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1(27)M. Juntti: Multicarrier Research © Centre for Wireless Communications, University of Oulu

CWC Prof. Markku Juntti

Zexian (Frank) Li, Marian Codreanu, Mikko Vehkaperä, Djordje Tujkovic, Matti Latva-ahoCentre for Wireless Communications

University of Oulu, Finland

FUTURA Workshop17 October, 2003

4G Research in FUTURA: Multicarrier Concepts

Centre for Wireless Communications tel. +358 8 553 2834P.O. Box 4500 fax +358 8 553 2845FIN-90014 University of Oulu [email protected] http://www.cwc.oulu.fi/


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Outline

■ Background

■ 4G research roadmap

■ 4G objective

■ MIMO-MC-CDMA Research

■ Adaptive MIMO-OFDM Research

■ Conclusions


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Background

■ Basic research point of view: 3G systems are “ready”.● Enhancement are still actively studied also in CWC Oulu.● Several more practically oriented research problems still exist

– consultation also possible.

! The main emphasis in wireless systems research is now on beyond 3G (B3G) or 4G techniques.

■ There is both need and time for basic research as well as applied studies in parallel.

● A unique chance to think before the system must be ready.● Basic research and feasibility study/considerations as well as

hardware demonstrations must go hand-in-hand.

■ Important current research theme globally.


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4G in CWC Research Strategy

Res

earc

h A

reas

Application Areas

Application Knowledge

Tech

nolo

gy K

now

ledg

e

Finnish Academy and long-term TEKES projects

EU, TEKES, industry and military projects

Tranceiver Techniques

Physical Layer Techniques

Wireless Networks

4G

Successful application oriented research needs strong basic research.


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4G Research Roadmap

-02 -10-06 -08 -12-04

FUTURA

4G research

L1 research

Networking research

6 NET

6 HOP

L1 basic solution

WINNER

L1 parameter selectionalgorithm selectionnetwork basic solution

4G system optimization5G system research

FUTURA II FUTURA III


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4G Laboratory

■ People, equipment and long term projects.

■ Focus on key enabling technologies of 4G systems and link level and implementation issues.

■ Main projects:● MIMO channel measurement and modelling● Investigation and implementation of advanced signal processing

algorithms● Multi-cell system simulation.


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4G Objective

4 >> 3

! 4G must be clearly more than 3G in terms of● services● applications● technology.

! 4G is not:● 3G + HSDPA + HSUPA ( = 3.5G ?) < 4G● 3G + WLAN < 4G● 3G + HSDPA + HSUPA + WLAN < 4G.


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Physical Layer

■ Carrier frequency: ~5 GHz.

■ Channel bandwidth / operator: 50 MHz.

■ Target data rate 100 … 1000 Mbits/s.

! High bandwidth efficiency (2 … 20 bits/s/Hz) needed.

■ Large bandwidth and high carrier frequency.

! Channel is extremely frequency-selective.

■ Multiplexing options: single-carrier (SC), multicarrier(MC) (including orthogonal frequency-division multiplexing (OFDM)).

■ Multiaccess options: TDMA, CDMA.

■ Duplexing options: FDD, TDD.


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Implications of Frequency-Selectivity

■ The number of separable multipath components is large.

■ The data rate is high.

! Intersymbol interference (ISI) is potentially a huge limiting factor for the performance.

● No. of rake fingers blows up in DS-CDMA.

■ Possible solutions:● efficient equalizer for a SC system

– conventionally complex● ISI resistant transmission schemes (MC and OFDM)

– stringent requirements for RF parts.


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Air Interface Options

■ Multicarrier● MC-CDMA

– user orthogonality required ! mainly downlink option● OFDM-TDMA● peak-to-average power ratio (PAPR) limitations● sensitive to frequency errors!mainly candidate for downlink.

■ Single-carrier with an equalizer● efficient equalizers potentially complex● novel turbo processing techniques ● frequency-domain equalization

– dual of multicarrier


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Implications of High Bandwidth Efficiency Requirement

■ Bandwidth efficiencies of the order 2 … 20 bits/s/Hz require novel transmission techniques.

