Research On Chaotic Pseudo-Random Sequence’s Generation And Its Application In Spread Spectrum Communication System

With the rapid development of science and technology,3G mobile communicationtechnology has evolved to a practical application stage. The technology that is most importantin the third-generation wireless communications technologies is CDMA spread spectrumcommunications technology. For suppressing multipath and multi access interference, it isrequired that the spread spectrum sequence is of good performance in auto-correlation andacross-correlation. For satisfying the requirement of the increasing number of users, thenumber of spread sequence is required to be numerous. Therefore, the performance of spreadspectrum communication system is directly determined by the performance of the spreadingsequence. Gold sequences and m-sequences have many inherent defects, such as: a limitednumbers, short cycle.Chaos provides a new method for generating of spreading sequences. It is randombehavior of deterministic dynamical systems, and is sensitive to initial conditions. Chaos canbe used to generate a huge amount of no-periodic sequences, which have good performance incorrelation and balance. Chaotic sequence is therefore of potential applications in spreadspectrum communication systems.The main research work in this thesis is to generate a chaotic sequence, which not onlyhas a better correlation, balance, randomness and periodicity, but also has a better complexity,confidentiality. In view of the chaotic sequence generated by a single low-dimensionaldiscrete chaotic map have many defects, such as: low complexity, poor anti-attack capability.In this thesis, a new chaotic sequence is generated, which is realized by combining Hybridmap and Chebyshev map and randomly selecting chaotic map and changing systematicparameters. The new sequence is greatly enhanced in complexity, security and anti-attack.Specifically, this thesis completed the following work:(1) Research of m-sequences,Gold sequences and several common chaotic sequences, whose characteristics are simulatedand analyzed, and included comments are also given.(2) To propose a method for generatinga mixed chaotic sequence, whose analysis and simulation are given; also, the comparedresults with Gold sequence, Chebyshev chaotic sequence and Hybrid chaotic sequence areincluded.(3) To establish a model of spread spectrum communication system, in which the new chaotic sequence is used to test the BER performance. Also, the compared results with msequence, Chebyshev chaotic sequence and Hybrid chaotic sequence are given.