Time Synchronization Network

Abstract

To provide a time synchronization network that can efficiently maintain time synchronization according to an absolute time.SOLUTION: In a time synchronization network to which a plurality of communication devices 11 having a communication function are connected, and that performs the time synchronization of each of the communication devices 11, the communication device 11 includes time information output means 120 that outputs time information by a stable internal clock 121, and time synchronization means 111 that corrects the time information of the time information output means 120 on the basis of time difference information between the communication device 11 and a communication device adjacent to the communication device 11.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a time synchronization network that performs time synchronization of communication devices. [Background technology]

[0002] In communications infrastructures that require robustness, communication nodes such as base stations and relay stations are laid and deployed to form a hierarchical mesh so that synchronization is always ensured. Also, in the field of power transmission and distribution, where efficiency as well as robustness are emphasized, smart management is achieved by synchronizing the amount of electricity used with absolute time, and overall optimization of electricity usage efficiency is also attempted by providing feedback to power generation facilities (Patent Document 1).

[0003] Synchronization is essential to ensure the stability and confidentiality of communications. For this reason, wireless communication terminals, such as mobile phones, use a protocol to establish communication by synchronizing with the base station they are connected to before sending or receiving packets.

[0004] The wireless communication terminals mentioned above adjust the timing of each communication as a communication event occurs. This synchronization is only between the wireless communication terminals communicating, and is not intended to allow multiple systems to share time, as is the case with absolute time synchronization. Absolute time synchronization is difficult because the internal clocks installed in wireless communication terminals have random frequency drift, making it possible to maintain time synchronization for only an extremely short period of time.

[0005] In recent years, atomic clocks that utilize the energy levels of alkali metal elements such as cesium (Cs) and rubidium (Rb) have been rapidly miniaturized (Non-Patent Documents 1, 2). The application of such small atomic clocks can significantly reduce the frequency drift of internal clocks installed in wireless communication terminals. Furthermore, even if frequency drift does occur, the drift rate can be maintained constant, making it easy to correct the frequency drift by linear interpolation.

[0006] In conventional communications using wireless communication terminals, the process is limited to sending and receiving packets between a base station and the terminal, but there is a constant demand for an increase in the amount of data handled and the speed of data calculations. If stable time synchronization can be maintained using the small atomic clocks mentioned above, it will become possible to link and virtualize terminals, or base stations and terminals, to aggregate big data, perform advanced calculations, and extract information. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2019-110417 [Non-patent literature]

[0008] [Non-Patent Document 1] N. Cyr, M. Tetu, M. Breton, “All-optical microwave frequency standard: a proposal,” IEEE Trans. Instrumentation and Measurement, vol. 42, pp. 640-649, 1993 [Non-patent document 2] S. Knappe, V. Shar, P. Schwindt, L. Hollberg, J. Kitching, LA Liew, J. Moreland, “A microfabricated atomic clock,” Appl. Phys. Lett., vol. 85, pp. 1460-1462, 2004. Summary of the Invention [Problem to be solved by the invention]

[0009] However, with the explosive growth of wireless communication terminals connected to networks, the frequency of time synchronization in time servers has become so large that it cannot be ignored in communication traffic. Furthermore, as networks become larger in scale, the uncertain network delays involved in time synchronization cannot be ignored.

[0010] Therefore, an object of the present invention is to provide a time synchronization network that can efficiently maintain time synchronization based on absolute time. [Means for solving the problem]

