卫星网络中基于网络编码的ARQ机制

随着航空航天技术的发展,越来越多的应用任务需要利用卫星通信进行信息传输。在卫星网络中,已有的研究成果大都采用了ARQ机制来降低卫星信道的数据丢失率。然而由于卫星信道具有长时延的特点,因此ARQ所采用的反馈重传机制会大幅增加卫星信道的传输时延。因此,针对卫星网络,提出了一种基于网络编码的ARQ(SatNC-ARQ)机制来减少卫星信道的丢包数,并通过减少重传次数来降低卫星信道的传输时延。在Sat-NC-ARQ中,卫星终端除了发送几个真实业务终端的数据包外,还会创建一个虚拟业务终端发送网络编码数据包,从而在接收方,只要接收到足够多的数据包,就能对所有的数据包进行解码,于是可以大幅降低卫星信道的传输时延以及丢包数。还对Sat-NC-ARQ所具有的一些性质进行了理论分析。仿真结果显示,相对于选择性重传ARQ机制,Sat-NC-ARQ机制能够降低大约11%的传输时延和86%的丢包数。     

无线网络中基于机会网络编码的加权广播重传

在无线广播网链路状态不同和丢包率高的条件下,基于机会网络编码的数据分发策略面临传输效率低和计算复杂度高的问题。针对这一问题,该文提出一种新的基于机会网络编码的加权广播重传(Weighted Opportunistic Network Coding Retransmission, WONCR)方案。该方案通过构建加权数据包分布矩阵(Weighted Packet Distribution Matrix, WPDM),在重传过程中采用新的调度算法进行编码数据包的选取,并将选取的数据包进行XOR编码后再重传。机会仿真结果表明,WONCR方案提高了传输效率,且计算开销较小,实现了无线广播网中高效、可靠的数据分发。     

基于自适应混合纠错的LVDS传输优化设计

数据在传输过程中由于多线程同步或者缓冲区溢出等问题经常发生丢包的问题，为改进该问题，本文提出基于 HARQ协议的传输方案，该协议发送方根据接收方反馈的信道状态调整数据包集大小，通过搭建的数据传输平台进行了验证，在传输距离为80ｍ时，误码率为0％，丢包率为10％时，信道输出率提高了14.5％，该传输方式在降低了因反复重传数据所造成的带宽损耗时也保证了接收的数据完整正确，真正提高了高速串行总线接口传输的可靠性。     

基于二进制网络编码的无线广播重传方法

为了提高无线广播网络中数据包的传输效率,提出了一种新的基于二进制网络编码的高效无线广播重传方法(WBRBNC).法基于数据包分布矩阵(PDM),在广播重传过程中使用一种新的数据包算法选取编码包,对这些丢包采用二进制网络编码方法进行编码,然后再进行广播,使一次广播重传可以使多个具有不同丢包的接收机受益.分析和仿真表明,该方法能有效保证接收节点的编码可解性,使重传次数显著减少,更接近于理论值,从而大大提高了传输效率.另外,该方法计算开销小,很适合应用在卫星广播网和无线传感器网等资源受限的系统中.     

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.     

基于机会式网络编码的低时延广播传输算法

为了提高无线网络中数据包广播传输的效率,本文提出了一种基于机会式网络编码的广播传输算法.该算法在发送端按一定顺序选择不同终端的丢包,并采用异或运算编码重传包,在终端采用从重传包中解码数据包的方法恢复丢包.该算法优先恢复时间重要性较高的丢包,并使多个终端同时从单个重传包恢复其丢包,因此有效地提高了广播传输效率并降低了传输...     

广播网络中基于补丁流的丢包恢复机制研究

现有的数字广播网络由于没有回传通道,发送端无法知悉传输过程中的丢包状况。接收端处在广播网络的不同位置,常常因处于小区边缘或受障碍物遮挡等原因造成信号减弱,从而导致丢包率提高。该文提出了一种基于pFEC (patching Forward Error Correction,补丁FEC)的丢包恢复机制,来解决单向广播网络的丢包问题。该方法利用蜂窝移动网络的双向信道来传输补丁流,提供自适应的FEC来降低丢包率。这种方式可以在广播业务中为不同位置的用户提供不同的丢包恢复能力。理论建模及仿真结果显示,在蜂窝移动网络丢包率不高的情况下,pFEC机制能够有效应对个别用户突发的丢包,从而提高广播业务整体的可靠性和服务质量。     

OBS网络中的新型竞争解决方案

提出一种解决光突发交换(OBS)网络节点中突发数据包冲突的方案.发生冲突时,在OBS层重传被丢弃突发数据包,然后给出评估这种重传机制丢包率的方法,并与偏射路由策略的性能进行比较,结果表明突发重传机制显著改善了丢包率.可以很好地实现服务质量(QoS)机制.     

