LED Wireless

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 fullcolor
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 link has
been carried out using an LED traffic-signal head as atransmitter. 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.