Selected Papers: Wireless Technologies for Ubiquitous

Overview of RFID Technologies for
Ubiquitous Services
Masashi Shimizu†, Mamoru Kobayashi,
and Masahiro Umehira
Abstract
The terms “ubiquitous”, “Auto-ID,” and “wireless tag” have recently become very popular and theyfrequently appear in the daily newspapers. Despite their popular use, it is very difficult to express theirreal functions because the definitions of these terms are not clear. This paper explains promising services
that are currently proposed, technical problems common to these services, and the direction in which
research should head in the future.

1. Introduction
Ubiquitous services are services that enable accessfrom anywhere to anything regardless of time andspace. They need every object to be connected to a
network in order to communicate. Since objects often
move, wireless communications should be used. The
communication tool that best suits these conditions is
the wireless tag. The functions that a wireless tag
requires depend on its role in a usage scenario. For
example, if tags are attached to all objects, as in the
Auto-ID center [1] described later, cost is a more
important issue than the functions provided by thetags. On the other hand, in the sensor networks provided by Dust Inc. [2], functions are much more
important than cost. This paper explains the functions
that wireless tags require in several proposed ubiquitous service examples.
2. From barcode to RFID
Auto-ID discriminates objects automatically, andpart of this service is already in use as barcodes or
optical character recognition (OCR). The introduction of the barcode was a revolutionary step because
it fundamentally changed physical distribution sys† NTT Network Innovation Laboratories
Yokosuka-shi, 239-0847 Japan
E-mail: shimizu.masashi@lab.ntt.co.jp

12

tems. It is now exceptionally rare to find a productthat has no barcode. The cost of a barcode is negligible because it is printed and barcode readers are very
cheap because they have a simple structure. However, barcodes do have a limited memory capacity: they
can identify a product category or manufacturer but
cannot distinguish each individual product.
The current readers are connected to networks. The
drawbacks to barcodes are that they are easy to copy
and must be passed in front of a reader. To addressthese problems, new trials are being conducted tomake the physical distribution system more efficient
or to manage customer information by affixing wireless tags to each product and establishing a connection to networks [3].
2.1 Passive tag
Wireless tags were originally designed to deter
shoplifting and not to manage products. A simple
shoplifting protection system cannot discriminate
each product as having a specific ID. However,recently developed wireless tags that can not only discriminate each product, but also write data in themselves are available at very economical costs (lessthan $1 per tag). Such a tag, which has an ID, is called
an RFID (radio frequency identification) tag. The
tag’s power is supplied by the reader to reduce thecost of the tag. These tags are called passive tags
because their power is supplied from a separate
source. Figure 1 shows the working principle behind
NTT Technical Review

ServicesElectromagnetic field

Vcc

Clock
Divider
MemoryOutput

IC

BPF

DEMO
OutputTag
BPF: band-pass filter, DEMO: demodulator

ReaderFig. 1. Basic circuit diagram for passive tag and reader.

passive tags. The power is supplied based on a similar principle to the transformer by electromagnetic
inductance between the wireless tag and a reader. The
reader transmits high-frequency modulated waves
that combine power with commands. The tag receives
and simultaneously detects the waves and uses themfor power. Depending on the system, a typical tag has
a simple microprocessor and a divider. It recognizes
received commands and replies with its own assigned
ID. The passive tag cannot drive an oscillator because
it has no battery. However, it receives powerful carrier waves and utilizes them instead of an oscillator. It
replies using frequency transformation through signals divided using the divider. The electromagnetic
inductance type tags can only transmit signals overone meter, but they can be used worldwide because
the frequencies are standardized from 100 to 135 kHz(LF: low frequency) and 13.56 MHz (HF: high frequency).
Recently, new types of passive tags have debuted.
They can receive high-frequency waves using anantenna, detect these waves, and use them as a power
supply instead of using electromagnetic inductance.
One characteristic of these new passive tags is theirsmall antenna for high frequency use. Based on theantenna pattern, the signals can be transmitted overlonger distances, such as 10 m, using the 900-MHz
band in the US [4]. However, because they are new,their frequencies have not yet been standardized. The
frequency of 2.45 GHz can be used worldwide, but its
maximum transmission range is only a few centimeVol. 1 No. 9 Dec. 2003

