Subject: [NEXTEL-1] Sharing spectrum the smarter way

From: [email-masked]
Date: Mon, 03 May 2004 02:33:14 -0400

Sharing spectrum the smarter way

Patrick Mannion
Apr 05, 2004

A seismic shift in radio design could break the spectrum-availability
bottleneck, proponents say, and open up a new frontier of opportunities
for radio designers and wireless application developers.

Cognitive radio - one that can sense its environment and location and
then alter its power, frequency, modulation and other parameters so as
to dynamically reuse available spectrum - is emerging, but some are
already calling it the holy grail of wireless design.

Derived from a doctoral thesis submitted in May 2000 by Joseph Mitola,
who is now at work on the military's cognitive-radio initiative, CR
could
in theory allow multidimensional reuse of spectrum in space, frequency
and time, obliterating the spectrum and bandwidth limitations that have
slowed broadband wireless development in the United States and
elsewhere.

This new technology is a kissing cousin of software-defined radio. With
SDR, the software embedded in a radio cell phone, for example, would
define the parameters under which the phone should operate in real-time
as its user moves from place to place. Today's cell phone parameters,
by contrast, are relatively fixed in terms of frequency band and
protocol.

But cognitive radio is even smarter than SDR. CR "is a radio that's
aware
of and can sense its environment; learn from its environment; and
perform functions for its user that best serve its user," said Bruce
Fette,
chief scientist at General Dynamics Decision Systems and technical
committee chairman of the SDR Forum.

Although the communications and wireless industries are just beginning
to hear about cognitive radio, the U.S. government is already showing
a keen interest in its possibilities.

The Federal Communications Commission is weighing the commercial
applications and the Defense Advanced Research Projects Agency is
proposing a military version.

The FCC in December officially began the effort to extricate the concept

from academia by issuing a notice of proposed rule making (NPRM)
calling for input on how CR could be realized. Now in the response
stage,
that NPRM underscores the unprecedented willingness of the commission
in recent years to explore innovative ways to open new spectrum to
commercial unlicensed use. Examples include the release of new spectrum
in the 5-GHz U-NII band last year, as well as the opening up of 7.5 GHz
of bandwidth for ultrawideband (UWB) signaling in the region between 3.1

and 10.6 GHz. Though the power levels allowed for UWB were extremely
low - a roof of - 41 dBm - the move marked the first time the FCC had
allowed unlicensed use across otherwise licensed bands.

"UWB was a first shot at this [reuse of spectrum]," said Bob Brodersen,
professor at the University of California, Berkeley's Wireless Research
Center.
"But CR is a more complete solution as it [actively] looks for unused
spectrum
and begins to transmit inside those bands." Cognitive radios coexist
with
primary users, he said, but get out of those bands if need be when the
primary users show up. "UWB just hid below the noise floor," Brodersen
said. "This one does it by jumping out really fast. Yet it can transmit
at
reasonable levels."

In his opening keynote at the CTIA Wireless show in Atlanta last month,
FCC chairman Michael Powell hammered home the need to open up new
spectrum and to enable spectrum reuse. The commission, he said,
formed the Spectrum Policy Task Force in 2000 "as we saw the potential
for wireless broadband."

But in the current system under which the FCC operates, formulated in
the
1920s, different bands are assigned to different services and licenses
are
then required to operate inside those bands. As a result, Powell said,
the
FCC has not "been able to faster optimize spectrum use. We're moving
cautiously but purposefully and will look at policies that will bring it
all
together for consumers."

UC Berkeley's Brodersen said that President Bush "also came out recently

with an edict on the same topic of better spectrum use. So politically,
there's
great support for this."

The FCC's Spectrum Policy Task Force (SPTF) came out with a report in
2002 that recommended the agency migrate toward a "policy-based"
solution where spectrum could be used on an opportunistic basis. "This
is a paradigm shift," said Jeffrey Schiffer, director of Intel Corp.'s
Wireless
Research Radio Communications Lab (Santa Clara, Calif.). "You can
characterize it as the most exciting thing in radio that's come along in

a long time, because of the opportunities that exist now and the
creativity
you can have around the ability to agilely move across the band and
operate legally in multiple different places, using things like policy
engines
as a means to check whether you're legal."

