1. Wireless Sensor Network and Applicaions(WSNA2002) A Coverage-Preserving Node Scheduling Scheme for Large Wireless Sensor Networks Di Tian, Nicolas D. Georganas

2. Outline  Introduction  Problem Formulation  Sponsored Coverage Calculation  Node Scheduling Scheme Based on Eligibility Rule  Simulation

3. Introduction  Wireless Sensor Network Sensing Computation Networking Applications: Battlefield surveillance Intruder alarming Ecological detection

4. Challenges  Properties of Sensors  Tiny  Powered by battery  Unattended  Large numbers Energy Constraints Powered by battery Hard to be recharged again Scale Constraints Large number of sensors Centralized control is unrelistic

5. Problem Formulation  The goal of this paper  Prolong system lifetime  To turn off redundant nodes while maintaining original sensing coverage

6. Sponsored Coverage Calculation  Sponsored Coverage Calculation  If the whole sensing area of a sensor is covered by the union set of its neighbors’, this node can be turned off. 1 5 2 4 3

7. Sponsored Coverage Calculation A. Fixed Sensing range r, and location information is known. B. Different sensing ranges, and location information is known.

8. Sponsored Coverage Calculation (Case A) NiNi NjNj d(i,j) r

9. Sponsored Coverage Calculation (Case A) S( i ) : the sensing area of node i

10. Sponsored Coverage Calculation (Case A) NiNi NjNj d(i,j) r rr θ

11. Sponsored Coverage Calculation (Case A) NiNi NjNj ψ j->i (x j,y j ) (x i,y i )

12. Sponsored Coverage Calculation (Case A)  The Union of sponsored coverage

13. Sponsored Coverage Calculation (Case A)  Coverage-based Off-duty Eligibility Rule  Turn off eligible node i if

14. Sponsored Coverage Calculation (Case B)  Four Cases

15. Sponsored Coverage Calculation (Case B)  Two Considered Cases:

16. Sponsored Coverage Calculation (Case B) θ riri rjrj d 餘弦定理 :

17. Node Scheduling Scheme Based on Eligibility Rule  The operation is divided into rounds, and each round begins with a scheduling phase, followed by a sensing phase.  Scheduling phase: turn off eligible nodes to save energy.  Sensing phase: perform sensing task time round SchedulingSensing

18. Node Scheduling Scheme Based on Eligibility Rule  Scheduling phase:  Neighbor Information Obtaining Step  Broadcast a Position Advertisement Message (PAM)  (ID, location)  Back-off Based Self-scheduling Step  Each node evaluates its eligibility for turning off by calculating the sponsored coverage

19. Node Scheduling Scheme Based on Eligibility Rule  Blind Points

20. Node Scheduling Scheme Based on Eligibility Rule  Back-off scheme  Let each node delay its determination until a random back-off time T d is reached.  Broadcast a Status Advertisement Message(SAM) to announce its status if it is eligible for turning off.  Enter ready-to-off state  may select the same random number

21. Node Scheduling Scheme Based on Eligibility Rule  To avoid a blind point further, let each node wait for a short period time T w after sending out SAM.  If one SAM is received during the ready-to-off period and the transmitter is one of its off-duty sponsors, the node will re-investigate its off-duty eligibility rule.

22. Finite State Machine for self- scheduling Phase Example

23. Simulation Results 100 nodes deployed in 50m x 50 m square space. Sensing range:10m

24. Simulation Results