time information and its corresponding timing as time information.

[0023] (External information input unit) The external information input unit 4 receives external information from the information synchronization device 1. External information refers to acoustic phenomena or electromagnetic phenomena such as light and radio waves, as well as other physical phenomena and physical quantities that exist in spacetime outside the information synchronization device 1. For example, sound and images (including moving images) are included in external information. The external information input unit 4 has the function of receiving external information acquired from the outside and inputting it in a time-series format via transducers, sensors, or receiving devices that are built into it.

[0024] External information may include timing, and the external information input unit 4 may input the count value or time of the system clock provided by the information synchronization device 1 as external information, corresponding to the moment a specific timing is detected.

[0025] The external information input unit 4 may receive signals from a Global Navigation Satellite System (GNSS) or a similar system and input standard time information and its corresponding timing or position information as external information. The external information input by the external information input unit 4 is referenced by each unit via the control unit 2.

[0026] (Position detection unit) The position detection unit 5 detects the position information of the device. The position detection unit 5 detects the position information of the device based on the information input from the control unit 2. The position information may be latitude, longitude, altitude, or relative spatial coordinates. The position information may also be a location, or a name that identifies the building or structure where the device is located. Furthermore, the position information may be an absolute position that can identify the location on its own, or a relative position such as an offset from a reference position. If it is a relative position, the reference position may be attached or specified separately.

[0027] The position information may also be the amount of movement for each position component of the device itself. In this case, the relative position is determined by integrating the input series of position information, but a reference position may be included or specified separately. The input position information of the device itself is referenced by each unit via the control unit 2.

[0028] (Information embedding section) The information embedding unit 6 embeds time information synchronized by the time synchronization unit 3 into the external information. Embedding means associating time information with specific timings contained in the external information input from the control unit 2. For example, the information embedding unit 6 embeds standard time information or system clock time information into the external information.

[0029] Furthermore, the information embedding unit 6 may embed the position information input from the control unit 2 into the external information. In this case, the position information may be linked to time information and embedded in the external information. In other words, the position information of the device at that time may be linked in synchronization with a specific timing included in the external information to which the information is embedded and the corresponding time information. The time information and position information embedded in the external information in this manner are referred to as spatiotemporal information.

[0030] The embedded time information, location information, or spatiotemporal information can be extracted. This extraction may be performed separately from the external information. The external information in which the time information, location information, or spatiotemporal information is embedded is referenced by each unit via the control unit 2.

[0031] Time information, location information, or spatiotemporal information may be embedded in external information in a form that is not perceived. "Not perceived" means that the person reviewing the reproduced external information cannot recognize the embedded spatiotemporal information. For example, by reproducing external information, even if the sound or image can be perceived by a person's sight or hearing, the time information, location information, or spatiotemporal information cannot be perceived. Any information hiding technique can be applied to achieve this.

[0032] Information hiding is a technique that conceals other information within the original information. The other information cannot be perceived from the original information. When time information, location information, or spatiotemporal information is embedded in external information through information hiding, the time information, location information, or spatiotemporal information cannot be perceived from the reconstructed external information. This prevents intentional alteration of time information, location information, or spatiotemporal information.

[0033] One example of information hiding is steganography. Steganography is a technique that hides information by altering the color information of pixels in an image or by altering the frequency components of an audio signal. The hidden information becomes undetectable to the human eye or ear.

[0034] Time information, location information, or spatiotemporal information may be embedded sequentially or in segments at the beginning, end, or in the middle of external information. For example, the information embedding unit 6 may embed one or more synchronized time pieces of information in the external information. Time information, location information, or spatiotemporal information may also be embedded in the external information in a multiplexed manner.

[0035] The information embedding unit 6 also has the function of embedding standard time information or system clock time information, also input from the control unit 2, into the reproducible information input from the control unit, synchronized with a specific timing contained in that information. Reproducible information refers to a series of data sampled in time series, such as audio, video, and other sensed external information. It can also include the data length (start and end of data), sampling rate, bit depth, and number of channels necessary for playback. Location information and spatiotemporal information can also be embedded, and the embedding format is the same as for external information. Reproducible information with embedded time information, location information, and spatiotemporal information is referenced by each unit via the control unit 2.

[0036] (External Information Recording Department) The external information recording unit 7 records external information in which time information, location information, or spatiotemporal information is embedded. The external information recording unit 7 records the external information input from the control unit 2 in a reproducible format in the storage area of ​​the storage unit 40, which will be described later. The external information recording unit 7 may also record the input external information after quantization or encoding. Embedding by the information embedding unit 6 may be performed when quantizing or encoding the input external information.

[0037] When the external information recording unit 7 records external information, it records it in association with an information identifier input from the control unit 2. This information identifier is unique and different from other information identifiers. The information identifier may be, for example, the date and time information of when the external information was input.

[0038] The external information recording unit 7 may store reproducible information in the storage area of ​​the storage unit 40, similar to external information, or it may record reproducible information input from the control unit 2 in the storage area. Similar to external information, the recorded reproducible information is assigned a uniquely identifiable information identifier. The stored external information and reproducible information are retrieved using the information identifier input from the control unit 2 and referenced by each unit via the control unit 2.

[0039] (External World Information Reproduction Department) The external information playback unit 8 synchronizes and plays back the external information recorded by the external information recording unit 7 in each information synchronization device 1, based on the time information embedded by the information embedding unit 6. The external information playback unit 8 plays back the external information input from the control unit 2 and outputs it to each unit via the control unit 2.

[0040] The external information playback unit 8 can extract embedded time information, location information, or spatiotemporal information, along with timing information, during or before playback of external information. The extracted time information, location information, or spatiotemporal information, along with the timing information, may be output to each unit via the control unit 2, along with the external information identifier.

[0041] The external information playback unit 8 may receive an offset time from the control unit 2, and playback the external information by synchronizing the extracted spatiotemporal information with the offset time.

[0042] The control unit 2 may extract time information, location information or spatiotemporal information, and timing information from multiple external information inputs, and then synchronously replay the external information. In this case, the multiple synchronously replayed external information may be aggregated into a new single external information, and the original time information, location information or spatiotemporal information, and timing information may be re-embedded. The aggregated external information is referenced by each unit via the control unit 2.

[0043] The external information playback unit 8 has the function of playing back playable information input from the control unit 2 and outputting it to each unit via the control unit 2. In this playback, time information, location information, or spatiotemporal information at the time of playback may be embedded via the information embedding unit 6 and output again to each unit via the control unit 2.

[0044] (External Interface) The external interface 9 connects to an external device and has the function of inputting and outputting information to and from the information synchronization system 100. The input information is referenced by each unit via the control unit 2. In addition, the information input from the control unit 2 to the external interface 9 is output to the external device.

