System and method for correcting the clock drift and maintaining the synchronization of low quality clocks in wireless networks

• US 7,072,432 B2
• Filed: 07/05/2002
• Issued: 07/04/2006
• Est. Priority Date: 07/05/2002
• Status: Expired due to Term

• Current Assignee: ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: MeshNetworks, Inc. (Motorola Solutions, Inc.)
• Inventors: Belcea, John M.
• Primary Examiner(s): Tran, Khai
• Assistant Examiner(s): CHANG, EDITH M
• Application Number:
  US10/188,982
• Publication Number:
  US 20040005902A1
• Time in Patent Office: 1,460 Days
• Field of Search: 375354-356, 375/371, 370/238, 370/280, 370/337, 370/352, 370/389, 370/516, 370/235, 370/503, 370/509, 455/426.1, 455/445, 455/502, 707/203, 713/400, 327/165, 327/292
• US Class Current: 375/356
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04J 3/0697 Synchronisation in a packet node
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A system and method for establishing and maintaining node clock synchronization in a wireless network. The system and method calculates the clock shift, clock drift and propagation delay values using a series of message exchanges and control algorithms between a selected reference node and a client node in a wireless network, then uses these values to synchronize the client node clock to the reference node clock.

Claims

1. A method for controlling clock synchronization between at least two nodes of a plurality of nodes in an ad-hoc wireless network, comprising:

controlling a client node of said plurality of nodes to select a reference node from said plurality of nodes and to send to said reference node a first communication, said client node having a client clock and said reference node having a reference clock;

controlling said reference node to receive said first communication and in response, send a first reply to said client node;

controlling said client node to receive said first reply and in response, send a second and third communication to said reference node; and

controlling said reference node to receive said second and said third communications and in response, calculate a first clock shift and propagation value existing between said client node and said reference node, and send information pertaining to said first clock shift and said propagation value to said client node in a second reply.

2. A method as claimed in claim 1, further comprising:

controlling said client node to select said reference node based upon network connectivity.

3. A method as claimed in claim 1, wherein said first communication comprises a request for clock synchronization.

4. A method as claimed in claim 3, wherein said first communication further comprises a CLOCKSYNC message including client clock and reference clock information, said CLOCKSYNC message requesting a clock synchronization session between said client node and said reference node.

5. A method as claimed in claim 1, wherein said first reply comprises a CLOCKTIME message including a first reference clock value.

6. A method as claimed in claim 5, wherein said first reference clock value comprises a reference clock value at a time of transmission of said first reply from said reference node to said client node.

7. A method as claimed in claim 6, wherein said reference clock value comprises a 32 bit value.

8. A method as claimed in claim 1, wherein said second communication comprises a CLOCKREPL1 message including a first client clock value, and said third communication comprises a CLOCKREPL2 message including a second client clock value.

9. A method as claimed in claim 8, wherein said first client clock value comprises a client clock value at a time of reception of said first reply from said reference node by said client node.

10. A method as claimed in claim 8, wherein said second client clock value comprises a client clock value at a time of transmission of said second communication from said client node to said reference node.

11. A method as claimed in claim 1, further comprising:

controlling said client node to synchronize said client clock with said reference clock using said first clock shift and said propagation value.

12. A method as claimed in claim 1, further comprising:

controlling at least one of said client node and said reference node to calculate a second clock shift and a second propagation value and in response, determine a clock drift of said client clock; and

further controlling at least one of said client node and said reference node to correct said clock drift of said client clock using said determined clock drift and a drift control algorithm.

13. A method as claimed in claim 12, wherein said drift control algorithm comprises a computer-readable medium of instructions for controlling clock drift correction at a node in the ad-hoc wireless network, said computer-readable medium of instructions comprising:

a first set of instructions, adapted to control at least one of said client node and said reference node to generate a drift correction value and correct said clock drift of said client clock using said drift correction value.

14. A method as claimed in claim 1, wherein:

said step of controlling said reference node to receive said first communication includes initializing said reference node, and said first reply to said client node includes a clock synchronization message.

15. A method as claimed in claim 1, wherein:

said step of controlling said client node to select said reference node includes initializing said client node;

said first reply to said client node includes a clock synchronization message; and

said method further includes the step of controlling said client node to correct said client clock using said propagation value sent from said reference node.

16. A method for controlling clock synchronization between at least two nodes of a plurality of nodes in an ad-hoc wireless network, comprising:

controlling a clock synchronization message exchange between a client node and a reference node of said plurality of nodes;

controlling said reference node to calculate a first clock shift and a propagation value existing between said client node and said reference node in response to said clock synchronization message exchange and provide information pertaining to said first clock shift and said propagation value to said client node; and

controlling said client node to synchronize a client clock at said client node with a reference clock at said reference node using said information.

17. A method as claimed in claim 16, further comprising:

controlling said client node to select said reference node for clock synchronization message exchange based upon network connectivity.

