Emeka Eyisi

Optimal Cross-Layer Design of Sampling Rate Adaptation and Network Scheduling for Wireless Networked Control Systems

Wireless Networked Control Systems (NCS) are increasingly deployed to monitor and control Cyber-Physical Systems (CPS). To achieve and maintain a desirable level of performance, NCS face significant challenges posed by the scarce wireless resource and network dynamics. In this paper, we consider NCS consisting of multiple physical plant and digital controller pairs communicating over a multi-hop wireless network. The control objective is that the plants follow the reference trajectories provided by the controllers. This paper presents a novel optimization formulation for minimizing the tracking error due to (1) discretization and (2) packet delay and loss. The optimization problem maximizes a utility function that characterizes the relationship between the sampling rate and the capability of disturbance rejection of the control system. The constraints come from the wireless network capacity and the delay requirement of the control system. The solution leads to a joint design of sampling rate adaptation and network scheduling, which can be naturally deployed over existing networking systems which have a layered architecture. Based on a passivity-based control framework, we show that the proposed cross-layer design can achieve both stability and performance optimality. Simulation studies conducted in an integrated simulation environment consisting of Matlab/Simulink and ns-2 demonstrate that our algorithm is able to provide agile and stable sampling rate adaptation and achieve optimal NCS performance.

Dynamic Tuning Retransmission Limit of IEEE 802.11 MAC Protocol for Networked Control Systems

Building networked control systems over wireless networks is an extremely challenging task, as the wireless communication characteristics such as random packet losses and delay, significantly affect the stability and the performance of the control systems. We present a novel approach to the design of wireless networked control system. This approach decomposes the design concerns into two factors and addresses them separately in two design spaces -- stability of the system is ensured using a passivity-based architecture at the control layer, while the performance of the system is optimized at the communication layer by adjusting the network operation parameters. This paper focuses on the design of IEEE 802.11-based wireless network. In particular, we present a MAC controller that dynamically adjusts the retransmission limit to track the optimal trade-off between packet losses and transmission delays and thus optimizes the overall control system performance. Simulation results show that our approach significantly improves the performance of the networked control systems.

Model-based control design and integration of cyberphysical systems: an adaptive cruise control case study

The systematic design of automotive control applications is a challenging problem due to lack of understanding of the complex and tight interactions that often manifest during the integration of components from the control design phase with the components from software generation and deployment on actual platform/network. In order to address this challenge, we present a systematic methodology and a toolchain using well-defined models to integrate components from various design phases with specific emphasis on restricting the complex interactions that manifest during integration such as timing, deployment, and quantization. We present an experimental platform for the evaluation and testing of the design process. The approach is applied to the development of an adaptive cruise control, and we present experimental results that demonstrate the efficacy of the approach.

NCSWT: An integrated modeling and simulation tool for networked control systems

Abstract Networked Control Systems (NCS) are becoming increasingly ubiquitous in a growing number of applications, such as groups of unmanned aerial vehicles and industrial control systems. The evaluation of NCS properties such as stability and performance is very important given that these systems are typically deployed in critical settings. This paper presents the Networked Control Systems Wind Tunnel (NCSWT), an integrated modeling and simulation tool for the evaluation of Networked Control Systems (NCS). NCSWT integrates Matlab/Simulink and ns-2 for modeling and simulation of NCS using the High Level Architecture (HLA) standard. The tool is composed of two parts, the design-time models and the run-time components. The design-time models use Model Integrated Computing (MIC) to define HLA-based model constructs such as federates representing the simulators and interactions representing the communication between the simulators. MIC techniques facilitate the modeling and design of complex systems by using abstractions defined in domain-specific modeling languages (DSMLs) to describe the systems. The design-time models represent the control system dynamics and networking system behaviors in order to facilitate the run-time simulation of a NCS. The run-time components represent the main software components and interfaces for the actual realization of a NCS simulation using the HLA framework. Our implementation of the NCSWT based on HLA guarantees accurate time synchronization and data communication. Two case studies are presented to demonstrate the capabilities of the tool as well as evaluate the impact of network effects on NCS.

