Can We Build a Wireless Communications Infrastructure That Values
Everyone’s Right to Communicate?
Vikki Cravens, Dharma
Dailey, Antwuan Wallace
PDF [204 KB]
Putting Equity On the Front Burner
If you believe that community based media is a good idea, then
you probably think that it’s a good idea for all communities.
Whether any community in particular will get access to community
radio
or TV is predicated on a number of factors. Radio licenses
may be available for community use, but most often are not.
Under existing rules, the most affordable and technically accessible
type of community
broadcasting, low power FM radio (LPFM), has a “secondary” status
– community low power stations can be moved or even bumped
completely off the dial by large commercial broadcasters.
Community based
television also lives under the shadow of industry. Because
the financing for community access TV comes from the fees
negotiated between municipalities and cable companies, the
cable industry
almost always gets a chance to wiggle out of its community
obligations
every time one of these local contracts comes up for renewal.
Additionally, the industry lobbies at the national level
to unfetter itself from
these obligations. Finally, in keeping with a trend already
well known to most community media advocates, those groups
and communities
which most need immediate access to powerful communication
infrastructures, such as groups warning of health crises,
environmental disasters,
or important political votes that effect the entire community,
almost never have an immediate way to communicate their messages
clearly.
Our thesis is that if it were possible for the
public to directly access the airwaves, without having to negotiate
with an intermediary –
the FCC or one of it’s sanctioned industry kingpins – then
perhaps it would be possible to expand vital community media
services
to all communities. It may even be possible for community-based
communications
providers, and home-grown communications tools built in-house
by organizations who need them, to grow and thrive on an
as-needed basis. We believe that current and future technological
advances
will make this scenario increasingly possible and economically
feasible. With a good legal case being made for this kind
of community
communications initiative, we hope that this groundwork can
inform grassroots action to bring it into being.
The goal of more equitable distribution of information by
the public and for the public should be of paramount importance
to any democratic
government. Yet, far too often in the United States, approaches
to public policy are made only in economic terms that favor
efficiency tradeoffs over equity tradeoffs. Those who ask
questions
about
equitable access to other necessary resources therefore rarely
ask questions about equitable access to wireless communications
infrastructures. However, we would argue that a
wireless communication infrastructure
based on the best of current wireless technologies – smart
radio – is a public good that can be consumed by everyone
including
those
who cannot pay. It is difficult to overstate
the social justice potential for a communication infrastructure
based on smart radio.
We must also discuss that in light of the drastic advances
in communication technology that are taking place, we need
to seriously
reconsider
what constitutes the public interest. As we approach “pervasive
connectivity” over the airwaves – that is, cheap and
ubiquitous communication – current thinking of what constitutes
public
access must be changed. In this new communications paradigm
at least two
important shifts are possible. First, our ideas about what
constitutes adequate access to communication must be radically
expanded upward,
to encompass these new possibilities in new technologies.
Second, we must fight for independent communication systems
thatcan
be created and controlled at the local level, without the
heavy hand
of government deciding who gets to communicate with whom,
and without the controlling hand of corporate monopolies.
These
local systems
need not all look the same, serve the same constituencies,
or be sustained in the same ways. Smart radio is flexible
enough to support
many models, including home grown and ad hoc communication.
I. “Assume Everyone Has the Right to Broadcast.”
The Technical Case
The Wi-Fi Accident
The first wave of smart radio was accidentally unleashed
directly on the public in 1999. WI-FI – two-way smart radios
that network
computers to each other and to the internet – was envisioned
by its creators as a way to network offices without wires,
but it
quickly became a way for neighbors – all over the world
– to share internet service. But WiFi is only a taste of what
is possible
with Low-Power Community Based Communications that use
Smart
Radio technology.
Leading Smart Radio expert Kevin Werbach believes the best way
for the airwaves to be allocated in the Smart Radio context is
to assume that
everyone has a “baseline
universal privilege to communicate.” In Radio
Revolution: The Coming Age of Unlicensed Wireless, Werbach states, “Using
a combination of the techniques outlined in this paper, it
is possible to imagine a world in which anyone can be a broadcaster.”
The 999,999 Missing Channels of Communication
The cluster of computer and networking innovations collectively
known as Smart Radio makes it possible for the airwaves
to be used for many, many times more channels of communication
than
could
be imagined just a few years ago. At a recent public
talk in DC, FCC Chief Engineer Ed Thomas said that he never
would
have
predicted
the current developments in wireless communications even
five years ago, but today “I’m amazed by what can be
put into a small box.”
