rfid taxonomy
DESCRIPTION
Hicss2005TRANSCRIPT
A Taxonomy for RFID
Taimur HassanSchool of Information Systems and
TechnologyClaremont Graduate University
Samir ChatterjeeSchool of Information Systems and
TechnologyClaremont Graduate University
Abstract
RFID systems come in a myriad of forms, each catering to a specific need. However, a systematic classification to reduce the confusion of potential adopters, researchers and enthusiasts is still lacking. This article proposes and evaluates a taxonomy of various RFID systems currently available. The taxonomy can be used for gaining an understanding of this technology, the factors for implementation of a successful RFID system, its strengths and weaknesses as well as scalability options. Both novice as well as experienced RFID researchers will benefit from this classification.
1. Introduction
Radio Frequency Identification (RFID) systems have been around from WWII era. In spite of the advancements, the basic principles for the technology have changed little. An RFID system has two basic hardware components, a transponder and an interrogator. They are most commonly referred to (and henceforth referred to) as tag and reader respectively. A reader emits a radio wave at a certain frequency that is received by the tag. The tag is designed to respond with data that is then read by the reader. The distance between the tag and reader can vary from a few centimeters to several meters. The adoption of RFID by Wal-Mart recently has made the topic headline news. The purpose of creating an RFID taxonomy is to classify and organize the large volume of knowledge on the subject so as to make it easier to navigate. The taxonomy can help create specifications for projects by providing a framework for comparing solutions from multiple vendors. Academics interested in RFID can use the taxonomy to get an overview of the which components of the technology can be researched on. Finally, the taxonomy serves users interested in general details and directs them to further resources. Accordingly, we propose the following dimensions: usage, frequency, data and physical as the fundamental classification requirements of a large array of RFID systems (See Fig. 1). These dimensions and their subsections are an initial start to a classification processes and are subject to iterative feedback and improvement. To comply with length limitations we have tried to present the more critical subsections of our taxonomy, while attempting to provide our readers references for more details. The rest of the paper is organized as follows: In Section 2, the taxonomy is presented, Section 3 evaluates the taxonomy by considering
sample real-world cases. Finally, we conclude in Section 4 by summarizing our contribution. Appendix A illustrates the dependencies between some of the branches of the taxonomy.
2. Taxonomy
RFID systems are available in many forms. In order for a taxonomy to be useful, functional themes need to be created that balance general with specific traits. In order to make the taxonomy easy to use, the classification should only require data openly available to the public and not proprietary and difficult to collect information. The taxonomy is illustrated in a tree node manner to closely resemble diagrams that classify species of plants and animals, for which taxonomies were originally created. The tree structure of the taxonomy may suggest each branch being mutually exclusive from other branches, which is not the case. Some of the relations will be discussed within the appendix. In case a node has two or more exclusive branches, i.e. indicating an OR type choice between the node branches, it will be indicated by a small circle on the node.
Figure 1: Top Tier
All RFID systems despite their varied prices, purpose and capabilities can be studied systematically using a small number of categories. These are the Usage, Physical, Frequency and Data dimensions.
2.1 Usage
Figure 2: Usage
All RFID systems usage fall under two main categories: monitoring and authorization. The intended use of the RFID system will significantly impact the choices selected in the rest of the taxonomy dimensions.
