Ch 15 Antenas Mimo Uni

8/3/2019 Ch 15 Antenas Mimo Uni

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UNI FIEE EE-525M Antenas 2011-1

Captulo 15

EE525M

UNI

Ing. Marcial Antonio Lpez Tafur [email protected]

Antenas MIMO

Aspiraciones

Enlaces de comunicaciones inalmbricos con velocidades detransmisin cercanas a 1 Gigabit/segundo.

Proveer enlaces de alta velocidad que puedan ofrecer unabuena Calidad de Servicio (Quality of Service - QoS) (que sercuantificada matemticamente)

Aspiraciones (Matematicas) deldiseador del sistema.

Altas velocidadesde datos

Calidad

AlcanzarCapacidad del canal (C)

Minimizar la Probabilidad deError (Pe)

Temas de la vida real

Minimizar complejidad/costo deimplementacin del sistema

propuesto.Minimizar la potencia de

transmisin requeridaMinimizar en ancho de banda

(espectro de frecuencia)usado

Configuraciones de antenas

Single-Input-Single-Output (SISO) antenna system

Tericamente, la barrera del 1Gbps puede ser alcanzadausando esta configuracin si usted est autorizado a usarmucha potencia y tanto ancho de banda como necesite!Extensivas pruebas han sido hechas sobre SISO bajorestricciones de potencia y BW. Una combinacin de tcnicasde modulacin inteligente, codificacin y multiplexacin han

dado buenos resultados pero lejos de la barrera del 1Gbps.

canalFlujo de datosdel usuario

Flujo de datosdel usuario

Configuracin de antenas MIMO


.

.

1

2

MT

.

.

.

1

2

MR

.

.

.

.

.

canal

Usar multiples antenas transmisoras y multiples antenasreceptoras para un solo usuario.

Este sistema promete enormes velocidades para los datos!


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El Concepto de MIMO

MIMO:Multiple Input/Multiple OutputConsiste en equipar tanto el extremotransmisor como el receptor con mltiplesantenas y procesar adecuadamente lassenales


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MIMO

Diversidad de antenasen recepcin

Mltiples antenasen transmisin y en recepcin

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9 10

11 12


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13 14

15 16

MIMOSe procesan las seales que se van a aplicar a las

diferentes antenas tanto en el extremo transmisor comoen el receptor, de tal modo que la calidad, detrminadapor el BER, o la tasa de transmisin, se pueden mejorar

El desvanecimiento selectivo producto de mltiplestrayectorias se puede contrarrestar, utilizandocodificacin espacial-temporal

El estndar 802.16e incluye MIMO, lo mismo que el802.11n, pendiente de aprobacin

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MIMO, SMART Antenna, ST CodingEl concepto fundamental es el de beamforming , es decir,la modificacin del haz de RF por medios electrnicos, que permiteincrementar la relacin S/N al enfocar la energa en la direccindeseada, una evolucin de los arreglos de antenas de vieja data.

Estas antenas inteligentes tambin permite minimizar la radiacin en

otras direcciones, con lo que se puede disminuir la interferencia y hastautilizarlo como tcnica de multiplexaje espacial

Unidades de datos

Will use the following terms loosely andinterchangeably,

Bits (lowest level): +1 and -1 Symbols (intermediate): A group of bits Packets (highest level): Lots and lots of

symbols


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Shannons Capacity (C) Given a unit of BW (Hz), the max error-free transmission rate is

C = log 2(1+SNR) bits/s/Hz Define

R: data rate (bits/symbol)RS: symbol rate (symbols/second)

w: allotted BW (Hz) Spectral Efficiency is defined as the number of bits transmitted per

second per HzR x R S bits/s/Hz

WAs a result of filtering/signal reconstruction requirements, R S W.Hence Spectral Efficiency = R if R S = W

If I transmit data at a rate of R C, I can achieve an arbitrarily low P e

Eficiencia espectral

Spectral efficiencies of somewidely used modulationschemes

The Whole point: Given an acceptable Pe , realistic power andBW limits, MIMO Systems using smart modulation schemesprovide much higher spectral efficiencies than traditional SISO

Esquema b/s/Hz

BPSK 1

QPSK 2

16-QAM 4

64-QAM 6

Modelo del sistema MIMO

y = Hs + n

User data stream

.

