State Intercom: November 1, 2001
Reliable, wireless, infrared
area networks demonstrated
engineers have shown that broadband, wireless, indoor, local area
communication networks that rely on non-line-of-sight infrared signal
transmission can offer low error rates as well as safe, low -- below one watt
-- power levels.
Kavehrad, professor of electrical engineering and holder of the W. L. Weiss
(AMERITECH) chair, said, "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.
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
Kavehrad and his colleagues at the 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. Svetla Jikova, research associate, collaborated with Kavehrad on
writing a paper on their work.
said, "This error rate is unmatched considering the offered transmission
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 na rrow beams, which strike the ceiling
and walls at points that form an invisible grid throughout the entire volume
of the room. Because the beams also are reflected at each of the strike
points, they can be used to send or receive information.
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
ensure continued coverage when some of the transmitter beams are blocked.
noted, "Others have attempted to develop local area networks with radio
frequencies. However, indoors, radio frequencies can pose a radiation hazard.
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."
University 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.
system is being patented by the University.
Barbara Hale can be reached at email@example.com.