RFID(Radio Frequency IDentification)

Radio-frequency identification (RFID) is the use of a wireless non-contact system that uses radio-frequency electromagnetic fields to transfer data from a tag attached to an object, for the purposes of automatic identification and tracking.

What is RFID

chip

Antenna

Applications of RFID

Payment by mobile phones Inventory systems Product tracking Transportation Infrastructure management Passports Transportation payments Animal identification Human identification Hospitals and healthcare Libraries Museums Schools and universities Sports

Animal Identification

E-Passport

Library Systems

Human Identification

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Since UPC first started in 1963 it became out of date with today's global economies and EPC is the Radio Frequency Identification (RFID) modern day equivalent of the older UPC.

EPC Gen 2 Architecture

Gen 2, EPC Gen 2, EPC C1G2 are the short names commonly used instead of "Electronic Product Code Class 1 Generation 2" standard.

"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.

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.

EPC Standard

A RFID system is made up of two parts: a tag or label and a reader.

RFID tags or labels are embedded with a transmitter and a receiver.

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 specific object. 

Working of RFID

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 memory bank.

The interrogator will then transmit the read results to an RFID computer program.

Working of RFID

There are two types of RFID tags: passive and battery powered. 

A passive RFID tag will use the interrogator’s radio wave energy to relay its stored information back to the interrogator.

 A batter powered RFID tag is embedded with a small battery that powers the relay of information. 

Types of RFID Tags

Reader functions:•Remotely power tags•Establish a bidirectional data link•Inventory tags, filter results•Communicate with networked server(s)•Can read 100-300 tags per second

Readers (interrogators) can be at a fixed point such as•Entrance/exit•Point of sale

Readers can also be mobile/hand-held

RFID readers

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 signal

•Antennas receive the modulated signal and send them to the Reader

•Reader decodes the data

• Results returned to the host application

RFID communication

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 tags.

The reader and tags use forms of ASK (Amplitude Shift Keying) modulation

They take turns to send bits, so the link is half duplex.

There are two main differences from other physical layers.

The first is that the reader is always transmitting a signal, regardless of whether it is the reader or tag that is communicating.

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 levels.

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.

Reader and tag backscatter signals

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 earliest protocols.

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

EPC Gen 2 Tag Identification Layer

Tags do not send their identifiers when they first reply.

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 expensive.

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 are responding.

The reader can also write data to tags as they are identified.

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 responses.

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 message fields.

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

Inventory efficiencyVulnerability to damage minimizedEasy to useHigh memory capacity

Disadvantages of RFID:

Security concernsHigh costUnread tags

Advantages of RFID: