an efficient subcarrier and power allocation algorithm for dual-service provisioning in ofdma based...

An Efficient Subcarrier and Power Allocation An Efficient Subcarrier and Power Allocation Algorithm for Dual-Service Provisioning Algorithm for Dual-Service Provisioning

in OFDMA Based WiBro Systems in OFDMA Based WiBro Systems

February 1, 2005

Mohmmad Anas, Kanghee Kim, Jee Hwan Ahn, and Kiseon [email protected]

Multimedia Communication Systems Lab.Dept. of Information and Communications, GIST

ICOIN 2005Jan 31st – Feb 2nd, 2005

Multimedia Communication Systems Lab.

[2/34]

Resource Allocation IssuesResource Allocation Issues Resource Allocation in OFDMA Systems

Subcarrier Allocation Different subcarriers are allocated to different users according to

subcarrier allocation strategy Power Allocation

Depending upon the user’s capacity requirement power is allocated to the user’s subcarriers

[OFDMA: Orthogonal Frequency Division Multiple Access]

Subcarrier Allocation

Power Allocation

Two set of flows

Flow 1

Flow 2

Mix of flows

Complete Channel State Information is known

1) How to allocate subcarriers for dual-service provisioning

2) How to allocate power for dual-service

provisioning


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ContributionsContributions An efficient resource (sequential subcarrier and power) allocatio

n algorithm is proposed for dual-service (GP and BE) provisioni

ng in OFDMA based systems.GP: Guaranteed Performance; BE: Best Effort; EQ: EQual power allocation;

PA: Power Allocation; RA: Resource Allocation

Proposed-EQ

Proposed-PA

Two set of flows having different required

QoS

GP Users

BE Users

Mix of flows

Complete Channel State Information is known

Proposed-RA


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ContentsContents

INTRODUCTION

OVERVIEW OF OFDMA SYSTEM

RESOURCE ALLOCATION IN OFDMA SYSTEM

Subcarrier Allocation for Dual-Class Users Power Allocation for Dual-Class Users

SIMULATION RESULTS

CONCLUDING REMARKS


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Research Background

Motivations and Objective

IINTRODUCTIONNTRODUCTION


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Broadband Wireless Applications NextG Mobile Communication Systems

Integration of Voice, Video, Image, Data etc.

User-level QoS Provisioning

OFDMA is chosen as PHY-MAC of several NextG standards IEEE 802.16-2004, ETSI HiperLAN/2, DVB etc.

Resource Allocation in OFDMA Systems Adaptive/Dynamic Resource Allocation is advantageous over

Fixed Resource Allocation Wireless Channel is time-varying and frequency-selective

Previous works mainly focus on joint subcarrier and power allocation problem for system-level QoS provisioning

Research BackgroundResearch Background


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Motivations and ObjectiveMotivations and Objective

Objective

OFDMA is PHY-MAC standard for several NextG communication systems

Resource Allocation in multiuser-OFDM/OFDMA is mostly studied for

system-level QoS provisioning

Joint subcarrier and power allocation for user-level QoS provisioning

is NP-hard problem [NP-hard: non-deterministic polynomial time hard]

[Shen’03] Joint resource allocation problem can be decoupled into

subcarrier allocation and power allocation problems with the reduction in

complexity almost by half and can be solve using canonical methods

Motivations

To present an efficient, decoupled subcarrier and power allocation

algorithm, for user-level QoS provisioning [QoS: data rate and BER]


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OFDMA Block Diagram

System Model

Traffic Model

OOverviewverview ofof OFDMA S OFDMA Systemsystems


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OFDMA Block DiagramOFDMA Block Diagram

Assumptions: - Base Station has perfect CSI

- Base station informs the mobile for Resource Allocation

- Subcarrier is not shared among users @ a certain time instant

OFDMATransceiver

SubcarrierSelector

Subcarrier and Power/Bit

Allocation Algorithm

OFDMATransceiver

b1

data

Subcarrier and bit information

Channel State Information (CSI), Hk,n

Subcarrier and bit allocation

Base Station User k

Subcarrier and power information

for mobile k

Channel Estimator

b2

bK


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System ModelSystem Model Assumption Each user experience independent fading, hk,n, with AW

