Dynamic Routing in Space-Ground Integrated Quantum Networks

Quantum networks emerge as fundamental frameworks for addressing various large-scale problems. There are two primary architectures: space-based quantum networks, which deploy satellites with free space channels to interconnect users, and ground-based quantum networks, which utilize optical fibers to interconnect users. In this paper, we explore space-ground integrated quantum networks that incorporate both satellites and optical fibers into the infrastructure. This integrated network features three forms of communication: using only free space links, only ground links, or a hybrid usage of free space and ground links. We formulate the routing problem in space-ground integrated quantum networks as an integer programming and propose two solutions: using a linear relaxation and a greedy algorithm. The linear relaxation algorithm allows timely scheduling of additional entanglement purification, whereas the greedy algorithm enables quick scheduling. Simulation results demonstrate their effective balancing between network throughput and communication fidelity.