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- Prashanth Mathihalli

Radio Frequency Identification technology dates back to World

War II. Attempting to reduce incidents of “friendly fire,” radio signals from one aircraft were beamed towards an approaching aircraft’s transponder; a

corresponding signal from the second plane identified it as a friendly aircraft. Sixty some years later RFID has finally begun to gain widespread

popularity, primarily because of recent reductions in size and cost, as well as more sophisticated functionality. This has led to the widespread

applications making it prominent.

This report on the study of RFID comprises of the following topics; Introduction to RFID, Description of devices, Operating frequencies,

Working of the devices, Antenna and tag orientation concepts, Tag classes, Communication standards, RFID Middleware, Stage by stage explanation of

a real time application example, Extension of study to UHF Gen 2 Tags, Gen 2 concepts and standards involved, Key features of Gen 2

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This is a flexible technology that is convenient, easy to use, and well-suited for automatic operation. It combines advantages not available with other identification technologies. It can be supplied as read-only or read/write, does not require contact or line-of-sight to operate, can function under a variety of environmental conditions, and provides a high level of data integrity. In addition, because the technology is difficult to counterfeit, RFID provides a high level of security.

RFID is similar in concept to bar coding. Bar code systems use a reader and coded

labels that are attached to an item, whereas RFID uses a reader and special RFID devices that are attached to an item. Bar code uses optical signals to transfer information from the label to the reader; RFID uses RF signals to transfer information from the RFID device to the reader. 1.1 Components of RFID System The principal components that constitute an RFID system are:

• RFID tag • Interrogator • Middleware

1.2.1 RFID Tag RFID tags consist of a microchip and a coupling element - an antenna. Most tags are only activated when they are within the interrogation zone of the interrogator; outside they "sleep". Tags can be both read-only (programmed during manufacture) or, at higher complexity and cost, read-write, or both. The tags contain memory. The size of the tag depends on the size of the antenna, which increases with range of tag and decreases with frequency. 1.2.2 Interrogator

Depending on the application and technology used, some interrogators not only read, but also remotely write to, the tags. For the majority of low cost tags (tags without batteries), the power to activate the tag microchip is supplied by the reader through the tag antenna when the tag is in the interrogation zone of the reader, as is the timing pulse - these are known as passive tags.

1.2.3 Middleware

Middleware is the interface needed between the interrogator and the existing

company databases and information management software. System Overview

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2. Description of devices and Operating frequencies 2.1 RFID tags The Tags form the preliminary or the first stage of an RFID system. This in lot of applications initiates the working of the system. The tags are of various kinds and posses respective features which are adopted based on the applications. They are affixed over the item to be identified.

The basic constituents of an RFID tag are a microchip embedded with a unique code called as the Electronic product code (EPC) and an antenna. The presence of the EPC over the tags facilitates the identification process in the system. The EPC is unique for each tag being manufactured and is embedded onto the chip during manufacturing and cannot be tampered with after production.

In action, the tags communicate with the interrogators or RFID readers using the antenna and transmit the EPC which is used to identify the item. Based on their ability to communicate they are classified as Active, Passive and Semi-passive.

• Passive tags use the reader field as a source of energy for the chip and for

communication from and to the reader. The available power from the reader field, not only reduces very rapidly with distance ,but is also controlled by strict regulations, resulting in a limited communication distance of 4 - 5m when using the UHF frequency band (860 Mhz – 930 Mhz).

• Semi-Passive (battery assisted backscatter) tags have built in batteries and therefore

do not require energy from the reader field to power the chip. This allows them to function with much lower signal power levels, resulting in greater distances of up to 100 meters. Distance is limited mainly due to the fact that tag does not have an integrated transmitter, and is still obliged to use the reader field to communicate back to the reader.

• Active tags are battery powered devices that have an active transmitter onboard.

Unlike passive tags, active tags generate RF energy and apply it to the antenna. This autonomy from the reader means that they can communicate at distances of over several kilometers. Passive tags are supposed to be the cheapest to produce, and must be within 4 feet

of the reader. Like active tags, semi-passive tags also contain a battery, but the tag lies dormant until receiving a signal from the reader. This has the desirable effect of conserving battery power.

