Researches On Chaotic Signal Generating, Processing With Applications In Communication Systems

In this dissertation, researches on chaotic signal generating, processing and application in communication systems are carried outHie main originality in this paper can be summarized as below: 1. Studies on chaos generation.(1) A new chaos family based on quadratic function is promoted, their Lyapunov exponents are calculated. In the proposed three types of chaos generator belonging to this chaos family, the period-doubling-bifurcation route to chaos is observed, and in the type-in chaos generator, the torus-breakdown route to chaos is also observed. It would be a firstly observed phenomenon that the period-doubling-bifurcation route to chaos and the torus-breakdown route to chaos coexist in a same system, and it is a rarely observed phenomenon that the route of torus-breakdown to chaos can be observed in a third-order ordinary differential system.(2) Piece-wise linear (PWL) circuit realizations of the class-DI-a chaos generator are suggested. In the circuit realizations, only one nonlinear element is needed, that is, only a three-segment PWL voltage-controlled vokage source or a two-segment PWL voltage-controlled voltage source is needed. In the context of the whole circuit structure, this circuit realization is more complex than that of Chua's circuit, but in the context of the complexity of the nonlinear element employed, it is the most simple chaos circuit while realized by a two-segment PWL element.(3) A modified Chua's circuit is proposed and a circuit implementation is also designed. Dynamics of this modified Chua's circuit are numerically studied and its Lyapunov exponents are also calculated.(4) A resistance-coupling method for designing new chaos generators by taking use of existing chaos generators is suggested, several new chaos generators realized by this way are studied and their dynamic are compared to those of original chaos generators, their Lyapunov exponents are also calculated.2. Studies on the processing of chaotic signal(1) A novel Volterra-TLS method based on Volterra series model, TLS criterion and iterative TLS algorithm is proposed. It is proved by numerically simulation that, when used for predicting the chaotic time series, the predicting precision of Volterra-TLS method is not inferior to the predicting precision of Volterra-NLMS method while its training and learning speed is faster and it is more ro^w; against noise interference.(2) A new perturbation method for noise reduction of chaotic signal is promoted, the approach consists of deploying a series of proper disturbance to the observing orbit YN = (yi,y2,.-.j//)?so as to gradually acquire the estimation XN - (Jc,,5c2,...,jcw) of the real orbit XN = (*i,X2,...,XAr). It is proved by numerically simulation that the disturbing method can still obtain fairly good noise reduction results even if the signal-to-noise ratio of input signals is low. 3. Studies on the application of chaotic signal in communication.(1) A new approach for chaotic secure analog communication is promoted, it is proved by both the computer simulation and hardware experiment that this new chaotic encryption method for analog secure communication is feasible.(2) A new digital frequency-hopping communication system based on cipher-quasi-chaotic sequence is proposed, which combines the cryptography and frequency-hopping technology. The system's protocol, base-band signal processing and modulation/demodulation algorithms of the radio-frequency part are designed, and the hardware experiment conducted on a prototype of the system show that the system functions well. The finite precision problem arising while taking use of chaotic signal to generate pseudo-random sequence is studied and the anti-tracking capability of the cipher-quasi-chaotic sequence is studied with the Volterra-TLS method proposed in this dissertation.