1 / 18

Wireless Embedded Systems (0120442x) Localization

Wireless Embedded Systems (0120442x) Localization. Chaiporn Jaikaeo chaiporn.j@ku.ac.th Department of Computer Engineering Kasetsart University. Materials taken from lecture slides by Karl and Willig. Overview. Basic approaches Trilateration Multihop schemes. Localization & positioning.

megan-downs
Download Presentation

Wireless Embedded Systems (0120442x) Localization

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Wireless Embedded Systems(0120442x) Localization Chaiporn Jaikaeo chaiporn.j@ku.ac.th Department of Computer EngineeringKasetsart University Materials taken from lecture slides by Karl and Willig

  2. Overview • Basic approaches • Trilateration • Multihop schemes

  3. Localization & positioning • Determine physical position or logical location • Coordinate system or symbolic reference • Absolute or relative coordinates • Metrics • Accuracy • Precision • Costs, energy consumption, … http://www.mathsisfun.com/accuracy-precision.html

  4. Main Approaches • Based on information source • Proximity • (Tri-/Multi-)lateration and angulation • Scene analysis • Radio environment has characteristic “signatures”

  5. Estimating Distances – RSSI • Compute distance from Received Signal Strength Indicator • Problem: Highly error-prone process PDF PDF Distance Signal strength Distance

  6. Estimating Distances – Others • Time of arrival (ToA) • Use time of transmission, propagation speed, time of arrival to compute distance • Time Difference of Arrival (TDoA) • Use two different signals with different propagation speeds • Example: ultrasound and radio signal

  7. Determining Angles • Directional antennas • Multiple antennas • Measure time difference between receptions

  8. Range-Free Techniques • Overlapping connectivity • Approximate point in triangle

  9. Overview • Basic approaches • Trilateration • Multihop schemes

  10. (x2,y2) r2 r1 r3 (x1,y1) (xu,yu) (x3,y3) Trilateration • Assuming distances to three points with known location are exactly given • Solve system of equations

  11. Trilateration as Matrix Equation • Rewriting as a matrix equation: • Example: (x1, y1) = (2,1), (x2, y2) = (5,4), (x3, y3) = (8,2), r1 = 100.5 , r2 = 2, r3 = 3

  12. Trilateration with Distance Errors • What if only distance estimation ri' = ri + iavailable? • Use multiple anchors • Overdetermined system of equations • Use (xu, yu) that minimize mean square error, i.e,

  13. Minimize Mean Square Error • Look at derivative with respect to x, set it equal to 0:  Normal equation • Has unique solution (if A has full rank), which gives desired minimal mean square error

  14. Overview • Basic approaches • Trilateration • Multihop schemes

  15. Multihop Range Estimation • No direct radio communication exists • Idea 1: Count number of hops, assume length of one hop is known (DV-Hop) • Idea 2: If range estimates between neighbors exist, use them • Improve total length of route estimation in previous method (DV-Distance)

  16. Iterative Multilateration

  17. Probabilistic Position Description • Position of nodes is only probabilistically known • Represent this probability explicitly • Use it to compute probabilities for further nodes

  18. Conclusions • Determining location or position is a vitally important function in WSN, but fraught with many errors and shortcomings • Range estimates often not sufficiently accurate • Many anchors are needed for acceptable results • Anchors might need external position sources (GPS) • Multilateration problematic (convergence, accuracy)

More Related