固定优先级调度的线性近似分析方法

通过线性逼近硬实时系统任务的工作负荷量的方法,一个更加接近精确响应时间的时间上限能有效地降低调度分析时间。同时该上限用于任务集的充分性可调度测试时具有线性时间的复杂度。这种线性上限的可调度性测试能够用于交互的系统工具设计、基于搜索的系统优化以及任务集的动态接纳新任务的设计中。并且新的调度系统模型无时间死线、抖动大小限制,适用范围更广。相关的实验也表明响应时间上限可调度性分析提高了准确调度测试的效率。     

基于改进型统一调度算法改善任务集的可调度性

实时系统要求任务在最差情况下能在其截止时间前获得结果,若超过了其截止时间,也会认为是错误的行为,所以改进任务可调度性分析、提高任务集可调度性尤其重要。统一调度能结合固定优先级调度的优点,防止不必要的抢占,降低资源额外销耗,能够提高任务集合的可调度性;但其任务的可调度性分析方法过于粗糙,影响任务最差响应时间分析的结果,降低了任务集的可调度性。针对存在的问题,基于统一调度,增加任务运行阶段数,重新建立任务模型,并提出通过分配任务抢占阈值、调整运行阶段的抢占阈值与长度,优化任务可容忍阻塞,改善任务集可调度性的算法。最后,实验表明,与统一调度算法及其他算法相比,所提出的调度算法能够有效改善任务集的可调度性。     

基于分区的航电系统调度分析工具实现

针对仅含纯周期任务集合、符合ARINC653多分区构架航电系统两级调度模型的可调度性判定问题,提出一种基于分区的航电系统调度分析工具。通过设定时钟变量模拟航电系统各分区中任务集调度过程,依据纯周期任务集及分区航电系统时间片分派特性确定仿真区间,设计优化的调度分析算法,判定航电系统分区级时间片分派的正确性及各分区中任务集的可调度性。测试及实例分析结果表明,该工具能自动、准确、快速地判定航电系统分区以及任务级调度模型的可调度性,并能以甘特图的方式绘制系统调度过程,较现有工具更为直观、高效。     

改进的抢占阈值调度任务响应时间分析方法

现有的基于抢占阈值调度的任务响应时间分析方法对实时任务系统进行可调度性判定时，对任务响应时间估计过低，造成任务错过期限的现象。针对上述缺点不足，该文提出改进的基于抢占阈值调度的任务响应时间分析方法，考虑了任务释放抖动和时钟嘀嗒调度的影响，使用改进的任务参数计算系统任务时间需求函数。仿真对比结果表明，改进后的方法较单纯固定优先级抢占阈值调度下的任务响应时间分析方法得到更加精确可调度性分析结果。     

基于时间需求迭代和排队模型的开放式实时系统可调度性分析算法研究

基于RM调度策略和可延期服务器调度的开放式实时系统,以往的可调度性分析算法造成较低资源利用率.结合时间需求分析和服务台休假M/M/1/K排队模型,考虑带宽保留服务器,提出一种高资源利用率的可调度性分析算法,对系统中所有周期任务进行可调度性分析测试.给出其在临界点的响应时间;根据非周期事件到来率和接收缓冲定量分析非周期事件的平均响应时间和事件丢失率.实验表明,提出的可调度性分析方法通过估计任务的响应时间范围,能够在较高资源利用率下,验证多任务系统的可调度性.     

改进的基于抢占阈值调度的任务响应时间分析方法

基于抢占阈值调度的任务响应时间分析方法是一种新型实时系统任务可调度性判定技术。然而已有的研究工作,有时对以前的任务请求检查过少,可能导致对响应时间估计过低。同时对任务响应时间的分析忽略了任务释放抖动和时钟嘀嗒调度对任务响应时间的影响,造成任务错过期限的现象,系统任务可调度性判定存在潜在的不精确因素。针对上述缺点不足,本文提出改进的基于抢占阈值调度的任务响应时间分析方法,在修正已有方法缺陷的同时,考虑任务释放抖动和时钟嘀嗒调度的影响,引入额外的时间需求,使用改进的任务参数计算系统任务时间需求函数。仿真对比结果表明,改进后的方法较单纯固定优先级抢占阈值调度下的任务响应时间分析方法得到更加精确可调度性分析结果。     

