Dual scheduling and quantised control for networked control systems with communication constraints

A novel integrated design scheme of average dwell time scheduling strategy, dynamic bandwidth allocation policy and quantised control for a collection of networked control systems (NCSs) with time delay and communication constraints is proposed in this paper. A scheduling policy is presented to accommodate the limitation of communication capacity which depends on the convergence rate of closed-loop system and divergence rate of open-loop plant. Linear programming technique is adopted to dynamically allocate bit rate for each node and the strategy is used to make trade-offs between the network utilisation and the control performance which provides an effective way of optimising the quality of control (QoC) and the quality of service (QoS) for NCSs. Mid-tread uniform quantisers update the quantisation rules according to the assignment of the bit rate and convert the quantised state into a kind of input saturation with bounded disturbances. Taking into account the effect of dual scheduling strategy and quantisation, the NCSs are modelled as discrete-time switched systems with bounded disturbances. Furthermore, a scheduling and quantised feedback control co-design procedure is proposed for the simultaneous stabilisation of the collection of networked subsystems. Finally, a simulation example is given to illustrate the effectiveness of the proposed method.     

网络控制系统中基于模糊反馈的消息调度

在网络带宽受限的情况下, 综合考虑了系统响应的误差和误差变化率, 设计了一个共享通信网络的模糊反馈调度器. 该调度器采用模糊最大优先调度算法对网络消息发送的优先级进行动态调整. 同时定义了一种归一化控制质量衡量指标来评价多回路系统的控制性能. 在此评价方法下, 对三种不同调度算法在不同随机时延序列下进行了仿真比较. 结果表明本文提出的调度算法优化了系统的控制性能, 并在不确定运行环境中具有更好的适应性.     

QoC elastic scheduling for real-time control systems

The elastic task model, a significant development in scheduling of real-time control tasks, provides a mechanism for flexible workload management in uncertain environments. It tells how to adjust the control periods to fulfill the workload constraints. However, it is not directly linked to the quality-of-control (QoC) management, the ultimate goal of a control system. As a result, it does not tell how to make the best use of the system resources to maximize the QoC improvement. To fill in this gap, a new feedback scheduling framework, which we refer to as QoC elastic scheduling, is developed in this paper for real-time process control systems. It addresses the QoC directly through embedding both the QoC management and workload adaptation into a constrained optimization problem. The resulting solution for period adjustment is in a closed-form expressed in QoC measurements, enabling closed-loop feedback of the QoC to the task scheduler. Whenever the QoC elastic scheduler is activated, it improves the QoC the most while still meeting the system constraints. Examples are given to demonstrate the effectiveness of the QoC elastic scheduling.     

Hybrid Scheduling and Quantized Output Feedback Control for Networked Control Systems

A novel co-design scheme of hybrid scheduling strategy, adaptive logarithmic quantizer and dynamic robust H-infinity output feedback controller for a class of networked control system (NCS)with communication constraints and time delay is proposed. The hybrid scheduling scheme integrates dead zone scheduling and Try Once Discard (TOD) scheduling so as to get the stronger adaptability and flexibility than the single scheduling. In this scheme, dead zone scheduling which updates the threshold according to mode-dependent control strategy is used for single node of NCS to reduce the network bandwidth utilization while TOD scheduling is used for the whole node of NCS in order to meet the requirements of communication constraints and guarantee the overall system performance.We develop the integrated design for the hybrid scheduling strategy, adaptive quantizer and dynamic robust output feedback controller to maintain asymptotic stability of the closed-loop NCS by using the multiple-Lyapunov function and switched system theory. The proposed method can improve the the quality of service (QoS) meanwhile ensure the quality of control (QoC) of overall systems, which make a better trade-off between network utilization and control performance. An simulation example demonstrates the efficiency of the proposed method.     

基于支持向量机的计算资源反馈调度

在实时控制系统(RTCS)中,计算资源一般受限。由于诸多不确定性因素和工作负载的动态变化,系统总是运行在不可预期的开放环境中。为保证系统的稳定运行,提出了一种基于支持向量机(SVM)的计算资源反馈调度方法。它周期性地监测系统计算资源,通过SVM在线预测,得到各个控制回路的下一个采样周期,从而实现系统计算资源的动态分配。通过仿真实验验证了该反馈调度方法的性能,并与理想情况、传统开环调度方法进行了比较,显示了其优越性。     

一种网络资源受限情况下的NCS 反馈调度方法

在网络控制系统中,网络负载的加重会使网络资源变得有限,从而使各个子系统的控制性能变 差．为了改善这一情况下系统的控制品质（quality of control, QoC）,本文提出了流动式死区反馈调度方法．通 过对死区节点的动态选择和对死区范围的连续分配,整个系统在网络资源有限的情况下总的控制品质得到了 提高．仿真结果表明,在网络资源紧缺时,该方法采用的流动式死区思想和死区范围连续化思想对系统QoC 的提高是有效的．     

