RFID (Radio Frequency Identification) Overview

Transcription

1 RFID (Radio Frequency Identification) Overview António Grilo Courtesy: Greg Leeming, INTEL Sridhar Iyer, ITT Bombay

2 Radio Frequency Identification Power from RF field Reader Antenna Reader->Tag Commands Reader Tag->Reader Responses Tags RFID Communication Channel 2

3 RFID Communications Host manages Reader(s) and issues Commands Reader and tag communicate via RF signal Carrier signal generated by the reader Carrier signal sent out through the antennas Carrier signal hits tag(s) Tag receives and modifies carrier signal sends back modulated signal (Passive Backscatter also referred to as field disturbance device ) Antennas receive the modulated signal and send them to the Reader Reader decodes the data Results returned to the host application 3

4 Radio Frequency IDentification Tag wirelessly sends bits of data when it is triggered by a reader Power source not required for passive tags a defining benefit Superior capabilities to barcode: Non Line of Sight Hi-speed, multiple reads Can read and write to tags Unit specific ID Four main frequencies: Frequency Distance Example Application LF 125khz Few cm HF 13.56Mhz 1m Auto- Immobilizer Building Access Focus of this presentation is on UHF UHF Mhz ~7m Supply Chain μwave 2.4Ghz 10m Traffic Toll 4

5 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 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 5

6 125 khz (135 khz) Late eighties: RFID-Projects gave initial boost Pigeons logging Immobilizer (cars) Logistics Gas bottles Beer barrels Garbage cans Container for toner (printer) Laundry services 6

7 125 khz (135 khz) Industry Tool identification Entertainment Casino Roulette Chips Access systems Turnstile (Ski, swimming pool) Door locks Working time recording 7

8 13,56 MHz Late nineties: Encryption and faster Payment systems Cafeteria, restaurants Access systems / Events Turnstile, Door locks Stadium, Theme parks Convention center (Mifare) Public transportation Bus, underground, ferries (South Korea, London) 8

9 868 MHz (UHF) Late nineties: Projects for UHF systems Logistics First projects had a poor hit rate (60%) Expensive labels National Identity ID card (China 1300Mio, 2005/6) License-plate number (50cm reading distance) 9

10 Basic Tag Operational Principles 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 Power decreases proportionally to 1/d 6 Far field (UHF, microwave): backscatter. Modulate back scatter by changing antenna impedance Power decreases proportionally to 1/d 2 Boundray between near and far field: d = 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 10

11 Limiting Factors for Passive RFID 1. Reader transmitter power Pt(reader) (Gov t. limited) 2. Reader receiver sensitivity Sr 3. Reader antenna gain Gr (Gov t. limited) 4. Tag antenna gain Gt (Size limited) 5. Power required at tag Pr(tag) (Silicon process limited) 6. Tag modulator efficiency Et 11

12 Implications Since in far field Pr(tag) 1/d 2, doubling read range requires 4X the transmitter power. Larger antennas can help, but at the expense of larger physical size because G{t,r} Area. More advanced CMOS process technology will help by reducing Pr(tag). At large distances, reader sensitivity limitations dominate. 12

13 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 13

14 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 14

15 Generic Tag Architecture (Highly Simplified) Write Path Receiver Antenna D S G Memory Protocol Engine 15

16 Possible UHF Reader RF Processor Micro- Controller Crystal DAC Power Control Host Device Baseband & Protocol PLL VCO Coupler PA Coupler FPGA DAC RFID READER RF Module Regulation ADC AGC Filters I/Q Demod Filter Coupler Power Detect Transmit path Receive Path Frequency Synthesizer Digital 16

17 Possible Digital Back End Ethernet RAM Power Supply Serial Port Flash LEDs IXP425 Processor RF Board Interface RF Module GPIO 17

18 Possible Reader Software Stack Network Interface Network management Custom Custom Application/ Protocol Reader Protocol Application RFID Reader API Library Platform API Libraries O/S High-Level Interfaces Low-Level Interfaces File Systems Network Protocols Hardware 18

19 Tag Details Freq. Range Read Range Market share Coupling LF KHz HF 10 cm 1M UHF Microwave MHz MHz GHz 2-7 M 1M 74% 17% 6% 3% Magnetic Magnetic Electro magnetic Electro magnetic Existing standards Application 11784/85, Smart Card, Ticketing, animal tagging, Access, Laundry , 15693,14443 A, B, and C Small item management, supply chain, Anti-theft, theft, library, transportation EPC C0, C1, C1G2, Transportation vehicle ID, Access/Security, large item management, supply chain Transportation vehicle ID (road toll), Access/Security, large item management, supply chain

