Cluster Tree Based Self Organization of Virtual Sensor Networks

Dilum Bandara1, Anura Jayasumana1, and Tissa Illangasekare2

1Department of Electrical and Computer Engineering, Colorado State University, CO 80523, USA.

2Division of Environmental Science and Engineering, Colorado School of Mines, Golden, CO 80401, USA.

dilumb@engr.colostate.edu

Supported in part by a grant from Army Research Office (ARO)

Outline Virtual Sensor Networks (VSNs) VSN formation Performance analysis Summary & future work

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Dedicated Wireless Sensor Networks Sense the physical world

at a far greater temporal and spatial granularity

Nodes are limited in sensing, processing, and communication capabilities

Severe power constraints Cost Homogeneous nodes

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Virtual Sensor Networks (VSNs)

Formed by a subset of nodes dedicated to a certain task/application

Other nodes provide support to create, maintain, and operate Multiple VSNs on a single WSN Heterogeneous

Jayasumana, Han, & Illangasekare, “Virtual

Sensor Networks,” 2007

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S

- VSN1 nodes - VSN2 nodes - Other nodes

Broadcast path from VSN1 member S to other VSN1 members

Example 1: Geographically overlapped applications

Heterogeneous nodes

Relay each others data

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Example 2: Multi-functional sensor networks

One physical sensor network for different functions Each node equipped

with multiple sensors SmartKG iBadge

platform Multiple applications

Smart neighborhood systems

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Example 3: Dedicated applications Some dedicated applications can benefit from the VSN

concept as well May involve dynamically varying subset of sensors & users

Jayasumana & Illangasekare, 2005

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Virtual Sensor Networks (VSNs)

Better resource efficiency through collaboration and resource sharing

Supports collaborative, resource efficient, and multipurpose WSNs We are proposing a cluster tree based approach for VSN formation

Jayasumana, Han, & Illangasekare, “Virtual

Sensor Networks,” 2007

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S

- VSN1 nodes - VSN2 nodes - Other nodes

Broadcast path from VSN1 member S to other VSN1 members

VSN support functions

Additional functions are required to handle splitting and merging phenomenons

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Function Usage

Form_Discover_VSN(msg) Nodes that detect a relevant event for the first time

Unsubscribe_VSN(msg) Unsubscribe if no longer need to be in a VSN

Unicast_VSN(destination, type, data)Muticast_VSN(type, data)Broadcast_VSN(data)

VSN communication

VSN message delivery Alternative strategies for node-to-sink and node-to-node

communication Random routing

Rumor routing – Braginsky and Estrin, (2002) Ant routing – Hussein and Saadawi (2003)

Geographic routing Hierarchical routing

Need some sort of an addressing scheme Imposing some structure within network is more attractive

E.g., Cluster tree – IEEE 802.15.4, GTC GTC – Generic Top-down Clustering algorithm

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Cluster tree formation with Generic Top-down Clustering (GTC) algorithm

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Bandara & Jayasumana, 2007

Hierarchical addressing scheme is developed to facilitate in-network communication

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Cluster tree based self-organization of VSNs

Cluster heads in VSNCluster heads that facilitate VSN

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Self-organization of VSNs (cont.)

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Virtual tree belong to plume 2

Cluster heads belong to plume 1Cluster heads belong to plume 2

Virtual tree belong to plume 1

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Simulator Discrete event simulator was developed using C 5000 nodes in a circular region with a radius of 500m 500 nodes detect the phenomenon in all the regions

(0, 0) (200, 0)

(200, 200)(0, 200)

Region 1

(0, 70)

(80, 70)

(0, 190) (80, 190)

(120, 200)

(120, 150) (200, 150)

Region 3

Region 2

(20, 150)(20, 180)

(80, 180)(80, 150)

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Performance analysis – Self-organization of VSNs

(a) Scenario 1, (b) Scenario 2PT= -12dBm

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Performance analysis – VSN formation overhead

Number of event nodes added over the time

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600

800Scenario 1Scenario 2Scenario 3

No hopsper agent

Probability of successful delivery

350 0.51

600 0.84

1000 0.91

Scenario 2 - 896 hops are required if CH-to-CH communication is multi-hop

Scenario 2 - Cost of discovering two VSN members with Rumor routing

Cluster tree based VSN formation guarantees that all VSN members identify each other

Lower overhead16WMSN 2008

Summary & future work Cluster tree based VSN formation scheme

Efficient Reliable Addressing scheme

Future work VSN management functions to detect multiple VSNs Merging 2 VSNs together Splitting a VSN into 2 VSNs

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Questions ?

Thank You…

Generic Top-Down Cluster & cluster tree formation (GTC) algorithm

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GTC - Cluster tree formation Cluster tree is formed by keeping track of parent & child relationships

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GTC algorithm (cont.) SHC – Simple Hierarchical Clustering HHC – Hop-ahead Hierarchical Clustering

SHC clustershopsmax = TTLmax = 1

Similar to IEEE 802.15.4 cluster tree

HHC clustersTTLmax = 2×hopsmax + 1

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HHC 5000 nodes Grid - 201×201 Grid spacing – 5m R = -20dBm Root node in the middle

Clusters

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Cluster tree

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Transmission power (dBm)-20 -18 -16 -14 -12 -10

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Performance analysis

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HHC Uniform clusters Better circularity Lower number of clusters Lower depth Message complexity O(n)

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Hierarchical addressing

Single point of failure at root node

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Cross-links based routing

Routing through cross links Reduce burden on the root node

Use hierarchical addresses

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Send message from U to K Hierarchical routing - 5 hops Cross links - 5 hops Circular path - 4 hops

Circular path based routing

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Circular path Connects clusters at the

same depth Reduce workload on root

node Use hierarchical addresses

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VSN formation algorithmHandle_VSN_Message(msg)

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//Initially n = 0, m = 0IF msg.source my.cluster_membersIF(msg.type my_data.VSNs)

my_data.VSNs(n) msg.typen n + 1Forward_To_Parent_CH(msg,

my.parent_CH)my_data.VSN_table(m) (msg.source,

msg.type)m m + 1

ELSEIF(msg.type my_data.VSN_table)

Forward_To_Parent_CH(msg, my_data.parent_CH)

my_data.VSN_table(m) (child_CH, msg.type)

m m + 1

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Already know phenomenon ?

Add sender’s branch ID to VSN table

Yes

Root node ?

No

Drop message

New event

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Send to parent CH

Yes

Routing schemeTree Only Tree + Cross-links Tree + Circular link

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Performance analysis – Number of messages

Cross-link and circular path base routing increase network capacity

Transmission power (dBm)-20 -18 -16 -14 -12 -10

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