[0045] External devices include information terminals such as PCs (personal computers) and smartphones that enable the above-mentioned input / output and communication described later. External devices also include input devices such as microphones for audio input and cameras for image input, and output devices such as speakers, headphones, earphones, and displays for audio output. Furthermore, external devices include devices that detect information indicating the state of the target, such as weather information such as temperature, humidity, and atmospheric pressure, biometric information such as heart rate and body temperature, and accelerometers and vibration meters. In addition, devices that detect location information, such as GPS receivers and access points, are also included as external devices.

[0046] The external interface 9 also has the function of interconnecting with other information synchronization devices 1 and inputting and outputting information within the information synchronization system 100. For example, the external interface 9 may have the functions of the communication unit 10 described later. The input information may be a control request to the device itself. The input information may also be reproducible information, in which case an information identifier for that information may be input along with it.

[0047] The output information may be external information, external information with embedded time information, location information, or spatiotemporal information, or embedded time information, location information, or spatiotemporal information. Furthermore, the output information may be external information corresponding to a specified information identifier or related information thereof. Also, the output information may be regenerated external information, in which case time information, location information, or spatiotemporal information may be embedded. Moreover, the output information may be the internal setting state of the information synchronization device 1, or its operating state.

[0048] In this way, the external interface 9 allows for the mutual input and output of external information between the information synchronization devices 1, and enables the mutual input and output of external information embedded with time information, location information, or spatiotemporal information.

[0049] (Communications Department) The communication unit 10 transmits and receives information with other information synchronization devices 1. In other words, the communication unit 10 transmits information to the outside of the information synchronization device 1, receives information from the outside of the information synchronization device 1, or does both.

[0050] (clock) The clock 20 oscillates at a predetermined frequency and outputs signals that provide operating timings to each part of the information synchronization device 1. For example, a fixed-frequency oscillator such as a crystal oscillator can be used as the clock 20. As a result, each part of the information synchronization device 1 operates in synchronization with the clock 20. The clock 20 may also receive a frequency control signal from an external source and variably control its oscillation frequency in response to this signal.

[0051] (clock) The clock 30 keeps time using the output signal of the clock 20 as its source and outputs the time relative to the startup of the information synchronization device 1. The timekeeping may also be synchronized with the frequency division of the input clock signal.

[0052] (Storage part) The storage unit 40 is a recording medium such as an HDD, SSD, memory, or register. The storage unit 50 stores the information necessary for processing by the information synchronization device 1. As described above, the external information recorded by the external information recording unit 7 is stored in the storage area of ​​the storage unit 50.

[0053] The memory unit 50 inputs and outputs arbitrary information and stores that information in a designated 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 retrieved in response to an external retrieval request, at which time the storage area of ​​the reference information is input, and the information in the storage area specified by that input is output. The storage of information may be maintained only while the device is operating, or it may be permanent, including when the device is stopped.

[0054] [Operation] The operation of the information synchronization system 100 of this embodiment, as described above, will be explained with reference to the flowchart in Figure 3.

[0055] The time synchronization unit 3 of each information synchronization device 1 synchronizes the information synchronization system 100 with a specific time, such as standard time (step S101). In addition, the position detection unit 5 of each information synchronization device 1 detects the position of its own device (step S102). In this flowchart, time synchronization and position detection may be performed simultaneously or in the reverse order.

[0056] When external information is input from the external information input unit 4 (YES in step S103), the information embedding unit 6 embeds synchronized time information into the input external information (step S104). At this time, the detected position information is also embedded into the external information. In other words, spatiotemporal information is embedded into the external information. The external information playback unit 8 plays back the external information by synchronizing the time and position based on the embedded spatiotemporal information (step S105). This makes it possible to uniquely identify and play back the spatiotemporal location in which the external information was input.

[0057] [Embedding and Extraction of Spatiotemporal Information] The embedding and extraction of spatiotemporal information are described in detail below. When inputting external information and when reproducing and outputting it, the external information is assumed to be discretized and sampled. At this time, the input and output timing of each sample is associated with the system clock, so that the time of each sample can be identified.

[0058] The spatiotemporal information embedded in the external information is to be uniquely associated with the timing of extraction. However, there may be a time difference between the extraction timing and the embedded time information. In such cases, the information embedding unit 6 also embeds this time difference, i.e., the offset, as part of the spatiotemporal information. By canceling this offset during extraction, synchronization between the external information and the embedded time information can be achieved.

[0059] [Synchronized playback of external information] Next, we will explain the synchronized playback of external information. First, as described above, multiple pieces of external information are input into a time-synchronized information synchronization system 100, and each piece of external information is embedded with similarly time-synchronized spatiotemporal information.

[0060] Prior to the playback of this external information, the time or timing at which each sample of external information corresponding to a specific time in the embedded spatiotemporal information will be played back is determined. By synchronizing the spatiotemporal information extracted from each piece of external information with the time, and canceling the offset between the determined playback time and the playback start sample time, synchronized playback can be achieved.

[0061] Such synchronous playback may be performed by a single information synchronization device 1, or it may be performed in a distributed manner among multiple time-synchronized information synchronization devices 1. Furthermore, external information that has been distributed and input on a single channel can be made multi-channel by synchronizing it with embedded spatiotemporal information and then playing it back in a synchronous manner.

[0062] Furthermore, by identifying the location of each information synchronization device 1, and by embedding and recording spatiotemporal information in time synchronization with the input external information, it is possible to uniquely identify and reproduce the spatiotemporal location including the location where the external information was input.

[0063] Furthermore, when playing back replayable information within the information synchronization system 100, spatiotemporal information is embedded in a time-synchronized manner, so that when the played-out output of that information is input, the spatiotemporal location from which the information was played can be identified.

[0064] [effect] (1) This embodiment is an information synchronization system 100 in which the time synchronization units 3 of a plurality of information synchronization devices 1 perform time synchronization based on time information, and the information synchronization device 1 has an external information input unit 4 that inputs external information, an information embedding unit 6 that embeds the time information synchronized by the time synchronization unit 3 into the external information, and an external information recording unit 7 that records the external information in which the time information has been embedded.

[0065] The information synchronization device 1 of this embodiment includes an external information input unit 4 for inputting external information, an information embedding unit 6 for embedding time information synchronized by the time synchronization unit 3 into the external information, and an external information recording unit 7 for recording the external information into which the time information has been embedded.

[0066] In this way, synchronized time information is embedded in the external information recorded in each information synchronization device 1, so that multiple pieces of external information can be recorded in a time-synchronized and replayable state. Therefore, the timing during replay can be matched, and there is no need to manually adjust for time differences between the information synchronization devices 1.

[0067] By aggregating various external information and uniquely associating it with the timing of each piece of external information based on embedded time information, it becomes possible to cue up and play back synchronized. For example, in large spaces such as natural environments or facilities, where there are many objects to observe or monitor, it is not possible to centralize the input devices that input external information such as sound, video, and sensor values ​​for each, and they must be scattered, it is not possible to associate the times with a single clock domain. Even in such cases, in this embodiment, synchronized playback becomes possible by embedding time information synchronized by the time synchronization unit 3 into the external information in each information synchronization device 1. The order in which sounds were emitted, the order in which actions were performed, and the order of biological responses can also be faithfully reproduced for each object to observe or monitor. Furthermore, it becomes possible to record and reproduce a so-called soundscape (soundscape) that is spatiotemporalally synchronized over a wide area.

