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 Beacon interval awake sleep Beacon window ATIM window

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-Interval Awake > BI/2 + BW

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

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 -0:01 0:05 0:01 10:09 - 0:05

Local Synchronization (1) Awake/sleep schedules A B C 1:00 2:00 3:00

Time Synchronization in 802.11 B C 1:00 2:00 3:00

Local Synchronization (2) 0:09 0:07 B 0:04 0:05 C 1:00 2:00 3:00

Local Synchronization (3) B C

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

Local Synchronization (3) B C D

Communications A B C

Which one? 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

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

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 All of them 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