A Taxonomy for Classifying RFID Systems

A Taxonomy for RFID

Taimur Hassan Samir Chatterjee
School of Information Systems and School of Information Systems and
Technology Technology
Claremont Graduate University Claremont Graduate University
taimur.hassan@cgu.edu samir.chatterjee@cgu.edu

Abstract data and physical as the fundamental classification
requirements of a large array of RFID systems (See
RFID systems come in a myriad of forms, each Fig. 1). These dimensions and their subsections are
catering to a specific need. However, a systematic an initial start to a classification processes and are
classification to reduce the confusion of potential subject to iterative feedback and improvement. To
adopters, researchers and enthusiasts is still lacking. comply with length limitations we have tried to
This article proposes and evaluates a taxonomy of present the more critical subsections of our taxonomy,
various RFID systems currently available. The while attempting to provide our readers references for
taxonomy can be used for gaining an understanding more details. The rest of the paper is organized as
of this technology, the factors for implementation of a follows: In Section 2, the taxonomy is presented,
successful RFID system, its strengths and weaknesses Section 3 evaluates the taxonomy by considering
as well as scalability options. Both novice as well as sample real-world cases. Finally, we conclude in
experienced RFID researchers will benefit from this Section 4 by summarizing our contribution.
classification. Appendix A illustrates the dependencies between
some of the branches of the taxonomy.
1. Introduction
2. Taxonomy
Radio Frequency Identification (RFID) systems have
been around from WWII era. In spite of the RFID systems are available in many forms. In order
advancements, the basic principles for the technology for a taxonomy to be useful, functional themes need
have changed little. An RFID system has two basic to be created that balance general with specific traits.
hardware components, a transponder and an In order to make the taxonomy easy to use, the
interrogator. They are most commonly referred to classification should only require data openly
(and henceforth referred to) as tag and reader available to the public and not proprietary and
respectively. A reader emits a radio wave at a certain difficult to collect information. The taxonomy is
frequency that is received by the tag. The tag is illustrated in a tree node manner to closely resemble
designed to respond with data that is then read by the diagrams that classify species of plants and animals,
reader. The distance between the tag and reader can for which taxonomies were originally created. The
vary from a few centimeters to several meters. The tree structure of the taxonomy may suggest each
adoption of RFID by Wal-Mart recently has made the branch being mutually exclusive from other branches,
topic headline news. The purpose of creating an which is not the case. Some of the relations will be
RFID taxonomy is to classify and organize the large discussed within the appendix. In case a node has two
volume of knowledge on the subject so as to make it or more exclusive branches, i.e. indicating an OR type
easier to navigate. The taxonomy can help create choice between the node branches, it will be indicated
specifications for projects by providing a framework by a small circle on the node.
for comparing solutions from multiple vendors. USAGE
PHYSICAL
Academics interested in RFID can use the taxonomy DIMENSIONS FREQUENCY
to get an overview of the which components of the DATA

technology can be researched on. Finally, the Figure 1: Top Tier
taxonomy serves users interested in general details
and directs them to further resources. Accordingly, we All RFID systems despite their varied prices, purpose
propose the following dimensions: usage, frequency, and capabilities can be studied systematically using a