2.11. Monitor: A desire to utilize RFID to determine whereabouts and/or take measurement would qualify as a monitoring activity and hence requires a
definition of granularity. Granularity is the level at which individual components can be uniquely resolved and depends upon the memory capabilities of a tag. As such, RFID systems can provide a class level or an entity level monitoring capability. If the RFID system has a class level granularity, it means that the RFID reader cannot identify an item, its type or group and can only monitor its presence within its interrogation zone. An example of this system is the inventory security tags utilized by department stores to discourage stealing of merchandise. Most RFID systems today are implemented to provide an entity level resolution capability to the customers. At this level, tags may have memory capacity to provide enough bits to identify not only the merchandise uniquely, but also their manufacturer, origin, various measurements attached to the entity (temperature, humidity etc). RFID systems in this category can be used very effectively to authenticate an item as well as its subcomponents. In authentication, the identity of an entity can be positively verified due to the inseparability of the RFID system from the item. A good example can be livestock or people embedded with RFID tags or an RFID label applied to a carton. Whenever the tag is detected by an RFID system, it is verified that the corresponding entity (livestock, merchandise) is present due to the inseparable nature of the tag. The same principle can extend to sub-entities, which can be defined as entities within an entity. An example can be a RFID enabled shipping container with many RFID enabled cartons inside. Another example can be an RFID enabled electronic component e.g. DVD player that has RFID enabled components. Monitoring at the sub-entity layer proves useful during assembly and maintenance of an entity as well as for inventory control. The degree of granularity desired should be determined before planning for an RFID system for example, some beverage manufacturers support tagging of beverage cartons, but not individual cans, which may or may not be acceptable for meeting the customer’s needs. However, with tagging of individual components, the need to collect, store and later utilize RFID data dramatically increases as well. Currently, researchers are using datamining to handle this data which can also include sensor measurements of an item and tracking data, which is the pinpointing of the approximate entity location. Measurement and tracking can occur after the entity is authenticated. Details on how a hospital in Taiwan combined temperature measurement with tracking capability of
their patients to combat the Asian flu crisis is discussed in [4].
2.1.2. Authorize: Such RFID systems are used to supplement traditional forms of authorization granting entities such as keys, passes, tickets etc. They are not suited for monitoring purposes because the RFID system has no way to verify the identity of the entity in possession of the RFID tag. This is because such tags are embedded inside cards, keys or passes not designed to be permanently attached to an entity, making it vulnerable to misplacement or theft.
2.2. Frequency
Figure 3: Frequency
The range of tasks, as well as the scalability of the RFID system is heavily dependent on the radio frequency the system uses. This is because frequencies can make a difference in range, data exchange speed, interoperability and surface penetration. Some frequencies are better at penetrating fluids and metals while others hinder scalability because of inconsistent regulations around the world. Within frequency, signal distance, spectrum range (the radio signal classification of the frequency), reader to tag frequency, tag to reader (the radio frequency at which a tag transmits its data to the reader), the interaction technique (the physics principles used to enable tag/reader communication) and regulations are important dimensions of the frequency selected for the RFID system.
2.2.1. Signal Distance: This represents the distance at which an RFID tag and reader can communicate effectively. This can be divided into the read range and write range as readers may read tags data at a different distance than it can write to the tag, depending upon tag architecture (discussed later). Because of the strengths and weaknesses that certain
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frequencies exhibit, low to high frequency levels are often used for distance up to a meter, while ultra high frequency levels and above are preferred for achieving ranges beyond a few meters and higher data transfer rate. Higher frequencies also need antennas that take less space and are more efficient than antennas used for low frequency [3].
2.2.2. Signal Range: RFID frequencies can be broken into four ranges:1. Low Frequency (9-135 KHz): Systems that use
this range of frequencies have a weakness of a read distance of only a few centimeters [3]. The frequency is typically used in subdermal animal identification due to its ability to penetrate the high moisture environment within an animal’s body.
2. High Frequency (13.56 MHz) : This very popular frequency range typically covers a distance from 1 cm to about 1.5 meter for tag reading and up to a meter for writing data to the tag. Tags that work at this range typically rely on the reader to power them. RFID systems using this frequency have a large user base and is supported by many RFID manufacturers such as Sony and Phillips.
3. Ultra High Frequency (0.3-1.2GHz) : This frequency range is used for supporting greater distance between tag and reader. These frequencies cannot penetrate metal and moisture as well as the lower frequency ranges, however they can transmit data faster and hence are good for reading multiple tags at once [3]. These frequencies fall in the ISM range and hence there are inconsistencies across countries as to their ranges (discussed later under regulations).
4. Microwave (2.45-5.8GHz) : The advantage of selecting such a high range is the resistance to strong electromagnetic fields such as electric motors and welding systems. Therefore, tags using these frequencies are often used for production lines in automotive systems. However they require more power and are expensive [3].
2.2.3 Reader frequency: Readers can come with the ability to capture only a single frequency or multiple frequencies. Multiple frequency readers are developed to query tags that use different frequencies or to comply with different standards.
