mimo ofdm emulation

7/30/2019 MIMO OFDM Emulation

1/28

MIMOw

irelesschannelem

ulation

Ro

gerPiqueras


2/28

MIMOwirelessch

annelem

ulation

Overview:

Wirelesss

ystems

Mobilecha

nnel

OFDM

2

MIMO

IEEE802.11n

Channelm

odels

Simulation

/Emulation

Wirelessc

hannelemulatio

n

Futurework


3/28

Wireless

systems

Whywireless

systems?

3


4/28

Mobilechannel

Themobilechannelisacomplex

channel:

Multipath,scattering

Dopplerspectrum

Shadowing

4


5/28

Mobilechannel

MultipathFrequencyselectiv

echannel

Timedomain

responseofthechannelconsistsonvariousrayshavingaco

mplex

Gaussiandistribution

Channelfrequencyresponseisno

tflat

Coherencebandwidth

5


6/28

Mobilechannel

Dopplerspectrum

/fading

Timevar

yingchannel

Changeinthe

carrierfrequencyduetorelativemovementbetweenthemobileand

the

BS

fDmax=v/C

oherencetime1/fDma

x

Fadingchanne

l

severechangesin

therecievedsignalpo

wereverycoherencet

ime

6

Howcanweovercomeormitigateth

enegativeeffectsofthemobilechannel?


7/28

Mobilechannel

Newtechniquestohandlefrequencyselectivityand

fadingchan

nels,

suchas...

OFDM

MIMO

7


8/28

Orthogona

lFrequenc

y-Division

Multiplexin

g

(OFDM)

OFDMconvertsawidebandsignal

intomultiplenarrowbandsignals

placedsidebysideinthefrequency

domain.

Partofthesignalismodulatedin

eachsubchannelandtransmitted

8

throughanalm

ostflatfadingchannel.

Ifoneofthesu

bchannelsisaffected

byaseverefading,simplynothingis

transmittedinthatsubchannel

Thisresultsinastrongresilency

againstfrequencyselectivechannels


9/28

MultipleIn

put-Multi

pleOutpu

t(MIMO)

Traditionallymultipleantennasplaced

atthereceiverto

applydiversity

Spatialdiversity(eachantennawill

seeadifferent

andindependent

channel)

Significantimm

unitytofading

Resultsimprov

easthenumberof

9

anennasncre

ase

Evenbetterresultsareachieved

whenmultipleant

ennasplacedalso

atthetransmitter

Totalavailabletransmitpowerissplit

uniformlyacrosstransmitantennas

Finiteoptimum

numberoftxantennas


10/28

IEEE802

.11n

OFDM

Resilencyaganistfre

quencyselective

channels

MIMO

Res

ilencyagainstfad

ingchannels

Mobilechanne

lisafadingand

frequencyselectivechannel

MIMO+OF

DMisagoodsolutionformobilecom

munications

1

0

IEEE802.1

1nstandard


11/28

IEEE802

.11n

IEEE802.1

1nstandard

WLANstandardimprovingthePhysicalLay

erand

MACLayerofthe

traditionalWLANs

IndoorMIMO/OFDMsystem

Range~

100met

ers

Maximumbitrate:600Mbps(3x3antennas)(typical

bitrate74Mbps)

Carrierfrequency

:2.4

or5GHz

1

1

Fullcompatibilityw

ithcurrentWLANs

Projecttodevelope

IEEE802.1

1nbeganin2003

Juststartingtobeinacommercialstage

Intelhasstartedtoadd802.1

1ninsomeo

fitsproducts

Forfuturecommerc

ialization,manytestsh

avetobedone

WirelesschannelonOF

DM-MIMOsystemssimulation


12/28

Channel

models

MxNMIMOchan

nelisequivalenttoM

Nimpulseresponse

s,

eachrepresenting

a

subchannel

ModelaSISOch

annel,thenextendtoMIMO(repeatMNtimesplusaddingoth

er

artifacts,

suchas

spatialcorrealtionbetweenantennaelem

ents...)

1

2


13/28

Channel

models

StatisticalModel

forIndoorMultipathPropagation(A.

Sale

h,

R.

Valenzuela)

Channelmeas

urement

1

3

Results(Powe

rDelayProfile)


14/28

Channel

models

Wirelessindoorch

annelmodeling

Multipath:cluste

ringofarrivingrays(angularclusters)

Channelmodele

dasanFIR

1

4

TX

v

RX

ArrivalTimes

t

Doubleexponentialdecayoftheimpulses(

clustersandrayswithina

cluster)


15/28

Channel

models

Clusteringofr

ays

Dopplerspectrum/Fading

Shadowfading

Pathlossmod

el

Freespacelo

ss(LFS

)uptoabrea

kpointdistance(dBP

)

1

5

Slopeof3.5

afterdBP

Addingthesee

lementstogether

SISOchanne

lmodel


16/28

Channel

models

Setofchannelm

odelsapplicabletoindoorWLAN

systems

1

6

Channelmode

lisaFIR

Exte

ndtoMIMO(matrixofMxNFIRs)

OtherMIMOchannelartifactsshouldbeadded


17/28

Channel

models(

MIMO)

MIMOmatrixformulation(foreachtap)

1

7

P

owerof

eachtap

RiceanK-factor(0

forNLOSt

aps)

LOS

[S](constantRice

Steeringmatrix)

NLOS

[X](timeva

rying

Rayleigh

and

Correlationmatrix)


18/28

Channel

models(

MIMO)

LOS

RiceS

teeringmatrix

Differenceinp

hasebetweenthera

ysarriving/leavingth

etxandrxantenna

elements

Constantmatrix

Onlyfirsttap(

LOS)

1

8

T

Tx

Tx

Tx

Tx

Tx

Rx

Rx

R

x

Rx

Rx

AoD

n

d

j

AoD

d

j

AoA

n

dj

AoA

d

j

S

=

]}

)1

sin[(

2

exp{

...

