深空通信中基于喷泉码的文件传输协议研究

发布时间：2018-06-04 11:52

本文选题：深空通信 + 传输层协议　；参考：《哈尔滨工业大学》2014年硕士论文

【摘要】：深空探测是人类在太空活动的主体，是探寻宇宙起源和扩展人类未来生存空间的必然举措。而维系航天探测器与地面通信系统的唯一纽带就是深空通信系统，，因此深空通信技术的发展直接影响着整个深空探测的前进方向。在深空探测任务中所采集到的信息都以文件的形式存储再发送，因此文件传输协议的优劣直接决定了深空通信系统的性能。由于深空通信收发双方具有极远的传输路径以及极高的丢包率，现有的TCP（Transmission Control Protocol）协议极差，已经不能满足深空通信的基本要求。而CFDP（CCSDS File Protocols）协议在一些短延时和低丢包率的信道环境中表现出了优良的性能，然而在信道时延及丢包率增加到一定阈值时，CFDP协议仍需要对丢失数据包进行多次重传，文件传输时延明显增加。经过分析论证得出反馈信息的传输次数直接决定了文件传输协议的性能，因此基于前向纠错技术的喷泉码可以引入到文件传输协议之中，这样就可以减少对丢失数据包的反馈。所以结合研究内容，本文针对深空通信环境的特点提出一种基于LT码的文件传输协议（Luby Transform based Protocol），解决了高丢包率、长传输时延造成反馈次数增多而引起链路性能的下降，减少了文件的传输时间，提高通信链路的吞吐率。此外在设计LT-P协议之前，对可能影响协议性能的因素进行了分析，包括译码算法的选择、度分布函数的分析以及LT译码开销的估算，并根据分析结果给出了相关建议。最后通过搭建的深空通信文件传输协议仿真平台的实验验证，TCP协议在单项路径传输时延大于1s的通信场景中表现最差；在单项路径传输时延以及丢包率小于一定阈值时，由于LT-P协议仍需要发送一定的额外开销来保证译码的成果，所以CFDP协议的性能要优于LT-P协议；而在单项路径传输时延较大时，由于CFDP协议需要对丢包信息进行多次反馈重传，因此CFDP协议性能明显下降，LT-P协议此时表现出了最佳性能。
[Abstract]:Deep space exploration is the main body of human activities in space and is an inevitable measure to explore the origin of the universe and expand the future living space of mankind. The only link between the space probe and the ground communication system is the deep space communication system, so the development of the deep space communication technology directly affects the forward direction of the whole deep space exploration. The information collected in the deep space exploration mission is stored and sent in the form of files, so the performance of the deep space communication system is directly determined by the merits and demerits of the file transfer protocol. Because of the extremely long transmission path and the extremely high packet loss rate, the existing TCP(Transmission Control protocol is extremely poor and can no longer meet the basic requirements of deep space communication. However, CFDP(CCSDS File protocols have good performance in some channel environments with short delay and low packet loss rate. However, when the channel delay and packet loss rate increase to a certain threshold, the CFDP(CCSDS File protocol still needs to retransmit the lost data packets many times. File transfer delay increased significantly. Through analysis and demonstration, it is concluded that the number of times of transmission of feedback information directly determines the performance of file transfer protocol, so the fountain code based on forward error correction technology can be introduced into file transfer protocol, which can reduce the feedback on lost data packets. Therefore, according to the characteristics of deep space communication environment, this paper proposes a file transfer protocol based on LT code, Luby Transform based protocol, which solves the problem of high packet loss rate, long transmission delay and increasing feedback times, which leads to the degradation of link performance. It reduces the transmission time of files and improves the throughput of communication links. In addition, the factors that may affect the performance of LT-P protocol are analyzed, including the selection of decoding algorithm, the analysis of degree distribution function and the estimation of decoding overhead, and the relevant suggestions are given according to the analysis results. Finally, through the experiment of the deep space communication file transfer protocol simulation platform, it is verified that TCP protocol performs the worst in the communication scene where the transmission delay of single path is greater than 1s, and when the transmission delay of single path and the packet loss rate are less than a certain threshold, Because the LT-P protocol still needs to send some extra overhead to ensure the decoding result, the performance of CFDP protocol is better than that of LT-P protocol, but when the transmission delay of single path is large, the CFDP protocol needs to retransmit the packet loss information many times. Therefore, the performance of CFDP protocol obviously drops and the LT-P protocol shows the best performance at this time.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN927

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