经典RM调度算法在无人机发动机试车台软件开发中的应用

现代无人机发动机测试项目多、实时性要求高,早期的基于非实时的片上系统不能很好地满足测试要求。本文以某型无人机发动机试车台软件系统实际开发为例,在软件开发中引入了经典RM调度算法,分析了经典RM算法的可调度性判定法则,描述了片上系统任务集设计过程,进行了RM可调度性理论判定。通过对任务集的实际可调度性测试表明：硬件利用率最大可达到93．8％,达到设计指标要求;系统运行稳定可靠,并取得预期效果。     

基于单调速率的可调度性判定改进算法

在单调速率调度策略的基础上,提出一种改进的任务集可调度性判定算法。该算法通过设定时钟变量模拟调度过程中的系统时钟,在时钟变量值增长过程中,根据任务优先级从高到低的顺序,分析各个任务的截止时间限的满足情况,判定任务的可调度性,从而确定任务集的可调度性。通过实例分析及与现有判定方法的比较,验证了该算法的正确性和高效性。     

回卷恢复模型下容错实时系统的可调度性分析

实时任务的超时完成将会导致灾难性后果,因此实时系统必须具备严格的实时性及可靠性保障.考虑实时系统的容错需求,本文基于回卷恢复模型,对容错实时系统的可调度性分析进行研究.在基于任务最环响应时间的可调度性分析方法中,容错优先级配置是决定系统可调度性的关键.为了改进系统的可调度性,提出一种容错优先级可降低的配置策略,并推导出此策略下任务最坏响应时间的计算公式,以判断系统的可调度性.降低策略下低优先级任务可挪用高优先级任务的空闲时间来满足自身的截止时限要求.仿真实验表明,降低任务的容错优先级可以有效提升系统的容错能力.     

基于最优虚拟截止日期多处理器混合时序调度

为提高混合临界系统实时调度有效性,提出基于最优虚拟截止日期的多处理器混合时序调度算法.将现有非抢占最早截止时间可调度性测试算法推广到混合临界多处理器系统,引入时序保证技术,确保系统在两个不同临界值间过渡;将所提可调度性测试扩展到混合临界系统,利用系统级截止期缩减参数控制,设计最优虚拟截止日期分配策略.仿真结果表明,采用最优虚拟截止时间分配策略可调度性测试可发现大量额外可调度任务集,实现混合临界多处理器非抢占调度性能提升.     

Dwell time and average dwell time methods based on the cycle ratio of the switching graph

A new method to find an upper bound on dwell time and average dwell time for switched linear systems is proposed. The method is based on computing the maximum cycle ratio and the maximum cycle mean of the directed graph that governs switchings. For planar switched systems, an upper bound for dwell time and average dwell time can be estimated by considering only the cycles of length two.     

A finite-time convergent dynamic system for solving online simultaneous linear equations

A new dynamic system is proposed and investigated for solving online simultaneous linear equations. Compared with the gradient-based dynamic system and the recently proposed Zhang dynamic system, the proposed dynamic system can achieve superior convergence performance (i.e. finite-time convergence) and thus is called the finite-time convergent dynamic system. In addition, the upper bound of the convergence time is derived analytically with the error bound being zero theoretically. Simulation results further indicate that the proposed dynamic system is much more efficient than the existing dynamic systems.     

An efficient response-time analysis for real-time transactions with fixed priority assignment

In the general context of tasks with offsets (general transactions), only exponential methods are known to calculate the exact worst-case response time (WCRT) of a task. The known pseudo-polynomial techniques give an upper bound of the WCRT. In this paper, we present a new worst-case response-time analysis technique (mixed method) for transactions scheduled by fixed priorities, and executing on a uniprocessor system. This new analysis technique gives a better (i.e. lower) pseudo-polynomial upper bound of the WCRT. The main idea is to combine the principle of exact calculation and the principle of approximation calculation, in order to decrease the pessimism of WCRT analysis, thus allowing improving the upper bound of the response time provided while preserving a pseudo-polynomial complexity. Then we define the Accumulative Monotonic property on which a necessary condition of feasibility is discussed. We also propose, to speed up the exact and mixed analysis, the dominated candidate task concept that allows reducing significantly the number of critical instants to study in an analysis.     

