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.
Power
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"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.
This story has been adapted from a news release issued by
Penn State.
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