2.2.4 Tag to reader frequency: When a tag receives a radio signal from the reader, it can respond in a frequency that is either a fraction of the reader
frequency (subharmonic), corresponding to the reader frequency, a multiple of the readers frequency (harmonic) or completely independent of the reader frequency (anharmonic). The tag to reader frequency is important to know because the frequency can be a cause of interference to an existing communication system even if the reader does not cause such interference. For example at 1/2 the frequency of a reader’s 128 KHz, a subharmonic tag will send back a signal at 64 KHz.
2.2.5 Interaction Technique: There are three techniques used for sending data to be received by a reader:1. Load Modulation : In this system, the inductive
field generated by the reader to power the tag is disrupted slightly by the tag, which is then detected by the reader and translated into data bits. This system is feasible in close proximity (one meter or less) due to a great reduction in the field’s strength with every increase in distance.
2. Backscatter : This system is typical for larger distances and microwave readers. In this system, the corresponding frequency is used by the tag to send data to the reader, through coordination with surrounding tags.
3. Surface Acoustic Wave : This technique uses the principle of microwave energy not passing through metal surfaces. The RFID chip is encoded lengthwise with vertical metal strips with a varying amount of gaps between them. When microwave energy passes the strip, it creates variable disturbances that can be detected by a reader and correspondingly be converted into binary data [3].
2.2.6 Regulations: Manufactures of RFID products have to adhere to regulations created by agencies such as the Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) that control the frequency spectrum within their designated regions. Differences in regulations make it more complicated and costly to manufacture equipment that complies with regulations. In Europe for example, the RFID UHF band range is 865-868 MHz while it is 950-956 MHz in Japan and 902-928 MHz in USA. Some RFID manufacturers handle the differences by designing their readers to handle the multiple frequencies and protocols. Nonetheless, implementing a global RFID system entails dealing with the different regulations and standards, which make the process expensive and complicated. An RFID standards organization, EPC
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has ratified a standard named ‘Gen 2’ that specifies regulations for global compatibility[17].
2.3. Physical
Figure 4: Physical (Diagram #1)
The physical dimension includes the tag and reader and their subcomponents, which due to their volume have been broken into three parts. The first two diagrams (including the one from above) cover the tag components while the last covers the reader components.2.3.1. Tag: Tags come in a variety of shapes and sizes. Each is designed for operating in various climates and conditions. Tags can be classified based on the following criteria:1. Power Source : A tag can either gain electric power
through an inductive field generated by a reader, or it can be powered internally with batteries. The former systems are called passive tags, while the latter are called active tags. The range of a passive tag varies from a few centimeters to a meter, while active tags can achieve very high ranges of 15 meters or more. Active tags are generally more costly than passive tags because extra range requires sophistication such as an algorithm for multiple-tag coordination and even a transmitter. So called semi-passive tags use a battery to power the microprocessor, but not the transmitter. Many operate in a hibernation state until awoken by a reader signal.
2. Environment : Tags have environmental limitations related to temperature and humidity. Typically manufactures include in their specifications the operating (the temperature range the tags perform optimally), storage temperatures (the range where tags can be safely stored) and the humidity range (expressed in percentage relative humidity).
3. Antenna : A tag’s antenna is needed to capture the signal as well and in some cases to act as a conductor of energy from the reader to the tag. An antenna’s shape and dimensions determines the
frequency range it captures as well as other performance characteristics. Four types of tag antennas are dipole, microstrip, slot and coil. Dipole antennas are straight piece of line whose length influences frequency range. Microstrip antennas, known also as patch antennas, prove advantageous for tags as they comprise of a printed circuit board with a rectangle at the end whose length and width influence frequency. Slot antennas are strips cut out of a metallic surface [3]. Coil antennas are wires arranged in either in a coiled planar fashion or wound up around a conductive core. The material tag antennas are made of are metal based or ink based. Copper antennas are common in tags due to their low price and good conductivity, however silver, gold and aluminum are also used, providing varying performance levels. The latest antenna manufacturing method is of using a special ink and circuit board printing technology that when dipped in a special solution that makes metal ‘grow’ on the surface of the ink. This technology is said to one day allow the mass production of tags at a very cost effective manner [7].
