Dimitrios Hristu-Varsakelis

Handbook of networked and embedded control systems

Preface Part I. Fundamentals Fundamentals of Dynamical Systems Control of Single-Input Single-Output Systems Basics of Sampling and Quantization Discrete-Event Systems Introduction to Hybrid Systems Finite Automata Basics of Computer Architecture Real-Time Scheduling for Embedded Systems Network Fundamentals Part II. Hardware Basics of Data Acquisition and Control Programmable Logic Controllers Digital Signal Processors Microcontrollers SOPCs: Systems on Programmable Chips Part III. Software Fundamentals of RTOS-Based Digital Controller Implementation-Aware Embedded Control Systems From Control Loops to Real-Time Programs Embedded Real-Time Control via MATLAB, Simulink, and xPC Target LabVIEW Real-Time for Networked/Embedded Control Control Loops in RTLinux Part IV. Theory An Introduction to Hybrid Automata An Overview of Hybrid Systems Control Temporal Logic Model Checking Switched Systems Feedback Control with Communication Constraints Networked Control Systems: A Model-Based Approach Control Issues in Systems with Loop Delays Part V. Networking Network Protocols for Networked Control Systems Control Using Feedback over Wireless Ethernet and Bluetooth Bluetooth in Control Embedded Sensor Networks Part VI. Applications Vehicle Applications of Controller Area Network Control of Autonomous Mobile Robots Wireless Control with Bluetooth The Cornell RoboCup Robot Soccer Team: 1999-2003 Index

Feedback control systems as users of a shared network: communication sequences that guarantee stability

We investigate the stability of a collection of systems which are governed by linear dynamics and operate under limited communication. We view each system and its feedback controller as users on an idealized shared network which grants access only to a few system-controller pairs at any one time. A communication sequence, which plays the role of a network admission policy, specifies the amount of time available for each system to complete its feedback loop. Using Lyapunov theory, we give a sufficient condition for the existence of a stabilizing communication sequence and show how one can be constructed in a way that minimizes network usage. Our solution depends on the parameters of the underlying system(s) and on the number of controller-plant connections that can be maintained simultaneously. We include simulation results illustrating the main ideas.

Interrupt-based feedback control over a shared communication medium

We investigate the simultaneous stabilization of a group of linear systems whose feedback loops are closed over an idealized shared medium. The capacity of that medium is constrained so that only a limited number of controller-plant connections can be accommodated at any one time. We introduce a feedback communication policy - inspired by previous work on queuing systems and real-time scheduling - for deciding which system(s) should be admitted into the network and for how long. The use of feedback in making communication decisions results in a set of autonomous dynamical systems which are coupled to one another due to the presence of communication constraints. We give conditions for the stability of the collection under the proposed communication policy and present simulation results that illustrate our ideas.

Towards remote evaluation of movement disorders via smartphones

Recent advances in mobile phone technology have placed an impressive array of sensing and communication equipment at the hands of an ever-growing number of people. One of the areas which can potentially be transformed by the availability of what is essentially a cheap, ubiquitous networked sensor, is that of remote diagnosis of movement disorders, such as Parkinsons disease. This work describes a smartphone-based method for detecting and quantifying the hand tremor associated with movement disorders using signals from the accelerometer and gyroscope embedded in the patients phone. Our approach is web-based and user-friendly, requiring minimal user interaction. In clinical experiments with twenty subjects, we found that by combining both accelerometer and gyroscope signals, we were able to correctly identify those with hand tremor, using very simple signal metrics.

Stabilization of Networked Control Systems: Designing Effective Communication Sequences

Abstract This paper discusses the stabilization of a networked control system (NCS) whose sensors and actuators exchange information with a remote controller over a shared communication medium. Access to that medium is governed by a pair of periodic communication sequences. Under the model utilized here, the controller and plant handle communication disruptions by “ignoring” (in a sense to be made precise) sensors and actuators that are not actively communicating. It is shown that under mild conditions, there exist periodic communication sequences that preserve the reachability and observability of the plant, leading to a straightforward design of a stabilizing feedback controller.

