## 5 Discussion
In particular, the horizontal and 3D RMS errors obtained in the multi-constellation mode are equal to 3.24 m and 5.73 m, respectively of Huawei P30 with respect to the 4.14 m and 7.07 m of Xiaomi Mi 8 and the 4.90 m and 8.05 m of Xiaomi Mi 9. Finally, regarding the evaluation of Galileo SPP positioning with E5a code observations, we found that, for Xiaomi Mi 9, the use of such signals instead of E1 ones led to a halving of the three-dimensional error: the 3D-RMS is 14.34 m using E1 measurements with respect to 7.91 m in the case of the E5a signal. The horizontal error has an evengreater improvement going from 8.44 to 3.17 m. These results could be compared with that obtained by Xiaomi Mi 9 in GPS L1 only configuration with a \(C/N_{0}\) weighting scheme where horizontal and three-dimensional error are of 6.82 m and 10.90 m, respectively. We report a poorer accuracy of the GPS L1 solution than the Galileo E5a one despite the fact that the smartphone tracked a slightly higher number of satellites for GPS (an average of 10.4) as compared to Galileo constellation (an average of 7.7; cf. Table 1). Such findings confirm a great benefit to standalone positioning from low-noise Galileo code observations on the E5a frequency band. If we confer the standalone positioning performance of recent smartphones given in this work to that reported in the past papers, we discover a progress in terms of the accuracy [41]. In one of the initial studies by [PERSON] et al. [42], accuracy levels of about 10 m and 20 m for horizontal and vertical components, respectively, of Huawei P10 were reported. A comprehensive assessment given in [43] revealed a diverse performance of the standalone positioning with the Samsung Galaxy series smartphones and a horizontal RMS up to 8 m for selected devices. We attribute the smartphone accuracy progress to the advancements in GNSS chips and antennas. More specifically, the results given in this paper highlighted the benefits from a multi-constellation solution, and what is even more noticeable is an application of low-noise E5a code signals that are acquired by recent dual-frequency smartphones. Conceptualization, U.R., J.P. and G.P. ; methodology, J.P., U.R. and G.P. ; software, J.P.; validation, U.R. and J.P.; formal analysis, U.R., J.P. and G.P. ; investigation, U.R. and J.P.; data curation, J.P.; writing--original draft preparation, U.R. and J.P.; writing--review and editing, J.P., U.R. and G.P. ; visualization, U.R. and J.P.; supervision, J.P. and G.P. All authors have read and agreed to the published version of the manuscript. [PERSON] is funded by the project No. POIR.04.01.04-00-0056/17, financed by the European Regional Development Fund within the Smart Growth Operational Program 2014-2020. The support is gratefully acknowledged. Not Applicable. The data presented in this study are available on request from the corresponding author. The study was conducted as a part of the International Association of Geodesy Working Group 4.4.3: \"Reliability of low-cost & Android GNSS in navigation and geosciences\". The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyzes, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.