时延约束动态不重组组播路由优化

针对时延约束的组播路由问题,提出了一种动态不重组组播路由算法NDMADC。算法将DGA和Floyd最短路径优化算法相结合,确保节点在满足时延约束的前提下动态选择到组播树有最小代价的路径加入组播会话。由于采用贪心算法思想,NDMADC算法保证了节点加入组播树时不需要组播树重组。仿真表明,该算法能正确地构造出满足时延约束的组播树,具有较低的代价和计算复杂度。     

一种基于最短路径优先的应用层组播算法

提出一种基于最短路径优先的应用层组播算法,将节点间的传输时延作为关键计算因素,在满足各节点度不大于3的前提下,构建出具有最短传输时延的组播树。实验结果表明,该算法构建的组播树均衡负载的能力较强,出现瓶颈的概率较低。     

一种高可靠性的组播树恢复方法

应用层组播树中某个非叶子节点失效后,需要重新构建组播树保证失效节点的子孙节点能够正确接收数据。针对这一问题,考虑满足高可靠性环境中保证恢复完整性的情况,提出一种基于备用父节点的组播树预先式恢复方法,即为每个非根节点找到一个备用父节点,使得当某一非叶节点失效时可以迅速的恢复组播树。首先建立模型并对其求解构造恢复方法,然后论证此方法保证组播树恢复的完整性,最后通过仿真实验验证了此方法的有效性以及其在恢复延迟和管理代价上的改进。     

应用层组播树分裂恢复算法研究

应用层组播树是由终端用户构造而成，其稳定性不能得到保证。由于终端用户失效导致组播树分裂，产生多个分支，因此需要快速恢复组播树，保证各组用户接收到组播数据。分析组播树分裂恢复特点，构造了带有时延和度约束的组播树分裂恢复问题数学模型。利用拉格朗日松弛方法分解此复杂问题，提出一种新的应用层组播树分裂恢复算法。仿真实验表明，此算法具有较快的收敛速度，而且算法稳定。     

基于时延约束的快速低代价组播路由算法

低代价最短路径树是一种广泛使用的组播树,通常不能满足实时多媒体应用中信息从源端到目的端传输的时延限制。针对该问题,提出基于时延约束的快速低代价组播路由算法,利用代价构建满足时延约束的初始树,将不满足时延约束的路径用最小时延路径代替。仿真结果表明,相比时延约束最短路径树算法,该算法的计算时间更少,组播树的总代价更低。     

一种满足时延和时延差约束的组播路由算法

针对时延和时延差约束的组播路由优化问题,提出一种最优代价组播路由算法。基于Dijkstra最短路径树算法,通过指示函数调整新加入节点的优先级,利用局部信息构建低代价组播树,使其能较好地平衡组播树代价、时延和时延差之间的关系。仿真实验结果表明,该算法能正确构造出满足时延和时延差约束的组播树,同时具有时间复杂度低、求解成功率高等综合性能。     

时延受限组播路由的最短路径加速算法求解

分析了时延受限的Steiner树问题,总结了在构建组播树过程中的代价和计算复杂度变化规律,并根据实际网络环境,从优化最短路径出发,提出了一种基于优化最短路径的时延受限组播路由算法AOSPMPH。该算法以MPH算法为基础,利用Floyd最短路径优化算法求出节点对之间的最短路径,选择满足时延要求的最小代价路径加入组播树,进而产生一棵满足时延约束的最小代价组播树。仿真结果表明,AOSPMPH不但能正确地构造时延约束组播树,而且其代价和计算复杂度与其他同类算法相比得到了优化。     

基于决策图贝叶斯优化算法的QoS组播路由算法

组播通信路由技术是视频广播、网络会议等分布式计算的关键技术 ,其目的是要寻找连接源节点和一组目的节点的一棵组播树 ,使得总体代价最小 .提出了一种基于决策图贝叶斯优化算法 (Bayesian Optim ization Algorithmwith Decision Graphs,简称 DBOA)的 Qo S组播路由算法 ,该算法利用新的编码和解码方法以及适当的适应度函数来求解带宽、时延及时延差别等 Qo S限制下最小代价组播路由问题 .仿真结果表明了该算法的可行性和有效性     

