Try-once-discard Research Articles

Co-design of dynamic scheduling and quantized control for networked control systems

A novel co-design scheme of dynamic scheduling strategy and quantized control for a class of time-delay networked control system with communication constraints is presented in this paper. Sufficient condition of bit rate is given to guarantee the convergence of quantization error by Lyapunov stability theory. The networked control system is modeled as a discrete-time switched system under the effect of Try-once-Discard (TOD) dynamic scheduling strategy and time-varying quantization, and a state feedback controller design method is given to guarantee asymptotic stability of the closed-loop system by using LMI techniques. Finally, two simulation results demonstrate the effectiveness of the proposed method.

Networked Control Systems in the Presence of Scheduling Protocols and Communication Delays

This paper develops the time-delay approach to Networked Control Systems (NCSs) in the presence of variable transmission delays, sampling intervals and communication constraints. The system sensor nodes are supposed to be distributed over a network. Due to communication constraints only one node output is transmitted through the communication channel at once. The scheduling of sensor information towards the controller is ruled by a weighted Try-Once-Discard (TOD) or by Round-Robin (RR) protocols. Differently from the existing results on NCSs in the presence of scheduling protocols (in the frameworks of hybrid and discrete-time systems), we allow the communication delays to be greater than the sampling intervals. A novel hybrid system model for the closed-loop system is presented that contains {\it time-varying delays in the continuous dynamics and in the reset conditions}. A new Lyapunov-Krasovskii method, which is based on discontinuous in time Lyapunov functionals is introduced for the stability analysis of the delayed hybrid systems. Polytopic type uncertainties in the system model can be easily included in the analysis. The efficiency of the time-delay approach is illustrated on the examples of uncertain cart-pendulum and of batch reactor.

Realization of Try-Once-Discard in Wireless Multihop Networks

In networked control systems, the Try-Once-Discard (TOD) protocol is of high interest because its properties can be characterized by Lyapunov functions. This feature makes it practical to incorporate TOD into Lyapunov-based design of linear and nonlinear control systems, yielding a self-contained theory for system stabilization. In previous work, candidates for TOD realizations for single-hop (wired and wireless) networks have been proposed. However, it has been a hitherto open question whether TOD can be realized in wireless multihop networks. In fact, it is far from obvious how dynamic value-based competition with deterministically bounded maximum delay, as required by TOD, is achievable in wireless multihop networks. In this paper, we give a positive answer to this question, by presenting a functionally complete realization of TOD in wireless multihop networks. Our solution is based on highly accurate multihop tick synchronization, and applies an algorithm for collision-protected network-wide value arbitration with deterministic delay. We provide experimental evidence for the feasibility of our solution on existing micro controller platforms, and assess our TOD realization in a batch reactor scenario.

Stability Analysis of Networked Control Systems Using a Switched Linear Systems Approach

In this paper, we study the stability of networked control systems (NCSs) that are subject to time-varying transmission intervals, time-varying transmission delays, and communication constraints. Communication constraints impose that, per transmission, only one node can access the network and send its information. The order in which nodes send their information is orchestrated by a network protocol, such as, the Round-Robin (RR) and the Try-Once-Discard (TOD) protocol. In this paper, we generalize the mentioned protocols to novel classes of so-called “periodic” and “quadratic” protocols. By focusing on linear plants and controllers, we present a modeling framework for NCSs based on discrete-time switched linear uncertain systems. This framework allows the controller to be given in discrete time as well as in continuous time. To analyze stability of such systems for a range of possible transmission intervals and delays, with a possible nonzero lower bound, we propose a new procedure to obtain a convex overapproximation in the form of a polytopic system with norm-bounded additive uncertainty. We show that this approximation can be made arbitrarily tight in an appropriate sense. Based on this overapproximation, we derive stability results in terms of linear matrix inequalities (LMIs). We illustrate our stability analysis on the benchmark example of a batch reactor and show how this leads to tradeoffs between different protocols, allowable ranges of transmission intervals and delays. In addition, we show that the exploitation of the linearity of the system and controller leads to a significant reduction in conservatism with respect to existing approaches in the literature.

Input–Output Stability of Networked Control Systems With Stochastic Protocols and Channels

This paper introduces a new definition of stochastic protocols for networked control systems (NCS) and the stochastic analog of the notion of uniform persistency of excitation of protocols first presented in the Proceedings of the 44th IEEE Conference on Decision and Control. Our framework applies directly to common wireless and wireline NCS, including those built on carrier-sense multiple access (CSMA) style protocols, with Ethernet and 802.11a/b/g as prime examples of this class. We present conditions for a general class of nonlinear NCS with exogenous disturbances using stochastic protocols in the presence of packet dropouts, random packet transmission times and collisions that are sufficient for LP stability from exogenous disturbance to NCS state with a linear finite expected gain. Within the same framework, we extend the results of Nesic and Teel (see IEEE Trans. Autom. Control, vol. 49, no. 10, pp. 1650-1667, Oct. 2004) to provide an analysis of deterministic protocols, including try-once-discard (TOD), in the presence of random packet dropouts and intertransmission times and provide a stochastic analog of the Lyapunov-theoretic stability properties for network protocols introduced therein.

Stability analysis of networked control systems

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.

P-1-119 - Surgical treatment for cervical internal carotid artery stenosis with ischemic heart disease

This paper is concerned with the problem of networked H∞ filtering under a weighted try-once-discard (TOD) protocol. Firstly, a weighted TOD protocol is investigated to orchestrate the sampled-data transmission from sensors to filter via a bandwidth-limited network. Taking into account the network-induced delay, the studied system is transformed into an impulsive system with an interval time-varying delay. Secondly, by using the Lyapunov–Krasovskii method, sufficient conditions for ensuring the exponential stability with a prescribed H∞ performance and the existence of suitable H∞ filter are obtained in the form of linear matrix inequalities (LMIs). Then, for minimizing H∞ performance, an algorithm is presented by using the binary search method. Finally, an example of quarter-car model with an active suspension is used to verify the validity of proposed method.