Non-preemptible last section assignment for reducing feedback latency in real-time control systems

A real-time control system design procedure consists of the controller design stage and the implementation stage. In the controller design stage, various digital control theories are used with assumptions, such as synchronous sampling, no sampling jitter and negligible feedback latency (latency from sensing to actuation). However, in the implementation stage, multiple control tasks are usually scheduled on a processor, which creates a finite sampling period, varying feedback latency and sampling jitter, and therefore the controller's performance is degraded. In this article, we investigate the relationship between control performance and timing parameters. In the course of this investigation, we found that the feedback latency is the dominant factor affecting control performance. In addition, we propose a rate monotonic (RM) scheduler with non-preemptible last section algorithm, which can reduce the feedback latency considerably. The proposed algorithm provides better control performance than a preemptive RM scheduler, in most cases. The effectiveness of the proposed algorithm is shown in illustrative examples.     

FF现场总线系统调度问题的研究

FF现场总线系统(FCS)为典型的分布式实时系统，分布在不同设备（包括总线） 的功能块和通讯任务相互作用完成复杂的控制方案，除了实时性要求，还要考虑执行顺序和 资源约束，调度问题为一NP 完全问题．本文分析了FF控制系统的特点，提出了类比于作业 车间调度问题（JSSP）的调度模型，针对特殊的模型，设计相应的编码和解码规则以及性能 指标，用遗传算法在满足上述约束下构建调度表，实现无抖动调度，最后分析了该方法下系 统的可调度条件．     

基于区间代数方法分析嵌入式系统抖动的稳定性

针对嵌入式实时调度系统,分析了控制任务的采样周期和延时不规则抖动属性及控制任务的稳定性能.针对抖动引起的时变不确定性,采用区间代数分析方法,构建系统的离散时间闭环区闻状态矩阵,通过对单个时不变矩阵范数的判断得到一个保守的系统稳定性充分判据.仿真实例表明,当抖动在有界范围内变化时,该方法简便有效.     

在WEB SERVER中实现响应时间预测和准入控制

WEB服务已经被广泛应用，我们必须为相应的增值服务提供可靠的服务质量保证。介绍了一个在WEB SERVER中进行准入控制的方法，该方法周期性地预测服务器负载，并根据预测结果实现系统资源的有效分配和准入控制。     

面向抖动优化的任务静态优先级指派算法

对任务相对截止时限进行优化设置是一种减少输出抖动的有效方法,但现有方法均是针对最早时限优先调度算法,不能适用于任务集采用静态优先级调度算法的场合.为此,提出通过优化优先级指派实现任务集的整体抖动最小化,并给出一种启发式的优先级指派算法.根据单调速率调度算法确定任务的初始优先级,以最小化局部抖动方式依次对任务的优先级进行再调整,从而得到近似最优的优先级指派.仿真实验结果表明,该算法能有效减少任务集的整体输出抖动.     

基于抖动激励的VoIP终端拥塞控制机制

针对基于H．323的VoIP系统，提出了一种抖动激励式终端拥塞控制机制，将语音分组的延迟抖动参数与RTCP协议相结合，控制动态改变语音编码方式及传输分组大小，从而缓解网络拥塞，降低传输延时和丢包率。     

TSN中时间感知整形器测试方案设计及实现

时间敏感网络（TSN）是支持工业互联网的以太网新标准。TSN通过引入时间感知整形器（TAS）来精确控制不同优先级别的数据帧转发,使以太网能够支持低时延、低时间抖动的确定性服务。对TSN的目的、发展现状以及主要标准进行了叙述,结合TAS的基本原理和工作流程,提出了TAS的测试方案,将其划分为几个独立的部分,采用观察测试流量通过每个部分后特征变化的测试方法,并完成了测试设计和测试验证,测试结果证明了测试方案的有效性。     

Fault‐tolerant RT‐Mach (FT‐RT‐Mach) and an application to real‐time train control

