Wireless Evolution To 3G · DS-CDMA with rake combining MC-CDMA with MMSE equalization Nc=256 SF=16, C=16 16 L=2 Uniform delay profile L=2 16 SC-CDMA for downlink w/full code-multiplexing

Broadband wireless communications techniques

2012/4/12 FA/Tohoku University 1

OUTLINE Wireless Evolution Challenge for Future Wireless Gigabit Wireless Concluding Remarks

Fumiyuki Adachi Wireless Signal Processing & Networking (WSP&N) Lab.

Dept. of Electrical and Communications Engineering,

Tohoku University, JapanE-mail: [email protected]

http://www.mobile.ecei.tohoku.ac.jp/

Lecture note #00

Matsushima

Tohoku U. Aobayama-campus

Wireless EvolutionTo 3G

From 2G to 3G systems Then, from 3G to 3.9G (LTE)

systems


F. Adachi, “Wireless past and future - evolving mobilecommunications systems,” IEICE Trans. Fundamentals, vol.E84-A, pp. 55-60，Jan. 2001.

Wireless Evolution To 3G In early 1980’s, communications systems changed from

fixed “point-to-point” to wireless “anytime, anywhere”communication.

Cellular systems have evolved from narrowband network ofaround 10kbps to wideband networks of around 10Mbps.

Now on the way to broadband networks of 100Mps (LTE).

2012/4/12 FA/Tohoku University 4We are here

Gigabitwireless

1980 1990 2000 Year

2G~64kbps

1G~2.4kbps

NarrowbandEra

Ser

vice

typ

eVo

ice

Mul

timed

ia

2010

3G~2Mbps

4G100M~1Gbps

W-CDMACDMA2000TD-SCDMA

HSDPA(W-CDMA)

~14Mbps0GVoice only

point-to-point

50~100Mbps

WidebandEra

BroadbandEra

3G LTE

2020

3.5G 3.9G

Cellular Networks Taking A Role of Fixed Networks No. of cellular+PHS phone

users exceeded that of fixedanalog telephone circuits inMarch 2000 in Japan Cellular: 51.141M PHS: 5.708M Fixed phone： 55.446M

This clearly shows that peoplewant to communicate withpeople, not with places

Cellular networks will take arole of the conventional fixednetworks, soon, worldwide


Year0

10

20

30

40

50

60

70

1985 1990 1995 2000 2005

Mobile

Fixed

61.22M@1997

No.

of

user

s (M

)

There was a big technical leap from 2G to 3Gsystems.

2012/4/12 8FA/Tohoku University

1GAnalog(FDMA)

2GDigital(TDMA)

Voice+data

Improved frequency utilizationNarrowband

3G/3.5GDigital(CDMA)

Increased peak rateIncreased throughput

Increased no. of channels

Broadband

Voice+Data

Big leap

~64kbps ~2Mbps~14Mbps

~2.4kbps

Evolution of Wireless Access Techniques Wireless access technique used in cellular systems has been

changed from FDMA to DS-CDMA. FDMA was used in 1G, TDMA in 2G, DS-CDMA in 3G OFDMA and SC-FDMA are used for downlink and uplink, respectively,

in 3.9G(LTE)


Time

FDMAf3f2f1

Freq

uenc

y

1G

TDMA

Time

1 3 1 2 3

2G Single-carrier

3.9G(LTE)

OFDMA，SC-FDMA

Frequency-domain processing

2

Time-domain processing

DS-CDMA3G Freq

uenc

y

Time

# 2# 3

Spreading code#1

Freq

uenc

y

20ms

Ex. 6.25kHz

Ex.

5MH

z

25kHz

3G Systems Using W-CDMA Data transfer rates in 2G systems are too slow for

downloading rich information distributed in the Internet. 3G cellular systems are designed to offer cellular users a

significantly higher data-rate services using W-CDMAtechnology (3.84cps/5MHz bandwidth). Indoor: 2Mbps Pedestrian: 384kbps Vehicular: 144kbps


F. Adachi, M. Sawahashi and H. Suda, “WidebandDS-CDMA for next generation mobilecommunications systems,” IEEE Commun. Mag., vol.36, pp. 56-69, Sept. 1998.

Indoors~2Mbps

Mobile~144kbps

IMT2000Network

Pedestrian~384kbps


Problem of 3G DS-CDMA Wireless Access

1G, 2G and 3G used FDMA, TDMA, and DS-CDMA, respectively All of them are based on time-domain signal

processing What signal processing should be used for

4G? Recently, multicarrier wireless techniques and

frequency-domain signal processing have beenattracting much attention

OFDMA, SC-FDMA, MC-CDMA, or DS-CDMA in4G?

F. Adachi, D. Garg, S. Takaoka, and K. Takeda, “BroadbandCDMA techniques,” IEEE Wireless Commun. Mag., Vol. 12, No.2, pp. 8-18, April 2005.

Single-Carrier DS-CDMA Transmit signal is spread over a broad bandwidth and

suffers from severe spectrum distortion due to severefrequency-selectivity of the channel.


(a) Transmitter

Datamodulation

Data

Time-domainspreading

Channelcoding &

interleaving

c(t)

Chipshaping

FrequencyfcCarrier frequency

Bandwidth (1+)/Tc

(b) Power spectrum

Channel Model


Transmitted radio waves are reflected or diffracted by somelarge buildings, creating resolvable paths having time delaysof multiple of (signal bandwidth)-1.

Each resolvable path is the sum of irresolvable pathscreated by local scatterers surrounding a mobile.

The path gain hl(t) varies in time according to themovement of mobile terminal since resolvable paths areadded constructively at one time and destructively atanother time.

Localscatterers

Large obstacles

Transmitter

ReceiverReflection/diffraction

c-4

Channel Impulse Response Multipath channel can be viewed as a time varying linear

filter having impulse response h(, t). Many impulses are received with different time delays when

one impulse is transmitted from a transmitter at time t. Frequency-selective fading channel is produced.


Time varyingFIRfilter

Transmit signals(t)

Received signalr(t)

1

0

)()(),(L

lll thth

time

Transmit pulse

Am

plitu

de

Wirelesschannel

0

Impu

lse r

esp

onse

Inverse ofthe signal bandwidth, 1/W

Time delay0

Observed pulses (each pulse consisting of many unresolvable pulses)

0 1 2

Rake Receiver for DS Receivers of present 3G systems use time-domain rake

combining, which is a channel matched filter. Rake combining can improve the BER performance if the

channel frequency-selectivity is not too strong (or thenumber L of resolvable paths is not too large).


F. Adachi, M. Sawahashi and H. Suda, “Wideband DS-CDMAfor next generation mobile communications systems,” IEEECommun. Mag., vol. 36, pp. 56-69, Sept. 1998.

c*(t) Recovered data

De-interleaving& channeldecoding

Datademodulation

*0h

Time-domain despreading

Coherent rake combining(a matched filter to channel)

0

L-1

*1Lh

Integrate& dump

l=1l=0

Delay Impu

lse

resp

onse

l=2

L=3Equalizermatched topropagationchannel

Limitation of Time-domain Rake Number of resolvable paths increases as the transmission

rate or the signal bandwidth increases. This increases the inter-path interference (IPI), thereby

degrading the BER performance. Furthermore, finite number of Rake fingers can collect only

a fraction of total power, reducing the power efficiency.


Time delay

Impu

lse

resp

onse

0

Wideband (~5MHz)

Broadband (25~100MHz)

BER Performance w/ Rake Combining As the number of resolvable

paths increases, the channel frequency-selectivity gets stronger.

The achievable BER performance of 3G SC(DS)-CDMA with rake combining degrades significantly due to strong IPI. For a heavily loaded channel,

even with L=2, a high BER floor appears if the code-multiplexing order is high.

On the other hand, MC-CDMA with MMSE-FDE provides much better performance. Performance improves as L

increases.


1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 5 10 15 20 25 30

Average received E b /N 0 (dB)

Ave

rage

BER

DS-CDMA withrake combining

MC-CDMA withMMSE equalization

N c =256SF =16, C =16

16

L=2

Uniform delay profile

L=2

16

SC-CDMA for downlink w/full code-multiplexing

QPSK

SC-CDMA with rake combining

Multi-carrier vs

Single-carrier

In 3G systems, DS-CDMA (or single-carrierCDMA) is adopted for both uplink anddownlink since it is a very flexible multi-access technique.

Which will be an optimal wireless accesstechnique in a severe frequency-selectivechannel, single-carrier CDMA or multicarrierCDMA or OFDMA for 4G wireless systems?


F. Adachi, D. Garg, S. Takaoka, and K. Takeda,“Broadband CDMA techniques,” IEEE WirelessCommun. Mag., Vol. 12, No. 2, pp. 8-18, April 2005

MC-CDMA MC-CDMA is a combination of OFDM and CDMA.

A simple one-tap FDE Very robust transmission against frequency-selective channel

A DS-CDMA chip block is transformed by IFFT into the frequency-domainsignal block (MC-CDMA).


(a) Transmitter

(b) Power spectrum FrequencyfcCarrier frequency

Bandwidth 1/Tc

Transmittingdata Channel

coding &interleaving

Datamodulation +CP

#0

c(t)

Time-domainspreading

IFFTS/P

Conversion to freq.-domain spread signal

#Nc-1

Frequency-domain equalization (FDE) is used to exploit thefrequency selectivity of the channel.

FDE based on the minimum mean square error (MMSE)criterion can provide the best downlink performance. MMSE weight is the one which minimizes the mean square error (MSE)

between the transmit subcarrier component and the received distortedcomponent.


(c) Receiver

-CPDe-interleaving

& channeldecoding

Datademodulation

W(0)

W(k)Recovered

data

Frequency-domainequalization

FFT

#0

#Nc-1

P/S

c*(t)

Time-domaindespreading

W(Nc-1)

Integrate& dump

Comparison of MMSE-, MRC-, and ZF- FDE MMSE provides the

best BERperformance. No. of subcarriers

Nc=256, spreadingfactor SF=256

Rayleigh fadingchannel with no.paths L=2 and 16,ideal channelestimation

Single user case(U=1)


MC-CDMA with U=1

10-5

10-4

10-3

10-2

10-1

100

0 5 10 15 20 25 30

AWGNMRCZFMMSE

Ave

rage

BER

Average received Eb/N0 (dB)

L=1L=16L=2

MMSE,MRCL=2

L=16

ZF

QPSK

DS-CDMA with Rake vs MC-CDMA with FDE As the number L of resolvable

paths increases, the channel frequency-selectivity gets stronger.

Achievable BER performance of 3G SC(DS)-CDMA with rake combining degrades significantly due to strong IPI. For a heavily loaded channel,

even with L=2, a high BER floor appears if the code-multiplexing order is high.

On the other hand, MC-CDMA with MMSE-FDE provides much better performance. Performance improves as L

increases.


1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 5 10 15 20 25 30


Ave

rage

BER

DS-CDMA withrake combining

MC-CDMA withMMSE equalization

N c =256SF =16, C =16

16

L=2

Uniform delay profile

L=2

16

SC-CDMA for downlink w/full code-multiplexing

QPSK SC-CDMA with rake combining

Frequency-domain Equalization (FDE) for DS-

CDMA

One-tap FDE can replace rake combining to ｐprovide much improved performance


F. Adachi, D. Garg, S. Takaoka, and K. Takeda,“Broadband CDMA techniques,” IEEE WirelessCommun. Mag., Vol. 12, No. 2, pp. 8-18, April 2005F. Adachi, Kazuki Takeda, and H. Tomeba,“Introduction of Frequency-Domain Signal Processingto Broadband Single-Carrier Transmissions in aWireless Channel,” IEICE Trans. Commun., Vol. E92-B,No.09, pp.2789-2808, Sep. 2009.

FA/Tohoku University 74

Can Single-Carrier CDMA (DS-CDMA) Survive in The Future? Can DS-CDMA (single-carrier CDMA) survive in the future?

This is an interesting question. My answer is “YES”. Single-carrier technique with spreading is believed to still

remain an important technique although single-carriertechnique without spreading will be used for uplink accessin 3.9G (LTE).

To take advantage of the frequency-selectivity, MMSE-FDEcan be applied to improve the BER performance of SC-CDMA, similar to MC-CDMA.


FDE Improves SC-CDMA Performance Coherent Rake combining can be replaced by one-tap FDE

Block transmission of Nc chips Insertion of cyclic prefix (CP) at the transmitter FFT/IFFT at the receiver


(b) Receiver

Receiveddata

･･･

Dat

ade

mod

.

Removalof CP IF

FTFFT

c*(t )

Time-domaindespreading

W(0)

W(k)

W(Nc-1)･･･

FDE

Integrate& dump

(a) Transmitter

Inse

rtio

n of

CPTransmit

data

Dat

a m

od.

Time-domain spreading

c(t )

DataCP

Copy

Nc chipsNg chips

*D.Falconer, S. Ariyavisitakul, A,Benyamin-Seeyar and B. Eidson,“Frequency Domain Equalizationfor Single-Carrier BroadbandWireless Systems,” IEEECommunications Magazine, Vol.40, No. 4, pp. 58-66, April 2002.

*F. Adachi, D. Garg, S. Takaoka,and K. Takeda, “BroadbandCDMA techniques,” IEEEWireless Commun. Mag., Vol. 12,No. 2, pp. 8-18, April 2005.

Similarity Between DS- and MC-CDMAWith FDE, both DS- and MC-CDMA can take

advantage of the channel frequency-selectivityand have a similar improved BER performance.

