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DESTABILIZATION EFFECTS OF adaptive QUANTIZATION IN ADPCM

IEEE TRANSACTIONS ON SPEECH AND AUDIO PROCESSING 1995年第2期3卷 137-141页

作者： WATKINS, CR BITMEAD, RR CRISAFULLI, S Cooperative Research Centre for Robust and Adaptive Systems Department of Systems EngineeringResearch School of Information Sciences and Engineering Australian National University Canberra Australia

adaptive quantization is used in many ADPCM systems to improve performance. We present an analysis dealing with the effect of adaptive quantizers on the stability of ADPCM systems as compared with ADPCM with nonadaptive quantization. Stability of the system is noted to equate with recovery from encoder internal state discrepancies. A sufficient condition for stability that leads to a relation between adaptation rate and stability is presented. This indicates that a price is paid for adaptation in terms of more stringent restrictions on the predictor to guarantee stability. The theorem further indicates that stability is related to the maximum rate of quantizer step size decrease and can be viewed as a theoretical justification for the shape of the Jayant ''one-word memory'' multiplier curve for adaptive quantization.

关键词： Quantization Stability analysis Pulse modulation Speech coding Bit rate Frequency response robustness adaptive systems Sufficient conditions Shape

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Optimal controller properties from closed-loop experiments (vol 34, pg 83, 1998)

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AUTOMATICA 1998年第9期34卷 1154-1154页

作者： Kammer, LC Bitmead, RR Bartlett, PL Department of Systems Engineering Cooperative Research Centre for Robust and Adaptive Systems Research School of Information Sciences & Engineering Australian National University Canberra ACT 0200 Australia

A model-free approach to linear quadratic (LQ) performance assessment is presented in this paper. First a test for LQ optimality, based on closed-loop signals, is presented. Its result indicates whether the controller should be adjusted. From the same test it is possible to determine the closed-loop pole positions which would be obtained by using the LQ optimal controller. These may then be used in a direct adaptive control scheme to adjust the controller. Both state and output feedback are addressed for discrete-time, single-input-single-output (SISO), linear, time-invariant processes. (Author abstract) 11 Refs.

关键词： Direct adaptive control Linear quadratic regulators Performance monitoring

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RISK-SENSITIVE FILTERING AND SMOOTHING FOR HIDDEN MARKOV-MODELS

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systems & CONTROL LETTERS 1995年第5期25卷 361-366页

作者： DEY, S MOORE, JB Cooperative Research Centre for Robust and Adaptive Systems Department of Systems Engineering Research School of Information Sciences and Engineering Australian National University Canberra ACT 0200 Australia

In this paper, we address the problem of risk-sensitive filtering and smoothing for discrete-time Hidden Markov Models (HMM) with finite-discrete states. The objective of risk-sensitive filtering is to minimise the expectation of the exponential of the squared estimation error weighted by a risk-sensitive parameter. We use the so-called Reference Probability Method in solving this problem. We achieve finite-dimensional linear recursions in the information state, and thereby the state estimate that minimises the risk-sensitive cost index. Also, fixed-interval smoothing results are derived. We show that L(2) or risk-neutral filtering for HMMs can be extracted as a limiting case of the risk-sensitive filtering problem when the risk-sensitive parameter approaches zero.

关键词： HIDDEN MARKOV MODEL RISK-SENSITIVE FILTERING INFORMATION STATE FIXED-INTERVAL SMOOTHING

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Exponential stability of filters and smoothers for Hidden Markov Models 4

Exponential stability of filters and smoothers for Hidden Ma...

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4th European Control Conference, ECC 1997

作者： Shue, L. Anderson, B.D.O. Dey, S. Department of Systems Engineering Cooperative Research Centre for Robust and Adaptive Systems Australian National University CanberraACT0200 Australia

ISBN: (纸本)9783952426906

In this paper, we address the problem of exponential stability of filters and fixed-lag smoothers for discrete-time and discrete-state Hidden Markov Models (HMMs). By appealing to a generalised Perron-Frobenius result for nonnegative matrices, we demonstrate exponential forgetting for both the recursive filters and smoothers, and obtain overbounds on the rate of forgetting. Simulation studies are carried out to substantiate the results.

关键词： Bandpass filters

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Controller Design: Moving from Theory to Practice

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IEEE Control systems 1993年第4期13卷 16-25页

作者： Anderson, Brian D.O. Department of Systems Engineering and Cooperative Research Centre for Robust and Adaptive Systems Research School of Physical Sciences and Engineering Australian National University Canberra ACT 0200 Australia

It is suggested that modern controller design packages often fall short of offering what is truly practical: lower order controllers, discrete-time controllers operating in a sampled-data loop, and finite word length (FWL) realizations of controllers with the FWL property minimally impacting closed-loop performance. Several methods for achieving these objectives are considered. The methods deal with controller complexity, transfer function matching, stability robustness, signal spectrum matching, fractional representations of open-loop unstable controllers, discrete time controllers, and realizing digital controllers.< >

关键词： Software packages Packaging Software design Videoconference Control systems Society Digital control Nonlinear equations robust control Design methodology Transfer functions

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Identification of nonlinear plants using left coprime fractional based representations 4

Identification of nonlinear plants using left coprime fracti...

