Auto-ID Center Tag Reading Protocols. Tuesday, 06 October 2015.Slide 1 Auto-ID Center Peter H. Cole Research Director Adelaide Auto-ID Research Laboratory

Auto-ID Center Tag Reading Protocols. Friday 21 April 2023. Slide 1

Auto-ID Center

Peter H. Cole

Research Director

Adelaide Auto-ID Research Laboratory

Auto-ID Center Tag Reading Protocols


What to expect

• There are three protocols to be explained

• In its entirety, that’s a lot of work

• So we are just giving the salient features

• The main aim is to explain how they work

That is, what goes on in the operation of the protocols

• Further detail is available in Auto-ID Center publications


Relevant prior presentations

• September 2002 CCAG Update/Discussion

Discussion of UHF Class 1 protocol

Technology Board September 2002

• Class 0 UHF tags

Detailed description of Class 0 UHF protocol

Technology Board February 2003

• Update on 13.56 MHz ISM Band Class 1 RFID Protocol Specification

Detailed description of Class 1 HF protocol

Technology Board February 2003


What is a protocol?

• A protocol is a primarily set of signalling waveforms, a command set, an operating procedure and a back end interface whereby the identities of population of tags in the field of a reader may be determined.

• Additional things may be done according to a protocol. These things may include writing the EPC to a tag when it is put into service, and do include disabling a tag when the attendant item is sold.

• Sometimes, for convenience and to avoid confusion, some limited wafer sampling testing commands are included.This does not mean we have abandoned the no global wafer test philosophy.


Auto-ID Center protocols

The Auto-ID Center has defined, in chronological order

• The Class 1 UHF protocol

• The Class 1 HF protocol

• The Class 0 UHF protocol


Why are they different?

• Different field properties at HF and UHF

Near and far field – different field confinement

Different field penetration in materials

Different silicon circuit possibilities and costs

Different electromagnetic regulations• Read only memory technologies enable miniaturisation• A high performance UHF system was available and was

modified by the Center to mange privacy concerns• In service evaluation under Auto-ID standards is essential


Classes

• We are discussing here only Class 0 and Class 1.

• Both are identify only tags.

• Both employ backscatter technology

• Will there be higher classes?

Yup, but I will not talk about them. It’s work in progress.


Objectives of identity tag protocols

• Open standard• Supported by multiple sources• Interoperable across suppliers• Good (margin of) performance• System performance reliable• Tags locked after writing• Orientation free tag reading• Global signalling acceptance

• Support cheap manufacture• Reader talks first• Support for late arrivals• Configurable communication • Minimum reader interference• Select specific tags• Tags may be killed• Secure forward link


Ingredients for protocols

• An air interface

• A command set

• A procedure for deploying the commands

• A back end interface for the reader

• We have context-dependent procedures


Constraints on protocols

• Electromagnetic compatibility regulations

Differ with frequency range and jurisdiction

Some convergence occurring

• Reader to reader interference

Readers confusing tags

Readers blocking other reader receives

• Simplicity (as reflected in chip size)

Maybe that influences reliability as well


Issues in designing a protocol

• Environmental noise

Mentioned here because often overlooked• Turn around time

All cheap passive backscatter tags are half duplex• Reader to reader interference

Tag confusion

Reader receiver blocking• Privacy (and the other user requirements)• The last two are specific Auto-ID Center concerns• There are many trade-offs


UHF and HF protocols

• We have two highly-integrated well-performing UHF protocols

Class 0 Read only memory

Class 1 Write then lock memory

Both are tree walking (next slide)

• We have a single well performing HF protocol

Class 1 HF write then lock memory

Slotted adaptive round collection (next slide)


Protocols: the major divide

• Slotted adaptive round data collectionA version of terminating alohaTags give effectively full replies in random time slots

• Tree walkingA systematic exploration of the tag population one or more bits at a time

• Differences are degree of randomness and mode of description

• Both are designed to read all tags, and quickly


Characteristics: contrasts

• 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

No information from one response about other tags


Characteristics: similarities

• Both can select subsets of tags for participation

• Overt selection may reveal what is selected

• Forms of less overt selection are possible

• Tag “sleeping” has a role in both


The HF protocol


Concept of the adaptive round

• Labels reply once per round, in randomly chosen slots• A group of n slots forms a round• The number of slots in a round varies as needed• The number of slots is adjusted to reduce collisions• Interrogator controls slot sizes; slot sizes vary as needed • Tags giving already collected replies moved to slot F

