power-efﬁcient opportunistic amplify-and-forward … · power-efﬁcient opportunistic...

2010 IEEE 71st Vehicular Technology Conference: VTC2010-Spring16-19 May 2010, Taipei, Taiwan

Power-Efficient Opportunistic Amplify-and-ForwardSingle-Relay Aided Multi-User SC-FDMA Uplink

Jiayi Zhang, Lie-Liang Yang, Lajos Hanzo

Communications Research GroupSchool of Electronics and Computer Science

University of Southampton, UK.Email: {jz07r, lly, lh}@ecs.soton.ac.uk

http://www-mobile.ecs.soton.ac.uk

Outline

IEEE VTC2010-Spring in Taipei

Outline

o The state-of-art

o Relay assisted SC-FDMA system model

o Signal detection at the BS and results

o Opportunistic cooperative relaying and results

o Conclusions

Key References


Slide 2 - Key References


Key References

o N. Benvenuto and R. Dinis and D. Falconer and S. Tomasin, “Single Carrier Modulation With NonlinearFrequency Domain Equalization: An Idea Whose Time Has Come–Again”, Proceedings of the IEEE,vol. 98, no. 1, pp. 69–96, Jan. 2010.

o J. Zhang, L.-L. Yang and L. Hanzo, “Multi-user performance of the amplify-and-forward single-relayassisted SC-FDMA uplink”, in Proceedings of IEEE VTC2009-Fall, 2009.

o L.-L. Yang, Multicarrier Communications, Wiley, 2009.

o H. G. Myung and J. Lim and D. J. Goodman, “Single carrier FDMA for uplink wireless transmission”,IEEE Vehicular Technology Magazine, pp. 30–38, Sept. 2006.

o A. Bletsas, A. Khisti, D. P. Reed and A. Lippman, “A simple cooperative diversity method based onnetwork path selection”, IEEE Journal on Selected Areas in Commuications, vol. 24, no. 3, pp.659–672, Mar. 2006.

o A. Sendonaris, E. Erikip and B. Aazhang, “User cooperative diversity - part I and II”, IEEE Transactionson Communications, vol. 51, pp. 1927–1948, Nov. 2003.

o D. Falconer, S. L. Ariyavisitakul, A. Benyamin-Seeyar and B. Eidson, “Frequency domain equalizationfor single-carrier broadband wireless systems”, IEEE Communications Magazine, pp. 58–66, Apr. 2002.

The State-of-Art


Slide 3 - The State-of-Art




Motivation

o 3GPP LTE-Advanced prospective

o Green radio awareness - power efficiency

o High transmission throughput requirement: broadband rather than narrowband

o Problem: have to mitigate both the shadow and Rayleigh/Rician fading overdispersive channels

The State-of-Art








Why SC-FDMA?

o Carrier modulation aware transmitter design

• Power amplifier (PA) requires low peak-to-average power ratio (PAPR) due to its limitedlinear range

RF, PAS/PDSP

RF module, PADSP

S/P SubcarrierMapping IDFT PA

RF

Conventional multi−carrier (MC) modulation

Conventional single−carrier (SC) modulation

IDFTSubband

DFT MappingRFPA

DSP

DSPSC−FDMA: DFT−spread OFDMA structure

Orthogonal frequency−division multiple−access (OFDMA)

Signal

Time

and PA PAPRHardware

generation complexityflexibility

Single

SingleTD Low

High Low

LowFlexible

modulation

(FD)

(TD)−domain

−domainFrequency

−moudulusConstant

Constant−moudulusmodulation

RF module Configure

Reconfig

diversity

Yes

No

Single Low Low

ReconfigFlexible

TD Multiple Low High No

Depend onreceiver

Multi−path

U -point

U -pointN -point

The State-of-Art










o Digital signal processing (DSP) at receiver

• Conventional SC receiver: time-domain equaliser (TDE) with hundreds of filter taps incase of long channel impulse responses imposed by frequency-selective fading

RF TDE

SC−TDE

Detection

− high DSP complexity

Multi−tap

• SC-FDE receiver transforms the received signal to the frequency-domain, as in OFDMand employs single-tap multiplicative frequency-domain equaliser (FDE)

• SC-FDE receiver includes IDFT operation after conventional OFDM receiver

FDESingle−tap

IDFTDetectionRF DFT

SubbandDemapping

(K−1) other users

OFDMA(OFDM) style

− low DSP complexity

− multi−path diversityUser 1

SC−FDMA(SC−FDE) receiver

N -pointU -point

The State-of-Art












o Multiple-access oriented subband mapping schemes

Subbands

Subbands

Distributed

Localised User 1

User 2

User 3

• Distributed mode provides higher multi-path diversity gain than localised mode.

