## 5 Simulation Experiment Results
### Simulation Setup  
The trajectory devised for simulations is a highly dynamic flight profile in the horizontal plane. A GNSS simulator was used to generate GPS L1 C/A RF signals corresponding to the reference trajectory. The RF signals were collected with an intermediate frequency collector. The IF collector converted the simulated RF signals into digital IF signals and stored them on a computer for post-processing.  
Figure 6(a) shows the horizontal trajectory. Figure 6(b),\(c\) shows the velocity and acceleration profiles of the simulation vehicle, respectively. The typical parameters of the simulation trajectory are as follows:  
* Starting position: longitude (108.9\({}^{\circ}\)), latitude (34.2\({}^{\circ}\)) and altitude (350 m);
* Trajectory duration: 110 s;
* Maximum velocity: 1500 m/s;
* Highly dynamic segment 1: linear acceleration = 100 g, time interval = (70, 71) s;
* Highly dynamic segment 2: centripetal acceleration \(>\) 100 g, time interval = (81, 90) s.  
Again, the MIMU data was also simulated based on the reference trajectory. The error parameter settings of the MIMU are provided in Table 1.  
The MIMU/GNSS UTC integration simulation program takes digital IF signals and the simulated MIMU data as input data. The UTC navigation simulation parameters are summarized in Table 2.  
If large frequency errors and large dynamics occur at the same time, the performance of the UTC navigation system will be greatly impaired. This test case is a severe challenge for the integrated navigation system, which can be regarded as a stringent assessment case. For this reason, in the simulation, a large frequency error was set to appear in the linear acceleration section of 100 g. In most applications, if the step change in frequency exceeds 50 Hz, the replica signal will no longer correlate with the incoming signal [9]. Hence, the large frequency error was set to 10 m/s, and the equivalent GPS L1 carrier frequency offset was 52.5 Hz.  
In the simulation, the \(C\)/\(N_{0}\) of all tracking channels was set to the same value (50 dB-Hz), so the tracking status of each tracking channel was similar. In the following, one of the tracking channels is chosen as an example to show the channel-dependent simulation results. Before the system was switched to the UTC mode, it was necessary to perform the scalar tracking and tight integration. The simulation results of the UTC integration were obtained starting from 40 s.  
\begin{table}
\begin{tabular}{c c c} \hline
**Items** & **Gyroscope** & **Accelerometer** \\ \hline Bias & 30\({}^{\circ}\)/h & 500 \(\mu\)g \\ Random walk & 0.3\({}^{\circ}\)/sqrt(h) 1  & 50 \(\mu\)g/sqrt(Hz) 1  \\ Time-dependent bias & 1\({}^{\circ}\)/h & 50 \(\mu\)g \\ Correlation time & 300 s & 300 s \\ Scale factor error & 500 ppm & 200 ppm \\ \hline \end{tabular}
\end{table}
Table 1: MIMU simulation error parameters.  
\begin{table}
\begin{tabular}{c c c} \hline
**Types** & **Parameters** & **Values** \\ \hline Initial errors & Initial attitude errors & (0.1; 0.1; 2)\({}^{\circ}\) \\ Initial velocity errors & Initial velocity errors & (0.1; 0.1; 0.1) m/s \\ Initial position errors & (3; 3; 5) m \\ \hline Prefilter process & Code phase & \(8\times 10^{-4}\) (code chip) 2  \\ noise variances & Carrier frequency & 0.1 (Hz) 2  \\  & Carrier frequency rate & 5 (Hz/s) 2  \\ \hline Update frequency & Integration filter & 10 Hz 1  \\  & Prefilter & 50 Hz 2  \\  & Code NCO & 50 Hz \\  & Carrier NCO & 1000 Hz \\ \hline \end{tabular}
\end{table}
Table 2: UTC navigation simulation parameters.  
Figure 7: Simulation reference trajectory: (**a**) horizontal trajectory; (**b**) velocity profiles; and (**c**) acceleration profiles.