-
Cognitive Radio
-
Spectrum (Licensed - Unlicensed)Spectrum utilizationWhite
SpacesConcept of Cognitive RadioSpectrum ManagementSpectrum
SensingSpectrum AccessConclusionFuture
DirectionsReferencesCognitive Radio
Cognitive Radio
-
Licensed SpectrumOperation of a wireless transmitter over
particular frequencies according to an authorization Spectrum
licenses come with a frequency assignmentApplications: Mobile
telephony, GPRS
Unlicensed SpectrumOperation of a wireless transmitter at
particular frequencies without authorizationPredefined rules to
mitigate interferenceApplications: WLAN, Wi-Fi
Cognitive Radio
Cognitive Radio
-
Spectrum is assigned to users with a license on a long term
basis normally for huge regions like whole countries Primary users
= rightful owners of a spectrum portion (LU - licensed)Secondary
users = users who access the spectrum opportunistically
AdvantagesExclusive access to spectrum in well-defined
areasAllow transmission in high power levelsProtection from
interference DisadvantagesLong payback time on infrastructureHigh
PricesSpectrum stays unused in some areas and periods of time
Cognitive Radio
Cognitive Radio
-
AdvantagesLow or no cost for spectrum accessAllowing multiple
users operate at the same frequencies Makes easier the
participation of new or small businesses
Disadvantagesno guarantee performancelimited QoSno legal
protection from interference
Cognitive Radio
Cognitive Radio
-
Increasing demand for radio spectrumMuch of the spectrum is idle
for a period of time and at large numbers of locations Goal:
Increase the efficiency of spectrum usageCognitive Radio
Cognitive Radio
-
White space (or spectrum hole)Is a band wider than 1Mhz that
remains unoccupied for 10 minutes or longerCR technology enables
their identification and useSecondary users jump from one white
space to another
Cognitive Radio
Cognitive Radio
-
A new class of radios was defined by the term cognitive
radioSeveral definitions (and variations) of Cognitive Radio
exist:Mitola- Cognitive radio signifies a radio that employs model
based reasoning to achieve a specified level of competence in radio
related domains.FCC - A cognitive radio (CR) is a radio that can
change its transmitter parameters based on interaction with the
environment in which it operates.E2R: Cognitive radios (CR) are
aware of the electromagnetic spectrum environment around them and
make adjustments to their transmission characteristics accordingly,
in a manner consistent with the tiered access rights model. Such
devices must be able to:sense the spectral environment over a wide
bandwidth,detect the presence/absence of legacy users (primary
users),adapt the parameters of their communication schemethe
communication does not interfere with primary users.
Cognitive Radio
Cognitive Radio
-
Cognitive radio is an emerging concept in wireless access, aimed
at improving the way radio spectrum is utilized.The principle of
cognitive radio is temporal, spatial and geographic re-use of
licensed spectrum. The idea is that an unlicensed (secondary) user
shall be permitted to use licensed spectrum, provided that it
transmits with low enough power and that it is so far from any
primary users that it does not interfere with. The motivation for
cognitive radio is various measurements of spectrum utilization,
that generally show that spectrum is underutilized. Cognitive
radios should be able to exploit spectrum holes by detecting them
and using them in an opportunistic manner. Cognitive radios could
be permitted to transmit if they cannot ``hear'' any primary
transmission: `transmit-if-you-cannot-hear-primary'' paradigm
Spectrum Etiquette (Listen before talk)
Cognitive Radio
Cognitive Radio
-
Cognitive Radio
Cognitive Radio
-
It knows where it isIt knows what services are available, for
example, it can identify then to use empty spectrum to communicate
more efficientlyIt knows what services interest the user, and knows
how to find themIt knows the current degree of needs and future
likelihood of needs of its userLearns and recognizes usage patterns
from the userApplies Model Based Reasoning about user needs, local
content, environmental contextFlexible architecturesCognitive Radio
Source: General Dynamic Decision Systems
Cognitive Radio
-
Cognitive Radio OrientEstablish PriorityPlanNormalGenerate
Alternatives(Program Generation)Evaluate AlternativesRegister to
Current TimeDecideAlternate ResourcesInitiate
Process(es)(Isochronism Is Key)ActLearnSave Global StatesSet
DisplaySend a MessageObserveReceive a MessageRead
