1. Modeling and Throughput Analysis for SMAC Ou Yang 4-29-2009

2. 2 Outline Motivation and Background Methodology - 1-D Markov Model for SMAC without retx - 2-D Markov Model for SMAC with retx Throughput Analysis - 1-D Markov Model for SMAC without retx - 2-D Markov Model for SMAC with retx Model Validation Conclusions

3. 3 Motivation Good to know the performance of SMAC - sleep at MAC layer or not? - which duty cycle should be chosen? No analytical model for SMAC - quantitative estimation of throughput - throughput under different scenarios

4. 4 Background – SMAC Protocol Duty-cycled MAC to reduce idle listening - fixed active period in a cycle - variable sleep period in a cycle - duty cycle = active period / cycle length

5. 5 Background – SMAC Protocol Synchronization - SYNC pkt carries sleep-awake schedule - broadcast SYNC pkt Medium access - RTS/CTS/DATA/ACK - carrier sensing ( virtual + physical ) - fixed contention window size

6. 6 Background – SMAC Protocol Reasons of packet loss (ideal channel) - SMAC without retx: RTS failed - SMAC with retx: retx over limit - queue overflow

7. 7 Methodology Assumptions - packet arrive independently - finite FIFO queue at each node - channel is ideal no hidden terminals no capture effects no channel fading

8. 8 Methodology 1-D Markov Model for SMAC without retx 0 pkts in the queue1 pkts in the queue2 pkts in the queueMaximum Q pkts in the queue

9. 9 Methodology 1-D Markov Model for SMAC without retx

10. 10 Methodology Example of the 1-D Markov Model 012 Transition Matrix P known unknown

11. 11 Methodology 2-D Markov Model for SMAC with retx Retx stage 0 Retx stage 1 Retx stage R 1 pkt in the queueQ pkts in the queue

12. 12 Methodology Example of the 2-D Markov Model 0,00,10,2 1,11,2 2,12,2 0,00,10,2

13. 13 Methodology Example of the 2-D Markov Model 0,00,10,2 1,11,2 2,12,2 1,11,2

14. 14 Methodology Example of the 2-D Markov Model 0,00,10,2 1,11,2 2,12,2 2,12,2

15. 15 Throughput Analysis Definition of throughput Solve 2 variables!

16. 16 Throughput Analysis – 1-D Markov Model According to the Markov Model - stationary distribution: - is the only unknown variable in - curve Assume each node behaves independently - prob. of to contend the media in a cycle - randomly select a backoff window in [0,W-1] - curve

17. 17 Throughput Analysis – 1-D Markov Model

18. 18 Throughput Analysis – 1-D Markov Model Intersections of and - - is obtained To solve similar to Assume each node behaves independently - prob. of to contend the media in a cycle - randomly select a backoff window in [0,W-1] - -

19. 19 Throughput Analysis – 2-D Markov Model According to the Markov Model - stationary distribution: - and are unknown variables in - surface Assume each node behaves independently - prob. of to contend the media in a cycle - randomly select a backoff window in [0,W-1] - curve

20. 20 Throughput Analysis – 2-D Markov Model is obtained!

21. 21 Model Validation Varying the number of nodes

22. 22 Model Validation Varying the queue capacity

23. 23 Model Validation Varying the contention window size

24. 24 Model Validation Varying the data arrival rate

25. 25 Discussions Effects of retransmissions - not obvious difference in throughput - extra traffic at the head of the queue Reasons - saturation: no improvement - far from saturation: trivial improvement - close to saturation: some improvement

26. 26 Conclusion 1-D Markov Model to describe the behavior of SMAC without retx 2-D Markov Model to describe the behavior of SMAC with retx Models well estimate the throughput of SMAC Application - estimate throughput - optimize the parameters of SMAC - trade off throughput and lifetime

27. 27 Thank you Q & A

28. 28 Methodology Example of the 1-D Markov Model 012 Transition Matrix P known unknown

29. 29 Background – Markov Model Markov model of IEEE 802.11