# Wide-Band Interference Mitigation in GNSS Receivers Using Sub-Band Automatic Gain Control +
## 6 Discussion  
The tracking results and PVT results showed that mitigation improved \(C/N_{0}\) and availability, respectively. The HDDM has superior mitigation capabilities with pulsed interference, and the AGC corrections had the least degradation with noise interference, showing its benefits in comparison to the state-of-the-art mitigation methods. However, the HDDM has inferior results with single-tone CW signals, but this limitation can be overcome  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Interference** & \multicolumn{4}{c}{**High-End (HE)**} & \multicolumn{4}{c}{**Low-Cost (LC)**} \\
**Number** & **Roof** & **No IM** & **With IM** & **HDDM** & **Roof** & **No IM** & **HDDM** \\ \hline \#1 CW & 0.43 & 0.42 & 0.58 & 1.49 & 1.56 & 2.42 & 8.22 \\ \#2 Fast Chirp & 0.44 & 3.26 & 1.00 & 1.89 & 1.60 & 4.64 & 1.75 \\ \#3 Slow Chirp & 0.47 & 1.01 & 0.67 & 1.10 & 2.37 & 2.12 & 3.22 \\ \#4 Fast Hop & 0.26 & 2.07 & 3.76 & 2.14 & 1.68 & 2.12 & 3.71 \\ \#5 Slow Hop & 0.26 & 1.48 & 5.12 & 2.10 & 1.82 & 2.38 & 3.01 \\ \#6 4 MHz Noise & 0.55 & 3.80 & 0.73 & 2.61 & 3.48 & 5.01 & 4.07 \\ \#7 35 MHz Noise & 0.30 & 1.37 & 1.91 & 3.44 & 1.73 & 3.78 & 3.61 \\ \#8 Slow Pulse & 0.35 & 1.79 & 1.72 & 2.78 & 1.39 & 1.70 & 4.98 \\ \#9 Fast Pulse & 0.42 & 2.50 & 1.14 & 5.63 & 1.61 & 2.49 & 3.99 \\ \hline Min. \#1 to \#9 & 0.26 & 0.42 & 0.58 & 1.10 & 1.39 & 1.70 & 1.75 \\ Mean \#1 to \#9 & 0.39 & 1.97 & 1.85 & 2.58 & 1.92 & 2.96 & 4.06 \\ Max. \#1 to \#9 & 0.55 & 3.80 & 5.12 & 5.63 & 3.48 & 5.01 & 8.22 \\ \hline \hline \end{tabular}
\end{table}
Table 3: 95% Horizontal position error R-95.  
with a notch filter [13]. Therefore, HDDM is a competitive method for IM. Furthermore, the HDDM is implemented on an FPGA running in real-time on a wide-band receiver, indicating the practical application of the method.  
The HDDM exhibited fair performance with FMCW signals, such as chirp signals and frequency hoppers, but the comparison is biased by the loss of the 1-bit DAC. Hence, strong conclusions cannot be made, and an improved test setup is proposed for future research. Nevertheless, the HDDM was not significantly worse than the state-of-the-art, even with the handicap. Theoretically, this loss should be about 2 dB from the 1-bit DAC [25]. However, a mean loss of 6 dB is measured. It could be attributed to oscillator leakage from the up-converter (i.e., a strong additional single-tone signal at the intermediate-frequency), which is not properly mitigated by the receivers. Further, the fact that the signal undergoes two RFFE could incur additional losses and deformations of the signal. Therefore, the total loss of 6 dB is within the expectations. However, using an improved DAC and up-converter would significantly improve the setup.  
The use of the HDDM-AGC with the LC receiver is especially interesting, as it provides external IM for a GNSS receiver. Therefore, it could provide mitigation capabilities to potentially any interference that does not include IM capabilities.  
All receivers were limited to only use GPS L1 C/A and Galileo E1 BC signals. Therefore, improved performance may be observed in the PVT if other unaffected signals are also tracked, or if multi-frequency techniques are employed. However, this setup limits a one-to-one comparison of the different receivers and does not represent the full capabilities of either the LC or HC receivers. Other combinations of signals or multi-band interferences could be interesting extensions of the study.