| With the rapid development of aerospace technology,many countries have started to develop deep space communications.Due to the celestial and satellite movement,communication links are often interrupted due to celestial occlusion,and the data will not be transmitted back in time during the link interruption period.As we can see,the traditional point-to-point direct communication and spacecraft relay cannot satisfy the communication demand.The space communication is changing from several independent systems towards the integration of multiple interconnected spatial information networks.It has been a trend to construct a deep space relay network.In the future,deep-space relay network will contain telemetry,remote control,voice,navigation and other real-time communication missions.It is required that the network could not only provide continuous and reliable network connection,but also can return the data from deep space to the ground station as soon as possible.Because the network topology reflects the communication delay of the entire network,and the network topology directly represents the link connection relationship between all network nodes,we need to study how to assign links between network nodes to construct a network topology with low communication delay.In this paper,for the purpose of reducing communication delay,the deep space link assignment problem will be studied from the following three aspects:First,considering the number of satellite communication terminals and the network connectivity constraints,the problem of network link assignment was studied with the objective of minimizing end-to-end average delay.To solve this problem,this paper proposed a link assignment algorithm based on the idea of competition-decision and a link assignment algorithm based on simulated annealing.The algorithm experiment simulation proved that the proposed algorithms could get smaller end-to-end delay than the greedy algorithm.Then,considering that in deep space network,it takes a long time to finish a link handover(the link will be considered in an interrupted state during the handover process),which brings a huge communication delay and seriously affects the communication quality in the meanwhile.Therefore,from the perspective of reducing the delay of link handover,and considering the communication terminal and network connectivity constraints as well,this paper established a mathematical model and proposed a link assignment algorithm with the aim of minimizing the delay of link handover.The effectiveness of the algorithm was proved by simulation experiment.Finally,considering that deep-space relay network has the characteristics of exposure,high dynamics,harsh operating environment and high maintenance costs,the network topology should also be more resilient.Therefore,based on the previous work,the network survivability was improved by backup paths while designing the link assignment algorithm.We proposed a link assignment algorithm with high survivability and minimizing the delay of link handover time.The effectiveness of the algorithm is then proved by experiment simulation. |
