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FILA: Fine-grained Indoor Localization

FILA: Fine-grained Indoor Localization. Kaishun Wu, Jiang Xiao, Youwen Yi, Min Gao , and Lionel M. Ni INFOCOM 2012 - Sowhat 2012.5.21. Outline. Introduction System Design Evaluation Discussion Conclusion. Outline. Introduction System Design Evaluation Discussion Conclusion.

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FILA: Fine-grained Indoor Localization

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  1. FILA: Fine-grained Indoor Localization Kaishun Wu, Jiang Xiao, Youwen Yi, Min Gao, and Lionel M. Ni INFOCOM 2012 - Sowhat 2012.5.21

  2. Outline • Introduction • System Design • Evaluation • Discussion • Conclusion

  3. Outline • Introduction • System Design • Evaluation • Discussion • Conclusion

  4. Motivation • WiFi-based indoor localization • RSSI range-based localization • Multipath • Variance of RSSIs – 5dB in 1 min at immobile receiver

  5. Objective An alternative metric to RSSI Capable to eliminate multipath effect Stable

  6. Outline • Introduction • System Design • Evaluation • Discussion • Conclusion

  7. Foundation of FILA OFDM Orthogonal Frequency Division Multiplexing CSI Channel State Information

  8. OFDM • Multicarrier modulation schemefor wideband wireless communication • Modulate data on multiple subcarriers in different frequencies • Transmit simultaneously

  9. CSI • Channel state/status information • Fine-grained value from the PHY layer • Describe how a signal propagate from TX to RX • Represent combined effect of scattering, fading and power decay with distance • Channel properties of each subcarrier • Amplitude • Phase

  10. System Architecture CSI Processing Calibration Location Determination

  11. CSI Processing Calibration Location Determination CSI ProcessingTime-domain Multipath Mitigation • 802.11n bandwidth ~40MHz > coherence bandwidth resolvable reflections • IFFT – channel response in frequency  time domain • Filter – keep 1st cluster truncation threshold = 50% of 1st peak value • FFT – channel response in time  frequency domain

  12. CSI Processing Calibration Location Determination CSI ProcessingFrequency-domain Fading Compensation • Prob. of simultaneous deep fading occurring on multiple uncorrelated fading envelopes> deep fading occurring on a single freq. system • ∵ channel bandwidth of 802.11n > coherence bandwidth∴ freq.-selective fading across all subcarriers  uncorrelated • Reduce the variance in CSIs owing to small scale factors • Weighted average

  13. CSI Processing Calibration Location Determination Calibration • Relationship between CSIeff and distance • σ: environment factor@TX, gain of baseband to RF band@RX, gain of RF band to basebandantenna gain • n : path loss fading exponent • Fast training algorithm • 2 anchors for training • Another anchor for testing

  14. CSI Processing Calibration Location Determination Location Determination • APs’ coordinate info. from network layer • Distance between AP/object • Effective CSI • Refined radio propagation model • Trilateration!

  15. Outline • Introduction • System Design • Evaluation • Discussion • Conclusion

  16. Hardware configuration • AP : TP-LINK TL-WR941ND router @ 2.4~2.4835GHz • Receiver: • HP laptop with 2.4GHz dual-core CPUIntel WiFi Link 5300 802.11n NICs • Modified driver to collecting CSI values from NICs • Placed on a plastic cart

  17. Experimental Scenarios • Chamber • 3m x 4m • Ideal free space indoor environment(only LOS signal exist without multipath reflections) • Research laboratory • 5m x 8m • 3 APs • Weekday afternoon(students seating or walking around)

  18. Experimental Scenarios • Lecture theatre • 20m x 20m • Corridor • 32.5m x 10m • Cover corridors, rooms and cubicles • Impact of the absence of LOS APs

  19. Robustness of The Refined Modal

  20. Temporal Stability of CSI

  21. Distance Determination Accuracy • ChamberResearch laboratoryLecture theatre • 10 different locations • Positions with serious multipath effect –Accuracy: FILA > RSSI-based by 10 times • Mean distance error

  22. Localization Accuracy in Single Room • Research laboratoryLecture theatre • 90% - 1m/1.8m ; median - 0.45m/1.2m

  23. Localization Accuracy in Multiple Rooms • Corridor • 6 APs in multiple rooms • Experiment procedure • Offline trainingFix the position of the object at reference nodes collect APs’coordinates and CSI • Moving @ 1m/s • Collect 20 CSIs and RSSIs at each position • Robust, median = 1.2m

  24. Latency • Latency = calibration + determination phase • Calibration • Data collectionAP transmit message every 0.8msCollect 20 CSIs20 * 0.8 = 16ms • Calibration processing = 2ms • Determination • IFFT, FFT with wireless NICs= ignorable • Signal processing + trilateration = 2ms • Total: 16ms + 2ms + 2ms = 20ms

  25. Outline • Introduction • System Design • Evaluation • Discussion • Conclusion

  26. Discussion • CSI + fingerprint-based method more accurate localization • Leverage available multiple APs to improve accuracy • Implement FILA on smart phone

  27. Outline • Introduction • System Design • Evaluation • Discussion • Conclusion

  28. Conclusion • Design and implement FILA • CSI with OFDM system • Compared to RSSI-Based in different scenarios • Capable to deal with multipath effect(time domain processing) • Stable (freq. domain processing) • Disadvantage • Unclear descriptions • Comparison of single room/multiple room

  29. Thanks for Listening ~

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