[0068] (2) The information synchronization device 1 has a position detection unit 5 that detects the position information of the information synchronization device 1, and the information embedding unit 6 embeds the position information detected by the position detection unit 5 into the external information. As a result, the information synchronization device 1 can record the position where the external information is input in a synchronized and playable state. The origin of the external information can be reproduced and played back. For example, the arrangement of multiple sound sources can be reproduced, making it possible to play back a sound that is close to the actual sound field.

[0069] (3) The information embedding unit embeds spatiotemporal information, which associates the position information detected by the position detection unit with the time information, into the external information. Therefore, external information can be recorded in a state in which spatiotemporal information, with time and position as elements, can be synchronized and reproduced.

[0070] (4) The time synchronization unit 3 synchronizes the time based on an external reference time. Therefore, time synchronization can be easily performed based on a unified standard.

[0071] (5) The information synchronization device 1 has an external information playback unit 8 that synchronizes and plays back external information recorded by the external information recording unit 7 in each information synchronization device 1 based on time information embedded by the information embedding unit 6. Therefore, multiple pieces of external information can be played back in time synchronization.

[0072] [Differentiation] (1) External information may be reproduced by the external information reproduction unit 8 of the information synchronization device 1 as described above, or by a reproduction device provided outside the information synchronization device 1 or outside the information synchronization system 100.

[0073] (2) The external information recorded by each information synchronization device 1 may be aggregated and recorded in any one of the information synchronization devices 1 or an external playback device, and then played back. The aggregated external information can be synchronized with the time embedded in each device, and all or part of it can be integrated and recorded or played back as new external information. The integrated external information may be analyzed or processed by prescribed means, and the results may be output to the next processing step inside the information synchronization system 100, or to the outside of the information synchronization system 100.

[0074] (3) Recorded external information, extracted time information, or location information may be referenced, managed, and made available from outside the information synchronization system 100.

[0075] (4) In the above embodiment, the time synchronization unit 3 synchronized with reference time information such as standard time or a reference clock. However, if such reference time information is unavailable, the time synchronization unit 3 may have a function to synchronize with a virtual clock virtually constructed on the synchronization network. Such an embodiment will be described below.

[0076] [Synchronization to virtual clock] Figure 4 is a block diagram showing the communication unit 10, Figure 5 is a block diagram of the time synchronization unit 3, and Figure 6 is a diagram showing the communication configuration between the information synchronization devices 1. In the following explanation, the device itself may be referred to as CLa, i, etc., and other devices as CLa, j, etc.

[0077] The information synchronization system 100 may consist of multiple time synchronization devices, and there are operating conditions that require each device to be time-synchronized when inputting or outputting external information. In this case, if all devices cannot independently synchronize with standard time, the time synchronization unit 3 within each device can be connected to a synchronization network to build a time synchronization system, and the operating conditions can be satisfied by synchronizing the entire system with a virtual clock. This time synchronization system is a subsystem of the information synchronization system 100.

[0078] A time synchronization system can achieve synchronization by having each information synchronization device 1 send and receive synchronization information without using standard time or a reference clock. A synchronization network is formed by time synchronization units 3 in multiple information synchronization devices 1, and synchronization can be achieved between all time synchronization units 3 while sending and receiving synchronization information bidirectionally. It is preferable that the synchronization network is a complete network. A complete network is a network in which each node can communicate directly with all other nodes. For example, the network NE shown in Figure 1 is assumed to be a complete network with N=5 nodes.

[0079] Below, we will provide further explanations for each of the above components in the configuration for such a synchronous network.

[0080] (Communications Department) As shown in Figure 4, the communication unit 10 includes a transmitter 11, a receiver 12, a transmission timing detection unit 13, and a reception timing detection unit 14.

[0081] Transmitter 11 is a device that transmits input information. Specifically, transmitter 11 decomposes the information into its smallest components in chronological order and then transmits the information to the outside. The packet length (amount of communication information) of the information is arbitrary and may differ for each communication.

[0082] The receiver 12 is a device that receives information from an external source. Specifically, the receiver 12 reconstructs the information received from outside the information synchronization device 1, which has been broken down into its smallest components in a time series, and outputs it to other components within the information synchronization device 1.

[0083] Here, the information communicated by the information synchronization device 1, that is, the information transmitted by the transmitter 11 and the information received by the receiver 12, includes synchronization information for synchronizing the time. The synchronization information consists of the synchronization timing or time information corresponding to the synchronization timing.

[0084] 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 synchronization device 1. This transmission timing is detected based on the clock period of the clock 20 (in other words, the period of the pulses oscillated by the clock 20). That is, the transmission timing is expressed based on an integer multiple of the clock period.

[0085] Furthermore, the transmission timing detection unit 13 can also output its detection result to other components within the information synchronization device 1. The information referred to 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.

[0086] The reception timing detection unit 14 detects the reception timing. The reception timing is the timing at which the information received by the receiver 12 is received from outside the information synchronization device 1. This reception timing is detected based on the clock period of the clock 20, which will be described later. In other words, the reception timing is expressed as an integer multiple of the clock period. The reception timing detection unit 14 also outputs its detection result to other components within the information synchronization device 1.

[0087] Figure 6 shows a configuration in which, using wired communication as an example, a specific bit position within a packet is detected as the transmission / reception timing during packet transmission between information synchronization devices 1, and the transmission interval and reception interval are determined from the adjacent transmission and reception timings, respectively.

[0088] Furthermore, while the transmission timing and reception timing may both detect the position of the same minimum component, they do not necessarily have to detect the same position as long as a predetermined relationship is maintained between the transmitting and receiving information synchronization devices 1, and any discrepancies in the detected element positions can be ignored or corrected.

[0089] Furthermore, the transmission timing may be detected a predetermined time before or after the actual transmission timing. 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 they may be set statically or dynamically from an external source.

[0090] (clock) The clock 20 has an inherent finite oscillation frequency tolerance. That is, the clock 20 has an error (e.g., 20 ppm) relative to a given oscillation frequency (e.g., 10 MHz). Even if the information synchronization devices 1 have the same nominal frequency, there are actually individual differences in the clock 20. In other words, there are frequency differences between the frequencies of the clock 20 of multiple information synchronization devices 1.

[0091] (clock) The timekeeping of clock 30 may be fixed or variable in terms of the advance per clock cycle. If variable, the clock frequency may be fixed or the drive frequency of clock 30 may be intermittently controlled. The time is referenced in a specified unit, which may be fixed within clock 30 or set statically or dynamically from an external source. The relative time output of clock 30 is provided, for example, in response to an external reference request.