• Localised mode may achieve multi-user diversity when invoking channel-dependentscheduling, it is more suitable for a system in which a few users require high bit-rate.

• Interleaved mode is a special case of the distributed mode, where subbands arearranged equidistantly from each other.

• The transmitted TD signal of localised mode requires a few subcarriers, while forinterleaved mode only single carrier is used.

The State-of-Art














Why Cooperation?

o Aims

• Achieving energy/power efficiency

• Increasing system throughput

• Extending cellular coverage

• Supports multiple users

• Guarantees a given quality of service (QoS)

o Relay selection: whom to cooperate with?

• Fixed - aiming for cooperative diversity, fixed relaying gain

• Random - limited relaying gain and selection diversity gain

• Distance-dependent - aiming for relaying gain

• Channel-dependent - aiming for both relaying and selection diversity gains -Opportunistic Relaying

Overview


Slide 8 - Overview


Slide 8 - Overview


Slide 8 - Overview


Slide 8 - Overview


Slide 8 - Overview


Slide 8 - Overview


Slide 8 - Overview


Opportunistic Amplify-and-Forward Cooperative Relaying forSC-FDMA Uplink

o Our proposed systems are capable ofproviding:• Multi-user (selection) diversity gain

• Cooperative (spatial) diversity gain

• Multi-path (frequency) diversity gain

o Additionally,• Free of multi-user interference (MUI)

and reduced AF relaying noise

• Low DSP complexity at the relay andBS

BS(destination)

MT(source)

MT(source)

MT(relay)

MT(relay)

Relay Assisted SC-FDMA System Model


Slide 9 - Relay Assisted SC-FDMA System Model
















Source MT Transmitter

o DFT-spread-OFDMA style transmitter

DFT PowerAllocation

T−domain T−domainF−domain

1 2 3 4 5 6

IDFTSubbandMapping Add CPPPPk

xxx(f)k

FFFN

xxx(t)kxxx

(t)k

FFFHU PS,k

xxx(f)k sss

(t)S,k

• k-th user’s N consecutive TD symbol in the vector xxx(t)k

• Bandwidth (BW) expansion factor M supports a maximum of M users

• N -point FFT matrix FFFN offers a normalised BW of N per user

• U -point IFFT matrix FFFHU provides the total normalised BW of U = N×M





















o Total transmitted signal power Pt is normalised to unity,the source MT’s transmitted power PSt,k = εS,kαS,kPt,power sharing factor αS,k = αR,k = 0.5, in terms of Equal Power Allocation (EPA),Power Control Error (PCE): log-normal distributed samples with zero mean andvariance of σ2

ε , i.e. εS,k(dB) ∼ N (0, σ2ε ).

o Subband mapping matrix PPPk of the k-th user• Interleaved mode - achieves multi-path diversity gain

Pk,un =

8<: 1, for u = nM + k

0, otherwise

o Transmitted signal before inserting cyclic-prefix CP

sss(t)S,k =

√PSt,kFFFHUPPPkFFFNxxx(t)

k

xxx(f)k

xxx(f)k+1

x(f)k,n

x(f)k,n+1

x(f)k+1,n

x(f)k+1,n+1

x(f)k,n

x(f)k+1,n

x(f)k+2,n

x(f)k,n+1

x(f)k+1,n+1

x(f)k+2,n+1

xxx(f)k + xxx

(f)k+1

N

N

U = N×M

Interleaved subband mapping























0 10 20 30 40 50 60 70−1.5

−1

−0.5

0

0.5

1

1.5SC−FDMA Discrete Time−Domain Waveform (N=8,M=8)

Normalised time

Am

plitu

de

signal point 1 real

signal point 1 imag

signal point 4 real

signal point 4 imag

−1.5 −1 −0.5 0 0.5 1 1.5−1.5

−1

−0.5

0

0.5

1

1.5SC−FDMA Time−Domain Constellations (BPSK)

I−real

Q−

imag

signal point 1signal point 4

0 10 20 30 40 50 60 70−1.5

−1

−0.5

0

0.5

1

1.5SC−FDMA Discrete Frequency−Domain Waveform (N=8,M=8)

