Analysis and Challenges in Wireless Networked Control System: A Survey

This paper integrates the IEEE 802.11 g ad-hoc wireless network and the control area network (CAN) in the present network control systems (NCS) or wireless - NCS (WNCS). Both the TCP and the CAN protocols are adopted as the communication gateway in a remote control system. The time delay between the application layer of the client and the application layer of the remote control target has been measured and analyzed in this paper. Experimental results on an AC 400 W servo motor indicate that the communication jam mainly causes the instability due to the induced time delay. In this paper, by applying the adaptive Smith predictor with the switching sampling time, satisfactory control performance of WNCS can be obtained even though the time delay seriously increases. Moreover, the feasibility of the proposed WNCS has been proven through experimental results.

The integration of wireless communication and control systems revealed wireless networked control systems (WNCSs). One fundamental problem in WNCSs is to have a wide coverage area. For the first time in the literature, we address this problem and we obtain the maximum coverage area by solving an optimization problem. In this technical note, we consider a WNCS where the output sensor measurements are transmitted over separate heterogeneous multi-hop wireless ad-hoc subnetworks. The observation process is divided into N parts and the system state is estimated using the Kalman filter. We present the critical arrival probability for a sensor measurement packet such that if the packet arrival probability is larger than the critical value, it is guaranteed that the estimator of the WNCS converges. We derive the maximum total coverage area of the heterogeneous wireless subnetworks having maximum cost-efficiency under the constraint of the convergence of the WNCS estimator.

The dynamism and portability of wireless installation allows for measurements to be obtained online in such environments hitherto considered challenging for wired measurements. WirelessHART standard has been in the open market for few years already. It has been acknowledged as a viable alternative to wired networks. By deploying wireless sensor network, the cost and period of wiring installation, maintenance and commissioning can be reduced. A Key issue associated with wireless networked control system is the packet dropout. This is prompted by the non-periodic update of measurements as a result of the use of wireless network in the control loop. The packet dropout can cause degradation and declining of the control performance and could possibly jeopardize plant safety. To overcome this phenomenon, this paper presents the application of filtered feedback PID control strategy. Analysis of the results obtained shows that the performance of the plant with the proposed method is better than the conventional PID control.

The Internet of things (IoT) becomes a new solution for the future industry. It aims to provide an intelligent environment to control systems in real time. We propose an embedded predictive application in the Wireless Networked Control Systems (W-NCS) to control a DC motor via RF links, under the presence of packet losses and limited size constraint of transmitted packets in the communication channel. To design an IoT predictive application in W-NCS, a Model Predictive Control (MPC) method is proposed. This strategy is developed and implemented in the embedded device by using the RIOT OS which granted maintenance costs of IoT products and offers a real-time support in the control of the systems. The proposed approach is tested in a wireless environment with an intention to be applied to tackle the problem of communication. The practical experiment results obtained demonstrate the effectiveness of the Networked Predictive Control (NPC) approach based on the W-NCS structure for this kind of problems.

This article considers a wireless networked control system (WNCS) consisting of a dynamic system to be controlled (i.e., a plant), a sensor, an actuator, and a remote controller for mission-critical Industrial Internet of Things (IIoT) applications. A WNCS has two types of wireless transmissions, i.e., the sensor’s measurement transmission to the controller and the controller’s command transmission to the actuator. In the literature of WNCSs, the controllers are commonly assumed to work in a full-duplex (FD) mode by default, i.e., being able to simultaneously receive the sensor’s information and transmit its own command to the actuator. In this article, we consider a practical half-duplex (HD) controller, which introduces a novel transmission-scheduling problem for WNCSs. A frequent scheduling of sensor’s transmission results in a better estimation of plant states at the controller and thus a higher quality of control command, but it leads to a less frequent/timely control of the plant. Therefore, considering the overall control performance of the plant in terms of its average cost function, there exists a fundamental tradeoff between the sensor’s and the controller’s transmissions. We formulate a new problem to optimize the transmission-scheduling policy for minimizing the long-term average cost function. We derive the necessary and sufficient condition of the existence of a stationary and deterministic optimal policy that results in a bounded average cost in terms of the transmission reliabilities of the sensor-to-controller and controller-to-actuator channels. Also, we derive an easy-to-compute suboptimal policy, which notably reduces the average cost of the plant compared to a naive alternative-scheduling policy.

A wireless networked control systems (NCS) is a control system whose feedback path is realized over a wireless communication network. The stability of such systems can be problematic given the random way in which wireless channels drop feedback messages. This paper establishes sufficient conditions for the almost sure stability of NCS under random dropouts. These conditions relate the burstiness in the dropout process to the nominal response of the controlled system. In particular, this means that the burstiness of the dropout process provides a convenient quality-of-service (QoS) constraint on the wireless channel that can be used to adaptively reconfigure the control system in a manner that guarantees the almost sure stability of the NCS. We also show how a probabilistic extension of the network calculus can be used to reconfigure multi-hop communication networks so this paper's sufficient stability condition is not violated.

