M步混合ARQ系统时延性能分析

为保证数据传输的可靠性,多种ARQ（自动请求重传）协议被提出和采用。论文针对多种ARQ／混合ARQ协议提出了一个一般化、系统化的时延分析模型,并采用信号流图理论及梅逊公式给出了M步混合ARQ控制系统的时延性能分析结果,为多种ARQ／混合ARQ协议的时延性能分析提供了一种系统化的有效分析方法。     

卫星通信传输延时误码率的比较研究

由于卫星通信传输时延大,因此误码造成丢帧后,增加的传输时间严重影响卫星通信。针对卫星通信普遍采用的卫星数字视频传输协议(DVB_S),通过比较分析自动重传(ARQ)、选择性重传(SR_ARQ)和主动性重传(CA_ARQ)3种重传机制的误码率与丢帧率的关系,给出了3种情况的理论延时性能,理论推导和仿真结果都表明CA_ARQ重传机制性能最为稳定,延时最小,更加适合卫星信道应用。     

适用于卫星网络的TCP跨层改进机制

该文提出基于跨层信息交互,将链路层ARQ重传状态信息通知TCP的机制,避免了链路层重传引起的时延变化对TCP的不利影响。该机制使用完全可靠选择性重传ARQ为TCP提供可靠的链路,避免卫星链路上发生丢包,并且不必要求链路层保证包按序递交,消除了重排序的等待时延,适合带宽时延积较大的卫星网络。仿真结果表明,能显著提高TCP在卫星网中的性能,特别是在误帧率较高条件下。     

预测反馈补偿法抑制帧中继网络时延抖动

对卫星通信帧中继网络时延抖动进行了深入的分析和研究,指出帧中继协议采用的可变帧长度以及卫星链路中缓冲区内等待帧个数变化是产生时延抖动的主要原因,并据此建立时延抖动数据模型,提出预测反馈补偿的方法抑制时延抖动,仿真实验结果表明,预测反馈补偿算法可以有效抑制帧中继网络时延抖动,根据QoS要求,可以采用不同的预测模型参数获得满足条件的时延抖动。     

一种基于新一代蜂窝移动通信的链路自适应方案

本文介绍了一种基于新一代蜂窝移动通信系统(简称4G)的链路自适应方案,能够很好的保证链路高吞吐量,而且有效抵抗突发误帧,使链路ARQ负荷相对很小;同时有效的提高了频带资源的利用率。     

LTE中ARQ的机制研究及算法改进*

本文主要研究了LTE中的ARQ机制,并针对ARQ确认算法中每次组装状态报告只是固定添加未接收到的PDU的SN号或分段信息而可能导致资源浪费的问题,提出了一种自适应确认算法,通过设定不同的基准参数,采用不同的偏移算法,有效的提高了系统的确认效率和资源利用率,从而使系统获得了较高的吞吐量。     

一种无线网络中基于ARQ的拥塞控制方法

提出了一种适用于无线网络的基于多拒绝自动请求重传（ARQ）算法的拥塞控制方法。谊方法结合随机早探洲（RED）算法,通过ARQ发送窗口和分割队列长度以及重传率进行拥塞控制。仿真表明,这种方法能预测链路拥塞,反馈链路拥塞程度,提高链路吞吐率。     

一种基于交织重组和星座重组的Type-Ⅱ型混合ARQ方案

为提高系统的通过率及译码效率，高速可靠数据传输系统采用混合ARQ方案。本文提出了一种基于交织重组和星座重组的混合ARQ方案，分析了系统的通过率、误帧率及重传时延。通过仿真说明本方案可获得较大的通过率增益，减小重传延时，提高了系统的传输可靠性。     

AOS自适应算法与虚拟信道复用结合的性能仿真

对CCADS AOS协议中的自适应帧生成算法进行研究,将包复用模块与虚拟信道复用模块作为一个整体进行考虑,仿真分析了分别采用高效率帧生成算法和自适应帧生成算法与虚拟信道调度算法相结合的平均包时延。仿真结果表明,采用自适应帧生成算法,并设置合理的门限值,比高效率帧生成算法与虚拟信道调度算法相结合的多路复用方法具有更小的包时延性能。     

导航设备时延测量技术分析

为了提高无线电卫星导航定位系统(RNSS)的精度,需要对导航设备时延进行精确测量。给出了导航设备的时延测量方法,研究了使用专用时延传递设备进行时延测试的实现方案,介绍了专用时延传递设备对接收链路和发射链路进行时延测量的方法,指出了该方法的创新性和实际测试过程中的应该注意的问题,给出了测试结果及误差分析。     

Two-layer modeling for local area networks

A two-layer performance model of a local-area network (LAN), consisting of a media-access control (MAC) layer submodel and transport layer submodels, is presented. A multiple-queue cyclic-service model of the token-passing MAC layer is used along with a closed-queueing network model for the transport layer. To deal with acknowledgement traffic with priority over data messages, a mean-value analysis (MVA) priority approximation is devised for the case where the priority can change at each queue. An iterative solution algorithm is proposed for this two-layer performance model. The method is applied to five models of communication systems: a symmetric-load, piggybacked acknowledgement model: a symmetric-load, explicit-acknowledgement model; full-duplex communication models (without and with priorities); and a client/server model. System performances measures such as throughput and mean-message delay, computed from the analysis, are compared to the simulation results over a wide range of parameters. In most numerical examples, the approximate analysis is shown to be within 90% confidence intervals in the mean-message delay, and within a few percent error in the throughput     

基于QualNet的无人机数据链时延仿真

概述了无人机数据链的网络组成,介绍了通信网络仿真软件QualNet的功能特点及其架构,并在该软件平台下建立无人机数据链时延仿真模型,分析远近程无人机在不同MAC信道接入协议下的平均端到端时延和平均抖动.仿真结果表明,设计无人机数据链时可优先采用TDMA接入协议.     