[0017] The time synchronization network according to the present invention is a time synchronization network to which a plurality of communication devices each having a communication function are connected, and which performs time synchronization for each of the communication devices. The time synchronization network includes an absolute time estimation device, which is an arbitrary communication device that estimates absolute time, and the communication devices; An absolute time estimation device adjacent to the communication device or A virtual hierarchical structure is formed for querying time information, and the communication device includes a time information output means for outputting time information based on a stable internal clock; Time information of the time information output means and an absolute time estimation device or communication device adjacent to the communication device represents the difference between the time information of The absolute time estimation device includes a time synchronization means for correcting time information based on time difference information, and a memory for storing the time difference information and the number of inquiry steps, and the absolute time estimation device includes an absolute time estimation means for performing a maximum likelihood point estimation process using a Kalman filter on the time difference information to estimate absolute time, time The time synchronization means is Inquiring about time information from an absolute time estimation device or a communication device adjacent to the communication device, receiving the time information and the number of inquiry steps in response to the inquiry about the time information, and adding 1 to the received number of inquiry steps; The time information of a communication device with a small number of inquiry steps is used as a reference, and a communication device with a large number of inquiry steps corrects its time information. With this configuration, even if a time server is not provided, accurate time synchronization can be performed based on the absolute time estimated by the absolute time estimation device. [Effects of the Invention]

[0018] The time synchronization network according to the present invention can suppress communication traffic and network delays, and efficiently maintain time synchronization based on absolute time. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating the overall configuration of a network. [Figure 2] FIG. 1 is a diagram showing the configuration of a sparse network as a time synchronization network according to a first embodiment. [Figure 3] FIG. 1 is a diagram showing the configuration of a dense network as a time synchronization network according to a first embodiment. [Figure 4] 1 is a block diagram showing a configuration of a communication device according to a first embodiment. [Figure 5] FIG. 2 is an explanatory diagram illustrating time synchronization in a time synchronization network according to the first embodiment. [Figure 6] 4 is a flowchart showing the operation of the communication device according to the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating a configuration of a time synchronization network according to a second embodiment. [Figure 8] FIG. 10 is a block diagram showing the configuration of a communication device according to a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating a configuration of a time synchronization network according to a third embodiment. [Figure 10] FIG. 10 is a block diagram showing the configuration of a communication device according to a third embodiment. [Figure 11] FIG. 10 is a diagram showing another configuration of the time synchronization network according to the third embodiment. [Figure 12] FIG. 10 is a diagram illustrating a configuration of a time synchronization network according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. However, each embodiment described below is intended to embody the technical concept of the present invention, and unless otherwise specified, the present invention is not limited to the following. Furthermore, in each embodiment, the same means are given the same reference numerals, and their description may be omitted.

[0021] [Overall network configuration] Referring to FIG. 1, the overall configuration of the network NW will be described as a premise for each embodiment. The network NW forms a time-synchronized communication network, and as shown in FIG. 1, includes a time-synchronized network 1, a core network 2, and an infrastructure network 3, which will be described later.

[0022] The core network 2 is a backbone network capable of large-capacity communications, and is sometimes called a backbone.

[0023] The infrastructure network 3 is a network that connects the time synchronization network 1 and the core network 2. The infrastructure network 3 is connected to the time synchronization network 1 in the form of a branch, regardless of whether it is wired or wireless. For example, the infrastructure network 3 includes a base station (master station device) 30 connected to the core network 2, and a base station (slave station device) 31 connected to the time synchronization network 1. The infrastructure network 3 may also include a repeater (relay device) 32 that relays between the base stations 30 and 31.

[0024] Here, in the network NW, accurate time information with time synchronization is transmitted from the core network 2 to the base station 30, relayed by the repeater 32, passes through the base station 31, and arrives at the time synchronization network 1. This time synchronization network 1 has a large number of communication devices 11 connected to an edge server 10 with computing power, and therefore efficiently maintains time synchronization as described below.

[0025] (First embodiment) [Time synchronization network configuration] The configuration of the time synchronization network 1 according to the first embodiment will be described with reference to FIG. As shown in Fig. 2, the time synchronization network 1 performs time synchronization for each communication device 11, and includes an edge server 10 and a communication device 11. Here, the time synchronization network 1 is a sparse network in which the edge server 10 and the communication device 11 are connected only to adjacent communication devices 11. Alternatively, the time synchronization network 1 may be a dense network in which the edge servers 10 and the communication devices 11 are interconnected, as shown in Fig. 3. In the following, the time synchronization network 1 will be described as a sparse network.

