Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 1
Auto-ID Center
Peter H. Cole
Research Director
Adelaide Auto-ID Research Laboratory
Auto-ID Center Tag Reading Protocols
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 2
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 3
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 4
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 Tag Reading Protocols. Thursday 20 April 2023. Slide 5
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 6
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 7
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.
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 8
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 9
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 10
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 11
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 12
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)
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 13
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 14
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 15
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 16
The HF protocol
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 17
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 18
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 19
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 20
Truncated label reply
N 16 24
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 21
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 22
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 23
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 24
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 25
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 26
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 27
The UHF protocols
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 28
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 29
More tree scanning concepts
Root
View ing point
Descent d istance
View ed nodes
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 30
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 31
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.
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 32
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 33
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 34
The Class 1 UHF protocol
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 35
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 36
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 37
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 38
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 39
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
// //
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 40
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)
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 41
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)
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 42
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 43
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 44
Summary: significant aspects
• 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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 45
The Class 0 UHF protocol
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 46
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 47
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 48
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
.......
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 49
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 50
Signalling variation
USA(min)
Europe(max)
12.5 sec
62.5 sec
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 51
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.
response end from tags
6us
1/2 bit cycle for reference
Reader ’null’ bit (fast bit rate)
Clock start
Total bit exchange time 12.5 s, fast mode
( No tag response )
9.5s
1/2 bit cycle for reference
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 52
Tag to reader link signals
Tag Backscatter on Reader Data Symbol
Clock start
Tag response
Total bit exchange time
Data Symbol
response end from tags
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.
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 53
Tag states
• Dormant
• Calibration
• Global command start
• Global command
• Tree start
• Tree traversal
• Traversal mute
• Singulated command start
• Singulated command
• Singulated command mute
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 54
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 55
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 56
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 57
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 58
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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 59
Summary: significant aspects
• 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
Auto-ID Center Tag Reading Protocols. Thursday 20 April 2023. Slide 60
The end