Two Types of Key-Compromise Impersonation Attacks against One-Pass Key Establishment Protocols

Key establishment protocols are among the most important security mechanisms via which two or more parties can encrypt their communications over an insecure network. This paper is concerned with the vulnerability of one-pass two-party key establishment protocols to key-compromise impersonation (K-CI) attacks. The latter may occur once an adversary has obtained the long-term private key of an honest party, and represent a serious — but often underestimated — threat, because a successful impersonation attack may result in far greater harm than the reading of past and future conversations. Our aim is to describe two main classes of K-CI attacks that can be mounted against all of the best-known one-pass protocols, including MQV and HMQV. We show that one of the attacks described can be somewhat avoided (though not completely eliminated) through the combined use of digital signatures and time-stamps; however, there still remains a class of K-CI threats for which there is no obvious solution.

Feedback Control with Communication Constraints

One of systems theory’s most useful and fundamental ideas is that of interconnecting simple systems in order to build complex ones. This is usually accomplished through the use of two important tools. One is a set of theoretical results that help predict the behavior and performance of the composed system given the properties of its components and the manner in which they are connected. The other is the ability to regard the interconnection as ideal in the sense that it neither corrupts nor delays data or—in situations where that is not the case—to “separate” its design from that of the other components (e.g., controllers). The development in recent years of embedded and network technologies has given rise to the area of Networked Control Systems (NCSs), where sensors, actuators and computing elements are connected by means of a network or other shared medium. At the same time, the attempt to expand the scope of systems theory into this new domain has made the assumptions stated above increasingly difficult to justify. The goal of this chapter is to expose some of the complications that arise when a control system includes a network (taken to mean a shared communication medium in the most generic sense) and to introduce a small collection of basic results on the control of systems that operate under communication constraints. The very technologies that enable one to construct NCSs impose limitations in communication that make the interconnection of components nontrivial from the point of view of control. Some of the issues that arise include

Biologically-inspired optimal control: learning from social insects

In the last few years, efforts to codify the organizing principles behind biological systems have been capturing the attention of a growing number of researchers in the systems and control community. This endeavour becomes increasingly important as new technologies make it possible to engineer complex cooperating systems, that are nevertheless faced with many of the challenges long overcome by their natural counterparts. One area in particular where biology serves as an inspiring but still distant example, involves systems in which members of a species cooperate to form collectives whose abilities are beyond those of individuals. This paper looks to the process by which ants optimize their foraging trails as inspiration for an organizing principle by which groups of dynamical systems can solve a class of optimal control problems. We explore the use of a strategy termed ‘local pursuit’, which allows members of the group to overcome their limitations with respect to sensing range and available information through the use of neighbour-to-neighbour interactions. Local pursuit enables the group to find an optimal solution by iteratively improving upon an initial feasible control. We show that our proposed strategy subsumes previous pursuit-based models for ant-trail optimization and applies to a large array of problems, including many of the classical situations in optimal control. The performance of our algorithm is illustrated in a series of simulations and experiments.

Experimenting with hybrid control

We have described an experimental facility designed to study aspects of multimodal intelligent control and reported on some of the related research activities. The purpose of the two-fingered robotic manipulator developed by the authors is to provide a reliable, versatile control system that will be useful both as an instructional aid and as a research tool.

Machine learning-based classification of simple drawing movements in Parkinson's disease

Abstract This work explores the use of a pen-and-tablet device to study differences in hand movement and muscle coordination between healthy subjects and Parkinson’s disease patients. We let volunteers draw simple horizontal lines and recorded the trajectory of the pen’s tip on the pad’s surface. The signals thus obtained were then processed to compute various features which correspond to the variability of the pen tip’s velocity, the deviation from the horizontal plane, and the trajectory’s entropy. Our goal was to establish simple and objective metrics which can be used to differentiate between normal and pathological movement. In a small-scale clinical trial, 44 age-matched subjects were divided in two groups, namely 20 healthy subjects (H), and 24 Parkinson’s disease (PD) patients. We applied a comprehensive machine learning approach to build a model that could classify unknown subjects based on their line-drawing performance. We were able to achieve an average prediction accuracy of 91% (88% sensitivity [ΤP], 95% specificity [ΤN]). Our results show that the proposed method is a good candidate for differentiating between healthy and Parkinson’s disease individuals, and shows promise in the context of telemedicine applications and tracking of the disease’s symptoms via inexpensive, widely available hardware.