正交分頻多重進接系統是運用正交分頻的傳輸概念，透過將不同子載波分配於不同的使用者來傳遞訊息，以達到多人存取的功用。由於都卜勒效應或者本地震盪器的不匹配，造成每位使用者所對應的頻率偏移也不相同，導致每一個使用者的訊號受到多重存取干擾影響而降低系統效能。故本篇論文針對QPSK以及16QAM調變下的正交分頻多重進接系統提出干擾消除演算法來有效地消除多重存取干擾，提出的方法包含循環式訊號分類之干擾消除法（Iterative Interference Cancellation by Signal Classification，IICSC）與使用者與訊號分類之干擾消除法（Interference Cancellation by User and Signal Classification，ICUSC）。論文中探討如何有效地在頻域分離出較可靠的訊號，並消除這些可靠訊號對其他訊號的多重存取干擾。由於在16QAM系統對多人存取干擾較為敏感，因此我們提出判斷法則來分離出受干擾較少的使用者，以達到有效的分離出可靠訊號。藉由減少對可靠訊號的干擾消除，在維持一定的系統效能下，可以有效地降低運算複雜度。從模擬結果顯示，所提出之演算法在系統效能上可以和平行干擾消除法（Parallel Interference Cancellation，PIC）相當，但所需運算量可以有效地降低。

Orthogonal frequency division multiple access (OFDMA) systems use the same concept of orthogonal frequency division multiplexing, assign different subcarriers to different users for multiple access requirements. Since the received signals from different users have different carrier frequency offsets (CFOs) induced by Doppler effect and frequency mismatching between transmitter’s and receiver’s oscillators, the system performance will be degraded by the multiple access interference (MAI). In this thesis, we present iterative interference cancellation by signal classification (IICSC) and interference cancellation by user and signal classification (ICUSC) algorithm for QPSK and 16QAM modulation schemes. We investigate the method to select significantly reliable signals and then cancel the corresponding MAI from other signals in frequency domain. In 16QAM modulation scheme, the system is more sensitive to MAI. Therefore, we propose a criterion to choose the users with less MAI and then select reliable signals from these users. Since these reliable signals are not required interference cancellation, we can reduce the total number of interference cancellation operations. From simulation results, the performance of our proposed methods is similar to that of parallel interference cancellation method, but the computational complexity of our proposed method is lower.

目錄
致謝 i
摘要 ii
Abstract iii
目錄 iv
圖索引 vi
表索引 x
第一章 簡介 01
1.1 背景介紹 01
1.2 研究動機 03
1.3 各章提要 04
第二章 系統模型 05
2.1 OFDM系統與早期FDM系統差異 05
2.2 OFDMA傳輸系統模型 06
2.3 OFDMA接收系統模型 08
第三章 運用於上行OFDMA系統之干擾消除技術 11
3.1多使用者干擾 11
3.2平行式干擾消除 12
3.3選擇性干擾消除 12
第四章 提出之訊號分類之干擾消除法 20
4.1 應用於QPSK調變系統的訊號分類之干擾消除法 20
4.1.1循環式訊號分類 20
4.1.2循環式干擾消除 21
4.1.3干擾消除複雜度計算 22
4.2 應用於16QAM調變系統的訊號分類之干擾消除法 25
4.2.1使用者與訊號分類 25
4.2.2干擾消除法 33
4.2.3干擾消除複雜度計算 34
第五章 模擬結果探討與分析 36
5.1 模擬環境 36
5.2 應用於QPSK調變系統的訊號分類之干擾消除法 36
5.2.1判斷線之探討 36
5.2.2循環式訊號分類之干擾消除法之探討 39
5.3 應用於16QAM調變系統的訊號分類之干擾消除法 45
5.3.1判斷線與使用者分類係數之探討 45
5.3.2使用者與訊號分類干擾消除法之探討 54
第六章 結論 67
參考文獻 68

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