AN ADAPTIVE MAC PROTOCOL FOR WIRELESS SENSOR NETWORKS

Wen-Hwa Liao, Hsiao-Hsien Wang, and Wan-Chi Wu

PIMRC’07

Outline

Introduction Related work Asynchronous MAC(AMAC) protocol Simulation Conclusion

Introduction

In WSNs, the sensors are used to sensing , calculating, and transmitting data.

Each sensor equips with battery and works individually.

The power of sensor is supplied by battery.

Introduction Because of technical limitations, the

power carried by sensor is very limited. To replace battery is very time

consuming and costly process. There are a lot of researches on energy

saving. Ex:

Hardware Operating mechanism

Introduction - motivation

The sleeping mechanism is one of the most effective energy saving method.

In order to conserve energy, the sensor turns its antenna off when it doesn’t have to transmit data.

Because the topology of WSNs may change frequently, the saving mechanism should be distributed and self-organized.

Related work - SMAC

Each sensor has its fixed wake-up schedule.

The sensor exchanges their schedules by broadcasting it to all its immediate neighbors.

W. Ye, J. Heidemann, and D. Estrin, “An Energy-Efficient MAC Protocol for Wireless Sensor Networks,” IEEE INFOCOM , 2002.

Listen ListenSleep Sleep

Time

Schedule

Related work - SMAC

A B

B’s schedule

Listen ListenSleep Sleep

Listen ListenSleep Sleep

A

BTime

Related work - PMAC

Sensor generates sleeping schedule based on its own traffic periodically. Pattern string

Bit 1 indicates wake-up Bit 0 means sleep

Period N time slots

The sensor also exchanges their schedules by broadcasting it to all its immediate neighbors.

TDMA systemT. Zheng, S. Radhakrishnan, and V. Sarangan, “PMAC: An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,” IEEE International Parallel and Distributed Processing Symposium (IDPDS), 2005.

Related work – PMAC schedule

Time is divided into super time frames (STF)

STF STF STF

Time

PRTF PETF

W

N slots

Period i Period i+1 Period i+2

0 0 1 10 0 …

Exchange the schedule of i+2

Related work - PMAC

δ is a predefine threshold. The time slot in a period will be repeated, if

pattern is small than the size of period N Schedule is composed of sleep-wakeup pat

tern Ex:

1, 011, 021, 041, · · · 0m1, 0m01, for m ≤δ 1,01,001,00001 ,δ=4

0δ 02 1, 0δ 03 1, · · · 0N−1 1. for δ≤m ≤N 0401,04001 δ=4

Related work - PMAC

PRTF PETF

W

6 slots

0 0 1 10 0 …

Pattern:001m= 2

δ=4 , N=6

Time

Pattern:00001m =4

Pattern:000001m =5

Update Pattern

PRTF PETF

W

6 slots

0 0 0 10 0 …

Time

Update Pattern

Related work - PMAC

The drawback of PMAC Sensor is necessary to exchange it

own schedule for neighbor discovery. PMAC is required to achieve clock

synchronous.

Related work – quorum based

R. Zheng, J. C. Hou, and L. Sha, “Asynchronous Wakeup for Ad Hoc Networks,” ACM International Symposium on Mobile Ad Hoc Networking & Computing (Mobihoc), 2003.

0 1 2 3

4 5 6 7

8 9 10 11

12 13 14 15Host A

Host B

r1 r2

c2

c1

Asynchronous method

AMAC – goal

Design a hybrid protocol time asynchronous schedule

Quorum system traffic-aware schedule

PMAC

AMAC -modify pattern string to adapt to quorum

Problem with PMAC between quorum The original Pattern is not compatible Ex:

Original pattern 001

0 0 1 0 0 1

0 0 1 0 0 1

0 0 1 0 0 1

0 0 1 0 0 1

0 0 1 0 0 1

0 0 1 0 0 1

AMAC -modify pattern string to adapt to quorum

Replace the original sleep-wakeup string bit

1 => 111…1 =>1n

0 => 000…1 =>0n-11

AMAC - modify pattern string to adapt to quorum

Origin PMAC pattern (000..)m-11

Exchange to new pattern {(0n-11)(0n-11) (0n-11)}m-1 1n

1N represents selected column in quorum

The other 0n-11 forms the selected row in quorum

0 0 0 0 1

0 0 0 0 1

0 0 0 0 1

… …

0 0 0 0 1

1 1 1 1 1

n

c

r

m

AMAC – traffic aware

Total time slot is also N slots N=n*m Pattern

(0n-11) 1n0 0 0 0 0 1

1 1 1 1 1 1

0 0 0 0 0 1

1 1 1 1 1 1

0 0 0 0 0 1

1 1 1 1 1 1

AMAC – different size

Pattern 000001 111111

Pattern 000101 000101

1111110 0 0 0 0 1

1 1 1 1 1 1

0 0 0 0 0 1

1 1 1 1 1 1

0 0 0 0 0 1

1 1 1 1 1 1

0 0 0 1 0 0

0 0 0 1 0 0

1 1 1 1 1 1

0 0 0 1 0 0

0 0 0 1 0 0

1 1 1 1 1 1

Simulation

100 sensors nodes Duty cycle 100 time slots Execution time 1000~10000 time

slot Schedule pattern is re-adjusted

after 100 time slots

Simulation

Simulation

Simulation

Simulation

Conclusion

AMAC has good adaptation ability doesn’t need time synchronous