The present document is the outcome of the study on use cases and potential new requirements for 5GS support of mobile base station relays mounted on vehicles, using 5G NR over the radio links toward UEs and macro RAN (connected to 5GC). This study covers aspects related to:

• Vehicle base station relays providing service to UEs inside the vehicle or in the vicinity of the vehicle;
• End-to-end service continuity during mobility scenarios (including mobility of the relays);
• Provisioning, policies and control, e.g. for
  • Provisioning of spectrum used by the relays, geographic area restrictions;
  • Control of relay operation, UEs access and connectivity via relays.
• Aspects related to roaming of relays, security, regulatory requirements (e.g. for emergency services), charging, spectrum interference.
• Gap analysis between the identified requirements and existing 5GS requirements or functionalities.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

Demand for improved 5G cellular coverage and connectivity continues to increase, which may be challenging in many outdoor and mobility scenarios. In some outdoor environments, the availability of vehicles equipped with mobile base station relays, either following a certain known/predictable itinerary (e.g. buses, trams, etc), or situated in convenient locations (e.g. outside stadiums, hot-spot areas, or emergency sites), could provide very opportunistic boost to cellular coverage and capacity when/where needed. Those relays, using 5G wireless backhaul toward the macro network, could indeed offer better 5G coverage and connectivity to neighbouring UEs. Vehicle relays are obviously very suitable also for improving connectivity for users or devices inside the vehicle itself, in different environments, e.g. for passengers in buses, car/taxi, or trains, ad-hoc/professional personnel or equipment. Yet other target scenarios are where vehicle relays can be used for reaching users or devices that would otherwise have no or very poor macro coverage, e.g. in case of first responders dislocated in indoor buildings/areas, using 5G relays placed on their nearby/outside vehicles to get required 5G coverage and connectivity. The technical benefits of using vehicle relays include, among others, the ability of the BS relay to get better macro coverage than a nearby UE, e.g exploiting better RF/antenna and power capabilities. Besides the value for network operators and end users, worthy incentives could be found for other parties as well, e.g. for vehicles manufacturers, vehicle/fleet owners or providers, to install and operate relays in their vehicles. In the context of this TR, from a high-level 5G system point of view, the target scenarios include moving vehicles equipped with small on board base station (BS) relays providing 5G coverage and communication to UEs (inside the vehicle and/or in its vicinity), and connected wirelessly to the 5G network via RAN (donor) nodes.

As shown in the figure above, the main connectivity assumptions are:

• 5G NR is used for the radio link between mobile BS relay and donor RAN node, as well as the radio link between BS relay and UE.
• The mobile BS relay connects, via donor RAN node, to the 5G Core network (5GC).
• Single-hop relay is the main/baseline scenario (multi-hop can be a possible option)

The study intends to cover use cases of BS relays mounted on ground/land type of mobile vehicles; nevertheless, some potential requirements may be general (for a "mobile base station relay"), i.e. could apply to BS relays mounted on different types of moving vehicles or devices. In the paragraphs that follow, next section (clause 5) captures several identified use cases and new potential requirements, covering (among others): basic operation of vehicle relays, relay configuration, UE access control, optimized connectivity and mobility, load balancing, support of location services, QoS and charging, service continuity during mobility (between relay and macro, or among relays or when macro node changes), multi-connectivity, ad-hoc coverage and topologies (e.g. for public safety), RAN/relay sharing, satellite backhauling. In addition to those, clause 6 covers further aspects and requirements, e.g. about support of roaming, regulatory requirements, emergency services, security, priority services. The two concluding sections (clause 7 and clause 8) contain the list of consolidated new potential requirements, from all use cases, and the final TR recommendations.