Interactive Multimedia Synchronization Model Based on Petri Nets

The multimedia synchronization is used to coordinate the timing of each multimedia object in the multimedia system. After studying different multimedia synchronization systems that have been published, an Interactive Synchronization multimedia based on Petri Nets model （ISPN） is proposed in this paper. The system is capable of describing the dynamic timing actions of multimedia objects vividly as well as controlling them interactively to maintain the system level synchronization balance.

A Multimedia Synchronization Model Based on Timed Petri Net

Multimedia synchronization is a significant requirement for distributed multimedia applications. In this paper, a multimedia synchronization model based on timed Petri nets is presented. Using this model one can give the abstraction and formal description for multimedia object compositions with time-constrained relations. Algorithms for asynchronous user interactions are also presented.

Temporal Models for Multimedia Synchronization

This paper provides a survey of selection of most common existing temporal models for multimedia synchronization, which are based on CSP, CCS, path expressions, and Petri net. Multimedia refers to the integrated generation, representation, processing, storage, and dissemination of information expressed in multiple time dependent and time independent media such as data, text, graphics, images, audio, and video. Synchronization assures a temporal order of events, which is a well-studied topic in the area of operating systems, parallel programming languages, and database technology.

Dual-scale multimedia dynamic synchronization model

Multimedia synchronization is the key technology in application of distributed multimedia.Solution of synchronization conflicts insides and among streams as well as that of user interaction,synchronization granularity refinement and synchronization precision improvement remain great challenges although great efforts have been invested by the academic circle.The construction method of a dual-scale dynamic synchronous model of multimedia presented in this article realizes multimedia synchronization on two sca...

Modeling Distributed Multimedia Synchronization with DSPN

Multimedia synchronization is the essential technology for the integration of multimedia in distributed multimedia systems. The multimedia synchronization model has been recognized by many researchers as a premise of the implementation of multimedia synchronization. In distributed multimedia systems, the characteristic of multimedia synchronization is dynamic, and the key medium has the priority in multimedia synchronization. The previously proposed multimedia synchronization models cannot meet these requirements. So a new multimedia dynamic synchronization model-DSPN,based on the timed4etri-net has been designed in this paper. This model can not only let the distributed multimedia system keep multimedia synchronization in a more precise and effective manner according to the runtime situation of the system, but also allow the. user to interact with the presentation of multimedia.

FINE-GRAINED DISTRIBUTED MULTIMEDIA SYNCHRONIZA-TION MODEL——ENHANCED FUZZY-TIMING PETRI NET

A fine grained distributed multimedia synchronization model——Enhanced Fuzzy timing Petri Net was proposed which is good at modeling indeterminacy and fuzzy. To satisfy the need of maximum tolerable jitter, the sufficient conditions are given in intra object synchronization. Method to find a proper granularity in inter object synchronization is also given to satisfy skew. Exceptions are detected and corrected as early as possible using restricted blocking method.

A New Multimedia Synchronization Model

Multimedia synchronization has been recognized by many researchers as a significant requirement for multimedia applications. Modeling and specifying timing requirements of the multimedia synchronization is a main problem of multimedia synchronization. In this paper, on the basis of overcoming the limitations of the other models, a new multimedia dynamic synchronization Petri net (DSPN), has been proposed. This model can let the multimedia system keep the multimedia synchronization in a more precise and effective manner.

Impacts of space-time-frequency synchronization errors onwide-band target echo characteristics of bistatic/multistatic radar

Bistatic/multistatic radar has great potential advantages over its monostatic counterpart. However, the separation of a transmitter and a receiver leads to difficulties in locating the target position accurately and guaranteeing space-timefrequency synchronization of the transmitter and the receiver.The error model of space-time-frequency synchronization in a motion platform of bistatic/multistatic radar is studied. The relationship between the space synchronization error and the transmitter platform position, receiver platform position, moving state, and beam pointing error, is analyzed. The effect of space synchronization error on target echo power is studied. The target scattering characteristics are restructured by many separate scattering centers of the target in high frequency regions. Based on the scattering centers model of the radar target, this radar target echo model and the simulation method are discussed. The algorithm of bistatic/multistatic radar target echo accurately reflects the scattering characteristics of the radar target, pulse modulation speciality of radar transmitting signals, and spacetime-frequency synchronization error characteristics between the transmitter station and the receiver station. The simulation of bistatic radar is completed in computer, and the results of the simulation validate the feasibility of the method.