!Multiple-input multiple-output (MIMO) system with antennas is necessary.

● A MIMO system with N transmit and receive antennas has N-fold capacity compared to single-input single-output (SISO) system.

■ Adaptive radio links (ARL)● Link adaptation can potentially increase the total system

throughput.● Requires co-operation between Layers 1–3.


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MIMO Research Roadmap

Application scenarios

Capacity Estimat.

MIMOchannels

Modelling

ST process with CSI@Tx ST coding

AdaptiveST cod

ST bit loading

SfC/MMSEBLAST

GroupWise

ArrProc

STblock,trellis

ST turbo

LayeredST arch.

MC-CDMAWCDMA OFDMSC-BBSC-NB


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MIMO-MC-CDMA Research

STTuCMenc

S/P

π

π

π

π

MM

N=2

STTuCMenc

M

Space-Freq.

Equaliz. and/or

despread.

M

π-1

π-1

π

π

P/S

STTuCMdec

STTuCMdec

Spreading OFDM mod

Spreading OFDM mod

Spreading OFDM mod

Spreading OFDM mod

M M M

OFDM dem

M

OFDM dem

OFDM dem

OFDM dem

Group-wise layered

transmission with space-frequency(SF) Turbo codes

Linear front end multiuser space-freq. equalization

followed by iterative IC and SF

decoding


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2-D channel encoder

GS/P

1

1

P

SpreadingCodes

Data Stream of the kth user

πc

PG

System Research Issues

ST channel encoder

1-D channel encoderS/P

Orthogonal Gold sequencesWalsh-Hadamard codesGold codesZadoff-Chu sequences2-D spreading MC-CDMA

OFDMmodulation

TransmitDiversity

Random& OptimalSubcarrier Interleaver

Different MultirateSchemes

Delay DiversityPhase DiversityCode DiversityScrambling DiversitySTBC

Ant #1

Ant #N


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Channel estimationPilot based or

semi-blind channel estimation

Receiver Research Issues

Receiveddata

P/S Despreading&Equalization

1−cπ

OFDMdemodulation

OFDMdemodulation1−

cπ

Despreadingand/or

1-D and/orSpace/time/frequency

Equalizer

MRC, EGC, ZFGeneralized MMSE

Parallel Interference CancellationSuboptimal ML receiver

Multiple antennas receiver

2-D channel encoderJoint ST decoder&demodulation

1-D channel decoder

Desireddata

Spreading Codes

More AdvancedReceivers


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STF MMSE/PIC Receiver

SISO

No coding


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Example: Sphere Detection

SISO

No coding


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STTuCM & SF-MMSE with soft PIC

4x4 MIMO

STTuCM

4 b/Hz/s


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STTuCM with Multiple Cells

STTuCM

4 b/Hz/s[Joint work with S. Tsumura, University of Osaka]


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Adaptive MIMO-OFDM Research

■ Comparison of● standard space time block coding (STBC)● selection diversity space time block coding (SD-STBC)● eigen-beamforming.

■ Performance measure: SNR at the antenna combiner output.

■ Assumptions:● TDD link● perfect channel state information (CSI) at RX● partial CSI at TX.


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Space-Time Block Coding (STBC)

Bit to symbol convert

S.T.B. Encoder

1 IFFT

1

Add CP and parallel-to-

serial convert

{ },1 1,k k Ks

=

IFFT T


serial convert

PRE - PROCESOR OFDM - MODULATOR

#1

#T

Input bits

FFT 1

Remove CP and serial-to-

parallel convert

FFT R


parallel convert

OFDM - DEMODULATOR

#1

# R

S.T.B. Encoder

C

{ }, 1,k C k Ks

= ( ){ } 1,C l Nl

=x

S.T.B. Decoder

1 ( ){ }1 1,l Nl

=y

S.T.B. Decoder

C ( ){ } 1,C l Nl

=y

{ },1 1,k k Kd

=%

{ }, 1,k C k Kd

=%

DetectorC

{ },1 1,�k k Ks

=

{ }, 1,�k C k Ks

=

Symbol to bit

convert

Detector1 Output

bits

POST - PROCESOR

( ){ }1 1,l Nl

=x


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Selection Diversity (SD) STBC


