A Sensibility-Based Sleeping Configuration Protocol for Dependable Wireless Sensor Networks

1. A Sensibility-Based Sleeping Configuration Protocol for Dependable Wireless Sensor Networks Chen Xinyu Group Meeting 2005-01-28 Dept. of Computer Science & Engineering

2. Outline • Introduction • Neighboring-sensor field sensibility • Sensibility-based sleeping configuration protocol • Performance evaluations • Conclusions

3. Wireless Sensor Networks • Composed of a large number of sensor nodes • Sensors communicate with each other through short-range radio transmission • Sensors react to environmental events and relay collected data through the dynamically formed network

4. Applications • Environment monitoring • Military reconnaissance • Physical security • Traffic surveillance • Industrial and manufacturing automation • Distributed robotics • … Ossama Younis and Sonia Fahmy: Distributed Clustering in Ad-hoc Sensor Networks: A Hybrid, Energy-Efficient Approach (InfoCom2004)

5. Requirements • Maintaining coverage • Every point in the region of interest should be sensed within given parameters • Extending system lifetime • The energy source is usually battery power • Battery recharging or replacement is undesirable or impossible due to the unattended nature of sensors and hostile sensing environments

6. Requirements (Cont’d) • Fault tolerance • Sensors may fail or be blocked due to physical damage or environmental interference • Produce some void areas which do not satisfy the coverage requirement • Scalability • High density of deployed nodes • Each sensor must configure its own operational mode adaptively based on local information, not on global information

7. Approach: Coverage Configuration • Coverage configuration is a promising way to extend network lifetime by alternately activating only a subset of sensors and scheduling others to sleep according to some heuristic schemes while providing sufficient coverage in a geographic region

8. Concerns • A good coverage-preserved and fault-tolerant sensor configuration protocol should have the following characteristics: • It should allow as many nodes as possible to turn their radio transceivers and sensing functionalities off to reduce energy consumption, thus extending network lifetime • Enough nodes must stay awake to form a connected network backbone and to preserve area coverage • Void areas produced by sensor failures and energy depletions should be recovered as soon as possible

9. Two Sensing Models • Boolean sensing model (BSM) • Each sensor has a certain sensing range, and can only detect the occurrences of events within its sensing range • General sensing model (GSM) • Capture the fact that signals emitted by a target of interest decay over the distance of propagation • Exploit the collaboration between adjacent sensors

10. Discussions for the BSM • Each sensor has a deterministic sensing radius • Allow a geometric treatment of the coverage problem • Miss the attenuation behavior of signals • Ignore the collaboration between adjacent sensors in performing area sensing and monitoring

11. Problem Formulation for the GSM • Point Sensibility s(Ni, p): the sensibility of a sensor Ni for an event occurring at an arbitrary measuring point p •  : the energy emitted by events occurring at point p •  : the decaying factor of the sensing signal • d(Ni, p) : the distance between senosr Ni and point p

12. All-Sensor Field Sensibility (ASFS) • Suppose we have a “background” distribution of n sensors, denoted by N1, N2, …, Nn, in a deployment region A • All-Sensor Field Sensibility for point p • With a sensibility threshold , the point p is covered if Sa(p) ≥ 

13. Discussions for the ASFS • Need a sink working as a data fusion center • Produce a heavy network load in multi-hop sensor networks • Pose a single point of failures

14. Neighboring-Sensor Field Sensibility (NSFS) • Treat each sensor as a sensing fusion center • Each sensor broadcasts its perceived field sensibility • Each sensor only collects its one-hop neighbors’ messages • Transform the original global coverage decision problem into a local problem

15. Responsible Sensing Region (RSR) • Voronoi diagram • Partition the deployed region into a set of convex polygons such that all points inside a polygon are closet to only one particular node • The polygon in which sensor Ni resides is its Responsible Sensing Region i • If an event occurs in i, sensor Ni will receive the strongest signal • Open RSR and closed RSR

16. Pessimistic Scan Region

17. Connectivity Requirement • Considering only the coverage issue may produce disconnected subnetworks • Simple connectivity preservation • Evaluating whether Ni’s one-hop neighbors will remain connected through each other or through its two-hop neighbors when Ni is removed

18. Ni’s Sleeping Candidate Condition • : Responsible Sensing Region of Nj • : the two-hop confined region of Ni • : communication path between Nj and Nk

19. Optimistic Scan Region

20. ineligible / STATUS eligible / STATUS uncertain II eligible / STATUS Twait Twait uncertain I ineligible Tround Tround Sensibility-Based Sleeping Configuration Protocol (SSCP) ready-to-on ready-to- sleeping sleeping on

21. Performance Evaluation with ns-2 • Boolean sensing model • ESS: extended sponsored sector • Proposed by Tian et. al. of Univ. of Ottawa, 2002 • Consider only the nodes inside the RSR of the evaluated node • General sensing model • SscpP: SSCP with the pessimistic scan region • SscpO: SSCP with the optimistic scan region

22. Bridge between BSM and GSM • Ensured-sensibility radius

23. Default Parameters Setting • The deployed area is 50m x 50m •  = 1,  = 3,  = 0.001 (r = 10m) • R = 12 m • The number of deployed sensor: 120 • Power Consumption: • Tx (transmit) = 1.4W, Rx (receive) = 1W, Idle = 0.83W, Sleeping = 0.13W

24. Performance Evaluation (1) • Sleeping sensor vs. communication radius

25. Performance Evaluation (2) • Network topology

26. Performance Evaluation (3) • Sleeping sensor vs. sensor number

27. Performance Evaluation (4) • Sleeping sensor vs. sensibility threshold

28. Performance Evaluation (5) • Network lifetime vs. live sensor when the MTBF is 800s, R is 12m

29. Performance Evaluation (6) • -coverage accumulated time • The total time during which  or morepercentage of the deployed area satisfies the coverage requirement

30. Conclusions • Propose NSFS with the GSM • transform a global decision problem to a local one • exploit the cooperation between adjacent sensors • Develop SSCPs to build dependable wireless sensor networks

31. Q & A Thank You