Localization With Mobile Anchor Points in Wireless Sensor Networks

Localization With Mobile Anchor Points in Wireless Sensor NetworksAuthors: Kuo-Feng Ssu, Chia-Ho Ou, and Hewijin Christine Jiau

Presented by:

Md. Kayser Nizam, Md. Habibur Rahman, Md. Monzur MorshedCourse:Sensor Networks and Wireless ComputingInstructor:Md. Saidur Rahman

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Main Idea of this paperIn this paper, authors described a range-free localization scheme using mobile anchor points equipped with GPS moves in sensor field and broadcasts its current position periodically.

For range-free localization, no extra hardware or data communication is needed.

Experiment results showed that authors scheme performed better than other range-free mechanisms.

LocalizationWhat is localization?Determining where a given node is physically located in a wireless sensor network (WSN).

Why do we need to localize a node?Identify the location at which sensor reading originate.A sensor reading consists of In novel communication protocols that route to geographic areas instead of ID.

Localization is a problem in WSNsNodes randomly deployedLocation unknown

Localization (cont.)Localization is essentialNecessary for data correlation (e.g. target tracking)Many MAC, routing, and other protocols use nodes' locationsHelps in understanding the utility of a WSN from its coverage areaIncrease network lifetime

Scalability of localization protocol is importantLarge networks especially need localizationMany using anchor nodes are non-scalable

Localization (cont.)Problem FormulationDefining a coordinate systemCalculating the distance between sensor nodes

Defining a Coordinate SystemGlobal Aligned with some externally meaningful system (e.g., GPS)RelativeAn arbitrary rigid transformation (rotation, reflection, translation) away from the global coordinate system

Localization (cont.)In general, almost all the sensor network localization algorithms share three main phases

DISTANCE ESTIMATION

POSITION COMPUTATION

LOCALIZATION ALGHORITHM

Distance EstimationANGLE OF ARRIVAL (AOA) method allows each sensor to evaluate the relative angles between received radio signals

TIME OF ARRIVAL (TOA) method tries to estimate distances between two nodes using time based measures

TIME DIFFERENT OF ARRIVAL (TDOA) is a method for determining the distance between a mobile station and nearby synchronized base station

THE RECEIVED SIGNAL STRENGTH INDICATOR (RSSI) techniques are used to translate signal strength into distance.

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Position ComputationThe common methods for position computation techniques are:

LATERATION techniques based on the precise measurements to three non collinear anchors. Lateration with more than three anchors called multi-lateration.

ANGULATION or triangulation is based on information about angles instead of distance.

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Classifications of Localization MethodsWireless Sensor Network localization algorithms into several categories such as:

Centralized vs DistributedAnchor-free vs Anchor-basedRange-free vs Range-basedMobile vs Stationary

Centralized vs DistributedCentralizedAll computation is done in a central server

DistributedComputation is distributed among the nodes

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Anchor-Free vs Anchor-BasedAnchor Nodes:Nodes that know their coordinates a priori By use of GPS or manual placementFor 2D three and 3D four anchor nodes are needed

Anchor-freeRelative coordinates

Anchor-basedUse anchor nodes to calculate global coordinates

Range-Free vs Range-BasedRange-FreeFor achieving coarse grained accuracy3 methods of distance estimationCentroidDV-hopGeometry conjecture

Range-BasedFor fine grained accuracyTOATDOARSSI AOA

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Generic Approach Using Anchor NodesDetermine the distances between regular nodes and anchor nodes. (Communication)

Derive the position of each node from its anchor distances. (Computation)

Iteratively refine node positions using range information and positions of neighboring nodes. (Communication & Computation)

Phase 1: Centroid

Anchors

Ref: Nirupama Bulusu, John Heidemann and Deborah Estrin. Density Adaptive Beacon Placement, Proceedings of the 21st IEEE ICDCS, 2001

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Phase 1: DV-hopC

AB

3 hopsavg hop: 5

System Environment

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Localization Scheme

Beacon Point Selection

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Location Calculation

Beacon Scheduling

Chord SelectionLocalization will be accurate if the selected beacon points are exact on the communication circleIncorrect beacon points could be chosen due to collision or inappropriate beacon intervals.Chords generated using the beacon points thus fails to estimate the position of the sensorWhen length of the chord is too short, probability of unsuccessful localization will increase rapidlyA threshold for the length of a chord is used to solve the problemThe length of a chord must surpass the threshold for reducing the localization error

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Obstacle Tolerance

Obstacle Tolerance (cont.)

Simulation Environment

Three metrics used to evaluate the performance of proposed localization mechanism

Average location errorAverage execution timeBeacon overhead

Performance Metrics

Simulation Parameters

Performance

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ConclusionIn this paper, authors found that ..

Range-free localization mechanism without using distance or angle information was also able to achieve fine-grained accuracy.

The sensor nodes can calculate their positions without additional interactions based on the localization information from mobile anchors and the principles of elementary geometry.

All computation is performed locally, and beacon overhead only occurs on mobile anchors so the mechanism is distributed, scalable, effective, and power efficient.

Execution time for localization mechanism can be shortened if the moving speed, the radio range, or the number of mobile anchor points in increased.

Thank you

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