MIM

O w

irele

ss c

hann

el e

mul

atio

n

Rog

er P

ique

ras

MIMO wireless channel emulation

�O

verv

iew

:

�W

irele

ss s

yste

ms

�M

obile

cha

nnel

�O

FD

M

MIM

O

2

�M

IMO

�IE

EE

802

.11n

�C

hann

el m

odel

s

�S

imul

atio

n/E

mul

atio

n

�W

irele

ss c

hann

el e

mul

atio

n

�F

utur

e w

ork

Wireless system

s

�W

hy w

irele

ss s

yste

ms?

3

Mobile channel

�T

he m

obile

cha

nnel

is a

com

plex

chan

nel:

�M

ultip

ath,

sca

tterin

g

�D

oppl

er s

pect

rum

�S

hado

win

g

4

Mobile channel

�M

ultip

ath �

Fre

quen

cy s

elec

tive

chan

nel

�T

ime

dom

ain

resp

onse

of t

he c

hann

el c

onsi

sts

on v

ario

us r

ays

havi

ng a

com

plex

Gau

ssia

n di

strib

utio

n

�C

hann

el fr

eque

ncy

resp

onse

is n

ot fl

at

�C

oher

ence

ban

dwid

th

5

Mobile channel

�D

oppl

er s

pect

rum

/fadi

ng �

Tim

e va

ryin

g ch

anne

l

�C

hang

e in

the

carr

ier

freq

uenc

y du

e to

rel

ativ

e m

ovem

ent

betw

een

the

mob

ile a

nd t

he

BS

�f D

max

=v/

λ�

Coh

eren

ce t

ime≈

1/f D

max

�F

adin

g ch

anne

l �se

vere

cha

nges

in th

e re

ciev

ed s

igna

l pow

er e

very

coh

eren

ce t

ime

6

How can we overcome or mitigate the negative effects of the mobile channel?

Mobile channel

�N

ew te

chni

ques

to h

andl

e fr

eque

ncy

sele

ctiv

ity a

nd

fadi

ng c

hann

els,

suc

h as

...

�O

FD

M

�M

IMO

7

�M

IMO

Orthogonal Frequency-Division Multiplexing

(OFDM)

�O

FD

M c

onve

rts

a w

ideb

and

sign

al

into

mul

tiple

nar

row

band

sig

nals

plac

ed s

ide

by s

ide

in th

e fr

eque

ncy

dom

ain.

�P

art o

f the

sig

nal i

s m

odul

ated

in

each

sub

chan

nel a

nd tr

ansm

itted

8

each

sub

chan

nel a

nd tr

ansm

itted

thro

ugh

an a

lmos

t fla

t fad

ing

chan

nel.

�If

one

of th

e su

bcha

nnel

s is

affe

cted

by a

sev

ere

fadi

ng,

sim

ply

noth

ing

is

tran

smitt

ed in

that

sub

chan

nel

�T

his

resu

lts in

a s

tron

g re

sile

ncy

agai

nst f

requ

ency

sel

ectiv

e ch

anne

ls

Multiple Input-Multiple Output (MIMO)

�T

radi

tiona

lly m

ultip

le a

nten

nas

plac

ed

at th

e re

ceiv

er to

app

ly d

iver

sity

�S

patia

l div

ersi

ty (

each

ant

enna

will

see

a di

ffere

nt a

nd in

depe

nden

t

chan

nel)