Both active and passive tags possess either read/write or read-only functionality.

Read-only tags usually function like license plates by identifying the object and pointing to more specific information stored in a database. Read/write tags allow the information stored on the tag to be edited, locked or completely erased, which makes them re-usable. Read/write tags also store more information on the tag and may not require a database lookup or any contact with an external system��

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The three operating frequency bands of the RFID system are LF, HF and UHF. RFID tags can also be classified by frequency band used. The following table summarizes the characteristics and example applications of each band.

Frequency band Frequency being

used Characteristics Typical

applications

LF - 100-500 kHz

125, 134 kHz Short to medium read range Inexpensive low reading speed

Access control Animal identification Inventory control Car immobilizer

HF - 10-15 MHz

13.56 MHz Short to medium read range potentially inexpensive medium reading speed

Access control Smart cards

UHF - 850-950 MHz 2.4-5.8 GHz

Dependent on country

Long read range High reading speed Line of sight required Expensive

Railroad car monitoring Toll collection systems

The tags are manufactured in various sizes and form to suite various applications. Some of the different formats are:

• Credit card size flexible labels with adhesive backs • Tokens and coins • Embedded tags – injection molded into plastic products such as cases • Wrist band tags • Hard tags with epoxy case • Key fobs • Tags designed specially for Palettes and cases • Paper tags

2.2 RFID Tag Packaging An ideal case of a Passive RFID tag in the form of a card is considered to explain the packaging process. The basic assembly process consists of first a substrate material (Paper, PVC, PET...), upon which an antenna made from one of many different conductive materials including Silver ink, Aluminum and copper is deposited. Next the Tag chip itself is connected to the antenna, using techniques such as wire bonding or flip chip. Finally a protective overlay made from materials such as PVC lamination, Epoxy Resin or Adhesive Paper, is optionally added to allow the tag to support some of the physical conditions found in many applications like abrasion, impact and corrosion.

2.3 RFID tag IC’s

RFID tag IC’s are designed and manufactured using some of the most advanced and smallest geometry silicon processes available. The result is impressive, when you consider that the size of a UHF tag chip is around 0.3 mm2

In terms of computational power, RFID tags contain basic logic and state machines

capable of decoding simple instructions. The challenges in designing are factors such as, achieving very low power consumption, managing noisy RF signals and keeping within strict emission regulations. Other important circuits allow the chip to transfer power from the reader signal field, and convert it via a rectifier into a supply voltage. The chip clock is also normally extracted from the reader signal. Most RFID tags contain a certain amount of NVM (Non volatile Memory) like EEPROM in order to store data. The amount of data stored depends on the chip specification, and can range from just simple Identifier numbers of around 96 bits to more information about the product with up to 32 Kbits. However, greater data capacity and storage (memory size) leads to larger chip sizes, and hence more expensive tags.

2.4 Tag communication

In order to receive energy and communicate with a reader, passive tags use one of the two following methods. These are near field which employs inductive coupling of the tag to the magnetic field circulating around the reader antenna (like a transformer), and far field which uses similar techniques to radar (backscatter reflection) by coupling with the electric field. The near field is generally used by RFID systems operating in the LF and HF frequency bands, and the far field for longer read range UHF and microwave RFID systems. The theoretical boundary between the two fields depends on the frequency used, and is in fact directly proportional to l/2p where l = wavelength. This gives for example around 3.5 meters for an HF system and 5 cm for UHF, both of which are further reduced when other factors are taken into account��

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2.4.1 Inductive coupling (Near fields)

LF and HF tags use inductive coupling between two coils (reader antenna and tag antenna) in order to supply energy to the tag and send information. The coils themselves are actually tuned LC circuits, which when set to the right frequency (ex; 13.56 MHz) will maximize the energy transfer from reader to tag. The higher the frequency the less turns required (13.56 MHz typically uses 3 to 5 turns). Communication from reader to tag occurs by the reader modulating (changing) its field amplitude in accordance with the digital information to be transmitted (base band signal). The result is the well known technique called AM or Amplitude Modulation. The tags receiver circuit is able to detect the modulated field, and decode the original information from it.

