## 4 Results
As shown in Figure 12b, interference suppression processing significantly improves the main-to-secondary peak ratio of the target signal, effectively suppressing interference residues in the background region. The main peak in the CAF becomes clearer and more distinguishable, thereby enhancing the accuracy of identifying the true pseudocode phase and Doppler frequency during the capture process and improving the accuracy and robustness of signal capture. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No.** & **Parameter** & **Value** & **No.** & **Parameter** & **Value** \\ \hline
1 & Signal Type & \
\begin{tabular}{c} GPS L1 \\ C/A \\ \end{tabular} & 7 &
\begin{tabular}{c} Frequency Search \\ Step Size \\ \end{tabular} & 300 Hz \\
2 & SNR & \(-\)20 dB & 8 & Tracking Duration & 1 s \\
3 & JNR & 30 dB & 9 &
\begin{tabular}{c} DLL Loop \\ Bandwidth \\ \end{tabular} & 1 Hz \\
4 & \
\begin{tabular}{c} Doppler \\ Frequency \\ Code Phase \\ Offset \\ \end{tabular} & 1500 Hz & 10 &
\begin{tabular}{c} PLL Loop \\ Bandwidth \\ \end{tabular} & 10 Hz \\
5 & \
\begin{tabular}{c} Code Phase \\ Offset \\ \end{tabular} & 479 chips & 11 &
\begin{tabular}{c} PLL Loop \\ Bandwidth \\ \end{tabular} & 20 Hz \\
6 &
\begin{tabular}{c} Code Phase \\ Search Step Size \\ \end{tabular} & 0.5 chip & 12 & Relevant Interval & 1 s \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameter settings for acquisition and tracking stage simulation. Figure 11: Performance comparison of the proposed algorithm under pulse jamming with different duty cycles. To further validate the performance of the interference suppression method proposed in this paper, a simulation analysis was conducted on the signal tracking performance after interference suppression. During the signal tracking phase, the coarse estimates of the signal Doppler frequency and pseudocode phase provided by the capture module were used as the initial input for the tracking loop. Through iterative correction by the loop filter, more precise measurement information was obtained, and the navigation message was demodulated. The frequency lock indicator (FLI) can be used to measure the frequency tracking performance of the frequency-locked loop (FLL) for the signal frequency, defined as  
\[\text{FLI}=\frac{\text{dot}^{2}-\text{cross}^{2}}{\text{dot}^{2}+\text{cross }^{2}} \tag{37}\]  
where  
\[\text{dot}=I_{P,k-1}I_{P,k}+Q_{P,k-1}Q_{P,k} \tag{38}\]  
\(I_{P,k}\) and \(Q_{P,k}\) represent the prompt-related values of the in-phase and the quadrature branches in the kth integration cycle, respectively. The value range of FLI is \([-1,1]\). When FLI approaches 1, it indicates that the frequency tracking is more stable and the accuracy is higher. The phase lock indicator (PLI) is used to evaluate the tracking accuracy of the PLL for the received signal carrier phase and is defined as  
\[\text{PLI}=\frac{I_{P,k}^{2}-Q_{P,k}^{2}}{I_{P,k}^{2}+Q_{P,k}^{2}} \tag{39}\]  
The PLI value ranges from \(-1\) to 1. The closer it is to 1, the higher the PLL tracking accuracy. Figure 13 shows the time-dependent changes in FLI and PLI within the 0.1 s to 0.2 s interval. As shown in the figure, when using the time-domain blanking method to suppress chirp interference, the values of FLI and PLI randomly fluctuate within the range of \([-1,1]\), indicating that both FLL and PLL fail to achieve effective frequency and phase tracking, and the loop is in an unlocked state. In contrast, after applying the KLT method and the method proposed in this paper, the values of FLI and PLI both stabilize near 1, indicating that the FLL and PLL have reached steady-state operating conditions, enabling accurate tracking of the carrier frequency and phase, and demonstrating excellent interference suppression and robust signal tracking performance. Figure 12: Capture results before and after interference suppression.