According to J. H. Snider’s Citizen’s Guide to the
Airwaves,
the same amount of airwaves that carried one TV channel
in 1960, can
today carry 10 channels. Similarly, the amount of the
airwaves that was tied up by a single mobile phone call
in the 1940s
today handles 100,000 phone calls. As time marches on
we can expect
even more improvements.“Yet all of these advances,” Snider
states, “may be little compared to what’s likely to
happen in the next decade. Another increase in spectrum capacity
by
a factor of 100,000 is quite possible.”
But these advances in wireless communication have not
been applied equally. Though some of the innovations
that make
so much more
communication possible have been around for decades and
many are already being used by some broadcasting based
industries,
the FCC
is only now considering whether these innovations will
be applied across the board. So the question must be
raised, will the
benefits of these new technologies be applied to direct
public
access?
What would community media look like it were multiplied
by 100,000 or
100,000 x 100,000?
Unlicensed – The More Fair Regime
WiFi is one of dozens of wireless radio devices including
portable phones, garage door openers, remote controls
and Mr. Microphones
that transmit and receive on special radio bands that
have been designated “unlicensed.” Unlicensed
does not mean – as some big telecoms are saying right
now – that
there
are no rules
and chaos reigns. Quite the contrary. On licensed radio,
people get permission to broadcast from the FCC. With
unlicensed radio,
a potential creator requests permission to build a
new device that takes advantage of unlicensed spectrum.
Creators submit
their design
for a device to the FCC for approval. Unlicensed devices
are required to follow strict specifications.Once a
creator can
prove that her
device meets the FCC’sengineering standards, she can
build any number of them can be made without requesting
license
permission for each unit. For example, people that
want to use unlicensed
devices – their portable phones, garage door openers
or wifi phones –
do not need to get prior permission to use them from
the FCC.
When communities take advantage of these new technologies
for their communication needs, innovative systems built
on an as-needed
basis
begin to flourish.
For example, the city of Cleveland is creating what
they call a citywide “municipal bicycle lane.” One
Cleveland is
a high speed city-wide network,designed to lower access costs for
all who use it. Scalable to neighborhoods or other cities, the
Cleveland project provides free wireless internet to the public
while lowering communications costs for participating non-profits
and government agencies. One Cleveland designers are focusing on
five core aspects for planning their “digital city”: “bridging
the digital divide, health care, arts and culture, scientific research
and e-government.” Operational savings for participating
educational, government, cultural, and healthcare organizations
is anticipated
to be 30-60%. Participating organizations are encouraged
to provide free public access to their neighbors and communities.
By creating access points in all public schools, universities,
and other public areas, the digital city planners hope
to create the digital infrastructure they believe is
critical to economic
growth. By creating this core network for the city,
the public
should benefit by opportunities for “learning, job
training, research, economic development, and community access
to culture,
healthcare, and e-government.
On a smaller scale along these lines, the Urban League
of Eastern Massachusetts is networking computer training
centers
and non-profits
in the Roxbury area of Boston, in order to more effectively
share resources such as expensive computer training
programs. In Urbana-Champaign,
Illinois a community wireless group is providing internet
on a sliding scale capping at $10 a month. And in southern
California,
eighteen Indian reservations in San Diego county are
using wireless to reunite their tribe across a distance
of over
200 miles with
hopes of making their project self-sustaining by providing
high-speed access to nonnative households.
If we want to see more community-based programs like
this come to fruit, we should clearly understand how
licenses
impact
a community’s ability to use communications infrastructure.
In
his Draft Principles
of Progressive Spectrum Management, Harold Feld points
out the public interest problems with licensing, in
light of
the new
technical possibilities: “Licensing spectrum...represents a fundamental
restraint on the ability of citizens to communicate with one another.
If licenses are exclusive, then citizens can only communicate with
each other via a government sanctioned intermediary. If that intermediary
has the right to choose how to deploy systems, or what content
gets carried on the system, then communities and individuals find
themselves at the mercy of government licenses. No matter what
technical capacities the system may support, or what content people
may prefer, or the rate at which communities would otherwise wish
to see services deployed, decisions on these matters rest wholly
with the licensee.” He continues, “Free citizens
should not have to go on bended knee, like serfs of old,
to those given
exclusive spectrum franchises by the government. Decentralized
control of spectrum has been advanced on economic grounds,
but it derives its fundamental justification from the principles
of
the First Amendment.”