ters due to the low power.
Since the passive tags provide simple functions, themanufacturing cost is low once a die chip has beencast. The chip cost is determined by the number produced and its size. Currently, 350-µm × 350-µm chips
are being manufactured. However, they do not workas the RFID themselves, as mentioned above,
because they require a coil or an antenna to receivehigh-frequency waves.
2.2 ePC tag
The Auto-ID center thinks that an important factor
in tag popularity is low cost. It proposes using the 96bit electronic product code (ePC) inherited from thecurrent barcode system and adding a serial number tothe tags. It will keep product history or detailed information on the network instead of storing it in the tag’s
memory to avoid having to expand the memory
capacity. Object name service (ONS) is a service thatmakes detailed information accessible through networks based on the ID and offers the information tolocations that require it after rapid certification via
the network. Servers called Savants respond toinquiries from various applications and tag ID. By
standardizing this information flow, Auto-ID
achieves lower operational costs and enables data distribution (Fig. 2). It is focused on standardized items
such as tag ID, ONS, and the physical makeup language (PML), a language on Savants, in addition todeveloping other features for various applications.
The ubiquitous ID center, the standardization orga13

Selected Papers

Common database(PML)
SensorTag

SavantInternet

Reader

Application

SavantePC=96 bits

Application
database

Commonresolution(ONS)

Standardization in Auto-ID
Competitive parts by vendors

Fig. 2. Standardization strategy of Auto-ID center.

nization for RFID in Japan, also has plans to simplify tag functions to decrease cost. It proposes its own
128-bit ID, and its plans for data distribution arealong the same lines as those of the Auto-ID center.
3. Problems holding up widespread use
Stores that sell small expensive goods that are easy
to shoplift such as CDs, videos, and DVDs alreadyuse wireless tags to deter shoplifting. However, thetag functions are disabled or the tags are removed
from the goods when the goods are purchased. Below
we explain the two main reasons for disabling the tag
functions upon purchase.
3.1 Maintenance for shoplifting protection
If the tag function continues to work after the goods
have been purchased, an alarm will sound when thecustomer enters another shop equipped with the sameanti-shoplifting system. There are several ways to
avoid this scenario. The most promising way is toread and store the tag IDs of all goods in a databasewhen stocking goods, and to write the ID and statusas purchased in the database when the goods are sold.
This can discriminate the reentry of goods into a store
from shoplifting. Furthermore, when people enter thestore with goods purchased in other stores, the store
system can recognize that the goods were not sold inthat particular store. However, if the current equipment is not upgraded and the ID is not stored whenstocking goods, alarms will continue to occur when
the customers enter a store with goods purchased atother stores. In other words, coexistence among existing equipment is a problem that must be addressed.

14

3.2 Problem of privacy
As powerful sponsors of the Auto-ID center, WalMart and Benetton responded quickly to concerns
about privacy. If the tags are affixed to all goods andtheir functions continue to work outside the store,
then anyone with a reader can obtain information
about those goods. The retailers had to treat this not
as a simple technical issue, but as a social issue withsignificant ramifications regarding customer satisfaction. Currently, the focus of introducing RFID is on
increasing the efficiency for retailers or manufacturers. The main obstacle to this system is expected to be
the issue of the invasion of customers’ privacy. If thissystem does not readily provide significant advantages to the customers, they are unlikely to accept it.
There are several proposals for privacy protection.
One of them is to use the Kill command feature proposed by the Auto-ID Center. Each tag has a uniquepassword, and when it receives the password, the tag
erases itself. This function is useful in protecting thecustomer’s privacy, but it raises some further problems. On the other hand, the encryption described
previously will give tags and readers a certain degreeof security. While there are several proposed encryption schemes, none is a complete solution. Some ofthem allow tag output to include relatively constantinformation, need to rewrite data to the tag memory
to avoid tracking, or require a conscious decision by
the user.
For active tags, these restrictions are not as strict asfor passive tags. For example, the active tag in car
keys used for wirelessly locking and unlocking thedoors from a short distance uses the code hopping
technique. Anyhow, the privacy issue is not simply
technical but has a human side. Solving it completely
will take a considerable amount of time.

