Wireless Networked Control Systems Research Articles

Network-Aware Design of State-Feedback Controllers for Linear Wireless Networked Control Systems

We study the problem of stabilizing the origin of a plant, modeled as a discrete-time linear system, for which the communication with the controller is ensured by a wireless network. The transmissions over the wireless channel are characterized by the so-called stochastic allowable transmission intervals (SATI), that is a stochastic version of the maximum allowable transmission interval (MATI). Instead of deterministic transmissions, SATI gives stability conditions in terms of the cumulative probability of successful transmission over N steps. We argue that SATI is well-suited for wireless networked control systems to cope both with the stochastic nature of the communications and the design of energy-efficient communication strategies. Our objective is to synthesize a stabilizing state-feedback controller and SATI parameters simultaneously. We model the overall closed-loop system as a Markov jump linear system and we first provide linear conditions for the stability of the wireless networked control systems in a mean-square sense. We then provide linear matrix inequalities conditions for the design of state-feedback controllers to ensure stability of the closed-loop system. These conditions can be used to obtain both the controller and the SATI. A numerical example is presented to illustrate our results.

New Constrained Predictive PID controller for packet dropouts in Wireless Networked Control Systems

A new constrained predictive PID controller is presented to achieve stability and performance robustness in Wireless Networked Control Systems (WNCS), where the communication is subject to dropouts in both communication directions: sensor to control and control to actuator transmission. The control strategy is based on a new PID controller with similar properties to Model-Based Predictive Control (MBPC). A Kalman filter used for output prediction and a consecutive dropouts compensator have also been added to the control scheme. The purpose of this approach is to develop an estimation algorithm and a control system that maintain information of the sensor packets and the control actions. Several experiments using the TrueTime network simulator showed that the predictive PID controller performs as good as the MBPC scheme with the advantage of having a simple structure.

Wireless Network Design for Control Systems: A Survey

Wireless networked control systems (WNCSs) are composed of spatially distributed sensors, actuators, and controllers communicating through wireless networks instead of conventional point-to-point wired connections. Due to their main benefits in the reduction of deployment and maintenance costs, large flexibility and possible enhancement of safety, WNCS are becoming a fundamental infrastructure technology for critical control systems in automotive electrical systems, avionics control systems, building management systems, and industrial automation systems. The main challenge in WNCS is to jointly design the communication and control systems considering their tight interaction to improve the control performance and the network lifetime. In this survey, we make an exhaustive review of the literature on wireless network design and optimization for WNCS. First, we discuss what we call the critical interactive variables including sampling period, message delay, message dropout, and network energy consumption. The mutual effects of these communication and control variables motivate their joint tuning. We discuss the analysis and design of control systems taking into account the effect of the interactive variables on the control system performance. Moreover, we discuss the effect of controllable wireless network parameters at all layers of the communication protocols on the probability distribution of these interactive variables. We also review the current wireless network standardization for WNCS and their corresponding methodology for adapting the network parameters. Finally, we present the state-of-the-art wireless network design and optimization for WNCS, while highlighting the tradeoff between the achievable performance and complexity of various approaches. We conclude the survey by highlighting major research issues and identifying future research directions.

Optimization of Resources for Wireless Network Control System Based on Sending Control Strategy

This paper studies the wireless network control system, describes the current situation of wireless network control system and describes the general approach to optimize the network. Then put forward the resources to optimize the design of wireless network control system. Build a system model, and establish the corresponding scheduling problem, and achieve optimal design. Through validate with the results from optimization design by simulation. The results show that the estimation performance optimization algorithm liberal radio network control system designed in this paper is better than the best TDMA strategy.

A sub-optimal method for routing redundancy design over lossy networks

In this paper we aim at rendering a wireless networked control system robust with respect to packet losses exploiting routing redundancy. More precisely, we send multiple copies of sensing and actuation data via different routing paths, associated to possibly different delays and packet loss probability, and assume that such data can be re-combined as a weighted linear combination. We extend previous results from the SISO state-feedback to the MIMO output-feedback architecture and provide a methodology to design such weights either to maximize or to constrain a robustness metric based on the notion of Asymptotic Mean Square Stability. Such a metric induces an objective or constraint function that is highly non-linear: we propose a more efficient sub-optimal design methodology that takes into account both the network parameters and the plant dynamics.