一种利用双路径组播树提高应用层组播稳定性的方案

应用层组播作为IP组播的替代方案,具有简单灵活、容易部署的优点,在分布式多媒体通信领域获得了广泛的应用.但其存在组播树稳定性的问题,发展受到了限制.该文提出一种双路径组播树方案,采用两个组播树传输和转发不同内容的数据,在节点加入或者退出组播组时,不需要重新构建组播树,其它节点仍然可以接收到可接受的多媒体数据,从而减少故障恢复的时间,提高应用层组播的稳定性,改善应用层组播的性能.最后通过计算机仿真,表明该方案在节点加入和退出时减少了故障恢复时间,维护了组播树的稳定性,具有良好的性能改善和显著的优点,适合多媒体业务传输.     

基于实时应用的组播路由算法研究

摘要实时多媒体应用要求组播接收者在一定的时延限制之内收到组播信息,这就对组播路由提出了新的要求。该文提出了一种基于实时应用的组播路由算法,该算法以较低的通信代价建立满足时延界限的接近最优的组播树。最后简要讨论了组播接收者的动态改变时如何重建组播树的问题。     

A disturbance reduction scheme for linear small delay systems with modeling uncertainties

A disturbance reduction scheme for linear delay systems with modeling uncertainties is presented in this paper. The linear systems in this study are assumed to be nominally stable, minimum phase and relative degree one systems. The control structure is based on Astrom's modified Smith predictor with a disturbance reduction scheme and an artificial neural network (ANN). Unlike other disturbance rejection methods, the proposed scheme does not require information about unknown disturbance frequencies. The ANN is used to approximate a product of an inverse of a time delay and a nonnegative gain and to augment the robustness of the proposed approach against modeling uncertainties including a time-varying delay. Connective weights of the ANN are trained on-line using a back-propagation algorithm according to a disturbance estimation error function. Simulation results show the effectiveness of the presented disturbance reduction scheme for linear delay systems with modeling uncertainties, subjected to both periodic and non-periodic unknown load disturbances.     

Modified Smith predictor with a robust disturbance reduction scheme for linear systems with small time delays

This paper presents a robust disturbance reduction scheme using an artificial neural network (ANN) for linear systems with small time delays. It is assumed that the nominal linear systems are stable, minimum phase and relative degree one systems. The proposed structure is an integration of a modified Smith predictor and an ANN‐based disturbance reduction scheme. Unlike other disturbance rejection methods, the proposed approach does not require information about unknown load disturbance frequencies. An ANN is used to approximate the unknown load disturbances and to enhance the robustness of the proposed disturbance reduction scheme against modelling errors in the estimated time delay and the process model. Connective weights of the ANN are trained on‐line using a back‐propagation algorithm until uncertainties resulting from unknown load disturbances and modelling errors are minimized. The simulation results show the effectiveness of the presented disturbance reduction scheme for controlling linear delay systems subjected to step or periodic unknown load disturbances.     

Robust task scheduling for volunteer computing systems

Performance perturbations are a natural phenomenon in volunteer computing systems. Scheduling parallel applications with precedence-constraints is emerging as a new challenge in these systems. In this paper, we propose two novel robust task scheduling heuristics, which identify best task-resource matches in terms of makespan and robustness. Our approach for both heuristics is based on a proactive reallocation (or schedule expansion) scheme enabling output schedules to tolerate a certain degree of performance degradation. Schedules are initially generated by focusing on their makespan. These schedules are scrutinized for possible rescheduling using additional volunteer computing resources to increase their robustness. Specifically, their robustness is improved by maximizing either the total allowable delay time or the minimum relative allowable delay time over all allocated volunteer resources. Allowable delay times may occur due to precedence constraints. In this paper, two proposed heuristics are evaluated with an extensive set of simulations. Based on simulation results, our approach significantly contributes to improving the robustness of the resulting schedules.     

Modified Smith predictor scheme for periodic disturbance reduction in linear delay systems

This paper presents a disturbance reduction scheme for linear systems with time delays. The linear systems in the study are assumed to be nominally stable, minimum phase, and relative degree one systems. The proposed scheme is a combination of Astrom’s modified Smith predictor with a disturbance reduction controller and a grey predictor. Unlike conventional disturbance rejection methods, the scheme proposed in this study does not require the estimation of disturbance frequencies. The grey prediction method is used to approximate the inverse of the time delay and to enhance the robustness of the disturbance reduction scheme against errors in the estimated delay time. The simulation results demonstrate the successful performance of the proposed disturbance reduction method for controlling a linear system with time delays, subjected to both step and periodic disturbances.     

