System and method for synchronizing ground clocks

Patent metadata

Field	Value
Publication number	US-9306727-B2
Application number	US-201414337675-A
Country	US
Kind code	B2
Filing date	Jul 22, 2014
Priority date	Jul 22, 2014
Publication date	Apr 5, 2016
Grant date	Apr 5, 2016

Abstract

A system and method of synchronizing clocks within a system having a plurality of base stations, wherein each base station includes a frequency locked clock. A fast moving emitter transmits pulses that are received at each base station. A time of arrival for each pulse received by each base station is recorded and the recorded times of arrival are communicated to at least one of the other base stations. The clocks are synchronized as a function of the recorded times of arrival received from each base station.

First claim

What is claimed is:

1. A method of synchronizing a plurality of frequency-locked clocks, the method comprising:
transmitting a train of pulses from a satellite-based or aerial fast moving emitter to each of a plurality of stationary base stations in line-of-sight communication with the emitter, the train of pulses being periodic and having a period such that the base stations receive each pulse within a single period, the base stations including respective frequency-locked clocks, the frequency-locked clocks having frequencies determined by a common atomic transition;
receiving the pulses at each base station;
recording a time of arrival for each pulse received by each base station;
communicating the recorded times of arrival to a processor;
calculating, with the processor, a synchronization offset for each frequency-locked clock, as a function of:
the time of arrival for each pulse at each base station,
a position of the emitter when transmitting each pulse, and
a position of each base station; and

synchronizing the frequency-locked clocks in response to the calculated synchronization offsets.

2. The method of claim 1 , wherein each pulse includes a pulse identifier and wherein recording the time of arrival includes recording the pulse identifier.

3. The method of claim 1 , wherein:
the plurality of base stations includes at least N base stations, N being an integer greater than 1; and
transmitting the train of pulses includes transmitting k pulses, k being an integer greater than 1.

4. The method of claim 3 , wherein, when the base station and emitter positions are unknown, N and k are selected to overdetermine a system of 4k+(4N−1) unknowns.

5. The method of claim 3 , wherein, when the base station positions are unknown but the emitter positions are known, N and k are selected to overdetermine a system of k+(4N−1) unknowns.

6. The method of claim 3 , wherein, when the base station positions are known but the emitter positions are unknown, N and k are selected to overdetermine a system of 4k+(N−1) unknowns.

7. The method of claim 3 , wherein, when the base station positions are known and the emitter positions are known, N and k are selected to overdetermine a system of k+(N−1) unknowns.

8. The method of claim 3 , wherein a fixed known time separates successive pulses; wherein a known baseline exists between a first base station and each of the other base stations, and wherein the emitter positions are known, N and k are selected to overdetermine a system of 4+(N−1) unknowns.

9. The method of claim 3 , wherein a fixed known time separates successive pulses; wherein a known baseline exists between a first base station and each of the other base stations, and wherein the emitter positions are known, N and k are selected to overdetermine a system of 4+3k+(N−1) unknowns.

10. The method of claim 3 , wherein calculating the synchronization offset for each base station includes correcting for an ephemeris error in determination of the emitter position at the time it transmitted each pulse.

11. The method of claim 3 , wherein calculating the synchronization offset for each base station includes correcting for an atmospheric delay error in determining time of arrival of a pulse at a base station.

12. The method of claim 3 , wherein calculating the synchronization offset for each base station includes correcting for a timing error introduced by one or more of the base station clocks.

13. A method of synchronizing a plurality of frequency-locked clocks within a system having a plurality of base stations, including a first base station, wherein each base station includes a frequency-locked clock, the frequency-locked clocks having frequencies determined by a common atomic transition, the method comprising:
receiving at the first base station, k pulses transmitted from a satellite-based or aerial fast moving emitter in line-of-sight communication with each of the plurality of base stations, k being an integer greater than 1;
recording a time of arrival for each pulse received by the first base station;
communicating the recorded times of arrival to a processor;
receiving, at the processor, recorded times of arrival for each of the k pulses from each of the other base stations;
calculating, with the processor, a synchronization offset for each frequency-locked clock, as a function of:
the time of arrival for each of the k pulses at each base station,
a position of the emitter when transmitting each of the k pulses, and
a position of each base station; and

synchronizing the frequency-locked clock of the first base station to a master clock in response to the calculated synchronization offsets.

14. The method of claim 13 ,
wherein the plurality of base stations includes at least N base stations, N being an integer greater than 1.

15. A non-transitory computer readable medium comprising a plurality of instructions that, in response to being executed on a computing device, cause the computing device to carry out a method for synchronizing a plurality of frequency-locked clocks within a system having a plurality of base stations, including a first base station, wherein each base station includes a frequency-locked clock, the frequency-locked clocks having frequencies determined by a common atomic transition, the method comprising:
receiving at the first base station, k pulses transmitted from a satellite-based or aerial fast moving emitter in line-of-sight communication with each of the plurality of base stations, k being an integer greater than 1;
recording a time of arrival for each pulse received by the first base station;
communicating the recorded times of arrival to a processor of the computing device;
receiving, at the processor, recorded times of arrival for each of the k pulses from each of the other base stations;
calculating, with the processor, a synchronization offset for each frequency-locked clock, as a function of:
the time of arrival for each of the k pulses at each base station,
a position of the emitter when transmitting each of the k pulses, and

a position of each base station; and
synchronizing the frequency-locked clock of the first base station to a master clock in response to the calculated synchronization offsets.

16. A system, comprising:
a satellite-based or aerial fast moving emitter configured to transmit a train of pulses, the train of pulses being periodic and having a period; and
a plurality of stationary base stations in line-of-sight communication with the emitter and configured to receive the train of pulses, each base station including a frequency-locked clock, the frequency-locked clocks having frequencies determined by a common atomic transition; each base station configured to record respective times of arrival of the pulses; and
a processor configured to:
receive the recorded times of arrival for each of the pulses from each of the base stations;
calculate a synchronization offset for each frequency-locked clock, as a function of:
the time of arrival for each of the pulses at each base station,
a position of the emitter when transmitting each of the pulses, and
a position of each base station; and

synchronize the frequency-locked clocks in response to the calculated synchronization offsets.

17. The system of claim 16 , wherein the pulses include a pulse identifier.

18. The system of claim 16 , wherein phases of the frequency-locked clocks accumulate at approximately the same rate.

Assignees

• Raytheon Co

Inventors

• Wilkinson Steven R
• Yurtsever Ulvi

Classifications

• H04B7/18519

  Operations control, administration or maintenance · CPC title

• H04B7/18517

  Transmission equipment in earth stations · CPC title

• H04L7/0012 Primary

  by comparing receiver clock with transmitter clock · CPC title

• H04B7/18515 Primary

  Transmission equipment in satellites or space-based relays · CPC title

• H04W56/00

  Synchronisation arrangements · CPC title