Clustering and look-up table calibration of receiver inter-system bias for QZSS and GPS integration

The Quasi-Zenith Satellite System (QZSS) from Japan will supplement the global positioning system (GPS) for more accurate and stable positioning, navigation and timing services. However, QZSS and GPS measurements are not free of inter-system bias (ISB) for various receiver brands. After estimating and clustering the receiver ISB values of GPS and QZSS for all three overlapping frequencies L1, L2 and L5, we show that the code ISB of the receivers can have at least two groups and the firmware versions of the groups may overlap with each other, making the look-up-table calibration difficult. Therefore, we propose to discriminate one code ISB value from the other for a specific receiver by the observations of a few epochs so that precise calibration can be implemented within a short time. The phase fractional ISB (F-ISB) calibration of QZSS and GPS is easier as their magnitudes are receiver-type and firmware-version related. Experiments for the code positioning show that the QZSS and GPS integration with the ISB calibrated by the looked-up values has an obviously smaller 3D distance root mean square, i.e. the root mean square of the radial distances from the true position to the calculated positions. The empirical success rate of the ambiguity fixing in precise positioning is also improved with the looked-up phase F-ISB values.