18. A method as claimed in claim 16, wherein said step of controlling said clock synchronization message exchange uses node tasks comprising at least one of the following:

a set of reference node tasks, adapted to initialize said reference node, further adapted to direct said reference node to exchange clock synchronization messages with said client node; and

a set of client node tasks, adapted to initialize said client node, further adapted to direct said client node to exchange clock synchronization messages with said reference node.

19. A method as claimed in claim 16, wherein said step of controlling said client node to synchronize the client clock comprises performing a drift control algorithm to control at least one of said client node and said reference node to generate a drift correction value and correct said clock drift of said client clock using said drift correction value.

20. A computer-readable medium of instructions for controlling clock synchronization between at least two nodes of a plurality of nodes in an ad-hoc wireless network, the computer-readable medium of instructions comprising:

a first set of instructions, adapted to control a client node of said plurality to select a reference node from said plurality of nodes and send to said reference node a first communication, said client node having a client clock and said reference node having a reference clock;

a second set of instructions, adapted to control said reference node to receive said first communication and in response, send a first reply to said client node;

said first set of instructions further adapted to control said client node to receive said first reply and in response, send a second and third communication to said reference node; and

said second set of instructions further adapted to control said reference node to receive said second and said third communications and in response, calculate a first clock shift and propagation value existing between said client node and said reference node, and send information pertaining to said first clock shift and said propagation value to said client node in a second reply.

21. A computer-readable medium of instructions as claimed in claim 20, wherein said first set of instructions are further adapted to control said client node to select said reference node based upon network connectivity.

22. A computer-readable medium of instructions as claimed in claim 20, wherein said first communication comprises a request for clock synchronization.

23. A computer-readable medium of instructions as claimed in claim 22, wherein said first communication further comprises a CLOCKSYNC message including client clock and reference clock information, said CLOCKSYNC message requesting a clock synchronization session between said client node and said reference node.

24. A computer-readable medium of instructions as claimed in claim 20, wherein said first reply comprises a CLOCKTIME message including a first reference clock value.

25. A computer-readable medium of instructions as claimed in claim 24, wherein said first reference clock value comprises a reference clock value at a time of transmission of said first reply from said reference node to said client node.

26. A computer-readable medium of instructions as claimed in claim 25, wherein said reference clock value comprises a 32 bit value.

27. A computer-readable medium of instructions as claimed in claim 20, wherein said second communication comprises a CLOCKREPL1 message including a first client clock value, and said third communication comprises a CLOCKREPL2 message including a second client clock value.

28. A computer-readable medium of instructions as claimed in claim 27, wherein said first client clock value comprises a client clock value at a time of reception of said first reply from said reference node by said client node.

29. A computer-readable medium of instructions as claimed in claim 27, wherein said second client clock value comprises a client clock value at a time of transmission of said second communication from said client node to said reference node.

30. A computer-readable medium of instructions as claimed in claim 20, wherein said first set of instructions is further adapted to control said client node to synchronize said client clock with said reference clock using said first clock shift and said propagation value.

31. A computer-readable medium of instructions as claimed in claim 20, wherein:

said first set of instructions are further adapted to control at least one of said client node and said reference node to calculate a second clock shift and a second propagation value and in response, determine a clock drift of said client clock; and

said first set of instructions further adapted to control at least one of said client node and said reference node to correct said clock drift of said client clock using said determined clock drift and a drift control algorithm.

32. A computer-readable medium of instructions as claimed in claim 31, wherein said algorithm comprises a third set of instructions, adapted to control at least one of said client node and said reference node to generate a drift correction value and correct said clock drift of said client clock using said drift correction value.

33. A computer-readable medium of instructions for controlling clock synchronization between at least two nodes of a plurality of nodes in an ad-hoc wireless network, the computer-readable medium of instructions comprising:

a first set of instructions, adapted to control a clock synchronization message exchange between a client node and a reference node of said plurality of nodes;

a second set of instructions, adapted to control said reference node to calculate a first clock shift and a propagation value existing between said client node and said reference node in response to said clock synchronization message exchange and provide information pertaining to said first clock shift and said propagation value to said client node; and

and a third set of instructions, adapted to control said client node to synchronize a client clock at said client node with a reference clock at said reference node using said information.

34. A computer-readable medium of instructions as claimed in claim 33, further comprising:

a fourth set of instructions, adapted to control said client node to select said reference node for clock synchronization message exchange based upon network connectivity.

35. A computer-readable medium of instructions as claimed in claim 33, wherein said first set of instructions uses node tasks comprising at least one of the following:

a set of reference node tasks, adapted to initialize said reference node, further adapted to direct said reference node to exchange clock synchronization messages with said client node; and

a set of client node tasks, adapted to initialize said client node, further adapted to direct said client node to exchange clock synchronization messages with said reference node.

36. A computer-readable medium of instructions as claimed in claim 33, wherein said third set of instructions is further adapted to performing a drift control algorithm to control at least one of said client node and said reference node to generate a drift correction value and correct a clock drift of said client clock using said drift correction value.