Method of synchronizing a reference clock of a ground station and a clock of a remote system

• US 6,633,590 B1
• Filed: 03/09/2000
• Issued: 10/14/2003
• Est. Priority Date: 03/11/1999
• Status: Expired due to Fees

• Current Assignee: Agence Spatiale Europeenne
• Original Assignee: Agence Spatiale Europeenne
• Inventors: Garofalo, Giovanni, Busca, Giovanni
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Fox, Jamal A.
• Application Number:
  US09/521,851
• Time in Patent Office: 1,314 Days
• Field of Search: 370/321, 370/324, 370/330, 370/336, 370/337, 370/350, 370/395.62, 370/503, 370/507, 370/511, 370/513, 375/356, 375/362, 375/363, 375/364, 375/365, 375/366, 375/371
• US Class Current: 370/507
• CPC Class Codes: H04B 7/2125 Synchronisation

Abstract

The invention relates to a method of synchronizing a reference clock of a first ground station and a local clock of a remote system, in particular a satellite. It includes:

a) acquisition in a first loop of synchronization between reference bursts received by the remote system and generated bursts synchronized with the local clock,

b) detection of the recognition word of the reference bursts received by the first remote system and generation of a time window containing N pulses of the reference clock,

c) acquisition of the average phase of said pulses and comparison with the phase of the local clock, and

d) in a second loop, synchronization of the phase of the local clock with said average phase.

The method can be reiterated to synchronize a second ground station with the first one via the remote system.

Claims

1. A method of synchronizing a reference clock of a first ground station and local clock of a first remote system, in particular a moving body and notably a satellite, the reference clock signals being contained in reference bursts transmitted by the ground station and received by the first remote system, said bursts beginning with a recognition word, the method including:

a) acquisition in a first loop of preliminary synchronization between said reference bursts received by the first remote system and bursts generated by the first remote system and synchronized with the local clock,

b) detection of the recognition word of the temporally synchronized reference bursts received by the first remote system and generation after detection of said recognition word of a time window containing a given number N of pulses of said reference clock,

c) acquisition of the average phase of said pulses received from the reference clock in the time window and comparison with the phase of the local clock, and

d) in a second loop, synchronization of the phase of the local clock with said average phase to achieve said synchronization of the local clock.

2. A method according to claim 1, including:

e) final synchronization of the reference bursts and said bursts generated by the remote system.

3. A method according to claim 1, wherein the acquisition of synchronization entails:

a1) in the first remote system, comparing the time of reception of the recognition words of the reference bursts transmitted by the ground station and the start of said bursts generated by the first remote system, and

a2) in the first ground station, adjusting the transmission of the reference bursts so that said reception time coincides with said start of said generated bursts.

4. A method according to claim 1, using a time-division multiple access multiplex uplink to transmit reference bursts between the first ground station and the first remote system.

5. A method according to claim 4, using a time-division multiplex downlink between the first remote system and the first ground station.

6. A method according to claim 1, wherein, after said synchronization of the local clock of the first remote system, the method iterates said synchronization such that the reference clock is said synchronized local clock of the first remote system and the local clock to be synchronized is a local clock of a second remote system, said iteration including:

a′

) acquisition in a third loop of synchronization between bursts transmitted by the first remote system, which constitute reference bursts beginning with a recognition word, and bursts generated by the second remote system and synchronized with the local clock of the second remote system,

b′

) detection of the recognition word of the bursts transmitted by the first remote system which are received by the second remote system and synchronized and generation after detection of said recognition word of a time window including a given number N′

of pulses received from said synchronized local clock of the first remote system,

c′

) acquisition of the average phase of said pulses received from said synchronized local clock and comparison with the phase of the local clock of the second remote system, and

d′

) in a fourth loop, synchronizing the phase of said local clock of the second remote system with said average phase to synchronize the local clock of the second remote system.

7. A method according to claim 6, including:

e′

) final synchronization of said reference bursts and said bursts generated by the second remote system.

8. A method according to claim 6, wherein N′

=N.

9. A method according to claim 6, wherein:

a′

1) in the second remote system, it compares the time of reception of the recognition words of the synchronized bursts transmitted by the first remote system and the start of the bursts generated by the second remote system, and

a′

2) in the first remote system, it adjusts the transmission of said transmitted bursts so that said time they are received by the second remote system coincides with the start of said bursts generated by the second remote system.

10. A method according to claim 6, wherein the second remote system is a second ground station having a reference clock synchronized with that of the first ground station.

11. A method according to claim 1, wherein the local clock of the first remote system is intrinsically less accurate than the reference clock of the first ground station.

12. A method according to claim 6, wherein said second remote system is a second satellite.

13. A method according to claim 7, wherein said second remote system is a second satellite.

14. A method according to claim 8, wherein said second remote system is a second satellite.

15. A method according to claim 9, wherein said second remote system is a second satellite.