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Farrukh JavedF-05-020/07-UET - PHD-CASE-CP-40
Spectrum Sensing and Allocation Techniques for Cognitive Radios
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Sequence of PresentationSection I – Cognitive Radios
IntroductionNext generation networksCognitive radios
Section II – Spectrum SensingTransmitter detectionCooperative detectionInterference based detectionSpectrum sensing challenges
Section III – Spectrum AllocationSpectrum analysisSpectrum decision
Section IV – Future of Cognitive RadiosConclusion
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Cognitive Radios
Section – I
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Motivation for Cognitive Radios
Spectrum Scarcity [1]
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Motivation for Cognitive Radios
Spectrum Utilisation [1]COGNITIVE RADIOS
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Motivation for Cognitive Radios
Measured Spectrum Occupancy Averaged over Six Locations
0.0% 25.0% 50.0% 75.0% 100.0%
PLM, Amateur, others: 30-54 MHzTV 2-6, RC: 54-88 MHz
Air traffic Control, Aero Nav: 108-138 MHzFixed Mobile, Amateur, others:138-174 MHz
TV 7-13: 174-216 MHzMaritime Mobile, Amateur, others: 216-225 MHz
Fixed Mobile, Aero, others: 225-406 MHzAmateur, Fixed, Mobile, Radiolocation, 406-470 MHz
TV 14-20: 470-512 MHzTV 21-36: 512-608 MHzTV 37-51: 608-698 MHzTV 52-69: 698-806 MHz
Cell phone and SMR: 806-902 MHzUnlicensed: 902-928 MHz
Paging, SMS, Fixed, BX Aux, and FMS: 928-906 MHzIFF, TACAN, GPS, others: 960-1240 MHz
Amateur: 1240-1300 MHzAero Radar, Military: 1300-1400 MHz
Space/Satellite, Fixed Mobile, Telemetry: 1400-1525 MHzMobile Satellite, GPS, Meteorologicial: 1525-1710 MHz
Fixed, Fixed Mobile: 1710-1850 MHzPCS, Asyn, Iso: 1850-1990 MHz
TV Aux: 1990-2110 MHzCommon Carriers, Private, MDS: 2110-2200 MHz
Space Operation, Fixed: 2200-2300 MHzAmateur, WCS, DARS: 2300-2360 MHz
Telemetry: 2360-2390 MHzU-PCS, ISM (Unlicensed): 2390-2500 MHz
ITFS, MMDS: 2500-2686 MHzSurveillance Radar: 2686-2900 MHz
Spectrum Occupancy
Spectrum Concentration [2] COGNITIVE RADIOS
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CognitionOxford English Dictionary definition of “cognition” as
“The action or faculty of knowing taken in its widest sense, including sensation, perception, conception, etc., as
distinguished from feeling and volition”Encyclopedia Encarta defines “cognition” as
“To acquire knowledge by use of reasoning, intuition or perception”
Encyclopedia of computer Sciences gives a three point computational view of “cognition” as
“1. Mental state and processes intervene between input stimuli and output responses
2. The mental state and processes are described by algorithms3. The mental states and processes lend themselves to
scientific investigations”
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Cognitive Radio Joseph Mitola introduced the idea of Cognitive Radio in 2000 as
“Situation in which wireless nodes and related networks are sufficiently computationally intelligent about radio resources and related computer to computer communication to detect the user communication needs as a function of user context
and to provide the resources most required”Simon Haykin explains the concept in six key words
AwarenessIntelligentLearningAdaptabilityReliabilityEfficiency
An intelligent radio capable of adapting itself to best suit its surrounding radio environment
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Operating Principal of CROverlay CRs utilise the concept of spectrum
holesUnderlay CRs use the concept of
interference temperature
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Overlay Cognitive Radios
Frequency
Pow
er
Time
COGNITIVE RADIOS
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Interference temperature TI is specified in Kelvin and is defined as
where PI (fc , B) is the average interference power in Watts centered at fc, covering bandwidth B measured in Hertz.
Boltzmann's constant k is 1.38 x 10-23
Any Un-licensed transmission must not violate the interference temperature limit at the licensed receivers. Mi is a fractional value between 0 and 1, representing a multiplicative attenuation due to fading and path loss between the unlicensed transmitter and the licensed receiver.
