Research On Satellite Link Optimization And Analysis Technology For Multi-layer Satellite Networks

With the rapid development of information technology,the status of satellite network becomes increasingly important in the global data communications.It can not only provide seamless global coverage and continuous high bandwidth performance,but also support flexible and scalable network configuration.Presently multi-layer satellite networks is one of the focus of attention and research about satellite network,satellite networks can generally divided into GEO satellite networks,MEO satellite networks and LEO satellite networks.GEO satellites located in geostationary Earth orbit,whose altitude is 35786 kilometers.In summary GEO satellites have the advantages of large coverage and big computing ability,on the other side the GEO satellite networks have a high propagation delay and are not suitable for transmitting real time information because of the altitude of orbit.Comparatively LEO satellites with lower orbit have low signal delay,however in LEO satellite networks,the coverage area is small and LEO satellite networks have a worse stability for the frequent changing of satellite-ground links.With the orbits whose altitudes between LEO satellites and GEO satellites,the MEO satellites' characteristics are in between.An efficient combination of different layers of satellite networks,both advantages of different layers of satellite networks,and avoid the disadvantages of them is an important way to make a better performance.With the increasing level of information technology and the frantic growth of information,both civilian and military,the demand for large capacity and high speed communication technology is very urgent.Therefore,multilayer satellite network transmission technology has become the frontier technology in the field of spatial information system and the research hotspot of scholars at home and abroad.In this paper,the link analysis and optimization technology in multi-layer satellite network is studied.Based on the research of the link analysis and optimization technology in multi-layer satellite network,this paper focuses on the satellite constellation design method,the carrier synchronization algorithm of satellite communication,the link margin analysis of inter-satellite laser link,and the optical communication acquisition tracking and pointing technology.The main research work of this thesis is as follows:(1)Aiming at the problems of insufficient coverage of satellite network,low elevation angle of communication and high real-time and reliability requirements of emergency communication,a multi-layer satellite constellation combining GEO,MEO and LEO satellites is proposed.The results show that Comparing with the current single-layer satellite network in orbit,the designed multi-layer satellite network constellation has significant advantages in terms of coverage multiplicity and communication elevation in the middle and low latitudes,and has strong inter-satellite link connectivity,so it is suitable for the transmission of emergency communication service at medium and low latitudes,lays a foundation for the research of inter-satellite link technology in this paper.(2)Aiming at the problems of large dynamic range of Doppler frequency offset and short communication time in satellite data transmission system based on multi-layer satellite network,etc.The paper studies the carrier synchronization methods under the situation of large Doppler frequency,presents a carrier synchronization method based on the improved COSTAS loop for Data Relay Satellite System.Simulation shows that the proposed carrier synchronization method brings out not only better BER performance compared with tradition COSTAS loop under large Doppler frequency,but also larger track range compared with tradition COSTAS loop.(3)Aiming at the problems of remote communication distance and limited onboard load capacity of satellite in multilayer satellite network,the communication distance,laser emission power,satellite load and other factors in satellite optical communication system are studied and analyzed.The laser link margin is obtained to meet the requirement of laser communication between different satellites in the integrated information network.The research results show that the current optical terminal performance can meet the requirements of the optical communication link of heterogeneous satellites in multi-layer satellite networks.(4)Aiming at the problem of lightweight and miniaturization of satellite optical communication terminals and inter-satellite optical communication in multi-layer satellite networks,researches and analysis beaconless light tracking and acquisition technology in satellite optical communication.The track and the capture process is designed,the influence of satellite platform attitude error,inter-satellite link communication distance and other factors on capture time and capture probability are simulated and deeply analyzed.The research shows that in the beaconless tracking acquisition scheme of the multi-layer satellite network optical communication,the probability of capture can meet the requirements of optical communication links of different orbit satellites in multi-layer satellite networks,and the current performance of optical terminal module and multilayer satellite network can be realized.