Communities Can Build, Own, and Control Their Communications
Infrastructure
So far, unlicensed devices are always low-power. This
means that the most smart radio devices like WiFi “whisper”
instead of “shouting” the way big broadcasters do. Whispering
has some big advantages. A lot more conversations can
take place in a room where everyone is whispering instead of shouting.
Low-power
networks have proved to be very reliable and powerful
in many situations. So-called “mesh” networks with lots of low-power
transmitters constantly whispering to their neighbors
– sending
and receiving –
are more reliable than old-fashioned point to point
networks. An important
advantage to the community-minded spectrum pioneer
is that
each transmitter
in the mesh network is relatively inexpensive to buy
and install compared to big transmitters that need special towers
to work.
The network grows bit by bit, cheap transmitter/receiver
by cheap
transmitter/receiver. As money becomes available the
network
grows. Each transmitter can be owned by the person
who throws it up on
the roof. And the more people who do so, the more coverage
everyone has and the better the network can run.
Trickle Down Media Democracy Doesn’t Work
Big Media and Big Telecoms complain loudly about the “command
and control” way that the FCC doles out permission
to use the airwaves. Command and control doesn’t work
well for media democracy either. One connecting thread
among the
various
community based wireless systems that are popping up
around the country is the excitement in the voices
of those involved
in building
them. These diverse organizers see the tantalizing
possibility of self-sustaining and self-reliant communications
at the
local level. Instead of being dependent on government
subsidies forever,
small for profits and non-profits all over the country
are finding ways to bring access to the public for
free in a
sustainable manner.
Smart radio has a role to play in correcting some of
the oversights of recent current communications policy.
Let’s
tour a few of
the failures:
The North End of Springfield, Massachusetts is one of
the poorest areas in the state. The public library
provides internet access,
but it is open for just one week day per week, from
9 am
to 5 pm. It is difficult to imagine successfully looking
for a
job
or working
on a school assignment with this level of “access.” Yet
from the fly-over perspective of policy makers, people
on the North End have “access.”
For some with pressing needs, “access” is not even
on the table. In the summer of 1995, over 700 people died
in Chicago in a record heat wave. (That’s more than twice
the number of people
that died in the Great Chicago Fire). Although it was
an unprecedented health crisis, the media at the time did not treat
it as such.
In Eric Klinenberg’s five year study of the deaths
published in his book Heat Wave he identifies the victims
as primarily poor,
socially-isolated, elderly men. Though health workers
were aware of the dire circumstances, the public at large was not
informed
because the story wasn’t reported. The media,
in their role as mediators of information,
missed the boat, with potentially dire consequences
for the city of Chicago, poised to suffer the same loss again.
A fitting epitaph
for these unfortunate men might be, “Trickle
down media democracy worked no better for us than trickle-down
economics.”
It is likely that if we had a team of Eric Klinenbergs
to study communities across the country, we would find
similar
stories
everywhere. In Immokalee, Florida, a public health
advisory circulated on the
local media told residents not to drink the water due
to bacterial contamination. Local officials had no
idea that
their health
advisory was functionally inaudible to the majority
of the town’s population –
its migrant workers – because there was no media that
served them. If local officials and local media are
unable to
see the communication
gaps that exist within their own community, how are
national policy makers supposed to shore these gaps?
Wherever old style communications infrastructure is
implemented, these problems persist. Sarah Kamal, who
works with international
organizations to build radio stations in rural areas
in Afghanistan, points out that even well-meaning experts
can make assumptions
that lead to very ineffective communication systems.
In
her article, “Disconnected From Discourse: Women’s
Radio Listening
in Rural
Samangan, Afghanistan” Kamal points out that the western
organizations that
are setting up radio in rural Afghanistan, made multiple
assumptions that did not take into account barriers
to relevant use of
radio by women there. Major factors such as linguistic
differences, time of day of programming, women’s access
to radios, and
relevance of programming were misunderstood by developers.
The discomfort
of western NGOs with the women’s desires to hear Islamic
programming was another difficulty. Kamal concludes, “Current
operational assumptions of western radio organizations
have created significant
gaps between what rural women require and what their
media system provides.”