The TL is to be decided by regulatory authority such as FCC or PTA
Interference temperature model
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Underlay Cognitive Radios
Interference Temperature Model [10]
SPECTRUM SENSING
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Interference Temperature LevelInterference temperature is the maximum
RF interference acceptable at a receiving antenna
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Basic Characteristics of Cognitive RadiosCognitive CapabilityRe-configurability
COGNITIVE RADIOS
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Cognitive CapabilityCognitive CycleSpectrum SensingSpectrum Allocation
Spectrum AnalysisSpectrum Decision
Cognitive cycle [3]
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Re - ConfigurabilityOperating FrequencyModulation SchemeTransmission PowerCommunication TechnologyDirectivity of Transmission
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Next Generation NetworksIntroductionProtocol Layers and Cognitive Radio
Functionalities
xG Network Functionalities [3]COGNITIVE RADIOS
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Spectrum Sensing
Section – II
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Spectrum Sensing Techniques
Spectrum Sensing
Transmitter DetectionMa
tched
Filter Detection
Energy Detection
Cyclo-
stationary Feature
Detection
Cooperative Detection
Interference Based
Detection
SPECTRUM SENSING
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Transmitter DetectionIntroduction
TechniquesMatched Filter DetectionEnergy DetectionCyclo – Stationary Feature Detection
SPECTRUM SENSING
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Matched Filter DetectionIntroductionOpportunities
Commonly UsedHigh Processing Gain
ChallengesMatched Filter BoundA priori knowledge of transmission is required
Tran
sm
itter D
ete
ctio
n
SPECTRUM SENSING
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Energy DetectionIntroductionOpportunities
Easy implementationMulti path and fading channel studies carried
outChallenges
Critical selection of thresholdSusceptible to noise power variationsCommunication type identification not
possibleReduced flexibility
Tran
sm
itter D
ete
ctio
n
SPECTRUM SENSING
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Cyclo – Stationary Feature DetectionIntroductionOpportunities
Robust against un-certain noise powersTransmitter information is not requiredNeural network application has been found
very feasibleChallenges
Computationally complexTransmission type identification is not
possibleReduced flexibility
Tran
sm
itter D
ete
ctio
n
SPECTRUM SENSING
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Transmitter Detection Un – Certainties Receiver Un-certaintyShadowing Un-certainty
Tran
sm
itter D
ete
ctio
n
(a) Receiver Uncertainty (b) Shadowing Uncertainty [3]
SPECTRUM SENSING
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Cooperative DetectionIntroduction
Centralised DetectionDistributed Detection
Cooperative Detection OpportunitiesNo receiver or shadowing un-certaintiesEffects of degrading factors mitigatedPrimary User’ interference reduced
Cooperative Detection ChallengesImplementation ComplexityConstrained ResourcesPrimary user un-certainty un-resolved
SPECTRUM SENSING
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Interference Based Detection
Interference Temperature Model [10]
SPECTRUM SENSING
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Opportunities and Challenges of Interference Based Detection Opportunities
Focus on primary receiver rather than primary transmitter
Frequency parameters of choice can be utilised
ChallengeReceiver temperature detectionDue to interference power constraints, the
underlay techniques can only be employed for short range communications
SPECTRUM SENSING
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Few GeneralisedSpectrum Sensing ChallengesMulti user environmentInterference temperature measurementSpeed of detection etc.
SPECTRUM SENSING
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Spectrum Allocation
Section – III
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Spectrum Allocation
SPECTRUM ALLOCATION
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Spectrum AnalysisChannel capacityPrimary user related informationxG user information
SPECTRUM ALLOCATION
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Channel CapacityPath LossWireless Link LayerLink Layer DelayNoise Info
Sp
ectru
m A
naly
sis
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User Related Information(Primary and xG Users)InterferenceHolding TimeUser Transmission Parameters
Sp
ectru
m A
naly
sis
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Spectrum Analysis Challenges and OpportunitiesChallenges
Heterogeneous Spectrum Sensing Non Cooperative Primary and xG usersVarying Transmission ParametersReal Time AnalysisDelays in Processing
Opportunities
Sp
ectru
m A
naly
sis
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Spectrum DecisionSpectrum managementSpectrum mobility Spectrum sharingUser related info
SPECTRUM ALLOCATION
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Spectrum ManagementDecision ModelMultiple Spectrum decisionReduced Transmission PowerCooperation with reconfigurationHeterogeneous Spectrum
SPECTRUM ALLOCATION
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Spectrum MobilityIntroductionChallenges
LatencySuitable AlgorithmAppearance of a Primary UserVertical and Inter-Cell Handoff SchemeSuitable Threshold for HandoffSpectrum Mobility in Time DomainSpectrum Mobility in Space
OpportunitiesPrioritised White SpaceSoft and Hard Handoff
SPECTRUM ALLOCATION
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Spectrum SharingArchitecture Based Classification
Centralised or DistributedChallenges and Opportunities
Access Behaviour ClassificationCooperative and Non-cooperative SharingChallenges and Opportunities
Access Technology ClassificationOverlay and Underlay TechniquesChallenges and Opportunities
Generalised Spectrum Sharing ChallengesCommon control ChannelDynamic radio rangeSpectrum Unit
SPECTRUM ALLOCATION
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Future of Cognitive Radios
Section IV
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Cognitive Radio AdvantagesAll of the benefits of software defined radioImproved link performanceAdapt away from bad channelsIncrease data rate on good channelsImproved spectrum utilizationFill in unused spectrumMove away from over occupied spectrumNew business propositionsHigh speed internet in rural areasHigh data rate application networks (e.g., Video-
conferencing)Significant interest from FCC, DoDPossible use in TV band refarming
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Cognitive Radio DrawbacksAll the software radio drawbacksSignificant research to realizeInformation collection and modelingDecision processesLearning processesHardware supportRegulatory concernsLoss of controlFear of undesirable adaptationsNeed some way to ensure that adaptations
yield desirable networks
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How can CR improve spectrum utilization?Allocate the frequency usage in a networkAssist secondary markets with frequency
use, implemented by mutual agreementsNegotiate frequency use between usersProvide automated frequency coordinationEnable unlicensed users when spectrum
not in useOvercome incompatibilities among existing
communication services
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Potential Applications of CRLeased networksMilitary usageEmergency situationsMesh networksLicensed user may enhance its
performanceImproving UWB transmission by avoiding
NBI
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Jeffery H Reed and Wills G Worcester
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ConclusionSpectrum Sensing and Allocation Techniques for Cognitive Radios