Non-Terrestrial Networks for 6G: Integrated, Intelligent and Ubiquitous Connectivity

To enable seamless 5G service continuity for mobile ground users traversing infrastructure-limited or obstructed regions, the integration of Non-Terrestrial Networks (NTNs) based on Low Earth Orbit (LEO) satellite constellations is being actively pursued. However, the mobility dynamics of ground terminals frequently result in sudden Line-of-Sight (LoS) loss, which undermines the feasibility of conventional handover preparation involving context transfer, synchronization, and identity continuity. Without pre-coordination, such transitions lead to uplink blindness, session interruption, and degraded performance. This paper addresses the handover problem under NTN-specific constraints by (i) defining a structured taxonomy of service continuity mechanisms suited for LoS-impaired conditions, (ii) introducing an analytical model that captures handover delay, authentication feasibility, and buffer dimensioning under varying visibility regimes, and (iii) quantitatively evaluating these metnisms in a high-mobility highway scenario. The results underline that while context mirroring ensures superior continuity under full coordination, handover with reactive preparation emerges as the most practical and resilient fallback under constrained NTN conditions.