Identifying a low-frequency oscillation in Galileo IOV pseudorange rates

Abstract

Galileo, the European global navigation satellite system, is in its in-orbit validation phase and the four satellites which have been available for some months now have allowed a preliminary analysis of the system performance. Previous studies have showed that Galileo will be able to provide pseudorange measurements more accurate than those provided by GPS. However, a similar improvement was not found for pseudorange rate observations in the velocity domain. This fact stimulated additional analysis of the velocity domain, and, in particular, an unintended oscillatory component was identified as the main error source in the velocity solution. The magnitude of such oscillation is less than 10 cm/s, and its period is in the order of few minutes. A methodology was developed to identify oscillatory components in the Galileo IOV pseudorange rate observables, and it was verified that the measurements from Galileo IOV PFM and Galileo IOV FM2 are affected by a small oscillatory disturbance. This disturbance stems from the architecture adopted for combining the frequency references provided by the two active clocks present in the Galileo satellites. The issue has been solved in Galileo IOV FM3 and Galileo IOV FM4, and the oscillatory component has been eliminated. We also propose a methodology for removing this unwanted component from the final velocity solution and for determining the performance that Galileo will be able to achieve. The analysis shows that Galileo velocity solution will provide a root-mean-square error of about 8 cm/s even in the limited geometry conditions achieved using only four satellites. This shows the potential of Galileo also in the determination of user velocity.

Selected properties of GPS and Galileo-IOV receiver intersystem biases in multi-GNSS data processing

“…The results are consistent with conclusions obtained by Borio et al (2015), who also detected oscillations in Galileo signals. Similarly, only E11 and E12 satellite signals were affected by the periodic effects.…”

“…Similar oscillating disturbances in Galileo observations were detected in pseudorange rate measurements by Borio et al (2015). In that case both Galileo E11 and E12 satellite measurements were affected by the periodic effects.…”

“…In that case both Galileo E11 and E12 satellite measurements were affected by the periodic effects. The study by Borio et al (2015) also showed the lack of oscillating disturbances in E19 signals. This is consistent with our study results since only ISB and phase observations related to E11 and E12 signals were affected by periodic phenomena.…”

“…This is consistent with our study results since only ISB and phase observations related to E11 and E12 signals were affected by periodic phenomena. The experiment conducted by Borio et al (2015) revealed changes over time of the oscillations' center frequency. The authors of that study stated that the source of the oscillations was the initial algorithm used for combining the frequency references provided by the two active clocks in the Galileo E11 and E12 satellites.…”

“…The authors of that study stated that the source of the oscillations was the initial algorithm used for combining the frequency references provided by the two active clocks in the Galileo E11 and E12 satellites. This problem was fixed in Galileo E19 and E20 satellites (Borio et al 2015).…”