IP: Ultrawideband Squeezes In

[Dave Farber <dave () farber net>]

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From: Dewayne Hendricks <dewayne () warpspeed com>

Ultrawideband Squeezes In

By Erika Jonietz    September 2002
<<http://www.technologyreview.com/articles/jonietz0902.asp>http://www.techno
logyreview.com/articles/jonietz0902.asp>

A newly approved radio technology promises wireless home electronics
and positioning systems accurate to the centimeter. But opponents say
it could also mean dead cell phones, thwarted satellite
reception-even plane wrecks.

Robert Fontana disappears into a hallway. Seconds later, a small
reddish blob of pixels appears and moves around a field of blue and
green on a computer monitor hooked up to a shoebox-sized device. The
splotch tracks Fontana's position in the building, even through the
two walls between him and the technology he's showing off: a tracking
and collision avoidance system that can "see" through barriers like
walls (or trees) and measure a target's position, bearing and speed.
Fontana, president of Germantown, MD-based Multispectral Solutions,
says what's inside his shoebox can one day help keep helicopters,
cars and other vehicles from ramming into obstacles like power lines
or people.
Behind the device is a radio technology called ultrawideband that for
decades was the province of military labs. But in the last few years,
startups, information technology companies and consumer electronics
giants have begun pushing ultrawideband beyond the radarlike systems
the military pioneered and into applications that could transform the
home. Sony and newcomer XtremeSpectrum in Vienna, VA, for instance,
are both pursuing the possibility of using ultrawideband transmission
to wirelessly link DVD players, stereos and TVs in home entertainment
systems. In the future, ultrawideband links could distribute
extremely information-rich content, endowing a home or office with
high-resolution 3-D virtual-reality simulation. Ultrawideband can
also zap data between computing devices up to 10 times faster than
today's rat's nests of wired links.

Other potential applications include tracking objects and people to
centimeter accuracy (even through walls) and ultrasensitive detectors
for everything from home security systems to virtual pet enclosures.
Ultrawideband tags could let robotic lawn mowers or vacuum cleaners
go about their tasks without ever hitting a tree or a sofa. "We've
got the most feasible technology for the George Jetson-like homes of
the future," says Bruce Watkins, president of Pulse-Link, an
ultrawideband startup in San Diego.

Ultrawideband, proponents say, will deliver all of this via cheap,
low-power radios. And, they contend-albeit over vigorous disagreement
from skeptics-it won't suffer from the interference problems that
plague many existing wireless devices. "It's a tremendous new
technology," says Geoffrey Anderson, vice president of Sony
Electronics' Advanced Wireless Technology Group. "Ultrawideband could
really be a huge benefit to the consumer market."

But the same qualities that enable such an array of applications also
make ultrawideband divisive. In February, the Federal Communications
Commission gave limited approval to the technology, opening the door
to its commercialization, if only a crack. The FCC process generated
almost 1,000 public comments-many more than most proposals elicit.
And while much of the feedback was supportive, cell phone makers and
service providers, Global Positioning System companies, satellite
radio firms, airlines, and a slew of civilian and military government
agencies all objected to the FCC's plans to approve ultrawideband.
Their beef: ultrawideband transmissions would interfere with the
radio frequencies they rely on. These groups cited consequences
ranging from the inconvenience of dropped cell phone calls to the
frightening scenarios of foiled guidance systems preventing planes
from landing in poor weather and wayward bombs that hit civilians.
"The price of that interference is going to be very severe if a bomb
is misdropped," says Badri Younes, assistant secretary of defense and
director of the U.S. Defense Department's office of spectrum
management.

For now, with few systems around for testing, discussions of
ultrawideband's promise and peril are largely theoretical. Although
the FCC and other agencies have done some testing of the technology,
the trials have mostly been conducted using lab devices-whose
ultrawideband signals may be stronger, or weaker, or otherwise very
different from those that will be produced by real-world devices.

With the new regulatory backing, companies will finally bring the
technology to market over the next few years, and the practical
answers needed to resolve the technical and political uncertainties
about ultrawideband's potential should emerge. Then we'll see whether
ultrawideband will transform the wireless world-or bring it crashing
down.

Pulses of Power

Ultrawideband was born in the military labs of the 1960s. Looking for
a way to let radar "see" through trees, researchers came up with the
idea of using extremely short pulses of radio energy. Fundamental
physics dictates that ultrashort pulses occupy a wide swath of the
radio frequency spectrum; at least some of these frequencies, the
theory went, were sure to penetrate leaves and branches.

Familiar wireless devices ranging from FM radios to cell phones to
wireless computer networks using the increasingly common 802.11b
standard all transmit continuous signals on narrow frequencies within
the radio spectrum. Digital cell phones on the Sprint PCS network,
for example, operate at around 1.9 gigahertz; 802.11b networks (and
newer cordless phones) operate at 2.4 gigahertz. These transmissions
occupy a thin slice of the spectrum and so generally do not interfere
with other systems that depend on radio wave transmissions.

Ultrawideband radios, however, work in a fundamentally different way,
emitting extremely short bursts of radio waves-just billionths or
trillionths of a second long. Each pulse covers up to several
gigahertz of radio spectrum. Information is transmitted by modulating
the timing, amplitude, polarity or some other aspect of the pulses.
An object's location can be inferred by methods like those used in
traditional radar systems, such as "listening" for the echo of a
directional signal and timing how long it takes to return, or
triangulating on a target with multiple transceivers. The extremely
short pulses used in ultrawideband make the position information
highly accurate, down to the centimeter scale-unlike GPS, which is
typically accurate only to tens of meters.

Sending information in pulses makes the radios much simpler, and
therefore cheaper, to build than typical transmitters. That's because
conventional narrowband radios require, among other design
complexities, multiple analog components to tune the frequencies they
emit. An ultrawideband transmitter, however, works like a tuning
fork. Striking a tuning fork causes it to vibrate, sending out sound
waves at a particular frequency. A semiconductor chip in an
ultrawideband radio "hits" an antenna with carefully timed electrical
pulses; the antenna responds by generating radio waves at every
frequency possible. "Ultrawideband systems are just brain-dead
simpler to build," says Carl Howe, an analyst at Forrester Research
in Cambridge, MA.

Simpler circuit designs and the pulsed nature of the transmissions
also allow ultrawideband radios to transmit at much lower power than
other wireless technologies. This gives ultrawideband an edge when it
comes to battery-powered devices, since other high-bandwidth
technologies require multiple power-consuming components (see "How
Ultrawideband Stacks Up"). And the wide swath of frequencies that
ultrawideband transmissions occupy helps them travel through walls;
even if one frequency is distorted or doesn't make it through, others
still carry the signal.

Ultrawideband Comes Through

An ultrawideband box could transmit different cable channels to TVs
throughout a home. Although walls block some of the frequencies used,
enough penetrate to reconstruct the signal.

Another advantage of ultrawideband is its relative immunity to
so-called multipath interference. When radio waves encounter
obstacles, they bounce off them; echoes that arrive at the receiver
out of phase with the original signal can cancel it out. A
cordless-phone user walking away from the phone's base station in his
or her home experiences this phenomenon as the fading of the caller's
voice. But with ultrawideband's extremely short pulses, the original
signal reaches the receiver in its entirety before the first echo
arrives. Today's microchips are sophisticated enough to tell the
difference between the two-or even to add them together to make the
signal stronger. So ultrawideband can operate well in echo-prone
places where conventional wireless systems suffer, such as living
rooms or crowded cities.

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