RFID (Radio Frequency Identification)Overview

António Grilo

Courtesy: Greg Leeming, INTEL

Sridhar Iyer, ITT Bombay

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Radio Frequency Identification

Tags

Reader

Power from RF field

ReaderAntenna

Reader->Tag Commands

Tag->Reader Responses

RFID Communication Channel

RFID Communications

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 (Passive Backscatter – also referred to as “field disturbance device”)

Antennas receive the modulated signal and send them to the Reader

Reader decodes the data Results returned to the host application

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Radio Frequency IDentification

Frequency Distance Example Application

LF 125khz Few cm Auto-Immobilizer

HF 13.56Mhz 1m Building Access

UHF 865-868Mhz ~7m Supply Chain

μwave 2.4Ghz 10m Traffic Toll

Four main frequencies:Four main frequencies:

• Tag wirelessly sends bits of data whenit is triggered by a reader

• Power source not required for passive tags… a defining benefit

• Superior capabilities to barcode:

– Non Line of Sight– Hi-speed, multiple reads– Can read and write to tags– Unit specific ID

Focus of this presentation is on UHF

RFID History

First Bar code patents – 1930s First use of RFID device – 2nd world war – Brittan used RFID-like

technology for Identify- Friend or Foe Harry Stockman October 1948 Paper – Communication by means of

reflected power ( The proceedings of the Institute of Radio Engineers) First RFID Patent - 1973 Auto-ID center founded at MIT – 1999

Standardization effort taken over by EPC Global (Electronic Product Code)

Current thrust primarily driven by Wal-Mart and DoD Automate Distribution:

Reduce cost (man power, shipping mistakes) Increase sales (keep shelves full) DoD Total Asset Visibility Initiative

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125 kHz (135 kHz)

Late eighties: RFID-Projects gave initial boost Pigeons logging Immobilizer (cars)

Logistics Gas bottles Beer barrels Garbage cans Container for toner (printer) Laundry services

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125 kHz (135 kHz)

Industry Tool identification

Entertainment Casino Roulette Chips

Access systems Turnstile (Ski, swimming pool) Door locks Working time recording

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13,56 MHz

Late nineties: Encryption and faster Payment systems

Cafeteria, restaurants

Access systems / Events Turnstile, Door locks Stadium, Theme parks Convention center (Mifare)

Public transportation Bus, underground, ferries (South Korea, London)

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868 MHz (UHF)

Late nineties: Projects for UHF systems Logistics

First projects had a poor hit rate (60%) Expensive labels

National Identity ID card (China 1300Mio, 2005/6) License-plate number (50cm reading distance)

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Basic Tag Operational Principles

• Near field (LF, HF): inductive coupling of tag to magnetic field circulating around antenna (like a transformer)• Varying magnetic flux induces current in tag. Modulate tag load to communicate with reader• Power decreases proportionally to 1/d6

• Far field (UHF, microwave): backscatter. • Modulate back scatter by changing antenna impedance• Power decreases proportionally to 1/d2

• Boundray between near and far field: d = wavelength / (2 pi) so, once have reached far field, lower frequencies will have lost significantly more energy than high frequencies

• Absorption by non-conductive materials significant problem for microwave frequencies

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Limiting Factors for Passive RFID

1. Reader transmitter power Pt(reader) (Gov’t. limited)2. Reader receiver sensitivity Sr3. Reader antenna gain Gr (Gov’t. limited)

4. Tag antenna gain Gt (Size limited)5. Power required at tag Pr(tag) (Silicon process limited)6. Tag modulator efficiency Et

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Implications

Since in far field Pr(tag) 1/d2 , doubling read range requires 4X the transmitter power.

Larger antennas can help, but at the expense of larger physical size because G{t,r} Area.

More advanced CMOS process technology will help by reducing Pr(tag).

At large distances, reader sensitivity limitations dominate.

