Time synchronization system, communication system, and time synchronization method

Abstract

Provided is a technology that suppresses degradation of the quality of time signals while reducing the number of highly accurate and stable clock sources. [Solution] The time synchronization system is a time synchronization system that supplies time information used for communication control to a communication system, and includes a first time transmitting device that generates and distributes first time information using either a first time correction signal based on a first received signal received from a satellite or an acquired first frequency synchronization signal, a reference frequency device that operates independently to generate a reference frequency with the desired quality, and a first frequency transmitting device that generates the first frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device.

Description

[Technical field]

[0001] The present invention relates to a technique for suppressing degradation in the quality of a time signal while limiting the number of highly accurate and stable clock sources. [Background technology]

[0002] Conventionally, there are wireless communication systems that use the time division duplex (TDD) method. This TDD method requires highly accurate time synchronization in order to use the same frequency for time-division uplink and downlink communications. Time synchronization of the base station of the wireless communication system is realized by generating a time signal from a signal received via an antenna from a GPS satellite (artificial satellite, GNSS satellite), distributing the time signal to multiple time receiving devices (BC), and the base station communicating using this time signal. In such wireless communication systems, there has been a demand for high quality time signals. For example, the quality of the time signal is required to satisfy both "steady-state accuracy" when the GPS satellite signal can be used, and "free-running accuracy" when the GPS satellite signal cannot be used. The quality of this time signal is determined by the frequency accuracy and stability of the transmitting device. In order to maintain the quality of the time signal when the GPS satellite signal cannot be used, a known configuration is to place a highly accurate and stable clock source (such as a cesium oscillator-type network synchronization device) at each base station that generates time information. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] ITU-T G.8272.1 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a highly accurate and stable clock source is provided for each base station that generates time information, there is a problem in that the cost required for the base station increases.

[0005] In view of the above circumstances, an object of the present invention is to provide a technique for suppressing deterioration in the quality of a time signal while reducing the number of highly accurate and stable clock sources. [Means for solving the problem]

[0006] One aspect of the present invention is a time synchronization system that supplies time information used for communication control to a communication system, and includes a first time transmitting device that generates and distributes first time information using either a first time correction signal based on a first received signal received from a satellite or an acquired first frequency synchronization signal, a reference frequency device that operates independently to generate a reference frequency with a desired quality, and a first frequency transmitting device that generates the first frequency synchronization signal that is directly or indirectly synchronized to the reference frequency supplied from the reference frequency device.

[0007] One aspect of the present invention is the time synchronization system described above, wherein the first time transmitting device receives the first frequency synchronization signal that complies with at least sync-E (Synchronous Ethernet).

[0008] One aspect of the present invention is the time synchronization system described above, wherein the first frequency transmission device supplies the first frequency synchronization signal conforming to sync-E to the first time transmission device.

[0009] One aspect of the present invention is the above-mentioned time synchronization system, wherein the first frequency transmission device generates the first frequency synchronization signal based on one of two frequency synchronization signals that are indirectly synchronized with the reference frequency supplied from the reference frequency device and are supplied via different paths.

[0010] One aspect of the present invention is the above-mentioned time synchronization system, which is provided with a second frequency transmission device that generates a second frequency synchronization signal corresponding to one of the two frequency synchronization signals based on a frequency synchronization signal that is directly or indirectly synchronized with a reference frequency supplied from the reference frequency device.

[0011] One aspect of the present invention is the above-mentioned time synchronization system, which is equipped with a second frequency transmission device that generates a third frequency synchronization signal based on a frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device, and the first time transmission device generates and distributes first time information using at least a first time correction signal based on a first received signal received from a satellite, the acquired first frequency synchronization signal, and the third frequency synchronization signal.

[0012] One aspect of the present invention is the above-mentioned time synchronization system, which is equipped with a second time transmission device that generates and distributes second time information using either a second time correction signal based on at least a second received signal received from a satellite or the acquired first frequency synchronization signal, and the first time transmission device generates and distributes first time information and a fourth frequency synchronization signal using at least the first time correction signal based on the first received signal received from a satellite or the acquired first frequency synchronization signal.

[0013] One aspect of the present invention is the above-mentioned time synchronization system, which includes a third time transmission device that generates and distributes third time information using at least a third time correction signal based on a third received signal received from a satellite, the acquired first frequency synchronization signal, and the acquired fourth frequency synchronization signal.

