Navigation Receiver Frequency Anti-jamming Technology And Performance Analysis

The GPS signal is CDMA using direct sequence spread spectrum (DSSS) to bi-phase modulate the carrier frequency. The GPS system has certain interference rejection capacities, but the interference immunity is limited by the processing gain. The performance of the system is strongly degraded when the interference power is greater than the interference margin. So, GPS satellite signal is vulnerable to malicious man-made interference, the system cannot work normally. It is very important to research signal processing techniques to suppress the interference. In this dissertation, we proposed the interference suppressions algorithm based on short-time Fourier transform and wavelet packet transform.GPS signal is a non-stationary signal, to process the non-stationary signal, we must use the time-frequency analysis. The STFT and the WPT are all a kind of the time-frequency analysis tool. STFT is a windowed Fourier transform, the wavelet packet decomposition and reconstruction are achieved by quadrature mirror filter Bank (QMF).The suppression algorithm based on STFT is the key to select the appropriate window function. The hamming window and Gaussian window are selected; the suppression algorithm based on WPT is the key to select the wavelet function and threshold value for interference suppression. According to the microscrope character of various wavelet bases, the symlet-10 is selected. According to the characteristics of transform domain and type of the interference, the appropriate threshold is selected.In this dissertation, we study interference suppression module, which includes forward transform, interference suppression in time-frequency domain and inverse transform. Interference suppression algorithm based on STFT can be summarized as following as: GPS signal is transformed from time domain to time-frequency domain by STFT, all data of every frequency are compared with the threshold, if that is greater than the threshold, which is polluted and cut it, and then the processed signal is transformed from time-frequency domain to time domain; Interference suppression algorithm based on WPT can be summarized as following as: the GPS signal including interference is decomposed into many sub-bands at the different levels by WPT. We analyze every sub-band and if every coefficient of the sub-band is greater than the threshold, the sub-band is polluted and it is removed, finally, reconstruct the interference free signal. Interference suppression process is completed. We add anti-jamming module into Monte Caro model, through this model we change our interferences such as Continuous Wave, Multi-Continuous Wave, Narrow Band Interference and Linear Frequency Modulate interference. We get the BER figures based on WPT and STFT algorithms, through the result we prove the efficiency of the WPT-based jamming suppression algorithm and improve the performance of GPS system.