## 5 Conclusions and Future Works  
### Conclusions  
This paper analyzes the communication, navigation, and TT&C service challenges faced by NS vehicles when entering the atmosphere. Based on the analysis of the current  
Figure 12: Simulation comparison results of the PSD and ACF curves for typical single signals and integrated signals. **(a)** Comparison of the PSD of the CMP-BOC (1,1) signal and its composite components. **(b)** Comparison of the ACF of the CMP-BOC (1,1) signal and its composite components. **(c)** Comparison of the PSD of the CMP-OFDM signal and its composite components. **(d)** Comparison of the ACF of the CMP-OFDM signal and its composite components. **(e)** Comparison of the PSD of the OFDM-BOC (1,1) signal and its composite components. **(f)** Comparison of the ACF of the OFDM-BOC (1,1) signal and its composite components. **(g)** Comparison of the PSD of the BPSK-BOC (1,1) signal and its composite components. **(h)** Comparison of the ACF of the BPSK-BOC (1,1) signal and its composite components.  
ICNT service requirements of NS, through the analysis of the frequency spectrum division by the ITU, high-speed communication in the NS, over-the-horizon relay in the NS, plasma and black barrier problems, as well as the maturity of the development of existing equipment, it is concluded that the K/Ka frequency band is currently a more suitable frequency band for the ICNT service requirements of NS. Based on the K/Ka frequency band, we have analyzed the impacts of key physical characteristics such as transmission loss, rain attenuation, and atmospheric loss in the NS on the signal transmission in the K/Ka frequency band. We explored the advantages of constant envelope signals in terms of spectral utilization rate, and proposed an overall design scheme for the ICNT based on the K/Ka frequency bands. The potential value of the scheme was verified through typical basic integrated signals. Finally, we drew the following research conclusions:  
1. The K/Ka frequency bands have huge potential advantages compared with the traditional L/S/C frequency bands. The K/Ka frequency bands are suitable for the ICNT in the NS.
2. The loss of K/Ka frequency band signals increases with the increase in frequency, and the path loss becomes greater as the elevation angle decreases.
3. The magnitude of rainfall loss depends on the signal frequency and the elevation angle of the beam. The larger the elevation angle, the smaller the rainfall attenuation. Conversely, the smaller the elevation angle, the greater the rainfall attenuation.
4. For K/Ka frequency band signals, the 1 min rainfall rate and rainfall attenuation are closely related to the frequency. The rainfall attenuation increases with the increase in frequency, and a higher rainfall rate usually leads to greater rainfall attenuation.
5. In the atmospheric loss of the near space, * For the K/Ka band signals, except for a relatively large absorption at 22.3 GHz due to the loss of oxygen molecules, the attenuation coefficients of both water vapor and oxygen molecules show a gradually increasing trend. * With the increase in frequency, the cloud and fog loss of K/Ka band signals is gradually increasing, and with the decrease in the antenna elevation angle, the loss is also gradually increasing. * The atmospheric attenuation of the K/Ka band gradually decreases with the increase in the antenna elevation angle. The lower the elevation angle, the stronger the atmospheric scintillation. * Factors such as the plasma sheath, multipath, Doppler effect, and noise will also have a certain degree of impact on the propagation of the signal. * Adopting constant envelope modulation can improve the frequency band utilization rate of the system to a certain extent. And the design scheme of integrating communication signals, navigation signals, and TT&C signals into the frequency points of a single K/Ka signal can enhance the overall performance of the system.