## 4 Results
### User Results
#### 4.2.1 Multi-Frequency  
To evaluate the performance of the generated forward-filtered PPP-RTK network products, observations of multi-frequency and multi-GNSS receivers with known long-term reference positions are processed. To enable a fair comparison between the constant phase bias and the reference phase clock approach, the same observations are processed in both approaches. More specifically, only satellites are processed at epochs where their classic code satellite clock estimate has a standard deviation of 15 cm in the constant phase bias approach. In total, 17 receivers observing all GNSS listed in Table 1 have been processed, and 23 hourly static and kinematic coordinate solutions have been computed for every receiver. The first hour has been discarded, as the results in the first hour would be degraded by the fact that significantly fewer satellites would be available for the user, especially in the first 20 min. Out of all computed solutions, one has been discarded, as the computed coordinate solution had a significant offset to the reference solution, most likely caused by a faulty ambiguity resolution. In Figure 5, the coordinate differences between the 1-hour static coordinate estimates and the long-term EUREF reference position and the mean position of all 23 hourly constant coordinate solutions are visualized. It can be seen that highly accurate static solutions can be computed in one hour, with the RMS of the horizontal components being around 5 mm and 7 mm for the north and east components, respectively, when compared to the reference and mean solutions. The RMS of the vertical offset is around three times larger than that of the horizontal offset and also has a significant bias of almost 1 cm when compared to the reference solution. Comparing the two different approaches regarding the receiver and satellite phase biases, the differences in the horizontal components are negligible and below 1 mm in all cases. Introducing a reference phase clock has increased the mean difference to the reference solution by 2 mm, while the precision has improved by slightly below 1 mm. Considering the negligible differences the two approaches have on the static receiver coordinate solution, the following results are only presented for the constant phase bias approach in order to keep the presented results concise. In Figure 6a, the temporal information of the generated static and kinematic solutions is visualized. It can be seen that even with no regional atmospheric corrections, fast ambiguity resolution is possible. For 77% of all solutions, ambiguity resolution was achieved in three epochs or fewer for both static and kinematic receiver coordinates. In 91% of all cases, a fixed solution could be computed after five epochs or fewer, and in 99% of solutions, in 20 epochs or fewer. The fastest TTFF is achieved in two epochs, which happened in 7% and 6% of all cases for the static and kinematic cases, respectively. It is important to note that this was achieved with an average of around 24 visible satellites. It was observed that some receivers had better performance regarding the quality of their solution and the TTFF. No significant differences in ambiguity resolution performance between static and kinematic receivers were observed; hence, the bar plots in Figure 6a mostly overlap. Note that a fixed solution is only computed when at least five satellites are fixed, although in more than 97% of all cases, the first fixed solution was computed with at least 10 fixed satellites. A satellite is considered fixed when all ambiguities about it are resolved. In 92% of all cases, more than 80% of satellites have been fixed at the last epoch. A failure to fix all satellites at the last epoch could be due to some satellites not being observed long enough or cycle slips that have been previously introduced but not repaired yet, but it does not necessarily imply a failure of the satellite clocks and biases to enable ambiguity resolution at the user level. Next, we take a closer look at the kinematic coordinate solutions.