Functional Split Evaluation in NTN for LEO Satellites

Functional split over non-terrestrial networks (NTN) is one of the key-enabling technologies in the next 5G+ and 6G networks, which allows the implementation of virtualized radio access network (vRAN), and the recent open RAN (ORAN) in NTN. Functional split is based on splitting the RAN functionalities into a centralized unit (CU) and a distributed unit (DU), aiming at reducing the processing requirements at the DU located close to the antenna. Even though functional split has been standardized and evaluated for terrestrial networks, its applicability in NTN has not been discussed up to now. Functional split is expected to be part of 3GPP NTN Rel-19, where regenerative payload is expected to be introduced in a new working item at the time of writing this paper. This work evaluates the different split options in NTN for low earth orbit (LEO) satellites based on NTN key performance indicators (KPIs) and highlights the challenges that hinders the implementation of functional splits in NTN. A new architecture is proposed to facilitate the implementation of functional splits in NTN while gaining the desired advantages compared to a transparent payload or a full gNB onboard.