Spectrum Sensing and Allocation Techniques for Cognitive Radios

Farrukh JavedF-05-020/07-UET - PHD-CASE-CP-40

Spectrum Sensing and Allocation Techniques for Cognitive Radios

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

Cognitive Radios

Section – I

Motivation for Cognitive Radios

Spectrum Scarcity [1]

Motivation for Cognitive Radios

Spectrum Utilisation [1]COGNITIVE RADIOS

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

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”

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

Operating Principal of CROverlay CRs utilise the concept of spectrum

holesUnderlay CRs use the concept of

interference temperature

Overlay Cognitive Radios

Frequency

Pow

er

Time

COGNITIVE RADIOS

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

Underlay Cognitive Radios

Interference Temperature Model [10]

SPECTRUM SENSING

Interference Temperature LevelInterference temperature is the maximum

RF interference acceptable at a receiving antenna

Basic Characteristics of Cognitive RadiosCognitive CapabilityRe-configurability

COGNITIVE RADIOS

Cognitive CapabilityCognitive CycleSpectrum SensingSpectrum Allocation

Spectrum AnalysisSpectrum Decision

Cognitive cycle [3]

Re - ConfigurabilityOperating FrequencyModulation SchemeTransmission PowerCommunication TechnologyDirectivity of Transmission

Next Generation NetworksIntroductionProtocol Layers and Cognitive Radio

Functionalities

xG Network Functionalities [3]COGNITIVE RADIOS

Spectrum Sensing

Section – II

Spectrum Sensing Techniques

Spectrum Sensing

Transmitter DetectionMa

tched

Filter Detection

Energy Detection

Cyclo-

stationary Feature

Detection

Cooperative Detection

Interference Based

Detection

SPECTRUM SENSING

Transmitter DetectionIntroduction

TechniquesMatched Filter DetectionEnergy DetectionCyclo – Stationary Feature Detection

SPECTRUM SENSING

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

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

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

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

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

Interference Based Detection

Interference Temperature Model [10]

SPECTRUM SENSING

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

Few GeneralisedSpectrum Sensing ChallengesMulti user environmentInterference temperature measurementSpeed of detection etc.

SPECTRUM SENSING

Spectrum Allocation

Section – III

Spectrum Allocation

SPECTRUM ALLOCATION

Spectrum AnalysisChannel capacityPrimary user related informationxG user information

SPECTRUM ALLOCATION

Channel CapacityPath LossWireless Link LayerLink Layer DelayNoise Info

Sp

ectru

m A

naly

sis

User Related Information(Primary and xG Users)InterferenceHolding TimeUser Transmission Parameters

Sp

ectru

m A

naly

sis

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

Spectrum DecisionSpectrum managementSpectrum mobility Spectrum sharingUser related info

SPECTRUM ALLOCATION

Spectrum ManagementDecision ModelMultiple Spectrum decisionReduced Transmission PowerCooperation with reconfigurationHeterogeneous Spectrum

SPECTRUM ALLOCATION

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

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

Future of Cognitive Radios

Section IV

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

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 services

Potential 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