多播网络中基于机会网络编码改进的重传方法

针对高链路分组丢失率下HLAR (hash lookup assisted retransmission)等重传方法存在的编码率低、算法性能下降等缺陷,提出了一种改进的基于机会网络编码的广播重传方法.该方法根据接收节点反馈的丢失分组情况,不仅能够通过散列查找快速选择丢失分组组合进行编码重传,并优先重传能让最多接收节点恢复其丢失分组的单个重传分组,而且基于邻域关联充分挖掘编码机会,允许节点从多个重传分组中恢复丢失分组,从而在保持较低算法复杂度的情况下,有效地提高重传性能.仿真结果表明,相对于已有算法,该方法能有效减少重传次数,提高传输效率.     

多播网络中基于网络编码的高效丢失恢复机制

网络编码为无线网络中可靠多播通信提供了有效解决途径。该文分析了网络中编码机会的变化规律,研究了解码失败的编码数据包对网络编码性能的影响,提出了新的基于网络编码的丢失恢复算法(NCLR)。NCLR要求节点缓存解码失败的编码数据包,并反馈信息给发送节点。根据各个节点的丢包情况,NCLR通过优先传输对编码性能影响较大的数据包,并在需要重传的已编码数据包和原始数据包中选择编码组合,来充分挖掘网络中的编码机会。仿真结果表明相对于已有算法,NCLR算法可以在重传次数和丢失恢复时延方面有显著性能改善。     

一种基于网络编码的重传算法研究

无线网络中,节点发送的数据分组传输失败后,执行重传机制。传统的重传机制ARQ由于在一次重传中只能发送一个丢失的数据分组,因此传输效率比较低。利用网络编码技术和AQR重传机制,我们可以在重传中使用网络编码,广播发送由多个丢失数据分组编码得到的编码分组,从而提高重传效率。本文中我们提出一种将网络编码应用于多个发送方多个接收方(MSMR)无线网络中的算法RMBNC。理论推导和仿真分析验证了我们提出的算法的有效性。     

LTE下行链路中基于网络编码的多进程联合HARQ

长期演进系统的下行链路物理层采用了以传输块为基本单元的混合自动重传请求机制,保证移动终端在各种测试场景下都能获得较好的数据通过率。在对传输块的每次接收处理过程中,单个传输块中的多路独立码块数据解码结果差异较大。接收端可以通过对各个码块数据做循环冗余校验测试,标志各个码块的译码结果。然而由于传统重传机制中反馈链路的容量限制,即便只有一个码块解码错误,接收端也将反馈请求发送端重传整个传输块。网络编码技术通过对不同传输块数据做组合编码,可以有效地提高整个网络的传输效率。针对长期演进系统下行链路的传输机制,我们提出一种基于网络编码的多进程联合重传方案。新的重传方案联合多个传输块的重传进程,在每个传输块完成首次传输后,新增一个网络编码重传反馈比特,指示后续是否启动一个新进程传输多个传输块的网络编码数据包。我们给出了具体的重传协议流程,收发端都可以高效地根据网络编码重传反馈比特指示,完成相应的发送和接收操作。结合长期演进系统标准中的典型测试场景,我们给出了数据通过率的仿真结果比较。在仅新增一个反馈比特的条件下,采用网络编码技术的多进程联合重传方案在数据通过率方面有较为明显的性能增益。      

一种新的基于多节点网络编码的无线广播重传算法

提出了一种基于网络编码的无线网络广播重传算法。该算法按照包丢失分布概率的特点生成新的重传序列,采用多节点的网络编码方法进行丢失包组合实现重传。通过数学分析和仿真证明,该算法能保证接收节点的编码可解性,同时重传次数可达到局部最优性;与传统重传方法相比,该算法可以有效地减少信息包的平均传输次数,从而提高传输效率。     

一种改进的网络编码广播重传算法

在无线网络广播传输中,为了提升效率提出改进的基于冗余避免的网络编码广播重传算法（INCBRRA）。对接收状态矩阵进行重排列后,再主动避免重传不可解码的编码组合,从而优先编码有助于接收节点解码的丢失数据包组合。分析结果表明,INCBRRA算法相比于现有算法能有效减少重传次数,提升了传输效率。     

基于随机网络编码的无线广播重传方案及性能分析

针对自动重复重传(ARQ)机制在无线广播系统中吞吐量性能不佳的缺陷,提出一种基于随机网络编码的广播重传方案RNC-ARQ.对于广播节点,采用随机线性码对所有丢失包进行编码组合重传.对于接收节点,当接收的编码包累积到一定数量后可通过解码操作恢复出原始数据.该方案可有效减少重传次数,改善无线广播的吞吐量性能.基于Gilbert-Elliott模型描述的突发错误信道,建立了信道状态和节点接收处理流程合并的多状态马尔可夫模型,并以此为基础推导了RNC-ARQ方案的吞吐量闭合解.最后,使用NS-2模拟器评估RNC-ARQ方案的性能,结果表明在突发差错信道下,基于随机网络编码重传方案的吞吐量优于传统的选择承传ARQ方案和基于异或编码的重传方案.     

