## 1 Introduction
In addition to the high position accuracies (decimeter-to-centimeter-level kinematic position accuracies and centimeter-to-millimeter-level static position accuracies), the PPP technology is characterized by the absent reference station, no limitation of operating distance, simple data processing, low cost, and flexibility [21; 22]. Thus, in the past two decades, PPP technology has been a research focus. Several studies also concentrated on PPP processing involving BDS-3 measurements. [PERSON] et al. [23] investigated the contribution of BDS-3 observations to the BDS-2 PPP using the datasets from three stations capable of tracking the full BDS-3 and BDS-2 constellations. Both the position accuracies and convergence speed of BDS-3/BDS-2 kinematic PPP were improved compared with the BDS-2 kinematic PPP. Based on the datasets from ten stations, [PERSON] et al. [24] also validated the superior performance of BDS-3/BDS-2 PPP in comparison to the BDS-2 PPP. In addition, continuous positioning became feasible for the stations located in Germany and North/South America after introducing the BDS-3 measurements into BDS-2 PPP processing. [PERSON] et al. [25] proposed a BDS-3/BDS-2 triple-frequency uncombined PPP model, in which the stochastic plus deterministic ionosphere model was used to constrain the estimated ionosphere delays. To indicate the potential of BDS-3 and BDS-2 integration, they also compared the BDS-3/BDS-2 PPP solutions with the standalone BDS-2 PPP solutions. [PERSON] et al. [26] assessed the performance of kinematic and static BDS-3 PPP using the datasets at two stations. After a convergence time of four hours, the horizontal and vertical position accuracies reached the centimeter level and decimeter level, respectively. Because of the latency of precise products of satellite clocks and orbits, the previous studies about BDS-3 PPP were confined to a post-processed mode. There has been a rapid growth in demand for real-time precise applications for the GNSS community in recent years [27; 28; 29; 30; 31], such as precision agriculture and tsunami warning system. The applications of BDS-3 post-processed PPP will be severely limited in these time-critical applications. The real-time stream CLK93 transmitted by Centre National d'Etudes Spatiales (CNES) starts to support the BDS-3 constellation, in addition to the BDS-2 constellation. Thus, it is feasible to investigate real-time PPP performance with BDS-3 observables. To fully take advantage of the BDS potential, the real-time PPP performance with BDS-3/BDS-2 observations in kinematic and static modes is evaluated in this study. To complete this, the availability of BDS-3/BDS-2 constellations (including the PNT service rate, the Position Dilution of Precision (PDOP), and the number of visible satellites), and the qualities of BDS-3/BDS-2 real-time precise products are also analyzed. For the purpose of comparison, the post-processed BDS-3/BDS-2 PPP solutions as well as the corresponding GPS results (including the real-time PPP solutions, post-processed PPP solutions, availability of satellite constellation, and qualities of real-time precise products) are also presented. This paper starts with the real-time BDS-3/BDS-2 PPP model. Next, we describe the current space segment of BDS-3/BDS-2 constellations. Subsequently, the results are provided and discussed. Finally, the main conclusion is summarized.