Inter-system biases in GPS and BDS combined relative positioning by double-differenced observations

The effects of inter-system biases (ISBs) in multi-global navigation satellite system (GNSS) combined positioning cannot be ignored in zero-differenced observations. Furthermore, for relative positioning of multi-GNSS from double-differenced observations, there also exists double-differenced ISB, and the influence on precise relative positioning cannot be ignored. The characteristics of double-differenced ISBs are analyzed by using a large volume of global positioning system (GPS) and BeiDou Navigation Satellite System (BDS) data for differential relative positioning. Different baselines result in different double-differenced ISBs; ISBs obtained from different days show consistency and periodicity for the same baseline. We propose a parameter estimation approach to realize consistency of relative positioning results for different GNSS systems, and thus improve their usability. The results show that the double-differenced ISBs are stable for the same period of time over consecutive days, and can be used for modeling and prediction.