Normalised frequency

Am

plitu

de

signal point 2 realsignal point 2 imagsignal point 3 realsignal point 3 imag

−1.5 −1 −0.5 0 0.5 1 1.5−1.5

−1

−0.5

0

0.5

1

1.5SC−FDMA Time−Domain Constellations (BPSK)

I−real

Q−

imag

signal point 2

signal point 3

























Channel Modelling

o 2D propagation map, direct link: source-destination (S-D),relaying links: source-relay (S-R), relay-destination (R-D)

o Reference distance: S-D link, normalised distances: δSR + δRD = 1

o Average path-loss: δ−ηSR and δ−ηRD

o Path-loss exponent η = 4, shadow fading ξ(dB) ∼ N (0, σ2ξ)

o Instantaneous path-loss: GSR = ξSRδ−ηSR and GRD = ξRDδ

−ηRD

RelaySource Destination

δSR δRD



























Assumptions

o BPSK modulation without channel coding

o AWGN CN (0, σ2N ) at the relay and BS

o Perfect Channel State Information at the Receiver (CSIR) of the BS

o Channel-Dependent Relay Selection (CD-RS) based on pilots

o Orthogonal subbands of the DFT-S-OFDM signals, avoiding MUI among the source MT

o A sufficiently long CP for each transmitted TD signal block, leading to zero inter-blockinterference (IBI)

o Each subband encounters independent and identically Rayleigh distributed block fading

o The K users’ signals are transmitted synchronously over the uplink channels





























Relaying Topologies

o Half-Duplex Time-Division Cooperation• Time slots

TS1: S→D and S→R, TS2: R→D

• Direct Transmission

rrr(t)SD =

K−1Xk=0

HHH(t)SD,ksss

(t)S,k + nnn

(t)D1

• Single-Dedicated-Relaying (SDR):K sources and K relays

rrr(t)

SR,k′ =√GSR

K−1Xk=0

HHH(t)SR,ksss

(t)S,k + nnn

(t)R,k

rrr(t)RD =

√GRD

K−1Xk′=0

HHH(t)

RD,k′sss(t)

R,k′ + nnn(t)D1

TS1

SK−1

TS1

D

R0TS2

S0

TS1

TS1TS2

RK−1































Cooperative Strategies

o Amplify-and-Forward combined with subband-based FD equalisation andremapping

SubbandDemap

DFT

CP

Remove

SubbandMapping

IDFTAdd CP

Matrix

Amplify

21 24

17181920

22 23

Subband FFFU

βββ(f)k

rrr(t)SR,k

sss(t)R,k

TS1

TS2

PPPTk

PPPkFFFH

U

• Subband-specific equalisation and amplification matrix

βββ(f)k = diag{β(f)

k0 , β(f)k1 , · · · , β

(f)

k(N−1)},

where the n-th element is the specific gain factor of the n-th subband

β(f)kn =

qPRt,k/[PSt,kGSR|h(f)

SR,kn|2 + σ2N ].

• The transmitted signal of the k-th relay during TS2

sss(t)R,k =

pPSt,kGSRFFFHUPPPkβββ

(f)k HHH

(f)SR,kxxx

(f)k + nnn

(t)R,k

Single Detection at the BS


Slide 16 - Single Detection at the BS






























Signal Processing at the BS’s Receiver

o MMSE Assisted Joint FD Equalisation and Combining (JFDEC)

SubbandDemap CP

Remove

789DFT

101112

U−pointN−pointIDFT

JFDECTS2:rrr

(t)RD

TS1:rrr(t)SD

PPPTk

yyy(f)D,k′yyy

(f)D,k′yyy

(t)D,k′

FFFHN w∗

D,k′(n+N)

w∗D,k′n

WWWHD,k′

FFFU

• The k′-th user’s received signals include direct and relay branches:

yyy(f)

D,k′ =pPSt,k′HHH

(f)

D,k′xxx(f)

k′ +nnn(f)D

• MMSE optimum weight matrixWWWD,k′ , jointly carry out single-tap FDE and diversitycombining of the direct and relay branches.



































o JFDEC-MMSE cont.

