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Identifying the Missing Tags in a Large RFID System

Identifying the Missing Tags in a Large RFID System. Tao Li (University of Florida, US) Shigang Chen (University of Florida, US) Yibei Ling (Telcordia Technologies, US). Outline. Introduction System Model Missing-tag Detection Protocols Simulation Results Conclusion. Introduction.

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Identifying the Missing Tags in a Large RFID System

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  1. Identifying the Missing Tags in a Large RFID System Tao Li (University of Florida, US) Shigang Chen (University of Florida, US) Yibei Ling (Telcordia Technologies, US)

  2. Outline • Introduction • System Model • Missing-tag Detection Protocols • Simulation Results • Conclusion Identifying the Missing Tags in a Large RFID System

  3. Introduction • RFID (radio-frequency identification) • Used in: • Warehouse management • Object tracking • Inventory control • Australia Goats Identifying the Missing Tags in a Large RFID System

  4. Introduction • Other topics: • Tag-collection problem • Tag-estimation problem • This paper studies missing-tag problem. • Few research papers has investigated this problem before. Identifying the Missing Tags in a Large RFID System

  5. Introduction • The most important thing is to minimize the detection time. • Two guidelines to achieve time efficiency: • Reduce radio collision • Report presence by each transmitting a bit instead of a whole tag duel. Identifying the Missing Tags in a Large RFID System

  6. Outline • Introduction • System Model • Missing-tag Detection Protocols • Simulation Results • Related Work • Conclusion Identifying the Missing Tags in a Large RFID System

  7. Problem and Assumption • A large RFID system of N tags. • Each tag carries a unique ID. • Each tag can perform certain computations and communicating with the RFID reader wirelessly. • RFID reader has access to database that stores the ID of the tags. Identifying the Missing Tags in a Large RFID System

  8. Time Slots • Empty slot, singleton slot, collision slot. • ttag for tag slot, tl for long-response slot, ts for short-response slot. ts <tl<ttag. • ts = 0.4ms,tl= 0.8ms,ttag = 2.4ms Identifying the Missing Tags in a Large RFID System

  9. Outline • Introduction • System Model • Missing-tag Detection Protocols • Simulation Results • Conclusion Identifying the Missing Tags in a Large RFID System

  10. Baseline Protocol • Because RFID reader has access to database, no need to read directly from tags. • For each tag: • Broadcast the tag ID: ttag • Wait to receive short response: ts • Total executing time: N(ttag+ts) Identifying the Missing Tags in a Large RFID System

  11. Two-Phase Protocol (TPP) • Reduce the number of tag IDs transmit. • Two phase: • Frame phase • Polling phase Identifying the Missing Tags in a Large RFID System

  12. ID ID ID H(id, r) H(id, r) H(id, r) Frame 0 to f-1 Frame Phase of TPP • RFID reader transmit <r, f> • r is a random number, f is the frame size • pseudo-randomly mapped H(id, r) -> [0, f-1] Identifying the Missing Tags in a Large RFID System

  13. Frame Phase of TPP • Hash function H(id, r): • String of 200 random bits stored in the tag • Return a certain number of bits after the rth bit in the ring. • If necessary, the number of bits can be larger than 200. Identifying the Missing Tags in a Large RFID System

  14. ID1 ID2 ID3 ID4 Frame 0 to f-1 Polling Phase of TPP • Perform the baseline protocol on the tags that are mapped to the collision slots in the frame. Identifying the Missing Tags in a Large RFID System

  15. Time Efficiency of TPP • Set the value of the protocol parameter f. • The executing time of TPP is T1. • The number of tags mapped to the collision slots is N1. Identifying the Missing Tags in a Large RFID System

  16. Time Efficiency of TPP Identifying the Missing Tags in a Large RFID System

  17. Time Efficiency of TPP • When N = 50,000, the optimal frame size is f = 104,028, and the minimum execution time of TPP is 95.04 seconds. Identifying the Missing Tags in a Large RFID System

  18. Two-Phase Protocol with Tag Removal (TPP/TR) • In TPP, two tags mapped to a collision slot, we have to broadcast both tags. • The information in the collision slot is totally unused. • Remove tags from collision slot to make it a singleton slot. Identifying the Missing Tags in a Large RFID System

