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Low Power,
Highly Reliable, Wireless, Infrared Local Area Networks Demonstrated
University Park, Pa. --- Penn State engineers have shown
that broadband, wireless, indoor, local area communication networks that rely
on non-line-of-sight infrared (IR) signal transmission can offer low error
rates as well as safe, low – below one Watt – power levels. Dr. Mohsen
Kavehrad, professor of electrical engineering and holder of the W. L. Weiss
(AMERITECH) chair, says, "Line-of-sight or point-to-point infrared
signal transmission, which is used, for example, in television remote
controls, is highly efficient at low power levels but suffers from the need
for alignment between the transmitter and receiver. If someone ‘shadows' or
blocks the remote control beam while you're trying to change the channel, the
signal can't get through.
"On the other hand,
non-line-of-sight transmission, which uses a broad diffuse beam, suffers less
from shadowing but usually forfeits the power efficiency, broadband and low
error rate values that infrared transmission can offer." Now, however,
Kavehrad and his colleagues at Penn State's Center for Information and
Communications Technology Research have developed a new link design that uses
a multi-beam transmitter with a narrow field of view receiver. The system has
a bit-error rate of only one error per billion bits and uses milliwatt
transmitted power levels. Kavehrad says, "This error rate is unmatched
considering the offered transmission capacity." The Penn State
researcher detailed the system Sunday, July 22, at the Fifth World
Multi-Conference on Systemics, Cybernetics and Informatics SCI 2001 meeting
in Orlando, Florida. His paper, "Some Recent Advances in Indoor
Broadband Infrared Wireless Communications," is co-authored by Dr.
Svetla Jivkova, research associate. To use the Penn State signaling scheme,
for example, to form a local area network for a group of computers in a room,
each machine is equipped with a low power infrared source and a holographic
beam splitter. The original low power beam is separated into several narrow
beams, which strike the ceiling and walls at points that form an invisible
grid throughout the entire volume of the room. Because the beams are also
reflected at each of the strike points, they can be used to send or receive
information. Since the beams created by the splitter are narrow, narrow
field-of-view receivers are used. Using a narrow field of view receiver makes
it easier to filter out noise. In addition, receivers consisting of more than
one element can insure continued coverage when some of the transmitter beams
are blocked. Kavehrad notes, "Others have attempted to develop local
area networks with radio frequencies. However, indoors, radio frequencies can
pose a radiation hazard."
"Infrared signals, on the
other hand, pose no such hazard, especially at the low powers used by our
system. However, since the sun is an infrared emitter, as well as fluorescent
and incandescent bulbs, light coming in through windows or from artificial
lighting can add background noise to the system. This noise, to some extent,
can be filtered at the receivers." The Penn State team developed a
framework for computer simulation under which properties of room, transmitter
and receiver are quantified. Using the simulation results, they showed that
the system has a bit-error rate of only one error per billion bits in 99
percent of the coverage area at bit rates up to a few hundred megabits per
second. In addition, the system uses transmitted power levels well below one
Watt.
The wireless infrared communication
system is being patented by the University. The research was supported by
grants from the National Science Foundation and the Pennsylvania technology
development program known as the Pittsburgh Digital Greenhouse.
Note: This story has been adapted from a news release
issued by Penn State for journalists and other members of the public. If you
wish to quote from any part of this story, please credit Penn State as the
original source. You may also wish to include the following link in any citation:
http://www.sciencedaily.com/releases/2001/07/010725081349.htm
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