Cognitive Radio System and Seamless Spectrum Handover

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Intelligent wireless communicationIntelligent wireless communication


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Outline

Why Cognitive Radio?

Objective

Motivation: Spectrum Scarcity

Whatis Cognitive Radio (CR) System

Key Challenges Basiccognitiveradio cycle

Licenses of SpectrumBand

CR Network Architecture

Licensed band

Unlicensed Band

IEEE 802.22 Cognitive Radio Main functions

Spectrum handoverin CR

Operation of conventionalspectrumhandover

Frequency v/s path loss

Frequency v/snormalized cellcoverage

Cognitive Radio SystemModel

Okumura-Hata Model

Equations for path loss Proposed spectrum handoverscheme

and operation

Performanceevaluation

Cell outageProbability

Totalno of handover

Advantage of proposed scheme

Conclusion

References

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Lack of RFspectrumband to meettheevermounting demand to meetisthe driving factor

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Highly reliablecommunicationwhenever andwherever needed

Effectiveutilization of radio spectrum

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Spectrum Utility

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Incognitiveradio systemtransreceiver adaptssurroundingenvironment and reconfiguresitself by changing itsinternal operatingparameters (e.g. transmitting power,carrier frequency ,modulationstrategy) inrealtimewith theknowledge of itsusers priorities andneeds.

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Analyze

Decide

Act

Sense

The Cognitive Radio ApproachThe Cognitive Radio Approach

Thecognitiveradio carries a level ofcognition orintelligencethat permitsdecision-making and learned patterns ofbehavior.

It detectswhether a particularsegment oftheradio spectrumiscurrently inuse andtojump into (or out of) thetemporarily-unused spectrumvery rapidly withoutinterfering with thetransmissions of other

users.


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Physical Architecture:Physical Architecture: An accurate detection of weaksignals of licensed

users over a widespectrumrange.

Implementation of RFwideband from-end and A/Dconverter (multi-GHzspeed)

ReRe--configurability:configurability: Adjusting operating parameters:

Operating frequency

Modulation

Transmission power

Communicationtechnology

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Cognitive capability:Cognitive capability:

Spectrumsensing (detecting spectrum holes)

Spectrum analysis/decision (determining data rates,

transmissionrate, and modes) Spectrummobility (if thecurrentspectrumband inuse

becomeunavailable)

Spectrumsharing (providing fairspectrumscheduling

among coexisting CR users)

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Thecognitive processstartswith the passivesensing of RF stimuliand culminateswith action.

There arethree tasks which cognitiveradio performs:1) Radio-scene analysis (carried outinthereceiver)

estimation of interferencetemperature of theradio environment detection of spectrum holes and fairsharing of itwithout harmful

interferencewith otherusers.

2) Channel identification (carried outinthereceiver) estimation of channel-stateinformation prediction of channelcapacity foruseby thetransmitter

3)Transmit-power control and dynamic spectrummanagement(carried outinthetransmitter) dynamic spectrummanagement allowstheradio terminalsto operatein

thebest available frequency band maintainsseamlesscommunicationrequirements during thetransitionto

betterspectrum

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Depending onthe parts of thespectrum availableforcognitiveradio,itis divided into

Licensed Band Cognitive Radio:

licensed band such as U-NII band or ISMband. The IEEE 802.22 working group is developing a standard

forwirelessregional area network (WRAN) which willoperateinunused televisionchannels

U

nlicensed Band Cognitive Radio: which can only utilizeunlicensed parts of radio frequency

spectrum.

Fore.g.,coexistence of IEEE 802.11 and Bluetooth.

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On licensed bandOn licensed band


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On unlicensed bandOn unlicensed band


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Spectrum sensingSpectrum sensing Detecting unused spectrum

Spectrum managementSpectrum management Capturing thebest availablespectrum

Spectrum analysis Interference/Path loss Linkerrors/delay Channel holding time

Spectrum decision Decisionmodel Multi-band decision

Spectrum mobilitySpectrum mobility Maintaining seamlesscommunication during thespectrum

transition Spectrum handoff

Spectrum sharingSpectrum sharing Providing fairspectrumscheduling method

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In cognitive radio system spectrum handoveroccurs when a secondary use changes frequencydue to the appearance o f a primary user.

