Networked Cyber-physical Systems Research Articles

Dynamic Watermarking: Active Defense of Networked Cyber–Physical Systems

The coming decades may see the large scale deployment of networked cyber–physical systems to address global needs in areas such as energy, water, health care, and transportation. However, as recent events have shown, such systems are vulnerable to cyber attacks. Being safety critical, their disruption or misbehavior can cause economic losses or injuries and loss of life. It is therefore important to secure such networked cyber–physical systems against attacks. In the absence of credible security guarantees, there will be resistance to the proliferation of cyber–physical systems, which are much needed to meet global needs in critical infrastructures and services. This paper addresses the problem of secure control of networked cyber–physical systems. This problem is different from the problem of securing the communication network, since cyber–physical systems at their very essence need sensors and actuators that interface with the physical plant, and malicious agents may tamper with sensors or actuators, as recent attacks have shown. We consider physical plants that are being controlled by multiple actuators and sensors communicating over a network, where some sensors could be “malicious,” meaning that they may not report the measurements that they observe. We address a general technique by which the actuators can detect the actions of malicious sensors in the system and disable closed-loop control based on their information. This technique, called “watermarking,” employs the technique of actuators injecting private excitation into the system, which will reveal malicious tampering with signals. We show how such an active defense can be used to secure networked systems of sensors and actuators.

Complex cyber-physical networks: From cybersecurity to security control

Complex cyber-physical network refers to a new generation of complex networks whose normal functioning significantly relies on tight interactions between its physical and cyber components. Many modern critical infrastructures can be appropriately modelled as complex cyber-physical networks. Typical examples of such infrastructures are electrical power grids, WWW, public transportation systems, state financial networks, and the Internet. These critical facilities play important roles in ensuring the stability of society as well as the development of economy. Advances in information and communication technology open opportunities for malicious attackers to launch coordinated attacks on cyber-physical critical facilities in networked infrastructures from any Internet-accessible place. Cybersecurity of complex cyber-physical networks has emerged as a hot topic within this context. In practice, it is also very crucial to understand the interplay between the evolution of underlying network structures and the collective dynamics on these complex networks and consequently to design efficient security control strategies to protect the evolution of these networks. In this paper, cybersecurity of complex cyber-physical networks is first outlined and then some security enhancing techniques, with particular emphasis on safety communications, attack detection and fault-tolerant control, are suggested. Furthermore, a new class of efficient secure control strategies are proposed for guaranteeing the achievement of desirable pinning synchronization behaviors in complex cyber-physical networks against malicious attacks on nodes. The authors hope that this paper motivates to design enhanced security strategies for complex cyber-physical network systems, to realize resilient and secure critical infrastructures.

Reliability of Sensor Nodes in Wireless Sensor Networks of Cyber Physical Systems

Sensors are a crucial component of any intelligent control system. Wireless sensor networks are one of the most rapidly developing information technologies and promise to have a variety of applications in Next Generation Networks, Internet of Things and for mission critical and safety relevant applications. Reliability is one of the most important attribute of such systems. In the paper Markov model for reliability analyses of sensor node in wireless sensor networks is proposed. It is shown that reliability of the sensor node depends on the strategy of it monitoring and is unimodal function of test period. For passive part of sensor node, the optimal time for test of functionality is defined.

Optimal Planning of Communication System of CPS for Distribution Network

IoT is the technical basis to realize the CPS (Cyber Physical System) for distribution networks, with which the complex system becomes more intelligent and controllable. Because of the multihop and self-organization characteristics, the large-scale heterogeneous CPS network becomes more difficult to plan. Using topological potential theory, one of typical big data analysis technologies, this paper proposed a novel optimal CPS planning model. Topological potential equalization is considered as the optimization objective function in heterogeneous CPS network with the constraints of communication requirements, physical infrastructures, and network reliability. An improved binary particle swarm optimization algorithm is proposed to solve this complex optimal problem. Two IEEE classic examples are adopted in the simulation, and the results show that, compared with benchmark algorithms, our proposed method can provide an effective topology optimization scheme to improve the network reliability and transmitting performance.

