Topological design and routing for low-Earth orbit satellite networks

We investigate a topological design and routing problem for low Earth orbit (LEO) satellite communication networks where each satellite can have a limited number of direct inter-satellite links (ISLs) to a subset of satellites within its line-of-sight. First, we model LEO satellite network as a FSA (finite state automaton) using satellite constellation information. Second, we solve a combined topological design and routing problem for each configuration corresponding to a state in the FSA. The topological design (or link assignment) problem deals with the selection of ISLs, and the routing problem handles the traffic distribution over the selected links to maximize the number of carried calls. This NP-complete mixed integer optimization problem is solved by a two-step heuristic algorithm that first solves the topological design problem, and then finds the optimal routing. The algorithm is iterated using the simulated annealing technique until the near-optimal solution is found. The link assignment table and the routing table that are pre-calculated off-line for each state are loaded into the satellites and a new set of these tables are retrieved at each state transition. The simulation result shows that the proposed method is applicable to practical LEO satellite networks.