Mega-constellation Low Earth Orbit (LEO) Satellite Networks (LSNs) have become an ongoing projection to realize the ubiquitous large-capacity wireless communication. With the rapid growth of satellite scale, the transmission efficiency of Mega-constellation LSNs is substantially decreased as the Average Shortest Path Length (ASPL) is dramatically increased, which not only encumbers the high-speed data transmission, but results in more processing delay, cost of satellite energy, rerouting probability and loss rate of packets. To this end, this paper proposes the structural optimization methods of Two-Layered Satellite Networks (TLSNs) to enhance the transmission efficiency of Mega-constellation LSNs. Differing from the traditional TLSNs, the proposed TLSNs emphasize on the highly integration between the different layers. The evaluated results confirm that the proposed methods not only effectively enhance the transmission efficiency of mega-constellation LSNs, but significantly increase the duration time of Inter-Layer Links (ILLs) and reduce the topological dynamics of TLSNs deriving from the switching of ILLs.

In this letter, we explore the link-adding method to improve communication robustness of networks. Firstly, a robustness measure called communication robustness (CR) is presented, which not only confirms the global effect of the largest connected component on the network communicability, but captures the local communicability of all small connected components. Secondly, we respectively put forward a simulated annealing algorithm, a heuristic algorithm called r-Weak Interconnection Algorithm (r-WIA) and a greedy algorithm to improve CR of networks, where the 2-WIA can fast improve the network robustness with low time complexity O(N2). Finally, the experimental results verify the effectiveness of the proposed algorithms.

Network structure has significant impact on its data transmission and robustness. This article presents a framework to evaluate the structure performance of dynamic networks, with a focus on measuring the topological dynamics and assessing its effect on routing, transmission efficiency, network robustness, and network capacity. Based on this framework, the structural performance of satellite networks including both single-layered and multilayered satellite networks is evaluated systematically. The performance results reveal that it is difficult to design the efficient and feasible transmission protocols for multilayered satellite networks for their high-dynamic topologies with irregular changes, which brings unpractical requirements on the routing update. To cope with this problem, a synchronization mechanism of the interorbital links for multilayered satellite networks is presented, which can significantly reduce and regularize the topological dynamics of multilayered satellite networks. Its advantages can effectively facilitate the realization of transmission protocols for multilayered satellite networks. Finally, the experimental evaluation results demonstrate the effectiveness of the proposed strategy.

In this letter, we prove that both the centralized and distributed routing schedule problems are NP-complete in 2D Mesh topology, which further enhance the complexity result of the routing schedule problem based on the complexity theory. Moreover, we prove that the Minimum Path Stretch Schedule (MIN-PSS), Maximum Path Contraction Schedule (MAX-PCS) and Maximum Constant Path Schedule (MAX-CPS) problems are NP-hard in predictable dynamic networks. Our conclusions provide the theoretical significance for the routing optimization.