To Sync or Not to Sync in Power Saving?
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To Sync or Not to Sync in Power Saving? Ten H. Lai
description
To Sync or Not to Sync in Power Saving?. Ten H. Lai. Essential Fundamental Simple Effective Fresh. Zen ( 禪 ) Networking. Problems Protocols. Problem, Problem, Problem!. ???. Energy Efficiency. Done at every level from physical to application. Energy-efficient routing. - PowerPoint PPT Presentation
Transcript of To Sync or Not to Sync in Power Saving?
To Sync or Not to Sync in Power Saving?
Ten H. Lai
Zen ( 禪 ) Networking
Essential Fundamental
Simple Effective Fresh
Problems
Protocols
Problem, Problem, Problem!
???
Energy Efficiency
Done at every level from physical to application.
Energy-efficient routing. Energy-efficient MAC. Energy-efficient everything.
Power Saving at MAC Layer
awake sleep
Beacon window ATIM window
Beacon interval
Time Sync Is Necessary/Important
Really ?What if it is difficult or impossible
to synchronize clocks?
To sync or not to sync?
Yes global synchronization
No no synchronization
Partially local synchronization
No Synchronization
“Power-Saving Protocols for IEEE 802.11-Based Multi-Hop Ad Hoc Networks”
INFOCOM 2002 Yu-Chee Tseng, Chih-Shun Hsu, Ten-Yueng
Hsieh National Chiao-Tung University
No Synchronization (0)
Basic idea: nodes have to awake for long enough time.
Extreme case: awake all the time.
No Synchronization (1)
Dominating-Awake-IntervalAwake > BI/2 + BW
No Synchronization (2)
• Periodical-Fully-Awake-Interval
T (=3) Beacon Interval
Beacon Window MTIM Window
Host A
Host B
No Synchronization (3)
Quorum-based
Local Synchronization
“An Energy-Efficient MAC Protocol for Wireless Sensor Networks”
INFOCOM 2002 Wei Ye, John Heidemann, Deborah Estrin UCLA
Local Synchronization (0)
Offset
10:10
10:04
10:09
0:01
- 0:05
-0:01
0:05
Local Synchronization (1)
Awake/sleep schedules
A
B
C
1:00 2:00 3:00
Time Synchronization in 802.11
A
B
C
1:00 2:00 3:00
Local Synchronization (2)
A
B
C
0:07
0:04
0:09
0:05
1:00 2:00 3:00
Local Synchronization (3)
A
B
C
Local Synchronization (4)
Nodes are free to choose their schedules Or synchronize with others Or adopt multiple schedules
Local Synchronization (3)
A
B
C
D
Communications
A
C
B
To sync or not to sync?
Yes (global sync)
No (no sync)
Partially (local sync)
Which one?
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
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%
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
No Synchronization – pro and con
Simple -- no need for clock sync
Less efficient in power saving Any other disadvantages?
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?
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.
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%
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
?
Time Sync in the “No Sync” Scheme
Simpler, more scalable, less energy efficient
Beacon window ATIM window
Local Synchronization: pro and con
Infocom 2002, Ye & Heidemann & Estrin Multiple schedules
Inefficient with multiple schedules Many issues unaddressed
To sync or not to sync?
Yes (global sync)
No (no sync)
Partially (local sync)
Which one?
Normal situation
Neighbor discovery
Transient situation
All of them
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.
?
Happy Ending
To sync or not to sync?
Yes (global sync)
No (no sync)
Partially (local sync)All of them
Problem, Problem, Problem!
???Power saving
MAC
Awake-sleep
global no partial sync