Even though real‐time systems have the stringent constraint of completing tasks before their deadlines, many existing real‐time operating systems do not implement fault tolerance capabilities. In this paper we summarize fault tolerant real‐time scheduling policy for dynamic tasks with ready times and deadlines. Our focus in this paper is the implementation, which includes fault‐tolerant scheduling, re‐scheduling, and recovery mechanisms in the FT‐RT‐Mach operating system, a fault‐tolerant version of RT‐Mach. A real‐time train control application is then implemented using the FT‐RT‐Mach operating system. Copyright © 1999 John Wiley & Sons, Ltd.     

一种新型的基于RED的逐节拥塞控制算法

随着Internet上各种多媒体应用的迅速发展,导致网络经常发生拥塞现象,严重影响网络传输的服务质量（QoS）,现有的拥塞控制采用以TCP为核心的基于窗口技术的端到端控制,具有丢包、响应速度慢等缺陷,提出的基于RED的逐节拥塞控制算法通过对拥塞的早期检测和在相邻节点进行拥塞控制等方法,使网络能对拥塞做出快速响应,有效地克服了现有拥塞控制方法的缺陷,实验结果表明,在相同配置下,采用该拥塞控制算法的网络在吞吐率和拌动等性能上均优于端到端拥塞控制。     

基于Smith预估的TCP拥塞控制策略及仿真

应用控制理论对网络数据传输过程进行了分析和建模,提出了一种基于回环时间RTT的P-Smith预估拥塞控制策略.该方法建立在RTT长相关性的基础上,可以在线实时调节控制器中的比例系数和时延参数以保证控制回路的稳定性以及发送速率的平滑性.仿真结果表明,使用该控制方案能使缓冲器队列长度快速收敛到目标值,发送速率具有良好的平滑性能,与传统的PID 控制器相比具有更好的稳定性和鲁棒性.     

采用抢占阈值调度的具有释放抖动和特定释放偏移的最大响应时间计算方法

当采用抢占阈值调度时,如果任务具有释放抖动并且对释放偏移有特定要求,任务最大响应时间的计算就很复杂.通过将对响应时间有影响的任务实例划分为4个集合,分别分析得出达到最大响应时间的各种条件,从而进一步得到具有释放抖动和特定释放偏移的周期任务最大响应时间的计算方法.试验结果表明：这种方法的运行时间要远低于采用模拟运行方法时的运行时间.     

时变时滞系统的参数辨识及自适应控制

基于最小二乘法一类辨识算法的自适应控制,一般只适用于时滞已知且时不变的被控过程,本文提出了一种包括可估计时变时滞在内的参数辨识方法,该方法扩展了最小二乘一类辨识算法及相应的自适应控制的应用范围,文中通过一个实例讨论了该方法在自适应控制中的应用,并谈及下一步的研究工作。     

基于PID控制的自适应媒体播放算法

针对视频播放中因缓冲区下溢带来的抖动问题,提出一种基于PID控制的自适应播放算法。算法结合PID控制和自适应播放算法,根据网络信道状态和缓冲区状态控制视频播放速率,并对播放速率的范围和相邻帧播放速率的突变进行控制,在减少缓冲区下溢概率的同时实现视频的平滑播放。该算法在减小缓冲区下溢概率、实现视频的平滑播放以及减少播放延迟方面均优于固定因子自适应播放算法。     

一类非自衡对象的PID控制

本文讨论非自衡对象PID控制器设计问题.首先在鲁棒控制理论的基础上定义了 最优性能指标,然后针对控制系统性能传递函数的特点发展了两种设计方法,通过引入2型滤 波器使系统满足了渐近跟踪的要求,并解析地得到了PID控制器.控制器的特点是标称性能 可以定量地估计,鲁棒性可以方便地调节.     

