Broadband Fm-dcsk Multiple Access Communication Technology Research

Chaos theory is attracting attention because of its broad-band and random property. But nowadays the application of chaos theory in communication system is not arrived at the level of traditional communication systems. Chaos theory can not be easily applied to practical communication projects. There are two main reasons for it. One is the difficulty of producing wide-band chaotic signal which accords with the practical needs, as a digital system is restricted in frequency range by the bandwidth of power-supplied parts or clock frequency and the analog system is also limited in frequency range by the working frequency of non-linear parts. The other is the difficulty to make chaotic signals synchronization, as the non-linear property of chaos signal results in too long synchronization time of chaos signal and too big fall of data transport speed and bit error rate. Then coherent demodulation of chaos communication system is difficult to implement. Therefore, the non-coherent communication system becomes a main direction of research of chaos communication theory. In this thesis, a research on the wide band chaotic multiple access communication system based on FM-DCSK modulation has been made, including analysis of the system performance and study on its application in spread-spectrum communication.First, As for the difficulty of producing wind band chaos signal, a circuit for generating ultra wide band chaotic signal is designed and analyzed by using parallel and cascading Colpitts circuits. Then it is testified that this kind of circuits can produce wide band signal even ultra wide band chaotic signal by means of results of simulation and analysis with the emulation software PSPICE. Then on, a communication system based on FM-DCSK modulation is designed. It is simulated and analyzed by the emulation software MATLAB. It is attested by the simulation data that the system has good multipath interference immunity and high data transport speed and low bit error rate. After that some improvements over this system is given to increase its data transport speed. Finally, consulting the code division multiple access technique in spread-spectrum communication, a multiple access communication system based on FM-DCSK modulation is designed. Then the performance of this system is simulated and analyzed by MATLAB and improved by means of time division multiple access technique.