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研究生:李欣鴻
論文名稱:利用展頻碼序列的選擇來降低OFDM-CDMA系統的峰均值比
論文名稱(外文):The Selection of Spreading Sequences to Reduce the Peak-to-Average Power Ratio in OFDM-CDMA System
指導教授:陳後守
學位類別:碩士
校院名稱:國立中興大學
系所名稱:電機工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:中文
中文關鍵詞:正交分頻-分碼多工系統峰值對平均值比
外文關鍵詞:OFDM-CDMAPeak-to-Average Power Ratio
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在無線通訊中,凡是訊號經過展頻後再傳送的系統,都一定會經歷頻率選擇性衰減。為了降低它對系統性能的影響,於是發展出多載波分碼多工,其主要利用正交分頻多工調變技術來切割通道,使得每個子通道皆呈現平坦衰減,同時簡化了系統接收器的複雜度。正交分頻分碼多工是一種結合分碼多工與正交分頻多工之傳輸技術。
OFDM-CDMA結合OFDM與CDMA兩種調變方式,因此具有對多路徑的頻率選擇通道有較佳的抵抗力高速資料傳輸、抗多路徑延遲擴展、頻譜利用率高的優點,此外也能提供高容量的系統服務,它已被視為第四代無線行動通訊系統設計上的一項重要技術。
由於OFDM-CDMA使用OFDM的結構,因此OFDM-CDMA訊號有很高的傳輸功率峰值對平均值比,所以易受無線通訊系統傳輸端的功率放大器非線性扭曲失真的影響,而嚴重降低訊號傳輸的品質。所以需要有大的動態範圍的線性放大器,才能保證接收到所有PAPR值較大的的訊號,而不會有訊號因超過其接收端放大器動態範圍而被截的現象。若能找到一些規則,使得選用的展頻碼組合,PAPR值都能限制在可接受的範圍,這樣就不需消秏過多的功率。
長度 的展頻碼及固定的使用者人數 之下,會有 種的展頻碼組合,這些不同的展頻碼組合,會有不同的PAPR值。本論文的研究方向有二,其一是找到一些規則,使得在任意 個使用者時,都能在 種展頻碼組合中,找到PAPR較低的組合。其二是,在原來固定的 個使用者下,當第 個使用者加入時,如何分配第 個展頻碼,使得這 個展頻碼的組合,其PAPR值仍然是較小的。
In wireless communication systems, the transimitted signals after spreading are always suffered by frequency-selective fading. To reduce this effect, the Orthogonal frequency Division Multiplexing - Code Division Multiple Access (OFDM-CDMA) systems are proposed, where the whole channel is divided into many flat fading sub-channel. The OFDM-CDMA systems is a combination of the CDMA and OFDM and thus have better resistance against frequency-selective fading against, Other advantage of OFDM-CMA is the transmission rate and high efficiency use in spectrum. Furthermore, OFDM-CDMA systems provide high capacity for the system service, and is considered to be an important technique in future B3G wireless communication system.
A major drawback of OFDM-CDMA is that it has a high Peak-to-Average power Ratio( PAPR). The larger peak power signal requires a liner amplifier with a larger dynamic range, which is very expensive and sometimes almost impossible to implement. It is desirable to reduce the peaks in OFDM-CDMA signals. Since the larger peaks degrade the efficiency of a linear amplifier . The purpose of the is to select the combination of spreading sequences with low PAPR, that there PAPR all limiting in the accept range.
There are total combination of spreading sequences for a down-link transmitter using a length spreading code. Each spreading sequence has different PAPR value and the search of a spreading sequence with low PAPR is a challenge problem. This thesis has two research. One aspect hope to find some rules, which can make system choose lower PAPR spreading sequences combination in the total spreading sequences under arbitrarily users. Another aspect is fixed original users than choose th spreading sequences when th user accede to the system, and these spreading sequences combination, which PAPR still lower.
中文摘要 i
Abstract iii
目錄 v
圖例目錄 ix
表格目錄 xv
第一章 序論 1
第二章 系統介紹 5
2.1 OFDM-CDMA傳送端架構 5
2.2訊號的PAPR性質 8
2.3 瞬間功率的自相關和互相關 10
2.4傳送位元數對展頻組合的影響 11
第三章 展頻碼介紹 16
3.1 正交展頻碼 16
3.1.1哈德展頻碼(Walsh-Hadamard Spreading code,WH) 16
3.1.2格雷展頻碼(Golay-Complementary Spreading code,CP) 16
3.2里得-米勒碼(Reed-Muller Code) 17
3.3里得-米勒碼與哈德碼 19
3.4哈德碼的奇、偶性質 22
3.5正交可變展頻係數(OVSF) 24
第四章 OFDM-CDMA的PAPR上限及下限 27
4.1概述 30
4.2全搜尋定義 30
4.3利用哈德碼奇、偶函數性質消除瞬間功率的互相關項 34
4.3.1哈德碼序列的奇、偶函數形式 34
4.3.2分奇偶函數的哈德碼序列取法 35
4.3.3使用有分奇偶函數型式的哈德碼組合 39
4.4互相關產生功率會加成的組合 41
4.4.1如何搜尋出哈德碼組合中互相關為會加成的型式 42
4.5 經平移產生的正交展頻碼 47
第五章 使用FLAT所對應的哈德碼組合 55
5.1概述 55
5.2何謂FLAT 56
5.2.1 如何找出FLAT 57
5.3使用FLAT所對應的展頻碼 58
5.3.1 FLAT所對應的哈德碼組合為分奇偶函數型數 59
5.3.2 會加成的展頻碼組點所對應的FLAT 62
5.4 各種 -flat的結果 64
5.4.1 2-flat 64
5.4.2 3-flat 67
5.4.3 4-flat 71
5.4.3 5-flat 72
第六章 漸增式搜尋法 74
6.1簡介 74
6.2全計算漸增式搜尋法 75
6.3有序的漸增式搜尋法 78
6.4最小自相關函數合搜尋法 87
6.5取絕對值後的互相關漸增式搜尋法 90
6.5.1概述 90
6.5.2搜尋法介紹及模擬結果 93
6.6 一次傳送多於1個位元時 97
6.6.1.全計算漸增搜尋法 97
6.6.2套用每次傳送一個位元的結果 98
6.6.3. 不同倍數的自相關和取絕對值後的互相關 100
第七章 結論 103
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