Digital Twin‐Based Optimization of Service Availability in LEO Mega Constellations Considering Handover Delays in Open RAN

ABSTRACT As non‐terrestrial networks (NTNs) become integral to future 6G systems, ensuring seamless connectivity and service continuity over low Earth orbit (LEO) satellite constellations is essential. This work investigates the impact of open radio access network (RAN) functional splits on handover performance in NTNs, focusing on minimizing service interruptions. We propose effective service time as a novel availability metric that accounts for end‐to‐end conditional handover (CHO) delay, radio link failures (RLFs), coverage gaps, and constellation‐specific propagation dynamics—factors often simplified or ignored. Unlike baseline models that assume ideal, instantaneous switching with no protocol delays or topology changes, our CHO mode reflects 3GPP‐compliant, real‐world constraints. Leveraging a digital twin‐based satellite handover framework, we evaluate availability across multiple constellations, geographic regions, and Open RAN architectures (gNB onboard, Split 2, and Split 7.2x). Results reveal that increasing satellite density beyond a threshold yields diminishing returns, as denser constellations suffer more frequent handovers and higher downtime. For instance, a medium‐density constellation with lower altitude achieves an average of 11 min of daily downtime, which rises to 13–16 min under a denser deployment. In contrast, a higher altitude but sparser constellation provides only 5–7 min of downtime, benefiting from fewer handovers. Our analysis revealed that the claim of availability in LEO is impractical, where we demonstrated that maximum can be achieved with lower altitude constellations. Moreover, functional splits impact performance: Transitioning from gNB onboard to Split 7.2x can reduce availability from say about – . Finally, we construct a four‐dimensional suitability map to identify optimal constellation–architecture pairings across a variety of service requirements defined by delay, modulation, reliability, and availability. Notably, stringent 50‐ms delay requirements are not supported by higher altitude constellations despite their higher availability, whereas lower altitude constellations can satisfy them. This study provides valuable insights into NTN design, highlighting the interplay between satellite constellation, network architecture, and service‐level guarantees.