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Received-Signal-Strength-Based Logical Positioning Resilient to Signal Fluctuation

Received-Signal-Strength-Based Logical Positioning Resilient to Signal Fluctuation. Thomas Locher Roger Wattenhofer Aaron Zollinger. Overview. Problem statement RSSI-based positioning Related work Logical positions instead of coordinates Experimental observations signal fluctuation

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Received-Signal-Strength-Based Logical Positioning Resilient to Signal Fluctuation

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  1. Received-Signal-Strength-Based Logical Positioning Resilient to Signal Fluctuation Thomas Locher Roger WattenhoferAaron Zollinger

  2. Overview • Problem statement • RSSI-based positioning • Related work • Logical positions instead of coordinates • Experimental observations • signal fluctuation • System • Calibration phase • Operation phase • Practical evaluation • Problems and limitations • Conclusion SAWN 2005

  3. b1 b2 b3 b1 b3 b2 Problem Statement • Positioning based on RSSI SAWN 2005

  4. Related Work • [Bahl, Padmanabhan, Infocom 2000] • [Bahl, Padmanabhan, Balachandran, MSR Tech.Rep. 2000] • [Youssef, Agrawala, Shankar, PerCom 2003] • [Youssef, Agrawala, CNDS 2004] • [Schwaighofer, Grigoras, Tresp, Hoffmann, Adv.Neur.Inf.Proc.Sys. 2004] • [Krishnan, Krishnakumar, Ju, Mallows, Ganu, Infocom 2004] • [Ganu, Krishnakumar, Krishnan, WCNC 2004] • [Roos, Myllymäki, Tirri, Misikangas, Sievänen, 3rd IEEE WLAN Workshop 2004] • … • Problems • Presence of base station position information • Antenna and radio propagation characteristics • (Moving) obstacles (walls, buildings, cars…) Compute coordinates of mobile user SAWN 2005

  5. Related Work • Important exception:Nibble [Castro, Chiu, Kremenek, Muntz, UbiComp 2001] • Information about not required Our approach Compute logical position of mobile user Room, floor, area… • base station positions • antenna/radio characteristics • obstacles SAWN 2005

  6. Overview • Problem statement • RSSI-based positioning • Related work • Logical positions instead of coordinates • Experimental observations • signal fluctuation • System • Calibration phase • Operation phase • Practical evaluation • Problems and limitations • Conclusion SAWN 2005

  7. Experimental Observations • The measured signal strengths vary over time • 15 minutes later: • 1 day later: Explicitly address signal fluctuation Factor 1.5! Factor 7.5! Factor 10! Factor 214! SAWN 2005

  8. Signal Distribution Over Time 3min 1h weak signal strong signal SAWN 2005

  9. Overview • Problem statement • RSSI-based positioning • Related work • Logical positions instead of coordinates • Experimental observations • signal fluctuation • System • Calibration phase • Operation phase • Practical evaluation • Problems and limitations • Conclusion SAWN 2005

  10. System Model Calibration phase Operation phase SAWN 2005

  11. (s1, v1), (s2, v2) (s2, v2), (s3, v3), (s4, v4) (s4, v4), (s5, v5) (s1, v1), (s3, v3), (s5, v5) Calibration Phase average b2 variance b4 b1 b3 b5 SAWN 2005

  12. if Operation Phase Recorded average Currently measured average Recorded variance Location withminimum Zi All locationswith Zi· Confidence interval p Maximum likelihood estimator SAWN 2005

  13. Overview • Problem statement • RSSI-based positioning • Related work • Logical positions instead of coordinates • Experimental observations • signal fluctuation • System • Calibration phase • Operation phase • Practical evaluation • Problems and limitations • Conclusion SAWN 2005

  14. Practical Evaluation 10 measurements over 1 second Calibration: 60 measurements over 6 seconds 80% confidence interval 20 measurements over 20 seconds Best matching location SAWN 2005

  15. Overview • Problem statement • RSSI-based positioning • Related work • Logical positions instead of coordinates • Experimental observations • signal fluctuation • System • Calibration phase • Operation phase • Practical evaluation • Problems and limitations • Conclusion SAWN 2005

  16. Factor ¼ 100! Factor ¼ 104! Problems and Limitations • Same room but different position • Orientation • Base station constellation and position granularity • Moving objects Inherentissues SAWN 2005

  17. Overview • Problem statement • RSSI-based positioning • Related work • Logical positions instead of coordinates • Experimental observations • signal fluctuation • System • Calibration phase • Operation phase • Practical evaluation • Problems and limitations • Conclusion SAWN 2005

  18. Conclusion • Coordinates logical location • Explicitly address high signal fluctuation • Proposed prototype system forming “first step” • Certain accuracy • But also problems SAWN 2005

  19. DistributedComputing Group Questions?Comments?

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