In particular, the FCC is looking at a means by which the 6-MHz-wide
licensed spectrum in the UHF band, currently assigned to TV
broadcasters,
can be reused in secondary markets as a path to last-mile data access .
This proposal would set power levels up to 8 dB higher than those
currently
allowed in those bands, thereby greatly increasing range and coverage
area.
In addition, said Schiffer, the propagation characteristics at the lower
UHF
frequencies are particularly attractive, offering the possibility of
longer
distance and lower power.

"Still, you have to operate in 6-MHz channels, so you won't get the
54 Mbits/ second you get with .11g or a [Wi-Fi]," he said. Nonetheless,
Schiffer says, data rates "will be respectable," especially in rural
areas
where channels can be concatenated.

But the FCC's interest also extends to higher frequencies. "If you look
at the entire RF frequency up to 100 GHz, and take a snapshot at any
given time, you'll see that only 5 to 10 percent of it is being used,"
said Ed Thomas, chief engineer at the FCC. "So, there's 90 GHz of
available bandwidth."

Military angle

The military, too, has latched on to the concept of cognitive radio
under the umbrella of the Darpa-funded XG - or Next Generation
Communications - program. Its aim is to develop technology that
allows multiple users to share spectrum in a way that coexists with,
and complements, sharing protocols included in today's Wi-Fi
technologies. "They're exploring the idea in the most extreme way,"
said John Notor, a system architect at Cadence Design Systems Inc.
(San Jose, Calif.) and a leading researcher in the area of CR. "They're
working on a 'dc-to-daylight' box covering a broad range of frequency
bands up to the microwave area and which can use any spectrum
at any time and adapt accordingly."

The government's interest in - and definition of - CR goes way
beyond spectrum reuse, said Fette of General Dynamics. Indeed,
CR and Darpa's XG technology are not identical, as many in the
industry believe, he said. "The spectral-efficiency technologies - as
exemplified by XG [and the FCC's efforts] - are one important
facet of CR, but not the only facet."

>From a military perspective, CR's ability to handle functions that
best serve its user translates to sufficient situational and mission
awareness to help the soldier reach an objective. "The kind of data
required for this is still in the labs," said Fette. "Academicians are
studying this and we want to work with them." Examples of data
for a soldier, he said, could include local topography, mission
objectives and time scales for those objectives, as well as knowledge
of - and access to - the radio networks in the area as well as
"the location of friendly - and enemy - positions and artillery."

WLAN launch pad

Researchers believe the technical foundations established by wireless
LANs provide a launching pad for CR. WLANs already incorporate
essential CR features such as dynamic frequency selection and transmit
power control. Also, while the RF front ends may require wideband
receivers and transmitters, Fette said, the hardware exists now, "and
the software is a matter of sitting down and doing the software
engineering"
to make functions like filtering, band selection and interference
mitigation
"available as plug-in software modules for the radios. That's stuff we
know how to do."

Fette sees the technology being implemented in a different style for the

commercial market, "but the FCC's interest in spectrum efficiency will
make that happen fairly quickly - in five years. And that's not so bad,"

he said.

That's not to say there are no technical hurdles to surmount. "Some
fundamental ideas need to be ironed out, such as interference
temperature,"
said Brodersen of UC Berkeley. Interference temperature, a metric the
FCC
included in its December rule-making notice, involves helping a radio
that's
intending to transmit determine how much interference it will cause on
other
radios in the locale to ensure the interference doesn't cross a certain
yet-to-be-determined threshold, said Brodersen. "But the problem is how
you, as a transmitter, can detect how much interference you're causing
this other receiver? That's a tough problem," he acknowledged.

Researchers are also grappling with how to identify channels and
so-called
"white space" within the TV spectrum, as well as the uncertainty
surrounding
FCC certification rules for radios with no assigned frequency bands.

Protocols and communications channels are also a thorny issue, since
they're required to help disparate radios negotiate optimum
communication
parameters to minimize their respective interference levels.

"We're working on a prototype CR right now, but the problem is the
protocol
and how to figure out how to set up these calls," said Brodersen,
referring
to
the kind of data that should go back and forth between the physical and
media-access control layers. "So you have to design a protocol stack
that's
very different from what we've had before as you have this sensing thing

built
into it now."

"There's some research to be done, especially in the incumbent profile
detection space," said Cadence's Notor. "Radios don't exist in
isolation.
Turn on a bunch of radios and how do they detect each other? How do
they get out of the way if a licensed user comes up? None of this has
been addressed in any standards I'm aware of."

 http://www.commsdesign.com/printableArticle/?articleID=18700443

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