Speaker : Lee Heon-Jong 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

Contents Introduction Coverage and connectivity Experimentation 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

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

Introduction Sensing coverage Connectivity 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

Introduction Past’s approach New idea of this paper 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

Problems Terminology Formulation of problem 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 p v Rs q |pv| Advanced Ubiquitous Computing

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

System life time System coverage life time System communication life time Advanced Ubiquitous Computing

Conclusion Coverage efficiency Coverage configuration 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