CooperativeCommunications inWirelessSystems Elza Erkip - - PowerPoint PPT Presentation

CooperativeCommunications inWirelessSystems

Elza Erkip

WirelessNetworks

Backbone Network

Wireless LAN Wireless Cellular

WirelessLAN Wireless Cellular Ad-hoc Network

Outline

• Relaychannel

– Relayinginwireless:Userelaysfordiversity – Traditionalmultihop versusmultihop withdiversity

• Conceptofcooperation:“Virtual”antennaarray
• Informationtheoreticmodelandanalysis
• Cooperativecodes

RelayChannel

• IntroducedbyVen der Meulen (1971)
• CoverandElGamal (1979):Innerandouterboundsonthe

capacity;capacityofdegradedrelaychannel

• Multiplerelays:

– Schein &Gallager – Gupta&Kumar – Xie &Kumar – Reznik,Kulkarni &Verdu – Gastpar &Vetterli – Gastpar,Kramer&Gupta

S R D

Multi-hopWirelessCommunications

Source Relay Destination d d § Directtransmission:

§ Relayedtransmission:

( )

α α α

Pd d P P

total

2 2 = =

α

Pd P

total

2 =

• Multi-hopreducespowerrequirementsandinterference
• Currenttrends:

– Onlyconsiderpathloss – Destinationonlyprocessessignalfromrelay

• Whataboutfading?Usemulti-hopfordiversity.

DiversityinMultihop

• Onesource/destination,tworelays
• Pathlossandfading
• Uncoded BPSK,bitbybitprocessing

– Relaysamplifyreceivedsignalandforward

• Direct
• Viarelays

– Totalpowerdividedequallyamongsourceandrelays

S S S S R1 R2 distance

s

R1 R2 D

time time

EffectofMultihop Diversity

2 4 6 8 10 12 10

• 6

10

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 SNR(dB) BER Directtx. Multihoptx. Diversitytx. Tx.div.3

UserCooperationDiversity

• Diversitythroughcooperationofmobiles

(Sendonaris,Erkip,Aazhang)

• Twomainideas

– Userelaystoprovidediversity – Collaborativescheme:Bothmobileshelpeachother (“partners”)

• Mobileantennasareomnidirectional

– Signalstransmittedtowardsthedestinationcanbe“overheard” atthepartner – Partnersprocessthisoverheardinformationandre-transmit towardsthedestination

• Totalresources(power,bandwidth)aresameasnon-cooperativecase

– Destinationprocessessignalsfrombothmobiles

• Spatialdiversitythroughpartner’santenna,a“virtual”

antennaarray

– Inter-userchannelisnoisy!

UserCooperation

Approach

• Informationtheory(Sendonaris,Erkip,Aazhang)

– Ageneralmodelillustratingthatcooperation resultsinthroughputanddiversitygains – Someidealizedassumptions

• Codedesign(Stefanov,Erkip)

– Morerealisticassumptions – Channelcodesthatexploitusercooperationgains

InformationTheoreticModel

1

E

2

E

1

X

1

Y

2

W

1

W Z

2

Y

1

Z Y

10

K

12

K

2

Z

21

K

20

K

2

X

User1 User2 D

• Kij :Fadingamplitudes
• Receiverstrackthefadingparameters,transmittersdon’t

CapacityAnalysis

• Assumptions

– Partnersreceiveandtransmitatthesametime

(sameassumptionasclassicalrelayofCover&ElGamal)

– Transmittershavephaseinformation:Coherent combiningispossible

• Modelissimilartomultipleaccesschannel

withgeneralizedfeedback

– DMCandGaussian(Carleial,Willems et.al.)

• Achievableregionunderfading

TransmitSignalStructure

• InformationW1 =(W10,W12)
• SignalX1 =(X10,X12,U1)

– X10:SendW10 atrateR10 todestination(D) – X12:SendW12 atrateR12 tomobile2(alsoheardatD) – U1:Cooperativesignalbasedon(W12,W12)totheBS

• Powerallocation:P1=P10+P12+PU1

AchievableRateRegionwithCooperation

} , | ) , {(

21 20 2 12 10 1 2 1

R R R R R R R R + = + =

2 , 1 E

2

=

• <

k N P K C R

k k k

2 , 1 E

2 ~ ~ 2~ ~

=

• +

< k N P K P K C R

k k k k k k k k k k

• +

< + N P K P K C R R

20 2 20 10 2 10 20 10

E

• +

+ < + + + N P P K K P K P K C R R R R

U U 2 1 20 10 2 2 20 1 2 10 21 12 20 10

2 E

2 21 20 2 1 12 10 1

,

U U

P P P P P P P P + + = + + =

Theclosureof where forsomepowerassignment

AchievableRateRegion(Symmetric)