[0014] A communication system according to one embodiment of the present invention is a communication system comprising the above-mentioned time synchronization system and a wireless communication station that regenerates the first time information supplied from the time synchronization system in a time receiving device and communicates using the regenerated first time information using time division reply control.

[0015] One aspect of the present invention is a time synchronization method for supplying time information used for communication control to a communication system, the time synchronization method including a process of distributing the first time information from a first time transmitting device that generates first time information using either a first time correction signal based on a first received signal received from an artificial satellite or an acquired first frequency synchronization signal, and generating the first frequency synchronization signal that directly or indirectly synchronizes with a reference frequency supplied from a reference frequency device that is self-operating and generates a reference frequency with a desired quality. Effect of the Invention

[0016] According to each aspect of the present invention, it is possible to provide a technique for suppressing degradation in quality of a time signal while reducing the number of highly accurate and stable clock sources. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram for explaining time synchronization in a comparative example of the present embodiment. [Diagram 3] FIG. 2 is a diagram for explaining time correction by a time distribution device (GMC) 111 of the present embodiment. [Figure 4] 1 is a schematic configuration diagram of a frequency synchronization network 200 in a wireless communication system 10 of the present embodiment. [Diagram 5] 1 is a configuration diagram of a frequency distribution network 200 related to the time distribution network of the present embodiment. [Figure 6] FIG. 13 is a diagram for explaining an application example of the present embodiment. [Figure 7] FIG. 2 is a diagram showing a configuration in which a frequency signal distribution path in this embodiment is configured redundantly. [Figure 8] FIG. 2 is a diagram for explaining distribution of frequency signals between GMCs in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding components are designated by the same reference numerals and the description thereof will be omitted as appropriate.

[0019] (First embodiment: basic configuration) FIG. 1 is a schematic configuration diagram of a wireless communication system according to an embodiment. The wireless communication system 10 is divided into subsystems 11, 12, . . . , 15 and the like.

[0020] Each of the subsystems 11, 12, ..., 15 is provided with an antenna for receiving radio waves from an artificial satellite 2 such as GNSS (GPS), and a time distribution network for extracting time information from the received signal. The subsystems 12, ..., 15 may be configured similarly to the subsystem 11, or may have different configurations. These subsystems indicate the range in which common time information is distributed. The following will continue the explanation of the wireless communication system 10, showing the subsystem 11 as an example of each subsystem. The devices in the subsystem 11 may be distributed across multiple buildings, such as communication buildings B11A and B11B.

[0021] The wireless communication system 10 includes a time synchronization system 1. The wireless communication system 10 includes, as a subsystem 11, base stations 122 and 123 (mobile base stations), a time distribution network 114, a time distribution device (Grand Master Clock, GMC) 111, and time receiving devices (Boundary Clock, BC) 112 and 113.

[0022] For example, base stations 122 and 123 are examples of mobile base stations located in communication buildings B11A and B11B, respectively. The base stations 122 and 123 relay communications of terminal devices (not shown) present within the areas where communication services are provided in the subsystem 11. For example, each of the base stations communicates with the terminal devices in a TDD (time division duplex) system using time information provided by time receiving devices (BC) 112 and 113, respectively. In order to synchronize the time of each base station in the subsystem 11, a time distribution device (GMC) 111, time receiving devices (BC) 112, 113, and a time distribution network 114 are provided. There may be multiple time receiving devices (BC) 112, 113 for each pair of the time distribution network and the time distribution device (GMC). In order to synchronize the times of the wireless communication stations in the wireless communication system 10, the subsystems 11, 12, . . . , 15 carry out communication processing in a state in which the times of the various wireless communication stations are synchronized with each other.

[0023] The time distribution device (GMC) 111 shown in FIG. 1 generates a time signal from a signal received from a GNSS satellite 2 via an antenna, and distributes the time signal to a plurality of time receiving devices (BC) 112, 113 associated with the time distribution device (GMC) 111. The time distribution device (GMC) 111 distributes the time signal using, for example, PTP (hereinafter, simply referred to as PTP), which is an example of a protocol for time synchronization. A time distribution network including the plurality of time receiving devices (BC) distributes the time signal generated by the time distribution device (GMC) 111 using, for example, PTP. In other words, the plurality of time receiving devices (BC) synchronize their time based on the time signal supplied from the time distribution device (GMC) 111. In this case, the time receiving devices (BC) 112, 113 are configured not to receive a frequency synchronization signal from devices other than the corresponding time distribution device (GMC) 111 and a time receiving device (BC) at a higher level than their own time receiving device (BC).