Alamouti S.T. Encoder

1 IFFT

1


serial convert

{ },1 1,2k ks

=

IFFT T


serial convert


#1

#T

Input bits

FFT 1


parallel convert

FFT 2


parallel convert

OFDM - DEMODULATOR

#1

# 2

( ){ }1 1,2ll

=x

Alamouti S.T. Encoder

C

{ }, 1,2k C ks

= ( ){ } 1,2C ll

=x

Alamouti Combiner

1 ( ){ }1 1,2ll

=y

Alamouti Combiner

C ( ){ } 1,2C ll

=y

{ },1 1,2k kd

=%

{ }, 1,2k C kd

=%

DetectorC

{ },1 1,2�k ks

=

{ }, 1,2�k C ks

=

Symbol to bit

convert

Detector1 Output

bits

POST - PROCESOR

Selection diversity

1

Selection diversity

C

Channel Estimation

( ) ( ) ( ){ }2 2

2 2, 1,...,

� �, arg max :, :,c c c ci j T

i j

i j i j=≠

= +H H Orthogonal pilot symbol 1,...,c C=

�cH


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Eigen-Beamforming


Eigenbeam-former

1�v

IFFT 1


serial convert 1s

Eigenbeam-former

� Cv

Cs IFFT T


serial convert


#1

# T( )C lx

Input bits

Detector1

Post-combining

H1u

FFT 1


parallel convert

1d%

Post-combining

HCu

Cd% FFT 2


parallel convert

POST - PROCESOR OFDM - DEMODULATOR

#1

# 2

( )1 ly

( )C ly

Channel Es timation

S.V.D. H��

c c c c=H U Λ V Orthogonal pilot symbol1, ...,c C=

�cH

DetectorC

1�s

�Cs

( )1 lx

Symbol to bit

convert

Output bits


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Performance Comparison

-10 -5 0 5 10 15 200

1

2

3

4

5

6

7

8

9

Eigen-Beamforming, R=2, T={2,4,8} antennas

SNR at TX side [dB]

SN

R g

ain

[dB

]

I. A.C.L.C.C.H.C.C.

8T =

4T =

2T =

-10 -5 0 5 10 15 200

0.5

1

1.5

2

2.5

3Selection Diversity STBC, R=2, T={4,8} antennas

SNR at TX side [dB]

SN

R g

ain

[dB

]

T=4,IACT=4,LCCT=4,HCCT=8,IACT=8,LCCT=8,HCC

! Eigen-beamforming outperforms both SD-STBC and standard STBC, even under high channel estimation errors at theTX side and even in the case of independent antenna fading.


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Conclusions

■ MC techniques are the main candidate for 4G downlink.

■ MC-CDMA appears to be flexible and robust● Trade-off between multiaccess and multiplexing (like DS-CDMA).● TDM: high data rates with QPSK ! alleviates PAPR problems.● No TX-CSI needed, but can potentially utilize if available?

■ Adaptive OFDM can provide high capacity with TX-CSI● Eigen-beamforming is near-optimal ST transmission scheme

– robust to TX-CSI imperfections.! Combine with MC-CDMA for low-mobility hot-spots?● Further studies in multicell environments needed:

– practical frequency reuse– co-existence with MC-CDMA?


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Further Research Issues

■ Performance evaluation in a cellular system

! air interface scheme selection.

■ Air interface design and parameter optimization:● modulation and coding● duplexing● radio resource managent.

■ Receiver algorithm design and optimization● performance-complexity trade-off● modularization.

■ Strong basic research is the key for the long-term success.


CWC

Thank You for Your Attention

Questions?

Comments?

Criticism?

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