# Machine Learning Techniques for Non-Terrestrial Networks
## 4 Non-Terrestrial Network Architectures
### Services for NTN
In this case, NTN acts as an eMMB backhauling to the locally deployed gNB, where UEs are easily connected with NR radio interface. UEs can experience eMMB shared services (e.g., 50 Mbit/s or more depending of the simultaneous active connections). The second case is when the NTN allows the connectivity of several sensors deployed in a wide area, such as remote and isolated areas (e.g., North Scandinavia, Siberia and long coasts). Sensors' throughput is in the order of tens of kbit/s. The third case is the monitoring of critical infrastructures (such as ports, bridges, airports and dams). This application assumes to have some sensors and actuators deployed in a remote but limited area that are able to locally communicate with a local access point (acting as a concentrator). The local links may exploit different wireless or wired technologies (e.g., ZigBee, Wi-Fi or other IEEE 802.15.x standards) according to the required data rates and sensors' constraints. The local access point connects with the NTN using NR. Differently from the first two cases, where HAPS and LEO may be the most suited NTEs, in the third case, also UAVs can be adopted, depending on the given criticisms of the monitored area. **Throughput increase. ** In some regions (e.g., suburban), the terrestrial network is available but the area served by a single gNB is wide, and thus the provided capacity is shared among all the active UEs. This limits the quality of experience (QoE) of the users above all in congested hours. The NTN can provide a second link to the users in the area, thus enabling a _throughput enhancement_ in their connection. A stringent collaboration should be performed by TN and NTN in the dual connectivity for the data rate split of each user. The stream merging from the TN link and from the NTN link is managed by the UE in downlink and by the gNB acting as a master cell in uplink. Acknowledgments and retransmissions are managed separately on the two links. For this service, HAPS can be normally used, but in some cases, such as traffic jams, vehicle accidents, or open-air gathering events, the throughput enhancement can be provided by deploying a dedicated UAV over the interested area. **Secondary link for backup. ** In some cases, connectivity is used to provide services to lone workers, trains, and small ships that should be guaranteed in wide areas. For example, the high-speed trains as well as regional trains have the necessity to constantly communicate with their remote-control center for sending their updated position and receiving the authorization to move on the rail. Connectivity provided by TNs cannot be available in rural and mountain areas since the base station deployment of the telecommunication operator is limited to urban/suburban zones. In order to guarantee the _service continuity_ and to optimize the rail infrastructure, NTN can cover the unserved areas through LEO sats or HAPSs. The NTN link is just as a backup complementing the terrestrial coverage and offering connectivity from few tens of kbit/s up to 1 Mbit/s per moving object. **Disaster relief. ** The adoption of the satellites has been largely investigated by the literature in the case that the TN has suffered significant damage from earthquakes, explosions, tsunamis or other natural disasters. NTN is able to fast provide connectivity (i.e., _throughput enhancement_) to rescue teams and civil protection up to 500 Mbit/s (or even more) in the affected area. Moreover, it can help missing people and survivors for their localization and limited communications, providing them _ubiquitous connectivity_. In the beginning, LEO satellites can be adopted in the affected area, but the radio capacity can be later improved by fast deploying UAVs and HAPSs. It is important to ensure that people can connect with their mobile phone rather than resetting communications only for law enforcement and military. **Broadcasting/ Multicasting. ** This service exploits the natural advantages of the satellites.