However, while the reader has the power to transmit and modulate its field, a

passive tag does not. The communication being achieved back from tag to reader is similar to a transformer, when the secondary coil (tag antenna) changes the load and the result is seen in the Primary (reader antenna).The tag chip accomplishes this same effect by changing its antenna impedance via an internal circuit, which is modulated at the same frequency as the reader signal. In fact it’s a little more complicated than this because, if the information is contained in the same frequency as the reader, then it will be swamped by it, and not easily detected due to the weak coupling between the reader and tag. To solve this problem, the real information is often instead modulated in the side-bands of a higher sub- carrier frequency which is more easily detected by the reader.

2.4.2 Backscatter reflection

Passive tags operating at the UHF and higher frequencies use similar modulation techniques (AM) as lower frequency tags, and also receive their power from the reader field. What is different however is the way that energy is transferred is, and the design of the antennas required to capture it. At this point, there is no further possibility of inductive coupling like in HF systems, because the magnetic field is no longer linked to the antenna. Transmission of this wave in the far field is the basis of all modern radio communication. In some systems such as transmission lines (coaxial cables), the propagation of these waves is restricted as much as possible via special shielding as they constitute a power loss. For antennas its the inverse, propagation is encouraged. When the propagating wave from the reader collides with a tag antenna in the form of a dipole, part of the energy is absorbed to power the tag and a small part is reflected back to the reader in a technique known as back-scatter. For the optimal energy transfer the length of the dipole must be equal to l/2, which gives a dimension of around 16 cm. The dipole is made up of two l/4 lengths.

Just as for lower frequency tags using near field inductive coupling, a passive UHF tag does not have the power to transmit independently. Communication from tag to reader is achieved by altering the antenna input impedance in time with the data stream to be transmitted. This results in the power reflected back to the reader being changed in time with the data i.e. it is modulated.

From an applications point of view, using the technique of far field back-scatter modulation introduces many problems that are not so prevalent in HF and lower frequency systems. One of the most important of these is due to the fact that the field emitted by the reader is not only reflected by the tag antenna, but also by any objects with dimensions in the order of the wavelength used. These reflected fields, if superimposed on the main reader field can lead to damping and even cancellation.

3. Antenna and Tag orientation The Antennas form an integral part of the RFID system. The parameter of the antennas being employed decides the operational features of the system. The entire working of the system can be modeled basing the antenna parameters.

Antennas are found on the Tags and Interrogators in various forms and adhere to several factors such as frequency, polarization, medium of operation, antenna material, application, etc. They usually enhance the communication distance between the tags and the interrogators. Antennas on the tags are used for communication data stored on them, whereas the antennas on Interrogators are used for identifying the tags. Hence the orientation of the tags and the antennas at the read location matters to the application.

Here is described a case of tag orientation for HF tags and antennas at a read

location for an Interrogator.

This case requires the tag to be parallel to the antenna as shown above for it to be identified and read by the Interrogator.

Here a Phase splitter is employed for two antenna structures being fed by a signal which is 90 degree out of phase with the original. This makes the tag readable in both directions.

This is the 3D case where tags are read in almost all the directions.

4. RFID Tag classes The Auto-ID center at MIT is the body that ratifies standards for all RFID tags. The group called as EPC-Global defines the classes. Based on the ability of tags to read and write data. Currently, several classes of tags fall under the EPC global defined library. The difference between Class 0 and Class 1 is in the data structure and operation. Class 0 tags are read only. Class 1 tags are one-time writeable. The EPC standards call for 5 classes of tags over time. The following table outlines the roadmap for the EPC tag class type: Class type Features Tag type

Class 0 Read Only

Passive (64 bit only)

Class 1 Write Once, Read Many (WORM)

Passive (96 bit min.)

Class 2 (Gen 2) Read Many (WORM) Passive (96 bit min.) Class 2 (Gen2)

Passive (96 bit min.)