Delay-jitter control in multimedia applications

The growing needs of multimedia communications are leading to new developments in providing real-time communication with guarantees. Several extensions have been proposed for different layers of the Open Systems Interconnection Reference Model to accomodate these needs. In this paper, we study methods for guaranteeing delay jitter bounds for high-speed networks in the network and application layers of this model. The method proposed for the network layer provides distributed jitter control. The method proposed for the application layer allows the destination application to control delay jitter. We use a simulation to compare the effects on delay jitter in each method for various scenarios, such as constant bit rate, cross traffic, and bursty data. In addition, the buffer space requirements for accommodating real-time channels are monitored at each node in the network.     

ADAPTIVE DYNAMIC MATRIX CONTROL FOR NETWORK‐BASED CONTROL SYSTEMS WITH RANDOM DELAYS

Random transfer delays in network‐based control systems (NCSs) degrade the control performance and can even destabilize the control system. To address this problem, the adaptive dynamic matrix control (DMC) algorithm is proposed. The control algorithm is derived by applying the philosophy behind DMC to a discrete time‐delay model. A method to estimate the network‐induced delays is also presented to facilitate implementation of the control algorithm. Finally, an NCS platform based on the TrueTime simulator is constructed. With it, the adaptive DMC algorithm is compared with the conventional DMC algorithm under different network conditions. Simulation results show that the proposed adaptive DMC algorithm can respond to various network conditions adaptively and achieve better control performance for NCSs with random transfer delays.     

Experimental Assessment of the Period Calibration Method: A Case Study

In this paper we present an experimental evaluation of the period calibration method (PCM) which was developed in Gerber et al. (1994, 1995) as a systematic design methodology for real-time systems. The objective of this experimental study is to assess design alternatives integrated into the method and their performance implication on resultant systems built via the PCM. Such design alternatives include scheduling jitter, sensor-to-output latency, intertask communication schemes, and system utilization. For this study, we have chosen a computerized numerical control (CNC) machine as our target real-time system, and built a realistic controller and a plant simulator. We show the detailed development process of the CNC controller and report its performance. The performance results were extracted from a controlled series of more than hundred test controllers obtained by varying four test variables. This study unveils several weaknesses of the PCM: (1) the communication scheme built into PCM incurs a large latency though average sensor-to-output latency is one of the most dominating factors in determining control quality; (2) scheduling jitter is taken seriously in PCM though its effect appears only when average sensor-to-output latency is sufficiently small; (3) loop processing periods are not properly optimized for control quality though they are another dominating factor of performance; and (4) transient overloads are not considered at all in PCM, even though they can seriously damage the performance of a system. Based on these results, we propose a new communication scheme and a transient overload handling technique for the improved period calibration method.     

线性离散时变系统的鲁棒自适应控制

利用滑模控制的概念,提出一种线性离散时变系统的自适应控制设计方法.在等价 控制信号外,用两个补偿项代替切换信号,避免了传统滑模控制中的抖动现象.文中证明了自 适应闭环系统的稳定性.     

基于RT-Linux的实时机器人控制器研究

本文结合机器人控制器的特点，提出了采用RT-Linux操作系统改进机器人控制实时性的方法，并对机器人控制器任务采用多线程机制进行实时域和非实时域的划分。最后给出了一个在RT-Linux操作系统下实现硬件设备实时驱动程序的实例。     

基于RTX的卫星姿轨控系统地面实时仿真系统

介绍了RTX的实时功能原理和RT—TCPIP的实时通讯机制，并且比较了Windows操作系统和基于RTX实时扩展操作系统在实时精度方面和实时通讯方面的性能。卫星姿轨控系统地面仿真试验系统在卫星研制过程中起着举足轻重的作用。针对该系统的实时性要求，讨论了基于RTX的实时仿真系统的软件设计和实现方法，并给出了仿真实验结果。实验结果证明，该系统实时性高，工作稳定可靠，满足实际实验要求。该文对实时性要求高的仿真系统具有一定的参考价值和指导意义，