Detection And Parameter Estimation Of Dsss Based On HHT

Direct sequence spread spectrum(DSSS) techniques have a number of advantages, such as anti-interference, low probability of interception and detection, anti-multipath effect, code division multiple access, and so on. They are increasingly replacing conventional communica- tion and obtaining extensively applications in both modern military and civil areas, for example, satellite communications, GPS and etc. Accordingly, how to detect and estimate DSSS signals in non-cooperative communication is a great challenge with a strong background of application.DSSS signals are wide-band weak ones. When SNR becomes lower, the performance of traditional detection and estimation methods take a turn for the worse so much as not working. Consequently, it calls for new detection and estimation technology to solve the difficult problem. Hilbert-Huang Transform (HHT) is applied to detect and estimate DSSS signals in this thesis. The main researches summarized as follows:1. The existing problems in HHT are summarized. Furthermore, a method called extremum balance forecast is proposed for end effects and has better performance.2. A method of detection and estimation is proposed on the basis that HHT is applied to analyse DSSS signals. Simulation results indicate that the proposed algorithm can work well on SNR below -20dB and improve compute efficiency. The method both offers an effective approach to detecting spread spectrum communication and exploits HHT application field.3. Combined empirical mode decomposition with correlation accumulate technique, an improved square detection method is raised that can pick up carrier frequency effectively. and the limit of SNR falls 11 dB comparing with traditional method.4. The improved approach of cyclic spectrum is proposed by making full use of self-adaptive decomposition and good concentration. Experimental results show that it can detect and estimate carrier frequency and chip rate of DSSS signals accurately in lower SNR.