  Future satellite networks are expected to have thousands of low Earth orbit
(LEO) satellites orbiting Earth at very high speeds. User equipment (UE)
communicating directly with LEO satellites will experience frequent handovers.
Managing the handover process is complicated due to the high frequency of
handovers and the availability of multiple LEO satellites as handover targets.
In addition, as the status of the communication link between a UE and an LEO
satellite varies in accordance with the visibility period of the satellite,
initiating handovers at the right time will significantly affect the quality of
service (QoS) of the communication provided. To address this problem, this work
proposes a graph-based customizable handover framework that considers both the
handover timing and target while selecting a handover sequence that maintains
QoS. A time-based graph is designed where the vertices represent the
satellites' instances over a certain period of time and the edges' weights are
the customizable handover criteria (i.e., data rate and delay in this work).
The appropriate sequence and timing of handovers that fulfill the required QoS
are obtained by finding the shortest path in the graph. Discussion and
simulations, which were conducted on the Starlink Phase I constellation, show
the low complexity and performance advantages of the proposed handover
framework.
