Handover Solutions for 5G Low-Earth Orbit Satellite Networks

Non-terrestrial networks (NTN) are foreseen as a key cornerstone for industry and academia. As part of this venture, low-Earth orbit (LEO) satellite networks are meant to be fundamental to closing the digital divide, enabling new market opportunities and providing fifth-generation (5G) new radio (NR) connectivity everywhere at any time. Despite the advantages of LEO deployments, these systems are characterized by a high mobility and a challenging propagation channel that compromises several procedures of the current 5G standards. One of the impacted areas is the radio mobility management, which is used to ensure continuous and satisfactory service while the users move across cells. Current research shows that the measurement-based 5G NR handover (HO) procedures, designed for terrestrial networks, fail to guarantee optimal mobility performance. In this work, we provide a performance analysis through systemlevel simulations of state-of-the-art HO procedures meant to enable 5G NR over LEO satellite networks with Earth-moving cells. Furthermore, this article presents a novel HO solution for intra-satellite mobility that exploits the predictability of the satellites movement and the antenna gain pattern of the satellite beams making user equipment (UE) radio measurements obsolete. The simulation results, which consider users in rural and urban scenarios, show that by exploiting the predictability of the satellites movement the UE eliminates service failures and undesired HO events, maximises the time of stay in a cell and it experiences improved downlink SINR. Finally, this article provides a sensitivity study on the mobility performance impact of additional sources of error not contemplated by the 3GPP, such as the antenna radiation error and the satellite pointing accuracy, and the impact of users' mobility.