[0092] (Storage part) The time on the clock 30 corresponding to the transmission or reception timing described later should be stored on a recording medium that can be accessed solely by hardware, without the need for a CPU or software, among the storage media constituting the storage unit 50. This is because it eliminates jitter caused by software. It is important that the association between the transmission / reception timing and the time is not affected by software jitter, and after the association between the transmission / reception timing and the time has been established, it may be stored in a low-speed access area.

[0093] (External Interface) The information input and output by the external interface 60 includes transmitted and received data such as synchronization information and the time of the clock 30.

[0094] (Time synchronization section) As shown in Figure 5, the time synchronization unit 3 includes a main control unit 31, a transmit / receive data interface (I / F) 32, a communication control unit 33, a scheduler 34, a time recording unit 35, a time acquisition unit 36, a time difference calculation unit 37, a virtual time difference calculation unit 38, and a synchronization control unit 39.

[0095] The main control unit 31 is coordinated with each part within the control unit 70 and controls the operation of each part within the control unit 70. The transmit / receive data interface 32 converts information from the storage unit 50 and the external interface 60 into a format that can be transmitted to the outside of the device. In addition, the transmit / receive data interface 32 converts information received from outside the device into a format suitable for the control unit 70 and the storage unit 50.

[0096] The communication control unit 33 controls the operation of the communication unit 10. The communication control unit 33 performs input and output of transmission and reception information between the communication unit 10 and the control unit 70.

[0097] The scheduler 34 sets the schedule (time) for the communication control unit 33 to transmit or receive information. For example, the transmitting scheduler 34 sets the information transmission interval and sets a schedule for detecting the timing of information transmission at a predetermined time.

[0098] The scheduler 34 in this embodiment sets the transmission of synchronization information, which is performed by the information synchronization devices 1 to obtain the transmission time and reception time of the synchronization information, to be executed within a predetermined time that can be considered to have a constant time difference. This predetermined time is the minimum interval time at which the frequency deviation between the local device CLa and the other device CLb affects the information propagation time between the local device CLa and the other device CLb, as will be described later. The frequency deviation is the difference in their respective clock frequencies. For example, the transmission timing of synchronization information, including the transmission time from the local device CLa to the other device CLb, and the transmission timing of synchronization information, including the transmission time from the other device CLb to the local device CLa, are set to be within the predetermined time.

[0099] The time recording unit 35 records the time when information is sent and received. In other words, the time recording unit 35 associates the transmission timing of the information detected by the transmission timing detection unit 13 with the time on the clock 30 at that transmission timing and stores it in memory. The time recording unit 35 also associates the reception timing of the information detected by the reception timing detection unit 14 with the time on the clock 30 at that reception timing and stores it in memory. This association is done, for example, when the time recording unit 35 receives a signal from the transmission timing detection unit 13 and the reception timing detection unit 14 indicating that the transmission and reception timings of the transmitted and received information have been detected, it refers to the time on the clock 30, and associates that time with the transmission and reception timings.

[0100] Thus, in this embodiment, "time" refers to the time on the clock 30 corresponding to the detected reception timing or transmission timing of the predetermined information element position of the information, and "duration" refers to the difference in said time.

[0101] The time acquisition unit 36 ​​acquires the transmission time of synchronization information from its own device CLa, the reception time when other devices CLb receive the synchronization information transmitted from its own device CLa, the transmission times of synchronization information from all other devices CLb, and the reception times when its own device CLa receives the synchronization information transmitted from all other devices CLb. The transmission time and reception time of its own device CLa are obtained from the memory of its own device CLa. The reception time and transmission time of other devices CLb are obtained from the synchronization information received by its own device CLa from other devices CLb and stored in its memory.

[0102] The time difference calculation unit 37 calculates the time difference between the clock 20 of the local device CLa and the clock 20 of all other devices CLb, based on the transmission time of the local device CLa, the reception time of the local device CLa, the transmission time of all other devices CLb, and the reception time of all other devices CLb, which are acquired by the time acquisition unit 36.

[0103] The virtual time difference calculation unit 38 calculates a virtual time difference, which is the time difference between the clock 20 of the device CLa and the virtual clock, based on the time difference between the clock 20 of the device CLa and the clocks 20 of all other devices CLa. In this embodiment, the virtual time difference is the average value of the time differences between the clock 20 of the device CLa and all other clocks 20. The virtual clock is not a clock that is actually in operation, but a virtual clock that can be considered a common time source for all information synchronization devices 1.

[0104] The synchronization control unit 39 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 38. In other words, the synchronization control unit 39 performs time synchronization using the virtual time difference as a correction value. Synchronization control is performed assuming that the propagation time between the clock 20 of its own device CLa and the virtual clock is symmetrical. For example, as will be described later, the time difference with the virtual clock is calculated, and the value of the clock 30's time is corrected based on that time difference. The correction may be made by controlling the clock 30 itself to correct the time. Alternatively, the clock 30 may correct the time based on the time difference when it outputs the time. That is, the clock 30's time itself may not be corrected, but the clock 30 may be controlled to output a time corrected for the difference when it outputs the time.

[0105] [Measurement of time difference when there is symmetry in propagation time] Next, the measurement of propagation time and time difference when there is symmetry in the propagation time will be explained with reference to Figure 7. Figure 7 shows the relationship between the time difference between the clocks and the information propagation time and the transmission and reception timing observed in information communication between a pair of devices, one local device CLa and the other device CLb, using wired communication as an example.

[0106] The synchronization information transmitted by the local device CLa, and the other synchronization information transmitted by the other device CLab, are for the purpose of timing synchronization. This synchronization information includes the transmission time of the local device CLa, but the content of this synchronization information and the other synchronization information is arbitrary.

[0107] As shown in Figure 7, the device CLa receives information at time t a,T It is transmitted to time t, and after propagation time d, it is transmitted to time t b,R Δt is received by another device, CLb. b Later, another device, CLb, received additional information at time t b,T It is transmitted to and, after the same propagation time d, the device CLa receives the signal at time t a,R It will be received.

[0108] Here, the interval between transmission and reception in the CLa device is defined as Δt. aLet the interval from reception to transmission in another device CLb be Δt b Let the transmission timing t of the own device CLa a,T The same timing as is observed as t' in another device CLb a,T For this reason, the time difference g between the clock 20 of another device CLb and the own device CLa at a certain moment can be obtained as shown in Equation (1). Furthermore, the time difference between the clocks of the own device CLa and another device CLb at the same moment with respect to another device CLb can be expressed as -g

[0109] TIFF2026055664000002.tif11161 Note that as described above, it is assumed that the propagation time d from the own device CLa to another device CLb and the propagation time d from another device CLb to the own device CLa are the same, that is, they are symmetric in the direction of information communication

[0110] From these conditions, the propagation time d can be obtained as shown in Equation (2).[[ID=...]] TIFF2026055664000003.tif15159

[0111] Therefore, the time difference g between the clocks 20 can be obtained as shown in Equation (3) using Equation (2). TIFF2026055664000004.tif14158

[0112] The synchronization control unit 39 of another device CLb can synchronize the time with respect to 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 39 of the own device CLa can synchronize the time with respect to another device CLb by repeatedly adjusting the clock frequency and time so that the time difference -g between the clocks 20 becomes minimum

[0113] If the clock frequencies of the local device CLa and the other device CLb are the same, that is, if the clock domain is single, time synchronization is possible by simply adjusting the time once. However, since there is generally a frequency difference between the two clocks, adjusting the clock frequency is essential for time synchronization. Even in systems where the clock frequency cannot be directly adjusted, time synchronization can be achieved by controlling the drive frequency of the clock 30 by repeatedly adjusting the amount of time advance per clock. In these frequency adjustments, closed-loop control is performed periodically, 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.

