# Initial Positioning Assessment of BDS New Satellites and New Signals
## 1 Introduction  
The second phase of the BeiDou navigation satellite system space segment (BDS-2) consists of Geosynchronous Earth Orbit (GEO), Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites and it started to provide regional service around the Asia-Pacific area, namely from 55\({}^{\circ}\)S to 55\({}^{\circ}\)N latitude and 55\({}^{\circ}\)E to 180\({}^{\circ}\)E longitude, since the end of 2012 [1]. BDS-2 aims to provide a better than 10 m (probability of 95%) positioning accuracy in horizontal and vertical, and timing precision better than 50 ns within the service area [2]. The performance of the BDS-2 system has been fully investigated by many researchers in the aspects of precise orbit determination (POD), observation noise, multipath, positioning performance including single point positioning (SPP), precise point positioning (PPP) and real-time kinematic (RTK) and so on [3; 4; 5; 6; 7]. Since 2015, China began to develop BDS-3 aiming to provide a global service. Five experimental satellites were launched for demonstration purposes during the period from 2015 to 2016. More BDS-3 satellites have been launched since 2017. Currently, the BDS system constellation consists of five GEO, seven IGSO and 21 MEO satellites, which includes 15 BDS-2 satellites and 18 BDS-3 satellites [8]. By the end of 2018, BDS was announced to be providing a global positioning, navigation and timing (PNT) service, which supports positioning accuracy of 10 m (95%) in horizontal and vertical throughout its global coverage, and timing accuracy better than 20 ns. By the end of 2020, the full BDS constellation will be completed with the continuous launching of additional BDS-3 satellites. The BDS signal in space range error (SISRE) will be better than 0.5 m with higher stability. Additionally BDS will provide a satellite-based augmentation service around China, an international search and rescue service, and a precise point positioning service [9]. Compared with BDS-2, the BDS-3 satellites show differences in three aspects: (1) in addition to B1I and B3I signals, BDS-3 satellites also transmit signals B1c and B2a, which are centralized at the same frequency as L1(GPS)/E1(Galileo) and L5(GPS)/E5a(Galileo), making BDS compatible with and interoperable with GPS and Galileo [8; 10]; (2) BDS-3 satellites are equipped with inter-satellite link (ISL) payloads in the Ka band which enable autonomous navigation and with ISL range measurements with accuracy less than 10 cm, the orbit overlap difference would be between 10 and 20 cm [11; 12; 13]; (3) BDS-3 employs a new generation of high-precision rubidium (Rb) clocks and passive hydrogen maser (PHM) clocks, which indicate a lower frequency drift than BDS-2. The frequency stability of the PHM clock shows about \(6\times 10^{-15}\) at an interval time of 1-day [14]. Current research mainly focuses on the space segment of the new BDS-3 satellites. With the implementation of the BDS-3 service, it is of great significance to investigate the positioning performance of the current BDS constellation. [PERSON] et al. [15] analyzed the benefit of BDS-3 experimental (BDS-3e) satellites, and indicate that BDS-3e satellites no longer suffer from satellite-induced elevation dependent code bias which was first discovered by [PERSON] and [PERSON] [5]. Meanwhile, B2a has a smaller code multipath and BDS-3e satellites would improve ambiguity resolution performance in RTK. [PERSON] et al. [16] further proved that with the help of BDS-3e satellites, the convergence time of PPP would also shorten for areas with fewer visible satellites. [PERSON] et al. [17] assessed the user equivalent range error (UERE) of BDS-3e, which is smaller than 0.73 m and the timing accuracy is usually better than 10 ns. To assess the possible positioning and navigation accuracy, a simulated BDS-3 constellation consisting of three GEO, three IGSO, and 24 MEO satellites was also designed to predict the dilution of precision (DOP) value of the final BDS-3 constellation [17; 18]. In 2019, [PERSON] et al.