Synchronization Of A Peer-To-Peer Communication Network

• US 20090016320A1
• Filed: 07/09/2007
• Published: 01/15/2009
• Est. Priority Date: 07/09/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tavildar, Saurabh, Wu, Xinzhou, Li, Junyi, Grokop, Leonard
• Granted Patent: US 8,811,372 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks
• CPC Class Codes: H04W 92/10 between terminal device and access point, i.e. wireless air interface
• CPC Class Codes: H04W 92/18 between terminal devices

Abstract

In an ad hoc peer-to-peer communications network, timing synchronization can be facilitated between two or more nodes based on respective timing adjustments. A sequence of timing synchronization time intervals can be determined based on a first timing reference received from a source. A symbol timing can be determined and included in a first signal transmitted during a dedicated time interval, which can be a chosen fraction of one of the timing synchronization time intervals. In the remaining portion of the time interval, such as a non-chosen fraction, a second signal that includes a second timing reference can be received. Based on the symbol timing and the second timing reference, a timing adjustment can be determined and timing of each node adjusted accordingly.

Claims

1. A method for time synchronization within a wireless communications network, comprising:

receiving a first timing reference from a source;

determining, based on the first time reference, a sequence of timing synchronization time intervals;

determining a symbol timing based on the first timing reference;

choosing a fraction in at least one of the timing synchronization time intervals to transmit a first signal with the symbol timing;

receiving at least a second signal during a non-chosen fraction of the at least one time interval, the second signal including a second timing reference;

determining a timing adjustment based on the symbol timing and the second timing references; and

adjusting the symbol timing based on the timing adjustment.

2. The method of claim 1, further comprises transmitting a third signal with the adjusted time reference during a fraction in a timing synchronization interval subsequent to the at least one timing synchronization interval.

3. The method of claim 1, wherein the source is at least one of a terrestrial base station transmitter, a terrestrial TV or radio transmitter, or a satellite transmitter, or combinations thereof.

4. The method of claim 1, further comprising:

receiving a plurality of signals during a non-chosen fraction of the at least one time interval, each including a timing reference, the plurality of signals including the second signal and the timing references of the plurality of signals including the second timing reference;

determining a composite timing reference value as a function of the timing references of the plurality of signals; and

determining the timing adjustment based on the first timing reference and the composite timing reference value.

5. The method of claim 4, wherein the composite timing reference value is an average of the timing references of the plurality of signals.

6. The method of claim 4, wherein the composite timing reference value is a weighted average of the timing references of the plurality of signals and a weight of each timing reference used in the calculation of the weighted average is a function of a received signal strength of a corresponding signal.

7. The method of claim 4, wherein the composite timing reference value is an earliest timing reference among the timing references of the plurality of signals.

8. The method of claim 4, further comprises prior to determining the timing adjustment, determining whether the composite timing reference is earlier than the symbol timing.

9. The method of claim 8, further comprising:

calculating an acceptance time interval, the acceptance time interval starting from a time instant that is a first amount earlier than the symbol timing and ending at another time instant that is a second amount later than the symbol timing; and

determining the timing adjustment to be zero if the composite timing reference is outside the acceptance time interval.

10. The method of claim 9, wherein the first and the second amounts are at most ⅕

of a symbol duration of the second signal.

11. The method of claim 9, wherein the second amount is zero.

12. The method of claim 8, further comprising:

determining the timing adjustment such that the symbol timing is to be delayed by a third amount in the step of adjusting the symbol timing based on the timing adjustment, if the symbol timing is earlier than the composite timing reference; and

determining the timing adjustment such that the symbol timing is to be advanced by a fourth amount in the step of adjusting the symbol timing based on the timing adjustment, if the composite timing reference is earlier than the symbol timing.

13. The method of claim 12, wherein the third and the fourth amounts are at most ⅕

of a symbol duration of the second signal.

14. A wireless communications apparatus, comprising:

a memory that retains instructions related to receiving a timing reference, determining a series of timing synchronization time intervals, determining a symbol timing, choosing a fraction of at least one of the series of timing synchronization time intervals to transmit a first signal that includes the symbol timing, receiving a second signal during a non-chosen fraction of the at least one time interval, determining a timing adjustment based on the symbol timing and the second timing reference, and changing the symbol timing based on the timing adjustment; and

a processor, coupled to the memory, configured to execute the instructions retained in the memory.