small number of categories. These are the Usage, proves useful during assembly and maintenance of an
Physical, Frequency and Data dimensions. entity as well as for inventory control. The degree of
granularity desired should be determined before
2.1 Usage planning for an RFID system for example, some
CLASS
PRESENCE beverage manufacturers support tagging of beverage
NOTIFICATION cartons, but not individual cans, which may or may
U MONITIOR not be acceptable for meeting the customer’s needs.
S ENTITYU1 AUTHENTICATE However, with tagging of individual components, the
A MEASURE need to collect, store and later utilize RFID data
G AUTHORIZEU2
E TRACK dramatically increases as well. Currently, researchers
are using datamining to handle this data which can
Figure 2: Usage also include sensor measurements of an item and
All RFID systems usage fall under two main tracking data, which is the pinpointing of the
categories: monitoring and authorization. The approximate entity location. Measurement and
intended use of the RFID system will significantly tracking can occur after the entity is authenticated.
impact the choices selected in the rest of the Details on how a hospital in Taiwan combined
taxonomy dimensions. temperature measurement with tracking capability of
their patients to combat the Asian flu crisis is
2.11. Monitor: A desire to utilize RFID to determine discussed in [4].
whereabouts and/or take measurement would qualify
as a monitoring activity and hence requires a 2.1.2. Authorize: Such RFID systems are used to
definition of granularity. Granularity is the level at supplement traditional forms of authorization granting
which individual components can be uniquely entities such as keys, passes, tickets etc. They are not
resolved and depends upon the memory capabilities of suited for monitoring purposes because the RFID
a tag. As such, RFID systems can provide a class system has no way to verify the identity of the entity
level or an entity level monitoring capability. If the in possession of the RFID tag. This is because such
RFID system has a class level granularity, it means tags are embedded inside cards, keys or passes not
that the RFID reader cannot identify an item, its type designed to be permanently attached to an entity,
or group and can only monitor its presence within its making it vulnerable to misplacement or theft.
interrogation zone. An example of this system is the
2.2. Frequency
inventory security tags utilized by department stores READ RANGE
SIGNAL
to discourage stealing of merchandise. Most RFID DISTANCEF1 WRITE RANGE
systems today are implemented to provide an entity
LF (9-195 Khz)
level resolution capability to the customers. At this SIGNAL HF (13.56 Mhz)
level, tags may have memory capacity to provide F RANGEF2 UHF (0.3-1.2 Ghz)
enough bits to identify not only the merchandise R MICROWAVE (2.45-5.8) Ghz
E READER TO SINGLE FREQUENCY
uniquely, but also their manufacturer, origin, various Q TAG MULTI-FREQUENCY
measurements attached to the entity (temperature, U SUBHARMONIC (1/n fold)
E TAG TO HARMONIC (n fold)
humidity etc). RFID systems in this category can be N READER
CORRESPONDING (n:n)
used very effectively to authenticate an item as well C ANHARMONIC
as its subcomponents. In authentication, the identity Y
INTERACTION LOAD MODULATION
of an entity can be positively verified due to the TECHNIQUE SURFACE ACOUSTIC WAVE
(COUPLING)F3
inseparability of the RFID system from the item. A BACKSCATTER
REGULATIONS
good example can be livestock or people embedded
with RFID tags or an RFID label applied to a carton. Figure 3: Frequency
Whenever the tag is detected by an RFID system, it is
verified that the corresponding entity (livestock, The range of tasks, as well as the scalability of the
merchandise) is present due to the inseparable nature RFID system is heavily dependent on the radio
of the tag. The same principle can extend to sub- frequency the system uses. This is because
entities, which can be defined as entities within an frequencies can make a difference in range, data
entity. An example can be a RFID enabled shipping exchange speed, interoperability and surface
container with many RFID enabled cartons inside. penetration. Some frequencies are better at
Another example can be an RFID enabled electronic penetrating fluids and metals while others hinder
component e.g. DVD player that has RFID enabled scalability because of inconsistent regulations around
components. Monitoring at the sub-entity layer the world. Within frequency, signal distance,
spectrum range (the radio signal classification of the

