With the advancement of the construction of space, space and ground integrated information networks, satellite communication systems nowhave a higher requirements for information transmission rate, satellite node storage capacity, satellite coverage and security. Traditional microwave communication methods are limited by bandwidth, speed, geographical location, spectrum, etc., and will be difficult to meet the ultra-high speed and ultra-large capacity communication requirements of multimedia broadband services for satellite networks. At the same time, laser communications are gradually becoming an important technical means for satellite communications due to its advantages of high transmission rate, high security and reliability, strong confidentiality, small terminal equipment, light weight and low power consumption. To achieve all-round coverage of communication signals, laser networking based on dynamic satellites and the establishment of high-speed, low-latency, high-reliability and large-capacity satellite communication systems will become the future development trend of satellite communication. In the future, space will inevitably gather a large number of products of human space activities, including rockets, satellites, and rocket ejections. As humans develop space, the increase in these space debris will also bring a series of hazards. Existing space debris research mainly focuses on how to avoid collisions with satellites and spacecraft in orbit. In addition, these space debris move randomly in space, which will block point-to-point laser communications. Therefore, more effective research on the reliability of satellite laser communication systems is needed.In order to solve the problem of inter-satellite link interruption that may be caused by space debris in low-orbit satellite laser communications, this paper proposes a Direction-enhanced Link State (DE-LS) routing algorithm. Firstly, the network topology of satellite communication is built. The polar orbit constellation model is selected. According to the orbital plane and the number of satellites, an initial and constant address is set for each satellite in the polar orbit constellation. Based on the changes in the satellite node addresses of the starting and ending points in different transmission tasks, the Direction Influencing Factor (DIF) is introduced. Then, based on the celestial motion patterns of satellites and space debris in polar orbit constellations. A joint simulation model of space debris and satellites is constructed to obtain the relative positions of satellites and debris at a given moment and to perform inter-satellite visibility analysis.. Based on the inter-satellite visibility data, a Direction Enhancement Index (DEI) is proposed corresponding to the four directions of each node. The direction impact factor and direction enhancement index are combined with the inter-satellite link distance and transmission delay to comprehensively represent the link cost. The cost is used as a measure to select the shortest path, and the shortest path is selected between each pair of satellite nodes in turn, and the number of routing hops is used as the evaluation index. The simulation experiment is carried out in the Walker constellation. Space debris and satellites are jointly modeled and simulated first. Then, in this environment, two situations are selected: the theoretical minimum number of hops in the same orbit is 4 hops and the theoretical minimum number in different orbits is 7 hops. Taking satellite communications No. 21 and No. 25 and satellite No. 21 and No. 55 as examples for routing selection, routing hop count and transmission delay are used as evaluation indicators, and compared with the Dijkstra routing algorithm, which also solves the shortest path. The simulation results show that the DE-LS algorithm can maintain the theoretical minimum number of hops when the link is interrupted. At the same time, it saves 14% of the hops and reduces the transmission delay by 17% compared with the Dijkstra algorithm, which reflects the effectiveness of DE-LS algorithm in avoiding faulty links.
当网络中出现碎片遮挡引起故障时,数据包往往因为通信路径的断裂而无法继续前向传输,此时需要重路由或者采用一定的动态路由策略来解决。关于卫星网络的故障管理,传统的方法是故障信息收集和全局广播,为路由计算提供基础,然后采用最短路径的方式进行路由计算。此类方式造成的开销较大,同时时效性较低,对于故障突发没有较好的恢复能力。基于此,LU Yong等提出基于有限状态自动机(Finite State Automata,FSA)的动态容错路由方法[6]来处理二维网格中节点故障,利用边界扩散和转发协议使得极轨卫星星座的通信故障率降低,但其构建故障区域较复杂且种类繁多,边界需要泛洪扩散的信息也较多,计算复杂度较高。文献[7]提出一种卫星网络链路状态路由(Satellite Networks Link State Routing,SLSR)方案,通过实时采集节点和链路故障信息,应对节点和链路故障异常,但是信息泛洪的开销要远大于原始链路状态算法的开销。QI Xiaoxin等[8]提出一种适用于倾斜轨道巨型星座的分布式生存路由算法,基于该星座网络拓扑的规律性,选取最小开销确定每对卫星节点对之间的主路径及多条备用路径。根据故障恢复机制,以降低链路故障时的端到端时延和信令开销,但其数据包容易因为拓扑早期的变化而被转发至非最优方案,从而产生更大的开销。赵扬提出了基于逻辑距离的概率分布式数据报路由算法[9],通过分析某链路故障对网络最小跳数的影响从而衡量其重要程度,保证数据在最少跳数前提下尽可能沿受失效链路影响最小方向前进,考虑负载均衡并提高对链路失效的抵抗能力,但其无法应对网络中实时的链路故障。
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