Co-simulation framework for design of time-triggered cyber physical systems

Designing cyber-physical systems (CPS) is challenging due to the tight interactions between software, network/platform, and physical components. A co-simulation method is valuable to enable early system evaluation. In this paper, a cosimulation framework that considers interacting CPS components for design of time-triggered (TT) CPS is proposed. Virtual prototyping of CPS is the core of the proposed frame-work. A network/platform model in SystemC forms the backbone of the virtual prototyping, which bridges control software and physical environment. The network/platform model consists of processing elements abstracted by real-time operating systems, communication systems, sensors, and actuators. The framework is also integrated with a model-based design tool to enable rapid prototyping. The framework is validated by comparing simulation results with the results from a hardware-in-the-loop automotive simulator.

A co-simulation framework for design of time-triggered automotive cyber physical systems

Abstract Designing cyber-physical systems (CPS) is challenging due to the tight interactions between software, network/platform, and physical components. Automotive control system is a typical CPS example and often designed based on a time-triggered paradigm. In this paper, a co-simulation framework that considers interacting CPS components for assisting time-triggered automotive CPS design is proposed. Virtual prototyping of automotive vehicles is the core of this framework, which uses SystemC to model the cyber components and integrates CarSim to model the vehicle dynamics. A network/platform model in SystemC forms the backbone of the virtual prototyping. The network/platform model consists of processing elements abstracted by real-time operating systems, communication systems, sensors, and actuators. The framework is also integrated with a model-based design tool to enable rapid prototyping. The framework is validated by comparing simulation results with the results from a hardware-in-the-loop automotive simulator. The framework is also used for design space exploration (DSE).

NCSWT: an integrated modeling and simulation tool for networked control systems

This paper presents the Networked Control Systems Windtunnel (NCSWT), an integrated modeling and simulation tool for the evaluation of networked control systems (NCS). NCSWT integrates Matlab/Simulink and ns-2 using the High Level Architecture (HLA). Our implementation of the NCSWT based on HLA guarantees accurate time synchronization and data communication in heterogenous simulations. NCSWT uses the Model Integrated Computing (MIC) techniques to define HLA-based model constructs such as federates representing the simulators and interactions between the simulators. NCSWT also uses MIC techniques to define models representing the control system and network dynamics for the rapid synthesis of simulations.

Energy-based attack detection in networked control systems

The increased prevalence of attacks on Cyber-Physical Systems(CPS) as well as the safety-critical nature of these systems, has resulted in increased concerns regarding the security of CPS. In an effort towards the security of CPS, we consider the detection of attacks based on the fundamental notion of a systems energy. We propose a discrete-time Energy-Based Attack Detection mechanism for networked cyber-physical systems that are dissipative or passive in nature. We present analytical results to show that the detection mechanism is effective in detecting a class of attack models in networked control systems (NCS). Finally, using simulations we illustrate the effectiveness of the proposed approach in detecting attacks.

A passivity approach for model-based compositional design of networked control systems

The integration of physical systems through computing and networking has become pervasive, a trend now known as cyber-physical systems (CPS). Functionality in CPS emerges from the interaction of networked computational and physical objects. System design and integration are particularly challenging because fundamentally different physical and computational design concerns intersect. The impact of these interactions is the loss of compositionality which creates tremendous challenges. The key idea in this article is to use passivity for decoupling the control design of networked systems from uncertainties such as time delays and packet loss, thus providing a fundamental simplification strategy that limits the complexity of interactions. The main contribution is the application of the approach to an experimental case study of a networked multi-robot system. We present a networked control architecture that ensures the overall system remains stable in spite of implementation uncertainties such as network delays and data dropouts, focusing on the technical details required for the implementation. We describe a prototype domain-specific modeling language and automated code generation tools for the design of networked control systems on top of passivity that facilitate effective system configuration, deployment, and testing. Finally, we present experimental evaluation results that show decoupling of interlayer interactions.

PaNeCS: A modeling language for passivity-based design of networked control systems

The rapidly increasing use of information technology in constructing real-world systems has led to the urgent need for a sound systematic approach in designing networked control systems. Communication delays and other uncertainties complicate the development and analysis of these systems. This paper describes a prototype modeling language for the design of networked control systems using passivity to decouple control design from network uncertainties. The modeling language includes an integrated analysis tool to check for passivity and code generators for simulation in MATLAB/Simulink using the TrueTime platform modeling toolbox and for running actual experiments. The resulting designs are by construction robust to platform effects and implementation uncertainties.