基于DVS技术的性能感知反馈调度算法

传统DVS算法在能量管理方面没有考虑实际系统性能的需求,这在一定意义上限制了其节能效果．针对这一问题,提出一种基于DVS技术的性能感知反馈调度算法．在反馈调度器中,分别采用DVS技术和模糊控制技术设计CPU电压调节模块和控制任务周期调节模块,实现对系统CPU速率和控制任务采样周期的动态调节．通过与基于固定采样周期的DVS反馈调度算法进行对比,结果表明该算法在保证系统控制性能的同时进一步降低了系统能耗．     

图书馆多媒体业务流的短时公平分组反馈调度方法

研究了一种新的基于短时公平的分组调度算法的问题. 基于短时公平性的分组反馈调度算法改进了WF2Q＋算法在短期内无法为新加入客户端提供公平服务的缺陷,增强了调度算法的适应性和公平性. 在本算法中,调度器中的各个客户端权值能够根据其获得的实际服务量状况在线调整,增强了系统的鲁棒性和自适应性,同时提高了系统实现短期公平性的能力,对各个客户端提供更为公平的服务质量（Quality of Service,QoS）.     

基于动态调度的网络控制系统设计方法

针对网络控制系统中存在多回路共享网络资源的问题,本文提出一种基于反馈和预测机理的动态调度策略,根据当前的网络状态在线调整控制系统的采样周期,以适应当前网络中信息流的变化,达到改善网络运行性能的目的．采用动态调度策略的网络控制系统为不确定变采样周期系统,经过等效变换,将系统等效为一类具有参数不确定性的离散系统．基于建立的模型,给出系统的鲁棒控制器参数化设计方法,并通过仿真实例验证了所提方法的有效性．     

多回路网络化控制系统级联反馈调度

针对动态环境下的多回路网络化控制系统，本文基于反馈控制与网络调度协同设计的思想，提出一种级联反馈调度策略．以优化系统整体控制性能为目标，根据可用带宽资源的动态变化，对控制回路采样周期进行在线调节，将截止期错过率控制在期望的较低水平，并对可用带宽进行优化分配．仿真实验结果表明，相对于传统设计方法，该方法能够明显改善整体控制性能．     

网络化控制系统中的抖动优化调度算法

在令牌型总线网环境下，提出折衷网络带宽资源占用和传输周期抖动的两步优化调度算法，在满足实时性要求的前提下，通过确定网络化控制系统中各控制闭环节点的采样周期及其在最小倍周期时段内的数据传输序列，在兼顾周期抖动对控制闭环动态性能影响的同时合理地调配了带宽资源，使系统具有较高的网络资源利用率。     

Feedback scheduling of model-based networked control systems with flexible workload

In this paper, a novel control structure called feedback scheduling of model-based networked control systems is proposed to cope with a flexible network load and resource constraints. The state update time is adjusted according to the real-time network congestion situation. State observer is used under the situation where the state of the controlled plant could not be acquired. The stability criterion of the proposed structure is proved with time-varying state update time. On the basis of the stability of the novel system structure, the compromise between the control performance and the network utilization is realized by using feedback scheduler.Examples are provided to show the advantage of the proposed control structure.     

Feedback–Feedforward Scheduling of Control Tasks

A scheduling architecture for real-time control tasks is proposed. The scheduler uses feedback from execution-time measurements and feedforward from workload changes to adjust the sampling periods of the control tasks so that the combined performance of the controllers is optimized. The performance of each controller is described by a cost function. Based on the solution to the optimal resource allocation problem, explicit solutions are derived for linear and quadratic approximations of the cost functions. It is shown that a linear rescaling of the nominal sampling frequencies is optimal for both of these approximations. An extensive inverted pendulum example is presented, where the performance obtained with open-loop, feedback, combined feedback and feedforward scheduling, and earliest-deadline first scheduling are compared. The performance under earliest-deadline first scheduling is explained by studying the behavior of periodic tasks under overload conditions. It is shown that the average values of the sampling periods equal the nominal periods, rescaled by the processor utilization.     

Bandwidth allocation and scheduling of networked control systems with exponential and quadratic approximations

This paper investigates bandwidth allocation and scheduling of networked control systems (NCSs) with nonlinear-programming techniques. The bandwidth utilization (BU) is defined in terms of sampling frequency. An exponential and a quadratic approximation are formulated to describe system performance versus the sampling frequencies. The optimal sampling frequencies are obtained by solving the approximations with Karush–Kuhn–Tucker (KKT) conditions. Experimental results verify the effectiveness of the proposed approximations and scheduling algorithms. The two approximations could find an optimal BU of an NCS with a given sequence of plants and maximize the total BU up to 98% of the total available bandwidth.     