[0026] The edge server 10 is a typical edge server used in edge computing, and performs desired processing on various data from the communication device 11 and transmits the data to the core network 2. The edge server 10 is also connected to the base station 31 and at least one communication device 11. In the example of FIG. 2, the edge server 10 is connected to two communication devices 11. In this embodiment, the edge server 10 also functions as a time server that presents absolute time to the communication device 11.

[0027] The communication device 11 is any device equipped with a communication function, and may also be called a communication node. For example, the communication device 11 may be a wireless communication terminal such as a mobile phone or a smartphone. Furthermore, the communication device 11 is not limited to a wireless communication terminal, but may also be an automobile or drone equipped with a wireless communication function, a sensor terminal that constitutes a sensor network, or a smart meter that measures power consumption.

[0028] When the communication device 11 has high mobility, such as an automobile or drone, time synchronization is required to link multiple edge servers 10. Furthermore, when analyzing image data from multiple drones, mobility and data linking are performed simultaneously, while contour extraction from the image data and obstacle avoidance are also performed in real time. Therefore, these calculation processes must also be linked between the edge servers 10, and accurate time information is essential. Furthermore, when measurements are taken using multiple sensor terminals, such as in a sensor network, continuous, multi-point time synchronization is required to ensure that the measurement data is meaningful.

[0029] [Communication device configuration] The configuration of the communication device 11 will be described with reference to FIG. As shown in FIG. 4, the communication device 11 includes a communication module 100, a calculation means 110, a time information output means 120, and a GNSS 130. It is assumed that each communication device 11 provided in the time synchronization network 1 has the same configuration.

[0030] The communication module 100 realizes the communication function of the communication device 11, and specifically, communicates with the edge server 10 and other communication devices 11. The communication module 100 can use any communication method depending on the type and purpose of the communication device 11. For example, the communication module 100 uses wireless communication such as Bluetooth (registered trademark) or Wi-Fi (registered trademark). Furthermore, if the communication device 11 is a smartphone, the data communication function of the communication module 100 can be used. Furthermore, the communication device 11 may communicate via a wired cable.

[0031] The calculation means 110 performs various calculations required by the communication device 11, and is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). As shown in FIG. 4, the calculation means 110 includes a time synchronization means 111 and a memory (storage means) 112.

[0032] The time synchronization means 111 corrects the time information output by the time information output means 120, which will be described later, based on the time difference information stored in the memory 112. Details of the time synchronization by the communication device 11 will be described later.

[0033] The memory 112 stores time difference information. This time difference information indicates the time difference between a communication device 11 and a communication device 11 adjacent to the communication device 11. Furthermore, if the communication device 11 is adjacent to an edge server 10, the time difference information indicates the time difference between the communication device 11 and the edge server 10.

[0034] The time information output means 120 outputs time information based on a stable internal clock 121 , and includes the internal clock 121 and a counter 122 . The internal clock 121 is a frequency source that generates a clock signal. The counter 122 counts the clock signal generated by the internal clock 121 and generates time information.

[0035] In this embodiment, the time information output means 120 is configured as an atomic clock. For example, the time information output means 120 may be an atomic clock that utilizes the energy levels of alkali metal elements such as cesium and rubidium (Non-Patent Documents 1 and 2).

[0036] Atomic clocks stabilize their internal clocks by utilizing absorption and emission spectra determined by the inherent energy levels of electron orbitals of atoms and molecules. Because frequency depends on the energy levels of atoms and molecules, which are essential physical quantities, they can provide extremely stable frequency standards. Stabilizing clock chips such as quartz oscillators using the aforementioned atomic clock technology can significantly reduce frequency drift. Even if frequency drift does occur, a constant drift rate can be maintained that facilitates linear interpolation. Therefore, by configuring the time information output means 120 with an atomic clock, time synchronization can be maintained through simple intermittent mutual comparison processing.

