本論文係針對直接序列劃碼多重存取(DS-CDMA)系統，以系統模擬方式，探討線性和非線性耙式均衡器的系統效能，特別是多重用戶干擾對耙式均衡器效能之影響，並且與單純使用耙式接收機做比較。在多重路徑衰變通訊中，為了兼顧消除字符間干擾，與CDMA耙式接收機的分集(diversity)優點，我們提出了耙式均衡器，並以模擬方式探討其在多重路徑通道多用戶情況下之效能。
由模擬結果，我們發現CDMA系統單獨使用耙式接收機雖有抗字符間干擾(Inter symbol Interference, ISI)，其抗字符間干擾能力完全會依賴處理增益；反觀耙式均衡器則可以消除大部份的ISI。此外，在多重用戶干擾(Multiple Access Interference, MAI)的情況下，我們也發現耙式均衡器的抗MAI能力也比耙式接收機來得好。在用戶數分別為2或3時，系統效能分別改善了8.8dB和14dB，所以在用戶數愈多時，耙式均衡器所提昇的效能就愈多。
關鍵字：直接序列劃碼多重存取、耙式接收機、耙式均衡器、多重用戶干擾、字符間干擾。

The performance of DS-CDMA systems equipped with linear and nonlinear RAKE Equalizers is investigated through system simulations, where we focus on the influence the multi-user interference (MAI), and the simulation results are compared with the RAKE receiver. The RAKE Equalizer is proposed not only to provide the capability of the inter-symbol interference (ISI) cancellation, but also to maintain the diversity feature of RAKE receiver. Simulations are performed to study the performance under multi-user interference and multi-path fading channels.
According to the simulation results, the CDMA system incorporated with RAKE receiver is able to reject parts of the inter-symbol interference (ISI), but the capability of ISI rejection relies on it’s processing gain. On the other band, the RAKE Equalizer can remove most of the ISI. In the presence of multi-user interference, the proposed RAKE Equalizer has better MAI rejection performance than that of the RAKE receiver. For two and three interfering users, the performance improvement of the RAKE Equalizer is 8.8 and 14dB, respectively. Consequently, the RAKE Equalizer has a better performance than RAKE Receivers, even when the number of interfering users increases.
Key Words : DS-CDMA, RAKE receiver, RAKE Equalizer, Multiple Access Interference, Inter symbol Interference.

目錄

封面內頁
簽名頁
授權書．．．．．．．．．．．．．．．．．．．．．．．．iii
中文摘要．．．．．．．．．．．．．．．．．．．．．．．iv
英文摘要．．．．．．．．．．．．．．．．．．．．．．．v
誌謝．．．．．．．．．．．．．．．．．．．．．．．．．．vi
目錄．．．．．．．．．．．．．．．．．．．．．．．．．．vii
圖目錄．．．．．．．．．．．．．．．．．．．．．．．．．x
表目錄．．．．．．．．．．．．．．．．．．．．．．．．．xii

第一章　緒論．．．．．．．．．．．．．．．．．．．．．．1
1.1 研究動機．．．．．．．．．．．．．．．．．．1
1.2文獻探討．．．．．．．．．．．．．．．．．．2
1.3內容大綱．．．．．．．．．．．．．．．．．．3
第二章　無線衰變通道．．．．．．．．．．．．．．．．．．4
2.1基本傳輸現像．．．．．．．．．．．．．．．．4
2.2路徑損失．．．．．．．．．．．．．．．．．5
2.3遮蔽效應．．．．．．．．．．．．．．．．．5
2.4多重路徑衰變．．．．．．．．．．．．．．．．6
2.4.1瑞雷分怖．．．．．．．．．．．．．7
2.4.2 萊斯分怖．．．．．．．．．．．．．．8
2.4.3 都卜勒效應．．．．．．．．．．．．9
第三章　展頻原理和CDMA系統．．．．．．．．．．10
3.1 展頻原理．．．．．．．．．．．．．．．．10
3.1.1 假雜訊序列．．．．．．．．．．．．．11
3.1.2 處理增益．．．．．．．．．．．．．．12
3.2直序展頻系統(DSSS)．．．．．．．．．．．13
3.2.1多使用者存取的情形．．．．．．．．16
3.3 CDMA系統．．．．．．．．．．．．．．19
3.3.1 遠近效應．．．．．．．．．．．．．20
3.3.2 功率控制．．．．．．．．．．．．．20
3.4 分集技術．．．．．．．．．．．．．．．21
第四章　CDMA的通道均衡與耙式均衡器．．．．．．．22
4.1通道的均衡與均衡的概念．．．．．．．．22
4.1.1強制為零(ZF)．．．．．．．．．．．．23
4.1.2最小均方差法(MMSE)．．．．．．．．24
4.1.3適應性演算法．．．．．．．．．．．．26
4.1.4最小均方演算法(LMS)．．．．．．．．26
4.2通道的均衡器．．．．．．．．．．．．．28
4.2.1橫向的均衡器(LTE)．．．．．．．．．28
4.2.2決策回授均衡器(DFE)．．．．．．．．29
4.2.3前置循環碼(Cyclic Prefix)．．．．．．．32
4.3耙式接收機．．．．．．．．．．．．．．34
4.4耙式均衡器．．．．．．．．．．．．．．38
第五章　效能模擬．．．．．．．．．．．．．．．．．．．41
5.1效能模擬的參數．．．．．．．．．．．．41
5.2系統效能的模擬．．．．．．．．．．．．41
5.2.1均衡器加入前置循環碼的架構．．．．41
5.2.2耙式接收機的模擬架構．．．．．．．42
5.3耙式均衡器的模擬架構．．．．．．．．．43
5.4 耙式接收機的效能模擬．．．．．．．．．．44
5.5耙式均衡器的效能模擬．．．．．．．．．．46
5.6在多重用戶干擾狀況下的模擬．．．．．．．48
5.6.1耙式接收機在多重用戶干擾下的系統架構．48
5.6.2耙式均衡器在多重用戶干擾下的系統架構．49
5.7在耙式均衡器在多重用戶干擾下的系統效能．50
5.8均衡器參數對系統效能的影響．．．．．．．53
5.8.1步階函數(step size)對收歛速度的影響．．．53
5.8.2分支數(tap)對均衡器系統效能的影響．．．55
第六章　結論．．．．．．．．．．．．．．．．．．．．．．58
參考文獻．．．．．．．．．．．．．．．．．．．．．．．．60


