在行動通訊系統中，經過展頻的分碼多重接取(CDMA)系統，訊號的頻寬會變得相當大。若訊號頻寬大於通道的同調頻寬，多重路徑延遲效應會造成訊號的失真。正交分頻多工(OFDM)技術利用平行傳輸的觀念將寬頻訊號分成多個窄頻訊號傳送，若依據通道環境來選擇適當的載波數，讓訊號頻寬小於通道的同調頻寬，即可克服多重路徑問題。
在未來的行動通訊中，傳輸多媒體資訊的需求日增，例如行動電話的語音傳輸以及無線區域網率中的高速數據傳輸等服務項目，因此不同目的使用者對於傳輸速率的需求產生不同。在最近幾年，多重傳輸速率的系統因應而生。

然而行動通訊的通道特性，是隨著移動速度及傳輸環境而作變化。因此，如以頻譜效率(bps/Hz)、資料位元錯誤率(BER) 、傳輸功率而言，並無單一固定模式的一組傳送及接收機(收發機)，在任何通道特性中，皆有最佳的效能表現。

在本論文中，將以電腦模擬的方式探討以編碼多重速率OFDM技術為基礎的通訊系統在不同無線環境中的傳輸性能表現，希望在不同的無線環境中找出較佳的傳輸模式。

In mobile radio systems, the bandwidth of spread spectrum signals for CDMA system is very wide. When the bandwidth exceeds the coherence bandwidth of the channel, the effect of multi-path fading become serious and the transmission signals are severely distorted. In OFDM systems, the available bandwidth is divided into a lot of small parts. By well selecting the number of sub-carriers according to the characteristics of the mobile channel will let the bandwidth of transmission signals smaller than the coherence bandwidth of channel. Then the multi-path fading problem can be overcome.

In future mobile communications, the demand for multimedia will grow spectacularly. For example, the need of voice transmission for mobile phone and the need of high data rate transmission for wireless local area network (WLAN). Therefore, multi-rate system was developed in the recent years.

Yet, the characteristics of mobile channel vary with the moving velocity of the systems and the environment of the mobile channel. Therefore no single transmission mode owns the best performance in terms of spectrum efficiency, bit error rate, and transmission power.

In this thesis, we study coded multi-rate OFDM systems in different mobile environment and evaluate their performance by means of computer simulation. Hoping to find better transmission modes in different mobile channel.

目錄 頁次

感謝詞………………………………………………………………i
中文摘要………………………………………………………………ii
英文摘要………………………………………………………………iii
目錄………………………………………………………………….iv
圖表目錄…………………………………………………………….vi

第一章 緒言………………………………………………………….1
1.1 文獻探討……………………………………………………1
1.2 研究動機……………………………………………………3

第二章 行動通道與正交分頻多工技術……………………………5
2.1 無線通道的傳輸現象…………………………………………5
2.2 無線通道的參數定義…………………………………………7
2.3 各式通道………………………………………………………10
2.3.1 加成性白色高斯雜訊(AWGN)通道………………………10
2.3.2 衰減(Fading)通道…………………………………………10
2.3.3 多重接取干擾(MAI)通道…………………………………14
2.4 正交分頻多工技術的發展與基本原理………………………16
2.4.1 正交分頻多工信號產生………………………………….19
2.4.2 保護時間的功能…………………………………………21
2.4.3 正交分頻多工系統的基本模型…………………………25

第三章 多重速率系統…………………………………………………28
3.1 多重速率系統簡介…………………………………………….29
3.2 多重速率DS-CDMA(直接序列分碼多重接取)系統………..30
3.2.1 DS-CDMA技術原理………………………………………..30
3.2.2多重速率DS-CDMA系統…………………………………..31
3.3 多重速率正交分頻多工系統………………………………….36
3.4 多重編碼速率系統…………………………………………….36
3.4.1編碼原理簡介……………………………………………….37
3.4.2迴旋碼……………………………………………………….38
3.4.3 RCPC碼與多重編碼速率系統……………………………..38
第四章 編碼多重速率正交分頻多工系統……………………………41
4.1編碼多重速率正交分頻多工系統模型……………………...41
4.2編碼多重速率正交分頻多工系統的偵測方式………………..42
4.3編碼多重速率正交分頻多工系統於AWGN通道之電腦模擬與分 析……………………………………………………………..45
4.4編碼多重速率正交分頻多工系統於衰減通道之電腦模擬與分析…………………………………………………………….49
4.5編碼多重速率正交分頻多工系統於強烈衰減通道之電腦模擬與分析………………………………………………………..53
4.6策略法則………………………………………………………….60

第五章 討論與建議……………………………………………………62

參考文獻……………………………………………………………….63

縮寫表…………………………………………………………………..68

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