1. p-Percent Coverage Schedule in Wireless Sensor Networks Shan Gao, Xiaoming Wang, Yingshu Li Georgia State University and Shaanxi Normal University IEEE ICCCN 2008 Acceptance Rate 25%

2. Outline Introduction Motivation Goal Problem Definition p-PERCENT COVERAGE SCHEDULING ALGORITHM Simulations Conclusion

3. Introduction In Wireless Sensor Networks (WSNs), there are some scenarios with different surveillance requirements and deployment environments –Full coverage A

4. Introduction But, full coverage is necessary? A 90% 70% 50% 10%40% 30% 80% 60%40%

5. Motivation Cover p-percent of the monitored area A 90% 70% 50% 10%20%30% 80% 60%40%

6. Goal A particular required coverage percentage such that the surveillance quality can be finely controlled and unnecessary energy consumption can be ulteriorly reduced –Could be turned off and network lifetime could be prolonged.

7. Problem Definition Extended p-Percent Coverage Problem(EPPC) –Given N sensors, a 2-dimensional area A which is divided into J subregions and a specific coverage percentage p j for each subregion Aj, find a set of n sensors to cover A and meanwhile, n is minimized. A j : The jth subregion in A p j : The predefined coverage percentage for Aj s i : The ith sensor R j,i : The region in Aj covered by si 80%

8. Problem Definition Network End-time of EPPC problem –Given an area A which is divided into J subregions and the weight w j assigned to the subregion A j, network lifetime ends at the time that the percentage of weighted area of subregions whose coverage can be guaranteed by living nodes is less than the user-input f.

9. Problem Definition Sensor Scheduling for p-Percent Coverage (SSPC) –Given a 2-dimensional area A and a set of sensors S, –Objective: Maximize L –Subject to:

10. Problem Definition Sensor Scheduling for p-Percent Coverage (SSPC) Network lifetime Working time of S k S k : The kth sensor subset K : The number of subsets S : The set of deployed sensors J : The number of subregions L i : The lifetime of s i 1 A B C 2 D E F 50% 20 19 20 18 15 16 s i : The ith sensor s i : 5 L i : E=15 1 Work i,k =1, if s i =5 is in S k =1 1 S k : 1 Guarantees the total working time of s i is less than its lifetime time t k : The lifetime of S k

11. Problem Definition Sensor Scheduling for p-Percent Coverage (SSPC) p j : The predefined coverage percentage for Aj R j,i,k : The region in A j covered by s i in S k ; if s i is not in S k, R j,i,k ’s area is zero. 1 A B C 2 D E F 50% 40 Decides network end-time Determines whether p j is guaranteed in A j. A j : The jth subregion in A F j,k =1, if [(40*6)/400] ≧ 50% 1 S k : 140 w j : Weight of subregion Area S k : The kth sensor subset K : The number of subsets S : The set of deployed sensors J : The number of subregions

12. Assume There are enough sensors deployed into the monitored area A All sensors have the same fixed sensing range Rs with different energy

13. p-PERCENT COVERAGE SCHEDULING ALGORITHM Centralized p-Percent Coverage Algorithm (CPCA) Distributed p-Percent Coverage Protocol (DPCP)

14. CPCA Checks whether A j is p j -percent covered A j : The jth subregion in A P j : The predefined coverage percentage for Aj

15. CPCA Connected C and is the farthest neighbor To find the next subregion to be considered 80% C

16. CPCA Not p j -percent coverage RS Aj Aj’ A j : The jth subregion in A A j’ : The extended jth subregion 80%

17. DPCA 3 Phases –Discover Discover neighbors –Construct Construct a subset of nodes to p-Percent cover each subregion –Connect Connect all subsets together Each phase is given a fixed period, Phase 2 and 3 have to begin at the predefined time despite At the very beginning, a node is randomly chosen and set as the first ROOT node where the algorithm begins to run.

18. DPCA Discover phase ROOT

19. DPCA Construct phase ROOT calculate cp, If cp >= p j, SUCCESS Calculate Worth ROOT

20. DPCA Construct phase Calculate Worth –The area covered only by is one of the most important criteria. The node which covers the most area should be chosen. ROOT parent B A ROOT d : is the distance between si and sj E : initial energy of a sensor e : residual energy λ and μ : tune the weight distance α1 α2

21. DPCA Construct phase Cp(coverage percentage) and the information of ROOT’S neighbors ROOT ROOT next BE_ROOT message ROOT parent

22. DPCA Connect phase –p j is satisfied. The ROOT node inform each node in C broadcasts a CONNECT message. ROOT

23. DPCA Connect phase –CONNECT_PATH messsage. –All nodes contained in the message’s routing information will be notified to be involved in each region’s C. ROOT

24. Simulations The surveillance area is a square and is separated into 3×3 subregions. The subregions’ size ranges from twice to 10 times of the sensing range. Nodes are proportionally deployed into each subregion according to pj. Each node has the same sensing range, 50 m, and the same communication range, 200 m

25. Simulations Network Lifetime

26. Simulations Coverage Accuracy

27. Conclusion Can remarkably prolong network lifetime compared with traditional full coverage algorithms.