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Types of Tags

Passive Operational power scavenged

from reader radiated power

Semi-passive Operational power provided by battery

Active Operational power provided by battery - transmitter built into

tag

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Electronic Product Code

Header - Tag version numberEPC Manager - Manufacturer ID

Object class - Manufacturer’s product IDSerial Number - Unit ID

With 96 bit code, 268 million companies can each categorize 16 million different products where each product category contains up to 687 billion individual units

Note: 64 bit versions also defined, 256 bit version under definition

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Generic Tag Architecture (Highly Simplified)

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ProtocolEngine

Receiver

Memory

Ante

nna

Write Path

D

S

G

Possible UHF Reader RF Processor

Transmit path Receive Path Frequency Synthesizer Digital

RFID READERRF ModuleDAC

Hos

t Dev

ice

ADC

Crystal

Micro-Controller

AGC Filters I/QDemod

PLL

VCO

DAC Power Control

PA

Filter Coupler

Coupler

PowerDetect

Coupler

FPGA

Regulation

Baseband&

Protocol

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Possible Digital Back End

Ethernet

IXP425Processor

Power Supply

RAM

Flash

RF Board Interface

GPIO

Serial Port

LEDsRF

Module

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Possible Reader Software Stack

RFID Reader API Library

CustomApplication/

Protocol

ReaderProtocol

ApplicationN

etw

ork

man

agem

ent

File Systems

NetworkProtocols

High-Level Interfaces

Low-Level InterfacesO/S

Hardware

Platform API Libraries

CustomApplication/

Protocol

CustomApplication/

Protocol

Network Interface

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Tag DetailsLFLF HFHF UHFUHF MicrowaveMicrowave

Freq. Freq. RangeRange

125 125 -- 134KHz134KHz 13.56 MHz13.56 MHz 866 866 -- 915MHz915MHz 2.45 2.45 -- 5.8 GHz5.8 GHz

Read Read RangeRange

10 cm10 cm 1M1M 22--7 M7 M 1M1M

Market Market shareshare

74%74% 17%17% 6%6% 3%3%

CouplingCoupling MagneticMagnetic MagneticMagnetic Electro magneticElectro magnetic Electro magneticElectro magnetic

Existing Existing standardsstandards

11784/85, 11784/85, 1422314223

1800018000--3.1, 3.1, 15693,14443 A, 15693,14443 A, B, and CB, and C

EPC C0, C1, EPC C0, C1, C1G2, 18000C1G2, 18000--66

1800018000--44

ApplicationApplication Smart Card, Smart Card, Ticketing, Ticketing, animal tagging,animal tagging,Access, LaundryAccess, Laundry

Small item Small item management, management, supply chain,supply chain,AntiAnti--theft, theft, library, library, transportationtransportation

Transportation Transportation vehicle ID, vehicle ID, Access/Security, Access/Security, large item large item management, management, supply chainsupply chain

Transportation Transportation vehicle ID (road vehicle ID (road toll), toll), Access/Security, Access/Security, large item large item management, management, supply chainsupply chain

Communication Protocols

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865MHz 867MHz200KHz

Transmission from other ReadersMax 4 sec TX then re-listen for 100 msec

Listen before talk Mandatory listen time of >5 msec before each transmission

ETSI EN 302 208 standard

Shared operation in band 865.0 – 868.0 MHz at transmit powers upto 2 W ERP. Operation in 10 sub-bands of 200 kHz. Power levels of 100 mW, 500 mW and 2 W ERP.

Mandatory “listen before talk” and “look before leap”.

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865.7 MHz 867.5 MHz

FT

865.1 MHz 867.9 MHz

100 mW

867.7 MHz865.5 MHz

LT

FT

LT LT

FT

600 kHz 600 kHz600 kHz

2 W

FT

LT

500 mW

865.0 MHz 865.6 MHz 867.6 MHz 868.0 MHz

Reader Collision Problem

Reader-Reader Interference Reader-Tag Interference

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Reader Collision and Hidden Terminal

The passive tags are not able to take part in the collision resolution or avoidance, as in other wireless systems

Consider: RTS-CTS for hidden terminal problem in 802.11 rfid: T is not able to send a CTS in response

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In case multiple readers try to read the same tag, the tag cannot respond selectively to a particular reader

TDMA Based Solution

Assign different time slots and/or frequencies to nearby readers Reduces to graph coloring problem (readers form vertices)

Only reader to reader interference Assign different operating frequencies

Only multiple reader to tag interference Assign different time slots for operation

Both types of interference First allot different time slots, then frequencies

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Beacon Based Solution

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A reader while reading tag, periodically sends a beacon on the control channel

Assumptions Separate control channel

between readers The range in the control

channel is sufficient for a reader to communicate with all the possible readers that might interfere in the data channel

Beacon Based Solution (contd.)

