臺灣博碩士論文加值系統

衛星通訊近幾年來受到廣泛的重視，由於高效率傳輸的日益需求，因此如何有效利用人造衛星的有限功率和頻寬，已成為人造衛星之數位傳輸系統的重要課題。在衛星通訊系統裡，我們希望將衛星通訊系統的放大器操作在飽和區裡，以提供功率的有效使用。由於飽和區具有非線性特性，因此衛星通訊通道可被視為非線性之通道。對於一個通訊通道而言，其輸入訊號往往具有帶通之特性，在這種情況下，若通訊系統為非線性，則其輸出訊號可能為多頻帶之帶通訊號。針對此多頻帶帶通訊號的取樣問題，前人的研究成果僅適用於三階之非線性系統。這使得該技術的應用受到相當侷限。以非線性衛星通訊通道為例，前人的研究顯示它可以用五階以內之伏特拉級數來描述。針對這一類的應用，我們至少需將非線性系統的帶通取樣技術推廣到五階之非線性系統才行。本論文將帶通取樣準則推廣到五階之非線性系統，並以電腦模擬結果驗證推導所得的帶通取樣準則之正確性。藉由本論文所推導出的帶通取樣準則挑選出適當的取樣頻率，則可避免對五階非線性系統取樣時產生膺頻現象。

Much attention has been given to satellite communications in recent years. Owing to the growing demand for high-efficiency data transmission and the power-limited nature of satellite communications, it is very important to make the best use of the limit power and bandwidth of a satellite to ensure efficient transmission. For a digital satellite system, operating the power amplifier of the satellite at or near the saturation point provides the most effective use of the power. However, due to the nonlinear characteristics of the power amplifier at its saturation point, the satellite communication channel is generally considered as a nonlinear channel. For a communication channel, an input signal often has bandpass characteristic. In this situation, if the communication system is nonlinear, the output signal could be a bandpass signal with multiple frequency bands. For sampling bandpass signals with multiple frequency bands, the result developed by previous researchers only applies to nonlinear systems up to the third order. This limits its application to nonlinear systems with a higher order. Take the satellite communication channel as an example, earlier research indicates that it can be described by a fifth-order Volterra series. For this kind of application, bandpass sampling techniques for nonlinear systems up to the fifth order will be appreciated. In this thesis, we develop bandpass sampling criteria for nonlinear systems up to the fifth order, and verify the accuracy of the bandpass sampling criteria by computer simulation. By choosing an appropriate sampling frequency using the developed bandpass sampling criteria, we can avoid the aliasing effect when taking samples of the output of fifth order nonlinear systems.

第一章 緒論 1
1.1 非線性系統輸出訊號之取樣 ..........................1
1.2 衛星通訊系統 ......................................2
1.3 研究動機與目的 ....................................2
1.4 各章節內容概要 ....................................3
第二章 非線性通訊通道與取樣原理 4
2.1 數位衛星傳輸 ......................................4
2.2 TWT放大器 .........................................5
2.3 伏特拉(Volterra)模型 ..............................9
2.3.1 以伏特拉模型描述非線性通訊通道 .................10
2.4 取樣原理 .........................................12
2.4.1 奈奎斯取樣定理 .................................12
2.4.2 帶通取樣定理 ...................................16
第三章 低階非線性系統之帶通取樣 20
3.1 簡介 .............................................20
3.2 二階非線性系統之帶通取樣準則 .....................21
3.3 三階非線性系統之帶通取樣準則 .....................29
第四章 高階非線性系統之帶通取樣 34
4.1 簡介 .............................................34
4.2 四階非線性系統之帶通取樣準則 .....................34
4.3 五階非線性系統之帶通取樣準則 .....................40
第五章 電腦模擬結果 51
第六章 結論及未來展望 58
6.1 結論 .............................................58
6.2 未來展望 .........................................58

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