Weak Signal Detection Based On Chaotic Oscillator

Weak signal detection is a new technology, which studies the principle and the method of detecting the weak signal under the strong noise bakground, weak signal exists widely in many areas, Such as the mechanical system appearance monitor, recognition of radar signal, medical signal processing and so on. Thus, weak signal detection becomes one of the most problems should be solved in these areas. The purpose of weak signal detection is to detcte useful signal from strong noise. It is an intergrated and sophisticated technique. Therefor, weak signal is become the hot topic in signal processing area.Chaos theory is a major branch of nonlinear science, its rise and development provides a new detection methods and clue for weak signal detection. Chaotic oscillator is a nonlinear system which demonstrates the typical chaos phenomemon, such as Duffing oscillator, Birkhoff-shaw oscillator and Lorzen oscillator and so on. As the chaosic oscillators'phase change is immune against the noise but sensitive to periodic signal, when the useful weak periodic signal is processed by chaosic oscillator, the useful weak signal can be detcted and recontrusted.There are two main tasks using chaosic to detect weak signal, the first one is studying new methods using the mature chaosic oscillators. Secondly, seeking new chaosic oscillators in order to expand chaotic oscillator detection applications. In this thesis, these two aspects are both studyed. First, studying the Birkhoff-shaw oscillator to detecte sine weak signal, and comparing with the Duffing oscillator in detection performance. Then, studying the Birkhoff-shaw oscillator using in square signal, pluse signal and mixed-signal, and through a lot of simulation experments to prove its feasibility.This thesis mainly incluedes the following:1. Based on the existing research results, combinating Melnikov method and Lyapunov exponent method to find the threshold of the chosic oscillator from chaosic state to stable state change. The last simulation prives this method is effetive, and it provides a theoretical basis for weak signal detection using chaosic oscillator.2. Studying specificly the method of weak sine signal detection using Birkhoff-shaw osciallator. Improved method of detecting the signal's amplitude in the situation of don't know the signal's frequency, and the simulation proved this method is usful and simply. According to Birkhoff-shaw oscillator's output component, find a new method to detecte the signal in the condation of frequency and amplitude are unknow, at last the simulation proved the method is correct and feasible.3. Preliminary study the possibility of Birkhoff-shaw oscillator detectes weak square signal, pluse signal and mixed-sianal. And the result of the simulation proves this osciallator can be used to detecte these signals, it proves that the Birkhoff-shaw can be uesd in general periodic signal detection. At last, compaired between Birkhoff-shaw and Duffing oscillator.4. The experiment and simulation using Birkhoff-shaw chaosic oscillator to detecte a variable frequency signal, shows that the method can apply to practice. At last design a virtul instrument base on Labview. And using this system to test these methods, the result proves they are correct.Weak signal detection based on chaosic oscillator is a new method, it has many advantages, especially in periodic signal detection. The simulations and experiments proved this method is correct and feasible. It provide a new method for the practice and engineering. However, much problem existing in this area should to be solved, and the study using chaosic oscillator to detecte weak signal has a long way to go.