[0024] The time synchronization according to the embodiment will be described with reference to FIG. 2 and FIG. First, an example of time synchronization in a comparative example of the embodiment will be described. FIG. 2 is a diagram for explaining time synchronization in a comparative example of the embodiment. FIG. 2(a) shows a configuration example in which a frequency signal is not supplied to the time distribution device (GMC) 111Z. The time distribution device (GMC) 111Z in the configuration example of FIG. 2(a) corrects the time signal it generates by using the time signal from the signal received from the artificial satellite 2 via the antenna. When the time distribution device (GMC) 111Z is no longer able to use the time signal from the signal received from the artificial satellite 2 via the antenna, it continues to generate and distribute a time signal using the free-running clock of the oscillator LO it has. In the above case, the time information thereafter contains a time error that depends on the frequency error of the free-running clock of the oscillator LO of the time distribution device (GMC) 111Z because there is no time signal for the above correction. In this way, the quality of the time signal generated by the free-running clock of the oscillator LO of the time distribution device (GMC) 111Z is largely dependent on the performance of the oscillator of the time distribution device (GMC) 111Z, and there is a limit to improving the quality of the time signal by only improving the performance of the time distribution device (GMC) 111Z.

[0025] Incidentally, the configuration example shown in Fig. 2(b) is known as a configuration example for suppressing such time errors. Fig. 2(b) shows a configuration example in which a frequency signal is supplied to a time distribution device (GMC) 111Z using an atomic clock as a frequency oscillation source. This configuration corresponds to the ePRTC (Enhanced Primary Reference Time Clock) method proposed in ITU-T G.8272.1 and the like. A cesium oscillator MC, which uses an atomic clock as a frequency oscillation source, is connected to the time distribution device (GMC) 111Z.

[0026] FIG. 3 is a diagram for explaining time correction by the time distribution device (GMC) 111 of the embodiment. The quality of the time signal distributed by the time distribution device (GMC) 111 must be of the desired quality for both "normal accuracy" when the signal from the antenna of the artificial satellite 2 is received and usable, and "free-running accuracy" when the signal from the antenna of the artificial satellite 2 is cut off or when the time distribution device (GMC) 111 is in a free-running state. Note that the state in which it is not possible to receive a signal from the artificial satellite 2 and the state in which it is not possible to use the time signal from the signal received via the antenna are sometimes collectively referred to as the "free-running" state.

[0027] For "normal accuracy", time information is generated based on timing information generated by a frequency signal from the oscillator LO or an external device (such as the frequency oscillator 220 described below), and the time information generated above is corrected using a time signal from a signal received via an antenna from the satellite 2. As a result, the time signal from the signal received via an antenna from the satellite 2 contributes to the time accuracy in the "normal state".

[0028] "Free-running accuracy" refers to the accuracy in a free-running state due to the loss of the time signal from the signal received via the antenna from the artificial satellite 2. In this free-running state, a time signal is generated within the time distribution device (GMC) 111 based on the immediately preceding time information and timing information.

[0029] When the clock is free-running, timing deviations based on the frequency signal from the oscillator LO or an external device accumulate, so the accuracy of the time information when the clock is free-running (free-running accuracy) depends on the frequency accuracy of the frequency signal from the oscillator LO or an external device.

[0030] In order to ensure the free-running accuracy of time information within the desired range, it is recommended that the time distribution device (GMC) 111 use a frequency signal from a cesium oscillator. This can improve the quality of the free-running time signal more than if the time distribution device (GMC) 111 were operated alone. However, if an atomic clock (cesium oscillator) is installed for each time distribution device (GMC) 111, the following issues arise, making it practically difficult to adopt the ePRTC method in a time distribution network.

[0031] Cesium oscillators are very expensive, and introducing a number of them equivalent to the number of GMC111 time distribution devices would result in enormous costs. - Cesium oscillators require a long period of aging before use (approximately 30 days may be required). In the ePRTC system, the signals that can be used for frequency synchronization between the frequency oscillator and the time distribution device (GMC) 111 are limited, and there are restrictions on the frequency oscillator and time distribution device (GMC) 111 that can be used. For example, only a 10 MHz analog signal is specified as the required specification for the signal.

