CMAC : An energy efficient mac layer protocol using convergent packet forwarding for wireless sensor networks

1. CMAC: An energy efficient mac layer protocol using convergent packet forwarding for wireless sensor networks SECON 2007 Sha liu, Kai-wei fan, Prasun sinha Department of computer science and engineering, Ohio state university Presentation: Jinhyung Lee Computer Network Lab

2. Contents 1 / 17 • Introduction • Contribution • Features • Evaluation • Conclusion • Discussion

3. Introduction 2 / 17 • MAC layer design goals for wsn • Long lifetime • Low latency • Low maintenance overhead • High throughput • Existing solutions • Synchronized MAC • SMAC, TMAC, DMAC • Consume a lot of energy on periodic synchronization • Unsynchronized MAC • BMAC, XMAC • Use long preambles

4. Contribution 3 / 17 • CMAC • Unsynchronized duty cycling • No synchronization overhead • Aggressive RTS, Anycast • Quickly make routing progress • Convergent packet forwarding • Avoid overhead of anycast • Achieved goals • Energy efficiency • Low latency • High throughput

5. Convergent MAC 4 / 17 • Aggressive RTS • Anycast packet forwarding • Convergent forwarding

6. Convergent MAC • Aggressive RTS • Anycast packet forwarding • Convergent forwarding

7. Aggressive RTS 5 / 17 Aggressive RTS Sender Sleep Sleep Sleep RTS RTS RTS RX Packet Sleep Sleep Receiver Sleep Sleep Sleep RX CTS Packet Sleep • Long preamble mechanism of BMAC • High latency • Breaks up long preamble into multiple rts packets • RTS burst • Sender receives a CTS, it sends packet immediately • Latency at each hop could be reduced by half

8. Aggressive RTS 6 / 17 RTS RTS Channel check • Assess channel quickly during each wake up time • To allow nodes to work at a very low duty cycle • If receiver wakes up during the gap between two RTSs • miss RTS burst

9. Aggressive RTS 7 / 17 RTS RTS RTS RTS (a) (b) Channel check Channel check RTS RTS Executed channel check Canceled channel check (c) Channel check • Double channel check • Check the channel twice to avoid missing activities • For each channel check, nodes sample up to 5 times • Between two channel checks, put to sleep mode • Interval must be shorter than RTS transmission time

10. Convergent MAC • Aggressive RTS • Anycast packet forwarding • Convergent forwarding

11. Anycast packet forwarding 8 / 17 • Nodes other than target receiver may • Wake up earlier • Can make some progress toward sink • Reduce latency • Anycast to the one closest to destination • Forwarding set • Neighbor nodes of the sender that are closer to the destination • Partition into 3 sub regions

12. Anycast packet forwarding 9 / 17 mini-slot CTS slot RTS Canceled RTS Sender CTS Node in R1 Node in R1 Canceled CTS Canceled CTS Node in R2 Canceled CTS Node in R3 • More than one node may contend to send cts • Each gap between two consecutive RTS is divided • 3 CTS slots for (R1, R2, R3) • Prioritize the cts packet transmission • Each CTS slot divided into mini-slots • Each node in the same region randomly picks up a mini-slot

13. Convergent MAC • Aggressive RTS • Anycast packet forwarding • Convergent forwarding

14. Convergent forwarding 10 / 17 • Anycast has higher overhead than unicast • Suboptimal routes • Anycast RTS/CTS • Switch from anycast to unicast if • Node is able to communicate with a node in R1 • Cannot find a better next hop than current one • Nodes stay awake for a short duration after receiving a packet • Synchronized wake-up scheduling • Timeout

15. Convergent forwarding 11 / 17

16. Experiments 12 / 17 • Testbed : kansei testbed • 105 XSM nodes • 7 x 15 topology, separation of 3 feet • Implementation parameters

17. Experiments 13 / 17 • Metrics • Throughput • Latency • Normalized energy consumption • Scenarios • Static event • Moving event • Comparison • CMAC 1%, BMAC 1% • CMAC 100%, BMAC 100%

18. Experiments – static scenario 14 / 17 Energy Consumption Throughput Latency

19. Experiments - moving scenario 15 / 17 Energy Consumption Throughput Latency

20. Simulation 16 / 17 Energy Consumption Throughput Latency

21. Conclusion 17 / 17 • CMAC • aggressive RTS, anycast, convergent packet forwarding • Supports high throughput, low latency and consumes less energy than existing solutions • Discussion • Noconsideration of node mobility • Awake duration after receiving packet is sensitive to performance • For low data rates, can’t converge from anycast to unicast • Too similar with XMAC

22. Thank You CS 710

23. Appendix CS 710

24. How long should nodes keep awake after receiving a packet? • Longer awake period →lower latency • But longer awake period may not be more energy efficient • Dependent on data rate and node density lambda: packet arrival rate in a Poisson arrival process

25. Performance of anycast if lack of convergence • Experiment settings: • Vary transmission ranges to create different node densities • Metric: • Latency normalized by distance (hops in unicast) • Results: • CMAC 1% achieves lower latency than BMAC 1%