Multi-GNSS Processing Combining GPS, GLONASS, BDS and GALILEO Observations

Coexistence and development of four kinds of Global Satellite Navigation System, GPS, GLONASS, BDS, and GALILEO have initially established. In order to benefit from multi-GNSS applications, including increase in usable SVs, signals and frequencies, increase in availability and coverage, more robust and reliable services, and so on, firstly we need to obtain the precise multi-GNSS orbit and clock in a unified space and time frame. Based on the knowledge of the EPOS and EPOS-RT (Earth Parameter and Orbit determination System in Real-Time) software package, Beijing Aerospace Control Center (BACC) has been working on his own software package for multi-GNSS data processing. This paper firstly introduces the multi-GNSS processing strategies in detail, and adopts additional inter system biases parameter (ISB) except the normal IGS and GFZ observation model and dynamic model. On the basis of above strategies and the observation data from a network of multi-GNSS capable receivers from the IGS Multi-GNSS EXperiment (MGEX) and a regional BDS station network operated by China, the experiments and simulation are carried out. The results are validated against products from other institutes and by overlap comparison. The impact on orbit and clock precision by combined processing against single system processing is investigated and the improvement on precise point positioning (PPP) is also evaluated.