[0032] A frequency distribution network 200 related to the time distribution network of the embodiment will be described with reference to FIG. 4 and FIG. FIG. 4 is a schematic configuration diagram of a frequency synchronization network 200 in the wireless communication system 10 of the embodiment. The frequency distribution network 200 includes, for example, a cesium oscillator 210 and frequency oscillators 222, 223, 224, and 225. In the following description, the frequency oscillators 222, 223, 224, and 225 may be collectively referred to as the frequency oscillator 220.

[0033] The cesium oscillator 210 includes a free-running oscillator and serves as the master clock for the frequency distribution network 200 .

[0034] The frequency oscillator 220 includes an oscillator circuit using an oscillator such as a quartz crystal or rubidium. Some oscillator circuits (e.g., PLL) that include an oscillator such as a quartz crystal or rubidium crystal require a certain amount of time from power-on until the oscillation stabilizes. However, this time is sufficiently shorter than the time required for the cesium oscillator 210 to stabilize, and does not require a long aging period.

[0035] This frequency oscillator 220 is a slave synchronization type transmitting device. The frequency oscillator 220 has an input port for a frequency signal and an output port for a frequency signal. The output port for a frequency signal of the frequency oscillator 220 has a port connected to a GMC and a port connected to another frequency oscillator 220. The number of input ports of the frequency oscillator 220 may be appropriately determined according to the number required.

[0036] The cesium oscillator 210 and the frequency oscillator 220 in the frequency distribution network 200 will now be described in more detail.

[0037] The first-stage cesium oscillator 210 is connected to a lower-stage (second-stage) frequency oscillator 220. The second-stage frequency oscillator 222 generates a frequency signal synchronized with the frequency signal supplied from the cesium oscillator 210. The second-stage frequency oscillator 222 is connected to a lower-stage (third-stage) frequency oscillator 222. The third-stage frequency oscillator 223 generates a frequency signal synchronized with the frequency signal supplied from the cesium oscillator 210. The third-stage frequency oscillator 223 is connected to a lower-stage (fourth-stage) frequency oscillator 223. The fourth-stage frequency oscillator 224 generates a frequency signal synchronized with the frequency signal supplied from the cesium oscillator 210. The fourth-stage frequency oscillator 224 is connected to a lower-stage (fifth-stage) frequency oscillator 224. The fifth-stage frequency oscillator 225 generates a frequency signal synchronized with the frequency signal supplied from the cesium oscillator 210. The fifth-stage frequency oscillator 225 is connected to a lower-stage (fifth-stage) frequency oscillator 225. The fifth-stage frequency oscillator 226 generates a frequency signal synchronized with the frequency signal supplied from the cesium oscillator 210.

[0038] The cesium oscillator 210 and the frequency oscillator 220 of each stage may be connected to a time distribution device (GMC) or the like. The cesium oscillator 210 and the frequency oscillator 220 supply frequency signals to the time distribution devices (GMC) 111, etc., connected to them. Each time distribution device (GMC) generates a time synchronization signal using the supplied frequency signal as necessary.

[0039] For example, as frequency signals for the interface between the cesium oscillator 210 and the frequency oscillator 220, the interface between the cesium oscillator 210 and the time distribution device (GMC) 111 etc., and the interface between the frequency oscillator 220 and the time distribution device (GMC) 111 etc., in addition to an analog 10 MHz signal specified by the ePRTC, a digital signal conforming to the Ethernet (registered trademark) standard can be applied.

[0040] FIG. 5 is a configuration diagram of a frequency distribution network 200 related to the time distribution network of the embodiment. The configuration shown in this figure is just one example. As described above, the frequency oscillator 220 and the time distribution device (GMC) 111 and the like use the cesium oscillator 210 as the ultimate master clock and generate frequency signals based on frequency signals from adjacent devices. The number of time distribution devices (GMC) 111 and the like connected to the frequency oscillator 220 is not limited to one, and may be multiple.

[0041] For example, the frequency synchronization network 200 may include a cesium oscillator 210 or a frequency oscillator 220 to which a time distribution device (GMC) 111 or the like is not connected.

[0042] Also, the frequency distribution network 200 shown in this figure may be replaced with a redundant configuration. A known form of redundant configuration can be applied to the method of change associated with this.

