【作者】 宋谱；

【导师】 吴伟陵；

【作者基本信息】 北京邮电大学 ， 信号与信息处理， 2009， 博士

【摘要】 随着移动通信和互联网的高速发展,无线多媒体业务需求的不断增长,人们对宽带无线接入的需求越来越迫切。人们期望,下一代(B3G/4G)移动通信系统能提供更高的数据速率,更大的系统容量支持更多的用户并且满足多种业务的不同服务质量(QoS)要求。故下一代移动通信系统需要应用更多先进的传输技术,以解决人们对带宽的需求和有限的无线资源之间的矛盾。其中网络编码(network coding)技术受到广泛关注。网络编码理论是网络通信研究领域中的一项重要突破,通过允许中继节点进行数据包级的编码,而不再是简单的信号存储转发,来有效提高整个网络的传输效率、容量和健壮性。一种新技术的出现,总是避免不了从简单应用到与其他现有技术相互结合设计的演进过程以获取更好的系统性能。网络编码也不例外。虽然网络编码的核心步骤在于编码操作,但其真正的性能优势体现在多用户的差异性上,相同的编码数据包被不同的用户接收,接收者根据存储数据包译出各自所需的信息,从而实现一次传输多个受益。而实现这一性能优势的物理条件在于广播或组播。因此论文从探讨无线网络编码的广播优势出发,综合考虑系统的可靠性和有效性,探讨了网络编码与无线通信系统各层关键技术相结合的有效方案,主要研究配置了网络编码模块系统的关键技术算法设计及性能分析等。论文的主要工作包括:网络编码技术可以有效地提高或达到网络中系统容量。为了在无线多跳系统中更好地获取网络编码增益,在网络层提出一种新的具有完全编码意识的路由机制CCAR(ComoleteCoding-Aware Routing):首先修正DSR(动态源路由Dynamic SourceRouting)协议进行路由发现,获得所有满足最大跳数约束的候选路径并判定网络编码机会;在路由选择阶段量化网络编码后传输的性能优势,提出ECTX(Expected Coding-aware Transmission Count)的判据,来选择一条最小代价的路径,真正实现了具有网络编码意识的无线路由。仿真结果表明该机制在无线多跳网络中,能够有效地增强节点对数据的处理能力,相比于不使用网络编码的系统,具有5%-20%的系统吞吐量增益。本路由机制具有很高的实用价值,可以应用在例如应急通信场景中,在不增加带宽等资源配置的前提下,用存储空间来换取系统吞吐率的有效提升。从而有效应对在短时间处理极繁重数据流量的业务需求。现有的基于多信道的无线路由协议选择的多条路径是节点不相交(node-disjoint)或链路不相交(link-disjoint),不能有效提高吞吐量,降低时延。为了提高系统频谱利用率,并解决多信道路由同频信道分集的难题,本文提出一种新的具有网络编码意识的多径多信道路由机制M-CCAR(Multi-path/channel Complete Coding-Aware Routing):在路径发现阶段,使用一种新的信道不相交(channel-disjoint)的路由发现算法,以获得所有满足最大跳数约束的候选路径并判定网络编码机会。在选路阶段量化网络编码后传输的性能优势,并综合考虑无线信道传输信道差错及干扰的影响,提出一种新的路由判据WCECTT(Weighted CumulativeCoding-aware ETT),真正实现了支持多信道的具有完全编码意识的多径路由。仿真结果表明该机制在无线多跳网络中,能够有效地增强节点对数据的处理能力,相比于不使用网络编码的多径路由算法,具有10%-20%的系统吞吐量增益。作为一种新型结合流间网络编码的多径多信道路由,可以应用在无线多跳网络中,从而有效提高系统吞吐量。无线传输具有很高的比特出错率和较大的传输时延。因此,在无线网络广播/组播中必须采用合适的策略来提高广播操作的可信赖性。然而在组播环境下实现可靠传输存在诸如重复恢复等难以解决的问题,使用网络编码可以在一定程度上解决这种问题。用网络编码进行组播差错恢复机制一般有两种做法:网络编码结合前向错误纠正(FEC),如喷泉码+网络编码;或网络编码结合自动重传请求(ARQ)。但是这些方案都存在一些重要缺陷:单纯FEC的差错恢复技术因为不能适应分组丢失的变化,分组丢失少时严重地浪费带宽,分组丢失严重时又不能恢复所有数据,因此很少被使用。现有的各种协议多采用反馈重传的方式保证组播的可靠性。单纯的ARQ技术只能检错,不能纠错,这样在比较恶劣的传输环境中重传效率依然很差。基于这些缺点,本文提出一种新的结合HARQ与网络编码的差错恢复机制,使用联合网络编码与信道译码的软信息合并技术,可以有效地应用于不同的传输信道环境,以保证重传效率,从而增强系统在恶劣环境下的鲁棒性。使用信息截止频率推导该机制的性能上界,最后给出仿真结果和分析。相比于前两种做法,能够更实际地应用于对实时性要求不高的无线单跳组播多播业务。更多还原