.

User data stream

.

.

.

.Channel

Matrix H

s1

s2

sM

s

y1

y2

yM

yTransmitted vector Received vector

.

.

h11

h12

Where H =

h11 h21 ..hM1h12 h22 ..

hM2h1M h2M ..hMM

. . .. .

MT

MR

hij is a Complex Gaussianrandom variable that modelsfading gain between the ithtransmit and jth receiveantenna

Tipos de canales

Desvanecimiento

Fading refers to changes in signal amplitude and phase causedby the channel as it makes its way to the receiver

Define T spread to be the time at which the last reflection arrivesand T sym to be the symbol time period

Time-spread of signal

Frequency-selective Frequency-flat

Tsym

Tspread

time

freq

1/TsymOccurs for wideband signals (smallTsym)

TOUGH TO DEAL IT!

Tsym

Tspread

time

freq

1/T symOccurs for narrowband signals (large Tsym)

EASIER! Fading gain is complex Gaussian

Multipaths NOT resolvable

Matriz de canal H In addition, assume slow fading MIMO Channel Response

Taking into account slow fading, the MIMO channel impulse response is constructed as,

Time-spread

Channel Time-variance

Because of flat fading, it becomes,

a and b are transmit andreceive array factor vectorsrespectively. S is thecomplex gain that isdependant on direction anddelay. g(t) is the transmitand receive pulse shapingimpulse response

With suitable choices of array geometry and antenna element patterns,H( ) = H which is an MR x MT matrix with complex Gaussian i. i. d random variables

Accurate for NLOS rich-scattering environments, with sufficient antenna spacing attransmitter and receiver with all elements identically polarized


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Capacidad de los canalesMIMO

y = Hs + n Let the transmitted vector s be a random vector to be very general and n is normalized

noise. Let the total transmitted power available per symbol period be P. Then,

C = log 2 (IM + HQH H) b/s/Hzwhere Q = E{ss H} a nd trace(Q) < P according to our power constraint

Consider specific case when we have users transmitting at equal power over the channeland the users are uncorrelated (no feedback available). Then,

CEP = log 2 [IM + (P/M T)HHH] b/s/HzTelatar showed that this is the optimal choice for blind transmission

Foschini and Telatar both demonstrated that as M T and M R grow,

CEP = min (M T,MR) log 2 (P/MT) + constant b/s/HzNote: When feedback is available, the Waterfilling solution is yields maximum capacity but converges to equal power capacity athigh SNRs

Capacidad (cont) The capacity expression presented was over one realization of the channel.

Capacity is a random variable and has to be averaged over infinite realizationsto obtain the true ergodic capacity. Outage capacity is another metric that isused to capture this

So MIMO promises enormous rates theoretically! Can we exploit thispractically?

Criterios de diseo MIMO

MIMO Systems can provide two types of gain

Spatial Multiplexing Gain Diversity Gain

Maximize transmission rate(optimistic approach)

Use rich scattering/fading toyour advantage

Minimize Pe (conservativeapproach)

Go for Reliability / QoS etc

Combat fading

System designs are based on trying to achieve either goal or a

little of both

If only I could have both! As expected, there is a tradeoff

Diversidad Each pair of transmit-receive antennas provides a signal path

from transmitter to receiver. By sending the SAME informationthrough different paths, multiple independently-faded replicasof the data symbol can be obtained at the receiver end. Hence,more reliable reception is achieved

A diversity gain d implies that in the high SNR region, my P edecays at a rate of 1/SNR d as opposed to 1/SNR for a SISOsystem

The maximal diversity gain d max is the total number ofindependent signal paths that exist between the transmitter andreceiver

For an (M R,MT) system, the total number of signal paths is M RMT

1 d d max = MRMT The higher my diversity gain, the lower my P e

Multiplexacin espacial

y = Hs + n y = Ds + n (through SVD on H)where D is a diagonal matrix that contains the eigenvalues of HH H

Viewing the MIMO received vector in a different but equivalentway,

CEP = log 2 [IM + (P/M T)DDH] = log 2 [1 + (P/M T) i] b/s/Hz

Equivalent form tells us that an (M T,MR) MIMO channel opens upm = min (M T,MR) independent SISO channels between thetransmitter and the receiver

So, intuitively, I can send a maximum of m different informationsymbols over the channel at any given time

=

m

i 1

Sistemas prcticos

Redundancy in time

Coding rate = rc Space- time redundancy over Tsymbol periods

Spatial multiplexing gain = rs

1

2

MT

Channelcoding

Symbolmapping

Space-Time

Coding

.

