Research On Resource Management For LEO Satellite Cooperative Communications

Comparing with the medium and high orbit satellites,Low Earth Orbit(LEO)satellites have lower orbital altitude,shorter transmission delay,and smaller path loss.The low earth orbit satellite services have been widely applied in many fields such as real-time communication,remote sensing and so on.In the existing LEO satellite systems,data transmission mainly depends on single LEO satellite.However,the error rate is very high and transmission rate is considerably low.So the LEO cooperative systems made up of multiple satellites is proposed.This system can obtain diversity gain,improve reliability,expand the coverage of communication and prelong service time.Based on the high dynamic and limited energy characteristics,cooperative relay selection and power allocation are studied in this thesis,and the main works can be summarized as follows:Aiming at the existing problem that the relay selection strategies is only suitable for the situation that the perfect CSI can be obtained,while the satellites can not obtain real-time CSI in high dynamic environment.The relay selection scheme is proposed based on the ergodic capacity.First,the closed form expression for the ergodic capacity of the cooperative link is deduced in LEO cooperative systems where the inter-satellite link and the satelliteterrestrial link obey different distribution channel models.Furthermore,in considerations of the fairness of the cooperative nodes,we adjust the priority of the cooperative satellites dynamically with weighted ergodic capacity to balance the quality of the communication and the consumption of the cooperation energy.The final results show that the proposed scheme can realize a better trade-off between reliability and fairness,and the service time of the satellites is improved to some extent synchronously.On this basis above,we focus on the power optimization problem where the existing loworbit satellite power allocation algorithm scheme has not been discussed in the time domain,which can not adapt to the high dynamic satellites.The thesis utilizes the information of satellite orbit and channel statistics,and a new power optimization scheme based on time slices is proposed.Firstly,according to the characteristics of the LEO satellite communication link,the over-time is separated into time slices,and the relative quantization error of the received signal-to-noise ratio(SNR)is defined to measure its performance.Then the dynamic power optimization problem is modeled as -dimensional transmit power combined optimization problem to maximize the total throughput of the LEO cooperative system based on the condition that the total power is limited.The closed-form expression for N-dimensional transmit energy of the cooperative satellites is obtained by convex optimization method.The results show that this method can improve the reliability of the system and prelong the service time of the satellite to a certain extent.