DTS: Dynamic TDMA scheduling for Networked Control Systems

Networked Control Systems (NCSs) are pervasively applied in modern industry. With increasing functionalities, modern NCSs tend to have dynamic workload by holding a variety of applications via a shared network. To handle workload variations and provide performance guarantees, dynamic network scheduling scheme is highly desired in NCSs. In this paper, we propose a network scheduling scheme, referred to as DTS, that can make on-the-fly decisions to schedule the applications in NCSs. DTS aims at NCSs that use time-triggered network as shared medium and Time division multiple access (TDMA) as network access method. DTS dynamically changes the network accessing sequence of the applications in a way to provide optimal system performance and maintain control stability in NCSs. DTS adopts a decentralized schedule mechanism where each application can make its local schedule decision, enhancing the scalability of NCSs. Simulation results demonstrate the effectiveness of the proposed scheme by improving the network bandwidth and providing better system performance in NCS comparing with the existing time-triggered scheduling schemes.     

Structural Properties,LQG Control and Scheduling of a Networked Control System with Bandwidth Limitations and Transmission Delays

The problem of simultaneous LQG control and scheduling of a Networked Control System (NCS) with constant network induced delays at input and output and bandwidth limitations is investigated. Delays are considered at plant as well as controller side. Sufficient conditions for controllability, stabilizability, reconstructibility and detectability of the underlying networked control system are drawn. The proposed conditions extend previous works on structural properties of NCS by capturing both plant and controller side delays together with bandwidth limitations. A framework for computing the optimal LQG controller for the NCS with a fixed scheduling is provided. The proposed modeling approach facilitates use of LQG as well as other control methods for NCSs with delays and bandwidth limitations. In order to optimize performance, a semi-online scheduling procedure is proposed based on an offline look up table. The look up table assigns an optimal schedule with associated optimal LQG controller to initial conditions. The proposed scheme improves previous results by online deployment of schedule and LQG control with stability guarantees and very low computational overhead. A simulation example with communication delays, packet losses and bandwidth limitations in both sensor and actuator sides is included. Static optimal periodic communication sequence, Optimal Pointer Placement (OPP) approach proposed in previous works, a random access scheduling method representing contention based access policies and the proposed method are simulated and compared.      

Traffic-prediction-assisted dynamic bandwidth assignment for hybrid optical wireless networks

Hybrid optical-wireless networks provide the inexpensive broadband bandwidth, vital for modern applications, as well as mobility, and scalability required for an access network. However, in order to provide satisfactory Quality of Service (QoS) on such a non-homogeneous network, innovative designs are required.This paper proposes a novel scheduling mechanism to significantly improve the delay guarantee, while maintaining high-level throughput, by predicting the incoming traffic to optical network units (ONU). The proposed scheduler managed to exploit the available information in hybrid optical-wireless networks, to enhance the ONU scheduler. This results in accurate prediction of incoming traffic, which leads to intelligent and traffic-aware, scheduling and dynamic bandwidth assignment (DBA).Based on the proposed architecture, two DBA algorithms are proposed and their performance is evaluated by extensive simulations. Moreover, the maximum throughput of such network is analyzed. The results show that by using the proposed algorithms, the delay bound of delay-sensitive traffic classes can be decreased by a factor of two, without any adverse effect on the throughput.     

Static output feedback control of networked control systems with packet dropout

This article deals with the problem of mean square stability of discrete-time networked control systems (NCSs) over a communication channel subject to packet dropout. By introducing a parameter-independent slack variable with lower triangular structure, the existence of a static output feedback controller is formulated in the form of linear matrix inequalities. Neither equality constraint nor iterative algorithm is involved through the derivation of the controller. Furthermore, a new algorithm is proposed to obtain the admissible packet dropout probability bound for the given controller gain. This is particularly important in the co-design of controller and scheduling for NCSs. The simplicity of the methods is demonstrated by numerical examples.     

Absolute stability and stabilization for Lurie networked control systems

This paper investigates the problem of absolute stability and stabilization for networked control systems (NCSs) with the controlled plant being Lurie systems (Lurie NCSs), in which the network‐induced delays are assumed to be time‐varying and bounded. By considering the relationship between the network‐induced delay and its upper bound, an improved stability criterion for networked control system is proposed. Furthermore, the resulting condition is extended to design a state feedback controller by employing an improved cone complementary linearization (ICCL) algorithm. A numerical example is worked out to illustrate the effectiveness and the benefits of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Stabilization of linear discrete‐time networked control systems via protocol and controller co‐design

This paper investigates the stabilization problem for networked control systems (NCSs) with communication constraint and packet loss. The communication constraint considered is that only one network node is allowed to access a shared communication channel during one time‐slot, and a feedback control is performed with only partially available measurements and control inputs. By taking random packet loss into consideration, a stochastic switched system model is presented to describe the NCS. A sufficient condition is derived for the NCS to be mean‐square exponentially stable, and it is shown that the system performance specified by the exponential decay rate critically depends on the network accessing rates (NARs) of the network nodes and the packet loss probability. The state feedback controller and scheduling protocol, which allocates the NARs, are co‐designed such that the NCS achieves a minimal decay rate. Finally, an illustrative example is given to show the effectiveness of the proposed design approach. Copyright © 2014 John Wiley & Sons, Ltd.