Nondeterministic Temporal Relations in Multimedia Data

Synchronization is a important issue in multimedia systems which integrate a variety oftemporally related media objects.One part of synchronization is the representation of tempo-ral information.With the emerging interaetive multimedia,deterministic temporal modelsare replaced by nondeterministic ones with more expressiveness.This paper classifies tempo-ral models by their expressiveness,and evaluates the relevant nondetermi.nistic temporal re-lations in multimedia data.Additionally,an interval-based nondeterministie model based ona complete temporal operator set is proposed,providing high-level abstractions and a highdegree of expressiveness for interactive multimedia systems.

永磁同步电机改进积分型时变滑模控制

为了提高永磁同步电机的控制性能,改善对于电机的控制方法,针对永磁同步电机的积分滑模控制进行研究,首先,提出积分滑模控制在运行中遭遇未知干扰后易产生转速超调的问题。然后,通过定义自调节的积分初值来消除运行过程中因积分累积所产生的超调,改善转速超调问题。其次,为了提高滑模控制在电机整个运动的全局阶段的收敛性,提出基于预测在线寻优的时变滑模控制,通过预测控制变量来选出当前时刻的最优滑模面,使得状态变量可以更快收敛到滑模面,进一步降低转速误差,提高系统的控制精度与控制速度。最后,建立扩张状态观测器来观测系统的未知干扰,对控制器进行补偿,提高整个控制系统的鲁棒性,并且通过仿真和实验验证了所提出方法的有效性。

基于ARIMA-TCN混合模型的高速铁路时间同步方法

列控系统作为高速铁路的核心系统,保持其系统的时间同步对于行车安全至关重要。针对现有时间同步方法易受时变上下行传输时延、随机时钟跳变等影响,导致主从时钟偏移估计不准确的问题,提出一种基于差分自回归移动平均-时域卷积神经网络(ARIMA-TCN)混合模型的高速铁路时间同步方法。首先,根据上下行链路传输速率的不对称比,建立高速铁路时钟的数学理论和实际观测模型。然后,使用拉依达准则识别处理跳变异常值,完成实际时间序列的预处理。再次,使用ARIMA模型平滑时间序列中不确定时延带来的噪声抖动,获得平稳的时间序列。最后,通过提出的注意力增强TCN模型进行预测补偿,完成时钟偏移的补偿校正。通过实验仿真,得到基站区间内位置、基站间距以及车速对高速铁路时间同步的影响性分析。实验结果表明:与对比方法相比,所提方法补偿后的均方根误差较最小二乘法减少了75%、较最大似然估计方法误差减少了44.4%,较BP神经网络方法误差减少了16.7%,验证所提方法具有更低的同步误差和更高的同步精度。

小偏差永磁同步电机双矢量模型预测控制

传统的永磁同步电机双矢量模型预测控制的合成电压矢量与参考电压矢量的偏差较大,且存在计算量大、开关频率高的缺点,在实际工况中难以实现良好的控制性能。为了解决上述问题,提出一种小偏差永磁同步电机双矢量模型预测控制策略,通过分析参考电压矢量的变化规律,构造新的电压矢量选择表,将电压矢量的选择范围从六个降为三个,减小计算量的同时也降低了开关频率;针对传统的作用时间计算方法存在的问题,提出基于偏差最小原则的作用时间计算方法,并详细证明了该方法的优越性。仿真和实验结果显示,所提出的方法能够有效减小计算量和降低开关频率,同时具有较好的稳态和动态性能。

基于神经网络的永磁同步电机模型预测电流控制

针对备选电压矢量有限导致永磁同步电机有限集模型预测电流控制性能较差及计算量较大的问题,提出基于神经网络的永磁同步电机模型预测电流控制。基于7个基本电压矢量和121个扩展电压矢量的永磁同步电机模型预测电流控制分别建立7分类和121分类神经网络。随着备选电压矢量的增加,模型预测电流控制性能提升,对应的神经网络控制性能也得到改善,但分类任务数也随之增加。对于多步模型预测控制,计算量随步长呈指数上升,但输出电压矢量不变。因此,基于两步模型预测电流控制建立7分类神经网络。仿真结果表明:以上神经网络控制均可行,性能与相对应的模型预测电流控制基本相当。实时性实验结果表明相较于单步模型预测电流控制,神经网络控制并不占优势,但相较于两步模型预测电流控制,神经网络实时性有明显优势,计算耗时减小29.58%,表明神经网络控制更适于多步模型预测电流控制。

