臺灣博碩士論文加值系統

本篇論文探討多載波分碼多重存取及正交頻率分碼多工信號之頻譜旁波特性。在此討論中，頻域展頻碼所具備的快速旁波衰減特性可確保信號頻譜旁波隨著頻率快速衰減。給定頻域展頻碼的長度，信號頻譜旁波衰減速率有一個與碼長有關的上限。將碼字適當地排列，所有正交可變展頻因子碼與正交互補格雷碼造成的信號頻譜旁波衰減速率可完全由其引數來描述。藉由此描述，可建立針對頻譜旁波抑制的正交可變展頻因子碼與正交互補格雷碼之碼字選取機制，而所有多相位碼所造成的頻譜旁波衰減特性則完全相同。最後，本篇論文亦提出一種針對頻譜旁波抑制的正交可變展頻因子碼樹管理策略，此策略同時可以解決展頻碼阻塞的問題。

In this thesis, the spectral sidelobe properties of MC-CDMA and OFCDM signals are investigated. Particularly, a general fast-sidelobe-decaying property of the frequency-domain spreading codes is observed to provide small power spectral sidelobes. Given the length of the frequency-domain spreading code, a limitation on the resulted sidelobe-decaying rate is also obtained. It is shown that, by proper arrangements, the spectral sidelobe properties of MC-CDMA or OFCDM signals with (frequency-domain spreading) OVSF and OCG codes can be completely described by their code indices. According to this description, new assigning principles for (frequency-domain spreading) OVSF and OCG codes subject to spectral sidelobe suppression are proposed. Also, all polyphase codes are shown to yield the same spectral sidelobe property. Furthermore, a new code tree management strategy for OVSF code is proposed aiming to maximize the sidelobe-decaying rate of the overall transmitted MC-CDMA or OFCDM signal, and in the meanwhile to eliminate the code-blocking problem completely.

Abstract .......... i
Contents .......... ii
List of Figures .......... iv
List of Tables .......... vi
1 Introduction .......... 1
1.1 Combining CDMA and OFDM .......... 1
1.2 Spreading Code Assignment .......... 4
1.3 Motivation .......... 7
2 Signal Models and Spectral Characteristics .......... 9
2.1 Signal Models .......... 9
2.2 Fast-Sidelobe-Decaying Property .......... 14
2.3 Limitation on Sidelobe-Decaying Order .......... 16
3 Sidelobe-Decaying Orders of Orthogonal Spreading Codes .......... 18
3.1 Overview of Orthogonal Spreading Codes .......... 18
3.2 Sidelobe-Decaying Orders of OVSF Codes .......... 22
3.3 Sidelobe-Decaying Orders of OCG Codes .......... 26
3.4 Sidelobe-Decaying Orders of Polyphase Codes .......... 31
4 Numerical Results and Applications .......... 37
4.1 Fractional Out-of-Band Power Characteristics .......... 37
4.2 Code Assignment With a Fixed Spreading Factor .......... 40
4.3 OVSF Code Tree Management .......... 44
5 Conclusion .......... 49
Bibliography .......... 51
Appendix .......... 53

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