Class 3 Read/Write with battery power to enhance range

Semi-Active

Class 4 Read/Write active transmitter

Active

CLASS 0 – READ ONLY. – Factory programmed These are the simplest type of tags, where the data, which is usually a simple ID number, (EPC) is written only once into the tag during manufacture. The memory is then disabled from any further updates. Class 0 is also used to define a category of tags called EAS (electronic article surveillance) or anti-theft devices, which have no ID, and only announce their presence when passing through an antenna field. CLASS 1 – WRITE ONCE READ ONLY (WORM) – Factory or User programmed In this case the tag is manufactured with no data written into the memory. Data can then either be written by the tag manufacturer or by the user – one time. Following this no further writes are allowed and the tag can only be read. Tags of this type usually act as simple identifiers

CLASS 2 – READ WRITE This is the most flexible type of tag, where users have access to read and write data into the tags memory. They are typically used as data loggers, and therefore contain more memory space than what is needed for just a simple ID number. CLASS 3 – READ WRITE – with on board sensors These tags contain on-board sensors for recording parameters like temperature, pressure, and motion, which can be recorded by writing into the tags memory. As sensor readings must be taken in the absence of a reader, the tags are either semi-passive or active. CLASS 4 – READ WRITE – with integrated transmitters. These are like miniature radio devices which can communicate with other tags and devices without the presence of a reader. This means that they are completely active with their own battery power source.

The chip manufacturer can only program the Class 0 tag; the Class 1 Version 1 tag can be programmed on the factory floor.

While functionally equivalent under the EPC global classification system, Class 0 and Class 1 use different hardware technologies to implement the Identity tag functionality. Class 0 tags are programmed when they are manufactured (referred to as “Read-Only” or “R/O”), assuring uniqueness of the tag ID. Class 1 tags can be programmed once, referred to as “Write Once Read Many” or “WORM”, by the user, providing operational flexibility.

Class 0 and Class 1 tags also use different protocols, or “air interfaces” to communicate. So, while both Identity tag implementations perform the required functions, they cannot communicate with each other. Tags of both classes can coexist in an environment, but require readers that “speak their language” to be identified.

4.1 EPC structure As described above each tag contains a unique code facilitating the identification process known as EPC. The structure of this code been embedded is described below. The EPC is a number made up of a header and three sets of data. The header identifies the EPC's version number, allowing for different lengths or types of EPC later on.

• The second part of the number identifies the EPC Manager, most likely the manufacturer of the product. • The third, called object class refers to the exact type of product, most often the Stock Keeping Unit (SKU). • The fourth is the serial number unique to the item, which can tell us, for example, exactly to which 330 ml can of Diet Coke we are referring. This makes it possible to quickly find products that might be nearing their expiration date.

Example of EPC 01.115A1D7.28A1E6.421CBA30A

01 Version of EPC ( 8 bit header) 115A1D7 Manufacturer Identifier

28 bits 28A1E6 Product Identifier

24 bits 421CB30A Item serial number

36 bits

5. RFID standards The international organization for standards has ratified standards for the RFID tags. The compliance depends on factors such as the operating frequency, type of tag and area of application. ISO Standards for Proximity Cards: ISO 14443 for “proximity” cards and ISO 15693 for “vicinity” cards both recommend 13.56 MHz as its carrier frequency. These standards feature a thinner card, higher memory space availability and allow numerous cards in the field to be read almost simultaneously using anti-collision, bit masking and time slot protocols.

• ISO 14443 proximity cards offer a maximum range of only a few inches. It is primarily utilized for financial transactions such as automatic fare collection, bankcard activity and high security applications. These applications prefer a very limited range for security.

• ISO 15693 vicinity cards, or Smart Tags, offer a maximum usable range of out to

28 inches from a single antenna or as much as 4 feet using multiple antenna elements and a high performance reader system.

ISO Standards for RFID Air interface. The ISO 18000 series is a set of proposed RFID specifications for item management that could be ratified as standards during 2004. The series includes different specifications that cover all popular frequencies, including 135 KHz, 13.56 MHz, 860-930 MHz and 2.45 GHz.

• 18000 – 1 Part 1 – Generic Parameters for Air Interface Communication for Globally Accepted Frequencies

• 18000 - Part 2: Parameters for Air Interface Communications below 135 KHz o ISO standard for Low Frequency

• 18000 - Part 3: Parameters for Air Interface Communications at 13.56 MHz o ISO standard for High Frequency o Read \ Write capability

• 18000 - Part 4: Parameters for Air Interface Communications at 2.45 GHz o ISO standard for Microwave Frequency o Read \ Write capability

• 18000 - Part 5: Parameters for Air Interface Communications at 5.8 GHz • 18000 - Part 6: Parameters for Air Interface Communications at 860 – 930 MHz

o ISO standard for UHF Frequency o Read \ Write capability o Targeted for same markets as EPC standards.