Real-life cyber-physical systems, such as automotive vehicles, building automation systems, and groups of unmanned vehicles are monitored and controlled by networked control systems. The overall system dynamics emerges from the interaction among physical dynamics, computational dynamics, and communication networks. Network uncertainties such as time-varying delay and packet loss cause significant challenges. This paper proposes a passive control architecture for designing wireless networked control systems that are insensitive to network uncertainties. We describe the architecture for a system consisting of a robotic manipulator controlled by a digital controller over a wireless network and we show that the system is stable even in the presence of time-varying delays. We present simulation results that demonstrate the advantages of the architecture with respect to stability and performance and show that the system is insensitive to network uncertainties.

Motivated by the potentially application merits of wireless networked control systems (WNCSs), this paper presents a network-based formation framework for multi-agent systems. First, we construct a discrete formation protocol by integrating 802.11b. Meanwhile, one agent is considered as the reference, and the other ones keep a desired formation with the reference via communication networks. Using Lyapunov stability theory, sufficient convergence conditions are derived, and the verification problem of the sufficient conditions can be transformed as a linear matrix inequality (LMI) feasibility problem. Solving this LMI feasibility problem, a networked-based feedback controller can be easily obtained. Finally, simulation studies are provided to demonstrate the effectiveness of the proposed method.

This paper investigates the design of a robust fault detection observer for Wireless Networked Control Systems (WNCS) subject to random packet delays introduced by the wireless communication networks. The concept of input-delay analysis is adopted for analyzing the impacts of the packet delay on the residual generation, and a robust observer design and optimization method is proposed to improve the robustness of fault detection against the network induced delay. For the purpose of realistic simulation, a mixed simulation is carried out, where the control system is simulated in MATLAB and the network-induced delays are achieved by simulating an IEEE 802.11b wireless network at the recently developed OMNeT++ platform. The simulation results validate the proposed robust fault detection observer design approach.

Markovian jumping systems have arisen naturally in the mathematical modeling of phenomena spanning disciplines in the social sciences, natural sciences, and engineering. This kind of stochastic dynamical systems can be employed to model the dynamics when parameters are subject to random abrupt changes due to sudden environment changes, subsystem switching, system noises, executor faults, and so forth. Much attention has been given to modeling, optimization, and real applications of such stochastic dynamical systems in the literature in recent years. As the advanced control and optimization will provide a basis for the design and application of such stochastic systems, these advanced techniques would result in substantial and sustainable benefits. The accepted papers in this special issue include stochastic stability, stabilization, stochastic control optimization, system modeling and identification methods, predictive control, signal processing, robust filtering, multiagent systems, networked control systems, time-delayed systems, neural networks, the Takagi-Sugeno fuzzy systems, simulated annealing, and fault detection methods.

Safety is the prime concern which drives the development of vehicular communication as support to intelligent transportation systems. The communication networks play a key role and supported by different components among which antenna plays a very crucial role. This paper presents a compact and new design of circular polarized (CP) patch antenna for use in wireless avionics intra-communications (WAICs) and intelligent transportation systems (ITS). Experimental results of the reflection coefficient, gain, and the radiation pattern is consistent with simulation. The prototype antenna can operate in a 4.4 GHz WAICs band with reflection coefficient under −15 dB and gain 8.3 dBi. In 5.9 GHz ITS band it operates with reflection coefficient under −15 dB and gain 8.8 dBi.

This paper focuses on network-based master-slave synchronization for delayed neural networks through a remote controller. The insertion of communication networks in a master-slave synchronization scheme inevitably induces network delays, packet dropouts and stochastic fluctuations. The data packets may be received with a different temporal order from that they are sent due to the fact that the network-induced delay is time-varying. A logic data processor and a logic zero order hold are proposed in the master-slave synchronization framework. Then an error system for the master system and the slave system is formulated. By combining a generalized Jensen integral inequality and a convex combination technique, some synchronization criteria are derived to ensure the mean-square global exponential synchronization of state trajectories for the master system and the slave system. The controller gain matrix is obtained by solving a minimization problem in terms of linear matrix inequalities using a cone complementary technique. As a special case in which only network-induced delays and packet dropouts are occurred in the signal transmission channels, some results are also presented. Finally, two illustrative examples are provided to show the effectiveness and applicability of the proposed scheme.