[0037] The time information output means 120 is not limited to an atomic clock, but may be configured with a correction function for frequency stabilization, such as a quartz oscillator with a thermostatic oven.

[0038] The GNSS 130 is a Global Navigation Satellite System (GNSS) receiver that measures the position of the communication device 11. For example, the position data measured by the GNSS 130 is transmitted to the edge server 10 via the communication module 100. The GNSS 130 is not an essential component, and may be provided when the communication device 11 is an automobile or a drone.

[0039] It goes without saying that the communication device 11 is not limited to the configuration shown in Fig. 4. For example, if the communication device 11 is a sensor terminal, it may be equipped with sensors such as a laser sensor, an infrared sensor, or an acceleration sensor, and may transmit measurement data from these sensors to the edge server 10. If the communication device 11 is a smart meter, it may be equipped with a means for measuring the amount of power used, and may transmit the measured power data to the edge server 10.

[0040] The time information corrected by the time information output means 120 can be used in any manner. For example, the time information can be used for time synchronization in the time synchronization network 1. The time information may also be added as a timestamp to the position data, image data, measurement data, or power data output by the communication device 11.

[0041] [Time synchronization in time synchronization networks] Referring to FIG. 5, the time synchronization in the time synchronization network 1 will be described. The time synchronization network 1 does not use a communication protocol in which each communication device 11 inquires about the time from the edge server 10, but instead uses a method of performing time synchronization based on time difference information with adjacent communication devices 11. In this case, in the time synchronization network 1, only the communication devices 11 adjacent to the edge server 10 inquire about the time from the edge server 10, so other communication devices 11 do not connect to the edge server 10, and communication traffic can be suppressed.

[0042] Here, the edge server 10 may periodically execute a time synchronization event. Note that the time synchronization event is an event that instructs each communication device 11 to perform time synchronization, and serves as a trigger for time synchronization. Furthermore, the edge server 10 may execute a time synchronization event in response to a synchronization request from each communication device 11. Then, upon receiving the time synchronization event, the communication device 11 performs time synchronization.

[0043] The time difference information alone does not allow determining which of the two adjacent communication devices 11 has more accurate time information, making it impossible to determine the reference time information. Therefore, the time synchronization network 1 uses the number of inquiry steps n to determine the reference time information. This number of inquiry steps n represents the number of times a time information inquiry has been made. Note that in Figure 5, the number of inquiry steps n is illustrated with a dashed arrow. In other words, this dashed arrow represents the query path for time information in the time synchronization network 1. In this way, the time synchronization network 1 forms a virtual hierarchical structure of inquiries, and the time information of the communication device 11 with a smaller number of inquiry steps n is used as the reference, and the communication device 11 with a larger number of inquiry steps n corrects its time information. It goes without saying that the inquiry route in FIG. 5 is an example and is not limited to this.

[0044] 5, the number of query steps n for the communication device 111 that queries the edge server 10 for time information, i.e., the first-tier communication device 111 adjacent to the edge server 10, is 1. Also, the number of query steps n for the communication device 112 that queries the communication device 111 for time information, i.e., the second-tier communication device 112 adjacent to the communication device 111, is 2.

[0045] Specifically, the first-layer communication device 111 inquires of the edge server 10 about time information t0 using the time synchronization means 111, and receives the time information t0 from the edge server 10 in response to this inquiry. Then, the communication device 111 calculates the difference between the time information t0 of the edge server 10 and the time information t1 of the time information output means 120 using the time synchronization means 111, and outputs the time difference information Δt 01 At this time, the communication device 111 stores the time difference information Δt 01 At the same time, the number of inquiry steps n=1 is also stored in the memory 112. Furthermore, the communication device 111 synchronizes the time difference information Δt 01 The time information t1 of the time information output means 120 is corrected by offset processing based on (t1=t0+Δt 01 ) The offset process is a process of offsetting the time information t1 of the time information output means 120 with the time difference information Δt 01 The only thing that needs to be shifted is the position.

