Integrated Coverage and Connectivity Configuration in Wireless Sensor Networks

1. Integrated Coverage and Connectivity Configuration in Wireless Sensor Networks Xiaorui Wang, Guoliang Xing, Yuanfang Zhang, Chenyang Lu, Robert Pless, Christopher Gill Speaker : Lee Heon-Jong Advanced Ubiquitous Computing

2. Contents • Introduction • Coverage and connectivity • Relationship between connectivity and coverage • Coverage and connectivity configuration • Rc >= 2Rs • Rc < 2Rs • Experimentation • Coverage configuration • Coverage and communication performance • System Life time • Conclusion Advanced Ubiquitous Computing

3. Introduction • Sensor network constraint : Energy • Power saving mode • Active and sleep scheduling • General goal • Minimize the number of active nodes • Guarantee QoS • Sensing coverage, network connectivity Advanced Ubiquitous Computing

4. Introduction • Sensing coverage • Monitoring quality • Different degree required by application • Coverage requirement change • Related with the number of faults to be tolerated • Connectivity • Minimum number of node to be removed to partition the graph into more than one connected component • larger number  greater connectivity • Redundant potential connectivity for fault tolerance • Greater connectivity for communication bottleneck Advanced Ubiquitous Computing

5. Introduction • Past’s approach • Separate approaches for each • Provided a fixed degree of coverage • New idea of this paper • Analytic guarantee for Sensing coverage with effective connectivity • Dynamically configured degree of coverage Advanced Ubiquitous Computing

6. Problems • Terminology • Rs, C(v), Rc • Convex region A of a coverage degree of K • every location inside A is covered by at least K nodes • Formulation of problem • Given a coverage region A, and sensor coverage degree Ks • Maximizing the number of nodes that are scheduled to sleep • Under constraints • A is at least Ks-covered • All active nodes are connected |pv| Rs v p q Advanced Ubiquitous Computing

7. Relationship between coverage and connectivity • Depends on the ratio of the communication range to the sensing range • Not guarantee each other • Coverage : whether any location is uncovered • Connectivity : all location of active nodes are connected • But can be handled by a configuration protocol if • Rc (Communication range) >= 2Rs (sensing range) Advanced Ubiquitous Computing

8. Relationship between coverage and connectivity • Sufficient condition for 1-coverage to imply connectivity • (Theorem 1) A region is sensor covered(at least 1-covered), the sensors covering region are connected if • Rc >= 2Rs • Sufficient condition for 1 covered network to guarantee one-connectivity Advanced Ubiquitous Computing

9. Relationship between coverage and connectivity • Relationship between the degree of coverage and connectivity • Boundary connectivity is Ks • (Lemma 1) for a Ks-covered convex region A, it is possible to disconnect a boundary node from the rest of the nodes in the communication graph by removing Ks sensors if Rc >= 2Rs Advanced Ubiquitous Computing

10. Relationship between coverage and connectivity • Relationship between the degree of coverage and connectivity (cont’d) • Tight lower bound on connectivity of communication graph is Ks • (Theorem 2) A set of nodes that Ks-cover a convex region A forms a Ks connected communication graph if Rc >= 2Rs • A disconnected network Advanced Ubiquitous Computing

11. Relationship between coverage and connectivity • Relationship between the degree of coverage and connectivity (cont’d) • Tight lower bound of Interior connectivity is 2Ks • (Theorem 3) For a set of sensors that Ks-cover a convex region A, the interior connectivity is 2Ks if Rc >= 2Rs • Two cases of disconnected situation of interior communication • First case : • the void does not • merge with boundary • prove one must remove at least 2Ks+1 sensors

12. Relationship between coverage and connectivity • Conclusion • Boundary connectivity (for nodes located within Rs distance to the boundary of the coverage region)  Ks • the interior connectivity  2Ks Second case : the void merge with boundary Advanced Ubiquitous Computing

13. Coverage and connectivity configuration when Rc >= 2Rs • CCP • Configuration protocol based on theorem 1, 2, 3 • Can configure network to the specific coverage degree requested by the application • Decentralized protocol that only depends on local states of sensing neighbors • Scalability enforcement • Applications can change its coverage degree at runtime without high communication overhead • Guarantee degrees of coverage at the same time connectivity Advanced Ubiquitous Computing

14. Coverage and connectivity configuration when Rc >= 2Rs • Ks-coverage Eligibility Algorithm • For Determination to become active • Example of Ks-eligibility Ineligible for Ks = 1 Eligible for Ks > 1 Advanced Ubiquitous Computing