2

frequency), reader to tag frequency, tag to reader (the However they require more power and are
radio frequency at which a tag transmits its data to the expensive [3].
reader), the interaction technique (the physics
principles used to enable tag/reader communication) 2.2.3 Reader frequency: Readers can come with the
and regulations are important dimensions of the ability to capture only a single frequency or multiple
frequency selected for the RFID system. frequencies. Multiple frequency readers are
developed to query tags that use different frequencies
2.2.1. Signal Distance: This represents the distance at or to comply with different standards.
which an RFID tag and reader can communicate
effectively. This can be divided into the read range 2.2.4 Tag to reader frequency: When a tag receives
and write range as readers may read tags data at a a radio signal from the reader, it can respond in a
different distance than it can write to the tag, frequency that is either a fraction of the reader
depending upon tag architecture (discussed later). frequency (subharmonic), corresponding to the reader
Because of the strengths and weaknesses that certain frequency, a multiple of the readers frequency
frequencies exhibit, low to high frequency levels are (harmonic) or completely independent of the reader
often used for distance up to a meter, while ultra high frequency (anharmonic). The tag to reader frequency
frequency levels and above are preferred for is important to know because the frequency can be a
achieving ranges beyond a few meters and higher data cause of interference to an existing communication
transfer rate. Higher frequencies also need antennas system even if the reader does not cause such
that take less space and are more efficient than interference. For example at 1/2 the frequency of a
antennas used for low frequency [3]. reader’s 128 KHz, a subharmonic tag will send back a
signal at 64 KHz.
2.2.2. Signal Range: RFID frequencies can be broken
into four ranges: 2.2.5 Interaction Technique: There are three
1. Low Frequency (9-135 KHz): Systems that use techniques used for sending data to be received by a
this range of frequencies have a weakness of a reader:
read distance of only a few centimeters [3]. The 1. Load Modulation: In this system, the inductive
frequency is typically used in subdermal animal field generated by the reader to power the tag is
identification due to its ability to penetrate the disrupted slightly by the tag, which is then
high moisture environment within an animal’s detected by the reader and translated into data
body. bits. This system is feasible in close proximity
2. High Frequency (13.56 MHz): This very popular (one meter or less) due to a great reduction in the
frequency range typically covers a distance from field’s strength with every increase in distance.
1 cm to about 1.5 meter for tag reading and up to 2. Backscatter: This system is typical for larger
a meter for writing data to the tag. Tags that distances and microwave readers. In this system,
work at this range typically rely on the reader to the corresponding frequency is used by the tag to
power them. RFID systems using this frequency send data to the reader, through coordination with
have a large user base and is supported by many surrounding tags.
RFID manufacturers such as Sony and Phillips. 3. Surface Acoustic Wave: This technique uses the
3. Ultra High Frequency (0.3-1.2GHz): This principle of microwave energy not passing
frequency range is used for supporting greater through metal surfaces. The RFID chip is
distance between tag and reader. These encoded lengthwise with vertical metal strips
frequencies cannot penetrate metal and moisture with a varying amount of gaps between them.
as well as the lower frequency ranges, however When microwave energy passes the strip, it
they can transmit data faster and hence are good creates variable disturbances that can be detected
for reading multiple tags at once [3]. These by a reader and correspondingly be converted
frequencies fall in the ISM range and hence there into binary data [3].
are inconsistencies across countries as to their
ranges (discussed later under regulations). 2.2.6 Regulations: Manufactures of RFID products
have to adhere to regulations created by agencies such
4. Microwave (2.45-5.8GHz): The advantage of as the Federal Communications Commission (FCC)
selecting such a high range is the resistance to and European Telecommunications Standards
strong electromagnetic fields such as electric Institute (ETSI) that control the frequency spectrum
motors and welding systems. Therefore, tags within their designated regions. Differences in
using these frequencies are often used for regulations make it more complicated and costly to
production lines in automotive systems. manufacture equipment that complies with

