Research On Link Resource Optimization And Routing Algorithm For Leo Satellite Laser Networking System

With the development of new launch technology,propulsion technology,and microsatellite batch manufacturing technology,low-orbit satellite constellations are being built at an unprecedented speed,and satellite communication is also developing towards networking.The inter-satellite laser communication with laser as the information carrier has the characteristics of fast transmission rate,high communication bandwidth,low power consumption,strong confidentiality,small size,lightweight,etc.,which can meet the ever-increasing demand for data rate and secure communication.It is the next breakthrough in the field of satellite communication.At present,domestic and foreign scholars have studied the relevant characteristics of optical satellite networks based on wavelength routing.However,there are still some problems to be solved: the number of on-board laser communication terminals is limited,so the resources of the links in the network are limited,and the number of visible satellites is more than that.The traditional Manhattan grid topology can’t make full use of the advantages of flexibility and freedom of laser link networking,so it is necessary to dynamically create an optimized topology according to the situation of visible satellites;The relativ e movement between satellites will cause the frequency offset in the received signal,which will accumulate in the routing in satellite networks supporting multi-hop.At the same time,when satellites change direction to establish communication links with other satellites,the Doppler frequency shift will produce a step change.Therefore,for the differential phase shift keying(DPSK)system using phase modulation,it is necessary to study the influence of the residual Doppler frequency shift on the bit error rate of the DPSK system;the routes corresponding to different network topologies need to be studied.Different network topologies have different routing algorithms.To adapt to the former,it is necessary to design routing and wavelength assignment algorithms according to the characteristics of satellite network topology.This paper takes LEO optical satellite network as the research object.In order to solve the above problems,this paper focuses on the topology design of LEO optical satellite network,the influence of Doppler frequency shift on the bit error rate of DPSK system,and the routing and wavelength assignment algorithm.The main research contents are as follows:A link assignment model based on vertex deleting using adjacency matrix(VDAM)is established.The adjacency matrix of network topology is used to assist link assignment,and links are selectively assigned to satellite nodes according to the weight of potential links,and delete the satellite nodes that have been assigned links from the current topology.The link assignment model solves the problems of large average hops and long propagation time in traditional network topologies;it solves the link assignment problem of the optical satellite network with the limit of the maximum allowable link hops of a single satellite;utilization ratio of onboard laser communication terminals is improved for scenarios with different numbers of onboard laser communication terminals.Taking the Ne LS constellation as an example,the proposed link assignment model is simulated and verified.In incessant link assignment,compared with the Manhattan Street Network(MSN)-LAS,Greedy-LAS and perfect match model(PMM)-LAS,the average hops of the network topology are reduced by 8.87%,3.13%,and 0.49%,respectively,and the average propagation delay is reduced by 17.24%,2.86%,and 0.8%,respectively.In intermittent link assignment,compared with the Greedy-LAS and PMM-LAS,the average number of hops are reduced by 10.45% and 6.89% on average;when the link assignment of communication terminals is not equal,compared with Greedy-LAS,the average number of hops is reduced by 5.92%,and the utilization ratio of communication terminals is 100%.A theoretical model of the residual Doppler shift of the satellite la ser networking system and the bit error rate of the DPSK modulated optical communication system is established.On this basis,the influence of the Doppler frequency shift step change on BER during topology reconstruction is analyzed;the influence of the Doppler frequency shift on BER under different link assignment models in the multi-hop optical satellite network is analyzed.The theoretical model has been simulated and verified,and the simulation results are consistent with the theoretical results.The results show that the bit error rate at the receiver of a single-hop link is mainly related to the Doppler step change when the link is reassigned.The bit error rate at the receiver of a multi-hop link is not only related to the Doppler step change but also to the accumulated Doppler frequency shift in the optical path.The results obtained here will be helpful in routing selection,link assignment,topology design,and system compensation.A multi-ant colony algorithm based on the hop-constrained heterogeneous sequential operation(HC-MACO)is proposed to solve the routing problem in the irregular network topology designed by the link assignment model of VDAM.The ant colony algorithm is combined with the layered graph model to realize the parallel calculation of routing and wavelength assignment,and the hop-constrained strategy improves the convergence speed of the algorithm.Compared with the classic Dijkstra+FF algorithm,it can reduce the blocking probability of the network and improve the resource utilization ratio on the basis of fast convergence.The effects of the number of available wavelengths,the number of service hops and the queuing rules on the communication performance of the optical satellite network are analyzed.In order to solve the problems of increasing blocking probability and decreasing wavelength utilization ratio caused by wavelength continuity constraint,a heuristic algorithm for wavelength converter placement is proposed for the irregular network topology,and the relationship between wavelength conversion gain and resource utilization ratio is analyzed.The research work of this paper lays a theoretical foundation for the networking of LEO optical satellite communication.The designed irregular topology makes full use of the flexibility of the laser terminal.An effective wavelength routing algorithm is provided for the irregular network topology.It also lays a theoretical foundation for the Doppler study of DPSK modulation communication systems.