23. Unified Estimation Model of Multi-system Biases Including BDS/GPS/GLONASS/Galileo

Beidou Navigation Satellite System (BDS) will increase the numbers of available observations to improve the solution accuracy, reliability and availability of precise positioning. Multi-system fusion with BDS is nowadays increasingly paid attention. However, the multi-system fusion focuses only on loose combination model, which means that each system has their reference satellite each other. This model will increase the probability of initialization because the reference satellite can be often changed during the process of positioning. If multi-system fusion has unified time and signal reference, that is, multi-system fusion selects the same satellite as the reference satellite, the problem will be covered. Therefore, the paper proposed an estimation model of multi-system biases for multi-system fusion. The estimation model will investigate differential code bias (DCB) of each system and inter-system biases (ISB) among systems. Multi-system data from IGS, MGEX and iGMAS were collected to analyze the effects of different types of the receivers on various biases, and then a unified multi-system biases estimation model was proposed. The results show that there are some biases of ISBs in GNSS systems and the biases are affected by stations. The variation of GLONASS satellites has a unified tendency and the ISBs of BDS has a fluctuation property, which need to be improved.