## 1 Introduction  
The third-generation BeiDou Navigation Satellite System (BDS-3), which is currently being deployed, is a global satellite navigation system. It is the third step of China's satellite navigation construction. The complete BDS-3 constellation will consist of 24 satellites in three orbital planes in medium Earth orbit (MEO) with an orbit inclination angle of \(55^{\circ}\); 3 satellites in geostationary Earth orbit (GEO) located at longitudes \(80^{\circ}\), \(110.5^{\circ}\), and \(140^{\circ}\); and 3 additional satellites in inclined geosynchronous orbits (IGSO) with an inclination of \(55^{\circ}\) over the Asia-Pacific region [1; 2]. By the end of 2019, 28 BDS-3 satellites have been launched into space. BDS-3 adds three new frequencies to the regional BeiDou satellite navigation system (BDS-2) [3], and three types of BDS-3 satellites are given different functions. Due to the geostationary characteristicsof GEO satellites and the resulting lower orbit accuracy, BDS-3 GEO satellites are mainly used to provide some featured services, such as satellite-based augmentation (SBAS), short message communication (SMC), and precise point positioning (PPP) [1]. The rest of the 24 MEO satellites and 3 IGSO satellites play a key role in providing the radio navigation satellite service (RNSS). However, the other side of the coin is that this hybrid constellation challenges precision orbit determination (POD) because MEO satellites require tracking stations distributed globally and IGSO/GEO satellites are only tracked by stations in the Asia-Pacific region. The normal operation of navigation satellites is accomplished by means of continuous tracking and control by the ground segment. To get rid of the dependence on the ground-based support, GPS has utilized an ultrahigh-frequency (UHF) inter-satellite link (ISL) technology to achieve autonomous navigation since the GPS IIR satellites [4; 5; 6; 7; 8]. Research shows that autonomous navigation can maintain navigation accuracy for six months without ground contact [8]. For BDS, the monitoring stations are distributed in mainland China for various reasons. Once the satellite loses the ground contact, the satellite will not be controlled, and thus orbit and clock accuracy will drop sharply. Therefore, the new BDS-3 satellites are equipped with ISL payload following GPS. This new payload enables intel-satellite communication and ranging by the Ka-band signal, which is suffered from less multipath and noise issues. ISL can be used to route the data from satellites out of the coverage region to satellites that are within the coverage region. Benefit from these new payloads, the satellite running outside mainland China can also be tracked and controlled indirectly. The operational control system (OCS) can make full use of both L band signals and Ka-band signal observations to generate the broadcast messages and to update messages [9]. Moreover, the ISL payloads provide BDS-3 with the potential for autonomous navigation. Many results of the BDS-3 experimental or BDS-3 satellites orbit determination with the real ISL measurements are published. [PERSON] et al. discussed the orbit determination with prior orbit constraints [10]. [PERSON] et al. presented a detailed evaluation of the combined orbit determination method, which indirectly achieves a 37-95% improvement in the orbit-only signal-in-space range error accuracy [11]. [PERSON] et al. applied the ISL data from BDS experiment satellites on the centralized autonomous orbit determination [12]. [PERSON] et al. analyzed the application of batch processing and extended Kalman filtering algorithm on BDS autonomous navigation [13]. [PERSON] et al. proposed an onboard extended Kalman filter constrained with high predicted orbit inclination and longitude of ascending node to resolve the constellation rotation error issue [14]. Precise orbit is the key to high-precision positioning applications and related scientific research.