Estimation and analysis of differential code biases for BDS3/BDS2 using iGMAS and MGEX observations

Abstract

In this contribution, the BDS3 differential code biases (DCBs) are estimated by using the iGMAS and MEGX networks and the performance of both satellite and receiver DCBs for BDS3 is evaluated with the observational data during the period of DOY 1–180, 2017. The characteristics of BDS3 and BDS2 DCB are compared, and the code inter-system biases (ISB) between BDS3 and BDS2 are also analyzed in detail. The comparison of our estimated BDS C2I-C6I and C2I-C7I DCBs and the DLR and IGG products shows a good agreement. For BDS2, the mean differences are within $$ \pm \,0.2\,{\text{ns}} $$ and STDs are within 0.15 ns. However, the BDS3 presents a larger difference, with the mean difference of about 0.35 ns, because fewer stations are included in the DLR/IGG processing. The comparison of BDS3 and BDS2 DCB shows that the receiver DCB differences between BDS3 and BDS2 are close to zero for the same network, i.e., iGMAS or MGEX. In other words, there is no significant systematic bias between BDS3 and BDS2 receiver DCB. However, when the iGMAS and MGEX networks are processed together, we found that the receiver DCB differences between BDS3 and BDS2 are not close to zero and present an obvious systematic bias between different networks. The further analysis of code ISB between BDS3 and BDS2 also shows a similar phenomenon. Therefore, the receiver DCB of BDS3 and BDS2 should be separately estimated or calibrated when iGMAS and MGEX networks are processed together. We also analyze the receiver DCB and code ISB between Galileo FOC and IOV satellites and found that there is no such systematic bias between Galileo FOC and IOV satellites. A 180-day analysis of estimated BDS3 and BDS2 DCB shows that the satellite DCBs of BDS3 are fairly stable, with a mean STD of about 0.18 ns. For BDS2, the IGSO DCBs are the most stable with a mean STD of about 0.09 ns, and the GEO DCBs exhibit the worst stability with a mean STD of about 0.18 ns. The mean STDs of receiver DCBs for BDS3 and BDS2 are 0.38 and 0.41 ns, respectively, and the STD of receiver DCBs of BDS3 is smaller than that of BDS2 at most stations.