This paper is concerned with a novel state estimator to track gas path performance in real time with one sensor failure and packet dropouts for aircraft engine in an advanced distributed architecture. It is common to sensor measurement lost in the distributed network, which results in the decrease of state tracking accuracy. A hybrid extended Kalman filter (HEKF) is proposed for engine performance anomaly detection and sensor fault accommodation from previous studies. Five groups of sensor measurement are divided along gas path related to five local filters, and the local estimated results are fused in the main filter. The reception state matrix is introduced to HEKF to deal with packet dropout, and nonlinear calculation is separated from a local filter to reduce computational burden in the field. Besides, fault diagnosis and isolation strategy of sensor subsets is developed and combined to HEKF by state consistency strategy of distributed network. The contribution of this study is to provide the novel HEKF algorithm to achieve real-time state estimation for sensor-fault-tolerant monitoring of aircraft engine with packet dropout in the distributed structure. The simulation and comparison are systematically carried out, and the superiority of the proposed methodology is confirmed.

This study proposes a new distributed networked control (DNC) scheme and its stability analysis framework for automatic generation control in networked interconnected power systems with participation of wind turbine. It is assumed that the remote control signals are measured at locations away from the control site and exchanged among a non‐ideal communication network with both time‐varying delays and random packet dropouts. First, a model is proposed for large‐scale DNC system consisting of subsystems, in which the states of each subsystem have their own time‐varying delay and there are also delay and packet dropouts in their interconnection links. Then, a linear matrix inequality (LMI)‐based method is proposed to design the distributed controller for better system performance. For this, a new Lyapunov–Krasovskii function is developed to conclude some LMI‐based delay‐independent theorem for designing control law. To evaluate the proposed method, a multi‐area power system with participation of wind turbine is considered. Simulation results show the capability of the proposed approach to enhance the performance of networked power system in the presence of load perturbation among a non‐ideal communication network with both time‐varying delays and random packet dropouts.

Smart buildings are equipped with computer systems that monitor and control diverse services such as air conditioning, indoor transportation, physical access control, and many others. Critical infrastructures like hospitals, airports, and data centers, leverage on such services to support their daily operations. However, the current popularity of smart buildings is founded on a decades-long history. Smart building systems have evolved from isolated networks using proprietary protocols to IT-integrated systems that use standardized communication protocols. They might even be connected to the Internet to allow remote building management. This transition has exposed smart buildings to a whole new set of security threats. For instance, there have been documented cases where attackers have managed to remotely disrupt the environmental conditions and physical access control of smart buildings. Due to the crucial role that smart buildings play in supporting organizations and the serious threat of cyber attacks against them, there is a pressing need to investigate how to improve their current security posture.<br/>The transfer of mature IT security solutions to smart building systems seems a natural approach to enhance their security, however, the fundamental differences between both domains often require significant adaptation effort or to develop completely new solutions. For this reason, in recent years, a growing body knowledge about smart buildings security has been developed. However, most of these solutions have focused on intrusion detection and little efforts have been made to prevent cyber attacks. An effective way to prevent cyber attacks against smart buildings is by preemptively handling security weaknesses in customized applications and configurations that run the system. Unfortunately, this is often overlooked by smart building administrators due to, e.g., lack of specialized tools, staff, and training. We identify not only a research gap regarding this important task, but also an urgent need to provide (semi-) automated tools that help overcome the limitations faced by smart building administrators. The implementation of these tools requires sophisticated methods that incorporate technical and business-related insights to handle weaknesses according to the organization’s best interest.<br/>In this thesis, we investigate how to implement the first stages of a vulnerability management process for smart building applications and configurations. Beyond just vulnerabilities, we consider the weaknesses that give rise to vulnerabilities. In particular, our contributions address the identification and assessment of security weaknesses for later remediation. These are two key activities to preemptively strengthen the security of smart buildings. The identification of weaknesses is the basis of any vulnerability management process as it provides the first insights about the current security state of a system. This is a challenging task because a deep understanding of the system’s inner workings is often needed to obtain meaningful findings. We propose two approaches to identify security weaknesses; one focused on smart building applications and another on smart building configurations. In the first case, we model the application as a graph data structure comprised of sensors, setpoints, actuators, and control function nodes. The relationships among these components reveal the architecture of the system, which can then be analyzed in the search for security weaknesses. In the second case, we look for component misconfigurations that can be observed in their behavior, i.e., the way they interact with other components in the system. Leveraging official documentation from the components’ manufacturers, we create a model of valid behavior for each of them, which is then compared with their actual behavior as observed in the network traffic. After identifying security weaknesses, we assess the sensitivity of the affected components, which is an important factor to prioritize weaknesses for later remediation. We propose a comprehensive approach to assess the sensitivity of smart building components based on technical and business-related features. The proposed methods are evaluated in real smart buildings and additional experiments are performed in testbeds and comparable simulated environments. These evaluations confirm the feasibility and effectivity of our (semi-) automated weakness identification and assessment approaches.