NTT Technical Review

Selected Papers

4. High-functionality tag
Because passive tags must be put on all products,
they must have a short radio range and simple functions to keep the cost low. The cost of a passive tag iscurrently under $1. Now, let us assume that a tag is
affixed to each carton delivered or stocked, rather
than each individual product. A tag cost of several
hundred dollars would be acceptable if one cartonholds a hundred items and the tag is reused ten times.
Of course, in this case, it is not possible to trace eachproduct and detect it being shoplifted. However, a tag
cost of several hundred dollars allows a battery-powered tag to be used. Then the tag can contain a sensor,
function as a reader, or record data to itself. Moreover, the radio range can be extended to approximately one kilometer if a radio license is obtained.
This does not involve privacy problems because thetags never come into the hands of customers.

mately five years if it transmits its ID once every
seven seconds based on the regulations for low-power
radio (500 µV/m at 3 m). Examples of asset tracking
using simple active tags will be introduced in theother papers in this issue.
4.2 Semi-passive tag
There are many semi-passive tag methods. Simple
active tags do not have a receiver function. To compensate for this, one proposal is a tag that has anunpowered receiver and waits until it receives a signal, in the same way that a passive tag does, and thenuses onboard battery power to transmit its ID anddata. This type of tag could be used to track containers or monitor the air pressure of car tires.
Figure 4 shows an example of a tag used to track
containers. Because the object bearing the tag is acontainer, the tag does not need to be especiallysmall, so it can have a large battery, which can have along life. The battery life depends on the transmission
duty cycle and the battery size, and this type can lastalmost five years.

4.1 Simple active tag
The transmission range of the RFID tags can beincreased by equipping the tag with a battery. This
type of tag is known as an active tag. The simplest
active tags only transmit
the ID periodically and don o t h a v e a r e c e i v e r.
Contents inside a tag
Active tags normally haveminimal functions toextend the battery life as
Readerlong as possible. For
example, the ID is onlyTagtransmitted for asset management or for palletrecognition. Therefore,(CompactFlash memory card shown for scale)
inexpensive sensors that
consume very little power
Fig. 3. Simple active tag and reader.
can be integrated into a
simple active tag. A
vibration sensor or a thermal sensor consumes
very little power andtransmits only one bit of
Tag or reader
information. The effecton battery life is veryslight if they are integrated into simple active tags.
Sensor for a container lid
Figure 3 shows an example of a simple active tag
20 cm
whose only function is totransmit its ID [5]. The
Fig. 4. RFID tag and reader for tracking containers.
battery will last approxiVol. 1 No. 9 Dec. 2003

15

Selected Papers

4.3 Sensor-equipped tag
American car manufacturers may be required tomonitor the air pressure in car tires for safety reasons.
An analog-to-digital (AD) converter is required tomeasure the physical value and transmit it. The tag
for monitoring air pressure can be constructed using
a simple active tag implemented only with an AD
converter and a small memory. This configuration
decreases the battery life, but the influence on the costis slight. There is significant demand for such a tag,because it could measure quality during the transportation of foods or valuables and record simple
measurements.

niques are developed based on the use of the 915MHz band of the ISM (Industry Science Medical)
band in the US (ZigBee plans to use 2.45 GHz too).
Therefore, these systems cannot be used outside the
US. These highly functional tags can establish multihop connections as tags communicate with eachother. Because multihop connections can expand theservice area, the investment in readers can be
decreased compared with simple active tags or passive tags. Naturally, the tag cost is higher, but it issuitable for applications that must work over a large
area using a few tags. The Dust system and ZigBee
are intended for use as sensor networks.

4.4 Multihop*1 tag
The most widely used wireless communications
standard is IEEE 802.11 for wireless LANs, which
can communicate over a few hundred meters when
there are no obstacles between the terminals. However, this standard has some drawbacks if it is used for
RFID.
q High power consumption caused mainly byusing high frequencies and aiming for a highdata rate rather than a long range.
w High probability of interference because manyusers already use such frequencies.
e High cost, which will be hard to decrease,because an expensive microprocessor isrequired for complex communication methods.
r Long link connection establishment timenecessitated by the advanced OS used.
It is of course possible to use a wireless LAN for
RFID tags for applications that require the functions
despite the short life or expense. For these reasons,some ideas were proposed to simplify IEEE 802.11
standards. Bluetooth [6] was initially planned to be avery simple protocol. However, as it was changed toaccommodate general-purpose use, many functions
were added. Its power consumption is becoming
much higher than originally planned because of its
complex signal processing. Since the number ofsimultaneously connected terminals is limited, it is
not suitable for use with RFID. ZigBee [7] isdesigned taking these criteria into consideration. It
has a less sophisticated operating system, a lower bit
rate, and simpler processing. These specifications canaccommodate the use of RFID. The Dust system issimilarly designed, but its specifications are uniqueand are not slated for standardization. These tech-

4.5 Infrared tag
The tag function must be “wireless”, but need notuse a “radio frequency”. Infrared tags, are inexpensive and free of wires, although they have high power
consumption. These tags are effective for applications that require directional transmission and reception. Some examples of promising applications using
infrared tags are introduced in the following papers.

