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Carrier Frequency Offset Compensation with Successive Cancellation in Uplink OFDMA
Systems
Tevfik Yucek,Student Member,IEEE,and Huseyin Arslan,Senior Member,IEEE
Wireless Communications, IEEE Transactions onVolume 6, Issue 10, October 2007 Page(s):3546 - 3551
學生 :陳威宇學號 :96325513
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Outline
• Introduction• System Model• Proposed Compensation Algorithm• Numerical Results• Conclusions• Reference
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Ⅰ. Introduction
• OFDMA - orthogonal frequency division multiple access
- subcarriers -> grouped into sets & assigned to different user
• CFO - carrier frequency offset - mismatch of the oscillators in the transmitter and the receiver
• In the uplink of an OFDMA - inter-carrier interference ,ICI multiple access interference , MAI
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Introduction ICI- the leakage or interference between a user’s own subcarriers
MAI-the power leakage from user’s subcarriers
• Two main approaches,can be used to mitigate the frequency offset in the uplink of OFDMA
- feedback and compensation method
• In this paper,present SIC (successive interference cancellation) method for frequency offset compensation assuming that
- perfect timing alignment - frequency offset of all uplink users are known at the receiver
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Ⅱ . System Model• OFDMA system with D users and N subcarriers• The IDFT output of ith user can be written as
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System Model• Assuming perfect time synchronization , discrete-time model of the rec
eived signal at the BS after removal of the CP can be written as
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System Model• The DFT output can be obtained as
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System Model• Assuming , the received signal in kth subcarrier can be written as
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System Model
• Clustered subcarrier assignment scheme where subcarriers are grouped into clusters
and each clusters is assigned to a different user
- Clustered =>size K
- total number of clustered is N/K
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Ⅲ. Proposed Compensation Algorithm
• Combination A. Decorrelation - remove the ICI effect B. Successive Cancellation - solve the MAI problem
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A. Decorrelation• In the receiver , the DFT output for cth cluster ,
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Decorrelation• The decorrelator output can be calculated using (8) as
• Using and the channel knowledge , the receiver can detect the transmitted information.
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B. Successive Cancellation• The interference of cth cluster
• The uth subcarrier`s value after removal of MAI from cth cluster becomes
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Successive Cancellation• proof
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Ⅳ . Numerical Results• An uplink OFDMA system parameter
subcarrier : 256 users: 8
clusters for each user : 8 transmission bandwidth : 10 MHz
channel : A of ITU-R channel model for vehicular environments with high antenna[13]
IMT-2000 frequency offset : independent for all user
random variable with uniform distribution(-єmax ,єmax)
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Numerical Results
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Numerical Results
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Numerical Results
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Numerical Results
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Ⅴ. Conclusions
• The proposed method , a combination of decorrelator and successive cancelation , can compensate the different frequency offsets of users with manageable complexity .
• We have proposed to apply SIC to only neighboring subcarriers in order to decrease the computational complexity.
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Ⅵ . Reference• [5] J Choi; C. Lee; H. W. Jung and Y. H. Lee; “ carrier fre
quency offset compensation for uplink of ofdm-fdma systems,”IEEE Trans. Commun. ,vol.53,no.7,pp. 1155-1165,July 2005
• [9] T. Yucek , “ Self-interference handling in OFDM based wireless communication systems,” Master’s thesis , University of South Florida,Nov.2003.