基于网络编码的无线网络广播重传方法

提出了一种适用于无线广播的基于网络编码的重传方法--NCWBR,通过网络编码组合不同的丢失包进行重传.理论分析表明,该方法能保证接收节点的编码可解性,同时重传次数较原方法更优;模拟测试结果表明,与逐个重传的方法相比,NCWBR有效地减少了信息包的平均传输次数,提高了传输效率.     

一种基于散列邻域搜索网络编码的机会中继重传方法

在无线多播网络中,传统的方法没有考虑某些接收节点与源节点及其他接收节点之间可能具有更好的链路质量.为此提出了一种基于散列邻域搜索网络编码的机会中继重传方法,该方法动态选择数据分组接收情况最好的且信道质量优于源节点的接收节点作为中继,并采用散列邻域搜索网络编码策略进行其他接收节点的丢失分组重传.仿真结果表明,相对于现有的其他网络编码重传方法,该方法能有效减少平均重传次数,提高重传效率,尤其当一些接收节点因受到干扰与源节点之间的信道质量变得很差时,该方法能取得很高的重传增益.     

中继协作无线网络中不完美反馈下基于网络编码的重传方案

无线广播网络传输过程中,目的节点反馈信息丢失或部分丢失导致发送节点不能了解目的节点的真实接收状态.为提高不完美反馈下无线网络的重传效率,本文提出中继协作无线网络中不完美反馈下基于网络编码的重传方案.本方案基于部分可观察马尔科夫决策过程对不完美反馈下的重传过程进行建模.发送节点根据系统观测状态和最大置信度更新系统估计状态,根据数据包发送顺序,优先选择最早丢失且能够恢复最多丢包的编码包重传.目的节点缓存不可解编码包以提升编解码机会.重传过程中源节点关注目的节点请求包需求,相同情况优先选择传输可靠性较高的中继节点,以提升传输有效性.仿真结果表明,在不完美反馈下相对于传统方案,本方案可有效提高重传效率.     

High efficient multipacket decoding approach for network coding in wireless networks

To improve the performance of transmission by reducing the number of transmission and network overhead of wireless single-hop networks, this paper presents a high efficient multipacket decoding approach for network coding (EMDNC) in wireless networks according to the idea of encoding packets which cannot be decoded and are stored in buffer by receiving nodes, the lost packets can be recovered from these encoded packets. Compared with the network coding wireless broadcasting retransmission (NCWBR), EMDNC can improve the efficiency of decoding and reduce the number of retransmission and transmission delay. Simulation results reveal that EMDNC can effectively reduce the number of retransmission and network overhead.     

Interleaved coding and sequential transmission scheme for packet‐level forward error correction over burst loss channels

Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications.     

联合蜂窝与D2D链路的网络编码广播重传方案

移动设备之间的合作以及利用蜂窝和D2D链路等多个接口有望满足日益增长的吞吐量需求。考虑设备配备有双接口的无线D2D广播（Network coding for dual interfaces,NCDI）场景,重传阶段,设备同时利用蜂窝与D2D链路来恢复丢失数据包。然而,如何合理的进行编码调度,充分发挥网络编码增益显得至关重要。为最小化重传次数,文章旨在设计联合蜂窝与D2D链路的网络编码广播重传方案。针对随机线性网络编码（RLNC）与立即可译网络编码（IDNC）,分别提出了NCDI-RLNC以及NCDI-IDNC方案。仿真结果表明,与其他方案相比,提出的两种方案均能够有效地提高重传效率、减少重传次数。      

D2D网络中基于立即可解网络编码的时延最小化重传方案

该文针对D2D无线网络中多终端并发协作重传冲突避免问题,提出一种基于立即可解网络编码的时延最小化重传方案。在重传阶段,充分利用D2D无线网络终端协作传输数据的优势,结合各终端数据包接收状态,综合考虑时延的影响因素,选取单次重传时延增量较小的数据包生成编码包,最小化重传时延。同时,构建终端冲突图,在图中搜索极大独立集,根据各终端的编码包权重值,选择最大加权独立集中的终端作为并发协作重传终端,从而降低重传次数。仿真结果表明,所提方案能够进一步改善D2D无线网络的重传效率。     