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4th European Control Conference, ECC 1997

作者： Linard, N. Anderson, B.D.O. Department of Systems Engineering and Cooperative Research Centre for Robust and Adaptive Systems RSISE Australian National University CanberraACT0200 Australia

ISBN: (纸本)9783952426906

It has been shown that the set of all nonlinear plants that can be stabilized by a known linear controller which also stabilizes a linear nominal model of the plant can be parametrized by a stable operator known as the Youla-Kucera parameter. This paper extends previous work by allowing the model of the nominal plant in the above scenario to be nonlinear, and hence explores the possibilities of converting the closed loop plant identification problem to one of open loop identification. The ideas rely on a concept of differential coprimeness for nonlinear fractional system descriptions.

关键词： Linear control systems

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Sampling rate versus quantisation in speech coders

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SIGNAL PROCESSING 1997年第3期56卷 209-218页

作者： Fulton, JA Bitmead, RR Williamson, RC Department of Engineering Faculty of Engineering and Information Technology Australian National University Canberra ACT 0200 Australia Co-operative Research Centre for Robust and Adaptive Systems Research School of Information Sciences and Engineering Australian National University Canberra ACT 0200 Australia

The use of Kalman filtering techniques to reconstruct down-sampled speech signals is investigated. We compare a full-sampled, coarsely quantised speech coding system with a down-sampled, finely quantised speech coding system transmitting at the same bit-rate. Testing reveals that the down-sampled system can outperform the full-sampled system. Sample rate, sample accuracy and decoding delay are traded to achieve improvements at a fixed bit-rate. (C) 1997 Elsevier Science B.V.

关键词： Speech coding

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Incorporating the true plant dynamics in a non-linear adaptation design for model reference adaptive control 4

Incorporating the true plant dynamics in a non-linear adapta...

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4th European Control Conference, ECC 1997

作者： Lee, Sang-Heon Mahony, Robert Department of System Engineering Cooperative Research Centre for Robust and Adaptive Systems RSISE Australian National University CanberraACT0200 Australia Cooperative Research Centre for Robust and Adaptive Systems RSISE Australian National University CanberraACT0200 Australia

ISBN: (纸本)9783952426906

In this paper, a non-linear approach to the design of model reference adaptive control is presented. The essence of the idea is to generate a full non-linear model of the plant dynamics and the parameter adaptation dynamics as a gradient descent algorithm with respect to a Riemannian metric. It is shown how a Riemannian metric can be chosen so that the modelled plant dynamics do in fact match the true plant dynamics. The approach is demonstrated by a case study of a simple single-pole and no zero, discretetime plant.

关键词： Nonlinear systems

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THRESHOLD EFFECTS IN MULTIHARMONIC MAXIMUM-LIKELIHOOD FREQUENCY ESTIMATION

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SIGNAL PROCESSING 1994年第3期37卷 309-331页

作者： WILLIAMSON, RC JAMES, B ANDERSON, BDO KOOTSOOKOS, PJ Department of Systems Engineering Research School of Information Sciences and Engineering Australian National University Canberra ACT 0200 Australia Industrial Systems Group Department of Electrical and Electronic Engineering Imperial College of Science Technology and Medicine Exhibition Road London SW7 2BT UK Cooperative Research Centre for Robust and Adaptive Systems 89 Labs DSTO Salisbury SA 5108 Australia

This paper derives a general expression for the mean square error in estimating the fundamental frequency of a multiharmonic signal from a finite sequence of noisy measurements. The distinguishing feature of this expression is that it is applicable at values of signal-to-noise ratio (SNR) within the threshold region, in contrast to earlier expressions (the Cramer-Rao bounds) that are valid only at high SNRs. Theoretical performance curves are thereby calculated (mean square error versus SNR) that establish the existence of a threshold effect. Until now, the existence of a threshold effect was demonstrable only by simulation. Examples are given comparing various multiharmonic estimation scenarios to the single tone case under comparable conditions. The theoretical performance curves in these examples are corroborated by Monte Carlo simulation.

关键词： FREQUENCY ESTIMATION THRESHOLD EFFECT OUTLIER ANALYSIS HARMONIC LOCKING

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ON SOME KEY ISSUES IN THE WINDSURFER APPROACH TO adaptive robust-CONTROL

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AUTOMATICA 1995年第11期31卷 1619-1636页

作者： LEE, WS ANDERSON, BDO MAREELS, IMY KOSUT, RL Department of Electrical and Electronic Engineering Victoria University of Technology Vic. 3000 PO Box 14428 MMC Australia Department of Systems Engineering Cooperative Research Centre for Robust and Adaptive Systems Australian National University Canberra ACT 0200 Australia Department of Engineering Faculty of Engineering Information Technology Australian National University Canberra ACT 0200 Australia Integrated Systems Inc. Santa Clara CA 95054 3260 Jay St United States

We examine a number of crucial questions that arise in the windsurfer approach to adaptive robust control. Considerations are limited to the case where the plant is stable and has no zeros on the imaginary axis. The key conclusion is that, given a strictly proper stable model of a strictly proper stable plant, we can improve the performance robustness of the closed-loop system through the windsurfer approach if the plant and the existing model have no unstable zeros within the designed closed-loop bandwidth and if the deterioration in performance robustness caused by increasing the closed-loop bandwidth results in a sufficiently high signal-to-noise ratio for a certain closed-loop output error. Situations that may cause the iterative identification and control design process to terminate prematurely are identified. A simulation example is used to illustrate the results discussed.

关键词： adaptive CONTROL robust CONTROL INTERNAL MODEL CONTROL IDENTIFICATION

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