The Application Research Of Chaotic Sequence In Spread Spectrum Communication System

With the development of science and technology, the 3G-based individual mobile communication has been put into pragmatic period and the CDMA-based spread spectrum has become the key technology in the third generation of the individual mobile communication system. The basis of the CDMA spread spectrum is the construction of the sound code with mutual correlation and self-correlation. And the code should contain spread spectrum sequence as more as possible in order to meet the demand of more customers. The performance of the spread spectrum sequence has the direct influence to the spread spectrum system and the spread spectrum sequence has become the key issue in spread spectrum communication system. The present spread spectrum communication system uses the m-code and Gold-system generated from the maximal length linear shift register, yet they still have the drawbacks of length and quantity limitation. The discovery of the chaotic dynamics provides the new ideas for the use and research of the spread spectrum sequence. Chaos is the certain acyclic phenomenon appeared in the non-linear dynamic system and it's similar with the stochastic process. It looks like irregular motion and it is limited yet not converged. It has sensitive reliance to the original values. Based on its non-periodicity, wide frequency and sensitivity to the original values, the chaos can be used in producing very long sequence and large-quantity code element. It makes the pseudo-random code has more advantaged than the traditional spread spectrum communication system and it makes the multiplexing to the maximum.This paper analyses all kinds of performance of the traditional m-code and Gold-mode and performance of the typical chaos mapping, such as Tent, Chebyshev. Logistic and the improved Logistic. On this basis, a new method can be used to produce chaos sequence, i.e. the chaos sequence can be produced by applying the discretization of the continuous chaos. Thus, the widely used continuous chaos can be used to produce chaos sequence and the range of the chaotic dynamics model can be greatly extended. This paper designs a switching chaos system and a ultra chaos system. The systems deal with the chaos signals according to certain rules and they produce chaos spread spectrum sequence. This paper also analyses characteristics of the mutual correlation, self-correlation, sidelobe, crest value and shift performance. We apply for the new methods to shift the chaos system and the ultra chaos system and we have got the result from the use of the FPGA platform, which is in accordance with the computer simulation. The application of FPGA platform is more convenient, reliable and transferable, and it explores the practical application of chaos spread spectrum sequence. Later we apply the experimental analysis on the optimized spread spectrum sequence on the MATLAB platform. By referring to the Monte Carlo communication system, we select the key parameters in influencing spread spectrum communication performance and analyse and simulate the error code performance. It proves that the designed shift sequence has more advantages in distinguishing the chaos sequence, ultra-chaos sequence, normal chaos sequence and Gold sequence. It provides great value for the research and development of the spectrum-spreading code and certain experimental evidence for the application of chaos system in communication system, which is quite beneficial for the development of the chaos communication.