## 5 Simulation Experiment Results
### Results and Analysis  
A CUTC integration simulation was performed as a benchmark for comparative analyses. The implementation details of the CUTC architecture are described in Section 2. The simulation parameter configuration is shown in Table 2.  
Figure 8a shows the carrier frequency tracking errors output by the frequency discriminator and the channel prefilter. The PRN code phase tracking errors are shown in Figure 8b. It is clear that the CUTC architecture cannot mitigate large frequency tracking errors in the tracking loop. The large frequency tracking errors induce the code tracking errors to increase. After 81 s, the highly dynamic circular maneuver causes the carrier frequency tracking and code tracking to lose lock. Figure 9a-c shows the attitude errors, the velocity errors and the position errors of the CUTC system, respectively. Large frequency errors cause attitude errors and velocity errors to increase rapidly. Position errors gradually diverge with time. In fact, after 81s, due to the loss of lock of tracking loops, integrated navigation errors are essentially inertial navigation errors. Next, we focused on the simulation analysis of the proposed EUTC system. The simulation of the EUTC integration also used the parameters shown in Table 2.  
Figure 10 shows the frequency and code phase errors of the EUTC navigation system. The simulation results presented demonstrate that the proposed EUTC architecture can eliminate large changes of carrier frequency errors in time. From the magnified view of Figure 10a, we can see that the adaptive prefilter can correctly estimate the frequency error of the abrupt change. When the frequency tracking error changes suddenly, the code tracking loop remains stable. Figure 11 shows the navigation errors of the proposed EUTC architecture. At the moment when large frequency errors occur, the pitch angle error and velocity errors (east and up) increase instantaneously. After 70 s, attitude and velocity errors quickly decrease, as shown in the figure. Moreover, Figure 11c shows that there is no significant change in position errors. Hence, the instantaneous increases in attitude and velocity errors have little effect on the overall navigation performance. Comparing Figures 9 and 11, we can conclude that the EUTC architecture can suppress the divergence of navigation errors caused by large frequency errors. Figure 8: Tracking errors for the CUTC integration simulation: (**a**) carrier frequency tracking errors; (**b**) code phase tracking errors. Figure 10: Tracking errors for the EUTC integration simulation: (**a**) carrier frequency tracking errors; (**b**) code phase tracking errors. Figure 9: Navigation solution errors of the CUTC integration simulation: (**a**) attitude errors; (**b**) velocity errors; and (**c**) position errors. Figure 12 shows the comparison of the 1 ms correlation amplitudes of the prompt correlators. After 80 s, the correlation amplitude of the CUTC system decays to trivial values, which implies that the tracking loop loses lock. In contrast, the correlation amplitude of the EUTC system is always maintained in the normal range. The EUTC system can maintain continuous operation of the tracking loop when a large frequency error occurs. Figure 13 shows the comparison of the estimated \(C/N_{0}\) of the two integrated architectures. We observe that the estimated \(C/N_{0}\) of the CUTC system rapidly drops to zero in the presence of a large frequency error. The estimated \(C/N_{0}\) of the EUTC system decreases only slightly in a short time. Figure 11: Navigation solution errors of the EUTC integration simulation: (**a**) attitude errors; (**b**) velocity errors; and (**c**) position errors. Figure 12: Comparison of 1 ms correlation amplitudes of the prompt correlators. After 70 s, the estimated \(C/N_{0}\) of the EUTC system recovers quickly. Hence, the EUTC integration can provide continuous and accurate \(C/N_{0}\) estimates. Finally, a simplified EUTC integration system was simulated to evaluate the performance of the adaptive prefilter.