3

regulations. In Europe for example, the RFID UHF specifications the operating (the temperature
band range is 865-868 MHz while it is 950-956 MHz range the tags perform optimally), storage
in Japan and 902-928 MHz in USA. Some RFID temperatures (the range where tags can be safely
manufacturers handle the differences by designing stored) and the humidity range (expressed in
their readers to handle the multiple frequencies and percentage relative humidity).
protocols. Nonetheless, implementing a global RFID 3. Antenna: A tag’s antenna is needed to capture the
system entails dealing with the different regulations signal as well and in some cases to act as a
and standards, which make the process expensive and conductor of energy from the reader to the tag.
complicated. An RFID standards organization, EPC An antenna’s shape and dimensions determines
has ratified a standard named ‘Gen 2’ that specifies the frequency range it captures as well as other
regulations for global compatibility[17]. performance characteristics. Four types of tag
antennas are dipole, microstrip, slot and coil.
2.3. Physical Dipole antennas are straight piece of line whose
length influences frequency range. Microstrip
POWER
BATTERY
READER OPERATING antennas, known also as patch antennas, prove
SOURCE
TEMPERATURE RANGE
DIPOLE
STORAGE advantageous for tags as they comprise of a
ENVIRONMENT
P
ANTENNA
HUMIDITY RANGE
SHAPE P1
MICROSTRIP
SLOT
printed circuit board with a rectangle at the end
H
Y
T MATERIAL
COIL
INTERFACE POWER whose length and width influence frequency.
S EPC DATA AIR
I
C
A
G METAL INK MEMORY
Slot antennas are strips cut out of a metallic
PROGRAMMABILITY
A
L
BASED RANGE
SHAPE
POWER
AIR surface [3]. Coil antennas are wires arranged in
SIGNAL
STANDARDS P2 INTERFACE
INITIALIZATION APPLICATION
FACTORY SET
WRITE ONCE
either in a coiled planar fashion or wound up
ISO DATA
LOG. MEM. FUNCTIONS
ENCODING
ANTICOLLISION
SIZE MULTI-WRITE
around a conductive core. The material tag
ASSIGNMENT
ENTITY ID AND MGT
TESTING SIZE antennas are made of are metal based or ink
MEMORY ASSIGNMENT
based. Copper antennas are common in tags due
Figure 4: Physical (Diagram #1) to their low price and good conductivity, however
silver, gold and aluminum are also used,
The physical dimension includes the tag and reader providing varying performance levels. The latest
and their subcomponents, which due to their volume antenna manufacturing method is of using a
have been broken into three parts. The first two special ink and circuit board printing technology
diagrams (including the one from above) cover the tag that when dipped in a special solution that makes
components while the last covers the reader metal ‘grow’ on the surface of the ink. This
components. technology is said to one day allow the mass
2.3.1. Tag: Tags come in a variety of shapes and production of tags at a very cost effective manner
sizes. Each is designed for operating in various [7].
climates and conditions. Tags can be classified based
on the following criteria:
4. Standards: RFID tags must comply with
standards created by agencies ISO (International
1. Power Source: A tag can either gain electric Standards Organization) and EPC (Electronic
power through an inductive field generated by a Product Code). Of these standards, ISO has
reader, or it can be powered internally with produced more than 180 very detailed
batteries. The former systems are called passive specifications. The ISO standards have been
tags, while the latter are called active tags. The divided into ‘families’ such as ISO 18000 and
range of a passive tag varies from a few ISO 15693 series. EPC standards are focused on
centimeters to a meter, while active tags can supply-chain, in particular defining a
achieve very high ranges of 15 meters or more. methodology for the capture, transfer, storage and
Active tags are generally more costly than access of RFID data. EPC classifies tags into
passive tags because extra range requires five ‘classes’ where an increase in class signifies
sophistication such as an algorithm for multiple- an increase in level of sophistication, for
tag coordination and even a transmitter. So example, class 0 refers to read only passive tags,
called semi-passive tags use a battery to power while class 4 refers to reprogrammable active
the microprocessor, but not the transmitter. tags. Class 5 standard is developed with
Many operate in a hibernation state until awoken backward compatibility of a reader with tags of
by a reader signal. older classes in mind. EPC has also published
2. Environment: Tags have environmental standards for RFID data exchange and processing
limitations related to temperature and humidity. under the title of ‘Savant’. Summaries for ISO
Typically manufactures include in their standards and the EPC classes can be found in

4

[16]. There are overlapped areas between the afterwards, as in the case of tags attached to some
two standards, however these standards differ in expensive store merchandise such as clothes and
approach and do not conflict. EPC has ratified a media. Embedded tags are designed to be or become
new global standard ‘Gen 2’ which is being a permanent part of the object they are to help
evaluated by ISO as the ISO 18000-6 standard. monitor, for example subdermal tags for livestock
Turner provides a comparison between EPC and tracking. Conveyed tags refers to tags that can be
ISO 18000-6 in [6]. carried by individuals inside a wallet or purse and
serve more of a authorization function such as RFID
enabled tickets and ATM cards.

Figure 5: Physical (Diagram #2)
5. Memory: Tags may be either memory-less, or
have either read only or read-write memory. Figure 6: Physical (Diagram #3)
Memory free tags can only indicate their
presence to a reader, e.g. surveillance tags 2.3.2. Reader: Readers have five important features,
discussed above. Tags with memory are costlier polarization, antenna, protocol, I/O interface and
and come in two types, read only and read- portability
writable, the latter having two types, one that is 1) Polarization: There are two types of fields that a
writeable only once and one allowing multiple reader can generate: linear and circular. Linear
writes. Tags with read-write memory can either readers create a focused and oriented
run without an internal power source or require a electromagnetic field used for a greater range and
battery to maintain the memory. Tags with larger deeper penetration for tags whose antennas must
memory size can be used to store more than a be in the specific orientation for them to receive
unique ID such as measurement and tracking the signal. Circular readers generate a non-
information. directional inductive field in order to power and
6. Logic: Tags can have: interrogate tags that have no specific orientation
a. No form of processing for example and the circular pattern of waves increase the
supermarket theft prevention tags that alert chances of the tag antenna capturing the signal.
guards to a possible theft in the presence of an However circular readers have a shorter read
inductive field. range than linear polarized readers.
b. A finite-state processor which can support 2) Antenna: For portability, a reader antenna can be
some cryptography e.g. stream cipher located within the circuitry (Internal) or it could
c. A microprocessor can have varying processing be attached externally to one or more antenna
capability depending on the requirement. ports provided by the reader.
High-end microprocessors may need greater 3) Protocol: Some readers are able to communicate
power than what a reader can provide, and as using only a single protocol. This means that
such are mostly found in active tags. A they can talk to either an ISO based tag or an
microprocessor can be part of a chipset EPC one. However in some situations e.g. for
manufactured by companies such as Texas compatibility with vendors using different
Instruments and Phillips. standard tags, the reader may need to know how
7. Application Method: The application of tags to communicate with both types of tags. Such
within an RFID system can be categorized as readers are called multiprotocol readers.
attached, removable, embedded and conveyed. The 4) Interface: RFID readers may be integrated into
difference between an attached and removable tag is business infrastructure via input and output ports
the reusability. For example, RFID label tags are such as Ethernet (RJ45), serial (RS232), Wi-Fi
designed to be attached to a single item for the (802.11), USB and other public or proprietary
purpose of tracking the item and are not designed to standards. These ports allow the reader to send
be removed and attached to another item. Removable and receive information and instructions to and
tags are designed to be removed and reused from current infrastructure, for example,