�S

igni

fican

t im

mun

ity to

fadi

ng

�R

esul

ts im

prov

e as

the

num

ber

of

ante

nnas

incr

ease

9

ante

nnas

incr

ease

�E

ven

bette

r re

sults

are

ach

ieve

d

whe

n m

ultip

le a

nten

nas

plac

ed a

lso

at th

e tr

ansm

itter

�To

tal a

vaila

ble

tran

smit

pow

er is

spl

it

unifo

rmly

acr

oss

tran

smit

ante

nnas

�F

inite

opt

imum

num

ber

of tx

ant

enna

s

IEEE 802.11n

�O

FD

M �

Res

ilenc

y ag

anis

t fr

eque

ncy

sele

ctiv

e ch

anne

ls

�M

IMO

�R

esile

ncy

agai

nst

fadi

ng c

hann

els

�M

obile

cha

nnel

is a

fadi

ng a

nd f

requ

ency

sel

ectiv

e ch

anne

l

MIMO+OFDM is a good solution for mobile communications

10

�IE

EE

802

.11n

sta

ndar

d

IEEE 802.11n

�IE

EE

802

.11n

sta

ndar

d

�W

LAN

sta

ndar

d im

prov

ing

the

Phy

sica

l Lay

er a

nd

MA

C L

ayer

of t

he tr

aditi

onal

WLA

N’s

�In

door

MIM

O/O

FD

M s

yste

m

�R

ange

~ 1

00 m

eter

s

�M

axim

um b

it ra

te: 6

00M

bps

(3x3

ant

enna

s) (

typi

cal

bit r

ate

74 M

bps)

�C

arrie

r fr

eque

ncy:

2.4

or

5 G

Hz

Ful

l com

patib

ility

with

cur

rent

WLA

Ns

11

�F

ull c

ompa

tibili

tyw

ith c

urre

nt W

LAN

s

�P

roje

ct to

dev

elop

e IE

EE

802

.11n

beg

an in

200

3

�Ju

st s

tart

ing

to b

e in

a c

omm

erci

al s

tage

�In

tel h

as s

tart

ed to

add

802

.11n

in s

ome

of it

s pr

oduc

ts

�F

or fu

ture

com

mer

cial

izat

ion,

man

y te

sts

have

to b

e do

ne

Wireless channel on OFDM-MIMO systems simulation

Channel models

�M

xN M

IMO

cha

nnel

is e

quiv

alen

t to

MN

impu

lse

resp

onse

s, e

ach

repr

esen

ting

a

subc

hann

el

�M

odel

a S

ISO

cha

nnel

, the

n ex

tend

to M

IMO

(re

peat

MN

tim

es p

lus

addi

ng o

ther

artif

acts

, suc

h as

spa

tial c

orre

altio

n be

twee

n an

tenn

a el

emen

ts...

)

12

Channel models

�S

tatis

tical

Mod

el fo

r In

door

Mul

tipat

h P

ropa

gatio

n (A

. Sal

eh, R

. Val

enzu

ela)

�C

hann

el m

easu

rem

ent

Res

ults

(P

ower

Del

ay P

rofil

e)

13

�R

esul

ts (

Pow

er D

elay

Pro

file)

Channel models

�W

irele

ss in

door

cha

nnel

mod

elin

g

�M

ultip

ath:

clu

ster

ing

of a

rriv

ing

rays

(an

gula

r cl

uste

rs)

�C

hann

el m

odel

ed a

s an

FIR

14

TX

v

RX

Arrival Tim

es

t

�D

oubl

e ex

pone

ntia

l dec

ay o

f the

impu

lses

(cl

uste

rs a

nd r

ays

with

in a

clu

ster

)

Channel models

�C

lust

erin

g of

ray

s

�D

oppl

er s

pect

rum

/Fad

ing

�S

hado

w f

adin

g

�P

ath

loss

mod

el

�F

ree

spac

e lo

ss (

L FS)

up to

a b

reak

poin

t dis

tanc

e (d

BP)

15

FS

BP

�S

lope

of 3

.5 a

fter

d BP

�A

ddin

g th

ese

elem

ents

tog

ethe

r �

SIS

O c

hann

el m

odel

Channel models

�S

et o

f cha

nnel

mod

els

appl

icab

le t

o in

door

WLA

N s

yste

ms

16

�C

hann

el m

odel

is a

FIR

�E

xten

d to

MIM

O (

mat

rix o

f MxN

FIR

s)

�O

ther

MIM

O c

hann

el a

rtifa

cts

shou

ld b

e ad

ded

Channel models (MIMO)

�M

IMO

mat

rix fo

rmul

atio

n (f

or e

ach

tap)

17

Power of

each tapRicean K-factor (0

for NLOS taps)

LOS

[S] (constantRice

Steering matrix)

NLOS

[X] (time varying

Rayleighand

Correlationmatrix)

Channel models (MIMO)

�LO

S �

Ric

e S

teer

ing

mat

rix

�D

iffer

ence

in p

hase

bet

wee

n th

e ra

ys a

rriv

ing/

leav

ing

the

tx a

nd r

x an

tenn

a

elem

ents

�C

onst

ant m

atrix

�O

nly

first

tap

(LO

S)

18

T

Tx

Tx

Tx

Tx

Tx

Rx

Rx

Rx

Rx

Rx

AoD

nd

j

AoD

dj

AoA

nd

j

AoA

dj

S

−

−

=

]})1

sin[(

2exp{

...

