###### Abstract  
The Chinese BeiDou-3 navigation satellite system (BDS-3) is capable of transmitting both old B1I, B3I signals and new B1C, B2a, B2b signals. Current BDS-3 precise orbits are generally calculated using a B1I/B3I combination considering overlap with the BeiDou-2 navigation satellite system (BDS-2). In this contribution, the observation quality of BDS-3 medium earth orbit (MEO) satellites and inclined geosynchronous orbit (IGSO) satellites are analyzed based on three aspects, i.e., carrier to noise ratio (C/N0), pseudo-range noise and pseudo-range multipath (MP). The C/N0 of the MEO satellite is 2-3 dB higher than that of the IGSO satellite at the same elevation angle. Meanwhile, the order of the Root Mean Square (RMS) values of both pseudo-range noise and MP is B1I \(<\) B1C \(<\) B3I \(<\) B2a \(\approx\) B2b. Three kinds of combinations, i.e., B1 CB2a, B1 CB2b and B1 IB3I, are selected for the BDS-3 precise orbit determination (POD) experiment. Orbits are assessed by the orbit-only signal-in-space range error (ISIRE) computed between pairs of the three kinds of combinations in this contribution, CODE and GFZ final orbits. Orbit-only SISRE assessment shows that B1 CB2a/CODE, B1 CB2b/CODE, B1 CB2a/GFZ and B1 CB2b/GFZ are at the same level with CODE/GFZ, and the orbit-only SISRE is at the level of 5 cm for MEOs and 9 cm for IGSOs, respectively. Meanwhile, B1 IB3I/CODE and B1 IB3I/GFZ are about 1-2 cm worse. Inter-solution comparison between B1 CB2a, B1 CB2b and B1 IB3I also indicate that B1 CB2a and B1 CB2b have good consistency, while B1 IB3I shows poor performance. Satellite laser ranging (SLR) residuals indicate that the mean RMS is 3-4 cm for the four BDS-3 MEOs for CODE final orbit, GFZ final orbit, B1 CB2a and B1 CB2b combinations, while the mean RMS value for B1 IB3I combination is a few millimeters worse, at approximately 4-5 cm. p 2022 20  
High-accuracy satellite orbit is the core technology for the operation and application of BDS. During the construction of BDS-2, analysis centers (ACs) of the International GNSS Monitoring and Assessment System (iGMAS), Center for Orbit Determination in Europe (CODE), Deutsches GeoForschungsZentrum (GFZ) and Technical University of Munich (TUM) have carried out much detailed research on POD of BDS-2. [PERSON] et al. [8] reported that the SLR residuals of the MGEX BDS-2 orbits were 5, 10 and 50 cm for MEOs, IGSOs, and GEOs, respectively. For BeiDou-3 experimental (BDS-3e) satellites, [PERSON] et al. [9] reported the POD results of BDS-3e and BDS-2 based on 9 iGMAS stations, and SLR residuals demonstrated that the orbit radial component were 10 cm and 40 cm for the BDS-3e IGSO and MEO satellites, respectively. For BDS-3 satellites, based on 100 MGEX and iGMAS stations, [PERSON] et al. [10] demonstrated that the SLR residual of the BDS-3 orbits was 4-6 cm. Meanwhile, several authors [11; 12; 13; 14; 15] have studied the BDS-3 POD based on inter-satellite links (ISLs), but ISL data are not used in the orbit product generation due to insufficient data openness. As the inheritor of the multi-GNSS experiment established by the IGS, the MGEX has established a global observation network capable of collecting multi-GNSS signals. Currently, five MGEX ACs, i.e., CODE, Shanghai Astronomical Observatory (SHAO, CAS), GFZ, Information and Analysis Center (IAC) and Wuhan University (WHU) have been offering multi-GNSS orbits with BDS-3 included [16; 17; 18; 19; 20]. [PERSON] et al. [21] have conducted an orbit consistency analysis and SLR analysis of the five MGEX ACs. It should be noticed that the B1I/B3I combination is widely used in the BDS-3 product solution among these ACs, in consideration of the overlap with BDS-2 [22; 23; 24].