TDMA mobile ad-hoc network (MANET) with second order timing and tracking

• US 7,974,402 B2
• Filed: 03/28/2007
• Issued: 07/05/2011
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: Stingray IP Solutions LLC (Acacia Research Corporation)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: PUN, NGAN-CHEUNG
• Primary Examiner(s): Afshar, Kamran
• Assistant Examiner(s): Zhang, Xiang
• Application Number:
  US11/692,361
• Publication Number:
  US 20080240050A1
• Time in Patent Office: 1,560 Days
• Field of Search: 370/324, 370/350, 370/395.62, 370/508, 370/249, 370/337, 370/503, 370/509, 370/519
• US Class Current: 379/350
• CPC Class Codes: H04J 3/0652 Synchronisation among time division multiple access [TDMA] nodes, e.g. time triggered protocol [TTP] bus network with centralized control in which slots are of a TDMA packet structure H04L12/4035
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 56/005 compensating for timing error by adjustment in the receiver
• CPC Class Codes: H04W 92/18 between terminal devices

Abstract

A communication system includes a plurality of mobile nodes forming a mobile ad-hoc network (MANET) and having a network clock time. A plurality of wireless communications links connects the mobile nodes together. Each mobile node includes a communications device and controller for transmitting and routing data packets wirelessly to other mobile nodes via the wireless communications link using a Time Division Multiple Access (TDMA) data transmission. Each mobile node includes a clock circuit having a digital clock time. A clock circuit is operative for processing a second order internal clock compensation factor as a learned and accumulated value for establishing a virtual clock time to correct any clock timing errors of the physical clock time from the network clock time.

Claims

1. A communications system, comprising:

a plurality of mobile nodes forming a mobile ad-hoc network (MANET) and having a network clock time;

a plurality of wireless communications links connecting the mobile nodes together;

each mobile node comprising a communications device and controller for transmitting and routing data packets wirelessly to other mobile nodes via the wireless communications link using a time division multiple access (TDMA) data transmission, each mobile node communicating at a selected guard time and further comprising a clock circuit having a physical clock time, wherein a clock circuit is operative for for establishing a virtual clock time based on a timing error adjustment obtained from a clock mean value subtracted from the physical clock time, wherein said virtual clock time is processed with the physical clock time to establish a second order internal clock compensation factor as a learned and accumulated value and obtain a virtual clock drift rate that is used to correct any clock timing errors of the physical clock time from the network clock time and reduce the guard time.

2. The communications system according to claim 1, wherein said virtual clock time is established over multiple iterations.

3. The communications system according to claim 1, wherein a clock circuit within a mobile node is operative for comparing its physical clock time to a clock mean value that has been established for mobile nodes within the MANET and establishing the virtual clock time.

4. The communications system according to claim 1, wherein a mobile node is operative for obtaining an average value for the physical clocks within mobile nodes of said MANET.

5. The communications system according to claim 4, wherein a mobile node is operative for determining a physical clock error for its clock by subtracting a mean value based on the calculated average value and scaling the virtual clock time that has been established by a correction value.

6. The communications system according to claim 5, wherein the internal clock compensation factor is bound by a decaying factor.

7. The communications system according to claim 5, wherein a plurality of mobile nodes within the MANET are operative for collecting timing offsets with reference to a common hypothetical clock and calculating standard deviations at each measurement period of the timing offset.

8. The communications system according to claim 1, and further comprising a timing reference that is propagated throughout the network for synchronizing a plurality of mobile nodes.

9. A mobile ad-hoc network (MANET), comprising:

a source mobile node, a destination mobile node, and a plurality of neighboring mobile nodes, each mobile node comprising a communications device and controller for transmitting and routing data packets wirelessly to other mobile nodes using a time division multiple access (TDMA) data transmission at a selected guard time;

each mobile node further comprising a clock circuit having a physical clock time; and

wherein a clock circuit is operative for establishing a virtual clock time based on a timing error adjustment obtained from a clock mean value subtracted from the physical clock time, wherein said virtual clock time is processed with the physical clock time to establish a second order internal clock compensation factor as a learned and accumulated value and obtain a virtual clock drift rate that is used to correct any clock timing errors of the physical clock time from a network clock time and reduce the guard time.

10. The communications system according to claim 9, wherein said virtual clock time in a mobile node is established over multiple iterations.

11. The communications system according to claim 9, wherein a clock circuit within a mobile node is operative for comparing its physical clock time to a clock mean value that has been established for neighboring mobile nodes and establishing the virtual clock time.

12. The communications system according to claim 9, wherein a mobile node is operative for obtaining an average value for the physical clocks within neighboring mobile nodes.

13. The communications system according to claim 12, wherein a mobile node is operative for determining a physical clock error for its clock by subtracting a mean value based on the calculated average value for physical clocks in neighboring mobile nodes and scaling the virtual clock time that has been established by a correction value.

14. The communications system according to claim 13, wherein the internal clock compensation factor is bound by a decaying factor.

15. The communications system according to claim 13, wherein timing offsets are collected by neighboring mobile nodes with reference to a common hypothetical clock to calculate standard deviations at each measurement period of the timing offset.

16. The communications system according to claim 9, and further comprising a timing reference that is propagated throughout the network for synchronizing a plurality of mobile nodes.

17. A method for communicating between mobile nodes within a mobile ad-hoc network (MANET) using a time division multiple access (TDMA) data transmission, comprising:

transmitting and routing data packets wirelessly to other mobile nodes via wireless communications links at a selected guard time, each mobile node comprising a communications device, controller and a clock circuit having a physical clock time;

establishing a virtual clock time based on a timing error adjustment obtained from a clock mean value subtracted from the physical clock time; and

processing the virtual clock time with the physical clock time to establish a second order internal clock compensation factor as a learned and accumulated value and obtain a virtual clock drift rate that is used to correct any clock timing errors of the physical clock time from a network clock time to reduce the guard time.

18. The method according to claim 17, which further comprises establishing the virtual clock time over multiple iterations.

19. The method according to claim 17, which further comprises comparing a physical clock time within a mobile node to a clock mean value that has been established for neighboring mobile nodes within the MANET and establishing the virtual clock time.

20. The method according to claim 17, which further comprises obtaining an average value for the physical clocks within mobile nodes of the MANET.

21. The method according to claim 20, which further comprises determining a physical clock error in a clock by subtracting a mean value based on the calculated average value for physical clocks and scaling the virtual clock time that has been established by a correction value.

22. The method according to claim 20, which further comprises collecting timing offsets with reference to a common hypothetical clock and calculating standard deviations at each measurement period of the timing offset.

23. The method according to claim 17, which further comprises propagating a timing reference throughout the network for synchronizing a plurality of mobile nodes.