## 3 Influence of Physical Properties of NS on Communication, Navigation, and TT&C Integration
### NS Rainfall Attenuation  
For wireless communication systems operating in frequency bands above 10 GHz, rainfall will be the most significant factor affecting their performance. In practical situations, rainfall is generally uneven in both time and space, and the inhomogeneity and randomness of rainfall make it extremely difficult and complex to accurately calculate rain attenuation. Currently, several relatively mature calculation methods internationally include the ITU-R, Lin, SAM, and Crane models, etc. [67; 68; 69; 70; 71], where the ITU-R rainfall attenuation prediction model is widely used internationally due to its characteristics such as easy to use, requiring fewer input parameters, and having relatively high calculation accuracy. For all path geometries in linear polarization and circular polarization, the ITU-R recommends that the average annual rainfall (mm/h) at a specific location for the space-to-ground path at 0.01% of the annual time is calculated as follows [71],  
\[\gamma_{R}=k(R_{0,01})^{\alpha} \tag{4}\]  
Figure 2: (**a**) The range of signal transmission loss in the K/Ka frequency band in the NS. (**b**) The signal transmission loss in the K/Ka frequency band at different elevation angles at the bottom layer of the NS. (**c**) The signal transmission loss in the K/Ka frequency band at different elevation angles at the top layer of the NS. where \(k=[k_{H}a_{H}+k_{V}a_{V}+(k_{H}-k_{V})\ \cos^{2}\!q\ \cos(2e)]/(2k)\), \(e\) is the polarization dip angle relative to the horizontal direction; when \(e=45^{\circ}\) is circular polarization, when \(e=0^{\circ}\) is horizontal polarization, and when \(e=90^{\circ}\) is vertical polarization, the specific parameters of horizontal polarization coefficient \(k_{H}\) and \(a_{H}\) and vertical polarization coefficient \(k_{V}\) and \(a_{V}\) can be determined according to the table [71], where \(R_{0.01}\) represents 0.01% of the average annual rainfall (mm/h) in that location. According to the statistical results given in the specific model of rain attenuation used in the prediction method specified in the ITU-R P.838-3 recommendation, for the K/Ka frequency band, the corresponding results of \(k_{H}\), \(a_{H}\), \(k_{V}\), and \(a_{V}\) are shown in Figure 3a. In addition, since rainfall usually occurs in the troposphere, that is, the airspace from the Earth's surface to an altitude of 18 km above the ground, so the signal propagation to the NS must pass through the troposphere. For circular polarization, when \(e=45^{\circ}\), \(k\) has no relation with the elevation angle \(\theta\). Therefore, simulations are carried out here according to the definitions of light drizzle (rainfall \(<0.1\) mm/24 h = 0.0042 mm/h), light rain (rainfall = 0.1 mm/24 h = 0.0042 mm/h to 9.9 mm/24 h = 0.4125 mm/h), moderate rain (rainfall = 10 mm/24 h = 0.4167 mm/h to 24.9 mm/24 h = 1.0375 mm/h), heavy rain (rainfall = 25 mm/24 h = 1.0417 mm/h to 49.9 mm/24 h = 2.0792 mm/h), rainstorm (rainfall \(>50\) mm/24 h = 2.0833 mm/h), severe rainstorm (rainfall \(>100\) mm/24 h = 4.1667 mm/h), and extremely severe rainstorm (rainfall \(>250\) mm/24 h = 10.4167 mm/h) [72]. The relationship between \(R_{0.01}\) and the K/Ka frequency band under different rainfall levels is shown in Figure 3b. For horizontal polarization and vertical polarization, \(k\) has a close relationship with the elevation angle. Therefore, simulations are carried out here under the condition of moderate rain, Figure 3c,d show the simulation results of the relationship between \(R_{0.01}\) and the K/Ka frequency band under the conditions of moderate rain and different elevation angles.