# Characterization of Carrier Phase-Based Positioning in Real-World Jamming Conditions
## 5 Discussion  
In this work, the impact of jamming on carrier phase-based PPK and NRTK solutions was studied. The purpose of this is to evaluate the robustness of existing RTK solutions to RFI.  
It is shown that jamming in reference stations may cause positioning errors of up to several meters in the rover receiver when a single-baseline PPK solution is analyzed. This however, is only the case with once-in-a-year incidents and, as shown in [8], most jamming incidents in GNSS reference stations will have little to no impact on RTK positioning.  
It is noted that the analyses in this paper build on data collected by stationary geodetic grade receivers and choke ring antennae, mounted in locations that will in general be distanced and elevated above the interference sources. Furthermore, the receivers (which are Septentrio PolaRx5s scintillation receivers) use an even more accurate clock than most reference station receivers. It is very possible that lower grade receivers using smaller antennas at street level would experience a more significant impact during similar jamming incidents.  
What is clear from the analyses is also that the processing methodology matters, and as such, the positioning results presented here would most likely be different if another processing software was used. Several results indicate that being able to use only unaffected GNSS constellations and frequencies in a positioning solution could lead to improved positioning, and that the way in which GNSS constellations are included in a positioning solution should be considered carefully.  
Especially, because most jammers target GPS L1/Galileo E1 [4; 5; 8], being able to do a solution not dependent on L1 (i.e., an L2 only or L2 + L5 solution) would in most cases completely negate the effects of jamming.  
It should be noted that, while using other frequencies bands than L1/E1 might currently pose a solution to the jamming problem, this may very well be temporary. As multi-frequency receivers become more and more common, most likely so will multi-frequency jammers as well.  
Thus, the results and some of the conclusions presented in this paper only apply to this specific setup, and one should be careful about stating anything about the general severity of the jamming incidents.  
It should be emphasized that, while jamming is not a big issue in the cases analyzed herein, interference and PPD jamming may well be an issue for other receivers. For instance, even if the reference station is not affected, a jammer on the rover side might severely impact the positioning solution, as was also shown in [23]. Several authors, including [14; 15], also showed that this was the case for code-based receivers.  
Furthermore, it was seen that, in a dense network such as TAPAS, the network solution is not severely impacted by a single station being jammed. It would, however, be interesting to investigate NRTK solutions more in-depth, and study the impact of jamming on the following:  
1. A sparse reference station network;
2. The reference station nearest to the rover;
3. Various NRTK solutions like FKP, PRS, MAC, or PPP-RTK.  
Thus, this contribution only provides a part of what is needed in order to fully evaluate the robustness of an NRTK solution.  
A final observation is that a sudden degradation of data, such as is seen in jamming Case 2, seems to cause a larger positioning error than steady continuous jamming. This could indicate that the sudden change in jamming power has a larger effect on the positioning performance than simply having strong steady RFI. Therefore, it should be investigated whether a moving jammer, or a jammer constantly being switched on and off, would have a larger impact on RTK positioning than a constant static jamming source.