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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 Kimanas@gist.ac.kr
Multimedia Communication Systems Lab.Dept. of Information and Communications, GIST
ICOIN 2005Jan 31st – Feb 2nd, 2005
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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.
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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
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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!
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