April 22, 2008 - Access Methods for RFID: EPC Global UHF

University of Kansas | School of Engineering

Department of Electrical Engineering and Computer Science

Milagros Figueroa April 2008 1

Access Methods for RFID: EPC Global UHF Class 1 Gen 2 -18000-6c standard




Outline

Objective: Understand the details of RFID with focus on EPC global UHF Class-1 Generation-2 -18000 6-c standard for passive RFID tags.

RFID Overview• Components of RFID systems• Types of RFID• Challenges and Motivation

Access Methods for RFID• EPC Global Class 1 Generation 2 or ISO18000-6c standard• Future of the Technology

Conclusions

References




What is RFID?

• Stands for Radio Frequency Identification

• Uses radio waves for identification

• One form of Automatic Identification

• Provides unique identification or serial number of an object (pallets, cases, items, animals, humans) [3]

From RFID Technical Tutorial, [3]

Components of a RFID system




RFID Reader

• Also known an interrogator

• Reader powers passive tags with RF energy

• Can be handheld or stationary

• Consists of:

• Transceiver

• Antenna

• Microprocessor

• Network interface

From RFID Solutions Online, [11]From RFID processes, [12]




RFID Frequency range

Frequency Band Description

< 135 KHz Low frequency

6.765 – 6.795 MHz HF

7.4 – 8.8 MHz HF

13.553 – 13.567 MHz HF

26.957 – 27. 283 MHz HF

433 MHz UHF

868 – 870 MHz UHF

902 – 928 MHz UHF

2.4 – 2.483 GHz SHF

5.725 – 5.875 GHz SHF





RFID Tag

Tag is a device used to transmit information such as a serial number to the reader without making physical contact.

All pictures from RFID Technical Tutorial, [3]




Types of RFID

Active RFID systems:• Active tags have their own transmitter and power source• Broadcast a signal to transmit the data stored on the microchip using a power source (battery, sunlight)• Operate at 455 MHz, 2.45 GHz, or 5.8 GHz• Long read range of 20 meters to 100 meters• Expensive – 10$ – 50$ per tag. [2]

Passive RFID systems:• Do not have a transmitter or power source. • Reflect back radio waves coming from the reader antenna• Operate at LF, HF and UHF• Short read range of few centimeters to 10 meters• Cheap – 20¢ – 40¢ per tag. [2]




Challenges and Motivation

• Passive RFID tags are very basic (cheap) so only changes in amplitude of the reader signal can be used. This means that advanced modulation like PSK or QAM are not available.

•Turning off the power from the reader reduces the power available to the tag

•Reader needs a modulation in which “power is on” most of the time; such modulations are wasteful users of spectrum, leading to relatively wide channels or low data rates.

•The tag reflection can be modulated in phase or amplitude, but the small tag reflection is combined with large reflections from the antenna and ambient.

• The resulting signal at the reader may change amplitude when the tag reflection changes phase, and so on.

• The reader can count edges from the tag but not the absolute or differential phase or amplitude. Tag and reader symbols must be chosen with these constraints in mind. [1]




RFID Standards

ISO/IEC (International Standards Organization and International Electrotechnical Commission)

• 18000–1: Generic air interfaces for globally accepted frequencies • 18000–2: Air interface for 135 KHz • 18000–3: Air interface for 13.56 MHz• 18000–4: Air interface for 2.45 GHz• 18000–5: Air interface for 5.8 GHz• 18000–6: Air interface for 860 MHz to 960 MHz• 18000–7: Air interface at 433.92 MHz

EPCglobal Inc• HF (13.56 MHz)

13.56 MHz ISM Band Class 1• UHF (868 – 928 MHz)

UHF Class-0UHF Class-1 Generation-1 (Class-1 Gen-1)UHF Class-1 Generation-2 (Class-1 Gen-2) [3]




Who is EPC Global?

•Not-for-profit organization developing commercial, world-wide RFID standards

•Joint venture between EAN International and the Uniform Code Council (UCC).