)}sin(

2exp{

1

·

]})1

sin[(

2exp{

...

)}sin(

2exp{

1

][

λπ

λπ

λπ

λπ

Rx antenna elements

Tx antenna elements

MxN matrix

Channel models (MIMO)

�N

LOS

�R

ayle

igh

and

Cor

rela

tion

mat

rix (

I)

�C

orre

latio

n be

twee

n tx

ant

enna

s an

d rx

ant

enna

s ([

Rtx

] and

[R

rx] m

atrix

es)

�F

rom

ant

enna

spa

cing

s to

theo

retic

al c

apac

ities

(L.

Sch

umac

her,

K. P

eder

sen,

P. M

orge

nsen

)

�P

ower

Ang

ular

Spe

ctru

m (

PA

S):

Uni

form

, Gau

ssia

n or

Lap

laci

an

19

θθ

θθ

ρπ π

θλπ

dA

APAS

ej

i

kdj

ij)

()·

()·

(·)

·sin(

2

∫ −

=

�U

nifo

rm li

near

ant

enna

arr

ay �

corr

elat

ion

of r

x/tx

sig

nals

bet

wee

n an

tenn

a el

emen

ts

Spacing between

antennas

Element electromagnetic

pattern

Channel models (MIMO)

�N

LOS

�R

ayle

igh

and

Cor

rela

tion

mat

rix (

II)

�C

orre

latio

n be

twee

n tx

ant

enna

s an

d rx

ant

enna

s ([

Rtx

] and

[R

rx] m

atrix

es)

�G

ener

atio

n of

the

corr

elat

ion

mat

rixes

20

Example: 4x4 MIMO channel

Channel models (MIMO)

�N

LOS

�R

ayle

igh

and

Cor

rela

tion

mat

rix (

III)

�R

ayle

igh

fadi

ng

�G

ener

atio

n of

a R

ayle

igh

vect

or

�S

hapi

ng o

f the

vec

tor

with

a F

IR (

orde

r=7)

to g

ener

ate

the

adeq

uate

Dop

pler

spe

ctru

m

�C

ombi

natio

n of

the

Cor

rela

tion

and

the

Ray

leig

h fa

ding

Kronecker product

Rayleigh vector

21

Kronecker product

Rayleigh vector

�A

ddin

g ot

her

artif

acts

�S

hado

w fa

ding

�D

oppl

er c

ompo

nent

due

to a

mov

ing

vehi

cle

(opt

iona

l)

�D

oppl

er c

ompo

nent

s du

e to

fluor

esce

nt li

ghts

(op

tiona

l)

Bell shape doppler

spectrum with a

200Hz Doppler

component

Simulation/Emulation

�IE

EE

802

.11n

stil

l in

test

ing

stag

e (a

lread

y be

ing

impl

emen

ted

by In

tel)

�P

erfo

rman

ce o

f adv

ance

d w

irele

ss te

chni

ques

suc

h as

MIM

O is

hig

hly

depe

ndan

t on

the

chan

nel

�N

eces

sity

of r

ealis

ing

cred

ible

test

s an

d va

lidat

ions

und

er r

ealis

tic c

ondi

tions

�In

effic

ienc

y of

rea

l mea

sure

men

ts (

mov

ing

the

rx a

long

a s

peci

fic in

door

loca

tion)

22

D.P. McNamara, M.A. Beach, P.N.

Fletcher, P. Karlsson, Initial

Investigation of MIMO Channels in

Indoor Enviroments

Necessity of replicating the wireless channel in the laboratory

Simulation/Emulation

�W

irele

ss c

hann

el r

eplic

atio

n in

the

labo

rato

ry

�T

radi

tiona

l opt

ion �

Sim

ulat

ion

�“E

asy”

sol

utio

n, b

ut...

