- 學位論文
以希爾伯特-黃轉換法為GPS接收機抑制調頻干擾
FM Interference Suppression for GPS Receivers via Hilbert-Huang Transform Approach
摘要
全球定位系統(GPS)可在各種導航、時頻同步等工程應用領域提供精確的位置與時間資訊。GPS雖能藉由展頻碼的程序增益，來抵抗一些寬頻的干擾(如熱雜訊與通道雜訊)或是低能量的窄頻干擾，但其仍無法應付更高能量的干擾，因此GPS接收機的干擾抑制研究，已成為一重要且實際的課題。 在本論文中，所探討的干擾訊號是調頻干擾。由於調頻干擾之頻率會隨著時間進行而改變，所以必須利用時頻分析方法偵測干擾的特性。時頻分析方法包含了短時傅立葉轉換(Short Time Fourier Transform, STFT)、蓋博轉換(Gabor Transform)、魏格納分佈(Wigner Distribution)及希爾伯特-黃轉換(Hilbert-Huang Transform, HHT)。經由模擬與比較得知HHT具有較佳的時頻解析度，所以我們運用HHT來呈現GPS調頻干擾的抑制效果。這個方法是以稱為經驗模態分解(EMD)的方式產生一組本質模態函數(IMF)為基礎。我們將最大能量的IMF當作是干擾並且將它移除。 接著，我們將利用弦波調頻干擾及線性調頻干擾作為干擾抑制之測試。經過軟體模擬可知在HHT的架構下，對於窄頻的調頻干擾已有不錯的抑制效果，且對於寬頻調頻干擾而言也能偵測出干擾源的特性。整體干擾抑制之效能較之前相關的研究提升許多。
並列摘要
The global position system (GPS) can provide accurate positioning and timing information in many applications. GPS can cope with wideband noise (such as thermal noise and channel noise) or low power narrowband interference with the processing gain of spreading code. However, GPS cannot reject high power interference completely. Therefore, interference suppression research of GPS receiver has become an important issue. In this thesis, we consider interference source as frequency modulation interference. Because frequency modulation interference is time-varying interference signal, we apply time-frequency analysis to detect characteristics of interference. The ways to analyze time-frequency include Short Time Fourier Transform (STFT), Gabor Transform, Wigner Distribution, and Hilbert-Huang Transform (HHT). Because Hilbert-Huang Transform has the best time-frequency resolution, we use HHT to simulate the performance of frequency modulation interference suppression. It is based on the empirical mode decomposition (EMD), which generates a set of intrinsic mode functions (IMF). We take the IMF which has the biggest energy as interference and remove it. Then, we use sinusoidal frequency modulation interference and linear frequency modulation interference to perform interference suppression test. Through software simulation, under HHT frame we can get excellent interference suppression result for narrowband frequency modulation interference and can detect interference characteristics for wideband frequency modulation interference. Compare to the previous research, the interference suppression ability in this research is superior.