15. The wireless communications apparatus of claim 14, the memory further retains instructions related to transmitting a next signal with the adjusted timing reference during a timing synchronization interval subsequent to the at least one timing synchronization interval.

16. The wireless communications apparatus of claim 14, the memory further retains instructions related to receiving a plurality of signals during a non-chosen fraction of the at least one time interval, wherein each of the plurality of signals includes a second timing reference, determining a composite timing reference value as a function of the timing references received in the plurality of signals, and determining a timing adjustment as a function of the first timing reference and the composite timing reference value.

17. The wireless communications apparatus of claim 16, the memory further retains instructions related to determining whether the composite timing reference is earlier than the symbol timing before determining the timing adjustment.

18. The wireless communications apparatus of claim 17, the memory further retains instructions related to calculating an acceptance time interval that starts at a time instant that is a first amount earlier than the symbol timing and ending at another time instant that is a second amount later than the symbol timing and determining the timing adjustment is zero if the composite timing reference is outside the acceptance time interval.

19. The wireless communications apparatus of claim 18, the memory further retains instructions related to determining the timing adjustment such that the symbol timing is to be delayed by a third amount in the step of adjusting the symbol timing based on the timing adjustment, if the symbol timing is earlier than the composite timing reference, and determining the timing adjustment such that the symbol timing is to be advanced by a fourth amount in the step of adjusting the symbol timing based on the timing adjustment, if the composite timing reference is earlier than the symbol timing.

20. A wireless communications apparatus that facilitates synchronization in a peer-to-peer communications network, comprising:

means for receiving a first timing reference;

means for determining a sequence of timing synchronization time intervals and a symbol timing based on the first timing reference;

means for choosing a fraction in at least one of the timing synchronization time intervals to transmit a first signal with the symbol timing;

means for receiving a second signal during a non-chosen fraction of at least one time interval;

means for determining a timing adjustment based on the symbol timing and the second timing reference; and

means for adjusting the symbol timing based on the timing adjustment.

21. The wireless communications apparatus of claim 20, further comprises means for transmitting a third signal with the adjusted time reference during a fraction in a timing synchronization interval subsequent to the at least one timing synchronization interval.

22. The wireless communications apparatus of claim 20, further comprising:

means for receiving a plurality of signals during a non-chosen fraction of the at least one time interval;

means for determining a composite timing reference value as a function of timing references included in each of the plurality of signals; and

means for determining whether the composite timing reference is earlier than the symbol timing; and

means for determining the timing adjustment based on the first timing reference and the composite timing reference value.

23. A machine-readable medium having stored thereon machine-executable instructions for:

receiving from a source a first timing reference;

determining a sequence of timing synchronization time intervals and a symbol timing based on the first timing reference;

selecting a portion of at least one of the timing synchronization time intervals to transmit a first signal that includes the symbol timing;

receiving at least a second signal that includes a second timing reference during a non-chosen fraction of the at least one time interval,

ascertaining a timing adjustment based on the symbol timing and the second timing reference; and

adjusting the symbol timing based on the ascertained timing adjustment.

24. The machine-readable medium of claim 23, the machine-executable instructions further comprises

receiving a plurality of signals during a non-chosen fraction of the at least one time interval;

determining a composite timing reference value as a function of timing references included in each of the plurality of signals;

determining whether the composite timing reference is earlier than the symbol timing; and

selectively determining the timing adjustment based on the first timing reference and the composite timing reference value.

25. In a wireless communication system, an apparatus comprising:

a processor configured to;

receive a first timing reference from a source;

determine, based on the first time reference, a sequence of timing synchronization time intervals;

determine a symbol timing based on the first timing reference;

choose a fraction in at least one of the timing synchronization time intervals to transmit a first signal with the symbol timing;

receive at least a second signal during a non-chosen fraction of the at least one time interval, the second signal including a second timing reference;

determine a timing adjustment based on the symbol timing and the second timing references; and

adjust the symbol timing based on the timing adjustment.