# 臺灣博碩士論文加值系統

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 正交分頻多工系統在現在的有線及無線通訊系統中都很常被使用到，它主要的概念就是將一個大的頻寬分成很多個小的頻寬，利用其正交性來克服干擾。但這樣的系統對於載波頻率偏移相當的敏感，因此在正交分頻多工系統當中，如果正確的估測出載波頻率偏移是一個非常重要的問題所在。 在本篇論文當中我們將會提出一個估測載波頻率偏移的方法，首先在傳送端我們將會使用虛擬載波來幫助我們推導出要最小化的函數，接著我們會將問題轉換成尋找最大公因式的問題，並且使用子空間演算法來求解最大公因式，然後求得載波頻率偏移的估測值，最後我們會把效能跟直接最小化目標函數所得到的效能來作一個比較。
 The OFDM system has been a widely adopted technique for both wired and wireless transmission. It is well-known that one of the most important problem for the OFDM system is the carrier frequency mismatch between the transmitter and the receiver. The frequency mismatch is always modeled as a CFO(carrier frequency offset) effect. Therefore how to estimate the CFO correctly is one of the most important problems for the OFDM systems.In this thesis, we will use a semiblind method for estimating the CFO in the OFDM systems. At the transmitter, some tones of the transmitted signal before applied to the normalized IDFT block are chosen to be the virtual carriers. The method is semiblind because we only need to know the locations of these virtual carriers but noneed to know what modulation scheme that the transmitted data uses. Using these virtual carriers, we can get our cost function. By minimizing the cost function, the CFO can be estimated.We convert the problem of minimizing the cost function into the problem of finding the GCD(greatest common divisor) polynomial. The method we use for finding the GCD polynomial is the subspace method. Finally the performance of the proposed method will be compared with the method that minimizes the cost function directly.
 List of Tables........................................viiList of Figures.......................................viiiAbstract..............................................xiAcknowledgements......................................xiii1.Introduction..........................................12.CFO effect on OFDM systems............................5 2.1 Introduction of OFDM systems..................6 2.1.1 CP-OFDM system..........................6 2.1.2 ZP-OFDM system.........................10 2.2 SINR of OFDM systems with CFO effect[7]......13 2.2.1 SINR formulation.......................13 2.2.2 SINR degradation due to CFO............183.Subspace method for finding GCD polynomial...........21 3.1 Introduction to subspace method[15][17]......22 3.2 Constrains and trade off of subspace method..26 3.3 Examples and simulations.....................294.CFO estimation using virtual carriers................37 4.1 Mathematical model in CP-OFDM system.........38 4.2 CFO estimation in CP-OFDM system.............39 4.2.1 Finding CFO as the root of polynomials.39 4.2.2 Finding CFO using JHA method[12].......41 4.2.3 Finding CFO by computing GCD...........47 4.2.4 Simulatino result......................50 4.3 CFO estimation in ZP-OFDM system.............54 4.3.1 Mathematical model.....................54 4.3.2 Simulation result......................575.Conclusion...........................................59Bibliography...........................................61
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 1 正交分頻多工系統於時變通道下使用導引符元估測載波頻率偏移量之方法 2 利用常數導引訊號完成正交分頻多工系統頻率同步之研究 3 應用於正交分頻多工系統之載波頻率偏移效應壓抑技術 4 正交分頻多工系統時頻多工收發機設計之IQ不平衡與載波偏移及通道估計/補償技術 5 結合時域和頻域載波頻率估測法以改善正交分頻多工系統之載波間干擾 6 針對WLAN OFDM系統之I/Q不平衡與載波頻率偏移補償與其電路設計與實現 7 正交分頻多工系統中利用不同導航符號之載波頻率飄移估測 8 正交分頻多工系統中載波頻率偏移與IQ不平衡之聯合估測與補償 9 使用共軛傳輸之OFDM系統的適應性接收機設計 10 多輸入多輸出正交分頻多工系統中頻率域封包欄位偵測與載波頻率偏移估計之實做 11 適用於OFDM系統中的基頻內層接收機技術 12 頻率偏移盲估測演算法應用於正交分頻多工系統之探討 13 正交分頻多工系統在頻率平坦通道中之頻率同步和通道估測研究利用最大概似率與最小平方估測法之研究

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