4. Standards : RFID tags must comply with standards created by agencies ISO (International Standards Organization) and EPC (Electronic Product Code). Of these standards, ISO has produced more than 180 very detailed specifications. The ISO standards have been divided into ‘families’ such as ISO 18000 and ISO 15693 series. EPC standards are focused on supply-chain, in particular defining a methodology for the capture, transfer, storage and access of RFID data. EPC classifies tags into five ‘classes’ where an increase in class signifies an increase in level of sophistication, for example, class 0 refers to read only passive tags, while class 4 refers to reprogrammable active tags. Class 5 standard is developed with backward compatibility of a reader with tags of older classes in mind. EPC has also published standards for RFID data exchange and processing under the title of ‘Savant’. Summaries for ISO standards and the EPC classes can be found in [16]. There are overlapped areas between the two standards, however these standards differ in approach and do not conflict. EPC has ratified a new global standard ‘Gen 2’ which is being evaluated by ISO as the ISO 18000-6 standard. Turner provides a comparison between EPC and ISO 18000-6 in [6].
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Figure 5: Physical (Diagram #2)
5. Memory: Tags may be either memory-less, or have either read only or read-write memory. Memory free tags can only indicate their presence to a reader, e.g. surveillance tags discussed above. Tags with memory are costlier and come in two types, read only and read-writable, the latter having two types, one that is writeable only once and one allowing multiple writes. Tags with read-write memory can either run without an internal power source or require a battery to maintain the memory. Tags with larger memory size can be used to store more than a unique ID such as measurement and tracking information.
6. Logic : Tags can have:a. No form of processing for example supermarket
theft prevention tags that alert guards to a possible theft in the presence of an inductive field.
b. A finite-state processor which can support some cryptography e.g. stream cipher
c. A microprocessor can have varying processing capability depending on the requirement. High-end microprocessors may need greater power than what a reader can provide, and as such are mostly found in active tags. A microprocessor can be part of a chipset manufactured by companies such as Texas Instruments and Phillips.
7. Application Method: The application of tags within an RFID system can be categorized as attached, removable, embedded and conveyed. The difference between an attached and removable tag is the reusability. For example, RFID label tags are designed to be attached to a single item for the purpose of tracking the item and are not designed to be removed and attached to another item. Removable tags are designed to be removed and reused afterwards, as in the case of tags attached to some expensive store merchandise such as clothes and media. Embedded tags are designed to be or become a permanent part of the object they are to help monitor, for example subdermal tags for livestock tracking. Conveyed tags refers to tags that can be
carried by individuals inside a wallet or purse and serve more of a authorization function such as RFID enabled tickets and ATM cards.
Figure 6: Physical (Diagram #3)
2.3.2. Reader: Readers have five important features, polarization, antenna, protocol, I/O interface and portability1) Polarization : There are two types of fields that a
reader can generate: linear and circular. Linear readers create a focused and oriented electromagnetic field used for a greater range and deeper penetration for tags whose antennas must be in the specific orientation for them to receive the signal. Circular readers generate a non-directional inductive field in order to power and interrogate tags that have no specific orientation and the circular pattern of waves increase the chances of the tag antenna capturing the signal. However circular readers have a shorter read range than linear polarized readers.
2) Antenna : For portability, a reader antenna can be located within the circuitry (Internal) or it could be attached externally to one or more antenna ports provided by the reader.
3) Protocol : Some readers are able to communicate using only a single protocol. This means that they can talk to either an ISO based tag or an EPC one. However in some situations e.g. for compatibility with vendors using different standard tags, the reader may need to know how to communicate with both types of tags. Such readers are called multiprotocol readers.
4) Interface: RFID readers may be integrated into business infrastructure via input and output ports such as Ethernet (RJ45), serial (RS232), Wi-Fi (802.11), USB and other public or proprietary standards. These ports allow the reader to send and receive information and instructions to and from current infrastructure, for example, information read from conveyor belts can be sent to an ERP system, while the reader can be sent signals to turn on or off from a server.
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5) Portability : RFID readers can either be fixed or handheld. Multi-port fixed readers can be advantageous for tracking multiple items at once as they can receive tag signals from multiple locations within a facility if the antennas are connected to the antenna ports via cable. Fixed readers can also come in a portal shape to detect tagged items passing through. Handheld RFID readers can incorporate an antenna, a UI and have uplink capability through serial or other interface e.g. Wi-Fi.