Their uplink transmitter/receiver structures aresimilar.


cu(t)

Scrambling

cscr(t)Transmit data

Dat

a m

od.

Inse

rtio

n of

CP

DS

MC

Nc-P

oint

IF

FT

Transmitter

Spreading

Descrambling

cscr(t)

Received

data

Despreading

cu(t)**

Dat

a de

mod

.

Nc-P

oint

FFT

Rem

oval

of

CP

FDE MC

DS

Receiver Nc-P

oint

IF

FT

Performance Comparison Among SC- and MC-CDMA and OFDM BER performance (single

user) can be significantly improved compared to the coherent rake receiver. Better BER performance than

OFDM even for full code-multiplexing (no. of users, U, is equal to SF=256).

However, there is still a big performance gap from the theoretical lower bound. This is due to residual ISI

after MMSE-FDE. Introduction of ISI

cancellation technique can reduce the performance gap.


# F. Adachi, D. Garg, S. Takaoka, and K. Takeda,“Broadband CDMA techniques,” IEEE Wireless Commun.Mag., Vol. 12, No. 2, pp. 8-18, April 2005

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 5 10 15 20 25


Ave

rage

BER

DS-FDE (MMSE)DS-rakeMC-FDE (MMSE)OFDM

QPSK data modulationRayleigh fadingL=16, uniformSF=256, C =256

SC-FDE (MMSE)SC-rake

Uncoded

Uncoded single user

SC-rake

OFDM

SC-,MC-FDE

Significant improvement

Lower bound

Wireless Evolutionto

3.9G (LTE)

FDMA was used in 1G, TDMA in 2G, DS-CDMA in3G

OFDMA and SC-FDMA are used for downlink anduplink, respectively, in 3.9G(LTE)


Before 4G, There Will Be 3.9G3G systems will continue to evolve to meet the

demands of (internet-related) broadband wirelessservices and substantially strengthen its downlinkdata rate capability. High-speed downlink packet access (HSDPA) of

~14Mbps/5MHz, called 3.5G systems, started in Japanin 2006.

Even 3.5G of ~14Mbps will sooner or later becomeinsufficient.

A 3.9G (3G LTE) will appear to provide broadband dataservices of 50~100Mbps/20MHz using 3G bands.


DS-CDMA(DL/UL)(~14Mbps)

OFDMA(DL),SC-FDMA(UL)(50~100Mbps)

3.5G (HSDPA) 3.9G (LTE)

3G band will be used No available bandwidth of around 100MHz (a hot matter

of WRC-07) Present 3G bandwidth (1.25~20MHz) will be used to

provide much faster rate data services Target: 100Mbps for downlink, 50Mbps for uplink

Difference from 3G wireless technology 3~3.5G：DS-CDMA (DL/UL) 3.9G (LTE): OFDMA(DL)/SC-FDMA(UL) Better transmission performance than 3G and good

commonality with WLAN

2012/4/12 FA/Tohoku University 92 2012/4/12 FA/Tohoku University 93

Evolution of Wireless Access Technique Cellular and WLAN (incl. WiMAX) are both using

OFDM technique Frequency-domain signal processing to exploit the

channel frequency-selectivity Standardization world

FDMA TDMA DS-CDMA SC-FDMAOFDMA

DS-CDMA OFDMA802.11b 802.11a, 11n

Cellular

WLAN

1G 2G 3G 3.9G (LTE)

WiMAX802.16

ITU world

IEEE world

Evolution of Wireless Access Techniques Wireless access technique used in cellular systems has been

changed from FDMA to DS-CDMA. FDMA was used in 1G, TDMA in 2G, DS-CDMA in 3G OFDMA and SC-FDMA are used for downlink and uplink, respectively,

in 3.9G(LTE)


Time

FDMAf3f2f1

Freq

uenc

y

1G

TDMA

Time

1 3 1 2 3

2G Single-carrier

3.9G(LTE)

OFDMA，SC-FDMA

Frequency-domain processing

2

Time-domain processing

DS-CDMA3G Freq

uenc

yTime

# 2# 3

Spreading code#1

Freq

uenc

y

20ms

Ex. 6.25kHz

Ex.

5MH

z

25kHz

Uplink and Downlink Access Techniques Are Different For a long time, the same access technique has been

adopted for the uplink and downlink. Different multi-access techniques between downlink and

uplink in LTE (this is the first time in the history) Downlink: MC-based multi-access is more appropriate since

high PAPR is not a big problem at the base station. Uplink: as the data rates increases, the PAPR problem

becomes more serious. SC-based multi-access is moreappropriate because of its lower PAPR.


Base station(DL)Higher peak power amp.(UP) Complex MMSE-FDE

Mobile terminal(UL) Lower peak power amp.(DL) Simple ZF-FDE

Wireless Access of 3.9G Different multi-access techniques between downlink and

uplink (this is the first time in the history) Downlink: OFDMA, ~100Mbps Uplink: SC-FDMA, ~50Mbps

Scheduling for packet access Multiuser diversity in wireless channel Hybrid ARQ using incremental redundancy (IR) strategy Non real time data services


Downlink UplinkBandwidth(MHz) 1.4/3/5/10/15/20IFFT/FFT block size

128/256/512/1024/1536/2048

Multi-access OFDMA SC-FDMAScheduling Multi-user diversity gainARQ Turbo-coded IR-HARQ

Downlink and uplink access schemes are different

OFDMA Downlink Resource allocation: one or more resource blocks of 1msec

and 12 subcarriers (180kHz) each are allocated accordingto each user’s channel condition (scheduling) to obtainmultiuser diversity gain

Proportional fairness (PF)* scheduling can maximize thethroughput while keeping fairness among users


Freq.

Freq.

User A User B User C

Cha

nnel

gai

n

12 subcarriers(180kHz)

* A. Jalali, R. Padovani, and R. Pankaj, “Data throughput of CDMA-HDR a high efficiency-high data rate personal communication wireless system,” Proc. IEEE VTC 2000-Spring, vol. 3, pp. 1854 -1858, Tokyo, 15-18May 2000.

S/P

P/S

IFFT

User A

+CPS/PUser B

Map

ping OFDMA

signal

Frequency-domain scheduling

Frequency and time -domain scheduling


A

A

A

A

A

B

B

B

B

B

B

B

B A

12 subcarriers(180kHz)

BS

User A

User B1ms

Tim

e

Frequency

Why Single-carrier (SC)Transmission for Uplink? SC has lower PAPR than

OFDM. No ISI at different symbol

positions. SC is suitable for the uplink

transmission. Less expensive power

amplifier is required.


-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

α= 0.00

-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

α= 1.00

-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

α= 0.50

SC

-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

OFDM

OFDMA

256 subcarriers

)2sin()(Im)2cos()(Re

)2exp()(Reveformcarrier wa Modulated

tftstftstfts

cc

c

SC signal has lessPAPR than OFDM.

Reason for this isbecause time-domainSC signal is a Nyquistfiltered signal whichhas the sameamplitude as theoriginal data symbol(ISI free) at every Tssecond (where Ts is thesymbol length).

2012/4/12 FA/Tohoku University 101PAPR(dB)

CCD

F

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

2 4 6 8 10 12

α=0.00

α=0.50

α=1.00

OFDM

OFDM

SC

SC-FDMA Uplink Uplink MAI

The MAI can be avoided by combining SC-FDE with either FDMA orCDMA while alleviating the complexity problem of MUD (remainingproblem is other-cell MAI).

SC-FDMA is a combination of SC-FDE and FDMA A block of data symbols to be transmitted is transformed into

frequency-domain signal which is then mapped onto a different set ofsubcarriers of OFDM.

To preserve the low PAPR property of SC-FDMA signals, equidistancespectrum mapping (either localized or equidistantly distributed) isused.


# R. Dinis, D. Falconer, C. T. Lam, and M. Sabbaghian, Proc.GlobeCom2004, vol.6, pp. 3808-3812, Dallas, TX, USA, 29Nov.-3 Dec. 2004

# K. Takeda and F. Adachi, Proc. IEEE VTC2005-Fall, Dallas,U.S.A., 26-28 Sept. 2005.

# M. Schnell, I. Broeck, and U. Sorger, ETT, Vol. 10, No.4,pp. 417-427, Jul.-Aug. 1999.

Transmitfiltering

M-pointDFT

Nc-pointIFFT

Coded data

0 M-1

・・・

1 2

User u

f

SC-FDMAsignal+CPMapping

Same as downlink OFDMA

Distributed FDMA Each user’s frequency components are mapped equal

distantly over entire signal bandwidth. Large frequency diversity gain can be obtained.

Localized FDMA Each user’s frequency components are mapped over

consecutive subcarriers. Lower frequency diversity gain, but larger multiuser

diversity gain can be obtained by scheduling.

Distributed FDMA vs Localized FDMA


Distributed

Localized

User #0#1#2#3

f

fUser #0 User #1 User #2 User #3

SC-FDMA vs OFDMA A different subcarrier group is assigned to a

different user. SC-FDMA vs OFDMA

In SC-FDMA, M-symbol block is transformed into thefrequency-domain signal of M components, which is thenmapped onto a subcarrier group assigned to that user.

In OFDMA, M symbols in a block are mapped onto asubcarrier group assigned to that user.


Transmit data

Data m

od.

＋CP

SC

OFDMN

c-Point

IFFT

Transmitter

M -Point D

FT

マッ

ピン

グ

Freq.

0d 1d 1Md

)0(D

)1(D)1( MD

Freq.

OFDMA

0 1 k 2cN 1cN

0 1 k 2cN 1cN

SC-FDMA


Frequency Diversity vs Multi-user Diversity Uplink SC-FDMA

Localized FDMA： multi-user diversity Distributed FDMA：frequency diversity

Multi-user diversity(freq./time-domain scheduling)

Frequency diversity

Distributed FDMA

Whole bandwidth

userA

userC

userB

userD

Localized FDMA

Whole bandwidth

Cha

nnel

gai

n

f

Different users’ spectra are mapped based on FDMA so that they are not overlapped to avoid the MAI.

At a BS, each user’s spectrum is extracted after FFT and then, joint FDE & diversity combining is carried out.

M-point D

FT

Mapping

Nc -point IFFT

Transmit data

Data m

od.

+CP

Joint FD

E/diversity com

bining

Joint FD

E/diversity com

bining –CP –C

P

Nc -point FFT

De-m

apping

M-point ID

FTM

-point ID

FT

User #U-1

Data

demod.

Data

demod.

Recovered dataUser #U-1

User #0

User #0

Antenna #0

#Nr–1

User transmitter

BS receiver


BER performance whenU=16 users aremultiplexed per block.M=16 subcarriers are

assigned to each user,which is equal to OFDMAsystem.

The distributed SC-FDMAobtains larger frequencydiversity gain and canachieve better BERperformance than thelocalized SC-FDMA．


1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 5 10 15 20

Ave

rage

BER


L=16-path uniformpower delay profile

SC-FDMA

QPSKNc=256 Ng=32U=16

Distributed

Localized2

4

Nr=1

3

10

1

0

2

1

0

/|)(|

)()(

)()()(ˆ

NEkH

kHkW

kRkWkR

s

N

mm

mMMSEm

N

mm

MMSEm

r

r

Wireless Evolution To

4G (LTE-Advanced) Cellular vs Wireless LAN


4G VisionBroadband services: data rates for mobile

services may be up to 100 Mbps and those fornomadic services may be up to 1Gbps.

Gigabit wireless: an important technology for therealization of 4G systems.


High(60~250km/h)

Low(Pede-strianspeed)

IMT2000 EnhancedIMT2000

New MobileAccess

New nomadic/LocalArea wireless access

Enhancement

Digital broadcast system

Inter-connection

1 10 100 1000Peak useful data rate (Mb/s)

New capabilities of systems beyond IMT-2000

Mobility

ITU-R WP8F (Ottawa, June 2002) :illustration of Capabilities of IMT2000 and Systems Beyond

Beyond IMT-2000

Wireless Evolution In early 1980’s, communications systems changed from

fixed “point-to-point” to wireless “anytime, anywhere”communication.

Cellular systems have evolved from narrowband network ofaround 10kbps to wideband networks of around 10Mbps.

Now on the way to broadband networks of 1Gbps (4G).

2012/4/12 FA/Tohoku University 118We are here

Gigabitwireless

1980 1990 2000 Year

2G~64kbps

1G~2.4kbps

NarrowbandEra

Ser

vice

typ

eVo

ice

Mul

timed

ia

2010

3G~2Mbps

4G100M~1Gbps

W-CDMACDMA2000TD-SCDMA

HSDPA(W-CDMA)

~14Mbps0GVoice only

point-to-point

3G LTE

50~100Mbps

WidebandEra

BroadbandEra

2020

There was a big technical leap from 2G to 3Gsystems.

In 4G systems, much higher throughput than 3Gsystems is demanded.


1GAnalog(FDMA)

2GDigital(TDMA)

Voice+data

Narrowband

3GDigital(CDMA)

4GDigital

(OFDMA?)

Increased peak rateIncreased throughput

Increased no. of channels

Broadband

Voice+Data

Big leap

3G LTEDigital(OFDMA

/SC-FDMA)

Big leap


What Is a Killer Application in 4G? It is quite difficult to predict which services will

become popular in the coming 10 years However, it is no doubt that Internet-related

services will dominate in 4G Another promising service in 4G is visual

communication Our natural communication way is to speak/hear and

look. Earlier generations of communication networks provided

voice services (speak/hear) only. Visual communication everywhere will be one of

important services.

