# Situational Awareness: Mapping Interference Sources in Real-Time Using a Smartphone App
## 6 On-Field Measurement Campaigns
### Interferences from a Complex System  
Another anomaly detected and analyzed thanks to NGeneApp is the interference in a complex integration system. The setup included a GNSS receiver, PCs, a GoPro camera, a Universal Software Radio Peripheral (USRP) and a rubidium clock. A photo taken during one of the performed data collections is shown in Figure 14, where the complex integration setup, including the GoPro camera and the USRP, is visible. During the experimental campaign, the researchers of NavSAS group observed some narrow-band interferences on the raw digital samples collected from the USRP. With the spectrum displaying in NGeneApp in real-time, the source of the interference was easily recognized by turning off each device at a time in the system. Finally, the camera was identified as the source of the narrow-band interference. Figure 15a shows the impact of the interference on the spectrum when the camera was turned on. When the GNSS antenna faced the camera at close range (about 10 cm) the spectrum was considerably distorted. After turning off the camera, the shape of spectrum became normal (Figure 15b).  
Figure 12: The PSD observed in the afternoon of 19 May 2017: in open sky (**a**,**b**) and when the Western part of the sky was obscured by buildings (**c**,**d**).  
Figure 13: The tracking correlation output of SVN 71 (PRN 26).  
In addition, another anomaly was noticed. In this regard, Figure 16 represents the PSD estimated by NGeneApp in case the USRP was triggered on (blue line) and off (red line). It is evident that although the shape of the spectrum is not distorted, the PSD looks noisier when the USRP is enabled. The effect can be clearly seen in Figure 17a: there is a sudden drop in the C/N\({}_{0}\) values of about 10 dB-Hz when the USRP starts recording data at about 95 s from the receiver start. However, the interference detector did not raise any warning. In fact, the test metrics produced by the GoF test were always above the detection threshold (i.e., no interference detection, see Figure 17b) meaning that such kind of anomaly did not produce any relevant distortion neither on the correlation function nor on the spectrum.  
Figure 14: The complex integration setup.  
Figure 15: The PSD observed when the camera is (**a**) on (from second 60 to second 120), (**b**) off (the rest) and (**c**) the total energy of error measured during the experiment.  
Furthermore, Figure 17c shows a sudden rise in the energy error of the PSD when the anomaly occurs but this increase is not sufficient to trigger the warning. However, when the disturbance occurred, the receiver was significantly affected, so that some channel lose track, for example, GPS PRN14, GPS PRN 25, GPS PRN 31. A possible explanation of this effect is a powerful uniform wideband noise generated by the USRP, which increases the noise floor of the received signal without distorting it. It is clear that, in order to cope with such kind of anomalies, the detection algorithms have to be complemented with additional monitors. For more details about the integration results of this experimental campaign, the interested reader can refer to [59].  
Figure 16: PSD evaluation when the USRP is turned on/off.  
Figure 17: Analysis of the anomaly from the USRP: (**a**) \(\mathrm{C/N_{0}}\) and (**b**) GoF \(p\)-values estimated for different PRNs, and (**c**) total energy error of the PSD.