20 Communication Protocols Listen before talk Mandatory listen time of >5 msec before each transmission Max 4 sec TX then re-listen for 100 msec Transmission from other Readers 865MHz 200KHz 867MHz 20

21 ETSI EN standard Shared operation in band MHz at transmit powers upto 2 W ERP. Operation in 10 sub-bands of 200 khz. Power levels of 100 mw, 500 mw and 2 W ERP. Mandatory listen before talk and look before leap MHz MHz MHz MHz 100 mw 2 W 500 mw FT FT FT FT LT LT LT LT 600 khz 600 khz 600 khz MHz MHz MHz MHz MHz MHz 21

22 Reader Collision Problem Reader-Reader Interference Reader-Tag Interference 22

23 Reader Collision and Hidden Terminal The passive tags are not able to take part in the collision resolution or avoidance, as in other wireless systems Consider: RTS-CTS for hidden terminal problem in rfid: T is not able to send a CTS in response In case multiple readers try to read the same tag, the tag cannot respond selectively to a particular reader 23

24 TDMA Based Solution Assign different time slots and/or frequencies to nearby readers Reduces to graph coloring problem (readers form vertices) Only reader to reader interference Assign different operating frequencies Only multiple reader to tag interference Assign different time slots for operation Both types of interference First allot different time slots, then frequencies 24

25 Beacon Based Solution A reader while reading tag, periodically sends a beacon on the control channel Assumptions Separate control channel between readers The range in the control channel is sufficient for a reader to communicate with all the possible readers that might interfere in the data channel 25

26 Beacon Based Solution (contd.) 26

27 Multiple Tags When multiple tags are in range of the reader: All the tags will be excited at the same time. Makes it very difficult to distinguish between the tags. Collision avoidance mechanisms: Probabilistic: Tags return at random times. Deterministic: Reader searches for specific tags. 27

28 Tag Collision Problem Multiple tags simultaneously respond to query Results in collision at the reader Several approaches Tree algorithm Memoryless protocol Contactless protocol I-code protocol 28

29 Tree Algorithm Reader queries for tags Reader informs in case of collision and tags generates 0 or 1 randomly If 0 then tag retransmits on next query If 1 then tag becomes silent and starts incrementing its counter (which is initially zero) Counter incremented every time collision reported and decremented every time identification reported Tag remains silent till its counter becomes zero 29

30 Tree Algorithm Example Reader informs tags in case of collision and tags generate 0 or 1 If 0 then tag retransmits on next query, else tag becomes silent and starts a counter. Counter incremented every time collision reported and decremented otherwise. 30

31 Tree Algorithm - Complexity Time Complexity O(n) where n is number of tags to be identified Message Complexity n is unknown θ(nlogn) n is known - θ(n) Overheads Requires random number generator Requires counter 31

32 Memoryless Protocol Assumption: tagid stored in k bit binary string Algorithm Reader queries for prefix p In case of collision queries for p0 or p1 Time complexity Running time O(n) Worst Case n*(k + 2 logn) Message Complexity k*(2.21logn ) 32

33 Memoryless Protocol Example Reader queries for prefix p In case of collision, reader queries for p0 or p1 Example: consider tags with prefixes: 00111, 01010, 01100, 10101, and

34 Contactless Protocol Assumption: tagid stored in k bit binary string Algorithm Reader queries for (i)th bit Reader informs in case of collision Tags with (i)th bit 0 become silent and maintain counter Tags with (i)th bit 1 respond to next query for (i+1)th bit Time complexity O(2 k ) Message complexity O(m(k+1)), where m is number of tags 34

35 Contactless Protocol Example Reader queries for (i)th bit Reader informs in case of collision Tags with (i)th bit 0 become silent and maintain counter Tags with (i)th bit 1 respond to next query for (i+1)th bit Example: tags with prefixes: 01, 10 and 11 35

36 I-Code Protocol Based on slotted ALOHA principle Algorithm Reader provides time frame with N slots, N calculated for estimate n of tags Tags randomly choose a slot and transmit their information Responses possible for each slot are Empty, no tag transmitted in this slot c 0 Single response, identifying the tag c 1 Multiple responses, collision c k 36

37 I-Code Protocol New estimate for n : lower bound ε lb (N, c 0, c 1,c k ) = c 1 + 2c k Using estimate n, N calculated N becomes constant after some time Using this N calculate number of read cycles s to identify tags with a given level of accuracy α Time complexity t 0 *(s+p) t 0 is time for one read cycle p number of read cycles for estimating N Message complexity n*(s+p) 37

38 ISO Standard Reference architecture and definition of parameters Parameters for air interface communications below 135 khz Parameters for air interface communications at 13,56 MHz Parameters for air interface communications at 2,45 GHz ( ) Parameters for air interface communications at 5,8 GHz (Type A, B, C) Parameters for air interface communications at MHz Parameters for active air interface communications at 433 MHz 38

