---------- Forwarded message ---------- Date: Sun, 14 Dec 2003 13:17:01 -0500 From: Dave Farber <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Subject: [IP] Beyond Wi-Fi: A New Wireless Age
Delivered-To: [EMAIL PROTECTED] Date: Fri, 12 Dec 2003 20:16:37 -0800 From: Dewayne Hendricks <[EMAIL PROTECTED]>
DECEMBER 15, 2003
SCIENCE & TECHNOLOGY
Beyond Wi-Fi: A New Wireless Age
Three technologies will boost the capacity of our airwaves -- and innovation, too <http://www.businessweek.com/magazine/content/03_50/b3862098.htm>
On the clear morning of June 10, Mark McHenry climbed onto the rooftop of a
seven-floor office building near Washington's busy Dupont Circle. Lugging
an unwieldy 10-foot antenna and a gray metal box, he and another engineer
set up an experiment to measure the actual usage of airwaves above the
Nation's Capital during peak business hours.
They were out to debunk a popular myth: With the explosion of wireless
devices, the air is nearly saturated with zinging TV, radio, cell-phone,
and BlackBerry signals, right? Not to mention satellite and
air-traffic-control signals, police dispatches, and mushrooming Wi-Fi
networks. And yet, the duo found that even in a heavily trafficked part of
the airwaves above the District of Columbia, only 19% to 40% of the
spectrum was occupied at any moment during an eight-hour period.
The experiment highlights a paradox that vexes the wireless industry.
Although nearly all of America's best ready-to-use spectrum is rented out
to tenants ranging from broadcasters to the U.S. military, most of the
time, it's unused -- just vacant space. ``It's as though every operator had
his own personal road to go to work instead of sharing the road,'' says
McHenry, president of tech startup Shared Spectrum Co. in McLean, Va. The
upshot: Wireless inventors with a new idea may not get access to the airwaves.
As any of these inventors might tell you, however, momentous changes are in
the air. Digital technologies have already allowed cellular operators to
pack more signals into each band than they could under the old analog
regime. Now, a wave of intelligent network technologies is sweeping from
university and military labs into the marketplace. The innovations are
known by various names, including smart antennas, mesh networks, and agile
radios -- all of them sharing the same basic breakthroughs in digital
signal processing. Together, they appear poised to knock down the lane
dividers on the spectrum highway, which were devised about 75 years ago
when federal regulators concluded that the airwaves were a scarce resource.
Regulators are applauding the liberation of the spectrum -- especially
after witnessing the meteoric rise of Wi-Fi. This wireless networking
standard, and the ubiquitous Internet ``hot spots'' it has spawned, took
off in the U.S. only because there was a swath of airwaves that regulators
left open for unlicensed gadgets such as microwave ovens and garage-door
openers. That's why the FCC is dismantling more fences. In mid-November, it
offered up a new slice of lightly regulated frequency in the 5-gigahertz
range. ``The more people who can play in the sandbox, the higher the
probability of technological innovation,'' says Federal Communications
Commission Chief Engineer Edmond Thomas.
DUG-IN RESISTANCE
Broadcasters, cell-phone carriers, and other longtime licensees of spectrum
rights won't give up their exclusive hold without a fight. ``If we have to
pay for spectrum and others can gain access to those very bands for free,
it becomes a parity issue,'' says Brian F. Fontes, vice-president for
federal relations at Cingular Wireless. Still, engineers, inventors, and
their financial backers are sure to keep up pressure on the FCC to use the
airwaves with greater efficiency and imagination. Together, new ideas about
intelligent devices and novel network architectures will open up a wireless
frontier. Here's what the engineers have in mind:
Smart Antennas: When the first AM radio tower went up in 1920 at KDKA in
Pittsburgh, the proud antenna on top beamed out signals 360 degrees around
it. Like a pebble thrown into a pond, it sent energy indiscriminately in
concentric ripples through the air.
What a waste, say many engineers today. If you could throw all that energy
in just the direction of the users you want to reach, the signal could
travel much farther and avoid unnecessarily jamming airwaves in other
directions. With a ``smart antenna,'' a narrow beam shoots a greater
distance in the same way that a water hose sprays farther when the gardener
puts a thumb over the nozzle. But that doesn't capture the intelligence of
these systems. Wireless consultant Nitin Shah prefers the analogy of a
spotlight following individual actors on a stage, as opposed to a room
light that illuminates everyone.
