RFID Object Localization
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Transcript of RFID Object Localization
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RFID Object Localization
Gabriel Robins and Kirti ChawlaDepartment of Computer Science
University of Virginia
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Outline
• What is Object Localization ?• Background • Motivation• Localizing Objects using RFID• Experimental Evaluation• Conclusion
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What is Object Localization ?
Goal: Find positions of objects in the environment
Problem: Devise an object localization approach with good performance and wide applicability
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Objects Environments
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Current Situation04/33
Lots of approaches and applications lead to vast disorganized research space
• Inapplicable
• Not general
• Mismatched
• Identify limitations
• Determine suitability
Techniques
Signal arrival angle
Signal strength
Signal arrival time
Signal phase
Technologies
Satellites
Lasers
Ultrasound sensors
Cameras
Applications
Outdoor localization
Indoor localization
Mobile object localization
Stationary object localization
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Localization Type05/33
Self Environmental
• Self-aware of position• Processing capability
• Not aware of position• Optional processing
capability
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Localization Technique06/33
• Signal arrival time• Signal arrival difference time• Signal strength• Signal arrival phase• Signal arrival angle• Landmarks• Analytics (combines above techniques with analytical
methods)
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RFID Technology Primer07/33
RFID reader RFID tag
• Passive• Semi-passive• Active
• Interact at various RF frequencies
Inductive CouplingBackscatter Coupling
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Motivating RFID-based Localization08/33
• Low-visibility environments• Not direct line of sight• Beyond solid obstacles• Cost-effective• Adaptive to flexible application requirements• Good localization performance
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State-of-the-art in RFID Localization09/33
Pure
RFID –based localization approaches
Hybrid
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Contributions10/33
• Pure RFID-based environmental localization framework with good performance and wide applicability
• Key localization challenges that impact performance and applicability
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Power-Distance Relationship11/33
Reader power Distance Tag power
NReader Power Wavelength
Reader Gain × Tag Gain ×Tag Power 4 × π × Distance
• Cannot determine tag position
• Empirical power-distance relationship
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Empirical Power-Distance Relationship12/33
Insight: Tags with very similar behaviors are very close to each other
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Tag Sensitivity13/33
• Variable sensitivities
• Bin tags on sensitivity
Average sensitiveHigh sensitive Low sensitive
Pile of tags
Key Challenges Results
25 % 54 % 8 %
13 %
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Reliability through Multi-tags14/33
Platform design
Results
Insight: Multi-tags have better detectabilities (Bolotnyy and Robins, 2007) due to orientation and redundancy
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Tag Localization Approach15/33
Setup phase Localization phase
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Algorithm: Linear Search16/33
• Linearly increments the reader power from lowest to highest (LH) or highest to lowest (HL)
• Reports the first power level at which a tag is detected as the minimum tag detection power level
• Localizes the tags in a serial manner• Time-complexity is: O(# tags power levels)
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Algorithm: Binary Search17/33
• Exponentially converges to the minimum tag detection power level
• Localizes the tags in a serial manner• Time-complexity is: O(# tags log(power levels))
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Algorithm: Parallel Search18/33
• Linearly decrements the reader power from highest to lowest power level
• Reports the first power level at which a tag is detected as the minimum tag detection power level
• Localizes the tags in a parallel manner• Time-complexity is: O(power levels)
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Reader Localization Approach19/33
Setup phase Localization phase
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Algorithm: Measure and Report20/33
• Reports a 2-tuple TagID, Timestamp after reading a neighborhood tag
• Sorted timestamps identify object’s motion path• Time-complexity is: O(1)
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Localization Error21/33
• Reference tag’s location as object’s location leads to error
• Number of selection criteria
Error-reducing Heuristics
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Experimental Setup22/33
1
4
2
3
Y-axis
X-axis
Track design Mobile robot design
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Experimental Evaluation23/33
• Empirical power-distance relationship• Localization performance• Impact of number of tags on localization performance
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Empirical Power-Distance Relationship24/33
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Localization Accuracy25/33
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Algorithmic Variability26/33
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Localization Time27/33
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Performance Vs Number of Tags28/33
Diminishing returns
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Comparison with Existing Approaches29/33
Hybrid
Hybrid
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Visualization30/33
Accuracy
Work area
Antenna control
Heuristics
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Deliverables31/33
Patent(s):1. Kirti Chawla, and Gabriel Robins, Method, System and Computer Program Product for Low-
Cost Power-Provident Object Localization using Ubiquitous RFID Infrastructure, UVA Patent Foundation, University of Virginia, 2010, US Patent Application Number: 61/386,646.
