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 2^Q-1
• CRC to protect the fields
• grown to resemble very small computers Internet of Things

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