# Worldwide Coverage Mobile Systems for
## 2 Satellites Constellations
### Design Parameters for Satellite Communications  
The design of a satellite communications links is based on the same parameters than any other radiofrequency link. The concrete values and characteristics depend on the type of constellation given the have particular features. There are a number of factors that affect satellite links, which can be divided into two categories: the conduit factors and the content factors. The former include parameters, such as the ground-space and space-ground distance, the effect on the propagation signal, the quality of the earth station equipment, and the impact of the frequency band of interest. The content factors are mainly related to the type of messages to be transmitted, and the type of devices involved. Basically, the link balance relates the transmitted power with the received power to guarantee the quality and reliability of the communication. An important property of satellite communications is that they are in direct line of sight. Therefore, the parameters that correspond to a communication in free space are those that are used, to which must be added the particular disturbances suffered by satellite communications. The essential parameters that characterize a transmission are antenna gain, beamwidth, path attenuation in free space, and the link power equation. The design must also take into account the noise of the communication system and how its effect on the radiofrequency link is quantified, for which terms, such as noise power, noise temperature, noise figure, and figure of merit are used. The carrier-to-noise ratio (C/N) is one of the parameters used to define the quality of the communication link. There are particular aspects that relate to the equipment used and that influence the link design, such as the sensitivity of the receivers. Table 4 shows the key performance indicator (KPIs) recommended by the 3 GPP for 5G. If we compare the link design for GEO, MEO, and LEO satellites, we will find parameters with different values due to the different characteristics of the link, in particular the distance, which will affect the attenuation in free space. Other parameters to take into account, depending on the application, are the delay produced by the link length and the latency. Table 5 shows the main parameters that are used to develop a satellite communication project. \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Peak data rate & 20 Gbps for DL \\  & 10 Gbps for UL \\ \hline Peak spectral efficiency & 30 bps/Hz for DL \\  & 15 bps/Hz for UL \\ \hline Control plane latency & 10 ms \\ \hline User plane latency & eMBB: 4 ms for UL \\  & 4 ms for DL \\  & URLL: 0.5 ms for UL \\  & 0.5 ms for DL \\ \hline Mobility interruption time & 0 ms \\ \hline Spectrum efficiency & 3\(\times\) (eMBB) \\ \hline Reliability & URLLC: \(1\times 10^{-5}\) (32 bytes with a user plane \\  & latency of 1 ms) \\  & eV2X: \(1\times 10^{-5}\) (300 bytes with a user plane \\  & latency of 3–10 ms) \\ \hline UE battery life & mMTC: beyond 10 years, 15 years desirable \\  & (200 bytes UL per day, 5 Wh) \\ \hline Connection density & 1,000,000 device/km\({}^{2}\) in urban environment \\ \hline Mobility & 500 km/h \\ \hline \hline \end{tabular}
\end{table} 
Table 4: 3 GPP 5G KPIs. Table 6 draws the design parameters for three examples based on the 3 GPP work [15]--satellites operating in the Ka band are much more susceptible to adverse weather conditions than those operating in the Ku band, and especially those operating in the C band. Working on platforms at higher frequencies allows the use of smaller on-board antennas, which provides the possibility of mounting multi-antenna systems, that is, arrays, on satellites. GEO satellites are those that incorporate larger antennas to produce the energy that is required to guarantee the quality of communication, typically 12 m and even 25 m in diameter, to provide adequate gain. One of the main disadvantages of GEO systems is latency, due to its greater distance from the ground.