2.4. Data
Figure 7: Data
In a typical RFID system, the type of data as well as the manner of data processing between the tag and reader is crucial to its function. Standards such as EPC class 1, version 2 (also called Gen 2) allow 96 bits for identification on a tag. These bits of information go through steps such as extraction, decoding, filtration, analysis and feedback within a very few seconds, involving everything from hardware such as tags, readers and conveyer belts to sophisticated software and backend IT systems such as ERP, hence making three dimensions of data important for an RFID system: security, multi-tag coordination and processing.
2.4.1. Security: Unprotected, sensitive data within tags can be eavesdropped by anyone with a radio receiver or network packet snooper when data is being transmitted between a reader and a backend server. Therefore, it is important to know the type of data protection scheme utilized.Three kinds of security scenarios are possible: 1) Public Algorithm : In this system, the tag and
reader employ encryption techniques that are well-tested and public information. Some common examples are shared key, derived key, 3DES and stream cipher. The choice of algorithm has a lot to do with the type of computing power available within the tag.
Computing-heavy algorithms require crypto-coprocessors and a power source, which can increase the costs of a tag [3]. Hence a balance needs to be struck between security and cost. Also, during the selection of a multi-organization RFID system, the use of the security algorithm should be coordinated between partners. Cost of multi-organization deployment can be kept in check by selecting hardware that conforms to well-known security algorithms.
2) Proprietary Algorithm : Some manufactures have developed data algorithms that are not based on published standards. With such a system, lock-in may become a problem if the customer wishes to utilize tags or readers provided by different vendors. The system may also have problems scaling across organizations as all suppliers or customers would have to utilize the same vendor’s equipment.
3) None : In such a case, the data on a tag is completely unencrypted and readable by a corresponding frequency reader. This may not be a problem in cases where the unique identifier of the tag has meaning only in the presence of a corresponding secure database. Once the data is read from the tag, the reader sends the unique tag identifier to a secure server where it is matched with a database record entry containing all the data regarding the identifier. Data is encrypted by the server and sent to the reader for display. This way, privacy is protected as no personal information ever gets exchanged. As long as a malicious party does not get a hold of the database, any identifier information obtained maliciously is meaningless.
2.4.2. Multi-tag Coordination: If a reader is capable of reading multiple tags at the same time, the tags require the use of a coordination scheme so as to allow all of their data to reach the reader uncorrupted. There are three types of techniques used:1) Space Division Multiple Access (SDMA): In this scheme, a frequency channel used in one zone is reused in another zone, similar to a cellular tower layout. The technique involves using a large number of readers and antennas to form an array to provide coverage of an area [3]. The technique is not commonly used.2) Frequency Division Multiple Access (FDMA): In FDMA, tags respond to a query by choosing multiple frequency channels for uplink. This requires a reader to have multiple frequency capability. The system is very expensive and used in custom applications [3].
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3) Time Division Multiple Access (TDMA): This is the most common technique used where each tag uplink is coordinated to send data during a specific period of time. Two common protocols that use this technique:
a. Aloha Protocol : The Aloha protocol works on a collision principle, where several tags send data packets at random intervals. If the packets collide, the tag waits for a random time period before retrying. Variant of this technique are S-Aloha and Frame Aloha protocol [3].
b. Binary Tree : In this protocol, data packets collide during transmission, however the reader resolves each collision one bit at a time through the use of a binary search tree algorithm. Each tag contains an ID associated with it. A reader specifies the range of tag IDs that must reply to a query, while all tags with IDs not covered in that range must stay silent. If a collision occurs because two tags choose the same time to upload data, the reader can detect the exact bit at which the collision occurred. By using a sophisticated binary search tree algorithm, the reader is able to read every tag [2].
2.4.3. Processing: Data from tags must go through a software that can filter, convert, correct and relay it to the appropriate enterprise systems. This layer of software is referred to as middleware. The middleware can reside on a reader or a server. Middleware located on a reader has capability to filter out some data at the source using programmable logic, but cannot perform sophisticated functions that can only be provided by server based middleware, for example communication with other types of devices such as bar code readers, RFID readers and even business process devices such as conveyer belts and ERP systems. Middleware can have either a single tier architecture or multi-tier architecture, the latter allowing greater flexibility in data and process integration. Some of the offerings of middleware are data and process management, application development and partner integration. A detailed evaluation and comparison of some current middleware solutions is done by Leaver [5].