[0043] Next, a wireless communication system capable of using the frequency distribution network 200 for time synchronization is illustrated as being deployed on a national level. A time distribution network corresponding to such a wireless communication system is deployed over a wide area, similar to the wireless communication system. For example, the entire frequency distribution network 200 is configured to synchronize with the reference frequency of the cesium oscillator 210, which is the master clock MC. At a lower level of the cesium oscillator 210, frequency transmission devices are provided in layers.

[0044] For example, a frequency distribution network 200 is configured in multiple layers as shown in FIG. A frequency synchronization network is configured to distribute a frequency signal with a cesium oscillator 210 as the first-stage master clock MC. Block representative frequency oscillators 222 (several units) are placed on the second stage of the frequency synchronization network, prefecture representative frequency oscillators 223 (several dozen units) are placed on the third stage, area representative frequency oscillators 224 are placed on the fourth stage, and frequency oscillators 225 for terminal buildings are placed on the fifth stage. By connecting these in a tree-like configuration, wireless communication systems can be efficiently deployed over a wide area.

[0045] An application example of the embodiment will be described with reference to FIG. FIG. 6 is a diagram for explaining an application example of the embodiment. The configuration shown in Fig. 6(a) is an example of a case where multiple time distribution devices (GMC) 111 are installed in the same building. The configuration shown in Fig. 6(b) is an example of a case where a time distribution device (GMC) 111 is installed in a small building where it is difficult to install both the time distribution device (GMC) 111 and a frequency oscillator device. This embodiment can be applied to either of these cases.

[0046] In this way, a configuration in which frequency signals are sent from the cesium oscillator 210 (master clock) or a subordinate frequency oscillator to a plurality of time distribution devices (GMC) 111 and the like is also possible.

[0047] In addition, if a balanced signal is used for the transmission, balanceThis is less susceptible to attenuation due to distance than when a balanced signal (10 MHz analog signal) is used for transmission. When spanning between buildings, as in the configuration shown in Figure 6(b), the configuration is simplified by using a balanced signal.

[0048] According to the time synchronization system 1 of the above embodiment, time information used for communication control is supplied to the communication system. The time transmission device (first time transmission device) generates and distributes first time information using either a first time correction signal based on a first reception signal received from an artificial satellite or an acquired first frequency synchronization signal. The reference frequency device self-operates to generate a reference frequency with desired quality. The frequency transmission device (first frequency transmission device) generates the first frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device. This makes it possible to reduce the number of reference frequency devices, which serve as highly accurate and stable clock sources, while suppressing degradation in the quality of the time signal.

[0049] The frequency transmitter 220 supplies a first frequency synchronization signal conforming to sync-E to the time transmitter (GMC) 111 and the like. The time transmitting device (GMC) 111 etc. may receive at least a first frequency synchronization signal conforming to sync-E (Synchronous Ethernet).

[0050] (Second embodiment: signal path redundancy configuration) A second embodiment will be described with reference to FIGS. In the above-mentioned first embodiment, a case where a tree-type route is used for the distribution route of the frequency synchronization signal has been described. In the case of such a tree-type, the signal route cannot be made redundant. Therefore, in this embodiment, a case where the distribution route of the frequency signal is made redundant will be described.

[0051] FIG. 7 is a diagram showing a configuration in which distribution paths of frequency signals are configured redundantly in the embodiment. In order to improve the stability of the entire frequency synchronization network, the distribution path of the frequency signal may be made redundant. As an example of a redundant configuration of a distribution path of a frequency signal, four forms (cases) will be illustrated.

[0052] Case 1: The frequency oscillator receives a frequency signal doubly by receiving a frequency signal from the cesium oscillator 210 (master clock) or two higher-level frequency oscillators, respectively. In this case configuration, the frequency oscillator can treat the two received signals on an equal footing. Case 2: The frequency oscillator receives a first signal from the cesium oscillator 210 (master clock) or a higher-level frequency oscillator and a second signal from a frequency oscillator of the same level. In this case of the configuration, the frequency oscillator can treat the first of the two received signals as the working system and the second signal as the protection system. Case 3: The GMC receives frequency signals from two frequency oscillators, resulting in double reception of frequency signals. Case 4: Normally synchronized to a signal from a frequency oscillator, but receives a signal from another GMC as a redundant signal.

