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RFID Collision 問題探討

RFID Collision 問題探討. 2010.12.31 王正誠. Outline. RFID 介紹 RFID collision problem 探討 Conclusion Future work Reference. 什麼是 RFID?. RFID Radio Frequency Identification 無線射頻識別 利用空間電磁感應或電磁傳播進行通信，以達到自動識別標識物體的目的. RFID 的組成元件. RFID 主要 有三個組成元件 電子標籤 (Tag)

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RFID Collision 問題探討

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  1. RFIDCollision 問題探討 2010.12.31 王正誠

  2. Outline • RFID 介紹 • RFID collision problem 探討 • Conclusion • Future work • Reference

  3. 什麼是RFID? • RFID • Radio Frequency Identification • 無線射頻識別 • 利用空間電磁感應或電磁傳播進行通信，以達到自動識別標識物體的目的

  4. RFID的組成元件 • RFID主要有三個組成元件 • 電子標籤(Tag) • RFID詢答器(RFID Transponder)、非接觸ID標籤(Contactless ID Tag) • 感應器(Reader) • 辨識器、讀碼器 • 天線(Antenna)

  5. RFID的組成元件–Tag • 依本身具電源與否區分為三類 • 主動式RFID • 電池型 • 通訊距離可達十公尺 • 可自行處理和傳送資料 • 被動式RFID • 免電池型 • 由讀寫器的天線接收電力後才能動作，通訊距離較短 • 不能自行處理和傳送資料

  6. RFID的組成元件–Tag(cont’d) • 半主動式RFID • 電池支援式 • 標籤內部數位電路供電 • 不能自行發送資料

  7. RFID的組成元件–Reader • 感應器(Reader) • 讀取電子標籤 • 射頻信號，不需要與電子標籤接觸及可讀取資料 • 感應器會與電腦連接，得到的資料傳送至系統作辨識或後續處理

  8. RFID的組成元件–Antenna • 天線(Antenna) • 傳遞電子標籤和感應器之間的射頻信號

  9. RFID的優點 • 儲存資訊量多 • 非接觸式、穿透性 • 可辨識數個RFID標籤、標籤可覆寫 • 使用期限長 • 體積小、多變的形狀 • 讀取速度快 • 安全性高

  10. RFID的缺點 • 有效距離 • 標籤和讀取裝置的通訊距離 • 成本價格較高 • RFID的標籤成本較傳統條碼高 • 易受干擾 • 電磁波無處不在

  11. RFID的應用 • 醫療 • 追蹤傳染性疾病患者、病患辨識、醫療廢棄物品追蹤 • 零售 • RFID標籤取代條碼標籤，追蹤商品，防缺貨 • 監控保全 • RFID技術與無線區域網路結合，取代傳統巡邏

  12. RFID的運作 • Differentiate between two main forms of communication. • Multi-access to a reader • Broadcast mode

  13. RFID的運作 – Multi-access • Data from many individual tag to reader

  14. RFID的運作 – Broadcast • At beginning of identification, reader broadcast to tags in its range and tags return message to reader.

  15. RFID的運作 – Broadcast (cont’d) • Three cases • Only one tag to respond reader. • At the same time have more tag to respond to the reader that result collision. • After reader’s broadcasting no tag respond.

  16. RFIDTag & Collision之間關係 • Active tag • Detect other between tagsto avoid collision. • Passive tags • Not detect other between tags to avoid collision.

  17. Anti-Collision Algorithm– FSA(1/3) • FSA (Framed Slotted ALOHA) • Reader broadcast aframe sizeto tags,all tags select a random number(less than frame size). • Tag have ownrandom number, slot equal to the number, tag transmit message to reader. • Tagtransmit to reader stagger. • Avoidcollisioncaused by tag. • Tags Reader 1 2 3 4

  18. Anti-Collision Algorithm– FSA (2/3) • When collision occur, reader skip collision tags until next cycle, and then readerbroadcast again and collision tagsselect randomnumber and transmit again. • Repeat step until all tags are identified by thereader.

  19. Anti-Collision Algorithm– FSA (3/3) • Issue • Additional memory to save the random number except the ID of tag.

  20. Anti-Collision Algorithm– Query tree (1/2) • Reader broadcasts a prefix and queries the tags. ID of tag is same as prefix, reader recognize it. • Query again until completing.

