cluster tree based self organization of virtual sensor...

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.

[email protected]

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

Outline

Virtual Sensor Networks (VSNs)

VSN formation

Performance analysis

Summary & future work

2WMSN 2008

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

3WMSN 2008


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

4WMSN 2008

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

5WMSN 2008

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

6WMSN 2008

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

7WMSN 2008


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

8WMSN 2008

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

9WMSN 2008

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

10WMSN 2008

Cluster tree formation with Generic

Top-down Clustering (GTC) algorithm

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DCB F GE

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11WMSN 2008

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 VSN

Cluster heads that facilitate VSN

12WMSN 2008

Self-organization of VSNs (cont.)

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Virtual tree belong to plume 2

Cluster heads belong to plume 1

Cluster heads belong to plume 2

Virtual tree belong to plume 1

13WMSN 2008

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)

14WMSN 2008

Performance analysis –

Self-organization of VSNs

(a) Scenario 1, (b) Scenario 2

PT= -12dBm

15WMSN 2008


VSN formation overhead

Number of event nodes added over the time

0 100 200 300 400 500

To

tal num

ber

of

hops

0

200

400

600

800

Scenario 1

Scenario 2

Scenario 3

No hops

per 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 overhead

16WMSN 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

17WMSN 2008

Questions ?

Thank You…

Generic Top-Down Cluster & cluster

tree formation (GTC) algorithm

C1

19

C2

C4

C3

WMSN 2008

GTC - Cluster tree formation

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

C1

C2

C4

C3

C1

C4C3C2

C10C8C7C6C5C9

20WMSN 2008

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

1

CID 1

5

7

4

3

2

9

8

10

6

CID 2

CID 3

CID 4

CID 5

CID 7

CID 6CID 9

CID 8

CID 10

CID 1

CID 7

CID 2

CID 4CID 6

CID 5

CID 3

1

4

3

2

98

76

5

CID 9

CID 10

CID 8

12

11

10

21WMSN 2008

HHC

5000 nodes

Grid - 201×201

Grid spacing – 5m

R = -20dBm

Root node in the middle

Clusters

22WMSN 2008

Cluster tree

23WMSN 2008

Transmission power (dBm)

-20 -18 -16 -14 -12 -10

Nu

mb

er

of

clu

ste

rs

0

300

600

900

1200

1500

1800

2100

SHC

HHC

RHHC

Hexagonal

Performance analysis

24


-20 -18 -16 -14 -12 -10

Cir

cu

larity

0

10

20

30

40

50

60

70

80

90

SHC

HHC

RHHC

Hexagonal

Depth

0 2 4 6 8 10 12 14 16N

um

be

r of

clu

ste

r h

ea

ds

0

20

40

60

80

100

120

140

160

SHC

HHC

RHHC

Hexagonal

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

WMSN 2008

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Hierarchical addressing

Single point of failure at root node

A(0)

D(20)C(10)B(00) F(40) G(50)E(30)

I

(100)

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(000)

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(110)

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(210)

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(010)

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(020)

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(030)

O

(050)

Q

(0100)

P

(0210)

25

25WMSN 2008

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Cross-links based routing

Routing through cross links

Reduce burden on the root node

Use hierarchical addresses

A(0)

D(20)C(10)B(00) F(40) G(50)E(30)

I

(100)

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(000)

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(210)

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(010)

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(020)

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(030)

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(050)

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(0100)

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(0210)

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26WMSN 2008

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

WMSN 2008

VSN formation algorithmHandle_VSN_Message(msg)

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12

//Initially n = 0, m = 0

IF msg.source my.cluster_members

IF(msg.type my_data.VSNs)

my_data.VSNs(n) msg.type

n n + 1

Forward_To_Parent_CH(msg, my.parent_CH)

my_data.VSN_table(m) (msg.source,

msg.type)

m m + 1

ELSE

IF(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

28WMSN 2008

Already know

phenomenon ?

Add sender’s branch

ID to VSN table

Yes

Root node ?

No

Drop message

New event

No

Send to parent CH

Yes

Routing scheme

Tree Only Tree + Cross-links Tree + Circular link

Num

ber

of

messages

10000

15000

20000

25000

30000

35000

40000

45000

50000

Scenario 1

Scenario 2

Scenario 3


-20 -18 -16 -14 -12 -10

Num

ber

of

messages

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Scenario 1

Scenario 2

Scenario 3


Number of messages

Cross-link and circular path base routing increase network capacity


-20 -18 -16 -14 -12 -10

Num

ber

of

mu

ltic

ast

me

ssa

ge

s

0

500

1000

1500

2000

2500

3000

3500

Scenario 1

Scenario 2

Scenario 3

29WMSN 2008

cluster tree based self organization of virtual sensor...

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