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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.