Synchronization of clocks in a satellite communication network by preassigning constants to stations of the network

Claim 3

A satellite communication network including a plurality of terrestrial stations, each station of said terrestrial stations establishing a bidirectional link to and from at least one selected station of said terrestrial stations through a satellite and comprises a local clock indicative of a current time from time to time, packet forming means for forming a transmission packet for transmission to said bidirectional link with said transmission packet made to additionally represent as a local time datum the current time indicated when supplied with data to be represented by said transmission packet, data extracting means for extracting a particular time datum from a reception packet received through said bidirectional link from said selected station, and a calculation unit connected to said local clock and to said data extracting means for calculating a propagation delay between said each station and said selected station through said bidirectional link, a first station of said terrestrial stations being used as said each station to transmit a first packet as said transmission packet to the bidirectional link established thereby, a second station of said terrestrial stations being used as said selected station to transmit a second packet as said transmission packet to a particular link established thereby as said bidirectional link by using said first station as said selected station relative to said second station with said second packet made to indicate the current time thereof as said particular time datum when the packet forming means thereof is supplied with data to be represented by said second packet, said first station receiving said second packet as said reception packet through said particular link, said satellite communication network comprising a reference station for establishing a unidirectional link to said terrestrial stations through said satellite, wherein: said reference station comprises a reference clock indicative of a reference time from time to time and announcing means for forming a common packet for transmission to said unidirectional link once in a predetermined duration of time to simultaneously announce said common packet to said terrestrial stations through said unidirectional link with said common packet made to indicate the reference time as a common time datum when said common packet is formed; said each station further comprising time setting means for extracting said common time datum as an extracted time datum from the common packet received through said unidirectional link and for setting said current time at a time instant indicated by a sum of said extracted time datum and a constant preassigned to said each station.

Claim 4

A satellite communication network including a plurality of terrestrial stations, each station of said terrestrial stations establishing a bidirectional link to and from at least one selected station of said terrestrial stations through a satellite and comprises a local clock indicative of a current time from time to time, packet forming means for forming a transmission packet for transmission to said bidirectional link with said transmission packet made to additionally represent as a local time datum the current time indicated when supplied with data to be represented by said transmission packet, data extracting means for extracting a particular time datum from a reception packet received through said bidirectional link from said selected station, and a calculation unit connected to said local clock and to said data extracting means for calculating a propagation delay between said each station and said selected station through said bidirectional link, a first station of said terrestrial stations being used as said each station to transmit a first packet as said transmission packet to the bidirectional link established thereby, a second station of said terrestrial stations being used as said selected station to transmit a second packet as said transmission packet to a particular link established thereby as said bidirectional link by using said first station as said selected station relative to said second station with said second packet made to indicate the current time thereof as said particular time datum when the packet forming means thereof is supplied with data to be represented by said second packet, said first station receiving said second packet as said reception packet through said particular link, said satellite communication network comprising a reference station for establishing a unidirectional link to said terrestrial stations through said satellite, wherein: said reference station comprises a reference clock indicative of a reference time from time to time and announcing means for forming a common packet for transmission to said unidirectional link once in a predetermined duration of time to simultaneously announce said common packet to said terrestrial stations through said unidirectional link with said common packet made to indicate the reference time as a common time datum when said common packet is formed; said each station further comprising time setting means for extracting said common time datum as an extracted time datum from the common packet received through said unidirectional link and for setting said current time at a time instant indicated by a sum of said extracted time datum and a constant preassigned to said each station.

Claim 5

A satellite communication network as claimed in Claim 2, wherein said time setting means comprises: time extracting means for extracting said extracted time datum from the common packet received through said unidirectional link; and a time setting unit for setting said current time at said time instant.

Claim 6

A satellite communication network as claimed in Claim 3, wherein said constant is given a value decided by calculating a distance on the earth between said each station and said reference station based on their longitudes and latitude, calculating a physical length of said unidirectional link from said reference station to said each station by using said distance, and calculating a time necessary for electromagnetic waves to travel said physical length.

Claim 7

A satellite communication network as claimed in Claim 3 or 4, said each station comprising a communication device for receiving said reception packet from said bidirectional link and said common packet from said unidirectional link, wherein said time extracting means is interposed between said communication device and said data extracting means.