[0114] Furthermore, propagation time and internal delays between transmission and reception timings can be ignored or compensated for depending on the system requirements. Also, instead of initiating the transmission of synchronization information from the local device CLa, the synchronization information may be transmitted from another device CLb. Additionally, while one interface is sufficient for information communication, a configuration using multiple interfaces simultaneously is also possible, for example, by implementing separate interfaces for transmission and reception.

[0115] [Effects of time zone and propagation time variations] The above explanation assumes that the time difference is constant and that the propagation time is symmetrical in the direction of information communication. However, the actual frequency deviation of the clock 20 between the information synchronization devices 1 differs from the nominal frequency and fluctuates moment by moment. Therefore, the time difference between the information synchronization devices 1 also fluctuates, and depending on the network system to which the local device CLa and the other device CLb are connected, the information propagation path and communication arbitration have an effect, and as shown in Figure 8, the propagation time is generally asymmetrical.

[0116] In other words, the time difference g between your device CLa and the other device CLab at a given moment. b / a Then, the time difference g between the same device CLa and another device CLb after a certain period of time has elapsed. a / b They will not be the same. Also, the information propagation time d from the local device CLa to the other device CLb. b / a This is the information propagation time d from another device CLb to the own device CLa.a / b It is generally not the same as [the other value]. Note that the time difference in Figure 8 is expressed in the same way as the time difference in Figure 7, g b / a and g a / b They have the same sign, and g b / a ·g a / b It is assumed to be ≥ 0. Furthermore, as mentioned above, the time difference and propagation time fluctuate moment by moment, and the time difference g observed at a given moment b / a [m] and propagation time d b / a [m] is the time difference g observed at different moments in time. b / a [n] and propagation time d b / a [n] are generally different in each case.

[0117] Here, from the relationship of each time in Figure 8, the propagation time d b / a d a / b and time difference g b / a ,g a / b Using this, we rearrange equations (2) and (3) to be as shown in equations (4) and (5), respectively. TIFF2026055664000005.tif15162TIFF2026055664000006.tif13162

[0118] In equation (2), the propagation time could be calculated assuming symmetry, but in equation (4), it can be seen that the average value of the propagation time includes a component of time zone variation. Similarly, in equation (3), the time zone could be calculated assuming that the time zone is constant, but in equation (5), it can be seen that the average value of the time zone includes a component of propagation time variation. When such components of time zone variation and propagation time are included, it leads to a decrease in the accuracy of time synchronization.

[0119] [Errors due to time zone differences and variations in propagation time] This explains the time synchronization errors caused by variations in time zone and propagation time in a time synchronization system. First, equations (4) and (5) are combined and transformed into matrix form as shown in equation (6). TIFF2026055664000007.tif13156

[0120] Here, the two-dimensional rotation matrix R θLet this be equation (7). TIFF2026055664000008.tif11161

[0121] Then, focusing on the common factor in equation (6), we get R in equation (7). θ By using this, equation (6) can be transformed into equation (8). TIFF2026055664000009.tif14162

[0122] As shown in Figure 9, the horizontal axis represents the time difference g when communication occurs from the local device CLa to the other device CLB. b / a and propagation time d b / a The vertical axis represents the time difference g when communication occurs from another device CLb to this device CLa. a / b and propagation time d a / b Consider a two-dimensional space whose components are (g b / a - g a / b ) T The time difference vector g, (d b / a d a / b ) T If we let this be the propagation time vector d, then the synchronization state vector s = (g) is an element of the time difference including the variation error and the propagation time as given by equation (8). d d g ) T This can be interpreted as the sum of the time difference vector g and the propagation time vector d, rotated by +π / 4 in the same space, and then scaled in each dimension.

[0123] In the operation of equation (8), the element g of the time difference vector g b / a , g a / b There is no change in 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 When this is the case, as shown in Figure 9, the synchronization state vector s is d g Ingredients and g d By orthogonally decomposing the components, it becomes clear that the time difference and delay time can be determined without including errors.

[0124] However, generally, as shown in Figure 10, the time difference vector g and the propagation time vector d each contain fluctuation errors in their respective elements. Therefore, because the errors of each other are combined in each of the orthogonal components, the operation of equation (8) alone cannot remove the errors from the time difference and propagation time, leading to a decrease in time synchronization accuracy.

[0125] Since equations (4) and (5) are linearly dependent, an analytical solution cannot be obtained without introducing other independent operations. However, measuring the transmission and reception timing of synchronization information alone does not allow for the discovery of new independent operations that result in the vector shown in Figure 9. Therefore, a different approach is needed to eliminate fluctuation errors.

[0126] [Relationship between time zone variations and frequency deviation] The oscillation frequency f of the clock 20 of each information synchronization device 1 used for time synchronization is the nominal frequency f N The frequency deviation e is included in the equation. Furthermore, the frequency deviation e fluctuates moment by moment depending on the mechanical and electromagnetic operating environment of clock 20. For this reason, the relationship between the oscillation frequency f[n] and the frequency deviation e[n] at 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. TIFF2026055664000010.tif10157

[0127] Figure 11 shows the relationship between transmission / reception timing, time difference, and propagation time when communicating information from the local device CLa to another device CLb.

[0128] The nominal frequency of clock 20 used for time synchronization is the same for both the local device CLa and the other device CLb. However, the frequency deviation is e a [n] Other devices CLb is e b [n]. In this case, the frequency deviation of the other device CLb as seen from the own device CLa is (e b [n]-e a [n]) is expressed as follows: the frequency ratio r b / a [n] is r b / a [n] = 1 + (eb [n]-e a [n]) can be expressed as follows. Similarly, the frequency deviation of our own device CLa as seen from another device CLb is (e a [n]-e b [n]) is expressed as follows: the frequency ratio r a / b [n] is r a / b [n] = 1 + (e a [n]-e b It can be expressed as [n]).

[0129] If the clock frequencies of the local device CLa and the other device CLB are different, the rate at which time progresses will also differ, resulting in a time difference moment by moment, g b / a [m]≠g b / a There are also observation timings where [n] occurs, and time calculations between devices require correction to account for frequency deviations. Failure to perform this correction will result in errors in time calculations, leading to a decrease in time synchronization accuracy.

