Study On The Method Of Nonlinear Spread-spectrum Signal Processing And Detection

Spread Spectrum Communication,compared with traditional means of communication,and due to its better confidentiality,better multiple access interference and better anti-interception capabilities,is widely used in the fields of military communications,civilian communications and aerospace monitoring and tracking.Spread Spectrum Communication as a highly confidential communication,its core is the choice of a good spreading code of pseudo-noise characteristics.Currently,the PN sequence(Pseudo-noise sequence)is widely used by Spread Spectrum Communication system as spreading codes,on account of the PN sequence's low complexity and less available code groups,it is easy for eavesdropper to copy and there will be a big security risk exists.Thus the generation and detection of nonlinear spread-spectrum signal become one of the key technology of Spread Spectrum Communication.Chaotic sequence used as the spread spectrum code of spread spectrum system is characterized as rich in symbols and good in secrity,etc.With the rapid development of communication technology and multimedia technology,research on the production and processing methods of chaotic signal becomes crucial.How to improve the sensitivity of the initial value of the iterative mapping,bifurcation and stochastic uncertainty is a hot issue on the generation of chaotic spread spectrum signal;Accurate estimation of the chaotic spread spectrum signal is the key to recover the original information to enable effective investigation and supervision as well as guidance of interference.This paper mainly focus on the research of new production and detection methods of chaotic spread spectrum signal.(1)A brief introduction to the type of spread spectrum communication system and its synchronization technology,as well as the analysis of the security and reliability of traditional spreading codes based on the design criteria of Spread spectrum sequence.(2)The research on theories of structural weakening,phase space reconstruction and composite mapping model.On the basis of these theories,the author proposes to improve Skew Tent mapping,Logistic mapping to improve.The simulation results proves that the chaotic performance indexes can be effectively improved by the new algorithm.(3)Chaotic time series must be quantized in order to use as a spread spectrum sequence.By the comparison of the respective advantages and disadvantages,the paper has analyzed some classical binarization methods,such as binary quantization method and bit quantization method more detailed.Through introducing the symbolic dynamic theory,combined with the properties of sequential symbolic,a new bit quantization method has been brought out based on symbolic sequences.With the combination of this method and the improved symmetrical two-dimensional Logistic map with two levels,this paper has introduced the process to generate pseudo random spread spectrum sequence,and further analysis about the relative merits of this sequence with the one produced by traditional method.(4)A simple spread spectrum communication system based on hardware has been designed and implemented.The spread spectrum signal has been produced and modulated on FPGA development platform Quartus II 13.1 of Altera,and then each module was designed and simulated.The new spread spectrum sequence proposed by this paper has been used in the system,contrasted with the traditional spread spectrum sequence.The test results show that the new method is more suitable than traditional one for DS-SS system.