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研究生:楊嘉豪
研究生(外文):Chia-Hao Yang
論文名稱:DS-CDMA結合OFDM之效能模擬
論文名稱(外文):Performanc Simulation of DS-CDMA and OFDM Combined in Radio Fading Channel
指導教授:李金椿
學位類別:碩士
校院名稱:大葉大學
系所名稱:電信工程學系碩士班
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:2005
畢業學年度:93
語文別:中文
論文頁數:74
中文關鍵詞:正交分頻多工直接序列劃碼多重接取耙式接收機字符間干擾
外文關鍵詞:OFDMDS-CDMARAKE receiverISIMAI
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本論文結合直接序列劃碼多重接取(Direct Sequence Code Division Multiple Access, DS-CDMA)與正交分頻多工(OFDM)兩種技術提出DS-CDMA-OFDM系統,以改善無線衰變通道之頻率選擇性衰變所造成之字符間干擾(Inter-Symbol Interference, ISI)與多用戶干擾(Multiple Access Interference, MAI)問題,其次以電腦模擬方式驗證其系統能量效益,並與備配耙式接收機之純DS-CDMA相比較。
所提出之DS-CDMA-OFDM系統係先展頻,再做OFDM調變,為因應高傳輸速率之需求,而同時又保證每個OFDM子載波的頻寬均小於通道的同調頻寬,OFDM的載波數目必須大於DS-CDMA的展頻因數(Spread factor, SF)。
從模擬結果發現,在單用戶情況下我發現DS-CDMA-OFDM系統的能量效益與備配耙式接收機的純DS-CDMA系統幾乎相同,但是在多用戶情況下,不論展頻因數的大小,所提DS-CDMA-OFDM系統效能均比純DS-CDMA系統強,如SF=32且以BER=10-2時,至少減少3dB、SF=64且以BER=10-3時,至少減少5.4dB。此外在多用戶情況下,DS-CDMA-OFDM系統對抗MAI能力與展頻因數成正比。因此,DS-CDMA-OFDM系統不僅具有降低ISI能力,而且具有抗MAI能力。
A DS-CDMA-OFDM system, which is a combination of DS-CDMA and OFDM technologies, is proposed to reduce the effect of Inter-symbol interference (ISI) caused by frequency selective fading radio channel and Multi-access interference (MAI). The energy efficiency of proposed system is investigated based on simulation, and the results is compared with a pure DS-CDMA having a RAKE receiver.
In the proposed DS-CDMA-OFDM system, the message is spread by a spreading code, and follows by OFDM modulation. To keep the bandwidth of the OFDM sub-carrier smaller than the channel coherence bandwidth in high data transmission rate, the number of the OFDM sub-carriers must be greater than the spreading factor (SF).
From the simulation results, for single user situation, we find that the energy efficiency of DS-CDMA-OFDM is approximately the same as the pure DS-CDMA system with RAKE receivers. For the multiple-user situation, the performance of the DS-CDMA-OFDM system is better than the pure DS-CDMA system irrespective of the spread factor. In a BER of 10-2 and an SF of 32, the energy efficiency of the DS-CDMA-OFDM system is at least 3 dB better than that of the pure DS-CDMA system, while at least 5.4 dB better for a BER of 10-3 and an SF of 64. We find that the MAI rejection capability of the DS-CDMA-OFDM system is proportional to the spread factor. In general, the proposed DS-CDMA-OFDM system is not only able to reduce the effect of ISI ability, but also to reject the MAI.
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.........................ix
表目錄.........................xii

第一章 緒論......................1
第二章 無線衰變通道...................4
2.1無線通道衰減形式...............5
2.1.1路徑損失效應.............. 6
2.1.2遮蔽效應................ 7
2.1.3多重路徑效應.............. 8
2.2無線通道衰變特性...............9
2.3多路徑通道之數學模型............ 12
2.4分集技術.................. 16
第三章 DS-CDMA與OFDM原理...........18
3.1展頻技術原理................ 18
3.1.1 DS-CDMA原理 ............ 22
3.1.2耙式接收器............... 24
3.2 OFDM原理.............. .. 28
第四章 DS-CDMA-OFDM系統............. .41
4.1 DS-CDMA-OFDM系統............ 41
4.1.1 DS-CDMA-OFDM發射模型........42
4.1.2 DS-CDMA-OFDM接收模型........46
4.2 DS-CDMA-OFDM傳輸頻寬.......... 48
第五章 系統效能模擬 .................. 51
5.1搭配耙式接收機之CDMA系統模擬架構 .... 51
5.2 DS-CDMA-OFDM系統模擬架構........ 52
5.3系統參數.................. 53
5.4單用戶之效能模擬結果............ 55
5.5多用戶干擾下之效能模擬結果.......... 56
5.6不同載波數目之效能模擬結果.......... 59
第六章 結論.....................60
參考文獻.......................61
圖 目 錄

