Enhancing Resource Utilization of Non-terrestrial Networks Using Temporal Graph-based Deterministic Routing

Non-terrestrial networks (NTNs) are expected to provide continuous and ubiquitous connectivity across the globe. We identify that deterministic routing is a promising technology to achieve high resource utilization and strict QoE guarantee in NTNs. However, due to the time-varying topology, dynamic bandwidth and long propagation, for establishing deterministic services, it is not only difficult in finding stable end-to-end (E2E) routing, but also complex for joint routing and scheduling. Towards this, we propose an optimal solution based on temporal graphs to enhance resource utilization and service capability of NTNs. First, an extended time-expanded graph (ETEG) with introduced virtual nodes and edges is constructed to uniformly model both heterogeneous resources and traffic requirements. Then, we recast the deterministic routing problem as an integer linear programming (ILP) problem, by linearizing the constraints containing variable-dependent summations, round-down operation and multiplication of nonlinear terms. With the solid upper bound by ILP-based scheduling, we further propose a low-complexity ETEG-based shortest time-featured path algorithm to jointly use transmission and storage resources to support dynamic queuing and cross-cycle transmission of packets, thereby determining the best outgoing link and forwarding cycle hop-by-hop. The optimality and complexity are analyzed, together with simulations to verify the superiority of proposed algorithm in traffic acceptance, E2E delay and running time.