Research On Chaotic Pseudo-random Sequence's Generation And Its Application In Spread Spectrum Communication

Pseudo-random sequence is a code sequence whose properties are similar to those of white noise. It is mainly used in cryptography and spread spectrum communication field. With the development of Code Division Multiple Access (CDMA) communication and the raising requirements of communication security, the traditional pseudo-random sequence, such as m sequence, Gold sequence, etc, can't meet the expanding requirements because it often has shortcomings of limited number of sequence and lower linear complexity. Chaos system not only is sensitivitive to initial conditions but also can generate high-quality pseudo-random sequences which is of high complexity profile property, so the generated sequences have good application prospect in spread spectrum communications. The topics that how to generate high-quality pseudo-random sequence and how to apply the sequence to spread spectrum communication are discussed in this paper. The main content of this paper are as follows.(1)The basic theory needed in this paper is summarized. Firstly, the nature of the Pseudo-random sequence and its performance indicators are generalized. Secondly, the properties of chaos system are analyzed including Lyapunov exponent, attractor, bifurcation, Permutation Entropy and so on. At last, the topics that the characteristics of spread spectrum communication, especially the Direct Sequence Spread Spectrum(DS-SS) communication, the shortcomings of traditional pseudo-random sequence used for spread spectrum communication and the advantage of chaotic sequence used for spread spectrum communication are analyzed.(2)An method is proposed to improve the traditional Henon map on the basic of a deep analysis of the common chaotic pseudo-random sequence. Internal structure of Henon map is changed by adopting absolute value term so that the charactoristics of the system including linear complexity and sensitivity to initial conditions are enhanced. Numerical results show that the Lyapunov exponent and Permutation Entropy of the modified Henon map have been improved and the modified Henon map can generate better-quality chaotic pseudo-random sequence.(3)Globally coupled map model is studied in order to try to generate high-quality pseudo-random sequence after analyzing the advantages of studying spatiotemporal chaos using the coupled map lattice model.The permutation entropy of coupled system is calculated under different parameters condition.The linear complexity of the model is scanned and the parameter space which is corresponding to the high linear complexity condition is found. The pseudo-random sequence of good quality is gained using universal algorithm to transform chaotic sequence into ones.(4)The generated chaotic sequence is applied to DS-SS comunication. the autocorrelation sidelobe and the cross-correlation RMS value which characterize the size of multiple path interference and multiple access interference generated by the spreading sequence are calculated. The simulation model of the DS-SS is established based on MATLAB (2007) platform. The generated spatiotemporal chaos sequence which is used in DS-SS is simulated.The bit error rate (BER) characteristic of the system is also analyzed.This thesis work has certain theoretical and engineering application value in the high-quality pseudo-random sequence generated by the chaotic system as well as in the applications of chaotic sequence in CDMA communication.