B e g in n in g o f ro u n d E n d o f ro u n d

S lo t F S lo t 0 S lo t 1 S lo t 2 S lo t 3 S lo t 4 S lo t n -1


Reply round timing

FS …… Fix Slot Command, CS …… Close Slot Sequence, RSOF.… Reply Start of Frame

BeginRound

RSOF

RSOF

Reply

FS CS CS CS

t5 t1t2 t3 t4

slot F slot 0 slot 1 slot 2 slot 3

t0

Reply

t3


Command set

Waveforms are not covered here but carefully selected• Begin round (with tag selection from the root)• Close slot (if slot empty)• Next slot (if response not correctly read)• Fix slot (if tag successfully read) (also begins a new slot)

Tags in fixed slot remain there with persistent memory• Complete reset

Brings tags our of fixed slot• There are also write and write lock commands• The protocol is fast


Truncated label reply

N 16 24


Electromagnetic compatibility aspects

• This is HF (13.56 MHz); at UHF its different• Signalling can there occupy greater bandwidth• But out to band rejection required may be extreme

dB V m

13.11 13.41 13.56 13.71 14.01+ /- 7kHz

8432.5

50.5

40.5

29.5

-11

-22

-1

EH

@ D = 30 mFIELD STRENGTH

+ /- 150kHz

+ /- 450kHz

dB A /m

42

9

-3.5

H

dB A /m

REVISED FCC PETITION

@ D = 10 mFIELD STRENGTH

EUROPEAN REGULATIONS

M Hz

| |X n

13.5 dB

f = nT1

2

1.5

O

TdV

V33.2 dB for d = 18% dipdepth and random 1,0

Unm odulated carrier level


What helps: spectral line spreading

-100 -80 -60 -40 -20 0 20 40 60 80 1000

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Rel

ativ

e am

plitu

de o

f sp

ectr

al li

nes

I n d e x n u m b e r o f sp e c tra l l in e s


Basic forward link signalling pulse

Min

6,0 µst2 3,0 µs

t3 0

Max

9,44 µst1

4,5 µsModulation

Index

t1

10% 30% hf, hr 0,1 (a-b) max

y 0,05 (a-b)

t1

t2

hfy

hr

t3

t

y

a

b

CarrierAmplitude • The frequency band

supports synchronous signalling

• Pulse position modulation is used

• The forward link baud rate is 25.48 kbit/s (fc/512)

• Dips from 18% to 45% are contemplated


Framing and data symbols

Short start of frame (SSOF)

Long start of frame (LSOF)

Common end of frame (CEOF)

Binary zero

Binary one

Close slot sequence

T = 512/fc = 37.76s


120

DESTROYED

UNPOWERED

READY

SLOTTED READ

FIXED SLOT

Destroy

In Field

Before response: Close Slot,Fix Slot

Begin Round and matching mask

Close Slot, Fix Slot, Begin Round

After response:Fix Slot with matching CRC16

Begin Round and matching mask

Write, Begin Round, and not matching mask

Begin Round and not matching mask

After response:, Close Slot, Fix Slot

without matching CRC16

State diagram


Summary: significant aspects

• Operation in near field – eavesdropping difficult

• Operable word wide under harmonised regulations

• Product selection from EPC header

• Economical secure residual reply signalling

• Performance near 200 tag/s


The UHF protocols


Some tree concepts

R o o t ( le v e l 0 , n o t in t r e e )L e v e l 1 M S B L S BL e v e l 2

L e v e l 3

L e v e l nP r o d u c t 0 1 0 0 1

Root (level 0 , not in tree)

Level 1 M SB

LSB

Level 2

Level 3

Level n

Product 01001


More tree scanning concepts

Root

View ing point

Descent d istance

View ed nodes


Some tree definitions

• Maximal tree

Complete set of EPC that could been defined for any use

• Global tree

All the EPC that have been placed into service

• Local tree

All the EPC in the field of the reader at any particular time


Alternative tree visualizations

• The Microsoft Windows style. Rotated, non-binary, horizontal, unidirectional when downward.

• If a partial selection is made, no branching over the region of selection, and branching above and below. No appropriate definition of root.


Variations on the simple picture

• Tree is very deep and crowded• Bottom not uniform

64 bit and 96 bit codes• CRC could be placed at bottom end

No branching in CRC region

The tree is then sparse at the root• CRC could be placed at the root

In the global tree, full branching from the root, but some branches disappear before the bottom

In the local tree, branches disappear anyway


Further general tree concepts

Root (no leve l)

Level 0 M SB

Level 1

Level 2

Level n-1

Produc t 01001 A tag code is defined by its descent string

0

0

0

1

1

Descent strings from root to tags are shown in heavy lines


The Class 1 UHF protocol


Textual description

• Based upon “atomic” transactions: almost no memory used in tag• Two important commands: ping, scroll• Ping selects a portion of the tree, and asks any tags matching that

partial selection to respond • Responses are arranged (by time) into groups so that several

descent strings (at least eight) are researched per atomic transaction

• Responses are encoded in a way that probably reveals whether a single tag or multiple tags are responding