圖 2.1 整體行動通訊簡略架構圖..............4
圖 2.2 多路徑所造成的ISI現象示意圖...........5
圖2.3 路徑損失示意圖.................6
圖 2.4 遮蔽效應簡易示意圖...............7
圖2.5 多重路徑示意圖.................8
圖2.6 建設性和破壞性示意圖..............9
圖2.7 道衰變特性示意圖................10
圖2.8 頻率選擇性衰落.................12
圖2.9 非頻率選擇性衰落................12
圖2.10簡單電波路徑的行進示意圖............14
圖2.11 多路徑通道模型.................15
圖3.1 訊息經展頻技術所得效應:(a)未展頻信號頻譜 (b)展頻後信號頻譜(包含其他用戶) (c)針對原用戶進行解展頻信號頻譜......................20
圖3.2 直接序列式展頻技術示意圖:(a)調變 (b)解調變...21
圖3.3 單一載波DS-CDMA發射機結構.........22
圖3.4 單一載波DS-CDMA接收機結構.........23
圖3.5 衰落呈現頻率選擇性衰落.............24
圖3.6 耙式接收器架構.................25
圖3.7 無重疊(un-overlap spectral)性...........29
圖3.8 重疊(overlap spectral)性.............29
圖3.9 多載波調變結構.................30
圖3.10多載波解調變結構...............31
圖3.11傳統FDM傳輸方式..............32
圖3.12接收方訊息式示意圖..............32
圖3.13 OFDM傳輸頻譜圖...............34
圖3.14利用IDFT/DFT取代多OFDM調變/解調....35
圖3.15 OFDM系統發射架構..............36
圖3.16每一路傳輸頻譜.................37
圖3.17 OFDM信號傳輸頻譜..............37
圖3.18通道對傳輸信號呈現選擇性頻率衰落示意圖.....38
圖3.19 OFDM系統接收架構..............39
圖4.1所提DS-CDMA-OFDM系統發射架構.......43
圖4.2展頻後的頻譜..................44
圖4.3每一個子載波信號所佔用的頻帶..........45
圖4.4 所提DS-CDMA-OFDM系統接收架構.......47
圖4.5 DS-CDMA-OFDM每一路傳輸頻譜........48
圖4.6 DS-CDMA-OFDM信號傳輸頻譜.........49
圖4.7 通道對DS-CDMA-OFDM信號呈現平坦衰落....49
圖5.1搭配耙式接收機之CDMA系統流程........52
圖5.2 所提出的DS-CDMA-OFDM系統流程.......53
圖5.3單一用戶、展頻增益為32.............55
圖5.4單一用戶、展頻增益為64.............56
圖5.5五個用戶、展頻增益為32.............57
圖5.6十個用戶、展頻增益為32.............57
圖5.7五個用戶、展頻增益為64.............58
圖5.8十個用戶、展頻增益為64.............58
圖 5.9針對不同展頻增益對應使用不同載波數目時之效能模擬.......................59
表 目 錄

表5.1在DS-CDMA系統下,多路徑通道參數........54
表5.2在DS-CDMA-OFDM系統下,多路徑通道參數.....54
參考文獻

[1] R. steele, C. C. Lee and P. Gould, GSM Cdmaone and 3G Systems, Wiley & Sons, 2001
[2] Lee W.C Y., Overview of cellular CDMA IEEE Trans. Veh. Technol., Vol. 40 , NO. 2, May 1991
[3] Vijay K. Garg, IS-95 CDMA and cdma2000, Prenitice-Hall, 2000
[4] G. L. Turin, Introduction to spread-spectrum antimultipath techniques and their application to urbran Digital radio, Proc. IEEE, vol. PROC-68, no. 3, pp. 328-353, Mar. 1980
[5] J. G. Proakis, Digital Communications, McGraw-Hill,4th , ch14, 2001
[6] S. Verdu, Multiuser Dection., Cambridge, U. K.: Cambridge University Press, 1998
[7] R. V. Nee and R. Prasad, OFDM for Wireless Multimedia Communication, Artech House, pp.20-41, 1999.
[8] Salzberg, B. R., “Performance of an efficient parallel date transmission system,” IEEE Trans.Commun., Vol.COM-15, 1967
[9] S. B. Weinstein and P. M. Ebert ,“Date Transmission by Frequency-Division Multiplexing Using the Discrete Fourier Transmission,” IEEE Trans. Commun., Vol. COM-19, pp.628-634, Oct.1971
[10]Pandharipande, “Principle of OFDM ,” Potentials IEEE Vol.21, Issue 2,pp. 16-19, Apr-May, 2003
[11]T. S. Rappaport, Wireless Communication, Prenitice-Hall, 2nd , ch5、ch7,2002
[12]Cilnt Smith and Daniel Coins, 3G Wireless Networks, McGraw-Hill, 2002
[13]L. Hanzo, M. Münster, B. J. Choi and T. Keller, OFDM and MC-CDMA for Broadband Multi-User Communication, WLANs and Broadcasting, Wiley &Sons, ch9,2003
[14]M. Kavehrad and P. J. McLane, “Performance of low Processing Gain DS/CDMA Systems with Random Spreading Sequences,” IEEE COMMUNICATION LETTER.. VOL. 2, No. 12, pp. 315-317, Dec. 1998
[15]L. Hanzo, L-L. Yang, E-L. Kuan and K. Yen, OFDM and MC-CDMA for Broadband Multi-User Communication, WLANs and Broadcasting, Wiley &Sons, ch9,2003
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