*1 Multihop: Multiple hopping. Hopping means data transmission
from a node to other node.

16

5. Common techniques among ubiquitous
services
As mentioned above, the appropriate function must
be selected for each application, and the perfect wireless tag has yet to be developed. Figure 5 and Table 1
show functions of RFID. It is necessary for all services to know “when”, “what”, “where”, and “result”.
The equipment should consume low power. Since areader is connected to a network, it can determine“when” by checking the time when it reads a tag. We
can easily handle “what” by using a unique ID to eachtag. The difficult issues pertain to “where” and“result”.
5.1 Position estimation
The global positioning system (GPS) is widelyused outdoors as a position estimation tool. It estimates the position from the arrival times of radio signals transmitted from satellites. Its accuracy decreases significantly indoors in principle because the radio
signals from satellites are attenuated and reflections
from walls or floors have a detrimental effect. To
solve this problem, some applications have beendeveloped. MIT’s Cricket [8], [9] and UCLA’s Ibadge [10], [11] estimate the position indoors byusing the difference in the transmission rate of ultrasonic waves compared with radio waves. These systems are designed for human navigation indoors and
NTT Technical Review

Selected Papers

1012

Transmitter

T R
ePC

ReceiverSensor

1011

Multihop
Encryption

Number of tags

1010

T B
Asset tracking

109
108
107

Battery

T R S B
Tire pressure

T R SM B
Sensor network

T R S B
Food tracking

T R S B
Container tracking

T R E
Access control

106

T R S E B
Children tracking
110Communications range (m)100Fig. 5. Wireless tag function for various applications.

None
None
None
None
Yes
Yes
Tag reader
Temp/light
None
none
None
None
MotionPressure/temp
Temp/motion
None
None

ke

ry
mo

r

r
or
ns

ive
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
None
Yes
Yes
Yes
None

Ma

∞
∞
∞
∞
<3 years<few months<few months<2 years<2 years<half year∞∞
<10 years<3 years<few months<few months
∞

Me

×
×
×
×
×
×
○
○
△
○
NA
×
×
×
×
×
×

ce

△
○
△
○
○
○
○
○
○
△
NA
×
×
×
×
△
×

Se

ry
tte
Ba

×
△
×
○
○
○
○
△
△
△
◎
×
×
×
×
×
×

Re

life

n
p
ho
ltiMu

oll
ti-c
An

cry

ptio

isio

n

eu

Yes
ePC Class 0 (13.56 MHz) <1 m
ePC Class 0 (915 MHz) <10 m No
ePC Class 1 (915 MHz) <10 m No
YesePC Class 2 (2.45 GHz) <1 m
<30 m NoePC Class 3
ePC Class 4<30 m NoePC Class 5<30 m No<300 m No
Smart Dust
Zig Bee<75 m Yes*/no<100 m Yes
Bluetooth<10 cm Yes
IC cardµ-Chip<10 cm Yes
Simple active tag<30 m No
Tire pressure monitor<30 m No
Food Tracking<30 m No
<10 m Yes
InfraredBar code<10 cm Yes

En

e
ng

wid
rld

Ra

Wo

Ty

pe

of

tag

se

Table 1. Features of wireless tags.

