Computer Network Lab. Integrated Coverage and Connectivity Configuration in Wireless Sensor Networks SenSys ’ 03 Xiaorui Wang, Guoliang Xing, Yuanfang Zhang, Chenyang Lu, Robert Pless, Christopher Univ.

Computer Network Lab. 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

Computer Network Lab. Introduction(1)  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

Computer Network Lab. Introduction(2)  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 larger number  greater connectivity  Redundant potential connectivity for fault tolerance  Greater connectivity for communication bottleneck

Computer Network Lab. Introduction(3)  Past’s approach  Separate approaches for each  New idea of this paper  Analytic guarantee for Sensing coverage with effective connectivity  Dynamically configured degree of coverage

Computer Network Lab. Problems  Terminology  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

Computer Network Lab. Relationship between connectivity and coverage  Depends on the ratio of the communication range to the sensing range  Not guarantee each other  But can be handled by a configuration protocol if  Rc (Communication range) >= 2Rs (sensing range)

Computer Network Lab.  Sufficient condition for 1-coverage to imply connectivity  (Theorem 1) A region is sensor covered, the sensors covering that region are connected if Rc >= 2Rs  Sufficient condition for 1 covered network to guarantee one- connectivity Relationship between connectivity and coverage (2) uv x y Rs 2Rs <= Not covered place

Computer Network Lab. Relationship between connectivity and coverage (3)  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 * Removing Ks nodes disconnects a covered network

Computer Network Lab. Relationship between connectivity and coverage (4)  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 * Disconnected network

Computer Network Lab. Relationship between connectivity and coverage (5)  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

Computer Network Lab. Relationship between connectivity and coverage (6) Second  the void merge with boundary  Conclusion  Boundary connectivity (for nodes located within Rs distance to the boundary of the coverage region)  Ks  the interior connectivity  2Ks

Computer Network Lab. 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

Computer Network Lab. Coverage and connectivity configuration when Rc >= 2Rs(1)  Ks-coverage Eligibility Algorithm  For Determination to become active  Example of Ks-eligibility

Computer Network Lab. Coverage and connectivity configuration when Rc >= 2Rs(2)  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

Computer Network Lab. Coverage and connectivity configuration when Rc >= 2Rs(3)  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

Computer Network Lab. Coverage and connectivity configuration when Rc >= 2Rs(4)  Ks coverage eligibility algorithm /*intersection point*/ cf) SN(v) : active node within 2Rs range from v

Computer Network Lab. Ks coverage eligibility algorithm  Complexity (O(n^3))  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  Hidden node discovery  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

Computer Network Lab. State transition of CCP Listen Sleep Active Periodically change 1. Ineligible 2. Listen timer expiration Eligible & join timer expiration Ineligible & Withdraw timer Expiration Eligible

Computer Network Lab. 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

Computer Network Lab. Experimentation  On Coverage Simulator (CS)  Coverage configuration - Ottawa protocol vs. CCP  Efficiency of CCP  The configurability of CCP  Coverage and communication performance  System life time

Computer Network Lab. Efficiency of CCP  Average coverage degree (Ks =1)

Computer Network Lab. Efficiency of CCP  Distribution of coverage degree  Comparison of active node number  CCP eligibility rule can preserve coverage with fewer active nodes

Computer Network Lab. The Configurability of CCP  Coverage degree vs. required coverage degree Irrespective of # of nodes Average/min decrease as required degree increase

Computer Network Lab. Coverage and communication performance  Simulation Environment  NS-2 with CMU wireless extensions  MAC layer with power saving support  400*400m 2 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

Computer Network Lab. Coverage and communication performance  SPAN  CCP  SPAN-CCP-2Hop  Network topology and coverage in a Typical run (Rc/Rs = 1.5) Medium size dots : sink and source at opposite sides Large size dots : active nodes

Computer Network Lab. Coverage and communication performance  Coverage degree vs. Rc/Rs  Packet delivery ratio vs. Rc/Rs Connectivity cannot guarantee coverage

Computer Network Lab. Coverage and communication performance  Number of active nodes vs. Rc/Rs

Computer Network Lab. 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%)

Computer Network Lab. System life time  System coverage life time  System communication life time

Computer Network Lab. 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 node 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