New sufficient conditions for the stability of slowly varyinglinear systems

The frozen-time approach is used to state some new sufficient conditions for the stability of linear time-varying systems. An upper bound on the norm of the time derivative of system matrix which, under different assumptions on frozen-time system eigenvalues, guarantees asymptotic stability or exponential stability of the system is established     

Performance analysis and scheduling of stochastic fork-join jobs ina multicomputer system

The authors model a parallel processing system comprising several homogeneous computers interconnected by a communication network. Jobs arriving to this system have a linear fork-join structure. Each fork of the job gives rise to a random number of tasks that can be processed independently on any of the computers. Since exact analysis of fork-join models is known to be intractable, the authors resort to obtaining analytical bounds to the mean job response time of the fork-join job. For jobs with a single fork-join and, probabilistic allocation of tasks of the job to the N processors, they obtain upper and lower bounds to the mean job response time. Upper bounds are obtained using the concept of associated random variables and are found to be a good approximation to the mean job response time. A simple lower bound is obtained by neglecting queueing delays. They also find two lower bounds that include queueing delays. For multiple fork-join jobs, they study an approximation based on associated random variables. Finally, two versions of the join-the-shortest-queue (JSQ) allocation policy (i.e., JSQ by batch and JSQ by task) are studied and compared, via simulations and diffusion limits     

Less conservative stability criteria for linear systems with interval time‐varying delays

The problem of the stability of a linear system with an interval time‐varying delay is investigated. A new Lyapunov–Krasovskii functional that fully uses information about the lower bound of the time‐varying delay is constructed to derive new stability criteria. It is proved that the proposed Lyapunov–Krasovskii functional can lead to less conservative results than some existing ones. Based on the proposed Lyapunov–Krasovskii functional, two stability conditions are developed using two different methods to estimate Lyapunov–Krasovskii functional's derivative. Two numerical examples are given to illustrate that the two stability conditions are complementary and yield a larger maximum upper bound of the time‐varying delay than some existing results. Copyright © 2013 John Wiley & Sons, Ltd.     

Consensus of multi‐agent systems with nonlinear dynamics and sampled‐data information: a delayed‐input approach

This paper is concerned with the problem of consensus in directed networks of multiple agents with intrinsic nonlinear dynamics and sampled‐data information. A new protocol is induced from a class of continuous‐time linear consensus protocols by implementing data‐sampling technique and a zero‐order hold circuit. On the basis of a delayed‐input approach, the sampled‐data multi‐agent system is converted to an equivalent nonlinear system with a time‐varying delay. Theoretical analysis on this time‐delayed system shows that consensus with asymptotic time‐varying velocities in a strongly connected network can be achieved over some suitable sampled‐data intervals. A multi‐step procedure is further presented to estimate the upper bound of the maximal allowable sampling intervals. The results are then extended to a network topology with a directed spanning tree. For the case of the topology without a directed spanning tree, it is shown that the new protocol can still guarantee the system to achieve consensus by appropriately informing a fraction of agents. Finally, some numerical simulations are presented to demonstrate the effectiveness of the theoretical results and the dependence of the upper bound of maximal allowable sampling interval on the coupling strength. Copyright © 2012 John Wiley & Sons, Ltd.     

一类控制问题的降阶控制器设计

基于线性矩阵不等式(LMI,1inear matrix inequalities),考虑了线性时不变对象的一类 控制问题的降阶控制器设计问题.给出了一个新的降阶控制器阶的上界,该上界适用于标准和 奇异控制两种情形.证明是构造性的,可以给出降阶控制器的构造方法.给出了简单的例子,说 明该方法的可行性和正确性.     

Analysis of time and frequency synchronization error for wireless systems using OFDM

1 Introduction The OFDM process includes the following two steps: splitting the high-rate serial bit stream into N parallel low-rate substreams, and modulating N substreams on N or-thogonal subcarriers by means of inverse fast Fourier transform (IFFT)[1―6]. Orthogonal superposition of subcarriers ensures the OFDM technique to have the higher bandwidth efficiency compared to other frequency division multiplexing[4]. Because OFDM can be arbitrarily combined with high-efficient digital m…