Understanding wireless networked control systems through simulation

Wireless sensor-actuator networks (WSANs) are being adopted in process industries because of their advantages in lowering deployment and maintenance costs. While there has been significant theoretical advancement in networked control design, only limited empirical results that combine control design with realistic WSAN standards exist. This paper presents a cyber-physical case study on a wireless process control system that integrates state-of-the-art network control design and a WSAN based on the WirelessHART standard. The case study systematically explores the interactions between wireless routing and control design in the process control plant. The network supports alternative routing strategies, including single-path source routing and multi-path graph routing. To mitigate the effect of data loss in the WSAN, the control design integrates an observer based on an Extended Kalman Filter with a model predictive controller and an actuator buffer of recent control inputs. We observe that sensing and actuation can have different levels of resilience to packet loss under this network control design. We then propose a flexible routing approach where the routing strategy for sensing and actuation can be configured separately. Finally, we show that an asymmetric routing configuration with different routing strategies for sensing and actuation can effectively improve control performance under significant packet loss. Our results highlight the importance of co- joining the design of wireless network protocols and control in wireless control systems.

There is a strong trend towards wireless networked Real-Time Control Systems. However, a variety of factors such as the variability of wireless channel capacities, multi-path fading, and ambient interference make it extraordinarily difficult to design and implement Wireless Control Systems (WCSs). To attack the uncertainty in available communication resource in WCSs, this chapter presents an Adaptive Feedback Scheduling scheme that takes advantage of the methodology of cross-layer design. The proposed approach exchanges information across the physical layer and the application layer in the presence of noise interference and link transmission rate variations. The overall QoC is guaranteed through controlling the deadline miss ratio of control loops. Design parameters of the feedback scheduler are adapted to dynamic changes in wireless channel capacity. To further improve the feedback scheduling performance, an event-driven invocation mechanism for feedback schedulers is suggested. Simulation results demonstrate that this approach is efficient to deal with channel capacity variations and noise interference, thus providing an enabling technology for wireless control in dynamic environments. It is also argued that in this context event-driven invocation mechanism improves the performance of the feedback scheduling system.KeywordsSampling PeriodTransmission RateMedium Access ControlControl PerformanceMedium Access Control ProtocolThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Emerging applications in IoT systems employ wireless communication networks to exchange data between spatially distributed components of a control system. As wireless networks are noisy and subject to packet losses - which might impact the operation of the control system - proper distribution of communication resources among components of the wireless control system sharing the communication network is essential to maintain the system operating reliably. Here, in particular, we study settings in which the decision maker must meet additional constraints on the control system while distributing communication resources. The existence of constraints and the infinite dimensionality of the problem make the resource allocation problem challenging. To reduce the dimensionality of the problem, we parameterize the resource allocation policy in terms of neural networks - high capability approximators - and leverage reinforcement learning techniques to design policies that do not require knowledge of plant dynamics or communication models. We further reformulate the resource allocation problem in the dual domain to handle the constraints, which leads naturally to a primal-dual policy gradient algorithm that alternates between updating the policy parameters via reinforcement learning iterations and updating a dual variable that enforces constraint satisfaction. We conclude the paper with numerical simulations that show the strong performance of the learned allocation policies against baseline resource allocation solutions.

Introduction. In order to ensure the sustainable functioning of critical infrastructures (CI), in conditions of the growth of various types of threats, security systems (SB) for various purposes, for example, technical SB, should be created on them. As such systems, first of all, there are security alarm systems, access control and some others. These systems are usually integral parts of the overall physical protection of CI, so they play an important role in ensuring the security of CI. One of the most important SB on the CI is the identification and access control system. In recent years, specialists in these systems have paid closer attention to the issues of ensuring the security of checkpoints for vehicles. It is known that they can be one of the most vulnerable places in the system of physical protection of the CI. Based on this, the task of improving identification and access control systems, including the vehicle, is currently an urgent scientific and practical task, and therefore require further study. Aims and Purposes. The purpose of this study is to develop a simplified conceptual design of the wireless identification and access control system of the vehicle on the CI. Methods. To achieve this goal, the methods of system analysis, elements of the theory of radio engineering, as well as methods of analysis, description, generalization, results of research works on the subject of research were used. Results and discussion. The existing systems of wireless identification and access control on CI are considered on the example of wireless identification and access control systems of the vehicle. Some ways of improving the safety and reliability of the operation of these systems are outlined. The analysis of ways to improve the systems of wireless identification and access control on CI is carried out on the example of wireless identification and access control systems of the vehicle. A simplified conceptual design of the wireless identification and access control system of the vehicle on CI has been developed. The main primary provisions of the system under development related to the circuit engineering stage of conceptual design are formulated. Conclusions. As a result of the conducted research, a simplified conceptual design of the wireless identification and access control system of the vehicle on CI has been developed. According to the authors, the developed simplified conceptual project, with appropriate adaptation, can be applied in practice for the purposes of ensuring the physical protection of CI. Keywords: critical infrastructure; identification systems; access control; wireless data transmission systems; conceptual project.

