C/N₀ degradation in presence of chirp interference: theoretical model

A growing threat for Global Navigation Satellite System (GNSS) service is Radio Frequency Interference (RFI). An important class of GNSS RFI signatures is time dependent frequency pattern signals, generically termed here as chirp signals radiated by Personal Privacy Devices which are jammers with a continuously growing (and illegal) use. The analysis of the impact of chirp signals on GNSS receivers is of the utmost importance in civil aviation. Civil aviation spectrum regulations characterize the Radio Frequency environment of the Safety-of Life GNSS service at signal processing level by comparing the effective carrier-to-noise power density ratio (C/N_0,eff), calculated from a degradation of the nominal C/N₀, to a C/N₀ threshold. Therefore, in this work the mathematical model of the theoretical C/N₀ degradation of the received useful signal in presence of a chirp signal is derived from the traditional calculation of the Spectrum Separation Coefficient (SSC) and the theoretical RFI chirp signal power spectrum density, whihc is also developed in this work. Moreover, the impact of the chirp signal characteristics on the SSC and C/N₀ degradation are commented. Finally, the applicability of the proposed model based on the SSC is also analyzed from the GNSS signal, receiver local replica and RFI chirp signal characteristics.