  19. Two-Phase Protocol with Tag Removal (TPP/TR) • Tow Phase: • Polling Phase (with tag removal) • Frame Phase • For each k-collision slot, randomly removes k-1 tags to turn the slot a singleton. Identifying the Missing Tags in a Large RFID System

  20. ID1 ID2 ID3 ID4 Frame 0 to f-1 Tag Removal • ID3 is removed, it will be broadcast in polling phase. • ID4 will be checked in frame phase. Identifying the Missing Tags in a Large RFID System

  21. Time Efficiency of TPP/TR • Set the value of the protocol parameter f. • The executing time of TPP/TR is T2. • The number of removal tags is N2. Identifying the Missing Tags in a Large RFID System

  22. Time Efficiency of TPP/TR Identifying the Missing Tags in a Large RFID System

  23. Time Efficiency of TPP/TR • When N = 50,000, the optimal frame size is f = 75,479. Identifying the Missing Tags in a Large RFID System

  24. Three-Phase Protocol with Collision Sensitive Tag Removal (TPP/CSTR) • When f is reasonably large, most collision slot are 2-collision slots. • Long response is needed. • The situation of the two tags response: • Empty: both are missing • Singleton: one is missing, check later • Collision: neither is missing. Identifying the Missing Tags in a Large RFID System

  25. Three-Phase Protocol with Collision Sensitive Tag Removal (TPP/CSTR) • Three Phase: • Polling Phase 1 (with tag removal) • Frame Phase • Polling Phase 2 • For each k-collision slot with k>2, randomly removes k-2 tags to turn the slot 2-collision. Identifying the Missing Tags in a Large RFID System

  26. ID5 ID1 ID2 ID3 ID4 Frame 0 to f-1 Tag Removal • ID3 is removed, it will be broadcast in polling phase 1. • ID4 and ID5 will be checked in frame phase and polling phase 2. Identifying the Missing Tags in a Large RFID System

  27. Time Efficiency of TPP/CSTR • Set the value of the protocol parameter f. • The executing time of TPP/TR is T3. • The number of removal tags is N3. • The number of tags broadcast in polling phase 2. Identifying the Missing Tags in a Large RFID System

  28. Time Efficiency of TPP/CSTR Identifying the Missing Tags in a Large RFID System

  29. Time Efficiency of TPP/CSTR • When N = 50,000, the optimal frame size is f = 38466. Identifying the Missing Tags in a Large RFID System

  30. Iterative ID-free protocol (IIP) • Transmitting tag IDs is an expensive operation. • IIP remove all the polling phase, it iteratively performs the frame phase. Identifying the Missing Tags in a Large RFID System

  31. Frame Phase in IIP • Transmitting a pre-frame vector: • ‘0’ for empty and singleton, ‘1’ for collision • A tag in a collision slot decide with 50% probability to not participate in the current frame. • Using H’(id,r). Identifying the Missing Tags in a Large RFID System

  32. Frame Phase in IIP • Transmitting a post-frame vector: • ‘0’ for empty and collision, ‘1’ for singleton • A tag in a singleton slot will not participate in the further execution. • Pre-frame or post-frame will be divide into segments of 96 bits (length of ID), and transmit in ttag. Identifying the Missing Tags in a Large RFID System

  33. Time Efficiency of IIP • Set the value of the protocol parameter f. • The executing time for a frame size of f of IIP is T4. • The expected number of tags whose presence will be verified by the frame is N’. • N* tags not confirm. Identifying the Missing Tags in a Large RFID System

  34. Time Efficiency of IIP Identifying the Missing Tags in a Large RFID System

  35. Time Efficiency of IIP • The average time for verifying the presence of one tag is Identifying the Missing Tags in a Large RFID System

  36. Time Efficiency of IIP • The optimal value the load factor is 1.516. Identifying the Missing Tags in a Large RFID System

  37. Outline • Introduction • System Model • Missing-tag Detection Protocols • Simulation Results • Conclusion Identifying the Missing Tags in a Large RFID System

  38. Simulation Results Identifying the Missing Tags in a Large RFID System

  39. Simulation Results Identifying the Missing Tags in a Large RFID System

  40. Outline • Introduction • System Model • Missing-tag Detection Protocols • Simulation Results • Conclusion Identifying the Missing Tags in a Large RFID System

  41. Conclusion • Monitoring the set of tags in a large RFID system and identifying the missing ones. • Proposing five missing-tag detection protocols with increasing time efficiencies. Identifying the Missing Tags in a Large RFID System

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