1,721,003 research outputs found
Predictor-based control of linear systems with large and variable measurement delays
No full textThis paper concerns the problem of the control of linear systems by means of feedback from delayed output, where the delay is known and time-varying. The main advantage of the approach is that it can be applied to systems with any delay bound, i.e. not only small delays. The predictor is based on a combination of finite-dimensional elementary predictors whose number can be suitably chosen to compensate any delay. The single-predictor element is an original proposal, and the class of delays to which the schema can be applied includes, but it is not limited to, continuous delay functions
Memoryless Approach to the LQ and LQG Problems with Variable Input Delay
No full textThis note studies the LQ and LQG problems for linear time invariant systems with a single time-varying input delay and instantaneous (memoryless) state feedback. We extend the memoryless state feedback solution proposed in [1] in two directions. We prove that in the deterministic case a memoryless state feedback can be in general optimal only up to a certain delay, for which we provide a sufficient, and sometimes strict, bound. Moreover, we show that this memoryless control is optimal also in the case of time-varying delays and that the quadratic cost functional has the same value as in the case without delay. For time varying delays the control law requires that the relationship between time points in which the input is generated and applied is known and invertible even if the delay function needs not to be differentiable or even continuous. Finally, we prove that the cost functional is bounded also in the stochastic case for the same delay interval as in the deterministic case, but with a larger cost than the delay-less LQG solution
A New Filtering Approach for Continuous-Time Linear Systems with Delayed Measurements
No full textThis paper introduces a new filter for linear continuous-time stochastic systems with delayed measurements. The approach is inspired by an observer designed for deterministic systems. The obtained solution is suboptimal and does not use distributed integration terms with advantages in terms of computational load. The relationship between the delay bound and the variance of the estimation error is formally characterized and confirmed by a numerical example
Analysis and experimentation over eterogeneous wireless networks
No full textWireless and mobile networks represent an enabling technology for ubiquitous access to information systems. However, there are critical issues that still prevent the widespread use of these technologies. In this paper we analyze and discuss our experience over a real ubiquitous network testbed capable to provide a seamless hand-off among heterogeneous networks. We describe Mobile IPv6/IPv4 interoperability and an efficient mechanism, based on link-layer information, for a seamless handoff among wired and wireless networks. We present the solutions adopted in setting up a real testbed and provide an evaluation of the observed performance, including a characterization of interoperability among three wireless access network technologies: 802.11 WLAN, GPRS, and UMTS
Optimal control of linear systems with large and variable input delays
No full textThis paper proposes an optimal control law for linear systems affected by input delays. Specifically we prove that when the delay functions are known it is possible to generate the optimal control for arbitrarily large delay values by using a DDE without distributed terms. The solution can be seen as a chain of predictors whose size depends on the maximum delay
White Noise Solution for Nonlinear Stochastic Systems: In memory of A.V. Balakrishnan
No full textThis paper proposes an alternative theory to the Ito calculus due to Balakrishnan: the white noise theory in Hilbert spaces. The proposed approach extends Blakrishnan's theory to a new class of nonlinear systems. The method uses the theory of differential geometry to devise a suitable map which transforms the starting system in an equivalent one; then the techniques of white noise theory is applied to this equivalent system. Finally, by means of the inverse map, the existence of a white noise solution for the starting system is proved
Delay identification for a class of nonlinear systems
No full textThe problem of state estimation for nonlinear systems with unknown state delays is still an open problem. In this paper, we propose to add a delay identifier to suitable high-gain observers in order to achieve simultaneous estimation of state and delay. In the case of one constant delay in the state, we provide sufficient conditions to guarantee the exponential convergence to zero of the errors, globally with respect to the initial choice of the system state variables and locally with respect to the initial delay estimation. We validate the method through an example concerning chaotic oscillators
Filtering Continuous-Time Linear Systems With Time-Varying Measurement Delay
No full textWe consider the filtering problem of LTI continuous-
time systems with known and bounded measurement delays. The
aim of the technical note is the design of a finite-dimensional
sub-optimal filter whose performance in terms of the estimation
error is comparable to optimal infinite-dimensional approaches.
We show that the proposed approach allows for a precise char-
acterization of the relationship between measurement delay and
the covariance of the estimation error. In the time-varying case no
restrictive hypotheses on the delay function are needed. The pro-
posed filter can therefore be applied to delay functions for which
traditional infinite-dimensional approaches cannot be straightfor-
wardly applied
Optimal linear and quadratic estimators for tracking from distance measurements
No full textWe consider the tracking problem of a point moving in a three-dimensional space using only measurements of distance from a set of reference points. The approach followed in this paper is to derive a linear map with multiplicative noise through a quadratic transformation of the distance measurements. A suitable rewriting by means of an output injection term makes the multiplicative noise of the linear map amenable to be processed by recursive estimators. These estimators are guaranteed to be internally stable and the variance of the estimation error is estimated. We compare the performance of the resulting algorithm for the linear and quadratic case with standard alternatives
Stabilization of strict-feedback nonlinear systems with input delay using closed-loop predictors
No full textIn this paper, we consider the control problem of strict-feedback nonlinear systems with time-varying input and output delays. The approach is based on the usual observer/predictor/feedback approach, but the novelty is the use of the closed-loop dynamics in the predictor. This approach allows to develop two designs, an instantaneous predictor and a delay differential equation-based predictor, that both attain the same performance in terms of system trajectories and input signal as in the case with no delays. The design based on delay differential equations allows to build a cascade of predictors to deal with arbitrarily large delay bounds. The resulting controller is much simpler to implement than classical infinite-dimensional predictors, and it is robust with respect to actuation and measurement disturbances. We illustrate the approach with an application to the control of a chaotic system with input delay. Copyright © 2016 John Wiley & Sons, Ltd
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