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.