.ds / Cdma Signal Blind Detection Technology

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 estimate the DS and DS/CDMA signals hidden in the noise. 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. DS/CDMA is the mixed signal of the users'DS signals in one communication system. These DS signals are modulated in the same mode, except the pseudo-noise (PN) sequence used to every user's signal. These DS signals have same characters on the frequency spectrums and some other transformed fields. The same situation happened between DS and DS/CDMA signals. As the result, it is very difficult to distinguish the DS signal of different user and very difficult to distinguish the DS signal and DS/CDMA signal without the knowledge of the PN sequence used by every user. But the distinguish job mentioned above is a big significance to communication interception. It is very necessary to research the methods of the DS/CDMA signals'blind detection and distinguishing approaches of the users'signals, even though the work is very difficult. 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, and the algorithm is simple...