.

R bits/symbol

rs : number of differentsymbols N transmittedin T symbol periods

rs = N/T

Spectral efficiency = (R*rc info bits/symbol)(rs)(Rs symbols/sec)

w

= Rrcrs bits/s/Hz assuming Rs = w

rs is the parameter that we are concerned about: 0 rs MT

** If rs = MT, we are in spatial multiplexing mode (maxtransmission rate)

**If rs 1, we are in diversity mode

Non-redundantportion of symbols


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V-BLAST Multiplexacin espacial(Vertical Bell Labs Layered Space-Time Architecture)

This is the only architecture that goes all out for maximum rate. Hope thechannel helps me out by splitting my info streams!

.

.

s1

s2

sM

s

User datastream .

.

User datastream.

.

y1

y2

yM

y

.

.

H V-BLASTProcessing

Split data into MT streams maps to symbols sendAssume receiver knows HUses old technique of ordered successive cancellation torecover signalsSensitive to estimation errors in Hrs = MT because in one symbol period, you are sending MTdifferent symbols

MT MR

V-BLAST(Resultados experimentales)

The prototype in an indoor environment was operated at a carrier frequency of1.9 GHz, and a symbol rate of 24.3 ksymbols/sec, in a bandwidth of 30 kHz withMT = 8 and M R = 12

Results shown on Block-Error-Rate Vs average SNR (at one received antennaelement); Block = 100 symbols ; 20 symbols for training

Each of the eight substreams utilized uncoded16-QAM, i.e. 4 b/symb/trans

Spec eff = (8 xmtr) ( 4 b/sym/xmtr )(24.3 ksym/s)30 kHz

= 25. 9 bps/Hz

In 30 kHz of bandwidth, I can push across 621Kbps of data!! Wirelessspectral efficiencies of this magnitude are unprecedented, and arefurthermore unattainable using traditional techniques

Receptores alternados

Can replace OSUC by other front-ends; MMSE, SUC,ML for instance

OSUC

ML

D-BLAST un poco de ambos(Diagonal Bell Labs Layered Space-Time Architecture)

In D-BLAST, the input data stream is divided into sub streams whichare coded, each of which is transmitted on different antennas timeslots in a diagonal fashion

For example, in a (2,2) system

receiver first estimates x2 (1) and thenestimates x1 (1) by treating x2 (1) asinterference and nulling it out

The estimates of x2 (1) and x1 (1) are fed to ajoint decoder to decode the first substream

After decoding the first substream, the receiver cancelsthe contribution of this substream from the received signalsand starts to decode the next substream, etc.

Here, an overhead is required to start the detection process;corresponding to the 0 symbol in the above example

Receiver complexity high

MT MR

Diversidad Esquema de Alamouti

Transmission/reception scheme easy to implement Space diversity because of antenna transmission. Time diversity

because of transmission over 2 symbol periods Consider (2, M R) system

Receiver uses combining and ML detectionrs = 1

V-BLAST SUC

Alamouti

If you are working with a (2,2)system, stick with Alamouti!

Widely used scheme: CDMA2000, WCDMA and IEEE 802.16-2004 OFDM-256

Comparaciones

Esquema EficienciaEspectral P eImplementacinComplejidad

V-BLAST ALTA ALTA BAJA

D-BLAST MODERADA MODERADA ALTA

ALAMOUTI BAJA BAJA BAJA


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Orthogonal Frequency DivisionMultiplexing (OFDM)

As the data rate increases in a multipathenvironment, the interference goes from flat fadingto frequency selective (last reflected componentarrives after symbol period). This results in heavydegradation

Most popular solution to compensate for ISI:equalizers

As we move to higher data rates (i.e.> 1 Mbps),equalizer complexity grows to level of complexitywhere the channel changes before you cancompensate for it!

