## 3 Results
### Precise Products for BDS, GPS, GLONASS, Galileo and QZSS
Following the named rules of RINEX version three files, \"COD\", \"ESA\", \"GBM\", \"GRG\", \"IAC\", \"JAX\", \"SHA\" and \"WUM\" are used by the analysis centers to identify the CODE, ESA, GFZ, CNES/CLS/GRGS, IAC, JAXA, SHAO and WHU post-processed precise products, respectively. In this study, \"CNT\" denotes the retrieved CNES real-time precise products. The abbreviations GLO, GAL and QZS refer to GLONASS, Galileo and QZSS, respectively. It is seen that, in addition to the legacy GPS and GLONASS, the precise products from all the analysis centers can also support the emerging Galileo and BDS-2, except for the \"GRG\" and \"JAX\" products. As for QZSS satellites, they are absent in the \"GRG\", \"SHA\" and \"CNT\" products, while the \"JAX\" products only include QZSS J01 satellite and do not support the other three QZSS satellites (J02, J03 and J07). There are significant differences in the support of GEO satellites for the various precise products. Both the \"COD\" and \"ESA\" precise products exclude BDS-2 and QZSS GEO satellites probably due to their worse orbit determination. Besides the \"GBM\" products, the analysis center GFZ also releases another set of precise products, which are identified by \"GFZ\". The \"GFZ\" products do not support BDS-3 satellites, and the B1/B2 dual-frequency IF combination is used to generate the BDS-2 precise satellite orbit and clock products. Based on the compatible B1/B3 dual-frequency signals, the \"GBM\" products include both the BDS-2 and BDS-3 satellites. On 14 June 2020, the \"GFZ\" products were replaced by the \"GBM\" products to be uploaded to the MGEX data centers. The \"GBM\" and \"WUM\" products can also support several BDS-3 GEO satellites, making them by far the most comprehensive products in support of all the available satellite constellations. Currently, only the \"COD\", \"GRG\" and \"JAX\" products do not cover the BDS-3 satellites. To sum up, only the \"ESA\", \"GBM\", \"IAC\" and \"WUM\" products can cover all the satellite systems at present, and the number of the supported GNSS/RNSS satellites in the four precise products can be up to 114, 123, 119 and 124 as of January 2021, respectively. However, the \"IAC\" products during the analysis period of this study are absent, and the continuous supply of \"IAC\" products usually cannot be guaranteed. It should be noted that this paper attempts to assess the performance of PPP with all available satellites (GPS+GLO+GAL+BDS-2+BDS-3+OZS) using reliable precise products under the current constellation status (in addition to the consistency analysis of precise products), and thus the \"COD\", \"GRG\", \"IAC\", \"JAX\" and \"SHA\" products are excluded from our analysis. In this study, the \"ESA\", \"GBM\" and \"WUM\" products are adopted to carry out the post-processed five-system PPP processing, and the consistency among them is also characterized. For completeness, the \"CNT\" products are employed to analyze the real-time four-system (GPS+GLO+GAL+BDS-2+BDS-3) PPP, and the consistency between real-time and post-processed products is also investigated. The software used for POD and PCE is different for different analysis centers, such as NAPEOS by ESA, EPOS by GFZ, and PANDA by WHU, but all employs the undifferenced dual-frequency IF combined code and phase observables. The frequency selection is L1/L2 for GPS and QZSS, G1/G2 for GLONASS, E1/E5a for Galileo, and B1/B3 for BDS-2 and BDS-3, respectively. With the covering of all the satellite systems by the \"IGS14.txt\" file provided by international GNSS service (IGS) [37], all the analysis centers gradually adopt it to correct the phase center offset (PCO) and variation (PCV), except for ESA. The analysis center ESA still employs the estimated PCO and PCV corrections by itself. Currently, more detailed information about the \"CNT\" products is not clear.