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Auto-ID Center

Auto-ID Center. Auto-ID Center Tag Reading Protocols. Peter H. Cole Research Director Adelaide Auto-ID Research Laboratory. 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

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Auto-ID Center

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  1. Auto-ID Center Auto-ID Center Tag Reading Protocols Peter H. Cole Research Director Adelaide Auto-ID Research Laboratory Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  8. 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 Objectives of identity tag protocols Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  13. Protocols: the major divide • Slotted adaptive round data collection • A version of terminating aloha • Tags give effectively full replies in random time slots • Tree walking • A 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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  16. The HF protocol Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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 Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  18. Begin Round Reply round timing FS CS CS CS Reply Reply RSOF RSOF t5 t0 t4 t1 t2 t3 t3 slot F slot 0 slot 1 slot 2 slot 3 FS F S CS C S RSOF …… ix lot Command, …… lose lot Sequence, .… Reply Start of Frame Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  20. Truncated label reply Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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 Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  22. What helps: spectral line spreading Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  23. Basic forward link signalling pulse • 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. Sunday, 05 October 2014.

  24. Long start of frame (LSOF) Short start of frame (SSOF) Common end of frame (CEOF) Binary zero Close slot sequence Binary one Framing and data symbols T = 512/fc = 37.76ms Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  25. State diagram 120 UNPOWERED In Field Destroy Write, Begin Round , DESTROYED READY and not matching mask Begin Round and matching mask Begin Round Begin Round and not matching mask and matching mask SLOTTED After response: READ Before response: Close Slot, Fix Slot , Close Slot,Fix Slot without matching CRC16 After response: Fix Slot with matching CRC16 Close Slot, Fix Slot, FIXED SLOT Begin Round Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  27. The UHF protocols Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  28. Some tree concepts Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  29. More tree scanning concepts Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  33. Further general tree concepts Descent strings from root to tags are shown in heavy lines Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  34. The Class 1 UHF protocol Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  36. Pointer, length and code matching 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. Sunday, 05 October 2014.

  37. Viewing and viewed levels Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  38. Basic reply waveform • 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. Sunday, 05 October 2014.

  39. Ping bins and scroll waveform Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  41. Class 1 UHF Tag: Ping Response Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  42. Simulated and actual ping responses Class 1 UHF protocol simulation output Signal from actual Class 1 UHF tag responding to ping command Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  43. Class 1 UHF tag scroll with collision (zoomed) CRC Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  45. The Class 0 UHF protocol Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  46. 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 Salient features Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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. Sunday, 05 October 2014.

  48. Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  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 Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

  50. Signalling variation 12.5 msec USA (min) 62.5 msec Europe (max) Auto-ID Center Tag Reading Protocols. Sunday, 05 October 2014.

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