A Novel Virtual Anchor Node-based Localization Algorithm for Wireless Sensor Networks

Pengxi Liu, Xinming Zhang, Shuang Tian, Zhiwei Zhao, Peng SunDepartment of Computer Science and TechnologyUniversity of Science and Technology of China

International Conference on Networking 2007

Outline Introduction Error analysis of typical localization

algorithms Virtual Anchor Node-based Localization

Algorithm (VANLA) Performance evaluation Conclusion

Introduction WSNs usually are arranged at special scout region, and sense special physics information in the region.

Sensor nodes are often deployed by random bestrewing. The application of WSNs is often related to the positions of nodes. So the localization of sensor nodes has become a hot topic in WSNs.

Introduction Most of the existent researches suppose

The network includes a small number of anchor nodes. The existence of various errors

The location precision will be restricted Some nodes even cannot be located.

The improvement of localization precision with lower cost less energy consumption less hardware support

Introduction The new algorithm finds out virtual anchors

to provide highly precise positions for unknowns nodes to assist in locating the rest unknowns along with primary real anchors.

Error analysis of typical localization algorithms The authors choose two concrete algorithms to

carry out error analysis. Euclidean

Range-Based

DV-hop Range-Free

Error analysis of typical localization algorithms - Euclidean

Each sensor has ability to measure their relative distance.

A

B

C

L1

D

α β

L3

L2

Error analysis of typical localization algorithms - Euclidean

The draw back of Euclidean The ranging error is the main flaw of Range-based algorithm. This error can be accumulated hop by hop.

Error analysis of typical localization algorithms – DV-hop

DV-hop Use the corrected factor ci to fixed the hop distance.

A

B

C

X

cA

Error analysis of typical localization algorithms – DV-hop

The draw back of DV-hop In practical application, the communication range of each node is not a standard circle ideally.

Error analysis of typical localization algorithms – DV-hop

A BC

n-hop n-hop

n*r n*r/2

The corrected factor is (3n*r/2*2n)=3r/4

Distance AC is n* 3r/4 =3n*r/4

The error is n*r-(3n*r/4)=n*r/4

This error can be accumulated hop by hop.

Virtual anchor node-based localization algorithm There can be only a few anchor nodes deployed in the network due to high cost and energy issue Virtual anchor node-based localization algorithm

The Selection of Virtual Anchor Node The Upgrade of Virtual Anchor Node

Virtual anchor node-based localization algorithm Assumption

The WSN is a dense network There are few anchor node in the

network The shape of the path with the

smallest hop count is asymptotic to a beeline

Virtual anchor node-based localization algorithm Scenario

AC

B

D

UE

y

Virtual anchor node-based localization algorithm The Selection of Virtual Anchor Node

A

B

C

HopA=1x

Compare Hop with “HopA=nA”

If the hop has not received or is smaller than present hop Store HopA=nA

HopA=nAHopB=nBHopC=nC

HopA=nAHopB=0HopC=nC

D

Virtual anchor node-based localization algorithm The Selection of Virtual Anchor Node

A

B

C

HopA=nAHopB=0HopC=nCHopD=nd

y

HopA=AyHopB=ByHopC=CyHopD=DyIF Ay+By=nAcandidate virtual anchor

D

Virtual anchor node-based localization algorithm

AB

If Max(hopA , hopB) – Min(hopA , hopB)= shortest pathAB, it is also an candidate anchor

y

HopA=nAHopB=nBnAB nB

nA= nAB+nBnA- nB =nAB

Virtual anchor node-based localization algorithm The Selection of Virtual Anchor

Node

A

B

C

D

Virtual anchor node-based localization algorithm The Upgrade of Virtual Anchor Node

A

B

C

D

UE

Virtual anchor node-based localization algorithm

AC

B

D

UE

Node UE can upgrade as a anchor node

Virtual anchor node-based localization algorithm Node UE can upgrade as a anchor

node

W

Y

X

ZUH

UF

UG

Virtual anchor node-based localization algorithm

AC

B

D

UE

Calculate UE’s position(Xb,Yb)

(Xa,Ya)

(Xd,Yd)

(Xc,Yc)(Xe,Ye)

Virtual anchor node-based localization algorithm

AC

B

D

UE

Calculate UE’s position

F

G

Performance evaluation Compiler: oCaml Language: caml OS: Cygwin

Performance evaluation Random deployment Field:32000m x 32000m Radius: 2200m 500nodes Ranging error 20%~50%

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation Random deployment Field:10000m x 10000m Radius: 2100m 500nodes

Performance evaluation

Conclusion In this paper, the authors proposed

a distributed algorithm for virtual anchor nodes upgrading it can increase the density of virtual

anchor nodes at low physical cost assist some algorithms which already

exist to enhance the precision of localization in

the network with dense nodes