• When a single tag seems to be responding, its full reply is sought by a Scroll command

• That tag is put to sleep to confirm it was the sole respondent • The tree is further explored in a manner guided by the occupancy

information already obtained• Sleep is persistent to ensure protocol immunity against field fading


Pointer, length and code matching

0 1 2 3 4 5 6 7 8 - - - - - - - - - -

Pointer

View ing level

Length View ed level

Region of code m atching

M SB of CRC LSB of EP C

CRC fo llowed by E PC

A portion of a descent string is defined by pointer, length and data values supplied in a reader command


Viewing and viewed levels

Root (no level)

The tags

Viewing point (pointer plus length)

Viewed nodes corresponding to the viewing point

More levels of the tree

Singly occupied nodes

Unoccupied nodes

Multipley occupied nodes

Tags descending from the viewed nodes respond

A node is defined by its descent string


Basic reply waveform

0

1

1 Bit Cell

• This is called F2F encoding• It has many desirable properties

No preamble needed for decoding

Signals well separated from reader carrier


Ping bins and scroll waveform

Bin 4(100)

EOF fromCMD

...Setup

Bin 0(000)

Bin 1(001)

Bin 2(010)

Bin 3(011)

Bin 5(101)

Bin 6(110)

Bin 7(111)

TtagreplyNom

// //


What’s in a ping bin?

• One or more superimposed eight bit tag responses• Responses come from all tags descended from the viewed node

corresponding to the ping bin• There may be no, one or more than one tag responding• The responses are eight bits long• Three bits re-identify ping bin position relative to viewing point

This is a deliberate redundancy aiding decoding of response• Five more bits identify the further descent string toward the tag• Interference between multiple responses is generally visible• If no interference is evident singultation on the partial selection

is likely• We probably then call for a complete tag response (scroll

command)


Class 1 UHF Tag: Ping Response

(Zoom of 6th/7th Bins)

-2.00E-01

-1.00E-01

0.00E+00

1.00E-01

2.00E-01

3.00E-01

1.70E-03 1.80E-03 1.90E-03 2.00E-03

Time (sec)

Sig

na

l (a

rb)

(Zoom of First two Bins)

-2.00E-01

-1.00E-01

0.00E+00

1.00E-01

2.00E-01

3.00E-01

1.10E-03 1.20E-03 1.30E-03 1.40E-03

Time (sec)

Sig

na

l (a

rb)

-2.00E-01

-1.50E-01

-1.00E-01

-5.00E-02

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

1.10E-03 1.30E-03 1.50E-03 1.70E-03 1.90E-03

Time (sec)

Sig

na

l (a

rb)


Simulated and actual ping responses

(Zoom of 6th/7th Bins)

-2.00E-01

-1.00E-01

0.00E+00

1.00E-01

2.00E-01

3.00E-01

1.88E-03 1.90E-03 1.92E-03 1.94E-03 1.96E-03

Time (sec)

Sig

nal (

arb)

Class 1 UHF protocolsimulation output

Signal from actual Class 1 UHF tag responding to ping command


Class 1 UHF tag scroll with collision (zoomed)

Zoom of scroll reply with collision

1.40E-03 1.50E-03 1.60E-03 1.70E-03 1.80E-03

Time (sec)

Sig

(a

rb.)

CRC



• Deep forward link modulation assists immunity to reader collisions

• Selection through CRC make the reader communication effectively meaningless to eavesdropping

• Eight bit ping bin responses provide a look down the tree and assist the detection of probably singulated tags

• Eight bit ping bin responses per bin tick are an appropriate use of turn-around time


The Class 0 UHF protocol


Salient features

• Factory programmed • UHF operation• USA and Europe• EPC data with CRC and

Kill• Fast tree scanning• Eavesdropping proof• Supports context

dependent protocols

• 96 and 64 bit varieties • Mixed tag populations• Selection of groups of

tags• Supports low cost

readers• Supports advanced tree

walking features• Analog set up, digital

thereafter


Signalling organisation

• RTF methodology• Reset before tag activity• Oscillator synchronisation after reset• Data command training after oscillator synchronisation• Global and singulated commands• Mandatory, optional and propriety commands• Fast tree descents on three symbols (zero, one null)• Three memory pages ID0, ID1 and ID2 for descent• ID2 contains EPC• ID1 contains factory programmed random descent string• ID0 contains locally generated random string


Power Up ...