GN with mean zero and variance, σ2 = N0(B/N)

Received SNR for the kth user’s nth subcarrier,2

, ,, , ,

0

| |k n k nk n k n k n

p hp H

BN

N

where, Hk,n: carrier-to-noise ratio

pk,n: power allocated to the kth user’s nth subcarrier

N0: noise power spectral density

B: total bandwidth

N: total number of subcarriers

[Goldsmith’97] for

,

,MQAM ,

1.51BER ( ) exp

5 2 1k n

k nk n q

,, 2log 1 bits/symbolk n

k nq

ln 5BER /1.5

, ,2; 0 30dBk n k nq


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Traffic ModelTraffic Model NextG broadband wireless communication expects mix of user

applications i.e., voice, video, image, and data

Assumptions: Mixture of two kind of users differentiated on the basis of QoS (data

rate and BER): Guaranteed Performance (GP) and Best Effort (BE)

GP Users: require bounded BER, and throughput guarantee

BE Users: require bounded BER, and NO throughput guarantee

Total number of users in the system is K

First K1 (known) users are GP users

Last (K-K1) users are BE users

All GP users have same BER requirements ( )

All BE users have same rate and BER requirements ( )

1

2


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Joint Subcarrier and Power Allocation Joint Problem Formulation

Decoupled Problem Formulation

Proposed-EQ

Proposed-RA Algorithm

RResourceesource A Allocation in llocation in OFDMAOFDMA SSystemystem

for for Dual-Service ProvisioningDual-Service Provisioning


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Joint Subcarrier and Power Allocation (I)Joint Subcarrier and Power Allocation (I)

Data rate of user k, , , ,2log (1 ) bps

k k

k n k n k nk

n n

q p HBR

T N

Problem Statement:

Maximize the sum capacity for BE (Best Effort) users under the constraints

of GP (Guaranteed Performance) users data rate requirements and total

transmitted power constraints.

where, Ωk: set of subcarrier allocated to kth user

T: OFDMA symbol duration i.e., 1/( / ) ( / ) secondsT B N N B


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Joint Subcarrier and Power Allocation (II)Joint Subcarrier and Power Allocation (II)

Joint Subcarrier and Power Allocation Problem Formulation:

,1

, ,2

,1 2

max log 1k n k

k

Kk n k n

pk K n

p HBN

, ,2

1

log 1k

k n k nk

n

p HBR

N

total

K

k nnk Pp

k

1

,

, 0 for all ,k np k n

1 11 2 1 2: : : : : :K KR R R

Maximization of sum capacity of BE users

Rate of ANY one GP user

Total Power Constraint

Other GP users rate are limited by the proportionality equation

[Hoo’98] NP-hard problem Decouple subcarrier and power allocation

Subject to:


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Decoupled Subcarrier and Power AllocationDecoupled Subcarrier and Power Allocation

Power Allocation Problem (for known subcarrier allocation) Formulation:

,1

, ,2

1 2

max log 1k n

k

Kk n k n

pk K n

p HBN

, ,2

1

log 1k

k n k nk

n

p HBR

N

total

K

k nnk Pp

k

1

,

, 0 for all ,k np k n

1 11 2 1 2: : : : : :K KR R R

Subcarrier allocation to service combined GP and BE users Power is assumed to be equally distributed for subcarrier allocation

Subject to:


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Proposed-EQ Algorithm (I)Proposed-EQ Algorithm (I)

Based on suboptimal subchannel allocation in [Rhee’00]

Proposed-EQ: Subcarrier allocation to combined GP and BE users… We assume power is equally distributed among subcarriers as in [Rhee’00]

1. Initialization (enforce zero initial conditions)

(a) set Rk=0, k= for k = 1, 2,…, K and A = {1, 2,…, N}

(b) p=Ptotal/N EQual power is allocated among subcarriers

2. For k = 1 to K1 (allocate best subcarrier for each GP user)

(a) find n satisfying | Hk,n| | Hk,j| for all j A

(b) let k = k {n}, A = A – {n}

(c)