An adaptive retransmission‐based multipath transmission mechanism for conversational video

Conversational video service is characterized by high bandwidth demand and low delay requirement. Bandwidth and transmission schemes play an important role in providing high‐quality delivery service for point‐to‐point conversational video service. Multipath transmission is regarded as an effective way to aggregate bandwidth. Transmission schemes need to ensure the strict time relation between information entities and to alleviate the negative impact of packet loss on video quality. To achieve this, existing transmission schemes may incur either a large delay or a large amount of duplicated packets that are not suitable for conversational video service. In this paper, we propose an adaptive retransmission mechanism–based multipath transmission (MT‐AR) for conversational video service delivery. MT‐AR takes advantage of historical reception experience to timely detect packet loss with a certain degree of misjudgement. Receiver requests sender to retransmit the lost packet if the lost packet benefits the decoding. Adaptive playout speed adjustment and alternative path retransmission cooperatively optimize the performance of retransmission. Receiver slightly extends playout speed to reserve time for retransmission and accelerates playout speed to alleviate negative impact of cumulative extension. Multiple paths support to conduct retransmission on an optimal path selected from alternative paths to avoid continuous congestion or error on the original path. Finally, we conduct extensive tests to evaluate the performance of MT‐AR. Experimental results show that MT‐AR can effectively improve the quality of experience of conversational video service by retransmission.     

Contention-based MAC protocols with erasure coding for wireless data networks

Contention-based medium access control (MAC) protocol is a key component for the success of wireless data networks. Conventional random access protocols like ALOHA and Carrier Sense Multiple Access (CSMA) suffer from packet collision which leads to low throughput. Aimed at improving the throughput performance, we propose to integrate erasure coding with contention-based MAC protocols for recovering collided packets. To demonstrate the effectiveness of this approach, we focus on combining erasure coding with slotted ALOHA and slotted non-persistent CSMA in this paper. The performances of the resulting protocols are evaluated by both analytical model and simulation. Simulation results match very well with analytical results and show that the system throughput is increased for low to medium traffic loading. Packet loss ratio is also improved considerably with our scheme when the maximum number of packet retransmission times is limited. However, the delay for our scheme is higher due to the longer waiting time in our scheme for recovering collided packets. It is also shown that delay can be significantly reduced if we choose appropriate coding parameters though throughput will be sacrificed.     

On Broadcast Stability of Queue-Based Dynamic Network Coding Over Erasure Channels

The transmission of packets is considered from one source to multiple receivers over single-hop erasure channels. The objective is to evaluate the stability properties of different transmission schemes with and without network coding. First, the throughput limitation of retransmission schemes is discussed and the stability benefits are shown for randomly coded transmissions, which, however, need not optimize the stable throughput for finite coding field size and finite packet block size. Next, a dynamic scheme is introduced for distributing packets among virtual queues depending on the channel feedback and performing linear network coding based on the instantaneous queue contents. The difference of the maximum stable throughput from the min-cut rate is bounded as function of the order of erasure probabilities depending on the complexity allowed for network coding and queue management. This queue-based network coding scheme can asymptotically optimize the stable throughput to the max-flow min-cut bound, as the erasure probabilities go to zero. This is realized for a finite coding field size without accumulating packet blocks at the source to start network coding. The comparison of random and queue-based dynamic network coding with plain retransmissions opens up new questions regarding the tradeoffs of stable throughput, packet delay, overhead, and complexity.      

在无线双向通信中基于CRC-NC抵抗污染攻击方案

本文提出一种CRC-NC (Cyclic Redundancy Check-Network Coding）方案．在无线双向通信网络中,该方案通过结合网络编码和循环冗余校验码技术,对接收到的消息的进行可信度检测,能有效地降低目的节点解码误码率,并抵抗污染攻击．该方案中节点与节点在中继节点的辅助下相互发送消息,并利用对方节点和中继节点发送的消息解码．若节点直接从对方节点获得的消息中有S个消息正确,该节点将对方节点发送的消息和中继节点发送的消息进行组合,并计算组合消息的汉明重量,从中选择K-S个最小的汉明重量所对应的由中继节点发送的消息解码．通过仿真结果表明,与基于随机选取方案和加密方案相比,该方案能有效的降低节点解码差错概率．