[0053] The characteristics of each of the above cases will be summarized below. The time synchronization system 1 is configured to synchronize with a reference frequency device that is free-running and generates a reference frequency with a desired quality.

[0054] In case 1, the frequency transmitting device 224A (first frequency transmitting device) generates a first frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device 220. For example, the time transmitting device 141B (first time transmitting device) generates and distributes first time information using at least either a first time correction signal based on a first received signal received from the artificial satellite 2 or the acquired first frequency synchronization signal.

[0055] In case 2, the frequency transmitting device 224C generates a first frequency synchronization signal based on one of two frequency synchronization signals that are indirectly synchronized with the reference frequency supplied from the reference frequency device 220 and are supplied via different paths. For example, the frequency transmitting device 224B (second frequency transmitting device) generates a second frequency synchronization signal corresponding to one of the two frequency synchronization signals based on a frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device 220.

[0056] In case 3, the frequency transmission device 224B (second frequency transmission device) generates a third frequency synchronization signal based on a frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device. The time transmission device 141D (first time transmission device) generates and distributes the first time information using at least one of the first time correction signal based on the first received signal received from the artificial satellite 2, the acquired first frequency synchronization signal, and the third frequency synchronization signal.

[0057] In case 4, the time transmitting device 141B (second time transmitting device) generates and distributes second time information and a fourth frequency synchronization signal using at least one of the second time correction signal based on the second received signal received from the satellite 2 and the first frequency synchronization signal acquired from the frequency transmitting device 224A. The time transmitting device 141A (third time transmitting device) generates and distributes third time information using at least one of the third time correction signal based on the third received signal received from the satellite 2, the first frequency synchronization signal acquired from the frequency transmitting device 224A, and the fourth frequency synchronization signal acquired from the time transmitting device 141B.

[0058] FIG. 8 is a diagram for explaining distribution of frequency signals between the time transmitting devices (GMC) 111 and the like in the embodiment. As shown in Fig. 1 above, the system is configured to transmit a time signal (PTP, etc.) and a frequency signal (Sync-E, etc.) from a time transmitting device (GMC) 111 to time receiving devices (BC) 112, 113. The system shown in Fig. 8 is configured to transmit and receive frequency signals between the time transmitting devices (GMC) 111, etc., in order to provide redundancy to the distribution path of the frequency signals.

[0059] For example, as shown in (a) of FIG. 8, a time transmitting device (GMC) 111 or the like may be configured to transmit a time signal (PTP or the like) and a frequency signal (Sync-E or the like) to another time transmitting device (GMC). In this case, the time transmitting device (GMC) that receives the time signal (PTP or the like) and the frequency signal (Sync-E or the like) may generate a time signal using the frequency signal (Sync-E or the like). Note that the time transmitting device (GMC) that receives the time signal (PTP or the like) may generate a time signal to be supplied to the time receiving devices (BC) 112, 113 or the like using the time signal (PTP or the like). The time transmitting device (GMC) 111 or the like may generate a time signal based on the time signal (PTP or the like) using the same generation method as the time receiving devices (BC) 112, 113 or the like.

[0060] 8(b), a time transmitting device (GMC) 111 etc. may be configured to transmit a frequency signal (Sync-E etc.) to another time transmitting device (GMC) 111 etc. In this case, the time transmitting device (GMC) 111 etc. that receives the frequency signal (Sync-E etc.) may generate a time signal using the frequency signal (Sync-E etc.).

[0061] In this way, the time synchronization system 1 of this embodiment supplies the communication system with time information used for communication control. The time transmission device (first time transmission device, GMC) 111 generates and distributes the first time information using either the first time correction signal based on the first reception signal received from the artificial satellite 2 or the acquired first frequency synchronization signal. The reference frequency device 210 generates a reference frequency with desired quality by itself. The frequency transmission device (first frequency transmission device) 220 generates the first frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device. This makes it possible to reduce the number of reference frequency devices, which serve as highly accurate and stable clock sources, while suppressing degradation in the quality of the time signal.