Communication infrastructures created using smart radio
could solve some of these problems. While the migrants
in Immokalee
now have
an LPFM station to disseminate information about the
next health crisis, the lengthy licensing process meant
that
the station
was not up in enough time to solve that particular
crisis. In the near
future, inexpensive ad hoc networks like the ones that
the US military is developing for battle will be able
to pop
up as cultural
and
civic needs emerge. It will be possible for the communications
budget of, say, a county public health agency to be
used to provide wifi phones to the chronically ill.
If such
a system
had been
in place in Chicago in 1995, hundreds of lives could
have been saved.
Today, in the North End of Springfield, Massachusetts,
students from Syracuse University, led by Professor
Murali Venkatesh
,have partnered with local community organizations
to design a wireless
network to replace the one-day-a-week access with real,
pervasive community-wide access. Key features of this
project include
an inherent design of sustainability, with the network
also serving
local businesses. Taking into account the needs of
this primarily poor, primarily Puerto Rican community,
the
design team is
looking for ways to make the network useful to non-English
speakers and
people with low or no literacy. In an era when this
Springfield community has little to no commercial media
representing
them, and at a time when that community’s access to
mediamaking is
at its lowest possible point, this project is designed
tomake it easy
for people in the community to generate local multimedia
content. It is the sincere hope of the Springfield
project organizers,
and of these authors, that the models and practices
established by
this community can be expanded to many community organizations
and their needs across the country, and the world.
As this group identifies its own needs, and creates
an infrastructure
tailored
especially to serve those needs in a sustainable way,
the
best practices of this model will start to become clear.
Beyond Community Media and Forward to the Real Impacts
of Community Communications
Communication is a powerful prophylactic. Over one
hundred years of psychological, sociological, and medical
research
from nearly
every sub-discipline and perspective all point in the
same direction: quality of life and length of life
is directly
related to the
quality of an individual’s social ties. The more ties,
and the stronger
the ties, the stronger an individual is in every measurable
way. We need to communicate in order to be healthy.
Current communications policy does not take this into
account. Take,for example, the phone system. The majority
of Americans
pay a fee to the phone companies so that low-income
users can access
the phone system for a reduced rate. But this reduced
rate often translates into reduced service and reduced
access.
While it
is desirable that low-income people are able to call
911 if their house is on fire, day to day communication
needs
become
undermined
by policies that undervalue the quality of life. A
holistic communication policy would recognize that
people who
are low-income, chronically
ill, or marginalized for whatever reason often have
stresses in
their social networks and should encourage as much
communication as is desired by such persons. Yet, the
current structure
is a subsidy to the phone industry that regressively
taxes most
users
while providing limited service options to the poor.
In essence, the policy says, “If your house is on fire call 911,
but if your roof leaks and your foundation is caving, we
can’t help
you.”
Smart radio and the age of pervasive connectivity can
change this arrangement. First, because the infrastructure
of
wireless communication
can accommodate multiple networks or cooperative sharing
of a single network, there is no need for us to have
to rely on
handouts
from
monopolies like the phone companies. Because the technology
is affordable enough for counties, municipalities,
small businesses or non-profits to build and use, the
design
of wireless networks
can be tailored to those who will actually be using
them. It must be recognized that what constitutes “meaningful” or “relevant” or “timely” or “necessary”
communication cannot be determined by those who stand
above the grassroots
level. Many of the problems that are embedded in well-intentioned
but
far away policy makers designing a network that attempts
to anticipate other peoples needs can be avoided by
building from
the ground
up – with the users able to tweak their network to
suit their needs.
II. Cost Does Equal Access. The Economic Case
In a September 17, 2003 piece in the Washington Post,
Rama Lakshmi reports “Radiophony, an Indian lobby group for community
radio, claims that villagers can set up a low-powered, do-it-yourself
radio station – with a half-watt transmitter, a microphone, antenna
and a cassette player – for approximately $25. The group says such
a station can reach about a third of a mile and cover a small village.” Old
fashioned low-powered analog radio is the communication choice
for the world’s poorest people because it is the least expensive
and easiest to use mass communication tool. Expanding the communication
tools that rely on wireless and expanding the communication channels
that are available via wireless should directly correlate with
more accessible communication to more people. As smart radio makes
possible “orders of magnitude” more communication
over the same old airwaves, our expectations of what slice
of the pie
the public gets to use should increase magnitudnally as well.
