Extending integration time for Galileo tracking robustness under ionosphere scintillation

As a wide array of services and applications are becoming more reliant on Global Navigation Satellite System (GNSS) technology, its continuity requirements are naturally becoming more stringent. The ionosphere scintillation phenomenon is one of the major concerns that threaten these continuity requirements. It results in amplitude, phase and frequency fluctuations of Radio Frequency (RF) signals traveling through space and piercing the ionosphere, hundreds of Km of altitude, where turbulent ionized gases or plasma that stem from solar winds modify the characteristics of electromagnetic signals. The objective of this paper is to study the impact of extending the coherent integration interval used in GNSS scalar tracking loops, in terms of maintaining tracking or synchronization of the European GNSS Galileo E1 Open Service (OS) signals. For that end, a first order optimum loop filter is designed in the digital domain, optimal in minimizing both transient energy and thermal noise tracking jitter. Moreover, a theoretical study of its stability and degree of stability is carried out through root locus and Bode plots. Its performance is also compared to that of traditional analog loop filters often used in literature. Carrier and code tracking loops using this optimum digital loop filter are tested on simulated weak Galileo signals as well as simulated scintillation affected signals. Fast and slow amplitude, phase scintillation are first considered separately to understand the mechanisms of each variable (amplitude/phase), and then both fluctuations are incorporated onto the simulated Galileo signal.