1. Assist. Prof. Peerapong Uthansakul, Ph.D. School of Telecommunication Engineering Suranaree University of Technology

2. Outline  Motivation  Background on time delay distribution  Time delay measurement  Positioning technique  Results and discussions  Conclusion uthansakul@sut.ac.th 2

3. Motivation  positioning methods based on WLAN infrastructure can be classified into four methods ◦ Time of Arrival (TOA) or Time Difference of Arrival (TDOA) ◦ Angle of Arrival (AOA) ◦ Received Signal Strength Indicator (RSSI) ◦ cell-ID. uthansakul@sut.ac.th 3

4. Motivation  Among those four parameters, TDOA or TOA are the best for indoor positioning systems in term of sensitivity to physical environment.  This is because the accuracy of positioning is distorted the least by multipath signals and distance between access point and user in comparing with AOA and RSS methods [16]. uthansakul@sut.ac.th 4

5. Motivation  However, they gain less attraction than the system using RSS.  This is due to the fact that RSS measurements can be obtained relatively effortlessly and inexpensively without the need for hardware and firmware modification [19]. uthansakul@sut.ac.th 5

6. Motivation  In [17-18], Gunther and Hoene attempt to measure time delay distribution without any modifications.  But their experiments were done under arranged scenarios. ◦ Non-operating access point => not practical ◦ Point-to-point measurement=>not practical ◦ No other active user => not practical uthansakul@sut.ac.th 6

7. Motivation  In this work, the following contributions can be found. ◦ Time delay measurements are investigated under operating WLAN system. ◦ The relation between measured time delay distribution and distance is presented. ◦ The utilizing method of measured data for positioning purpose is proposed. uthansakul@sut.ac.th 7

8.  WLAN is based on CSMA/CA  Time delay of successful transmission  Time delay uthansakul@sut.ac.th 8 Background on time delay distribution

9.  Probability of time delay uthansakul@sut.ac.th 9 Background on time delay distribution

10.  The method to collect the time delay of successful transmission is done by ping command from computer notebook.  The measurements are performed at 4 th level of C-Building at SUT.  There are 4 access points on this level.  The user knows IP address of all access points. uthansakul@sut.ac.th 10 Time delay measurement

11. uthansakul@sut.ac.th 11 Time delay measurement

12.  At each location, 100 trial time delays are collected in order to compute the probability of time delays.  there is no modification needed at both access point and user hardware.  As a result, it can be directly implemented to any existing WLAN system without extra costs. uthansakul@sut.ac.th 12 Time delay measurement

13. uthansakul@sut.ac.th 13 Time delay measurement

14.  Relation between distance and time delay distribution ??  By using average time delay of first transmission attempt (j = 0), a good agreement can be met.  The results are confirmed by measuring 5 times a day, 2 different days. uthansakul@sut.ac.th 14 Time delay measurement

15. uthansakul@sut.ac.th 15 Time delay measurement

16.  In this work, the empirical approach is adopted to find an appropriated parameter for translating time delay into distance.  Two steps of positioning technique: ◦ Determine conversion between time delay and distance ◦ Apply triangle locating uthansakul@sut.ac.th 16 Positioning technique

17.  Relation between distance and time delay uthansakul@sut.ac.th 17 Positioning technique

18.  Triangle locating uthansakul@sut.ac.th 18 Positioning technique

19.  Measurement area uthansakul@sut.ac.th 19 Results and discussions The average error is 3.96 m

20.  Outside Measurement area uthansakul@sut.ac.th 20 Results and discussions The average error is 3.12 m

21.  This paper has been demonstrated the new technique for WLAN positioning system.  The proposed technique provides the most convenient method to know the position of user without any extra cost of firmware and hardware.  The measurement results confirm the success of using proposed method. uthansakul@sut.ac.th 21 Conclusion

22. Thank you for your attention ! uthansakul@sut.ac.th 22 End