Wi-Fi has already demonstrated that smart radio can
be inexpensive and accessible for communities in
the United
States. The
cost to implement the community network in Springfield,
Mass today
is estimated
to be $60,000. That’s still a far cry from the $25
dollar LPFM stations in India. Like all computer
technology the cost of
smart radios is likely to decrease over time. The
largest computer chip manufacturer, Intel, is already
making
smart radio chips.
Companies
like Cisco, Microsoft, and Sony and are betting heavily
on wireless
technology. Wireless networks are not as easy to
use or implement as old-fashioned radio- yet. The
wonderful
opportunities
that smart radio brings to us will have arrived when
they come down
to the
price and ease of use of LPFM.
Use of “consumer grade” technology means the
communications infrastructure is affordable to many,
and – if we work at it –
maybe everybody. There are ways that the cost of
smart radio can be made
unnecessarily expensive for the little guy. Imagine,
for example, that the government passed a rule that said anyone
that drove
on a public road must drive a Mercury Cougar. Ridiculous?
Unfair? Yet, this is analogous to what the FCC mandated
AM
and FM broadcasters
to do. A proprietary technology called IBOC, partially
owned by
ClearChannel must be used by any AM or FM broadcaster
who wants to broadcast digitally. Big Media and the Big Telecoms
must
not be allowed to lock the public out of use of the
airwaves
by locking
up control of key technologies. When the government
mandates that everyone who wants to use the airwaves must use a
specific
corporation’s
product, it gives that corporation a veto on free speech.
Another way the public could be cut out of the wireless
loop is through “propertizing” of the
airwaves. “Propertizing” is
a term thrown about in Washington by a group called “the
propertizers” and it describes the mental hopscotch
that needs to be played en route to privatizing the
airwaves. Yes, the
same great minds who dreamed up pollution credits
for mid-west air and for-profit water for South American
peasants have their
eyes set on the airwaves. Variations on the theme
include transferring the work of the FCC over to
a private entity, permanently selling
off the rights to broadcast to the highest bidder,
and secondary markets for spectrum – like the ones
we have for energy (think Enron).
Imagine ClearChannel or The Carlyle Group “owned” the
color green and anyone who wanted to use green had
to pay them a fee. That is a literal analogy of what
the propertizers
want
to do.
III. Ye Olde Dumb Network. The First
Amendment Case
If it is possible that new communication technologies
can evolve into infrastructures that allow people
broad-based direct
cultural and civic participation via the airwaves,
as many of us believe
to be the case, than the arguments of 70 years ago
that allowed for monopoly control of communications
over the
airwaves
may no longer be legally excusable. According to public
interest
telecomm
lawyer Harold Feld of Media Access Project, “The First
Amendment prohibits the government from granting exclusive
rights in communication
unless the physical characteristics of the medium require
exclusivity as a precondition for productive use.”
The framers of the constitution did more than pay
lip service to free speech. When we begin to talk
about
building a
state-of-the-art communication infrastructure that
values everyone’s right
to communicate,
the response is usually an instantaneous and guttural, “THAT
WILL NEVER HAPPEN!” But this is completely untrue.
It already happened at least once.
When the American Revolutionaries met for their first
big meeting at the Continental Congress, it isn’t
surprising that one of
the very first things on the table was putting in
place their own communication
system that would not be subject to the King. A former
royal postmaster who had lost his job for his political
beliefs
and who was also
printer and publisher of The Pennsylvania Gazette
– Ben Franklin – was charged with setting up an alternative
postal
service.
Back in the 1700s, mail was not only for letters
to
grandma,
it was
the only way for information or news to circulate.
In those days, censorship could be heavy handed.
Saying the wrong
thing could
get you burned at the stake or locked up for life.
King
George also used other clever laws like taxes on
newspapers to control
the flow of content and dissent. Even if one were
able to speak ones mind, political dissenters would
be subject
to
spying
as traditionally in Europe the mail system was also
a spy system for the royalty.
It is truly astonishing and revolutionary that after
they won their war, the Americans did not replicate
the Europeans,
but
instead
embarked on creating a communication system that
reflected the Enlightenment value of Free Speech.
Mail carriers
were not spies.