(d) while A ≠ , repeat Step 2 until the Rate requirements for GP users are

fulfilled

,2

1

log 1 k nk k

pHBR R

N


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Proposed-EQ Algorithm (II)Proposed-EQ Algorithm (II)

3. For k = K1+1 to K (allocate left subcarriers to BE users)

(a) find n satisfying | Hk,n| | Hk,j| for all j A

(b) let k = k {n}, A = A – {n}

(c)

4. While A ≠ (iteratively give lowest rate BE user first choice)

(a) find k satisfying Rk ≤ Ri for all i, K1+1 ≤ i ≤ K

(b) for the found k, find n satisfying | Hk,n| | Hk,j| for all j A

(c) for the found k and n, let k = k {n}, A = A – {n}

(d)

,2

2

log 1 k nk k

pHBR R

N

,2

2

log 1 k nk k

pHBR R

N

Omitting Step 2.(d) and Step 3 in proposed-EQ reduces it to method in [Rhee’00]


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Proposed-RA Algorithm (I)Proposed-RA Algorithm (I)

Proposed-RA: Resource allocation to provide service to combined

GP and BE users

Proposed-EQ is used as subcarrier allocation algorithm

An efficient power allocation algorithm for dual-service (combined GP

and BE users) provisioning is proposed: Proposed-PA

start

Distribute power amongGP users and BE users

proportional to the numberof subcarriers allotted to

each service

1

' 1Power allocated to GP users,

K

kk

temp total

NP P

N

" 'Power allocated to BE users, temp total tempP P P

Proposed-EQ Algorithm

Proposed Power AllocationAlgorithm


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Proposed-RA Algorithm (II)Proposed-RA Algorithm (II)

Allocate power to GP userssubcarrier under total powerconstraint of P’temp according

to the optimal waterfillingsolution

Above found P” is thendistributed equally amongthe subcarriers allotted to

BE users

stop

1 1

1

'',

21, 2, ,2

1

Capacity of each BE user,

log 1k

k nk Kk K K K

nk

k K

HB PR

NN

( )reqk kR R R

' 'temp tempP P P ' '

temp tempP P P

( )if ( )reqk kR R R ( )if ( )req

k kR R R

NoNo

Yes' '

'' '

temp

total temp

P P

P P P


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Resource Allocation in OFDMA System Simulation Parameters

Optimal Power Allocation

Proposed-RA vs. Proposed-EQ

SSimulationimulation R Resultsesults


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Simulation ParametersSimulation Parameters

SystemOFDMA System, Number of Subcarriers, N = 64

Number of Users, K = [4, 8, 12, 16]

Channel6-tap exponentially decaying power profile with Rayleigh fading

Max. delay spread 5 s

Doppler frequency 30 Hz

GP Users BE Users

Number of Users First 50% Last 50%

Required BER 10-5 10-3

Required data rate 1 bps/Hz Not applicable

Example Voice, Video Internet Data


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Proposed-EQ vs. Proposed-RA (I)Proposed-EQ vs. Proposed-RA (I)

(a) (b)

1 2 1 20

5

10

User Index

Cap

acit

y [b

it/s

/Hz]

1 2 1 20

5

10

User Index

Cap

acit

y [b

it/s

/Hz]

BE Users

GP Users

BE Users

GP Users

1 2 3 4 1 2 3 40

2

4

User Index

Cap

acit

y [b

it/s

/Hz]

1 2 3 4 1 2 3 40

2

4

User Index

Cap

acit

y [b

it/s

/Hz]

BE Users

GP Users

BE Users

GP Users

Figure 3. Capacity vs. user index. (a) K = 4; (b) K = 8

Proposed-EQ Proposed-RA

Observations: We notice that GP users adapt to their data rates (1 bps/Hz) after proposed-RA a

lgorithm. While the BE user’s capacity performance is same for proposed-EQ and proposed-RA.


