Efficient Error Recovery Techniques in a Novel Multimedia Streaming Framework with Peer-Paired Collaboration

Research on application-level multicast seeks to combine the merits of unicast and IP multicast while avoiding their drawbacks. Efficient error recovery in such a system is still a difficult problem. Current research is primarily focused on developing local error recovery techniques, but these techniques would not work with shared losses, which often occur in application-level multicast. This paper presents a novel multimedia streaming framework called peer-paired pyramid streaming (P3S) which is basically a hybrid client/server and peer-to-peer structure. In P3S, clients are hierarchically organized with those at the same level coupled as peer pairs. P3S uses some controlled delay between packets that are vulnerable to shared losses to reduce the shared losses. The technique is verified by both theoretical and experimental results.     

Streaming Media over a Color Overlay Based on Forward Error Correction Technique

The number of clients that receive high-quality streaming video from a source is greatly limited by the application requirements, such as the high bandwidth and reliability. In this work, a method was developed to construct a color overlay, which enables clients to receive data across multiple paths, based on the forward error correction technique. The color overlay enlarges system capacity by reducing the bottlenecks and extending the bandwidth, improves reliability against node failure, and is more resilient to fluctuations of network metrics. A light-weight protocol for building the overlay is also presented. Extensive simulations were conducted and the results clearly support the claimed advantages.     

光传输系统中FEC码型的分析与研究

对适用于光传输系统中前向纠错（FEC）码型进行了一系列理论分析,提出了光传输系统中FEC码型的主要构造方法, 为光传输系统中FEC码型的构造和仿真研究打下了坚实的基础。并对光传输系统中带内FEC码型与带外FEC码型的纠错性能进行了比较分析,分析表明,为了适应光传输系统日益发展的要求而研究具有更强纠错性能的超强FEC码型的必要性。     

前向纠错编码传输机制的优化

为了提高前向纠错(FEC)编码在抖动参数上的性能,提出了一种改进发送端与接收端之间的信息交互方式的动态FEC传输机制(DFEC).新机制中,发送端收到反馈信息后,只调整数据的冗余度而不会为了等待反馈信息停止数据传送.在NS2平台上的仿真结果对比证实,所提出的DFEC传输机制可以改善接收端在抖动参数上的性能,为提高实时视频传输的端到端的服务质量提供了一种新方法.     

基于解码失真分析的最优前向纠错码码率分配策略

研究了H．263 视频在Rayleigh衰减无线信道中传输的信源／信道码率分配策略，目标是确定出前向纠错码(FEC)的最优编码速率，减小视频解码失真．对二阶Markov无线信道模型中符号级RS(n，k)编码残余分组出错率进行了分析，提出了一种估算解码失真的解析方法，并根据失真结果探讨了一种最优FEC编码速率策略．实验结果表明，残余分组出错率和解码失真的分析是合理的，最优FEC码率分配策略提高了无线视频传输质量．     

Strategies of Collaboration in Multi-Swarm Peer-to-Peer Content Distribution

In modern Peer-to-Peer (P2P) content distribution applications, multiple swarms typically exist, each corresponding to the dissemination of one content among interested peers. A common design in the existing P2P applications is to allow peers in one swarm to help each other, while different swarms are only coupled when sharing the upload bandwidth at the dedicated content servers/publishers. In recent years, a number of proposals have emerged which advocate inter-swarm collaboration and resource sharing, where peers in one swarm may contribute their storage and bandwidth resources to help peers in the swarm of another content. Such inter-swarm collaboration can improve content availability and optimize resource uti-lization in the entire system, at the cost of additional overhead for content preloading and inter-swarm coor-dination. This paper presents a survey of studies on effective inter-swarm collaboration mechanisms in the existing literature. This paper first discusses strategies of collaboration in P2P file sharing applications, and then presents multi-channel collaborative design for P2P live and Video-on-Demand (VoD) streaming. In particular, this paper elaborates our recent design of collaboration strategies among multiple streaming channels in a P2P VoD system, and shows that the server cost can be reduced by up to 25% while high streaming qualities are guaranteed in the entire system, even during extreme scenarios such as unexpected flash crowds. This paper also discusses representative approaches to implement inter-swarm collaborations in various P2P content distribution systems.     

感知编码的错误弹性音频流的改进方案

介绍了感知编码的一些基本概念,总结了早期错误弹性音频流的基本原理及关键技术。提出了一种感知编码的错误弹性音频流的改进方案,并对改进方案的仿真结果作了总结和分析,结果表明,提出的方案大大增强了增益因子丢包的鲁棒性。     

精密并联机器人系统误差的分析与补偿

为减小机构末端定位误差,提高精密并联机器人运动精度,以6-HTRT并联机构为结构模型,分析了机构的各种制造误差。首先在机构上开发了一种新型虎克铰链,同时采用了预紧装置;然后在控制系统中引入DSP高性能数据处理器;最后,用矢量构造的方法计算机构速度Jacobian矩阵,用数值法计算位置正解,用构造法计算误差Jacobian矩阵,对机构末端误差进行补偿。通过以上措施,可以使系统的精度提高到机构重复运动精度的3倍左右,满足精密并联机器人工作的精度要求。其中,软件误差补偿算法不受并联机构类型的限制,有较大的适用范围。     

基于插值算法的数控机床复合误差补偿技术

为提高数控机床的加工精度,提出了基于线性插值法和牛顿插值法的数控机床几何与热的复合误差建模方法,并利用数控系统外部机床坐标系的偏置功能,应用自行研发的综合误差实时补偿系统进行误差在线实时补偿.结果表明:所提出的模型具有计算简便、预测精度高等优点,可用于各种复杂加工场合中的数控机床几何误差与热误差的实时补偿.     

