# A Routing Optimization Method for LEO Satellite Networks with Stochastic Link Failure
###### Abstract  
In this paper, for an Low-Earth Orbit (LEO) satellite network with inter-satellite links, a routing optimization method is developed in the case of stochastic link failure. First, a discrete-time strategy is used for the satellite network to acquire several static topological graphs during a cycle. Based on the static topological graphs regarding stochastic link failure, a constraint model is established that constructs the task revenue, switching times and routing cost as indicators. Then, an improved Genetic Algorithm based on A* is proposed to optimize the topology under the constraint model. In particular, to reduce the cost of computation, a new generation strategy for the initial solution is presented which combines the roulette wheel operator and the A* algorithm. Finally, the effectiveness of the proposed method is illustrated by a group of numerical simulations for the network with stochastic link failure.  
routing optimization; stochastic link failure; LEO satellite networks +
Footnote †: journal:  
0000-0001-5399-2222-3/00/00001-5399-2222-3/00  
laser link (ISLL), a random link allocation scheme was proposed, which randomly generates a connected network topology and has the goal of maximizing the number of links, showing that the logical connections to be formed depend on the line-of-sight visibility of satellites.  
In terms of ISLL, due to the platform vibration, internal system noise and pointing error, there is a possibility of failure in satellite links [19]. In [20,21]; with the assumption of constant probability of failure and transmitted power, the modified Rayleigh method was used to calculate the pointing error and the optimal root-mean-square width of the Gaussian beam. In [22], based on the space optical communication link equation, the signal-to-noise ratio equations were given for the inter-satellite coherent optical receiving system with different aberrations.  
In this paper, for an LEO satellite network, we establish the model with stochastic link failure, based on the task revenue, switching times and routing costs. To tackle this challenging problem, an improved Genetic Algorithm (GA) is proposed which changes the means of initial solution generation. The main contributions of this work are stated as follows:  
1. Different from previous studies [23,24], we consider the case of ISLL failure by treating communication tasks as stochastic events and calculate the probability of failure in the network.
2. To optimize the topology of the network, the improved Genetic Algorithm based on A* (GA-AS) is proposed, including a new initial population generation strategy that produces initial solutions to provide an optimization direction, resulting in effectively reducing the computation cost.  
The remainder of this paper is organized as follows. The LEO satellite network model, including optimization constraints and objective functions, is established with stochastic link failure in Section 2. In Section 3, the GA-AS is proposed and the improved A* strategy is explained in detail. Simulation results under different task scales and population size are presented in Section 4. Finally, conclusions are provided in Section 5.