Applied Research Based On Chaotic Theory In CDMA Communication System

As a complex nonlinear dynamics behavior,chaos is a general phenomenon in nature and is one of the most important discoveries in the 20th century later.Chaos,which is generated by non-linear dynamical system,possesses many unusual characteristics and these characteristics enable chaos to have a great charming prospect and practical value in secure communication field.Recently,chaotic communication has become a new and promising subject,so this dissertation selects it as research direction,and analyses emphatically the applications of chaos in CDMA communication system.The main works are as follows:(1) Chaotic phenomena and its related problems are summarized,and these problems,such as the relation of spread-spectrum code in CDMA communication system and chaotic sequences,and the relation of chaotic synchronization and system secret performance,are discussed.(2) The three numeric methods,including formula method , histogram method and feature vector method, of calcucation invariant probability distribution for chaotic map is derived,and their characteristics are discussed each other, these results of the computer simulation are in agreement with those of theoretic analysis.(3) The principles and methods of chaotic communication are reviewed and commented systematically.First,several main chaotic synchronization methods are discussed,then the methods and ways of chaotic communication are explored,including analogue chaotic communication,digital chaotic communication and direct chaotic communication.This is the article basis, and it startes from follow-up case study.(4) The mathematical expressions of statistical properties of chaotic sequences generated by Chebyshev-map are derived. Their statistical properties are identical withthose of white noise, and they are suit to be spread-spectrum address sequences.The appropriate number of chips contained in one information bit is gained for these chaotic spread-spectrum sequences.This provides the theoretical basis for chaotic sequences as address code.(5) The optimal neural network model of chaotic generation are built to generate chaotic spread-spectrum sequences,and its optimized methods are proposed.Results show that these optimized chaotic sequences are much better than traditional sequences(for example Gold sequences) and those generated by chaotic map. So this provides a new method for the engineering application of chaotic sequences.(6) The particular model of CDMA communication system based on spatiotemporal chaos is proposed,which is based on the communication efficiency and the method of secure communication is given up.The results illustrate that the system possesses high security ability and strong synchronization ability,and is easy to be realized;and chaotic CDMA communication system is superior to Gold one in the anti-jamming property.