Research On SDN-based Low-Earth Orbit Satellite Network Architecture Design And Optimization

In recent years,low-Earth orbit(LEO)satellite networks have developed rapidly.Various LEO constellation projects such as Starlink and Oneweb emerging one after an-other are drawing more and more attention.However,traditional satellite networks have some problems,such as rigid and closed architecture,complex configuration and upgrad-ing,which makes new protocols or technologies difficult to implement and integrate with ground networks.The software defined network(SDN),a new architecture initially pro-posed in terrestrial networks,improves the flexibility of network control and management through the decoupling of the control and data planes.Therefore,the SDN-based LEO satellite network has become one of the research hotspots.Taking network architecture as the main line,this paper focuses on the design and optimization methods of the network architecture for specific problems existing in the SDN-based LEO satellite networks,such as the topology configuration design in the space segment,gateway placement optimiza-tion in the ground segment,SDN performance modeling and evaluation,SDN controller placement and so on.The main achievements of this paper are as follows:1.The overall architecture of SDN-based LEO satellite networks is carried out.Firstly,the overall architecture of SDN-based LEO satellite networks is proposed,and the structure of multiple controllers,co-located deployment between switches and con-trollers,in-band mode are discussed.Secondly,the time-varying graph model is used to mathematically abstract the network space segment,which is also the core part,to specify the satellite numbering method,and to illustrate the constellation configuration.On the basis of that,the spatial-temporal accuracy of LEO satellite networks is analyzed in order to solve the discrete approximation problem in theoretical analysis and simulation,and the user coverage division results and the conditions that the total simulation time should satisfy are obtained.Thirdly,the user traffic in the access segment is analyzed by taking the global population and flight distributions as the estimation data set,and the traffic distribution model of sub-satellite points is established.Finally,the network simulation and optimization platform is designed,including the satellite orbit dynamics part based on STK and MATLAB,the network numerical calculation and optimization platform based on Isight and Gurobi,and the network simulation platform with EXata and OMNe T++.It can effectively solve the problems caused by the lack of top-level architectural design in the previous studies,and it can also practically realize the design scheme of LEO satellite network architecture based on SDN.2.A topology design method for space segment of LEO satellite network is proposed.Firstly,the space segment topology design problem is proposed,which is de-termined by the constellation configuration and the establishment mode of inter-satellite links(ISLs).Secondly,taking the Walker constellation as an example,the coverage belt analysis method for constellation configuration design and the establishment mode of ISLs are discussed.Through the standardized formulation of the network topology,the network transmission analysis process is determined,and the design variables of the prob-lem are summarized.Thirdly,the design method of space segment topology configuration of LEO satellite networks is proposed,and the performance evaluation model of network topology configuration is established from three aspects: coverage performance,ISL es-tablishment performance and transmission performance.The principle of network access stability is proposed and proved.Accordingly,the analytical expression of network trans-mission performance is given.Finally,taking the Iridium constellation as a reference,the results of topology configuration design are presented.3.Aiming at the gateway deployment problem in the ground segment of LEO satellite networks,a gateway deployment optimization method based on traffic esti-mation is proposed.Firstly,a combinatorial optimization model of gateway deployment in the ground segment of LEO satellite networks is established.Given the alternative set of gateway sites,the design variable is defined as a binary multidimensional vector.The number of gateways and the traffic load balancing of them are selected as the optimiza-tion objectives,and thus a multi-objective nonlinear optimization model is established by considering the constraints of network physical layer such as frequency interference,antenna number and satellite bandwidth.The model is simplified by using weighted sum-mation method and penalty function method.Secondly,taking the database of global Internet exchange points as the alternative set of gateway sites to reduce the network de-lay and bandwidth resource overhead,the gravity model in the traffic estimation method is adopted to estimate the traffic matrix between gateways and satellites.Thirdly,the mod-ified discrete particle swarm optimization algorithm is used to solve the gateway place-ment optimization problem,and the complexity of it is reduced by fixing the number of gateways.Finally,the proposed method is applied to real satellite constellations,and the corresponding optimal gateway deployment solution is given.4.A priority queuing theory-based performance modeling and evaluation method for SDN-based LEO satellite networks is proposed.Firstly,based on the priority queu-ing theory,the research on SDN performance modeling and evaluation in SDN-based LEO satellite networks is carried out.The classical M/M/1/m queuing model and the priority-based M/M/1/m queuing model are derived,and the evaluation indices of the queuing system are obtained.Secondly,according to the SDN characteristics of LEO satellite networks,the problem of sharing the channel between control and data planes when con-trollers and switches are co-located is considered,and the performance of SDN controller and switch of satellite network is modeled.The system capacity,controller performance and switch performance are analyzed through simulation.Finally,the time latency anal-ysis results between controllers and switches are obtained by using the simulated traffic of on-orbit satellites.5.A static placement and dynamic assignment method for SDN controller in LEO satellite networks is proposed.Firstly,aiming at the placement of SDN controllers in LEO satellite network,a static placement and dynamic assignment(SPDA)method is proposed.The switch migration process is described in detail,the periodic topology of satellite constellation is analyzed,and an improved time snapshot division method is pro-posed.Secondly,the SPDA method is mainly divided into two parts: the first is to place SDN controllers on some fixed satellites by formulating a mixed integer programming model;the second is to dynamically assign switches to existing controllers according to switch-controller latency and traffic load of controllers.The static placement problem is modeled as a mixed integer programming problem.The static deployment solution of the controller is obtained through the network numerical calculation and optimization platform.Based on that,a heuristic algorithm is proposed to obtain the results of the dy-namic assignment of the controllers.Real satellite constellations are adopted to evaluate the performance of our controller placement solution.The results show that the SPDA outperforms existing methods in terms of reducing the switch-controller latency and it has good load balancing performance.In a word,this paper deeply studies the architecture design and optimization of SDN-based LEO satellite networks,proposes the overall network architecture and simulation platform design scheme,and studies the space segment topology configuration design method,ground segment gateway placement optimization method,SDN performance modeling and evaluation method,and SDN controller static placement and dynamic as-signment method.The related results have a certain application prospect,and can provide a theoretical reference for the design and construction of LEO satellite networks in the future.