- 學位論文
GPS接收機抗窄頻干擾之頻域設計
Design of Narrowband Anti-jamming GPS Receivers in Frequency Domain
摘要
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。不過在某些場合，GPS接收機受到外界射頻訊號(radio frequency, RF)的干擾。使GPS接收機發生定位精確度降低的現象，更甚者使接收機同步功能失鎖而無法接收衛星訊號。有鑑於此，GPS接收機的抗干擾研究，已成為一重要且實際的課題 本文專注在頻域GPS抗窄頻干擾方法的研究，在System View軟體上模擬整個抗干擾環境。其方法的主要精神是利用快速傅利葉轉換（ fast Fourier transform）將經過RF端降到中頻的數位訊號轉到頻譜上，透過干擾濾除電路將窄頻干擾的頻帶資料濾除，最後由反快速傅利葉轉換（inverse fast Fourier transform）將資料還原到時域。此時的窄頻干擾訊號已經被消除，僅剩熱雜訊和GPS訊號進入接收機，經過解調變和解展頻處理之後就可得到導航資料。 為了研究此抗干擾架構的可行性，我們利用Altera Startix EP1S25 F780C5 FPGA在 Quarstus II軟體上模擬整個抗干擾電路。透過FPGA電路的合成，驗證了利用快速傅利葉轉換，干擾濾除電路和反快速傅利葉轉換來達到抗干擾的目的。
並列摘要
Abstract GPS is an accurate navigating system and generally used in civilian or military applications. But GPS receiver performance is usually degraded by intentional or unintentional RF interference. The jamming signal may cause the navigation error and even saturate the receiver. This thesis focuses on the cancellation of narrowband jamming. Excising method in frequency domain is our architecture in the anti-jamming studies. Fast Fourier transform (FFT) can translate time sequence after A/D converter to frequency domain Excision processing removes jamming power in the spectrum. Inverse fast Fourier transform (IFFT) reconstruct the time sequence after jamming excision. We use System View, a powerful communication software package, to generate the GPS signals, PRN codes, thermal noise and jamming signals, etc. The jamming method, despread and demodulation operations are also constructed by the same software package. The simulation can shows that overlap fast Fourier transform (OFFT) is a powerful approach to reject the narrowband interference. After anti-jamming processing, the signal to noise ration (SNR) is improved. So, GPS receiver can get navigation data successfully. In order to implement the hardware circuits, we choose Altera Stratix FPGA EP1S25 F780C5 to build three main blocks (FFT, excision and IFFT). Quarstus II can help us to simulate the anti-jamming processing in hardware circuit. Taking a single tone interference as an example to test this hardware implementation, the results are satisfactory.