Efficient RFID-Based Mobile Object Localization

Kirti Chawla, Gabriel Robins, and Liuyi Zhang

Department of Computer ScienceUniversity of Virginia, Charlottesville, USA

{kirti, robins, lz3m}@virginia.edu

This work is supported by U.S. National Science Foundation (NSF) grant: CNS-0716635 (PI: Professor Gabriel Robins)For more details, visit: www.cs.virginia.edu/robins

2/26

Novel Application Scenarios

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Overview

RFID Localization

Activity Recognition

Real-time Tracking Elderly Care

Pervasive Media

RFID-based Object Localization

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Overview

RFID Localization

Reader Localization Tag Localization

Stationary Reader Localization Tag Reader Localization

Mobile Reader Localization Mobile Tag Localization

Localization Challenges

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Overview

RF Interference Occlusions

Reader LocalityTag Spatiality

Tag Sensitivity

Tag Orientation

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Tag Power

Reader Power Distance

2Tag Power Frequency= Reader Gain Tag Gain

Reader Power 4 π Distance

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Intersection of Detectability Regions

Calibration phase Localization phase

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Multi-Tag Platform

Calibration under Proximity Calibration under Rotation

Platform Design

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Linear Search for Tags

Time = O(# tags power levels)

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Binary Search for Tags

Time = O(# tags log(power levels))

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Start

Initialize power level of all tags to maximum

Linearly decrement power level for all tags

Stop

Power level = 0 ?

Power level of a tag

“fixed” ?

YESNO

YESNO

Tag has optimal power level

Parallel Search for Tags

Time = O(power levels)

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Start

Stop

Tag Found ?

YESNO

Return “Not Found” Return Tag-ID and Timestamp

Measure and Report

Time = O(1)

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Reference Tag Target Tag

Error

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Heuristics: Absolute Difference

are neighbors

are neig

such that

M

1 I JJI=1

M M

2 I J I KJ,KI=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

J,K

H : Min( Δ (R ))

H : Min( Δ (R ) + Δ (R ))

H : Min( Δ (R ) + Δ (R ))

H : Min( Δ (R ) + Δ (R )) Δ (R ) < Δ (R )

hbors

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are planar orthogonally oriented

are neighbors

5 J KJ,K,S,QJ KS Q

6 J KJ,K,S,QJ KS Q

J,K

S, Q

H : Min (Δ (T) + Δ (T))

H : Min (Δ (T) + Δ (T))

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Heuristics: Root Sum Square Absolute Difference

are neighbors

such that

M2

7 I JJI=1

M M2 2

8 I J I KJ,KI=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

H : Min( Δ (R ) )

H : Min( Δ (R ) + Δ (R ) )

H : Min( Δ (R ) + Δ (R ) )

H : Min( Δ (R ) + Δ (R ) ) Δ (R ) < Δ (R )

are neighbors

M

1

J,K

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1

4

2

3

Y-axis

X-axis

Track Design Mobile Robot Design

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Constant Distance/Variable Power

Variable Distance/Constant Power

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Constant Distance/Variable Power

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Variable Distance/Constant Power

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Localization Accuracy

Localization Speed

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Accuracy vs. Tag Density

Accuracy vs. Power-Step Size

Diminishing returns

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TechniqueAverage Time (minutes)

Test area (m2)

Localization Error (m)Setup Phase Localization Phase

Chae and Han [5] Not Reported Not Reported 48.36 0.23Choi and Lee [8] Not Reported Not Reported 14.4 0.016 – 0.024Hansel et al [11] Not Reported Not Reported 784 1 – 10

Han et al [12] Not Reported Not Reported 1 0.09Koch et al [14] Not Reported Not Reported 60 0.1

Milella et al [18] Not Reported Not Reported 70 0.64Santa et al [20] Not Reported Not Reported 2 0.2

Seo and Lee [21] Not Reported Not Reported 5 0.2 – 1.6Vorst et al [23] Not Reported Not Reported 125 0.2 – 0.6

Linear Search (HL) 29.78 1.42 8 0.29Linear Search (LH) 161.23 5.28 8 0.27

Binary Search 47.24 1.95 8 0.31Parallel Search 1.67 1.67 8 0.35

Measure and Report 0 0 8 0.25Combined Approach 161.23 10.32 8 0.18

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Accuracy

Work Area

Antenna Control

Heuristics

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Open Research Problems

Tag Spatiality Impact on Localization Accuracy

and Speed

Simultaneous Multiple Object Localization

Activity Recognition

Novel Applications

Questions ?

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