[0046] The second-layer communication device 112 uses the time synchronization means 111 to inquire about time information t1 of the adjacent communication device 111, and receives the time information t1 and the number of inquiry steps n=1 of the communication device 111 in response to this inquiry. Then, the communication device 112 adds 1 to the number of inquiry steps n of the communication device 111 using the time synchronization means 111 to calculate the number of inquiry steps n=2 of the communication device 112. Furthermore, the communication device 112 uses the time synchronization means 111 to calculate the difference between the time information t1 of the communication device 111 and the time information t2 of the time information output means 120, and outputs time difference information Δt 12At this time, the communication device 112 stores the time difference information Δt 12 At the same time, the number of inquiry steps n=2 is also stored in the memory 112. Furthermore, the communication device 112 synchronizes the time difference information Δt 12 The time information t2 of the time information output means 120 is corrected by offset processing based on (t2=t1+Δt 12 ).

[0047] Here, the communication device 11 in FIG. A ,11 B Here, the edge server 10, the communication device 111 in the first layer, the communication device 112 in the second layer, the communication devices 113 and 114 in the third layer, and the communication device 115 in the third layer are considered to perform time synchronization. B In this case, the communication device 11 inquires about the time information in the order A The number of inquiry steps n=4, and the communication device 11 B Since the number of inquiry steps n=3, the communication device 11 B Time information t B Based on this, communication device 11 A Time information t A In this case, the communication device 11 A Time information t A communication device 11 B Time information t B communication device 11 A ,11 B Time difference information Δt AB The time is offset by t A =t B +Δt AB ). In this way, in the time synchronization network 1, each communication device 11 autonomously repeats time synchronization with adjacent communication devices 11, thereby making it possible to maintain stable and efficient time synchronization.

[0048] [Communication device operation] The operation of the communication device 11 will be described with reference to FIG. As shown in FIG. 6, in step S1, the time synchronization means 111 inquires of the adjacent communication devices 11 about time information. In step S2, the time synchronization means 111 receives time information from the adjacent communication device 11 in response to the inquiry in step S1.

[0049] In step S3, the time synchronization means 111 calculates the difference between the time information of the time information output means 120 and the time information received in step S2, and stores this in the memory 112 as time difference information. In step S 4 , the time synchronization means 111 corrects the time information of the time information output means 120 by performing offset processing based on the time difference information in the memory 112 .

[0050] [Actions and Effects] As described above, in the time synchronization network 1, the internal clock 121 is stable, so frequency drift is suppressed, and even if frequency drift occurs, the drift rate can be maintained constant. Therefore, in the time synchronization network 1, time information can be corrected based on time difference information between adjacent communication devices 11, so there is no need for all communication devices 11 to connect to the edge server 10. As a result, in the time synchronization network 1, communication traffic and network delays can be suppressed, and time synchronization based on absolute time can be efficiently maintained.

[0051] On the other hand, if the internal clock is not stable like in a conventional crystal oscillator, disturbances such as external vibrations, temperature, and humidity can cause random frequency drift in each device, making it impossible to maintain a constant drift rate. In this case, the time information of each device will shift independently, making it difficult to correct the time information using the time difference information between adjacent devices.

[0052] Furthermore, in the time synchronization network 1, the time information output means 120 is configured with an atomic clock, so the internal clock is more stable and frequency drift can be significantly suppressed. Furthermore, in the time synchronization network 1, each communication device 11 stores the time difference information in the memory 112, so that each communication device 11 does not need to obtain the time difference information from outside, and communication traffic can be further reduced.

[0053] (Second embodiment) [Time synchronization network configuration] With reference to FIG. 7, the configuration of a time synchronization network 1B according to the second embodiment will be described, focusing on differences from the first embodiment. The time synchronization network 1B differs from the first embodiment in that the memory server 12 stores time difference information of each communication device 11. As shown in Fig. 7, the time synchronization network 1B includes an edge server 10, a communication device 11B, and a memory server 12. Below, the memory server 12 will be described first, and then the configuration of the communication device 11B will be described.

