THE STABILITY OF INTER-SYSTEM BIAS OVER TIME FOR POSITIONING USING GPS AND GALILEO

Abstract

The introduction of new overlapping signals from GPS and Galileo, such as L1 and E1 and L5 and E5a, presents new opportunities for enhanced precision and reliability in positioning. However, it also introduces new challenges that need to be addressed. One of the primary challenges in processing GPS and Galileo observations is the requirement for Inter-System Bias (ISB) estimation. An important aspect has become the examination of the stability of the ISB parameter over time. Both short-term and long-term stability must be investigated. For this purpose, experiments were conducted on 20 permanent IGS stations in 10 pairs. Using the Modified Ambiguity Function Approach (MAFA) method, the stability of the ISB parameter over time was investigated, both for short-term (daily) and long-term periods. When selecting pairs, care was taken to ensure that the distances between the receivers in the pair were shorter than 10 kilometers (this allowed us to reduce the influence of the atmosphere on the obtained results). Observation data were obtained from the permanent GNSS stations mentioned above for 2020 and 2021. Calculations were conducted for the GPS and Galileo systems conjoined observations. The obtained results showed that for both the short-term period, which is a day, and for the more extended period of time (few months), the ISB exhibits significant stability. This means that once determined, the ISB can be used for several months for a given pair of receivers.