Wireless Voice to Wireless Video


1G Voice

2G Voice Text & data (e-mailing, data access)

3G Video Picture&video

4GVideocommunications Video data

3.5G3.9G

Non-Real timeservice

Real time communications

Voice

Wireless Everywhere How to offer both cellular and nomadic users a

broad range of wireless multimedia services,everywhere?

Almost impossible to build a new, single superwireless system to meet all demands for a broadrange of wireless services

A good solution may be a seamless and secureintegration of various wireless networks, thoseare optimized to each environment


Evolution of Wireless Access In 3G, FDMA was used in 1G, TDMA in 2G, DS-CDMA. In 3.9G(LTE), OFDMA and SC-FDMA will be used for

downlink and uplink, respectively. In 4G, what wireless access technique is used?


1G

TDMA2G

Time

Single-carrier

3.9G(LTE)

OFDMA，SC-FDMA

Time-domain signal processing

Frequency-domainSignal processing

Time

f3f2f1

Freq

uenc

y 6.25kHzFDMA

Freq

uenc

y

Time

1 3 1 2 32

Ex. 20ms

CDMA3G

Freq

uenc

y

# 2# 3

Spreading code#15M

Hz

?4G

25kHz

ITU allocated the spectrum for 4G systems in Dec.2007. 450~470MHz (20MHz), 790~806MHz (16MHz),

2.3~2.4GMHz (100MHz), 3.4G~3.6GHz Global use(200MHz)


DS-CDMA(DL/UL)(~14Mbps)

OFDMA(DL),SC-FDMA(UL)(50~100Mbps)

OFDMA, SC-FDMAMC-CDMA, or SC-CDMA?

(100M~1Gbps)

3.5G 3.9G

4GWRC’07

New band for 4G

3G band


Cellular vs WLAN Until 3G,

Cellular systems WLANCellular and WLAN systems have been advancing

independently Will this continue?

Cellular systems

WLAN

Everywhere Wide coverage area Demand: increasing

data rate

High speed, but hotspot coverage

Demand: extension of coverage area


Convergence of Cellular and Wireless LAN Will Happen? Cellular Wireless LAN

Cellular

DS-CDMA

WLAN

OFDM

Next GenerationWirelessDS-CDMA?MC-CDMA?

Single-carrier?OFDM?

+ Broadband data

+ Mobility

Present Year of around 2015?

IP-based Wireless Access Network Wireless access network may become closer to

present wireless LAN but with nationwide mobilitymanagement.


Basestation

WNC

IP-basedcore network

LR

WNC: Wireless Network ControlLR: Location Register

IP-basedwireless access

network


Heterogeneous Networks Cellular provides wide area coverage, but WLAN

provides hot spot coverage WLAN has a power problem Perhaps, hot spot coverage can only be possible due to

power problem Cellular world

Counterpart of WLAN is 3.9G/4G However, the development of 3.9G will take 5 years.

WLAN world WLAN is quite difficult to cover the whole nation WiMAX has appeared, but needs time to become a

popular system

4G wireless systems may not be based on a singlestandard

A global wireless system that consists of manydedicated wireless systems inter-connected bybroadband Internet technology


Broadcasting

WLAN

Cellular

Broadcasting

WLAN

Advancement

Advancement

Advancement

2G, 3G cellular

3.5G, 3.9G cellular

WiMAX4G (Gigabit)Cellular

Technical Goal Of Wireless The available bandwidth and power are limited The ultimate goal of wireless technology is to

provide extremely high rate data services uniformly over an areawith as much low energy and narrow bandwidthas possible


1GAnalog(FDMA)

2GDigital(TDMA)

3G/3.5GDigital(CDMA)

Big leap

~64kbps ~2Mbps~14Mbps

~2.4kbps

4G/5GDigital

Ultimate goal

Extremely high datarate with as much

low energyand

narrow bandwidthas possible

Wireless Network for Cloud Computing


Cloud Computing Network

Wireless Access Network

User terminals (ultrahigh memory capacity, high speed data communication)

Big wireless pipe (>1Gbps)Low delay (~10ms)

A variety of data services through Internet

ITU allocated the spectrum for 4G systems in Dec. 2007. 450~470MHz (20MHz) 790~806MHz (16MHz) 2.3~2.4GMHz (100MHz) 3.4G~3.6GHz for Global use (200MHz)

200MHz bandwidth in the global frequency band must beshared by several operators (at least 2) and reusedeverywhere.

The single frequency reuse is possible with either SC orOFDM.

However, probably, an effective frequency reuse factor canbe around 25% an effective bandwidth/BS is only around12.5MHz/link under severe co-channel interference.

1Gbps/12.5MHz/BS is equivalent to 80bps/Hz/BS!!


LTE-Advanced May Not Be Sufficient Peak data rate:1Gbps/BS

Total bit rate per one BS There may be many users accessing the same BS Therefore, data rate per user is less than 1Gbps

1Gbps/BS is not enough in densely populatedarea Active user density: one user/(50x50)m2

1km cell 1,256 users/BS 0.8Mbps/user

Ultimate goal >1 Gbps/BS wireless access (>10Mbps/user) Extremely low transmit power (least interference to

other users) Uniform transmission quality over a service area


How To Achieve ～1Gbps with Limited Bandwidth and Power? Future wireless networks may require >1Gbps/BS

capability. LTE advanced networks (4G) are expected to

provide broadband packet data services of up to1Gbps. However, available bandwidth is limited. In December 2007, ITU allocated 3.4~3.6GHz band for

4G services. Only 200MHz is available for global use. This must be shared by at least 2 operators and by the

up/down links. Although one-cell reuse of 100MHz ispossible, effective bandwidth which can be used at eachBS is only around 12.5MHz/link.

Development of advanced wireless techniquesthat achieve a spectrum efficiency of>80bps/Hz/BS with least transmit power isdemanded.


Important Technical Issues Severe channel Advanced equalization

Limited bandwidthMIMO multiplexing

Limited transmit power Distributed antenna network (DAN)


Limited Bandwidth Problem


0

0.1

0.2

0 5 10 15 20 25 30 35 40

(dB)

S1

)6(1

)1(log3

5.3

212

4 7N=3

×S/3

F3F2

F1

F3F1

F3F4

F1F2

F3F1

F4F5

F6F1

F2F7

F3

F6F7

F1F1

F1

N=7 N=4

N=3N=1

Resources (bandwidth, power) are limited Spectrum efficiency is most important

Frequency reuse is indispensible Cluster size of 4~7 may maximize the cellular Therefore, each BS can only utilize a fraction of the

system bandwidth

How To Achieve ～1Gbps with Limited Bandwidth? Use of higher level of modulation has a limitation

1024QAM provides only 10bps/Hz. In addition, the achievable BER performance severely

degrades.


16QAM(4bps/Hz)

4QAM(2bps/Hz) 1024QAM

(10bps/Hz)

MIMO Multiplexing May Be A Savior Independent data streams are transmitted simultaneously

from transmit antennas using the same carrier frequency. SDM is to increase achievable data rate within the limited

bandwidth, i.e., the channel capacity in bps/Hz.


Coding S/P Signal]detection Decod.

Multipathchannel

Nt antennas Nr antennas

Channel Model


Transmitted radio waves are reflected or diffracted by somelarge buildings, creating resolvable paths having time delaysof multiple of (signal bandwidth)-1.

Each resolvable path is the sum of irresolvable pathscreated by local scatterers surrounding a mobile.

The path gain hl(t) varies in time according to themovement of mobile terminal since resolvable paths areadded constructively at one time and destructively atanother time.

Localscatterers

Large obstacles

Transmitter

ReceiverReflection/diffraction

d-4

Channel Impulse Response Multipath channel can be viewed as a time varying linear

filter having impulse response h(, t). Many impulses are received with different time delays when

one impulse is transmitted from a transmitter at time t. Frequency-selective fading channel is produced.


Time varyingFIRfilter

Transmit signals(t)

Received signalr(t)

1

0

)()(),(L

lll thth

time

Transmit pulse

Am

plitu

de

Wirelesschannel

0

Impu

lse r

esp

onse

Inverse ofthe signal bandwidth, 1/W

Time delay0

Observed pulses (each pulse consisting of many unresolvable pulses)

0 1 2

0.01

0.1

1

10

0 1 2 3 4 5 6 7 8 9 10

0.01

0.1

1

10

0 10 20 30 40 50 60 70 80 90 100

Frequency (MHz)

Frequency (MHz)

Cha

nnel

gai

nC

hann

el g

ain

Frequency-selective Channel The transfer function

H(f, t) of broadband channel at time t is not constant and varies over the signalbandwidth.

Challenge is totransmit broadbanddata with high qualityover such a severefrequency-selectivechannel.


L=16Uniform power delay profilel-th path time delay=100l + [-50,50)ns


Transmit Power Problem Peak power is in proportion to “transmission rate” x “fc2.6

[Hata-formula]” where fc is the carrier frequency. Assume that the required transmit power for 8kbps@2GHz is 1Watt for

a communication range of 1,000m. The required peak transmission power for [email protected] needs to be

increased by 1Gbps/8kbps x (3.5GHz/2GHz)2.6 = 535,561 times, that is,536kWatt.

Obviously, this cannot be allowed.

To keep the 1W power, the communication range should bereduced by 43 times(i.e., 1,000m 23m). Femto cellularnetwork.


# M. Hata, “Empirical formula for propagation loss in land mobile radio services”, IEEE Trans. Veh. Technol., VT-29, pp. 317-325, 1980. 2012/4/12

8kbps@[email protected]

1000m23m

For broadband communications, communicationrange shrinks significantly because of thetransmit power limitation.

Fundamental change is necessary in wirelessaccess network.


Radio control station

Network

Base station

Network

Base station

Advances in SC-FDE


F. Adachi, Kazuki Takeda, and H. Tomeba, “Frequency-Domain Equalization for Broadband Single-CarrierMultiple Access,” IEICE Trans. Commun., Vol.E92-B,No. 05, pp. 1441-1456, May 2009.F. Adachi, Kazuki Takeda, and H. Tomeba,“Introduction of Frequency-Domain Signal Processingto Broadband Single-Carrier Transmissions in aWireless Channel,” IEICE Trans. Commun., Vol. E92-B,No.09, pp.2789-2808, Sep. 2009.

Why Single-carrier (SC)Transmission for Uplink? SC signal has lower PAPR

than OFDM. No ISI at different symbol

positions. SC is suitable for the uplink

transmission. Less expensive power

amplifier is required.


-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

α= 0.00

-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

α= 1.00

-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

α= 0.50

SC

-4

-3

-2

-1

0

1

2

3

4

55 57 59 61 63 65

OFDM

OFDMA

256 subcarriers

)2sin()(Im)2cos()(Re

)2exp()(Reveformcarrier wa Modulated

tftstftstfts

cc

c

SC signal has lessPAPR than OFDM.

Reason for this isbecause time-domainSC signal is a Nyquistfiltered signal whichhas the sameamplitude as theoriginal data symbol(ISI free) at every Tssecond(where Ts is thesymbol length).

2012/4/12 FA/Tohoku University 151PAPR(dB)

CCD

F

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

2 4 6 8 10 12

α=0.00

α=0.50

α=1.00

OFDM

OFDM

SC

Single-carrier Frequency-domain Equalization (SC-FDE) Simple one-tap FDE

Block transmission of Nc symbols Insertion of cyclic prefix (CP) at the transmitter FFT/IFFT for FDE at the receiver


(b) Rx

(a) Tx

+CPTransmit

data block

Data m

od.

*D.Falconer, S. Ariyavisitakul, A, Benyamin-Seeyar and B. Eidson, “FrequencyDomain Equalization for Single-Carrier Broadband Wireless Systems,” IEEECommunications Magazine, Vol. 40, No. 4, pp. 58-66, April 2002.

*F. Adachi, D. Garg, S. Takaoka, and K. Takeda, “Broadband CDMA techniques,”IEEE Wireless Commun. Mag., Vol. 12, No. 2, pp. 8-18, April 2005.

Received data block

･･･Data

Dem

od.

Nc -point IFFT

W(0)

W(k)

W(Nc-1)

･･･

FDE

Nc -point FFT

-CP

SC-FDE can take advantage of the channel frequency-selectivity and can improve the BER performance.

Transceiver structure of SC-FDE is similar to OFDMtransceiver. Difference is the location of IFFT.


CP Nc symbols

Ng symbols

Copy

Received data

Data dem

od.

-CP

FDE

OFDM

SC

ReceiverN

c-Point

IFFT

Nc–Point

FFT

Transmit data

Data m

od.

＋CP

SC

OFDM Nc-Point

IFFTTransmitter

Transceiver can be designed based on OFDM For SC, FFT and IFFT are added at transmitter and receiver,

respectively.


Receiver

Transmit data

Data m

od.

＋CP

SC

OFDM

Nc-Point

IFFT

Transmitter

Nc-Point FFT

Received data

Data dem

od.

