.ds / Cdma Signal Blind Detection And Separation Technology Research

Direct sequence spread spectrum (DS) signals have been widely used for secure communication and mobile communication known as Code Division Multiple Access (CDMA) system. Because DS signals have many advantages such as anti-jamming capability, low probability of interception, multiple access capability and so on. Accordingly, the interception and radio monitoring for spread spectrum communication have been of great research interests. And the chief task is to detect and separate the DS/CDMA signals hidden in the noise and interference.Several methods of sequence spread spectrum signals direction have been developed, such as energy detection, correlation detection, cepstrum detection, cyclic spectral, higher order cumulant detection, etc. These methods developed from the research of detection and estimation for DS signals. But applying these methods to detect the DS/CDMA signals have not been done and analyses have not been made. At the same time, there are many methods for blind source separation, but there is not an ideal solution to multiuser separation in DS condition. Regardless using Nerve Net, ICA or ME method, it is difficult to separate the mixed DS/CDMA signal in low SNR condition.At first, to estimating common parameters, in this dissertation three detection methods-square detection, spectrum correlation detection and cepstrum detection are applied to detect the DS/CDMA signal. These three methods have different advantages and disadvantages respectively. Every method can estimate a different parameter of the signal with good performance. The square detection can picks up the carrier frequencies, which is simple and has great performance. But this method can't recognize the signal as spread spectrum signal. The spectral correlation detection method can estimates the chip rate of signal's PN sequence. The shortcoming of spectral detection is its complexity and in need of long time to compute. A simple and powerful approach is cepstrum detection method, which can estimate PN sequence's time period. Using this parameter and the PN chip rate estimated by spectral correlation method, we can get another parameter, length of the PN sequence. And then, we utilize Delay and...