15. Coverage and connectivity configuration when Rc >= 2Rs • Ks-coverage Eligibility Algorithm • (Theorem 4) A convex region A is Ks-covered by a set of sensors S if • Intersection points between sensors or between sensors and A’s boundary exist in a region A • All intersection points between any sensors are at least Ks-covered • All intersection points between any sensor and A’s boundary are at least Ks-covered Advanced Ubiquitous Computing

16. Coverage and connectivity configuration when Rc >= 2Rs • Coverage patch S (same coverage area) • (conclusion of theorem 4) Region A is Ks covered • Coverage degree of a region  coverage degree of all the intersection points in the same region Advanced Ubiquitous Computing

17. Ks-coverage eligibility algorithm • Ks coverage eligibility algorithm /*intersection point*/ • SN(v) : all the active node within 2Rs range from v Advanced Ubiquitous Computing

18. Ks-coverage eligibility algorithm • Complexity : O(N3) • Locations of all sensing neighbors required • table of known sensing neighbors based on beacon from its communication neighbors • Beacon message (HELLO) • Rc >= 2Rs • Its own location is included • Rc < 2Rs • Hidden node happens • Aware of its multi-hop neighbors(two approaches) • Broadcast HELLO with TTL • All known neighbor information in HELLO  CCP case • Trade off between beacon overhead and the number of active nodes maintained by CCP Advanced Ubiquitous Computing

19. State transition of CCP - Beacon is received- State evaluating Listen Sleep timer expiration (Periodically change) 1. Eligible & join timer expiration2. broadcast JOIN beacon 1. Ineligible 2. Listen timer expiration Eligible • Beacon is received & update table- State evaluating Active Sleep Ineligible & Withdraw timer Expiration Advanced Ubiquitous Computing

20. Coverage and connectivity configuration when Rc < 2Rs • Does not guarantee connectivity by CCP • Integration of CCP with SPAN • SPAN • Decentralized coordination protocol for energy consumption while maintaining a communication backbone composed by active nodes • CCP eligibility rule guarantee the coverage, and for connectivity, SPAN eligibility rule is adapted Advanced Ubiquitous Computing

21. Experimentation • Coverage configuration - Ottawa protocol vs. CCP • Efficiency of CCP • The configurability of CCP • Coverage and communication performance • System life time Advanced Ubiquitous Computing

22. Efficiency of CCP • Average coverage degree (Ks =1) Advanced Ubiquitous Computing

23. Efficiency of CCP • Distribution of coverage degree • Comparison of active node number  CCP eligibility rule can preserve coverage with fewer active nodes Advanced Ubiquitous Computing

24. The Configurability of CCP • Coverage degree vs. required coverage degree Average/min decrease as required degree increase Be in Proportional ratio Advanced Ubiquitous Computing

25. Coverage and communication performance • Simulation Environment • NS-2 with CMU wireless extensions • 802.11 MAC layer with power saving support • 400*400m2 coverage region with 160 nodes randomly distributed • 10 sources and 10 sinks in opposite sides of the region with CBR flow to destination node (128byte packets with 3Kbps) • 2Mbps bandwidth and a sensing range of 50m • TwoRayGround radio propagation model • Requested coverage degree Ks = 1 • Comparison protocols • SPAN • CCP • SPAN+CCP • CCP-2Hop • SPAN+CCP-2Hop Advanced Ubiquitous Computing

26. Coverage and communication performance • Network topology and coverage in a Typical run (Rc/Rs = 1.5) • SPAN • CCP • SPAN-CCP-2Hop Small size dots : inactive nodes Medium size dots : sink and source at opposite sides Large size dots : active nodes Advanced Ubiquitous Computing

27. Coverage and communication performance • Coverage degree vs. Rc/Rs • Packet delivery ratio vs. Rc/Rs Advanced Ubiquitous Computing

28. Coverage and communication performance • Number of active nodes vs. Rc/Rs Advanced Ubiquitous Computing

29. System life time • Lifetime goes up if many factors can be controlled • SPAN + CCP • Coverage lifetime, communication lifetime • Until ratio’s dropping below the threshold (90%) Advanced Ubiquitous Computing

30. System life time • System coverage life time • System communication life time Advanced Ubiquitous Computing

31. Conclusion • Coverage efficiency • One coverage with smaller number of active nodes than OTTAWA • Irrespective of node density • Coverage configuration • Effectively enforcement of different coverage degrees • Active nodes remain proportional to requested coverage degree • Integrated coverage and connectivity configuration • Rc>=2Rs • Good performance with CCP • Rc<2Rs • SPAN + CCP-2Hop : most effective protocol for communication and coverage Advanced Ubiquitous Computing