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