Inter-system Bias: Stability and impact on multi-constellation positioning

Global Navigation Satellite Systems (GNSSs) operate using independent time scales. For this reason, the determination of inter-system time offsets is required to enable multi-constellation solution. In this paper, two different approaches for the determination of the inter-system bias are considered and their performance is evaluated using measurements from three multi-constellation receivers. From the results obtained, it can be noted that the Galileo to GPS Time offset (GGTO) is more stable than the GPS/GLONASS inter-system bias which is characterized by a small drift. Different receivers provide different estimates of the inter-system bias, however the intersystem bias can be considered constant over a short time interval, hence an additional equation can be introduced in the estimation process. The use of pseudo-measurement on the intersystem bias significantly improves multi-constellation positioning performance.