Low-complexity time synchronization for energy-constrained wireless sensor networks: Dual-Clock delayed-message approach

Due to the ability of sensor nodes to collaborate, time synchronization is essential for many sensor network operations. With the aid of hardware capabilities, this work presents a novel time synchronization method, which employs a dual-clock delayed-message approach, for energy-constrained wireless sensor networks (WSNs). To conserve WSN energy, this study adopts the flooding time synchronization scheme based on one-way timing messages. Via the proposed approach, the maximum-likelihood (ML) estimation of time parameters, such as clock skew and clock offset, can be obtained for time synchronization. Additionally, with the proposed scheme, the clock skew and offset estimation problem will be transformed into a problem independent of random delay and propagation delay. The ML estimation of link propagation delay, which can be used for localization systems in the proposed scenario, is also obtained. In addition to good performance, the proposed method has low complexity.     

Decentralized low-order ADRC design for MIMO system with unknown order and relative degree

Many industrial processes are multi-input multi-output (MIMO) systems, in which the order and/or the relative degree are uncertain, and the parameters cannot be obtained accurately. In this paper, for such MIMO systems, the decentralized low-order active disturbance rejection control (ADRC) scheme is designed with tuning method, and the whole design procedure is verified on the plants with/without the time delay. A necessary condition is derived based on the definition of numerator’s zero-order coefficient (NZC) matrix for the closed-loop stability. It is proved that the low-order ADRC scheme can reject the interaction disturbance and guarantee the closed-loop stability for the open-loop stable MIMO plants. This design method is capable of guaranteeing the integrity for the open-loop stable plant with diagonally dominant NZC matrix, which has also discussed in the simulations. Several numerical new methods have given to show the further capability of the ADRC scheme to obtain better performances for the systems with/without time delay.     

Adaptive passive control with varying time delay

This paper presents a passive control scheme for a force reflecting bilateral teleoperation system with a varying time communication delay. To improve the stability and performance of the system, the master and slave must be coupled dynamically via a transmission network through which the force and velocity are communicated bilaterally. However, the time delay caused by various factors, such as the transmission distance, network congestion, and communication bandwidth, is a long-standing impediment to bilateral control that can destabilize the system. In this study, we investigated how a varying time delay affects the stability of a teleoperation system. A new optimal adaptive approach based on a passive control scheme was designed bilaterally for both the master and slave sites. Extra variables were transmitted together with the wave variables in the scattering system. The proposed scheme achieved both passive control, and an acceptable tracking performance. The tracking performance was demonstrated using a computer simulation of varying time delays in a bilateral teleoperation system.     

Stabilization of bilaterally controlled teleoperators with communication delay: An ISS approach

A new approach to the stabilization of bilaterally controlled teleoperators in the presence of time delay in the communication channel is presented. A control scheme is proposed which makes the teleoperator system input-to-state stable regardless of the delay in the communication channel. It is shown that in the case of digital implementation of the control system, the input-to-state stability property is preserved in the 'semiglobal' sense. Simulation results are presented which confirm the stability properties of the proposed telerobotic scheme.     

基于服务质量需求的存储系统动态优先权调度策略

多媒体应用要求存储系统提供保证服务质量的数据访问服务，响应时间超过延迟上限的访问请求必须小于一定的比例．基于服务质量需求的动态优先权调度策略（QADPS）根据多媒体应用接受存储系统服务的历史信息，计算多媒体应用的服务质量失败距离；并为失败距离较小的多媒体应用分配较高的调度优先权．QADPS根据多媒体应用的不同服务质量需求，实现了有差别的调度：多媒体应用的服务质量需求越严格，它的访问请求被调度的机会越高．QADPS能够在保证服务质量的前提下，支持更多的并发多媒体应用．     

Design of adaptive PID regulators based on recursive estimation of the process parameters

This paper introduces a new approach based on a stochastic-deterministic recursive adaptive scheme, estimating the process parameters and the time delay at the same time and using design formulae for automatic tuning of PID regulator parameters.