Joint Optimization of Wireless Network Energy Consumption and Control System Performance in Wireless Networked Control Systems

Communication system design for wireless networked control systems requires satisfying the high reliability and strict delay constraints of control systems for guaranteed stability, with the limited battery resources of sensor nodes, despite the wireless networking induced non-idealities. These include non-zero packet error probability caused by the unreliability of wireless transmissions and non-zero delay resulting from packet transmission and shared wireless medium. In this paper, we study the joint optimization of control and communication systems incorporating their efficient abstractions practically used in real-world scenarios. The proposed framework allows including any non-decreasing function of the power consumption of the nodes as the objective, any modulation scheme and any scheduling algorithm. We first introduce an exact solution method based on the analysis of the optimality conditions and smart enumeration techniques. Then, we propose two polynomial-time heuristic algorithms based on intelligent search space reduction and smart searching techniques. Extensive simulations demonstrate that the proposed algorithms perform very close to optimal and much better than previous algorithms at much smaller runtime for various scenarios.

Implementation and Evaluation of Wireless Networked Control Systems using Modbus

The recent introduction of wireless transmitters in the industry has driven a new interest in measuring and control techniques, but most applications are restricted to open loop monitoring applications. The reason is the lack of reliability due to problems inherent to the transmission medium, such as loss of information, time varying delays, slow and sometimes-aperiodic update measurements and interference. In order to enable and make the wireless networked control systems (WNCS) more reliable, many control techniques have been researched, including the PIDPlus representing a modified PID algorithm developed for use in systems in which the sampling frequency requirement cannot be guaranteed. This paper presents the implementation of the Modbus protocol for WNCS applications. The Modbus TCP was embedded in dedicated hardware enabling the transmission of data via Ethernet TCP/IP and Wi-Fi. A comparison of PID controllers for the WNCS subjected to variable delays and sampling, and packet losses were done. Experimental results in a pilot plant prove the efficiency of the implementation of a wireless control loop using a Wi-Fi network with embedded Modbus protocol and PIDPlus controller

A probabilistic mix-critical task scheduling algorithm for wireless networked control system

As a special application of real-time systems, a wireless networked control system (WNCS) is a control system wherein the control loops are closed through a wireless communication network. In WNCSs, tasks have different time constraints as well as critical requirements, therefore, how to schedule mix-critical tasks is extremely important. However, traditional mix-critical task scheduling algorithms for WNCSs usually suffer from long transmission delay and high failure rate, which hinders the performance of WNCSs. In this paper, we propose a probabilistic real time scheduling (PRTS) algorithm for solving scheduling problems. We introduce a schedulability analysis scheme for testifying whether a group of tasks can be scheduled or not. Then the scheduling algorithm PRTS is developed, which aims at enhancing the successful rate of scheduling and reducing the real-time transmission delay. At last, several simulations are conducted to show the advantages of our scheme. Simulation results reveal that PRTS has a higher ability in solving the mix-critical task scheduling problem. We conclude that PRTS is feasible to be used in WNCS.

A probabilistic mix-critical task scheduling algorithm for wireless networked control system

A probabilistic mix-critical task scheduling algorithm for wireless networked control system

Realization of Actuator‐Fault Estimation for Distributed Wireless Networked Control Systems

AbstractThis paper addresses a study of fault estimation for distributed wireless networked control systems (WNCSs) with actuator multiple faults during industrial automatic processes. Firstly, the model of WNCSs is formulated as linear time periodic systems (LTPSs) according to the periodicity of subsystems in WNCSs. Afterwards, the distributed fault estimation (FE) method for LTPSs is concerned. The strategy of avoiding the problem of structure‐limitation in the FE gain and the realization of the proposed method in the real process are especially detailed. Finally, the proposed FE method is verified on a wireless network control (WiNC) platform.

