# Performance Characterization of GNSS/IMU/DVL Integration under Real Maritime Jamming Conditions
## 5 Results
### Lab Experiment  
For the lab experiment, an antenna receiver setup identical to the one of the maritime jamming measurement campaign described in Section 4 was used. The antenna has been mounted on the roof of the DLR office building in Neustrelitz (Germany). In Figure 5, the schematic overview of the experimental setup is given. One receiver (type Javad Delta) was acting as a reference using only the original GNSS signals from the antenna. As an input for the other receiver, a combined signal from the same GNSS antenna and the jammer was used. The antenna output of the jammer was connected using a HF cable, and an attenuated jamming signal was merged with the original GNSS signal. The jammer together with the attenuator and the GNSS signal combiner were placed in a shielding box ensuring that no measurable jamming radiation could be detected outside the laboratory. For each experiment, a 48 h (February 2017) measurement data with a 2 Hz update rate have been recorded. Two jamming scenarios were investigated with a total attenuation of 53 dB (Scenario A) and 42 dB (Scenario B), respectively. In Figure 6, the impact of the jamming signal on the correlation between the carrier-to-noise density ratio (CN0) and the elevation angle is shown. For the unjammed reference, the mean of CN0 values varies approximately between 40 dBHz @ 5\({}^{\circ}\) elevation angle and 57 dBHz @ 90\({}^{\circ}\) elevation angle. For Scenario A, the 2D density distribution is shifted by approximately -10 dBHz, and fewer low elevation satellites are tracked. For Scenario B, the 2D density distribution is shifted again by approximately -10 dBHz (compared to Scenario A) and mainly higher elevation satellites remain visible. This corresponds fairly well with the difference of 11 dB of the attenuation of the jamming signal between Scenarios A and B. In Scenario B, only satellites above \(\sim\)30\({}^{\circ}\) elevation are tracked by the receiver, resulting in only 4-5 satellites at each point in time. From the comparison of the three graphs in Figure 6, one can deduce that, for that receiver, a rather soft CN0 threshold for the tracking of the satellites exists, which lies between 25 and 30 dBHz. In the absence of jamming, low-elevation satellites show a signal strength gain of approximately 10 dBHz, compared to the signal strength under the effects of a jamming attack. In order to determine the pseudorange statistics, the antenna position as well as the receiver clock offset of the reference was determined by a static precise point positioning (PPP) calculation with the RTKLib software [42] in post-processing using precise satellite orbit and clock information from the IGS service. The pseudorange errors were calculated as the difference between the expected and the observed ranges using broadcast ionospheric and tropospheric corrections (the same corrections which have been used within the filter design in Part 2 of this section) while taking into account the receiver clock offset from the PPP solution. The obtained data were binned according to the associated CN0 as measured by the receiver or to the elevation values, and for each  
Figure 5: A schematic overview of the setup used in laboratory conditions. was determined. Note that in this simplified approach we focus only on the standard deviation of the distribution and ignore the non-zero mean offset. However, pseudorange biases, which vary within the evaluated time span of 48 h, ultimately will also contribute to the calculated standard deviation. In Figure 7, the standard deviation of the errors is plotted against the elevation angle for both the original (no jamming) and for the two jamming scenarios. The crosses mark data points with an underlying test statistic including more than 1000 pseudorange errors, and the small dots mark data points with a sample population fewer than 1000 data points for that bin. The unjammed reference data show expected behavior, with increasing standard deviation for decreasing elevation angles.