5

information read from conveyor belts can be sent computing power available within the tag.
to an ERP system, while the reader can be sent Computing-heavy algorithms require crypto-
signals to turn on or off from a server. coprocessors and a power source, which can
5) Portability: RFID readers can either be fixed or increase the costs of a tag [3]. Hence a balance
handheld. Multi-port fixed readers can be needs to be struck between security and cost.
advantageous for tracking multiple items at once Also, during the selection of a multi-organization
as they can receive tag signals from multiple RFID system, the use of the security algorithm
locations within a facility if the antennas are should be coordinated between partners. Cost of
connected to the antenna ports via cable. Fixed multi-organization deployment can be kept in
readers can also come in a portal shape to detect check by selecting hardware that conforms to
tagged items passing through. Handheld RFID well-known security algorithms.
readers can incorporate an antenna, a UI and have 2) Proprietary Algorithm: Some manufactures have
uplink capability through serial or other interface developed data algorithms that are not based on
e.g. Wi-Fi. published standards. With such a system, lock-in
may become a problem if the customer wishes to
2.4. Data 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
Figure 7: Data read from the tag, the reader sends the unique tag
identifier to a secure server where it is matched
In a typical RFID system, the type of data as well as with a database record entry containing all the
the manner of data processing between the tag and data regarding the identifier. Data is encrypted
reader is crucial to its function. Standards such as by the server and sent to the reader for display.
EPC class 1, version 2 (also called Gen 2) allow 96 This way, privacy is protected as no personal
bits for identification on a tag. These bits of information ever gets exchanged. As long as a
information go through steps such as extraction, malicious party does not get a hold of the
decoding, filtration, analysis and feedback within a database, any identifier information obtained
very few seconds, involving everything from maliciously is meaningless.
hardware such as tags, readers and conveyer belts to
sophisticated software and backend IT systems such 2.4.2. Multi-tag Coordination: If a reader is capable
as ERP, hence making three dimensions of data of reading multiple tags at the same time, the tags
important for an RFID system: security, multi-tag require the use of a coordination scheme so as to
coordination and processing. allow all of their data to reach the reader uncorrupted.
There are three types of techniques used:
2.4.1. Security: Unprotected, sensitive data within 1) Space Division Multiple Access (SDMA): In this
tags can be eavesdropped by anyone with a radio scheme, a frequency channel used in one zone is
receiver or network packet snooper when data is reused in another zone, similar to a cellular tower
being transmitted between a reader and a backend layout. The technique involves using a large number
server. Therefore, it is important to know the type of of readers and antennas to form an array to provide
data protection scheme utilized. coverage of an area [3]. The technique is not
Three kinds of security scenarios are possible: commonly used.
1) Public Algorithm: In this system, the tag and 2) Frequency Division Multiple Access (FDMA): In
reader employ encryption techniques that are FDMA, tags respond to a query by choosing multiple
well-tested and public information. Some frequency channels for uplink. This requires a reader
common examples are shared key, derived key, to have multiple frequency capability. The system is
3DES and stream cipher. The choice of very expensive and used in custom applications [3].
algorithm has a lot to do with the type of