Optimal fault-tolerant control for UAV systems with time delay and uncertainties over wireless network

This paper presents an optimal fault-tolerant control scheme for time-delay systems in wireless network. In order to solve the problem of time delay caused by wireless transmission, time delay compensation item is added to the sliding surface to eliminate the impact of state time delay. Aiming at the modeling uncertainties of the systems, sufficient conditions for asymptotic stability of ideal sliding mode of the system are given based on LMI (linear matrix inequality) technique. To deal with the actuator faults, optimal index of quadratic form is designed to optimize the control law of the nominal system, and then the sliding mode switching control law is constructed to complete the optimal fault-tolerant control for time delay systems with the actuator faults. Finally, the proposed method is applied to the wireless network control system of the quad-rotor UAV (Unmanned Aerial Vehicle). The experiment results show that the proposed method in this paper has obvious advantages compared with the traditional method.

Event‐triggered output tracking control for wireless networked control systems with communication delays and data dropouts

This study addresses the event-triggered output tracking control under wireless network environments. First, an improved event-triggered communication scheme and a sampled-state-error dependent tracking model for wireless networked control systems is presented. In this scheme and model, (a) the sensor takes samples in a periodic manner; (b) an improved event-triggering condition is applied in the communications to determine whether the sampled data is transmitted to the controller or not; and (c) the closed-loop tracking system with a networked state-dependent controller is modelled as an augmented time-delay system. Second, by constructing a novel Lyapunov–Krasovskii functional, two theorems are derived with guaranteed H∞ tracking performance subject to imperfect wireless communications. The tracking performance is based on two permissible limits on the signal transmission. That is, the maximum allowable communication delay bound and maximum allowable number of successive data dropouts. Finally, a satellite tracking example is given to show the effectiveness of the proposed method.

Modelling and stabilization of a wireless network control system with time delay

This paper investigates the problem of modelling and stabilization for a wireless based network control system with time delay. A model for the discrete-time system with time-varying delay is established to describe the system, and a static controller is designed that takes the feedback from both state and output into account. Based on Lyapunov stability theory and the linear matrix inequalities method, a new criterion is presented for stabilizing the discrete-time system with time-varying delay, and the corresponding controller parameter is obtained. A numerical example is given to demonstrate the effectiveness of the proposed approach.

A Higher Energy-Efficient Sampling Scheme for Networked Control Systems over IEEE 802.15.4 Wireless Networks

This paper proposes a higher energy-efficient mixed sampling scheme (MSE) for networked control systems (NCSs) over IEEE 802.15.4 wireless networks. Compared with some existing periodic event-triggered sampling (ETS) schemes with a delayed sampling estimation, this delay is no longer existing in MSE since there is a dynamic adjustable threshold in MSE to compensate for this delay. Compared with some existing self-triggered sampling (STS)/ETS schemes, MSE does not require continuous measurement of the system states and does not suffer from the conservativeness induced by a self-triggered estimation. By using the proposed MSE, one can improve the energy efficiency in energy-constrained wireless NCSs (WiNCSs) by reducing the number of transmitted packets and increasing the idle-listening period of wireless sensor nodes. An inverted pendulum (Feedback 33-005-PCI) controlled over IEEE 802.15.4 wireless networks is given to demonstrate the effectiveness of the proposed method.

Design Considerations for Wireless Networked Control Systems

In traditional networked control systems, wired communication networks are used for the transmission of information between the communicating systems. With the increasing demand for distributed systems and the growth in the scale of the applications, the use of wireless communication networks offers significant advantages over their wired counterparts. To facilitate the deployment of a fully automated closed-loop wireless networked control system (WNCS), this paper addresses several design considerations for a proposed topology for potential use as a closed-loop WNCS. The topology consists of a plant system having sensor and actuator nodes, a controller system having input and output nodes, an intermediate network system having interconnected nodes, and wireless communication links for the information transfer between the different nodes of the plant, controller, and network systems. More specifically, the design considerations addressed in the paper are: the condition requirements needed to facilitate the design of optimal controller and network systems, the joint design of optimal controller and network systems to control the plant system, and the structured model reduction of the closed-loop WNCS to reduce its scale. Finally, simulation examples are provided to demonstrate the applicability of discussed design considerations.

