【作者】 陈旭东；

【导师】 朱清新；

【作者基本信息】 电子科技大学 ， 计算机应用技术， 2008， 博士

【摘要】 随着应用的推动,实时系统变得越来越复杂和灵活,比如像普适计算,自适应控制,视频会议等应用都具有高度的动态性与时变性。因此,实时系统的研究重点也从静态调度过渡到动态调度、从可预测环境过渡到不可预测环境、从周期性任务过渡到非周期性任务。本文着重研究动态系统的实时调度问题,具体内容如下:首先简要回顾了动态系统实时调度的研究现状,重点对反馈控制实时调度和实时排队论进行了介绍。然后介绍了一种静态的资源管理方法。在任务集具有速率约束时,该方法能以线性时间复杂度生成任务的可调度性上下界,并确定任务集的一个可行解。在此基础上,设计了一种简单的随机启发式算法来获得一个可行解,该可行解可以作为其他算法(如遗传算法、模拟退火算法、人工神经网络等)的初始点来进一步获得更精确的解。也可用其他的方法来获得可行解。接着讨论了如何把反馈控制用于实时调度中。首先把反馈理论中的自平衡概念引入到动态实时系统中,并在此基础上提出了针对单处理器非周期任务集的自平衡模型,该模型从实时计算系统本身出发,采用一种模型化实时系统的新方法,把许可控制和QoS降级相结合,运用反馈控制技术来确保系统的性能和提高系统的吞吐率。然后针对端到端结构的分布式实时系统提出了一种线性二次最优控制模型,该模型通过两个控制环来确保系统的实时性和性能。再接着讨论了基于排队论的实时调度。任务到达和执行时间均是随机的非周期软实时系统可以看作是一个随机服务系统。首先给出了先来先服务调度策略的一些结果;然后在此基础上构造了针对DM调度算法的最优控制模型,此时非周期软实时系统是一个多优先级的单服务台排队系统。该模型能在统计意义上保障系统的实时性,同时兼顾系统的服务质量和提高系统吞吐率。最后分析了缓冲阈值对系统性能的影响,并设计了相应的控制模型。最后对一个应用实例进行了研究,即无线局域网作为有线网络的扩展时的压缩视频实时传输问题。也就是一边是有线网,一边是无线局域网时,如何确保传输的实时性和接收端播放的连续性。在TMN8测试模型的基础上,讨论了一种适用于无线局域环境的速率自适应转码算法。该算法采用了随机控制技术来适应无线信道带宽的随机变化。我们进行了较详细的性能分析,最后的仿真试验结果说明该算法能够兼顾视频传输的实时性和播放质量要求。和TMN8的比较也说明我们的算法更能适应带宽的变化和充分利用信道资源。更多还原

【Abstract】 An increasing number of real-time applications are more and more complex and flexible. The characteristic of these applications related to multimedia, adaptive control and videoconference and so on is dynamic and time-varied. So, the emphasis of research on real-time system is from static scheduling to dynamic scheduling, from predictable environment to unpredictable environment, from periodic tasks to aperiodic tasks. This thesis gives emphasis to the real-time of dynamic system, and the main contents are as follows.Firstly, it gives a brief review to the research status of dynamic system real-time scheduling; mostly introduces the feedback control real-time scheduling and real-time queueing.Then, it proposes a static resource management method. This method can generate the upper and the lower bounds of tasks in linear time complexity in the absence of rate constraints, and find a feasible solution of task set. And then we design a very simple stochastic heuristical algorithm to maximize the weighted reward of task set. The better approach is to compute an initial solution by our stochastic heuristical algorithm and then search the more precise solution by other algorithms such as Genetic Algorithm, Simulating Anneal, and Artificial Neural Network and so on. The feasible solution can also be got by other methods.And then, it discusses some results on feedback real-time scheduling. The self-regulation in the feedback control theory is first introduced into the dynamic real-time system. A dynamic real-time scheduling model based on self-regulation used to single processor aperiodic task set is proposed. This model adopts a novel method modeling real-time system to integrate admission control with QoS degradation, and uses feedback control technique to meet timeliness requirements, and improve the system throughput. And then, proposes a linear quadratic stochastic optimal control model used to the end-to-end distributed real-time system. This model uses two feedback loops to guarantee the system’s performance.And then, it discusses a method based on real-time queueing. The aperiodic soft real-time system where tasks’ arriver time and execution time are stochastic can be regarded as a stochastic service system. Firstly, we construct a dynamic optimal control model for FCFS scheduling strategy; then, we present the more useful model for DM scheduling algorithm, so, the aperiodic soft real-time system is a single server queue system with multiple priorities. The model can statistically guarantee the schedulability of real-time systems, at the same time it can guarantee the QoS(Quality of Service) and improve throughput of systems. Finally, analyses the influence of buffer threshold on system’s performance, and designs the control model with buffer threshold.Lastly, it introduces an instance research, namely, the end-to-end transmission of video stream from wired channel to wireless channel. The target is to guarantee the real-time transmission, at the same time guarantee the playout quality. We propose a frame layer adaptive rate control algorithm for the wireless transcoder based on the TMN8 test model. The algorithm adopts stochastic control technique to adapt the variation of wireless bandwidth. We analyze the performance in detail. Experiment results demonstrate that the algorithm can improve the synthetic performance of rate control through the compromise between the end-to-end delay and the playout quality. To be compared with TMN8, the proposed algorithm can guarantee the continuity of video communication under the condition of great variation of bandwidth.更多还原