Robust filtering and feedforward control based on probabilistic descriptions of model errors,

A new approach to robust estimation of signals, prediction of time{series and robust feedforward control is considered. Signal and system parameter deviations are represented as random variables, with known covariances. A robust design is obtained by minimizing the squared estimation error, averaged both with respect to model errors and the noise. A polynomial equations approach, based on averaged spectral factorizations and averaged Diophantine equations, is derived. Mild solvability conditions guarantee the existence of stable optimal lters and feedforward regulators. The robust design turns out to be no more complicated than the design of an ordinary Wiener lter or LQG regulator. The proposed approach avoids two drawbacks of robust minimax design. First, probabilistic descriptions of model uncertainties may have soft bounds. These are more readily obtainable in a noisy environment than the hard bounds required for minimax design. Furthermore, not only the range of uncertainties, but also their likelihood is taken into account; common model deviations will have a greater impact on an estimator design than do very rare \worst cases". The conservativeness is thus reduced. Subtitle: If model errors are represented by stochastic variables, performance robustness can be optimized by using a polynomial equations approach. Simple closed{form solutions are presented. They minimize quadratic criteria, averaged with respect to model error distributions.