A Survey of Mobility Management in Non-Terrestrial 5G Networks: Power Constraints and Signaling Cost

Mobility management is a critical and challenging requirement for 5G networks and their successors, as numerous highly mobile user equipment (UE), including massive Internet-of-Things (IoT) devices, generate extreme traffic volumes. In the integration of non-terrestrial networks (NTNs) with 5G, mobility management is of utmost importance to track these highly mobile UE/IoT throughout the network coverage area for the purpose of data-packet delivery. In this context, we thoroughly discuss the integration of satellite-based NTNs with 5G technology, which has become increasingly active in recent years, and studies are still ongoing to develop innovative frameworks to provide seamless connections to the extremely increasing density of high-mobility UE/IoT. The goal of this integration is to extend coverage and improve reliability beyond current 5G networks, enabling ubiquitous connectivity in remote areas and delivering high-speed data to UE/IoT. However, this integration poses numerous challenges in terms of mobility management, especially concerning the power constraints and signaling overhead of UE/IoT, as these devices are limited in battery power and processing capabilities. Handling these challenges is crucial to ensure successful integration and provide seamless connectivity to UE/IoT. In this paper, we highlight recent research efforts and potential solutions in these areas, contributing to the ongoing development of non-terrestrial 5G networks and improving global connectivity. To the best of our knowledge, this paper is the first study to emphasize and critically assess different mobility management solutions for satellite-based 5G NTNs, evaluating their impact on UE/IoT battery power consumption and signaling overhead, with implications extending to 6G networks.