New anti-jamming technique for GPS and GALILEO receivers using adaptive FADP filter

Abstract

Anti-jamming techniques to improve Global Positioning System (GPS) receiver's robustness have been mainly developed in military applications. None of civilian techniques can procure sufficient robustness against occasional or intentional jammers for civil GPS or GALILEO navigation receivers. The amplitude domain processing (ADP) filtering is a technique based upon Capon works and Neyman-Pearson theory. Several experiments concerning the ADP filtering have been considered at the 3DETSNAV division of LACIME laboratory at Ecole de technologie superieure (ETS), which have proved that the technique is reliable in order to eradicate powerful interference present in the spread spectrum signal. However, the results show that the ADP filter has a real limitation when submitted to multiple interference scenarios. This paper shows that working in the frequency domain is more efficient because jamming signals added to a white Gaussian noise are easier to detect and to attenuate when represented in the frequency domain. The present paper gives mathematical elements to complete the ADP theory in the frequency domain and presents the performances of an ADP in the frequency domain (FADP) filter simulated in a Matlab Simulink environment. The filter is tested with a signal composed of a GPS C/A code (Gold sequence) drowned in a white Gaussian noise in presence of one or several additional jammers (CWI, PWI, chirp). Several analyses are made upon the filter output (signal to noise ratio, attenuation and power spectral density measurements). The results of the analysis show that the FADP can eradicate any kind of jammers of 20 dB above white Gaussian noise. Correlation losses are measured; they are always under 0.5 dB. In the presence of one or two jammers, the performances of the FADP filter are better than those of the ADP filter. The FADP filter can procure up to 20 dB processing gain with a maximum of 10 dB loss on SNR in worse jamming scenario. When the number of jammers increases, the performances remain convenient, whereas the time-domain ADP filter becomes unable to be effective. In this paper, measurements are made with a number of jammers up to 15.