What is RFID
(RFID) is the use of a wireless noncontact system that uses radiofrequency electromagnetic fields to
transfer data from a tag attached to an
object, for the purposes of automatic
identification and tracking.
RFID is also called dedicated short
EPC Gen 2 Architecture
Each RFID tag contains a unique code that facilitating
the identification process & is known as EPC
EPC is the new Electronic Product Code that
replaces the older UPC (Universal Product Code)
found on many item labels and is a set of numbers plus
a bar code.
Since UPC first started in 1963 it became out of date
with today's global economies and EPC is
the Radio Frequency Identification (RFID) modern
day equivalent of the older UPC.
In most instances, EPCs are encoded on RFID tags
which can be used to track all kinds of objects
including: trade items, fixed assets, documents, or
reusable transport items.
"Class-1" refers to the functionality of the tag while
"Gen-2" refers to the physical and logical standards of
tag and the encompassing system. These standards are
maintained by EPCglobal.
Gen 2, EPC Gen 2, EPC C1G2 are the short names
commonly used instead of "Electronic Product
Code Class 1 Generation 2" standard.
Working of RFID
A RFID system is made up of two parts: a tag or label and
RFID tags or labels are embedded with a transmitter and
The RFID component on the tags have two parts: a
microchip that stores and processes information, and an
antenna to receive and transmit a signal.
The tag contains the specific serial number for one
To read the information encoded on a tag, a two-way radio
transmitter-receiver called an interrogator or reader emits a
signal to the tag using an antenna.
The tag responds with the information written in its
The interrogator will then transmit the read results to an
RFID computer program.
Types of RFID Tags
There are two types of RFID tags: passive and battery
A passive RFID tag will use the interrogator’s radio
wave energy to relay its stored information back to the
A batter powered RFID tag is embedded with a small
battery that powers the relay of information.
•Remotely power tags
•Establish a bidirectional data link
•Inventory tags, filter results
•Communicate with networked
•Can read 100-300 tags per second
Readers (interrogators) can be at a
fixed point such as
•Point of sale
Readers can also be mobile/hand-held
Host manages Reader(s) and issues Commands
• Reader and tag communicate via RF signal
• Carrier signal generated by the reader
• Carrier signal sent out through the antennas
• Carrier signal hits tag(s)
• Tag receives and modifies carrier signal– “sends back” modulated
•Antennas receive the modulated signal and send them to the Reader
•Reader decodes the data
• Results returned to the host application
EPC Gen 2 Physical Layer
The physical layer defines how bits are sent between the
RFID reader and tags.
In the U.S., transmissions are sent in the unlicensed 902–
928 MHz ISM band. This band falls in the UHF (Ultra High
Frequency) range, so the tags are referred to as UHF RFID
The reader and tags use forms of ASK (Amplitude Shift
They take turns to send bits, so the link is half duplex.
There are two main differences from other physical
The first is that the reader is always transmitting a
signal, regardless of whether it is the reader or tag that is
Naturally, the reader transmits a signal to send bits to
tags. For the tags to send bits to the reader, the reader
transmits a fixed carrier signal that carries no bits.
The tags harvest this signal to get the power they need
to run; otherwise, a tag would not be able to transmit in
the first place.
To send data, a tag changes whether it is reflecting
the signal from the reader, like a radar signal bouncing
off a target, or absorbing it.
This method is called backscatter.
It differs from all the other wireless situations
Backscatter is a low-energy way for the tag to create
a weak signal of its own that shows up at the reader.
For the reader to decode the incoming signal, it must
filter out the outgoing signal that it is transmitting.
The second difference is that very simple forms of
modulation are used so that they can be implemented on a
tag that runs on very little power and costs only a
few cents to make.
To send data to the tags, the reader uses two amplitude
Bits are determined to be either a 0 or a 1, depending on
how long the reader waits before a low-power period.
The tag measures the time between low-power
periods and compares this time to a reference measured
during a preamble.
Tag responses consist of the tag alternating
its backscatter state at fixed intervals to create
a series of pulses in the signal.
Anywhere from one to eight pulse periods
can be used to encode each 0 or 1, depending
on the need for reliability.
EPC Gen 2 Tag Identification Layer
•To inventory the nearby tags, the reader needs to
receive a message from each tag that gives the
identifier for the tag.
•The reader might broadcast a query to ask all tags
to send their identifiers.
The closest protocol for the current situation,
in which the tags cannot hear each others’
transmissions, is slotted ALOHA, one of the
This protocol is adapted for use in Gen 2 RFID
In the first slot (slot 0), the reader sends a
Query message to start the process.
Each QRepeat message advances to the next
slot. EPC Gen 2 Tag Identification Layer
Tags do not send their identifiers when they first
Instead, a tag sends a short 16-bit random number
in an RN16 message.
If there is no collision, the reader receives this
message and sends an ACK message of its own.
At this stage, the tag has acquired the slot and sends
its EPC identifier.
The reason for this exchange is that EPC identifiers are
long, so collisions on these messages would be
Instead, a short exchange is used to test whether the
tag can safely use the slot to send its identifier.
Once its identifier has been successfully transmitted,
the tag temporarily stops responding to new Query
messages so that all the remaining tags can be identified
If the reader sees too many slots with no responses or too
many slots with collisions, it can send a Qadjust message to
decrease or increase the range of slots over which the tags
The reader can also write data to tags as they are
Tag Identification Message Formats
The message is compact because the downlink rates are limited,
from 27 kbps up to 128 kbps.
The next flags, DR, M, and TR, determine the physical
layer parameters for reader transmissions and tag
Then come three fields, Sel, Session, and Target, that
select the tags to respond.
In this way, multiple readers can operate in overlapping
coverage areas by using different sessions.
Next is the most important parameter for this command, Q.
This field defines the range of slots over which tags will
respond, from 0 to 2Q−1. Finally, there is a CRC to protect the
the Query message is much shorter than most packets too.
The tag responses simply carry data, such as the EPC identifier.
Originally the tags were just for identification purposes
Advantages of RFID:
Vulnerability to damage minimized
Easy to use
High memory capacity
Disadvantages of RFID: