Selected Papers

Infrared Signboard
Shuichi Yoshino† and Masashi Shimizu
Abstract
The infrared signboard system lets consumers receive digital information (such as URLs and emailaddresses) from a signboard at a distance. It uses infrared communication technology originally developed for remote control devices to achieve a reasonable communication range and low equipment cost.

1. Introduction
As the information society has advanced, there
have been discussions about objects that transmit
information directly without human control [1]. In
the real world, there are many objects that might want
to send messages to persons. We studied the model inwhich signboards communicate with persons as“object-to-person” communication.
These days, advertising signboards in trains or on
walls often include printed Web or e-mail addresses
for the company or product. However, consumers
must write them down or memorize them and later
input them into an Internet access terminal, which istroublesome and inconvenient. What is needed is ameans of easily acquiring such information fromsignboards in a directly usable form.
To solve this problem, some systems use mobilephones with built-in digital cameras, which are available now [2]. They can get information from advertisements directly by capturing a two-dimensional
barcode and processing the image or by acquiring
digital data from text in advertisements using image
recognition technology. These systems require theuser to move close to the signboard, so they are suitable for advertisement media that the user can takeaway (e.g., magazines and newspapers) and a systemthat needs authentication. They are not suitable forstreet signboards or advertisements in trains. The
communication range can be extended by using wire† NTT Network Innovation Laboratories
Yokosuka-shi, 239-0847 Japan
E-mail: yoshino.shuichi@lab.ntt.co.jp

Vol. 1 No. 9 Dec. 2003

less communication devices, such as Bluetooth or awireless LAN, but such equipment is expensive.
Inexpensive equipment is one of the important factors
in enabling a system to become popular because, inthe case of advertising, its effect depends on the number of consumers that can make good use of it. Therefore, the equipment cost should be as low as possible.
We studied wireless technologies to find a way to
expand the communication range using inexpensive
devices. In this paper, we describe our infrared signboard, which features a large communication range,
signal multiplexing, and inexpensive equipment as aresult of using infrared communication technologies
originally developed for remote control systems.
2. Proposed system
2.1 System configuration
The infrared signboard consists of the signboard
and its peripheral equipment (Fig. 1). The signboard
equipment can i) receive a request signal transmitted
from a user terminal to a signboard indicating that theuser wants to receive information from the signboardand ii) transmit the requested information. The user
terminal can transmit the request signal and receive
the desired information. If the user terminal is connected to a network (for example by wireless Internetaccess), the consumer can access an online web site
within moments of seeing the signboard.
2.2 Communication media
There are several choices for the wireless communication media to use between the signboard equipment and user terminals. To expand the communica37

Selected Papers

Signboard
Online site
Signboard equipment

NetworkqSend request signal
wReceive
information
signalWireless systembase station
User terminal

eAccess the online site associatedwith received information

Wireless device connected to a
network e.g. cellular phone or PDA

Fig. 1. System configuration.

tion range, we could use radio systems such as wireless LAN or Bluetooth [3], [4], but these would makethe system construction cost high. To keep the costlow, we might use wireless tags [5], but if the user
terminal is to receive information from the signboard
anytime, it must incorporate a receiver, which makes
the terminal expensive. Moreover, to avoid interference with nearby radio devices, the user terminal andthe signboard equipment should control the directivity of the radio waves and the carrier frequency.
To achieve a reasonable communication range at alow system cost, we chose a remote control system
based on infrared communication technology. The
communication direction is controlled optically.
There are several existing systems using infrared
such as IrDA (infrared data association) [6], infrared
wireless LAN, and remote control devices for consumer audio/visual equipment. In our intended appli-cation, the transmitted information is text strings(e.g., email addresses and Web addresses (URLs: uniform resource locators)), so the system does not needbroadband communication. The bandwidth ofinfrared wireless LAN and IrDA systems is more thanenough, but their power consumption is very large.
Therefore, we chose to use a remote control infraredcommunication system that offers devices at low costwith low power consumption. Table 1 compares various communication media.
One problem with infrared remote control systems
is their low data transmission rate: only a few hundred
bits per second because they are designed to transmit
very little data. We want to transmit no less than 256
characters in 1 s to give our system good usability, so
we need to raise the bit rate to several thousand bits
per second. We achieved high-speed communicationin our system by redesigning the transmitted codes

Table 1. Comparison of communication media.
MediaCommunication
range

Speed

Wireless LANRadio

Several hundredmeters

Up to 11 Mbit/s(IEEE802.11b)

Depends on antenna
Several hundred dollars
Several hours
characteristics

BluetoothRadio

Up to 10 m
(Class 1)

Up to 1 Mbit/s

A few days

Depends on antenna
Several hundred dollars
characteristics

A few tens ofmeters

Several hundred bit/s A few years

Depends on antenna
Several hundred dollars
characteristics

SystemWireless active tag Radio

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Battery life

IrDA

Infrared 1 m

Up to 4 Mbit/s

Remote control

Infrared Several meters

Several hundred bit/s A few years

Directivity

A few months Optically tunable
Optically tunable

System cost using
commercial equipment

Under 100 dollars
Under 50 dollars

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Selected Papers

and enhancing the modulation speed.
There are two choices for the communication
scheme between the signboard equipment and user
terminals: one-way communication in which thesignboard broadcasts information periodically or
two-way communication in which it transmits information upon receiving a request signal from a user
terminal. Since signboards will not always be set up
in places where electrical sockets are available, wemust consider the maintenance of batteries to keep
the proposed system running. Thus, the power consumption of the signboard equipment is an importantissue. The two-way communication scheme uses lesspower.

