發(fā)布時(shí)間：2018-03-21 04:46

  本文選題：深空通信　切入點(diǎn)：LTP協(xié)議　出處：《哈爾濱工業(yè)大學(xué)》2014年碩士論文　論文類型：學(xué)位論文

【摘要】：深空信道存在長延時(shí)、高誤碼率、中斷頻繁等不同于地面信道的特點(diǎn),給工作在其上的通信系統(tǒng)帶來了巨大的挑戰(zhàn)。就通信協(xié)議而言,上述特點(diǎn)對深空通信協(xié)議的工作流程、反饋機(jī)制、差錯(cuò)控制方式等方面提出了較高的要求�，F(xiàn)階段廣泛使用的深空通信協(xié)議有CCSDS空間通信協(xié)議參考模型與DTN協(xié)議族,其中DTN協(xié)議族可視作CCSDS協(xié)議族在深空通信體系中繼化與網(wǎng)絡(luò)化趨勢下的補(bǔ)充。LTP協(xié)議作為DTN協(xié)議族中的匯聚層與傳輸層協(xié)議,可在深空信道下實(shí)現(xiàn)點(diǎn)對點(diǎn)可靠傳輸,但其同時(shí)存在工作于深空信道下保障數(shù)據(jù)可靠傳輸延時(shí)較長的問題。其根本原因在于LTP協(xié)議使用ARQ機(jī)制保障數(shù)據(jù)可靠傳輸,但是在高誤碼率與長延時(shí)的深空信道上,該機(jī)制因所需反饋重傳次數(shù)較多且每次重傳鏈路延時(shí)較長等原因而效率較低。本文考慮將面向數(shù)據(jù)包的、系統(tǒng)碼形式的長糾刪碼引入LTP協(xié)議中,發(fā)端發(fā)送經(jīng)過編碼后的數(shù)據(jù)包組,收端收到經(jīng)信道部分刪除后的數(shù)據(jù)包組,首先進(jìn)行譯碼操作,憑借長糾刪碼的前向糾刪能力恢復(fù)部分?jǐn)?shù)據(jù)包,隨后再對未能成功恢復(fù)的數(shù)據(jù)包進(jìn)行反饋重傳操作。此時(shí)原LTP協(xié)議的ARQ差錯(cuò)控制機(jī)制被替換為H-ARQ機(jī)制,使用H-ARQ機(jī)制可減少優(yōu)化后協(xié)議所需反饋重傳的次數(shù),進(jìn)而減少總傳輸延時(shí),在深空信道上可較大幅度地提高傳輸效率。常用的糾刪編碼有RS碼、LDPC碼、噴泉碼等,考慮RS碼編譯碼復(fù)雜度相對較高,噴泉碼的有關(guān)理論尚不夠成熟,本文選擇LDPC碼作為長糾刪碼。本文保持優(yōu)化后協(xié)議的Segment類型與原LTP協(xié)議一致,僅對DS與RS的數(shù)據(jù)包格式加以修改以傳遞長糾刪碼的編碼信息,在修改時(shí)使用原LTP協(xié)議Segment的Extension區(qū)域?qū)ο嚓P(guān)信息加以存儲,最大限度地保持了優(yōu)化后協(xié)議與原LTP協(xié)議的兼容性。本文實(shí)現(xiàn)了優(yōu)化前后的LTP協(xié)議并進(jìn)行了仿真實(shí)驗(yàn),實(shí)驗(yàn)結(jié)果顯示,優(yōu)化后協(xié)議的延時(shí)性能優(yōu)于原LTP協(xié)議,驗(yàn)證了優(yōu)化設(shè)計(jì)的可行性與有效性。通過分析實(shí)驗(yàn)結(jié)果,本文得到了優(yōu)化后協(xié)議的適用條件、不同長糾刪碼參數(shù)對優(yōu)化后協(xié)議性能的影響、以及優(yōu)化后協(xié)議的最優(yōu)配置方案。本文還討論了優(yōu)化后協(xié)議所傳輸數(shù)據(jù)的可靠性以及綜合考慮數(shù)據(jù)鏈路層性能后協(xié)議的最優(yōu)傳輸模式。
[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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN915.04

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