基于3G网络的图像传输系统设计

设计并实现了基于3G网络的图像传输系统,特别提出一种适用于静态图像传输的基于用户数据报协议(UDP)和重传的传输方案。该传输方案在传输层采用UDP,可保证数据传输的实时性;在应用层对控制数据和图像数据采用不同的分类重传方法,可保证数据传输的可靠性。进一步,通过对数据包的大小以及数据包发送速率进行优化,降低了丢包率。最后,在实际环境中实现并测试了设计的系统。测试结果表明,该系统能够高效、可靠地传输静态图像。     

基于合作分集的新型自动重传协议

研究了一种基于合作分集的新型链路层自动重传协议——合作ARQ协议,传输错误的数据包将由一个中继节点进行重传。根据接收端处理重传数据包的不同方式,探讨了2种协议:1)合作简单ARQ协议,目的节点在收到重传的数据包之后丢弃原始的数据包;2)合作混合ARQ协议,目的节点将重传的数据包和原始数据包进行分集合并。分析了独立慢衰落信道下合作ARQ协议性能,仿真成果证明,合作ARQ协议相比传统ARQ协议能够降低链路层的丢包率,提高了系统的传输性能。     

带有接入阈值和超时隙的认知无线网络频谱分配策略

为了提高认知用户的响应性能,并降低传输中断的概率,通过限制进入系统的认知用户数据包数量,并令授权用户以超时隙为单位优先使用信道,提出一种带有接入阈值和超时隙的集中式认知无线网络频谱分配策略。结合时隙序号及系统中认知用户数据包的数量建立2维离散时间Markov链模型,给出认知用户数据包的平均延迟、吞吐量及信道切换率等性能指标的表达式。建立系统收益函数,针对不同的超时隙大小给出接入阈值的优化设置方案,并利用优化结果,进行系统实验。实验结果显示:合理的接入阈值和超时隙大小可以有效提高认知用户的传输质量。     

Erasure coding for reliable adaptive retransmission in wireless broadcast/multicast systems

In this paper, we present new adaptive automatic repeat request (ARQ) schemes for wireless broadcast/multicast combining erasure coding (EC) and packet retransmission. Traditional approaches rely on retransmitting the lost packets in a point-to-point or point-to-multipoint mode. The main idea behind the presented protocols is to retransmit adaptive combinations of the lost packets using EC, which can help several receivers to recover the lost information with fewer retransmission attempts. We propose two versions of EC-based ARQ protocols, and investigate theoretically the corresponding transmission bandwidths in different contexts. We show through simulation results the efficiency of the proposed protocols with respect to conventional ARQ strategies and new published ARQ works for broadcast/multicast. Finally, a new sliding window NACK feedback policy is presented for the case of a high number of receivers to avoid the feedback implosion problem.     

中继网络中减少反馈的多用户调度算法

针对多用户中继网络中上行反馈负荷过大的问题,本文提出了一种减少信道状态信息反馈的半分布式调度算法（RRFD）。基于反馈中断概率及总用户数,基站与中继分别设置信道状态反馈门限。每一调度周期内,通过与门限的比较,用户决定是否反馈相应链路信息,基站根据用户反馈情况决定系统采用何种传输模式。文中还对AF协议下采用该算法时的反馈用户数及平均可达速率等性能指标进行了理论推导。仿真结果表明,系统性能与数学推导相一致,与此同时,本文提出的算法可极大程度（90%以上）的减少系统反馈量,并显著降低了系统反馈中断概率,减小了容量损失。      

SR架构下的软件定义信息中心网络概率路由策略

传统的TCP/IP路由以IP地址为中心,信息传输效率低下,难以满足网络用户需求.信息中心网络(Information-Centric Network,ICN)开始成为研究热点,ICN以内容为中心,可以高效传输信息.为了利用软件定义网络(Software Defined Network,SDN)和分段路由技术的优势,提高...     

