基于遍历容量的低轨卫星协作通信中继选择算法

在低轨卫星通信系统下行链路中引入协作技术，可获得协作分集增益，从而减小信道衰落的影响。目前在目标通信区域内多星的覆盖率非常高，合适的中继卫星选择策略对于提升卫星通信网络的整体性能至关重要。针对这一问题，本文提出一种基于遍历容量的中继选择算法。该算法借助卫星轨道信息以及统计信道信息，综合考虑卫星本身载荷受限和高动态的特点，通过公平性因子进行遍历容量和能耗之间的折中，选择具有最佳权重遍历容量的节点作为协作卫星。并在此过程中，得到了卫星间协作链路信噪比概率密度闭式表达式，该表达式用来求解协作链路遍历容量。仿真分析表明，该方法可以动态的调整协作卫星的优先级，在误比特率性能和公平性之间可以达到很好的平衡，并且可以在低EIRP情况下提高卫星的服务时间。 

Ergodic capacity based relay selection algorithm in LEO satellite cooperative communication

Cooperative diversity transmission technique is introduced in the downlink of the Low Earth Orbit (LEO) satellite communication system. This technique can achieve cooperative diversity gain to reduce the influence of channel fading. In addition target coverage area always has multiple satellites. Suitable relay satellite selection strategy is critical for LEO satellite systems to enhance the overall performance. A ergodic capacity based relay selection scheme is proposed to solve this problem. The algorithm, with the Satellite orbit information, compromises between ergodic capacity and power consumption, and then chooses the satellite which has the best weighted ergodic capacity from the optional set as the cooperative satellite of this time, considering the characteristics of the satellite limited load and high dynamic. And in the process，exact closed-form is derived for the probability density function of SNR of cooperative link. This is used to obtain the first exact integral solution for the ergodic capacity. Simulation results show that this scheme can dynamically adjust the priority of cooperative satellites and achieve a good balance between BER and fairness performance. The proposed method can extend the satellite service time, especially when EIRP is low.