Cross-Layer Application-Specific WSN Design over SS-Trees

1. Cross-Layer Application-Specific WSN Design over SS-Trees -Prepared by Amy

2. Outline • Background Introduction • Sleep Scheduling Issues & the SS-Tree Concept • SS-Tree Operational Stages • SS-Tree Computation • SS-Tree Operational Specifics & Sleep Scheduling • Conclusions and Future Work

3. Background Introduction • Wide-area surveillance WSN applications • expected lifetime • limited battery supply • Energy Efficiency is paramount • Adaptive sleep schedules to minimize energy lost

4. Background Introduction • Sleep scheduling: • shorten the time radio transceiver engaged in idle listening • Good impact: • reduced overhearing • Ensuing problem: • link table entries expire prematurely • control and data packet compete for resources • real-time data reporting function reduced

5. Background Introduction • Ultimate Design Goal: • Balance: • sensing requirements • end-to-end data communication overhead • network control effectiveness • With energy efficiency • Through a cross-layer sleep scheduling scheme

6. Sleep Scheduling Issues • Not recommended: • Random sleep scheduling • detrimental effect on network connectivity and topology control efficiency • Global sleep scheduling • network-wide communication blackout • Groups of leaf nodes sleep scheduling • non-leaf nodes depleting battery reserves sooner

7. Sleep Scheduling Issues • Using coordinated sleep scheduling • Realize the benefits: • reduced overhearing • reduced packet collision • simplified topology • Without sacrifice: • network connectivity • sensing capabilities

8. SS-Tree Concept

9. SS-Tree Concept • Advantages: • Avoid overburdening any set of nodes from being the sole virtual backbone • Increase monitoring sensitivity (greater event reporting windows) without altering communication duty cycle(reporting frequencies)

10. SS-Tree Concept--issues to be considered Gaps appearing in between the active period of adjacent SS-Tree

11. SS-Tree Concept--issues to be considered -- Blackout duration -- Sleep period -- number of mutually adjacent SS-Trees -- Active period Number of distinct live path To guarantee 100% real-time event reporting capability Not feasible due to limited nodal density And high SS-Tree computation complexity Not necessary to approach real-time Intuition suggests the number of SS-Tree Should less than the average nodal degree

12. SS-Tree Concept--issues to be considered Drawback: timer-driven Data cannot be simultaneously Gathered from all SS-Trees

13. SS-Tree Operational Stages

14. SS-Tree Operational Stages • Network Initialization: • gather network connectivity information, • compute the SS-Trees • disseminate the sleep schedules • Sleep: • shut down the radio transceiver • processor and sensing unit remain active • Hibernation: • Shutting down all hardware components • except for a tiny low-power wakeup timer

15. SS-Tree Operational Stages • Active: • all data reporting • network maintenance tasks are performed • Failure Recovery: • data sink repair or reconstruct SS-Trees • Neighborhood Update: • neighboring nodes exchange local information • for each other’s sleep schedule

16. SS-Tree Computation

17. SS-Tree Computation • A greedy depth-first approach • From the bottom-up on a branch-by-branch basis • Proceeds in a number of iterations • In each iteration an end-to-end minimum cost path is appended to one of the SS-Trees.

18. SS-Tree Computation

19. SS-Tree Computation

20. SS-Tree Computation

21. SS-Tree Computation

22. SS-Tree Operational Specifics & Sleep Scheduling • Major task – determine an optimal sleep schedule that maximizes energy efficiency • Short active period -> high transmission latency • Longer active period -> increase sleep time between two consecutive active periods • Determine an upper bound of active period • balance low communication duty cycle • monitoring sensitivity • end-to-end packet transmissions

23. SS-Tree Operational Specifics & Sleep Scheduling Network Layer Routing

24. SS-Tree Operational Specifics & Sleep Scheduling • Some flexible strategies in manipulating application requirements: • Compact query formats • shrink packet size by formatting data types • reduce hop-by-hop transmission time • Aggressive data aggregation • duplicate suppression • reduce unnecessary packet exchange • Hop-by-hop ACK in MAC layer • instead of end-to end ACK in transport layer • reduce energy expenditure

25. SS-Tree Operational Specifics & Sleep Scheduling

26. SS-Tree Operational Specifics & Sleep Scheduling • Medium Access Control • Prefer single-channel unslotted CSMA • simplicity • greater scalability • looser time synchronization requirements • Bypass the RTS/CTS handshake • long end-to-end propagation delay

27. SS-Tree Operational Specifics & Sleep Scheduling Timing components constituting a single active period Round-trip time recorded for node I on its respective SS-Tree

28. SS-Tree Operational Specifics & Sleep Scheduling

29. SS-Tree Operational Specifics & Sleep Scheduling

30. SS-Tree Operational Specifics & Sleep Scheduling

31. SS-Tree Operational Specifics & Sleep Scheduling IACK works better in reducing the time when the size of C/D packet is comparable to that of EACK

32. Conclusion and Future Work • Following issues will be explored: • For a given random topology, what is the maximum number of SS-Trees that can be constructed to minimize the number of shared nodes? • For a given number of nodes, what is the optimal method of deployment that ensures 100% coverage of the subject area while maximizing the number of available SS-Trees with minimum shared nodes? • What are the suitable neighborhood discovery and failure recovery strategies for the SS-Tree design?

33. The End