6

3) Time Division Multiple Access (TDMA): This is
the most common technique used where each tag Background: Three different transportation agencies
uplink is coordinated to send data during a specific in Hong Kong introduced the ‘Octopus’ transport
period of time. Two common protocols that use this ticketing service. The service consists of RFID cards
technique: bought by customers, which can have an initial stored
a. Aloha Protocol: The Aloha protocol works on currency value based on the amount paid by customer
a collision principle, where several tags send during purchase. The card can be used in place of
data packets at random intervals. If the packets cash aboard any of Hong Kong’s transportation
collide, the tag waits for a random time period services (bus, tram, railway) equipped with 13.56
before retrying. Variant of this technique are MHz tag readers with a range of few centimeters.
S-Aloha and Frame Aloha protocol [3]. Customers have two options, purchase an anonymous
b. Binary Tree: In this protocol, data packets card with no identification feature or purchase a
collide during transmission, however the reader personalized card with an identification photo [9].
resolves each collision one bit at a time through The cards are based on Sony FeliCa smart-card
the use of a binary search tree algorithm. Each system [10] that utilizes standard physical and logical
tag contains an ID associated with it. A reader architecture.
specifies the range of tag IDs that must reply to
a query, while all tags with IDs not covered in 3.1.1 Usage: This system is used primarily as an
that range must stay silent. If a collision occurs authorization tool. However, as customers can
because two tags choose the same time to personalize their ID with pictures, it can also become
upload data, the reader can detect the exact bit a valid authentication form. The interrogation zone is
at which the collision occurred. By using a only a few centimeters to prevent accidental
sophisticated binary search tree algorithm, the deduction of value from customers not intending on
reader is able to read every tag [2]. ride the transportation. Due to the small interrogation
range between tag and reader, the tag is infeasible for
2.4.3. Processing: Data from tags must go through a tracking.
software that can filter, convert, correct and relay it
to the appropriate enterprise systems. This layer of 3.1.2. Frequency: The desire for a small read range
software is referred to as middleware. The as well as a requirement to change value of the
middleware can reside on a reader or a server. currency amount stored in the tag’s memory makes
Middleware located on a reader has capability to filter 13.56 MHz a good choice for a frequency as it
out some data at the source using programmable provides enough power for read-write operations as
logic, but cannot perform sophisticated functions that well as data encryption. The frequency 13.56 MHz is
can only be provided by server based middleware, for shared between reader and tag and vice versa. The
example communication with other types of devices tag uses load modulation to send its data to the reader,
such as bar code readers, RFID readers and even meaning it creates a detectable interruption in the
business process devices such as conveyer belts and induction field of the reader.
ERP systems. Middleware can have either a single
tier architecture or multi-tier architecture, the latter 3.1.3. Physical: The power source in the FeliCa card
allowing greater flexibility in data and process is the reader. A microprocessor is required to
integration. Some of the offerings of middleware are compute the encryption requirement of the tag. The
data and process management, application reader needs to update currency information in the
development and partner integration. A detailed card; therefore, read-write memory is present. The
evaluation and comparison of some current application of the tag is on the surface of the smart
middleware solutions is done by Leaver [5]. card. The reader is circular and requires the customer
to place the card within a few centimeters of the
3. Evaluation reader’s inductive field.

3.1.4. Data: In this last dimension, we can see that
In order to evaluate the taxonomy, three RFID cases because the system is intended for one customer
were selected. The information gathered was based authorization at a time, the hardware will not
on official press releases, technical specification accommodate a multi-tag reading scenario. Each tag
documents of the RFID equipment suppliers as well will have to be addressed and updated individually by
as official standards. the reader. Also, as a public algorithm is used for
encryption, the tag can be used in organizations
3.1 Hong Kong ‘Octopus’ Case outside transportation as long as they have readers