39 EPCglobal Tag Classes Class-1: Identity Tags Class-2: Higher functionality tags Class-3: Battery-Assisted Passive Tags Class-4: Active Tags 39

40 Competing UHF Protocols (EPC only) Read Rate Read or Read/Write Tag Cost Privacy Security Global Standard Class 0 NA: 800 reads/sec EU: 200 reads/sec Read Only $$ 24 bit password Reader broadcasts OID or Anonymous modes with reduced throughput No Class 0+ NA:800 reads/sec EU:200 reads/sec Read & Write $$ See above See above No Class 1 NA:200 reads/sec EU: 50 reads/sec Read & Write $ 8 bit password Reader broadcasts partial OID No Class 1 Gen 2 (UHF Gen2) NA:1700 reads/sec EU: 600 reads/sec Read & Write? 32 bit password and concealed mode Authentication and Encryption Yes 40

41 Class 0 Protocol 41

42 Class 0 Signalling 42

43 Default Class 0 Reader Communication Sequence Tag power up, reset, and calibration process Tag Singulation Process Reader power up Repeated after each frequency hop Reset: 800 micro sec uninterrupted continuous wave Oscillator calibration: micro sec pulses Data calibration: 3 pulses ( data 0, data 1, data null ) Single Binary Transversal Once tag has been singulated, reader can send commands to it or begin next BT cycle 43

44 Tag Singulation Process read individual tag from group of all tags in range of reader Basic process: 1. All tags within range of reader backscatter their MSB to the reader. 2. Reader responds with either a 1 or a If tag bit equals reader bit, tag backscatters the next bit in it s code. If instead, tag bit does not equal reader bit, tag goes mute for remainder of singulation. 4. Process continues until reader has completely read a single tag. 5. Reader conducts consecutive singulations until all tags in its range are read. 6. Reader can interrupt the singulation process to send commands to a single tag, a subset of all tags in range, or globally to all tags in range. 44

45 EPC Gen 2 Protocol EPC Gen 2 is a UHF protocol EPC Gen 2 Protocol is likely to become a global standard Gen 2 protocol was designed to optimize performance in different regulatory environments around the world 45

46 EPC Gen 2 Protocol EPC Gen 2 Protocol is allows readers to operate in 3 different modes Single-reader mode Multi-reader mode Dense-reader mode Dense mode is designed to prevent readers from interfering with one another Dense mode uses a backscatter method called Miller subcarrier 46

47 EPC Gen 2 Protocol - Memory Gen 2 tags are field programmable Gen 2 tags have 4 memory areas: 3 required: EPC Password Tag identification 1 optional Memory areas can be locked temporary or permanently 47

48 EPC Gen 2 Protocol Q Algorithm Q Algorithm allows readers to query tags even if two tags have the same EPC or do not contain EPC at all The query mechanism is based on random number generation The reader does not have to transmit EPC, preventing eavesdropping 48

49 Sessions Each Gen 2 tags can have 4 separate sessions for communicating Sessions is a means for preventing interference (e.g. caused by different readers) 49

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52 Savant Savant is a middleware specification developed by the Auto-ID Center Savant acts as a nervous system of an RFID network After readers pick up EPC codes, Savant manages and moves the data 52

53 Savant Savant uses distributed architecture and is organized into a hierarchy of individual savants that manages the process of gathering and distributing data Tasks savant can do: Data smoothing Reader coordination Data forwarding Data storage Task Management 53

54 Object Name Service (ONS) The Object Name Service (ONS) provides a global lookup service to translate an EPC into one or more Internet Uniform Reference Locators (URLs) where further information on the object may be found These URLs often identify an EPC Information Service, though ONS may also be used to associate EPCs with web sites and other Internet resources relevant to an object ONS provides both static and dynamic services. Static ONS typically provides URLs for information maintained by an object s manufacturer Dynamic ONS services record a sequence of custodians as an object moves through a supply chain ONS is built using the same technology as DNS, the Domain Name Service of the Internet Source: Auto-ID/EPCglobal 54

55 Physical Markup Language (PML) The Physical Mark-Up Language (PML) is a collection of common, standardized XML vocabularies to represent and distribute information related to EPC Network enabled objects The PML standardizes the content of messages exchanged within the EPC network. It is a part of the Auto-ID Center s effort to develop standardized 283 interfaces and protocols for the communication with and within the Auto-ID infrastructure The core part of the physical mark-up-language (PML Core) provides a standardized format for the exchange of the data captured by the sensors (readers) in the Auto-ID infrastructure 55

56 Reader Protocol The Reader Protocol specifies the interaction between a device capable of reading (and possibly writing) tags, and application software 56