Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy.

Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our Privacy Policy and User Agreement for details.

Like this presentation? Why not share!

- Localization in WSN by Yara Ali 2730 views
- A Survey on Localization of Wireles... by Karthik Mohan 372 views
- Wireless sensor networks localizati... by IJCNCJournal 2969 views
- Location In Wsn by netfet 3787 views
- Node localization by ad-hocnet 161 views
- Localization of WSN using a single ... by haroonrashidlone 63 views

2,417 views

2,096 views

2,096 views

Published on

No Downloads

Total views

2,417

On SlideShare

0

From Embeds

0

Number of Embeds

0

Shares

0

Downloads

135

Comments

0

Likes

2

No embeds

No notes for slide

- 1. Localization With Mobile AnchorLocalization With Mobile Anchor Points in Wireless Sensor NetworksPoints in Wireless Sensor Networks Authors: Kuo-Feng Ssu, Chia-Ho Ou, and Hewijin Christine Jiau Presented by: Md. Kayser Nizam, Md. Habibur Rahman, Md. Monzur Morshed Course: Sensor Networks and Wireless Computing Instructor: Md. Saidur Rahman
- 2. Main Idea of this paperMain Idea of this paper In 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.
- 3. LocalizationLocalization What 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 <time, location, measurement> • In novel communication protocols that route to geographic areas instead of ID. Localization is a problem in WSNs • Nodes randomly deployed • Location unknown
- 4. Localization (cont.)Localization (cont.) Localization is essential • Necessary for data correlation (e.g. target tracking) • Many MAC, routing, and other protocols use nodes' locations • Helps in understanding the utility of a WSN from its coverage area • Increase network lifetime Scalability of localization protocol is important • Large networks especially need localization • Many using anchor nodes are non-scalable
- 5. Localization (cont.)Localization (cont.) Problem Formulation • Defining a coordinate system • Calculating the distance between sensor nodes Defining a Coordinate System • Global • Aligned with some externally meaningful system (e.g., GPS) • Relative • An arbitrary rigid transformation (rotation, reflection, translation) away from the global coordinate system
- 6. Localization (cont.)Localization (cont.) In general, almost all the sensor network localization algorithms share three main phases DISTANCE ESTIMATION POSITION COMPUTATION LOCALIZATION ALGHORITHM
- 7. Distance EstimationDistance Estimation ANGLE 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.
- 8. Position ComputationPosition Computation The 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.
- 9. Classifications of LocalizationClassifications of Localization MethodsMethods Wireless Sensor Network localization algorithms into several categories such as: Centralized vs Distributed Anchor-free vs Anchor-based Range-free vs Range-based Mobile vs Stationary
- 10. Centralized vs DistributedCentralized vs Distributed Centralized • All computation is done in a central server Distributed • Computation is distributed among the nodes
- 11. Anchor-Free vs Anchor-BasedAnchor-Free vs Anchor-Based Anchor Nodes: • Nodes that know their coordinates a priori • By use of GPS or manual placement • For 2D three and 3D four anchor nodes are needed Anchor-free • Relative coordinates Anchor-based • Use anchor nodes to calculate global coordinates
- 12. Range-Free vs Range-BasedRange-Free vs Range-Based Range-Free • For achieving coarse grained accuracy • 3 methods of distance estimation • Centroid • DV-hop • Geometry conjecture Range-Based • For fine grained accuracy • TOA • TDOA • RSSI • AOA
- 13. Generic Approach Using AnchorGeneric Approach Using Anchor NodesNodes Determine 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)
- 14. Phase 1: CentroidPhase 1: Centroid Idea: Do not use any ranging at all, simply deploy enough beacons Anchors periodically broadcast their location Localization: Listen for beacons Average locations of all anchors in range Result is location estimate Good anchor placement is crucial! Anchors Ref: Nirupama Bulusu, John Heidemann and Deborah Estrin. Density Adaptive Beacon Placement, Proceedings of the 21st IEEE ICDCS, 2001
- 15. Phase 1: DV-hopPhase 1: DV-hop • Anchors • flood network with own position • flood network with avg hop distance • Nodes • count number of hops to anchors • multiply with avg hop distance C A B 1 1 1 1 2 2 2 3 3 4 4 3 hops avg hop: 5
- 16. System EnvironmentSystem Environment • Sensor network consists of sensor nodes and mobile anchor points • Randomly distributed • Can receive messages from sensor nodes and mobile anchor points • Mobile anchor points can traverse for assisting sensor nodes to determine their locations • Each mobile anchor point has a GPS receiver and sufficient energy for moving and broadcasting beacon • Messages during the localization process.
- 17. Localization SchemeLocalization Scheme • Inspired by the perpendicular bisector of a chord conjecture. • Perpendicular bisector of any chord passes through the center of the circle • Localization problem can be transformed based on the conjecture • Sensor node location: center of the circle • Sensor nodes communicate with mobile anchors through the radius of the circle
- 18. Beacon Point SelectionBeacon Point Selection • At least three endpoints on the circle should be collected for establishing two chords • Anchor point periodically broadcasts beacon messages when it moves • Beacon message contains the anchor node’s id, location, and timestamp • Node maintains a set of beacon points & a visitor list • Beacon point is considered as an approximate endpoint on the sensor node’s communication circle
- 19. Location CalculationLocation Calculation
- 20. Beacon SchedulingBeacon Scheduling • Broadcasting in wireless ad hoc networks may cause destructive bandwidth congestion, contention, and collision • Collision at sensor nodes could occur due to beacon messages in the mechanism • Solution: the scheduling for broadcasting beacon messages is jittered. • Randomized scheduling prevents the beacon collision at sensor nodes so each node can efficiently obtain beacon messages from different mobile anchor points.
- 21. Chord SelectionChord Selection Localization will be accurate if the selected beacon points are exact on the communication circle Incorrect 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 sensor When length of the chord is too short, probability of unsuccessful localization will increase rapidly A threshold λ for the length of a chord is used to solve the problem The length of a chord must surpass the threshold for reducing the localization error
- 22. Obstacle ToleranceObstacle Tolerance • Obstacles in the sensor field cause radio irregularity in the sensor network • Radio irregularity could degrade the performance of localization protocols so most localization schemes require a non-obstacle sensing area • Original mechanism may choose inappropriate beacon points if obstacles exist
- 23. Obstacle Tolerance (cont.)Obstacle Tolerance (cont.) • Enhanced beacon point selection based on the characteristic of concentric circles is developed for tolerating the presence of obstacles • Exploiting chords on one of its concentric circles can also compute the center of the circle • B3, B4, and B5 are on the same concentric circle and can form two suitable chords to determine the center of the circle • Signal strength of a received beacon is in inverse proportion to the distance with the sender
- 24. Simulation EnvironmentSimulation Environment Six sets of simulations for evaluation: •Beacon scheduling •Threshold for the length of a chord •Radio range •Moving speed •Number of anchor points •Obstacles
- 25. Three metrics used to evaluate the performance of proposed localization mechanism • Average location error • Average execution time • Beacon overhead Performance MetricsPerformance Metrics
- 26. Simulation ParametersSimulation Parameters
- 27. PerformancePerformance
- 28. ConclusionConclusion In 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.
- 29. Thank you

No public clipboards found for this slide

×
### Save the most important slides with Clipping

Clipping is a handy way to collect and organize the most important slides from a presentation. You can keep your great finds in clipboards organized around topics.

Be the first to comment