1. Stochastic sleep scheduling (SSS) for large scale wireless sensor networks Yaxiong Zhao Jie Wu Computer and Information Sciences Temple University

2. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

3. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

4. Fixed sleep scheduling A fixed scheduling is shown in the figure – The interval between “on” periods is fixed – The length of “on” periods is fixed – The ratio of “on” to “off” periods is tunable Determines the energy efficiency of the scheduling Lower ratio => larger delay and lower energy consumption

5. Stochastic sleep scheduling (SSS) The interval between “on” periods is random The length of “on” periods is random The ratio of “on” to “off” periods is tunable Minimal coordination between sensors – Good for large scale networks

6. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

7. SSS scheduling model The ratio of “on” to “off” periods is given “r” Two random variables “ON” and “OFF” with expectations “T on ” and “T off ” – The ratio of T on /T off = r – Long term energy efficiency is guaranteed The “on” period is drawn from ON and OFF

8. The delay introduced by SSS Due to the randomness – There always be a delay – Between two successive sensors In this paper – We try to characterize the end-to-end delay between sensors – Guide the design and choice of the parameters

9. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

10. Greedy routing Routing algorithms determine the delay Greedy routing is used – A sensor forwards the packet to the neighbor that has shorter minimal distance to the destination – If multiple sensors are available Randomly choose one

11. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

12. Chain of sensors Source and destination are connected by a series of sensors The Probability Density Function of a n-hop chain is given above The simulation results is given besides

13. Grid networks The distribution of end-to-end delay is more complicated in Grid networks Three parts – Regular part – Expanding part – Contracting part – They have different distribution of forwarding sensors

14. Grid networks (cont’d) Transition matrix between different levels in different parts – A sample matrix for expanding part is given We can multiply multiple matrices to obtain the distribution Sample transition matrix

15. Simulation Results Analytic results and simulation results

16. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

17. Adaptive listening Instead of continuously listen the channel – Listen the channel periodically with short cycle – We need to determine the cycle length so that the probability of detecting the availability of channel is guaranteed – The interval between listening should be less than the “on” period of the intended neighbor Its probability should be larger than a certain threshold

18. Simulation results Energy consumption is greatly reduced

19. Outline Motivation Basic scheduling model Analysis of delay in networks of regular topology – Greedy routing algorithm – Chain and grid SSS-based MAC protocol – Adaptive listening Conclusion and future work

20. Concluding remarks SSS can be made controllable – End-to-end delay in networks using SSS is acceptable – Minimal control overhead A practical MAC protocol based on SSS is presented – Monitoring overhead is reduced using adaptive listening

21. Future work In SSS, sensors are completely agnostic of each other – Introducing a certain amount of coordination can improve the performance More extensive theoretical analysis is needed – For networks with random topologies – Take into consideration traffic pattern, routing algorithms, and mobility

22. Q&A Thanks for listening