The analysis of the irregular signal is usually based on the assumed linear stochastic model.The development of chaos theory provides a useful alternative,since chaotic signal also shows similar characteristics.If the signal under investigating is chaotic in nature,or the underlying system can be approximately modeled by a chaotic dynamical system,novel signal analysis methods based on the deterministic nature of the signals can be developed.The opportunity lies largely in the fact that the structure (or the lack of structure) of the power spectrum of the signals can now be interpreted by other intrinsic properties of the underlying nonlinear system,rather than only the autocorrelation.For example,the different components in frequency representation may be coherent,which can be exploited by modeling the underlying dynamical system.