For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905. The definitions given in [2] are also applicable in this report. The definitions given in [3] are also applicable in this report Satellite: Satellite network: Satellite RAT: 5G Satellite RAT: 5G satellite access network: Terrestrial: Terrestrial network:

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905. 5QI ALM AMF CN D2D eMBB eMBMS FFS GEO gNB GSM HEO HFT HQ IoT LEO LI LTE MEO mMTC MNO Nb-IoT NGSO NR QI QoS RAN RAT SE SMF SNO TR TS TV UE VIP

On the basis of the analysis of the characteristics of satellite networks, it is possible to define 3 main categories that will be used in the following parts of the documents. Categories are not exclusive from each other: a use case may contribute to one or more categories. The following sub-clauses define and illustrate the corresponding categories:

The deployment of terrestrial networks can be driven by the coverage of population centres rather than by the coverage of geographical areas. This can lead to the creation of geographical areas where access to the 5G services through the radio coverage of a terrestrial network will not be possible In such cases, UE's whether associated with pedestrian users, or embarked on moving land mobile terrestrial platforms (e.g. a car, a coach, a truck, a train), airborne platforms (e.g. a commercial or a private jet) or maritime platforms (e.g. a maritime vessel) can experience conditions where 5G services cannot be offered continuously by a single or a combination of terrestrial networks during the journey of the UE. Use cases described under this category will address the opportunity for users to be provided a continuous access to services granted by the 5G system, whilst moving between terrestrial and satellite networks. Use cases including fleets of such UE's (whether dispersed or locally grouped) would also be included in this category.

Terrestrial networks may not be available due either to economic rationales (expectation for revenues not meeting the minimum threshold for profitability), or disasters (e.g. Earthquakes, floods) leading to a temporary outage or total destruction of the terrestrial network infrastructures that need to be restored. A number of potential users may wish to access 5G services in these "un-served" or "underserved" areas by terrestrial networks, but will be prevented to do so, unless 5G satellite access networks provide such a service. Example uses cases are:

• Internet of Things (for Agriculture, Critical Infrastructures Metering & Control -pipelines, Asset Tracking/ Tracing)
• Public Safety and associated emergency networks
• Home access

In comparison with terrestrial networks, satellite networks have a large coverage, typically corresponding to tens of thousands of cells of a terrestrial network. Satellites are therefore efficient in multicasting or broadcasting a similar content over a large area, and potentially directly to user equipment. Similarly, a satellite network can also contribute to off-loading traffic from terrestrial networks during the busy hours by multicasting or broadcasting non time sensitive data in non-busy hours. Use cases associated to this category would be for instance the distribution of rich to very rich TV content due to new media encoding format (e.g. 3D, Ultra High Definition).