If spectrum handover is from high to lowfrequency than cell coverage area is expanded & ifit is from low to high frequency than cell outageoccurs.

Spectrum handover may result in

degraded system performance because of the differentpropagation loss or path loss of the different frequency.

cell outage which in turn disruption of service.

redundant intercell handover.

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High frequenciessuffer fromlarge path lossand incase of low frequencies, path lossisrelatively small.

Path losscanbe formulated from followingequation.

Path loss(dB)=20log F + 20log D +32.5

where,F= frequency inMHzD=distanceinKm

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According to equation of path losswecanseethat for higher frequenciescellcoverage area isreduced.


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Applicable to/under conditions:

Multicellcognitiveradio system

Each basestation (BS) canuse a differentfrequency based onspectrumsensing tominimizetheinterference.

Systemmodelisbased onOkumura-Hata

model and itis applicableto thetransmissionsinsidecities.

Thismodelissuited forboth point-to-pointand broadcasttransmissions.

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Mostwidely used model forradio frequencypropagation for predicting thebehavior ofcellulartransmissioninbuiltup areas.

Thismodel Includestheeffects of diffraction,reflection and scattering caused by citystructures.

Hata Model predictsthetotal path loss along alink of terrestrialmicrowave or othertype ofcellularcommunications.

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Where,

LU = Path lossin Urban Areasin dB

hB = Height of basestation antenna inm (valid 30 to 200 m)

hM = Height of mobilestation antenna inm (valid 1 to 10 m)

f = Frequency of TransmissioninMHz (valid 150 to 1,000 MHz)

CH = Antenna heightcorrection factord = Distancebetweenthebase and mobilestationsinkm (valid 1 to20 km)

K0 = 0 forurban area

= 3 dB for denseurban area

K1 =69.55 for frequency range 150 f 1000 MHz=46.3 for frequency range 1500 f 2000 MHz

K2 =26.16 for frequency range 150 f 1000 MHz

=33.9 for frequency range 1500 f 2000 MHz

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(1)Enforcing condition of intercell handover:

(Low to high frequency case)

Where,f = original frequency of theserving BS

fi = the frequency of a neighborBS indexed by i

th1 = threshold fortriggering intercell handover

th2 = threshold for determining intercell handover = SNR

Intercell handovercanbeenforced beforechanging the frequency to avoid cell outage.

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(2)Stopping condition of intercellhandover:(High to low frequency case)

Where,f = original frequency of theserving BS

fi = the frequency of a neighborBS indexed by i.

th1 = threshold fortriggering intercell handover

th2 = threshold for determining intercell handover = SNR

Suspension of theintercell handover of a terminal attheedge of a cellcanbeenforced in orderto avoid redundantintercell handoverif coverageisexpanded.

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Applied undercondition:

Spectrumrange: 54 MHz< f < 698 MHz

Bandwidth of each channel: 6 MHz

During spectrum handover,thenew frequencyisselected randomly

Terminals arelocated randomly

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= Cell outage probability of conventional scheme

= Cell outage probability of proposed scheme

= = intercell handover parameter= 0 dB


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Where,

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Note: In proposed schemeredundant handoverisreduced by 30% according to aboveformula.


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As original frequency of serving BS isrelativelyhigh,lowto high transition probabilitydecreases.

Probability of coverageexpanded is high.

Reduced intercell handover.

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The proposed scheme forthecognitiveradiosystemreducesthecell outage probability and

thetotalnumber of handovers. Hence,itcanprovideseamlessserviceincognitiveradiosystem.

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http://en.wikipedia.org/wiki/Cognitive_radio

http://ieeexplore.ieee.org

IanF. Akyildiz,et al., NeXtgeneration/dynamicspectrumaccess/cognitiveradio wirelessnetworks: A survey,ComNet2006

Li-Chun Wang and Anderson Chen, Onthe Spatial. Coexistence ofInfrastructure-Based and Ad Hocconnections for a Cognitive RadioSystem

S. Haykin, Cognitive Radio,JSAC 2005

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Cognitive Radio System and Seamless Spectrum Handover

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