Sensitivity of GNSS Receivers

GNSS receiver synchronization systems in carrier phase (frequency) (PLL, FLL) and code delay (DLL) have been considered taking into account mutual interaction in high-precision phase mode (centimeter accuracy level) and in a rougher, but more noise-immune code mode (meter accuracy level). Satellite signals can be of two types: data type - inversely modulated by a priori unknown binary symbols, or pilot type - without such modulation, and also with different types of modulation (BPSK, BOC, etc.). Tracking errors and minimal SNR (Signal-to-Noise density Ratio) values are estimated, which can still ensure standard operation of these systems (and hence the entire receiver). There are considered two traditional combinations of code and carrier synchronization, namely: PLL + coherent DLL; FLL + non-coherent DLL; and a rather nontraditional combination: PLL+ non-coherent DLL. According to the study, the last combination (PLL + non-coherent DLL) has been recommended for synchronization of GNSS receivers to ensure the best sensitivity of them. It is shown that the dynamic properties of PLL and FLL from the point of view of their guiding DLL are equivalent in a linear mode, however, FLL provides much greater dynamic stability than PLL at high SNRs.