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Beaming
Data Holds Promise, With Limits, for Networking
New York Times;
New York, N.Y.; Aug 23, 2001; David F. Gallagher;
Abstract:
Dr.
[Mohsen Kavehrad] and a colleague, Dr. Svetla Jivkova, have been researching a
system that sends pencil-thin infrared beams bouncing around a room, connecting
computers to one another and to a central transmitter and receiver that is
wired to a larger network. The researchers said the technology could transmit
two gigabits a second, or about a thousand times as much data as a cable modem,
with few transmission errors.
One way around the problem is to bounce wide infrared beams off the
ceiling, scattering the reflections around the room. This allows receivers to
be pointed in any direction. While some networking products already use this
approach, Dr. Kavehrad said the scattered beams created something similar to an
echo, causing data loss and limiting the network's speed.
Dr. [Joseph M. Kahn], who did research on infrared networking for much
of the last decade, said he had based some of his work on research by Dr.
Kavehrad. In a report, he and his colleagues demonstrated about a year ago that
an infrared network could handle a separate video stream for every passenger on
a jetliner. But he said he had moved on to other things.
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Copyright New York Times Company Aug 23, 2001 |
RESEARCHERS of infrared
networking would like to bounce data off your nose. Or your desk. Or the coffee
machine.
Their goal is
to use beams of infrared light, reflecting from all surfaces in a room, to
create high-speed information networks. While local networks using radio waves,
like Apple's AirPort system, have been getting the attention, scientists
working on infrared say that in the long run, light might be a better and
faster alternative.
''Radio cannot
compete with this performance,'' said Dr. Mohsen Kavehrad, a professor of
electrical engineering at Pennsylvania State University.
Dr. Kavehrad
and a colleague, Dr. Svetla Jivkova, have been researching a system that sends
pencil-thin infrared beams bouncing around a room, connecting computers to one
another and to a central transmitter and receiver that is wired to a larger
network. The researchers said the technology could transmit two gigabits a
second, or about a thousand times as much data as a cable modem, with few
transmission errors.
Anyone who has
used a remote control to change the channel has seen infrared in action. The
technology is also used in laptop computers and Palm-type devices for wireless
communication over short distances. But these links work best when the
transmitter is pointed at the receiver, something that would not be practical
when linking an entire office or offering network access in a public place like
an airport or a restaurant.
One way around
the problem is to bounce wide infrared beams off the ceiling, scattering the
reflections around the room. This allows receivers to be pointed in any
direction. While some networking products already use this approach, Dr.
Kavehrad said the scattered beams created something similar to an echo, causing
data loss and limiting the network's speed.
The Penn State
researchers think they have solved the echo problem by using a holographic
filter to produce thin beams that create a large grid as they reflect around
the room. The university is seeking a patent on the technology.
''It's a really
cheap and easy way of producing these multiple beams,'' he said. ''Having the
pencil beams allows you to send the signals very fast, and not relying on just
one of them allows you to move around, and you can do this whole thing at low
power levels.''
Researchers at the
University of Kassel and at the University of Siegen, both in Germany, have
approached the problem differently, focusing on improving the receiver's
ability to separate signals from echoes and interference. The researchers say
the resulting network would be fast enough to allow everyone in a meeting to
receive and transmit video streams on their laptops simultaneously for
videoconferencing.
Providing
enough bandwidth for activities like videoconferencing is one area where
infrared has an advantage; the radio spectrum is tightly regulated so only
certain frequencies can be used for data transmission. Manufacturers can push
into higher frequencies in search of free space, but at the same time, the
components needed become more expensive.
Infrared has no
such problems, because its frequencies, which are just below visible light on
the electromagnetic spectrum, are unregulated. And because infrared
transmissions do not penetrate walls, there is no chance of interference or
overlap in neighboring rooms. That also can be a security advantage;
radio-frequency networks open the possibility of eavesdropping, perhaps by
someone sitting in the parking lot with a laptop and an antenna.
But infrared's
inability to pass through walls and other objects may also be its downfall. The
technology requires at least one receiver and transmitter in each room to be
connected to a wired network. This makes it an unlikely choice for, say,
someone wanting to stay online wirelessly while moving a laptop among different
rooms. And forget about going online from the backyard via infrared -- the
beams need surfaces, particularly ceilings, to bounce from.
Joseph M. Kahn,
a professor of electrical engineering and computer sciences at the University
of California at Berkeley, said the first users of new networking equipment
have been companies and schools, and ''they don't want to put an access point
in each room.''
Dr. Kahn, who
did research on infrared networking for much of the last decade, said he had
based some of his work on research by Dr. Kavehrad. In a report, he and his
colleagues demonstrated about a year ago that an infrared network could handle
a separate video stream for every passenger on a jetliner. But he said he had
moved on to other things.
''It has some
technical advantages,'' he said, ''but it just hasn't taken off commercially,
and I see no signs that that's going to change, unfortunately.''
In addition, he
said, companies are investing more money in radio research, limiting
advancements in infrared.
Meanwhile,
radio-based networking is entering the mainstream. Much of the focus is on a
standard known as 802.11b or Wi-Fi, the technology used in Apple's AirPort and
other low-cost networking products. Starbucks is putting Wi-Fi into its stores,
allowing customers to surf while sipping.
One thing that
might give a lift to infrared would be research demonstrating that the radio
energy used in mobile phones and other devices is actually hazardous to human
health, Dr. Kahn said.
Studies so far
have been inconclusive, and there is only a slim chance that something more
definitive will appear, he said. At the low level of energy needed for
networking, researchers say, infrared beams cannot hurt the eyes or anything
else.
Dr. Kavehrad
said that he was concerned about the long-term effects of bathing people in
radio waves and that infrared light offered a safer alternative.
''We've lived
under God-given sunlight for zillions of years,'' he said.
[Illustration]
Photo
(Mary Ann Smith)
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Reproduced with permission of the copyright owner.
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