## 5 Simulation Analysis
### Simulation Results
#### 5.2.3 Comparison with MEO Constellation Algorithms  
To compare the navigation and positioning performance of LEO and MEO constellations, we compared and analyzed the navigation and positioning results in LEO and MEO scenarios under the condition of reasonable setting parameters, without a loss of generality. We focused on a comparison of LEO 1 satellite + altimeter and MEO 1 satellite + altimeter integrated navigation and positioning. Figure 8 shows the navigation and positioning results of the LEO and MEO constellations.  
Figure 8: _Cont._  
According to Figure 8, we can find that compared with the INS and MEO 1 satellite + altimeter, the LEO 1 satellite + altimeter can effectively overcome the divergence of INS. Compared with standard LEO 3 s positioning, although LEO 1 satellite + altimeter has fluctuations in local details, the final navigation trajectory is very close to the real trajectory of the aircraft. The STD of the trajectory error is 0.0182 m, reaching a cm level, and its positioning error is similar to the standard LEO, which shows that the LEO constellation is more suitable for the algorithm proposed by us and verifies the superiority of the LEO constellation as a navigation system. It is not difficult to imagine that its advantages are self-evident compared with the high orbit constellation.  
From Tables 8-10, compared with the MEO 1 satellites + INS algorithm, we can find the following:  
1. In the scenario without an altimeter, since the LEO constellation has less pseudorange measurement noise and pseudorange rate measurement noise than the MEO constellation, the LEO constellation is more sensitive to the UKF algorithm. As a result, the overall performance of the LEO constellation algorithm in some directions is slightly worse than the overall performance of the MEO constellation, but the overall performance of the LEO constellation algorithm is still better than the overall performance of the MEO constellation algorithm.
2. In the scenario of an altimeter, the performance of the LEO constellation algorithm is significantly better than the performance of the MEO1 constellation algorithm, especially in the down direction. Position and velocity errors have absolute advantages, and the accuracy of the mean is increased by 99.85% and 97.36% and STD is increased by 97.67% and 82.08%, respectively. In the final trajectory error, the mean value and STD of the altitude accuracy are increased by 99.96% and 99.49%, respectively.  
From the above analysis, we can find that, due to the inherent characteristics of system error, such as the pseudorange measurement noise and pseudorange rate measurement noise of the LEO constellation and the MEO constellation, the position error of the MEO constellation in a certain direction may be slightly lower than the position error of the LEO constellation. However, due to the long period of time it takes for the MEO satellite to pass the zenith, the geometric accuracy characteristics cannot be updated quickly. Therefore, the MEO satellite is unable to overcome the divergence problem of INS. In comparison, the LEO constellation does not have such problems, so it is more suitable for the navigation and positioning requirements under the integration of communication and navigation, and the LEO constellation can effectively improve the accuracy of navigation and positioning without much cost.