• UCC standardized Universal Product Code (UPC) barcodes in US

• EAN standardized barcodes in Europe

• Technology already in used by organizations such as Walmart stores and US Department of Defense (DOD)

•The EPCglobal protocols assume the tag carries a unique identifier, the electronic product code (EPC). [13]

•EPC's can be either 64 or 96 bits long

•Divided into: • Header: defines data type, indicates code partitions, used to partition sub-domains

• Manager: indicates originator of EPC

• Type of Object: as needed by the segment/application

• Serial Number: as determined by the segment application [4]




Electronic Product Code (EPC)

96 bits can uniquely label all products for the next 1,000 years [3]




EPCglobal UHF Specification History

•EPCglobal UHF Class-0

•EPCglobal UHF Class-1 Generation-1

•EPCglobal UHF Class-1 Gen-2 (Gen-2)ISO 18000 suite specifies the air interface for a variety of RFID applications

– 18000-6A

– 18000-6B

– 18000-6C: currently is the most common worldwide standard for UHF passive tags in supply chain applications.

18000-6A and 18000-6B are distinct UHF tag protocols. A few aspects of the standards are common, but the modulations, symbol sets, and command sets and mostly incompatible.

Gen 2 standard is completely incompatible with first-generation class 0 and class 1 readers and tags.[1]




EPCglobal UHF Class-1 Gen-2: PIE Encoding and Tari

• Binary ‘0’: short high level pulse followed by low pulse of equal length

• Binary ‘1’ : longer high pulse followed by the same low pulse width.

• This symbol set is known as PIE encoding and provides a high average RF power delivered to the tag.

•The length of a binary '0' is defined as Tari, and is used as a reference for several other times in the standard.

•The data rate can vary from 27 to 128 Kbps (Tari from 25 to 6.5 microseconds)

•The most significant bit of the most significant word is always sent first. [1]





EPCglobal UHF Class-1 Gen-2: Physical and Link Layers

READER-TO-TAG• Modulation• Double sideband amplitude shift keying (DSB-ASK) • Single-sideband ASK (SSB-ASK)• Phase reversal ASK (PR-ASK)

• Encoding - Pulse interval encoding (PIE)• Data rate based on Tari• Tari 25 microsecond (TYPICAL SETTING)

40 Kilobits per second (Kbps) maximum27 Kbps average

• Tari 12.5 microsecond80 Kbps maximum53 Kbps average

• Tari 6.25 microsecond160 Kbps maximum107 Kbps average [4]




EPCglobal UHF Class-1 Gen-2: FM0 and MMS

• FM0Binary '0' has a transition in the middle of a symbolBinary '1' does not.

•Miller-modulated subcarrier (MMS).Signal is multiplied by a square wave with either 2,

4, or 8 periods for each FM0 symbolThe data rate for a fixed link frequency is reduced

by the MMS multiplier. Data rate is reduced intentionally

• If we set a link frequency of 100 KHz, FM0 provides a data rate of 100 Kbps, but MMS with a multiplier of M=4 only provides 25 Kbps.

• MMS offers some advantages over FM0. In spectral terms, the energy in an MMS signal is concentrated away from the carrier, making it easier to detect in the presence of phase noise and possible interference from other readers. [4]

From The RF in RFID [1]




EPCglobal UHF Class-1 Gen-2: Physical and Link Layers

TAG-TO-READER• Communication between the tag and reader is packetized• Backscatter modulation

• Varies reflection coefficient of antenna• Switch load on antenna in time with bits, which varies input impedance• Varies amount of energy reflected from tag to reader• 80 to 90 dB less signal than reader-to-tag (10,000 times weaker!)

