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Swadhin Mishra

Cognitive Radio Networks

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Network Evolution

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Network EvolutionSoftware-dene radio (SDR): a collection

of hardware and software technologiesthat enable recongurable systearchitectures for wireless networks and

user terinals!Cognitive radio (CR) " a radio that is

aware of and can sense its environent#learn fro its environent# and ad$ust itso%eration according to soe ob$ectivefunctionSDR is the building block of CR

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&ireless Network ChallengesMobility is inherent with untetheredResources are constrainedS%ectru 'scarcity bandwidth * delay

issues

Environent changesMobility di+erent surroundings (indoor#

urban# rural)

,arying %hysical %ro%erties&ireless counication %ath changes over

tie

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&ireless Network Challenges

S%ectru 'scarcity bandwidth * delayissues

•License for a large region, usuallycountry-wide•Large chunk of licensed spectrum

e!pensive licenses"•#arriers to new ideas•$rohibited spectrum access by unlicensedusers•%S& bands are unlicensed

•'L() bands at *+ ./, 0 ./•1em orar short ran e licenses

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Cognitive RadioCognitive radio is a wireless

counication syste which is aware of theenvironent and its changes and can ada%tits transission %araeters accordingly!

Cognitive Ca%ability: -he ability to sense theunused s%ectru at a s%ecic tie andlocation (s%ectru hole)

Recongurability: -he ability to receive and

transit at di+erent fre.uency band enablesthe cognitive radio to recongure its%araeters and select the best band!

(n intelligent wireless communication system that isaware of its environment and uses the methodology ofunderstanding-by-building to learn from theenvironment and (dapt to statistical variations in theinput stimuli, with two primary ob2ectives in mind3 4"

highly reliable communication whenever and whereverneeded5 *" e6cient utili/ation of the radio spectrum+

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S%ectru hole

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Cognitive Radio /latfors0le1ible in R0 carrier fre.uency (23 4 5 678)0le1ible in bandwidth (several 93s M78)0le1ible in wavefor;<= and =<; driven

6enerated<%rocessed by %rograable =S/and<or 0/6;s>bserves: -ra?c characteristics easured at network

layer

Error rate * characteristics (M;C layer#network layer# trans%ort layer)

Receive characteristics (/hysical layer# M;Clayer)

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Cognitive Radio /latfors

@nAuences:/hysical layer

0re.uency * bandwidth -ransit %ower Bea width * direction =ata rate# code# * chi%%ing rate

M;C %rotocol 0EC strength Retransit schee M- si8e Encry%tion * %araeters

Network layer Routing %rotocol ;ddressing %lan(s) ;CDs

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Cognitive radio network/riary network– /riary users:  /riary users have the license to o%erate in certain s%ectru

bands

/riary base station: Controls the access of %riary users to s%ectru

Secondary networkSecondary users:  Secondary users have no licensed bands assigned to the!

Secondary base4station: ; 1ed infrastructure co%onent with cognitive radio ca%abilities

and %rovides single ho% connection to secondary users!S%ectru broker : Scheduling server shares the s%ectru resources between

di+erent cognitive radio networks!

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Cognitive radio network

Dicensed user< high%riority user :/riary ser (/)

nlicensed user <cognitive user :Secondary ser (S)

@dle fre.uency <

channel band:S%ectru hole#white s%ectru#

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CRN ;rchitecture

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CRN ;rchitecture

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0unctionalities of a CRNSpectrum sensing: Cognitive radio user has

the ability to sense the unused s%ectru at anytie and location!

 Spectrum management: Based on theavailability of the s%ectru and other %olicies#CR user allocates the best available s%ectruband!

 Spectrum mobility: CR user shall vacate thes%ectru in the %resence of any %riary user

and ove to ne1t best available s%ectru bandSpectrum sharing: CR network has to %rovide

a fair and o%tial s%ectru allocation ethodaong ulti%le CR users!

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Challenges@nterference avoidance>S awareness

Sealess counication

  Re.uires a cross layer design

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S%ectru Sharing in Cognitiveradio networksSpectrum sensing: -he secondary user can

only allocate a s%ectru if its not used by anunlicensed user!

 Spectrum allocation: ;llocation of a channelnot only de%ends on s%ectru availability butalso de%ends on internal and e1ternal %olicies!

 Spectrum access: Since there are ulti%le

secondary users trying to access the s%ectru#their access should be coordinated to avoidcolliding in overla%%ing %ortions of the s%ectru

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S%ectru Sharing in Cognitiveradio networks1ransmitter-receiver handshake: ;fter

deciding a %ortion of the s%ectru# thereceiver of this counication should also

be indicated!

Spectrum mobility: @f the s%ecic %ortion

of the s%ectru is needed by a licensed

user# the counication needs becontinued in another vacant %ortion!

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1.()9 :;<

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References

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FLG Q! iao and 0! 7u# Cognitive radio networks! ;uerbach /ublications# K33!

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FJG D! Chen# S! @ellao# M! Cou%echou1# /! 6odlewski# /! da ,inci# and @! Milan# ';n;uction 0raework for S%ectru ;llocation with @nterference Constraint in CognitiveRadio Networks!