Alternate solution: Multi-carrier Modulation (MCM)where channel is broken up into subbands such thatthe fading over each subchannel becomes flat thuseliminating the problem of ISI

Multi-carrier Modulation

FDMA OFDM

Efficiencia espectral del OFDM

Rs symbols/s

Rs/ 3 symbols/s

The spectral efficiency of an OFDM-(PSK/ASK) system is same as comparedto using the (PSK/ASK) system alone

Spec eff = log 2 M bits/s/Hz

However, you have successfullyconverted an ugly channel into a channelthat you can use

easy to implement

Used in IEEE 802.11A, .11G,HiperLAN, IEEE 802.16

MIMO-OFDM OFDM extends directly to MIMO channels with the IFFT/FFT and CP operations

being performed at each of the transmit and receive antennas. MIMO-OFDMdecouples the frequency-selective MIMO channel into a set of parallel MIMOchannels with the inputoutput relation for the ith (i = 0, 2,,L-1) tone,

yi = H is i + n i i = 0, 2,, L-1

IEEE 802.11 MAC (DCF Mode) As a result of the CSMA/CA with RTS/CT S MAC protocol, two issues

arise-the unfairness problem-extreme throughput degradation (ETD)

Throughtput T2 3 > Throughtput T0 1

Unfairness

Both throughtput T2 3 and throughtputT0 1 are equally affected

ETD

MIMO-Based Solutions

Use multiple transmit and receive antennas Again, MIMO provides

-increase in rate-decrease in P e (as a result of diversity, interference cancellation

abilities etc)Simply use 802.11 with MT=MR=2.VBLAST-ZF is an optionTwo data streams transmittedfrom node 0 to 1 instead of 1.Increases transmission rate.Increases overall capacity ofnetworkDoes not address unfairness andETD

MIMO-Based SolutionsMIMA-MAC Protocol

Mitigating Interference using Multiple Antennas (MIMA) MAC protocol[Tang, Park, Nettles, Texas at Austin, submitted to Proc. ACM Mobicom , Philadelphia, PA, USA on Sep. 26 Oct. 1, 2004]

Each transmitter views it as a (1,2)MIMO system.

Unfairness (SDT): node 1concentrates on node 0 andsupresses node 2. Increase inthroughput Tro 1

ETD (ODT): node 1 concentrates onnode 0 and supresses node 3 stream.node 2 concentrates on node 3 andsupresses node 0 stream. Increase inthroughput Tro 1 and Tr3 2


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Resultados de la simulacin

SDT

Unfairness

ODT

Throughputdegradation 44

UMA

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802.16e Tasas de hasta 63 Mb/s Dl,28 Mb/s Ul por sector en

un canal de 10 MHz, gracias al empleo de MIMO ysistemas de codificacin y modulacin avanzados.

QoS imbuida, adjudicacin de recursos de tiempo,frecuencia y espacio en base a cada trama

Canales de ancho de banda variable desde 1,25MHzhasta 20 MHz, en las bandas 2,3 GHz, 2,5 GHz y 3,5GHz, gracias al empleo de Scalable OFDMA(SOFDMA)

Seguridad utilizando EAP, autenticacin yencriptacin

Movilidad con latencias inferiores a 50ms Utiliza TDD inicialmente, luego FDD y HD FDD

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WiMAX Fijo

Basado en 802.16 d, estndarcompletado en 2004. Tiene buenalcance, puede transmitir an con lalnea de vista obstruida.

Las pruebas de interoperabilidad sehicieron a la frecuencia de 3,5 GHz,pero tambin existen equipos enotras bandas, como la de 5 GHz

No es muy atractivo en pasesdesarrollados donde enfrentanumerosas competidores y unmercado saturado.

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WiMAX mvil

Basado en el estndar 802.16 e, aprobado en dic.2005, permite movilidad hasta 80 km/h, pero adistancias muy reducidas del orden de unos 3 km.Inicialmente en las bandas de 2,3 y 2,5 GHz

Samsung, est demostrando la tecnologa WiBro enTurn en las olimpiadas de invierno, muchas otrasempresas estn apuntando a un mercado muyinteresante en pases desarrollados

Texas Instruments anunci un DSP de 1 GHz basadoen 802.16e

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WiMAX mvil

Airspan anunci un dispositivo USB basado en elestndar 802.16 e,. Inicialmente en las bandas de 2,3y 2,5 GHz