• Modulation• Amplitude shift keying (ASK) • Phase shift keying (PSK)

• Encoding – Reader chooses type• FM0• Miller (M=2, 4, or 8)

• Data rates are variable• FM0 [single reader mode] – 40 Kbps up to 640 Kbps• Miller (M=2) [multi-reader mode] – 20 Kbps up to 320 Kbps• Miller (M=4) [dense reader mode] – 10 Kbps up to 160 Kbps• Miller (M=8) – 5 Kbps up to 80 Kbps• Typical rates in the lab vary between 60-70 Kbps using Miller (M=4) [4]




Class-1 Gen-2 Anti-Collision Protocol (Media Access Control)

•Select phase: Selection of a specific Tag population•Inventory phase: Based on slotted Aloha collision resolution. •Access phase: Reader interacts with tags requesting EPC number and any other information.

•Process:• Reader issues a QUERY command• Each tag rolls a many-sided die, where the

number of sides is set by the reader. • A tag that rolls a 0 replies immediately while all

other tags record their numbers in a counter and say nothing.

• The reader, after either receiving a reply or no response, will issue a QUERY REP command, causing all the tags to decrement their counters by 1

• Any tag reaching a counter value of 0 responds. [4]

From The RF in RFID [1]




Class-1 Gen-2 Anti-Collision Protocol (Media Access Control)

•If the number of sides is chosen properly, one and only one tag will respond to most of the QUERY REP commands.

•A tag replies by sending a 16-bit random number RN16.•If the reader hears the random number it echoes that number as an ACK, causing the tag to send its EPC and error check, along with some protocol control bits (PC). •The PC bits provide the length of the EPC stored in the tag, as well as some information pertaining to the numbering system and optionally the type of object to which the tag is attached (the application family identifier (AFI)). •The reader can then send commands specific to that tag, or continue to inventory other tags. From The RF in RFID [1]




Future of the technology

EPC Global plans to release additional classes of tags for applications that require additional features

• Class-2 higher functionality tags introducing authenticated access control, extended user memory and a lengthened TID

• Class-3 semi-passive tags introducing an internal power source and sensing circuitry

• Class-4 active tags are planned to introduced active communications, tag-to-tag communications, and ad hoc networking [13]




Conclusions

• EPC Global Class1 Gen 2 standard incorporates requirements of prominent organizations and allow global operation.

• This standard includes more advanced hardware specifications that are improvements over earlier RFID technologies.

• Global operation is achieved by using UHF band (860-960MHz).

• There are more choices of modulation and encoding giving manufacturers and users more freedom in choosing how tag and readers operate.

• It also allows tags to be built at a lower cost , with a smaller size, and with improved read performance [13]




References

1. D. Dobkin . The RF in RFID: physical layer operation of passive UHF tags and readers. April 2007

2. D. Stevanovic. Radio Frequency Identification(RFID). April 2007

3. D. Thompson. RFID Technical Tutorial. 2006

4. EPC Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz – 960 MHz, ver. 1.0.9, EPCglobal Inc., Jan. 31, 2005. Available: http://www.epcglobalinc.org/.

5. L. Burdet. RFID Multiple Access Methods. Seminar “Smart environments” 2004

6. Z. Zhou, H. Gupta, S. Das, and X. Zhu. Slotted scheduled tag access in multi-reader RFID systems. Technical report, Stony Brook U., 2007.

7. M. Kodialam and T. Nandagopal. Fast and reliable estimation schemes in RFID systems. MobiCom, 2006.

8. http://en.wikipedia.org/wiki/Channel_access_method

9. http://en.wikipedia.org/wiki/RFID21

10. http://www.autoid.org/2002_Documents/sc31_wg4/docs_501-520/520_18000-7_WhitePaper.pdf

11. RFID Solutions Online. www.rfidsolutionsonline.com/nl/435580/-1

12. RFID Processes, LLC. www.rfidprocesses.com/prod02.htm

13. G Barber, E. Tsibertzopolus, B. Hamilton. An Analysis of Using EPCGLOBAL Class-1 Generation-2 RFID Technology for Wireless Asset Management. 2005

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April 22, 2008 - Access Methods for RFID: EPC Global UHF