【Abstract】 With rapid development of mobile communication and internet network, the requirement of broadband wireless access is increasing to meet the dramatically growing demands for wireless multimedia services.The next-generation mobile communication systems(B3G/4G) provide high data-rate,support more subscribers and guarantee quality-of-service(QoS). Hence advanced technologies will be applied in the B3G/4G system to provide higher frequency efficiency within limited wireless bandwidth, among which network coding system is promising technology.Network coding theory is an important break-though in network communication and development.The core idea of network coding is that the gateway nodes in network not only focus on simple store-and-forward,but also encode the information that passes by;therefore,the coding process has enlarged the capacity and stability of entire network.Typical evolution process of novel techniques,like network coding, almost always involves from some simple application independent with other existing techniques to some joint designing mechnisms to obtain further performance advantages.Although the key steps of network coding is the coding process,the instinct benefit lies in the difference of muti-user part, specifically,through which the same network coded packets is broadcasted or multicasted to more than one receivers,different receivers can decode individual information needed using its former information possessed respectively.In one word,more than one receiver can gain after one coding transmission by the means of multicasting or broadcasting.Based on this observation,this dissertation seeks to apply the method of network coding with some existing techniques in wireless communication system,mainly focusing on research and analysis in system performance and implementation alternatives.The mainly works include: In recent years,the coding-aware routing mechanism attracts the interest of many people to further magnify the gains achieved by network coding in wireless networks.This paper aims at revealing a unifying framework for routing in the presence of the awareness of network coding,which we call "coding-aware routing".In this paper,we propose a practical routing mechanism CCAR(Complete Coding-Aware Routing) which fairly quantify the network coding gain while considering the wireless transmission conditions.In general,there are two steps that should be realized in coding-aware routing mechanism:one is finding coding opportunity in the routing discovery phase and the other one is determining the optimum path from the coding-available paths and the coding- unavailable ones.We implement the CCAR routing in wireless mesh system in C++ with extensive evaluation,and the simulation results illustrate that compared with the ones which oblivious of coding gains using,transmission efficiency can be sharply increased in the whole network and achieves 5%-20%throughput gains.The problem of intra-channel diversity in multi-channel routing can be relived efficiently using new proposed technology called "Network coding", and hence spectral efficiency can be increased.In this framework,we presented a method for computing source-destination routes and utilizing the best coding opportunities from available ones so as to maximize the throughput,which called M-CCAR(Multi-Path/channel Complete Coding-Aware Routing).In general,there are two steps that should be realized in coding-aware routing mechanism:the first one is finding the set of candidate path using a modified DSR protocol and making aware of coding opportunity in the routing discovery phase and the other one is determining the optimum path from the coding-available paths and the codingunavailable ones using the novel routing metric of WCECTT(Weighted Cumulative Coding-aware ETT).We implement the M-CCAR routing in wireless mesh system in C++ with extensive evaluation,and the simulation results illustrate that compared with the ones which oblivious of coding gains using,transmission efficiency can be sharply increased in the whole network and achieves 10%-20%throughput gains.A novel scheme joint with chase combining and network coding for broadcast flows in a multi-user system is presented.An information-theoretic performance bound is also developed to explain and predict the coding gains of the Soft combining in network coding-based Multicasting scheme using random coding bounding techniques.It is found from the simulation results that the transmission efficiency is sharply increased in the whole network especially in fairly severe fading circumstance.Research supported in part by National Basic Research Program of China(973 Program) 2007CB310604 and Project 2009CB320401,Project 60772108 and 60702048 supported by National Natural Science Foundation of China.This work has also been supported by the Doctor Fund of Beijing University of Posts and Telecommunications.更多还原