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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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