[0054] The memory server 12 stores the time difference information of each communication device 11B. Therefore, the memory server 12 includes a memory (not shown) for storing the time difference information. The time difference information itself is the same information as in the first embodiment.

[0055] [Communication device configuration] The configuration of the communication device 11B will be described with reference to FIG. 8, the communication device 11B includes a communication module 100, a calculation means 110B, a time information output means 120, and a GNSS 130. Note that the means other than the calculation means 110B are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0056] The calculation means 110B includes a time synchronization means 111B, but does not include a memory 112 (FIG. 4) because it does not store time difference information.

[0057] The time synchronization means 111B corrects the time information output by the time information output means 120 by performing offset processing based on the time difference information stored in the memory server 12. The time synchronization means 111B is the same as that in the first embodiment except that it uses the time difference information of the memory server 12 instead of the time difference information of the memory 112, so further explanation will be omitted.

[0058] [Actions and Effects] As described above, in the time synchronization network 1B, similarly to the first embodiment, communication traffic and network delays can be suppressed, and time synchronization based on absolute time can be efficiently maintained. Furthermore, in the time synchronization network 1B, each communication device 11B does not need to store time difference information, so the configuration of the communication device 11B can be simplified and the time difference information can be easily managed.

[0059] (Third embodiment) [Time synchronization network configuration] With reference to FIG. 9, the configuration of a time synchronization network 1C according to the third embodiment will be described, focusing on differences from the first embodiment. The time synchronization network 1C differs from the first embodiment in that the edge server 10C does not function as a time server and instead sets a reference communication device (absolute time estimation device) 13. As shown in Figure 9, the time synchronization network 1C includes the edge server 10C, a communication device 11, and the reference communication device 13.

[0060] The edge server 10C is the same as that in the first embodiment except that it does not have the function of a time server. In other words, the edge server 10C is a general edge server.

[0061] As described above, in the time synchronization network 1C, there is no time server that presents absolute time, so absolute time is estimated by one of the communication devices 11. The communication device 11 that estimates this absolute time is called the reference communication device 13. For example, in the time synchronization network 1C, a maximum likelihood point estimation process using a Kalman filter is performed on the time difference information of each communication device 11 to estimate absolute time. Note that in the time synchronization network 1C, any communication device 11 can be set as the reference communication device 13. In the example of FIG. 9, the communication device 11 adjacent to the edge server 10C is set as the reference communication device 13. Also, a communication device 11 that is not adjacent to the edge server 10C may be set as the reference communication device 13.

[0062] That is, in the time synchronization network 1C, a reference communication device 13 is set as the parent communication device 11, and time synchronization can be performed by combining time difference information starting from this reference communication device 13. At this time, the reference communication device 13 calculates a virtual absolute time so that the amount of time adjustment of each communication device 11 is minimized. Also, a synchronization event may be executed periodically starting from the reference communication device 13.

[0063] Note that a communication device 11 adjacent to the reference communication device 13 corrects its time information by offset processing based on the time difference information between this communication device 11 and the reference communication device 13. That is, when this communication device 11 queries the reference communication device 13 for time information using the time synchronization means 111, it receives time information from the reference communication device 13 in response to this query. In other respects, the communication device 11 is the same as in the first embodiment, so a description thereof will be omitted.

[0064] [Configuration of the reference communication device] The configuration of the reference communication device 13 will be described with reference to FIG. The reference communication device 13 has a function of estimating absolute time in addition to the function of the communication device 11 described above. As shown in FIG. 10, the reference communication device 13 includes a communication module 100, a calculation means 110C, a time information output means 120, and a GNSS 130.

[0065] The calculation means 110C includes a time synchronization means 111 and an absolute time estimation means 113. The time synchronization means 111 is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0066] The absolute time estimation means 113 estimates the absolute time by statistical processing of the time difference information. First, the absolute time estimation means 113 acquires time difference information from the communication devices 11. At this time, the absolute time estimation means 113 may acquire time difference information from all of the communication devices 11. Furthermore, when there are multiple communication devices 11, the absolute time estimation means 113 can suppress errors caused by transmission noise by acquiring time difference information only from adjacent communication devices 11.

