Study On Applications Of Chaos In Image Secure And Weak Vital Signals' Frequencies Detection

Chaos is a kind of dynamical behavior derived from deterministic nonlinear systems. As a result of the chaotic signals'properties, such as relatively wide spectrum, sensitive dependence on initial values, pseudorandom, high complexity, long-term unpredictability and etc, they have been extensively applied on many scientific fields, such as communication, signal processing, information security, medicine, meteorology and etc. In recent years, the application of chaos in the fileds of communication and information security becomes a research hotspot in academe and industry.This dissertation focuses on the study on applications of chaos in image secure and weak vital signals'frequencies detection.1. Study on chaos based image encryption algorithmBecause of the characteristics of image information, such as strong data redundancy, large amount of data, strong correlation of adjoining pixels and etc, conventional encryption algorithms aimed at text information do not entirely adapt to image encryption, for example, DES, IDEA, RSA and etc. The recent research indicates that chaos based image encryption algorithms have evident advantages in security and applicability.An image encryption algorithm based on alternating subsection-disordered diploid chaotic sequences is proposed. The proposed algorithm imports the auxiliary secret key generated by original image. The alternating subsection-disordered diploid chaotic cipher sequences are generated by the auxiliary secret key, the initial keys and the diploid chaotic systems. Cryptogram matrix which consists of the cipher sequences encrypts original images. The simulation show that the proposed algorithm is of excellent encryption effect and high security。2. Study on the application of chaotic theory in weak vital signals'frequencies detectionAs to conventional methods of weak singal detection based on the linear principle, the input SNR(signal-to-noise ratio) threshold is limited and it is hard to decrease. Whereas chaos based method takes advantage of the fundamental properties of nonlinear, sensitivity and immunity to noises. The chaotic detection technique extracts information from instability and imbalance, which could remedies the shortages of conventional ways and reduces the SNR threshold.The principle of low velocity target weak signal detection based on chaotic oscillator is amply introduced. Based on the principle, a method of weak vital periodic signals' frequencies detection based on chaotic oscillator is proposed. The proposed method based on the combination of autocorrelation and the improved chaotic oscillators array and succeeds in detecting two weak vital periodic signals whose frequencies are unknowable in the context of high level noises. The SNR threshold of the proposed method is lower than either autocorrelation or chaotic oscillator detection and the error precision is reasonable. The proposed method is able to apply on the signal processing part in life-detection radar.The healthy mobile phone project is indicated in the appendix, which gives an application example of chaos based detection in ECG(electrocardiogram) signal.