3. Evaluation
In order to evaluate the taxonomy, three RFID cases were selected. The information gathered was based on official press releases, technical specification
documents of the RFID equipment suppliers as well as official standards.
3.1 Hong Kong ‘Octopus’ Case
Background: Three different transportation agencies in Hong Kong introduced the ‘Octopus’ transport ticketing service. The service consists of RFID cards bought by customers, which can have an initial stored currency value based on the amount paid by customer during purchase. The card can be used in place of cash aboard any of Hong Kong’s transportation services (bus, tram, railway) equipped with 13.56 MHz tag readers with a range of few centimeters. Customers have two options, purchase an anonymous card with no identification feature or purchase a personalized card with an identification photo [9]. The cards are based on Sony FeliCa smart-card system [10] that utilizes standard physical and logical architecture.
3.1.1 Usage: This system is used primarily as an authorization tool. However, as customers can personalize their ID with pictures, it can also become a valid authentication form. The interrogation zone is only a few centimeters to prevent accidental deduction of value from customers not intending on ride the transportation. Due to the small interrogation range between tag and reader, the tag is infeasible for tracking.
3.1.2. Frequency: The desire for a small read range as well as a requirement to change value of the currency amount stored in the tag’s memory makes 13.56 MHz a good choice for a frequency as it provides enough power for read-write operations as well as data encryption. The frequency 13.56 MHz is shared between reader and tag and vice versa. The tag uses load modulation to send its data to the reader, meaning it creates a detectable interruption in the induction field of the reader. 3.1.3. Physical: The power source in the FeliCa card is the reader. A microprocessor is required to compute the encryption requirement of the tag. The reader needs to update currency information in the card; therefore, read-write memory is present. The application of the tag is on the surface of the smart card. The reader is circular and requires the customer to place the card within a few centimeters of the reader’s inductive field.
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3.1.4. Data: In this last dimension, we can see that because the system is intended for one customer authorization at a time, the hardware will not accommodate a multi-tag reading scenario. Each tag will have to be addressed and updated individually by the reader. Also, as a public algorithm is used for encryption, the tag can be used in organizations outside transportation as long as they have readers that utilize standardized security algorithms. Hence, the octopus card is currently being accepted by many businesses in Hong Kong.
How the taxonomy helps: If the managers of ‘Octopus’ want to increase efficiency, improve services and reduce costs of the transportation system, the taxonomy can be consulted to understand what changes can be brought about to achieve these goals. For example, they can program their middleware to collect information such as when passengers switch from bus to train, peak times etc, to help improve their business process. In such case, operations researchers, IT analysts and academics involved will need a source that proves a good classification reference for RFID systems in order to understand the options available.
3.2 Sainsbury Case
Background: Sainsbury is a UK retailer that wanted to implement RFID technology within its supply chain. Cartons with inventory arrive at Sainsbury’s distribution depot. An RFID system based on Phillips I-Code chips detects the arrival of the cartons and reads the inventory system at a read distance of more than a meter [11]. The system can read multiple tags in a single read session. The write distance is about a meter. Each tag has a unique identifier for securing data against malicious change, however no data encryption is supported.
3.2.1 Usage: A read range of 1.5 meters allows monitoring (authentication) of carton within a distribution center, as well as tracking for security purpose. This is possible due to the deployment of portal scanners that automatically detect the presence of tags when they are brought within the read range. This system also allows tracking of the exact location of the cartons within a warehouse.
3.2.2 Frequency: The read distance of the tags is about 1.5 meters, however, there is a limitation on write range. In order to be able to change data within the passive tag, it must be within a meter distance
from the reader. The frequency used is the popular 13.56 MHz, both ways. An inductive field is used for coupling, the readers are single frequency.
3.2.3 Physical: The tags require power from the reader. Each tag contains a microprocessor that can support basic read-write functionality. The tags are applied to the surface of cartons. The reader uses circular-polarization with a read range of 1.5 meters in all directions. It means that a portal reader can cover an area equal to the warehouse entrance [12].