FDE

OFDM

SC

Nc-Point

IFFT

Nc-Point FFT

-CP

CP Nc symbols

Ng symbols

Copy


Time-domain signal and noise after FDE

(b) MRC

-5

0

5

0 50 100 150 200 250

Time t

s(t)

-10

0

10

0 50 100 150 200 250

Time t

Re[

(t)]

0.01

0.1

1

10

0 50 100 150 200 250

Subcarrier index k

H(k

)

-5

0

5

0 50 100 150 200 250

Time t

s(t)

-10

0

10

0 50 100 150 200 250

Time t

Re[

(t)]

0.01

0.1

1

10

0 50 100 150 200 250

Subcarrier index k

H(k

)

(c) ZF

-5

0

5

0 50 100 150 200 250

Time t

s(t)

-10

0

10

0 50 100 150 200 250

Time t

Re[

(t)]

0.01

0.1

1

10

0 50 100 150 200 250

Subcarrier index k

H(k

)

(a) MMSE

Equivalent channel

ZFMRCMMSE

Signal

Noise

BER Performance Improvement BER performance of SC can

be significantly improved with MMSE-FDE.

However, there is still a big performance gap from the theoretical lower bound. Due to residual ISI after

MMSE-FDE. Introduction of ISI cancellation

technique can reduce the performance gap.


F. Adachi, K. Takeda, and H. Tomeba, “Introduction of Frequency-DomainSignal Processing to Broadband Single-Carrier Transmissions in a WirelessChannel,” IEICE Trans. Commun., Vol. E92-B, No.09, pp.2789-2808, Sep.2009.

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20

Ave

rage

BER


MMSE

ZF

MRC

L=16-pathuniform powerdelay profileQPSKNc=256Ng=32

EGC

Matchedfilter boundLower bound

Performancegap

MMSE ,

)/()()(

MRC ),(EGC |,)(|/)(

ZF ),(/1

)(

10

2

*

*

*

NEkHkH

kHkHkH

kH

kW

s

Performance gap fromthe MF bound increasesfor higher multileveldata modulation. Performance gap from

MF bound at BER=10-3

QPSK: 6.5dB 16QAM: 8.5dB

64QAM: 11.5dB

157

0 5 10 15 20 25 30105

104

103

102

101

10

MF bound

MMSE-FDE

Average received Eb/N0(dB)

Aver

age

BER

QPSK

16QAM

64QAM

Nc=64Ng=16L=16-path

2012/4/12 FA/Tohoku University

Performancegap

Nc-P

oint

FFT

–CP

Nc-P

oint

FFT

–CP

Joint FDE/antenna diversity combining

Antenna #0

#Nr–1

)(0 kW

)(1 kWrN

Nc-P

oint

IFF

T

Dat

a de

mod

.

Recovered data

Joint FDE & Antenna Diversity Combining Transmitter/receiver structure


Transmit data

Dat

a m

od.

+CP

* F. Adachi, K. Takeda, and H. Tomeba, “Frequency-Domain Equalization for Broadband Single-Carrier Multiple Access,” IEICE Trans. Commun., Vol.E92-B, No. 05, pp. 1441-1456, May 2009.

* F. Adachi, K. Takeda, and H. Tomeba, “Introduction of Frequency-Domain Signal Processing to Broadband Single-Carrier Transmissions in a Wireless Channel,” IEICE Trans. Commun., Vol. E92-B, No.09, pp.2789-2808, Sep. 2009.

BER performance Antenna diversity is

powerful to improvethe BER performance.


MMSE ,/|)(|

)(

ZF,|)(|

)(

)(

)()()(ˆ

10

1

0

2

1

0

2

,

1

0,

NEkH

kH

kH

kH

kW

kRkWkR

s

N

mm

m

N

mm

m

mMMSE

N

mmmMMSE

r

r

r

　　

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 5 10 15 20

Ave

rage

BER

Average received Eb/N0 per receive antenna (dB)

L=16-path uniformpower delay profile

QPSKNc=256Ng=32

MMSE

ZF

Nr=1(No diversity)

Nr=2

Nr=4

Nr=3

F. Adachi, Kazuki Takeda, and H. Tomeba, “Introduction ofFrequency-Domain Signal Processing to Broadband Single-Carrier Transmissions in a Wireless Channel,” IEICE Trans.Commun., Vol. E92-B, No.09, pp.2789-2808, Sep. 2009.

Frequency-domain Block Space-time Transmit Diversity(STTD) Alamouti’s STTD for frequency-nonselective channel

Simple 2-antenna space-time transmit diversity (STTD) is aspace-time block coding that does not need transmit channelknowledge and can alleviate the complexity problem of mobileterminal.

Similar diversity gain to MRC receive diversity is obtained butwith 3 dB power penalty.

Transmit diversity can alleviate the complexity problem whenusing receive antenna diversity


se sose -s*o

so s*eSTT

Den

codi

ng

Antenna #0

A pair of2 symbols

time time

Antenna #1

h0

h1 STT

Dde

codi

ng

re rotime

)ˆ,ˆ( oe ss),( oe ss

S. M. Alamouti, “A simple transmit diversity technique for wireless communications,” IEEE J. Sel. Areas Commun., vol. 16, no. 8, pp.1451-1458, 1998.

Frequency-domain Block STTD STTD encoding is applied to each frequency component of a

pair of two symbol blocks to be transmitted. Equivalent time-domain STTD encoding is derived.


so(t)t STTD

encoding+ CP

n=0

n=1se(t)

so(t)

se(t) )( tNs co

)( tNs ce

t

tso(t)

se(t) )( tNs co

t

t

A pair of two symbol blockseven odd

Nc symbolseven odd

STTD-encoded symbol blocks

Nc +Ng symbols

CPTransmitantennas

)( tNs ce

Transmitter

Receiver

K. Takeda, T. Itagaki, and F. Adachi, "Application of space-time transmit diversityto single-carrier transmission withfrequency-domain equalization and receiveantenna diversity in a frequency-selectivefading channel," IEE Proc.-Commun., vol.151, No.6, pp. 627-632, Dec. 2004.

Nc-P

oint

FFT

–CP

Nc-P

oint

FFT

–CP

Antenna #0

#Nr–1

Recovered data

BER Performance With Frequency-domain Block STTD


1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 5 10 15 20 25 30


Ave

rage

BER

L =16N r =1

STTDno STTD

=0dB=2dB=8dB=dB

with MMSE-STTD (Nt=2, Nr=1)

MMSEfor

,

1|)(||)(|

)(

MRCfor ,)(

for ZF |)(|

)(

)(

1

0

1

0

2,1

2,0

,1/0

,1/0

1

0

1

0

2,

,1/0

,1/0

c

gsN

mmm

m

m

n

N

mmn

m

m

NN

NEkHkH

kH

kH

kH

kH

kW

r

r

Frequency-domain blockMMSE-STTD gives afurther improved BERperformance.

An MMSE-STTD gain of3.2dB at BER=10-4 isobtained when =0 dB.

Cyclic Delay Transmit Diversity (CDTD) Well known transmit

diversity is cyclic delaytransmit diversity (CDTD).

The same signal block istransmitted simultaneouslyfrom Nt transmit antennaswith different cyclic timedelays.

Weak frequency selectivechannel can betransformed into strongerselective channel to obtainlarger frequency diversitygain.


J. H. Winters, “Diversity gain of transmit diversity inwireless systems with Rayleigh fading,” IEEE Trans.Veh. Technol., Vol. 47, pp.119-123, Feb. 1998.

(a) Transmitter

Datamodulation

Data

n=0

n=Nt-1+CPNt-1

+CP

Dat

ade

mod

. Data･･

･

(b) Receiver

m=0

m=Nr-1

IFFT

FFT

W0(Nc-1)

WNr-1(Nc-1)

W0(0)

W0(Nc-1)

Rem

oval

of

CP

Rem

oval

of

CP

0(t)

Nr-1

(t)


STTDとDTDの特性比較

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 5 10 15 20 25 30


Ave

rage

BER

=0dB=8dB=dB

L =16N r =1

STTDDTDNo transmitdiversity

Nt=2

CDTD

QPSKNc=256

As the channel frequency-selectivity gets stronger (as gets smaller), the BERperformance improves forboth MMSE-STTD and -CDTD.

When =8 dB, the requiredEb/N0 for BER=10-4 is 2.5dBsmaller with MMSE-STTD thanwith MMSE-CDTD. This isbecause the equivalent no. ofreceive antennas is two timeslarger with MMSE-STTD.

When =0 dB (the channelselectivity is strong enough),MMSE-CDTD gain is as smallas 0.4dB, but MMSE-STTDgain is as much as 3.2dB.

Iterative ISI Cancellation Residual ISI replica is generated and subtracted from the

received signal.

MMSE weight


10

)()(

)1()()()(

)()(

)(

)()()(

)(ˆ)/1(

ˆ

~ˆ/2~ˆ

replica ISI residual theis ~ where

~ˆ~

cNkc

ii

iiiss

i

ii

i

iii

kHNA

ATE

HWH

sFIHM

RWR

M

MRR

　　

　

# Kazuaki Takeda and F. Adachi, “Throughput of multicode DS-CDMA HARQ using MMSE turbo equalization” IEICE Technical report, RCS2006-167, pp.59-64, Nov. 2006.

# K. Ishihara, K. Takeda, and F. Adachi, “Frequency-domain Multi-stage Soft Interference Cancellation for DS-CDMA Uplink Signal Transmission,” IEICE Trans. Commun., Vol.E90-B, No.5, pp. 1152-1161, May 2007.

.estimatesoft its andblock signal ed transmittebetween therror squared average theis |)(~)(| where

)/(|)(|)()(

bygiven is ,~or error vect theofelement each of

error squared average theminimizes which weight,MMSE The

2)1()1(

10

2)1(

*)(

)()()(

tstsE

NEkHkHkW

A

iis

ii

iii

　

FsRE

-CP

Nc-

poin

t FF

T

Nc-

poin

t IF

FT

ReceivedSignal block

Soft replicaN

c -point FFT

Residual ISIreplica

MMSEweight

・・

・・

・・

・・

・・

・・

)()( kW i

)(kR

)(~ )1( kS i

)()( kM i

)1(~ is

)(ˆ )( kR i )(~ )( kR i

-+

MMSE-FDE/w residual ISI cancellation can improve the BER performance.

But, the performance improvement is smaller for a higher multilevel modulation. Performance gap from

MF bound @BER=10-4

QPSK: 2dB 16QAM: 5dB 64QAM: 12dB


0 5 10 15 20 25 3010-5

10-4

10-3

10-2

10-1

100

MF bound

MMSE-FDE


Aver

age

BER

QPSK

16QAM

64QAM

Nc=64Ng=16L=16-path

Performancegap

K. Takeda and F. Adachi, “Frequency-domain ICICancellation with MMSE Equalization for DS-CDMADownlink,” IEICE Trans. Commun., Vol.E89-B,No.12, pp.3335-3343, Dec. 2006.

Frequency-domain Block Signal Detection BER performance of the broadband single-carrier signal

transmissions significantly degrades due to the stronginter-symbol interference (ISI).

Frequency-domain block signal detection which combinesfrequency-domain equalization (FDE) and maximumlikelihood detection (MLD) is very promising.


y YFrequency-

domain block signal

detection

-CP

Nc-

poin

t FF

T

Dat

aD

emod

. Received

data

Data

Dat

am

od. d

+CP

timed(0) d(2) d(Nc-1)∙∙∙

Nc-symbol transmit block

Frequency-selective

channel H

NdHFY s

s

TE2

T. Yamamoto, K. Takeda, and F. Adachi, “A Study of Frequency-Domain Signal Detection forSingle-Carrier Transmission,” Proc. IEEE VTC 2009 Fall, 20-23 Sept, 2009, Araska, US.

Equivalent channel

MMSE-FDE Combined With SIC

...

...

......

...

...

Iteration stage0th layer

1th layer

...

Nc-1th layer

Initial stage

...

0th layer

Nc-1th layer

1th layer

no cancellation

cancellation

d(0) d(1) d(2) ・・・ d(Nc-1)

d(0) d(1) d(2) ・・・ d(Nc-1)

d(0) d(1) d(2) ・・・ d(Nc-1)

d(0) d(1) d(2) ・・・ d(Nc-1)

d(0) d(1) d(2) ・・・ d(Nc-1)

d(0) d(1) d(2) ・・・ d(Nc-1)

cancellation

cancellation

cancellationcancellation

cancellation

no cancellation


Interference cancellation

One-tap MMSE-FDE detectionReplica

generation

Decision resultY

172

T. Yamamoto, K. Takeda, and F. Adachi, “A Study of Frequency-Domain Signal Detection for Single-Carrier Transmission,” Proc. IEEE VTC 2009 Fall, 20-23 Sept, 2009, Araska, US.

Hard decision iterative SIC


1.0E-01

1.0E-02

1.0E-03

1.0E-04

1.0E-050 5 10 15 20

QPSKNcNg=16

Theoretical lower bound


Ave

rage

BER

One-tap MMSE-FDE

Hard decisioniterative V-BLAST

i=0i=1i=2i=3

MMSE detection

1.0E-01

1.0E-02

1.0E-03

1.0E-04

1.0E-055 10 15 20 25

16QAMNcNg=16



Ave

rage

BER

One-tap MMSE-FDE

Hard decisioniterative V-BLAST

i=0i=1i=2i=3

MMSE detection

(b) 16QAM (a) QPSK

Soft decision iterative SIC One iteration is sufficient. More than one iterations do not provide

noticeable additional performance improvement.


