在正交分頻多工存取中, 頻譜資源分割給多個正交的子載波, 且子載波被分配給不
同的使用者同時傳輸, 然而正交分頻多工與正交分頻存取有著相同的問題, 對於破壞這
些子載波正交性的載波頻域偏移相當的敏感, 而也因載波頻率位移的緣故, 造成載波間
干擾和多重存取干擾。
為了減輕在正交分頻多工存取上鏈系統上的載波間干擾和多重存取干擾的影響, 在
本論文中我們提出迭代式接收器之最小均方誤差等化器, 此接收器由兩個不同的最小均
方誤差等化器所組成。在第一部分, 我們採用線性最小均方誤差等化器, 並且利用干擾消
除以最小均方誤差等化器所回傳的軟性對數概似比值來消除接收訊號的干擾, 而干擾消
除以最小均方誤差等化器稱之為第二部份, 而在第二部分中, 由於載波間干擾的重建會
因上一部分的決策錯誤而導致錯誤的傳遞, 為了降低錯誤訊息傳遞的可能, 在最小均方
誤差等化器中將為了使得錯誤傳遞的可能降到最低, 藉由對數概似比值來轉換成決策錯
誤的機率, 錯誤協方差矩陣可更準確被求出。 基於渦輪原理下透過對數概似比值的交換
可更有效的傳遞訊息, 因此將渦輪原理應用於我們所提出的演算法中, 可使第一部份和
第二部份的訊息交換來得更有效率, 爾後我們進行模擬來驗證所提出之低複雜度方法與
先前比之方法比較能有更優異之錯誤率效能 。

In orthogonal frequency division multiple access (OFDMA) systems, the total
spectral resource is partitioned into multiple orthogonal subcarriers. These subcarriers are then assigned to different users for simultaneous transmission. However,similar as OFDM, OFDMA is very sensitive to carrier frequency offsets that destroy the orthogonality among the subcarriers and as a consequence introduceinter-carrier interference (ICI) and multiple access interference (MAI).
To alleviate the effect of ICI and MAI in the OFDMA uplink systems, in this
thesis we propose an iterative receiver which consists of two parts which based on the turbo principle, effectively interchange the soft information in between. In the first part, we adopt the linear minimum mean square error (MMSE) equalizer to cancel the interference in the received signals with the aid of soft log-likelihood ratio (LLR) fed from the second part. The second part consists of an interference cancellation and an MMSE equalizer. The MMSE equalizer is employed to minimize the error progation effect, incurred due to the incorrect ICI regenerated by the output of the first part, by converting LLR to the decision error probability so as to attain more accurated error covariance matrix. Conducted simulations show that the proposed scheme, with lower computational complexity, provides comparable or even superior performance compared with previous works .

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