Samsung, est demostrando la tecnologa WiBro enTurn en las olimpiadas de invierno, muchas otrasempresas estn apuntando a un mercado muyinteresante en pases desarrollados

Texas Instruments anunci un DSP de 1 GHz basadoen 802.16e

Alcatel firm convenio con Samsung para WiBromundial


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WiMAX Movilidad

Velocidades: ~ 75 km / h Roaming entre estaciones bases Enrutamiento entre estaciones de suscritor

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OFDM/TDMA vs. OFDMA

OFDM/TDMA en 16dUn usuario a la vezMultiacceso con subcanalizacines opcional

Viable slo para fijo

frecuencia

p o t e n c

i a

Ruido

Seal

OFDMA en 16eMultiacceso consubacanalizaci es estndarIntercambio entre S/N yvelocidad Viable para CPE interiores,porttiles o mviles

frecuencia

p o t e n c

i a

Ruido

Subcanalizacin de alta potenciaPero se desperdicia espectro

Espectro desperdiciado

S/N baja yalcancelimitado

Multiacceso entiempo y

frecuenciapermite altacapacidad y

gran alcance

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Parmetros de S-OFDMA

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Incompatibilidad

Las versiones fija y mvil de WiMax no soncompatibles porque utilizan esquemas deacceso al medio diferentes, aunque ambosestn basados en OFDM

802.16d usa TDMA 802.16e usa OFDMA Se definen diferentes perfiles, que incluyen

bandas de frecuencia, mtodo de duplexing,etc.

No se descarta que algn fabricante ofrezcasistemas compatibles

6/29/2011 Pietrosemoli 53

WiBro es un estndar coreanoalineado con 802.16e

Demostrado enAgosto 2005.permite handoffa alta velocidadTres operadoresde corea pagaron100 M$ c/u por el uso

del espectro en 2,3 GHzdurante 7 aos.En Venezuela seInstalar a finales de2006

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Adjudicacin de Frecuencias paraWiBro


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Red basada en IP

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IEEE 802.20 La misin de IEEE 802.20 es desarrollar las

especificaciones de una interfaz de aire basada enpaquetes optimizada para el transporte de serviciosbasados en IP.

Especificar las capas fsicas y de control de acceso almedio en frecuencias inferiores a 3,5 GHz con tasas detransmisin efectivas por usuario de hasta 1 Mb/s avelocidades de hasta 250 km/h.

La eficiencia espectral y el nmero de usuarios activossimultneos sern significativamente mayores que losofrecidos por los sistemas celulares existentes.

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8 0 2 . 1 1 8 0 2 . 1 1 8 0 2 . 1 1 8 0 2 . 1 1 M M D S M M D S M M D S M M D S 8 0 2 . 1 6 d 8 0 2 . 1 6 d 8 0 2 . 1 6 d 8 0 2 . 1 6 d 8 0 2 . 1 6 e 8 0 2 . 1 6 e 8 0 2 . 1 6 e 8 0 2 . 1 6 e

C D M A 1 x / 1 x E V C D M A 1 x / 1 x E V C D M A 1 x / 1 x E V C D M A 1 x / 1 x E V - -- -

D O D O D O D O

W C D M A W C D M A W C D M A W C D M A

a p l i c a c i a p l i c a c i a p l i c a c i a p l i c a c i

n nn n

L A N : R e d e s

l o c a l e s

f i j a s

M A N f i j a

p a r a d a t o s y

V o I P ;

M A N f i j a p a r a

d a t o s y V o I P ;

M A N m v i l p a r a

v o z y d a t o s

W A N a l t a

v e l o c i d a d , v o z

y d a t o s

W A N a l t a

v e l o c i d a d , v o z

y d a t o s

a l c a n c e a l c a n c e a l c a n c e a l c a n c e

< 1 0 0 m N L O S

1 0 k m L O S

1 0 K m N L O S

4 0 K m L O S

P T P < 5 0 K m L O S

P M P < 1 0 K m N L O S

3 k m N L O S

8 0 0 m ~ 5 0 K m

N L O S

5 0 0 m ~ 1 0 K m

N L O S

e s p e c t r o e s p e c t r o e s p e c t r o e s p e c t r o

T D D

2 . 4 / 5 . 8 G H z

B a n d a l i b r e

F D D / T D D

2 . 5 / 3 . 5 / 5 . 8 /

1 0 . 5 G H z

F D D / T D D /

2 - 1 1 G H z

a m b a s

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2 - 6 G H z

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4 5 0 / 8 0 0 M / 1 . 9 / 2 . 1