一种基于扩时的直接序列扩频系统抗脉冲干扰方法

为了提高直接序列扩频系统在脉冲干扰条件下的误码性能,提出了一种基于扩时技术的抗脉冲干扰新方法.对基于扩时技术的直接序列扩频（DSSS）系统模型及其脉冲抑制能力进行了分析,并提出了一种抗脉冲性能优越的扩时码方案.仿真结果表明,在误码率要求为10^-6时,该方法和理想交织加纠错的方法相比,抗脉冲干扰能力提高了4 dB,并且不会降低信息传输速率,硬件实现容易.     

自适应纠错编码抗衰减对策研究

在Ka及以上高频段卫星通信系统中,下行链路采用自适应纠错编码作为抗衰减对策将是一种很好的选择。文中首先给出了自适应纠错编码抗衰减系统的总体方案;提出了将收缩码与RS码加交织构成的自适应级联码作为前向纠错编码方式,能保证绝大部分地区卫星下行链路99.8%的系统可用度;最后对自适应编译码选择方案的实现进行了说明。     

数控车床两轴联动系统空间误差建模技术

利用齐次变换对数控车床两轴联动系统的几何误差进行了系统分析,根据小溜板坐标系的不同建立方法分两种情况分析了整个建模过程,论述了两轴间的正交误差对空间误差的影响,建立了两轴联动系统空间误差的数学模型,并利用该数学模型计算出某台数控车床两轴联动系统的空间误差.该分析方法可应用到其他机器设备空间误差的建模中.     

A Numerical Error Modeling Method for Parallel Kinematic Machines and Its Applications

<正>Introduction Unlike serial machines, which suffer from the accumulation of joint errors, parallel kinematic machines (PKMs) are considered to have high accuracy[1]. However, recent investigations have shown that the PKM is not necessarily more accurate than a serial machine with the same manufacturing and assembling     

Efficient User Authentication and Key Management for Peer-to-Peer Live Streaming Systems

Recent development of the peer-to-peer(P2P)live streaming technique has brought unprecedented new momentum to the Internet with the characters of effective,scalable,and low cost.However,before these applications can be successfully deployed as commercial applications,efficient access control mechanisms are needed.This work based on earlier research of the secure streaming architecture in Trust-Stream, analyzes how to ensure that only authorized users can access the original media in the P2P live streamin...     

舵机频率特性的测试误差分析与修正

为了提高舵机频率特性的测试精度,分析了测试系统输入输出通道产生的系统误差,特别是由A/D芯片多路转换、一路采集工作方式造成的信号相位滞后误差,并提出误差修正方法,即通过测量测试系统的频率特性来修正系统幅频和相频误差,并进行了试验.试验结果表明,对于测试系统造成的信号幅值衰减和相位滞后,可根据测试系统自身的幅频和相频特性测试数据,对直接计算值进行误差修正.     

无线传感器网络数据传输纠错方法的应用

在无线传感器网络实际应用中,传输信道容易受到干扰,不可避免形成突发错码.为了确保数据传输的可靠性,提出一种简便实用的数据传输纠错方法,结合卷积码技术和交织技术对数据进行纠错,并在传感器节点上实现卷积交织及卷积编码纠错功能.该方法不仅译码简单,设计复杂度低,而且可抗较高的信道误码,是一种良好的、便于软件实现的前向纠错编码技术.实验结果验证了该方法的实用性与合理性.     

QoS-Aware Virtual Machine Scheduling for Video Streaming Services in Multi-Cloud

Video streaming services are trending to be deployed on cloud. Cloud computing offers better stability and lower price than traditional IT facilities. Huge storage capacity is essential for video streaming service. More and more cloud providers appear so there are increasing cloud platforms to choose. A better choice is to use more than one data center, which is called multi-cloud. In this paper a closed-loop approach is proposed for optimizing Quality of Service (QoS) and cost. Modules of monitoring and controlling data centers are required as well as the application feedback such as video streaming services. An algorithm is proposed to help choose cloud providers and data centers in a multi-cloud environment as a video service manager. Performance with different video service workloads are evaluated. Compared with using only one cloud provider, dynamically deploying services in multi-cloud is better in aspects of both cost and QoS. If cloud service costs are different among data centers, the algorithm will help make choices to lower the cost and keep a high QoS.     

视频通信中频域和空域相结合的错误掩盖技术

针对由于信道误码导致帧内编码图像中出现的错误块，提出频域和空域相结合的掩盖算法．该算法基于图像局部平滑性和边界连续性。首先以相邻正确图像块的低频系数估计该错误块的直流分量并进行离散余弦反变换，实现对错误块的初步恢复．同时利用Sobel梯度算子检测相邻正确块中边界信息，进而估计错误块内的边界方向及其幅度．以马尔可夫随机场作为图像的先验模型，并基于最大后验估计实现对初步处理后的错误块进行空域优化．实验结果表明，和同类方法相比，该算法不仅能得到更好的掩盖图像质量，而且其计算量大幅度地减少．     

基于机器视觉的印刷电路板误差校正方法

利用贴片机视觉系统,首先通过示教的方法消除第1块印刷电路板(PCB)的定位误差,然后利用对PCB板基准点的图像识别与计算,消除其余PCB板的定位误差和制造误差,从而保证了贴片机的重复贴装精度.本文提出的PCB板误差校正方法和步骤用于所研制的全视觉贴片机样机上,对细间距表面元件的贴装精度可以控制在±50μm以内.