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.
EDITORS: Dr. Kavehrad is at 814-865–7179 or mkavehrad@psu.edu by
email.
