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Ad Hoc Positioning System (APS) Using AOA

Ad Hoc Positioning System (APS) Using AOA. Dragos ¸ Niculescu and Badri Nath INFOCOM ’03. Seoyeon Kang September 23, 2008. Outline. Introduction Angle of arrival(AOA) theory Ad hoc positioning system(APS) algorithm Error control Simulation Future work & conclusion. Introduction.

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Ad Hoc Positioning System (APS) Using AOA

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  1. Ad Hoc Positioning System (APS)Using AOA Dragos¸ Niculescu and BadriNath INFOCOM ’03 Seoyeon Kang September 23, 2008

  2. Outline Introduction Angle of arrival(AOA) theory Ad hoc positioning system(APS) algorithm Error control Simulation Future work & conclusion

  3. Introduction • Ad hoc networks • Challenges • Background • Problem definition

  4. Ad hoc networks • Decentralized wireless network • Each node is willing to forward data for other nodes • Each node acts as a router • Large number of unattended nodes with varying capability • Ranging, compass, AOA, etc.

  5. Challenges Cost of deployment Capability and complexity of nodes Routing without the use of large conventional routing table Etc.

  6. Challenges • Availability of position would enable routing without the use of large routing tables • How to get position information • Using capabilities • How to export capabilities in network

  7. Background NORTH • Orientation • Heading • Defined by the angles it forms with the axes of a reference frame

  8. Background Ultrasound receiver x1 x2 • Angle of arrival(AOA) • To sense the direction from which a signal is received • By knowing ranges x1, x2, and distance L • The node can infer the orientation Θ

  9. Background • Related works with other capabilities • Time of arrival(TOA) • Time difference of arrival(TDOA) • Signal strength • Based on AOA • Less computational resources and infrastructures

  10. Problem definition How all nodes determine their orientation and position in an ad-hoc network where only a fraction of the nodes have positioning capabilities, under the assumption that each node has the AOA capability

  11. AOA theory • Terms • Problem definition • Finding headings • Finding positions • Triangulation using AOA

  12. Terms • Bearing • Angle measurement with respect to another object • Radial • Reverse bearing • Angle under which an object is seen from another point

  13. Problem definition • Given imprecise bearing to neighbor • By AOA capability • A small fraction of the nodes have self positioning capability • Landmarks • Find headings and positions for all nodes

  14. Finding headings A’s heading :

  15. Finding positions • Triangulation using AOA • Given • Positions for the vertices of a triangle • Angles at which an interior point “sees” the vertices Reduction to trilateration

  16. Finding positions • Review of trilateration • Given • Positions for the vertices of a triangle • Distances to vertices

  17. Finding positions • For each pair of landmarks • Create an trilateration • A triangulation problem of size n  a trilateration problem of size

  18. Finding positions L4 L5 L1 D(x,y) L2 L3 • Using triplets of landmarks • trilateration problems of size 3 • Less memory

  19. APS(ad hoc positioning system) Algorithm • Concepts of original APS • Information is forwarded in a hop by hop fashion • Each node estimates position based on landmarks • Extend to angle measurements • DV-Bearing • DV-Radial

  20. Orientation forwarding DV-Bearing

  21. Orientation forwarding DV-Radial

  22. Orientation forwarding Tradeoffs between DV-Bearing and DV-Radial

  23. Network density What kind of node density is needed in order to achieve a certain condition with high probability

  24. Error control Bearing measurements are affected by errors Forwarding may amplify and compound smaller errors into larger errors

  25. Limitingthe propagation of packets Set TTL to limit error propagation

  26. Threshold to eliminate triangles • Ignore small angles • Tradeoff – coverage vs. positioning error

  27. Elimination of outliers Compute centroid and remove outliersthen recompute

  28. Simulation 1000nodes Avg. degree=10.5 Gaussian noise 20% landmarks Threshold 0.35(≈ 20˚) DV-Bearing TTL=5 DV-Radial TTL=4 Isotropic topology

  29. Positioning error 1.0 means that the position is one hop away from true position

  30. Bearing error Howforwarding method compounds and propagates error

  31. Heading error Errorin the absolute orientation averaged over all nodes

  32. Coverage Percentageof regular nodes which are able to resolve for a position

  33. Tracking example

  34. Future work • Extension to mobility • A moving landmark provides more information • Error estimation • Transmitting of the error estimation with DV data • Weights for each landmark • Multimodal sensing • With compasses and accelerometers

  35. Summary • A method that infers position and orientationin ad hoc network with only few landmarks • Orientation forwarding • DV-Bearing and DV-Radial • Triangulation using AOA • Advantages • Do not require additional infrastructures • Less computational resources • Scalable

  36. Thank you

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