圖目錄

圖2.1多重路徑示意圖．．．．．．．．．．．．．．．．．7
圖2.2多重路徑衰減通道的數學模型．．．．．．．．．．．7
圖2.3行動通訊天線移動接收電波圖．．．．．．．．．．．9
圖3.1回授移位暫存器架構．．．．．．．．．．．．．．11
圖3.2(a) BPSK的直序展頻的發射機．．．．．．．．．．14
圖3.2(b) BPSK的直序展機接收機．．．．．．．．．．．14
圖3.3(a) BPSK的直序展頻調變的波形．．．．．．．．．15
圖3.3(b) BPSK的直序展頻解調的波形．．．．．．．．．16
圖3.4(a) DS/CDMA多用戶通道圖．．．．．．．．．．．17
圖3.4(b) DS/CDMA多用戶接收機．．．．．．．．．．．17
圖3.5遠近效應的示意圖．．．．．．．．．．．．．．．20
圖4.1橫向均衡器(LTE)的架構．．．．．．．．．．．．．29
圖4.2決策回授均衡器(DFE)的架構．．．．．．．．．．．31
圖4.3前兆及後兆之離散通道的脈衝響應．．．．．．．．．31
圖4.4前置循環碼的架構．．．．．．．．．．．．．．．．33
圖4.5前置循環碼碼消除區塊間干擾的示意圖．．．．．．．33
圖4.6 RAKE接收機．．．．．．．．．．．．．．．．．．35
圖4.7耙式均衡器系統架構．．．．．．．．．．．．．．．38
圖5.1均衡器搭配前置循碼的系統模擬流程．．．．．．．．42
圖5.2耙式接收機的系統模擬流程．．．．．．．．．．．．43
圖5.3耙式均衡器的系統模擬流程．．．．．．．．．．．．44
圖5.4瑞雷衰變通道下，線性均衡器加前置循環碼(PG=15)．．45
圖5.5瑞雷衰變通道下，線性均衡器加前置循環碼(PG=7)．．45
圖5.6瑞雷衰變通道下RAKE Equalizer(DFE, PG=15)．．．47
圖5.7瑞雷衰變通道下RAKE Equalizer(DFE, PG=7)．．．．47
圖5.8耙式接收機加多重用戶干擾的系統模擬流程．．．．．49
圖5.9耙式均衡器加多重用戶干擾的系統模擬流程．．．．50
圖5.10瑞雷衰變下RAKE Equalizer (PG=15, users=2)．．．51
圖5.11瑞雷衰變下RAKE Equalizer (PG=15, users=3)．．．51
圖5.12瑞雷衰變下RAKE Equalizer (PG=7, users=2)．．．．52
圖5.13 LTE在不同步階函數的收歛速度．．．．．．．．．54
圖5.14 DFE在不同步階函數的收歛速度(FFF的α=0.065)．54
圖5.15 LTE在不同tap數的系統效能(Eb/N0=6dB)．．．．56
圖5.16 DFE中FBF在不同tap數的系統效能(Eb/N0=6dB)．57

表目錄

表5.1處理增益為7和15時的Eb/N0．．．．．．．．46
表5.2處理增益為7和15時的Eb/N0．．．．．．．．48
表5.3處理增益為7和15時的Eb/N0(users=2)．．．．52
表5.4處理增益為15時的Eb/N0(users=3)．．．．．．．．52
表5.5 LTE的步階函數的收斂速度和大小．．．．．．．．55
表5.6 DFE中FBF的步階函數的收斂速度和大小．．．．55

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