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MIMOw
irelesschannelem
ulation
Ro
gerPiqueras
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MIMOwirelessch
annelem
ulation
Overview:
Wirelesss
ystems
Mobilecha
nnel
OFDM
2
MIMO
IEEE802.11n
Channelm
odels
Simulation
/Emulation
Wirelessc
hannelemulatio
n
Futurework
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Wireless
systems
Whywireless
systems?
3
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Mobilechannel
Themobilechannelisacomplex
channel:
Multipath,scattering
Dopplerspectrum
Shadowing
4
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Mobilechannel
MultipathFrequencyselectiv
echannel
Timedomain
responseofthechannelconsistsonvariousrayshavingaco
mplex
Gaussiandistribution
Channelfrequencyresponseisno
tflat
Coherencebandwidth
5
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Mobilechannel
Dopplerspectrum
/fading
Timevar
yingchannel
Changeinthe
carrierfrequencyduetorelativemovementbetweenthemobileand
the
BS
fDmax=v/C
oherencetime1/fDma
x
Fadingchanne
l
severechangesin
therecievedsignalpo
wereverycoherencet
ime
6
Howcanweovercomeormitigateth
enegativeeffectsofthemobilechannel?
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Mobilechannel
Newtechniquestohandlefrequencyselectivityand
fadingchan
nels,
suchas...
OFDM
MIMO
7
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Orthogona
lFrequenc
y-Division
Multiplexin
g
(OFDM)
OFDMconvertsawidebandsignal
intomultiplenarrowbandsignals
placedsidebysideinthefrequency
domain.
Partofthesignalismodulatedin
eachsubchannelandtransmitted
8
throughanalm
ostflatfadingchannel.
Ifoneofthesu
bchannelsisaffected
byaseverefading,simplynothingis
transmittedinthatsubchannel
Thisresultsinastrongresilency
againstfrequencyselectivechannels
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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
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IEEE802
.11n
OFDM
Resilencyaganistfre
quencyselective
channels
MIMO
Res
ilencyagainstfad
ingchannels
Mobilechanne
lisafadingand
frequencyselectivechannel
MIMO+OF
DMisagoodsolutionformobilecom
munications
1
0
IEEE802.1
1nstandard
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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
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Channel
models
MxNMIMOchan
nelisequivalenttoM
Nimpulseresponse
s,
eachrepresenting
a
subchannel
ModelaSISOch
annel,thenextendtoMIMO(repeatMNtimesplusaddingoth
er
artifacts,
suchas
spatialcorrealtionbetweenantennaelem
ents...)
1
2
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Channel
models
StatisticalModel
forIndoorMultipathPropagation(A.
Sale
h,
R.
Valenzuela)
Channelmeas
urement
1
3
Results(Powe
rDelayProfile)
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Channel
models
Wirelessindoorch
annelmodeling
Multipath:cluste
ringofarrivingrays(angularclusters)
Channelmodele
dasanFIR
1
4
TX
v
RX
ArrivalTimes
t
Doubleexponentialdecayoftheimpulses(
clustersandrayswithina
cluster)
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Channel
models
Clusteringofr
ays
Dopplerspectrum/Fading
Shadowfading
Pathlossmod
el
Freespacelo
ss(LFS
)uptoabrea
kpointdistance(dBP
)
1
5
Slopeof3.5
afterdBP
Addingthesee
lementstogether
SISOchanne
lmodel
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Channel
models
Setofchannelm
odelsapplicabletoindoorWLAN
systems
1
6
Channelmode
lisaFIR
Exte
ndtoMIMO(matrixofMxNFIRs)
OtherMIMOchannelartifactsshouldbeadded
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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)
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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
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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
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Channel
models(
MIMO)
NLOS
RayleighandCorrelationm
atrix(II)
Correlationbetweentxantennasand
rxantennas([Rtx]and
[Rrx]matrixes)
Generation
ofthecorrelationmatrixes
2
0
Example:4x4MIMOchannel
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Channel
models(
MIMO)
NLOS
RayleighandCorrelationm
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
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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
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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
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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
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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
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Wireless
channel
emulatio
n
Improvements
Eachextrasub
-channelisonlyana
dditionalmultiplier
Lesscomputationalcomplexity
Scalable(nochangesneededifthe
lengthofthechannelFIRvaries)
2
6
,
4FFTengines
attheinputoftheem
ulator
16multipliers(1pereachsubchann
el)
4IFFTengines
attheoutputoftheemulator
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Wireless
channel
emulatio
n
Someresults...
FPGAimplementationofthetimedom
ainemulatorvsthefrequencydomainemula
tor
2
7
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Futurework
Optimizeand
reducecompu
tationalcomplexity
Hybridtime/frequencychanne
lemulator
2
8
...