PW-MAC: An Energy-Efficient Predictive-Wakeup MAC Protocol for Wireless Sensor Networks

1. PW-MAC: An Energy-Efficient Predictive-WakeupMAC Protocol for Wireless Sensor Networks Jeong Young-Hwan

2. Paper Information • Paper Title • PW-MAC: An Energy-Efficient Predictive-Wakeup MAC Protocol for Wireless Sensor Networks • This paper appears in •  INFOCOM, 2011 Proceedings IEEE • Be affiliated to with • Department of Computer Science, Rice University, Houston, TX, USA • Authors • Lei Tang, Yanjun Sun, Omer Gurewitz, David B. Johnson

3. Contents • 1. Introduction • 2. Related Work • 3. Predictive Wake-up MAC (PW-MAC) • 3.1 Predictive Wake-up • 3.2 Prediction-based Retransmission • 3.3 Controling Prediction Error • 4. Simulation • 5. Conclusion

4. 1. Introduction • Minimize sensor node energy consumption • By enabling senders to predict receiver wakeup times, even given the challenges of unpredictable hardware and OS delay and clock drift. • An efficient prediction-based retransmission mechanism • to achieve high energy efficiency when wireless collisions occur and packets need to be retransmitted. • The prediction error caused by hardware and OS latency can be much larger than that caused by clock drift. • To enable a sender to wake up shortly before a receiver does, they introduce an on-demand prediction error correction mechanism, allowing a sender to resynchronize with a receiver when needed. • The results of experiments on a testbed of MICAz motes to evaluate the performance of PW-MAC compared with other MAC protocols • i.e., X-MAC, WiseMAC, and RI-MAC • under singlehop and multihop traffic flows, under hidden-terminal scenarios, and under scenarios in which nodes have wakeup schedule conflicts.

5. 2. Related Works • B-MAC (Sender-initiated) Sender sends a preamble longer than the receiver wake-up interval to notify receiver the pending transmission. Receiver wakes up, hears the preamble, and Next stays awake to receive data packets Wake-up

6. 2. Related Works • X-MAC(Original)

7. 2. Related Works • X-MAC (Sender-initiated) • The UPMA implementation of X-MAC Next Wake-up • Sender preamble is replaced by shorter data packets. • Receiver sends an ACK after receiving a data packet, without preamble hearing the entire preamble.

8. 2. Related Works • WiseMAC (Sender-initiated) • WiseMAC shortened the long preamble, taking advantage of fixed node wake-up interval to enable sender to predict the receiver wake-up times.

9. 2. Related Works • B-MAC, X-MAC, and WiseMAC • B-MAC and X-MAC have large sender duty cycle. • The fixed wakeup interval of WiseMAC can often causes collisions. • Preambles often collide when there are multiple hidden transceivers. • No efficient retransmission mechanism

10. 2. Related Works • RI-MAC (Receiver-initiated)

11. 3. PW-MAC: Predictive Wake-up MAC • Receiver-initiated protocol, no global clock synch. • Independent pseudo-random wakeup scheduling to reduce collisions. • Minimizes idle-listening and overhearing both at senders and at receivers by predictive pseudorandom wakeup. • Also a prediction-based retransmission mechanism to achieve high energy efficiency even when collisions occur. • Achieves high performance on real hardware by controlling the prediction error caused by hardware and OS latency and clock drift.

12. 3. PW-MAC: Predictive Wake-up MAC • Linear congruential generator(LCG) • Represents one of the oldest and best-known pseudorandom number generator algorithms • The generator is defined by the recurrence relation:

13. 3. PW-MAC: Predictive Wake-up MAC • Parameters in common use • In this paper, m=1000, a=nodeID*20, c=7

14. 3. PW-MAC: Predictive Wake-up MAC 3.1 PW-MAC: Predictive Wake-up MAC • Prediction state obtained by a node S to predict a node R’s wakeups includes: • Pseudorandom number generator parameters and current seed of R. • The time difference between S and R.

15. 3. PW-MAC: Predictive Wake-up MAC 3.1 PW-MAC: Predictive Wake-up MAC • By waking up right before a receiver does, a sender minimizes its idle listening and overhearing. The prediction state of R learned by S comprises the parameters and current seed of the pseudo-random number generator of R (6 bytes in total), as well as the current time difference between S and R (4 bytes)

16. 3. PW-MAC: Predictive Wake-up MAC 3.2 Prediction-based Retransmission

17. 3. PW-MAC: Predictive Wake-up MAC 3.3 Controling Prediction Error

18. 3. PW-MAC: Predictive Wake-up MAC 3.3 Controling Prediction Error

19. 4. Evaluation on MICAz motes • Experiment of Wake-up Schedule Conflicts

20. 4. Evaluation on MICAz motes • Hidden Terminal Experiment • In hidden scenario, with WiseMAC, the two senders’ repeated collisions retransmissions cause persistent collisions.

21. 4. Evaluation on MICAz motes • Sender Duty Cycle with Increasing Hop-Length and Num-Flows

22. 4. Evaluation on MICAz motes • Delivery Latency with Increasing Hop-Length and Num-Flows

23. 4. Evaluation on MICAz motes • Delivery Ratio with Increasing Hop-Length and Num-Flows

24. 5. Conclusion • PW-MAC achieves high energy efficiency both at senders and at receivers. • Predictable pseudorandom wake-up schedules. • Prediction-based retransmission mechanism maintains high energy efficiency even when collisions occur. • PW-MAC outperformed other tested protocols under colliding-schedule, hidden-terminal, and multihop experiments on a testbed of MICAz motes.

25. Thank you