Wireless self-backhauling relays considered in 3GPP generally assume a terrestrial (fixed) base station providing wireless access to the relay nodes. In this use case, access to a very remote mobile relay is supported by means of a non-terrestrial platform.
This introduces two complicating factors:
The latency for signalling across the network (between the relay nodes and the node providing access to the relay) will be much higher than in terrestrial networks.
The non-terrestrial platform providing relay connectivity itself may be mobile (in all cases except a GEO NTN access node.)
This could be needed - for example, to support vehicular relays that are out of coverage of terrestrial networks, e.g. in remote areas. Even where terrestrial coverage exists, the vehicular relay may use satellite coverage.
Where satellite access is described in this use case, both the transparent and regenerative NG-RAN architectures could apply. [y]
Two vehicles drive across a remote landscape, 100s of km from any settlement. There is no terrestrial coverage. Some vehicles are equipped to support satellite access and provide passengers of the vehicle with coverage by way of mobile vehicular relay.
In Figure 1, the two vehicles are roughly 1 km apart, driving in the same direction. The satellite platform is also in motion (see the displacement during T1 to T2 - which is not drawn to scale.) Satellite access is available for both vehicles. Even as the satellite moves, the vehicles continue to be in coverage and serve their passengers with relayed coverage.
At T3, the black satellite will no longer be able to provide coverage to the vehicles. A separate satellite platform (shown in gray) that is part of the same satellite network follows. Even as the first platform cannot offer coverage, the second takes its place. There is thus continuity of service by means of a sequence of transitions to make use of different satellite platforms offering access to the vehicular mobile relays.
This use case does not differentiate (at the service level) between the situation where the satellites are transparent (in which case the donor RAN is terrestrial), or whether the satellite is regenerative (in which case the donor RAN is the satellite platform itself.)
NR Rel-16 introduces a relaying architecture enabling routing across a backhaul network of relay nodes which uses NR-Uu interface to interconet relay nodes, enabling data transfer from network access node to the end-user, and back: IAB. In Rel-17, IAB is currently being enhanced, although relay (IAB-node) mobility is not being taken into account.
The 5G System shall be able to support mobile vehicle relays using NR satellite access to connect to a remote donor RAN node via a satellite link.
The 5G System shall be able to support a mobile vehicle relay using NR satellite access with service continuity in the scenario where there is a transition from one serving satellite to another serving satellite.
A nationwide company, 5G-travels, provides long-distance bus transport service and has recently installed 5G mobile BS relays on their bus fleet, for enhanced 5G connectivity to their passengers. Two national cellular MNOs, PLMN-A and PLMN-B, already using RAN sharing in several areas of the country, make commercial arrangements with the bus company and among themselves, for sharing the use of the bus relays, such that their customers can have access to their respective HPLMN, without roaming.
The following aspects and options are assumed in this use case:
Each PLMN operator has his own 5G core network; both core networks are connected to a certain number of shared donor RAN nodes, deployed along the bus routes, which provide wireless connectivity to the vehicle relays on the buses.
Spectrum and RAN resources used for UEs and wireless relays access could be managed by either PLMN A or B, or by a hosting operator different from operator A or B
The vehicle relays will broadcast both PLMN-IDs of the sharing operators, appearing to their users/UEs like their home PLMN network.
Based on user subscription/UE identity, the shared RAN can route traffic of PLMN-A and PLMN-B customers to/from their corresponding PLMN core network.
It is assumed that other passengers, without subscription or roaming agreement with either PLMN-A nor B, will not get access via the bus relays. If roaming agreement is in place, in-bound roamers would also be allowed to access the vehicle relay.
Two users, from South-ville, are taking an inter-regional bus, for visiting their parents living up in North-ville, over the weekend:
Ms Red, who is a PLMN-A subscriber
Mr. Blue, who is a PLMN-B subscriber
Before entering the bus, their UEs are connected to the fixed macro-RAN (which may or may not be shared between PLMN-A and PLMN-B), and their UEs will display "PLMN-A" and "PLMN-B", respectively.
Upon entering the bus, their UE's display shows "PLMN-A_BUS" and "PLMN-B_BUS", respectively, and both users receive a short message announcing the new "enhanced 5G-bus service" offered by their respective HPLMN operator, which they can use without additional charge.
During the few hours trip, both Ms Red and Mr Blue use their smartphones to keep entertained, make few calls, check emails, social media etc.
Mr Blue and Ms Red enjoy the very good 5G connectivity and service quality during the whole trip, much better than last month's trip, when the enhance 5G-Bus service was not available.
At the arrival, when leaving the bus, their UEs will re-select and/or connect from the relay to the macro-RAN (which may or may not be shared between PLMN-A and PLMN-B)
Basic support of RAN sharing is defined for 5G NG-RAN (since Rel-15), including service requirements (e.g. in TS 22.101) and stage-2/3 capabilities (e.g. TS 23.501, TS 38.331); nevertheless, they do not cover or assume specific consideration for the case of shared wireless access via mobile base stations.
The 5G system shall be able to support RAN sharing between multiple PLMNs for UEs connected to 5G network via mobile base station relays (e.g. mounted on vehicles)
The 3GPP System shall support end-to-end service continuity for a UE active connection to RAN via a mobile base station relay (e.g. mounted on a vehicle) when there is a change between a shared RAN (e.g. inside the vehicle) and a non-shared RAN (e.g. outside a vehicle), or when RAN sharing changes (for the same mobile relay) between different sharing PLMNs.