Measurement of signal parameters using nonlinear observers

Recursive measurements of signal parameters that are nonlinear functions of observations require nonlinear observers. A method to design absolutely stable observers for multiple-output time-varying nonlinear free dynamic systems is presented. Because of the high computational burden of absolutely stable observers the authors have developed a computationally efficient globally, but not absolutely, stable observer measuring the frequency and the Fourier coefficients of bandlimited periodic signals. Simulation and realization results are also provided