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Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 2010.12.31 Slide 2 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 RFID RFID collision problem Conclusion Future work Reference 2 Slide 3 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 RFID Radio Frequency Identification 3 Slide 4 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 RFID 1. (Tag) RFID (RFID Transponder) ID (Contactless ID Tag) 2. (Reader) 3. (Antenna) 4 Slide 5 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 1. RFID 2. RFID 5 Slide 6 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 3. RFID 6 Slide 7 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 (Reader) 7 Slide 8 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 (Antenna) 8 Slide 9 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 1. 2. 3. RFID 4. 5. 6. 7. 9 Slide 10 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 1. 2. RFID 3. 10 Slide 11 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 RFID RFID 11 Slide 12 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 Differentiate between two main forms of communication. Multi-access to a reader Broadcast mode 12 Slide 13 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 Data from many individual tag to reader 13 Slide 14 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 At beginning of identification, reader broadcast to tags in its range and tags return message to reader. 14 Slide 15 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 Three cases 1.Only one tag to respond reader. 2.At the same time have more tag to respond to the reader that result collision. 3.After readers broadcasting no tag respond. 15 Slide 16 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 Active tag Detect other between tags to avoid collision. Passive tags Not detect other between tags to avoid collision. 16 Slide 17 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 FSA (Framed Slotted ALOHA) Reader broadcast a frame size to tags, all tags select a random number(less than frame size). Tag have own random number, slot equal to the number, tag transmit message to reader. Tag transmit to reader stagger. Avoid collision caused by tag. Tags 17 Reader 12 34 Slide 18 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 When collision occur, reader skip collision tags until next cycle, and then reader broadcast again and collision tags select random number and transmit again. Repeat step until all tags are identified by the reader. 18 Slide 19 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 19 Issue Additional memory to save the random number except the ID of tag. Slide 20 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 20 Reader broadcasts a prefix and queries the tags. ID of tag is same as prefix, reader recognize it. Query again until completing. Slide 21 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 21 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. Slide 22 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 DFSA (Dynamic Framed Slotted ALOHA) Estimate through algorithm can estimate remaining number tags after each round of identification. Frame size change according to result. 22 Slide 23 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 23 Issue Frame size is no longer fixed, make whole identification process more efficient. Slide 24 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 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. 24 Slide 25 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 n : passive tags(have unique ID) Reader does not know number of tags but can estimate. N i : frame size at the beginning Reader broadcast frame size N i to tags, tag generate a number between 1 and N i. n c : estimate number of collision tag Reader use n c to differentiate frame size N c, tag generate number between 1 and N c. 25 Slide 26 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 26 Slide 27 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 Referring to [2], range of frame size can be decided. Frame size is close number of tag, efficiency of identification is better. 27 Slide 28 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 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; 28 Slide 29 Wireless and Broadband Networks Laboratory Department of Computer Science and Information Engineering National Taipei University of Technology / 38 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