Computer Network Lab.

Integrated Coverage and Connectivity Configuration Integrated Coverage and Connectivity Configuration in Wireless Sensor in Wireless Sensor NetworksNetworks

SenSys’03

Xiaorui Wang, Guoliang Xing, Yuanfang Zhang, Chenyang Lu, Robert Pless, Christopher Gill

@Washington Univ.

Computer Network Lab.

ContentsContents

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)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)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)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.

ProblemsProblems

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 Relationship between connectivity and coveragecoverage

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 coverin

g that region are connected if• Rc >= 2Rs

Sufficient condition for 1 covered network to guarantee one-connectivity

Relationship between connectivity and Relationship between connectivity and coverage (2)coverage (2)

u v

x

y

Rs

2Rs <=

Not covered place

Computer Network Lab.

Relationship between connectivity and Relationship between connectivity and coverage (3)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 t

o 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 Relationship between connectivity and coverage (4)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 Relationship between connectivity and coverage (5)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 reg

ion A, the interior connectivity is 2Ks if Rc >= 2Rs Two cases of disconnected situation of interior communicati

on

• First case

the void does not

merge with boundary

Computer Network Lab.

Relationship between connectivity and Relationship between connectivity and coverage (6)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 Coverage and connectivity configuration when Rc >= 2Rswhen 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 Coverage and connectivity configuration when Rc >= 2Rs(1)when Rc >= 2Rs(1)

Ks-coverage Eligibility Algorithm For Determination to become active Example of Ks-eligibility

Computer Network Lab.

Coverage and connectivity configuration Coverage and connectivity configuration when Rc >= 2Rs(2)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 Coverage and connectivity configuration when Rc >= 2Rs(3)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 Coverage and connectivity configuration when Rc >= 2Rs(4)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 algorithmKs coverage eligibility algorithm

Complexity (O(n^3)) Locations of all sensing neighbors required table of known sensing neighbors based on beacon from its co

mmunication 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 node

s maintained by CCP

Computer Network Lab.

State transition of CCPState 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 Coverage and connectivity configuration when Rc < 2Rswhen 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.

ExperimentationExperimentation

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 CCPEfficiency of CCP

Average coverage degree (Ks =1)

Computer Network Lab.

Efficiency of CCPEfficiency 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 CCPThe 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 Coverage and communication performance 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 de

stination 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 Coverage and communication performanceperformance

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 Coverage and communication performanceperformance

Coverage degree vs. Rc/Rs Packet delivery ratio vs. Rc/Rs

Connectivity cannot guarantee coverage

Computer Network Lab.

Coverage and communication Coverage and communication performanceperformance

Number of active nodes vs. Rc/Rs

Computer Network Lab.

System life timeSystem 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 timeSystem life time

System coverage life time System communication life time

Computer Network Lab.

ConclusionConclusion

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 co

verage