## 2 NS Communication, Navigation, and TT&C Integrated Frequency Selection
They are also convenient for compatibility with 5G and 6G mobile communications, and can form a communication network that coordinates with the ground cellular network [46; 47]. Figure 1 shows the application scenarios of various frequency bands within the frequency range from 1 GHz to 40 GHz. It is not difficult to observe the advantages of the spectral resources in the K/Ka frequency bands. (2) High-speed Communication  
Regarding NS vehicles, especially low-dynamic vehicles, one of their main uses is to achieve persistent regional information acquisition and anti-interference capabilities. Therefore, they must have strong high-speed communication capabilities, which requires the communication, navigation, and TT&C systems of the NS platform to adopt higher frequency bands and yield wider bandwidths [48]. Taking the 27.5-28.35 GHz (downlink) band divided by the ITU as an example, it has a total bandwidth of 0.85 GHz [49]. If the transmission bandwidth \(B\) is selected according to the requirement of 1.3\(R_{c}\) (\(R_{c}\) is the transmission channel symbol rate), for binary phase shift keying (BPSK) modulation, the symbol rate that can be transmitted is 650 Mbps, and for quadrature phase shift keying (QPSK) modulation, it can reach 1.3 Gbps. In addition, high-frequency bands \begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Type** & **Applicable Conditions** \\ \hline \multirow{4}{*}{ITU-R P.531} & \multirow{4}{*}{Recommendations of ITU-R Series P.} & It is used to analyze the influence of the ionosphere on near-space communication, and to provide the basis of propagation characteristics for the spectrum usage in high-frequency bands such as Ka/V frequency bands. \\  & & \\ \cline{1-1}  & An international treaty that regulates the use of the global radio frequency (RF) spectrum and satellite orbits. & It covers more than 40 different radio communication services, with frequencies ranging from 8.3 kHz to 3000 GHz. \\ \cline{1-1}  & & It is used for high-altitude platform station (HIBS), Earth station in motion for non-GEO satellite (ESIM), and space weather observation. \\ \cline{1-1}  & & An international treaty that regulates the use of the global radio frequency (RF) spectrum and satellite orbits. & Updates and supplements to the Radio Regulations, Edition of 2020. \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._also help to reduce the bit error rate (BER) of communication; due to the increase in the carrier frequency \(f_{0}\), the relative bandwidth \(B/f_{0}\) decreases. Thus, within the same \(B\), the linearity of the phase-frequency characteristic and the uniformity of the amplitude-frequency characteristic of the radio frequency front-end in the high-frequency band are improved, which is beneficial to reducing the BER of communication. From the perspective of future practical applications, since the L, S, and C frequency bands are already quite crowded and the spectrum resources are facing exhaustion, it is not advisable to use low-frequency bands such as L, S, and C anymore. Undoubtedly, the K/Ka bands are the best choice. (3) Over-the-horizon relay  
When the NS platform is beyond the radio line-of-sight (LOS) range of the ground TT&C station, especially when the reusable space shuttle re-enters the atmosphere, the plasma sheath and blackout effect will occur. Therefore, the communication and TT&C must adopt the relay mode. General relays are divided into three types: ground relay, air relay, and satellite relay. However, for the NS platform, due to its altitude, ground relay and satellite relay are of little significance. In particular, the S-band of the relay satellite only supports low-speed communication below 1 Mbps [50], so it is not suitable for the communication needs of the NS platform. The C-band of communication satellites and the L-band of navigation satellites are narrow and very crowded, and are also not suitable for the requirements of high-speed communication and precise navigation.