This paper addresses the challenges of feeder link switching in non-terrestrial networks (NTNs) by leveraging low Earth orbit (LEO) mega-constellations with multiple shells and multiple gateway (GW) deployments. Due to the high mobility of LEO satellites and frequent feeder link disruptions, it is critical to maintain reliable feeder link connectivity. To tackle these challenges, we propose a novel bilevel optimization framework that combines virtual network embedding (VNE) with advanced feeder link switching strategies. To manage the trade-off between link quality and switching frequency, lower-level optimization maximizes the data transmitted per feeder link connection using a path-finding algorithm with bisection search. The upper-level VNE problem enhances the connectivity between the satellites in the LEO mega-constellation and the ground infrastructure by constructing a dedicated virtual network for NTN GWs. Simulation results based on the Starlink Gen II constellation demonstrate that our proposed method consistently ensures 100% satellite activation, while baseline benchmarks achieve 93% satellite activation rates in the real-world GW deployments. Our optimization framework is well-suited for multiple shell deployments of LEO mega-constellations with multiple GW supports, paving the way for globally connected NTNs.

This paper proposes a globally scalable multicontroller software-defined networking (SDN) framework tailored for low Earth orbit (LEO) mega-constellation. To handle the rapidly changing topology and massive scale of such networks, the novel topology virtualization technique and dynamic mapping strategy are introduced. The framework creates a stable logical network abstraction of the moving satellites that shields the control-plane from constant topological changes. Unlike conventional approaches that require frequent intercontroller cooperation, we formulate a location-based linear assignment problem and derive a closed-form mapping solution to directly assign satellites to SDN controllers without additional cooperation. Extensive evaluations on the Starlink Gen II constellation demonstrate that our framework achieves efficient load balancing among Earth-fixed cells across LEO mega-constellation while significantly reducing computational complexity. Our main contribution is to address the critical challenges of mobility management in dynamic, global-scale LEO mega-constellation, thereby paving the way for enhanced global coverage and efficient use of resources in next-generation communication systems.

In cellular networks, authorities may need to physically locate user devices to track criminals or illegal equipment. This process involves authorized agents tracing devices by monitoring uplink signals with cellular operator assistance. However, tracking uncooperative uplink signal sources remains challenging, even for operators and authorities. Three key challenges persist for fine-grained localization: i) devices must generate sufficient, consistent uplink traffic over time, ii) target devices may transmit uplink signals at very low power, and iii) signals from cellular repeaters may hinder localization of the target device. While these challenges pose significant practical obstacles to localization, they have been largely overlooked in existing research.