Friday, November 23, 2012

Notes - RFID

The following are notes from Computer Networks written by Tanenbaum 5th edition.
  • RFID(Radio Frequency Identification)
  • EPC(Electronic Product Code)
    • commercialized by EPCglobal
EPC Gen 2 Architecture
  • communicates via the RFID Reader which sends out a signal that gets scatted back by a RFID tag
  • EPC gives each tag 96 bit EPC identifier 
  • readers have all the intelligence, much more powerful and do all signal processing
EPC Gen 2 Physical Layer
  • sent in the UHF(Ultra High Frequency) range
  • readers and tags use ASK(Amplitude shift keying) modulation to encode bits
EPC Gen 2 Tag Identification layer
  • situation is multiple access problem
  • closest protocol is slotted ALOHA protocol
  • tags pick a random slot to reply with
  • sends a short 16 bit random number for collision reader receives and sends ACK to acquire slot and send EPC identifier
  • adjust number of slot, reader can send QAdjust message to change slot adjust level for RFID tags
Tag Identification Message Formats
  • Form of the Query Message
    • Command field identifies this as query
    • DR, M, TR determine physical layer parameters
    • Sel, session and target select the tags to respond tags keep track of up to 4 concurrent sessions
    • Q defines the range of slots that tags can respond to 0 to 2Q-1
    • CRC to protect the fields
    • grown to resemble very small computers Internet of Things

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