Journal Publication(s): 2. Kirti Chawla, and Gabriel Robins, An RFID-Based Object Localization Framework,
International Journal of Radio Frequency Identification Technology and Applications, Inderscience Publishers, 2011, Vol. 3, Nos. 1/2, pp. 2-30.
Conference Publication(s):3. Kirti Chawla, Gabriel Robins, and Liuyi Zhang, Efficient RFID-Based Mobile Object
Localization, Proceedings of IEEE International Conference on Wireless and Mobile Computing, Networking and Communications, 2010, Canada, pp. 683-690.
4. Kirti Chawla, Gabriel Robins, and Liuyi Zhang, Object Localization using RFID, Proceedings of IEEE International Symposium on Wireless Pervasive Computing, 2010, Italy, pp. 301-306.
Grant(s): 5. Gabriel Robins (PI), NSF Grant on RFID Pending
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Conclusion32/33
• Pure RFID-based object localization framework• Key localization challenges• Power-distance relationship is a reliable indicator• Extendible to other scenarios
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Thank You
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Backup Slides
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Key Localization Challenges35
RF interference Occlusions
Reader localityTag spatiality
Tag sensitivity
Tag orientation
Back
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Single Tag Calibration36
Constant distance/Variable power
Variable distance/Constant power
Back
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Multi-Tag Calibration: Proximity37
Constant distance/Variable power
Variable distance/Constant power
Back
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Multi-Tag Calibration: Rotation 138
Constant distance/Variable power
Back
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Multi-Tag Calibration: Rotation 239
Variable distance/Constant power
Back
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Error-Reducing Heuristics40
Heuristics: Absolute differenceM
1 I JJI=1
M M
2 I J I KJ,K I=1 I=1J K
M M
3 I J I KJ,KI=1 I=1J K
M M M M
4 I J I K I J I KJ,KI=1 I=1 I=1 I=1J K
J, K are neighbors
J, K are neig
H : Min( Δ (R ))
H : Min( Δ (R ) + Δ (R ))
H : Min( Δ (R ) + Δ (R ))
H : Min( Δ (R ) + Δ (R )) such that Δ (R ) < Δ (R )
hbors
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Error-Reducing Heuristics41
Heuristics: Minimum power reader selection
5 J KJ,K,S,QJ KS Q
6 J KJ,K,S,QJ KS Q
J, K are planar orthogonally oriented
S, Q are neighbors
H : Min (Δ (T) + Δ (T))
H : Min (Δ (T) + Δ (T))
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Error-Reducing Heuristics42
Heuristics: Root sum square absolute difference
M2
7 I JJ I=1
M M2 2
8 I J I KJ,K I=1 I=1J K
M M2 2
9 I J I KJ,KI=1 I=1J K
M M M2 2 2 2
10 I J I K I J I KJ,KI=1 I=1 I=1 I=J K
J, K are neighbors
H : Min( Δ (R ) )
H : Min( Δ (R ) + Δ (R ) )
H : Min( Δ (R ) + Δ (R ) )
H : Min( Δ (R ) + Δ (R ) ) such that Δ (R ) < Δ (R )
M
1
J, K are neighbors
Back
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Error-Reducing Heuristics43
Localization error
Root sum square absolute difference
Meta-Heuristic
Minimum power reader selection
Absolute difference
Other heuristics
Back