STS: A Real Time Scheduling Algorithm for Temporal-Spatial Tasks in Wireless Networked Control Systems

In this paper, a hybrid spatial and temporal scheduling algorithm for wireless networked control system, which takes the distance between robot and task region as well as the deadline of a task into consideration is proposed. In our method, we quantify spatial and temporal factors for eventually getting the priority queue. Based on the priority queue, the robot is able to execute the tasks sequentially. At last, extensive simulations are conducted to show the advantages of our spatial and temporal scheduling algorithm. Simulation results show that, on the premise of ensuring high successful scheduling rate, compared with previous method, our scheme show merits in terms of task requesting throughput, successful task solving ratio, average responding delay.

Computation and Communication Evaluation of an Authentication Mechanism for Time-Triggered Networked Control Systems.

In modern networked control applications, confidentiality and integrity are important features to address in order to prevent against attacks. Moreover, network control systems are a fundamental part of the communication components of current cyber-physical systems (e.g., automotive communications). Many networked control systems employ Time-Triggered (TT) architectures that provide mechanisms enabling the exchange of precise and synchronous messages. TT systems have computation and communication constraints, and with the aim to enable secure communications in the network, it is important to evaluate the computational and communication overhead of implementing secure communication mechanisms. This paper presents a comprehensive analysis and evaluation of the effects of adding a Hash-based Message Authentication (HMAC) to TT networked control systems. The contributions of the paper include (1) the analysis and experimental validation of the communication overhead, as well as a scalability analysis that utilizes the experimental result for both wired and wireless platforms and (2) an experimental evaluation of the computational overhead of HMAC based on a kernel-level Linux implementation. An automotive application is used as an example, and the results show that it is feasible to implement a secure communication mechanism without interfering with the existing automotive controller execution times. The methods and results of the paper can be used for evaluating the performance impact of security mechanisms and, thus, for the design of secure wired and wireless TT networked control systems.

Quantized stabilization of wireless networked control systems with packet losses

This paper considers stabilization of discrete-time linear systems, where wireless networks exist for transmitting the sensor and controller information. Based on Markov jump systems, we show that the coarsest quantizer that stabilizes the WNCS is logarithmic in the sense of mean square quadratic stability and the stabilization of this system can be transformed into the robust stabilization of an equivalent uncertain system. Moreover, a method of optimal quantizer/controller design in terms of linear matrix inequality is presented. Finally, a numerical example is provided to illustrate the effectiveness of the developed theoretical results.

Delay compensation using Smith predictor for wireless network control system

Wireless Sensor Network (WSN) is widely used in the industrial Network Control System (NCS). It relies on the IEEE 802.15.4 MAC protocol to transfer data at low rate. Experimental and theoretical studies proved that the wireless channel produces a time delay. In the NCS, this delay may cause system instability and performance degradation. Delay compensation schemes are used to reduce the delay effects.In this paper, a delay compensation scheme using classical and adaptive Smith predictor is applied to wireless NCS. The Markov model is proposed to compute the estimated network delay used in the classical predictor. In the adaptive predictor, the channel delay statistics using shift register is proposed to update the estimated delay. To evaluate the proposed schemes, a DC-motor controller system based on IEEE 802.15.4 is built using True Time Matlab software. The system performance with and without the proposed delay compensation scheme is studied. It is also compared to other delay compensation schemes. The results show that the proposed scheme improves the NCS performance significantly and reduces the effect of the delay on the system.

Optimal DoS Attack Scheduling in Wireless Networked Control System

Recently, many literature works have considered the security issues of wireless networked control system (WNCS). However, few works studied how the attacker should optimize its attack schedule in order to maximize the effect on the system performance due to the insufficiency of energy at the attacker side. This paper fills this gap from the aspect of control system performance. We consider the optimal jamming attack that maximizes the Linear Quadratic Gaussian (LQG) control cost function under energy constraint. After analyzing the properties of the cost function under an arbitrary attack schedule, we derive the optimal jamming attack schedule and the corresponding cost function. System stability under this optimal attack schedule is also considered. We further investigate the optimal attack schedule in a WNCS with multiple subsystems. Different examples are provided to demonstrate the effectiveness of the proposed optimal denial-of-service attack schedule.