## 5 Discussion and Outlook
The estimation of all receiver and satellite phase biases as constants compared to introducing a reference phase clock has led to negligible differences in the estimation of the user point position. With the introduction of the GPS L5 satellite phase bias as a random walk parameter, a notable difference in the temporal variation between the L5 and L1 biases for GPS BLOCK IIIA and IIF satellites has been observed, in the sense that BLOCK III biases appeared to have a significantly higher temporal variation, confirming the findings in [11]. For real-time applications, where latency between the network products and the user solution is expected, modeling the uncertainty of network parameters over time becomes relevant. Especially the modeling of the VCM of the network products becomes increasingly relevant as latency increases, as shown in [33]. In this study, only satellites with a satellite clock estimate of a standard deviation of 15 cm or better were considered for the user processing since satellite clocks and biases were considered deterministic corrections. In cases where the VCM or an approximation thereof is used for the network parameters, this condition can be discarded. For a regional network, this would generally increase the number of available satellites for the user and eliminate or reduce the errors introduced by neglecting the VCM of the network parameters. The functional model can be further improved by also using GLONASS satellites. Generally speaking, FDMA GLONASS satellites have a weaker functional model regarding the estimation of integer-valued ambiguities (see [5]), but nevertheless, a strengthening of the functional model is to be expected when more satellites are available. In addition to the GLONASS observations, the functional model can be further strengthened by introducing pseudo-observations in the form of ionospheric slant delays computed by regional network stations and interpolated to the user position like it was done, e.g., in [37; 38]. Of further interest would be the density of reference stations required to compute the regional atmospheric corrections to significantly strengthen the functional model and possibly enable instantaneous or more reliable ambiguity resolution in combination with the methods used in this study. With these improvements in the functional model, the availability of a fixed solution in just a few epochs can hopefully be further increased. The author acknowledges support by the Deutsche Forschungsgemeinschaft (DFG--German Research Foundation) and the Open Access Publishing Fund of Technical University of Darmstadt. **Data Availability Statement:** EPN reference frame solution [15], CODE final orbits and ERP [16], Tropospheric modeling functions used in this study can be found at [39], GNSS-observations used are publicly available at: [[https://epncb.eu/ftp/obs/](https://epncb.eu/ftp/obs/)]([https://epncb.eu/ftp/obs/](https://epncb.eu/ftp/obs/)) (accessed on 15 February 2023), MLAMBDA functions used [24]. The results may be provided by the author at reasonable request. **Acknowledgments:** The author acknowledges the European Permanent GNSS Network for making GNSS observation data and the reference frame realization available. Furthermore, the author acknowledges the Center for Orbit Determination in Europe (CODE) for providing the multi-GNSS satellite orbits used in this work. **Conflicts of Interest:** The author declares no conflict of interest.