臺灣博碩士論文加值系統

目前的第二代行動通訊系統具有傳輸速度慢、系統效能(QoS)差、服務類型少(只有語音和數據)與系統容量低等缺點，而第三代行動通訊系統不但能改善上述的缺點，且其中又以直序展頻分碼多工(DS-CDMA)最被看好，其主要是犧牲頻寬，來換取抗多重路徑、抗雜訊、保密性佳和高容量等優點，然而使用者間的多重進接干擾(MAI)是限制QoS和容量的最主要因素，故傳統上，是使用多使用者偵測(MUD)來降低或消除MAI的影嚮。
解相關偵測器雖可完全去除MAI的影嚮，且具有其複雜度和使用者的個數呈線性關係和不須知道訊號能量等優點，但其卻有雜訊增強的現象，因而使得性能變差。本論文引入重疊視窗和決策迴授的觀念，來增進其效能，為了降低複雜度，使用遞迴最小平方(RLS)來取代反矩陣做去相關動作。重疊視窗是將前一視窗中未做決策的位元留至下一視窗再做決策。決策迴授主要用於具有遠近效應的環境中，使得最弱的使用者其效能能因較強使用者其MAI的消除而變好。由電腦模擬結果可知，可知結合重疊視窗和決策迴授較傳統的解相關偵測器其位元錯誤率低，因此，可有效增進通訊品質。

The second generation mobile communication system has shor-tcomings, such as low data rate, poor quality of service(Qos),
limited service types -- speech and data only, and low system capacity. But the third generation mobile communication system
overcomes the shortcomings above, and direct-sequence code division multiple access (DS-CDMA) is one of the best candi-dates.It has advantages; for example, anti-mulpath, anti-noise, keeping a secret well and high capacity at the cost of band-width. However, multiple access interference (MAI) between the users contributes to the limitation of Qos and capacity. Trad-itionally, the multiuser detection (MUD) scheme is applied to reduce or eliminate the MAI.
Although the decorrelating detector can remove the MAI comp-letely, has linear complexity in the number of users, and does not need the knowledge of users' signal energy, but it has noise enhancement, causing poor performance. A new structure that combines the overlapping window with decision feedback to improve the performance of the detector is proposed in the thesis. When removing the correlation between users, we replace the inverse matrix with the algorithm of recursive least square(RLS) in order to reduce the computation complexity of the detector. The overlapping window has the properties that allow the states of data bits undecided in the previous window to be decided in the next window. Decision feedback has the charact-
eristic that in the environment of near-far effect, the perform-ance of the weakest SNR user can be improved due to the remove of MAI of the stronger SNR users. Simulation results have shown that the bit-error-rate of the detector using overlapping window
and decision feedback is better. Therefore, it can make the communication quality perfect.

第一章 序論
1.1 背景簡介 …………………………………………………………1
1.2 研究動機和目的 …………………………………………………2
1.3 各章節內容概述 …………………………………………………4
第二章 可加性高斯白雜訊通道下的同步多使用者偵測之回顧
2.1 可加性高斯白雜訊通道下的同步DS-CDMA模型…………………5
2.2 最佳多使用者偵測………………………………………………10
2.3 次最佳多使用者偵測……………………………………………12
2.3.1 線性解相關偵測器………………………………………14
2.3.2 線性最小均方誤差多使用者偵測………………………16
2.4 連續干擾消除……………………………………………………17
2.5 平行干擾消除……………………………………………………19
2.6 多使用者偵測的比較……………………………………………20
第三章 多重路徑衰落通道下的非同步解相關偵測器其視窗長度選擇法
3.1 己存在的非同步解相關偵測器其視窗長度選擇法……………23
3.1.1 傳統解相關偵測器………………………………………23
3.1.2 單撃型解相關偵測器……………………………………27
3.1.3 增進單擊型解相關偵測器………………………………29
3.1.4 加倍視窗型解相關偵測器………………………………31
3.2 多重路徑下解相關偵測器其視窗長度選擇法…………………33
3.3 重疊視窗與其偵測方式…………………………………………36
3.4 視窗長度選擇及其偵測方式的比較……………………………38
第四章 結合決策迴授和重疊視窗的RLS型解相關偵測器
4.1 多重路徑衰落通道下的非同步DS-CDMA 模型…………………40
4.2 通道模型…………………………………………………………43
4.3 RLS 型解相關偵測器……………………………………………45
4.4 決策迴授…………………………………………………………48
4.5 模擬結果和分析…………………………………………………60
4.5.1 基本假設…………………………………………………60
4.5.2 結果與分析………………………………………………60
第五章 結論與未來發展
5.1 結論……………………………………………………………67
5.2 未來發展………………………………………………………68
參考文獻…………………………………………………………………69

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