23

�M

IMO

sys

tem

s �

The

cha

nnel

mat

rix [H

] has

to b

e ge

nera

ted

at le

ast

ever

y

cohe

renc

e tim

e!

�A

mor

e re

alis

tic s

imul

atio

n w

ill r

equi

re m

any

sam

ples

per

coh

eren

ce t

ime

�Huge computational complexity

(tha

t eve

n grows quadratically

with

the

num

ber

of

tx a

nd r

x an

tenn

as)

Simulation is not enough �

Real time emulation

Wireless channel emulation

�C

hann

el e

mul

ator

�A

pla

tform

tha

t rep

licat

es a

n ac

tual

wire

less

cha

nnel

and

all

its a

rtifa

cts

in th

e la

b

envi

rom

ent

�D

ue to

the

larg

e am

ount

of r

eal-t

ime

oper

atio

ns d

eman

ded,

usu

ally

impl

emen

ted

as

high

spe

ed d

edic

ated

har

dwar

e pl

atfo

rms

�T

radi

tiona

l app

roac

h

�R

epre

sent

the

chan

nel a

s a

FIR

filte

r Calculation of

channel

PC

24

�R

epre

sent

the

chan

nel a

s a

FIR

filte

r

com

plia

nt to

the

PD

P

�E

mul

atio

n co

re p

erfo

rms

conv

olut

ion

in

time

over

the

inco

min

g da

ta a

nd t

he

chan

nel r

espo

nse

�R

eplic

ate

for

the

num

ber

of s

ubch

anne

ls

(MxN

)

�C

ompu

tatio

ns a

re a

funt

ion

of th

e ch

anne

l

resp

onse

leng

th a

nd in

crea

se

quad

ratic

ally

with

M a

nd N

channel

matrices as a

function of

channel

profile

Emulation

process in

real tim

e

Hard-

ware

Download

Channel profile

DBB signal

Emulated base-band

output signal

Wireless channel emulation

�N

ew s

cala

ble

solu

tions

�Frequency domain channel emulation

�A

rea

l-tim

e w

irele

ss c

hann

el e

mul

ator

for

MIM

O s

yste

ms

(H. E

slam

i, A

. Elta

wil)

�G

ener

ate

the

freq

uenc

y re

spon

se f

or e

ach

subc

hann

el (

Hij(

f))

�O

ne s

ampl

e of

the

chan

nel s

tate

eve

ry c

oher

ence

tim

e

�F

or a

ccur

ate

emul

atio

ns, m

ultip

le s

ampl

es c

an b

e ge

nera

ted

ever

y co

here

nce

time

�1

FF

T/IF

FT

per

eac

h tx

/rx

elem

ent

(M F

FT,

N IF

FT

) as

opo

se t

o on

e F

IR p

er e

ach

subc

hann

el

25

subc

hann

el

�E

mul

ator

cor

e is

a s

ingl

e

mul

tiplie

r fo

r ea

ch s

ubch

anne

l

Wireless channel emulation

�Im

prov

emen

ts

�E

ach

extr

a su

b-ch

anne

l is

only

an

addi

tiona

l mul

tiplie

r

�Le

ss c

ompu

tatio

nal c

ompl

exity

�S

cala

ble

(no

chan

ges

need

ed if

the

leng

th o

f the

cha

nnel

FIR

var

ies)

�F

or e

xam

ple,

for

a 4

x4 M

IMO

sys

tem

26

�F

or e

xam

ple,

for

a 4

x4 M

IMO

sys

tem

�4

FF

T e

ngin

es a

t the

inpu

t of t

he e

mul

ator

�16

mul

tiplie

rs (

1 pe

r ea

ch s

ubch

anne

l)

�4

IFF

T e

ngin

es a

t the

out

put o

f the

em

ulat

or

Wireless channel emulation

�S

ome

resu

lts...

�F

PG

A im

plem

enta

tion

of th

e tim

e do

mai

n em

ulat

or v

s th

e fr

eque

ncy

dom

ain

emul

ator

27

Future work

�O

ptim

ize

and

redu

ce c

ompu

tatio

nal c

ompl

exity

�H

ybrid

tim

e/fr

eque

ncy

chan

nel e

mul

ator

�...

28

�...