Research On Hyper-chaotic Secure Communication With Two Transmitted Channels And Chaotic Spreading Sequences Generated By The Extended Chaotic Maps

Based on the fundamental characteristic of chaotic signals, which are similar to stochastic signal, extremely sensitive dependence upon initial conditions and not being predicted for long time, and so on, we study the application of chaotic signals to analog secure communication systems and digital CDMA communication systems in this thesis. The main work of this thesis is presented as follows.1. Chaos synchronization is the foundation of the application of chaos to analog secure communication. We present several chaos synchronization methods and make a compare among them when applying to secure communication systems, and then introduce a synchronization method in unidirectionally coupled hyper-chaotic systems using a single variable. This method can realize hyper-chaos synchronization under a single analog or discrete variable coupling, adapting to apply to secure communication.2. A hyper-chaotic secure communication scheme with two transmitted channels is presented. This scheme takes full advantage of the complexity of hyper-chaotic signals, the precise synchronization performance of the synchronization method in unidirectionally coupled chaos systems using a single variable, the high interference cancellation of the communication systems with two transmitted channels, and the double encryption scheme to the information. So this scheme harmonizes the security, synchronization performance and the interference cancellation of chaos secure communication. It can be realized as follows: In transmitter, the digital chaotic key is generated by one hyper-chaotic signal, the information is encrypted by chaotic key and then masked by one or several hyper-chaotic signals, the encrypted signal is transmitted through one channel, the other channel is used to transmitted the coupled variable which realizes hyper-chaos synchronization. In receiver, based on synchronization of the transmitter and receiver, the chaotic key can be regenerated and the information can be recovered with high SNR(Signal Noise Rate). The simulation results show that this scheme is effective.3. In the study of digital method of chaos application to secure communication, in view of the performance of the spreading sequences for spread-spectrum communication system, a novel method of obtaining chaotic digital sequences generated by the extended chaotic map is given. Then an advanced method is givenafter the performance analysis of the above digital chaotic spreading sequences. The simulation results show that the advanced sequences have ideal balance performance and higher security, so they can reduce the spectrum leaking in spread-spectrum communication, and they suit to apply to CDMA communication systems.4. In order to analyze the security of chaos secure communication, we study the prediction of chaotic sequences. Three linear methods of the local prediction are introduced. Aiming at avoiding the disadvantage of the linear method, a nonlinear adaptive prediction method using Volterra filter is analyzed. Then a new adaptive predictor is introduced which is realized by predicting firstly and filtering secondly. This method can not only adaptively adjust the parameters of the second-order.