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