The GETA Sandals: A Footprint Location Tracking System Kenji Okuda, Shun-yuan Yeh, Chon-in Wu, Keng-hao Chang, and Hao-hua Chu National Taiwan University

What is GETA?   a kind of the traditional Japanese sandals

Outline   Motivation   Related works   Basic idea   Design, implementation and evaluation   (three versions try and error)   Conclusion   Current works

Motivation   Infrastructure cost (barriers for the user) (deployment, calibration, maintain)   Active Badge: IR receivers   Active BAT: Ultrasonic receivers + RF   Cricket: Ultrasonic beacons + RF   RADAR: WiFi network   Smart floor: pressure sensors   Goal   Infrastructure free (not succeed so far in this paper-> low infrastructure)   High accuracy

Related Works   Lee et al. proposed a method   by recognizing a sequence of incremental motions.   E.g. 5 steps north followed by 14 steps east.   Only can tell from place to place   e.g. living room, bedroom   Point research provides a vehicle self- tracking system

Basic idea of Foot-print Approach ( 0, 0 ) ( 180, 200 ) SpSp S1S1 S2S2 S3S3 S4S4 S5S5 Sp=S1+S2+S3+S4+S5Sp=S1+S2+S3+S4+S5

How to sum up those vectors mathematically Coordinate system 1 Coordinate system 1 ’ (x1, y1) (x2, y2) (xc2, yc2) (xc1, yc1) θ Coordinate system 2 Need coordinate transformation for each left foot step.

Three try-and-error versions

Design version I Bottom viewside view Ultrasonic Transmitters Ultrasonic Receivers

Why using two transmitters P1 (known) P2 (Unknown) T1 d1 d2 d3 d4 Can be rotated!! fixed (fixed)

Why using two transmitters P1 (known) P2 (determined) T1 Can Not be rotated any more ! T2

Problems of Design I   Poor accuracy!   The interference of the signals from two transmitters.   Measures the incorrect vectors   Miss-detection of the user’s steps   All the calculations become failure.   Can not distinguish the user is moving forward or backward!

Design version II Bottom viewside view Ultrasonic Transmitter Ultrasonic Receivers Pressure sensor Orientation Sensor

Design II Performance Evaluation

Two Main Error Sources θ err P1 P2 Real path Calculated path Error Displacement P2 Steps Error Real path Calculated path Error Displacement P1 Fig1. Ultrasonic device errFig2. Orientation sensor err

The solution of design II Passive RFID tag Adds a RFID reader in the GETA and put some tags in the environment. Real Path of the user Calculated Path of the user

Design version III Orientation Sensor RFID Reader Pressure Sensor Ultrasonic Receivers board (with 2 Ultrasonic receivers) Ultrasonic transmitter

Hardware Sensors of Design III   Pressure sensors   Phidgets   Ultrasonic device   NAVINote (an electronic pen product)   Resolution : 0.2 mm   Orientation sensor   InterSense InterTrax2   Resolution : 0.02 degree   RFID Reader   SkyeTek M1   Read range: ~5cm

Design III Performance Evaluation The positioning error under different tag density over the walking distance.

Conclusion   A interesting self tracking method.   Low infrastructure cost.   The error of the orientation dominants our system accuracy.   Still have some limitations   E.g. climbing the stairs, walking crossover..

Current Works   Increase the accuracy (reducing the orientation error)   Solve the obstruction problem   Going down/up stair problem   Enhance the wearability (wireless)

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