Communication apparatus, time synchronization system, and time synchronization method

Abstract

A communication apparatus ( 13 ) according to the present invention is provided with: a storage unit ( 131 ) that stored in advance difference information ( 1311 ), which is the difference between first time information (t 1 ) and second time information (t 2 ), said first time information (t 1 ) being received from a synchronization source communication apparatus ( 11 ) as a time synchronization source connected to a transmission system ( 12 ) wherein transmission delay time is different depending on the direction of transmission, and said second time information (t 2 ) obtained from a time synchronization origin ( 14 ) other than the transmission system ( 12 ); and a time synchronization means ( 132 ) that carries out, when the second time information (t 2 ) cannot be obtained from the time synchronization origin ( 14 ), time synchronization with the synchronization source communication apparatus ( 11 ) using the difference information ( 1311 ) read out from the storage unit ( 131 ).

1 - 10 . (canceled) 
     
     
         11 . A communication device, comprising:
 a storage unit for storing in advance difference information between first time information and second time information, the first time information being received from a synchronization source communication apparatus as a time synchronization source connected to a transmission system wherein transmission delay time is different depending on the direction of transmission and the second time information obtained from a time synchronization origin other than the transmission system; and   a time synchronization unit for carrying out, when the second time information cannot be obtained from the time synchronization origin, time synchronization with the synchronization source communication apparatus using the difference information read out from the storage unit.   
     
     
         12 . The communication apparatus of  claim 11 , further comprising: a difference information calculation unit for calculating the difference information between first time information and second time information and for storing the difference information in the storage unit. 
     
     
         13 . The communication apparatus of  claim 12 , wherein the time synchronization unit carries out time synchronization with the synchronization source communication apparatus on the basis of the first time information and the second time information when the second time information can be obtained from the time synchronization origin. 
     
     
         14 . The communication apparatus of  claim 12 , wherein the difference information calculation unit stores bidirectional transmission delay times of the unit itself and the synchronization source communication apparatus, as the difference information, into the storage unit. 
     
     
         15 . The communication apparatus of  claim 11 , wherein the time synchronization origin is a satellite positioning system. 
     
     
         16 . The communication apparatus of  claim 11 , wherein the time synchronization origin is a transmission system in which bidirectional transmission delay times are symmetrical. 
     
     
         17 . A time synchronization system, comprising:
 a transmission system in which transmission delay time is different depending on the direction of transmission;   a first communication apparatus that is connected to the transmission system, as a time synchronization source;   a time synchronization origin other than the transmission system; and   a second communication apparatus that is connected to the transmission system and the time synchronization origin and carries out time synchronization on the basis of time information of the first communication apparatus, wherein the second communication apparatus comprises:   a storage unit for storing in advance difference information between first time information received from the first communication apparatus and second time information obtained from the time synchronization origin; and   a time synchronization unit for carrying out, when the second time information cannot be obtained from the time synchronization origin, time synchronization with the first communication apparatus using the difference information read out from the storage unit.   
     
     
         18 . The time synchronization system of  claim 17 , wherein the second communication apparatus further comprises a difference information calculation unit for calculating the difference information between first time information and second time information and for storing the difference information in the storage unit. 
     
     
         19 . The time synchronization system of  claim 18 , wherein the time synchronization unit carries out time synchronization with the first communication apparatus on the basis of the first time information and the second time information when the second time information can be obtained from the time synchronization origin. 
     
     
         20 . A time synchronization method, comprising:
 receiving first time information from a synchronization source communication apparatus, as a time synchronization source, connected to a transmission system wherein transmission delay time is different depending on the direction of transmission;   obtaining second time information from a time synchronization origin other than the transmission system;   calculating difference information between the first time information and the second time information;   storing the difference information in a storage unit;   after that, reading out the difference information from the storage unit when the second time information cannot be obtained from the time synchronization origin; and   carrying out time synchronization with the synchronization source communication apparatus using the difference information read out from the storage unit.   
     
     
         21 . The time synchronization system of  claim 18 , wherein the difference information calculation unit stores bidirectional transmission delay times of the unit itself and the first communication apparatus, as the difference information, into the storage unit.