The GETA Sandals A Footprint Location Tracking System

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: Wi. Fi 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 selftracking system

Basic idea of Foot-print Approach S 4 S 3 S 5 ( 180, 200 ) Sp S 2 ( 0, 0 ) S 1 Sp=S 1+S 2+S 3+S 4+S 5

How to sum up those vectors mathematically Coordinate system 1’ (x 2, y 2) Need coordinate transformation for each left foot step. (x 1, y 1) θ Coordinate system 2 (xc 2, yc 2) (xc 1, yc 1) Coordinate system 1

Three try-and-error versions

Design version I Ultrasonic Transmitters Bottom view Ultrasonic Receivers side view

Why using two transmitters Can be rotated!! d 3 P 2 (Unknown) d 4 T 1 (fixed ) d 1 fixed P 1 d 2

Why using two transmitters Can Not be rotated any more ! P 2 (determined) T 2 T 1 P 1

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 Pressure sensor Ultrasonic Transmitter Bottom view Orientation Sensor Ultrasonic Receivers side view

Design II Performance Evaluation

Two Main Error Sources Fig 1. Ultrasonic device err P 1 Fig 2. Orientation sensor err θerr P 2 P 1 Real path Calculated path Error Displacement Error Real path Calculated path Error Displacement P 2 Steps

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

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 § Inter. Sense Inter. Trax 2 § Resolution : 0. 02 degree § RFID Reader § Skye. Tek M 1 § Read range: ~5 cm

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)

Thank you Questions? or send me E-mail r 93124@csie. ntu. edu. tw Thank you !