| Space is another new area of activities and development for human following the land, the sea and the air. As the vital nexus between the integrated information systems of land, ocean, air and sky, the Space Information Network is a strategic infrastructure. However, limited resources, as well as wireless communications make the performance of the network closely bound up with its topology. Unreasonable network topology will reduce network capacity, increase packet transmission delay and weaken network robustness when faced by node failures. Hence, topology control is an effective measure of great significance to improve the overall performance of the Space Information Network.The characteristics of the Space Information Network, such as self-organizedm, with large amount of redundancy, task partition, more long-distance links and high link error rate, are considered to propose a distributed fault-tolerant topology control algorithm based on a hierarchical network. The algorithm has three phases, which are intracluster topology control, intercluster topology control and topology maintenance. The aim of the first phase is to ensure the intracuster network k-connected through maintaining k optimal node-disjoint paths between a node and the nodes in its vicinity, as well as remove redundant links. In the second phase, the topology, consisted of the selected border nodes which can communicate with nodes belonging to the adjcacent clusters and the links empowered based on transfer delay between them, can be mapped into bipartite graph, and then to maintain k node-disjoint paths between adjacent custers by calculating the optimal matching of the empowered bipartite graph. After calculating the topology, nodes adjust their transmission power based on symmetry mechanism. The aim of the third phase is to guarantee good network performance in the running phase.The network simulation software NS2 and emulation platform were adopted to evaluate the proposed control algorithm. Simulation results demonstrate the algorithm can optimize network topology and improve network wide-performances, such as reducing the average node degree and interference effectively to increase efficiency of wireless channels and throughput of networks. saving nodes'energy to prolong the life of the network, reducing the probability of using long-distance links to reduce the communication delay, and guaranteeing good invulnerability and fault tolerance for the network with the overhead not increasing. |
