A Multi-hop Control Network (MCN) consists of a plant where the communication between sensor, actuator and computational unit is supported by a wireless multi-hop communication network, and data flow is performed using scheduling and routing of sensing and actuation data. We address the problem of characterizing controllability and observability of a MCN, by means of necessary and sufficient conditions on the plant dynamics and on the communication scheduling and routing. We provide a methodology to design scheduling and routing, in order to satisfy controllability and observability of a MCN for any fault occurrence in a given set of configurations of failures.
There exists a wide literature on Networked Control Systems, see for example @cite_3 , @cite_17 , @cite_5 , @cite_0 and references therein. The literature on robust stability of networked control systems (see e.g. @cite_12 , @cite_11 , @cite_15 ) generally addresses stability analysis in presence of packet loss and variable delays, but does not take into account the non--idealities introduced by scheduling and routing communication protocols of multi-hop control networks. When relating our paper with the current research about the interaction of control networks and communication protocols, most efforts in the literature focus on scheduling message and sampling time assignment for sensors actuators and controllers interconnected by wired common-bus networks, e.g. @cite_13 , @cite_20 , @cite_1 , @cite_16 , @cite_4 . The authors in @cite_21 use model predictive control to stabilize a plant over a multi-hop control network, by only considering delay introduced by the routing policy.
@cite_11 @cite_4 @cite_21 @cite_1 @cite_3 @cite_16 @cite_0 @cite_5 @cite_15 @cite_20 @cite_13 @cite_12 @cite_17
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In this paper, the stability of a Networked Control System (NCS) with time-varying delays is analyzed. A discrete-time state-space model is used to analyze the dynamics of the NCS. The delay is introduced by the network itself and is assumed to be upperbounded by a fraction of the sample-time. A typical motion control example is presented in which the time-variation of the delay results in an unstable system, although for each fixed delay the system is stable. Conditions in terms of LMIs are presented guaranteeing the robust asymptotic stability of the discrete-time system, given bounds on the uncertain time-varying delay. Moreover, it is shown that the robust stability conditions also guarantee asymptotic stability of the intersample behavior. Additionally, LMIs are presented to synthesize a feedback controller that stabilizes the system for the uncertain time-varying delay. The results are illustrated on an example concerning a mechanical model of a motor driving a roller in a printer. This paper provides a general framework for analyzing the stability of general nonlinear networked control systems (NCS) with disturbances in the setting of stability. Our presentation provides sharper results for both gain and maximum allowable transfer interval (MATI) than previously obtainable and details the property of uniformly persistently exciting scheduling protocols. This class of protocols was shown to lead to stability for high enough transmission rates and were a natural property to demand, especially in the design of wireless scheduling protocols. The property is used directly in a novel proof technique based on the notions of vector comparison and (quasi)-monotone systems. We explore these results through analytical comparisons to those in the literature, as well as through simulations and numerical comparisons that verify that the uniform persistence of excitation property of protocols is, in some sense, the ldquofinestrdquo property that can be extracted from wireless scheduling protocols. Remote control over wireless multi-hop networks is considered. Time-varying delays for the transmission of sensor and control data over the wireless network are caused by a randomized multi-hop routing protocol. The characterstics of the routing protocol together with lower-layer network mechanisms give rise to a delay process with high variance and stepwise changing mean. A new predictive control scheme with a delay estimator is proposed in the paper. The estimator is based on a Kalman filter with a change detection algorithm. It is able to track the delay mean changes but efficiently attenuate the high frequency jitter. The control scheme is analyzed and its implementation detailed. Network data from an experimental setup are used to illustrate the efficiency of the approach. Describes a new framework for distributed control systems in which estimators are used at each node to estimate the values of the outputs at the other nodes. The estimated values are then used to compute the control algorithms at each node. When the estimated value deviates from the true value by more than a pre-specified tolerance, the actual value is broadcast to the rest of the system; all of the estimators are then updated to the current value. By using the estimated values instead of true value at every node, a significant saving in the required bandwidth is achieved, allowing large-scale distributed control systems to be implemented effectively. The stability, performance, and expected communication frequency of the reduced communication system are analyzed in detail. Simulation and experimental results validating the effectiveness and communication savings of the framework are also presented. First, we review some previous work on networked control systems (NCSs) and offer some improvements. Then, we summarize the fundamental issues in NCSs and examine them with different underlying network-scheduling protocols. We present NCS models with network-induced delay and analyze their