臺灣博碩士論文加值系統

近年來，無線通訊系統根據不同的應用範圍與使用環境，創造出許多截然不同的標準。但因應未來無線通訊的需求，接下來的幾年中，無線通訊網路將整合2G，2.5G以及3G等無線通訊規格，並將其整合並創造為一個新的標準。軟體無線電技術是整合不同通訊系統的可能方法。軟體無線電設計的構想是將接收機中之類比與數位轉換器(ADC)盡可能地接近天線，以減少所需的類比前端電路，將最多的接收機功能以軟體實現。在軟體無線電的架構下，適當的使用帶通取樣技術可以有效降低取樣頻率。然而，接收機之類比前端，通常包含有低雜訊放大器，而低雜訊放大器常會產生不可避免的非線性失真。當我們選擇取樣頻率時，若沒有考慮到非線性失真的影響，則帶通取樣訊號的品質必定會變差。因此，我們不宜以傳統的帶通取樣技術來實現傳統的軟體無線電接收機。本論文使用一種新方法找到能迴避非線性頻譜所造成的干擾。這個方法是將欲得訊號的頻譜與非線性失真頻譜視為多組輸入訊號，然後考慮選擇不會讓這些頻譜在取樣後產生頻譜重疊之帶通取樣頻率。如此一來可保證取樣後的訊號中欲得訊號與非線性失真訊號在頻譜上是分離的，
藉此達到降低非線性失真效應的目的。藉由將所提出的方法應用於B3G之軟體無線電接收機，我們得以驗證所提出之方法的正確性與可行性。


關鍵字：帶通取樣、軟體無線電、低雜訊放大器、非線性現象、數位前端

Abstract
In recent years, various wireless communication systems were developed for different applications and in different environments. In the near future, it is very likely that the 2G, 2.5G, and 3G standards will be integrated into an entirely new standard. The software defined radio(SDR) is a potential technique to accomplish such integration. The idea of SDR is to place the analog-to –digital converter as near to the antenna as possible, so as to minimize the required analog front end (AFE) circuit. This ensures that most functions of the SDR can effectively reduce the required sampling frequency. However, the low noise amplifier in the AFE will generate nonlinear distortions. In the circumstances, there will be harmonic and inter-modulation bands which can interfere with the desired band. Therefore, using the conventional bandpass sampling technique does not yield a good result. In this thesis, we propose a new approach to find the valid bandpass sampling frequencies for SDR front end with nonlinearities. By considering the nonlinear distortion bands as part of the multiband input signal, we find suitable bandpass sampling frequencies which yield an aliasing-free sampled output. This guarantees that the nonlinear distortion bands are not overlapped with the desired signal band is the sampled signal. Hence, the effects of the nonlinearities can be reduced. By applying the proposed method to the B3G SDR
receiver , the goodness of the proposed method is verified.

Keywords：Bandpass sampling, Software defined radio , Low-noise amperfier, Nonlinear distortion, Digital front end

1 緒論
1.1 B3G時代與軟體無線電系統
1.2 研究動機與目的

2 無線通訊系統的發展趨勢
2.1 B3G時代與軟體無線電系統
2.2 使用軟體無線電實現B3G系統
2.3 利用數位前端的方式整合前端方塊
2.4 用帶通取樣原理完成數位降頻
2.5 接收級放大器所產生的非線性行為

3 抗非線性失真之帶通取樣法
3.1 使用多組訊號帶通取樣技術克服單組訊號經非線性放大後之干擾
3.2 以另一種方式求取三組射頻訊號之帶通取樣技術

4 抗非線性失真之多組射頻訊號帶通取樣法
4.1 抗非線性失真之兩組射頻訊號帶通取樣法
4.2 兩組三階非線性帶通取樣演算法
4.3 三組三階非線性射頻訊號帶通取樣條件分析

5 多模軟體無線電接收機之電腦模擬
5.1 以軟體無線電實現之多模架構
5.2 接收GSM三頻訊號
5.3 對任意鄰近GSM訊號接收
5.4 接收B3G之多模訊號
5.5 模擬雙模與三模SDR接收機

6 結論

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