[0062] Although one embodiment of the present invention has been described above, the embodiment of the present invention is not limited to the above. For example, the methods exemplified in each embodiment and its modified examples may be combined in a combination other than the exemplified combination. In addition, the embodiment of the present invention may be a modification of the above embodiment as follows. [Explanation of symbols]

[0063] 1. Time Synchronization System 10 Wireless communication systems (communication systems) 11, 12, 13, 14, 15 Subsystems 111, 112, 113, 121, 131, 141, 151 Time distribution device (GMC) 200 Frequency Distribution Network 210 Cesium oscillator (master clock) 220, 222, 223, 224, 225 Frequency oscillator

Claims

1. A time synchronization system that supplies time information used for communication control to a communication system using a frequency distribution network including a plurality of frequency transmission devices, a self-running reference frequency device for generating a reference frequency with a desired quality; a first frequency transmitting device that generates a first frequency synchronization signal that is directly or indirectly synchronized with a reference frequency provided by the reference frequency device; a second frequency transmitter that generates a third frequency synchronization signal that is directly or indirectly synchronized with the reference frequency; a first time transmitting device that generates and distributes first time information using a first time correction signal based on at least a first reception signal received from an artificial satellite, the acquired first frequency synchronization signal, or the acquired third frequency synchronization signal; Equipped with The first time transmitting device generating the first time information using either the first frequency synchronization signal or the third frequency synchronization signal and time information from the first reception signal from the satellite when the device is in a first state in which the first reception signal from the satellite can be obtained; When in a second state in which the first reception signal from the artificial satellite cannot be obtained, the time information is generated and transmitted in place of the time information based on the first time correction signal by using either the first frequency synchronization signal or the third frequency synchronization signal and time information based on the first time correction signal that has already been obtained. Time synchronization system.

2. The first frequency transmitting device is The first frequency synchronization signal is generated based on one of two frequency synchronization signals that are indirectly synchronized with the reference frequency provided by the reference frequency device and are provided via different paths. The time synchronization system according to claim 1 .

3. a second frequency generating device that generates a second frequency synchronization signal corresponding to one of the two frequency synchronization signals based on a frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device; The time synchronization system according to claim 2 .

4. a second frequency generating device for generating a third frequency synchronization signal based on a frequency synchronization signal that is directly or indirectly synchronized with the reference frequency supplied from the reference frequency device; Equipped with The first time transmitting device generating and distributing first time information using at least one of a first time correction signal based on a first reception signal received from an artificial satellite, the acquired first frequency synchronization signal, and the third frequency synchronization signal; The time synchronization system according to claim 1 .

5. A second time transmitting device that generates and distributes second time information using at least one of a second time correction signal based on a second reception signal received from an artificial satellite and the acquired first frequency synchronization signal. Equipped with The first time transmitting device generating and distributing first time information and a fourth frequency synchronization signal using at least one of a first time correction signal based on a first reception signal received from an artificial satellite and the acquired first frequency synchronization signal; The time synchronization system according to claim 1 .

6. A third time transmitting device that generates and distributes third time information using at least one of a third time correction signal based on a third reception signal received from an artificial satellite, the acquired first frequency synchronization signal, and the acquired fourth frequency synchronization signal. The time synchronization system according to claim 5 .

7. A time synchronization system according to any one of claims 1 to 6, a wireless communication station that reproduces the first time information supplied from the time synchronization system in a time receiving device and communicates using the reproduced first time information under time division reply control; A communication system comprising:

8. A time synchronization method for supplying time information used for communication control to a communication system using a frequency distribution network including a plurality of frequency transmission devices, comprising: A first frequency synchronizing signal is generated by a first frequency transmitting device, the first frequency synchronizing signal being directly or indirectly synchronized with a reference frequency supplied from a reference frequency device which generates a reference frequency with a desired quality in a self-running manner; generating a third frequency synchronization signal, which is directly or indirectly synchronized with the reference frequency, by a second frequency transmitting device; A process of distributing the first time information from a first time transmission device GMC that generates first time information using a first time correction signal based on a first reception signal received from an artificial satellite, the acquired first frequency synchronization signal, or the acquired third frequency synchronization signal. Including, The first time transmitting device generating the first time information using either the first frequency synchronization signal or the third frequency synchronization signal and time information from the first reception signal from the satellite when the device is in a first state in which the first reception signal from the satellite can be obtained; When in a second state in which the first reception signal from the artificial satellite cannot be obtained, the time information is generated and transmitted in place of the time information based on the first time correction signal by using either the first frequency synchronization signal or the third frequency synchronization signal and time information based on the first time correction signal that has already been obtained. Time synchronization method.

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