Spectrum Sensing and Allocation Techniques for Cognitive Radios

Farrukh JavedF-05-020/07-UET - PHD-CASE-CP-40Spectrum Sensing and Allocation Techniques for Cognitive Radios1Sequence of PresentationSection I Cognitive RadiosIntroductionNext generation networksCognitive radiosSection II Spectrum SensingTransmitter detectionCooperative detectionInterference based detectionSpectrum sensing challengesSection III Spectrum AllocationSpectrum analysisSpectrum decisionSection IV Future of Cognitive RadiosConclusion2Cognitive RadiosSection I 3Motivation for Cognitive Radios

Spectrum Scarcity [1]4-Spectrum is managed by FSA(Fixed Spectrum Access) techniques-Extensive utilisation has resulted in spectrum scarcity

Motivation for Cognitive Radios

Spectrum Utilisation [1]COGNITIVE RADIOS5-The scarcity leads us to consider a re-consideration of spectrum allocation techniques-The FSA mgmt is convinient but resulted in under utilised spectrum-Some bands very congested and most not-Avg usage between 15 to 85 %Motivation for Cognitive Radios

Spectrum Concentration [2]COGNITIVE RADIOS6-Jean Piere Hubaux-Goes on to comment that 100 billion Euoros are spent to buy spectrum for 3rd GenerationCognitionOxford 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 volitionEncyclopedia Encarta defines cognition asTo acquire knowledge by use of reasoning, intuition or perceptionEncyclopedia of computer Sciences gives a three point computational view of cognition as1. Mental state and processes intervene between input stimuli and output responses2. The mental state and processes are described by algorithms3. The mental states and processes lend themselves to scientific investigations7Cognitive RadioJoseph Mitola introduced the idea of Cognitive Radio in 2000 asSituation 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 requiredSimon Haykin explains the concept in six key wordsAwarenessIntelligentLearningAdaptabilityReliabilityEfficiencyAn intelligent radio capable of adapting itself to best suit its surrounding radio environment

8-The CR utilises the flexibility of an SDR supplemented by the knowledge of prevailing radio environment through a sensing system. The transceiver should be able to sence the dictates of its prevailing spectrum conditions and change its transmission parameters accordinglyOperating Principal of CROverlay CRs utilise the concept of spectrum holesUnderlay CRs use the concept of interference temperatureOverlay Cognitive RadiosTimeCOGNITIVE RADIOSInterference 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 10-23Any 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 modelUnderlay Cognitive Radios

Interference Temperature Model [10]SPECTRUM SENSING

Interference Temperature LevelInterference temperature is the maximum RF interference acceptable at a receiving antennaBasic Characteristics of Cognitive RadiosCognitive CapabilityRe-configurabilityCOGNITIVE RADIOS14Cognitive CapabilityCognitive CycleSpectrum SensingSpectrum AllocationSpectrum AnalysisSpectrum DecisionCognitive cycle [3]

15Re - ConfigurabilityOperating FrequencyModulation SchemeTransmission PowerCommunication TechnologyDirectivity of Transmission16Next Generation NetworksIntroductionProtocol Layers and Cognitive Radio Functionalities

xG Network Functionalities [3]COGNITIVE RADIOS17-Explain the DSA or XG networks as hetrogenous networks which use cognitive radio as nodal pts-Works in parallel to primary networks and other xG-Aim is Optimum utilisation of spectrum -One network as suggested by Akyldiz is shownSpectrum SensingSection II Spectrum Sensing TechniquesSPECTRUM SENSINGTransmitter DetectionIntroduction

TechniquesMatched Filter DetectionEnergy DetectionCyclo Stationary Feature Detection

SPECTRUM SENSINGMatched Filter DetectionIntroductionOpportunitiesCommonly UsedHigh Processing GainChallengesMatched Filter BoundA priori knowledge of transmission is requiredTransmitter DetectionSPECTRUM SENSINGEnergy DetectionIntroductionOpportunitiesEasy implementationMulti path and fading channel studies carried outChallengesCritical selection of thresholdSusceptible to noise power variationsCommunication type identification not possibleReduced flexibilityTransmitter DetectionSPECTRUM SENSINGCyclo Stationary Feature DetectionIntroductionOpportunitiesRobust against un-certain noise powersTransmitter information is not requiredNeural network application has been found very feasibleChallengesComputationally complexTransmission type identification is not possibleReduced flexibilityTransmitter DetectionSPECTRUM SENSINGTransmitter Detection Un Certainties Receiver Un-certaintyShadowing Un-certaintyTransmitter Detection

(a) Receiver Uncertainty (b) Shadowing Uncertainty [3]SPECTRUM SENSINGCooperative DetectionIntroductionCentralised DetectionDistributed DetectionCooperative Detection OpportunitiesNo receiver or shadowing un-certaintiesEffects of degrading factors mitigatedPrimary User interference reducedCooperative Detection ChallengesImplementation ComplexityConstrained ResourcesPrimary user un-certainty un-resolvedSPECTRUM SENSINGInterference Based Detection

Interference Temperature Model [10]SPECTRUM SENSINGOpportunities and Challenges of Interference Based Detection OpportunitiesFocus on primary receiver rather than primary transmitterFrequency parameters of choice can be utilisedChallengeReceiver temperature detectionDue to interference power constraints, the underlay techniques can only be employed for short range communicationsSPECTRUM SENSINGFew GeneralisedSpectrum Sensing ChallengesMulti user environmentInterference temperature measurementSpeed of detection etc.SPECTRUM SENSINGSpectrum AllocationSection III Spectrum Allocation

SPECTRUM ALLOCATIONSpectrum AnalysisChannel capacityPrimary user related informationxG user information SPECTRUM ALLOCATIONChannel CapacityPath LossWireless Link LayerLink Layer DelayNoise InfoSpectrum AnalysisUser Related Information(Primary and xG Users)InterferenceHolding TimeUser Transmission ParametersSpectrum AnalysisSpectrum Analysis Challenges and OpportunitiesChallengesHeterogeneous Spectrum Sensing Non Cooperative Primary and xG usersVarying Transmission ParametersReal Time AnalysisDelays in ProcessingOpportunitiesSpectrum Analysis

Spectrum DecisionSpectrum managementSpectrum mobility Spectrum sharingUser related infoSPECTRUM ALLOCATIONSpectrum ManagementDecision ModelMultiple Spectrum decisionReduced Transmission PowerCooperation with reconfigurationHeterogeneous Spectrum

SPECTRUM ALLOCATIONSpectrum MobilityIntroductionChallengesLatencySuitable AlgorithmAppearance of a Primary UserVertical and Inter-Cell Handoff SchemeSuitable Threshold for HandoffSpectrum Mobility in Time DomainSpectrum Mobility in SpaceOpportunitiesPrioritised White SpaceSoft and Hard HandoffSPECTRUM ALLOCATIONSpectrum SharingArchitecture Based ClassificationCentralised or DistributedChallenges and OpportunitiesAccess Behaviour ClassificationCooperative and Non-cooperative SharingChallenges and OpportunitiesAccess Technology ClassificationOverlay and Underlay TechniquesChallenges and OpportunitiesGeneralised Spectrum Sharing ChallengesCommon control ChannelDynamic radio rangeSpectrum UnitSPECTRUM ALLOCATIONFuture of Cognitive RadiosSection IVCognitive 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

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

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 servicesPotential Applications of CRLeased networksMilitary usageEmergency situationsMesh networksLicensed user may enhance its performanceImproving UWB transmission by avoiding NBI

Jeffery H Reed and Wills G Worcester ConclusionSpectrum Sensing and Allocation Techniques for Cognitive Radios