Direct Sequence Spread Spectrum Signal Detection Based On Chaos Theory

Since the Direct Sequence Spread Spectrum (DSSS) signal is always transmitted in seriously noisy environment, the DSSS signal detection with low signal-to-noise ratio is an important content of DSSS electronic countermeasures. Normally, the signal detection in this situation is non-cooperative and lacks adequate prior information; therefore, it is a type of blind detection or approximate blind detection.With the development of nonlinear science, chaos theory has become more and more important in many fields. It is found that a kind of chaotic system is extremely sensitive to weak signals and immune to noise under certain conditions, which has a great potential in improving the performance of signal detection. And the application of chaos theory to DSSS signal detection is a creational research in information countermeasures, which is a creation in the application field of chaos theory and impels the development of DSSS signal detection technology.The dissertation studies on Chaotic Oscillator Systems——Duffing Oscillators and Lorenz Oscillators, and proves that DSSS signal is chaotic. According to the principle of Intermittent Chaos, the system of Duffing Chaotic Oscillators Array is creatively constructed for blind detection of DSSS/BPSK signal in very low signal-to-noise ratio (SNR) below -30dB. Computer simulations prove that the new method is effective,and in comparison with many previous methods, the DSSS/BPSK signal can be detected successfully at a lower detection-threshold by this method, which enhances the performance.Furthermore, the dissertation combines the new method based on chaos theory with normal linear methods such as the time-domain correlation detection method and the high-order cumulant detection method. So the detection performance is advanced more. The detection threshold is about -40 dB.Lyapunov Characteristic Exponent (LCE) is one of the most important characteristic quantities of chaos, and also is an important criterion for the identification of chaos. According to the analysis of Chaotic Oscillator Detection System, the dissertation proposed an improved RHR method for LCE's calculation. Comparison to QR method and RHR method, the new method greatly improves the efficiency of calculation.