PHYSICS, NETWORKS AND STANDARDS IN RFID

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• PHYSICS, NETWORKS AND STANDARDS IN RFID

Peter H. Cole Professor of RFID Systems at the
University of Adelaide and Director of the
Auto-ID Laboratory _at_ Adelaide
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• PART 1
• INTRODUCTION

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Outline

• Introduction
• General RFID concepts
• Electromagnetic Fields and propagation
• Design issues in RFID systems
• Electromagnetic coupling in the far field
• Electromagnetic coupling in the near field
• Coupling volume theory
• Auto-ID and EPCglobal concepts
• Protocols in RFID reading
• Problems of small tags

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• Good news
• Presentation ist stark reduziert

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Tag reading
The black spot
With passive tags a very weak reply is obtained
Some application illustrations will be given
shortly
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Traffic Monitoring
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Waste Collection
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EAS Gates
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Tags use electromagnetic fields

• Coupling is via electromagnetic fields
• There is little margin for poor performance
• We must understand their properties

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• PART 2
• ELECTROMAGNETIC FIELDS AND PROPAGATION

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Laws in differential form
Vortex
Source
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Laws in empty space
Vortex
Source
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Electromagnetic propagation
Electric and magnetic fields orthogonal,
proportional and in time phase.
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Electromagnetic waves

• They propagate with the velocity of light
• (Light is an electromagnetic wave)
• Velocity c is 300,000,000 m/s
• Wavelength - frequency relation is c fl
• Propagation constant b 2p/l
• But not all electromagnetic fields are
  propagating waves some are just local energy
  storage fields

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Fields of a Magnetic Dipole(oh dear)
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The radian sphere

• At br 1, r l/2p, and
• The phase factor e-jbr is one radian
• Inside this sphere the near field predominates
• Outside this sphere the far field predominates

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Boundary Condition electric field
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Boundary Condition magnetic field
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Microelectronic backscatter

• Concept can be applied from 10 MHz to 10,000 MHz
• Low propagation loss points to coupling using the
  far field
• Low power consumption requires a low frequency
  microcircuit
• Reply is by modulation of the interrogation
  frequency

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Planar printed coil
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Ferrite cored solenoid
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Electric field bow tie
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Electric field box structure
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• PART 4
• ELECTROMAGNETIC COUPLING IN THE FAR FIELD

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Far field coupling theory 1
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Far field coupling theory 2
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Far field coupling theory 3
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• PART 5
• ELECTROMAGNETIC COUPLING IN THE NEAR FIELD

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Near field coupling 3

• In the near field we just have coupled coils

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Near field coupling 4
Simple result for weakly coupled coils
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Coupling volume theory 1

• Coefficient of coupling k depends on the coil
  sizes and positions
• Quality factor depends on materials
• We want to separate these effects
• We want to obtain for k2 a product of factors
  depending separately on the interrogator coil
  geometry and the tag coil geometry
• The power-like measure driving field is the
  reactive power density per unit volume at the tag
  position

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Coupling volume theory 2
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Coupling volume theory 3
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Coupling volume theory 5
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Coupling volume theory 7
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Significant conclusions

• Coupling volumes for well shaped planar electric
  and magnetic field labels are size dependent and
  similar
• Radiation quality factors for both types of label
  formed within a square of side L are size
  dependent and similar
• These are calculated results for sensibly shaped
  antennas

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• PART 8
• RFID PROTOCOLS

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What is a protocol?

• Signalling waveforms
• Command set
• Operating procedure
• A back end interface
• whereby the identities of a population of tags
  in the field of a reader may be determined, and
  the population otherwise managed.

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Protocols the major divide

• Tree walking
• More forward link signalling
• Prolonged periods of interrupted signalling
• Partial information of tag population remains
  relevant
• Adaptive round (terminating aloha)
• Less forward link signalling
• Long periods of un-modulated reader carrier
• Reader signalling is less
• No information from one response about others

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Tree scanning concepts
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Adaptive round concepts 2

• What we saw was the Class 1 Generation 1 HF
  protocol
• Adaptive round concept now appears in may places
• Next protocol is a complex example of an adaptive
  round

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• PART 9
• C1G2 PROTOCOL

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The C1G2 protocol

• Labels have an adjustable probability of replying
  on each query or repeated query
• Probability is adjusted to about a third
• Empty slots, singly occupied slots and multiply
  occupied slots are roughly equi-probable
• A wide range of forward and reverse signalling
  parameters are defined
• Some of them allow for narrow band reply
  signalling well separated from the interrogation
  carrier

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C1G2 Features

• Tag must be able to communicate from 860 MHz to
  960 MHz
• Tags must understand 3 different modulation
  schemes
• Double Sideband Amplitude Shift Keying DSB-ASK
• Single Sideband Amplitude Shift Keying SSB-ASK
• Phase Reversal Amplitude Shift Keying PR-ASK
• Coding is by Pulse Interval Encoding (PIE)
• TgtR data rates 40, 80, 160, 320 and 640 kbits
• Selection
• Access Kill Passwords
• EPC up to 256 bits
• Dense reader channelised signalling

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Three basic Operations

• Select.
• The operation of choosing a tag population for
  inventory and access.
• A Select command may be applied successively to
  select a particular tag population based on
  user-specified criteria.
• Inventory.
• The operation of identifying tags.
• An interrogator begins an inventory round by
  transmitting a Query command in one of four
  sessions. One or more tags may reply.
• The interrogator detects a single tag reply and
  requests the PC, UII, and CRC-16 from the tag.
• Inventory comprises multiple commands.
• An inventory round operates in one and only one
  session at a time.
• Access.
• The operation of communicating with (reading from
  and/or writing to) a tag.
• An individual tag must be uniquely identified
  prior to access.
• Access comprises multiple commands, some of which
  employ one-time-pad based cover-coding of the
  RgtT link.

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Selecting

• The selection process employs a single command,
  Select, which an interrogator may apply
  successively to select a particular tag
  population based on user-defined criteria,
  enabling union (U), intersection (n), and
  negation () based tag partitioning.
• Interrogators perform n and U operations by
  issuing successive Select commands. Select can
  assert or de-assert a tags SL flag, or it can
  set a tags inventoried flag to either A or B in
  any one of the four sessions.

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Inventory

• Reader Talks First
• Sets up communication parameters, defines a round
• Round Size (Q value), slots are numbered from 0
  to 2Q-1
• Tags select a slot within a round to offer a
  reply
• Tag States
• Ready
• Arbitrate
• Reply
• Acknowledge
• Open
• Secured
• Killed

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Replies
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Access and Kill Passwords

• Kill password
• 32-bit value stored in Reserved memory
• Default (unprogrammed) value is zero.
• An interrogator uses a tags kill password once,
  to kill the tag and render it silent thereafter.
• Access password
• 32-bit value stored in Reserved memory.
• Default (unprogrammed) value is zero.
• Tags with a nonzero access password shall require
  an interrogator to issue this password before
  transitioning to the secured state.

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• PART 15
• CONCLUSIONS

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What to take away 1

• Simplicity of passive RFID for identity
• The weakness of the label reply
• Electric and magnetic field concept
• Source and vortex concepts
• Frequency wave length relation c fl
• Near and far field concepts
• Radian sphere size and significance
• Boundary conditions near metal

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What to take away 2

• Varieties of fast reading protocol
• EPCglobal networking concepts
• Standardised EPC
• Standardised readers, tags and protocols
• Standardised communication between roles
• Problems of small tags
• Only retain sensitivity with high Q

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• Questions?