1. A Stochastic Frame Based Approach to RFID Tag Searching Ann L. Wang Dept. of Computer Science and Engineering Michigan State University Joint work with Muhammad Shahzad and Alex X. Liu 1

2. A Basic RFID System Tag Tag chips or integrated circuits(ICs) Tag antennas Reader Reader antenna Reader control & application software 2

3. Problem Statement 3 Known Tag Set A Unknown Tag Set B Confidence Interval Confidence Interval RFID Tag Searching Protocol Present Tag Set C IDS |B|

4. RFID Tag Searching Applications 4

5. Limitations of Prior Art Several tag searching protocols – CATS [ToN’ 2013] – ITSP [INFOCOM’ 2013] – TSM [GREENCOM’ 2013] – BKC [ICNP’ 2014] Non compliance with C1G2 standard Can not identify present tags 5

6. RFID Tag Searching Protocol(RTSP) Key features – Easy to deploy C1G2 ( Electronic Product Code Class 1 Generation 2) RFID Standard compliant – Privacy preserving – Faster than Tree Hopping (TH) [SIGMETRICS 2013] 6

7. Communication Protocol Overview 011C011 frame size f =7, R 326447 1234567 011C011011C0110111011 Empty slot : NO TAG REPLY Singleton slot : ONE TAG REPLIED Collision slot : MORE THAN ONE TAGS REPLIED H(ID1,f,R) = 3 7

8. Communication Protocol Overview Frame size f – From C1G2, maximum value is 65535 Persistent probability p – The probability a tag choose to respond in a slot is f * 1/p 8

9. RTSP - Intuition 1 st round 2 nd round 3 rd round N th round 9

10. |A| = 200, |B| = 300, f = 300 Expected number of slot pair is an increasing function of number of present tags |C| Number of slot pair can be used to estimate number of present tags |C| RTSP - Intuition 10

11. Expected Value of Observed Slot Pairs The probability of i th slot equals to one in both frames (A ＆ B) can be defined as ： 11

12. Expected Value of Observed Slot Pairs 0110101 0101011 12

13. 0110101 0101011 Expected Value of Observed Slot Pairs 13

14. 0110101 0101011 Expected Value of Observed Slot Pairs 14

15. Estimated number of present tags Expected observed number of slot pairs Expected Value of Observed Slot Pairs 15

16. System Parameters 16

17. System Parameter – Confidence Interval |A| = 200, n=10, f= 600 False positive Confidence interval 17

18. System Parameter – Confidence Interval Minimize execution time: n x f Number of rounds: 18

19. RTSP Example Size of tag set A: 20 Size of tag set B: 12 With known IDS 19

20. RTSP Example Frame size f = 15, R 0111001 0001 0101011 011 0 111 110 0111001 0101 0111011 011 1 111 110 1 11101011 011 1 0 1 1 110 1 11101 011 11 110 1 1 1111011 000 1 Optimal Frame size f = 12, R 20

21. System Evaluation - Execution time Execution time vs. |B| Execution time vs. |A| 21

22. Execution time vs. C System Evaluation - Execution time 22

23. System Evaluation - Accuracy Observed confidence interval vs. |A| Observed confidence interval vs. |B| 23

24. Experimental Evaluation Execution time & Accuracy TH ITSP RTSP 24

25. Execution Time & Accuracy Execution time vs. |A| Accuracy vs. |A| 25

26. Execution Time & Accuracy Execution time vs. |B| Accuracy vs. |B| 26

27. Execution Time & Accuracy Execution time vs. |C| Accuracy vs. |C| 27

28. Questions? 28