• 18000 – Part 7: Parameters for Air Interface Communications at 433.92 MHz o Manifest tag for Department of Defense (DOD)

ISO Standards for Animal Identification • ISO 11748 / 11785: Standard for Animal Identification ISO Supply Chain Standards These are used to identify different types of logistics containers and packaging, in addition to individual items. • ISO 17358 - Application Requirements, including • Hierarchical Data Mapping • ISO 17363 - Freight Containers • ISO 17364 - Returnable Transport Items • ISO 17365 - Transport Units • ISO 17366 - Product Packaging • ISO 17367 - Product Tagging (DoD) • ISO 10374.2 - RFID Freight Container Identification

6. RFID Interrogator or Reader

Readers or interrogators are a key element in any RFID system, and will therefore be part of the product evaluation and selection process.

6.1 Main Criteria for readers

• Operating Frequency (HF or UHF) – some companies are developing Multi frequency readers

• Protocol Agility – Support for different Tag Protocols (ISO, EPC, proprietary) – • Different regional regulations

- UHF frequency agility 902 – 930 MHz in the US and 869 MHz in Europe - Power Regulations: 4 Watts in the US and 500mW in Europe - Manage Frequency Hopping in the US and Duty Cycle in Europe

• Networking to host capability: - TCP/IP - Wireless LAN (802.11) - Ethernet LAN (10base T) - RS 485

• Ability to network many readers together - Via concentrators - Via middleware

• Ability to upgrade the reader Firmware in the field - via internet - via Host interface

• Managing multiple antennas - Typically 4 antennas/reader - How antennas are polled or multiplexed

• Adapting to antenna conditions - Dynamic auto-tuning

• Interface to middleware products • Digital I/O for external sensors and control circuits

6.2 RFID Reader Antennas In an RFID system, reader antennas are supposed to be tougher in designing since they are subjected to various elements which govern their operation. For low power proximity range (< 10cm) HF applications such as access control, antennas tend to be integrated in with the reader. For longer range HF (10cm < 1m) or UHF (< 3m) applications, the antenna is nearly always external and connected at some distance to the reader via a shielded and impedance matched coaxial cable.

6.2.1 Design

Antenna principles and designs are radically different in LF, HF frequency range

than in UHF. In fact it’s not strictly true that inductive coupled systems like HF use antennas, because they work in the near field where there is no Electromagnetic propagation.

The majority of the RFID antennas need to be tuned to the resonance of the

operating frequency. This leaves them prone to many external effects, which can seriously impact the communication distance by de-tuning the antenna. Causes vary depending on the operating frequency and can be due to anything from;

• RF variations • Skin-effects • Losses due to metal proximity • Antenna cabling losses • Signal fading • Proximity of other reader antennas • Environmental variations, • Harmonic effects • Interference from other RF sources • Eddy fields • Signal reflections • Cross talk

The problem of antenna de-tuning caused by the effects mentioned above, can be corrected by dynamic auto-tuning circuits which work with feedback from the antennas resonance tuning parameters. This scheme guarantees stability and maximum performance for the selected frequency. 6.2.2 Performance Designing antennas with optimal performance in terms of communication distance will need to take into account the following main parameters;

• Operating frequency range • Impedance (typically, 50 Ohms) • Maximum allowed power • Gain • Radiation pattern (polarization XY, circular)

These are the key elements which create the RF field strength and field patterns (read zones) which are in turn affected by the efficiency, and type of coupling used (Inductive, Radiation...) between reader and tag.