1.0E-01

1.0E-02

1.0E-03

1.0E-04

1.0E-050 5 10 15 20

QPSKNcNg=16



Ave

rage

BER

One-tap MMSE-FDE

Soft decisioniterative V-BLAST

i=0i=1i=2i=3

MMSE detection

1.0E-01

1.0E-02

1.0E-03

1.0E-04

1.0E-055 10 15 20 25

16QAMNcNg=16



Ave

rage

BER

One-tap MMSE-FDE

Soft decisioniterative V-BLAST

i=0i=1i=2i=3

MMSE detection

(b) 16QAM (a) QPSK

T. Yamamoto, K. Takeda, and F. Adachi, “Frequency-Domain Block Signal Detection for Single-Carrier Transmission,” IEICE Trans. Commun., Vol.E93-B, No.08, pp. 2104 – 2112, Aug. 2010.

Frequency-domain QRM-MLD Maximum likelihood detection employing QR decomposition

and M-algorithm (called QRM-MLD) can achieve near MLDperformance with much reduced computational complexity.

Cyclic prefix insertedSC transmission (CP-SC)


Data

Dat

am

odul

atio

n

+CP

Nc-

poin

t D

FT

FDBD

usi

ng

QRM

-MLD

Received

data

Dat

a de

-m

odul

atio

n

d s Y(TA)

QR decomposition M

LD u

sing

M

-alg

orith

m

QH

R

QRFH

Y Decisionvariable

H

F

Data symbols(0)CP(0) Data symbols(1)CP(1)

Ng symbolsNc symbols

DFT block size

QR decomposition is applied to Y to transform detect thesymbols in decreasing order of reliability using MLD.

MLD


Y QR decomposition

Multiplication of QH

MLD based on M-algorithm

Decision result

QRHF YQY Hˆ

NQ

0

NQRdYQY

H

cNN

N

N

s

s

c

H

s

sH

Nd

dd

R

RRRRR

TE

NY

YY

TE

cc

c

c

)1(

)1()0(

2

)1(ˆ

)1(ˆ)0(ˆ

2ˆ

1,1

1,11,1

1,01,00,0

．

1

0

2

01,1

2

1

1

)1(2)1(ˆ2ˆ )(

and level modulation thedenotes where

)(minargˆ

c

ccc

cNc

N

n

n

ncnNnN

s

sc

s

sN

NX

nNdRTEnNY

TEL

X

L

RdYd

ddd

In case of iterativeSIC&MMSED, as thenumber of iterationsincreases, the BERperformance improves andapproaches that of thetheoretical lower bound.

Much better performancecan be achieved by usingQRM-MLD than by usingiterative SIC&MMSED.

However, a large M isrequired.


[Iterative SIC&MMSED]T. Yamamoto, K. Takeda, and F. Adachi, “A Study of Frequency-Domain Signal Detection for Single-Carrier Transmission,” Proc. IEEE VTC 2009 Fall, 20-23 Sept, 2009, Araska, USA.[QRM-MLD]T. Yamamoto, Kazuki Takeda, and F. Adachi, "Single-carrier transmission using QRM-MLD with antenna diversity," Proc. The 12th International Symposium on Wireless Personal Multimedia Communications (WPMC2009), Sendai, Japan, 7-10 Sep. 2009.


1.0E-01

1.0E-02

1.0E-03

1.0E-04

1.0E-050 5 10 15 20

Aver

age

BER MMSE-FDE

QRM-MLD


Iterative SIC&MMSED

QPSKNc=64Ng=16L=16-path uniform

i=1i=0

M=16 M=64M=256

i=2

QPSK

In case of iterativeSIC&MMSED, as thenumber of iterationsincreases, the BERperformance improves andapproaches that of thetheoretical lower bound.

Much better performancecan be achieved by usingQRM-MLD than by usingiterative SIC&MMSED.

However, a large M isrequired.



1.0E-01

1.0E-02

1.0E-03

1.0E-04

1.0E-055 10 15 20 25

Aver

age

BER MMSE-FDE

QRM-MLD


Iterative SIC&MMSED

16QAMNc=64Ng=16L=16-path uniform

i=1i=0

M=16 M=64M=256

i=2

16QAM

[Iterative SIC&MMSED]T. Yamamoto, K. Takeda, and F. Adachi, “A Study of Frequency-Domain Signal Detection for Single-Carrier Transmission,” Proc. IEEE VTC 2009 Fall, 20-23 Sept, 2009, Araska, USA.[QRM-MLD]T. Yamamoto, Kazuki Takeda, and F. Adachi, "Single-carrier transmission using QRM-MLD with antenna diversity," Proc. The 12th International Symposium on Wireless Personal Multimedia Communications (WPMC2009), Sendai, Japan, 7-10 Sep. 2009.

Cyclic prefix inserted SC (CP-SC) transmission Last Ng symbols in transmit symbol block are used as CP to

make the received signal block as a circular convolution oftransmit symbol block and channel.

Since last Ng symbols are unknown, a large number ofsurviving symbols in QRM-MLD is requried.

Two types of CP


Data

Dat

a m

od.

+CP

Nc-

poin

t D

FT

FDBD

usi

ng

QRM

-MLD

Received

data

Dat

a de

mod

.

-CPd Y(CP)

Data symbols(0)CP(0) Data symbols(1)CP(1)

Ng symbolsNc symbols

DFT block size

Training sequence aided SC (TA-SC) Last Ng symbols in DFT block are known and therefore, more

accurate signal detection using QRM-MLD is possible than CP-SC.

However, DFT size is larger than the case of CP-SC, increasingthe complexity.


Data

Dat

a m

od.

+TS

Nc+

Ng-

poin

t D

FT

FDBD

usi

ng

QRM

-MLD

Received

data

Dat

a de

mod

.

d s Y(TA)

Data symbols(0)TS Data symbols(1)TS

Nc symbols Ng symbols

DFT block size

T. Yamamoto, K. Takeda, and F. Adachi, “Frequency-domain Block Signal Detection with QRM-MLD for Training Sequence-aided Single-carrier Transmission,” EURASIP Journal on Advances in Signal Processing, Vol. 2011, Article ID 575706, Vol. 2011, doi:10.1155/2011/575706.

Frequency-domain QRM-MLD Maximum likelihood detection employing QR decomposition

and M-algorithm (called QRM-MLD) can achieve near MLDperformance with much reduced computational complexity.

Training sequence aided SC(TA-SC)


Data

Dat

am

odul

atio

n

+TS

Nc+

Ng-

poin

t D

FT

FDBD

usi

ng

QRM

-MLD

Received

data

Dat

a de

-m

odul

atio

n

d s Y(TA)

QR decomposition M

LD u

sing

M

-alg

orith

m

QH

R

QRFH

Y Decisionvariable

H

F

Data symbols(0)TS Data symbols(1)TS

Nc symbols Ng symbols

DFT block size

5 10 15 20 25

16QAMNc=64Ng=16


Aver

age

BER MF

bound

10-1

10-2

10-3

10-4

10-5

M=4M=16M=256

CP-SCTA-SC

Frequency-domain QRM-MLD

MMSE-FDE

When TA-SC is used,the required number ofsurviving paths in theM-algorithm is greatlyreduced whileachieving almost thesame BER performanceas CP-SC.

The overall complexityrequired for SCfrequency-domainQRM-MLD blockdetection in TA-SC isreduced to about 7.4%of that in CP-SC incase of 16QAM.


T. Yamamoto, K. Takeda, and F. Adachi, “Frequency-domain Block Signal Detection with QRM-MLD for Training Sequence-aided Single-carrier Transmission,” EURASIP Journal on Advances in Signal Processing, Vol. 2011, Article ID 575706, Vol. 2011, doi:10.1155/2011/575706.

Overlap FDE The insertion of CP reduces the throughput by a factor of

1/(1+Ng/Nc).

Without CP insertion, the inter-block interference (IBI) isproduced.


DataCPCopy

Nc symbolsNg symbols

NoiseIBI residualISI residual)()(12ˆ

FDEMMSEafter signaldomain -Time

2

IBI theis )( where

2signal Received

1

0

1

0mod)(

1

0mod)(

n

N

kcc

sn

L

llnnNnlnl

c

sn

nn

L

lNlnl

c

sn

skHkWNT

Es

uusshTE

t

nshTEr

c

cl

c

　

　

：

　

IBI

Block average equivalent channel gain

*Kazuki Takeda, H. Tomeba, K. Takeda, and F. Adachi, “DS-CDMAHARQ with Overlap FDE,” IEICE Trans. Commun., Vol. E90-B,No.11, pp.3189-3169, Nov. 2007.

*K. Takeda, H. Tomeba, and F. Adachi, “Iterative Overlap FDE forDS-CDMA without GI,” Proc. 2006 IEEE 64th Vehicular TechnologyConference (VTC), Montreal, Quebec, Canada, 25-28 Sept. 2006.

Impulse response of circular FDE filter concentrates at the vicinity of t=0. This means that the residual

IBI after FDE is localized only at the both ends of FFT block.

This property can be exploited to mitigate the IBI after FDE.

Overlap FDE


0

0.1

0.2

0.3

0.4

0.5

-128 -64 0 64 128

t

Inpu

lse re

spon

se a

fter F

DE MMSE-FDE

N c =256L =16E b /N 0=10dB

FFT blockFFT block

time

FFT block

A partial sequence of Msymbols is picked up

*Kazuki Takeda, H. Tomeba, K. Takeda, and F.Adachi, “DS-CDMA HARQ with Overlap FDE,” IEICETrans. Commun., Vol. E90-B, No.11, pp.3189-3169,Nov. 2007.

*K. Takeda, H. Tomeba, and F. Adachi, “IterativeOverlap FDE for DS-CDMA without GI,” Proc. 2006IEEE 64th Vehicular Technology Conference (VTC),Montreal, Quebec, Canada, 25-28 Sept. 2006.

If M128 is used, the residual IBI can be minimized and theBER performance close to MMSE-FDE with CP insertion canbe achieved.


1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

0 5 10 15 20

Ave

rage

BER


L=16-pathuniform power delay profileQPSKNc=256

Conventional MMSE-FDEusing Ng=32-GI

Overlap FDEM = 64

128192224240256

M symbols

FFT block window

0 Nc-1

Joint overlap FDE & ICI cancellation provides good BERperformance close to the lower-bound.


1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 5 10 15 20Average received E b /N 0 (dB)

Ave

rage

BER

QPSKN c =256, M =160

L =16SF =U =16

Lowerbound

Overlap FDEonly

Iterativejoint overlap FDE& ICI cancellationi =1

2 3 4

Number of iteration

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 5 10 15 20Average received E b /N 0 (dB)

Ave

rage

BER

QPSKN c =256, M =160

L =16SF =1

Lowerbound

Overlap FDEonly

Iterativejoint overlap FDE& ICI cancellation

i =1 2 3 4

Number of iteration

(a) SF=U=1 (b) SF=U=16

Application of Overlap FDE to DS-CDMA Overlap FDE

improves the throughput of SC HARQ.

Since CP insertion is not required, overlap FDE can be applied to the present HSDPA using SC-CDMA. Much higher

throughput can be achieved.

The 3G air interface does not need to be changed at all.


0

0.5

1

1.5

2

-5 0 5 10 15 20 25 30

Thro

ughp

ut (

bps/

Hz)

Average received Es/N0 (dB)

L=16-pathuniform power delay profileQPSKTurbo coded HARQType II S-P2Nc=256, SF=C=16

Overlap FDE (M=64)

Conventional FDEusing Ng=32-chip GI

Coherent rake combining

Frequency-domain Transmit Filtering Frequency-domain

filtering is a partial spreading of the transmit signal in the frequency domain. Frequency domain filtering

increases the number of frequency components from Nc to (1+)Nc.

Lower PAPR is achieved at the price of wider signal bandwidth.

Larger frequency-diversity gain can be obtained through joint MMSE-FDE & spectrum combining.


Transmit data

Dat

a m

od.

＋CP

Nc-P

oint

FF

T

Transmitter

Freq

uenc

y-do

mai

nFi

lter

2Nc-P

oint

IF

FT

Filtering

Nc frequency components

(1+)Nc frequency components

NcNc/2Nc/2Nc 0

NcNc/2Nc/2Nc 0Frequency index k

Am

plitu

de o

f si

gnal

spec

trum

Am

plitu

de o

f si

gnal

spec

trum

Joint MMSE-FDE & Spectrum Combining Weight that minimizes the restored signal spectrum after

spectrum combining and transmitted signal spectrum

196

1

0

1

1

2

*

1

1

)(

)()(

weightMMSE theis )( where

12/~2/,)()()(ˆ

NENpkH

pNkHpNkW

kW

NNkpNkWpNkRkR

s

pc

cc

ccp

cc

Nc 2Nc0-Nc-2Nc Frequency index k

Am

plitu

de o

f si

gnal

spe

ctru

m

)(ˆ kR

)( kR

Nc frequency components


T. Obara, K. Takeda, and F. Adachi, "Joint Frequency-domain Equalization & Spectrum Combining for The Reception of SC Signals in the Presence of Timing Offset," Proc. IEEE VTC2010-Spring, Taipei, Taiwan, 16–19 May 2010.

When transmit filtering is used,the BER performance of SC-FDE is sensitive to the timingoffset between transmitterand receiver. As the roll-off factor of the transmit

filter increases, larger frequencydiversity gain can be achieved.

However, the performance degradesif the timing offset exists.

