# Wide-Band Interference Mitigation in GNSS Receivers Using Sub-Band Automatic Gain Control +
## 5 Results
### Tracking Results: C/N0  
In each plot, the highest elevation satellite is selected to ensure stable tracking over the entire duration of the test. Figure 7 shows the \(C/N_{0}\) and the difference of \(C/N_{0}\) compared to the roof antenna for each receiver type for the fast chirp. All signals create some V-shape, which correspond to the increase and later decrease in \(I/N_{0}\). The HE Roof antenna also has a dip at the highest interference power, indicating that the RF splitter setup described in Figure 3 has limited isolation. The isolation is experimentally determined to be about 45 dB: within the specified 20 to 24 dB values of the RF combiner and splitter. Nevertheless, such results are expected when a large range of \(I/N_{0}\)s is tested. A bar indicates whether interference is detected per device in each plot. Blue indicates no detection, and red designates interference is present. Figure 7 detects interference from an \(I/N_{0}\) of about 65 dBHz for the \"No IM\" case. It also detects interference signals in the roof antenna, highlighting the isolation issue again. The detection is less in the HDDM-AGC case. It can be due partly to the IM but also to the AGC that normalizes the spectrum: the detector--amongst other methods--employs an energy detection that requires tuning. The AGC partially counters it, resulting in fewer detections. Nevertheless, the HDDM-AGC still results in some interference detection at high \(I/N_{0}\)s.  
Figure 7: Interference #2 (fast chirp): 10 MHz bandwidth and chirp repetition rate of 10 μs. (**a**) \(C/N_{0}\) for the highest elevation satellite. (**b**) Delta \(C/N_{0}\) for the highest elevation satellite. The delta \(C/N_{0}\) Figure 7b compares the roof antenna of each receiver type to the other receivers of the same type. Therefore, it shows the loss caused by the interference and mitigation during tracking. The HE with the HDDM-AGC has a loss of 6 dB at low \(1/N_{0}\). It is attributed to the quantization noise introduced by the 1-bit DAC used by the R&S up-converter. Unfortunately, it makes the comparison unfair as the HDDM-AGC has a permanent handicap. However, despite this limitation, the HDDM-AGC has comparable or improved IM capabilities in some instances, e.g., between 10 and 14 min. The delta \(C/N_{0}\) provides a straightforward receiver comparison, and only these plots are shown in the remainder of this section. Figure 8 shows the delta \(C/N_{0}\) for the frequency hopper signal. In this case, the HE \"with IM\" and the HDDM-AGC have a constant offset from the 1-bit DAC, indicating similar IM capabilities. Figure 9 shows the effect to narrow bandwidth noise and Figure 10 for wide-band noise. The interference cannot be mitigated in both cases as it is not sparse in any domain. Hence, any mitigation attempt only results in signal losses. In the narrow bandwidth case of Figure 9, the HDDM-AGC successfully notices the limitation and does not mitigate the signal, and tends to the unmitigated case. The HE \" with IM\" tries to mitigate the signal and ultimately cuts out the GNSS signals as well, resulting in inferior performance. Contrarily, in the wide-bandwidth case of Figure 10, all methods recognize that the interference cannot be mitigated, and no losses are perceived. These two cases show that noise interferences are impossible to mitigate if they encompass the GNSS signal of interest, but identifying when to mitigate is the key to minimizing the losses. In Figure 9 the LC \"No IM\" has almost no loss at high \(I/N_{0}\), which can be only explained as an error in the receiver output. Figure 11 shows the response to a slow pulse and Figure 12 for a fast pulse. In both cases, the HDDM-AGC shows improved performance at high \(I/N_{0}\). The HE \"with IM\" responds better for the faster pulse, indicating that it responds best with agile interferences.