基于时间序列的改进型永磁同步电机三矢量无模型预测电流控制策略

针对永磁同步电机驱动系统传统的三矢量模型预测电流控制策略参数鲁棒性差的问题,提出一种基于时间序列的改进型三矢量无模型预测电流控制策略,以消除参数失配的影响,提高系统的鲁棒性。首先,建立时间序列数据驱动模型,将输入输出数据拟合为离散传递函数,并结合递归最小二乘法在线估计模型待定系数,预测所需变量。此外,对矢量扇区进行重新分类,以优化三矢量组合的选择过程。引入矢量占空比直接计算方法,抑制电机参数入口对占空比计算环节的不确定性影响,进一步提高系统的鲁棒性。最后,仿真和实验结果表明,所提出的策略能有效提高模型参数的鲁棒性,dq轴电流纹波减小,电机参数变化引起的干扰得到有效抑制。

扩展时间流Petri网多媒体同步模型

多媒体同步的一个主要问题是多媒体同步时间要求的描述与建模。文中基于时间流Ｐｅｔｒｉ网模型（ＴＳＰＮ），通过分析ＴＳＰＮ 模型的不足之处，提出了一种新的多媒体同步模型——扩展时间流Ｐｅｔｒｉ网模型（ＸＴＳＰＮ）．ＸＴＳＰＮ 不但可以完全、准确地描述媒体流内和流间的时间行为，而且通过引入容许阻塞时间、回溯算法等对ＴＳＰＮ进行扩展，可以有效地克服网络随机延迟、阻塞和丢包等因素的不良影响，提高了模型的建模能力和对分布式网络环境的适应能力．

基于线性时态逻辑的Petri网模型检测

Petri网是一种重要的数学工具,它能有效地对并发系统进行描述和建模。线性时态逻辑LTL则是描述和验证并发系统特性的一种重要的形式化工具,它能方便准确地描述并发系统的重要性质,如安全性和活性。文章深入描述了线性时态逻辑、Büchi自动机、Petri网和同步积之间的内在联系,并探讨了基于线性时态逻辑的Petri网模型检测策略。与其它方法比较,这种模型检测的策略结合了线性时态逻辑和Petri网模型的不同优点,增强了Petri网的模型分析和验证能力。最后,通过对一个并发系统形式化的模型检测分析,验证了相应的结论。

基于同步时间Petri网的细粒度多媒体同步模型研究

多媒体同步是分布式多媒体信息系统的关键问题。在分析和比较几种已有的典型的多媒体同步模型的基础上,本文提出了一种新的模型:同步时间Petri网(简记为STPN)。STPN不仅能完整、准确地对媒体流内和媒体流间的时间层次行为进行形式化描述,而且解决了时间流Petri网中存在的死托肯问题。特别地,通过引入抑止弧,STPN有效地克服了随机延迟、阻塞、丢包等因素的不良影响。尤其当丢失率较高时,STPN更能体现其优越性和鲁棒性。

多媒体同步的Petri网模型

多媒休系统中通常包括各种媒休类型,例如,文本、语音、图象、音频和视频。

基于Petri网的分布式多媒体同步模型研究

Petri网作为一种描述系统行为的形式化工具 ,在各类多媒体系统中有着较多的应用 ,尤其擅长于描述多媒体的同步问题 ,出现了诸如 OCPN(对象组合 Petri网 )等多媒体同步模型 ,然而 ,这些模型却不足以处理分布式环境中的多媒体同步问题 .本文提出了一种新的扩充 Petri网模型并分析了其模型化的能力和性质 ,利用该模型可以较好地解决分布式环境中的多媒体同步问题 .

自回归和EWMA在齿轮箱早期异常检测中的应用

针对齿轮箱传统故障分析方法难以及时发现早期故障的问题,进行基于自回归模型和统计过程控制方法的齿轮箱早期异常检测方法研究。采用时域同步平均算法(Time Synchronous Averaging,TSA)去除原始振动信号中的噪声,并建立自回归(Autoregressive Model,AR)模型计算残差;提取残差的标准差、峭度与均方根作为指标,初步判断齿轮早期故障;选取残差的标准差进行统计过程分析,分别建立均值控制图(Xbar)、单值-移动极差控制图(I-MR)、指数加权移动平均(EWMA)控制图来判断齿轮早期异常发生点。研究结果表明,EWMA控制图检测到第62个文件开始超出控制限,而其他两种控制图均从第65个文件出现异常,说明EWMA控制图相比其他方法能够更早的检测出齿轮早期故障发生的异常点,进一步验证了AR模型与EWMA控制图相结合进行早期异常检测的有效性。