p -Percent Coverage Schedule in Wireless Sensor Networks

1. p-Percent Coverage Schedule in Wireless Sensor Networks Shan Gao, Xiaoming Wang, Yingshu Li Georgia State University andShaanxi 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 40% 70% 60% 90% 50% 80% 30% 10% 40%

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

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 pjfor each subregion Aj ,find a set of n sensors to cover A and meanwhile, n is minimized. Aj : The jthsubregion in A pj : The predefined coverage percentage for Aj si : The ithsensor Rj,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 wj assigned to the subregion Aj,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 Sk 1 50% 2 Guarantees the total working time of siis less than its lifetime A 20 D 18 B 19 E 15 tk: The lifetime of Sk Sk: 1 Sk: The kthsensor subset si: 5 K : The number of subsets C 20 F 16 Li: The lifetime of si Li: E=15 si: The ithsensor J : The number of subregions Worki,k=1, if si=5 is in Sk=1 time S : The set of deployed sensors

11. Problem Definition • Sensor Scheduling for p-Percent Coverage (SSPC) Decides network end-time 1 50% 2 Determines whether pjis guaranteed in Aj . 40 40 A D Sk: 1 Fj,k=1, if [(40*6)/400] ≧50% 40 40 B E K : The number of subsets J : The number of subregions Sk: The kthsensor subset 40 40 Aj: The jthsubregion in A C F S : The set of deployed sensors wj: Weight of subregion pj: The predefined coverage percentage for Aj Area Rj,i,k :The region in Ajcovered by siin Sk; if si is not in Sk, Rj,i,k’s area is zero.

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 Ajis pj-percent covered Aj : The jthsubregion in A Pj : The predefined coverage percentage for Aj

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

16. CPCA • Not pj-percent coverage Aj’ RS Aj 80% Aj : The jthsubregion in A Aj’ : The extended jthsubregion

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 >=pj, SUCCESS • Calculate Worth ROOT

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

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

22. DPCA • Connect phase • pj 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.