15-446 Networked Systems Practicum

Lecture 6 – RFID technology

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• Basic RFID

• NFC (RFID + Storage)

• Next Generation RFIDs (RFID + Computation + Storage)

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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

Basic Tag Operational Principles

NN

SS

TAG

Rea

der

Rea

der

TAG

BackscatterBackscatter

• 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• field energy decreases proportionally to 1/R3 (to first order)

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

• Boundry between near and far field: R = 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

Inductive CouplingInductive Coupling

Tag DetailsLF HF UHF Microwave

Freq. Range

125 - 134KHz 13.56 MHz 866 - 915MHz 2.45 - 5.8 GHz

Read Range

10 cm 1M 2-7 M 1M

Market share

74% 17% 6% 3%

Coupling Magnetic Magnetic Electro magnetic

Electro magnetic

Existing standards

11784/85, 14223

18000-3.1, 15693,14443 A, B, and C

EPC C0, C1, C1G2, 18000-6

18000-4

Application

Smart Card, Ticketing, animal tagging,Access, Laundry

Small item management, supply chain,Anti-theft, library, transportation

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

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

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

Real Tags

Real Tags

Real Tags

Electronic Product Code

Header - Tag version number EPC Manager - Manufacturer ID Object class - Manufacturer’s product ID Serial 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

Class 1 Gen 2 tags

• 900 Mhz

• 10m range

• Downlink = information + energy• 26.7 – 128kbps

• Uplink = energy sent down as continuous wave (CW) + modulate reflection coefficient of antenna

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Multiple Tags?

• What happens when multiple tags are in range of the transceiver?

• All the tags will be excited at the same time.

• Makes it very difficult to distinguish between the tags.

Collision Avoidance

• Similar to network collision avoidance

• Probabilistic• Tags return at random times

• Deterministic• Reader searches for specific tags

CIG2 MAC

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Traditional RFID Market Segments

Auto ImmobilizersAuto Immobilizers

Access ControlAccess ControlAnimal TrackingAnimal Tracking

Automated Vehicle IdAutomated Vehicle Id

• Isolated systemsIsolated systems• Simple readsSimple reads• Slow growthSlow growth

The New Mkt SegmentConsumer Pkg Goods Supply Chain

Wal-Mart•June ’03 announcement•Pallet/Case tagging

Top 100 suppliers Jan ’05Other 30K by end of ’06

•4 Billion tags/year•300k direct readers•18 Million indirect readers

• End to end systemsEnd to end systems• Complex readsComplex reads• Emerging marketEmerging market

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RFID in the Supply-Chain

Today: Outside the Supply Chain

• Basic RFID

• NFC (RFID + Storage)

• Next Generation RFIDs (RFID + Computation + Storage)

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NFC Phy

• 13.56MHz frequency, 14kHz band

• Range 4cm (max 20cm)

• Active (2 transmitters) and Passive (1 transmitter + load modulation) mode

• Data rate = 106, 212 or 424kbps

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NFC Tag Types

• Type 1 and 2• 96 or 48 bytes, 106kbps• Read/write or read only • Expansion to 2kbyte

• Type 3• 2kbyte• 212kbps• Read-only

• Type 4• 32kbyte• 106-424 kbps• Read-only

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• Basic RFID

• NFC (RFID + Storage)

• Next Generation RFIDs (RFID + Computation + Storage)

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• Collection of small, battery-powered sensing devices (motes)

• Peer-to-peer communication (multi-hop network)• Range of monitoring applications:

• habitat monitoring, structural integrity of bridges• volcanic activity, forest fires, etc.

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UHF RFID EPC Class Gen 2

• Powered reader infrastructure plus simple passive tags

• Direct reader to tag communication• 4W EIRP from readers, tags “backscatter,” range of up

to ~30ft • Applications around inventory / supply chain

management

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• Combine the best of both: • Small / inexpensive passive tags that sense/compute

(WISPs) and communicate directly with apps in infrastructure (via readers)

• Key advantages:• Ubiquitous, long-lived instrumentation, business simplicity,

flexibility

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Milk App

Cold chain monitoring: •Track many small items, e.g., bags of blood, items in fridge, with cheap and/or disposable tag •Use proximity of readers to sense temperature and vital statistics when refrigerated most of the time •Use stored energy (super-cap) to sense for brief periods when items are away from reader and exposed

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Intermittent Power

• How do we run programs on WISPs with intermittent power?

• WISP power model: • Gathers energy from

readers, when in range (~15ft) at unpredictable times

• Has limited on board storage (capacitor << battery)

• Expends energy to sense/compute and communicate

• Slowly loses stored energy

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• WISP API to expose power state to application code• “Enough power yet to complete this step?”

• Divide large computation into multiple small stages• Store state in non-volatile memory or on readers

• Coordinate to match reader power to WISP needs• Continue to provide for a sufficient interval

• Implications • Lower reliability due to unpredictable contacts, power

durations • Variable frequency of operation due to “pre-charge”

period

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