# Characterization of Carrier Phase-Based Positioning in Real-World Jamming Conditions
## 4 Analysis and Results
### Analysis 3: Effects of Using Multiple Constellations
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Case 2, Baseline 2** & **East [m]** & **North [m]** & **Up [m]** \\ \hline _GPS_ & 0.0882 & 0.0515 & 0.2938 \\ _GPS_ + _GLO_ & 0.1345 & 0.0590 & 0.4434 \\ _GPS_ + _Gal_ & 0.0208 & 0.0122 & 0.0722 \\ _GPS_ + _GLO_ + _Gal_ & 0.1227 & 0.0517 & 0.4045 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Position standard deviation in east, north, and up direction during the jamming incident of Case 2, baseline 2 (12.1 km)—the full 3D positioning error is shown in Figure 11. The solution is based on L1 + L2 phase data. The solution with the least error and largest errors are highlighted in green and red, respectively. Figure 11: Solution 3D error (**top**) and number of satellites in the solution (**bottom**) for various L1 + L2 PPK solutions to Case 2, baseline 2 (12.1 km). 17:42:07: Galileo is reintroduced to the 3 CS. that this is simply because of the fact that adding noisy observations to the processing might very well lead to a worse solution. However, it was shown in Analyses 1 and 2 that carrier phase tracking is stable during these incidents, and that a carrier phase-based solution sees very little noise. It is, in other words, not the observations themselves that are the issue. The increased std of the 3 CS stems from the processing, and two issues can be identified:  
1. IE seems to blindly prioritize certain constellations over others. 2. The inclusion of additional constellations to the solution may momentarily lead to a heavily increased positioning error. These issues are not general to carrier phase-based positioning. They are specific to this particular setup, and are caused by the unique combination of processing software and the sudden decrease in the number of observations caused by jamming. The issues occur because IE, naturally, is not built for this purpose. For any ordinary (jamming free) case of post processing, these issues should be non-existent. It is also important to note, though, that in both Case 1 and Case 2, the increased stds of the 3 CS are due to short periods (-2 min) with large errors (see Figures 10 and 11), primarily caused by the above two issues. While these issues are specific to the setup, they are still relevant, as there are more general conclusions to be drawn from an investigation of them. Looking at the first issue, IE is proprietary software, and we do not know for certain that constellations are in fact prioritized, but the results here suggest that this is the case. This is most clearly seen in Figure 11 in the period 17:41-17:42, as emphasized by the zoom. Here, following the start of the HIP, the number of satellites on all solutions drops to zero--except the GPS + Galileo solution. This indicates that the full 3 CS is prioritizing a GPS + GLO fix, which is not possible at the time, over a GPS + Galileo fix, which is possible. The results from Case 1 also suggest that IE favors a GPS + GLO solution. Following the start of the jamming incident at 11:17, the 3 CS reverts to a GPS + GLO solution. This is clearly shown in the bottom of Figure 10, as the number of satellites in the 3 CS and GPS + GLO solutions is exactly the same in the period of (approximately) 11:18-11:30. Thus, IE seems to prioritize constellations in the following way: 1. GPS, 2. GLOASS, 3. Galileo. This is not an issue in Case 1, where GLOASS is the better choice, but in Case 2, it leads to markedly worse results in the period 17:40-17:45. The second issue, inclusion of additional constellations, is visible in both Figures 10 and 11. When Galileo is reintroduced, the 3D positioning error spikes. Interestingly, in Case 1, as shown in the top zoom of Figure 10, reintroducing Galileo to the 3 CS makes it worse than the RFI heavy GPS + Galileo solution, although the only change to the 3 CS is the addition of the interference-free GLONASS constellation. The inclusion of additional constellations may temporarily increase errors in a way that technically does not make sense.