稀疏編碼多重存取系統(Sparse Code Multiple Access, SCMA)是為了因應第五代行動通訊(5th Generation Mobile Networks)所提出的技術，有著增進頻寬使用效率(Spectrum Efficiency)的特點。在SCMA系統中，每個使用者都會被分配不同碼簿(Codebook)，碼簿由多組碼字(Codeword)所組成，由使用者輸入SCMA Encoder的資料，選擇對應的碼字進行傳送。而每個使用者依照輸入訊號所選擇的碼字，經過通道之後，於接收端會因為使用者間的碼字間的非正交性而造成多重使用者干擾(Multiple User Interference, MUI)。在碼簿建構方面，我們利用稀疏完美高斯整數序列(Sparse Gaussian Integer Perfect Sequence, SGIPS)設計碼簿，把不同使用者所傳送出的碼字間的最短距離最大化做為設計的目標，提升多用戶偵測器(Multiple User Detector, MUD)的效能，另外，在頻域(Frequency Domain)建構碼字，利用SGIPS在對應的時域(Time Domain)有等振幅的特性，可以降低峰均值功率比(Peak-to-Average Power Ratio, PAPR)的問題。在接收端由於來自各個使用者的訊號會疊加在一起，所以我們利用SCMA的估測器進行解碼，可是傳統的估測器複雜度會隨著使用者數量以及碼簿的大小呈現指數成長，所以我們採用高斯干擾近似演算法(Gaussian Approximation of Interference, GAI)的演算法，把其他使用者所造成的干擾量模擬成高斯分佈，我們的複雜度可以從原本的指數成長降低成線性成長且維持近乎相同的效能。

Sparse code multiple access (SCMA) is proposed for 5th generation mobile networks. Because SCMA has good spectrum efficiency. Each user is assigned a SCMA codebook, which is made of codeword. The user’s information bits are directly encoded to codewords selected from a predefined codebook set. The selected codeword will overlapped at the receiver resulting in seriously multiple user interference. Therefore, we apply Sparse Gaussian Integer Perfect Sequence to design SCMA codebook. In order to improve the performance of multiple user detector, our target is to make the minimum Euclidean distance between every codeword selected by different user maximized. In the other hand, we use the properties of SGIPS that we construct codebook in frequency domain and the sequence is maintained equal amplitude in the corresponding time domain resulting in low peak to average power ratio. Because the codewords from different user will combined each other, we decode the message by SCMA decoder. But the complexity of traditional SCMA decoder will increase exponentially when both the size of codebook and the number of user. We proposed Gaussian Approximation of Interference algorithm to design receiver and model the interference as Gaussian distribution. By this way, we could reduce the complexity efficiently.

目錄
論文審定書 i
公開授權書 ii
誌謝 iii
中文摘要 iv
Abstract v
目錄 vi
圖次 viii
表次 x
第一章 導論 1
1.1 研究動機 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之基本架構 9
2.3低密度分碼多重存取之基本架構 11
2.4稀疏分碼多重存取之基本架構 12
第三章 碼簿設計 14
3.1碼簿設計 14
3.2使用稀疏高斯完美整數序列之碼簿設計方法 15
第四章 接收端設計 23
4.1 SCMA估測器設計 23
4.2 GAI估測器設計 24
4.3 複雜度比較 28
第五章 模擬結果與討論 29
5.1 Smooth Factor與Cross Entropy收斂值關係 29
5.1 SCMA 接收機 與GAI 接收機效能比較 32
5.2 峰均值功率比 34
5.3 錯誤率比較 36
第六章 結論 38
參考文獻 39
中英對照表 44
縮寫對照表 50

圖次
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 7
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 10
圖2-7 MC-CDMA系統接收端架構圖 10
圖2-8 LDS 系統架構圖 12
圖2-9 LDS 展頻碼示意圖 12
圖2-10 SCMA 上鏈傳輸系統架構圖 13
圖2-11 SCMA碼簿構造 13
圖3-1 不同的旋轉係數組合 20
圖3-2 不同的位移係數組合 20
圖3-3 長度為16與使用者數量為24的GI-SCMA碼簿 21
圖3-4 長度為32與使用者數量為48的GI-SCMA碼簿 22
圖4-1 GAI估測器設計FACTOR GRAPH 25
圖4-2 GAI估測器設計演算法 25
圖5-1 兩組基底序列與SMOOTH FACTOR 31
圖5-2 四組基底序列與SMOOTH FACTOR 31
圖5-3 SCMA CODEBOOK 33
圖5-4 SCMA接收機與GAI接收機效能比較 34
圖5-5 兩組基底序列的PAPR比較 35
圖5-6 四組基底序列的PAPR比較 35
圖5-7 兩組基底序列與LDS比較 37
圖5-8 四組基底序列與LDS比較 37

表次
表 3-1 兩組基底序列之不同位移係數間重疊關係 19
表 3-2 四組基底序列之不同位移係數間重疊關係 19

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