There are many approaches to such antennas under study at universities and
corporate labs -- including a commercial product from San Francisco startup
Vivato Inc. By clustering 128 pencil-size antennas, Vivato can project
signals as far as 2.5 miles. They achieve this by squishing a tiny bit of
energy -- roughly 100 milliwatts, or half the power of a cell phone -- into
narrow seven-to-eight-degree beams. Each antenna, starting at a different
moment, sends out its own signals on regular radio waves. When the waves of
one start waning, those of another might be cresting. Taken together, these
waves can form rays specially shaped to reach a particular target. With the
help of software, the antennas can change the shape and direction of these
rays at a moment's notice when targets move. In this way, Vivato expects to
extend the range of Wi-Fi, currently limited to about 300 feet. ``Smart
antennas are the future of spectrum sharing for wireless,'' says Greg
Raleigh, CEO of Airgo Networks Inc. in Palo Alto, Calif., which makes a
more complex extension of this technology. ``Ten years from now, they'll be
in every wireless device.''
Mesh Networks: Just as smart antennas free up more airwaves than
traditional towers, a new routing technology makes even today's most
efficient digital networks look like spectrum hogs. With cell-phone systems
today, for example, users must be within the range of a cell tower, also
known as a base station, to get a link. The cell tower is the central hub
connecting the phones around it.
With so-called mesh networks, one transmitter can get a connection from the
antenna next to it, even if neither is in the range of the hub. All that's
required is a connection between users, circuitous or not, that leads to a
hub -- which may be an Internet access point or a cell tower. To explain
this idea, engineers often invoke the analogy of a crowded cocktail party.
Instead of shouting across the room to tell your spouse it's time to go
home, thus drowning everyone else out, the guests transmit the message
person by person in whispers across the room.
In the case of mesh networks, each device -- whether it's a laptop
computer, as in most prototypes today, or a futuristic cell phone --
becomes the equivalent of a base station or network hub. As soon as one of
the devices is switched on, it puts out a signal announcing its presence
and searches for signals from others. Once the newcomer finds a group of
networked devices, it knocks on the door, and the others welcome it to the
group. True, wired Internet switches achieve the same effect. But the
challenges multiply in the wireless world, where changing topography is
ever a threat. If a building goes up across your street, a mesh network
would spot the obstruction and route itself around it.
Various companies have experimented with ad hoc networks like these -- so
far, without much commercial success. For one thing, the demands of a mesh
network can drain everyone's batteries. Even if your laptop doesn't want to
communicate across the network at the moment, it ends up being used as a
hopping station for other people's messages. Despite that, Nokia (NOK ),
Microsoft (MSFT ), Intel (INTC ), and others hope to use the technology to
extend the range of Wi-Fi. And it's not just commercial ventures that are
interested. In San Mateo, Calif., the Police Dept. is testing a system from
a local startup, Tropos Networks, to connect laptops in police cars across
the downtown area.
Agile Radios: On the blue waters of San Diego Bay, engineers have
implemented the first phase of an experiment that could lead to the biggest
radio breakthrough of all. Twelve sailors on the USS Coronado, a Navy
flagship, are testing a radio from General Dynamics Corp. (GD ) that can
communicate in 10 different frequency bands. That matters because the
military has access to many swaths of spectrum, but different branches of
the Armed Forces use different radios, which often can't talk to one
another. The gizmo on the Coronado uses software to transmit and receive in
multiple frequences, thus breaking down the barriers. ``Think of these
radios as a computer with an antenna,'' says John D. Bard, CEO of Space
Coast Communication Systems Inc. in Melbourne, Fla., which is writing new
radio software.
AN ULTRASMART MACHINE
The military's work in software-defined radio is the prelude to what many
consider the ultimate solution for the wireless future: the agile radio.
This device can hop in and out of empty spaces in the spectrum, operating
in a variety of different bands, in spaces nobody else is using. The
Defense Advanced Research Projects Agency (DARPA) is funding the
development of this ultrasmart machine, which would be able to scan the
airwaves and determine the vacant spaces on its own. As other users pile
into these frequencies, the agile radio would see the traffic and instantly
seek out ``white space'' in other bands.
It will take at least 10 years to create a workable agile radio, according
to Vanu Bose, CEO of Vanu Inc, which is developing software-defined radios.
For one thing, it must be smart enough to ensure that the vacant bands are
indeed available, and not cause interference with existing users. ``We have
to prove we can coexist,'' says Preston Marshall, DARPA's program manager
for the agile radio. But if such a sensitive radio can be made, researchers
say users can harvest up to 10 times more out of the airwaves.
The lure of such bountiful yields has turned federal regulators into
evangelists for these potentially disruptive technologies. At first, the
FCC is likely to move slowly, releasing small blocks of spectrum that are
under lease to the military and others. But once the dam is compromised,
there is no stopping the deluge. On the flood plain, wireless innovators
may realize their wildest dreams -- and citizens will gain access to a new
frontier in the sky.
By Catherine Yang in Washington
Archives at: <http://Wireless.Com/Dewayne-Net> Weblog at: <http://weblog.warpspeed.com>
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