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。     

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。     

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.     

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。      

Turbo编码调制技术在物理层网络编码中的应用研究

在双向中继信道中,基于编码调制技术提出了一种Turbo编码调制技术(T-TCM)与物理层网络编码的联合实施方案.本方案采用了T-TCM,即将TCM中的卷积码用Turbo码代替,两个分量编码器用符号交织器分开.中继节点利用卷积码和网络编码的线性性质直接估计网络编码的码字,并在中继节点采用了基于符号的MAP译码算法.本方案将信道编码技术、调制技术以及物理层网络编码三者联合设计,不仅增加了无线网络的吞吐量,还提高了网络的频谱利用率.     

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。     

非完全无线报文重传分析研究及其分治策略

网络编码为无线网络报文重传问题WPRTPs(Wireless Packet ReTransmission Problems)提供了有效解决途径.现有关于WPRTP问题的研究主要针对完全无线网络报文重传问题P-WPRTPs(Perfect WPRTPs),而尚未发现对非完全无线网络报文重传问题IP-WPRTPs（ImPe...     

无线Mesh网络中跨层协作的路由策略

网络编码可以提高无线Mesh网络的吞吐量,但是网络编码在无线Mesh网络中实际应用获得最大网络利用率是需要解决的问题。提出一种多路径策略,能够通过将网络编码和TCP进行最大化融合提高网络的利用率。网络编码被加入到现有的网络系统,通过解决速率控制问题和分组调度问题,调整源节点的数据编码分块,降低数据包重传的次数,提高网络的吞吐量。     

基于网络编码的PON中编码机制优化设计

接入网业务本地化趋势使得NC(网络编码)在PON(无源光网络)中的应用越来越广泛,而数据包长度不同将导致网络编码包传输过程中的带宽浪费问题。为了提高带宽利用率,减少OLT(光线路终端)能耗,提出了一种新型的包队列编码方式及其实现方案。仿真结果表明所提出的编码机制及其实现方案提高了带宽利用率,有效地降低了解码包对ONU(光网络单元)内存的占用,优化了系统的下行吞吐量并提高了OLT端的节能效率。     

适合TCP的网络编码重传机制

通过理论分析,看出基于反馈的重传方法比定量重传的方法有更低的解码延迟。提出了一种新型的基于反馈的网络编码(FNC)重传机制,利用seen机制中的隐含信息来获取接收方解码所需的重传分组个数,并改变了编码规则使部分分组可以提前解码。该机制不仅可以处理有固定误码率的随机分组丢失,还可以有效地应对大量突发性分组丢失。仿真结果显示,该机制在高误码率下也能保持较高的吞吐量,且极大地减少了解码延迟,传输过程基本不受分组丢失的影响,有效地对拥塞控制协议隐藏了链路错误。算法简单有效,更适于在实际系统中应用。     

A hybrid network coding technique for single-hop wireless networks

In this paper, we investigate a hybrid network coding technique to be used at a wireless base station (BS) or access point (AP) to increase the throughput efficiency of single-hop wireless networks. Traditionally, to provide reliability, lost packets from different flows (applications) are retransmitted separately, leading to inefficient use of wireless bandwidth. Using the proposed hybrid network coding approach, the BS encodes these lost packets, possibly from different flows together before broadcasting them to all wireless users. In this way, multiple wireless receivers can recover their lost packets simultaneously with a single transmission from the BS. Furthermore, simulations and theoretical analysis showed that when used in conjunction with an appropriate channel coding technique under typical channel conditions, this approach can increase the throughput efficiency up to 3.5 times over the automatic repeat request (ARQ), and up to 1.5 times over the HARQ techniques.     

基于机会式网络编码的高效广播传输算法

为了提高无线网络广播传输的效率,针对单跳无线网络提出了采用编码方法的广播传输算法。在传统的无线广播传输模型的基础上,分别实现了基于机会式网络编码的单组合分组广播传输算法和多组合分组广播传输算法。它们采用不同的策略选择多个丢失分组编码组合成重传分组,并通过从编码组合数据分组中恢复丢失分组的方式来提高广播传输的吞吐量。仿真结果表明,新算法在不同无线信道传输模型下相比已有的算法有效地降低了广播传输所需的传输带宽。     

To‐send‐or‐not‐to‐send: An optimal stopping approach to network coding in multi‐hop wireless networks

Network coding is all about combining a variety of packets and forwarding as much packets as possible in each transmission operation. The network coding technique improves the throughput efficiency of multi‐hop wireless networks by taking advantage of the broadcast nature of wireless channels. However, there are some scenarios where the coding cannot be exploited due to the stochastic nature of the packet arrival process in the network. In these cases, the coding node faces 2 critical choices: forwarding the packet towards the destination without coding, thereby sacrificing the advantage of network coding, or waiting for a while until a coding opportunity arises for the packets. Current research works have addressed this challenge for the case of a simple and restricted scheme called reverse carpooling where it is assumed that 2 flows with opposite directions arrive at the coding node. In this paper, the issue is explored in a general sense based on the COPE architecture requiring no assumption about flows in multi‐hop wireless networks. In particular, we address this sequential decision making problem by using the solid framework of optimal stopping theory and derive the optimal stopping rule for the coding node to choose the optimal action to take, ie, to wait for more coding opportunity or to stop immediately (and send packet). Our simulation results validate the effectiveness of the derived optimal stopping rule and show that the proposed scheme outperforms existing methods in terms of network throughput and energy consumption.     

