Clock synchronization among network stations
Communicating among stations in a network includes providing repeated beacon transmissions from at least some of the stations including a first station. The first station is assigned to a first level. Any stations that can reliably receive transmissions from the first station are assigned to a second level. Any stations not assigned to any of the preceding levels that can reliably receive transmissions from the preceding level are assigned to each of one or more higher levels. Timing information at each station in a given level is synchronized according to transmissions received from at least one station in the preceding level.
1. A system for communicating among stations in a network, the system comprising:
a first station assigned to a first level in the network;
a second station assigned to a second level and configured to receive a transmission from the first station; and
a third station assigned to a third level and configured to receive a transmission from the second station, wherein the third station is configured to synchronize a first timing information based on the transmission received from the second station, wherein synchronizing the first timing information comprises synchronizing a prediction of a periodic time reference based on a second timing information included in the transmission received from the second station.
2. The system of claim 1 , wherein synchronizing the first timing information at the third station further comprises synchronizing a first clock used to sample transmissions received at the third station.
3. The system of claim 1 , wherein synchronizing the first timing information at the third station further comprises synchronizing a first clock used to prepare transmissions from the third station.
4. The system of claim 1 , wherein the transmission received from the second station includes at least one of: a timestamp of a second clock at the second station, and time delay information indicating a time delay between the periodic time reference and a time associated with the transmission from the second station.
5. The system of claim 4 , wherein synchronizing the first timing information at the third station comprises synchronizing a first clock at the third station based on the timestamp in the transmission received from the second station.
6. The system of claim 4 , wherein synchronizing the first timing information at the third station includes: tracking a position in an AC line cycle, and using the time delay information in the transmission received from the second station to predict future occurrences of the periodic time reference relative to the AC line cycle position.
7. The system of claim 6 , wherein the position in the AC line cycle includes a zero crossing.
8. The system of claim 6 , further comprising using a predicted future occurrence of the periodic time reference in response to not receiving the transmission from the second station at an expected time.
9. The system of claim 4 , wherein synchronizing the first timing information at the third station includes: tracking a first clock at the third station, and using the time delay information in the transmission received from the second station to predict future occurrences of the periodic time reference relative to the first clock.
10. The system of claim 9 , further comprising updating the first clock using information from a beacon transmission.
11. A first station for communicating in a network, the first station comprising:
a transmitter configured to transmit a beacon in the network; and
a receiver assigned to a first level in the network, the receiver configured to:
receive a transmission from a second station in a preceding level, and
synchronize a first timing information according to the transmission received from the second station in the preceding level, wherein synchronizing the first timing information comprises synchronizing a prediction of a periodic time reference based on a second timing information included in the transmission received from the second station.
12. The first station of claim 11 , wherein the receiver is further configured to synchronize the first timing information by synchronizing a first clock at the first station used to sample the transmission received from the second station.
13. The first station of claim 11 , wherein the receiver is further configured to synchronize the first timing information by synchronizing a first clock at the first station used to prepare the beacon for transmission from the transmitter.
14. The first station of claim 11 , wherein the transmission received from the second station includes at least one of: a timestamp of a second clock at the second station, and time delay information indicating a time delay between the periodic time reference and a time associated with the transmission from the second station.
15. The first station of claim 14 , wherein the receiver is further configured to synchronize the first timing information by synchronizing a first clock at the first station based on the timestamp in the transmission received from the second station.
16. The first station of claim 14 , wherein the receiver is further configured to synchronize the first timing information by tracking a position in an AC line cycle, and use the time delay information in the transmission received from the second station to predict future occurrences of the periodic time reference relative to the AC line cycle position.
17. The first station of claim 16 , wherein the position of the AC line cycle includes a zero crossing.
18. The first station of claim 16 , wherein the receiver is further configured to use a predicted future occurrence of the periodic time reference in response to not receiving a transmission at an expected time.
19. The first station of claim 14 , wherein the receiver is further configured to synchronize the first timing information by tracking a first clock at the first station, and use the time delay information in the transmission received from the second station to predict a future occurrence of the periodic time reference relative to the first clock.
20. The first station of claim 15 , wherein the first clock is updated using information from the beacon transmission.
21. A method performed by a first station for communicating in a network, the first station assigned to a first level in the network, the method comprising:
receiving, at the first station, a transmission from a second station in a preceding level in the network; and
synchronizing a first timing information based on the transmission received from the second station in the preceding level, wherein synchronizing the first timing information includes synchronizing a prediction of a periodic time reference based on a second timing information included in the transmission received from the second station.
22. The method of claim 21 , wherein synchronizing the first timing information further comprises synchronizing a first clock at the first station used to sample the transmission received from the second station.
23. The method of claim 21 , wherein synchronizing the first timing information further comprises synchronizing a first clock at the first station used to prepare a beacon for transmission from the first station.
24. The method of claim 21 , wherein the transmission received from the second station includes at least one of: a timestamp of a second clock at the second station, and time delay information indicating a time delay between the periodic time reference and a time associated with the transmission received from the second station.
25. The method of claim 24 , wherein synchronizing the first timing information further comprises synchronizing a first clock at the first station based on the timestamp in the transmission received from the second station.
26. The method of claim 24 , wherein synchronizing the first timing information further comprises tracking a position in an AC line cycle, and using the time delay information in the transmission received from the second station to predict future occurrences of the periodic time reference relative to the AC line cycle position.
27. The method of claim 26 , wherein the position of the AC line cycle includes a zero crossing.
28. The method of claim 26 , further comprising using a predicted future occurrence of the periodic time reference in response to not receiving a transmission at an expected time.
29. The method of claim 24 , wherein synchronizing the first timing information further comprises tracking a first clock at the first station, and using the time delay information in the transmission received from the second station to a predict future occurrence of the periodic time reference relative to the first clock.
30. The method of claim 29 , further comprising updating the first clock using information from a beacon transmission.