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Special Issue on Distributed Signal processing for Security and Privacy in Networked Cyber-Physical Systems

Energy-Event-Triggered Hybrid Supervisory Control for Cyber-Physical Network Systems

This technical note develops energy-event-triggered hybrid supervisory control techniques to address robust and fast energy equipartition for cyber-physical network systems, and discusses the application of the proposed approach to power systems. First, we present a hybrid controller with a distributed feedback and supervisory energy-event-triggered resetting law to achieve the robust disturbance rejection performance of physical networks by mimicking thermodynamic systems. The proposed controller architectures are constructed in such a way that each controller has a one-directional energy transfer from a plant to itself, and exchanges energy with its neighboring controllers. Specifically, if the cyber-physical system is lossless, this controller can prevent cascading behaviors. Second, we propose a consensus hybrid controller that mitigates the disturbance effect by decentralizing the disturbance on one plant to all the other plants when stabilizing it. In addition, a new combined hybrid controller based on the two precedent hybrid controllers is proposed to achieve cascade prevention and fast energy equipartition for lossless cyber-physical network systems. Finally, we apply our hybrid control technique to power systems, and simulation studies are carried out to show the efficacy of the proposed approach.

Simulation alternatives for the verification of networked cyber-physical systems

Several embedded system applications are used to control physical processes thus leading to the concept of Cyber-Physical System. Sensing, computation and actuation are combined by involving a set of highly heterogeneous components, i.e., digital and analog hardware, software, energy sources, and external physical systems (e.g., a room to be heated, a mechanical component). Moreover, we see the growing use of networks to connect several sub-systems in a more efficient way; this contributes to introduce a further level of heterogeneity due to the presence of messages exchanged over communication channels. All these aspects should be taken into account in the design process to find highly optimized solutions; in particular, simulation is a key technique for their verification. However, the heterogeneity of components, together with the presence of the network, forces to adopt complex and slow co-simulation techniques to carry on the simulation of the entire system.This work aims at proposing SystemC as unified framework to model and simulate Networked Cyber-Physical Systems. Concerning the modeling of continuous-time components and a specific class of discrete-time components, the different Models of Computation provided by the Analog/Mixed-Signal (AMS) extension of SystemC are used. Regarding the network, SystemC and the SystemC Network Simulation Library are used to model communications at different abstraction levels. The approach is validated by considering a networked control system. First, the accuracy and speed of SystemC simulation is compared to Matlab/Simulink simulation. Second, different simulation alternatives are compared to co-simulation. Finally, we show that the simulation speed-up achieved by all-SystemC modeling allows to explore several design alternatives and the accurate modeling of the communication network can improve the design of the controller.

A priority-aware frequency domain polling MAC protocol for OFDMA-based networks in cyber-physical systems

Wireless networking in cyber-physical systems (CPSs) is characteristically different from traditional wireless systems due to the harsh radio frequency environment and applications that impose high real-time and reliability constraints. One of the fundamental considerations for enabling CPS networks is the medium access control protocol. To this end, this paper proposes a novel priority-aware frequency domain polling medium access control (MAC) protocol, which takes advantage of an orthogonal frequency-division multiple access (OFDMA) physical layer to achieve instantaneous priority-aware polling. Based on the polling result, the proposed work then optimizes the resource allocation of the OFDMA network to further improve the data reliability. Due to the non-polynomial-complete nature of the OFDMA resource allocation, we propose two heuristic rules, based on which an efficient solution algorithm to the OFDMA resource allocation problem is designed. Simulation results show that the reliability performance of CPS networks is significantly improved because of this work.

Traffic Generation Rate Control of Wireless Sensor and Actuator Networks

The traffic generation rate of the network used for cyber-physical systems is a crucial design parameter since it directly affects the stability of physical systems and the congestion level of communication systems. In this paper, we propose a novel modeling framework of the general wireless sensor and actuator networks of cyber-physical systems where the sensor-controller and controller-actuator sides communicate over a lossy network. The performance model is then used to derive the optimal traffic generation rate of sensors and controllers for minimizing the maximum outage probability of the stability constraint of the control systems while guaranteeing a schedulability constraint. The resulting problem is a non-linear optimization problem which allows to obtain the global optimum. An efficient approximation converts the proposed optimization problem into a linear programming problem. One interesting finding is that the optimal solution assigns higher traffic generate rate on the controller-actuator link compared to the one of the sensor-controller link since the actuating-link is more critical to guarantee the stability of the control systems.