ButtonsOutsideWorldNewStatesThe Cognition
CyclePriorStatesPre-processParseImmediateUrgentInfer on Context
Hierarchy
Cognitive Radio
-
Spectrum sensingDetermine which portions of the spectrum is
available and detect the presence of licensed users when a user
operates in a licensed bandSpectrum decisionSelect the best
available channelSpectrum sharingCoordinate access to this channel
with other usersSpectrum mobilitya SU changes its frequency of
operation when a PU appears in the same bandCognitive Radio
Cognitive Radio
-
CooperationCR users determine their actions based on observed
information exchanged with their neighborsimprove accuracy, fair
sharing, PU interference
Common control channel (CCC)Spectrum management functions rely
on exchanging information between CR users over a common control
channelIn-Band CCClocal coverageOut-of-Band CCCglobal
coveragecluster-based architectures for local coverage
Cognitive Radio
Cognitive Radio
-
PU Detectionenergy detectionsense presence/absence based on
received signals energy(+) easy to implement() cannot differentiate
signal types feature detectionsense presence/absence by extracting
specific features(+) most effective scheme for CRAHNs()
computationally complex, long sensing time Sensing
Controlcontroller coordinates PU detectionHow quickly a CR user can
find the available spectrum bandHow long and how frequently a CR
user should sense the spectrumChallenges [4]Support of Asynchronous
SensingOptimization of Cooperative Sensing
Cognitive Radio
Cognitive Radio
-
Source SENDORA ProjectCognitive Radio
Cognitive Radio
-
Radio Environment
SPECTRUMDECISION
SPECTRUMSENSING
SPECTRUMANALYSIS
RF stimuli
RF stimuli
Spectrum holes information
Spectrum holes information
Channel Capacity
Transmitted signal
-
Objectivechoose the best spectrum band according to the QoS
requirements & spectrum characteristicsFunctionalitiesSpectrum
Characterizationreceived signal strength, interference, user
numberSpectrum Selectionallocate the best spectrum band (QoS)
availableRouting Protocolswitch the spectrum or
not?Reconfigurationadjust operating parameters
Cognitive Radio
Cognitive Radio
-
ObjectiveMaintain QoS for SU without interfering to the
PUFunctionalitiesResource Allocationchannel selection and power
allocation without interferenceSpectrum Accesscoordination of
access in order to avoid collisionsrandom access, time slotted,
hybridSpectrum Sensing SupportPU transmission distinguished from
other CR usersChallengesTopology Discoveryuse of non-uniforms
channels by different CR users makes it difficultCognitive
Radio
Cognitive Radio
-
Objectivechange the SU frequency if a PU requires the specific
portionFunctionalitiesSpectrum Handoffstarts with link failure: PU
activity or quality degradationusers transfer their connections to
an unused bandConnection Managementsustain the QoS during spectrum
switchingavoid temporary disconnectionChallengesSwitching Delay
MinimizationAdaptive Framework for Spectrum HandoffCognitive
Radio
Cognitive Radio
-
Sensing PeriodicityPeriodically sense the band in case a PU
transmits Sensing has to be interleaved with data
transmissionSensing period: maximum time of SU unawareness
delayDetection SensitivityThe minimum SNR at which the primary
signal may still be accurately detected by the CRInterference
causes SIR to fall harmful: If SIR falls below a certain
thresholdStrong dependency between the detection sensitivity and
the maximum power it is allowed to transmit in a licensed bandWe
should be able to manage the total interference according to the
networks detection sensitivityCognitive Radio
Cognitive Radio
-
Channel UncertaintyChannel fading and shadowingCRs have to
distinguish a faded or shadowed primary signal from a white space
Noise UncertaintyLimited accuracy on noise power
estimationcalibration errors thermal noise changescalculation of
detection sensitivity with the worst case noise assumptionCognitive
Radio
Cognitive Radio
-
Aggregate-Interference Uncertainty multiple cognitive radio
networks operating over the same licensed bandenergy detection:
nearby CR Networks sense each other and avoid simultaneous
transmissionsystem-level coordination among CR networks overcomes
uncertainty at increased implementation costCognitive Radio
Cognitive Radio
-
Pros and Cons(+) higher detection sensitivityusers employ less
sensitive detectorsovercomes channel uncertainty() additional
communication overheadband manager collects measurements broadcast
decision to all SUcontrol channel needed() user reliability?
