基于纠删编码的LTP协议优化设计

发布时间：2018-03-21 04:46

本文选题：深空通信　切入点：LTP协议　出处：《哈尔滨工业大学》2014年硕士论文　论文类型：学位论文

【摘要】：深空信道存在长延时、高误码率、中断频繁等不同于地面信道的特点,给工作在其上的通信系统带来了巨大的挑战。就通信协议而言,上述特点对深空通信协议的工作流程、反馈机制、差错控制方式等方面提出了较高的要求。现阶段广泛使用的深空通信协议有CCSDS空间通信协议参考模型与DTN协议族,其中DTN协议族可视作CCSDS协议族在深空通信体系中继化与网络化趋势下的补充。LTP协议作为DTN协议族中的汇聚层与传输层协议,可在深空信道下实现点对点可靠传输,但其同时存在工作于深空信道下保障数据可靠传输延时较长的问题。其根本原因在于LTP协议使用ARQ机制保障数据可靠传输,但是在高误码率与长延时的深空信道上,该机制因所需反馈重传次数较多且每次重传链路延时较长等原因而效率较低。本文考虑将面向数据包的、系统码形式的长纠删码引入LTP协议中,发端发送经过编码后的数据包组,收端收到经信道部分删除后的数据包组,首先进行译码操作,凭借长纠删码的前向纠删能力恢复部分数据包,随后再对未能成功恢复的数据包进行反馈重传操作。此时原LTP协议的ARQ差错控制机制被替换为H-ARQ机制,使用H-ARQ机制可减少优化后协议所需反馈重传的次数,进而减少总传输延时,在深空信道上可较大幅度地提高传输效率。常用的纠删编码有RS码、LDPC码、喷泉码等,考虑RS码编译码复杂度相对较高,喷泉码的有关理论尚不够成熟,本文选择LDPC码作为长纠删码。本文保持优化后协议的Segment类型与原LTP协议一致,仅对DS与RS的数据包格式加以修改以传递长纠删码的编码信息,在修改时使用原LTP协议Segment的Extension区域对相关信息加以存储,最大限度地保持了优化后协议与原LTP协议的兼容性。本文实现了优化前后的LTP协议并进行了仿真实验,实验结果显示,优化后协议的延时性能优于原LTP协议,验证了优化设计的可行性与有效性。通过分析实验结果,本文得到了优化后协议的适用条件、不同长纠删码参数对优化后协议性能的影响、以及优化后协议的最优配置方案。本文还讨论了优化后协议所传输数据的可靠性以及综合考虑数据链路层性能后协议的最优传输模式。
[Abstract]:Deep space channel has the characteristics of long delay, high bit error rate, frequent interruption and so on, which brings great challenges to the communication system working on it. As far as the communication protocol is concerned, the above characteristics are of great importance to the workflow of the deep space communication protocol. The feedback mechanism, error control methods and other aspects have put forward higher requirements. At present, the widely used deep space communication protocols include CCSDS space communication protocol reference model and DTN protocol family. DTN protocol family can be regarded as the supplement of CCSDS protocol family under the trend of relay and network of deep space communication system. As the convergent layer and transport layer protocol of DTN protocol family, it can realize point to point reliable transmission in deep space channel. But at the same time, it has the problem of ensuring the reliable data transmission delay in the deep space channel. The fundamental reason is that the LTP protocol uses the ARQ mechanism to guarantee the reliable data transmission, but in the deep space channel with high bit error rate and long delay, the main reason is that the LTP protocol uses the ARQ mechanism to guarantee the reliable data transmission. The mechanism is inefficient because of the high number of feedback retransmissions and the long delay of each retransmission. In this paper, we consider introducing the packet oriented long erasure codes in the form of system codes to the LTP protocol. The sender sends the encoded packet group, the receiving end receives the packet group that has been deleted by the channel part, the first decoding operation is carried out, and the partial packet is recovered by the forward erasure ability of the long erasure code. The ARQ error control mechanism of the original LTP protocol is replaced by the H-ARQ mechanism, and the number of feedback retransmissions required by the optimized protocol can be reduced by using H-ARQ mechanism. In order to reduce the total transmission delay and improve the transmission efficiency in deep space channels, the commonly used erasure codes include RS code LDPC code, fountain code and so on. Considering the relatively high complexity of RS code encoding and decoding, the theory of fountain code is not mature enough. In this paper, LDPC codes are chosen as long erasure codes. The Segment type of the optimized protocol is consistent with the original LTP protocol, and the data packet format of DS and RS is modified to transmit the encoding information of long erasure codes. The Extension region of the original LTP protocol Segment is used to store the relevant information, and the compatibility between the optimized protocol and the original LTP protocol is maintained to the maximum extent. The LTP protocol before and after the optimization is realized and the simulation experiment is carried out, and the experimental results show that the optimized protocol is compatible with the original LTP protocol. The delay performance of the optimized protocol is superior to that of the original LTP protocol, which verifies the feasibility and effectiveness of the optimized design. The effect of different length erasure code parameters on the performance of the optimized protocol, This paper also discusses the reliability of the data transmitted by the optimized protocol and the optimal transmission mode after considering the performance of the data link layer.
【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】：TN915.04

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