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Proposed-EQ vs. Proposed-RA (II)Proposed-EQ vs. Proposed-RA (II)

(c) (d)

1 2 3 4 5 6 1 2 3 4 5 60

1

2

User Index

Cap

acit

y [b

it/s

/Hz]

1 2 3 4 5 6 1 2 3 4 5 60

1

2

User Index

Cap

acit

y [b

it/s

/Hz]

BE Users

GP Users

BE Users

GP Users

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 80

1

2

User Index

Cap

acit

y [b

it/s

/Hz]

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 80

1

2

User Index

Cap

acit

y [b

it/s

/Hz]

BE Users

GP Users

BE Users

GP Users

Figure 4. Capacity vs. user index. (a) K = 12; (b) K = 16

Proposed-EQ Proposed-RA

Observations: We notice that GP user’s QoS requirements (1 bps/Hz) are satisfied after propos

ed-RA algorithm.


[24/34]

Proposed-EQ vs. Proposed-RA (III)Proposed-EQ vs. Proposed-RA (III)

Figure 5. min-user’s capacity of GP and BE users vs. number of users

Observations:

min-user’s capacity of GP

users (A, B) remain consta

nt while those of BE users

(C, D) decreases with the i

ncrease in number of user

s.

Adaptive resource allocati

on (C, D) performs better t

han static resource allocati

on i.e., TDMA (E).

4 6 8 10 12 14 160

2

4

6

8

Number of Users (K)

min

(Rk)

[bit/s

/Hz]

proposed-RA-GP

proposed-EQ-GP

proposed-RA-BE

proposed-EQ-BE

TDMA

A:

B:

C:

D:

E:C, D

A, B

E


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Conclusions

CCONCLUDING ONCLUDING RREMARKSEMARKS


[26/34]

ConclusionsConclusions

QoS aware subcarrier and power allocation for OFDMA based broadband wireless communication system is studied Proposed a subcarrier allocation algorithm to service dual-class

users differentiated on the basis of data rate and BER: Proposed-EQ The suboptimal subchannel allocation method in [Rhee’00] is the

motivation for proposed-EQ algorithm

Proposed an efficient power allocation algorithm for dual-class users

(combined GP and BE) provisioning assuming subcarrier allocation

determined by the proposed-EQ: Proposed-RA

Result shows that proposed-RA works well to provide

guaranteed performance to GP users and to maximize the sum-

capacity for BE users for given BER.


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ReferencesReferences

[Wong‘99] C.Y. Wong, R.S. Cheng, K.B. Letaief, and R.D. Murch, “Multiuser OFDM with Adaptive Subcarrier, Bit, and Power Allocation”, IEEE JSAC, Vol. 17, No.10 (1999)

[Rhee‘00] W. Rhee, and J.M. Cioffi, “Increase in Capacity of Multiuser OFDM system Using Dynamic Subchannel Allocation,” IEEE VTC-Spring (2000)

[Yin‘00] H. Yin, and H. Liu, “An Efficient Multiuser Loading Algorithm for OFDM-based Broadband Wireless Systems,” IEEE GLOBECOM (2000)

[Jang‘03] J. Jang, and K.B. Lee, “Transmit Power Adaptation for Multiuser OFDM Systems,” IEEE JSAC, Vol.21, No. 2 (2003)

[Shen‘03] Z. Shen, J.G. Andrews, and B.L. Evans, “Optimal Power Allocation in Multiuser OFDM Systems,” IEEE GLOBECOM (2003)

[Hoo‘98] L. Hoo, J. Tellado and J.M. Cioffi, “Dual QoS Loading Algorithm for DMT Systems Offering CBR and VBR Services,” IEEE GLOBECOM, Vol. 1 (1998)

[Goldsmith‘97] A.J. Goldsmith and S.G. Chua, “Variable-Rate Variable-Power MQAM for Fading Channels,” IEEE Trans. On Communications, Vol. 45 (1997)

[Shakkottai‘03] S. Shakkottai, T.S. Rappaport, and P.C. Karlsson, “Cross-layer Design for Wireless Networks,” IEEE Communications Magazine, vol. 41 (2003)


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Thank you!

an efficient subcarrier and power allocation algorithm for dual-service provisioning in ofdma based...

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