3.2.4. Data: The Phillips tag used in Sainsbury’s inventory control does not have any security function except a unique ID that is used to address and change data for each tag. The tag used is economical, and even if the tag data is maliciously changed, it does not warrant the use of a high-end microprocessor or crypto coprocessor, as there is no currency involved as in the case of the FeliCa smart card. The Phillips RFID system utilizes a special form of the Aloha anticollision protocol called Frame Aloha where the reader coordinates the transmission of tag data, giving higher throughput than the regular Aloha protocol [12][13].
How the taxonomy helps: The usage taxonomy for Sainsbury shows that authentication and tracking is currently taking place only. For Sainsbury managers, the next step can be collecting measurement data regarding the tagged items, for example temperature, humidity levels etc. This information can help the chain and customers select only the items that have not been exposed to long periods of unsatisfactory conditions. The RFID system is not using a global standard currently. For now, the chain may only be working with a limited supplier base for RFID enabling their supply-chain. However, in order for Sainsbury to be able to accept RFID tagged items from all over the world, they will need to shift to more multi-protocol readers which will allow them to accept RFID tagged items from global suppliers who use equipment complying with different standards.
The data taxonomy shows what kind of capabilities a middleware can have and may help managers realize its capabilities and the type of architecture needed.
3.3. VeriChip
Background: VeriChip is a miniature implantable RFID tag that can be used as a way of (monitoring) authenticating the implant receiver. The tag is placed
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under the skin and can be used with a special reader at a distance of a few centimeters or through a portal reader [14].
3.3.1 Usage: With an implanted chip, monitoring (authentication, tracking and measurement) of a subject can take place. VeriChip provides two types of proprietary scanners. There is a portable version where the read range for the tag/reader needs to be within a few centimeters. The reader will have to be held close to the tag in order to upload any data. Another version is a fixed ‘portal’ reader which can detect an embedded chip when it passes through the portal, enabling very rudimentary tracking ability. VeriChip is planning GPS enabled RFID chips that can be easily tracked, even outside. Currently, the system is being considered for supporting functionality such as authorization by chip and payments etc.
3.3.2. Frequency: The frequency utilized by the VeriChip is 125 KHz, which is approved for subdermal use in livestock. This frequency is a good choice as it is better for use in high moisture environments such as under skin and tissue with the drawback of the data exchange rate being slower than at high frequencies. Also, the read range is a few centimeters. The frequency used is the same both ways.
3.3.3. Physical: The VeriChip tag is powered by the reader and has a low-end microprocessor that does not support any security functionality. The memory is read only. The tag application method is insertion under the skin. The reader used works at 125 KHz and circular [15].
3.3.4 Data: The VeriChip system cannot interrogate multiple tags. There is no security encryption involved to protect data on the tag. The only data available is a unique ID that only makes sense through the use of a proprietary database and reader provided by VeriChip to subscribers. The ID of the tag uniquely identifies a subject who receives an implant. The unique ID is entered into a database and associated with whatever information the customer wishes the database to carry, for example social security, blood type etc. The unique ID does not conform to any standard. Once it is uploaded into the proprietary reader, the reader retrieves the corresponding subject data from the database and displays it.
How the taxonomy helps: The managers at VeriChip may eventually want to offer credit card companies a device that can read a customer tag’s unique ID and automatically charge the account for purchases at stores. The taxonomy will provide the managers information on what frequency parameters such as, range, read-write distance should be adopted. Furthermore, if the reader is to be offered globally, what types of frequency regulations will need to be kept in mind. If VeriChip managers want to expand functionality of their embedded tags, they can use the taxonomy to understand what types of characteristics can the new reader have e.g. fixed or handheld, number of ports etc. Security of the account information retrieved for the user to pay for merchandise would be very important. Also the taxonomy can help answer where the middleware should reside, for example, for their purposes, the middleware is better off on the reader because the RFID reader does not need to control the business process as it only serves as an authentication tool.
4. Conclusion
Though this RFID taxonomy covers most of the current RFID implementations it will still require many iteration before it can become the definite source of classifying RFID systems. Possible updates could include more information standards, costs, antenna and middleware.
