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针对基于协作节点的分层移动IPV6协议(PHMIPv6)在域间切换时,因未充分考虑非合作节点而可能导致的预切换操作失败问题,该文通过计算移动节点与协作节点的链路终止时间(LET)并引入时间阈值,保证所选择的协作节点能够及时执行预切换过程并返回新的转交地址,有效缩短切换准备时长;另外,在切换完成后,以协作节点为中继,移动节点与新的接入点在上下行建立包括蜂窝网络和Ad hoc网络的异构协作信道,充分利用协作分集技术来提高小区边缘的通信质量.应用NS2搭建了仿真环境,并分别从预切换成率、丢包数、切换时延等三个方面验证了该切换机制在性能上的优越性. 相似文献
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下一代网络(NGN)是一种采用不同无线接入技术的融合网络,在这种融合的网络环境中,不同无线接入技术间的垂直切换成为重要的研究课题。但是现有的垂直切换算法少有考虑用户业务对网络的实际需求偏好以及用户的移动性,大多以网络端的属性值作为切换判决指标。为了解决上述问题,提出了一种基于业务需求的速度自适应垂直切换算法,并通过速度因子以及网络属性因子矩阵来补偿因节点运动而对无线链路质量造成的损耗,自适应调整业务对网络属性因子需求的权重,从而支撑节点做出有效的切换判决,最终实现速度自适应的能更好地服务于应用业务的垂直切换。仿真实验表明,该算法能有效地克服乒乓效应,且与其他切换算法相比有较高的数据包吞吐率。 相似文献
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频谱切换技术可以降低无线传输干扰、优化网络结构,成为无线网络研究的热点。现有频谱切换技术忽视了频谱切换执行顺序对网络性能的影响,无法保证网络在切换过程中的连通性和吞吐量。为了最大化网络吞吐量,提出一新的频谱切换调度问题(SHSTM:Spectrum Handoff Scheduling for Throughput Maximization),并证明SHSTM是NP难问题。为解决SHSTM问题,提出联合频谱切换调度和QoS重路由的跨层优化算法JSHSQ-R。在JSHSQ-R中,频谱切换分多轮执行。为了减少切换延时并保证网络连通性,该算法基于加权最小生成树来确定每轮需要切换的链路,并在切换过程中为数据流进行重路由来满足数据流的QoS需求。在NS2上进行了大量仿真实验,结果表明所提算法能够充分利用无线网状网多接口多信道资源,并能为多流提供较高的网络吞吐量保证。 相似文献
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为了解决多描述视频编码器在丢包信道下的漂移问题,本文提出了一种新的基于分布式视频算法的多描述视频编码方案。实验结果表明,借助于分布式编码的稳健性,这一新方案能有效地避免漂移问题。为了解决多描述视频编码器在丢包信道下的漂移问题,提出了一种新的基于分布式视频算法的多描述视频编码方案。实验结果表明,借助于分布式编码的稳健性,这一新方案能有效地避免漂移问题。 相似文献
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针对多种传输速率的链路共存于同一信道时引发的性能瓶颈,以及单接口多信道网络中接收端忙的问题,在DCF协议的框架内提出一种适用于WLAN Mesh网络的分布式多信道速率自适应媒体控制接入(MAC)协议。该协议允许发送节点的邻居节点通过协作应答的方式告知相应接收节点所处信道,接收节点根据当前信道质量合理选择传输速率和传输信道反馈给发送节点。通过上述机制,将不同传输速率的链路分配在不同的信道上。仿真结果证明,该协议能避免不同传输速率链路之间的相互干扰,解决接收端忙问题。与现有典型多信道速率自适应MAC协议相比,能有效提高网络的总吞吐量。 相似文献
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为了解决当前许多基于IEEE 802.11标准的速率自适应协议所面临着的快速变化链路中的切换滞后问题、碰撞问题及重复速率抖动问题,提出了一种混合速率自适应算法(MRA)。MRA算法通过高优先级速率自适应算法(HPRA)快速获得非最优化的传输速率来解决快速切换问题,通过低优先级速率自适应算法(LPRA)在一定时间后获得最优化的传输速率,其中利用获得的SNR参数减小碰撞问题带来的影响,并建立短时间内出现反复速率切换便在一定时间内禁止切换的机制来避免重复速率抖动问题的出现。仿真实验结果表明,无论在快速变化的链路中还是在相对平静的链路情况下,该算法的性能较当前的知名算法都有明显的提高。 相似文献
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针对无线传感器网络节点能量受限问题,提出了一种新的自适应更新异步MAC协议——AU-MAC协议。该协议以睡眠与工作状态切换、异步方式和自适应更新相结合的办法有效延长了网络寿命,减少了节点能耗。AU-MAC协议通过采用发方监听、接方激活数据传输,提高了信道利用的有效性。并且,它以建立邻居节点信息表,引入自适应更新机制,来减少空闲监听。在NS2网络仿真平台对提出的AU-MAC协议的性能进行了仿真评估。仿真结果表明,AU-MAC协议在保持相当的吞吐量以及端—端延迟的基础上,使无线传感器网络的能量有效性得到了改善。 相似文献
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《Computer Networks (1976)》1979,3(4):267-286
In this paper a new switching technique called virtual cut-through is proposed and its performance is analyzed. This switching system is very similar to message switching, with the difference that when a message arrives in an intermediate mode and its selected outgoing channel is free (just after the reception of the header), then, in contrast to message switching, the message is sent out to the adjacent node towards its destination before it is received completely at the node; only if the message is blocked due to a busy output channel is a message buffered in an intermediate node. Therefore, the delay due to unnecessary buffering in front of an idle channel is avoided. We analyze and compare the performance of this new switching technique with that of message switching with respect to three measures: network delay, traffic gain and buffer storage requirement. Our analysis shows that cut-through switching is superior (and at worst identical) to message switching with respect to the above three performance measures. 相似文献
