Tackling Satellite Mobility in LEO-Based Non-Terrestrial Networks

Non-Terrestrial Networks (NTNs) will constitute a cornerstone of the next-to-come Sixth-Generation (6 G) technology. Specifically, Low-Earth Orbit (LEO) satellite constellations play a crucial role, either as a stand-alone networking solution or as a complement to terrestrial networks, in providing network access and services anywhere and anytime with lower latency than geostationary satellites. However, LEO's narrow coverage areas and mobility will likely cause service interruptions whenever the link between the NTN platform and NTN-Gateway (GW) (i.e., the feeder link) becomes unavailable. The Third Generation Partnership Project (3GPP) has defined a set of feeder link switch over procedures, which may lead to a long procedure duration and, hence, long service interruptions, especially in the case of NTN-GWs located far from each other. To cope with the mentioned issues, this paper proposes a novel feeder link switch over procedure, which exploits intersatellite links (ISLs) to implement, through a chain of LEO satellites, virtual visibility between a LEO satellite and an NTN-GW that are not in direct sight. This aims at reducing the time of feeder link switch over and avoiding service disruptions. The advantages of the proposed "ISL-aided" feeder link switch over procedure over the one defined by 3GPP are assessed via simulative campaigns.