1 / 31

Outline

BackPos : Anchor-free Backscatter Positioning for RFID Tags with High Accuracy Tianci Liu , Lei Yang , Qiongzheng Lin, Yi Guo , Yunhao Liu. Outline. Background & Motivation Proposed Approach Evaluation Discussion & Conclusion. Backscatter system. UHF Wave. Tags. Reader. Antenna.

albin
Download Presentation

Outline

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. BackPos: Anchor-free Backscatter Positioning for RFID Tags with High AccuracyTianci Liu, Lei Yang, Qiongzheng Lin, Yi Guo, Yunhao Liu

  2. Outline • Background & Motivation • Proposed Approach • Evaluation • Discussion & Conclusion

  3. Backscatter system UHF Wave Tags Reader Antenna Four elements of UHF backscatter system

  4. Backscatter system Expensive and do most of the jobs. EPC C1Gen2 Transmit/receive signals Polarized, ‘fat’(e.g. ) From 300MHz to 3GHz EPC C1Gen2: 900MHz~915MHz No battery and weak Tiny and cheap. 5 cents to 15 cents

  5. Locating every unique RFID tag Locating a tag means almost locating everything

  6. Existing approaches By distance estimation. RSS as distance indicator. Influenced by environment, tag orientation and diversity.

  7. Existing approaches By reference tags(anchor). Compare fingerprint: RSS(LANDMARC), multipath profile(PinIt) A lot of deployment work Granularity of anchors largely determines accuracy.

  8. Outline • Background & Motivation • Proposed Approach • Evaluation • Discussion & Conclusion

  9. Signal features COTS readers provide RSS & phase are available, e.g. Impinj readers RSS: not reliable Phase:

  10. Empirical studies of phase Gaussian distribution. Deviation: Phase v.s. frequency Phase is stable.

  11. Empirical studies of phase 8 orientations. Remain at a same level Phase v.s. tag orientation Phase is unrelated to tag orientation.

  12. Phase in backscatter system Periodicity Linear Phase v.s. distance

  13. Challenges of using phase • Stable, unrelated to orientation, related to distance • Tag diversity: • Should be applicable for all tags without measuring first • Periodicity: • Can not get from directly

  14. BackPos - tag diversity • Use phase difference from different antennas • Eliminate periodicity • Get distance difference from phase difference

  15. Eliminate periodicity • Distance difference restrict • : one • : two possible • Naive approach • Triangle constraint • between antennas

  16. Eliminate periodicity • Naive approach • Triangle constraint: 𝜆/4 between antennas • 𝜆≈32𝑐𝑚 (𝑓≈910𝑀𝐻𝑧) w=25cm w=25cm Triangle restrict does not work

  17. BackPos - periodicity • Use feasible region to relax antenna distance constraint • Antenna has reading zone • Just positions in reading zone satisfy distance difference restrict Reading zone

  18. BackPos - periodicity • Use feasible region to relax antenna distance constraint • Feasible region: region that all positions satisfy distance difference restrict. • Cover reading zone intersections of antennas Feasible region

  19. BackPos - periodicity • Hyperbola constraint • and are two focus points • Angle between two asymptote line: : Hyperbola restrict

  20. BackPos– distance difference • => • or 3 Two possible : two half hyperbola for each antenna pair

  21. BackPos– hyperbola intersection • For three antennas: • , -> , • , -> , Three possible points: Hyperbola intersection

  22. BackPos– estimated position • Reader: 4 antenna ports • If readings are accurate: • With error:

  23. Outline • Background & Motivation • Proposed Approach • Evaluation • Discussion & Conclusion

  24. Implementation & Evaluation • COTS reader • Impinj R420 with 4 antennas • 138.1cm high • COTS tags • Alien ‘2×2’ & ‘Square’ • Ground Truth • Laser meter: ~1𝑚𝑚 • Scenario • room 25cm 25cm

  25. Positioning accuracy Target position: (−43.2, 283.4) Distance difference error: <1𝑐𝑚 Positioning error: 12.8𝑐𝑚 Distance difference accuracy Positioning accuracy

  26. Positioning v.s positions 9 targets in a circle Error increases as 𝑦 increases Positioning accuracy v.s positions

  27. Positioning v.s positions 9 targets in a circle Error increases as 𝑦 increases Positioning accuracy v.s positions

  28. Positioning v.s tag diversity Random choose positions for targets ‘2×2’ & ‘Square’ Positioning accuracy v.s tag diversity

  29. Outline • Background & Motivation • Proposed Approach • Evaluation • Discussion & Conclusion

  30. Discussion & Conclusion • Explore phase in backscatter systems • Propose BackPos • No reference tags, 12.8cm • Implement and evaluate BackPos with COTS devices • Limitations: • Not suitable for NLOS scenarios • 4 antennas

  31. Thank you!Questions?

More Related