[0130] In Figure 11, the average frequency ratio of the other device CLb as seen from the own device CLa from timing m to timing n is r. b / a If we let [n,m], then the relationship in equation (10) can be expressed. TIFF2026055664000011.tif20158

[0131] 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 expressed as [m]), and it can be seen that the time difference changes due to the effect of frequency deviation.

[0132] In equation (10), the frequency deviation does not affect the propagation time and therefore no correction is required. This is because the nominal frequency f of clock 20 N For two devices with apparent frequency deviation e[n], the minimum time L required for a time difference to occur in the observation times of both devices is given by L. g [n] can be expressed as shown in equation (11), but generally the propagation time is this minimum time L g This is because it is smaller than [n]. Note that the period T N= 1 / f N is defined as such. TIFF2026055664000012.tif13158

[0133] That is, L g [n] is the time T for one period corresponding to the nominal frequency with respect to the observed time difference between devices. N is the interval time during which addition or subtraction is performed. Therefore, within this interval time, the time difference changes by at most ±T N and does not change further.

[0134] Also, L g [n] changes moment by moment and cannot be directly obtained. However, if the allowable frequency deviation of clock 20 is e, the absolute value of the apparent frequency deviation between devices using the same type of clock 20 does not exceed |2e|. Therefore, L g = T N / |2e| is set as the minimum time for the time difference to be constant in these clocks 20.

[0135] [Formation of Virtual Clock] Next, the formation of a virtual clock v for synchronizing the clocks 20 of all information synchronization devices 1 will be described. In the following description, the symbols of the "devices" that are information synchronization devices 1 and the "clocks" included therein are made to match.

[0136] When the transmission time of the synchronization information of the self-device i including clock i is t<s i,T , {t i,T} j is set as the time of the other device j including clock j at the same timing as t i,T . The same timing means the ideal single timing at which the times of each clock i, j are observed with a propagation time of 0 in the observation system including clocks i, j. By definition, t i,T can also be described as {t i,T} i .

[0137] The time difference g i,T between clock j observed from clock i at the timing when the synchronization information is transmitted at time t j / iWe define this as shown in equation (12). TIFF2026055664000013.tif14158

[0138] N information synchronization devices 1 are connected to a synchronization network NE, and one of these information synchronization devices 1, device i, implements a clock i. The transmission time of the synchronization information of device i is t. i,T The sum of the transmission times of the synchronization information of all devices k at the same time, that is, the sum of the transmission times of all information synchronization devices 1, can be expressed by equation (13). TIFF2026055664000014.tif15159

[0139] By rearranging equation (13), we obtain equation (14). In equation (14), the first term on the far right side corresponds to the sum of the time differences between the local device i and all N information synchronization devices 1 as seen from the local device i. Note that the local device i is included in all information synchronization devices 1, but the time difference between local devices i is 0. The second term on the far right side is the transmission time of the synchronization information of the local device i multiplied by N. TIFF2026055664000015.tif16156

[0140] From equation (12), equation (14) can be expressed as equation (15). TIFF2026055664000016.tif16156

[0141] 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 synchronization devices 1, and the first term on the right side is the average value of the time difference between the device i and all information synchronization devices 1 as seen from the device i itself. TIFF2026055664000017.tif15156

[0142] At this time, the left side of equation (16) is t i,TAssume the existence of a device v that includes a clock v which has the same timing as the others. This clock v is called a virtual clock v. If the first term on the right side of Equation (16) is regarded as the time difference between the observed virtual clock v from clock i, then based on device v, Equation (16) can be rewritten as Equation (17), which is a transformation of Equation (12). That is, by looking at the time differences between clock i and all other clocks and taking their average, a virtual clock v can be formed. TIFF2026055664000018.tif11156

[0143] This t i,T At the same timing as this, if device j transmits synchronization information at time t j,T then t j,T ={t i,T} j and t i,T ={t j,T} i as well. Therefore, {t i,T} v ={t j,T} v and it can be said that the same device v exists both from device i and device j.

[0144] Even when device j transmits synchronization information at a timing different from t in Equation (17) at time t i,T if Equation (17) holds for another device j, each device connected to this synchronization network NE can synchronize with the assumed device v by performing time synchronization control to cancel the time difference g j,T with the virtual clock v. v / k

[0145] The relationship between such a virtual clock and the clocks of the information synchronization device 1 is schematically shown in FIG. 12. The horizontal axis in FIG. 12 represents the passage of absolute time, and the vertical axis represents the time differences of each clock. The virtual clock is shown as Cv, and the clocks of the information synchronization device 1 are shown as C1 to C3. Among the four points enclosed by each of the three dotted ellipses in FIG. 12, the line connecting the points obtained by taking the average of the time differences of C1 to C3 becomes the virtual clock Cv.

[0146] For clock C1's t1,T and the virtual clock Cv {t 1,T} v The time difference is g v / 1 , clock C2 t 2,T and the virtual clock Cv {t 2,T} v The time difference is g v / 2 , clock C3 t 3,T and the virtual clock Cv {t 3,T} v The time difference is g v / 3 The clocks C1, C2, and C3 each have a time difference of g. v / 1 , g v / 2 , g v / 3 If you cancel it, you should be able to sync.

[0147] However, Figure 12 only shows the time difference with errors, including propagation time deviation and frequency deviation, eliminated. In reality, errors are included in the time difference. These errors are schematically shown in Figure 13. Figure 13 shows that clock C1 and clock C2 have a minimum unit of ±1 / f N This shows the discrepancy. Such errors will be discussed later.

[0148] [Effect of time zone fluctuations on virtual clocks] It is common for different devices i and j to transmit synchronization information at different times. Furthermore, the propagation time of the synchronization information is longer than zero, and the reception timing differs from the transmission timing. The interval between these timings corresponds to the time L over which time difference variations due to clock frequency deviations are observed. g Let's consider the case where it is kept within the limit.

[0149] Without losing generality, the nominal frequency of the clock implemented in each device is f N In this case, since each clock operates independently, device k takes time L g Within this range, the possible time variation (time difference variation from an ideal clock with a permissible frequency deviation of 0) Δk is given by {-1 / f N ,0,1 / f N It is one of the following: That is, even if L gEven if the time difference is repeatedly observed at shorter intervals, the smallest unit in which time difference variation can be observed is ±2 / f. N It may be possible to observe changes in this.

[0150] Similarly, the time variation Δv that the virtual clock v formed in the synchronous network NE, to which N devices are connected, can take during this interval can be determined by equation (18). TIFF2026055664000019.tif15152

[0151] However, the sum of Δk follows a ternary distribution, and its probability distribution is shown in Figure 14. Therefore, the probability that both sides of equation (18) hold is at most 1 / 3 each. N Therefore, Δk is always -1 / f N or 1 / f N This applies only if that is the case. In other words, at most 2 / 3 N This is the probability. Note that Δk can take {-1 / f N ,0,1 / f N The values ​​} are assumed to appear with equal probability, and in Figure 14, they are normalized to a range of ±1. The probabilities of being -0.5 or less and 0.5 or greater are 8 × 10 for N=10. -2 , if N=20 units, 8 × 10 -3 , if N=50 units, 1 × 10 -5 , if N=100 units, 5 × 10 -10 That is the case.

