# IPCB: Intelligent Pseudolite Constellation Based on High-Altitude Balloons
## 7 Simulations and Discussions
### Discussion about IPCBs with Different Initial Horizontal Layouts  
The initial horizontal layout of an IPCB also has a significant impact on its geometry performance. This section adjusts the initial latitude of IPB5 and IPB6 from south to north, as illustrated in Figure 12, while other conditions remain untouched. The planning results are compared in Figures 13-15.  
Figures 13-15 and Table 4 show that IPCB can obtain better performance in deploying IPBs with high altitudes to positions near the airspace center (layout 3) than to positions near airspace borders (Layout 1 and Layout 5).  
Figure 13: Flight altitude comparison for IPCBs with different initial horizontal layouts: (**a**) Layout 1; (**b**) Layout 2; (**c**) Layout 4; (**d**) Layout 5. (Flight altitude for IPCB with initial Layout 3, please refer to Figure 6).  
Furthermore, Figure 15 shows that IPCBs with Layout 1 and Layout 5 have approximate initial GDOPs. However, their performance displays a different tendency as time goes on. A similar case occurs in IPCBs with Layout 2 and Layout 4. Data in Table 5 also shows that Layout 1 performs better than Layout 5, and Layout 2 performs better than Layout 4. These phenomena may be derived from the winds used in the simulations. In the feasible flight altitude range (21-24 km), the meridional winds are all southerly, leading to all the IPBs moving northward. So, IPCBs with low initial latitudes perform better than IPCBs with high initial latitudes. It is especially obvious in Layout 5, in which IPB5 and IPB6 fly out of the approved airspace quickly due to the short distance between their initial positions and the north border of the airspace.  
Figure 14: _Cont._  
In winds with quasi-zero wind layers, the direction reversion rule of zonal wind can be employed to improve IPCB geometry configuration. In contrast, no proper rule of meridional wind can be employed. To achieve good performance throughout the whole service duration, the wind is suggested to be treated as a notable factor in the initial horizontal layout design of IPCB.  
Figure 14: Horizontal trajectory comparison for IPCBs with different initial horizontal layouts: (**a**) Layout 1; (**b**) Layout 2; (**c**) Layout 4; (**d**) Layout 5. (Horizontal trajectory for IPCB with initial Layout 3, please refer to Figure 7).  
Figure 19: GDOP comparison for IPCBs in winds with/without quasi-zero wind layers.  
Figure 17: Flight altitude of the IPCB in the wind without a quasi-zero wind layer.  
Figure 18: Flight trajectory of the IPCB in the wind without a quasi-zero wind layer.  
From Figures 17-19, it can be seen that in winds without a quasi-zero wind layer, zonal trajectory direction reversion does not occur since wind direction reversion does not occur. In addition, the wind velocity is bigger than the wind velocity in Section 7.2, so some IPBs fly out of the approved airspace in a short time, such as IPB2 and IPB3 in Figure 18. This leads to a decrease in the number of available IPBs in the IPCB and deterioration in the IPCB geometry configuration. In order to lengthen IPBs' flight time in the approved airspace, the planning algorithm tends to adjust IPBs' flight altitude to 23\(\sim\)24 km, where wind velocity is small, as IPB1, IPB 4, IPB 5, and IPB6 in Figure 17 illustrate.  
By comparing planning results in this section with results in Section 7.2, it can be seen that the results in winds with quasi-zero wind layers are significantly better than those in winds without quasi-zero wind layers. It indicates the significance of the quasi-zero wind layer in improving IPCB geometry performance.  
To improve IPCB performance in winds without quasi-zero wind layers, measures such as altering the initial layout, increasing the initial number of IPBs, or supplementing IPBs dynamically can be taken.  
Since IPCB achieves its flight mainly by buoyancy and winds, it is sensitive to its running environment. Environment fluctuations or different environment models may bring different results, which can be analyzed in detail in the future.