臺灣博碩士論文加值系統

為了應付OFDM於時變通道中所造成之通道效應，通道追蹤已成為重要之探討課題。通常會有兩種方法來解決此通道效應之問題，第一種方法將於傳輸訊號中插入領航訊號(Pilot)，不過如此將造成頻寬效率下降。第二種方法為利用Preamble加上決策迴授機制的方法，於頻寬效率上是優於第一種方式，不過第二種方法的缺點為，在兩個連續的Payloads之中還是需要插入一個Preamble，假若我們的Frame長度太小，同樣會降低頻寬效率。因此，我們提出半盲目通道追蹤法來提升頻寬效率。傳統的通道追蹤是利用決策迴授機制的方法，不過此法最大的缺點是會有錯誤傳播情形發生，造成系統性能降低。因此於本論文中，我們提出半盲目通道追蹤法並結合兩種不同的切換機制與傳統的通道追蹤方法利用BER(Bit Error Rate)於性能上做一比較，從模擬的結果中可得知，我們所提出的通道追蹤方法可得到較佳之性能。

To deal with the channel effect in an OFDM time-varying channel, channel tracking is an important issue. We can have two methods to solve the channel effect problem. First, we use pilots to be inserted in transmitted signals, which significantly reduce the bandwidth efficiency. Second, we use a preamble along with decision feedback methods, which has better bandwidth efficiency than the first method. However, the drawback of the latter method is the requirement of a preamble between two successive data payloads. If the length of the frame is small, the bandwidth efficiency is also restricted. Therefore, we propose a semi-blind channel tracking method to improve the bandwidth efficiency. It is well-known that the decision feedback channel tracking method has the error propagation problem which can degrade the system performance. In contrast, the semi-blind channel tracking method applies a decision error criterion to change the use of the error control signal without the error propagation problem. Simulation results show that the proposed semi-blind channel tracking scheme has better BER performance than the decision feedback method.

章節目錄
第一章 序論 1
1.1. 前言 1
1.2. 研究動機 2
1.3. 內容大綱 2
第二章 正交分頻多工系統之簡介 3
2.1. 正交分頻多工系統之基本原理 3
2.2. 循環字首 4
2.3. OFDM之優缺點 5
2.4. 通道模型 7
2.4.1. 傑克斯通道模型簡介 7
2.4.2. 功率延遲數據圖(Power Delay Profile) 9
2.4.3. 自迴歸通道模型簡介 11
第三章 正交分頻多工系統之通道追蹤 14
3.1. 802.11a之通道估測法 14
3.2. 頻域之通道追蹤利用決策迴授機制 16
3.3. 時域之通道追蹤利用決策迴授機制 17
3.4. 平滑化通道估測 19
3.5. 半盲目通道追蹤法 21
3.5.1. MCMA與相位回復演算法 22
3.5.2. Generalized Sato Algorithm(GSA) 26
3.5.3. Stop-and-Go Algorithm(SGA) 27
3.6. 半盲目通道追蹤法與直接決策模型之切換準則 28
3.6.1. 通道追蹤模型切換 28
3.6.2. 切換法則 29
第四章 模擬與分析 36
4.1. 系統以及通道模型之參數設定 36
4.2. 不同Blind通道估測法利用自動切換準則之性能比較 42
4.3. MCMA與直接決策模式之切換準則模擬與分析 44
4.4. 通道追蹤演算法之位元錯誤率性能模擬與分析 55
第五章 結論和未來展望 65
參考文獻 67

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