# Assessment of BeiDou-3 and Multi-GNSS Precise Point Positioning Performance
## 1 Introduction  
In addition to GPS and GLONASS equipped with the global positioning capability, both the BeiDou navigation satellite system (BDS) and Galileo have global positioning capability with the launchof the BDS-3 and Galileo satellites. Especially, BDS has developed from a regional to global system with the open service of the global basic navigation service of BDS-3 in December 2018 and the Galileo constellation has reached 26 satellites in space. The construction of the BDS follows the \"three-step\" strategy, including the demonstration system BDS-1, the regional system BDS-2, and the global system BDS-3 [1]. BDS-1 contains three Geostationary Earth Orbit (GEO) satellites, the first of which was launched in 2000 and the entire BDS-1 system was completed in 2003 [2]. The master control station using the Radio Determination Satellite System (RDSS) of BDS-1 [3] can determine the user location. BDS-2 contains five GEO satellites, seven Inclined Geosynchronous Satellite Orbit (IGSO) satellites, and four Medium Earth Orbit (MEO) satellites, which can provide positioning and navigation services for users over the whole Asian-Pacific region by the end of 2012 [4]. The construction of BDS-3 began in 2015. BDS-3 contains five GEO, 27 MEO, and three IGSO, and it will provide positioning and navigation services to global users by 2020 [5]. The European Galileo is the third Global Navigation Satellite System (GNSS), which can offer a continuous, flexible, and precise positioning service. When compared with BDS, the development of the Galileo follows the two steps. Four In-Orbit Validation (IOV) satellites have been successfully launched and they are in orbit. Currently, the IOV phase is closed and it is a transition phase to Full Operational Capability (FOC) [6]. The Galileo constellation has reached 26 satellites in space, completing the constellation in July 2018. In addition that, GPS and GLONASS perform global precise point positioning (PPP) calculations, BDS and Galileo also have this ability already with the launch of BDS-3 and Galileo new satellites. The assessment of the precise positioning ability of the GPS, BDS-2, BDS-2/BDS-3, GLONASS, Galileo, and multi-GNSS has become very meaningful in GNSS development. Especially, the technology of BDS-3 and GNSS combined PPP has become very important in the development of multi-GNSS integration. In the terms of the assessment of the precise positioning ability of the different navigation system, many scholars have made some achievements. [PERSON] et al. indicated that the contribution of Galileo can improve the positioning accuracy by 23.7%-29.96% and 10.59%-11.07% and can reduce the convergence time by 45.48% and 11.04% for GPS-only and GPS/GLONASS kinematic PPP, respectively [7]. [PERSON] et al. concluded that integrating the BeiDou experimental satellites (BDS-3e) could slightly improve the horizontal precision for BDS-2-only or GPS/BDS-2 combined solutions by comparing GPS/BDS-2, GPS/BDS-2/BDS-3, BDS-2, and BDS-3 PPP [8]. The addition of BDS-2, Galileo and GLONASS systems to the standard GPS-only PPP can reduce the convergence time and improve the positioning accuracy, and the position series of multi-PPP are much more stable than the GPS-only solutions [9; 10]. The previous research on the assessment of GNSS performance based on multi-GNSS PPP mainly focused on BDS-2 and its benefit to other navigation systems. Although the relative positioning and PPP technology were used to conclude that the BDS-3e could contribute to improving performance of precise positioning [2; 11], there are few researches regarding the assessment of BDS-2/BDS-3 PPP and its contribution to multi-GNSS based on the raw BDS-3 observation. In addition, the previous discussion on the assessment of GNSS performance mainly focused on the positioning accuracy and convergence time, with less consideration for zenith troposphere delay (ZTD) accuracy.