[0152] Therefore, the time difference variation Δg between the virtual clock v observed from device k and the device k. v / k =Δv-Δk is -2 / f N <Δg v / k <2 / f N It can take on the range of Δg. v / k = ±2 / f N The reason this cannot be true is due to the conditions under which the equality in equation (18) holds. In other words, Δ i = -1 / f N , Δ k≠i = 1 / f N At that time Δ v =(N-2) / Nf N And Δg v / kThe maximum value is (2N-2) / Nf N <2 / f N Take Δ i = 1 / f N like Δ k Similarly, when the sign of Δg is reversed, v / k The minimum value is -(2N-2) / Nf N >-2 / f N Take it.

[0153] Using this time difference, g i / j =-(g j / i +Δg j / i If expressed as ), the expected value of the first term on the far right of equation (5) when device i observes other device j can be expressed as in equation (19), taking into account the change in the definition of time difference in equation (12). This is Δ v From the probability distribution (Figure 14), the second term of the second right side is Δg v / i / 2 is -1 / 2f N Beyond 1 / 2f N Since it can be considered to take the range less than 1 / f N It can be rounded to zero using as the unit. TIFF2026055664000020.tif16154

[0154] Therefore, the time variation of each device is at most ±1 / f N If the observations in equation (19) are completed within the period in which only this occurs, the time difference with the virtual clock can be determined without causing a time difference error due to fluctuations in the clock's frequency deviation.

[0155] Under these conditions, the time difference g calculated by equation (17) at different timings for each device k is v / k This represents the time difference relative to the same virtual clock.

[0156] [Effect of propagation time variations on the virtual clock] Until now, the ideal time difference g without error j / i The observation was based on the assumption that the propagation time d is greater than 0 and different from the actual value, as shown in equation (5). j / i d i / j Time differences can be observed through this process.

[0157] g a / b =g b / a +Δg b / a ,Δd b / a =d b / a -d a / b Let's rewrite equation (5) as equation (20). TIFF2026055664000021.tif12152

[0158] For device i and other devices k connected to the synchronous network NE, time L g By completing the transmission and reception of synchronization information within the time frame, and paying attention to the change in the definition of time difference in equation (12), we can derive equation (20) and take the expected value of these equations to arrive at equation (21). TIFF2026055664000022.tif15157

[0159] In other words, the error due to 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 propagation time deviation between device i and each of the other devices k. Therefore, time synchronization with the virtual clock can reduce errors due to propagation time deviation of the synchronization information.

[0160] Furthermore, the propagation time deviation Δd at the timing of device i j / i [i] and the propagation time deviation Δd at the timing of device j i / j [j] is Δd j / i [i]=-Δd i / j If the relationship [j] is maintained when transmitting and receiving synchronization information, the expected value of the time difference error due to propagation time deviation can be calculated using equation (22). Δd i / j [j] is Δd j / i [i] has opposite signs but the same absolute value, so it becomes 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 with the virtual clock, and this is 0. In other words, each information synchronization device 1 assumes that the communication unit 10 transmits and receives synchronization information while maintaining a relationship in which the absolute value of the propagation time deviation at the timing of its own device i is equal to the absolute value of the propagation time deviation at the timing of other devices j. TIFF2026055664000023.tif16158

[0161] In other words, the expected value of the synchronization phase difference due to time synchronization to the virtual clock across the entire synchronous network NE is 0, achieving balanced and accurate time synchronization.

[0162] [Operation] Based on the embodiment described above, the procedure for multiple devices connected to the synchronization network NE to synchronize their time with the virtual clock formed in this synchronization network NE will be explained with reference to the flowchart in Figure 15 and the explanatory diagram in Figure 16. In the following explanation, any one of the information synchronization devices 1 will be referred to as the local device i, and the other information synchronization devices 1 will be referred to as other devices j. The flowchart in Figure 15 shows the processing flow in the local device i.

[0163] First, as shown in Figure 16, the communication control units 33 of the local device i and the other device j, according to the scheduler 34, inform the communication unit 10 of a time L that can be considered to have a constant time difference. g The system performs multicast transmission of synchronization information within a certain timeframe, and then unicast transmission of the synchronization information. As a result, the time acquisition unit 36 ​​of the device i acquires four transmission and reception times (step S201). The four transmission and reception times are the transmission time of the synchronization information from the device i. i,T , when this was received by another device j, the reception time t j / i,R , the transmission time of synchronization information from all other devices j t j,T The reception time t when device i receives the synchronization information transmitted from all other devices j. i / j,R That is the case.

[0164] More specifically, device i transmits synchronization information via multicast, and other devices j≠i receive this synchronization information. At this time, device i t i,T Other devices j are t j / i,R Obtain (Process 1). Similarly, other devices j≠i simultaneously transmit synchronization information, and device i receives this synchronization information. At this time, other device j is t j,T The device i is t i / j,RObtain (Process 2). All local devices i and other devices j can consider Processes 1 and 2 to be performed with a constant time difference for a certain period of time L. g We will execute it within [time].

[0165] Then, device i sends process 1 to other device j≠i. i,T and process 2 t i / j,R Synchronization information including is sent via unicast, and other device j receives this synchronization information (process 3). As a result, device j t j,T ,t j / i,R ,t i,T ,t i / j,R This can be obtained. Furthermore, another device j≠i sends process 2 t to its own device i. j,T and process 1 t j / i,R Synchronization information including is sent, and device i receives this synchronization information. As a result, device i t i,T ,t i / j,R ,t j,T ,t j / i,R This can be obtained (process 4). All information synchronization devices 1 perform processes 3 and 4.

[0166] Next, the time difference calculation unit 37 of the device i calculates the time difference g with all other devices j≠i using equation (23). d,j / i We find the answer (step S202). TIFF2026055664000024.tif14158

[0167] Then, the virtual time difference calculation unit 38 of the device i uses equation (24) to calculate the time difference g with the virtual clock v. d,v / i Calculate the (virtual time difference) (Step S203). TIFF2026055664000025.tif17157

[0168] Device i has a time difference g at the current time. d,v / i The time or clock frequency is adjusted to add to it, and the time is synchronized with the virtual clock v (step S204).

[0169] If all information synchronization devices 1 perform steps S102, S103, and S104 and continue time synchronization, wait for a predetermined period and return to step S101. Through this procedure, Δd j / i [i]=-Δd i / j The transmission and reception of synchronization information is achieved while maintaining the relationship [j].

[0170] [effect] In this embodiment, the time synchronization unit 3 performs time synchronization based on a virtual clock, which is a virtual clock that can be considered a common time source for each information synchronization device 1.