Timing Offset Problem

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

5 7 9 11 13 15 17 19

= 0.220.51.0

Ideal timing( = 0)

QPSKNc = 256Ng = 32L =16-path uniform

]5.0,5.0[

Aver

age

BER


Conventional MMSE-FDE

Timing offset

* T. Obara, H. Tomeba, Kazuki Takeda, and F. Adachi,“Impact of Timing Offset on DS-CDMA with Overlap FDE,”The 5th IEEE VTS Asia Pacific Wireless CommunicationsSymposium (APWCS2008), Tohoku University, Sendai,Japan, 21-22 Aug., 2008.


Non Zero (ISI)

Timing offset

0 Ts 2Ts 3Ts 4TsTs2Ts3Ts4Tst

Out

put o

f rec

eive

filte

r

BER Performance As the filter roll-off factor increases, the signal bandwidth

widens and hence, larger frequency diversity gain isobtained.


1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0 10 20

Aver

age

BER


QPSKNc=256, Ng=32L=32-path uniform=0

□ =0△ 0.5× 1

=0

=1

100

10-1

10-2

10-3

10-4

102 4 6 8

QPSK

OFDM=0

=0.25

=0.5

=0.75=1

PAPR0 (dB)

Pr(P

APR

>PA

PR0)

Robust Against Timing Offset Joint MMSE-FDE & spectrum combining is robust against

the receive timing offset. MMSE weight removes the phase rotation produced by timing offset. BER performance is almost insensitive to the timing offset.

202

Symbol rate MMSE-FDE

=0.5

Symbol rate MMSE-FDE

Joint MMSE-FDE & spectrum combining

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

5 10 15 20

Aver

age

BER


QPSKNc = 256Ng = 32L=32-path uniform=0.5

∈[0.5, 0.5]

Freq. diversity gain

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

5 10 15 20

Aver

age

BER


QPSKNc = 256Ng = 32L=32-path uniform=1

∈[0.5, 0.5]

=1

Joint MMSE-FDE & spectrum combining

Freq. diversity gain


MIMO Combined With FDE


Even using FDE, reliable communication over an entire service is quite difficult due to shadowing and distance dependent path losses.

Furthermore, effective bandwidth per each link seems to be around 12.5MHz. How to achieve 1Gbps using the limited bandwidth?

MIMO Multiplexing Next generation (4G) wireless systems are

expected to provide broadband packet dataservices of up to 1Gbps. However, availablebandwidth is limited. In December 2007, ITU allocated 3.4~3.6GHz band for


up/down links. Although one-cell reuse of 100MHz ispossible, effective bandwidth which can be used at eachBS is only around 12.5MHz/link. 1Gbps/12.5MHz isequivalent to 80bps/Hz/BS!!

Future 5G wireless systems require >1Gbps/BScapability. Development of a highly spectrum efficient wireless

transmission technology of >80bps/Hz/BS is demanded.2012/4/12 FA/Tohoku University 259 FA/Tohoku University 260

Is Super-high Level Modulation Helpful? To achieve 1Gbps/BS using 12.5MHz で bandwidth, the

required spectrum efficiency is1Gbps/12.5MHz=80bps/Hz/BS!

We need to adopt 280QAM. However, this is impractical. BER increases as the modulation level increases.

16QAM(4bps/Hz)

256QAM(8bps/Hz)

1024QAM(10bps/Hz)

260FA/Tohoku University

Signal constellation

2012/4/12

MIMO Multiplexing It is not a practical approach to use super-high level modulation

like 280QAM. Independent data streams are transmitted simultaneously from

transmit antennas using the same carrier frequency. Multiplexing is to increase achievable data rate within the limited

bandwidth, i.e., the channel capacity in bps/Hz.


Coding S/P Signaldetection Decod.

Multipathchannel

Nt antennas Nr antennas

G. J. Foschini and M. J. Gans, “On limits of wireless communicationsin a fading environment when using multiple antennas,” WirelessPersonal Commun., Vol.6, No. 3, pp.311-335, Mar. 1998.

Single-carrier MIMO Multiplexing Joint MMSE frequency-domain equalization (FDE) and

parallel interference cancellation (PIC) is repeated for de-multiplexing while achieving frequency-diversity gain.


Frequency-domainiterative PIC

-CP

･･･

-CP

Nr antennasReceived

data

･･･ Nt

Nt antennas

+CP

･･･

+CP

S/P

Data Mod.

P/S

･･･

･･･

LLR cal.

･･･

･･･2D MMSE-FDE

Nt signals

Frequency-domain Time-domain

Nr signals

Nt signals

SISO channel

Nr

Nt

TFFTPIC… …

… …

......

...

...

SIMO channel

Nt signals

FFT

i=0

i>0

Replica

generation

IFFT･･････

… …

… …

...

...

......

MIMO channel

･･･

A. Nakajima, D. Garg and F.Adachi, “Frequency-domainiterative parallel interferencecancellation for multicode DS-CDMA-MIMO multiplexing,” Proc.IEEE VTC’05 Fall, Vol.1, pp. 73-77,Dallas, U.S.A., 26-28 Sept. 2005.A. Nakajima and F. Adachi,“Iterative FDIC using 2D-MMSEFDE for turbo-coded HARQ in SC-MIMO multiplexing,” IEICE Trans.Commun. Vol. E90-B, No.3,pp.693-695, Mar. 2007.

Throughput of SC MIMO Multiplexing MIMO signal detection

using FDE and FDIC provides higher throughput than OFDM.


FDIC

Replica gene.

Start

LLR comp.

Output

MMSE FDE Weight comp.

# A. Nakajima, D. Garg and F. Adachi, “Frequency-domain iterative parallel interference cancellation formulticode DS-CDMA-MIMO multiplexing,” Proc. IEEEVTC’05 Fall, Vol.1, pp. 73-77, Dallas, U.S.A., 26-28Sept. 2005.

# A. Nakajima and F. Adachi, “Iterative FDIC using 2D-MMSE FDE for turbo-coded HARQ in SC-MIMOmultiplexing,” IEICE Trans. Commun. Vol. E90-B, No.3,pp.693-695, Mar. 2007.

0

1

2

3

4

5

6

7

8

-5 0 5 10 15 20 25

Th

rou

ghp

ut (

bit

/s/H

z)

Average received Es/N0 per receive antenna (dB)

SC (4, 4)MIMO SDM with iterative FDIC(i=4)HARQ type-II S-P2QPSK, Nc=256, Ng=32L=16-path uniform power delay profile

SC w/ FDIC

SC w/o FDIC

OFDMw/ FDIC

OFDM w/o FDIC Single transmit antenna limit

0

1

2

3

4

5

6

7

8

-5 0 5 10 15 20 25 30

Average received E s /N 0 per antenna (dB)

Thro

ughp

ut (b

ps/H

z)

MC-CDMA (4,4)SDM with iterative FDIC, QPSK,SF (=U )=256, N c=256, N g =32, L=16, S-P2, i=4

OFDM

MC DS

OFDM

w/ FDICw/o FDIC

MC, DS

MC, DS

w/o FDIC

w/ FDIC

Throughput of Spread MIMO Multiplexing Spread MIMO multiplexing

w/FDIC provides the throughput superior to non-spread SC. Much better throughput than OFDM

in a high Es/N0 region. Almost the same throughput as

OFDM in a low Es/N0 region.


FDIC

Replica gene.

Start

LLR comp.

End

2D-MMSE FDE

Multicodedespreading

Multicodespreading

Weight comp.

A. Nakajima, D. Garg and F. Adachi, “Frequency-domain iterative parallelinterference cancellation for multicode DS-CDMA-MIMO multiplexing,”Proc. IEEE VTC’05 Fall, Vol.1, pp. 73-77, Dallas, U.S.A., 26-28 Sept. 2005.A. Nakajima and F. Adachi, “Iterative FDIC using 2D-MMSE FDE for turbo-coded HARQ in SC-MIMO multiplexing,” IEICE Trans. Commun. Vol. E90-B,No.3, pp.693-695, Mar. 2007.

0

1

2

3

4

5

6

7

8

-5 0 5 10 15 20 25

Th

rou

ghp

ut (

bit

/s/H

z)

Average received Es/N0 per receive antenna (dB)

SC (4, 4)MIMO SDM with iterative FDIC (i=4)HARQ type-II S-P2QPSK, Nc=256, Ng=32L=16-path uniform power delay profile

SC w/ FDIC

SC w/o

FDIC

OFDMw/ FDIC

OFDM w/o FDIC

MIMO Multiplexing MIMO multiplexing is powerful.

But, use of too many antennas at a mobile terminal is notpractical

Furthermore, strong co-channel interference exists due tofrequency reuse.


dB.in loss shadowing theis andexponent losspath theis MT, and BSbetween distance theis where

,10

1, if,min

1log,min

,min11log,min

10/

2

1

0

1

0

2

2

rr

NNNN

NNN

hNNN

NNC

t

rtrt

rrt

N

n

N

nnn

rttrt

r

r

t

ttr

　

　　　　　　　

　

SNRTransmit

capacity Channel

One Possible Solution How to implement many antennas in a hand

portable unit? Wearable antenna on your head?


Wearable antennaNo space available at a small hand portable unit

MIMO Cannot Solve Power Problem Transmit power is another important issue Broadband radio requires prohibitively large

transmit power


dB.in loss shadowing theis andexponent losspath theis MT, and BSbetween distance theis where

,10

1, if,min

1log,min

,min11log,min

10/

2

1

0

1

0

2

2

rr

NNNN

NNN

hNNN

NNC

t

rtrt

rrt

N

n

N

nnn

rttrt

r

r

t

ttr

　

　　　　　　　

　

SNRTransmit

capacity ChannelReceived

SNR


Peak power is in proportion to “transmission rate” x “fc2.6

[Hata-formula]” where fc is the carrier frequency. Assume that the required transmit power for 8kbps@2GHz is 1Watt for

a communication range of 1,000m. The required peak transmission power for [email protected] needs to be

increased by 1Gbps/8kbps x (3.5GHz/2GHz)2.6 = 535,561 times, that is,536kWatt. Obviously, this cannot be allowed.

To keep the 1W power, the communication range should be reducedby 43 times(i.e., 1,000m 23m).

A new wireless access network architecture needs to bedeveloped.


# M. Hata, “Empirical formula for propagation loss in land mobile radio services”, IEEE Trans. Veh. Technol., VT-29, pp. 317-325, 1980.

2012/4/12

8kbps@[email protected]

1000m23m

F. Aachi, “Wireless past and future - evolvingmobile communications systems,” IEICE Trans.Fundamentals, vol. E84-A, pp. 55-60，Jan. 2001.E. Kudoh and F. Adachi, “Power and FrequencyEfficient Wireless Multi-hop Virtual CellularConcept,” IEICE Trans. Commun., Vol.E88-B,No.4, pp.1613-1621, Apr. 2005.

Wireless EvolutionTo

5G (Gigabit Wireless)

Voice to Video Cloud Computing Network >1Gbps access capability 3 important technical issues

Limited bandwidth MIMO multiplexing Severe channel Advanced equalization Transmit power Distributed antenna

network (DAN)


Wireless Network for Cloud Computing


Cloud Computing Network

Wireless Access Network

User terminals (ultrahigh memory capacity, high speed data communication)

Big wireless pipe (>1Gbps)Low delay (~10ms)

A variety of data services through Internet

LTE-Advanced May Not Be Sufficient Peak data rate:1Gbps/BS




Ultimate goal >1 Gbps/BS wireless access (>10Mbps/user) Extremely low transmit power (least interference to

other users) Uniform transmission quality over a service area


How To Achieve ～1Gbps with Limited Bandwidth? LTE advanced networks (4G) are expected to

provide broadband packet data services of up to1Gbps. However, available bandwidth is limited. In December 2007, ITU allocated 3.4~3.6GHz band for


up/down links. Although one-cell reuse of 100MHz is possible, an

effective bandwidth which can be used at each BS isonly around 12.5MHz/link. 1Gbps/12.5MHz is equivalentto 80bps/Hz/BS!!

Future wireless networks may require >1Gbps/BScapability. Development of advanced wireless techniques that

achieve a spectrum efficiency of >80bps/Hz/BS withleast transmit power is demanded.


Important Technical Issues Severe channel Advanced equalization

Limited bandwidthMIMO multiplexing



Reduced Communication Range For broadband communications, communication

range shrinks significantly because of thetransmit power limitation.



Radio control stationCore

Network

Base station

CoreNetwork

Base station

Frequency Efficiency Let the total information bit rate be Ctotal (bps), the total

bandwidth be B (Hz), and the cluster area size be A (km2). Since the information service of bit rate Ctotal is provided in

the area of size A using the total bandwidth B, the cellularefficiency can be defined


)km(bps/Hz 11 , , since and

s)channel(bpper ratebit n informatioHz)bandwidth( channel

)(km size cell

Let

)km(bps/Hz

2

2

2

SNWC

NCCNWBNSA

CWS

ABC

total

total

　

　　　

　　

E.g. N=7

F4F5

F6F1

F2F7

F3

f

B

2012/4/12 285

)km(bps/Hz 11 2SNW

C　

Reducing the cluster size N (e.g., N=7→4→3→1）by reducing the required SIR(a) Error control, antenna diversity(b) Cell sectorization, beam tilting

Reducing the cell size：Macro cell system (cell radius of several km)micro cell system (cell radius of several 100m)pico cell system (cell radius of several 10m)

FA/Tohoku University

Communication range reduces from 1,000m to23m, resulting in a nano-cell network of radius of23m.

Radio resource control based on present cellulararchitecture becomes troublesome.