Control of content was exclusively in the hands of
the “end
user,”the“consumer” or as they used to say the “individual.” One
of the first acts of the first federal congress was to create
a subsidized communication system to tie the whole country
together,
including unprofitable rural areas. As Robert McChesney,
Paul Starr and others point out, in its day, the postal system
was
the best
way to provide the maximum amount of people with the most
free speech.
Today, important decisions are being made at the
national and international levels about where the
controls should
be placed
on who can communicate
with whom. Much of the decisions revolve around what
kind of networks can be built. Network theorist David
Isenberg
calls
for a “Stupid
Network” – one where the network pays
no attention to what’s coming over it, and where
all of the intelligence exists at “the
edge of the network” – the user and the user’s
computer. Franklin would say, “Been there,
done that.”
Convergence is here
At the New America Foundations Pervasive Connectivity
conference this April, FCC Chief Engineer Ed Thomas
said, “People have
been talking about convergence for fifteen years.” “Convergence
is now here.” Of course, Mr. Thomas is talking about
the convergence of communication systems. But it also means
that those
of us who desire a communications infrastructure that widens
and deepens the circle of meaningful participation can converge
as
well. Radio activists are no longer just radio activists,
tv activists are no longer just tv activists, and computer
activists
are no
longer just computer activists. The possibilities of smart
radio and questions of fair use of spectrum even reach out
to the environmental
movement. Common Assets Defense Fund takes the position that
spectrum is a natural resource.
As the wireless infrastructure opens new possibilities,
many questions that go to the heart of public interest
in communication
deserve
to be revisited: How quickly and how easily can
communities/individuals solve a communications
need or desire? What governmental
entities or what corporations do they need to go
through in order to
resolve a communication need? What communication
systems promote the
highest degree of communication self-reliance for
communities? How do we
assess the depth and breadth of meaningful civic
and cultural communication? In light of so many
more channels
of communication
possible – what
can we do with them? How far can consumer grade
technology and consumer based infrastructure be
pushed in the
direction of putting
citizens in the decision-making position? Who will
decide what level of civic and cultural participation
we can
engage in
and with whom we can engage?
The wisdom among our communications architects
in Washington is that the public does not understand,
does not care
to understand, and cannot be made to understand
what
is at
stake in current
spectrum
reform debates. Smart radio has created a feast
of communication possibilities. We must change
current
wisdom by demanding
a seat at the banquet even if we have to slip in
through the
backdoor
sideways.
Fact-Sheet on New Spectrum Technologies
Today’s digital technologies differ from the devices
of the past, which required regulation to prevent
interference among
signals.
There are several ways in which new “smart” digital
devices transmit and receive data in ways that distinguish
between signals, allowing users to share the airwaves.
Cognitive Radio: Same thing as Smart Radio. Use “cognitive
radio” when you want to sound obnoxious. Smart Radios are
software defined. They would be better named Polite Radios because
they cooperate very well with other wireless devices by “listening” before
they transmit a signal. They can detect other nearby signals
and avoid interfering with them. The imaginatively named
Next Generation
of smart radio is being developed by the Department of Defense.
It will allow the DOD to set up complete communications systems
without any interference to or from any existing broadcasting.
Software Defined Radio: using software to process
the radio signals, these radios can also receive
and transmit
across
a broad range
of frequencies. Software radio is highly adaptable.
For example, cellular telephone radio can transmit
broadcast
television
signals. They can change transmission protocols
on the fly and do many
other nifty things.
WIFI: “A cordless phone for computers.”– Eli
Noam.
Mesh Networks are based on small low-power two
way radios. Each node in the network is both
receiving and transmitting –
capturing
and retransmitting data – sent by other devices
in
the network. Each node that is added strengthens
the network’s
capacity
by sharing the workload.
Spread-spectrum refers to several techniques
to transmit a signal over a wide range of
frequencies. Spread
spectrum signals
are
transparent to other users.
Open Spectrum – describes mechanisms that
allow for facilitated spectrum sharing.
and key words
are unlicensed,
underlay,
ultrawideb and and spread-spectrum. Unlicensed
spectrum sets aside frequency
bands for use with no exclusive rights.
Unlicensed exists today, in the
bands shared by computer devices such as
cordless phones, and these bands are used
by wifi (wireless
internet)
networks.
Underlay allows unlicensed users to coexist
in licensed bands, by making their signals
invisible
and nonintrusive
to other
users. Ultrawideband devices transmit
pulses of very short duration
in order to avoid interfering with preexisting
users of that same
spectrum band.
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