Energy efficiency analysis of IEEE 802.15.6 based wireless body area networks in scheduled access mode

This paper investigates the energy efficiency of IEEE 802.15.6 based wireless body area networks in the scheduled access mode. We assume that the hub operates in beacon mode with superframes and the nodes obtain scheduled allocation intervals consisting of finite number of allocation slots from the hub. In this paper, first of all, we present analytical models to compute the energy efficiency of the network for various scheduled allocation and acknowledgement policies assuming ideal channel conditions. The numerical and simulation results show that energy efficiency can be improved by (1) increasing the number of uploads in an active superframe, (2) increasing the payload size, (3) adopting block acknowledgement policy instead of immediate acknowledgement policy or (4) by decreasing the periodicity of allocations. We then present an analytical model to evaluate the energy efficiency in the presence of channel error. An approximate analytical solution for optimal frame size that maximize the energy efficiency of the network in error prone channel is obtained. For each node, we also provide analytical expression for the optimal allocation interval per superframe that maximize the energy efficiency of the network. Through extensive simulation studies, we establish that, in an error prone channel, the energy efficiency can be improved if the nodes make use of computed optimal frame size and optimal allocation interval for the uplink data transfer.     

Queuing analysis of cooperative GBN-ARQ in wireless networks with peers contending for a common helper

This paper presents a new queuing model for performance analysis of go-back-N automatic repeat request (GBN-ARQ) protocol in cooperative wireless networks. In the model, cooperative medium access control (CoopMAC) protocol and dynamic radio link adaptation are taken into consideration. We analyze the probability distribution of the total delay witnessed by packets at the source side. Multi-rate transmissions are considered for all links with link adaptation. An enhanced Markov model is introduced in our model, which encompasses the following aspects: CoopMAC protocol at the MAC sub-layer; GBN-ARQ protocol at the logical link control sub-layer and the transmission using decode-and-forward cooperative diversity at the physical layer. The stochastic process of random feedback delay because of peers contending for a common helper is analyzed. The queuing system is modeled as a GI/M/1 Markov chain to acquire statistics of the exact queue length and the total delay. We analyze the effects of Doppler frequency shift and packet arrival rate on the total delay. The analysis is validated by simulation.     

Delay constraint multipath routing for wireless multimedia ad hoc networks

According to the disadvantages of real time and continuity for multimedia services in ad hoc networks, a delay constraint multipath routing protocol for wireless multimedia ad hoc networks, which can satisfy quality of service (QoS) requirement (QoS multipath optimized link state routing [MOLSR]), is proposed. The protocol firstly detects and analyzes the link delay among the nodes and collects the delay information as the routing metric by HELLO message and topology control message. Then, through using the improved multipath Dijkstra algorithm for path selection, the protocol can gain the minimum delay path from the source node to the other nodes. Finally, when the route is launched, several node‐disjoint or link‐disjoint multipaths will be built through the route computation. The simulation and test results show that QoS‐MOLSR is suitable for large and dense networks with heavy traffic. It can improve the real time and reliability for multimedia transmission in wireless multimedia ad hoc networks. The average end‐to‐end delay of QoS‐MOLSR is four times less than the optimized link state routing. Copyright © 2014 John Wiley & Sons, Ltd.     

TCP/IP Performance over 3G Wireless Links with Rate and Delay Variation

Wireless link losses result in poor TCP throughput since losses are perceived as congestion by TCP, resulting in source throttling. In order to mitigate this effect, 3G wireless link designers have augmented their system with extensive local retransmission mechanisms. In addition, in order to increase throughput, intelligent channel state based scheduling have also been introduced. While these mechanisms have reduced the impact of losses on TCP throughput and improved the channel utilization, these gains have come at the expense of increased delay and rate variability. In this paper, we comprehensively evaluate the impact of variable rate and variable delay on long-lived TCP performance. We propose a model to explain and predict TCPs throughput over a link with variable rate and/or delay. We also propose a network-based solution called Ack Regulator that mitigates the effect of variable rate and/or delay without significantly increasing the round trip time, while improving TCP performance by up to 100%.     

SSCOP信令传输时延分析与检测

SSCOP协议是ATM宽带网络信令系统数据链路层的一部分,SSCOP信令链路为ATM网络元素之间提供可靠的信令信息传输。信令链路传输时延是ATM网络传输质量的一个重要参数,SSCOP协议的很多重要参数的取值都依赖于传输时延的大小。介绍一种SSCOP信令链路传输时延的检测方法,通过构造一种特殊的SSCOP报文来测试信令网络的传输质量,并计算信令报文的传输时延。对提高ATM信令系统的网络质量和优化SSCOP协议参数具有一定的现实意义。     

A Novel Rate Control Method for Low Delay Applications

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Internet中支配延迟的特征行为研究

通过对CAIDA机构授权的原始海量样本数据处理得到单向链路延迟,在此基础上计算了路径上最大的链路延迟对端到端延迟的比例以及路径上链路个数分布,基于此定义了支配延迟.针对链路延迟对端到端延迟的影响进行分析,表明支配延迟之间的差异是导致端到端延迟呈现多峰分布的主要原因.支配延迟更多地出现在路径的中间部分和AS自治域内部,说明延迟瓶颈从网络的接入部分向传输部分转移,得出传输延迟在总延迟中的影响逐渐减小,路径中的支配延迟将主要由传播延迟决定的结论.