Online Seminar on Control and Information
Speaker Title and Abstract
5:30 PM CET
via Zoom
 Alexander Pogromsky
(Dynamics and Control Group,
Department of Mechanical Engineering, Eindhoven University of Technology)

  Seminar Slides and Video Link

Data Rate Limits for the Remote State Estimation Problem
Abstract : The past few decades have witnessed a substantially growing attention to networked control systems and related problems of control and/or state estimation via communication channels with constrained bit-rates.
One of the fundamental concerns in this context is to find a minimal data rate between the communication peers under which remote state estimation is feasible; in other words, the receiver is able to reconstruct the current state of the remote system in the real time regime if and only if data about this state is updated by means of a bit flow whose intensity exceeds that “threshold” rate. Loosely speaking, this communication rate has to exceed the rate at which the system “generates information”, while the latter concept is classically formalized in a form of entropy-like characteristic of the dynamical system at hands. The related mathematical results are usually referred to as Data Rate Theorems. Keeping in mind relevance of communication constraints in modern control engineering, constructive methods to compute or finely estimate those entropy-like characteristics take on crucial not only theoretical but also practical importance.
The primary goal of the talk is to present an approach to a solution of the bit-rate constrained remote observation problem along with the tight estimates of a particular version of the entropy-like characteristic, the so called restoration entropy. The talk will focus on upper and lower estimates of the restoration entropy derived by the second  Lyapunov method.

5:30 PM CET
Alexander L. Fradkov and Boris R. Andrievskii
(Institute for Problems of Mechanical Engineering of RAS, St. Petersburg, Russia)

 Seminar Slides (part I / part II)
             and Video Link

Synchronization and State Estimation of Nonlinear Physical Systems under Communication Constraints
Abstract: An exposition of the results on synchronization and state estimation of nonlinear systems over the limited-band communication channel is given. Relevance of passifiability condition for controlled synchronization of master-slave nonlinear systems for first order and full-order coder/decoder pairs is demonstrated. The algorithm for state estimation of spatially distributed systems based on the local measurements and quantization of the transmitted data is developed, and its limit opportunities are studied. The numerical and experimental results for various physical systems are presented. They  demonstrate practical applicability of the theoretical statements and high efficiency of the proposed estimation and synchronization schemes.
5:30 PM CET
 Raphaël Jungers
(Université Catholique de Louvain)

 Seminar Slides and Video Link

Quantized Control of Switched Linear Systems
Abstract: Network Control Systems have found applications in a broad range of areas, like intelligent transportation, remote surgery, IoT, etc. Due to the digital nature of the network, all data must be quantized before transmission, resulting in quantization error that can affect the performance of the observing/controlling scheme. Consequently, a major challenge in the design of such networked systems is to determine the minimal communication data rate required to achieve a given control objective. Despite the increasing attention devoted to quantized control in the last decades, the topic seems to have not received much attention in the case of switched and hybrid systems until very recently. In this work, we study the question of finite data-rate control for the class of switched linear systems, i.e., systems described by a finite set of linear modes, among which the system can switch over time. We focus on both theoretical and practical aspects of this issue: we provide necessary and sufficient conditions, which combine the data rate of the controller and the switching parameters of the system, to achieve stabilization. Moreover, we describe practical implementations of controllers that stabilize the system, and whose data rate can be arbitrarily close to the optimal data rate. Finally, we will present numerical examples and perspectives for future research in this field.

5:30 PM CET
 Luca Schenato (University of Padova, Italy)

  Seminar Slides and Video Link

Control over Wireless: An Unfinished Journey
Abstract: The proliferation of large scale smart multi-agent systems, also known as Internet-of-Things, Networked Control Systems, Wireless sensor and actuator networks, Cyber-physical Systems, etc., are the pillars of the so-called fourth industrial revolution referred as Industry 4.0. In particular the need for small, reconfigurable, mobile industrial robots in the foreseen future smart factories calls for a more extensive use of wireless communication not only to collect data
for off-line monitoring and predictive maintenance, but also for real-time control in machine-to-machine and human-robot interaction. The interplay between wireless communication and control has created great enthusiasm in both control and communication community in the past 15
years and a wealth of theoretical results have appeared. Nonetheless, wireless communication for control in the industrial realm is still limited, with the notable exception of the process industry and smart building, where control bandwidth requirements are not very high. In this talk I will review some of the fundamental theoretical results obtained in the field of control over wireless, and I will try to suggest some of the reasons for its limited adoption in high-bandwidth applications in industrial scenarios. I will also present our current effort in bridging the gap between theory and practice and I will show preliminary theoretical and experimental results on how off-the-shelf Wi-Fi communication paired with model-based control tools can potentially bridge this gap.
5:30 PM CET
Mohammad Khojasteh
(Massachusetts Institute of Technology)