Radio resource controle Core network

Core netowork

Base station

Nano-cell network

Nano-cell Network


4G(LTE-Advanced) Is Still Not Sufficient Peak data rate:1Gbps/BS





Evolution Into 5G5G systems are required to provide much faster

packet data services of a peak rate of >1Gbps.>1Gbps with extremely low transmit power is a

requirement.


We are here

Broadbandwireless

1980 1990 2000 Year

2G~64kbps

1G~2.4kbps

Ser

vice

typ

eVo

ice

Mul

timed

ia

2010

3G~2Mbps

4G100M~1Gbps

IMT-2000

HSDPA

~14Mbps0GVoice only

point-to-point

3G LTE

50~100Mbps

NarrowbandEra

WidebandEra

BroadbandEra

?Gigabitwireless

5G>1Gbps

2020

5G System Requirement >1 Gbps/BS wireless access

(>10Mbps/user) Extremely low transmit power (least

interference to other users) Uniform transmission quality over a

service area


Distributed Antenna Network (DAN)

A new wireless access network with >1Gbpswhile achieving extremely low transmit powerand providing uniform transmission qualityover a service area.

This can be achieved by introducing thedistributed antenna concept.


Important Technical Issues Limited bandwidth Spatial reuse of the same frequency

bps/Hz bps/Hz/BS or bps/Hz/km2

Frequency reuse + MIMO multiplexing Severe channel Advanced equalization



Frequency Reuse To increase the bandwidth/BS (or bps/Hz/km2),

interference management is essential The same frequency must be reused because of

limited available bandwidth From the spectrum efficiency (bps/Hz/BS) point of view,

the same frequency needs to be reused at locations asclose as possible

Cochannel interference is a limiting factor on frequencyefficiency

Cochannel interference management becomes acrucial issue to realize spectrum efficientbroadband networks


Reduced Communication Range For broadband communications, communication

range shrinks significantly because of thetransmit power limitation.



Radio control stationCore

Network

Base station

CoreNetwork

Base station

CoreNetwork

Base station

Coordinated Multi-point Transmission (CoMP) To improve the communication quality for a user

near the cell edge, the coordinated multi-pointtransmission (CoMP) was introduced. Improved SINR (increased capacity) with limited

transmit power This is the first step towards the realization of

distributed antenna network (DAN).


3. Distributed Antenna Network

Distributed antenna network is designed torealize a nano-cell network with increasedspectrum efficiency and reduced transmit power.

Many antennas belonging to a base station (SPC:signal processing center) are distributed aroundSPC.

Each distributed antenna forms a cell Resource allocation control (frequency, time,

power) for distributed antennas is carried out bySPC.



Path lossShadowing

ㇾ Fading

ㇾ Path lossㇾ Shadowingㇾ Fading

Co-located antennas Distributed antennas

Distributed Antenna Network (DAN) Many antennas cooperate and act as cooperative

spatial multiplexing, diversity, or relay The problems can be mitigated which result from distance-

dependent path loss and shadowing loss as well as thefrequency-selective fading

Significant reduction in transmit power is possible


DANSignal Processing

Center

Optical fiber cable

Distributed antenna

Distributed relay

Spatialmultiplexing/diversity

Relay with network coding

Huge transmit power Low spectrum efficiency Non-uniform quality

Huge transmit power Low spectrum efficiency Non-uniform quality

Very low transmit power High spectrum efficiency Uniform quality



High bit rate services with very low transmit power/uniform quality over a service area Distributed antenna network (DAN)

High bit rate with limited bandwidthdistributed MIMO

multiplexing/diversity/relay/beamforming

Formulation of Personal Cell Center of personal cell is a user Personal cell moves according to user movement


Huge transmit power Low spectrum efficiency No-nuniform quality

Huge transmit power Low spectrum efficiency No-nuniform quality



BS is the center of cell

Each user is the center of cell

Uniform Quality Uniform quality over an BS area


Distance from BS

Thro

ughp

ut

Present Cellular

Uniform qualityover an BS area

Cell edge

Distributed Antenna Network (DAN) Many antennas are spatially distributed around a signal

processing center (SPC), which is a gateway to the network With a high probability, some antennas close to an MT can always be

visible Antennas are connected with a SPC by a means of optical or wireless

links


SPC

SPC

SPC

SPC

Distributed Antenna Layer to form a user centric cell

Signal Processing Layer

0.01

0.1

1

10

0 1 2 3 4 5 6 7 8 9 10

0.01

0.1

1

10

0 10 20 30 40 50 60 70 80 90 100

Frequency (MHz)

Frequency (MHz)

Cha

nnel

gai

nC

hann

el g

ain

Frequency-selective Channel The transfer function

H(f, t) of broadband channel at time t is not constant and varies over the signalbandwidth.

This channel is called the frequency-selective channel.

Advanced equalizationis necessary.


L=16Uniform power delay profilel-th path time delay=100l + [-50,50)ns

Distributed MIMO Transmit Diversity With Pre FDE (Downlink)The distributed MIMO diversity increases

significantly the channel capacity while significantly reducing the transmit power.


W0(k)

Cha

nnel

co

ding

Dat

a m

od.

Opt

. m

od.

Distributed antennas

Tran

smit

bina

ry

data

Opt. fibercable

FFT

FFT

WNt-1(k)

IFFT

IFFT

+CP

+CP

Opt

. de

-m

od.

Opt

. de

-m

od.

Distributed Antenna NetworkMT

BS

F. Adachi, K. Takeda, T. Obara, and T. Yamamoto,“Recent Advances in Single-carrier Frequency-domain Equalization and Distributed AntennaNetwork,” (invited) IEICE Trans. Fundamentals,Vol.E93-A, No.11, pp.2201-2211, Nov. 2010.

SC-MRT transmit diversity(downlink) Arbitrary number of transmit

antennas for single receiveantennas

The use of only around 5antennas near a user providesa sufficient improvement.


# H. Matsuda, H. Tomeba, and F. Adachi,“Channel capacity of distributed antenna systemusing maximal ratio transmission,” The 5thIEEE VTS Asia Pacific Wireless CommunicationsSymposium (APWCS2008), Tohoku University,21~22 Aug., 2008.

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 1 2 3 4 5 6 7 8 9 10Channel capacity C (bit/s/Hz)

Prob

[C<a

bsci

ssa]

=3.5, =7.0

Es/N0=10dBL=16-path uniform

t

tt

t

t

MRT diversity

transmit diversity(downlink)


c

N

k

N

nt

N

nt

s

N

nt

tt

NknW

knHNE

knH

knHknW

c t

t

t

t

t

t

1

0

1

0

2

1

0

2

1

02D

1

0

2

*

),(

constraintpower transmit under the

0 ,

,

1max

,

,,

bygiven weight,MRT-joint WF called weight FDE pre following the

using maximized iscapacity downlink Theantenna. receive single for the used be

can antennas transmit ofnumber arbitrary An

　　

　

H. Matsuda, K. Takeda, and F. Adachi, “Downlink Transmit Diversity For Broadband Single-carrier Distributed Antenna Network,” to be presented at IEEE VTC 2010 Spring, Taipei, May 2010.

1.0E-02

1.0E-01

1.0E+00

0 1 2 3 4 5 6 7 8 9 10

= 3.5 = 7.0L = 16Es/N0 = 10 dBNc = 256

C (bps/Hz)

Prob

[C<a

bsci

ssa]

Nt = 12

3

5

10

2D-WF1D-WFMRT

WF-MRTWFMRT

Joint WF-MRT

Frequency-domain STBC-JTRD(downlink) Space-Time Block Coded Joint Transmit/Receive Diversity

(STBC-JTRD) is suitable for downlink application since itallows an arbitrary number of transmit antennas. Transmit FDE (channel state information (CSI) is necessary at

TX) to obtain frequency-diversity gain. Only simple addition/subtraction and complex conjugation

operations are required at the receiver.


Terminal

Dat

a m

od.

#0

#Ndan-1

STB

C-JT

RD

en

code

r

IFFTFFT

・・・

・・・

+CP

SPC

Ndan distributedantennas

#1

Dat

a de

mod

.

#0

STB

C-JT

RD

de

code

r

IFFT

FFT

・・・

・・・

CP

#Nmt -1Nmt receiveantennas

Cooperative Diversity (STBC-JTRD) (downlink) An arbitrary number of transmit antennas can be used.

Suitable to downlink transmission. Pre FDE to achieve frequency-diversity gain (channel state

information (CSI) is necessary). Receiver needs simple addition/subtraction and complex

conjugation operations only.

309

N (no. of transmit

antennas)

M (no. of receive

antennas)J Q Coding

rate

Arbitrary

1 1 1 12 2 2 13 3 4 3/44 3 4 3/4


# R. Matsukawa, T. Obara, K. Takeda, and F. Adachi, “Single-carrier Distributed Antenna Network Downlink Using JointTransmit/Receive Diversity,” Proc. 12th IEEE InternationalConference on Communication Systems 2010, Singapore, 18-19 November, 2010.

# H. Matsuda, R. Matsukawa, T. Obara, K. Takeda, and F.Adachi, “Channel Capacity of Distributed Antenna NetworkUsing Space-Time Block Coded-Joint Transmit/ReceiveDiversity,” Proc. 12th IEEE International Conference onCommunication Systems 2010, Singapore, 18-19 November,2010.

* H. Tomeba, K. Takeda and F. Adachi, “Space-Time BlockCoded Joint Transmit/Receive Diversity in a Frequency-Nonselective Rayleigh Fading Channel,” IEICE Trans. Commun.,Vol.E89-B, No.8, pp.2189-2195, Aug. 2006.

#H. Tomeba and F. Adachi, “Frequency-domain Space-TimeBlock Coded-Joint Transmit/Receive Diversity for The SingleCarrier Transmission,” Proc.10th IEEE InternationalConference on Communication Systems (ICCS 2006),Singapore, 30 Oct. – Nov. 2006.

J blocks Q blocks

time…

・・・

・・・

・・・

timeWTransmit FDE

Cooperative Diversity (STBC-JTRD) (downlink) M=2 STBC-JTRD encoding/decoding


)()()()(

)()(

)(ˆ

*0,11,0

*1,10,0

1

0

kRkRkRkR

kDkD

kD

)()()(2

)()()()(

)(1,10.1

1,00.0

kkkTE

kRkRkRkR

k

s

s NSH

R

)}(),({ 10 kDkD )(kD

)(kW

)(kSTransmit FDEEncoding

Received signal

Decoding

Transmitsignal

)()()()()()(

)(

where)()()(

)()()()()(

with

)()(

)()(

)()()()(

)(

1,11,10,1

1,01,00,0

1,10,1

1,10,1

1,00,0

*01

*10

kHkHkHkHkHkH

k

kkAk

kDkDkDkDk

kk

kSkS

kSkSkSkS

k

danN

danN

danNdanN

H

jtrdstbc

H

HW

D

DWS

　

　　

　

Cooperative Diversity (STBC-JTRD) (downlink) Joint WF-MRT weight that maximizes the channel

capacity

MMSE weight


MRT WF

21

1

0

1

0

2,

10

2D1

0

1

0

2,

0,)(

)2/(max

)(

1)(

mt danmt danN

m

N

nnm

sN

m

N

nnm

mrtwf

kH

NE

kH

kA

11

0

1

0

1

0

2, )(1)(

N

EkH

MkA s

N

m

N

nnm

mmsemt dan

Cooperative Diversity (STBC-JTRD) (downlink) STBC-JTRD encoding when Nt=Nr=2

312

*

0,0*1

*0,1

*0

*0,11

*0,00

0,1

0,0

hdhdhdhd

ss

*

1,0*1

*1,1

*0

*1,11

*1,00

1,1

1,0

hdhdhdhd

ss

1

021,1

21,0

20,1

20,0

*0,11,0

*1,10,0

1

0ˆˆ

dd

hhhh

rrrr

dd


Models of DAN and CN DAN

Ntotal=7 antennas areassumed.

Ndan antennas are selectedfrom Ntotal=7 antennas,based on the local averagereceived signal power (i.e.,the antenna selection isbased on the path loss plusshadowing loss).

CN Ndan antennas are selected

from Ntotal antennas co-located at the BS, basedon the instantaneousreceived signal power.


Increasing the number of transmit antennas reduces the 10% outage capacity.

The use of 2 receive antennas maximizes the capacity.

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10Ndan

10%

outa

ge c

apac

ity (

bps/

Hz)

Transmit Es/N0 = 10dB=3.5, =7.0, L=16Nc=256

○ Nmt = 1□ 2△ 3◇ 4

Nmt =1

2

3, 4


Joint MRT-WF weight

H. Matsuda, R. Matsukawa, T. Obara, Kazuki Takeda, and F. Adachi, "Channel Capacity of Distributed Antenna Network Using Space-Time Block Coded-Joint Transmit/Receive Diversity," Proc. 12th IEEE International Conference on Communication Systems (ICCS 2010), Singapore, 17-19, Nov. 2010.

BER Distribution Increasing the number

of transmit antennas reduces the BER outage probability (probability of BER exceeding the allowable BER) significantly.

Also effective is increasing of no. of receive antennas.


0.001

0.01

0.1

1

1.00E-04 1.00E-03 1.00E-02 1.00E-01

Prob

[BER

>abs

ciss

a]

BER

Transmit Es/N0=5dBL = 16 = 3.5= 7.0

Nt=1

2

3

4

Nr = 12

MMSE weight

R. Matsukawa, T. Obara, K. Takeda, and F. Adachi, "Single-carrier Distributed Antenna Network Downlink Using Joint Transmit/Receive Diversity," Proc. 12th IEEE International Conference on Communication Systems (ICCS2010), Singapore, 17-19, Nov. 2010.