Efficient Medium Access Control for Cyber–Physical Systems With Heterogeneous Networks

A cyber-physical system (CPS) consists of a group of interlinked networked objects. CPSs are characteristically different from the traditional internetworked systems (e.g., Internet) due to the operating environment and their applications, which impose high reliability constraints on them. One of the fundamental considerations for enabling this technology is the medium access control (MAC). The traditional IEEE 802.11-based MAC layer solutions need to be revamped. In order to increase the efficiency of data transmission, we introduce a new approach, which argues the replacement of the traditional backoff algorithm of 802.11. The proposed approach attempts to address some of the obligations posed by CPS networks. At the core of the proposed solution is the introduction of the adaptability factor to the traditional backoff procedure, which can help CPS networks operate under diverse environmental conditions. In order to survive the high degrees of dynamism of these networks, each of the nodes is equipped with a learning automaton, which adapts to the changing environment and provides the node with the most optimized value. The consistent outperformance of the proposed approach when compared with similar existing approaches under different simulation scenarios exhibits its efficacy. The critical parameters, such as packet delivery ratio and delay, are improved by up to 40% and 27%, respectively, over the traditional protocols.

A Secure Service Provisioning Framework for Cyber Physical Cloud Computing Systems

Cyber physical systems (CPS) are mission critical systems engineered by combination of cyber and physical systems respectively. These systems are tightly coupled, resource constrained systems and have dynamic real time applications. Due to the limitation of resources, and in order to improve the efficiency of the CPS systems, they are combined with cloud computing architecture, and are called as Cyber Physical Cloud Computing Systems (CPCCS). These CPCCS have critical care applications where security of the systems is a major concern. Therefore, we propose a Secure Service provisioning architecture for Cyber Physical Cloud Computing Systems (CPCCS), which includes the combination of technologies such as CPS, Cloud Computing and Wireless Sensor Networks. In addition to this, we also highlight various threats/attacks; security requirements and mechanisms that are applicable to CPCCS at different layers and propose two security models that can be adapted in a layered architectural format.

Energy Equipartition Stabilization and Cascading Resilience Optimization for Geospatially Distributed Cyber-Physical Network Systems

This paper develops three novel hybrid stabilization techniques addressing fast energy equipartition for cyber-physical network systems, establishes an optimization-based network topology design framework to achieve cascading resilience and efficiency of geospatially distributed physical networks, and discusses the future application of the proposed approach to power network systems. Thus, the main contributions of this paper are three-fold. First, we present three hybrid distributed stabilization architectures for cyber-physical network systems to achieve the robust performance of geospatial physical networks by mimicking the dynamic behavior of thermodynamic systems. The proposed stabilization architectures are constructed in such a way that each stabilizer has a one-directional energy transfer from a plant to itself, and exchanges energy with its neighboring stabilizers. Second, to balance resilience to cascading failures and efficiency of energy flow in geospatially distributed physical networks, we propose an entropy metric-based multiobjective optimization framework for network topology design to characterize this resilience-efficiency trade-off design in networks. Moreover, we propose a novel cascade-connectivity swarm optimization algorithm which combines swarm intelligence and graph theory together to solve this multiobjective optimization problem. Finally, we apply our hybrid stabilization techniques and topology design algorithms to power network systems, and simulation studies are carried out to show the efficacy of the proposed approach.

Implementing virtual platform for global‐scale cyber physical system networks

SummaryThe need for global‐scale cyber physical system (CPS) is increasing with the evolution of CPS research. A global‐scale CPS requires additional considerations beyond the well‐known CPS requirements, such as security, reliability, and timely delivery, which cannot be easily satisfied when a CPS becomes global scale. Building an entire dedicated network for a global‐scale CPS cannot be a solution, because it requires a large capital outlay in order to be actualized. To overcome these obstacles, we implement a virtual platform named Xebra that includes effective CPS middleware for realizing a global‐scale CPS and isolation techniques based on virtualization. In this paper, we discuss the requirements for realizing global‐scale CPS network, and also, we introduce our implementation as a virtual platform with its performance evaluation. Copyright © 2014 John Wiley & Sons, Ltd.

