| With the development of human aerospace technology,the future deep space exploration missions will inevitably become more and more complex.It is of great significance to build standards and platforms that can provide information services for exploration missions of different types,stages and needs,and form a unified communication and information service system.Based on this,this thesis proposes a hybrid protocol system combining CCSDS protocol and DTN network to realize the application of CCSDS protocol in planetary area and DTN network in deep space link and other large delay scenarios,so as to give full play to their respective advantages and make the space network run under the more adaptive and optimized top-level services.This thesis first analyzes several main characteristics of deep space communication links,introduces the space communication network protocol system proposed by CCSDS,introduces the basic concept,operation mode and cluster layer protocol of the delay and break tolerant network.Then the basic scenarios and service requirements of deep space communication network are analyzed by taking Mars exploration as examples,then proposes a hybrid protocol system combining CCSDS and DTN network for deep space exploration.Aiming at the problem of delay and frequent high and medium interruptions in deep space links,the bundle protocol in DTN is added as the cluster layer under the CCSDS protocol architecture,which improves the transmission efficiency of data packets in deep space links,reduces unnecessary data retransmission and saves link resources;For inter satellite and planetary surface links,BOC + BPSK signal system is adopted in the physical layer to improve the transmission efficiency of data and measurement and control information between relay satellite and detector,and reduce the power consumption and volume of nodes;In addition,SCPS-TP and Proximity-1 protocols in CCSDS system are extended in the transmission layer and link layer,and their specific implementation schemes are described and designed in detail.For the hybrid protocol system proposed above,this thesis takes Mars exploration as the basic scenario,builds a simulation test platform in Omnet + +,designs simulation nodes such as ground control center,ground station,Mars relay star and probe,and tests the function of the protocol system.The test results show that the protocol system can correctly carry out end-to-end data interaction in the link with large delay and frequent interruption,The cluster layer bundle protocol is introduced to reduce the delivery time of documents by at least one round-trip cycle when the communication link is interrupted.According to the Earth-Mars link,the delay is about 5 ～ 25 min.For the Mars surface network link,three nodes of Mars relay star and two Mars probes are designed using FPGA,equipped with Proximity-1 link protocol andBOC + BPSK signal system.The space communication environment with high dynamic,high bit error and noise interference is simulated through the channel simulator.The feasibility of the link layer protocol and physical layer signal system and the transmission performance under different receiving power and data transmission rate are tested with the real data stream.From the test results,the signal acquisition time is about 60 ms,the data transmission rate can reach 5.11 mbps and the bit error rate is about 1.4e-7 when the signal-to-noise ratio is10 dB,Meet the recommended indexes of CCSDS in the blue book of spatial signal frequency and modulation system.The research of this thesis aims to provide a certain reference for the development of deep space communication network protocol and the construction of interplanetary Internet,and has a certain reference significance for the construction and development of deep space exploration network in China in the future. |
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