6.2.3 Types RFID antennas used generally are classified into following types:

• Gate antennas (orthogonal use) • Patch antennas • Circular polarized • Omni directional antennas • Stick antennas (directional) • Di-pole or multi-pole antennas • Linear polarized • Adaptive, beam-forming or phased array element antennas

7. RFID Middleware The RFID tags would deliver a huge volume of data which needs to be processed. This would slow down or crash a system running enterprise software. RFID middleware acts as a tool that is used to manage the data. They serve as a software buffer which sits almost invisible between the RFID readers, and the servers storing the product information. RFID middleware consists of a set of software components that acts as bridge between RFID system components (tags and readers) and the host application software. It performs two primary functions:

• Monitors the device • Manages RFID specific infrastructure and data flow

It allows companies to process relatively unstructured tag data taken from many RFID readers, and direct it to the appropriate information systems. They are able to perform many different operations, such as

• Monitor the RFID reader, devices. • Manage false reads • Cache data • Query an Object Naming Service (ONS)

8. Description of a Real time Example – Access control system Access control is one of the simple and effective applications using RFID. It provides lot many features to the end users because of its simplicity to use and handle the data which serves as a source for other application other than access control. A diagrammatic description of the system is shown below.

The system comprises of the following devices:

• Proximity card • Interrogator • Control device • Server

The function of the system is to provide a definite access control in an area of applications such as office buildings. The employees would be provided with the proximity cards which would be programmed with respective access privileges. The system is a smart sentinel. It not only performs access control but the data derived out can be used for other administrative purposes.

• The user would need to present the proximity cards to the interrogators at the

point of entry to the interrogators. • The interrogators would read the EPC from the cards and would forward the

code to the decision making device. • A database is maintained in a central server, which stores all the user details

corresponding to the assigned EPC codes and defined access points. • The control device communicates with the server for authentication process; the

user is provided access as per the defined privileges. • Correspondingly a different database would be updated with details such as

entry time, exit time, point of entry, etc. The details could be used for other applications such as in a payroll calculation.

The proximity cards would be an LF or an HF smart cards operating at 134 kHz or

13.56 MHz respectively. Based on the application suitable card is selected and a corresponding ISO standard is adopted.

The system is a security device along with access control, since all users would need to

present the proximity cards and an addition of a secondary device such as biometric device or even a keypad ensures a definite security cover.

In the case of a larger area, the interrogators at different locations are capable of

forming a network and communicate with each other for authentication process. A middleware handles the data being obtained. More advanced interrogators have wireless connectivity and are capable of relaying data over the web.

9. Introduction to UHF Gen 2 The UHF Gen 2 RFID standard ratified by EPC global is new state of art technology all by itself.

The current thrust of EPC global is known as UHF Generation 2 (UHF Gen 2), a

Write Once Read Many tag with more memory (96 bits vs. 64 bits) than preceding Class 0 and Class 1 tags. UHF Gen 2 provides a bridge to the eventual Class 2 High Memory full Read Write tag. Prior to UHF Gen 2, Class 0 and Class 1 were being utilized for EPC, but they were not interoperable. Consequently, a retailer utilizing an EPC solution – such as Wal-Mart – would need different RFID readers to read different tags or force all of their suppliers into one technology. UHF Gen 2 will merge the Class 0 and Class 1 standards for a global, interoperable EPC standard.

Presently deployed Gen 1 UHF RFID systems are based on a number of competing

protocols, most notably Class 0 and Class 1.The current incarnations of these protocols are proprietary. Beyond that, they lack the features, reliability, and horsepower to adequately serve a growing number of applications—particularly when taking worldwide operability into account.

MIT's Auto-ID Center recognized the problems and proposed the solution, a single

open standard that 1) Would create an environment of interoperability and international regulatory compliance, and 2) Would raise the bar on RFID system performance in a significant way. These two values formed the backbone of what they proposed as the next generation of UHF RFID— UHF Gen 2

10. Key features of Gen 2 The key qualities of UHF Gen 2 are listed below.

1. Superior Tag Population Management Gen 2 defines the interactions between readers and tags over a robust air interface with three primary command-driven procedures: Select, Inventory, and Access. Select – Prior to conducting an inventory, a user may wish to first conditionally isolate only those tags that exhibit, say, a particular date code, manufacturer code, or other variable of interest. By targeting only that segment of the tag EPC memory that contains those particular kinds of descriptive bits, the reader can quickly narrow down the field, making for a more efficient inventory operation. The Select command offers a quick sorting of the tag population, where the reader (using union, intersection, and negation operators on a set of user-defined selection criteria) chooses a subpopulation of the tags within its field. Inventory – The Inventory operation—identifies tags, one at a time, resolving conflicts among tag responses, and sets an appropriate "inventoried" flag within each of the tags as they're counted. Access – Available only following an Inventory operation, Access involves more than simply sorting and counting tags; Access commands allow the reader to write individual tag memory fields directly (with EPC and/or password data), set the desired memory lock bits, or kill the tag.