7

that utilize standardized security algorithms. Hence, 3.2.4. Data: The Phillips tag used in Sainsbury’s
the octopus card is currently being accepted by many inventory control does not have any security function
businesses in Hong Kong. except a unique ID that is used to address and change
data for each tag. The tag used is economical, and
How the taxonomy helps: If the managers of even if the tag data is maliciously changed, it does not
‘Octopus’ want to increase efficiency, improve warrant the use of a high-end microprocessor or
services and reduce costs of the transportation system, crypto coprocessor, as there is no currency involved
the taxonomy can be consulted to understand what as in the case of the FeliCa smart card. The Phillips
changes can be brought about to achieve these goals. RFID system utilizes a special form of the Aloha
For example, they can program their middleware to anticollision protocol called Frame Aloha where the
collect information such as when passengers switch reader coordinates the transmission of tag data, giving
from bus to train, peak times etc, to help improve higher throughput than the regular Aloha protocol
their business process. In such case, operations [12][13].
researchers, IT analysts and academics involved will
need a source that proves a good classification How the taxonomy helps: The usage taxonomy for
reference for RFID systems in order to understand the Sainsbury shows that authentication and tracking is
options available. currently taking place only. For Sainsbury managers,
the next step can be collecting measurement data
3.2 Sainsbury Case regarding the tagged items, for example temperature,
humidity levels etc. This information can help the
Background: Sainsbury is a UK retailer that wanted to chain and customers select only the items that have
implement RFID technology within its supply chain. not been exposed to long periods of unsatisfactory
Cartons with inventory arrive at Sainsbury’s conditions. The RFID system is not using a global
distribution depot. An RFID system based on Phillips standard currently. For now, the chain may only be
I-Code chips detects the arrival of the cartons and working with a limited supplier base for RFID
reads the inventory system at a read distance of more enabling their supply-chain. However, in order for
than a meter [11]. The system can read multiple tags Sainsbury to be able to accept RFID tagged items
in a single read session. The write distance is about a from all over the world, they will need to shift to
meter. Each tag has a unique identifier for securing more multi-protocol readers which will allow them to
data against malicious change, however no data accept RFID tagged items from global suppliers who
encryption is supported. use equipment complying with different standards.
The data taxonomy shows what kind of
3.2.1 Usage: A read range of 1.5 meters allows
capabilities a middleware can have and may help
monitoring (authentication) of carton within a
managers realize its capabilities and the type of
distribution center, as well as tracking for security
architecture needed.
purpose. This is possible due to the deployment of
portal scanners that automatically detect the presence 3.3. VeriChip
of tags when they are brought within the read range.
This system also allows tracking of the exact location Background: VeriChip is a miniature implantable
of the cartons within a warehouse. RFID tag that can be used as a way of (monitoring)
authenticating the implant receiver. The tag is placed
3.2.2 Frequency: The read distance of the tags is under the skin and can be used with a special reader at
about 1.5 meters, however, there is a limitation on a distance of a few centimeters or through a portal
write range. In order to be able to change data within reader [14].
the passive tag, it must be within a meter distance
from the reader. The frequency used is the popular 3.3.1 Usage: With an implanted chip, monitoring
13.56 MHz, both ways. An inductive field is used for (authentication, tracking and measurement) of a
coupling, the readers are single frequency. subject can take place. VeriChip provides two types
of proprietary scanners. There is a portable version
3.2.3 Physical: The tags require power from the
where the read range for the tag/reader needs to be
reader. Each tag contains a microprocessor that can
within a few centimeters. The reader will have to be
support basic read-write functionality. The tags are
held close to the tag in order to upload any data.
applied to the surface of cartons. The reader uses
Another version is a fixed ‘portal’ reader which can
circular-polarization with a read range of 1.5 meters
detect an embedded chip when it passes through the
in all directions. It means that a portal reader can
portal, enabling very rudimentary tracking ability.
cover an area equal to the warehouse entrance [12].
VeriChip is planning GPS enabled RFID chips that

