Research On Transmission Technology In Moon-to-earth Communication Based On GEO Relay

Moon is the only natural satellite of the Earth,and rich in material resources and energy.It also can be used as the best platform for human to study the universe and the Earth.The platform is more convenient for other deep space exploration activities.In the lunar exploration,the normal operation of communication system is an important guarantee for the successful lunar exploration mission.In order to make use of deployed satellites formation and spacecraft resources on the Earth space at present,this paper proposed the signal receiving platform combined space-based with ground-based antenna array.This platform uses geosynchronous orbit(GEO)satellite formation with ground stations to form cooperative receiving array,which collects the signal energy in a wider range,improves the effectiveness of space communication,and services on the future lunar exploration activities,such as,landing on the back of the moon,manned lunar landing.Based on this background,the influence of satellite formation and its perturbation is studied.Then,the communication scene is modeled,and the influence of perturbation factors is introduced.Finally,the system outage probability and the average symbol error rate index are studied and analyzed.The main research work of this paper is divided into the following three aspects:The GEO satellite formation is designed to achieve 24 hours of ground continuous monitoring for the lunar landing plan of the three phase lunar exploration project of China.By the constraint of the space round formation configuration,the motion equation of deputy satellite is derived from the equation of the chief satellite and relative motion between them.The GEO satellite is mainly affected by the Earth gravitational perturbation,third body gravitational perturbation and solar radiation perturbation.This paper analyzes the effect of three kinds of perturbation factors on the track of satellite.The theoretical analysis and simulation results show satellite perturbation makes the distance constantly changing between signal receiver and sender,and causes the formation configuration gradually divergent.Combining with Kashi and Qingdao stations form the joint receiving platform that is used to receive the communication signals from Chang'e 3.The results show that the proposed joint receiving platform combined space-based with ground-based can realize uninterrupted communication of Chang'e 3,and improve the effectiveness of communication links through the GEO satellite formation.The transmission channel model based on moon-to-earth communication downlink was built based on the joint receiving platform combined space-based with ground-based antenna array.Compared to the current research on hybrid satellite terrestrial cooperative networks,the cooperative relay node is extended to space from ground firstly.In this model,the source node is the lunar node,the relay node is a GEO formation satellite which is connected with the source node and destination node and has the best channel state.The destination node is the ground station which has the best connection with the source node or relay node in the ground station group and the channel state is the best.Using the maximum ratio combining and selection combining principle at the destination node,the relay node adopts with amplify-and-forward protocol.Each node is equiped with the single antenna.Then the end-to-end output signal to noise ratio(SNR)is derived.Then,each communication link in the model are analyzed,and the antenna pointing error and pointing loss are discussed.The analysis results show that the satellite perturbation makes the distance continuously changing between signal receiv er and sender,which causes antenna pointing loss and antenna pointing error,and affects the communication performance.In addition,the influence of satellite perturbation on the reliability and effectiveness of communication system is analyzed firstly.In the transmission model based on moon-to-earth communication downlink,assuming the source-relay node experiences Rician distribution,source-destination node and relay-destination node follow Shadowed Rician distribution,the theoretical expressions of a verage symbol error rate and outage probability are derived through the integral operation and approximate treatment.We also consider the satellite perturbation.Due to the perturbation causes by satellite antenna pointing error,which leads to changes on the fading channel model parameters.Furthermore,the changes cause vary on average symbol error rate and outage probability.Then,the rationality of the model is verified by simulation.And the relationship between satellite perturbation and outage probability and average symbol error rate is shown intuitively.There is the fact that satellite is always affected by various perturbation forces in the space environment.Thus,the influence of satellite perturbation on the communication system performance is considered in this paper,which is more in line with the actual signal transmission environment.