The design of a wireless water level control system is introduced and discussed in detail. In this system, the wireless Proportional Integral (PI) controller is developed using the LabVIEW graphical user programming language. Zigbee wireless technology is chosen for the wireless data transfer system. The experimental testbed was built and the system software and hardware were implemented. In order to compare the performance of the wired and wireless system, a corresponding wired water level control system was built. Experimental results show that under the same PI parameters, the settling time of the wired system is 3.3 times faster than the wireless system. However, the percent overshoot using the wireless controller is 4% smaller.

Recent years have witnessed adoption of wireless sensor-actuator networks (WSANs) in process control. Many real-world process control systems must handle various emergency alarms under stringent timing constraints in addition to regular control loops. However, despite considerable theoretical results on wireless control, the problem of incorporating emergency alarms in wireless control has received little attention. This paper presents, to the best of our knowledge, the first systematic approach to incorporate emergency alarms into wireless process control. The challenge in emergency communication lies in the fact that emergencies occur occasionally, but must be delivered within their deadlines when they occur. The contributions of this work are three-fold: (1) we propose efficient real-time emergency communication protocols based on slot stealing and event-based communication; (2) we build an open-source WirelessHART protocol stack in the Wireless Cyber-Physical Simulator (WCPS) for holistic simulations of wireless control systems; (3) we conduct systematic studies on a coupled water tank system controlled over a 6-hop 21-node WSAN. Our results demonstrate our real-time emergency communication approach enables timely emergency handling, while allowing regular feedback control loops to effectively share resources in WSANs during normal operations.

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.

Although wireless control is one of the key technologies for future industries, most wireless networks are only used for monitoring. When wireless networks are applied to transmit control commands, the uncertain link qualities and limited network resources may destroy the performance of multi-loop control systems. Hence, it is critical to allocate these resources to optimize the control performance as the network condition changes and plants evolve. This article presents comprehensive optimal scheduling strategies for wireless control systems based on adaptive dynamic programming. First, we propose an effective adaptive dynamic programming scheduling (ADPS) strategy to solve the optimal scheduling problem based on the single-step control performance at runtime while significantly reducing computational complexity. Moreover, to overcome the “short-sightedness” of single-step performance prediction, we extend ADPS to ADPS-m ( m ulti-step prediction), which optimizes multi-step performance by incorporating a longer-horizon evolution of the plants. Furthermore, we propose ADPS-H ( H eterogeneous flow scheduling) to support heterogeneous flows with different data rates and sizes and ADPS-H-m ( m ulti-step prediction for H eterogeneous flow scheduling), which schedules heterogeneous flows in a longer prediction horizon. We prove that all these scheduling strategies can achieve optimality and stability under mild assumptions. Extensive experiments integrating TOSSIM and MATLAB/Simulink are performed to evaluate all of the proposed methods in case studies of four- and ten-loop control systems. The simulation results demonstrate that these strategies can effectively improve the control performance at lower computing costs under both cyber and physical disturbances. Under the noise level of \(-\) 76 dBm, for the four-loop case, ADPS achieves the same control performance as the linear programming while saving 99.5% of the execution time. ADPS-m further improves the control performance by up to 27.0% compared with ADPS at the prediction horizon of 3, and ADPS-H-m improves the performance by up to 32.3% and 8.4% compared with round-robin and ADPS-H, respectively. The ten-loop case indicates the effectiveness and scalability of the proposed approaches.

