08-03-2011, 03:27 PM
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INTRODUCTION
Billions of visible LEDs are produced each year, and
the emergence of high brightness AlGaAs and AlInGaP devices
has given rise to many new markets. The surprising growth of
activity in, relatively old, LED technology has been spurred by
the introduction of AlInGaP devices. Recently developed
AlGaInN materials have led to the improvements in the
performance of bluish-green LEDs, which have luminous
efficacy peaks much higher than those for incandescent lamps.
This advancement has led to the production of large-area full-
color outdoors LED displays with diverse industrial
applications.
The novel idea of this article is to modulate light
waves from visible LEDs for communication purposes. This
concurrent use of visible LEDs for simultaneous signaling and
communication, called iLight, leads to many new and interesting
applications and is based on the idea of fast switching of LEDs
and the modulation visible-light waves for free-space
communications. The feasibility of such approach has been
examined and hardware has been implemented with
experimental results. The implementation of an optical page link has
been carried out using an LED traffic-signal head as a
LED Wireless
transmitter. The LED traffic light can be used for either audio
or data transmission.
Audio messages can be sent using the LED
transmitter, and the receiver located at a distance around 20 m
away can play back the messages with the speaker. Another
prototype that resembles a circular speed-limit sign with a 2-ft
diameter was built. The audio signal can be received in open air
over a distance of 59.3 m or 194.5 ft. For data transmission,
digital data can be sent using the same LED transmitter, and the
experiments were setup to send a speed limit or location ID
information.
The work reported in this article differs from the use
of infrared (IR) radiation as a medium for short-range wireless
communications. Currently, IR links and local-area networks
available. IR transceivers for use as IR data links are widely
available in the markets. Some systems are comprised of IR
transmitters that convey speech messages to small receivers
carried by persons with severe visual impairments. The Talking
Signs system is one such IR remote signage system developed at
the Smith-Kettlewell Rehabilitation Engineering Research
center. It can provide a repeating, directionally selective voice
message that originates at a sign. However, there has been very
little work on the use of visible light as a communication
medium.
LED Wireless
The availability of high brightness LEDs make the
visible-light medium even more feasible for communications.
All products with visible-LED components (like an LED traffic
signal head) can be turned into an information beacon. This
iLight technology has many characteristics that are different
from IR. The iLight transceivers make use of the direct line-of-
sight (LOS) property of visible light, which is ideal in
applications for providing directional guidance to persons with
visual impairments. On the other hand, IR has the property of
bouncing back and forth in a confined environment. Another
advantage of iLight is that the transmitter provides easy targets
for LOS reception by the receiver. This is because the LEDs,
being on at all times, are also indicators of the location of the
transmitter. A user searching for information has only to look
for lights from an iLight transmitter. Very often, the device is
concurrently used for illumination, display, or visual signage.
Hence, there is no need to implement an additional transmitter
for information broadcasting. Compared with an IR transmitter,
an iLight transmitter has to be concerned with even brightness.
There should be no apparent difference to a user on the visible
light that emits from an iLight device.
It has long been realized that visible light has the
potential to be modulated and used as a communication channel.
The application has to make use of the directional nature of the
communication medium because the receiver requires a LOS to
LED Wireless
the audio system or transmitter. The locations of the audio
signal broadcasting system and the receiver are relatively
stationary. Since the relative speed between the receiver and the
source are much less than the speed of light, the Doppler
frequency shift observed by the receiver can be safely neglected.
The transmitter can broadcast with viewing angle close to 180 .
This article aims to present an application of high-brightness
visible LEDs for establishing optical free-space links.
INTRODUCTION
Billions of visible LEDs are produced each year, and
the emergence of high brightness AlGaAs and AlInGaP devices
has given rise to many new markets. The surprising growth of
activity in, relatively old, LED technology has been spurred by
the introduction of AlInGaP devices. Recently developed
AlGaInN materials have led to the improvements in the
performance of bluish-green LEDs, which have luminous
efficacy peaks much higher than those for incandescent lamps.
This advancement has led to the production of large-area full-
color outdoors LED displays with diverse industrial
applications.
The novel idea of this article is to modulate light
waves from visible LEDs for communication purposes. This
concurrent use of visible LEDs for simultaneous signaling and
communication, called iLight, leads to many new and interesting
applications and is based on the idea of fast switching of LEDs
and the modulation visible-light waves for free-space
communications. The feasibility of such approach has been
examined and hardware has been implemented with
experimental results. The implementation of an optical page link has
been carried out using an LED traffic-signal head as a
LED Wireless
transmitter. The LED traffic light can be used for either audio
or data transmission.
Audio messages can be sent using the LED
transmitter, and the receiver located at a distance around 20 m
away can play back the messages with the speaker. Another
prototype that resembles a circular speed-limit sign with a 2-ft
diameter was built. The audio signal can be received in open air
over a distance of 59.3 m or 194.5 ft. For data transmission,
digital data can be sent using the same LED transmitter, and the
experiments were setup to send a speed limit or location ID
information.
The work reported in this article differs from the use
of infrared (IR) radiation as a medium for short-range wireless
communications. Currently, IR links and local-area networks
available. IR transceivers for use as IR data links are widely
available in the markets. Some systems are comprised of IR
transmitters that convey speech messages to small receivers
carried by persons with severe visual impairments. The Talking
Signs system is one such IR remote signage system developed at
the Smith-Kettlewell Rehabilitation Engineering Research
center. It can provide a repeating, directionally selective voice
message that originates at a sign. However, there has been very
little work on the use of visible light as a communication
medium.
LED Wireless
The availability of high brightness LEDs make the
visible-light medium even more feasible for communications.
All products with visible-LED components (like an LED traffic
signal head) can be turned into an information beacon. This
iLight technology has many characteristics that are different
from IR. The iLight transceivers make use of the direct line-of-
sight (LOS) property of visible light, which is ideal in
applications for providing directional guidance to persons with
visual impairments. On the other hand, IR has the property of
bouncing back and forth in a confined environment. Another
advantage of iLight is that the transmitter provides easy targets
for LOS reception by the receiver. This is because the LEDs,
being on at all times, are also indicators of the location of the
transmitter. A user searching for information has only to look
for lights from an iLight transmitter. Very often, the device is
concurrently used for illumination, display, or visual signage.
Hence, there is no need to implement an additional transmitter
for information broadcasting. Compared with an IR transmitter,
an iLight transmitter has to be concerned with even brightness.
There should be no apparent difference to a user on the visible
light that emits from an iLight device.
It has long been realized that visible light has the
potential to be modulated and used as a communication channel.
The application has to make use of the directional nature of the
communication medium because the receiver requires a LOS to
LED Wireless
the audio system or transmitter. The locations of the audio
signal broadcasting system and the receiver are relatively
stationary. Since the relative speed between the receiver and the
source are much less than the speed of light, the Doppler
frequency shift observed by the receiver can be safely neglected.
The transmitter can broadcast with viewing angle close to 180 .
This article aims to present an application of high-brightness
visible LEDs for establishing optical free-space links.
