Describing the messages being exchanged between a reader and RFID tag.

1. 1
Radio Frequency Identification
(Part 2)
Amjad Y. Majid
Przemysław Pawełczak
Wireless Networking [ET4394]

2. 2
EPCglobal Class 1 Generation 2

3. 33
EPC
• ISO 18000-6C
• Specially for passive UHF backscatter RF tags
• Features
• Reader talk first
• Tags can be read, written, and killed in the field
• A killed tag does nothing and remains killed forever
• Flexible data rates
• Provides methods for spectral control to avoid interference
• Uses a Slotted-Aloha algorithm to mitigate data collisions
Source: EPC Protocols Gen2 UHF RFID v2.0.0, EPCGlobal, nov 2013
Source: The Fundamentals of Backscatter Radio and RFID Systems, Disney Research Pittsburg, 2009

4. 4
Reader to Tag
Messages

5. 55
EPC C1 Gen2 (R=>T)
http://www.gs1.org/
Reader Tag
● Query: starts an inventory round
● QueryRep: indicates the beginning of a slot
● QueryAdjust: adjusts the number of slots
● Command: Can be Read, Write, BlockWrite
Inventory
Access
(Read/Write)

6. 66
EPC C1 Gen2 Overview
● EPC goal is to enable the reader to
identify all tags
● Collisions may occur
● Slotted Aloha
○ Within a slot only one tag should
reply
Antenna
Tags

7. 77
EPC (R=>T) Inventory
http://www.gs1.org/
Reader
Tag
Tag
Tag
Reader
Reader
no Reply Good Reply
Reader
Collision
Reader

8. 88
Messages Preambles
http://www.gs1.org/

9. 99
Query Message
http://www.gs1.org/

10. 1010
Message Preamble
http://www.gs1.org/

11. 1111
Modulation (Reader signals)
http://www.gs1.org/

12. 1212
Data Encoding
http://www.gs1.org/

13. 13
Tag to Reader
Backscattering

14. 1414
EPC (T=>R) Messages
http://www.gs1.org/
Reader Tag
● RN16
● EPC
● handle

15. 1515
Signal Preamble
http://www.gs1.org/

16. 1616
Data Symbols
http://www.gs1.org/

17. 1717
TCP Sniffer
QueryRep:S2 3986
TAG::1010v101010011100110 4854
ACK:010101001110011011 5394
Antenna USRP Matlab GnuRadio Output

18. 18
Thank you for your attention!