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    Title: 正交分頻多工系統中脈衝雜訊的壓制與消除
    Other Titles: Suppression and Cancellation of Impulsive Noises in Ofdm Systems
    Authors: 易志孝
    Contributors: 淡江大學電機工程學系
    Keywords: Orthogonal frequency division multiplexing;impulsive noise;additive white Gaussian noise channel;frequency selective fading channel;channel capacity;symbol error rate;impulsive noise suppression;impulsive noise cancellation;channel coding;iterative decoding
    Date: 2011
    Issue Date: 2012-05-22 21:53:40 (UTC+8)
    Abstract: 正交分頻多工在近年來已經成為非常熱門之高資料速率無線通訊傳輸的技巧。當正交分頻多工技 術被用於數位電視廣播系統與電力線傳輸系統時,除了頻率選擇衰減與白色高斯雜訊外,脈衝雜訊也 是影響系統效能的一個關鍵因素。一般說來,與單載波系統相比較,正交分頻多工系統對脈衝雜訊有 較好之抵抗能力。但因脈衝雜訊一旦出現後,其振幅往往超過高斯雜訊許多,若無適當之補償,系統 效能將受其影響而衰減。在此研究計畫中,我們將研究脈衝雜訊對正交分頻多工系統效能的影響並提 出一個抑制與消除此雜訊的方法。 在正交分頻多工系統中,脈衝雜訊對系統的影響可經由適當之信號處理而降低。常用低複雜度的 信號處理方式為信號消隱、信號剪裁、與前兩者的組合。因為上述的信號處理等同於將收到的正交分 頻多工信號經過一個非線性函數轉換,將使原本正交分頻多工信號喪失正交性,因而產生載波間干 擾。本專題研究的第一個主題即為設計一個循環式的載波間干擾消除演算法來解決此一問題。我們將 提出固定與可變門檻值的循環式的載波間干擾消除演算法,並推導此一演算法的符元錯誤率下界以評 估其效能。 利用非線性函數處理接收的正交分頻多工信號,雖可有效降低脈衝雜訊對系統效能的影響,但卻 無法完全消除每個子載波上所殘留的脈衝雜訊。為了進一步改善系統效能使其接近於不含脈衝雜訊的 情況,本專題研究的第二個主題在於設計一個循環式的脈衝雜訊檢測器及估計器並使用此估計結果來 消除脈衝雜訊。此循環式接收機的收斂條件與其系統參數對其效能的影響需要進一步分析與評估。 最後,本專題研究的第三個主題為將上述針對正交分頻多工系統在脈衝雜訊通道下接收機的設計 推廣至編碼正交分頻多工系統。我們將考慮兩種編碼系統:第一種為以捲積碼或渦輪碼為基礎的位元 交織編碼系統;第二種為以里德所羅門碼加上消除解碼的編碼系統。研究的重點將放在不同編碼系統 抵抗脈衝雜訊能力的分析與系統參數的最佳化。
    Orthogonal frequency division multiplexing (OFDM) has become a popular transmission technique for high-data-rate wireless communications in recent years. The OFDM transmission technology has been adopted in digital television broadcasting and power-line communication systems where the additive white Gaussian noise (AWGN), frequency selective fading, and impulsive noise are all key factors to affect system performance. In general, OFDM systems have better immunity to impulsive noises compared to single carrier systems. However, if impulsive noises are not properly compensated, they will still degrade system performance significantly due to their large noise power. In this research project, we will study the effect of impulsive noises on the performance of OFDM systems and propose a method to suppress and cancel impulsive noises. In an OFDM system, the impulsive noise can be effectively reduced by adequate signal processing. The commonly employed low-complexity signal processing methods are signal blanking, signal clipping, and the combination of blanking and clipping. Since the aforementioned signal processing methods are equivalent to passing the received OFDM signal to nonlinear transformations, the orthogonality of OFDM signal is destroyed and the intercarrier interference (ICI) is created. The first topic of this research project is to design an iterative ICI cancellation algorithm to solve this problem. We will propose an iterative ICI cancellation algorithm with both fixed and variable blanking/clipping thresholds and derive the genie-aided symbol error rate (SER) lower bound to evaluate its performance. Although the nonlinear signal processing schemes can effectively mitigate the effects of impulsive noises on the performance of OFDM systems, there still exist residual impulsive noises at each subcarrier. To make the system performance approach to the impulsive noise free case, the second topic of this research project is to design an iterative impulsive noise detector and estimator. The impulsive noise is cancelled based on the impulsive noise estimates. The convergence conditions and the influence of system parameters on performance will be further analyzed and evaluated. Finally, the third topic of this research project is to extend the proposed OFDM receiver designs in impulsive noise channels to coded OFDM systems. We will consider two kinds of coding systems. The first one is the convolutional code or turbo code based bit-interleaved coded modulation (BICM) system. The second one is the Reed-Solomon code with erasure decoding scheme. We will analyze the resistance capability and optimize system performance of different coded OFDM systems in impulsive noise channels.
    Appears in Collections:[電機工程學系暨研究所] 研究報告

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