臺灣博碩士論文加值系統

多載波調變在頻率選擇衰減的通道中是一種有效的通訊技術，正交頻率分散多工即是其中一例，它在高速無線傳輸的環境中可以成功地對抗多路徑衰減效應。然而，多載波系統最大的缺點就是有峰均值比的問題，這會對某些譬如像放大器之類的元件造成不可避免的效率損失。
在本論文中，我們提出一種新的方法來降低多載波調變訊號的峰均值比。利用位元分載的操作，我們略為調整原來的分載來降低其峰均值比。從模擬的結果發現，當64個分支載波數時，使用我們提出的演算法，只需要三次遞迴就可將峰均值比降低到5dB。此外，複雜度的降低與附帶資訊的傳輸等議題也在本論文中探討，從結果得知，我們可以用少許峰均值比的增加來換取顯著運算複雜度的降低，而附帶資訊的增加量比起其他降低峰均值比的方法也在可接受的範圍內。因此總結地說，我們提出的方法可以有效地降低峰均值比，並且不會對多載波系統帶來過多錯誤率效能的損失。

Multi-carrier modulation is an effective technique for communication in frequency selective fading channels. Orthogonal frequency division multiplexing (OFDM) is one example that successfully combats multi-path fading for high data rate wireless communications. However, multi-carrier systems suffer from the peak-to-average power ratio (PAPR) problem, which causes efficiency loss in devices, such as the transmitter power amplifier. In this thesis, we propose a new method for lowering the PAPR of multi-carrier modulated signals. Our method performs bit loading with PAPR consideration. We slightly perturb the “optimal” loading in order to reduce PAPR. Simulation results show that PAPR as lower as 5dB is achievable using 3 iterations of the proposed algorithm when number of sub-carriers is 64. Complexity reduction and side information transmission issues are also investigated in the thesis. Our results show that it is possible to trade a slight loss of PAPR performance for significant reduction in computational complexity. The overhead caused by side information transmission is also acceptable compared to other PAPR reduction methods. We thus conclude that the proposed method is an effective scheme that can significantly reduce PAPR without sacrificing too much error performance of a multi-carrier system.

Chapter 1 Introduction
Chapter 2 OFDM Basics
2.1 Multi-path Fading Channel
2.2 Basic Concept of OFDM
Chapter 3 PAPR Problem
3.1 Introduction
3.2 PAPR Problem in OFDM Systems
3.3 PAPR Reduction Methods
Chapter 4 PAPR Reduction Using Bit-Loading Method
4.1 Bit Loading in Multi-carrier Systems
4.2 PAPR Reduction Using Bit-Loading
4.3 Complexity Reduction Method and Side Information Transmission
Chapter 5 Simulation Results
5.1 Simulation Environment
5.2 Simulation Results
5.3 Discussion
Chapter 6 Conclusion
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