GEMS: GAT-Embedded Mobility for Dual Connectivity in Integrated Terrestrial and Non-terrestrial Networks

Non-terrestrial networks (NTNs) are advancing with multi-shell dense satellite constellations, offering sufficient capacity and enabling system-level integration with terrestrial networks (TNs). In this context, adding and maintaining secondary satellite links via dual connectivity (DC) in integrated TN-NTN systems enhances service quality for users underserved by TN coverage. However, satellites operating in diverse orbits and altitudes exhibit heterogeneous signal characteristics and coverage windows, posing challenges for maintaining effective DC configuration under time-varying TN-NTN coverage overlap. To address this, we propose a mobility-aware DC configuration and continuity management framework for dynamic TN-NTN environments. First, all DC admissions are modeled as an optimal user equipment (UE)-satellite bipartite graph matching problem for spatial NTN link allocation. The graph is then temporally extended to capture satellite mobility and handover (HO) opportunities. A graph attention network (GAT) generates UE-specific mobility-aware edge weights, enabling path-level DC configuration that balances instantaneous throughput gains with long-term service continuity. System-level evaluations with practical satellite constellations demonstrate the proposed framework significantly outperforms existing repeated and snapshot-wise DC configuration methods in both service rate and signaling efficiency. By fully exploiting TN-NTN coverage asymmetry and mobility dynamics, the proposed scheme ensures robust and sustained DC performance across diverse scenarios.