• The n-th and (n+N)-th element of the JFDECWWWD,k′ can be expressed as

wD,k′n =h

(f)

D0,k′n

σ2N

|h(f)

D0,k′n|2

σ2N

+|h(f)

D1,k′n|2

ND1,n+ P−1

St,k′

!−1

,

wD,k′(n+N) =h

(f)

D1,k′n

ND1,n

|h(f)

D0,k′n|2

σ2N

+|h(f)

D1,k′n|2

ND1,n+ P−1

St,k′

!−1

• TD decision variable vectoryyy

(t)

D,k′ = FFFHNWWWHD,k′yyy

(f)

D,k′

• The k′-th user’s overall received SINR

γk′ =

8<: 1

N

N−1Xn=0

24 1 + γSD,k′n+“γ−1SR,k′n + γ−1

RD,k′n

”−1

35−19=;−1

− 1





































Simulation Results

o Power reduction of JFDEC receiver by ignoring path-loss and shadowing

10-5

2

5

10-4

2

5

10-3

2

5

10-2

2

5

10-1

2

5

1

0 2 4 6 8 10 12 14 16 18 20

. ..

.

.

10-5

2

5

10-4

2

5

10-3

2

5

10-2

2

5

10-1

2

5

1B

ER

0 2 4 6 8 10 12 14 16 18 20

Eb/N0 (dB)

SC-FDMA AF (N=M=K=L=8)

SimulationSemi-analysis

. Non-Coop, GaussianNon-Coop, RayleighSDR, FDE-EGCSSR, FDE-EGCSDR, JFDECSSR, JFDEC

Power Reductionat BER=10

-4up to

2dB

4dB

Opportunistic Cooperative Relaying


Slide 19 - Opportunistic Cooperative Relaying





































o Opportunistic relaying- allows a single relay to be selected from a cluster of J(J > 0) inactive MTs, the so-called Relay

Candidates (RC), depending on which MT provides for the best end-to-end link quality between the

source and destination

RelayCandidate

Source

Target Relay

Base Station

SU−RS MU−RS









































Relay Selection Schemes

o Single-User Relay Selection (SU-RS) for the SDR

• High number of idle MTs, more RCs may be considered

• Each source MT is capable of seeking a target relay from a cluster of J RCs which areindependent of the other source MT’s RC

j(opt)k = arg max

j∈[0,J−1]{γj,k}

o Multi-User Relay Selection (MU-RS) for the SDR

• Low number of inactive MTs results in an insufficient number of available RCs

• A cluster of K source MTs is assocated with a cluster of J(J≥K) RCs, the system onlyrequires a total of K relays

j(opt)k,i = arg max

j∈[0,J−1],k∈[0,K−1]{γj,k}











































Simulation Results

• BER performance of relay selection schemes- for path-loss exponent η = 4, 4 source MTs and total 16 RCs case

10-5

2

5

10-4

2

5

10-3

2

5

10-2

2

5

10-1

2

5

1

0 2 4 6 8 10 12 14 16 18 20

. ..

.

.

10-5

2

5

10-4

2

5

10-3

2

5

10-2

2

5

10-1

2

5

1B

ER

0 2 4 6 8 10 12 14 16 18 20

Eb/N0 (dB)

SC-FDMA SDR AF JFDEC (N=M=L=8, K= =4)

2=0dB,

2=0dB

2=4dB,

2=0dB

. Non-Coop, GaussianNon-Coop, RayleighEPA, RRSEPA, SU-RSEPA, MU-RS













































Simulation Results

• Power reduction of relay selection schemes- for path-loss exponent η = 4, 4 source MTs and total 16 RCs case

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

16

18T

rans

mit

pow

erpe

rbi

t(dB

)

2 4 6 8 10 12 14 16 18 20

Sum-Rate (bits/transmission)

SC-FDMA SDR AF JFDEC (N=M=L=8, K= =4)

2=0dB,

2=0dB

2=4dB,

2=0dB

Non-CoopEPA, RRSEPA, SU-RSEPA, MU-RS

Power reduction(without shadowing)

Power reduction(with shadowing)

4.75

dB

5dB

6.75

dB

8.08

dB7.

75dB

9.67

dB

Conclusions


Slide 23 - Conclusions












































Conclusions

o Cooperative SC-FDMA was studied• Proposed diversity-optimised FDE receiver

– achieved 4dB power reduction

• Relay selection schemes for opportunistic relaying– Over fading channels free freom shadowing:

SU-RS provides 6.8dB power reductionMU-RS provides 7.8dB power reduction

– Over 4dB shadow fading channels:SU-RS provides 8dB power reductionMU-RS provides 9.7dB power reduction

power-efﬁcient opportunistic amplify-and-forward … · power-efﬁcient opportunistic...

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