## 2 The Model for GNSS/INS/LEO/5G Integrated Navigation
### Simulation Method of Each Signal Source  
#### 2.3.1 GNSS and LEO Constellation Simulation  
Both GNSS and LEO constellation simulations in this paper are Walker constellations and aim to optimize constellation coverage with a given number of satellites. Walker constellation is proposed after [PERSON]'s improvement in literature [31], forming a constellation system widely used in the field of orbit design [32]. The parameters of the Walker constellation include the number of satellites \(T\), the number of orbits \(P\), and the number of satellites per orbit \(S\). All \(P\) orbital planes have the same orbital inclination \(i\) (relative to the equatorial plane). On each orbital plane, \(S\) satellites are evenly distributed on the orbital plane with an angular distance of \(360^{\circ}/S\). The ascending points of each orbital plane are evenly distributed on the equatorial plane with an interval of \(360^{\circ}/P\). In order to maintain the relative position relationship between satellites of different orbital planes, the strategy of the equal time interval between satellites of adjacent orbital planes passing through their ascending intersection is adopted. Therefore, the relative phase must be an integer multiple of \(360^{\circ}/T\), \(F\) can be any integer between 0  
Figure 4: Schematic diagram of simulation scene (**a**) Open scene; (**b**) Semi-occluded scene; (**c**) Surrounding occluded scene; (**d**) Headspace occluded scene. and \(P-1\). By giving three parameters \(T\), \(P\), \(S\), and orbital inclination \(i\), the constellation form can be completely determined, namely the Walker constellation. Table 2 shows the parameters of the GNSS/LEO Walker constellation simulation. The constellation distribution operation diagram after STK software simulation is shown in the following figure. The simulation results after GNSS and LEO were simulated and connected with the ground are shown in Figure 5.  
The visibility analysis is shown in Figures 6-8. As can be seen from Figures 6-8, the selected target area is 139.776\({}^{\circ}\) E-139.802\({}^{\circ}\) E and 35.569\({}^{\circ}\) N-35.687\({}^{\circ}\) N, and the visibility of the target area is 100% within 24 h of simulation. According to the global visibility analysis report of the GNSS+LEO constellation in Figure 8, it can be concluded that the GNSS and LEO constellation simulated in this paper can provide satellite-ranging signal data source for integrated navigation in the target area. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **GNSS** & **LEO** \\ \hline Number of satellite—\(T\) & 30 & 120 \\ Number of orbits—\(P\) & 6 & 12 \\ Number of satellites per orbit—\(S\) & 5 & 10 \\ Number of relative phase multiple—\(F\) & 1 & 1 \\ Angle of orbital inclination—\(i\) & 55 deg & 40 deg \\ Altitude of orbit—\(h\) & 20,183.65 km & 1139.9 km \\ \hline \hline \end{tabular}
\end{table} 
Table 2: GNSS/LEO Walker constellation parameters. Figure 5: GNSS_LEO constellation STK simulation results. Based on the GNSS/LEO constellation simulation to obtain the satellite position and speed, the pseudo-range measurement value of satellite navigation can be obtained using Formula (23) below:  
\[\hat{\rho}=\rho+\delta\rho_{I}+\delta\rho_{T}+\delta\rho_{SIS}+\delta\rho_{ct}+ \delta\rho_{sc}+\delta\rho_{c}+\delta\dot{\rho}_{cd}\times\Delta t \tag{23}\]  
where \(\hat{\rho}\) is the measured value of satellite navigation pseudo-range. \(\rho\) is the theoretical distance between satellite position and receiver. \(\delta\rho_{I}\) is the ionospheric error. \(\delta\rho_{T}\) is tropospheric error. \(\delta\rho_{SIS}\) is the spatial signal propagation error, which is mainly caused by multipath, non-line-of-sight, and diffraction phenomena. \(\delta\rho_{ct}\) is code tracking error. \(\delta\rho_{sc}\) is the clock error of satellite. \(\delta\rho_{c}\) is the clock error of receiver. \(\delta\rho_{cd}\) is the receiver clock drift. \(\Delta t\) is the time interval for satellite navigation. Figure 6: Global visibility analysis of GNSS constellation.