  Seminar Slides and Video Link

Event-Triggered Stabilization over Digital channels
Abstract: In many cyber-physical systems (CPS), control occurs under communication constraints, where observations are corrupted by noise and subjected to delay. Data-rate theorems represent a cornerstone of CPS theory and have been studied for more than two decades. These theorems essentially state that the minimum communication rate to achieve stabilization is equal to the plant's entropy rate. On the other hand, the need to use distributed resources efficiently in CPS has led to event-triggering control techniques based on the idea of sending information opportunistically between the controller and the plant. After reviewing the basics of the data rate theorems, we illustrate how they are to be modified in the presence of an event-triggered implementation. In the same way that subsequent pauses in spoken language are used to convey information, it is also possible to transmit information in communication networks not only by message content but also with its timing. In this talk, we discuss how event-triggering strategies provide timing information by transmitting in a state-dependent fashion. In fact, the event-triggering paradigm brings a new perspective, leading to insights on the information-theoretic value of timing in communication that can be used for control. We will conclude the talk by discussing some open problems.
5:30 PM CET
Daniel Liberzon
(University of Illinois at Urbana-Champaign)

Title: Estimation entropy for nonlinear and switched systems
Abstract: In this talk we will discuss estimation entropy for continuous-time nonlinear systems, which is a variant of topological entropy formulated in terms of the number of functions that approximate all system trajectories up to an exponentially decaying error. We will establish an upper bound on the estimation entropy in terms of the sum of the desired convergence rate and the system's expansion rate multiplied by the system dimension, as well as a lower bound. We will describe an iterative procedure that uses quantized and sampled state measurements to generate state estimates that converge to the true state at the desired exponential rate. The average bit rate utilized by this procedure matches the derived upper bound on the estimation entropy, and no other algorithm of this type can perform the same estimation task with bit rates lower than the estimation entropy. As an application of this estimation procedure, we will study the problem of determining, from quantized state measurements, which of two competing models of a dynamical system is the true model. We will show that under a mild assumption of exponential separation of the candidate models, detection always happens in finite time. Recent work on entropy of switched systems will also be discussed. 

Nicolas Garcia (Queen's University)
Title: Ergodicity and Asymptotic Stationarity of Controlled Stochastic Nonlinear Systems under Information Constraints
Abstract: The presence of real-world scenarios where controllers must make control decisions with quantized or noisy state information has motivated the subfield of control under communication constraints. For stochastic systems, an important problem is to characterize the smallest data rate or channel capacity above which stabilization is possible. This problem has been extensively studied for linear (noiseless and stochastic) systems, with a reoccurring theme being the characterization of the minimum data rate as the log-sum of the unstable eigenvalues. For non-linear stochastic systems, however, the problem has not been extensively studied. In this talk, we present several converse results, in the form of lower bounds necessary for ergodic and AMS (asymptotic mean stationarity) stabilization for discrete-time non-linear stochastic systems. These results were established using a modification of invariance entropy for the case of systems with noise, which will be discussed in detail. For noiseless systems, invariance entropy characterizes the difficulty of rendering a subset of the state space invariant, based on the number of open-loop control sequences required to do so. This idea is applied for the stochastic case, where we relax the control objective to probabilistic invariance. This notion, combined with a volume growth approach, is used to obtain the results. Comparison with information theoretic methods will also be made. Although the talk will mostly focus on systems controlled over noiseless channels, the noisy channel case will be briefly mentioned.

Photius Stavrou (KTH-Stockholm)

Oron Sabag (Caltech)

Gireeja Ranade (University of California at Berkeley)


Umesh Vaidya (Clemson University)  


    Massimo Franceschetti
    Christoph Kawan

    Alexey Matveev
    Serdar Yüksel
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