Master Reset

Oscillator Calibration

Reader Transmit Once Only

General Protocol Structure

Data Calibration BT BT BT BT

Repetitive Binary Traversals

Full Communication Architecture (not to scale)

Total ID0/ID1 Length = 80 bits, maximum

Data Null,

0

Binary Traversal Architecture, ID0 & ID1 - (not to scale)

min block length = 10 bits

1 bit

Global Cmds

Total Tag ID Length = 80, 112 bits

Data Null,

0

msb Identification Number lsb

Manager, Product and Serial Numbers Header CRC

Binary Traversal Architecture, ID2 - (not to scale)

ID length = 64, 96 bits CRC = 16 bits

1 bit

4 ID Bits

1 bit parity

4 ID Bits

1 bit parity

4 ID Bits

1 bit parity

4 ID Bits

1 bit parity

.......


Start of tree traversal

• Data 0 given by reader in tree start state

Responses come from tag MSB

• Data 0 or 1 given by reader: causes descent L or R

Tags which has responded with matching 0 or 1 stay in, and respond according to their MSB-1; other tags go temporarily inactive

• Data 0 or 1 again given by reader: causes descent L or R

• etc

Root (leve l 0 , not in tree)

Level 1 M SB

LSB

Level 2

Level 3

Level n

Product 01001


Signalling variation

USA(min)

Europe(max)

12.5 sec

62.5 sec


Zero, one and null signals

Reader bit ’0’ (fast bit rate)

Clock start

Total bit exchange time - 12.5 s, typ.

3s

response end from tags

1/2 bit cycle for reference

Reader bit ’1’ (fast bit rate)

Clock start

Total bit exchange time 12.5 s, typ.


6us


Reader ’null’ bit (fast bit rate)

Clock start

Total bit exchange time 12.5 s, fast mode

( No tag response )

9.5s



Tag to reader link signals

Tag Backscatter on Reader Data Symbol

Clock start

Tag response

Total bit exchange time

Data Symbol


response start from tags

Standard is bit 0: 2.2 MHz, bit 1: 3.3 MHz, chosen as approximate mid points of carrier positions.

In region I, these frequencies are divided by 2.


Tag states

• Dormant

• Calibration

• Global command start

• Global command

• Tree start

• Tree traversal

• Traversal mute

• Singulated command start

• Singulated command

• Singulated command mute


Command summary

• Mandatory commands

Both tags and readers must implement

Occupy particular part of command space• Optional commands

None yet defined, but command space left for them• Proprietary commands

Must not interfere with mandatory or optional commands

Command space left for them as well


Global and singulated mandatory commands

• ResetIDFlag {00 000001 1} (reset all identified flags to not read)used in managing groups of tags

• SetNegotiationPage {00 000010 1} {argument} (choose negotiation string)regulates security and speed

• SetRegionOfOperation {00 000011 0} {argument} (set backscatter prmtrs)Used to set region I or region II etc

• ForceDormant {00 000100 1} (immediately enter Dormant State)used in managing groups of tags

• ForceMute {00 000101 0} (immediately enter Mute State) used in managing groups of tags

• Read {00 000110 0} {argument} (read new data from an indexed page)Used in reading EPC without forward link disclosure


Singulated only mandatory commands

• Kill {01 111111 1} {argument} (Permanently disable tag)

Not yet implemented, but will be• Optional commands

None yet defined, but space left• Proprietary (defined by the manufacturer )

commands


Advantages of the protocol

• Very low gate count (high performance, less expensive)• Very high tag read rates, beneficial in inventory use• Protection against eavesdropping• Robust against noise• Contention free collision handling• Designed for multi-reader, dense tag populations• Group commands available & flexible• Flexible to current regulation and expected (Region 1)• Tags ignore mistimed commands• Tags go to a safe state if a command cannot be decoded


Advantages of the protocol

• Facilitates dynamic, adaptive data rates• Predictable, linear performance regardless of pop. size• Flexible for both high performance & inexpensive

readers• Eliminates delays changing from Tx to Rx mode• Minimal Interference between forward & backscatter

links• Promotes reception at very long backscatter ranges• Coherent in nature – higher RF link margins• Flexible for future command expansions



• Compact factory programmed read only memory• Descents of the tree take place one level at a time• High reply sub-carrier frequencies make this possible

The projection of interrogator signalling spectrum on the receiver pass band is small

• Very fast singultation, around 1000 tags/s in USA• Very flexible in signalling: trainable for different jurisdictions• Three descent strings for various levels of privacy• Artefacts are accompanied by very good electromagnetic

engineering

Latter aspect is not strictly part of the protocol

and could be applied to other protocols


The end

Documents

Auto-ID Center Tag Reading Protocols. Tuesday, 06 October 2015.Slide 1 Auto-ID Center Peter H. Cole Research Director Adelaide Auto-ID Research Laboratory