Characteristics of Onefold Clocks of GPS, Galileo, BeiDou and GLONASS Systems.

Qingsong Ai,Lukasz Borowski,Kamil Maciuk,Paulina Lewinska

doi:10.3390/s21072396

Abstract

This research is focused on searching for frequency and noise characteristics for available GNSS (Global Navigation Satellite Systems). The authors illustrated frequency stability and noise characteristics for a selected set of data from four different GNSS systems. For this purpose, 30-s-interval clock corrections were used for the GPS weeks 1982–2034 (the entirety of 2018). Firstly, phase data (raw clock corrections) were preprocessed for shifts and removal of outliers; GLONASS and GPS satellites characterize a smaller number of outliers than BeiDou and Galileo clock products. Secondly, frequency and Hadamard deviation were calculated. This study concludes that the stability of GPS and Galileo is better than that of BDS (BeiDou Navigation Satellite System) and GLONASS. Regarding noise, the GPS, Galileo, and BDS clocks are affected by the random walk modulation noise (RWFM), flashing frequency modulation noise (FFM), and white frequency modulation noise (WFM), whereas the GLONASS clocks are mainly affected only by WFM.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
We find that the short-term (τ = 100 s) medium–long‐term (τ = 10,000 s) stability of GPS, Galileo, and BDS were at the level of and−13medium–long-term (τ = 10,000 s) stability of GPS, Galileo, and BDS were at the level of
The Multi-GNSS EXperiment (MGEX) products of all currently available GNSS clocks were analyzed in this paper

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Along with the development of other satellite systems such as the European Galileo system, the Chinese BeiDou, or the Japanese QZSS (Quasi-Zenith Satellite System), IGS initiated the introduction of the Multi-GNSS EXperiment (MGEX) products. It is worth mentioning that MGEX clock offset products and orbits are provided by several analysis centers [2]. The authors present a quality analysis of the precise clock products provided by the MGEX, based on the occurrence of clock offset. The obtained results are used to analyze the stability and noise of GPS, GLONASS, Galileo, and BeiDou satellites. This paper contributes to the existing knowledge by analyzing four different GNSS clocks and completing a long-term analysis (1 year) with a very low sampling interval (30 s), which leads to more than 1 M observations per satellite. The adopted methodology includes the Hadamard deviation, the MAD (Median Absolute Deviation) method, and the lag 1 ACF (autocorrelation function) for clock correction data preprocessing for noise identification

Materials and Methods

Stability of GNSS Satellite Clock Offset

Noise Determination

Conclusions