Low-Blocking Dynamic Topology Control for LEO Satellite Networks with Real-time Connectivity

When people and things around the world are always connected in future, satellite networks will perform higher throughput and ensure real-time connectivity. To realize such a future, this research proposes a topology control method that reduces the blocking probability for real-time demands in a low-earth-orbit (LEO) satellite network system, which deploys an optical inter-satellite link (OISL) for increasing capacity. In conventional studies on dynamic topology control, effects of the routing layer and OISL-switching penalties were not accurately taken into account in the time-dependent system, making it difficult to discuss the impact of topology on the blocking probability. Therefore, we start by analyzing blocking causes in a time-dependent multilayer system comprising routing and physical-link layers and including OISL-switching penalties. The blocking causes can be classified into three types, and we found that the biggest issue in achieving real-time connectivity is blocking caused by the switching penalties. To reduce the switching-induced blocking, we introduce the concept of "connectivity depth" and propose an algorithm to maintain the connectivity depth to solve the problem. The proposed method showed the best blocking probability compared to conventional methods, regardless of the constellation type such as Walker-Delta or Walker-Star, and achieved blocking probability of less than 1e-3. Even in more dynamic Walker-Delta type constellations, the proposed method improved switching-induced blocking probability by 54-80% compared to the conventional methods.