AchievableRateRegion(Asymmetric)

ProbabilityofOutage

BenefitsofCooperation

• Higherdatarates
• Reducedoutage

Providesanincentiveforrelaying

• Increasedbatterylife
• Extendedcoverageforcellular
• Worksevenwheninter-userchannelisbadorone

userisclosertothebasestation Forbothmobiles

RealisticConstraints

• Hardtotransmit/receiveatthesametime

– Withoutcooperation – Withcooperation N N N/2 N/2 N/2 N/2

M1 M2forM1 M2 M1forM2 M1

M2

CooperationUsingTime-Sharing

(Laneman,Tse,Wornell)

• Worksforsame/separatereceivers
• Outageprobabilityanalysisforslowfading
• Partnercan

– Amplifyandforward

• Amplifiesnoise,twoleveldiversity

– Decodeandforward

• Perfectdecodingisastrictconstraint,oneleveldiversity

– Adaptivedecodeandforward

• Partnerdecodesonlywhenitcan,twoleveldiversity
• Channelcodesforcooperation?

ChannelCodingforCooperation

(Stefanov,Erkip)

• Withcooperation

N/2 N/2 N/2 N/2 M1 M2forM1 M2 M1forM2

• Tocooperate,M1onlytransmitshalfofitscodedbits.
• ThisisreceivedatM2andatthedestination.
• M2decodesM1’sinformation,re-encodesandtransmitsremaininghalf
• fthecodedbits.
• M2forwardsonlywhenithascorrectinformation(checkedbyCRC),otherwise

M1continues.

• ProtocolsimilartoHunter&Nosratinia.

BlockFadingModel

• Quasi-staticchannels

Blockfadingwhencooperationtakesplace

• Canusecodesdesignedforblockfadingchannels

(Knopp &Humblet)

– Maximizediversityandcodingadvantages

• Additionalconstraints

– Firsthalfofthecodehastobegoodinthequasi-staticinter- userchannel – Codehastobegoodinthequasi-staticchannelwhen cooperationdoesnottakeplace

N/2 N/2 M1 M2forM1

CooperativeCodingPerformanceAnalysis

• Frameerrorratewiththeabovecooperationprotocol

– Pf

C :FERforthecooperativeprotocol

– Pf

in :FERforinter-userchannel

– Pf

BF :FERfortheblockfadingchannelresultingfromcooperation

– Pf

QS :FERforthedirect(non-cooperative)channel

– SNRi:ReceivedSNRforuseriatthedestination,i=1,2 – SNRin:ReceivedSNRintheinter-userchannel – K:Codeparameters

1 2 1

) 1 ( SNR K SNR K SNR SNR K P P P P P P P P

QS in in BF QS f in f BF f QS f in f BF f in f C f

+ ≤ + ≤ + − =

CooperativeCoding(Similarusers)

CooperativeCoding(Asymmetriccase)

EffectofCooperationonRouting

– Traditionalrouting

• Onlypathlossisconsidered:ChooseM3asrelay

– Cooperativediversity

• Formedium-highSNR,M2resultsinlowererrorrate
• Goodinter-userchanneldominates

M1 M3 M2 D

RoutingwithCooperativeDiversity

OtherRelatedProjectsatPoly

• Cooperativespace-timecoding(Stefanov,

Erkip)

– Cooperativecodesformobileswithmultipleantennas – Asymmetric:Cooperationamongmobileswithdifferent numberofantennas(overlaycodes)

• Choiceofpartners:Geometryofcooperation

(Lin,Erkip,Stefanov)

• Diversityinrelayingprotocols (Yuksel,Erkip)
• Visitourwebpage:eeweb.poly.edu/~elza

References

1. A.Sendonaris,E.Erkip andB.Aazhang,“Usercooperationdiversity-partI: Systemdescription.”Toappear,IEEETransactionsonCommunications. 2. A.Sendonaris,E.Erkip andB.Aazhang,“Usercooperationdiversity-partII: Implementationaspectsandperformanceanalysis.”Toappear,IEEE TransactionsonCommunications. 3. A.Stefanov andE.Erkip,“Cooperativecodingforwirelessnetworks.”In ProceedingsofIEEEConferenceonMobileandWirelessCommunications Networks,Stockholm,Sweden,September2002. 4. A.Stefanov andE.Erkip,“Ontheperformanceanalysisofcooperativespace- timecodedsystems.”ToappearIEEEWirelessCommunicationsand NetworkingConference(WCNC2003), NewOrleans,Lousiana,March2003. 5. A.Stefanov andE.Erkip,“Cooperativespace-timecodingforwireless networks.”Toappear,2003InformationTheoryWorkshop,Paris,France,April 2003.