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Infrared light does the work for you when
you change a television channel using a remote control. It wasn’t always that
way; an ungainly cable connected the first clickers to the television set.
Researchers at Pennsylvania State University are looking to make infrared wireless computer
networks better competition for cabled networks
by harnessing the light channeling abilities of holograms.
Infrared light is very fast. It can transmit data at several times the rate
of today's cable-bound networks, and far more than wireless radio networks.
Infrared’s main drawback, however, is that the light signals must have a
clear path to travel.
While radio frequencies can go through walls, infrared signals are limited to
line-of-sight contact. A person walking in front of a remote control, for
instance, will block the signal. Both radio and infrared waves are also prone
to data transmission delays and signal distortions.
The Penn State system addresses the line-of-sight and distortion problems by
passing the infrared signals through a hologram, which scatters them towards
the ceiling. "The [holographic element] at the transmitter splits a
single laser beam into many beams aimed at different directions in such a way
that a regular grid of small size light spots is created on the
ceiling," said Mohsen Kavehrad, a professor of electrical engineering at
Penn State.
The infrared signals then reflect back down to the receivers at different
angles. A 10-by-10 grid will allow the signals to cover an average-sized
square room, and more than one grid can be used to cover larger rooms,
Kavhrad said.
In contrast, existing infrared networks use a single, wide-pattern laser beam
that shines on the walls and ceilings. The light-signals reach the receiver
at different times after bouncing off several surfaces and traveling
different distances. This jumble of signals causes distortion.
The Penn State receiver is tuned to recognize each angled signal, but uses
just one at a time to receive data. "The transmitting pattern and the
receiving pattern are matched in such a way that the receiver receives
signals from only one or two light spots," said Kavehrad. This
eliminates the usual signal distortion at the receiver, he said.
The receiver hologram also acts like a curved mirror, concentrating the
signal. Unlike a regular mirror, however, the hologram channels only a narrow
range of light wavelengths, or colors. This filters out background light,
which can also distort signals, said Kavehrad.
Radio-based devices like IBM’s Bluetooth transmit data at less than 1 megabit
per second, and common ethernet cable transmits data at 100 megabits per
second. The infrared network's theoretical capacity is 2,000 megabits, which
translates to several hundred megabits per second in practice, Kavehrad said.
The system also does not use much power; it requires less than a watt of
power to operate, said Kavehrad.
This research is a nice advance, said Joseph M. Kahn, a professor in the
department of electrical engineering and computer sciences at the University
of California at Berkeley. "It’s an interesting application of
technology to generate those narrow beams," he said.
There is also an issue of where infrared fits in competitively with
radiowaves, he said. Although infrared’s high transmission rate opens up
possibilities, it is still a drawback that the signals cannot pass through
walls and so require an access point in each room, he said. "Typically,
people are looking to cover a building or a larger geographical area at the
lowest cost rather than trying to bump the highest data rate. So at the
current stage, people would prefer... radio solutions," he said.
If people wanted high data rates of 100 megabits per second in each room,
infrared would play a role, he said. "But the demand isn’t there
yet."
The system could be commerically available in about a year, said Kavehrad.
The researchers’ immediate goal is to install a system in their own lab.
Kavehrad’s colleague was Svetla Jivkova, a research associate at Penn State.
They published the paper in the proceedings of the 5th World Conference on
Systemics, Cybernetics and Informatics (ISAS/SCI 2001) held in Orlando,
Florida between July 22 - 25, 2001. The research was funded by the National
Science Foundation (NSF), Pittsburgh Digital Greenhouse and IBM’s Shared
University Resources programs (SUR).
Timeline: 1 year
Funding: Corporate; Government
TRN Categories: Wireless Communication
Story Type: News
Related Elements: Technical paper, "Some Recent Advances in
Indoor Broadband Infrared Wireless Communications," presented at the
ISAS/SCI-2001, Orlando, Florida, July 2001.
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