Studies Of Secret Communication Based On The Chaotic Observer

Nowadays, communication has been an indispensable part of people's life. Meanwhile, as the importance of improving the quality of communication, and by the prograss of society, people gradually pay more attention to the personal secrets in communication. Thus, secret communication has become a hot spot in the field of common communications. Based on the current studies and key techoniques of secret communication, this paper, combining with domestic and foreign relevant field of studies, proposes a new secret communication method, which is based on the chaos theory. Expounding the advantage of chaos application in secret communication by introducing its history, current studies and main characteristics, this paper designs a secret communication system, which is based on the chaotic observer. Finally, the simulation and experiment verify the feasibility and effectiveness of the proposed system.The organization of the thesis is as follows.First, this paper reviews the current studies and development of chaos theory and chaotic synchronization theory, analyses some methods of chaotic synchronization and their limitation, and presents some mathematical conclusions, which will be used in designing the observers.Second, based on the relevant studies of traditional secret communication and chaotic theory application, this paper constructs a new chaotic communication system framework. To ensure the security and reliability of the system, this paper uses the classical Lorenz chaotic system in encryption system. However, simply using chaos masking method to encrypt voice signal has some shortages. Because the main energy of chaotic signal of the system is in the low frequency, and direct superposition cannot cover voice signal sufficiently. Through the spectrum analysis of voice signal and chaotic signal, this paper proposes the pre-processing of chaotic signal by the designing low-pass amplified filter.Additionally, to realize the chaotic synchronization of system, this thesis designs two types of observers to recover the audio signal based on the Luenberger observer theory. The validation is verified by critical of mathematics proof and the effectiveness is proved by simulation and experiment. Moreover, after the comparing between the two types observers, this paper finally chooses the observer with unknown parameter as the synchronization solution of secret communication system.Finally, experiment for the system application is carried out by using Texas Company's TMS320C5416 DSK. After analyzing the system performance index, data capacity and actual human ear's sound frequency range, this paper formulates the basic workflow of experiment, sets the system operation parameters, and makes the pre-processing of voice signal by the designing band-pass filter. According to the requirement of encryption method and synchronization, this paper designs the software system. Finally, the experiment results demonstrate that designed secret communication system is feasible.