The Research And Design Of Low Level Protocol For Low Earth Orbit Satellite Digital Trunking System

The low earth orbit satellite digital trunking communication system uses the "Satellites work in the sky and transparently transpond signals from networks work on the ground" communication mode.They system combines the low communication delay,high channel utilization,wide coverage of low earth orbit satellite mobile communication systems and good privacy,rich feature of digital trunking communication systems.Remote control of the industrial networking,unmanned combat,resource exploration and other needs in the future will be met by this system.It is indispensable to the national defense,public safety,transportation,mining enterprises,oil field and farms,which have high demands for sensitive information.With the channel business of low earth orbit satellite communications developing and increasing,channel occupancy of C band(6/4 GHz),X band(8/7 GHz),and Ku band(14/12 GHz)is becoming increasingly crowded.The researches on Ka band(30/20 GHz)low earth orbit satellite communications get more and more attention.However,there are lacks of Loo model about Ka-band mobile satellite communication in the existing literatures.Adaptive coding and modulation techniques can dynamically change satellite communication coding and modulation strategies to ensure system reliability and throughput in different channel environments.But there are still a lot of room for improvement in three existing coding and modulation switching strategies.In the low earth orbit satellite digital trunking communication system,the low-level protocols are the core of the communication system.Designing a set of low-level communication protocols adapted to the system plays a decisive role in the overall system.In order to solve the above problems,the Ka-band satellite channel modeling,adaptive coding and modulation techniques,low-level protocols of low earth orbit satellite digital trunking communication system design were researched in this thesis.The main work of this thesis is as follows:(1)The mathematical probability statistics of the Loo model in the Ka-band mobile communication satellite channel was analyzed,the joint mode of shadowing and multipath effect in the existing channel model was improved,a new Ka-band mobile satellite channel model was proposed to make it more realistic in this thesis.The new channel model provides supports for the adaptive coding and modulation techniques and determination of low-level protocol design specifications.(2)According to the proposed Ka-band mobile satellite channel model,four modulation and coding strategies were chosen for adaptive switching in the combination of BCH,RS coding and MPSK modulation schemes.The shortcomings of the commonly used modulation and coding switching algorithms and their causes were analyzed.An improved variance correction of average signal-noise ratio modulation and coding strategy was proposed,and its applicability of low earth orbit satellite digital trunking communication system was verified.(3)Based on signal-noise ratio estimation,the key technologies of modulation and coding selection and switching strategy in adaptive coding and modulation,a low-level protocol for low earth orbit satellite digital trunking communication system was designed,including the protocol stack model and its hierarchical structure,physical channel,logical channel,frame structure,burst type,interleaving,frame synchronization,burst coding and decoding.The design principle and simulation process were presented.At last,the correctness and adaptability of the low-level protocol were verified.