# Performance Characterization of GNSS/IMU/DVL Integration under Real Maritime Jamming Conditions
## 5 Results
### Results of the Maritime Jamming Campaign  
#### 5.2.1 GPS Single Point Positioning Results  
Figure 9 provides an overview of GPS Single Point Positioning (SPP) results for the analyzed time frame of nearly two hours for all three antennas/receivers on board the BALTIC TAUCHER II. During this time, the vessel BALTIC TAUCHER II passed the vessel AARON (the vessel with the jammer installed) several times with increasing passing distances, as shown Figure 9a. For the entire time, except during the turning maneuvers, the PPD jammer was activated. The idea behind the deactivation of the jammer during the turning maneuvers was to start each passing of the jammer under undisturbed and, therefore, repeatable conditions. Although the turning maneuvers were performed at a distance of more than three kilometers, the on/off switching of the jammer is clearly visible from the reported maximum CN0 values, as shown in Figure 9b. When the jammer was switched off, between 9 and 11 GPS satellites have been tracked, as is easily seen in Figure 9c. At the points of maximum separation between the two vessels, the horizontal positioning error of approximately 2 m had been achieved with geometric dilution of precision (GDOP) values between 1 and 2 for all three antennas and receivers. Therefore, with the sufficient separation from the jammer, the positioning performance lies in the expected range of non-augmented code-based SPP. Note that the zone where pure GPS-positioning is prevented by the jammer is not easy to clearly define (see Figure 9f). The places where GPS positioning is possible already vary significantly between the three antennas. Additionally, a dependency on whether one is approaching the jammer or is veering away is observed. Obviously, in the former case, the GPS position solution is available on a smaller distance to the jammer when compared to the latter one. This, however, is not too surprising due to the signal acquisition and tracking mechanisms, as implemented by a typical commercial receiver. Usually, keeping track of a satellite can be performed under CN0 conditions inferior to those of the acquisition of a new satellite. Moreover, a relatively large variability in the impact of the jammer on the CN0 value can also be found in Figure 9b. The observed behavior can be, at least to some extent, explained by the specific experimental conditions. The jammer was mounted on the vessel AARON at a height comparable to the GPS antenna on the test vessel. As the jamming signal was coupling into the antenna at nearly zero degree elevation, the impact of the jamming signal strongly varied with the elevation angle (\(\approx\)0.25 dB/\({}^{\circ}\)). During the experiment, the Baltic Sea was quite rough (wave heights between 1 and 2 m) so that the vessel was rolling and pitching significantly. The variations in roll and pitch angles of the vessel translate directly to the variations in the effective elevation of the jammer with respect to the GPS antenna body frame and, hence, into the variations of the power of the injected jamming signal. Besides this, the mounting of the GPS antenna, which was not on the topmost position of the vessel (see Figure 4), could cause shadowing effects of the jamming signal by structures of the vessel itself depending on the trajectory segment. A careful analysis of Figure 9d,e reveal that large position errors seem to happen only when GDOP is large (i.e., GDOP \(>\) 5). This could also be confirmed by analyzing the dependency of the HPE on the GDOP during these two hours. In Figure 10, the mean HPE is plotted with the GDOP. The statistics here include all measurements from all three antennas during the analyzed 2 h time span. In order to account for the fact that large GDOP values are less frequently observed, the bin size for large GDOP values has been enlarged accordingly. In Figure 10, a relatively good correlation between HPE and GDOP can be found.