Performance Evaluation of the 5G NR Conditional Handover in LEO-based Non-Terrestrial Networks

The development of non-terrestrial networks (NTN) aims to satisfy the requirements of ubiquitous and seamless coverage for fifth-generation (5G) services. Low Earth orbit (LEO) satellites introduce challenging mobility requirements to the 5G New Radio (NR) radio resource management procedures. Current research shows that the baseline 5G NR UE-assisted network-controlled handover (HO) procedure, meant for terrestrial scenarios, fails to ensure continuous and satisfactory service in LEO-based NTN. The conditional handover (CHO), specified by 3GPP in Rel-16, was designed for terrestrial networks to enhance mobility robustness by making HO decisions earlier. In this work, we conduct system-level simulations to evaluate the 5G NR mobility performance of the CHO in a LEO-based NTN with Earth-moving cells scenario. The simulation results show that the CHO procedure reduces the radio link failures and handover failures to 0 but increases the unnecessary HO rate by more than 60% in comparison with the baseline HO, which leads to an increase of the signalling and measurement reporting. Finally, future research directions are identified to address the increase of the signalling overhead by exploiting the predictability of the satellite’s movement.