效率感知的无线网络编码机制

网络编码在无线网络中的应用可以显著提高无线网络的吞吐量和容量。然而,当前大多数的无线网络编码机制在进行编码操作时,都没有考虑将不同长度的报文编码在一起时的效率问题。该文研究了在进行网络编码操作时如何获得最优的每字节编码效率,并设计了编码效率感知的无线网络编码机制(coDing Efficiency awarE Network coding, DEEN),以提升每字节的编码效率。模拟结果表明,DEEN协议能够有效地提升无线网络的容量。     

卷积网络编码

网络编码作为一种新的编码技术在提高传输效率、均衡负载、节省资源及数据安全等方面有很大优势。对于确定型通信网络,线性网络编码已被证明是一种简单高效的编码方式。然而,对基于无线网络的通信则不然,这主要是因为无线网络组成元素的可移动性,链路的不稳定性,传输的广播特性及资源共享性。针对无线网络特性,卷积网络编码应运而生,并表明比分组网络编码存储需求更少、译码时延及复杂度更小,成为网络编码在无线应用研究方面的焦点。首先介绍了卷积网络编码的研究进展,以及迫切需要解决的问题。然后从卷积网络编码的基本模型,研究方向,已有的编译码算法及与经典卷积编码的关系几个方面展开,为今后的卷积网络编码及其应用研究廓清思路。     

Throughput and resource optimization for adaptive coding‐based random access networks with correlated sources

Modern wireless communication networks frequently have lower application throughput due to higher number of collisions and subsequent retransmission of data packets. Moreover, these networks are characterized by restricted computational capacity due to limited node‐battery power. These challenges can be assessed for deploying fast, reliable network design with resource‐restrained operation by means of concurrent optimization of multiple performance parameters across different layers of the conventional protocol stack. This optimization can be efficiently accomplished via cross‐layer design with the aid of network coding technique and optimal allocation of limited resources to wireless links. In this paper, we evaluate and analyze intersession coding across several source–destination pairs in random access ad hoc networks with inherent power scarcity and variable capacity links. The proposed work addresses the problem of joint optimal coding, rate control, power control, contention, and flow control schemes for multi‐hop heterogeneous networks with correlated sources. For this, we employ cross‐layer design for multiple unicast sessions in the system with network coding and bandwidth constraints. This model is elucidated for global optimal solution using CVX software through disciplined convex programming technique to find the improved throughput and power allocation. Simulation results show that the proposed model effectively incorporates throughput and link power management while satisfying flow conservation, bit error rate, data compression, power outage, and capacity constraints of the challenged wireless networks. Finally, we compare our model with three previous algorithms to demonstrate its efficacy and superiority in terms of various performance metrics such as transmission success probability, throughput, power efficiency, and delay.     

复数域网络编码中最大似然解码算法的改进

针对复数域网络编码中继网络,提出一种改进的中继处的最大似然解码算法。当传统的最大似然解码算法使用在复数域网络编码中继网络中时,计算复杂度会随着信息星座图映射方式的改变而大大增加。为了降低计算复杂度,在前人研究的基础上提出一种改进的最大似然解码算法,该算法利用无线中继网络通信系统的非对称性,在解码时,先进行预判决,然后进行精确判决,这样可以大大降低计算复杂度,提高了系统性能。     

An efficient network coded ARQ for multisource multidestination relay networks over mixed flat fading channels

This paper proposes a new reliable automatic repeat request (ARQ) transmission protocol for wireless multisource multidestination relay networks over mixed fading channels. Conventional application of ARQ protocols to retransmit lost or erroneous packets in relay networks can cause considerable delay latency with a significant increase in the number of retransmissions when networks consist of multiple sources and multiple destinations. To address this issue, a new ARQ protocol based on network coding (NC) is proposed where the relay detects packets from different transmission sources, then uses NC to combine and forward lost packets to their destinations. An efficient means for the retransmission of all lost packets is proposed through two packet-combination algorithms for retransmissions at the relay and sources. The paper derives mathematical formulation of transmission bandwidth for this new NC-based ARQ protocol and compares analytical and simulation results with some other ARQ protocols over both mixed Rayleigh and Rician flat fading channel. The mixed fading model permits investigation of two typical fading scenarios where the relay is located in the neighbourhood of either the sources or the destinations. The transmission bandwidth results show that the proposed NC-based ARQ protocol demonstrates superior performance over other existing ARQ schemes.     

联合自适应调制编码与ARQ的跨层设计

为了提高无线系统数据速率,目前广泛地采用物理层自适应调制编码(AMC)和链路层自动重发请求(ARQ)协议相结合的跨层设计,这种设计方法能大大提高系统频谱利用率。本文在瑞利衰落信道模型下,在给定包时延和丢包率的情况下,推导出了联合AMC和ARQ的跨层设计频谱利用率的公式。同时也与纯AMC和纯ARQ的情况作了比较。