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Multiple Tags

When multiple tags are in range of the reader: All the tags will be excited at the same time. Makes it very difficult to distinguish between the tags.

Collision avoidance mechanisms: Probabilistic:

Tags return at random times.

Deterministic: Reader searches for specific tags.

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Tag Collision Problem

Multiple tags simultaneously respond to query Results in collision at the reader

Several approaches Tree algorithm Memoryless protocol Contactless protocol I-code protocol

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Tree Algorithm

Reader queries for tags Reader informs in case of collision and tags generates 0 or 1

randomly If 0 then tag retransmits on next query If 1 then tag becomes silent and starts incrementing its counter

(which is initially zero) Counter incremented every time collision reported and

decremented every time identification reported Tag remains silent till its counter becomes zero

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Tree Algorithm – Example

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Reader informs tags in case of collision and tags generate 0 or 1•If 0 then tag retransmits on next query, else tag becomes silent and starts a counter.

Counter incremented every time collision reported and decremented otherwise.

Tree Algorithm - Complexity

Time Complexity – O(n) where n is number of tags to be identified

Message Complexity n is unknown – θ(nlogn) n is known - θ(n)

Overheads Requires random number generator Requires counter

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Memoryless Protocol

Assumption: tagID stored in k bit binary string Algorithm

Reader queries for prefix p In case of collision queries for p0 or p1

Time complexity Running time – O(n) Worst Case – n*(k + 2 – logn)

Message Complexity – k*(2.21logn + 4.19)

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Memoryless Protocol – Example

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Reader queries for prefix p In case of collision, reader queries for p0 or p1 Example: consider tags with prefixes: 00111, 01010, 01100, 10101,

10110 and 10111

Contactless Protocol

Assumption: tagID stored in k bit binary string Algorithm

Reader queries for (i)th bit Reader informs in case of collision

Tags with (i)th bit 0 become silent and maintain counter Tags with (i)th bit 1 respond to next query for (i+1)th bit

Time complexity – O(2k) Message complexity – O(m(k+1)), where m is number of

tags

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Contactless Protocol – Example

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Reader queries for (i)th bit Reader informs in case of collision

Tags with (i)th bit 0 become silent and maintain counter Tags with (i)th bit 1 respond to next query for (i+1)th bit

Example: tags with prefixes: 01, 10 and 11

I-Code Protocol

Based on slotted ALOHA principle Algorithm

Reader provides time frame with N slots, N calculated for estimate n of tags

Tags randomly choose a slot and transmit their information Responses possible for each slot are

Empty, no tag transmitted in this slot – c0

Single response, identifying the tag – c1

Multiple responses, collision – ck

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I-Code Protocol

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New estimate for n : lower bound εlb(N, c0, c1,ck) = c1 + 2ck

Using estimate n, N calculated N becomes constant after some time Using this N calculate number of read cycles s to identify tags

with a given level of accuracy α

Time complexity – t0*(s+p) t0 is time for one read cycle p number of read cycles for estimating N

Message complexity – n*(s+p)

ISO 18000 Standard

18000-1 Reference architecture and definition of parameters 18000-2 Parameters for air interface communications below 135 kHz 18000-3 Parameters for air interface communications at 13,56 MHz 18000-4 Parameters for air interface communications at 2,45 GHz (18000-5) Parameters for air interface communications at 5,8 GHz 18000-6 (Type A, B, C) Parameters for air interface communications at

860-960 MHz 18000-7 Parameters for active air interface communications at 433

MHz

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EPCglobal Tag Classes

Class-1: Identity Tags

Class-2: Higher functionality tags

Class-3: Battery-Assisted Passive Tags

Class-4: Active Tags

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Competing UHF Protocols (EPC only)Read Rate Read or

Read/WriteTagCost

Privacy Security Global Standard

Class 0 NA: 800 reads/secEU: 200 reads/sec

Read Only $$ 24 bit password

Reader broadcasts OID or Anonymous modes with reduced

throughput

No

Class 0+ NA:800 reads/secEU:200 reads/sec

Read & Write $$ See above See above No

Class 1 NA:200 reads/secEU: 50 reads/sec

Read & Write $ 8 bit password Reader broadcasts partial OID

No

Class 1 Gen 2(UHF Gen2)