  21. Anti-Collision Algorithm– Query tree (2/2) • Issue • Not like ALOHA, need extra memory to save number of tag. • Whole identification process check ID with prefix one by one. ID of tags is similar, identification process of tag maybe cost long time. But ALOHA type not impact by ID.

  22. Anti-Collision Algorithm–DFSA(1/2) • DFSA (Dynamic Framed Slotted ALOHA) • Estimate through algorithm can estimate remaining number tags after each round of identification. • Frame size change according to result.

  23. Anti-Collision Algorithm–DFSA(2/2) • Issue • Frame size is no longer fixed, make whole identification process more efficient.

  24. Simple & Efficient Anti-Collision Algorithm (1/8) • Based on ALOHA. • Solve collision immediately when collisions occur. • When collision occur, system restart another identification process(new cycle and abandon previous cycle). • Estimate collision tags and reader broadcast a new frame size to tags. Tag generate random number again and transmit message. • Reduce collision tag to collide again in next round to make more collisions.

  25. Simple & Efficient Anti-Collision Algorithm (2/8) • n:passive tags(have unique ID) • Reader does not know number of tags but can estimate. • Ni:frame size at thebeginning • Reader broadcast frame size Ni to tags, tag generate a number between 1 and Ni. • nc :estimate number of collision tag • Reader use ncto differentiate frame size Nc, tag generate number between 1 and Nc.

  26. Simple & Efficient Anti-Collision Algorithm (3/8)

  27. Simple & Efficient Anti-Collision Algorithm (4/8) • Referring to [2], range of frame size can be decided. • Frame size is close number of tag, efficiency of identification is better.

  28. Simple & Efficient Anti-Collision Algorithm (5/8) • Command “throw_away” • Execute of proposed method. • What reader do when reader detects collision? • c: greater than zero, mean collisions occur • ad:count value to aim at collision tags //Reader: //broadcast “throw_away” if (c > 0) tag_respond = tag(throw_away); if (tag_respond > 0) ad = ad + 1; tag(ad); start a new round; broadcast Nc;

  29. Simple & Efficient Anti-Collision Algorithm (6/8) • What tag do when the reader broadcasts command “throw_away” to collision tag? • ct :limit collision tags to respond to reader //Tag: //Receive initial parameters from reader ct = 1; transmission: receive frame size; generate random number; //must <= frame size if (ct == ad) transmit message; ct = 0; if (receive “throw_away”) ct = ct + 1; goto transmission;

  30. Simple & Efficient Anti-Collision Algorithm (7/8) • Worst case

  31. Simple & Efficient Anti-Collision Algorithm (8/8) • Analyze probability of worst case • Number of tags is between 3 and 32

  32. Simulation Results (1/3) • 10≦n≦300, Ni =16

  33. Simulation Results (2/3) • Ni ={16,64,128}

  34. Simulation Results(3/3) • 10≦n≦1000, Ni =16

  35. Conclusion • The method of anti-collisionalgorithm of RFID system • Base on ALOHA protocol. • Cost fewer slots than DFSA about 54% and efficiency of whole process is about 35%when number of tags is increased to 1000.

  36. Future work • Anti-collisionalgorithm for RFID • Position of RFID

  37. Reference [1] Chuen-Ching Wang, Te-Yuan Wang, Tien-Hao Lien, Rong-Ming Su, "A Simple and Efficient Anti-collision Algorithm for RFID System," iih-msp, pp.300-305, 2010 Sixth International Conference on Intelligent Information Hiding and Multimedia Signal Processing, 2010 [2] Wen-Tzu Chen, Guan-Hung Lin “An Efficient Anti-Collision Method for Tag Identification in a RFID System,” IEICE Transactions on Communications, Volume E89-B, no.12, pp.3386-3392, Dec. 2006. [3]Klaus Finkenzeller,RFID Handbook Fundamentals and Applications in Contactless Smart Cards and Identification,Second Edition,Wiley,2003. [4] 龔哲幀著，「主動式RFID室內定位追蹤演算法與系統設計」，碩 士論文，國立台北科技大學資訊工程研究所，台北，2010。

  38. Thank You For Listening • Q & A

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