Claim 8

A satellite communication network comprising a plurality of terrestrial stations, each station of said terrestrial stations establishing a bidirectional link to and from at least one selected station of said terrestrial stations through a satellite and comprising a local clock indicative of a current time from time to time, packet forming means for forming a transmission packet for transmission to said bidirectional link with said transmission packet made to additionally represent as a local time datum the current time indicated when supplied with data to be represented by said transmission packet, data extracting means for extracting a particular time datum from a reception packet received through said bidirectional link from said selected station, and a calculation unit connected to said local clock and to said data extracting means for calculating a propagation delay between said each station and said selected station through said bidirectional link, a first station of said terrestrial stations being used as said each station to transmit a first packet as said transmission packet to the bidirectional link established thereby, a second station of said terrestrial stations being used as said selected station to transmit a second packet as said transmission packet to a particular link established thereby as said bidirectional link by using said first station as said selected station relative to said second station with said second packet made to indicate the current time thereof as said particular time datum when the packet forming means thereof is supplied with data to be represented by said second packet, said first station receiving said second packet as said reception packet through said particular link, one of said terrestrial stations being used as a center station for establishing a common link as said bidirectional link with each of said terrestrial stations used as said selected station, wherein: said center station comprises a reference clock indicative of a reference time from time to time and announcing means for forming a common packet for transmission to said common link once in a predetermined duration of time to simultaneously announce said common packet to said terrestrial stations through said common link with said common packet made to indicate said reference time as a common time datum when said common packet is formed; said each station further comprising time setting means for extracting said common time datum as an extracted time datum from the common packet received through said common link and for setting said current time at a time instant indicated by a sum of said extracted time datum and a constant preassigned to said each station.

Claim 9

A satellite communication network comprising a plurality of terrestrial stations, each station of said terrestrial stations establishing a bidirectional link to and from at least one selected station of said terrestrial stations through a satellite and comprising a local clock indicative of a current time from time to time, packet forming means for forming a transmission packet for transmission to said bidirectional link with said transmission packet made to additionally represent as a local time datum the current time indicated when supplied with data to be represented by said transmission packet, data extracting means for extracting a particular time datum from a reception packet received through said bidirectional link from said selected station, and a calculation unit connected to said local clock and to said data extracting means for calculating a propagation delay between said each station and said selected station through said bidirectional link, a first station of said terrestrial stations being used as said each station to transmit a first packet as said transmission packet to the bidirectional link established thereby, a second station of said terrestrial stations being used as said selected station to transmit a second packet as said transmission packet to a particular link established thereby as said bidirectional link by using said first station as said selected station relative to said second station with said second packet made to indicate the current time thereof as said particular time datum when the packet forming means thereof is supplied with data to be represented by said second packet, said first station receiving said second packet as said reception packet through said particular link, one of said terrestrial stations being used as a center station for establishing a common link as said bidirectional link with each of said terrestrial stations used as said selected station, wherein: said center station comprises a reference clock indicative of a reference time from time to time and announcing means for forming a common packet for transmission to said common link once in a predetermined duration of time to simultaneously announce said common packet to said terrestrial stations through said common link with said common packet made to indicate said reference time as a common time datum when said common packet is formed; said each station further comprising time setting means for extracting said common time datum as an extracted time datum from the common packet received through said common link and for setting said current time at a time instant indicated by a sum of said extracted time datum and a constant preassigned to said each station.

Claim 10

A satellite communication network as claimed in Claim 6, wherein said time setting means comprises: time extracting means for extracting said extracted time datum from the common packet received through said common link; and a time setting unit for setting said current time at said time instant.

Claim 11

A satellite communication network as claimed in Claim 7, wherein said constant is given a value decided by calculating a distance on the earth between said each station and said center station based on their longitudes and latitudes, calculating a physical length of said common link between said each station and said common station by using said distance, and calculating a time necessary for electromagnetic waves to travel said physical length.

Claim 12

A satellite communication network as claimed in Claim 7 or 8, said each station comprising a communication device for receiving said reception packet from said bidirectional link and said common packet from said common link, wherein said time extracting means is interposed between said communication device and said data extracting means.