CDMA (code division multiple access). These
schemes can achieve effective multiplexing but theequipment tends to be expensive. The infrared communication scheme for remote control devices doesnot use any access control scheme to keep the costlow. In our system, we use a simple multiple access
scheme that divides the communication space bycontrolling the directivity of the infrared beam, as
shown in Figs. 2 and 3. The signboard equipment is
Signboard equipment

Infrareddevice2.3 Multiplexing scheme
A signboard is usually set up in plain view so as
many people as possible can see it. Consequently, thesignboard equipment must transmit its information to
many people simultaneously. Therefore, we gave oursystem a multiplexing function. There are several
kinds of multiple access schemes among radio systems for multiplexing user terminals at the base station, such as FDMA (frequency division multipleaccess), TDMA (time division multiple access), andCommunication
space

User terminals

Fig. 2. Multiplexing scheme.

Signboardequipment 1

Signboardequipment 2User terminal B

User terminal A

Userterminal A

Userterminal B

Signboardequipment 1

Signboardequipment 2

Request signal (ID-B)
Discard information
because the ID
does not match.

Request signal (ID-A)
Information (ID-B, Data-2)
Information (ID-A, Data-1)

Fig. 3. Communication concept.

Vol. 1 No. 9 Dec. 2003

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Selected Papers

equipped with infrared devices that have limited
directivity. The communication space in front of thesignboards is covered by mounting these devices in asemicircle. If they were mounted in a hemispheroid,
they could cover not only the horizontal space but
also the vertical space. The proposed scheme provides two-way communication by equalizing thedirectivity of the transmitting and receiving devices.
The user terminal’s address is included in the request
signal and the information signal to avoid interference with other devices in the neighborhood. A given
user terminal receives only information signals containing its own address.

tion of the receiver at the signboard equipment.
3.2 User terminals
Two examples of user terminal configurations areshown in Fig. 5. We developed small external devices(user terminals) that can connect to two popular typesof mobile communication devices having built-ininterfaces: a PDA (personal digital assistant) and acellular phone (PDC: personal digital cellular). Bothdevices were designed as external devices because
they are prototype models. However, they have fewparts, so if our system becomes popular, the user terminal hardware could be incorporated into future ver-3. Development
130 mm

3.1 Signboard equipment
The signboard equipment we developed is shownin Fig. 4. It has 11 pairs of infrared devices, set up 15
degrees apart. Each pair consists of an infrared transmitter and receiver that cover the same communication space. The transmitter is located directly below
the receiver. The signboard equipment stores letter
strings associated with the signboard and supports
both one-way and two-way communication. In thecase of two-way communication, after a request signal from the user terminal has been received, thetransmitter located directly below the receiver sends
the information signal together with the terminal’s
address to the user terminal. Also, when the signboard equipment selects one-way communication, it
can transmit information with a broadcast address at
certain intervals. The uplink and downlink communication speeds are different in the two-way communication mode. The request signal (uplink) uses very little data because it consists only of the terminal
address, so we chose a slow modulation speed
scheme for the uplink to reduce the power consump-Receivers

51 mm

TransmittersFig. 4. Signboard equipment.

External interface
External interface

Cellular phone
PDA

User terminal

User terminal
PDA (personal digital assistant)

Cellular phone

Fig. 5. Examples of user terminals.

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Selected Papers

sions of such mobile devices.
The user terminal has a laser pointer to indicate thedirection in which the infrared radiation is being
emitted. If users see the light of another laser pointeron the signboard, they recognize that someone else
nearby is also receiving information, so the laserpointer provides an anti-collision function in the proposed system. The user terminal stores a specificaddress associated with the connected device andsends this address when it transmits a request signal.
When the user terminal receives information from thesignboard, it checks the address in the received information. If the address matches the user terminal’saddress, it forwards the received information to theconnected network device (wireless PDA or cellularphone) via the external interface. Therefore, the user
can get useful information without having to manually input it. Also the user terminal supports both communication schemes provided by the signboardequipment. We experimentally confirmed that thecommunication distance was up to 10 m.

References
[1]

[2]
[3]

[4]
[5]
[6]

M. Shimizu, M. Kobayashi, and M. Umehira “Overview of Wireless
Technologies for Ubiquitous Services,” NTT Technical Review, Vol.
1, No. 9, pp. 12-18, 2003.
http://www.nttdocomo.co.jp/IEEE. LAN/MAN standards of the IEEE computer society. Wireless
LAN medium access control (MAC) and physical layer (PHY) specification. IEEE Standard 802.11, 1997.
http://www.bluetooth.com/
Klaus Finkenzeller, “RFID handbook,” John Wiley & Sons, Ltd.
http://www.irda.org/

4. Conclusion
Shuichi Yoshino

Our infrared signboard system lets a consumer get
useful information easily from a signboard. We
developed the signboard equipment and the user terminal. To ensure inexpensive devices and a reasonable communication range between the signboard
and consumer we used infrared as a wireless medium
and the infrared communication technology designed
for remote control devices as the communication
scheme. We developed a multiplexing communication system by mounting several infrared devices.
The user terminal we developed can forward received
information to another device directly because it has
an external interface to connect to network devices
such as wireless PDAs or cellular phones. We experimentally confirmed that the communication distanceis up to 10 m. This system lets consumers connect toan online site associated with a signboard without
inputting text strings and without getting close to thesignboard.

Vol. 1 No. 9 Dec. 2003

Senior Research Engineer, Wireless Systems
Innovation Laboratory, NTT Network Innovation Laboratories.
He received the B.E. and M.E. degrees inmechanical engineering from Kanazawa University, Ishikawa, in 1990 and 1992, respectively.
He joined NTT Laboratories in 1992 and worked
on satellite Internet system development. He iscurrently engaged in R&D on wireless networking technology for ubiquitous services.

Masashi Shimizu
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.

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