| The Space & Ground Integrated Information Network consist of various spacecraft,near space vehicles,ground stations and other equipment through interplanetary and satellite links.In the global remote sensing,observation and Information transmission,etc.with great social,economic and military value.With the development of integrated information network,the rapid growth of the number of space vehicles,various types of monitoring and control tasks and data transmission tasks are also increasing,which on the space measurement and control system put forward higher requirements.For a long time,land-based and ocean-based Telemetry Track and Command(TT&C)systems are the major TT&C methods in China,and the infrastructures include telemetry stations and telemetry ships.Due to the limited coverage of ground-based facilities and the short skip-over time of low orbit spacecrafts,the land-based and sea-based TT&C system don't have the ability of continuous long time tracking.With the successful launch of TianLian No.1 series GEO satellites,China has became the second country with the quasifully covered low-orbit relay satellite system,following the United States.However,the bandwidth resource in relay satellites is limited,and how to share link resources efficiently between multiple users is a key problem in multiple access protocols and resource allocation strategies.Though the number of spacecraft is increasing and the requirement of business' s timeliness is improving,the relay satellite's payload is still limited.Thus the existing weekly scheduling scheme will not be able to meet future business demands.In order to solve these problems,the key technology in the space-based TT&C network is discussed and some innovational algorithms are proposed in this thesis.The contributions of this thesis are as follows:1.The space-based TT&C network system and applications of space-based TT&C network are studied in this thesis.The existing satellite multiple access technologies as well as bandwidth allocation algorithms are reviewed.The advantages and disadvantages of various algorithms are summarized.2.A space-based TT&C system model,a channel model and a business model are established in this thesis,The Combined Free/Demand Assignment Multiple Access(CFDAMA)protocol and its multiple reservation request strategies are studied in depth,and the performance is simulated and analyzed.After that,an improved CFDAMA-CFRP protocol is proposed,in which a chaotic exponential prediction method for self-similar service is applied to reduce the average delay and a random access strategy based on contention resolution is used to resolve conflict efficiently.Based on the theoretical analysis and simulation results,it is shown that the CFDAMA-CRFP protocol proposed in this thesis can provide better access performance under self-similar burst business model conditions compared with the traditional CFDAMA protocol.3.In view of limited payload in relay satellites,a more efficient on-demand access system(DAS)for space-based TT&C network is designed in this thesis.The DAS's procedure can be divided into three processes,including user aircraft random access process,user aircraft forward control process and user aircraft business file download process.In addition,a reliable file transfer scheme is proposed to improve the reliability of file transmission as well as the utilization of the forward link.Moreover,the platform of the space-based TT&C network demand access system is implemented,the software platform implements the configuration function of any topology and the three business processes in the system are tested in the simulation scenario. |
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