臺灣博碩士論文加值系統

本論文探討二維正交可變展頻因子（Two-Dimensional Orthogonal Variable Spreading Factors, 2D-OVSF）碼於正交分頻多工存取（Orthogonal Frequency Division Multiple Access, OFDMA）行動通訊系統之上鏈（Uplink）效能。當無線通道具有頻率選擇性衰減（Frequency Selective Fading）及都普勒效應（Doppler Effect）時，其分集性效益（Diversity Gain）可提升系統效能，但在多用戶（Multiuser）系統中，正交展頻碼會失去正交性，而導致多重存取干擾（Multiple Access Interference, MAI），並使OFDMA行動通訊系統之多用戶效能惡化。因此本文針對分集性效益與多重進接干擾對系統效能之影響進行理論分析，並進一步以電腦模擬驗證之。模擬結果顯示，應用2D-OVSF碼在OFDMA上鏈系統中，針對不同頻率選擇性衰減及都普勒效應之通道環境，適當地選用頻域與時域之展頻因子，可提升多用戶系統效能。

This study evaluates the performance of two-dimensional orthogonal variable spreading factors (2D-OVSF) codes on uplink of orthogonal frequency division multiple access (OFDMA) mobile communication systems. For wireless channel with frequency selective fading and Doppler frequency shift, the diversity gain can enhance system performance. However, in the multiuser environment the performance is degraded due to multiple access interference (MAI) resulting from the loss of orthogonality between users. Therefore, firstly, this thesis analyzes the effect of diversity gain and MAI on bit error rate (BER) and then verifies the derived results via simulations. Simulation results indicate that appropriate selection of time and frequency spreading factors of 2D-OVSF codes for OFDMA uplink can improve performance of multiuser systems.

中文摘要 i
英文摘要 ii
誌謝 iii
目錄 iv
表目錄 vii
圖目錄 viii
第一章 緒論 1
1.1 研究動機與目的 1
1.2 研究方法 2
1.3 各章節內容摘要 2
第二章 正交分頻多工系統簡介 3
2.1系統演進 3
2.2正交分頻多工系統 3
2.2.1正交分頻多工系統架構 5
2.2.2正交性 6
2.2.3離散傅立葉轉換 7
2.2.4保護區間 7
2.3正交分頻多工在頻率選擇性衰減通道之效能 11
2.4正交分頻多工優缺點 12
2.5耙式接收器 12
2.5.1全部接收型耙式接收器 14
2.5.2局部接收型耙式接收器 14
2.5.3選擇型耙式接收器 14
2.5.4限制選擇型耙式接收器 14
第三章 無線通訊系統通道模型 16
3.1通道模型簡介 16
3.2多重路徑傳播效應 17
3.3瑞利分布 18
3.4頻率選擇性衰減 18
3.5都普勒效應 19
3.5.1緩慢衰減 22
3.5.2快速衰減 22
3.6頻率選擇性衰減通道模型 23
第四章 二維OVSF碼 24
4.1 OVSF碼和2D-OVSF碼簡介 24
4.2碼樹 25
4.2.1 OVSF碼樹 25
4.2.2時域分散和頻域展頻長度相等的2D-OVSF+碼樹 26
4.2.3時域分散和頻域展頻長度不同的2D-OVSF+碼樹 28
4.3 2D-OVSF‾碼 30
4.4 2D-OVSF碼間的正交性 31
4.4.1 M等於N時2D-OVSF+碼的正交性 32
4.4.2 M不等於N時2D-OVSF+碼的正交性 33
4.4.3 2D-OVSF‾碼的正交性 35
4.5通道效應對OVSF碼及2D-OVSF的影響 36
4.5.1選擇性衰減在上傳通道對OVSF碼的影響 36
4.5.2選擇性衰減在上傳通道對2D-OVSF＋碼的影響 39
4.5.3選擇性衰減在上傳通道對2D-OVSF—碼的影響 42
第五章實驗結果 45
5.1模擬架構 45
5.1.1系統參數 45
5.1.2通道設定 45
5.1.3效能評估 46
5.2通道效應對正交分頻多工的影響 46
5.2.1通道延遲小於保護區間 47
5.2.2通道延遲大於保護區間 50
5.3用戶數I=1之模擬 53
5.4用戶數I=2之模擬 55
第六章 結論與未來展望 57
參考文獻 58
縮寫中英對照 61

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