Exploiting classification for fountain data estimation in wireless sensor networks

In order to correct and avoid channel error, fountain codes were the best solution by limiting feedback channels and reducing energy consumption. Multi‐hops transmission is the principal limitation of the deployment and the use of these codes. Indeed, relayed transmission conducts to the generation of useless data, named overflow leading to a waste of energy, the most critical issue, and the big challenge in WSN. In this paper, based on a clustered architecture and estimation, we consider a distributed estimation scheme composing of sensor members and the cluster head. In order to reduce the number of a useless encoded packet generated as well as the impact of the overflow, we determine the optimal minimal number of encoded packets needed for data decoding. Sensor observations are encoded using fountain codes, and then messages are collected at the cluster head where a final estimation is provided within learning method. Then messages are collected at the cluster head where a final estimation is provided with a classification based on Bayes rule. The main goal of this paper is to determine the number of encoded packets by exploiting the classification model for fountain data estimation to minimize the overflow and extend the network lifetime.     

Fountain-inspired erasure coding for real-time traffic

An erasure correction strategy based on fountain coding is proposed for traffic with real-time requirements. A sliding window marks the range of non-expired data. Each new block entering the window is once sent as such, followed by probabilistically sending a repair packet. The repair packets are formed as a random combination of the blocks in the current window using a degree distribution as in LT coding. The performance of the method with a given channel loss probability is analyzed using a Markov chain model. The state space, however, has to be truncated for computational tractability. The truncation error is verified to be small enough by simulations. By using the analytical model the optimal degree distribution is found to be of single-degree type. The performance of the proposed scheme is compared with deterministic settings, in which repair packets are sent after fixed number of systematic packets. Further comparison is made against Raptor coding, and we note that using the presented strategy can result in better performance in some situations.     

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.     

Optimal resource allocation for two-stage connectionless access with collision detection

Connectionless access allows massive machine type communication (mMTC) devices to transmit small packets without establishment of radio bearers,significantly reducing device power consumption and control signaling overhead.Two-stage connectionless access (TSCLA) improves throughput and resource efficiency by optimally allocating resources between scheduling request (SR) phase and data transmission phase,which can be used for bigger packets and high traffic load.Based on this,a comprehensive theoretical analysis of one kind of TSCLA with collision detection was conducted to investigate its performance limit and devise its optimal resource allocation scheme.In addition,to avoid the complexity of user number estimation,a dynamic resource allocation algorithm with feedback control was proposed.Numerical results are provided to validate the effectiveness of aforementioned theoretical results and show that comparing with the genie aided algorithm known exactly the number of users,the performance loss of the proposed algorithm is within 4%.These works together provide good references for appropriate resource dimensioning for mMTC related protocols.     

Selfish users in energy constrained ALOHA systems with power capture

We consider a slotted ALOHA setting where backlogged, energy-constrained users selfishly select the probability with which they transmit packets. Packets are successfully received, even in case of collision, if the signal to interference plus noise ratio at the access point exceeds some threshold (power capture). The user problem of finding appropriate transmission probabilities is formulated as a static non-cooperative game and the performance limits for stationary and mobile scenarios are determined. The equilibrium analyses show that for stationary scenarios, users with high pathgains share the channel fairly while others never transmit. In the mobile case users utilize a binary strategy where they try to monopolize the channel when their pathgain exceeds some threshold that depends on system parameters (number of users, transmission costs, etc.). Otherwise they shut their transmitters off. Compared to traditional nondiscriminatory distributed multiaccess protocols the operating points achieved by selfish users generally increase sum-utility although this comes at the expense of larger user performance variations.     

数字喷泉码及其应用的研究进展与展望

 基于TCP协议的大部分网络通信都将接收到的数据包当作一个有序序列进行处理.TCP协议的这种有序序列模式限制了其在大量数据传输或将数据分布到大量用户的应用.基于数字喷泉码的数据传输模式不需要有序的数据序列,从而简化了网络中数据的传输方式,使得数字喷泉码成为一类适用于可靠通信的有效编码技术,而具有广阔的应用前景.本文综述了几类典型数字喷泉码的原理及其优缺点;探讨了这几类数字喷泉码的具体应用;指出了数字喷泉码研究中需要解决的一些关键问题.最后,对数字喷泉码的发展前景及研究方向进行展望.