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An Uplink Resource Allocation Algorithm For OFDM and FBMC Based Cognitive Radio Systems
Musbah Shaat & Faouzi Bader
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
Castelldefels-Barcelona, Spain
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Outline
• Introduction.
• System model.
• Optimization problem.
• Proposed subcarrier allocation algorithm.
• Proposed power allocation algorithm.
• Simulation results.
• Conclusions.
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Introduction
• The spectrum scarcity is considered as one ofthe serious problem.
• Cognitive radio (CR) aims to increase thespectrum utilization.
• Multicarrier communication has beensuggested as a candidate for cognitive radio(CR) systems.
• OFDM suffers from high interference to theprimary user (PU) and the cyclic prefixinsertion decreases the system capacity.
• FBMC doesn’t need any CP insertion and canovercome the interference problem.
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Introduction, cont.
/ IFFTPrefix
insertion / /FFTPrefix
removing/Input
Stream
Output
Stream
Channel
OFDM Transmitter
S
/P
IFFT
Polyphase
Network
( PPN )
P
/S
P
/S
FFT
Polyphase
Network
( PPN )
S
/P
Synthesis Filter Bank Analysis Filter Bank
S/P
IFFTPrefix
insertion
P
/S
P/S
FFTPrefix
removing
S/P
S/P
IFFT
Polyphase
Network
( PPN )
P/S
P/S
FFT
Polyphase
Network
( PPN )
S/P
Input
Stream Stream
Channel
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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System Model
• The CR system coexist with the PU’s radio inthe same geographical location.
• The Uplink scenario will be considered.
• Each of the two system causes interference toeach other.
CR base station
(CBS)
Secondary User
(SU1)
(SU3)
(SU3)
Transmission
Interference
Primary System
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System Model, Cont.
• The SU and PU band are exist side by side.
• Mutual interference is a limiting factor affect theperformance of both systems.
• The CR can use non-active primary bands.
• The introduced interference to the primary bandshould be below where is the interferencetemperature limit.
th thI T B thT
1 2………. N
Frequency
PU Band
B
f
CR Band CR Band
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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System Model, Cont.
• The interference introduced by the subcarrier to PU band is the integration of the PSD of the subcarrier across the PU band
• The PSD expression depends on the used multicarrier technique.
4 5 6 7 8 9 10 11 12-0.2
0
0.2
0.4
0.6
0.8
1
1.2Amplitude
FILTER BANK
OFDM
Sub-channel
thithi
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
8Problem Formulation
• The objective is to maximize the total data rate of the CR system subject to the interference introduced to the PU band and per-user power constraints
• where
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
9Problem Formulation, Cont.
• The problem is combinatorial optimization problem.• The complexity grows with the input size.• The problem is solved in two steps
1. Subcarriers are assigned to the users.2. Power allocated to the different subcarriers
(virtually as single user multicarrier system)
1 2………. N
Frequency
PU Band
B
f
CR Band CR Band
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Proposed Subcarrier Allocation Algorithm
• Assume that every subcarrier is allowed to introduce the same amount of interference to the primary system
• The maximum power that can be allocated to the ith subcarrier when it is allocated to the mth SU is
• Let to be the set of unassigned subcarriers.
subcarriers allocated according to Max. Power
subcarriers allocated according to Average Power
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Proposed Subcarrier Allocation Algorithm, Cont.
• The assigning procedures of a particular subcarrier
are as follows:
1. For every User m , Evaluate
If
else
2. Compute the amount of increment in the data rate
when the subcarrier is assigned to the SU
and
and
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Proposed Subcarrier Allocation Algorithm, Cont.
• Find satisfying and
set
, and .
• Remove the subcarrier form the set and repeat until the set is empty.
• The final set of allocated subcarriers to the SU is
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Proposed Power Allocation Algorithm
• Once the subcarriers are allocated to the users, the multiuser system can be viewed virtually as a single user multicarrier system. The problem can be reformulated as follows:
• Where in and refers to the user who’s already got the subcarrier .
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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• Problem P2 is convex with the Lagrangian :
• Applying KKT condition and solving for the optimal
• Can be solved numerically using ellipsoid or interior point method with a polynomial time complexity.
Proposed Power Allocation Algorithm, Cont.
(*)
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
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Simulation Results
• Optimal: the subcarriers are allocated by exhaustive enumeration while the power is allocated by (*)
• Wang: the method proposed inWang et al., “An uplink resource allocation scheme for OFDMA-based cognitive radio networks,” International Journal of Communication Systems, vol. 22, no. 5, pp. 603–623, 2009.
• Classical: the subcarriers are allocated according to the scheme used in non-cognitive OFDM while the power is allocated by (*).
Gao et al., ““Efficient subcarrier, power, and rate allocation with fairness consideration for OFDMA uplink,” IEEE Trans. Wireless Communications, vol. 7, no. 5, pp. 1507–1511, May 2008.
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications
16Simulation Results (Interference. Vs. Capacity)
-60 -50 -40 -300
1
2
3
4
5
6
7
Interference (dBm)
Capacity (
bit/H
z/s
ec)
Optimal-OFDM
Optimal-FBMC
Proposed-OFDM
Proposed-FBMC
Wang-OFDM
Wang-FBMC
Classical-OFDM
Classical-FBMC
17Simulation Results (Interference. Vs. Capacity)
-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 00
1
2
3
4
5
6
7
8
9
10
Interference Threshold (dBm)
Capacity (
Bit/H
z/s
ec)
Proposed
Wang
Classical
OFDM
FBMC
18Simulation Results (No. of Users Vs. Capacity)
0 5 10 153
4
5
6
7
8
9
10
11
No. Users
Capacity (
Bit/H
z/s
ec)
Proposed
Wang
Classical
OFDM
FBMC
19Conclusions
• Efficient resource allocation algorithm for uplink in multicarrier based CR networks was presented.
• The allocation process is separated into two steps.
1. In the first step, the subcarriers are allocated to the users .
2. In the second step, the per-user power budget is distributed among the subcarriers .
• The proposed algorithm with low computational complexity outperforms other algorithms and achieves a very good performance.
• The obtained results contribute in recommending the use ofFBMC physical layer in the future cognitive radio systems.
• Developing a resource allocation algorithm that considersmany interference constraints as well as the users quality ofservice (QoS) will be the guideline of our future research.
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Thanks for your kind attention!
Contact Email:
{musbah.shaat,faouzi.bader}@cttc.es
5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications