Chaotic Spread Spectrum Technology And Its Applications In Ttc

Chaos is a convinced and similar random process that appears in the nonlinear system. It is also a nonperiodic and irregular process. It is not convergent but have a bound. Also, it is sensitive to its initial values. With all these specical properties, chaos has good application prospects in the field of secure communication and spread spectrum communication. In the field of TTC, the technology based on PN using spread spectrum principle has been widely used. The traditional spread spectrum TTC pseudo codes are mainly m sequence and Gold sequence, or composite sequence composed of these two kinds of sequences. In some areas, TTC must guarantee security and confidentiality, but m sequence and Gold sequence can't satisfy these requirements because of their low complexity. So finding nonlinear and high complexity pseudo codes becomes a new topic in the TTC field. With the development of chaos theory and technology, the chaotic signal or quantified chaotic sequence has been paid extensive attention and widely used due to some of their good characteristics, such as noise-like, nonperiodic, nonlinear. Therefore using chaotic sequence becomes a new development direction in the TTC field, and the research about it has very universal theoretical and practical value.First of all, this paper introduces the basic theories of chaos, including the definition of chaos, and the properties of chaos, and emphatically introduces the applications of chaos in the TTC communication.Then four basic chaotic mappings are introduced which are Chebyshev Map, Tent Map, Logistic Map and improved Logistic Map. The statistical properties of four kinds of typical chaotic sequences are analysed. The performances of autocorrelation and crosscorrelation are simulated respectively. The selection problems of initial values and fractal parameters about the four kinds of chaotic sequence are discussed. The quantization methods about chaotic sequence are researched, and then we make an optimization for the chaotic sequence from the aspects of balance, autocorrelation and crosscorrelation. Finally the selection process and methods are given.Anti-interference performances of the chaotic spread spectrum communication system are researched. According to the chaotic spread spectrum principle, we set up Simulink model, and analyse the BER performance of the chaotic spread spectrum system under white noise, single frequence interference, low frequence pulse interference, and part frequency interference respectively through simulation.Then this system is compared with the traditional Gold frequence spread spectrum communication system. The simulation results show that the chaotic spread spectrum communication system has good anti-interference performances.The chaotic spread spectrum technology with Rake reception is reseached. A new calculation method of BER is derived through the analysis of the existing methods about the calculation of BER in the multi-user chaotic spread sprctrum system with Rake reception. And the BER formula is given in the forms of energy distribution,the number of multi-paths,the number of users and average power of chaotic sequences. Then we make a simulation, and the results show that this method is accurate.Finally, the basic principle of pseudo-code ranging and two ranging methods are introduced. Meanwhile, the DCSK system and chaotic self-synchronization scheme are emphatically introduced and reseached. According to the principle of pseudo-code ranging, using the existing spread spectrum technology, synchronization technology and the chaos features, two chaotic ranging schemes are designed: chaotic ranging scheme based on matched filter, and chaotic ranging scheme based on DCSK. Theoretical analysis and expatiation to the advantages and disadvantages of the two ranging schemes are made, and the function and performances are simulated. The theoretical analysis and simulation results show that these two schemes are feasible.