Cognitive Radio
Cognitive Radio
-
Multiple CR users share the spectrum resource by determining who
will access the channel, or when a user accesses the channelThere
are 3 types of access protocols:Random access protocols - No need
time synchronization- Based on the carrier sense multiple access
with collision avoidance (CSMA/CA) principleTime slotted protocols-
Need of network-wide synchronization, where time is divided into
slots for both the control channel and the data transmissionHybrid
protocols - Partially slotted transmission, in which the control
signaling generally occurs over synchronized time slotsCognitive
Radio
Cognitive Radio
-
Interaction between the network and transport layers with the
link layer Cooperation among the different users Research
challenges: i) Control channel design ii) Adaptation to PU
transmissionCognitive Radio
Cognitive Radio
-
Cognitive radio networksmay solve current wireless network
problems resulting from the limited available spectrumcreate a new
class of users who intelligently share spectrum when it its
idleSpectrum Sensinghas performance limitations by the
uncertainties at various levelsis a multifaceted problem demanding
coordinated efforts of the regulatory and technical sidese.g.
Cooperative Sensing which requires flexible policySpectrum
Managementmanagement functions help with interaction among CR
userscooperation among multiple users ensures protection to PU and
optimizes CR network performanceCognitive Radio
Cognitive Radio
-
An overview of the state of the art for medium access protocols
in cognitive radio networksSpectrum management, spectrum sensing
and spectrumaccess were discussedThere is further work needed in
devising accurate models that account for false alarm and missed
detection probabilities in one framework The simplified ON/OFF PU
traffic model may not be suitable in a practical environment where
the licensed users may be cellular, contention-based, or have other
possible access technologies Cognitive Radio
Cognitive Radio
-
The information from multiple layers must be
seamlesslyintegrated in the working of the MAC protocolCompletely
integration of the sensing function with more accuracySignificant
scope for devising protocols that adapt the CR transmissions based
on the type of the interferer Newer performance metrics that
capture the CR specific improvements should be devised and used for
evaluating the different MAC protocols
CRs are an open area of research with industrial and academic
interest for the next few yearsCognitive Radio
Cognitive Radio
-
http://en.wikipedia.org/wiki/Cognitive_radio
Spectrum Management in Cognitive Radio Ad Hoc Networks,
Akyildiz, I.F. and Lee, W.Y. and Chowdhury, K.R., IEEE Network,
2009 Spectrum sensing in cognitive radio networks: requirements,
challenges and design trade-offs, Amir Ghasemi, Elvino S. Sousa,
IEEE Communications Magazine, 2008
Sliding-Window Algorithm for Asynchronous Cooperative Sensing in
Wireless Cognitive Networks, Chengqi Song, Qian Zhang, IEEE
Communications Society, ICC 2008 proceedings PDF
Cognitive Radio
Cognitive Radio
-
Any Questions???Cognitive Radio
Cognitive Radio
***An extension of SDR employs model based reasoning about user
needs, local content and environmental contextThink of it as a PDA
with a radio that is so smart that it solves simple stuff on its
own round peg - round hole;
******