)}

sin(

2

exp{

1

]}

)1

sin[(

2

exp{

...

)}

sin(

2

exp{

1

]

[

Rxantennaelements

Txantennaelements

MxNmatrix


19/28

Channel

models(

MIMO)

NLOS

RayleighandCorrelationm

atrix(I)

Correlationbetweentxantennasand

rxantennas([Rtx]and

[Rrx]matrixes)

Fromanten

naspacingstotheoreticalcapacities(L.

Schumacher,K.

Pedersen,

P.

Morgensen)

PowerAngularSpectrum(PAS):Uniform,

GaussianorLaplacia

n

1

9

d

A

A

PAS

e

j

i

kd

j

ij

)

(

)

(

)

(

)

sin(

2

=

Uniformline

arantennaarray

corre

lationofrx/txsignalsbetw

eenantennaelements

Spacingbetween

antennas

Elementelectromagnetic

pattern


20/28

Channel

models(

MIMO)

NLOS


atrix(II)

Correlationbetweentxantennasand

rxantennas([Rtx]and

[Rrx]matrixes)

Generation

ofthecorrelationmatrixes

2

0

Example:4x4MIMOchannel


21/28

Channel

models(

MIMO)

NLOS


atrix(III)

Rayleighfading

Generation

ofaRayleighvector

ShapingofthevectorwithaFIR(order=7)togeneratetheadequateDopplerspectrum

Combinationo

ftheCorrelationandth

eRayleighfading

Kronecke

rroduct

Raleihvector

2

1

Addingotherar

tifacts

Shadowfading

Dopplercom

ponentduetoamoving

vehicle(optional)

Dopplercom

ponentsdueto

fluorescentlights(optional)

Bellshaped

oppler

spectrumw

itha

200HzDoppler

component


22/28

Simulatio

n/Emula

tion

IEEE802.1

1nstill

intestingstage(alread

ybeingimplementedb

yIntel)

Performanceofad

vancedwirelesstechniquessuchasMIMOis

highlydependantonth

e

channel

Necessityofrealisingcredibletestsandvalidationsunderrealisticconditions

Inefficiencyofre

almeasurements(moving

therxalongaspecificindoorlocation)

2

2

D.P.McNam

ara,M.A.Beach,P.N.

Fletcher,P.Karlsson,Initial

InvestigationofMIMOChannelsin

Indo

orEnviroments

Necessityofreplicatingthe

wirelesschannelin

thelaboratory


23/28

Simulatio

n/Emula

tion

Wirelesschannelreplicationinthelaboratory

Traditionaloption

Simulation

Easysolution

,but...

2

3

MIMOsystems

Thechannelmatrix[H]hastobegeneratedatleastevery

coherencetime!

Amorerealisticsimulationwillr

equire

manysamplespercoherencetime

Hugecomput

ationalcomplexity(th

atevengrowsquadra

ticallywiththenumberof

txandrxanten

nas)

Simu

lationisnotenoug

h

Realtimeemulation


24/28

Wireless

channel

emulatio

n

Channelemulato

r

Aplatformthatreplicatesanactualwirelesschannelandalli

tsartifactsinthelab

enviroment

Duetothelarg

eamountofreal-timeoperationsdemanded,

usuallyimplementedas

highspeeddedicatedhardwareplatfo

rms

Traditionalapproa

ch

Calculationof

PC

2

4

complianttothe

PDP

Emulationcore

performsconvolutionin

timeoverthein

comingdataandthe

channelrespon

se

Replicateforthenumberofsubchannels

(MxN)

Computationsa

reafuntionofthechannel

responselength

andincrease

quadraticallywithMandN

canne

matricesasa

functionof

channel

profile

Emulation

processin

realtime

Hard-

ware

Download

Channelprofile

DBBsignal

Emulatedbase-band

outputsignal


25/28

Wireless

channel

emulatio

n

Newscalablesolutions

Frequenc

ydomainchannele

mulation

Areal-timewirele

sschannelemulatorforMIMOsystems(

H.

Eslami,A.

Eltawil)

Generatethefrequencyresponsefor

eachsubchannel(Hij(f

))

Onesample

ofthechannelstateeverycoherencetime

Foraccurateemulations,

multiplesam

plescanbegeneratedeverycoherencetime

1FFT/IFFTpereachtx/rxelement(M

FFT,

NIFFT)asoposetooneFIRpereach

subchannel

2

5

Emulatorcore

isasingle

multiplierforeachsubchannel


26/28

Wireless

channel

emulatio

n

Improvements

Eachextrasub

-channelisonlyana

dditionalmultiplier

Lesscomputationalcomplexity

Scalable(nochangesneededifthe

lengthofthechannelFIRvaries)

2

6

,

4FFTengines

attheinputoftheem

ulator

16multipliers(1pereachsubchann

el)

4IFFTengines

attheoutputoftheemulator


27/28

Wireless

channel

emulatio

n

Someresults...

FPGAimplementationofthetimedom

ainemulatorvsthefrequencydomainemula

tor

2

7


28/28

Futurework

Optimizeand

reducecompu

tationalcomplexity

Hybridtime/frequencychanne

lemulator

2

8

...

mimo ofdm emulation

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