Research On Link Selection Optimization For Efficient And Reliable Satellite-Ground Transmission

With the rapid development of space technology,space information resources have become particularly vital.Countries around the world have successively carried out the research and construction of space information networks.It is of both theoretical and practical importance to realize efficient and reliable information transmission for space information networks.In this context,focusing on satellite-to-ground transmission of the space information network,this dissertation studies the optimization of link selection based on relay cooperation,ground station(GS)diversity and satellite diversity,respectively.Our main contributions are summarized as follows:Firstly,we propose a novel capacity maximized relay cooperation mechanism for a two-layered satellite network which consists of geostationary Earth orbit(GEO)relay satellites and low Earth orbit(LEO)satellites.Specifically,we formulate a theoretical model of the network capacity under the proposed relay cooperation strategy.Furthermore,we optimize the system capacity under the ideal scenario,LEO access capability constrained scenario,and LEO on-orbit data constrained scenario,where the closed-form or semi-closed form solutions to the considered integer programming problems under different scenarios are obtained through rigorous mathematical analysis.Finally,we perform simulations to show that the proposed relay cooperation scheme exhibits superior performance when compared to the conventional methods.Then,regarding single-satellite free-space optical(FSO)networks,GS diversity is used to reduce the link outage probability caused by clouds,thus improving the network availability.We first formulate the problem of maximizing the network availability for a single-satellite FSO network.Then,we perform binary constraints relaxation and smooth function approximation to obtain a more tractable formulation.We further propose a gradient projection algorithm to solve the transformed problem,after which a binary solution is successfully obtained.By comparing with the existing algorithms,it is confirmed that the proposed method can achieve approximately optimal network availability performance with much lower computational complexity.Finally,we employ the additional satellite diversity gain provided by the multi-satellite FSO network to further reduce the impact of clouds on the satellite-ground link outage and to improve network availability.Firstly,the network availability optimization problem for a single satellite network is extended to multi-satellite networks.Next,we develop a minorization-maximization algorithm to deal with the rather complicated design problem under the multi-satellite network,by constructing a surrogate function as the lower bound of the objective function.In this way,we only need to calculate one semi-closed form solution per iteration.The proposed algorithm approaches the performance of gradient projection algorithm and exhaustive search without involving stepsize selection.