1. Saran Jenjaturong, Chalermek Intanagonwiwat Department of Computer Engineering Chulalongkorn University Bangkok, Thailand IEEE CROWNCOM 2008 acceptance rate 25%

2. Outline Introduction Set Cover-Based Density Control Algorithm Performance Evaluation Conclusion

3. Require a high density of sensors to accurately collect data Introduction

4. Overlapping Introduction Redundancy node

5. Resolve the overlapping problem Density control algorithm Finding redundant nodes To avoid appearance of blind area The node scheduling algorithms approximation algorithm called a greedy algorithm Nodes with the maximum number of covered areas Previous works did not considered about node’s remaining energy Introduction Blind area

6. Introduction A Set Cover-Based Density Control Algorithm Goal To prolong network lifetime, the energy consumption must be somehow reduced

7. Network Model Nodes are deployed in a two-dimensioned plane Each node knows its own location Each node has the same communication range twice as far as the sensing range Has the same initial energy quantity Has the same consumption rate

8. Set Cover-Based Density Control Algorithm Redundancy determination Activation node scheduling

9. Redundancy determination Activation node scheduling Perimeter coverage Redundancy determination XEDFABC

10. Overlapping segment of perimeter EDFABC Redundancy determination X Activation node scheduling

11. Redundancy determination X FEGACD ZY B Blind area Redundancy determination Activation node scheduling

12. A set with the most members will be selected first These nodes will run out of energy before others Activation node scheduling F E D C B A Z G X Y

13. Universe = {a,b,c} X={a,b} Y={a,b,c} Z={b,c} X FEGACD ZY B a b c Redundancy determination Activation node scheduling

14. Crossing points are viewed as the vertices of an area search graph Area searching protocol XZ 1 2 4 3 5 Crossing point Y

15. Clockwise order referring to the center of circle Area searching protocol YXZ 1 2 4 3 5 Crossing point 1254 531 432 X Y Z

16. Area search tree (4) (3) (2) (1) 1321253 (4) (3) (2) (1) 1321 Area searching protocol 1254 531 432 X Y Z (1,3,2,1) (3,2,5,3) (3,4,5,3) (5) (4) (3) (2) (1) 132153453

17. Y node is to be sleep mode Y node is to be active mode Some nodes may be decided to be active by one node but the other nodes may prefer them to sleep. Activation node scheduling F E D C B A Z G X Y

18. Collect solutions from nbrs Calculate wait-to- sleep timer Turn into sleep mode Calculate set cover solution Voting protocol Send votes to nbrs votes timeout Receive decision message from nbrs Go to next roundWait-to-sleep timeout E D C B A Z G X Y F

19. Performance Evaluation Simulator : TOSSIM Programming language : nesC Monitoring area : 100x100 units

20. Performance Evaluation H. Zhang and J. C. Hou, "Maintaining Sensing Coverage and Connectivity in Large Sensor Networks," International Journal of Wireless Ad Hoc and Sensor Networks, vol. 1, pp. 89-124, 2005.

21. Performance Evaluation H. Zhang and J. C. Hou, "Maintaining Sensing Coverage and Connectivity in Large Sensor Networks," International Journal of Wireless Ad Hoc and Sensor Networks, vol. 1, pp. 89-124, 2005.

22. F. Ye, G. Zhong, J. Cheng, S. Lu, and L. Zhang, "PEAS: A Robust Energy Conserving Protocol for Long- lived Sensor Networks," in Proceedings of the 23rd International Conference on Distributed Computing Systems: IEEE Computer Society, 2003, pp. 28-37. D. Tian and N. D. Georganas, "A Coverage-Preserving Node Scheduling Scheme for Large Wireless Sensor Networks," in Proceedings of the 1 st ACM International Workshop on Wireless Sensor Networks and Applications Atlanta, Georgia, USA: ACM, 2002, pp. 32-41. Performance Evaluation Sleep!! SchedulingClusteringSensing Sleep!!

23. Performance Evaluation

25. Conclusion Require a high density of sensors to accurately collect data Set cover-based density control algorithm Greedy approximation algorithm weighted by the remainingenergy of nodes To prolong network lifetime, the energy consumption must be somehow reduced Area searching protocol Determining the covering areas of a node