Research On Key Technology Of Gateway Station In Geostationary Earth Orbit Satellite Mobile Communication System

Geostationary earth orbit(GEO)satellite mobile communication system which utilizes GEO communication satellites as relays adopts advanced technologies such as space division multiplexing,cellular-like network management and control.This system has many advantages,including large capacity,providing service for small terminals,simple network control,seamless coverage and so on,which enables the system can be widely used in forestry,fishery,water conservancy,meteorology,military communications and so on.In recent years,such as flood,earthquake,typhoon,tsunami emergencies happen frequently,as well as the state visit,Olympic security,and other major activities is increasing.The satellite mobile terminals plays a more and more important role in the field of emergency communication support,and the application prospect of satellite mobile communication system is also wider and wider with the increasing demand of users.GEO satellite mobile communication system is mainly composed of gateway station,communication satellite and various mobile terminals.As the most important equipment of this system,gateway station is the center of system management,exchange and control,which is responsible for the processes of system signal access,user authentication management,business admission control,data exchange and so on.In this paper,the current development of satellite mobile communications at home and abroad is first introduced and the overall framework of gateway station is further studied by referring to the design ideas of ground mobile communication system.Then,several key technologies of the gateway station are proposed and corresponding solutions are put forward.Finally,through the joint efforts of team members,the first gateway station of satellite mobile communication system was designed and implemented,which is not only autonomous totally by our country but also capable of supporting millions of users.In the design and implementation processes of gateway station,the author not only participates in the overall framework design of gateway station,but also is responsible for the networking design and hardware selection of the access network.Besides,the author proposed and broke through three key technologies,including multi-carrier demodulation,system synchronization,and system testing.The main contribution is as follows:Firstly,through the research of multi-carrier demodulation technology,the efficient digital signal processing structure is adopted.In order to improve resource utilization efficiency and extend the system flexibly,signal sampling,data transmission between processing units,low-pass filtering and carrier demodulation are combined and arranged in a unified way.The demodulation processing of nearly a hundred carriers is achieved in a single processing borad,which not only greatly simplifies the hardware architecture of multi-carrier system but also cuts the cost of gateway station.Secondly,through non-central system synchronization technology,the problems of timing and synchronization for TDMA satellite mobile communication system is solved.The problems includes timing offset problem caused by satellite's relative position change,Doppler shift problem caused by satellite motion,synchronization problem between multiple gateway stations,and the timing and frequency synchronization problem between multiple baseband and RF processing equipment.Thirdly,faced with such a huge and complex system,a test scheme based on software simulation as well asreal equipment is proposed for the development and acceptance test of the gateway station.This paper sortsand analyzs the schemes,methods and results of the tests,and the results verify the function and performance of the gateway station.In the end,the paper combines the development of software-defined network(SDN),network function virtualization(NFV),and "cloud" base stations in terrestrial mobile communications,and how to achieve network virtualization and how to improve spectrum utilization.Efficiency,how to provide a more open platform and so on put forward a look forward to the structure of a new generation of gateway stations.