The GETA Sandals: A Footprint Location Tracking System

1. 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

2. What is GETA? • a kind of the traditional Japanese sandals

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

4. 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

5. 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

6. Basic idea of Foot-print Approach ( 180, 200 ) S5 S4 Sp S3 S2 Sp=S1+S2+S3+S4+S5 S1 ( 0, 0 )

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

8. Three try-and-error versions

9. Ultrasonic Receivers Ultrasonic Transmitters Bottom view side view Design version I

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

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

12. 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!

13. Orientation Sensor Pressure sensor Ultrasonic Transmitter Ultrasonic Receivers Bottom view side view Design version II

14. Design II Performance Evaluation

15. P1 Real path Calculated path Error Displacement Two Main Error Sources Fig1. Ultrasonic device err Fig2. Orientation sensor err θerr P2 P1 Real path Calculated path Error Displacement Error P2 Steps

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

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

18. 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

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

20. 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..

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

22. Thank you Questions? or send me E-mail r93124@csie.ntu.edu.tw Thank you !