2. Robust Signaling Protocol A vastly more reliable RF link protocol, this eliminates the case of ghost reads. A Gen 2 reader uniquely identifies a single tag within a population. When a reader issues a Query command, the tag must respond within an extremely narrow window—just 4-millionths of a second wide. If the tag does not respond within that timeframe, the reader assumes that no tag is present, and issues another Query command. The reader continues to poll in this manner until it receives a valid response. This tight window represents the first hurdle in a series of "communication qualifiers" designed to eliminate false triggering on noise and other spurious emissions. When a tag does respond, it does so with a preamble—a distinctive waveform that the reader is able to reliably discern and identify, even in noisy environments. If the reader does not recognize the preamble as the leading part of the tag's response, it is ignored. As data begins to flow from tag to reader in the form of well-defined symbols, memory retained in the waveform is used to identify bad sequences, or alternatively, to make decisions on ambiguous bits and fix them.

Once the transmission is complete, the reader reviews the waveform and checks the PC (Protocol Control) bits at the top of the transmission, used to compare the number of bits it received with the number of bits the tag says it sent. If the two numbers match, then the reader can be fairly confident of a valid transmission. The reader then compares the CRC (cyclic redundancy check) at the end of the transmission and verifies its integrity. Only then is the reader satisfied that it has read a valid EPC.

3. Dense-Reader Operation Any truly practical vision of RFID deployment will require the fielding of many readers, all of which might be operating simultaneously. Faint-voiced tags will have little, if any, hope of being heard above the noise and interference. Gen 2 gets around the problem of "dense" readers by isolating tags and readers through a frequency channelization scheme If a reader’s signal (which is many orders of magnitude greater than that of the tags) were to leak into adjacent tag lanes, it would mask the tags' low-power transmissions, burying them in RF noise, and preventing other readers from seeing them at all. By restricting reader transmissions to occur within strictly delineated lanes (or channels), tags can be heard clearly, even though as many as 50 active readers might be operating simultaneously in 50 available channels.

4. Cover-Coding of the Forward Link

Maintaining a secure link between reader and tag is essential to safeguard data transmitted over an air interface. It's especially critical in the reader-to-tag direction, because reader transmissions occur at substantially higher power levels than those of the tags, who effectively whisper their responses back to readers. The reader requests a random number from the tag. The reader then mixes that random number with its data before transmitting the result to the tag. The tag decodes the mixing (reversing the operation) and extracts the original information. A simple scheme, but it effectively protects both data and password transactions by obscuring data transmissions in a purely random manner.

5. A 32-bit Kill Password Incorporated to address privacy concerns, the kill command permanently disables a tag from talking back to a reader, rendering it useless. The ability to kill a tag, though, exposes the network to the possibility of unauthorized kills. To prevent it, a password protection scheme was adopted. Class 1's 8-bit kill password, for example, left it exposed to only 256 possibilities—hardly a password at all. While Class 0 improved things significantly with a 24-bit password, Gen 2 raised the hacker's bar to 32 bits—more than 4,000,000,000 possibilities.

6. Sessions Dramatically Boost Productivity Capitalizing on the enabling power of the dense-reader mode, Gen 2 also introduces the concept of sessions, where as many as four different readers may access the same population of tags through a time-interleaved process. That's an extremely useful capability. Consider the case where a shelf-mounted reader in the midst of a counting operation (assigned to, say, session 1), is interrupted by another reader entering the field—possibly a handheld reader—to perform its own inventory operation (in session 2, perhaps). Dock door and forklift readers, assigned to sessions 3 and 4 respectively, and might also jump in for a round. Because Gen 2 tags maintain a separate "inventoried" flag to keep track of each of these various random and independent sessions, they're able to seamlessly resume their participation in the previous (pre-interruption) inventory round, picking up right where they left off, and never miss a beat.