stability using stability regions and a hybrid systems technique. Following that, we discuss methods to compensate network-induced delay and present experimental results over a physical network. Then, we model NCSs with packet dropout and multiple-packet transmission as asynchronous dynamical systems and analyze their stability. Finally, we present our conclusions. In this paper, we consider a robust network control problem. We consider linear unstable and uncertain discrete time plants with a network between the sensor and controller and the controller and plant. We investigate the effect of data drop out in the form of packet losses. Four distinct control schemes are explored and sufficient conditions to ensure almost sure stability of the closed loop system are derived for each of them in terms of minimum packet arrival rate and the maximum uncertainty. I. INTRODUCTION In the past decade, networked control systems (NCS) have gained much attention from both the control com- munity and the network and communication community. When compared with classical feedback control system, networked control systems have several advantages. For example, they can reduce the system wiring, make the system easy to operate and maintain and later diagnose in case of malfunctioning, and increase system agility (20). Although NCS have advantages, inserting a network in between the plant and the controller introduces many problems as well. For instance, zero-delayed sensing and actuation, perfect information and synchronization are no longer guaranteed in the new system architecture as only finite bandwidth is available and data packet drops and delays may occur due to network traffic conditions. These must be revisited and analyzed before networked control systems become prevalent. Recently, many researchers have spent effort on these issues and some significant results were obtained and many are in progress. Many of the aforementioned issues are studied separately. Tatikonda (19) and Sahai (13) have presented some interesting results in the area of control under communication constraints. Specifically, Tatikonda gave a necessary and sufficient condition on the channel data rate such that a noiseless LTI system in the closed loop is asymptotically stable. He also gave rate results for stabilizing a noisy LTI system over a digital channel. Sahai proposed the notion of anytime capacity to deal with real time estimation and control for a networked control system. In our paper (17), the authors have considered various rate issues under finite bandwidth, packet drops and finite controls. An optimal bit allocation scheme is given in (16) under the networked setting. The effect of pacekt drops on state estimation was studied by Sinopoli, et. al. in (3). It has further been investigated by many researchers including the present authors in (15) and (6). We introduce a novel control network protocol, try-once-discard (TOD), for multiple-input-multiple-output (MIMO) networked control systems (NCSs), and provide an analytic proof of global exponential stability for both the new protocol and the more commonly used (statically scheduled) access methods. Our approach is to first design the controller using established techniques and considering the network transparency, and then analyze the effect of the network on closed-loop system performance. When implemented, an NCS consists of multiple independent sensors and actuators competing for an access to the network, with no universal clock available to synchronize their actions. Since the nodes act asynchronously, we allow access to the network at anytime, but assume each access occurs before a prescribed deadline, known as the maximum allowable transfer interval. Only one node may access the network at a time. This communication constraint imposed by the network is the main focus of the paper. The performance of the new TOD protocol and the statically scheduled protocols are examined in simulations of an automotive gas turbine and an unstable batch reactor. In this paper, stability and disturbance attenuation issues for a class of networked control systems (NCSs) under uncertain access delay and packet dropout effects are considered. Our aim is to find conditions on the delay and packet dropout rate, under which the system stability and H sup spl infin disturbance attenuation properties are preserved to a desired level. The basic idea in this paper is to formulate such networked control system as a discrete-time switched system. Then the NCSs' stability and performance problems can be reduced to corresponding problems for the switched systems, which have been studied for decades and for which a number of results are available in the literature. The techniques in this paper are based in the discrete-time switched systems and piecewise Lyapunov functions. The defining characteristic of a networked control system (NCS) is having one or more control loops closed via a serial communication channel. Typically, when the words networking and control are used together, the focus is on the control of networks, but in this article our intent is nearly inverse, not control of networks but control through networks. NCS design objectives revolve around the performance and stability of a target physical device rather than of the network. The problem of stabilizing queue lengths, for example, is of secondary importance. Integrating computer networks into control systems to replace the traditional point-to-point wiring has enormous advantages, including lower cost, reduced weight and power, simpler installation and maintenance, and higher reliability. In this article, in addition to introducing networked control systems, we demonstrate how dispensing with queues and dynamically scheduling control traffic improves closed-loop performance.