G H z

r e g u l a d a

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2 . 1 G H z

r e g u l a d a

B W B W B W B W 2 0 M H z

3 . 5 / 7 M H z 1 . 5 - 2 0 M H z

1 . 5 - 5 M H z 1 . 2 5 M H z 5 M H z

T a s a T a s a T a s a T a s a

5 4 M b p s

( C a n a l 2 0 M H z )

< 7 5 M b p s

2 0 M H z

< 7 5 M b p s

2 0 M H z

< 1 5 M b p s

( 5 M H z )

< 2 . 4 M / 1 5 3 k b p s

d o w n l i n k / u p l i n k

< 1 4 . 4 M / 2 M b p s

( d o w n l i n k / u p l i n k )

E s t n d a r E s t n d a r E s t n d a r E s t n d a r

E s t n d a r

G l o b a l ,

T e r m i n a l e s

m u y

e c o n m i c o s

N o

e s t n d a r

C o s t o s o

E s t n d a r c o n

d i f e r e n t e s

p e r f i l e s ,

W i M a x

E s t n d a r

a p r o b a d o e n 2 0 0 5

c o n d i f e r e n t e s

p e r f i l e s , W i M a x

E s t n d a r m a d u r o ,

t e r m i n a l e s m u y

e c o n m i c o s

E s t n d a r m a d u r o ,

t e r m i n a l e s

e c o n m i c o s

Comparacin de las tecnologas inalmbricas


WWAN


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Estndares IEEE802.16 10 - 66 GHz, punto a punto

Lnea de vista,802.16a Extensin a 2-11 GHz, NLOS

(Non line of sight), Punto a Multipunto802.16d Actualizacin de 802.16 y 802.16aPerfiles

802.16e Extensin para movilidad y roaming

802.21 Handoff independiente del medio ( 802.3,802.15, 802.11, 802.16 )

802.20 Mobile Broadband Wireless Access MBWA Compite con tecnologas celulares Velocidades hasta 250 km/h An sin aprobar

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Estndares 802.16

802.16 802.16d 802.16e

Lnea de vista Casi l nea de vista(NLOS) Casi lnea de vista(NLOS)10 66 GHz 2 11 GHz 2 6 GHz32 134 Mbps 75 Mbps 15 Mbps2 5 kilmetros 5 8 km

Mx. 50 km2 5 km

Fijo Fijo Movilidadmetropolitana,Roaming

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Comparacin 802.11 802.16

Rango Optimizado para 100m Hasta 50 km

Bandas defrecuencia

Sin licencia, canales fijosde 20 MHz

Con o sin licencia,Canales de ancho variable

Eficienciaespectral 2,7 bps / Hz 5 bps / Hz

Acceso alMedio

CSMA/CA (Aleatorio)TDD

Por solicitud (determinstico)TDD o FDD

Calidad deServicio

Pendiente con el estndar802.11 e

Cuatro tipos de QoS, buen soportepara voz y video interactivo

Seguridad Limitada, WEP, WAPMejorada, 3DES, AES

EscalabilidadReduccin geomtrica delrendimiento versus nmerode usuarios

Soporte de cientos de usuarios porcanal RF


Ejemplo de 802.20: Flash OFDM de Flarion

Arquitectura distribuida totalmente IP Soporta QoS Utiliza dos canales apareados de 1,25 MHz Picos de 3,2 Mb/s DL, 900 kb/s UL Latencia de 50 ms 31 conversaciones VoIP simultneas, 126 usuarios

de datos 250 km/h, handoff (traspaso) continuo de voz y

datos

Sumario / Conclusiones

MIMO Systems are getting us closer to the1Gbps landmark (aspiration 1)

At the same time, they provide reliablecommunications (aspiration 2)

Different architectures available for use Developing efficient network protocols for

a MIMO PHY layer is an area of openresearch

66

Muchas gracias por su atencin

UNI FIEELima Per

Ch 15 Antenas Mimo Uni

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