正交分頻多工存取系統(orthogonal frequency division multiple ac-
cess, OFDMA) 中, 對於破壞這些子載波正交性的載波頻域偏移相當的
敏感, 而也因載波頻率偏移 (carrier frequency offsets, CFOs) 的緣故,
造成載波間干擾 (inter-carrier interference, ICI) 和多重存取干擾 (mul-
tiple access interference, MAI)。而在接收端也容易造成 I/Q 不平衡 (in-
phase/quadrature-phase imbalance) 的干擾, 此將造成振幅及相位的失
真, 這將導致實部項與虛部項之振幅不一致, 而且兩項之相位也不能剛好
為90度, 此些影響將不僅產生鏡像干擾及載波間干擾, 並且對於載波頻率
偏移的估測也會造成錯誤。
為了減輕載波頻率偏移和 I/Q 不平衡的影響, 於本論文中, 我們考
慮將先將 I/Q 不平衡及載波頻率偏移做最大似然估測法, 再結合最小均
方誤差偵測器並佐以連續干擾消除法 (successive interference cancella-
tion, SIC) 的應用在交錯的正交分頻多工存取上鏈系統上。 對每個傳輸符
元, 在第一部分中, 我們使用最大似然估測法先對 IQ 不平衡做干擾參數
的估測, 接著再對載波頻率偏移一樣以最大似然估測法來估測參數, 然後
有效地利用連續干擾消除法減少過去符元的干擾所造成的錯誤, 此步驟能
有效地重建出較一個接近原始之訊號, 最後再以最小均方誤差徹底的減少
干擾和殘留決策的錯誤, 如此我們所提出之法便能有效得到較精確的估測
值以及更為優良的接收效能, 最後我們對發展之演算法, 進行電腦模擬與
效能分析, 而實驗結果也驗證所提之法確實較優於過去存在之法。 儘管如
此, 我們也可得知在得到這些成果的同時, 還能保有相近的複雜度。

The orthogonal frequency division multiple access (OFDMA) sys-
tems are very sensitive to carrier frequency offsets (CFOs) that de-
stroy the orthogonality among the subcarriers . Also, the in-phase/q
uadrature-phase (I/Q) imbalance may produce amplitude and phase
mismatch producing the unwanted image interference to affect the
desired signal and degrading the accuracy of CFO estimation.
In this thesis, we present a maximumlikelihood(ML)-based scheme
for joint estimation of CFO and I/Q imbalance in the uplink of in-
terleaved OFDMA systems. In light of the fact that the received
signal is contaminated by multiple access interference (MUI) and
inter-carrier interference (ICI), the successive interference cancella-
tion (SIC) are employed before proceeding the parameter estimation.
For every transmitted symbol, SIC is first invoked to alleviate the
MUI and ICI, the CFO and I/Q imbalance are then estimated based
on the successively refined signals. Thereafter, to mitigate the inter-
ference caused by the undetected symbol, a minimum mean-square
error (MMSE) multiuser detector is employed to determine the out-
put. As such, the CFO and I/Q imbalance estimates are refined
sequentially. While the overall computational complexity is slightly
higher, the developed scheme, as shown by simulations, provides su-
perior performance compared with pervious works.

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