The classification of RFID is necessary due to the wide variety of currently available systems. Academics, practitioners and enthusiasts will appreciate an organized source of information on RFID systems and the references to more detailed sources. This taxonomy will also present them information in a systematic and visual manner, reducing confusion. Calman [1] wrote that a systematic study of a field is a precursor to any detailed research of the field and that some classification knowledge gives a ground plan for the study of the entire field. He concluded that a classification system discourages generalization based on results of one observation or experiment. Such disambiguation would be a great achievement for this taxonomy. With the advent of smaller RFID enabled circuitry [8], cheaper manufacturing techniques [7] and hence their consequent ubiquity, the need for an RFID classifier is ever increasing.
5. References[1] Calman, W, T, The Classification of Animals,
Methuen & Co. Ltd, 1949
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[2] Engels, D. W, Sarma, S, The Reader Collision Problem, Auto-ID Center, IEEE SMC, 2002
[3] Finkenzeller, K, RFID Handbook: Fundamentals and applications in contactless smart cards and identification, 2nd Edition, John Wiley & Sons Ltd, 2003
[4] Janz, B, Pitts, M.G, Otondo, R.F, Information Systems and Health Care II: Back to the Future with RFID: Lessons Learned – Some Old, Some New, CAIS, Vol. 15, 2005
[5] Leaver, S, Evaluating RFID Middleware, Forrester Research, Aug 2004, www.forrester.com/Research/Document/0,7211,34390,00.html
[6] Turner, C, EPC and ISO 18000-6, RFID Journal, March 2003, www.rfidjournal.com/article/articleview/325/1/2/
[7] Twist, J, ‘Magic ink’ that makes metal grow, BBC Online, Jul, 2004
[8] Usami, M, An Ultra Small RFID Chip, IEEE Radio Frequency Integrated Circuits Symposium 2004
[9] Octopus Cards, www.octopuscards.com[10] FeliCa RC-S860 Contactless Smart Cart Security
Target, v1, Sony, Aug. 2002[11] Phillips Semiconductors,
http://www.vlsi.com/news/content/file_755.html, Philips Semiconductors announces availability of ISO 15693-compatible I-CODE smart label and reader IC products, Oct., 2001
[12] I-Code SLI Smart Label IC Functional Specification SL2 ICS20, Phillips Semiconductors, Rev 3.0, Jan. 2003
[13] Anti-collision and transmission protocol, ISO/IEC FCD 15693-3, Mar. 2000
[14] VeriChip, http://www.verichipcorp.com/ [15] Find Me LLC, www.findmellc.com, VeriChip
Reseller[16] Anonymous, A summary of RFID Standards,
RFID Journal, www.rfidjournal.com/article/articleview/1335/2/129/
[17] Class 1 Generation 2 UHF Air Interface Protocol Standard Version 1.0.9, http://www.epcglobalinc.org/standards_technology/EPCglobalClass-1Generation-2UHFRFIDProtocolV109.pdf
Appendix A
There are dependencies within some of the nodes in the taxonomy. Nodes with dependencies have been assigned ids in the taxonomy and will be discussed in the order of the four dimensions:
UsageID RELATION(S) DESCRIPTIONU1 P3, P4 Monitoring entities by unique
id requires a tag with memory
and a processorU2 P5 Authorization to resources
can take place with conveyable tags (e.g. e-ticket, ATM Card) or even embedded (e.g. VeriChip)
FrequencyID RELATION(S) DESCRIPTIONF1 F2 Read and Write range are
influenced by the frequency range utilized for communication b/w reader and tag
F2 F3 Load modulation is typical for low to high frequency range while surface acoustic waves backscatter are used for UHF and Microwave
PhysicalID RELATION(S) DESCRIPTIONP1 F2 The antenna shape is
influences the frequency range it can operate in
P2 P3, P5, P7 ISO AND EPC standards influence tag and reader specifications such as memory, shape, protocol amongst othersData
ID RELATION(S) DESCRIPTIOND1 P3,P4 Cryptography requires read-
write memory [3] as well as a processor
D4 D5 The scope of a middleware’s management capability is increased if it is resident on a server than a reader
11