NA:1700 reads/secEU: 600 reads/sec

Read & Write ? 32 bit password and concealed mode

Authentication and Encryption

Yes

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Class 0 Protocol

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Class 0 Signalling

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Default Class 0 Reader Communication Sequence Tag Singulation ProcessTag power up, reset, and calibration process

Single Binary Transversal

Repeated after each frequency hop

Once tag has been singulated, reader can send commands to it or begin next BT cycle

Reset: 800 micro sec uninterrupted continuous waveOscillator calibration: 8 116 micro sec pulses

Data calibration: 3 pulses ( data “0”, data “1”, data “null”)

Reset: 800 micro sec uninterrupted continuous waveOscillator calibration: 8 116 micro sec pulses

Data calibration: 3 pulses ( data “0”, data “1”, data “null”)

Readerpower up

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Tag Singulation Processread individual tag from group of all tags in range of reader

Basic process:

1. All tags within range of reader backscatter their MSB to the reader.

2. Reader responds with either a 1 or a 0.

3. If tag bit equals reader bit, tag backscatters the next bit in it’s code . If instead, tag bit does not equal reader bit, tag goes mute for remainder of singulation.

4. Process continues until reader has completely read a single tag.

5. Reader conducts consecutive singulations until all tags in its range are read.

6. Reader can interrupt the singulation process to send commands to a single tag, a subset of all tags in range, or globally to all tags in range.

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EPC Gen 2 Protocol

EPC Gen 2 is a UHF protocol EPC Gen 2 Protocol is likely to become a global standard Gen 2 protocol was designed to optimize performance in

different regulatory environments around the world

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EPC Gen 2 Protocol

EPC Gen 2 Protocol is allows readers to operate in 3 different modes Single-reader mode Multi-reader mode Dense-reader mode

Dense mode is designed to prevent readers from interfering with one another

Dense mode uses a backscatter method called “Miller subcarrier”

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EPC Gen 2 Protocol - Memory

Gen 2 tags are field programmable Gen 2 tags have 4 memory areas:

3 required: EPC Password Tag identification

1 optional Memory areas can be locked temporary or permanently

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EPC Gen 2 Protocol – Q Algorithm Q Algorithm allows readers to query tags even if two tags

have the same EPC or do not contain EPC at all The query mechanism is based on random number

generation The reader does not have to transmit EPC, preventing

eavesdropping

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Sessions

Each Gen 2 tags can have 4 separate sessions for communicating

Sessions is a means for preventing interference (e.g. caused by different readers)

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Savant

Savant is a middleware specification developed by the Auto-ID Center

Savant acts as a “nervous system” of an RFID network After readers pick up EPC codes, Savant manages and

moves the data

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Savant

Savant uses distributed architecture and is organized into a hierarchy of individual savants that manages the process of gathering and distributing data

Tasks savant can do: Data smoothing Reader coordination Data forwarding Data storage Task Management

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Object Name Service (ONS) The Object Name Service (ONS) provides a global lookup

service to translate an EPC into one or more Internet Uniform Reference Locators (URLs) where further information on the object may be found

These URLs often identify an EPC Information Service, though ONS may also be used to associate EPCs with web sites and other Internet resources relevant to an object

ONS provides both static and dynamic services. Static ONS typically provides URLs for information maintained by an object’s manufacturer

Dynamic ONS services record a sequence of custodians as an object moves through a supply chain

ONS is built using the same technology as DNS, the Domain Name Service of the Internet

Source: Auto-ID/EPCglobal 54

Physical Markup Language (PML) The Physical Mark-Up Language (PML) is a collection of

common, standardized XML vocabularies to represent and distribute information related to EPC Network enabled objects

The PML standardizes the content of messages exchanged within the EPC network.

It is a part of the Auto-ID Center’s effort to develop standardized 283

interfaces and protocols for the communication with and within the Auto-ID infrastructure

The core part of the physical mark-up-language (PML Core) provides a standardized format for the exchange of the data captured by the sensors (readers) in the Auto-ID infrastructure

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Reader Protocol

The Reader Protocol specifies the interaction between a device capable of reading (and possibly writing) tags, and application software

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