Uplink FD-STTD

2012/4/12 316

Mobile Terminal

Nmt=2

cc

cc

NtNstsNtNsts

mod)()(mod)()(~

*01

*10S

FA/Tohoku University

Dat

a m

od.

STT

Den

codi

ng +CP

+CP

#0

#1s1(t) s0(t)

2 symbol blocks DAN SPC

Estimated symbol blocks

Dat

a de

mod

.

STT

D

deco

ding

with

FD

E

・・・

-CP#0

#Ndan-1

#1

+

s1(t)^ s0(t)

^

FFT

FFT

S.M. Alamouti, “A simple transmit diversity technique for wireless communications,” IEEE Journal on Selected Areas in Communications, Vol. 16, No. 8, pp. 1451–1458, October 1998.

Up and Downlink Comparison The same BER

performancefor up anddownlinks


0.001

0.01

0.1

1

1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01

Prob

[BER

>abs

ciss

a]

BER

FD-STTD(Uplink , MMSE weight)FD-STBC-JTRD(Downlink, MMSE weight)

Ndan =1

23

4

10-1

10-2

10-3

Transmit Es/N0 = 5dB=3.5, =7.0, L=16Nc=256, Ng=32Nmt=2 ＊

Throughput DAN can achieve much higher throughput

throughput at the cell edge is about 2.6 (bps/Hz) in DAN while it isabout 1.2 (bps/Hz) in CN.

Type II S-P2 (Incremental Redundancy) using rate-1/3 turbo coding.


Spatial distribution of throughput when (Ndan, Nmt) = (4, 2) for DAN using 7 distributed antennas, 16QAM, and Es/N0=0 (dB)

Thro

ughp

ut (

bps/

Hz)

16QAMEs/N0=0 (dB)(Ndan,Nmt)=(4, 2)

MMSE weight

Increasing Ndanachieves higherthroughput due toits larger spatialdiversity gain. The use of more

than Ndan=4provides only amarginal increasein the throughput.

By increasing Ndanfrom 1 to 4, thetransmit power canbe reduced byabout 6dB.


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-10 -5 0 5 10 15 20Normalized transmit Es/N0 (dB)

DAN=3.5, =7.0, L=16

16QAM, Nc=256, Ng=32Nmt=2

Ndan= 12

4, 7

1%-o

utag

e th

roug

hput

(bps

/Hz)

◇ Ndan = 1□ 2△ 4× 7

Cooperative AF Relay Cooperative relay can

extend the coverage A simple protocol is 2-slot

amplify and forward (AF) .


Cooperate AF relay

SPCMT

RSi

rMi riB

rMB

1.0

MTRS,SPC RSSPC

1st slot 2nd slot

time

Frame

Cooperative 2-slot AF relay does not always improve the throughput. In a good channel

condition, the direct communication provides higher throughput.

Switching betweendirect and relaying(D/AR switching)provides always higherthroughput. Cooperative AF relay is

used only if it provides larger channel capacity than the direct communication.


Capacity improvement by D/AR switching

0

2

4

6

8

10

12

14

16

-10 0 10 20 30

Out

age

capa

city

(bps

/Hz)

(dB)

U=1, K=6Nc=128, M=64L=16=7.0(dB), =3.5

■ D/AR switching○ Cooperative AF relaying△ Direct communication

t

50% outage

1% outage

Cooperative AF Relay To better exploit the frequency selectivity of the channel,

spectrum division/adaptive subcarrier allocation (SDASA) isproposed. Each user’s M frequency components after DFT are divided into D

sub-blocks of of M/D components each. They are mapped over Nc/(M/D) resource blocks (Nc subcarriers)

based on the channel conditions of MT-RS-BS and MT-BS.


An example of SDASA when (M, D, Nc) = (8, 4, 16)

M. Nakada, K. Takeda, and F. Adachi, “Channel capacity of SC-FDMA cooperative AF relay using spectrum division & adaptive subcarrier allocation,” Proc. IC-NIDC 2010, pp.579-583, Sept. 2010.

Frequency

Channel gain

Nc =16

Sub-block

① ② ③ ④ ⑤ ⑥ ⑦ ⑧

Resource block

k

Cooperative AF Relay The additional use of

SDASA obtains the frequency diversity gain.

It can further reduce the required transmit power compared to the D/AR switching without SDASA.


Additional capacity improvement by SDASA

0

2

4

6

8

10

12

14

16

-10 0 10 20 30

Out

age

capa

city

(bps

/Hz)

(dB)

◆ With SDASA (D=4)■ Without SDASA

U=1, K=6Nc=128, M=64L=16s=7.0(dB), a=3.5D/AR switching

1%

50%

t

327

Cooperative Beamforming Multiple distributed antennas are used to reduce

the other user interference using the same carrierfrequency.

Omuniantenna

Directional beam

Distributed antenna(a group of antennas)


Center


Cooperative Beamforming Multiple distributed antennas are used to reduce

the other user interference using the same carrierfrequency.

Omuniantenna

Directional beam

Distributed antenna(a group of antennas)


Center


Cooperative Beamforming SC-FDAAA acts as an adaptive beamformer as

well as one-tap FDE based on the MMSE criterion Beamforming can suppress MAI while FDE

suppresses ISI.


-GI

Data m

od.

+GI

-GI

Data D

emod.

Data m

od.

+GI

SPCUser#0

User #U-1

*W. Peng and F. Adachi, “Frequency Domain Adaptive Antenna Array Algorithm for Uplink Transmission,” Proc. The 20th Personal, Indoor and Mobile Radio Communications Symposium 2009 (PIMRC’09), Tokyo, Japan, 13-16 Sept., 2009.

Cooperative Beamforming Using a group of Nr receive antennas, up to Nr

users can be accommodated with satisfactoryperformance even in a strong frequency-selectivechannel.


0 2 4 6 8 10 12 14 16 18 20

10-4

10-3

10-2

10-1

100


Ave

rage

BE

R

U=12

3

4

5

L=16, Nr=4

*W. Peng and F. Adachi, “Frequency Domain Adaptive Antenna Array Algorithm for Uplink Transmission,” Proc. The 20th Personal, Indoor and Mobile Radio Communications Symposium 2009 (PIMRC’09), Tokyo, Japan, 13-16 Sept., 2009.

*W. Peng and F. Adachi, “Single-carrier Frequency Domain Adaptive Antenna Array for Cellular Systems,” Proc. 2010 IEEE 72nd Vehicular Technology Conference (VTC2010-Fall), Ottawa, Canada, 6-9 Sept. 2010.

SC-FDAAA

Two DAN SC-FDAAA schemes The distributed SC-FDAAA

generates the SC-FDAAA weightfor each active cluster ofantennas respectively and thencombines the post SC-FDAAAsignals.

On the other hand, the unifiedSC-FDAAA generates the AAAweight for all active clusters ofantennas.

The unified SC-FDAAA schemeachieves better performancethan the distributed SC-FDAAAscheme.


Distributed antenna clustersfor SC-FDAAA

Cooperative Beamforming Frequency-domain cooperative beamforming allows the

single frequency-reuse (FRF=1). U=2 case．


0 2 4 6 8 10 12 14 16 18 20

10-6

10-5

10-4

10-3

10-2

10-1

Transmit SNR(dB)

Ave

rage

BE

R

FRF=1FRF=3FRF=4FRF=7

Uplink TransmissionTwo active clusters of four antennas(D)=2

Unified SC-FDAAA

Distributed SC-FDAAAMulti-cell

F6F1

F2

F3F5F4

F7

FRF=7

F1F1

F1

F1F1F1

F1

FRF=1

U=2 case

Cooperative Multiplexing Distributed antennas can be used for spatial

multiplexing to significantly increase the datarate.


Distributed antenna

DANSPC

Cooperative Multiplexing TS-SC MIMO multiplexing using QRM-MLBD


Nc+Ng-pointDFT

QRD of equivalent channel matrix

…

Nda

ndi

strib

uted

ant

enna

s

Nc+Ng-point DFT

Y1

YNdan

…

… Mul

tiplic

atio

n of

QH

MLD

usi

ng M

-al

gorit

hmY

De-

mod

ulat

ion

SPC

Info. bits

Dat

am

odul

atio

n +TSd

S/P

…

+TS

d1

dNmt

s1

sNmt

…

Nmt antennas

Mobile terminal

T. Yamamoto, K. Takeda, and F. Adachi, “Training sequence-aided QRM-MLD block signal detection for single-carrier MIMO spatial multiplexing,” Proc. IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June, 2011.

Cooperative Multiplexing Uplink transmission using Nmt transmit antennas

(MT) and Ndan distributed receive antennas (SPC) Antenna distribution model: Nmt=Ndan=2


1.0

2/3

R1

R2 1.0R

DAN Conventional cellular system

Cooperative Multiplexing Received signal representation at mth antenna


symbols of vector TS:)]1(),...,0([

antennat th transmi ofblock symbol data : )]1(),...,(),...,0([

with

][

vectornoisedomain -frequency:antenna ddistribute )~1(th and antenna transmit MT

)~1(th between matrix channeldomain -frequency : size ofmatrix DFT :

where

2

antenna ddistribute)~1(th at the vector signal receiveddomain -frequency The

,

)(

1

)(,

gT

gnnn

Tcnnnn

TTn

Tnn

m

dan

mtnm

JJ

N

nmn

NNnm

s

sm

dan

NNuu

nNdtdd

NmmNnn

J×J

TE

Nmm

mtgc

u

d

uds

N

HF

NsFHY

Cooperative Multiplexing Overall received signal representation


1×)+( size of vector noise overall:

)+(×)+( size ofmatrix channel equivalent:

where

2

2

1×)+( size of signal receiveddomain -frequency Overall

1

11

,1,

,11,11

gcdan

gcmtgcdan

Ns

s

NNNNN

N

s

s

N

gcdan

NNNNNNNNN

TE

TE

NNN

mt

danmtmtdandan

mt

dan

NH

Ns

sH

N

N

s

s

FHFH

FHFH

Y

YY

　　

Cooperative Multiplexing QRM-MLBD consists of three steps

OrderingQR decompositionMLD using M-algorithm.

Ordering


1× size of symbolth at vector TS: )(

1× size of symbolth at vector data:)(

where

)]1()()0(),1()()0([

vector) theof bottom at the symbols training theall relocate (to orderingafter vector symbol transmit The

danT

danT

Tg

TTTc

TTTorder

Ntt

Ntt

NtNt

u

d

uuuddds

　　

　

Cooperative Multiplexing QR decomposition


)+(×)+( size ofmatrix ngular upper tria :

)+(×)+( size ofmatrix unitary :with where

2ˆ

signal receiveddomain -frequency ed transformThe

gcmtgcmt

gcmtgcdan

Horder

s

sH

NNNNNNNNNNNN

TE

RQ

QR=H

NQRsYQY

　　

　

Cooperative Multiplexing MLD using M algorithm


stagelast at the metricpath smallest thehavingpath back the by tracingon demodulati Data (c)

metricspath thecomparingby paths surviving as selected are paths best thestage,each In (b)

diagram treein the distanceEuclidean minimum thehavingpath best for the Searching (a)

M

101010101010

10

10

10

CN

DAN

MMSED

QRM-MLBD

M=1M=4M=16

NcNg=16Transmit Es/N0=10dB16-path uniform

Nmt=Ndan=2QPSK

BER

Prob

[BER

>abs

ciss

a]

Cooperative Multiplexing DAN can significantly

improve thetransmission qualitycompared to the caseof co-located antennasat BS (conventionalcellular system).M is the number of

surviving candidate symbols in the Malgorithm of QRM-MLD.

As M increases, the achievable link performance improves but, the complexity for the signal detection reduces.


DAN achieves higher throughput than CN The cell edge throughput is about 3bps/Hz higher with DAN

than with CN. CN can achieve high throughput only near SPC.


Thro

ughp

ut (b

ps/H

z)

2.0

3.0

4.0

5.0

6.0

7.0

Es/N0=5dB(b) CN

(a) DAN

Spatial distribution of throughput

02.0

3.0

4.0

16QAMNdan=Nmt=2NcNg=16=3.5, =7dB16-path uniform

Normalized transmit Es/N0 (dB)

10%

out

age t

hrou

ghpu

t (bp

s/Hz)

5 10 15 20 25

5.0

6.0

7.0

DAN

CN

QRM-MLBD(M=16)MMSED

DAN can reduce thenormalized transmitEs/N0 required forachieving the samethroughput as CN. Es/N0 reduction from CN is

as much as about 10dBfor a 10%-outagethroughput of 5bps/Hz.

QRM-MLBD can improvethe throughputcompared to the MMSEdetection. Es/N0 reduction from

MMSED is as much asabout 9dB in DAN for a10%-outage throughput of5bps/Hz.


Some Concluding Remarks Next generation (4G) and future (5G) wireless networks will

require Giga-bit wireless technology of >1Gbps and>80bps/Hz/BS under severe MAI and co-channelinterference.

Wireless Signal Processing Frequency-domain equalization & MIMO may be indispensible

techniques. But, still insufficient! Reducing transmit power

Distributed antenna network (DAN) with multiplexing, diversityor relay can solve the transmit power problem while increasingthe spectrum efficiency.

Other promising solutions? Lots of interesting and important research topics remain

before the born of next generation wireless systems.


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