Investigation of anti-jamming techniques for GPS systems

GPS is a satellite-based radio navigation system that aims to enable users to obtain high-accuracy position, speed, and time information in various military and civilian applications. GPS signals, which reach users at low power levels, can be vulnerable to the disruptive effects of high-power interference signals. Therefore, the development of anti jamming techniques has been necessary in GPS receivers. Anti-jamming can be implemented in the antenna domain, digital domain, and analog domain depending on the signal processing domain in the GPS receiver. Within the scope of this thesis, an anti-jamming technique has been developed in the analog domain to suppress jamming signals. The aim was to mitigate the jamming signals before reaching the front-end of the GPS receiver by designing an adaptive analog notch filter. All the design and analysis studies was performed using the MATLAB simulation tool. Jamming performance of single-tone CW, multi-tone CW, and linear chirp jammers have been analyzed on GPS C/A signals and effective jamming parameters have been determined. Analog band-stop/notch filters have been designed using Butterworth, Chebyshev Type I, and Elliptic filter design approaches and performance analyses have been conducted based on the center frequency and bandwidth parameters of the filters. In the performance analyses, it has been concluded that the Butterworth filter is the most effective filter against the jamming signal. The analog Butterworth notch filter has been adapted using the MUSIC and STFT spectral estimation methods. The adaptive analog notch filter method with MUSIC has been used to mitigate single-tone CW and multi-tone CW jamming signals, while the adaptive analog notch filter method with STFT has been used to mitigate linear chirp jamming signals. Performance evaluations of the proposed anti-jamming method have been conducted by comparing the BER analysis results obtained before and after anti-jamming.