The Key Technologies Of Data Transmission In Spacecraft Cluster Network With Interferometric SAR Missions

Spacecraft cluster with interferometric SAR missions is an innovative application of spacecraft system in Earth observation,which effectively combines the advantages of distributed cooperative work pattern and multidimensional SAR interferometry technology,but there are still many deficiencies in the related research.Therefore,some thorough research on the key technologies of data transmission strategy of spacecraft cluster network with interferometric SAR missions has carried on.The main contents of this dissertation are consist of the following parts:Based on the spacecraft dynamic model with J2 perturbation and HILL equation,the motion model of spacecraft cluster is established.And with the graph theory,the basic graph structure of SCN is constructed,and a research method of the multiple-time slot and static topology control strategy is proposed for the time-varying network topology.Also,the data flow in SCN is described and defined with the M/M/1 model in queuing theory,and its transmission properties under the case of multi-hop is analyzed.Based on the graph theory and queuing theory,models of SCN,the interferometric SAR missions and its Poisson data flow are established,and the network topology construction methods within and between clusters are given according to the antenna direction and the signal free space attenuation models.Using the network simulation software NS-3,the SCN simulation model is established and its validity is also verified.Then,from two perspectives of topology time-varying and different network load,the problems of the current routing algorithms applied in SCN are analyzed,and the improvement methods of data transmission performance in SCN are clarified.According to the spacecraft relative motion model,the spacecraft distribution model of a bounded space in SCN is established,and the parameters of this bounded space,such as distribution density and volume,are analyzed.Then,based on the proposed multipletime slot and parallel transmission strategy and the optimal multi-hop routing method,the network capacity mathematical model under delay constraints is constructed.Also,the relationship among the average delay,the routing parameters and the network capacity is analyzed.Finally,the effectiveness of the proposed network capacity model is validated by comparing with the simulation results.Based on the first-order radio frequency energy consumption model,a model of single hop and multi-hop data transmission is proposed for SCN with interferometric SAR missions.Then,based on the ESMT graph theory and the proposed reliability link metric,a reliable and dynamic topology control method for the collaborative missions is proposed.The simulation results show that the topological control strategy based on the reliability priority of the graph structure can improve the stability of the information interaction of the spacecraft under dynamic motion.Using ARIMA and wavelet neural network combined prediction model,the linear and nonlinear parts of the network load in SCN are predicted.Considering the uncertainty of inter-cluster communication link,a method for estimating the survival time of intercluster links is proposed using the Doppler frequency shift during information interaction.Based on the traditional OLSR algorithm and reliable topology control strategy proposed in this dissertation,a load-balancing data routing strategy(OLSR-LB)combining central control and distributed transmission is constructed to solves the problem of load balancing of network data transmission by introducing the average load forecasting mechanism in topology time slots as well as local congestion processing method.The simulation results show that the load balancing OLSR-LB routing strategy can adapt to the dynamic change of the topology of the spacecraft cluster network and the variation of load,which has certain engineering application value.