Packet priority assignment for wireless control systems of multiple physical systems

The PIDPLUS algorithm is one of the candidates to be used in wireless automation systems. The control performance of this algorithm under packet losses is investigated in the paper. First, the performance of PIDPLUS is evaluated with respect to packet loss rates for a general first-order plus time-delay process, a model widely used for controller tuning. This simulation study reveals how the performance is affected by packet losses in a wireless control system. Secondly, we will elaborate on the implementation of PIDPLUS and discuss its design, tuning and performance in wireless control systems in light of an unstable case process. The results suggest that PIDPLUS can well be used for wireless control, but better performance could be attained by further development of the controller tuning methodology.

Industrial automation is embracing wireless sensor-actuator networks (WSANs). Despite the success of WSANs for monitoring applications, feedback control poses significant challenges due to data loss and stringent energy constraints in WSANs. Holistic control adopts a cyber-physical system approach to overcome the challenges by orchestrating network reconfiguration and process control at run time. Fundamentally, it leverages self-awareness across control and wireless boundaries to enhance the resiliency of wireless control systems. In this article, we explore efficient holistic control designs to maintain control performance while reducing the communication cost. The contributions of this work are five-fold: (1) We introduce a holistic control architecture that integrates Low-power Wireless Bus (LWB) and two control strategies, rate adaptation and self-triggered control ; (2) We present heuristics-based and optimal rate selection algorithms for rate adaptation; (3) We design novel network adaptation mechanisms to support rate adaptation and self-triggered control in a multi-hop WSAN; (4) We build WCPS-RT, a real-time network-in-the-loop simulator that integrates MATLAB/Simulink and a physical WSAN testbed to evaluate wireless control systems; (5) We empirically explore the tradeoff between communication cost and control performance in holistic control approaches. Our studies show that rate adaptation and self-triggered control offer advantages in control performance and energy efficiency, respectively, in normal operating conditions. The advantage in energy efficiency of self-triggered control, however, may diminish under harsh physical and wireless conditions due to the cost of recovering from data loss and physical disturbances.

In order to overcome the power frequency electromagnetic interference existing in the wireless liquid level control system and realize the accurate control to the liquid level, a compound digital filter algorithm is proposed and implemented. This article discusses the topology of the wireless liquid level control system, the form and characteristics of the electromagnetic interference signal, the architecture of the digital filter and the algorithm flow chart, finally compares and analyzes actual operation results. The digital filtering algorithm runs effectively and can achieve the purpose of filtering the electromagnetic interference.

Monitoring and control of critical parameters is of paramount importance for most of the industrial processes. But laying cables from various sensors and actuators to monitoring stations increases cost and complexity. This problem calls for wireless implementations for monitoring and control applications. This paper presents a low cost wireless temperature monitoring and control system based on ZigBee wireless communication protocol. The system uses Microchip's PIC18F458 microcontroller as the field unit and NI LabVIEW interface as the monitoring unit. It utilizes a precision temperature sensor IC, which being a low cost sensor provides a reliable output within its operating range. The system follows a request-response methodology, where the field unit responds to the requests made by the monitoring unit.

An industrial wireless monitoring and control system, capable of supporting energy-harvesting devices through smart sensing and network management, designed for improving electro-refinery performance by applying predictive maintenance, is presented. The system is self-powered from bus bars, and features wireless communication and easy-to-access information and alarms. With cell voltage and electrolyte temperature measurements, the system enables real-time cell performance discovery and early reaction to critical production or quality disturbances such as short-circuiting, flow blockages, or electrolyte temperature excursions. Field validation shows an increase in operational performance of 30% (reaching 97%) in the detection of short circuits, which, thanks to a neural network deployed, are detected, on average, 10.5 h earlier compared to the traditional methodology. The developed system is a sustainable IoT solution, being easy to maintain after its deployment, and providing benefits of improved control and operation, increased current efficiency, and decreased maintenance costs.

This paper designs and makes up a wireless monitoring and control system based on the wireless communication with several single chips and the nRF905 modules. Transferring data and instructions via wireless interface, the system can control the opening and closing operation of a high voltage circuit breaker and measure the characteristic parameters. The reliability tests on the system under a series of typical interferes in vacuum switch cabinets are carried out. Parallel experiments on the data communication demonstrators without EMI are also conducted for comparison. Furthermore, signal intensity experiments is designed to review the wireless communication effect with different distances. By the tests designed and conducted, it is confirmed that the wireless measure and control system designed to monitor and control the high voltage circuit breaker is feasible