- 學位論文
GPS接收機抗窄頻干擾之時域設計
Design of Narrowband Anti-jamming GPS Receivers in Time Domain
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。它是利用直接展頻的一種架構，因此，此系統能藉由C/A碼的展頻處理增益，來對付ㄧ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，但是它無法應付高能量的窄頻干擾，因此我們需要一個抗干擾濾波器在解展頻之前來先將干擾去除。 在本論文將提出定點數的橫貫式適應性濾波器與定點數的格式適應性濾波器，將它們應用在抗干擾的系統中。為了能配合真實狀況，我們將考慮以下四種窄頻干擾，包括連續波單頻干擾(CWI)、連續波多頻干擾(Multi-tone CWI)、掃頻干擾(Periodically swept (linear FM) CWI )與脈波干擾(Pulsed CWI)。因為干擾為未知的，我們利用適應性估測器能在線上即時學習的特性，來即時預估所遭遇之窄頻干擾。 接著，我們將模擬並比較兩種架構的適應性濾波器，在抗干擾的應用上的優缺點；之後，將其應用於各種干擾的環境來模擬，模擬結果以訊號雜訊比的改善值(SNR Improvement)來顯示出其抗干擾有不錯成效。最後，將設計橫貫式的抗干擾濾波器以FPGA來實現，並測試其結果。
並列摘要
The globe position system (GPS) can provide accurate positioning and timing information useful in many applications. The communication technology used in GPS is a direct sequence spread spectrum (DS-SS) structure. Using C/A Gold codes, it can cope with wideband noise (such as thermal noise and channel noise) or low power narrowband interference by its processing gain. But DS-SS can not reject high power narrowband interference completely. So we need an anti-jamming filter to reject the narrowband interference by using adaptive filters prior to dispreading. This paper proposed a fixed-point transversal adaptive filter and a fixed-point lattice adaptive filter for the application in GPS anti-jamming system. Four types of narrowband jammers, i.e. continuous wave interference (CWI), multi-tone CWI, swept CWI, and pulsed CWI, are considered in order to emulate realistic conditions. As the jammings are unknown, the adaptive predictor is employed to accurately predict the narrowband signals based on a real-time learning method. In order to compare the two kinds of anti-jamming filter, we need simulation. Simulation results show that the proposed methods achieve good performance in terms of SNR improvement in broad class of interference environments. Finally, we implement the transversal anti-jamming filter in FPGA.