- Scientists at Bell Labs have developed
a technology called BLAST (Bell Labs Layered Space-Time) that may boost
the carrying capacity of fixed wireless links 10- to 20-fold.
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- In wireless communications systems, radio
waves don't travel directly from the transmitting antenna to the receiving
antenna. Instead, the waves stream out, bounce off objects in the environment,
scatter wildly, take a variety of paths and arrive at the receiving antenna
at slightly different times.
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- Signals arriving at different times can
produce multiple images -- the familiar TV screen "ghosts" and
cross-over "bleed" on the radio. These superimposed and jumbled
signals degrade wireless transmissions.
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- The Bell solution to the problem is to
exploit it. BLAST does that by treating each scattered signal path within
a single transmission frequency as a separate subchannel, each carrying
its own distinct datastream.
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- With BLAST, 10 to 20 transmitting antennas
are placed an inch or so from one another. Each antenna transmits its own
unique signal; adjacent antennas could be transmitting music, tax data
and Star Trek reruns. The separated transmission points mean each signal
gets sent out along a unique trajectory.
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- On the receiving end, 10 to 20 tuned
antennas arrayed inches from one another distinguish the mutually interfering
transmissions. Then innovative signal processing algorithms clarify the
signals, so, for instance, we don't get Spock singing Elvis.
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- Thus, by using many transmitting antennas,
and an equal number of receivers, the bandwidth within a single frequency
can be increased dramatically.
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- "The breakthrough proves the feasibility
of a technology which leapfrogs what we assumed about the limitations of
radio communications," says Jim Brewington, president of Lucent's
Wireless Networks Group.
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- BLAST doesn't work well yet for mobile
applications such as cellular phones because the products are too small
for the required antenna arrays.
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- Initially skeptical of the claims, Geoff
Kuenning, assistant professor of electrical engineering at UCLA, revised
his opinion to conclude, "I would expect BLAST to have applications
in telephony, cable television, point-to- point computer networking and
possibly in communications satellites. In the longer term, I would not
be surprised if some of the restrictions on mobile applications were resolved."
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