7. Significantly Faster Singulation Rates Readers and their associated tag populations have a lot of business to transact. At least one throughput-gating parameter is the effective data rate, which also determines the time it takes to singulate, or identify, a single tag within a population. Typical Gen 1 data rates run from 55 to 80 kbps. Gen 2, though, provides for data rates as high as 640 kbps (a throughput of 1600 tags per second).

8. Variable Read Rates The rate of data flow between reader and tag is governed by a number of factors: environmental conditions (including noise level and physical structures), region of operation, the number of active readers in the area, and even the speed of tagged materials moving through the distribution center. A very adaptable system, Gen 2 allows the fine-tuning of the RFID network—including the varying of data rates—to optimize performance across all possible combinations of operating conditions. Whether the need is for fast reads of pallets moving through a dock door, or slower reads in a noisy environment of dense readers.

9. Greater Configuration Control The modulation and data encoding schemes of choice, like the selection of data rates, also depend on a set of environmental considerations. As such, Gen 2 provides options in both reader-to-tag link and tag-to-reader link directions, allowing performance calibration of the Gen 2 system to the demands of its operating environment. Gen 1 system, on the other hand, are limited to a fixed communication format, where one size may not necessarily fit all.

10. Worldwide Operation Both Gen 1 and Gen 2 systems cover the 860 to 960 MHz operational band—the superset of international frequencies—but the way the two standards deal with that spectrum is worlds apart. As far as Europe is concerned, Gen 1 doesn't deal with it very well. Compared with North America's fairly wide frequency allocation of 902 to 928 MHz, Europe's is pretty slim— just 865 to 868 MHz. As such, European RFID deployments tolerate much less interference, and require much tighter spectral control than Gen 1 systems can deliver. Gen 2, on the other hand, takes the European standards fully into account; it works well in North America, Japan, Europe, and elsewhere, making Gen 2 a truly international standard, hence its strong advocacy within ISO.

11. Conclusion

In this study of mine, I have researched about RFID, the architectural concepts, standards tied to the RFID applications, and in particular tried to extend it to recent revelation UHF Gen 2 Tags, the parameters and features involved in modeling them. I substantiate my study by the description of a real time example, which highlights the functioning of this technology in one common application in the best effective way possible.

RFID is in its spring. It is slowly gaining its own niche is the field of automatic identification and security. RFID will likely have much more influence on everyday lives around the world more than what is it doing at present. It may few more months to years to realize its full potential, but ready or not; RFID is here to stay and will eventually become widely adopted.

References: ��

1. “A Basic introduction to RFID technology and its use in the supply chain”-

Steve Lewis, Whitepaper – www.laranrfid.com

2. “Gen 2 Story”, Whitepaper – www.impinj.com

3. “An introduction to RFID”, Whitepaper – Data systems international

4. “RFID: What is it all about?”, Whitepaper - Leonard Miller – National institute of

standards and technology

5. RFID for Dummies – Patrick J. Sweeney

6. “RFID standards”, White paper - www.scanscource.com

7. AIM (Automatic Identification Manufacturers), “Radio frequency identification –

RFID: a basic primer”, September 1999.

8. AIM (Automatic Identification Manufacturers), “Draft paper on the characteristics

of RFID-systems, July 2000.

9. AIM Inc., White Paper, Version 1.2, August 23, 2001.

10. AIM, “International technology overview – the AIM RFID initiative,” 1998.

11. Aim global Draft Paper on the Characteristics of RFID-Systems, p. 4, 9, July 2000.

12. Aim global, www.aimglobal.org/technologies/rfid/,

www.aimglobal.org/technologies/rfid/resources/papers/rfid_basics_pri mer.htm,

2003.

13. HighTechAid Available from: www.hightechaid.com/standards/18000.html

14. EPCGlobal, Standards & Technology 2005. www.epcglobalinc.org

15. “Intermec” white papers -

http://www.intermec.com/eprise/main/Intermec/content/Products/Products_L

istFamily?Category=RFID

Note: This report is compiled from a search conducted over the internet. It is being used as a reference material to learn basics of RFID and is not used for any commercial purposes to benefit monetarily any individual or organization. I wish not to violate any copyright issues or patents.