8

can be easily tracked, even outside. Currently, the middleware is better off on the reader because the
system is being considered for supporting RFID reader does not need to control the business
functionality such as authorization by chip and process as it only serves as an authentication tool.
payments etc.
4. Conclusion
3.3.2. Frequency: The frequency utilized by the
VeriChip is 125 KHz, which is approved for Though this RFID taxonomy covers most of the
subdermal use in livestock. This frequency is a good current RFID implementations it will still require
choice as it is better for use in high moisture many iteration before it can become the definite
environments such as under skin and tissue with the source of classifying RFID systems. Possible
drawback of the data exchange rate being slower than updates could include more information standards,
at high frequencies. Also, the read range is a few costs, antenna and middleware.
centimeters. The frequency used is the same both The classification of RFID is necessary due to the
ways. wide variety of currently available systems.
Academics, practitioners and enthusiasts will
3.3.3. Physical: The VeriChip tag is powered by the appreciate an organized source of information on
reader and has a low-end microprocessor that does not RFID systems and the references to more detailed
support any security functionality. The memory is sources. This taxonomy will also present them
read only. The tag application method is insertion information in a systematic and visual manner,
under the skin. The reader used works at 125 KHz reducing confusion. Calman [1] wrote that a
and circular [15]. systematic study of a field is a precursor to any
detailed research of the field and that some
3.3.4 Data: The VeriChip system cannot interrogate classification knowledge gives a ground plan for the
multiple tags. There is no security encryption study of the entire field. He concluded that a
involved to protect data on the tag. The only data classification system discourages generalization based
available is a unique ID that only makes sense on results of one observation or experiment. Such
through the use of a proprietary database and reader disambiguation would be a great achievement for this
provided by VeriChip to subscribers. The ID of the taxonomy. With the advent of smaller RFID enabled
tag uniquely identifies a subject who receives an circuitry [8], cheaper manufacturing techniques [7]
implant. The unique ID is entered into a database and and hence their consequent ubiquity, the need for an
associated with whatever information the customer RFID classifier is ever increasing.
wishes the database to carry, for example social
security, blood type etc. The unique ID does not 5. References
conform to any standard. Once it is uploaded into the [1] Calman, W, T, The Classification of Animals,
proprietary reader, the reader retrieves the Methuen & Co. Ltd, 1949
corresponding subject data from the database and [2] Engels, D. W, Sarma, S, The Reader Collision
Problem, Auto-ID Center, IEEE SMC, 2002
displays it.
[3] Finkenzeller, K, RFID Handbook: Fundamentals
How the taxonomy helps: The managers at VeriChip and applications in contactless smart cards and
identification, 2nd Edition, John Wiley & Sons
may eventually want to offer credit card companies a
Ltd, 2003
device that can read a customer tag’s unique ID and [4] Janz, B, Pitts, M.G, Otondo, R.F, Information
automatically charge the account for purchases at Systems and Health Care II: Back to the Future
stores. The taxonomy will provide the managers with RFID: Lessons Learned – Some Old, Some
information on what frequency parameters such as, New, CAIS, Vol. 15, 2005
range, read-write distance should be adopted. [5] Leaver, S, Evaluating RFID Middleware,
Furthermore, if the reader is to be offered globally, Forrester Research, Aug 2004,
what types of frequency regulations will need to be www.forrester.com/Research/Document/0,7211,3
kept in mind. If VeriChip managers want to expand 4390,00.html
functionality of their embedded tags, they can use the [6] Turner, C, EPC and ISO 18000-6, RFID Journal,
taxonomy to understand what types of characteristics March 2003,
can the new reader have e.g. fixed or handheld, www.rfidjournal.com/article/articleview/325/1/2/
number of ports etc. Security of the account [7] Twist, J, ‘Magic ink’ that makes metal grow, BBC
information retrieved for the user to pay for Online, Jul, 2004
merchandise would be very important. Also the [8] Usami, M, An Ultra Small RFID Chip, IEEE
Radio Frequency Integrated Circuits Symposium
taxonomy can help answer where the middleware 2004
should reside, for example, for their purposes, the

9

[9] Octopus Cards, www.octopuscards.com influences the frequency
[10] FeliCa RC-S860 Contactless Smart Cart Security range it can operate in
Target, v1, Sony, Aug. 2002 P2 P3, P5, P7 ISO AND EPC standards
[11]Phillips Semiconductors, influence tag and reader
http://www.vlsi.com/news/content/file_755.html, specifications such as
Philips Semiconductors announces availability of memory, shape, protocol
ISO 15693-compatible I-CODE smart label and amongst others
reader IC products, Oct., 2001 Data
[12] I-Code SLI Smart Label IC Functional
Specification SL2 ICS20, Phillips
ID RELATION(S) DESCRIPTION
Semiconductors, Rev 3.0, Jan. 2003 D1 P3,P4 Cryptography requires read-
[13] Anti-collision and transmission protocol, ISO/IEC write memory [3] as well as a
FCD 15693-3, Mar. 2000 processor
[14]VeriChip, http://www.verichipcorp.com/ D4 D5 The scope of a middleware’s
[15]Find Me LLC, www.findmellc.com, VeriChip management capability is
Reseller increased if it is resident on a
server than a reader
[16]Anonymous, A summary of RFID Standards,
RFID Journal,
www.rfidjournal.com/article/articleview/1335/2/1
29/
[17] Class 1 Generation 2 UHF Air Interface Protocol
Standard Version 1.0.9,
http://www.epcglobalinc.org/standards_technolog
y/EPCglobalClass-1Generation-2UHFRFIDProto
colV109.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:
Usage
U1 P3, P4 Monitoring entities by unique
id requires a tag with memory
and a processor
U2 P5 Authorization to resources
can take place with
conveyable tags (e.g. e-ticket,
ATM Card) or even
embedded (e.g. VeriChip)
Frequency
F1 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
Physical
P1 F2 The antenna shape is

10

A Taxonomy for Classifying RFID Systems

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