None Phillips
Yes Matrics
None Alien
None Alien
Yes Unknown
Yes Unknown
Yes Unknown
Yes Dust
Yes Many
Yes Many
Yes Many
None Hitachi
None Many
None ManyYes Many
None Many
None Many* ZigBee defines three frequency bands: 2.45-GHz band is worldwide, 800-and 900-MHz bands are for Europe and theUSA, respectively.
Green rows are our predictions.
Bluetooth usually is used for embedded devices. There are few cases of use for active tags.

have a high data rate connection between a terminal
and a network. It is difficult to obtain information on
goods by using their tags because the battery life isvery short. We have developed an indoor position
estimation system for objects that incorporate longlife tags. Details are given in the following papers.
5.2 Incorporating sensors
It is necessary to incorporate a sensor in the tag orreader to learn the “result”. It is very effective, espeVol. 1 No. 9 Dec. 2003

cially for physical distribution management, to incorporate a sensor and a memory in a tag so that it canknow the history of the object. In this case the sensor
power consumption is strongly limited, just as withradio components. Currently, temperature sensors,
light sensors, and vibration sensors run on relatively
little power, and they can be integrated into a wireless
tag.

17

Selected Papers

6. Future work
Masashi Shimizu

We are focusing development on an active RFID
that incorporates high functionality. Currently, we aredeveloping a system using commercial active RFID,
but we plan to construct a single-chip tag to achieve
low cost and long battery life. We also plan to develop a tag that enables position estimation with an errorof only a few centimeters using ultrasound and has abattery life of over five years.
7. Conclusion
There are various types of RFID and it is necessary
to select a type of tag that is best suited for a particular purpose. We have developed some applications
using active tags that have high functionality and thevalue of these functions may increase in the future.
These applications are introduced in the following
papers.
References[1]

J. Yamato and T. Asahi, “MIT Auto-ID Center Advances the Standardization of RFID Tags,” NTT Technical Review, Vol. 1, No. 5,
pp. 95-97, http://www.autoidcenter.org/[2] http://www.dust-inc.com/[3] http://www.newsfactor.com/perl/story/21957.html[4] http://www.alientedtechnology.com/[5] http://www.rfcode.com/[6] http://www.bluetooth.com/[7] http://www.zigbee.org/[8] http://nms.lcs.mit.edu/projects/cricket/[9] Nissanka B. Priyantha, A. Chakraborty, and H. Balakrishnan, “TheCricket Location-Support system,” Proc. 6th ACM MOBICOM,
Boston, MA, U.S.A., Aug. 2000.
[10] http://nesl.ee.ucla.edu/projects/ibadge/[11] S. Park, I. Locher, and M. Srivastava, “Design of a Wearable Sensor
Badge for Smart Kindergarten,” 6th International Symposium on
Wearable Computers (ISWC2002), Seattle, WA, U.S.A., Oct. 7-10,
2002.

18

Senior Research Engineer, Supervisor, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories.
He received the B.E. and M.E. degrees inmechanical engineering from Keio University,
Yokohama, in 1986 and 1988, respectively. In
1988, he joined NTT Wireless Systems Laboratories, Yokosuka, Japan. Since then, he has been
engaged in research on the pointing control for
deployable space antennas and surface error
compensation through feed distributions control.
His recent interest focuses on active RFID and its
applications. He is a member of the Institute ofElectronics, Information and Communication
Engineers (IEICE).

Mamoru Kobayashi
Senior Research Engineer, Wireless Systems
Innovation Laboratory, NTT Network Innovation Laboratories.
He received the B.E. and M.E. degrees in electronic engineering from Shizuoka University,
Shizuoka, in 1987 and 1989, respectively. In
1989, he joined NTT Wireless System Laboratories, Yokosuka, Japan. Since then, he has been
engaged in research on channel control for satellite communications systems. He recently joined
the research group on active RFID and its applications.

Masahiro Umehira
Director, Wireless Systems Innovation Laboratory, NTT Network Innovation Laboratories.
He received the B.E., M.E., and Ph.D. degrees
from Kyoto University, Kyoto in 1978, 1980,
and 2000, respectively. Since joining NTT in
1980, he has been engaged in R&D of modems
and TDMA equipment for satellite communications, TDMA satellite communication systems,
wireless ATM, and broadband wireless accesssystems for mobile multimedia services. He iscurrently responsible for R&D of next-generation broadband fixed/nomadic/mobile wirelesssystems, future satellite communication systems,
and ubiquitous services using wireless technologies. From 1987 to 1988, he was with the Communications Research Center, Department ofCommunications, Canada, as a visiting scientist.
He is a member of IEEE and IEICE. He received
the Young Engineer award and Achievement
award from IEICE in 1987 and 1999, respectively. He also received the Education, Culture,
Sports, Science and Technology Minister’saward in 2001.

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