多載波分碼多重存取系統(Multi-Carrier Code Division Multiple Access,
MC-CDMA)在上鏈傳輸時，受到頻率選擇性衰減通道(Frequency Selective Fading
Channel)影響，使用者所屬的展頻碼之間的正交性會被破壞，造成嚴重的多重存
取干擾(Multiple Access Interference, MAI)；有學者提出一種 precoded MC-CDMA
系統，能將 MAI 減少到只有前後使用者會影響主要訊號，而傳統 MC-CDMA 的
MAI 是來自於其他所有使用者。經適當地擺放資料能夠避免掉 MAI 問題，且其
將展頻矩陣與反快速傅立葉轉換(Inverse Fast Fourier Transform, IFFT)結合成一
低密度之轉換矩陣。此轉換矩陣由稀疏完美高斯整數序列(Sparse Perfect Gaussian
Integer Sequence, SPGIS)建構而成，所以能得到額外的好處：有效降低峰均功率
比(Peak-to-Average Power Ratio, PAPR)及降低傳送端及接收端的運算複雜度；此
系統雖能完全避免多重存取干擾，卻限制了資料傳輸量。在這篇碩論中，我們觀
察接收訊號、傳送訊號、通道路徑之間的關係，並以高斯隨機變數來近似 MAI
和雜訊，試圖以機率的角度來處理訊號。在處理接收訊號時，利用該隨機變數的
統計性質來消除 MAI 對接收訊號的影響，進而計算出每個符元的傳送機率。由
於我們利用高斯隨機變數近似干擾項及雜訊項，且利用符元與通道路徑之間的關
係做一連串的干擾消除處理。故我們將這樣子的訊號處理方式稱為利用機率概念
的干擾消除(Probability based Interference Cancellation, PbIC)演算法；由模擬結果
可以發現，我們成功地提升了舊方法的資料傳輸量，同時在位元錯誤率效能方面
也比較好。在特定環境參數下，此演算法效能甚至能逼近最大概似機率(Maximum
Likelihood, ML)偵測接收機效能。最後，在運算複雜度分析部分可以看出，PbIC
演算法複雜度比 ML 偵測接收機少非常多。

Multi-carrier code division multiple access (MC-CDMA) system will be effect
by multipath channel in uplink transmission and tend to destroy orthogonality among
users lead to multi-access interference (MAI). Thus, the performance of MC-CDMA
will degrade greatly. In order to deal with MAI, authors proposed new MC-CDMA
structure, called precoded MC-CDMA, it can decrease MAI and only from two user.
By the way, the MAI from all other user in conventional MC-CDMA. The system
used sparse perfect Gaussian integer sequences (SPGIS) as low density spreading
matrix that combine spreading matrix and IFFT matrix. The precoded MC-CDMA has
several advantage such as low PAPR, low computational complexity. Although the
method of novel symbol vector location also can remove MAI term. But, throughput
be limited. In this work, we develop algorithm that can mitigate the MAI. We tried to
improve the performance of precoded MC-CDMA such as BER and throughput using
probability based interference cancellation (PbIC) algorithm. By the way,
performance of our algorithm approach ML detection performance and the
computational complexity of PbIC is lower than ML detection. We briefly illustrate
the principle of PbIC algorithm. We observed the relation of transmitted symbols,
channel path and received symbols. Then, the Interference term and noise term of
receive signal be approximated to Gaussian distribution random variable. We used
statistical property of interference to mitigate the MAI term and determined the
probability of transmitted symbols. Finally, we can detect symbols correctly.

論文審定書.....................................................................................................................i
誌謝................................................................................................................................ii
中文摘要.......................................................................................................................iii
Abstract........................................................................................................................iv
目錄................................................................................................................................v
圖次..............................................................................................................................vii
表次................................................................................................................................viii
第一章 導論................................................................................................................1
1.1 研究動機與貢獻............................................................................................4
1.2 論文架構........................................................................................................4
第二章 系統模型........................................................................................................5
2.1 正交分頻多工系統之基本架構....................................................................5
2.2 多載波分碼多重存取系統之基本架構......................................................10
第三章 轉換矩陣之設計..........................................................................................12
3.1 展頻碼矩陣與轉換矩陣..............................................................................12
3.2 使用稀疏完美高斯整數序列之轉換矩陣產生方法..................................13
第四章預編碼多載波分碼多重存取上鏈系統使用干擾消除演算法 .....................17
4.1 傳送端架構..................................................................................................17
4.2 接收端架構..................................................................................................19
4.3 利用機率概念的干擾消除演算法..............................................................22
4.4 訊號和雜訊加上干擾的比值推導和分析..................................................33
4.5 複雜度分析與比較......................................................................................35
第五章 模擬結果與討論..........................................................................................39
第六章 結論..............................................................................................................46
參考文獻......................................................................................................................47
中英對照表..................................................................................................................53
縮寫對照表..................................................................................................................59
圖 2-1 多載波系統 ........................................................................................................6
圖 2-2 傳統 OFDM 傳送端...........................................................................................6
圖 2-3 傳統 OFDM 接收端...........................................................................................6
圖 2-4 S/P 轉換示意圖 .................................................................................................7
圖 2-5 使用 IDFT 之等效 OFDM 傳送端....................................................................9
圖 2-6 MC-CDMA 系統傳送端架構圖 .....................................................................11
圖 2-7 MC-CDMA 系統接收端架構圖 .....................................................................11
圖 4-1 預編碼多載波分碼多重存取上鏈系統傳送端 ..............................................18
圖 4-2 預編碼多載波分碼多重存取上鏈系統接收端 ..............................................19
圖 4-3 干擾訊號來源示意圖 ......................................................................................25
圖 4-4 多重存取干擾來源示意圖 ..............................................................................26
圖 4-5 利用機率概念的干擾消除演算法運作方塊圖 ..............................................27
圖 4-6 利用機率概念的干擾消除演算法解碼過程 ..................................................32
圖 5-1 完整使用所有展頻碼導致 MAI 效應 ............................................................39
圖 5-2 適當擺放資料方式避免 MAI 效應 ................................................................39
圖 5-3 Precoded MC-CDMA 使用不同方法的錯誤率效能比較 L=10....................41
圖 5-4 Precoded MC-CDMA 使用不同方法的錯誤率效能比較 L=20....................42
圖 5-5 PbIC 和 ML 的錯誤率效能比較 L=4 .............................................................43
圖 5-6 PbIC 在不同權重因子下的錯誤率分析 ........................................................44
圖 5-7 PbIC 在不同權重因子暨不同疊代次數與錯誤率分析 ................................45
表 4-1 PbIC 與 ML 在改變使用者數量時比較各方法的計算複雜度....................38
表 4-2 PbIC 與 ML 在改變通道長度時比較各方法的計算複雜度........................38
表 4-3 PbIC 與 ML 在改變碼長時比較各方法的計算複雜度................................38

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