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First presentation of Research
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Introducing Adaptive and Cognitive Radios
Joe Mitola of Mitre Corporation and Wayne Bonser of Air ForceResearch Labs were the visionaries who started this organizationand brought the industry together to work these hard designproblems, and to begin establishing the new standards it wouldrequire.
He recognized that it is feasible for a radio to become aware of itsuser, aware of its network (choices and features), and aware of itsspectral environment.
In fact, it could then be adaptive, and ultimately could have thesoftware to learn various adaptations to its current environment that
are desirable support to the user, network, operators, spectrumowners, and regulators.
Dr. Mitola introduced the terms aware, adaptive, and idealCognitive
Radio (iCR) to reflect the different levels of cognitive capability.
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Cognitive and adoptive radio
the cognitive meaning which is related to thinking, reasoning,
and remembering
is a smart radio that has the ability to sense the external
environment, learn from the history, and make intelligent
decisions to adjust its transmission parameters according to thecurrent state of the environment.
It is important to remark that a CR is not what in the literature is
called adaptative radio. A CR can not only adapt to the best
spectrum settings but also store past data, learn, and positively
evolve. Indeed, adaptation is a subset of CR characteristics, andan adaptative radio is not necessarily cognitive at all.
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Cognitive radio..
Two main accepted characteristics
(1) Cognitive capability, which refers to
sense the information from its radio
environment and identify the best andmore appropriate spectrum and
operating parameters and
(2) Reconfigurabilitythat enables the
radio components to be dynamicallyprogrammed according to cognitive
decisions.
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Cognitive radio network
is a network made up of CRs
by extending the radio link
features to network layer
function and above. By means
of CRs cooperation, the
network is able to sense its
environment, learn from the
history, and accordingly decide
the best spectrum settings.
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Simple scenario
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Support for the Network
Radios, just like computer networks, generally have a full protocol
stack running from the physical layer to the application.
Of these layers, only the physical and MAC layers are intimately
designed and specific to radio/wireless protocols.
the physical layer and MAC layer are very specific to radio/wirelessapplications, and optimization of these layers as a real time activity
based on measurements of local spectrum is the dominant part of
Cognitive Radio research and design at this time.
The radio can also select the most appropriate network for the
service requests of the user. For example, the radio can select a
Bluetooth network access for a local printer, rather than using the
WiFi access point, while using the WiFi access point for internet
database searches. Similarly, voice or video traffic can be provided
through the most appropriately resourced network.
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Support for the Network Operator
Some network operators have recognized the benefit of
convergence of wireless services delivered through multiple access
networks. Thus, cellular, WiFi, WiMAX, Bluetooth, broadcast digital
audio, and video are bundled so that the service provider selects
which resource is most efficiently able to accommodate a userscurrent needs, and that the transition across different network
access is both seamless and economical for the user and for the
network operator
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Support for the Regulatory Organization
Nearly 200 different countries has different regulatory rules andprocedures for designing radios, defining spectral mask of eachradio application waveform, manufacturing radios, and acquiringrights to use various parts of spectrum.
Cognitive radios include a policy engine. The policy engines role isto be aware of the utilization rules for all countries where theequipment is licensed, and to assure that the radio only operates inthose allowed modes in those geographic regions.
Other policies: network usage policy, network operator policy, andeven manufacturer policy.
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Support for the Spectrum Owner & Users
Measurements suggest that cognitive radio systems should be ableto increase traffic density at ratios between 7:1 and over 20:1
In addition to supporting significant increase in users, use ofspectrum awareness and adaptation techniques can also indicateinterference properties, multipath properties, signal strength, and inturn, these real time measurements can guide adaptation of thetransmission waveforms to be more robust, providing the userimproved quality of service in multiple dimensions.
Cellular connectivity may swap with WiFi or WiMax connectivity asthe user moves about his activities.
Since the availability, range, throughput, and economics are vastlydifferent models, users will come to expect the system to make costeffective and performance sensitive decisions. Eventually users willexpect these decisions to be automatic.
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Economics of Cognitive Radio
Many things are technically possible, but what justifies
the time and effort to advance various degrees of
cognitive functionality into the radio network, either in
subscriber equipment or in the network infrastructure is
the economics
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Value ofSpectrum
Spectrum is the lifeblood of communication systems. The telecommunications industry is now a 1 Trillion(1012) dollar per
year industry,6 and the wireless part is growing very rapidly, while
the wired telecommunication services are experiencing a relatively
flat business.
in many rural areas, a single broadcast TV source may be nearly
200 miles away and there is little or no local TV service) there are
significant opportunities to provide internet and telecommunication
services using this under-utilized spectrum
.
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Smart Antennas
One way to get enhanced spectral density and user density is withsmart antennas.
Smart antennas can provide narrow beam patterns for eithertransmitter or for receiver or both. In the Industrial Scientific andMedical (ISM) band frequencies of 2.4 GHz, practical narrow beamantennas can provide 9 dB of gain, and reduce interference to othercommunication activity off the sidelobes of the antenna beampatterns
Smart antenna techniques may be economically costly for certainapplications, and may be impractical for certain form factors
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MIMO
Multi-Input Multi-Output (MIMO) is a communication technique inwhich the multipath properties of the channel are utilized to supportgreater data throughput
In a MIMO system, the transmitter transmits multiple channels ofdata traffic through multiple antennas; the receiver learns thechannel behavior between the transmitters multiple antennas andthe receivers multiple antennas, and uses signal processing tocompute what waveform was transmitted by each transmittingantenna, and the corresponding data stream.
In this way, the same frequency is reused in the same geographicregion to deliver greater amounts of data traffic than could beexpected from a single transmitting and receiving antenna (SISO)system. Some MIMO systems also have the ability to learn tosuppress interference from unrelated transmitters, further enhancingnetwork performance.
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Spectrum Subleasing, Sharing
In dense urban applications, there is opportunity to sublease
spectrum from spectrum owners whose loading is temporarily light.
Such owners can define access rules, and economics of such
transactions, as well as rules to take back spectrum should demand
or emergency arise. SDR Forum, IEEE, and others are working to establish standardized
protocols to enable such transactions.
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Architecture of a cognitive radio.
includes a cognitive function to
analyze existing spectrum
users, and measure properties
of its own communication
channels, and a set of rules expressed
through a policy engine which
define what the radio is
allowed to do, and what it is
not allowed to do..
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Scenario
Cognitive radios are aware of their surroundings and
bandwidth availability and are able to dynamically tune
the spectrum usage based on location, nearby radios,
time of day and other factors. This provides for a moreefficient use of the spectrum as well as reducing power
consumption, and enabling high priority communications
to take precedence if needed.
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Varied devices will be
able to detect other
radios around them andwork together to
optimize the use of
spectrum, allocate
resources and moreeasily communicate to
their peers.
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