A Hybrid Trust Management Framework for Wireless Sensor and Actuator Networks in Cyber-Physical Systems

To secure a wireless sensor and actuator network (WSAN) in cyber-physical systems, trust management framework copes with misbehavior problem of nodes and stimulate nodes to cooperate with each other. The existing trust management frameworks can be classified into reputation-based framework and trust establishment framework. There, however, are still many problems with these existing trust management frameworks, which remain unsolved, such as frangibility under possible attacks. To design a robust trust management framework, we identify the attacks to the existing frameworks, present the countermeasures to them, and propose a hybrid trust management framework (HTMF) to construct trust environment for WSANs in the paper. HTMF includes second-hand information and confidence value into trustworthiness evaluation and integrates the countermeasures into the trust formation. We preform extensive performance evaluations, which show that the proposed HTMF is more robust and reliable than the existing frameworks.

System Architectures, Protocols and Algorithms for Aperiodic Wireless Control Systems

Wide deployment of wireless sensor and actuator networks in cyber-physical systems requires systematic design tools to enable dynamic tradeoff of network resources and control performance. In this paper, we consider three recently proposed aperiodic control algorithms which have the potential to address this problem. By showing how these controllers can be implemented over the IEEE 802.15.4 standard, a practical wireless control system architecture with guaranteed closed-loop performance is detailed. Event-based predictive and hybrid sensor and actuator communication schemes are compared with respect to their capabilities and implementation complexity. A two double-tank laboratory experimental setup, mimicking some typical industrial process control loops, is used to demonstrate the applicability of the proposed approach. Experimental results show how the sensor communication adapts to the changing demands of the control loops and the network resources, allowing for lower energy consumption and efficient bandwidth utilization.

Distributed programming framework for fast iterative optimization in networked cyber-physical systems

Large-scale coordination and control problems in cyber-physical systems are often expressed within the networked optimization model. While significant advances have taken place in optimization techniques, their widespread adoption in practical implementations has been impeded by the complexity of internode coordination and lack of programming support for the same. Currently, application developers build their own elaborate coordination mechanisms for synchronized execution and coherent access to shared resources via distributed and concurrent controller processes. However, they typically tend to be error prone and inefficient due to tight constraints on application development time and cost. This is unacceptable in many CPS applications, as it can result in expensive and often irreversible side-effects in the environment due to inaccurate or delayed reaction of the control system. This article explores the design of a distributed shared memory (DSM) architecture that abstracts the details of internode coordination. It simplifies application design by transparently managing routing, messaging, and discovery of nodes for coherent access to shared resources. Our key contribution is the design of provably correct locality-sensitive synchronization mechanisms that exploit the spatial locality inherent in actuation to drive faster and scalable application execution through opportunistic data parallel operation. As a result, applications encoded in the proposed Hotline Application Programming Framework are error free, and in many scenarios, exhibit faster reactions to environmental events over conventional implementations. Relative to our prior work, this article extends Hotline with a new locality-sensitive coordination mechanism for improved reaction times and two tunable iteration control schemes for lower message costs. Our extensive evaluation demonstrates that realistic performance and cost of applications are highly sensitive to the prevalent deployment, network, and environmental characteristics. This highlights the importance of Hotline, which provides user-configurable options to trivially tune these metrics and thus affords time to the developers for implementing, evaluating, and comparing multiple algorithms.

A distributed logic for Networked Cyber-Physical Systems

We describe a distributed logical framework designed to serve as a declarative semantic foundation for Networked Cyber-Physical Systems. The framework provides notions of facts and goals that include interactions with the environment via external goal requests, observations that generate facts, and actions that achieve goals. Reasoning rules are built on a partially ordered knowledge-sharing model for loosely coupled distributed computing. The logic supports reasoning in the context of dynamically changing facts and system goals. It can be used both to program systems and to reason about possible scenarios and emerging properties.The underlying reasoning framework is specified in terms of constraints that must be satisfied, making it very general and flexible. Inference rules for an instantiation to a specific local logic (Horn clause logic) are given as a concrete example. The key novel features are illustrated with snippets from an existing application—a theory for self-organizing robots performing a distributed surveillance task. Traditional properties of logical inference and computation are reformulated in this novel context, and related to features of system design and execution. Proofs are outlined for key properties corresponding to soundness, completeness, and termination. Finally, the framework is compared to other formal systems addressing concurrent/distributed computation.