1. AN ADAPTIVE MAC PROTOCOL FOR WIRELESS SENSOR NETWORKS Wen-Hwa Liao, Hsiao-Hsien Wang, and Wan-Chi Wu PIMRC ’ 07

2. Outline Introduction Related work Asynchronous MAC(AMAC) protocol Simulation Conclusion

3. 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.

4. 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

5. 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.

6. 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 Sleep Time Schedule

7. Related work - SMAC A B B ’ s schedule Listen Sleep Listen Sleep A B Time

8. 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 system T. 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.

9. Related work – PMAC schedule Time is divided into super time frames (STF) STF Time PRTFPETF W N slots Period iPeriod i+1 Period i+2 0 01 100 … Exchange the schedule of i+2

10. 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 pattern Ex: 1, 0 1 1, 0 2 1, 0 4 1, · · · 0 m 1, 0 m 01, for m ≤δ 1,01,001,00001,δ=4 0 δ 0 2 1, 0 δ 0 3 1, · · · 0 N−1 1. for δ≤m ≤N 0 4 01,0 4 001 δ=4

11. Related work - PMAC PRTFPETF W 6 slots 0 01 100 … Pattern:001 m= 2 δ=4, N=6 Time Pattern:00001 m =4 Pattern:000001 m =5 Update Pattern PRTFPETF W 6 slots 0 00 100 … Time Update Pattern

12. 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.

13. 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. 0123 4567 891011 12131415 Host A Host B r1r1 r2r2 c2c2 c1c1 Asynchronous method

14. AMAC – goal Design a hybrid protocol time asynchronous schedule Quorum system traffic-aware schedule PMAC

15. AMAC - modify pattern string to adapt to quorum Problem with PMAC between quorum The original Pattern is not compatible Ex: Original pattern 001 001001 001001 001001 001001 001001 001001

16. AMAC - modify pattern string to adapt to quorum Replace the original sleep-wakeup string bit 1 => 111 … 1 =>1 n 0 => 000 … 1 =>0 n-1 1

17. AMAC - modify pattern string to adapt to quorum Origin PMAC pattern (000..) m-1 1 Exchange to new pattern {(0 n-1 1)(0 n-1 1) (0 n-1 1)} m-1 1 n 1 N represents selected column in quorum The other 0 n-1 1 forms the selected row in quorum 00001 00001 00001 … … 00001 11111 n c r m

18. AMAC – traffic aware Total time slot is also N slots N=n*m Pattern (0 n-1 1) 1 n 000001 111111 000001 111111 000001 111111

19. AMAC – different size Pattern 000001 111111 Pattern 000101 000101 111111 000001 111111 000001 111111 000001 111111 000100 000100 111111 000100 000100 111111

20. Simulation 100 sensors nodes Duty cycle 100 time slots Execution time 1000~10000 time slot Schedule pattern is re-adjusted after 100 time slots

21. Simulation

25. Conclusion AMAC has good adaptation ability doesn ’ t need time synchronous