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This paper studies the adaptive consensus problem of networked mechanical systems with time-varying delay and jointly-connected topologies. Two different consensus protocols are proposed. First, we present an adaptive consensus protocol for the connected switching topologies. Based on graph theory, Lyapunov stability theory and switching control theory, the stability of the proposed algorithm is demonstrated. Then we investigate the problem under the more general jointly-connected topologies, and with concurrent time-varying communication delay. The proposed consensus protocol consists of two parts: one is for the connected agents which contains the current states disagreement among them and the other is designed for the isolated agents which contains the states difference between the current and past. A distinctive feature of this work is to address the consensus control problem of mechanical systems with unknown parameters, time-varying delay and switching topologies in a unified theoretical framework. Numerical simulation is provided to demonstrate the effectiveness of the obtained results. 相似文献
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针对一类非线性离散时间动态系统, 提出了一种新的非线性自适应切换控制方法. 该方法首先把非线性项分解为前一拍可测部分与未知增量和的形式, 并充分利用被控对象的大数据信息和知识, 把非线性项前一拍可测数据与未知增量都用于控制器设计, 分别设计了线性自适应控制器, 带有非线性项前一拍可测数据补偿的非线性自适应控制器以及带有非线性项未知增量估计与补偿的非线性自适应控制器. 三个自适应控制器通过切换函数和切换规则来协调控制被控对象. 既保证了闭环系统的稳定性, 同时又提高了闭环系统的性能. 分析了闭环切换系统的稳定性和收敛性. 最后, 通过水箱液位系统的物理实验, 实验结果验证了所提算法的有效性. 相似文献
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Behrouz Shahgholi Ghahfarokhi Neda Moghim Shayan Eftekhari 《Multimedia Tools and Applications》2017,76(22):23239-23271
Channel zapping delay is a big challenge in delivering TV service over the Internet infrastructure. Previous research works have studied this delay, its components, and solutions to decrease it. Unfortunately, the best proposed solutions reduce the delay at the expense of increasing bandwidth usage or decreasing the received video quality. After channel switching, the Set Top Box (STB) or player application should buffer sufficient frames before starting to play the received video. However, the buffering process takes place at the playback rate and leads to a delay which is inversely related to the buffer duration. Regarding Information Centric Networking (ICN) paradigm, this paper introduces a new channel zapping protocol that aims to remove the synchronization and buffering delays while maintaining the bandwidth utilization and also the received video quality. The general idea of the proposed solution is to exploit the in-network caching feature of the ICN to retrieve the frames from the network at the network speed. Although the analyses show that the proposed zapping protocol eliminates the delay dependency to the buffer duration, network throughput becomes the bottleneck instead. So, novel solutions have been proposed to reduce the queuing delay as the main component of network delay. These solutions include two new caching algorithms, a new cache replacement algorithm, and applying scheduling methods to the forwarding queues. Simulation results show that increasing link rates, using the proposed caching and cache replacement algorithms, and applying an appropriate scheduling method will greatly reduce the zapping delay without sacrificing the bandwidth or video quality. 相似文献
