## 1 Introduction  
Among the global navigation satellite systems (GNSS) that have been built in the world, the Chinese BDS-3 is the first to realize the whole constellation inter-satellite links (ISL) function [1]. ISL not only ensure the precise orbit determination (POD) performance under the condition of limited regional ground stations but also supports the autonomous navigation of the constellation, which greatly enhances the overall operational capability of the BDS-3 [2,3]. The existing research about the ISL measurement used for POD can be mainly divided into two categories: One is to combine ISL measurements and carrier phase observations of GNSS receivers at ground stations to realize the precise orbit determination, namely joint POD. The other focuses on the autonomous orbit determination only using ISL measurement, namely AOD. For the first type, [PERSON] et al. [4] conducted a POD experiment by combining ISL measurements with carrier phase observations from six GNSS receivers distributed in regional stations. The results show that the orbit-related spatial ranging accuracy was improved by 37-76%, compared to using only pseudorange and phase observations from ground stations, which indicates that introducing ISL measurement can improve the orbit accuracy determined with regional stations. [PERSON] et al. [5] added ISL measurements to GNSS observations from 16 global ground stations for orbit determination. The results show that the 3D overlap accuracy of the orbit is improved by 42%, and the orbit accuracy is up to 9.2 cm, which indicates that ISL can improve the orbit accuracy based on a small number of global ground stations. [PERSON] et al. [6] discussed the contribution of ISL measurements to the phase observations from various quantities and distributions of ground stations, pointing out that almost equivalent POD performance can be achieved when ISL measurements combine 10 regional and 10 global ground stations, respectively. All of the above have shown that, by introducing ISL measurements, the POD can reduce the dependence on ground stations. What is more, centimeter-level orbit can be achieved with regional ground stations. For the second type, POD with only ISL measurements, there are obvious systematic biases, as is known. [PERSON] et al. [7] analyzed its characteristics and proposed an improved method, while the user's ranging error still reached 3 m in 9 days. Moreover, [PERSON] et al. [8] analyzed the effect of the a priori orbit on the autonomous orbit determination, such as the predicted orbit of the telemetry tracking control system and of the international GNSS Monitoring And evaluation System (iGMAS). They concluded that, under the a priori orbit of 45 m, the orbit accuracy with four ISL measurements can reach about 2 m. [PERSON] et al. [9,10] further explored the performance of autonomous POD and time synchronization with ISL measurements from all BDS-3 satellites. They verified that, on one hand, the radial overlap error of the satellite orbit is better than 15 cm. On the other hand, the clock error accuracy of the satellite is better than the ones solved with only GNSS observations from ground stations. Moreover, [PERSON] et al. [11] recently provided a comprehensive review of the existing research on POD, confirming the two conclusions above. Nevertheless, there are still some overlooked issues that need to be taken seriously and addressed, namely the influencing factors on and corresponding effectiveness of the performance of AOD. For example, the a priori orbit may greatly affect the orbital accuracy in AOD. What is more, although introducing the ISL measurement into GNSS observations from ground stations can improve the orbital accuracy in a certain extent, it needs a complex and rigorous algorithm. That is to say, the algorithm to detect the cycle slip and to realize the ambiguity resolution for the GNSS carrier observations must be implemented correctly, otherwise the orbital accuracy will deteriorate sharply in joint POD [12,13].