## 7 Conclusions  
The ERP constitute a crucial component in defining the global reference frame, and GNSS serves as a vital technology for obtaining ERP, including PM, its rates, and LOD. The latest IGS Repro3 ERP products provided the IGS contribution to the latest ITRF2020, but without consideration of the BDS observations. In this study, the ERP and the orbits generated from the BDS-3 B1I/B3I observations and B1C/B2a observations were calculated in the ITRF2020. The evaluation of these parameters was conducted, and the validation of 22 BDS-3 MEO orbits using SLR was also performed. Firstly, we evaluated the signal quality from several indicators. SNR is an important index of characterizing the signal strength. The B2a signal has the largest SNR, then the second one is B3I and the SNR of B1C is comparable with B1I. The other indicator of observation quality is multipath. The ranking of multipath errors is B3I \(<\) B2a \(<\) B1C \(<\) B1I. Ambiguity resolution is one of crucial steps in GNSS data processing with phase observations, and the B1C/B2a combination has a higher percentage of ambiguity fixing than the B1I/B3I combination. The mean percentage of all fixed ambiguities including WL and NL is 78.9% for the B1I/B3I combination and the mean percentage for the B1C/B2a combination is higher, which is 86.5%. Subsequently, the precision of the satellite orbits was compared by using orbit overlapping. The RMS for the B1C/B2a-based BDS-3 orbit overlapping was calculated for radial component, along component, cross component, and 1D component, yielding values of 1.58 cm, 2.09 cm, 1.86 cm, and 1.86 cm, respectively. It is noteworthy that the RMS values for the BDS-3 orbit overlapping, employing the B1I/B3I combination, are slightly higher compared with the B1C/B2a solution. This discrepancy may be thanks to the higher percentage of ambiguity fixing to integers in the B1C/B2a combination. Satellite Laser Ranging, as one of key space technologies, can realize the orbit accuracy validation of GNSS satellites independently. The mean RMS of SLR residuals is 5.72 cm for 3-day arc orbits of 22 BDS-3 satellites from the B1C/B2a solution and 4.40 cm for BDS-3 satellite orbits without consideration of satellites C22, C43, and C44, which are both slightly better than the B1I/B3I combination and CODE MGEX products. Finally, we assessed the accuracy of ERP estimates from the aspect of internal and external accuracy, particularly focusing on the formal errors in ERP estimation and the disparities between the estimated ERP values and the 20C04 products. The mean formal errors of the 3-day arc ERP estimates derived from B1C/B2a combination observations are approximately 10 \(\mu\)as for PM, 12 \(\mu\)as/d for PM rates, and 0.7 \(\mu\)s/d for LOD. Comparatively, the utilization of B1C/B2a-based solutions results in a reduction of mean formal errors by about 17% for pole coordinates, 22% for LOD, and 21% for pole coordinate rates when compared with B1I/B3I-based solutions. Regarding the external accuracy, the mean differences of the 3-day arc ERP estimates from the BDS-3 B1C/B2a combination, with reference to IERS 20C04, are 48 \(\mu\)as for X PM, 19 \(\mu\)as for Y PM, 17 \(\mu\)as/d for X PM rate, 5 \(\mu\)as/d for Y PM rate, and 4.0 \(\mu\)s/d for LOD.