[0067] Next, the absolute time estimation means 113 performs statistical processing on the acquired time difference information. Here, the absolute time estimation means 113 may perform a simple least squares method as statistical processing. Alternatively, the absolute time estimation means 113 may perform least squares processing with weighting according to the performance of each communication device 11 (e.g., calculation speed, time information error) (weighted least squares method). When performing statistical processing, it is preferable that the absolute time estimation means 113 use a Kalman filter to sufficiently remove noise and perform statistical processing on the time difference information as undegraded digital information. Absolute time can be estimated by this procedure.

[0068] [Actions and Effects] As described above, in the time synchronization network 1C, similarly to the first embodiment, communication traffic and network delays can be suppressed, and time synchronization based on absolute time can be efficiently maintained. Furthermore, the time synchronization network 1C can perform accurate time synchronization based on the absolute time estimated by the reference communication device 13 even if it does not include a time server.

[0069] In the time synchronization network 1C of Fig. 9, one of the communication devices 11 is set as the reference communication device 13, but this is not limited to this. As shown in Fig. 11, the time synchronization network 1C may also include an absolute time estimation device 13C that is independent of the communication device 11. This absolute time estimation device 13C includes absolute time estimation means 113 similar to that of Fig. 10 and can estimate absolute time. In this case, the communication device 11 can correct its time information using the absolute time estimated by the absolute time estimation device 13C. Furthermore, the time synchronization network 1C can be applied not only to the first embodiment but also to the second embodiment.

[0070] (Variation) Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these and includes design modifications and the like within the scope of the present invention.

[0071] In the first embodiment described above, the edge server is described as having the function of a time server, but this is not limiting. As shown in Fig. 12, the time synchronization network 1D may include a time server 14 independent of the edge server 10D. In this case, the time server 14 presents absolute time to the adjacent communication devices 11.

[0072] In the above-described embodiments, the range of the time synchronization network (local network) is not defined, but the range of the local network may be set in advance by a domain. Also, the range of the local network may be set autonomously according to the response time of the beacon. [Explanation of symbols]

[0073] NW Network 1,1B,1C,1D time synchronization network 2 Core Network 3 Infrastructure Network 10,10C Edge Server 11,11B Communication equipment 12 Memory Server 13 Reference communication device (absolute time estimation device) 13C Absolute time estimation device 14 Time Server 30 Base station (parent station device) 31 Base station (slave station equipment) 32 Repeater (relay device) 100 Communication Module 110,110B,110C calculation means 111,11B Time synchronization means 112 Memory (storage means) 113 Absolute time estimation means 120 Time information output means 121 Internal Clock 122 counters 130 GNSS

Claims

[Claim 1] A time synchronization network in which a plurality of communication devices each having a communication function are connected and which synchronizes the time of each communication device, The time synchronization network includes an absolute time estimation device, which is any of the communication devices that estimate absolute time, and the communication device, and forms a virtual hierarchical structure that queries an absolute time estimation device or a communication device adjacent to the communication device for time information; The communication device a time information output means for outputting the time information based on a stable internal clock; a time synchronization means for correcting the time information based on time difference information representing a difference between the time information of the time information output means and the time information of an absolute time estimation device or a communication device adjacent to the communication device; a memory for storing the time difference information and the number of inquiry steps; The absolute time estimation device an absolute time estimation means for performing a maximum likelihood point estimation process using a Kalman filter on the time difference information to estimate the absolute time; The time synchronization means inquiring of the time information from an absolute time estimation device or a communication device adjacent to the communication device; receiving the time information and the number of inquiry steps in response to the inquiry about the time information; Adding 1 to the number of received inquiry steps; A time synchronization network, characterized in that the time information of the communication device with a small number of inquiry steps is used as a reference, and the communication device with a large number of inquiry steps corrects the time information.

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