[0171] More specifically, the time synchronization unit 3 includes a communication control unit 33 that causes the communication unit 10 to send and receive synchronization information within a predetermined time period during which the time difference between the information synchronization devices 1 can be considered constant, a time acquisition unit 36 ​​that acquires the transmission time of synchronization information from one of the information synchronization devices 1, which is the self-device CLa, the reception time when the synchronization information transmitted from the self-device CLa is received by another information synchronization device 1, which is another-device CLa, the transmission time of synchronization information from all other-device CLa, and the reception time when the self-device CLa receives the synchronization information transmitted from all other-device CLa, and the transmission time of the self-device CLa acquired by the time acquisition unit 36. The system includes: a time difference calculation unit 37 that calculates the time difference between the clock 20 of the local device CLa and the clocks 20 of all other devices CLa based on the reception time, the transmission time of all other devices CLa, and the reception time of all other devices CLa; a virtual time difference calculation unit 38 that calculates a virtual time difference between the clock 20 of the local device CLa and a virtual clock, which is a virtual clock that can be considered a common time source for all information synchronization devices 1, based on the time difference between the clock 20 of the local device CLa and all other clocks CLa; and a synchronization control unit 39 that synchronizes the clock 20 of the local device CLa with the virtual clock based on the virtual time difference calculated by the time difference calculation unit 37.

[0172] In this way, by assuming a virtual clock based on the time difference between the clock 20 of the local device CLa and the clock 20 of the other device CLb, it becomes possible to absorb fluctuations in the propagation time of information communication and reduce errors in synchronization control using only information communication between the information synchronization devices 1, without using a reference clock such as GMC or relay devices such as BC and TC. By having the communication unit 10 send and receive synchronization information within a predetermined time when the time difference between the information synchronization 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. In this embodiment, as described above, the average value of the time difference with the clock 20 of the other device CLb is used as the time difference between the clock 20 of the local device CLa and the virtual clock.

[0173] The communication units 10 of the local device CLa and other devices CLb are connected via a complete network. Therefore, the time difference with all other devices CLb except the local device CLa can be determined. Thus, it is preferable that the synchronous network NE be a complete network.

[0174] However, the physical configuration does not need to be a complete network; even a star-shaped synchronous network NE centered around a single hub is sufficient as long as the communication method of the synchronous information can achieve a complete network.

[0175] Furthermore, 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, synchronization errors will occur because the equation (16) obtained for each information synchronization device 1 will not be the same. Moreover, even if any one of the information synchronization devices 1 fails, the current time synchronization can be maintained by degrading the synchronization network NE to form a complete network.

[0176] The communication control units 33 of the local device CLa and the other device CLb cause the communication unit 10 to simultaneously transmit synchronization information within a predetermined time. As a result, the time acquisition unit 36 ​​can efficiently acquire four transmission and reception times.

[0177] The communication unit 10 transmits and receives synchronization information while maintaining a relationship where the absolute value of the propagation time deviation at the timing of its own device CLa is equal to the absolute value of the propagation time deviation at the timing of the other device CLb. As a result, the expected value of the synchronization phase difference with the virtual clock is 0, meaning that time synchronization centered on the virtual clock can be achieved.

[0178] [Other embodiments] The present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriate combinations of the multiple components disclosed in the above embodiments. [Explanation of Symbols]

[0179] 1. Information synchronization device 2 Control Unit 3. Time synchronization section 4. External Information Input Unit 5 Position detection unit 6. Information embedding section 7 External Information Recording Unit 8 External World Information Reproduction Department 9. External Interfaces 10 Communications Department 11 Transmitter 12 Receiver 13 Transmission timing detection unit 14 Reception timing detection unit 20 clock 30 Clocks 31 Main Control Unit 32. Data transmission / reception interface 33 Communication Control Unit 34 Scheduler 35 Time Recording Section 36 Time acquisition part 37 Time difference calculation unit 38 Virtual Time Difference Calculation Unit 39 Synchronization Control Unit 100 Information Synchronization System

Claims

1. An information synchronization system in which the time synchronization units of multiple information synchronization devices perform time synchronization based on time information, The aforementioned information synchronization device is External information input unit for inputting external information, An information embedding unit embeds the time information synchronized by the aforementioned time synchronization unit into external information, An external information recording unit that records external information with embedded time information, An information synchronization system characterized by having the following features.

2. The information synchronization device has a position detection unit that detects the position information of the information synchronization device, The information synchronization system according to claim 1, characterized in that the information embedding unit embeds the position information detected by the position detection unit into the external information.

3. The information synchronization device has a position detection unit that detects the position information of the information synchronization device, The information synchronization system according to claim 1, characterized in that the information embedding unit embeds spatiotemporal information, which associates the position information detected by the position detection unit with the time information, into the external information.

4. The information synchronization system according to claim 1, characterized in that the time synchronization unit synchronizes with external reference time information.

5. The information synchronization system according to claim 1, characterized in that the time synchronization unit performs time synchronization based on a virtual clock, which is a virtual clock that each information communication device can consider as a common time source.

6. The aforementioned time synchronization unit, A communication control unit causes the communication unit to send and receive synchronization information within a predetermined time period during which the time difference between the aforementioned information synchronization devices can be considered constant. A time acquisition unit that acquires the transmission time of the synchronization information from the device itself, which is one of the information synchronization devices; the reception time when the synchronization information transmitted from the device itself is received by another information communication device other than the device itself; the transmission time of the synchronization information from all of the other devices; and the reception time when the device itself receives the synchronization information transmitted from all of the other devices. A time difference calculation unit calculates the time difference between the clock of the device and the clocks of all other devices based on the transmission time of the device itself, the reception time of the device itself, the transmission time of all other devices, and the reception time of all 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 device and the virtual clock, based on the time difference between the clock of the device and all other clocks, A synchronization control unit synchronizes the clock of the device with the virtual clock based on the virtual time difference calculated by the virtual time difference calculation unit, The information synchronization system according to claim 5, characterized by having the following features.

7. The information synchronization system according to claim 1, characterized in that each information synchronization device has an external information playback unit that synchronizes and plays back external information recorded by the external information recording unit based on time information embedded by the information embedding unit.

8. A time synchronization unit that performs time synchronization based on time information with other information synchronization devices, External information input unit for inputting external information, An information embedding unit embeds the time information synchronized by the aforementioned time synchronization unit into external information, An external information recording unit that records external information with embedded time information, Sharp information synchronization device.

9. It has a position detection unit that detects the position information of the information synchronization device, The information synchronization device according to claim 8, characterized in that the information embedding unit embeds the position information detected by the position detection unit into the external information.

10. It has a position detection unit that detects the position information of the information synchronization device, The information synchronization device according to claim 8, characterized in that the information embedding unit embeds spatiotemporal information, which associates the position information detected by the position detection unit with the time information, into the external information.

11. The information synchronization device according to claim 8, further comprising an external information playback unit that synchronizes and reproduces external information recorded by the external information recording unit based on time information embedded by the information embedding unit.

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