# Machine Learning Techniques for Non-Terrestrial Networks
## 4 Non-Terrestrial Network Architectures
### Services for NTN  
Due to satellite and HAPS characteristics (e.g., latency, pathloss and Doppler shift), classical three use cases envisaged by 5G (i.e., enhanced multi-broad band, eMMB, massive machine type communications, mMTC, and ultra-reliable and low latency communications, uRLLCs) and defined in [29] are slightly modified in [30], providing revised and adjusted requirements for satellite use cases. They are reported in Table 2, where it is assumed a bandwidth of up to 30 MHz over one satellite beam. In the following, we present the most-suited services that an NTN system is able to provide based on its characteristics and grouped within the three novel areas: _service continuity_, _throughput enhancement_ and _ubiquitous connectivity_. After their description, we also provide possible service requirements, which is the most suited NTE to provide it. Based on this grouping, telecommunication operators may properly implement changes or integration with terrestrial network elements in order to provide services in a specific vertical market. **Moving cell connectivity. ** Several platforms used for public/private transport are moving objects worldwide, including ships, airplanes, trains, and river boats. Connectivity service is not provided to their passengers or provided intermittently, such as in high-speed trains. The adoption of NTNs can overcome the coverage issue, thus providing the basic service of _ubiquitous connectivity_. Since the considered mobile platforms are located in open spaces and travel at considerable speed, LEO and HAPS are of greater interest for the connectivity service. It is considered to connect each passenger with a data rate of 50 Mbit/s. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**NTE** & **Altitude** & **Footprint Size** & \(D_{max}\) & **RTT** \\ \hline GEO & 35,786 km & 200–3500 km & 40,581 km & 541.46 ms (service and feeder links) \\  & & & & 270.73 ms (service link only) \\ MEO & 7000–25,000 km & 100–1000 km & 16,000 km & 213 ms (8000 km) (service and feeder links) \\  & & & (\(h_{0}=8000\) km) & 107 ms (8000 km) (service link only) \\ LEO & 300–1500 km & 100–1000 km & 1932 km & 25.77 ms (600 km), 41.77 ms (1200 km) \\  & & & (\(h_{0}=600\) km) & (service and feeder links) \\  & & & 3131 km & 12.89 ms (600 km), 20.89 ms (1200 km) \\  & & & (\(h_{0}=1200\) km) & (service link only) \\ HAPS & 8–50 km & 5–200 km & 115 km & 15.53 ms (20 km) (service and feeder links) \\  & & & (\(h_{0}=20\) km) & links) \\  & & & & 0.77 ms (20 km) (service link only) \\ UAV & 1–10 km & 1–50 km & 30 km & \(<\)67 μs (service and feeder link), \\  & & & (\(h_{0}=5\) km) & \(<\)33 μs (service link) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters for NTN types and scenarios [2; 27]. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Requirement** & **Value** & \\ \hline Peak data rate & 70 Mbit/s (in downlink), & 2 Mbit/s (in uplink) \\ User experienced data rate & 1 Mbit/s (in downlink), & 100 kbit/s (in uplink) \\ Area traffic capacity & 8 kbit/s/km\({}^{2}\) (in downlink), & 1.5 kbit/s/km\({}^{2}\) (in uplink) \\ Latency & 10 ms (user plane), & 40 ms (control plane) \\ Latency for SRI in high-altitude satellites & 650 ms (user plane), & 1150 ms (control plane) \\ Connection density & 500 devices per km\({}^{2}\) & \\ Reliability & 0.999 & \\ Mobility & 250 km/h (car), 500 km/h & (train), 1200 km/h (airplane) \\ Mobility interruption time & 50 ms & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Requirements in NMT-2020 for satellite radio interface [29]. **Unserved/Under-served and isolated areas. ** There exist several areas in the world that have limited or no access to the internet. NTN can solve the _ubiquitous connectivity_ but its applicability depends on the specific context in which the connectivity is provisioned. Three main cases or applications are considered. The first one is the connectivity of remote access points hard to be reached out by fiber optics.