1. To Sync or Not to Sync in Power Saving?
Ten H. Lai

2. Zen (禪) Networking Essential Fundamental Simple Effective Fresh
Problems
Protocols

3. Problem, Problem, Problem!
???

4. Energy Efficiency Done at every level from physical to application.
Energy-efficient routing.
Energy-efficient MAC.
Energy-efficient everything.

5. Power Saving at MAC Layer
Beacon interval
awake sleep
Beacon window ATIM window

6. Time Sync Is Necessary/Important
Really ?
What if it is difficult or impossible to synchronize clocks?

7. To sync or not to sync? Yes global synchronization
No no synchronization
Partially local synchronization

8. No Synchronization
“Power-Saving Protocols for IEEE Based Multi-Hop Ad Hoc Networks”
INFOCOM 2002
Yu-Chee Tseng, Chih-Shun Hsu, Ten-Yueng Hsieh
National Chiao-Tung University

9. No Synchronization (0)
Basic idea: nodes have to awake for long enough time.
Extreme case: awake all the time.

10. No Synchronization (1)
Dominating-Awake-Interval
Awake > BI/2 + BW

11. No Synchronization (2)
Periodical-Fully-Awake-Interval

12. No Synchronization (3)
Quorum-based

13. Local Synchronization
“An Energy-Efficient MAC Protocol for Wireless Sensor Networks”
INFOCOM 2002
Wei Ye, John Heidemann, Deborah Estrin
UCLA

14. Local Synchronization (0)
Offset
10:10
10:04
-0:01
0:05
0:01
10:09
- 0:05

15. Local Synchronization (1)
Awake/sleep schedules A B C
1: : :00

16. Time Synchronization in 802.11B C
1: : :00

17. Local Synchronization (2)
0:09
0:07 B
0:04
0:05 C
1: : :00

18. Local Synchronization (3)B C

19. Local Synchronization (4)
Nodes are free to choose their schedules
Or synchronize with others
Or adopt multiple schedules

20. Local Synchronization (3)B C D

21. Communications A B C

22. Which one? To sync or not to sync? Yes (global sync) No (no sync)
Partially (local sync)
Which one?

23. Analysis of energy saving (1)
No data traffic
Parameters
Parameter
Value
Beacon Interval length
100ms
Beacon window length
3ms
ATIM window length
7ms
PFAI T value 4
Quorum-based n value 6
Avg. num. of sch. in border nodes for Local Synch.
2.7
Total nodes in Local Synch.
100

24. Analysis of energy saving (2)
Clock synchronization method
Awake time ratio
No Synchronization
DAI
53%
PFAI
32.5%
Quorum-based
35.4%
Global Synchronization
10%
Local Synchronization
2 schedules
19%
3 schedules
28.4%
4 schedules
37.87%

25. Global Synchronization: pro and con
Best performance in energy saving
Have to assume:
Formation: MANET initiated by a single node.
Connectivity: MANET remains connected.
Overhead

26. No Synchronization – pro and con
Simple -- no need for clock sync
Less efficient in power saving
Any other disadvantages?

27. No Synchronization: Analysis
B has a packet for A in interval 14.
Q: When should B send it?
In every blue.
Or when blue meet gray.
Q: When will blue meet gray  ?

28. 金剛經的智慧 所謂 … 即非 … 是名 … The so called no synchronization
is not no synchronization;
it’s named no synchronization.

29. No Synchronization: Analysis
Clock synchronization method
Awake time ratio
No Synchronization
DAI
53%
PFAI 
32.5%
Quorum-based 
35.4%
Global Synchronization
10%
Local Synchronization
2 schedules
19%
3 schedules
28.4%
4 schedules
37.87%

30. No Synchronization – pro and con
Less efficient in power saving
Simple -- no need for clock sync
Simpler – clock sync is simpler and more scalable, but less energy efficient ?

31. Time Sync in the “No Sync” Scheme
Simpler, more scalable, less energy efficient
Beacon window ATIM window

32. Local Synchronization: pro and con
Infocom 2002, Ye & Heidemann & Estrin
Multiple schedules
Inefficient with multiple schedules
Many issues unaddressed

33. All of them To sync or not to sync? Which one? Yes (global sync)
No (no sync)
Partially (local sync)
Which one?
Normal situation
Neighbor discovery
Transient situation
All of them

34. Proposed Protocol ? Normally, use the global sync scheme.
Switch to the no sync scheme when necessary (for neighbor discovery).
Use the partial sync scheme while merging. ?

35. Happy Ending All of them To sync or not to sync? Yes (global sync)
No (no sync)
Partially (local sync)
All of them

36. Problem, Problem, Problem!
Power saving
???
MAC
Awake-sleep
global no partial sync