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该文研究将智能天线应用于Internet无线接入网络的中心接入点(CAP)。提出了基于轮询的自适应波束形成多址接入协议(PB-ABFMA).该协议中,CAP接收或发送数据分组前,由CAP引导用户节点发送训练序列,CAP的智能天线据此计算出与用户节点对应的权矢量.CAP以轮询及动态TDMA方式为各节点安排发送时隙。采用微时隙为处于空闲状态的节点保持连接以降低时延.设计了一种简单有效的竞争接入算法,保证新用户能快速接入信道.针对Internet中主要的“请求一回应”(request-reply)式业务,分析了协议的信道利用率与平均“请求一回应”时延.结果表明,PB-ABFMA协议能有效支持智能天线应用并具有较高的信道利用率与良好的时延性能。 相似文献
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In this paper a new switching technique called virtual cut-through is proposed and its performance is analyzed. This switching system is very similar to message switching, with the difference that when a message arrives in an intermediate node and its selected outgoing channel is free (just after the reception of the header), then, in contrast to message switching, the message is sent out to the adjacent node towards its destination before it is received completely at the node; only if the message is blocked due to a busy output channel is a message buffered in an intermediate node. Therefore, the delay due to unnecessary buffering in front of an idle channel is avoided. We analyze and compare the performance of this new switching technique with that of message switching with respect to three measures: network delay, traffic gain and buffer storage requirement. Our analysis shows that cut-through switching is superior (and at worst identical) to message switching with respect to the above three performance measures. 相似文献
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《Computers & Operations Research》2002,29(13):1793-1806
In this paper, we propose an efficient algorithm to find a collision-free time slot schedule in a time division multiple access frame. In order to minimize the system delay, the optimal schedule must be defined as the one that has the minimum frame length and provides the maximum slot utilization. The proposed algorithm is based on the sequential vertex coloring algorithm. Numerical examples and comparisons with the algorithm in previous research have shown that the proposed algorithm can find near-optimal solutions in respect of the system delay.Scope and purposeAn ad-hoc network was introduced in order to apply packet switching communication to a shared radio channel. Using a radio channel as the broadcast medium to interconnect users, an ad-hoc network provides flexible data communication services among a large number of geographically distributed, possibly mobile, radio units. In an ad-hoc network, since all users share a single channel by multiple access protocol, unconstrained transmission may lead to the time overlap of two or more packet receptions, called collision, resulting in damaged useless packets at the destination. Collided packets increase the system delay because they must be retransmitted. Therefore, the transmission for each station must be scheduled to avoid any collision, that is, collision-free transmission should be guaranteed. The time division multiple access (TDMA) technology can be used to schedule collision-free transmission. In this paper, we propose an efficient algorithm to find a collision-free time slot schedule in a TDMA ad-hoc network. 相似文献