# Characterization of Carrier Phase-Based Positioning in Real-World Jamming Conditions
## 4 Analysis and Results
### Analysis 5: Impacts of a Dual-Frequency Solution  
The purpose of this analysis is to evaluate the benefits of using dual-frequency GNSS data during jamming as compared with using a single-frequency only. In this analysis, there will be a clear distinction between jamming Cases 1 and 2 owing the single-frequency versus multi-frequency nature of the jamming incidents. Looking first at Case 1, Table 8 shows the effect of including GPS L2 observations in the single-frequency jamming case. It is clear that, during jamming, it makes almost no difference to include the extra frequency. The major reason for this is most likely the lack of L1 data. In IE, a dual-frequency solution utilizes a combination of L1 and L2 data, thus if observations on one frequency are missing, a solution is impossible. Figure 14: A comparison of the ambiguity resolution (AR) status (quality factor) for the shortest and the very long baseline in Case 2. The AR status levels indicate different levels of accuracy explained in [38]: 1 = Fixed, 2–4 = Converging float, 5–6 = DGPS, 0 = No solution. Furthermore, IE in this setup uses the L2W observations. These observations are based on codeless tracking, and thus depend on the L1 observations, so naturally, when GPS L1 is jammed, so is GPS L2W. For Case 1, L2C observations are jamming-free, thus using L2C could have led to improved accuracy in all dual-frequency solutions. In this analysis, the GPS solutions are identical, except at the very end of the incident where the L1 + L2 solution is faster in re-acquiring a fix, leading to slightly smaller deviations. Looking at solutions using both of the heavily affected constellations, GPS and Galileo, some of the same tendencies are apparent. In Table 8, it is seen that including a second frequency makes little difference. However, Figure 15 provides a further look into these solutions, with plots of 2D and 3D positioning error, and it is clear from Figure 15 that using two frequencies in this case actually makes a considerable difference. While precision and std are almost the same in both the single- and dual-frequency case, accuracy is clearly improved in the dual-frequency solution. It is also clear that there are still large gaps where a position has not been calculated. A dual-frequency solution is simply not possible owing to the lack of L1 observations. As previously mentioned, it does make sense that single-frequency solutions based only on L2 are not possible, given that the PPK software is not meant to handle jamming. However, if GNSS positioning in general is handled this way, it introduces a major vulnerability to L1 jamming, which is unfortunate as L1 jamming happens quite often [8]. As GLONASS is basically unaffected by jamming in Case 1, including this constellation has a huge effect on positioning accuracy compared with using GPS only. Looking at Table 8, it is clear that hardly anything is gained by including carrier phase observations from an additional frequency, though this is mostly because the L1 solution is already very good. _Summary: To conclude on the single-frequency case, having more frequencies available may improve accuracy of the solution. In this setup, however, it actually makes little difference. This is partially due to the fact that the processing software must include the jammed L1 frequency, which, in this case, may result in having only very few observations available. Being able to make solutions based solely on unaffected frequencies would most likely be a huge benefit._  
Turning now to Case 2, it is not possible to do a solution based only on clean observations because all constellations and frequencies are affected. As Analysis 2 showed that a GPS + Gal solution had the best accuracy, this analysis will be based on these two constellations. Table 9 shows the deviation from the known rover position for baseline 2 in jamming Case 2, and the numbers show that including a second frequency does make a significant difference.